Liver Toxicity Induced by Exposure to Bisphenol Analogs at Environmentally Relevant Levels: Insights from a Literature Review on Multiple Species

Abstract

Bisphenol analogs and their derivatives have been identified in human tissue and our living environment. There are major concerns over exposure to bisphenol analogs, especially the low-dose- and mixture-related toxicities, as they are considered potential endocrine-disrupting chemicals that may cause adverse effects in multiple organ systems. The liver is a critical organ responsible for an array of functions, e.g., metabolism, immunity, digestion, detoxification and vitamin storage, in addition to being a leading chemical target site. In this literature review of multiple species, we discussed the metabolism of bisphenol analogs in the liver, which was followed by discussions of bisphenol analog-induced liver toxicity in various species, including humans, rodents (mice and rats) and other species (chicken, pig, sheep, etc.). Further, the mechanisms of action and markers of liver damage such as oxidative stress, apoptosis, inflammation and fibrosis were discussed. It was concluded that bisphenol analogs can produce toxic effects on the liver in different species through various mechanisms, including epigenetic modifications and disruptions of the cell signaling pathways, gene expression, microbiome and metabolome. More research should be conducted to study the toxicity of bisphenol analogs other than bisphenol A and the underlying mechanisms of action, and in particular the potential for causing dysbiosis. Understanding the mechanisms of liver injury holds promise for improving the prediction of liver toxicity from bisphenol analogs and other environmental chemicals, and their risk assessment and legislation.

1. Introduction and Methods

Bisphenols, which contain two hydroxyphenyl groups, are a class of well-known endocrine-disrupting chemicals (EDCs) found in plastics and epoxy resins. Exposure to bisphenol analogs in the general population occurs through multiple routes, including oral uptake, dermal contact and inhalation [1], with total daily adult human exposure being <1 µg/kg [2]. There are more than fifteen bisphenol analogs that are being commercially applied, with bisphenol A (BPA) being predominant [3,4]. Bisphenol analogs (Figure 1), such as bisphenol B (BPB), bisphenol C (BPC), bisphenol E (BPE), bisphenol F (BPF), bisphenol G (BPG), bisphenol P (BPP), bisphenol S (BPS), bisphenol Z (BPZ), bisphenol AF (BPAF), bisphenol AP (BPAP), bisphenol BP (BPBP, also known as dihydroxytetraphenylmethane) and bisphenol PH (BPPH), have also been identified in human tissue, various fresh water and marine fish species and our environment [5,6]. BPA can be detected in most tissues, with the highest concentrations found in adipose tissue, followed by the liver and brain [7]. Although many studies have been conducted on BPA, assessment of its exposure risks remains insufficient due to the lack of comprehensive cross-species comparison. In addition, the toxicity information on other bisphenol analogs is scarce. A survey of adults and children in the US population revealed the presence of BPA in urine at higher levels than other bisphenol analogs such as BPS and BPF [8]. However, an emerging concern is that several bisphenol analogs, such as BPS, BPAF, BPB and BPZ, display higher bioaccumulation than BPA, and some of these analogs are much less biodegradable than BPA. Further, these analogs can also induce the activation of estrogen receptors (ERs) and lead to developmental and reproductive dysfunction [4]. For instance, BPE and BPF exhibit estrogenic activity like that of BPA, while BPB and BPZ are more active [9]. There are additional concerns over the low-dose- and mixture-related effects, as these bisphenol analogs may cause synergistic toxicity in multiple organ systems, e.g., the liver [10]. The responses of different species to bisphenol analogs vary due to their unique physiology, metabolism and genetics, and a literature review on multiple species can help elucidate the mechanisms of toxicity and extrapolate animal toxicity data to human risk assessment.

BPA is the most studied bisphenol analog regarding its adverse effects on many organ systems, including the liver [11,12]. It has been reported that BPA can be detected in human fetal livers as early as the 3rd month of life [13], suggesting potential developmental toxicity. Aside from BPA, other bisphenol analogs are currently not regulated, largely because fewer studies have examined their potential toxicities. We have previously reviewed the toxicities of several bisphenol analogs, e.g., BPS and BPF, on the reproductive, nervous and immune systems [4]. However, the liver is the organ of first-pass metabolism to metabolize and detoxify toxic chemicals/metabolites to protect organisms from potentially toxic insults. The liver comprises approximately 2% of body weight in an adult human, and about 25% of the total cardiac output passes through the liver. It is the first organ that encounters blood from the gastrointestinal tract [14]. Due to the close association of the estrogen signaling pathway with lipid metabolism, the liver represents a major site for the generation and action of toxic metabolites following exposure to bisphenol analogs and the manifestation of acute and chronic adverse effects. However, toxicological information regarding other bisphenol analogs on the liver has not been systemically reviewed. Because of their different metabolic processes, it is possible that bisphenol analogs employ different mechanisms from that of BPA to produce their toxic effects on the liver. Thus, we conducted a comprehensive review of the current literature that describes the liver toxicity of bisphenol analogs and their related mechanisms in various species, including human, rodent, chicken, pig and sheep (Figure 1).

Literature searches of different bisphenol analogs and their effects were carried out in various platforms, including Google Scholar, MEDLINE, PubMed and the Directory of Open Access Journals, for all studies from the earliest available indexing year through 15 January 2025. We used various search terms corresponding to bisphenol exposure and liver injury, including, but not limited to, “bisphenol A”, “bisphenol A toxicity”, “bisphenol analogs/analogue”, “bisphenol developmental”, “bisphenol liver”, “bisphenol microbiome”, “bisphenol metabolism”, “bisphenol S”, “bisphenol F” and “bisphenol mixtures”.

2. Metabolism of Bisphenol Analogs

Bisphenol analogs are primarily metabolized and detoxified in the body through glucuronidation catalyzed by UDP-glucuronosyltransferases (UGTs) in the liver and intestine, leading to excretion in the urine as a glucuronide conjugate (phase II metabolism). The detoxification process for bisphenol analogs, e.g., BPA, in the liver is initiated in the endoplasmic reticulum [15]. In addition to glucuronidation, sulfation also plays a role in bisphenol metabolism. Although the conjugated metabolites do not show ER activities [16], a concern regarding the metabolism of bisphenol analogs by UGTs is related to the ability of glucuronidated metabolites to change back into the active parent compounds through deconjugation, which is carried out by β-glucuronidases that are present in adult, fetus and placenta [17]. Additionally, the metabolisms of bisphenol analogs can also be carried out by the cytochrome P450 monooxygenase system, the phase I pathway, in the liver [18]. This process can produce several different metabolites, with the most common being the hydroxylated form, leading to liver cell damage [19]. To make the process more complicated, bisphenol analogs such as BPA can affect the expression of P450 isoforms in rat liver [20]. BPA inhibits certain P450 isoforms and affects the conjugation of other drugs [21]. In human fetal liver, the reduced expressions of both the phase I and phase II genes correlated with higher BPA levels, possibly due to increased methylation by BPA [22].

BPA, BPS and BPF are the bisphenol analogs with the most available metabolism data to date. The phase I metabolites of BPA include hydroxy-BPA (catechol), BPA-ol, BPA orthoquinone, 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (dimerization), hydroxycumyl alcohol and isopropenyl phenyl (IPP). The phase I + II metabolites of BPA include BPA-ol-glucuronide, hydroxy-BPA-glucuronide/sulfate, methoxylated BPA-glucuronide/sulfate and hydroxy-BPA-glucuronide. The phase II metabolites of BPA include BPA glucuronide, BPA sulfate and BPA sulfate/glucuronide [19,23,24,25,26,27,28,29,30]. The phase I metabolites of BPS include hydroxy-BPS (catechol) and dihydroxy-BPS. The phase I + II metabolites of BPS include hydroxy-BPS-glucuronide and hydroxy-BPS-sulfate. The phase II metabolites of BPS include BPS-glucuronide, BPS-sulfate, BPS sulfate/glucuronide and BPS diglucuronide [31,32,33,34]. A study of BPF in rats has also shown the formation of many metabolites [35]. The phase I metabolites of BPF include ortho-hydroxy-BPF (catechol), meta-hydroxy-BPF (catechol), dihydroxy BPF, BPF dimer, dihydroxybenzo phenone and 4-(hydroxymethyl) phenol. The phase I + II metabolites of BPF are hydroxy-BPF-sulfate. The phase II metabolites of BPF include BPF-glucuronide, BPF-sulfate and BPF-disulfate [19,35,36,37]. When the glucuronidation rates between BPS, BPF and BPAF were compared in adult human liver and intestinal microsomes, it was found that BPAF and BPS were glucuronidated at the highest and lowest rates, in the intestine and liver, respectively [38]. For BPB, similar to BPA, it could be activated to have estrogenic activity by rat liver S9 fraction [39].

There are species differences in the metabolism of bisphenol analogs. The expression of liver and intestine UGT enzymes varied widely among humans, monkeys, dogs, rats and mice [40]. The relative levels of in vitro clearance values for BPA in monkey, dogs, rats and mice were 7-, 12-, 34- and 29-fold compared to that of humans, respectively. It has also been shown that the hepatocyte clearance of BPS and its derivatives was slower in humans than rodents [33]. In pigs, oral BPS was mostly absorbed and transported into the liver, where 41% of the parent compound was glucuronidated, with a bioavailability of 57.4%. On the other hand, only 77% of the oral BPA was absorbed, with a low bioavailability following the first-pass glucuronidation either in the gut (44%) or in the liver (53%) [41]. In rats, enterohepatic circulation of BPA glucuronide leads to a slow rate of excretion. However, in humans, BPA does not undergo enterohepatic circulation because it is rapidly conjugated and excreted [42]. In fact, BPA glucuronide was the only metabolite found in the urine and blood of human volunteers who were administered 5 mg BPA orally in a hard gelatine capsule [42].

There are age differences in the metabolism of bisphenol analogs. When the internal doses of BPA (both free and conjugated) were measured in the first- and second-trimester human fetal liver samples [12], it was found that the levels of free BPA were three times higher than that of the conjugated BPA, which might be due to a reduced BPA metabolism. As compared to sex-matched adult liver controls, the gene expression of UGTs, sulfotransferases and steroid sulfatases displayed reduced levels, whereas β-glucuronidase were unchanged [12]. There are also large variations in the ability to glucuronidate BPA by the human feto-placental unit. Fetal age can have a significant effect on BPA-glucuronide levels, but not on free or total BPA, in placental samples. For example, the maternal liver and/or the placenta has the ability to conjugate BPA changes during early to mid-gestation [43]. In sheep, Gingrich et al. [44] reported large differences in half-life, maximum concentration and total body clearance of BPA, BPS and BPF in both maternal and fetal circulations. Longer half-lives were observed in fetal compared to maternal circulation for all three bisphenols, while BPS had the longest fetal half-life.

In mice, including the fetuses, pups and dams, liver UGT activity toward BPAF is weaker than BPA and BPF, and BPAF tends to accumulate in the fetus [45]. Although hepatic UGT activity toward BPF was also weak in the fetuses and newborn pups, it was at the same level as BPA in dams. When the distribution of BPF was studied in female SD rats (pregnant and non-pregnant), the results suggested that the excretion of BPF occurred mostly in urine (at least six different metabolites with sulfate conjugate of BPF being predominant), and to a lesser degree in feces. The liver accumulated the largest amounts of BPF, and it could pass the placental barrier [46]. UGT1A9, primarily a hepatic enzyme, mainly contributes to BPS glucuronidation, whereas UGT1A10, an intestine enzyme that is homologous to UGT1A9, is the most active UGT in BPF glucuronidation [47].

Other factors such as the health condition, sex and routes of exposure also affect the metabolism of bisphenol analogs. Rat liver expression of UGT2B1 mRNA is higher in females than males, resulting in higher BPA glucuronidation in the microsome reaction of female rats [48]. Further, the expression of UGTs might be reduced by androgen, resulting in a slower clearance of bisphenol analogs and higher serum levels by men and women with hyperandrogenemia compared to women without [49]. Yalcin et al. observed a decreased ability of BPA elimination via sulfonation in obese or diabetic patients and in patients with fatty or cirrhotic livers [50]. In addition, internal levels of aglycone BPA in neonatal rats treated orally were substantially lower than from subcutaneous injection [51]. Following BPA exposure from gestational day 1 to the seventh day after delivery by subcutaneous injection, Mita et al. found that liver BPA levels in female mouse offspring were higher than those of males, while the BPA levels in the central nervous system of the male offspring were higher than those of females [52].

Bisphenol analogs can also be biotransformed by Cupriavidus basilensis SBUG 290, the biphenyl-degrading bacterium [53]. Importantly, among four biotransformation products tested, including BPE-OH, BPC-CH₂OH, BPC-CH₂OH-OH and BPPH-COOH, none were estrogenically active. Further, there were 91 bacterial strains reported in the literature that could degrade bisphenol analogs [54], including Pseudomonas, Sphingomonas, Cupriavidus and Bacillus. Bacteria can also modulate the biotransformation of bisphenol analogs through the metabolites produced. For example, gut microbial metabolite p-cresol could alter the biotransformation of BPA [55].

3. Liver Toxicity of Bisphenol Analogs in Different Species

Liver toxicity can manifest in several ways, including changed liver enzymes and altered liver cell morphology. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) are two sensitive indicators of hepatocyte injury. A persisting injury or scar formation in the liver can lead to cirrhosis [56]. Non-alcoholic fatty liver disease (NAFLD) is becoming the leading cause of chronic liver disease worldwide. It ranges from simple steatosis to steatohepatitis and potentially progresses to cirrhosis and hepatocellular carcinoma (HCC). The mortality rates in patients with type 2 diabetes and NAFLD are very high because of cardiovascular disease involvement in these patients [57]. Many studies have demonstrated the relationship between exposure to EDCs like bisphenol analogs and the development of liver diseases like NAFLD [58]. Although bisphenols are rapidly metabolized, concerns remain regarding their potential to dysregulate the endocrine system due to their mimicking hormones even at low levels [10]. In addition, the phase I metabolites are likely estrogenic [19]. The toxicities of bisphenol analogs depended on multiple factors, such as the ability to detoxify the compound, metabolic rates (e.g., half-life within the system, how fast the organism can clear the compound/metabolites from the system), toxic metabolites, mixture effect, estrogenic effects of the parental compound, endocrine disrupting properties other than ER-signaling and windows of exposure during the development of organisms. The liver is one major target organ for bisphenol analogs, and studies in different species showed highly variable transcriptomic patterns following exposure to bisphenol analogs [59,60]. Thus, a comparison of liver toxicity in different species would provide insights into the mechanisms of hepatotoxicity induced by various bisphenol analogs.

3.1. Liver Toxicity of Bisphenol Analogs in Humans

Human exposure to bisphenol analogs, such as BPA, from canned food is estimated to be as high as 6.6 μg/person/day [61]. Evidence for hepatotoxicity in humans mainly comes from epidemiology and clinical studies (Table 1). Among the identified human studies, most of them were population-based epidemiological studies and focused specifically on BPA. An et al. [62] reported that the rate of abnormal levels of ALT, but not of AST and gamma-glutamyl transferase/transpeptidase (GGT), was increased according to the increases in urinary BPA levels in Korean adults [62]. However, Lee et al. reported positive correlations between urinary BPA and levels of AST, ALT and GGT in Korean elderly populations, and higher urinary BPA levels were associated with more abnormal liver functions [63]. In workers of two semiautomatic epoxy resin factories in China, higher BPA levels were also associated with clinically abnormal levels of GGT [64]. Additionally, the correlations between serum BPA and AST and between serum BPA and direct bilirubin in children were significant in certain areas of China [65]. In a study conducted in Punjab, one of the most populated provinces in Pakistan, higher levels of ALT and AST were observed among BPA-positive diabetic participants than BPA-negative diabetics. Similarly, BPA-positive non-diabetic participants also had higher levels of ALT and AST than BPA-negative non-diabetics [66].

Using data from the National Health and Nutrition Examination Survey (NHANES) 2003–2004, in which 1455 US adults (18–74 years old) with available urinary BPA and urine creatinine measurements participated, the cross-sectional analysis found that higher BPA concentrations correlated with abnormal liver enzyme levels, including lactate dehydrogenase, GGT and alkaline phosphatase [67]. A follow-up study found that urinary BPA correlated with liver enzyme levels in the 2003–2004 survey, but with fewer correlations in the 2005–2006 survey, although overall associations were still present for alkaline phosphatase and lactate dehydrogenase [68]. Using data from the NHANES between 2003 and 2016 with 11,750 adults, Zhang et al. found that the increment of BPA positively correlated with alkaline phosphatase and total bilirubin, while inversely with albumin [69]. A negative association between urinary BPA and serum total protein and albumin has also been reported by Luo et al. [70].

