Maternal exposure to environmental chemicals, such as endocrine disrupting chemicals (EDCs), can increase disease risk later in life. This concept is known as the developmental origins of health and disease (DOHaD) [1
]. One of the most commonly environmental EDC exposures is bisphenol A (BPA). Though the U.S. Food and Drug Administration and European Food Safety Authority have banned BPA from infant formula bottles, many plastic food and drinking containers still contain BPA. BPA has been reported to be associated with the development of cardiovascular disease and hypertension in both children and adults [2
]. A previous study showed that exposure to BPA during pregnancy is associated with higher blood pressure (BP) of children [3
]. However, the impacts of maternal BPA exposure on BP in adult offspring remain unclear.
High-fat (HF) consumption is closely linked to the development of hypertension [4
]. Our previous report demonstrated that a maternal plus post-weaning HF diet induced hypertension in adult male offspring [5
]. Development is a plastic process that is sensitive to environmental insults including nutrition, stress, drugs, and environmental pollutants. These environmental insults may interact with each other, resulting in an increased susceptibility to similar diseases. Since a second insult or challenge could deteriorate earlier programming effects induced by the first insult, we hypothesized that BPA exposure enhances offspring vulnerability to HF diet-induced programmed hypertension.
BPA acts as an endogenous estrogen by interacting with estrogen receptors [6
]. Estrogen acts as a vasodilator by regulating the nitric oxide (NO) system [7
]. Additionally, BPA is a ligand for the aryl hydrocarbon receptor (AHR). The AHR is involved in the transcription of distinct genes that are associated with hypertension [8
]. Our previous studies suggest that the NO and AHR signaling pathways both contribute to the pathogenesis of hypertension of developmental origins [9
Conversely, several therapeutic strategies by so-called reprogramming have been applied to reverse the programming processes and prevent the development of hypertension [11
]. Resveratrol is a naturally occurring phytoalexin found in various plants, especially berry fruits, and it is a popular nutritional supplement. Resveratrol possesses many beneficial effects include anti-inflammatory and antioxidant properties, anti-obesogenic and anti-atherosclerotic effects, anti-carcinogenic activity, the inhibition of platelet aggregation, the improvement of endothelial function, the restoration of NO bioavailability, and the ability to serve as an AHR antagonist [12
]. Emerging evidence supports the idea that resveratrol might serve as a reprogramming strategy to prevent a variety of disorders, including hypertension [12
]. Additionally, resveratrol has been reported to prevent BSA-induced vascular toxicity [13
BP is regulated by a complex process that is controlled mainly by the kidney. The developing kidney is vulnerable to suboptimal early-life environments, which may produce renal programming and programmed hypertension [11
]. We investigated whether combined maternal BPA and HF exposure induced programmed hypertension in adult male offspring via the activation of AHR signaling and disturbing NO pathways and whether resveratrol can protect against hypertension programmed by combined BPA and HF exposure, with a focus on the kidney.
This study casts a new light on the links of the ADMA–NO pathway, oxidative stress, and the AHR signaling pathway in the kidney by which maternal resveratrol treatment attenuates hypertension programmed by combined BPA and HF exposure in adult male offspring. The key contributions of this work are presented as follows: (1) Maternal BPA exposure exacerbates hypertension programmed by dams exposed to an HF diet in adult male offspring; (2) resveratrol treatment moderates hypertension programmed by BPA or HF + BPA; (3) there was a synergistic effect of the HF diet and BPA exposure on inducing oxidative damage in offspring kidneys, which resveratrol treatment prevented; (4) HF + BPA-induced programmed hypertension is related to decreases of NO bioavailability, increases of oxidative stress, and the activation of the AHR signaling pathway; and (5) resveratrol restores NO bioavailability, reduces oxidative stress, and antagonizes AHR signaling so that HF + BPA-induced hypertension is prevented in adult male offspring.
Early BPA exposure has been associated with an increased risk of developing obesity, diabetes, and cardiometabolic diseases [16
]. As far as we know, no previous research has investigated whether early exposure to BPA and/or HF diet increases the vulnerability of offspring to hypertension in later life. In the current study, BPA was administered at a dose of 50 μg/kg bodyweight/day based on the estimated human exposure levels and the current oral reference dose set by the US Environmental Protection Agency (USEPA) [18
]. Though this dose is likely to be without a considerable risk of deleterious effects during a lifetime [18
], our data show mother rats exposed to low doses of BPA during pregnancy and lactation not only caused the elevation of BP in their adult offspring but also aggravated hypertension programmed by the maternal HF diet. Our results are agreement with previous studies showing that different insults could be synergistically contributing to renal programming and programmed hypertension [9
]. Of note is that the increases of BP were mitigated by maternal resveratrol therapy. Though resveratrol has been reported to lower BP in adult hypertension [20
], few studies are available regarding dams exposed to resveratrol protecting programmed hypertension in their adult offspring [12
]. To our knowledge, this is the first report showing that resveratrol administration during pregnancy and lactation periods protects adult offspring against hypertension programmed by combined maternal BPA and HF exposure.
