Metabolic Syndrome (MS), obesity and type 2 diabetes have drastically increased to epidemic levels worldwide in the last few decades. The World Health Organization has defined obesity as an increment in adipose tissue (AT) mass which may or may not be detrimental to health [1
]. These illnesses have been attributed mainly to changes in lifestyle, including dietary habits. Fructose rich diet (FRD) consumption has been shown to be associated with insulin resistance [2
], hyperadiposity, hypertriglyceridemia, hyperleptinemia [3
], hyperglycemia, hyperinsulinemia, impaired glucose tolerance [4
] and hepatic steatosis [5
], in both animal models and humans.
Diseases in adulthood may originate during an individual’s development, due to changes in the environment in which the individual is subjected to [6
]. Factors that may alter the environment can include maternal nutrition, either during gestation and lactation [7
]. Several studies highlighted the undesirable consequences of maternal unbalanced diet intake during gestation and/or lactation for the offspring’s health in adult life [9
]. Different works have focused on the effects of feeding mothers a FRD during gestation and lactation, showing that their offspring displayed an increased risk of developing obesity in adult life [11
]. We previously reported deleterious metabolic-endocrine function of pups born to FRD-fed lactating mothers [13
]. These pups developed changes in the hypothalamic circuitry controlling appetite, impaired peripheral insulin sensitivity, and both hyperleptinemia and visceral adipocyte hypertrophy [13
Carbohydrates are major metabolites involved in fetal growth and metabolism, and it is accepted that fructose is present in fetal circulation [14
]. The intake of refined sugar, particularly high-fructose corn syrup, has increased in the United States from a yearly estimate of 8.1 kg/individual at the beginning of the 19th century up to 65 kg/person in 2010 [15
]. However, limited data exist on the consequences of FRD intake through the mother for the offspring’s metabolic programming [16
]. Indeed, most of the international literature showed studies wherein experimental designs were devoted to mothers consuming FRD throughout gestation and lactation or only while lactating [11
It was reported recently that adult male offspring born to FRD-fed dams throughout gestation developed insulin resistance, dyslipidemia, a distorted pattern of peripheral adipokines and enhanced oxidative stress [21
]. Interestingly, later in life, the offspring normalized leptinemia, but became hypoadiponectinemic [22
]. Conversely, a recent study showed that FRD intake by gestating mothers resulted in pronounced maternal dysfunctions but no major undesirable metabolic effects on offspring, even after following their progress up to 6 months of age [23
The current study was designed to test whether or not the feeding of mothers with a FRD throughout gestation modifies endocrine-metabolic biomarkers and in vivo and in vitro AT functions in adult male progeny. Moreover, we aimed to determine in utero fructose exposure impact on adult rats challenged or not with a FRD during adult lifetime.
Our results clearly demonstrate a deleterious effect on male offspring’s endocrine-metabolic and adiposity functions induced by feeding pregnant rats a FRD. The consequences of this diet intake by the pregnant mother were evident when pups reached 60 days of age. At that time, male offspring showed dyslipidemia, hyperleptinemia, impaired glucose tolerance and adipocyte hypertrophy; several dysfunctions were further aggravated after offspring were re-challenged with FRD for three weeks.
Epidemiological and experimental studies demonstrated a relationship between maternal nutrition and long-term metabolic consequences in the offspring. Under-/malnourishment [31
] or over-nourishment [34
] in pregnant mothers induces in their offspring severe endocrine, metabolic and adiposity dysfunctions. In effect, FRD intake during both pre- and early post-natal periods impairs INS and LEP cell signaling, thereby modifying carbohydrate metabolism in the progeny [11
]. Previous studies have shown that mothers consuming a FRD during both gestation and lactation resulted in offspring characterized by dyslipidemia [36
] and insulin resistance [37
]. Other studies showed that offspring consumption of a rich carbohydrate-milk during lactation increased plasma levels of INS and LEP, and also BW, resulting in pancreatic disorders [12
]. Moreover, FRD-intake by pregnant rats was reported to affect both mother and fetal metabolism by enhancing lipogenesis and hepatic endoplasmic reticulum stress [38
]. The deleterious consequences of FRD administration to pregnant mothers have been previously addressed. This diet is able to induce altered glucose tolerance, hyperinsulinemia and reduced placental vascular area, thus leading to high risk for the mother of developing gestational diabetes and preeclampsia [24
]; moreover, their fetuses (embryonic day 20) displayed increased BW. Interestingly, these dysfunctions were fully prevented by metformin co-treatment [24
], thereby indicating that impaired overall insulin sensitivity in the mother seems to be mainly responsible for these FRD effects.
A relevant observation made throughout the present study is that the detrimental consequences on AT endocrine function seen in F animals (which never consume FRD) are similar to those developed by CF animals. In both situations, a higher basal leptinemia and hypertrophic adipocytes from RPAT were found. However, while FRD administration to the adult offspring is able to enhance adiponectinemia in CF animals, we found that in F animals there was no change in plasma adiponectin concentration. These findings highlight that the AT seems to be the main target for this diet-noxa, and highlight the importance of the perinatal environment for an individual’s development.