After examining 2104 participants from the NHANES 2003–2008, Teppala et al. found that the levels of urinary BPA positively correlated with metabolic syndrome [71]. Dallio et al. showed that BPA levels were higher in NAFLD subjects from Naples than controls [72]. An et al. [62] also reported that urinary BPA levels positively correlated with NAFLD risks in Korean adults. In plasma samples from individuals affected by NAFLD in southern Italy, unconjugated BPA was detected in all samples, also suggesting an association between BPA exposure and liver health [73]. Kim et al. also showed that the levels of urinary BPA correlated with NAFLD in US adults [74]. In adolescents, Verstraete et al. found that there was an increased risk of suspected NAFLD with higher levels of BPA exposure [75]. Moreover, BPA seemed to be higher in non-alcoholic steatohepatitis patients than steatosis subjects. Additionally, there was a correlation between BPA plasma levels and hepatic inflammation [72]. Another epidemiological study in Naples also showed that the plasma BPA levels exhibited a positive association with visceral obesity and low-grade inflammation, the important risk factors for NAFLD [76]. A meta-analysis revealed that a 1 ng/mL increase in BPA correlated with an 11% higher risk of obesity [77]. Interestingly, from the Cancer Genome Atlas and the Comparative Toxicogenomics Database, Liu et al. identified some genes that were simultaneously associated with immune-related pathways and BPA exposure [78]. Furthermore, in a group of women with polycystic ovary syndrome, the increased BPA levels were highly correlated with hepatic steatosis and laboratory liver tests, as well as with low-grade chronic inflammation, e.g., the levels of CRP and IL-6 and the degree of spleen enlargement [79].

In terms of possible mechanisms, Federico et al. highlighted the role of BPA-induced oxidative stress in NAFLD patients as there was a proportional relationship between thiobarbituric acid reactive substances (TBARS), a measure of lipid peroxidation, and serum BPA levels in NAFLD patients [80]. Kim et al. reported that the genetic polymorphisms of oxidative stress-related genes, e.g., COX2, EPHX1, CAT and SOD2, could modify the association of urinary BPA with liver function [81]. Specifically, significant associations of BPA with abnormal liver function were observed in individuals with COX2 GG genotype, CAT genotype, CAT CT genotype, SOD2 TT genotype or SOD2 GG genotype. Further, a correlation between BPA levels and liver abnormality was found in elderly people with the polymorphisms of repair genes, e.g., PARP4 G-C-G haplotype, XRCC3 G-A-G haplotype or RAD51 T-A-A haplotype [82]. Using the University of Washington Birth Defects Research Laboratory Fetal Biobank, an epigenome-wide analysis of human fetal liver DNA methylation revealed that BPA levels were positively associated with methylation in CpG islands and negatively associated with the methylation degree in CpG shores, shelves and repetitive regions [83,84]. Furthermore, BPA levels are associated with complex linear and non-monotonic as well as sequence-dependent changes in DNA methylation. This could support the theory that exposure to even low doses of BPA in children might adversely affect liver function later in life [85].

Several studies also investigated bisphenol analogs other than BPA. Li et al. measured 10 bisphenol analogs in serum, blood, and urine samples from 197 HCC patients and 100 non-HCC patients [86]. It was found that levels of bisphenol analogs increased with age in all patients regardless of HCC status, and the levels of some bisphenol analogs were higher in non-HCC patients than HCC patients [86]. A positive correlation was found between GGT and BPAP in the blood of HCC patients. In non-HCC patients, there was a positive correlation between GGT and BPG in sera, between GGT and BPF in blood, and between GGT and BPG and BPAP in urine [86]. Further, a positive correlation was observed between BPZ (or BPAF, BPAP) and ALT in the sera of HCC patients. In non-HCC patients, a positive correlation, although weak, was observed between BPBP (or BPG) and ALT in the sera [86]. Additionally, a weak positive correlation was found between BPB and alpha-fetoprotein, while a weak negative correlation between BPBP and alpha-fetoprotein was found in the urine of HCC patients. In non-HCC patients, there was a weak positive correlation between BPAP and alpha-fetoprotein, as well as between BPF and alpha-fetoprotein in the sera [86]. Ding et al. also showed that bisphenol analogs (BPA, BPS, BPZ, BPAF, BPAP, BPBP, BPPH) have some significant positive correlations with levels of GGT and ALT in HCC patients, especially BPBP levels in bile [87].

Some studies provide evidence of an interrelationship between NAFLD and exposure to bisphenol analogs other than BPA. In a population-based study in Korea, BPS was among the group of investigated EDCs that had the most effects on metabolic syndrome [88]. Peng et al. reported that elevated levels of BPA and BPS were significantly associated with NAFLD in a population-based, cross-sectional study [89]. Further analysis indicated that serum glycolipids might be related to the association. Liang et al. also reported that the BPS levels in sera and urine were associated with NAFLD risks. For each increased unit of BPS level, the NAFLD risk was increased 3.16-fold (serum) and 3.98-fold (urine) [90]. However, in another study, BPS showed a negative association with ALT [91]. Additionally, urine BPA, but not BPS, exhibited a positive correlation with liver standardized uptake value, an indicator of increased glucose metabolism that was associated with inflammation, certain liver diseases or potentially the presence of malignant lesions [92] in male patients who underwent ¹⁸F-fluorodeoxyglucose PET/CT imaging [93].

Wang et al. reported an increased serum BPF level in the NAFLD patients [94], suggesting a potential positive association between BPF levels and NAFLD. In addition, BPF was among the group of investigated EDCs that had the greatest effects on NAFLD as defined by the fatty liver index (≥60) in a study conducted in Korea [88]. Similarly, Wang et al. also showed that BPF exposure was positively correlated with NAFLD severity and triglyceride level in these patients [95]. In a case–control study to determine the association of 12 bisphenol analogs in children using three biological matrices (nails, saliva and urine), it was found that BPF in nails correlated with overweight/obesity [96]. In contrast, the highest detected levels of BPAF in saliva had an inverse association with overweight/obesity. No associations were detected between other bisphenol analogs, including BPA, and overweight/obesity [96]. However, Peng et al. reported that BPF levels were not associated with NAFLD in a population-based, cross-sectional study [89].

Table 1. Selected liver toxicity studies on bisphenol analogs in humans.

Compounds	Data Source/Diseases	#Participants	Age	Years/Period	Liver Effects	Reference
BPA	The Korean National Environmental Health Survey III	3476 adults: 1474 men and 2002 women	~53 years old	2015–2017	Urinary BPA levels are positively associated with the risk of NAFLD. The rate of abnormal ALT was in accordance with the increases in BPA levels.	[62]
BPA	The Korean Elderly Environmental Panel	560 elderly people	Aged 60 or over	2008–2010	Higher urinary BPA concentrations were associated with increased abnormal liver function: significant relationships between urinary BPA and levels of AST, ALT and GGT.	[63]
BPA	Workers in two semiautomatic epoxy resin factories, China	28 participants	38.9 ± 11.3 years old	Not available	Higher BPA correlated with clinically abnormal levels of glutamic-oxaloacetic transaminase and GGT.	[64]
BPA	Northern district of Guizhou Province, China	1006 children	5 to 14 years old	July to August 2018	The correlation between BPA and AST was significant in Bozhou district; the correlation between BPA and direct bilirubin was significant in Huichuan district.	[65]
BPA	Punjab, Pakistan	400 participants	43.9  ±  13.6 years old	Not available	Higher levels of ALT and AST were observed among BPA-positive participants than that of BPA-negative ones.	[66]
BPA	NHANES	1455 US adults	18 to 74 years old	2003–2004	Higher urinary BPA correlated with clinically abnormal levels of the liver enzymes, including lactate dehydrogenase, GTT and alkaline phosphatase.	[67]
BPA	NHANES	2948 US adults	18 to 74 years old	2003–2006	Higher urinary BPA correlated with clinically abnormal levels of the liver enzymes, including alkaline phosphatase and lactate dehydrogenase.	[68]
BPA	NHANES	11,750 adults	Mean age 43.9 years old	2003 to 2016	The increment of BPA positively associated with alkaline phosphatase and total bilirubin, while inversely with albumin.	[69]
BPA	NHANES	2179 adults	Not available	2011 to 2016	A negative association between urinary BPA and serum total protein and albumin.	[70]
BPA	NHANES	2104 US adults	≥18 years old	2003–2008	Levels of urinary BPA were positively associated with metabolic syndrome.	[71]
BPA	NAFLD with or without T2DM in Naples	60 patients and 60 controls	54–57 years old	2016	BPA levels were higher in NAFLD subjects than controls. BPA levels appeared to be higher in non-alcoholic steatohepatitis patients than simple steatosis subjects.	[72]
BPA	NAFLD and HCC in Regione Campania (Southern Italy)	30 NAFLD and 11 HCC	23–80 years old	Not available	The subjects with liver diseases had higher BPA levels in both urine and plasma samples, suggesting an association between BPA exposure and liver health.	[73]
BPA	NHANES	7605 participants (48.4% male)	Mean age 47 years old	2005–2014	The rate of NAFLD and abnormally elevated ALT levels were positively associated with urinary BPA.	[74]
BPA	NHANES	944 adolescents	12–19 years old	2003–2010	Higher levels of BPA were associated with increased risks of suspected NAFLD, but not with elevation of ALT.	[75]
BPA	Obesity and metabolic syndrome (Naples)	76 adult male Caucasian subjects	53.5 ± 5.7 years old	Not available	Plasma BPA levels positively associated with visceral obesity and low-grade inflammation, which are important risk factors of NAFLD.	[76]
BPA	Polycystic ovary syndrome (Naples)	40 with PCOS and 20 healthy age-matched women	27.7 ± 6.8 years old	2009–2011	Increased BPA levels correlated with hepatic steatosis and abnormal liver tests, as well as with chronic inflammation.	[79]
BPA	NAFLD in Naples	32 male patients and 30 controls	44.5 ± 18.3 years old	Between January and October 2017	Plasma BPA, and both urine free and total BPA levels are higher in NAFLD patients. There was a proportionality relationship between TBARS and serum BPA levels.	[80]
BPA	The Korean Elderly Environmental Panel	560 elderly people	Aged 60 or over	2008–2010	The genetic polymorphisms of COX2, EPHX1, CAT and SOD2 modified the association between BPA levels and liver functions.	[81]
BPA	The Korean Elderly Environmental Panel	560 elderly people	Aged 60 or over	2008–2010	There was an association between BPA levels and liver abnormality in elders with the polymorphisms of repair genes.	[82]
BPA	The NIH-funded UW Birth Defects Research Laboratory Fetal Biobank	50 human fetal liver samples	Gestational days 70 to 120	Not available	BPA levels positively correlated with methylation in CpG islands and negatively with that in CpG shores, shelves, and repetitive regions. Further, BPA levels correlated with complex linear and non-monotonic as well as sequence-dependent changes in DNA methylation.	[83]
BPA	The Ewha Birth and Growth Cohort Study	164 children	At 3–5, 7–9 and 10–13 years of age	Between 2001 and 2015	Urinary BPA concentrations at 7–9 years, but not that at 3–5 years, correlated with the serum liver enzymes at 10–13 years of age.	[85]
BPA, BPB, BPF, BPG, BPS, BPZ, BPAF, BPAP, BPBP, BPPH	HCC patients	197 HCC patients and 100 non-HCC patients	Mean age of HCC patients (54 years old), non-HCC (47 years old)	Between 2021 and 2023	There was a positive correlation between GGT and BPAP in the blood of HCC patients. In non-HCC patients, there was a positive correlation between GGT and BPG in sera, between GGT and BPF in blood, and between GGT and BPG and BPAP in urine.	[86]
BPA, BPS, BPZ, BPAF, BPAP, BPBP, BPPH	HCC patients	149 patients with HCC	≥60 (50) 40–60 (78) ≤40 (21)	Between 2021 and 2023	Bisphenol analogs have some significant positive correlations with levels of GGT and ALT, especially BPBP levels in bile.	[87]
Various EDCs	The Korean National Environmental Health Survey Cycle 4	2942 adults	54 years old	2018–2020	BPS was among the investigated EDCs that had the most effects on metabolic syndrome. BPF was among the investigated EDCs that had the greatest effects on NAFLD.	[88]
BPA, BPS, BPF	NHANES	960 participants	≥20 years old	2013–2016	Elevated levels of BPA and BPS, but not BPF, correlated with NAFLD.	[89]
BPS	The Korean National Environmental Health Survey IV	2961 adults	≥19 years old	2018 to 2020	BPS showed a negative association with ALT.	[91]
BPF	NAFLD patients	117 controls; 145 patients	21–76 years old	2018	There were increased serum BPF levels in the NAFLD patients.	[94]

Table 1. Selected liver toxicity studies on bisphenol analogs in humans.

Compounds	Data Source/Diseases	#Participants	Age	Years/Period	Liver Effects	Reference
BPA	The Korean National Environmental Health Survey III	3476 adults: 1474 men and 2002 women	~53 years old	2015–2017	Urinary BPA levels are positively associated with the risk of NAFLD. The rate of abnormal ALT was in accordance with the increases in BPA levels.	[62]
BPA	The Korean Elderly Environmental Panel	560 elderly people	Aged 60 or over	2008–2010	Higher urinary BPA concentrations were associated with increased abnormal liver function: significant relationships between urinary BPA and levels of AST, ALT and GGT.	[63]
BPA	Workers in two semiautomatic epoxy resin factories, China	28 participants	38.9 ± 11.3 years old	Not available	Higher BPA correlated with clinically abnormal levels of glutamic-oxaloacetic transaminase and GGT.	[64]
BPA	Northern district of Guizhou Province, China	1006 children	5 to 14 years old	July to August 2018	The correlation between BPA and AST was significant in Bozhou district; the correlation between BPA and direct bilirubin was significant in Huichuan district.	[65]
BPA	Punjab, Pakistan	400 participants	43.9  ±  13.6 years old	Not available	Higher levels of ALT and AST were observed among BPA-positive participants than that of BPA-negative ones.	[66]
BPA	NHANES	1455 US adults	18 to 74 years old	2003–2004	Higher urinary BPA correlated with clinically abnormal levels of the liver enzymes, including lactate dehydrogenase, GTT and alkaline phosphatase.	[67]
BPA	NHANES	2948 US adults	18 to 74 years old	2003–2006	Higher urinary BPA correlated with clinically abnormal levels of the liver enzymes, including alkaline phosphatase and lactate dehydrogenase.	[68]
BPA	NHANES	11,750 adults	Mean age 43.9 years old	2003 to 2016	The increment of BPA positively associated with alkaline phosphatase and total bilirubin, while inversely with albumin.	[69]
BPA	NHANES	2179 adults	Not available	2011 to 2016	A negative association between urinary BPA and serum total protein and albumin.	[70]
BPA	NHANES	2104 US adults	≥18 years old	2003–2008	Levels of urinary BPA were positively associated with metabolic syndrome.	[71]
BPA	NAFLD with or without T2DM in Naples	60 patients and 60 controls	54–57 years old	2016	BPA levels were higher in NAFLD subjects than controls. BPA levels appeared to be higher in non-alcoholic steatohepatitis patients than simple steatosis subjects.	[72]
BPA	NAFLD and HCC in Regione Campania (Southern Italy)	30 NAFLD and 11 HCC	23–80 years old	Not available	The subjects with liver diseases had higher BPA levels in both urine and plasma samples, suggesting an association between BPA exposure and liver health.	[73]
BPA	NHANES	7605 participants (48.4% male)	Mean age 47 years old	2005–2014	The rate of NAFLD and abnormally elevated ALT levels were positively associated with urinary BPA.	[74]
BPA	NHANES	944 adolescents	12–19 years old	2003–2010	Higher levels of BPA were associated with increased risks of suspected NAFLD, but not with elevation of ALT.	[75]
BPA	Obesity and metabolic syndrome (Naples)	76 adult male Caucasian subjects	53.5 ± 5.7 years old	Not available	Plasma BPA levels positively associated with visceral obesity and low-grade inflammation, which are important risk factors of NAFLD.	[76]
BPA	Polycystic ovary syndrome (Naples)	40 with PCOS and 20 healthy age-matched women	27.7 ± 6.8 years old	2009–2011	Increased BPA levels correlated with hepatic steatosis and abnormal liver tests, as well as with chronic inflammation.	[79]
BPA	NAFLD in Naples	32 male patients and 30 controls	44.5 ± 18.3 years old	Between January and October 2017	Plasma BPA, and both urine free and total BPA levels are higher in NAFLD patients. There was a proportionality relationship between TBARS and serum BPA levels.	[80]
BPA	The Korean Elderly Environmental Panel	560 elderly people	Aged 60 or over	2008–2010	The genetic polymorphisms of COX2, EPHX1, CAT and SOD2 modified the association between BPA levels and liver functions.	[81]
BPA	The Korean Elderly Environmental Panel	560 elderly people	Aged 60 or over	2008–2010	There was an association between BPA levels and liver abnormality in elders with the polymorphisms of repair genes.	[82]
BPA	The NIH-funded UW Birth Defects Research Laboratory Fetal Biobank	50 human fetal liver samples	Gestational days 70 to 120	Not available	BPA levels positively correlated with methylation in CpG islands and negatively with that in CpG shores, shelves, and repetitive regions. Further, BPA levels correlated with complex linear and non-monotonic as well as sequence-dependent changes in DNA methylation.	[83]
BPA	The Ewha Birth and Growth Cohort Study	164 children	At 3–5, 7–9 and 10–13 years of age	Between 2001 and 2015	Urinary BPA concentrations at 7–9 years, but not that at 3–5 years, correlated with the serum liver enzymes at 10–13 years of age.	[85]
BPA, BPB, BPF, BPG, BPS, BPZ, BPAF, BPAP, BPBP, BPPH	HCC patients	197 HCC patients and 100 non-HCC patients	Mean age of HCC patients (54 years old), non-HCC (47 years old)	Between 2021 and 2023	There was a positive correlation between GGT and BPAP in the blood of HCC patients. In non-HCC patients, there was a positive correlation between GGT and BPG in sera, between GGT and BPF in blood, and between GGT and BPG and BPAP in urine.	[86]
BPA, BPS, BPZ, BPAF, BPAP, BPBP, BPPH	HCC patients	149 patients with HCC	≥60 (50) 40–60 (78) ≤40 (21)	Between 2021 and 2023	Bisphenol analogs have some significant positive correlations with levels of GGT and ALT, especially BPBP levels in bile.	[87]
Various EDCs	The Korean National Environmental Health Survey Cycle 4	2942 adults	54 years old	2018–2020	BPS was among the investigated EDCs that had the most effects on metabolic syndrome. BPF was among the investigated EDCs that had the greatest effects on NAFLD.	[88]
BPA, BPS, BPF	NHANES	960 participants	≥20 years old	2013–2016	Elevated levels of BPA and BPS, but not BPF, correlated with NAFLD.	[89]
BPS	The Korean National Environmental Health Survey IV	2961 adults	≥19 years old	2018 to 2020	BPS showed a negative association with ALT.	[91]
BPF	NAFLD patients	117 controls; 145 patients	21–76 years old	2018	There were increased serum BPF levels in the NAFLD patients.	[94]