Certain mechanisms contributing to the protective effects of resveratrol against HF + BPA-induced hypertension have been observed, such as the reduction of oxidative stress, the restoration of NO bioavailability, and the abrogation of AHR activation. Early-life oxidative stress attributed to NO–ROS imbalance is considered as a key mechanism underlying programmed hypertension [14
]. A variety of prenatal insults have been associated with oxidative stress to lead to renal programming and programmed hypertension [21
], including a maternal HF diet [5
]. Though research has reported that BSA exposure can induce oxidative stress, resulting in kidney damage [22
], no study to date has examined whether hypertension programmed by maternal BPA exposure is associated with oxidative stress. Our data address that BPA not only increases 8-OHdG staining, an oxidative stress damage marker, but also exacerbates HF-induced increases of 8-OHdG staining. Conversely, resveratrol improves oxidative stress, represented by lower 8-OHdG staining in both the BPA + R and HF + BPA + R groups. These findings tie in well with previous studies wherein the beneficial effects of resveratrol were noted as, at least in part, due to its antioxidant properties [9
Another protective mechanism of resveratrol on BPA + HF-induced programmed hypertension may be related to the restoration of NO bioavailability. Conflicting a previous study showing that BPA at the dose ranged from 1 to 100 μM increased NO2−
production in murine endothelial cells [23
], we found that the urinary level of NO2−
was decreased in the BPA-treated offspring. NO is a vasodilator. We observed that both indices of NO bioavailability, l
-arginine-to-ADMA ratio and the NO2−
level, were reduced in the BPA + HF group. Additionally, BPA + HF caused the elevation of BP and was associated with decreased renal protein levels of eNOS and nNOS, an increased plasma ADMA level, and decreased DDAH activity. Our data support a close link between the ADMA–NO pathway and programmed hypertension, which concurs with previous studies from our laboratory and other [14
]. On the contrary, resveratrol therapy increased the plasma l
-arginine level, restored the decreased protein levels of eNOS and nNOS, improved renal DDAH activity, and the increased NO2−
level. Our data are in agreement with previous studies showing that the early restoration of the ADMA–NO pathway, prior to hypertension in favor of NO, is able to prevent the development of hypertension in different hypertensive models [14
Additionally, the beneficial effects of resveratrol therapy could be due to the antagonization of the AHR signaling pathway. Like other EDCs, BPA is a ligand for the AHR. It has been reported that the AHR agonist ligand 2,3,7,8-tetrachlorodibenzo-p
-dioxin (TCDD) has induced a high BP, and, in this process, AHR target genes like Ahrr
may be involved [8
]. The AHR repressor (AHRR) is an AHR-regulated gene and a negative regulator of the AHR by competing with the AHR for the binding of the AHR nuclear translocator (ARNT) [8
]. Our results demonstrated that BPA significantly increased the protein level of the AHR as well as the mRNA expression of Ahrr
in the HF + BPA-treated offspring kidneys. These findings indicate that BPA activates the AHR signaling pathway, which appears to be correlated with the elevation of BP. Though the AHR has been reported to protect high-fat diet-induced adverse phenotypes in adult mice [26
], this notion is not supported by our data, which showed that a maternal HF diet had no effect on the AHR signaling pathway in the offspring. Nevertheless, these HF + BPA-induced increases of the AHR protein and the mRNA expression of Ahrr
were restored by resveratrol therapy. The present observations suggest that resveratrol may act as an AHR antagonist and inhibit BPA-induced AHR target gene expression.
One limitation in the current study is that we did not conduct control + R, BPA + R, and HF + R groups. One reason is because resveratrol has no prior history of toxicity in humans [27
]. Additionally, we mainly focused on studying the reprogramming effect of resveratrol on the two-hit HF + BPA model rather than the one-hit model. However, whether maternal resveratrol therapy might cause long-term reprogramming changes in offspring prenatally exposed to BPA or HF alone remains to be clarified. Next, we did not examine different doses and exposures of BPA. Given that BPA effects could be very different for low and high doses [28
], it would be interesting to determine whether various exposure protocols of BPA lead to differential phenotypes of adult offspring. Moreover, we did not examine other organs involved in BP control, such as the vasculature, heart, and brain. The beneficial effects of maternal resveratrol therapy might be derived from these organs.