It is well known that AT endocrine dysfunction associated to obesity is closely related to adipocyte size, rather than to pad mass [39
], and hypertrophic adipocytes are characterized by impaired insulin sensitivity [40
] and changes in the adipokine secretory pattern, including higher leptin production [39
]. Therefore, enhanced adipocyte size could well explain the hyperleptinemia found in F animals despite AT mass decrease. Changes in LEP concentration could contribute to impaired peripheral insulin sensitivity [42
]. In the present study, the male offspring born to FRD-fed gestating mothers displayed an apparent paradoxical situation; although, they have a lower AT mass it has large adipocytes. These results could indicate a lower number of adipocytes. It has been found that, in both humans and animal models, AT development occurs mainly during late pregnancy and early postnatal life [43
]. In fact, the ability to generate new adipocytes in adult life is limited; as a consequence, the number of adipocytes remains relatively stable. Therefore, it is possible to speculate that lower adipocyte numbers is a consequence of the alterations in APC determination during the AT development, leading to a decrease in adipocyte generation [43
]. Then, considering this unusual situation, we next examined the cellular composition of the RPAT SVF to determine whether cell hypertrophy and low pad mass could be a result of a lower APC number. Interestingly, a low number of APCs, CD34+
] was found in F RPAT pads. This diminished APC number could be responsible for an impaired adipogenic potential [45
], and therefore leading to the development of hypertrophic adipocytes. To our knowledge, this is the first study that shows changes in APC numbers induced by excessive prenatal fructose intake.
Indeed, malnutrition during perinatal life could trigger changes in DNA methylation and in histone acetylation/methylation, causing transcriptional changes of key factors involved in adipogenesis (C/EBPα, PPARγ) [47
]. Examples of this emerge from several studies, such as those findings indicating that, during differentiation of 3T3-L1 cells, there is a modification in the DNA methylation degree (i.e.
, PPAR, C/EBP, LEP, GULT4) [49
] and in histone methylation/acetylation [53
], thus demonstrating the relevance of epigenetic regulation during the adipogenic process. It is reasonable to speculate that, at least partially, AT dysfunction found in offspring born from FRD mothers could be a consequence of epigenetic changes. Further research is needed to better clarify the role of epigenetic modifications in our model. Given the endocrine-metabolic alterations that we found in 60 day-old animals from FRD-fed mothers, we proposed studying the response of these rats to a direct challenge with FRD in adult life. For this purpose, we treated C and F 60 day-old rats with a FRD or a normal diet for three weeks (achieving 81 days of life), which has been widely used as an animal model of the human MS [30
]. When older (81-day-old) pups were studied, surprisingly, we found a remarkably deteriorated AT function and metabolic state in FC pups. These rats had higher basal plasma levels of TG and GLU than CC rats, despite no changes in insulinemia, whereas offspring’s hyperleptinemia and RPAT hypertrophic adipocytes remained. In this regard, it has been previously reported that FRD intake in rats induced severe basal hyperglycemia, with concomitant normoinsulinemia, accompanied by a high risk of cardiovascular events [55
]. In our experiments with 81 day-old rats, we noticed that the FRD challenge to control animals (CF), increased circulating levels of TG, LEP and ADIPOQ, as well as RPAT pad mass and adipocyte size, confirming our previous data [30
]. Nevertheless, the consequences of direct FRD administration to male offspring born to FRD-fed mothers (FF rats) were even more serious: they showed increased caloric intake, body weight, and plasma levels of GLU, TG and LEP, thus indicating they could be developing diabetes type 2.
Unlike the FC group and similar to findings in the 60-day-old F male offspring, there was no increase in peripheral levels of ADIPOQ. It is well known that ADIPOQ acts as an insulin-sensitizing factor [56
]. In fact, ADIPOQ regulates glucose metabolism by improving insulin signaling pathway [57
], enhancing liver and muscle glucose uptake, decreasing hepatic glucose output [58
] and enhancing fatty acid oxidation [60
]. Therefore, an increase in ADIPOQ plasma levels observed in 81 day-old control animals challenged with FRD (CF rats in Table 3
) might play a protective role in carbohydrate metabolism. These results are in full agreement with those previously reported from our laboratory [30
]. The lack of a physiological increase in adiponectin secretion in FF animals is highly indicative of the loss of its protective effect on carbohydrate dys-metabolism, contributing to the worsening of overall metabolic derangements.
Overall, the present study shows that maternal consumption of fructose during gestation alters offspring’s development causing metabolic and AT dysfunctions. At 60 days of age, rats born to FRD-fed mothers showed impaired insulin sensitivity and profound AT dysfunction, evidenced by hypertrophic adipocytes that secrete in vitro larger amounts of LEP, although with decreased AT mass. This paradoxical situation could be the result, at least partially, of the reduced APC number, present in RPAT from F rats. At 81 days old, the results of FC rats corroborate that the impact of FRD on pups worsened the metabolic profile throughout their lifetime, even when they were not directly exposed to this diet. These changes are clearly aggravated when the offspring directly consume FRD during adulthood.
Considering that hypertrophic expansion of AT mass is a key marker for AT dysfunction, we further conclude that high fructose consumption by pregnant mothers primes the first male generation with a high risk of developing MS, obesity and type 2 diabetes. To our knowledge, this study is the first to report changes in adipose precursor cells numbers, induced by in utero diet manipulation. However, the impact of high fructose in utero on overall developmental programming of individuals requires deeper research.