Taken together, the above review indicates that there is some evidence that exposure to bisphenol analogs may contribute to liver toxicity in humans, which is consistent with a meta-analysis that population exposure to BPA was positively correlated with the risk of NAFLD [97]. Notably, BPA is implicated in NAFLD more than hepatitis B virus as a cause of chronic liver disease globally [98]. Except for two studies focused on males [76,80] and one study on females [79], other identified studies had both males and females, and no sex differences were noted. While the methodology and analysis in these studies were strong, their inherent limitations must be recognized due to their cross-sectional nature. Thus, further research is required, particularly longitudinal studies, to elucidate the link between both prenatal and postnatal exposures to bisphenol analogs and liver toxicity.

3.2. Liver Toxicity of Bisphenol Analogs in Rodents

There are many studies on liver toxicity by BPA in rodents [11], due to their small size, ease of handling, short lifecycles, cost-effectiveness and genetic and physiological similarities to humans. A maximum daily intake of 50 μg/kg of body weight (bw)/day BPA was established by the US Environmental Protection Agency and the European Food Safety Authority (EFSA) in 2009 and 2006, respectively [99]. However, the EFSA has since reduced the safe level of BPA based on new data and refined methodologies to 4 µg/kg of bw/day in 2015 and to 0.2 ng/kg of bw/day in 2023 [99]. Based on the formula for converting doses from human to mice [100], the 4 μg/kg of bw/day BPA was equivalent to an oral dose of 48 μg/kg in mice. Therefore, focuses of this section are placed on studies of bisphenol analogs at environmentally relevant levels, and studies of bisphenol analogs at doses above 50 μg/kg are excluded. This is important as it has been argued that the BPA toxicological effects observed in rodents might overpredict the possible outcomes in humans [101,102].

3.2.1. Adult Exposure in Mice

Among the identified studies on bisphenol analogs in mice following adult exposure (Table 2), one of the three strains, e.g., C57BL/6, CD-1 and Swiss albino mice, was employed in most studies, with some of these studies using both male and female mice. The starting ages of mice were between 3 and 12 weeks, and strictly speaking, some of these studies might have included a period of developmental stage. The exposure time ranged from once/day for 5 days to 6 months. Some studies had more than one dose under the 50 μg/kg level. When adult C57BL/6 mice were orally exposed to 5 and 50 μg/kg of BPA in gelatin pellets for 28 days, there were some changes in gene expression in the liver [103]. In males, increased expression of sterol regulatory element-binding transcription factor 1 (SREBF1), a gene that controls cholesterol homeostasis and lipid metabolism, was observed in the 5 μg/kg dose group. In females, decreased expressions of fatty acid synthase (FASN, an enzyme that synthesizes fatty acids from acetyl-CoA and other precursors), acetyl-CoA carboxylase (ACC, a biotin-containing enzyme that catalyzes the carboxylation of acetyl-CoA to malonyl-CoA), CYP2B10 and UGT1A1 were observed in the 50 μg/kg dose group, while HMG-CoA reductase (HMGCR, an enzyme that regulates the production of cholesterol and other isoprenoids) and CYP1A1 were up- and downregulated, respectively, in the 5 μg/kg dose group [103]. Li et al. also reported that BPA exposure (50 μg/kg) though diet increased the expression of hepatic HMGCR and sterol regulatory element binding proteins (SREBP)-2 [104]. Lin et al. showed that BPA-induced hepatic steatosis and lipid accumulation correlated with an increased expression of genes involved in de novo lipogenesis. Further, BPA induced a decrease in miR-192 that might enhance the expression of SREBF1 and lead to increases in de novo lipogenesis [105].

Consistent with increased fatty acid and cholesterol biosynthesis, as discussed above, a transcriptomic study in male CD-1 mice exposed to BPA (5 and 50 μg/kg/day) for 28 days through food consumption also revealed a specific impact on the hepatic transcriptome, particularly on genes of lipid synthesis [106]. BPA strongly induced the expression of patatin-like phospholipase domain containing 3 (PNPLA3), a gene related to the severity of nonalcoholic steatohepatitis [107]. The expression of thyroid hormone responsive Spot14 homolog (THRSP-SPOT14), a small nuclear protein that responds rapidly to thyroid hormone to increase lipogenesis in human hepatocytes, was also increased [108]. The expressions of peroxisome proliferator-activated receptor (PPAR)-γ and liver X receptor (LXR) α were also increased in the liver of mice exposed to BPA at 50 μg/kg, while that of PPAR-α was decreased in mice exposed to 5 μg BPA/kg/day [106]. PPAR consists of three different subtypes (α, β/δ, γ), all of which play important roles in regulating lipid and glucose metabolism in different tissues, including the liver [109]. LXRs play complex roles in liver diseases and are important regulators of cholesterol, fatty acid, and glucose homeostasis. LXRα is expressed in several tissues, with liver having the highest expression. LXRα knockout mice are healthy on a low-cholesterol diet. However, they develop enlarged fatty livers as well as exhibiting degeneration of liver cells, high cholesterol levels in liver and impaired liver function on a high-cholesterol diet [110]. Gao et al. also reported the induction of LXRα in the liver tissues of female C57BL/6 mice following exposure to BPA (50 μg/kg) through drinking water [111].

The gut–liver axis plays an important role in liver toxicity [112], including the onset of NAFLD. Dietary BPA exposure in male CD-1 mice at 50 μg/kg bw/day for 24 weeks induced hepatic steatosis and promoted dysbiosis and activated the gut–liver axis [113]. The abundance of Proteobacteria phylum, a marker of dysbiosis, was increased, whereas the abundance of Akkermansia genus, a gut microbe associated with increased gut barrier functions and anti-inflammatory factors, was markedly decreased. BPA increased the expression of TLR4 and phosphorylation of NF-κB in the liver as well as the production of inflammatory cytokines, including IL-1β, IL-18, TNF-α and IL-6 [113]. Hong et al. also reported that the abundance of Proteobacteria and the Firmicutes/Bacteroidetes ratio were increased by BPA, while the abundances of genera Bacteroides, Parabacteroides and Akkermansia, which are associated with bile acid metabolism, were reduced [114,115]. In addition, BPA inhibited the activation of special receptors such as farnesoid X receptor and Takeda G protein-coupled receptor 5 in the ileum and liver, and these receptors help regulate the homeostasis of bile acid, glucose and energy [115].

In the identified adult mouse studies, some have focused on bisphenol analogs other than BPA (Table 2). Chi et al. [116] reported that long-term BPS exposure for 154 days at about 1.5 μg/day increased liver weight and induced dyslipidemia, obesity, hepatic lipid accumulation, gut dysbiosis and intestinal lesions in female mice. Similar to BPA, the induction of LXRα in mice following exposure to BPS was observed [111]. Xie et al. showed that BPS exposure (50 μg/kg) promoted the progression of NAFLD in high-fat diet (HFD)-treated male mice, manifesting as elevated serum ALT and AST levels and more and larger lipid droplets in liver tissues as well as increased liver/body weight ratio [117]. Liang et al. also showed that mice had lipid accumulation in the liver after BPS exposure for 20 weeks at a physiological relevant dose [90]. Mornagui et al. reported that BPS exposure in drinking water at 25 and 50 μg/kg for 10 weeks induced hypertriglyceridemia, liver injury and histopathological changes, including inflammation, hepatocyte necrosis and steatosis [118]. However, similar BPS exposure in a male mouse study showed that BPS stimulated glycogenolysis and/or gluconeogenesis in the liver and increased the expressions of glucose 6-phosphatase and phosphoenolpyruvate carboxykinase, but did not affect pro-inflammatory markers [119]. A metabolomics analysis in male mice that were exposed to BPA, BPF, and BPAF at a dose of 50 μg/kg bw/day for eight consecutive weeks under HFD also showed aberrant fatty acid and lipid metabolism in the liver [120], but BPF and BPAF exposure reduced lipid accumulation in the liver of HFD-fed mice by lowering glyceride and cholesterol levels. However, BPF elevated plasma AST levels. Furthermore, significant increases in both absolute and relative liver weights were observed in all treated groups except for BPA [120].

Bisphenol analogs in food and beverages account for most daily human exposure. Among the identified adult mouse studies (Table 2), many studies used oral exposure, e.g., diet, drinking water and gavage. However, a couple of studies employed intraperitoneal injection [121,122]. Intraperitoneal administration is a justifiable route for toxicological and proof-of-concept studies in which the goal is to evaluate the effect(s) of target engagement rather than toxicokinetics. They were included mainly for the purpose of comparison. However, it should be noted that intraperitoneal administration may bypass the first-pass metabolism from the gut, although the toxicant is still subject to first-pass metabolism by the liver. Al-Griw et al. [121] showed that intraperitoneal BPA treatment in Swiss albino mice at 50 μg/kg twice a week for 6 weeks produced increases in the body and liver weights in both sexes. Such treatment also increased liver damage markers ALT, ALP and GGT. It also induced liver histopathological changes, including higher apoptotic indices in both sexes [121]. Moon et al. reported that intraperitoneal BPA treatment at 50 μg/kg/day for 5 days in male C57BL/6 mice altered the structure of hepatic mitochondria [122]. The hepatic levels of malondialdehyde, a naturally occurring product of lipid peroxidation, were increased after BPA treatment, while the expression of glutathione peroxidase 3 was decreased [122]. In addition, Wang et al. have shown that exposure to BPF at 50 μg/kg/day via subcutaneous injection for 30 days induced alterations that were consistent with NAFLD in mice, such as lipid droplet accumulation and increased levels of triglycerides and fatty acids in the liver [94]. Additionally, altered interstitial structures with loose connective tissues were found in the liver. The cholesterol, however, was not significantly changed [94].

Taken together, in agreement with possibly increased NAFLD risk associated with BPA exposure in humans, the liver toxicological effects following bisphenol analog exposure in adult mice included increases in the liver weights [103,105,113,114,121], changes in liver gene expression [103,104,106], increases in the liver damage markers (e.g., ALT, alkaline phosphatase and GGT), hepatic steatosis and disturbed liver fatty acid and cholesterol metabolism [104,105,115,123,124,125], accumulations of cholesteryl esters and of triglycerides [106,125], altered bile acid metabolism [115], liver inflammation [113,124,126] and liver pathological and histopathological changes [105,121,123]. Additionally, BPA could exacerbate HFD-induced alterations of the lipid metabolism, liver triglycerides accumulation and mitochondrial dysfunction by increasing oxidative stress and reducing antioxidant defense [127]. In addition to the gut–liver axis, hepatic nuclear receptor activation is one of the mechanisms mediating metabolic effects of bisphenol analogs. Further, oxidative stress is also an important mechanism for the association between exposure to bisphenol analogs and liver damage. Finally, some sex-dependent effects were noted, e.g., more liver toxicity was observed in males [103,121].

There are also some liver toxicological effects associated with bisphenol analog exposure that do not fit in the overall conclusion listed above. For example, BPA might promote hyperuricemia via activating xanthine oxidase. In male CD-1 mice, BPA exposure at 50 μg/kg increased the level of uric acid in both serum and liver with enhanced activity of liver xanthine oxidase [128]. When male C57BL/6 mice were orally treated with BPA (1, 10 and 50 μg/kg) for 35 days by gavage, there were significant decreases, instead of increases, in liver weight in all the dose groups [123], and no significant differences were found at all doses for IL-1β, phospholipase A2, AST and ALT. However, there were significant differences for pyruvate dehydrogenase (decrease), lactate dehydrogenase (decrease), fatty acyl-CoA synthetase (increase) and carnitine transferase-1 (decrease). Wang et al. also showed that BPA exposure could decrease the body weights in mice as well as their liver weights, but increased the levels of oxidative stress indicators and pro-inflammatory cytokines [126]. On the other hand, antioxidant indicators were reduced [126]. Perreault et al. reported that exposure to BPA at ∼50 µg/kg/day suppressed hepatic glucokinase activity in the 6-month-old male C57BL/6 mice [129]. Yang et al. showed that BPA exposure could also dysregulate autophagy in livers in addition to increasing hepatic lipid accumulation [130]. Yu et al. reported that the administration of BPF in mice at 40 μg/kg by gavage once daily for 30 consecutive days markedly increased the levels of kynurenine in the liver [131]. Further, the expression of 2,3-dioxygenase and kynurenine 3-monooxygenase, the key enzymes in the kynurenine metabolic pathway, were significantly increased in the liver, suggesting a possible depression-like change along the “liver–brain” axis. Zhang et al. showed that BPF exposure increased body weight gain in mice but had no effects on liver weights; however, it elicited some ballooning degeneration in the liver [132].

3.2.2. Developmental Exposure in Mice

Developmental exposure refers to the impact of environmental chemicals or other agents on the developing organism, including the prenatal, postnatal and juvenile periods, during its growth and development. A major concern is the profound and permanent effects that developmental exposure to bisphenol analogs can have on the future wellbeing of offspring, e.g., the developmental origins of health and disease hypothesis. Table 3 summarized liver toxicity studies on bisphenol analogs in mice following developmental exposure. One standout toxicity endpoint was that there existed a linkage between early-life exposure to BPA and the development of hepatic tumors [133]. Similar to BPA exposure in adult mice, changes in the liver weights following developmental exposure were also a major toxicity endpoint. In fact, increased liver weight in mice from the two-generation study at 0, 0.018 or 0.18 ppm (~0, 3 or 30 µg BPA/kg/day) reported by Tyl et al. [134] was chosen for hazard characterization by EFSA. van Esterik et al. also reported that adult male offspring showed dose-dependent increases in body and liver weights when mice were exposed during gestation (3 weeks) and lactation (3 weeks) via maternal feed to BPA at concentrations of 0.017, 0.056 and 0.17 mg/kg, which corresponded to 3, 10 and 30 μg/kg bw/day [135]. However, the livers of males did not exhibit any adverse effects histopathologically, including lipid accumulation. In contrast, female offspring showed a dose-related decrease in liver weight [135]. Nishizawa et al. also reported no significant changes in the protein levels of cytochrome P450 1A1 and the glutathione S-transferase Ya subunit in the livers of late-stage embryos when murine embryos were exposed in utero to BPA (0.02, 2 μg/kg/day) orally [136].

Similar to adult BPA exposure, changes in liver gene expression and disturbed liver fatty acid and cholesterol metabolism were observed following developmental BPA exposure in mice. Diamante et al. reported that prenatal exposure to BPA at 5 μg/kg/day in both male and female mouse offspring dysregulated the expression of liver genes in the pathways of oxidative phosphorylation, PPAR signaling and fatty acid metabolism, as well as the gut microbiota in an age- and sex-dependent manner [137]. Another developmental study by Long et al. showed that BPA exposure at 1 µg/kg during gestation affected the expression of genes related to lipid metabolism, leading to a sex-dependent hepatic lipid accumulation in offspring, and both male and female mice displayed fatty liver [137]. Additionally, BPA-exposed male offspring had lipid accumulation and dysregulated glucose metabolism, and also gained more weight and had higher hepatic triglyceride levels when subjected to HFD [138]. Ke et al. also showed that lactational and postnatal exposure of male mice to BPA (0.5 μg BPA/kg/day) for 10 months increased the hepatic accumulation of triglycerides and cholesterol [139]. In addition, the liver cells exhibited increased expressions of the genes related to lipid synthesis and SREBF1 and SREBF2, and decreased DNA methylation of SREBF1 and SREBF2 [139]. Susiarjo et al. reported that developmental exposure to 10 µg/kg/day of BPA significantly altered 13 metabolites in male mouse fetal liver [140]. Further, the fetal liver from the BPA group had reduced expression of Shp, a corepressor that inhibits Lrh1 or Hnf4-α.

Table 2. Selected liver toxicity studies on bisphenol analogs in mice—adult exposure.

Compounds	Model/Diseases	Exposure Starting Age	Exposure Window/Time	Dose/Concentration	Routes of Administration	Diet	Liver Effects	Reference
BPF	Male C57BL/6 mice	8 weeks old	30 days	50 μg/kg bw/day	Subcutaneous injection	Phytoestrogen-free diet	BPF-induced alterations were consistent with NAFLD in mice, such as lipid droplet accumulation and increased levels of triglycerides and fatty acids.	[94]
BPA	Male and female C57BL/6 mice	8–12 weeks old	4 weeks (28 days)	5 and 50 μg/kg bw/day	Oral (in gelatin pellets)	Regular chow (soy protein free diets)	BPA increased relative liver weight in males at the 50 μg/kg dose and the expression of SREBF1 at the 5 μg/kg dose; in females, BPA decreased expression of FASN, ACC, CYP2b10, and UGT1a1 at the 50 μg/kg dose, while HMGCR and CYP1a1 were up- and downregulated, respectively, at the 5 μg/kg dose.	[103]
BPA	Male C57BL/6 mice	7 weeks old	16 weeks	50 μg/kg/day	Oral (Diet: 0.5 mg/kg BPA)	MD12062 diet and BPA diet	BPA increased hepatic cholesterol content and the expression of HMGCR and SREBP-2. BPA decreased the DNA methylation levels of SREBP-2 and increased the expression levels of SREBP-1c and stearoyl-CoA desaturase 1 in the liver.	[104]
BPA	Male C57BL/6 mice	3 weeks old	90 days	50 μg/kg bw/day	Gavage	Likely standard chow (not mentioned)	BPA increased liver weight and triglyceride. BPA-induced hepatic steatosis and lipid accumulation were associated with increased expressions of genes in de novo lipogenesis. A diffuse vacuolization phenotype was observed in the liver, due to the accumulation of lipid droplets.	[105]
BPA	Male CD-1 mice	6 weeks old	4 weeks (28 days)	5 and 50 μg/kg bw/day	Oral (Diet)	Standard diet as the control	BPA had a strong impact on liver transcriptome, particularly on genes in lipid synthesis, including genes involved in de novo fatty acid synthesis (ACLY, ACACA, ACACB, FASN) and elongation (ELOVL6), in triglyceride synthesis (GPAT) and cholesterol synthesis (MVD, LSS). BPA also upregulated LXR mRNA levels and affected liver lipid metabolism.	[106]
BPA, BPS	Female C57BL/6 mice	5 weeks old	10 weeks	50 μg/kg bw/day	Drinking water (0.25 mg/L)	Likely standard chow (not mentioned)	Induction of LXRα by BPA and BPS was observed, which highly correlated with the aberrant metabolism profiles in liver tissues.	[111]
BPA	Male CD-1 mice	6 weeks old	24 weeks (6 months)	~50 μg/kg bw/day	Oral (Diet: 0.5 mg/kg BPA)	MD12062 normal diet and BPA diet	BPA increased liver weight, lipid contents and fat accumulation and the expression of inflammatory cytokines. The diversity of gut microbiota was reduced.	[113]
BPA	Male CD-1 mice	6 weeks old	24 weeks (6 months)	~50 μg/kg bw/day	Oral (Diet: 0.5 mg/kg BPA)	Normal diet and BPA diet	BPA increased liver weight, the relative abundance of Proteobacteria and Firmicutes/Bacteroidetes ratio while Akkermansia was reduced.	[114]
BPA	Male CD-1 mice	6 weeks old	24 weeks (6 months)	50 μg/kg bw/day	Oral (Diet: 0.5 mg/kg BPA)	A standard diet (AIN93-G) and BPA diet	BPA induced hepatic steatosis and reduced the relative abundance of Bacteroides, Parabacteroides and Akkermansia.	[115]
BPS	Female C57BL/6J mice	3 weeks old	22 weeks (154 days)	50–100 μg/kg bw/day	Oral (Diet: 0.5 mg/kg BPS)	Normal chow diet and BPS diet	BPS increased liver weight and caused dyslipidemia, obesity, hepatic lipid accumulation, intestinal lesions and dysbiosis.	[116]
BPS	Male C57BL/6 mice	5 weeks old	16 weeks	50 μg/kg bw/day	Drinking water	High-fat diet	BPS promoted the progression of NAFLD, which was reflected by the increased liver/body weight ratio, elevated serum ALT and AST levels, and more and larger lipid droplets in liver tissues.	[117]
BPS	Male Swiss mice	NA	10 weeks	25 and 50 μg/kg bw/day	Drinking water	Standard diet	BPS induced hypertriglyceridemia, increased liver injury markers, and initiated histopathological changes.	[118]
BPS	Male mice	NA	10 weeks	25 and 50 μg/kg	Drinking water	Standard diet	BPS exposure increased the expression of G6Pase and PEPCK in the liver. BPS also stimulated glycogenolysis and/or gluconeogenesis.	[119]
BPA, BPF, BPAF	Male C57BL/6 mice	Starting at eight-weeks old	8 weeks	50 μg/kg bw/day	Drinking water	High-fat diet (HFD)	BPF and BPAF reduced lipid accumulation in HFD mouse liver by lowering glyceride and cholesterol levels. An increase in both absolute and relative liver weights was observed in all treated groups except for BPA. BPF also elevated plasma AST levels.	[120]
BPA	Swiss albino mice (Male and female)	4.5 weeks old	6 weeks	50 μg/kg bw/day (twice a week)	Intraperitoneally	Likely standard chow (not mentioned)	In both sexes, BPA produced increases in the liver weights and the levels of ALT, ALP and GGT. It also induced liver histopathological changes. More effects were observed in males.	[121]
BPA	Male C57BL/6 mice	4 weeks old	Once/day for 5 days	50 μg/kg bw/day	Intraperitoneally	Likely standard chow (not mentioned)	BPA treatment impaired the structure of the hepatic mitochondria. The hepatic levels of malondialdehyde were increased, while the expression of glutathione peroxidase 3 was decreased.	[122]
BPA	Male C57BL/6 mice	6 weeks old	5 weeks (35 days)	1.0, 10 and 50 μg/ kg bw/day	Gavage	Likely standard chow (not mentioned)	No significant differences were found for IL-1 beta, phospholipase A2, AST, and ALT; however, there were significant differences for pyruvate dehydrogenase (decrease), LDH (decrease), fatty acyl-CoA synthetase (increase), and carnitine transferase-1 (decrease).	[123]
BPA	Male CD-1 mice	6 weeks old	8 weeks	5 and 50 μg/kg bw/day	Oral (Diet: 0.05 and 0.5 mg/kg)	Standard diet as the control	BPA increased liver fat contents, accompanied by more pro-inflammatory M1 Kupffer cells and enhanced secretion of inflammatory cytokines.	[124]
BPA	Male CD-1 mice	6 weeks old	8 months	5 and 50 μg/kg bw/day	Drinking water	A standard diet (A04, from SAFE Diet, Augy, France)	Consistent with the hypercholesterolemia, BPA induced hepatic overexpression of key genes involved in cholesterol biosynthesis, namely, HMGCR.	[125]
BPA	Male CD-1 mice	3-week-old	10 weeks	50 μg/kg bw/day	Drinking water	Standard rodent chow	BPA decreased the body weights as well as the liver weights. The levels of oxidative stress indicators and pro-inflammatory cytokines were increased. Antioxidant indicators were reduced.	[126]
BPA	Male C57BL/6 mice	6 weeks old	3 weeks	50 μg/kg bw/day	Oral	High-fat diet (HFD)	BPA augmented HFD-induced alteration of lipid metabolism, liver triglyceride accumulation and mitochondrial dysfunction by increasing oxidative stress and reducing antioxidant defense.	[127]
BPA	Male C57BL/6 mice	6 months	2 weeks	50 μg/kg bw/day	Drinking water (1.75 mM BPA)	Likely standard chow (not mentioned)	BPA suppressed hepatic glucokinase activity.	[129]
BPA	Male CD-1 mice	6 weeks old	8 weeks	5 and 50 μg/kg bw/day	Oral (Diet)	Standard diet	BPA increased hepatic lipid accumulation and dysregulated the process of autophagy in livers.	[130]
BPF	Male C57BL/6J mice	6 weeks old	30 consecutive days	40 μg/kg b.w./day	Gavage	Likely standard chow (not mentioned)	BPF increased kynurenine level in the liver and the expression of 2,3-dioxygenase and kynurenine 3-monooxygenase.	[131]
BPF	Male C57BL/6J mice	5–6 weeks	30 days	50 μg/kg/day	Gavage	Diet did not contain alfalfa or soybean meal	BPF increased body weight gain but had no effects on liver weights; however, it elicited some ballooning degeneration in liver.	[132]

Abbreviations: ACACA, acetyl-CoA carboxylase alpha; ACACB, acetyl-CoA carboxylase beta; ACLY, ATP citrate lyase; ALP, alkaline phosphatase; ELOVL6, long-chain FA elongase 6; FASN, fatty acid synthase; GPAT, glycerol-3-phosphate acyltransferase; HMGCR, 3-hydroxy-3-methylglutaryl coenzyme A reductase; LDH, lactate dehydrogenase; LSS, lanosterol synthase; MVD, mevalonate (diphospho) decarboxylase.

Table 2. Selected liver toxicity studies on bisphenol analogs in mice—adult exposure.

Compounds	Model/Diseases	Exposure Starting Age	Exposure Window/Time	Dose/Concentration	Routes of Administration	Diet	Liver Effects	Reference
BPF	Male C57BL/6 mice	8 weeks old	30 days	50 μg/kg bw/day	Subcutaneous injection	Phytoestrogen-free diet	BPF-induced alterations were consistent with NAFLD in mice, such as lipid droplet accumulation and increased levels of triglycerides and fatty acids.	[94]
BPA	Male and female C57BL/6 mice	8–12 weeks old	4 weeks (28 days)	5 and 50 μg/kg bw/day	Oral (in gelatin pellets)	Regular chow (soy protein free diets)	BPA increased relative liver weight in males at the 50 μg/kg dose and the expression of SREBF1 at the 5 μg/kg dose; in females, BPA decreased expression of FASN, ACC, CYP2b10, and UGT1a1 at the 50 μg/kg dose, while HMGCR and CYP1a1 were up- and downregulated, respectively, at the 5 μg/kg dose.	[103]
BPA	Male C57BL/6 mice	7 weeks old	16 weeks	50 μg/kg/day	Oral (Diet: 0.5 mg/kg BPA)	MD12062 diet and BPA diet	BPA increased hepatic cholesterol content and the expression of HMGCR and SREBP-2. BPA decreased the DNA methylation levels of SREBP-2 and increased the expression levels of SREBP-1c and stearoyl-CoA desaturase 1 in the liver.	[104]
BPA	Male C57BL/6 mice	3 weeks old	90 days	50 μg/kg bw/day	Gavage	Likely standard chow (not mentioned)	BPA increased liver weight and triglyceride. BPA-induced hepatic steatosis and lipid accumulation were associated with increased expressions of genes in de novo lipogenesis. A diffuse vacuolization phenotype was observed in the liver, due to the accumulation of lipid droplets.	[105]
BPA	Male CD-1 mice	6 weeks old	4 weeks (28 days)	5 and 50 μg/kg bw/day	Oral (Diet)	Standard diet as the control	BPA had a strong impact on liver transcriptome, particularly on genes in lipid synthesis, including genes involved in de novo fatty acid synthesis (ACLY, ACACA, ACACB, FASN) and elongation (ELOVL6), in triglyceride synthesis (GPAT) and cholesterol synthesis (MVD, LSS). BPA also upregulated LXR mRNA levels and affected liver lipid metabolism.	[106]
BPA, BPS	Female C57BL/6 mice	5 weeks old	10 weeks	50 μg/kg bw/day	Drinking water (0.25 mg/L)	Likely standard chow (not mentioned)	Induction of LXRα by BPA and BPS was observed, which highly correlated with the aberrant metabolism profiles in liver tissues.	[111]
BPA	Male CD-1 mice	6 weeks old	24 weeks (6 months)	~50 μg/kg bw/day	Oral (Diet: 0.5 mg/kg BPA)	MD12062 normal diet and BPA diet	BPA increased liver weight, lipid contents and fat accumulation and the expression of inflammatory cytokines. The diversity of gut microbiota was reduced.	[113]
BPA	Male CD-1 mice	6 weeks old	24 weeks (6 months)	~50 μg/kg bw/day	Oral (Diet: 0.5 mg/kg BPA)	Normal diet and BPA diet	BPA increased liver weight, the relative abundance of Proteobacteria and Firmicutes/Bacteroidetes ratio while Akkermansia was reduced.	[114]
BPA	Male CD-1 mice	6 weeks old	24 weeks (6 months)	50 μg/kg bw/day	Oral (Diet: 0.5 mg/kg BPA)	A standard diet (AIN93-G) and BPA diet	BPA induced hepatic steatosis and reduced the relative abundance of Bacteroides, Parabacteroides and Akkermansia.	[115]
BPS	Female C57BL/6J mice	3 weeks old	22 weeks (154 days)	50–100 μg/kg bw/day	Oral (Diet: 0.5 mg/kg BPS)	Normal chow diet and BPS diet	BPS increased liver weight and caused dyslipidemia, obesity, hepatic lipid accumulation, intestinal lesions and dysbiosis.	[116]
BPS	Male C57BL/6 mice	5 weeks old	16 weeks	50 μg/kg bw/day	Drinking water	High-fat diet	BPS promoted the progression of NAFLD, which was reflected by the increased liver/body weight ratio, elevated serum ALT and AST levels, and more and larger lipid droplets in liver tissues.	[117]
BPS	Male Swiss mice	NA	10 weeks	25 and 50 μg/kg bw/day	Drinking water	Standard diet	BPS induced hypertriglyceridemia, increased liver injury markers, and initiated histopathological changes.	[118]
BPS	Male mice	NA	10 weeks	25 and 50 μg/kg	Drinking water	Standard diet	BPS exposure increased the expression of G6Pase and PEPCK in the liver. BPS also stimulated glycogenolysis and/or gluconeogenesis.	[119]
BPA, BPF, BPAF	Male C57BL/6 mice	Starting at eight-weeks old	8 weeks	50 μg/kg bw/day	Drinking water	High-fat diet (HFD)	BPF and BPAF reduced lipid accumulation in HFD mouse liver by lowering glyceride and cholesterol levels. An increase in both absolute and relative liver weights was observed in all treated groups except for BPA. BPF also elevated plasma AST levels.	[120]
BPA	Swiss albino mice (Male and female)	4.5 weeks old	6 weeks	50 μg/kg bw/day (twice a week)	Intraperitoneally	Likely standard chow (not mentioned)	In both sexes, BPA produced increases in the liver weights and the levels of ALT, ALP and GGT. It also induced liver histopathological changes. More effects were observed in males.	[121]
BPA	Male C57BL/6 mice	4 weeks old	Once/day for 5 days	50 μg/kg bw/day	Intraperitoneally	Likely standard chow (not mentioned)	BPA treatment impaired the structure of the hepatic mitochondria. The hepatic levels of malondialdehyde were increased, while the expression of glutathione peroxidase 3 was decreased.	[122]
BPA	Male C57BL/6 mice	6 weeks old	5 weeks (35 days)	1.0, 10 and 50 μg/ kg bw/day	Gavage	Likely standard chow (not mentioned)	No significant differences were found for IL-1 beta, phospholipase A2, AST, and ALT; however, there were significant differences for pyruvate dehydrogenase (decrease), LDH (decrease), fatty acyl-CoA synthetase (increase), and carnitine transferase-1 (decrease).	[123]
BPA	Male CD-1 mice	6 weeks old	8 weeks	5 and 50 μg/kg bw/day	Oral (Diet: 0.05 and 0.5 mg/kg)	Standard diet as the control	BPA increased liver fat contents, accompanied by more pro-inflammatory M1 Kupffer cells and enhanced secretion of inflammatory cytokines.	[124]
BPA	Male CD-1 mice	6 weeks old	8 months	5 and 50 μg/kg bw/day	Drinking water	A standard diet (A04, from SAFE Diet, Augy, France)	Consistent with the hypercholesterolemia, BPA induced hepatic overexpression of key genes involved in cholesterol biosynthesis, namely, HMGCR.	[125]
BPA	Male CD-1 mice	3-week-old	10 weeks	50 μg/kg bw/day	Drinking water	Standard rodent chow	BPA decreased the body weights as well as the liver weights. The levels of oxidative stress indicators and pro-inflammatory cytokines were increased. Antioxidant indicators were reduced.	[126]
BPA	Male C57BL/6 mice	6 weeks old	3 weeks	50 μg/kg bw/day	Oral	High-fat diet (HFD)	BPA augmented HFD-induced alteration of lipid metabolism, liver triglyceride accumulation and mitochondrial dysfunction by increasing oxidative stress and reducing antioxidant defense.	[127]
BPA	Male C57BL/6 mice	6 months	2 weeks	50 μg/kg bw/day	Drinking water (1.75 mM BPA)	Likely standard chow (not mentioned)	BPA suppressed hepatic glucokinase activity.	[129]
BPA	Male CD-1 mice	6 weeks old	8 weeks	5 and 50 μg/kg bw/day	Oral (Diet)	Standard diet	BPA increased hepatic lipid accumulation and dysregulated the process of autophagy in livers.	[130]
BPF	Male C57BL/6J mice	6 weeks old	30 consecutive days	40 μg/kg b.w./day	Gavage	Likely standard chow (not mentioned)	BPF increased kynurenine level in the liver and the expression of 2,3-dioxygenase and kynurenine 3-monooxygenase.	[131]
BPF	Male C57BL/6J mice	5–6 weeks	30 days	50 μg/kg/day	Gavage	Diet did not contain alfalfa or soybean meal	BPF increased body weight gain but had no effects on liver weights; however, it elicited some ballooning degeneration in liver.	[132]

Abbreviations: ACACA, acetyl-CoA carboxylase alpha; ACACB, acetyl-CoA carboxylase beta; ACLY, ATP citrate lyase; ALP, alkaline phosphatase; ELOVL6, long-chain FA elongase 6; FASN, fatty acid synthase; GPAT, glycerol-3-phosphate acyltransferase; HMGCR, 3-hydroxy-3-methylglutaryl coenzyme A reductase; LDH, lactate dehydrogenase; LSS, lanosterol synthase; MVD, mevalonate (diphospho) decarboxylase.

Several studies have demonstrated that developmental exposure to BPA induced changes in liver DNA methylation, a key epigenetic mechanism that can have lasting effects on the genome [84]. Anderson et al. found epigenetic alterations in liver tissues from female mouse offspring (10 months old) following perinatal BPA exposure [141]. Further analysis identified an enrichment of significant differentially methylated regions in metabolic pathways. Kim et al. also found that offspring maternally exposed to BPA during gestation and lactation had alterations of the mouse methylome in the liver [142]. Signal transducer and activator of transcription 3 (STAT3), a transcription factor, plays an important role in liver injury and regeneration, hepatic inflammation and the development of HCC [143]. Interestingly, STAT3 exhibited a dose-dependent change in DNA methylation in BPA-exposed mice [144]. Further analysis revealed that the metabolic consequences in the liver were associated with BPA-induced hypermethylation of the neuronal signaling pathways because they were linked to energy regulation and metabolic function [145].

In addition to oral administration of BPA, other routes of exposure have also been employed (Table 3). Using Alzet osmotic pumps implanted subcutaneously, Cabaton et al. showed that BPA at 0.025, 0.25 or 25 µg/kg bw/day disrupted global metabolism, e.g., energy metabolism and brain function, in perinatally exposed male offspring [146]. Esplugas et al. also reported that neonatal exposure to BPA at 25 μg/kg bw subcutaneously in male C57BL/6J mice induced liver damage evidenced by oxidative stress [147]. Aberrant retinoid metabolism such as decreases in retinoic acid receptor signaling and liver retinoids are implicated in numerous diseases of the liver, including HCC and NAFLD [148]. When male mice were exposed in utero to BPA following maternal subcutaneous doses of 10 μg/kg bw/day during gestational days 9–16, retinoid concentrations and the expression of key genes in the retinoid system were altered in the liver at postnatal day (PND) 30 [149]. García-Arevalo et al. reported that gestational exposure to BPA subcutaneously in mice perturbed the cytokine balance and increased the expression of the PPAR-γ gene in the liver and the levels of non-esterified fatty acids, as well as adipogenesis and lipid accumulation in the adipose tissue and liver [150]. Shimpi et al. also showed that BPA exposure at 25 μg/kg/day during pregnancy using osmotic minipumps and postnatally through drinking water in mice induced lipid accumulation in offspring liver, which might be attributed to the hypomethylation of lipogenic genes [151]. However, El Hamrani et al. found no structural modification and hepatic microvesicular steatosis of the liver and no changes in lipid composition in male offspring at 8 weeks of age when dams were injected with 20 μg/kg/day of BPA intraperitoneally during gestation and lactation [152].

In the identified developmental mouse studies, some have focused on bisphenol analogs other than BPA (Table 3). Although no changes in the liver weight were observed, life-long BPS exposure in mice at 1.5 μg/kg bw/day increased hepatic triglyceride content and changed gene expression, including in those that were involved in protein translation and complement regulation following HFD challenge [153]. Additionally, such exposure altered the hepatic DNA methylation pattern, e.g., hypomethylation in autosomes and hypermethylation in sex chromosomes of male mice [154]. When the liver transcriptome and methylome were further compared, it was found that the biological pathways disrupted by BPS were mainly related to metabolism, e.g., energy metabolism, detoxification, and protein and steroid metabolism [155]. Perinatal BPS exposure also subcutaneously induced steatosis, with hepatocytes exhibiting vacuolation, cytoplasmic loosening and hypochromasia as well as granular degeneration and necrosis in male C57BL/6 offspring [156]. In addition, Ivry Del Moral et al. also showed that perinatal and chronic exposure to low doses of BPS results in obesogenic effects in male C57BL/6 mice, particularly when combined with HFD [157]. While many studies suggested that perinatal BPS exposure showed greater metabolic and microbial disturbances in males, a study reported greater effects in females [158]. When ICR mice were exposed to 5 μg/kg bw/day of BPS through drinking water from gestational day one to the weaning of the pups, there were no changes in liver weight and liver organ index as well as no obvious liver histopathology in male offspring. However, liver weight was increased in females. While no significant changes were found in serum and liver biochemical parameters as well as in HMGCR expression, the expression of USP2, a deubiquitinating enzyme, was lowered following BPS exposure [158].

Taken together, through the above-cited literature, it is evident that, similar to adult exposure, developmental exposure to bisphenol analogs can also induce liver damage. While liver toxicities were observed in both male and female offspring, some studies suggested more toxicities observed in males. However, it was noted that developmental exposure-induced liver toxicities were less severe than those observed during adult exposure in mice. Marchlewicz et al. have reported that gestational exposure to high-fat diets and BPA alters metabolic outcomes in both dams and offspring but only produces hepatic steatosis in dams [159]. Nonetheless, the toxic effects of developmental exposure to bisphenol analogs cannot be undermined, especially the long-term effects and low-dose effects on other systems, e.g., neurotoxicity.

3.2.3. Adult Exposure in Rats

In toxicology studies, rats are generally considered a preferred model compared to mice due to their larger size, longer lifespan and closer physiological similarities to humans. These characteristics often make rats better suited for studying chronic toxicity and the long-term effects of chemicals. Table 4 summarized liver toxicity studies on bisphenol analogs in rats following adult exposure. It was noted that adult exposure to BPA induced less severe liver toxicities than in mice. For example, when adult male Wistar rats were treated with dietary BPA (50 μg/kg/day) for 35 weeks, no effect in lipid metabolism was observed. In addition, there were no differences in body weight gain, total energy intake, liver weight index or % body fat in both standard diet- and HFD-fed sub-groups [160]. In a separate study, the administration of BPA (5 and 25 μg/kg) to rats by gavage for 35 days resulted in decreased body weights and reduced levels of liver enzyme alkaline phosphatase and AST, while the level of ALT was not changed [161]. However, Chen et al. reported an increased excretion of the water-soluble vitamin biotin and riboflavin in rats when BPA was given at the dose of 0.5 μg/kg/day by gavage for 8 weeks [162]. In addition, higher levels of methionine adenosyltransferase Iα (Mat1a) and methionine adenosyltransferase IIα (Mat2a) and S-adenosylmethionine (SAMe) were also observed in the liver of BPA-treated rats [162]. Mat1a and Mat2a encode critical isoenzymes that catalyze the formation of SAMe, the major biological methyl donor involved in the choline metabolism.

One consistent finding among the BPA-exposed rats was increased oxidative stress. Exposure to BPA at 5 and 50 µg/kg bw/day caused oxidative stress [163], but liver tissues appeared normal, and there were no significant changes in lipid droplets. Morsi et al. also showed that male Wistar albino rats had altered tissue levels of malondialdehyde, superoxide dismutase and nitric oxide, disturbed gene expression profiles, and apoptotic changes following BPA exposure at 1–2 μg/kg bw/day in drinking water for 45 consecutive days [164]. In addition, Bindhumol et al. reported that male Wistar rats had decreased activities of antioxidant enzymes, e.g., superoxide dismutase, catalase, glutathione reductase and glutathione peroxidase, and increased levels of hydrogen peroxide and lipid peroxidation following oral exposure to BPA at 0.2, 2 and 20 μg/kg bw per day for 30 days [165]. However, no significant changes in ALT activity in liver mitochondrial and microsome-rich fractions were observed [165]. One consequence of increased oxidative stress would be DNA damage. Indeed, Panpatil et al. showed increases in the formation of micronuclei in the liver of male Wistar rats following exposure to BPA (50 µg/kg) by gavage for 4 weeks [166]. Additionally, increases in oxidative stress can also induce aberrant gene expression, as there was enhanced expression of HO-1 (25 μg/kg) and GADD45B (5 and 25 μg/kg) genes following BPA exposure [167].

Table 3. Summary of liver toxicity studies on bisphenol analogs in mice—developmental exposure.

Compounds	Model/Diseases	Age	Exposure Window/Time	Dose/Concentration	Routes of Administration	Diet	Liver Effects	Reference
BPA	Pregnant CD-1 mice	Two-generation studies	Whole life	3 and 30 μg/kg bw/day	Oral/diet	Purina certified ground rodent diet	BPA increased kidney and liver weights.	[134]
BPA	C57BL/6JxFVB hybrid mice	23 weeks	During mating, gestation, and lactation	3, 10 and 30 μg/kg bw/day	Oral/diet	NIH-07 diet	Adult male offspring showed dose-dependent increases in body and liver weights. The liver of males did not reveal any effects histopathologically. Female offspring showed a dose-dependent decrease in liver weight.	[135]
BPA	Pregnant ICR mice	E14.5 or E18.5	E6.5–13.5 or E6.5–17.5	0.02 and 2 μg/kg bw/day	Oral	Standard diet	No significant changes in cytochrome P450 1A1and the glutathione S-transferase Ya subunit in the livers of late-stage embryos.	[136]
BPA	Pregnant C57BL/6J mice	Adult (male and female pups)	For 19–21 consecutive days during gestation	5 μg/kg bw/day	Oral	Select rodent diet 50 IF/6F 5V5R	BPA affected the expression of genes related to liver oxidative phosphorylation, PPAR signaling and fatty acid metabolism, as well as the gut microbipta in an age- and sex-dependent manner.	[137]
BPA	C57BL/6 mice	14 weeks old	Gestational exposure (E7.5–16.5)	1 μg/kg bw/day	Gavage	Standard rodent chow then high-fat diet at 6 weeks old	BPA affected the expression of genes related to lipid metabolism, leading to a sex-dependent lipid accumulation in the liver of male offspring and fatty liver in both sexes.	[138]
BPA	Male ICR (CD1) mice	10 months	Lactational and postnatal exposure after weaning	0.5 μg/kg/day	Drinking water (2.5 μg/L BPA)	Standard diet	BPA increased triglycerides and cholesterol levels in the liver. Hepatocytes showed increased expression of genes related to lipid synthesis and SREBF1 and SREBF2, and decreased DNA methylation in SREBF1 and SREBF2.	[139]
BPA	F0 pregnant C57BL/6J mice	E18.5 male fetuses	From mating until GD 18.5	10 µg/kg bw/day	Oral	Modified AIN 93G diet containing BPA or control diet	Thirteen metabolites differed between control and BPA groups. BPA fetal liver had significantly reduced Shp expression in comparison to the controls.	[140]
BPA	Pregnant mice	PND 22	Two weeks prior to mating	5–10 μg/kg bw/day	Oral/diet (50 μg BPA/Kg)	AIN-93G diets as the control	Offspring maternally exposed to BPA during gestation and lactation had alterations of liver methylome.	[142]
BPA	Pregnant CD-1 mice	Male pups at PND 2 or PND 21	From GD 8 through day 16 of lactation	0.025, 0.25, or 25 µg BPA/kg bw/day	Alzet osmotic pumps (sc)	Standard food (Harlan Teklad)	BPA disrupted energy metabolism and brain function in perinatally exposed CD-1 mouse pups.	[146]
BPA	Male C57BL/6J mice	2 months old	A single injection at PND 10	25 μg/kg bw/day	Subcutaneous	Standard food (Panlab, Barcelona, Spain)	BPA induced liver damage evidenced by oxidative stress.	[147]
BPA	Pregnant OF-1 mice	Male pups at PND 30	Gestational day 9–16	10 μg/kg bw/day	Subcutaneous	2014 Teklad Global 14% protein rodent maintenance diet	BPA increased the level of all-trans-retinoic acids and the expression of Adh1, Fgf21, Aox1 and Cyp1a2 (biosynthesis of retinoic acid).	[149]
BPA	Pregnant OF-1 mice	Male pups at 17 or 28 weeks of age	Gestational day 9–16	10 μg/kg bw/day	Subcutaneous	At age of one month, mice were on a chow diet or HFD for 13 or 24 weeks	BPA increased PPARγ and Prkaa1 genes in the liver, while decreased the expression of Cd36; Hepatic triglyceride levels were increased.	[150]
BPA	Pregnant CD-1 mice	At week 5 and week 39 (pups)	From GD 8 through PND 16 and PND 21–35	25 μg/kg bw/day	Osmotic minipumps in utero and drinking water postnatally	Harlan Teklad Rodents Diets® 2018 chow	BPA increased hepatic lipid content along with increased Nrf2 and pro-lipogenic enzymes in females; BPA exposure induced hypomethylation of the Nrf2 and Srebp-1c promoters in liver.	[151]
BPA	Swiss mice	PND 56 (male and female pups)	During gestation and lactation	20 μg/kg bw/day	Intraperitoneal	Standard normal diet	No structural modification and hepatic microvesicular steatosis in the liver, no differences in lipid composition.	[152]
BPS	F0 pregnant C57BL/6J mice	Multi-generation studies (F0–F3)	From GD 0 until weaning of offspring	1.5 μg/kg bw/day	Drinking water	Standard diet based on the 4RF21 diet (estrogen-free)	BPS produced no significant changes in liver weight regardless of generations.	[153]
BPS	Pregnant C57BL/6J mice	22-week-old male pups	From embryo day 0 until 22 weeks old	1.5 μg/kg bw/day	Drinking water	At 8 weeks old, all male pups were fed with a high-fat diet	BPS increased hepatic triglyceride content and changed gene expression (1366 genes modified more than 1.5-fold).	[154]
BPS	Pregnant C57BL/6J mice	23-week-old male pups	From embryo day 0 until 22 weeks old	1.5 μg/kg bw/day	Drinking water	Standard diet (4RF21)	BPS dysregulated 374 genes in the liver; BPS also induced hypomethylation in the differentially methylated regions (58.5%).	[155]
BPS	C57BL/6 mice	Postnatal week 12	From GD 0 until weaning	50 μg/kg bw/day	Subcutaneous	At postnatal week 4, offspring were shifted to a high-fat diet	Male offspring showed greater metabolic and microbial disturbances. In the liver, BPS induced cytoplasmic loosening and hypochromasia, with hepatocytes exhibiting vacuolation. There were granular degeneration, steatosis and hepatocyte necrosis.	[156]
BPS	Pregnant C57BL/6J mice	Up to 23-week-old	From gestational day 0	0.2, 1.5, and 50 μg/kg bw/day	Drinking water	Fed with a standard or HFD	BPS increased body weight in male offspring fed with a HFD at 1.5 and 50 μg/kg doses.	[157]
BPS	Pregnant ICR mice	PND 70	From GD 1 until the pups were weaned (40 days)	5 µg/kg bw/day	Drinking water	The growth and reproduction compound feed	BPS did not change liver weight and liver organ index, and liver histopathology in male offspring, but liver weight was increased in females. In addition, the expression of USP2 was lower following BPS exposure.	[158]

Table 3. Summary of liver toxicity studies on bisphenol analogs in mice—developmental exposure.

Compounds	Model/Diseases	Age	Exposure Window/Time	Dose/Concentration	Routes of Administration	Diet	Liver Effects	Reference
BPA	Pregnant CD-1 mice	Two-generation studies	Whole life	3 and 30 μg/kg bw/day	Oral/diet	Purina certified ground rodent diet	BPA increased kidney and liver weights.	[134]
BPA	C57BL/6JxFVB hybrid mice	23 weeks	During mating, gestation, and lactation	3, 10 and 30 μg/kg bw/day	Oral/diet	NIH-07 diet	Adult male offspring showed dose-dependent increases in body and liver weights. The liver of males did not reveal any effects histopathologically. Female offspring showed a dose-dependent decrease in liver weight.	[135]
BPA	Pregnant ICR mice	E14.5 or E18.5	E6.5–13.5 or E6.5–17.5	0.02 and 2 μg/kg bw/day	Oral	Standard diet	No significant changes in cytochrome P450 1A1and the glutathione S-transferase Ya subunit in the livers of late-stage embryos.	[136]
BPA	Pregnant C57BL/6J mice	Adult (male and female pups)	For 19–21 consecutive days during gestation	5 μg/kg bw/day	Oral	Select rodent diet 50 IF/6F 5V5R	BPA affected the expression of genes related to liver oxidative phosphorylation, PPAR signaling and fatty acid metabolism, as well as the gut microbipta in an age- and sex-dependent manner.	[137]
BPA	C57BL/6 mice	14 weeks old	Gestational exposure (E7.5–16.5)	1 μg/kg bw/day	Gavage	Standard rodent chow then high-fat diet at 6 weeks old	BPA affected the expression of genes related to lipid metabolism, leading to a sex-dependent lipid accumulation in the liver of male offspring and fatty liver in both sexes.	[138]
BPA	Male ICR (CD1) mice	10 months	Lactational and postnatal exposure after weaning	0.5 μg/kg/day	Drinking water (2.5 μg/L BPA)	Standard diet	BPA increased triglycerides and cholesterol levels in the liver. Hepatocytes showed increased expression of genes related to lipid synthesis and SREBF1 and SREBF2, and decreased DNA methylation in SREBF1 and SREBF2.	[139]
BPA	F0 pregnant C57BL/6J mice	E18.5 male fetuses	From mating until GD 18.5	10 µg/kg bw/day	Oral	Modified AIN 93G diet containing BPA or control diet	Thirteen metabolites differed between control and BPA groups. BPA fetal liver had significantly reduced Shp expression in comparison to the controls.	[140]
BPA	Pregnant mice	PND 22	Two weeks prior to mating	5–10 μg/kg bw/day	Oral/diet (50 μg BPA/Kg)	AIN-93G diets as the control	Offspring maternally exposed to BPA during gestation and lactation had alterations of liver methylome.	[142]
BPA	Pregnant CD-1 mice	Male pups at PND 2 or PND 21	From GD 8 through day 16 of lactation	0.025, 0.25, or 25 µg BPA/kg bw/day	Alzet osmotic pumps (sc)	Standard food (Harlan Teklad)	BPA disrupted energy metabolism and brain function in perinatally exposed CD-1 mouse pups.	[146]
BPA	Male C57BL/6J mice	2 months old	A single injection at PND 10	25 μg/kg bw/day	Subcutaneous	Standard food (Panlab, Barcelona, Spain)	BPA induced liver damage evidenced by oxidative stress.	[147]
BPA	Pregnant OF-1 mice	Male pups at PND 30	Gestational day 9–16	10 μg/kg bw/day	Subcutaneous	2014 Teklad Global 14% protein rodent maintenance diet	BPA increased the level of all-trans-retinoic acids and the expression of Adh1, Fgf21, Aox1 and Cyp1a2 (biosynthesis of retinoic acid).	[149]
BPA	Pregnant OF-1 mice	Male pups at 17 or 28 weeks of age	Gestational day 9–16	10 μg/kg bw/day	Subcutaneous	At age of one month, mice were on a chow diet or HFD for 13 or 24 weeks	BPA increased PPARγ and Prkaa1 genes in the liver, while decreased the expression of Cd36; Hepatic triglyceride levels were increased.	[150]
BPA	Pregnant CD-1 mice	At week 5 and week 39 (pups)	From GD 8 through PND 16 and PND 21–35	25 μg/kg bw/day	Osmotic minipumps in utero and drinking water postnatally	Harlan Teklad Rodents Diets® 2018 chow	BPA increased hepatic lipid content along with increased Nrf2 and pro-lipogenic enzymes in females; BPA exposure induced hypomethylation of the Nrf2 and Srebp-1c promoters in liver.	[151]
BPA	Swiss mice	PND 56 (male and female pups)	During gestation and lactation	20 μg/kg bw/day	Intraperitoneal	Standard normal diet	No structural modification and hepatic microvesicular steatosis in the liver, no differences in lipid composition.	[152]
BPS	F0 pregnant C57BL/6J mice	Multi-generation studies (F0–F3)	From GD 0 until weaning of offspring	1.5 μg/kg bw/day	Drinking water	Standard diet based on the 4RF21 diet (estrogen-free)	BPS produced no significant changes in liver weight regardless of generations.	[153]
BPS	Pregnant C57BL/6J mice	22-week-old male pups	From embryo day 0 until 22 weeks old	1.5 μg/kg bw/day	Drinking water	At 8 weeks old, all male pups were fed with a high-fat diet	BPS increased hepatic triglyceride content and changed gene expression (1366 genes modified more than 1.5-fold).	[154]
BPS	Pregnant C57BL/6J mice	23-week-old male pups	From embryo day 0 until 22 weeks old	1.5 μg/kg bw/day	Drinking water	Standard diet (4RF21)	BPS dysregulated 374 genes in the liver; BPS also induced hypomethylation in the differentially methylated regions (58.5%).	[155]
BPS	C57BL/6 mice	Postnatal week 12	From GD 0 until weaning	50 μg/kg bw/day	Subcutaneous	At postnatal week 4, offspring were shifted to a high-fat diet	Male offspring showed greater metabolic and microbial disturbances. In the liver, BPS induced cytoplasmic loosening and hypochromasia, with hepatocytes exhibiting vacuolation. There were granular degeneration, steatosis and hepatocyte necrosis.	[156]
BPS	Pregnant C57BL/6J mice	Up to 23-week-old	From gestational day 0	0.2, 1.5, and 50 μg/kg bw/day	Drinking water	Fed with a standard or HFD	BPS increased body weight in male offspring fed with a HFD at 1.5 and 50 μg/kg doses.	[157]
BPS	Pregnant ICR mice	PND 70	From GD 1 until the pups were weaned (40 days)	5 µg/kg bw/day	Drinking water	The growth and reproduction compound feed	BPS did not change liver weight and liver organ index, and liver histopathology in male offspring, but liver weight was increased in females. In addition, the expression of USP2 was lower following BPS exposure.	[158]

While BPA-treated rats seemed not to exhibit as much liver toxicity as BPA-treated mice, some evidence supported that BPA might synergize with other factors. When female Fischer 344 rats were exposed to BPA via drinking water at 0.025 and 0.25 mg/L (~2.5–50 μg/kg/day) containing 5% fructose [168], the magnetic resonance imaging showed that liver fat content was higher in the BPA-exposed groups than in the fructose control group. In the liver, fructose is metabolized to promote the synthesis of fat. In addition, Nagarajan et al. showed that oral exposure to BPA at 50 μg/kg bw/day for 30 days elevated the content of TBARS in both the plasma and liver of the Nω-nitro-l-arginine methyl ester-induced hypertensive male albino Wistar rats [169]. In a follow-up study, Nagarajan et al. reported that similar BPA exposure potentiated/aggravated hypertension-induced hepatic fibrosis, oxidative stress, angiotensin-converting enzyme activity, dysfunction of the antioxidant system, dyslipidemias and expression of inflammatory factors [170].

In the identified adult rat studies, there are several that focused on bisphenol analogs other than BPA (Table 4). Azevedo et al. showed that, similar to BPA, long-term exposure to BPS promoted glucose intolerance and changed hepatic mitochondrial metabolism in male Wistar rats [171]. When male Wistar rats were exposed to BPA or BPS at 50 μg/kg bw/day for 38 weeks in drinking water, no significant differences were observed for AST and ALT levels [172]. However, BPA exposure increased serum levels of total cholesterol and HDL-cholesterol, with BPS-treated rats exhibiting hypertriglyceridemia. Both BPA and BPS increased levels of serum lipid markers and enhanced the expression of glycerol kinase-like protein 1, an enzyme involved in triglyceride synthesis. Additionally, BPS treatment increased the expression of a liver lipogenic enzyme and had a greater obesogenic effect than BPA, suggesting that BPS might be more toxic in terms of metabolic disturbance [172].

Taken together, through the above-cited literature, it is evident that adult exposure to bisphenol analogs in rats also has some toxic effects on the liver, although they are less severe than that in mice following adult exposure. Further, the synergistic effects with diet and underlying conditions demand future investigations. However, it should be noted that, among the identified studies, only one study used female rats, in which BPA-exposed rats had more liver fat content than the controls [168].

3.2.4. Developmental Exposure in Rats

Table 5 summarizes liver toxicity studies on bisphenol analogs in rats following developmental exposure. In a proof-of-concept study using the Alzet osmotic pumps as the route of exposure, Tremblay-Franco et al. showed that metabolisms of glucose, lactate and fatty acids were modified with time in Sprague Dawley rats perinatally exposed to BPA at 0.25–25 μg/kg bw/day [173]. Consistent with BPA-induced impairment of glucose metabolism, BPA exposure by gavage in F0 pregnant rats at a daily dose of 40 μg/kg bw during gestation and lactation periods downregulated the expression of glucokinase gene in F2 liver by inducing changes in its DNA methylation [174]. Suppressed hepatic glucokinase activity was also observed in BPA-exposed adult mice [129]. Ma et al. [175] showed that BPA exposure (50 μg/kg/day) by gavage throughout gestation and lactation in Wistar rats induced promoter hypermethylation, and thus reduced the expression of hepatic glucokinase. Moreover, increased promoter hypermethylation of glucokinase became more profound in BPA-treated offspring with time, although the hepatic global DNA methylation was decreased [175]. When pregnant Wistar rats were exposed to 50 μg BPA/kg bw/day from embryonic day 3 to 18, the treatment caused masculinization of the hepatic transcriptome in females. Further, the relative liver weight was increased in females at PND 1 while it was decreased in males at PND 21 [176]. When BPA was evaluated at concentrations of 0.015 and 0.3 ppm (approximately 1 and 20 µg/kg/day of BPA) administered in the diet to Sprague Dawley rats for three generations, decreased male liver weight and increased female liver weight were observed in F₂ at 20 μg/kg dose [177].

Table 4. Summary of liver toxicity studies on bisphenol analogs in rats—adult exposure.

Compounds	Model/Diseases	Exposure Starting Age	Exposure Window/Time	Dose/Concentration	Routes of Administration	Diet	Liver Effects	Reference
BPA	Male Wistar rats	9 weeks old	35 weeks	50 μg/kg bw/day	Oral (diet)	Standard chow or high-fat diet	BPA did not affect lipid metabolism.	[160]
BPA	Male Wistar rats	Older than 2 months	35 days	5 and 25 μg/kg bw/day	Gavage	Likely standard chow (not mentioned)	The levels of alkaline phosphatase and AST were decreased by BPA, while the level of ALT was not changed.	[161]
BPA	Male Sprague Dawley rats	6–8 weeks	8 weeks	0.5 μg/kg bw/day	Gavage	Likely standard chow (not mentioned)	BPA increased biotin and riboflavin excretion; higher levels of Mat1a and Mat2a, and SAMe were also observed in rat liver.	[162]
BPA	Male Wistar albino rats	8 weeks old	8 weeks	5 and 50 μg/ kg bw/day	Oral	Likely standard chow (not mentioned)	BPA caused oxidative stress, but liver tissues appeared normal. No significant difference among the groups in lipid droplets.	[163]
BPA	Male Wistar rats	NA	45 days	1–2 μg/ kg bw/day	Drinking water (4.5 and 8 µg/L BPA)	Likely standard chow	BPA altered MDA, SOD, NO tissue levels in the liver, disturbed gene expression, and induced apoptosis.	[164]
BPA	Albino male rats of Wistar strain	45 days old	30 days	0.2, 2 and 20 μg/kg bw per day	Orally in olive oil	Standard commercial laboratory chow	No significant changes in ALT activity in mitochondrial and microsome-rich fractions, but BPA induced reactive oxygen species generation in the liver.	[165]
BPA	Male Wistar rats	9–10 weeks old	4 weeks	50 μg/kg bw/day	Gavage	Standard rodent chow	BPA group exhibited higher DNA damage in liver with increased formation of micronuclei.	[166]
BPA	Male Wistar rats	10 to 12 weeks old	35 days	5 and 25 μg/ kg bw/day	Gavage	Likely standard chow (not mentioned)	There were increased expressions in HO-1 (25 μg/kg) and GADD45B (5 and 25 μg/kg) genes, indicating increases in oxidative stress.	[167]
BPA	Female Fischer 344 rats	5 weeks old	From 5 to 15 weeks old	2.5–50 μg/kg/day	Drinking water (0.025 and 0.25 mg/L)	Likely standard rodent chow (not specified)	BPA-exposed rats had more liver fat content than the fructose controls.	[168]
BPA	Hypertensive male albino Wistar rats	8–10 weeks old	30 days	50 μg/kg bw/day	Oral	Likely standard chow (not mentioned)	BPA elevated the TBARS content in plasma and liver.	[169]
BPA	Hypertensive male albino Wistar rats	8–10 weeks old	30 days	50 μg/kg bw/day	Oral	Likely standard chow (not mentioned)	BPA potentiated hypertension-induced hepatic fibrosis, oxidative stress, ACE activity, dysfunctional antioxidant system, dyslipidemia and expression of inflammatory factor.	[170]
BPA, BPS	Male Wistar rats	3 weeks old	38 weeks	50 μg/kg bw/day	Drinking water	Standard diet	Long-term BPA or BPS exposure promoted glucose intolerance and changed hepatic mitochondrial metabolism.	[171]
BPA, BPS	Male Wistar rats	4 weeks-old	20 weeks	50 μg/kg bw/day	Drinking water	Standard diet	BPA increased serum levels of total cholesterol and HDL-cholesterol, while BPS induced hypertriglyceridemia. BPS increased the expression of a liver lipogenic enzyme and had a greater obesogenic effect than BPA.	[172]

Abbreviations: ACE, angiotensin-converting enzyme; GADD45B, growth arrest and DNA damage-inducible, beta; HO-1, heme oxygenase-1; MDA, malondialdehyde; NO, nitric oxide; SOD, superoxide dismutase.

Table 4. Summary of liver toxicity studies on bisphenol analogs in rats—adult exposure.

Compounds	Model/Diseases	Exposure Starting Age	Exposure Window/Time	Dose/Concentration	Routes of Administration	Diet	Liver Effects	Reference
BPA	Male Wistar rats	9 weeks old	35 weeks	50 μg/kg bw/day	Oral (diet)	Standard chow or high-fat diet	BPA did not affect lipid metabolism.	[160]
BPA	Male Wistar rats	Older than 2 months	35 days	5 and 25 μg/kg bw/day	Gavage	Likely standard chow (not mentioned)	The levels of alkaline phosphatase and AST were decreased by BPA, while the level of ALT was not changed.	[161]
BPA	Male Sprague Dawley rats	6–8 weeks	8 weeks	0.5 μg/kg bw/day	Gavage	Likely standard chow (not mentioned)	BPA increased biotin and riboflavin excretion; higher levels of Mat1a and Mat2a, and SAMe were also observed in rat liver.	[162]
BPA	Male Wistar albino rats	8 weeks old	8 weeks	5 and 50 μg/ kg bw/day	Oral	Likely standard chow (not mentioned)	BPA caused oxidative stress, but liver tissues appeared normal. No significant difference among the groups in lipid droplets.	[163]
BPA	Male Wistar rats	NA	45 days	1–2 μg/ kg bw/day	Drinking water (4.5 and 8 µg/L BPA)	Likely standard chow	BPA altered MDA, SOD, NO tissue levels in the liver, disturbed gene expression, and induced apoptosis.	[164]
BPA	Albino male rats of Wistar strain	45 days old	30 days	0.2, 2 and 20 μg/kg bw per day	Orally in olive oil	Standard commercial laboratory chow	No significant changes in ALT activity in mitochondrial and microsome-rich fractions, but BPA induced reactive oxygen species generation in the liver.	[165]
BPA	Male Wistar rats	9–10 weeks old	4 weeks	50 μg/kg bw/day	Gavage	Standard rodent chow	BPA group exhibited higher DNA damage in liver with increased formation of micronuclei.	[166]
BPA	Male Wistar rats	10 to 12 weeks old	35 days	5 and 25 μg/ kg bw/day	Gavage	Likely standard chow (not mentioned)	There were increased expressions in HO-1 (25 μg/kg) and GADD45B (5 and 25 μg/kg) genes, indicating increases in oxidative stress.	[167]
BPA	Female Fischer 344 rats	5 weeks old	From 5 to 15 weeks old	2.5–50 μg/kg/day	Drinking water (0.025 and 0.25 mg/L)	Likely standard rodent chow (not specified)	BPA-exposed rats had more liver fat content than the fructose controls.	[168]
BPA	Hypertensive male albino Wistar rats	8–10 weeks old	30 days	50 μg/kg bw/day	Oral	Likely standard chow (not mentioned)	BPA elevated the TBARS content in plasma and liver.	[169]
BPA	Hypertensive male albino Wistar rats	8–10 weeks old	30 days	50 μg/kg bw/day	Oral	Likely standard chow (not mentioned)	BPA potentiated hypertension-induced hepatic fibrosis, oxidative stress, ACE activity, dysfunctional antioxidant system, dyslipidemia and expression of inflammatory factor.	[170]
BPA, BPS	Male Wistar rats	3 weeks old	38 weeks	50 μg/kg bw/day	Drinking water	Standard diet	Long-term BPA or BPS exposure promoted glucose intolerance and changed hepatic mitochondrial metabolism.	[171]
BPA, BPS	Male Wistar rats	4 weeks-old	20 weeks	50 μg/kg bw/day	Drinking water	Standard diet	BPA increased serum levels of total cholesterol and HDL-cholesterol, while BPS induced hypertriglyceridemia. BPS increased the expression of a liver lipogenic enzyme and had a greater obesogenic effect than BPA.	[172]

Abbreviations: ACE, angiotensin-converting enzyme; GADD45B, growth arrest and DNA damage-inducible, beta; HO-1, heme oxygenase-1; MDA, malondialdehyde; NO, nitric oxide; SOD, superoxide dismutase.

Consistent with BPA-induced dysregulation of the fatty acid metabolism, BPA exposure from gestational day 3.5 until PND 22 at 0.5 or 50 µg/kg in Fischer 344 rat offspring altered the fatty acid composition in males by decreasing liver triglycerides [178]. However, Yang et al. [179] showed that both triglycerides and total cholesterol in the serum and liver were increased in BPA-exposed offspring, the liver fatty acid oxidation related genes were downregulated, and the fatty acid synthesis-related genes were upregulated when the Sprague Dawley rats were exposed to BPA (50 μg/kg bw/day) from day 5 to day 19 of gestation. In addition, the relative liver weight was increased at PND 56 in male offspring [179]. Lejonklou et al. showed that BPA exposure from gestational day 3.5 to PND 22 induced sex-specific gene expressions in adipose tissues and increased plasma triglyceride levels in males and adipocyte cell density in females when pregnant F344 rats were exposed to BPA via their drinking water, corresponding to 0.5 or 50 μg/kg BW/day [180]. Offspring born to Wistar rats exposed to 50 μg/kg/day BPA throughout gestation and lactation on the standard diet had moderate hepatic steatosis and altered expression of insulin signaling elements in the liver, but with normal liver function [181]. On the HFD, the BPA offspring showed a nonalcoholic steatohepatitis-like phenotype, e.g., extensive lipid accumulation, large lipid droplets, hepatocyte degeneration, impaired liver function, increased inflammation and mild fibrosis in the liver, consistent with profound hepatic oxidative stress [181].

Consistent with the observations from mouse developmental studies, Xia et al. found that perinatal BPA at 50 µg/kg/day increased the ALT level and enhanced cell apoptosis in the liver of rat offspring at 15 and 21 weeks, which was further supported by increases in the activities of caspase-3 and caspase-9 and levels of cytochrome c [182]. Jiang et al. showed that perinatal BPA exposure resulted in mitochondrial dysfunction in early life and contributed to hepatic steatosis in rat offspring [183]. When pregnant Wistar rats were exposed to BPA (40 μg/kg/day) during gestation and lactation, micro-vesicular steatosis in the liver, upregulated lipogenesis pathway and increased ROS generation and cytochrome c release were found in offspring at 15 weeks old. Extensive fatty accumulation in the liver and elevated serum ALT were observed in BPA-exposed offspring at 26 weeks [183]. Tonini et al. [184] reported that, following in utero exposure to BPA at 2.5 µg/kg/day, the liver of female rat fetuses exhibited modulations of proteins involved in cholesterol and fatty acid biosynthesis and trafficking, and alterations to the inflammatory process [184]. Linillos-Pradillo et al. also showed that perinatal BPA exposure (36 μg/kg bw/day) in female PND 6 rat offspring increased oxidative stress levels and triggered an inflammatory response and apoptosis pathways in the liver [185]. In addition, when lactating and weaned Wistar rats were exposed to BPA (100 μg/L) in drinking water during gestation and lactation, the expression of inflammatory cytokine Sirt1, its natural antisense long non-coding RNA (Sirt1-AS LncRNA) and histone deacetylase 1 (Hdac1) were affected [186]. Lastly, there are other mechanisms that might be responsible for BPA-induced developmental toxicity in rats. For example, alterations of the gut–liver axis through changing the gut microbiota in rat offspring administered 50 μg/kg/day of BPA have been reported [187].

Some studies focused on bisphenol analogs other than BPA. When 21-day-old male rats were exposed to BPS (5 and 20 μg/L of drinking water) for 14 days (e.g., juvenile exposure), no effects on inflammation, apoptosis and mitochondrial function were found. Further, there were reduced levels of the reactive oxygen species and nitrite content, indicating hepatoprotection [188]. However, when pregnant Wistar rats were exposed to BPS and BPA (0.4, 4.0 μg/kg bw) from gestational day 4 to 21 by gavage, prenatal BPS-exposed male offspring showed a more obesogenic effect, e.g., impaired hepatic clearance of lipids, compared with BPA at PND 90 [189]. In addition, BPS exposure increased liver weight and caused liver discoloration and liver lobe alteration more than BPA [189]. Similar to the developmental exposure in mice, Zhang et al. also showed that BPS treatment in pregnant rats caused profoundly altered liver histology, showing lipid droplets, which was accompanied by metabolic changes, decreased miR-29a-3p expression and microvesicular steatosis in the offspring [190]. In terms of BPF, Linillos-Pradillo et al. reported that oral exposure at 36.5 μg/kg bw/day perinatally affected liver defense mechanisms (antioxidant enzymes and glutathione system), increased ROS levels and produced lipid peroxidation in lactating dams as well as in female and male offspring at PND 6 [191]. Further, lactating dams treated with BPF showed a significant increase in iNOS and HO-1d, activation of NLRP3 components and the release of pro-inflammatory cytokines. Similar effects were observed in female and male PND 6 offspring after perinatal exposure [192].

These studies collectively demonstrate that bisphenol exposure in rats during perinatal periods can have significant, sex-specific impacts on liver development and function, potentially leading to long-term metabolic consequences.

3.3. Liver Toxicity of Bisphenol Analogs in Other Species (Chickens, Pigs, Sheep, Etc.)

The primary de novo lipogenesis in human and chicken livers is similar, which makes chicken an ideal animal model for studying the progression of lipid metabolism in the liver [193,194]. Direct dosing with BPA (50 μg/L BPA corresponding to 10 μg/kg bw/day) in 8-day old chicks has been conducted in a 4-week drinking water study [195], and BPA exposure increased body weight and both absolute and relative liver weight (Table 6). Further analyses showed that BPA increased hepatocyte volume and the activities of both AST and ALT in sera, and disrupted hepatocyte morphology [195]. BPA treatment also increased levels of hepatic triglyceride, total cholesterol and low-density lipoprotein cholesterol, while decreasing that of high-density lipoprotein cholesterol [195]. Moreover, BPA treatment altered the expression of hepatic genes involved in fatty acid β-oxidation, synthesis and absorption, suggesting severe hepatic injury. Additionally, the study found that the BPA group had higher expressions of IL-1β, IL-18 and TNF-α in the liver [195]. BPA was shown to bind to G protein-coupled estrogen receptor (GPER) and activated GPER expression in the liver, and the inhibition of GPER attenuated BPA-induced lipid metabolism dysregulation, inflammatory response and ferroptosis. It was possible that BPA bound to GPER and reduced the binding of estrogen and thus diminished its protective action on hepatic steatosis [195]. However, it should be noted that exposure to BPA and BPS at 50 μg/kg bw/day for three months in adult chickens had no significant effects on either the absolute weights or the relative weights of livers [196,197], suggesting that developmental exposure might be more detrimental. Additionally, Hanafy et al. did not find significant changes in ZP1 gene expression in the liver of Japanese quail following BPA exposure in both immature male quail and maternally exposed embryos [198].

Pigs are also a good model for toxicological studies due to their similar physiology to humans, ease of breeding and lower emotional attachment from the public. Thoene et al. exposed developing pigs to BPA at a dose of 50 μg/kg bw/day, and they found that the histological appearance of BPA liver was characterized by central vein and hepatic sinusoid dilatation and vascular congestion. Moreover, significant increases in the levels of ALT and AST were observed [199]. When the livers were examined for the expression of selected neuronal markers in the parasympathetic nervous system, it was noted that the number of galanin⁺/vesicular acetylcholine transporter⁺ nerves in the BPA group was significantly higher than that of the control samples [199]. The vesicular acetylcholine transporter is a marker for the parasympathetic nervous system. Galanin may potentiate the effects of norepinephrine to affect glucose production in the liver [200]. Further, increased expressions of these neuronal markers have previously been correlated with childhood obesity and diabetes [201,202]. Additional studies showed that such BPA exposure dysregulated porcine liver sympathetic innervation, and thus it might change the oxygenated blood supply and disrupt metabolism and the activity of hepatic parenchymal cells [203,204]. Furthermore, there were increased nerve fibers in the liver sympathetic nervous system colocalized with the neural marker PACAP that correlated with specific pathophysiology after exposure to BPA [205].

In addition to chickens and pigs, there were also some studies in sheep that have used doses at environmentally relevant levels due to their long lifespan, similarity to humans in size and ease of management. In a proof-of-concept study using subcutaneous injection as the route of exposure, Vyas et al. showed that the liver weight index was reduced in female sheep fetuses following BPA treatment prenatally at a dose of 500 μg/kg, but not at 50 μg/kg [206]. However, when the livers collected from 21-month-old female sheep offspring born to mothers treated with 50 μg/kg/day of BPA from days 30 to 90 of gestation were studied, the effect size analysis showed a reduction in the expression of pro-inflammatory markers (e.g., IL-1β, IL-6 and CCL2) and an increase in TNF-α and the macrophage marker CD68. Further, a significant increase in oxidized tyrosine moieties, a marker of oxidative stress, was observed [207].

Table 5. Summary of liver toxicity studies on bisphenol analogs in rats—developmental exposure.

Compounds	Model/Diseases	Age	Exposure Window/Time	Dose/Concentration	Routes of Administration	Diet	Liver Effects	Reference
BPA	Sprague Dawley rats	PND 21, 50, 90, 140 and 200	From day 9 of gestation to PND 28	0.25; 2.5 and 25 μg/kg BW/day	Alzet osmotic pumps (subcutaneously)	Standard rodent chow	BPA modified the metabolism of glucose, lactate and fatty acids with time.	[173]
BPA	F0 female SD rats	F2 offspring at 9 and 20 weeks old	GD0 to PND 21	40 μg/kg bw/day	Gavage	Standard rat food	F0 maternal BPA exposure downregulated the expression of glucokinase gene in F2 liver by inducing DNA methylation change.	[174]
BPA	Wistar rats	Male offspring at 3 and 21 weeks old	GD 0 until weaning at 3 weeks	50 μg/kg bw/day	Gavage	Standard rodent chow	Hepatic global DNA methylation was decreased by BPA, along with overexpression of DNA methyltransferase 3B at week 3. However, there was promoter hypermethylation, and thus reduced expression of hepatic glucokinase.	[175]
BPA	Pregnant Wistar rats	Newborn (PND 1) and weaning (PND21)	From embryonic day 3 to 18	50 μg/kg/day	Gavage	Standard solid diet	Prenatal BPA exposure caused masculinization of the hepatic transcriptome in females. The relative liver weight was increased in females at PND 1 while it was decreased in males at PND 21.	[176]
BPA	SD rats (Three-generation study)	up to ∼ 17 weeks	Whole life	Approximately 1 and 20 µg/kg/day	Oral/diet	Purina Certified Rodent Chow	BPA decreased male liver weight and increased female liver weight in F2 at 20 μg/kg/day.	[177]
BPA	Pregnant Fischer 344 rat	5 and 52 weeks old	GD3.5 until PND 22	0.5 and 50 µg/kg bw/day	Drinking water	Standard chows	BPA at 0.5 µg/kg altered the fatty acid composition and decreased liver triglycerides in male offspring.	[178]
BPA	Pregnant Sprague Dawley rats	Male offspring at PND 21 and 56	From day 5 to day 19 of gestation	50 μg/kg/day	Gavage	Likely standard rodent chow (not specified)	BPA increased the relative liver weight at PND 56, the levels of triglycerides and total cholesterol in serum and liver.	[179]
BPA	Pregnant F344 rats	PND 22	GD3.5 until PND 22	0.5 and 50 µg/kg bw/day	Drinking water	Standard chows	BPA induced sex-specific gene expressions in adipose tissue and increased plasma triglyceride levels in males and adipocyte cell density in females.	[180]
BPA	Wistar rats	27 weeks old	GD 0 to the end of lactation at PND 21	50 μg/kg/day	Gavage	Standard rodent chow or high-fat diet after weaning	On the standard diet, BPA offspring had moderate hepatic steatosis, but with normal liver function. On HFD, BPA offspring showed a nonalcoholic steatohepatitis-like phenotype.	[181]
BPA	Genitor Wistar male rat pups	At 3, 15 and 21 weeks old	GD 0 to PND 21	50 μg/kg/day	Gavage	Standard rodent chow	BPA increased ALT level and enhanced cell apoptosis in the liver of rat offspring at 15 and 21 weeks.	[182]
BPA	Pregnant Wistar rats	Male offspring at postnatal 3, 15 and 26 weeks	During gestation and lactation	40 μg/kg bw/day	Oral (Likely gavage)	Standard chows	Perinatal BPA exposure in rat offspring resulted in mitochondrial dysfunction in early life and contributed to hepatic steatosis.	[183]
BPA	Sprague Dawley rats	Fetus on GD20	30 days before coitus and continued until GD20	2.5 µg/kg/day	Drinking water	Standard rodent chow	BPA modulated the expression of proteins involved in cholesterol and fatty acid biosynthesis and trafficking in the liver.	[184]
BPA	Long-Evans rats	Female PND 6 offspring	All the time starting at premating	36 μg/kg bw/day	Oral/diet	A diet of natural ingredients low in phytoestrogens	BPA increased oxidative stress and triggered inflammatory responses and apoptosis pathways in the liver.	[185]
BPA	Pregnant Wistar rats	PND 17 and 60	During gestation and lactation and postnatal	10–20 μg/kg/day	Drinking water (100 μg/L)	Likely standard rodent chow (not specified)	BPA affected the expression of inflammatory cytokine Sirt1, its natural antisense long non-coding RNA and histone deacetylase 1.	[186]
BPA, BPS	Male Long-Evans rats	21-day-old	14 days	1 and 4 μg/kg bw/day	Drinking water (5 and 20 μg/L)	Likely standard rodent chow (not specified)	BPA induced hepatoxicity by depleting glutathione; BPS did not affect apoptosis, inflammation and mitochondrial function but reduced the reactive oxygen species and nitrite content.	[188]
BPA, BPS	Pregnant Wistar rats	PND 90	GD 4 to 21	0.4 and 4.0 μg/kg bw/day	Gavage	Standard rodent chow	BPS produced a more obesogenic effect and altered liver lobes more than l BPA; BPS exposure increased absolute liver weight and caused liver discoloration.	[189]
BPF	Long-Evans rats	Male and female (PND 6 offspring	All the time starting at premating	36 μg/kg bw/day	Oral/diet	A diet of natural ingredients low in phytoestrogens	Dams treated with BPF had increases in iNOS and HO-1d, activation of NLRP3 components and the release of pro-inflammatory cytokines. Similar effects were found in female and male PND 6 offspring.	[192]

Table 5. Summary of liver toxicity studies on bisphenol analogs in rats—developmental exposure.

Compounds	Model/Diseases	Age	Exposure Window/Time	Dose/Concentration	Routes of Administration	Diet	Liver Effects	Reference
BPA	Sprague Dawley rats	PND 21, 50, 90, 140 and 200	From day 9 of gestation to PND 28	0.25; 2.5 and 25 μg/kg BW/day	Alzet osmotic pumps (subcutaneously)	Standard rodent chow	BPA modified the metabolism of glucose, lactate and fatty acids with time.	[173]
BPA	F0 female SD rats	F2 offspring at 9 and 20 weeks old	GD0 to PND 21	40 μg/kg bw/day	Gavage	Standard rat food	F0 maternal BPA exposure downregulated the expression of glucokinase gene in F2 liver by inducing DNA methylation change.	[174]
BPA	Wistar rats	Male offspring at 3 and 21 weeks old	GD 0 until weaning at 3 weeks	50 μg/kg bw/day	Gavage	Standard rodent chow	Hepatic global DNA methylation was decreased by BPA, along with overexpression of DNA methyltransferase 3B at week 3. However, there was promoter hypermethylation, and thus reduced expression of hepatic glucokinase.	[175]
BPA	Pregnant Wistar rats	Newborn (PND 1) and weaning (PND21)	From embryonic day 3 to 18	50 μg/kg/day	Gavage	Standard solid diet	Prenatal BPA exposure caused masculinization of the hepatic transcriptome in females. The relative liver weight was increased in females at PND 1 while it was decreased in males at PND 21.	[176]
BPA	SD rats (Three-generation study)	up to ∼ 17 weeks	Whole life	Approximately 1 and 20 µg/kg/day	Oral/diet	Purina Certified Rodent Chow	BPA decreased male liver weight and increased female liver weight in F2 at 20 μg/kg/day.	[177]
BPA	Pregnant Fischer 344 rat	5 and 52 weeks old	GD3.5 until PND 22	0.5 and 50 µg/kg bw/day	Drinking water	Standard chows	BPA at 0.5 µg/kg altered the fatty acid composition and decreased liver triglycerides in male offspring.	[178]
BPA	Pregnant Sprague Dawley rats	Male offspring at PND 21 and 56	From day 5 to day 19 of gestation	50 μg/kg/day	Gavage	Likely standard rodent chow (not specified)	BPA increased the relative liver weight at PND 56, the levels of triglycerides and total cholesterol in serum and liver.	[179]
BPA	Pregnant F344 rats	PND 22	GD3.5 until PND 22	0.5 and 50 µg/kg bw/day	Drinking water	Standard chows	BPA induced sex-specific gene expressions in adipose tissue and increased plasma triglyceride levels in males and adipocyte cell density in females.	[180]
BPA	Wistar rats	27 weeks old	GD 0 to the end of lactation at PND 21	50 μg/kg/day	Gavage	Standard rodent chow or high-fat diet after weaning	On the standard diet, BPA offspring had moderate hepatic steatosis, but with normal liver function. On HFD, BPA offspring showed a nonalcoholic steatohepatitis-like phenotype.	[181]
BPA	Genitor Wistar male rat pups	At 3, 15 and 21 weeks old	GD 0 to PND 21	50 μg/kg/day	Gavage	Standard rodent chow	BPA increased ALT level and enhanced cell apoptosis in the liver of rat offspring at 15 and 21 weeks.	[182]
BPA	Pregnant Wistar rats	Male offspring at postnatal 3, 15 and 26 weeks	During gestation and lactation	40 μg/kg bw/day	Oral (Likely gavage)	Standard chows	Perinatal BPA exposure in rat offspring resulted in mitochondrial dysfunction in early life and contributed to hepatic steatosis.	[183]
BPA	Sprague Dawley rats	Fetus on GD20	30 days before coitus and continued until GD20	2.5 µg/kg/day	Drinking water	Standard rodent chow	BPA modulated the expression of proteins involved in cholesterol and fatty acid biosynthesis and trafficking in the liver.	[184]
BPA	Long-Evans rats	Female PND 6 offspring	All the time starting at premating	36 μg/kg bw/day	Oral/diet	A diet of natural ingredients low in phytoestrogens	BPA increased oxidative stress and triggered inflammatory responses and apoptosis pathways in the liver.	[185]
BPA	Pregnant Wistar rats	PND 17 and 60	During gestation and lactation and postnatal	10–20 μg/kg/day	Drinking water (100 μg/L)	Likely standard rodent chow (not specified)	BPA affected the expression of inflammatory cytokine Sirt1, its natural antisense long non-coding RNA and histone deacetylase 1.	[186]
BPA, BPS	Male Long-Evans rats	21-day-old	14 days	1 and 4 μg/kg bw/day	Drinking water (5 and 20 μg/L)	Likely standard rodent chow (not specified)	BPA induced hepatoxicity by depleting glutathione; BPS did not affect apoptosis, inflammation and mitochondrial function but reduced the reactive oxygen species and nitrite content.	[188]
BPA, BPS	Pregnant Wistar rats	PND 90	GD 4 to 21	0.4 and 4.0 μg/kg bw/day	Gavage	Standard rodent chow	BPS produced a more obesogenic effect and altered liver lobes more than l BPA; BPS exposure increased absolute liver weight and caused liver discoloration.	[189]
BPF	Long-Evans rats	Male and female (PND 6 offspring	All the time starting at premating	36 μg/kg bw/day	Oral/diet	A diet of natural ingredients low in phytoestrogens	Dams treated with BPF had increases in iNOS and HO-1d, activation of NLRP3 components and the release of pro-inflammatory cytokines. Similar effects were found in female and male PND 6 offspring.	[192]

Table 6. Summary of selected liver toxicity studies on bisphenol analogs in other species.

Compounds	Model/Diseases	Age	Exposure Window/Time	Dose/Concentration	Routes of Administration	Diet/Medium	Liver Effects	Reference
BPA	Chicks	8-day old	28 days	10 μg/kg	Drinking water	Typical laboratory conditions	BPA activates G protein-coupled estrogen receptor, disrupts lipid metabolism and induces ferroptosis in the liver.	[195]
BPA, BPS	Laying hens	Adult	3 months	50 μg/kg bw/day	Gavage	Typical laboratory conditions	No significant effects on either the absolute weights or the relative weights of livers.	[196]
BPA	Hy-Line Brown laying hens	450 days old	90 days	50 μg/kg	Not known	High-energy and low-protein diet	No significant effects on liver weight, NAFLD activity score, AST, ALT, TG, TC, HDL and LDL.	[197]
BPA	Juvenile porcine model	8 weeks	28 days	50 μg/kg bw/day	Oral (BPA capsules)	Typical laboratory conditions (not specified)	BPA liver had central vein and hepatic sinusoid dilatation and vascular congestion, and increases in ALT and AST and the number of galanin+/vesicular acetylcholine transporter+ nerves.	[198]
BPA	Juvenile porcine model	8 weeks	28 days	50 μg/kg bw/day	Oral (BPA capsules)	Typical laboratory conditions (not specified)	Oral BPA increased the number of liver sympathetic nerve fibers that co-localized with cocaine and amphetamine regulated transcripts and galanin.	[203,204]
BPA	Juvenile porcine model	8 weeks	28 days	50 μg/kg bw/day	Oral (BPA capsules)	Typical laboratory conditions (not specified)	BPA increased nerve fibers that colocalized with PACAP in the liver sympathetic nervous system.	[205]
BPA	Pregnant Suffolk sheep	GD90	From days 30 through 90 of gestation	50 and 500 μg/kg bw/day	Subcutaneous injection	A pelleted diet	Liver weight was reduced in prenatal BPA (500 μg/kg)-treated female fetuses.	[206]
BPA	Pregnant sheep	2–5 years old	Between days 30 and 90 of gestation	50 μg/kg	Subcutaneous injection	Typical laboratory conditions (not specified)	In liver, there were reduced expressions of pro-inflammatory markers IL-1, IL-6 and CCL2, and increases in TNF-α and the macrophage marker CD68 and oxidized tyrosine moieties.	[207]

Table 6. Summary of selected liver toxicity studies on bisphenol analogs in other species.

Compounds	Model/Diseases	Age	Exposure Window/Time	Dose/Concentration	Routes of Administration	Diet/Medium	Liver Effects	Reference
BPA	Chicks	8-day old	28 days	10 μg/kg	Drinking water	Typical laboratory conditions	BPA activates G protein-coupled estrogen receptor, disrupts lipid metabolism and induces ferroptosis in the liver.	[195]
BPA, BPS	Laying hens	Adult	3 months	50 μg/kg bw/day	Gavage	Typical laboratory conditions	No significant effects on either the absolute weights or the relative weights of livers.	[196]
BPA	Hy-Line Brown laying hens	450 days old	90 days	50 μg/kg	Not known	High-energy and low-protein diet	No significant effects on liver weight, NAFLD activity score, AST, ALT, TG, TC, HDL and LDL.	[197]
BPA	Juvenile porcine model	8 weeks	28 days	50 μg/kg bw/day	Oral (BPA capsules)	Typical laboratory conditions (not specified)	BPA liver had central vein and hepatic sinusoid dilatation and vascular congestion, and increases in ALT and AST and the number of galanin+/vesicular acetylcholine transporter+ nerves.	[198]
BPA	Juvenile porcine model	8 weeks	28 days	50 μg/kg bw/day	Oral (BPA capsules)	Typical laboratory conditions (not specified)	Oral BPA increased the number of liver sympathetic nerve fibers that co-localized with cocaine and amphetamine regulated transcripts and galanin.	[203,204]
BPA	Juvenile porcine model	8 weeks	28 days	50 μg/kg bw/day	Oral (BPA capsules)	Typical laboratory conditions (not specified)	BPA increased nerve fibers that colocalized with PACAP in the liver sympathetic nervous system.	[205]
BPA	Pregnant Suffolk sheep	GD90	From days 30 through 90 of gestation	50 and 500 μg/kg bw/day	Subcutaneous injection	A pelleted diet	Liver weight was reduced in prenatal BPA (500 μg/kg)-treated female fetuses.	[206]
BPA	Pregnant sheep	2–5 years old	Between days 30 and 90 of gestation	50 μg/kg	Subcutaneous injection	Typical laboratory conditions (not specified)	In liver, there were reduced expressions of pro-inflammatory markers IL-1, IL-6 and CCL2, and increases in TNF-α and the macrophage marker CD68 and oxidized tyrosine moieties.	[207]

4. Conclusions and Future Directions

In summary, studies in humans, rodents and other species including chickens, pigs and sheep have shown that exposure to bisphenol analogs can lead to hepatic metabolomic perturbations. Specifically, BPA exposure might be related to impaired liver functions in humans. The mechanisms of toxicity involved both genomic pathways that alter gene expression as well as nongenomic pathways that involve receptor-mediated signaling or interactions. In addition, studies in various animal species also indicated that several mechanisms are potentially involved in bisphenol analog-induced hepatic dysfunctions, such as oxidative stress, apoptosis, altered signaling pathways, liver–gut axis, fibrosis and inflammation. Dysregulated lipid metabolism could be induced by bisphenol analogs in liver cells in all species examined following both adult and developmental exposures. Further, lipid accumulation might be due to the effects of oxidative stress resulting from mitochondrial dysfunction that causes decreased fatty acid degradation. Similar to BPA, other bisphenol analogs can contribute to liver toxicity by disrupting hepatic metabolism, promoting lipid accumulation, causing oxidative stress and thus leading to liver toxicity.

Among the species included in this review, e.g., human, mouse, rat, chicken, pig and sheep, there are differences in liver toxicity that may be related to species-specific metabolic capacity, BPA clearance, estrogen signaling or other physiological variables. For example, the relative levels of in vitro clearance values for BPA in rats and mice were 34- and 29-fold compared to that of humans, respectively [40], and lesser liver toxicity in rats than mice was noted following both adult and developmental exposures. Although BPA does not undergo enterohepatic circulation in humans [42], whether slow clearance relative to rodents contributes to its toxicity warrant further investigation. While estrogen is crucial for lipid metabolism in the liver in different species, mouse models do not recapitulate the increase in plasma triglyceride in response to estrogen treatment in humans [208]. Unfortunately, the molecular regulatory network of estrogen in the liver of various species is still poorly understood.

While rodent models are valuable tools for understanding human health/disease and toxicity, it is important to acknowledge that they are not perfect representations of humans, and that caution is needed when extrapolating results to human conditions. The studies of chickens have a “dual benefit” for the improvement of health and disease prevention in both humans and agriculturally important domestic birds. However, several limitations exist when translating findings from avian studies to humans, including species-specific differences in physiology, genetics and immune responses. In addition, there are challenges in accurately replicating human diseases in chickens. Similarly, studies of pigs and sheep offer “dual benefits”, but there are differences between humans and these models in the immune system, gut microbiome, brain structure and function and certain physiological processes, which can affect the interpretation and applicability of findings.

While our review provides strong evidence that bisphenol analogs indeed induce similar liver toxic effects in different species, its complex metabolism and variations across species pose challenges for biomonitoring. Exposure to bisphenol analogs involves concurrent or sequential exposures to mixtures of bisphenol analogs and other chemicals. Multiple mechanisms of action and the infinite possible combinations of mixtures present a formidable challenge with bisphenol exposures. When the mixture of bisphenol analogs at the average ratio of human exposure was used to conduct in vitro cell studies, it was shown that the mixture had a larger effect on cell viability than BPA [209]. On the other hand, biotransformation of bisphenol analogs can be changed by coexposure, as binary exposures to other phenolic xenobiotics produce inhibitory effects on the BPA metabolism due to competition for metabolizing enzymes [210]. Exposure to a mixture containing dioxin, polychlorobiphenyl, phthalate and bisphenol could reduce the impact of ovariectomy on glucose intolerance and insulin resistance in mice, enhance the expression of the hepatic Erα, and attenuate ovariectomy-induced inflammation [211].

It is imperative to conduct more research to understand the effects of underlying conditions, e.g., malnutrition [212] and diet [213], on liver toxicity induced by bisphenol analogs and other EDCs. Patients with Parkinson’s disease have decreased abilities to glucuronide bisphenol analogs [214]. Lifetime exposure to bisphenol analogs may contribute to the pathogenesis of neurological pathologies such as Alzheimer’s disease [215]. Above all, it is important to recognize the linkage between exposure to bisphenol analogs and liver toxicity, as the liver plays a critical role in many processes and pathogenesis of the various non-communicable diseases of modern times, like NAFLD, diabetes and hypertension. More research into the mechanisms of liver injury will also improve the prediction of liver toxicity from bisphenol analogs and other chemicals, and their risk assessment and legislation.