Effect of Bisphenol-A (BPA) on insulin signal transduction and GLUT4 translocation in gastrocnemius muscle of adult male albino rat

Bisphenol a downregulates GLUT4 expression by activating aryl hydrocarbon receptor to exacerbate polycystic ovary syndrome

BACKGROUND

Bisphenol A (BPA) levels are high in women with polycystic ovary syndrome (PCOS). The mechanism by which BPA induces abnormal glucose metabolism in PCOS patients is largely unknown.

METHODS

Serum and urine samples were collected from women with and without PCOS (control) at the reproductive medicine center with informed consent. Non-PCOS patients who received in vitro fertilization were recruited for collection of ovarian follicular fluid and granular cells. Wild-type C57BL/6 and AhR -/- mice were used to verify the effects of BPA on PCOS. Real-time PCR, western blotting, and ELISA were conducted to analyze the function of BPA. Chip-qPCR verified the role of AhR in GLUT4 transcription. Flow cytometry was performed to determine glucose uptake.

RESULTS

A positive correlation was observed between BPA concentration and serum BPA levels in PCOS patients. BPA aggravated the changes in PCOS with abnormal glucose metabolism, impaired fertility, and increased body fat. Mechanistically, we showed that BPA activated AhR and led to decreased glucose transport via GLUT4 downregulation in ovarian granular cells. Therefore, the use of inhibitors or knockout of AhR could effectively rescue BPA-induced metabolic disorders in PCOS mice.

CONCLUSIONS

Our results revealed that BPA suppressed GLUT4 expression and induced abnormal glucose metabolism by activating AhR, causing insulin resistance, and is thus a potential contributor to the development of PCOS. Therefore, AhR could be a potential new therapeutic target for PCOS. Video Abstract.

Bisphenol A (BPA) and Cardiovascular or Cardiometabolic Diseases

Bisphenol A (BPA; 4,4'-isopropylidenediphenol) is a well-known endocrine disruptor. Most human exposure to BPA occurs through the consumption of BPA-contaminated foods. Cardiovascular or cardiometabolic diseases such as diabetes, obesity, hypertension, acute kidney disease, chronic kidney disease, and heart failure are the leading causes of death worldwide. Positive associations have been reported between blood or urinary BPA levels and cardiovascular or cardiometabolic diseases. BPA also induces disorders or dysfunctions in the tissues associated with these diseases through various cell signaling pathways. This review highlights the literature elucidating the relationship between BPA and various cardiovascular or cardiometabolic diseases and the potential mechanisms underlying BPA-mediated disorders or dysfunctions in tissues such as blood vessels, skeletal muscle, adipose tissue, liver, pancreas, kidney, and heart that are associated with these diseases.

Alterations induced by Bisphenol A on cellular organelles and potential relevance on human health

Bisphenol A (BPA) is a chemical partially soluble in water and exists in a solid state. Its structural similarity with estrogen makes it an endocrine-disrupting chemical. BPA can disrupt signaling pathways at very low doses and may cause organellar stress. According to in vitro and in vivo studies, BPA interacts with various cell surface receptors to cause organellar stress, producing free radicals, cellular toxicity, structural changes, DNA damage, mitochondrial dysfunction, cytoskeleton remodeling, centriole duplication, and aberrant changes in several cell signaling pathways. The current review summarizes the impact of BPA exposure on the structural and functional aspects of subcellular components of cells such as the nucleus, mitochondria, endoplasmic reticulum, lysosome, ribosome, Golgi apparatus, and microtubules and its consequent impact on human health.

Enhancing de novo ceramide synthesis induced by bisphenol A exposure aggravates metabolic derangement during obesity

OBJECTIVE

Exposure to bisphenol A (BPA) has been shown to increase the prevalence of obesity and its related insulin resistance (IR). Ceramide is a sphingolipid known to facilitate the production of proinflammatory cytokines and subsequently exacerbate inflammation and IR during the progression of obesity. Here, we investigated the effects of BPA exposure on ceramide de novo synthesis and whether increased ceramides aggravate adipose tissue (AT) inflammation and obesity-related IR.

METHODS

A population-based case-control study was conducted to explore the relationship between BPA exposure and IR and the potential role of ceramide in AT in obesity. Next, we used mice reared on a normal chow diet (NCD) or a high-fat diet (HFD) to verify the results from the population study and then investigated the role of ceramides in low-level BPA exposure with HFD-induced IR and AT inflammation in mice treated with or without myriocin (an inhibitor of the rate-limiting enzyme in de novo ceramide synthesis).

RESULTS

BPA levels are higher in obese individuals and are significantly associated with AT inflammation and IR. Specific subtypes of ceramides mediated the associations between BPA and obesity, obesity-related IR and AT inflammation in the obesity group. In animal experiments, BPA exposure facilitated ceramide accumulation in AT, activated PKCζ, promoted AT inflammation, increased the expression and secretion of proinflammatory cytokines via the JNK/NF-κB pathway, and lowered insulin sensitivity by disrupting IRS1-PI3K-AKT signaling in mice fed a HFD. Myriocin suppressed BPA-induced AT inflammation and IR.

CONCLUSION

These findings indicate that BPA aggravates obesity-induced IR, which is partly via increased de novo synthesis of ceramides and subsequent promotion of AT inflammation. Ceramide synthesis could be a potential target for the prevention of environmental BPA exposure-related metabolic diseases.

Environmentally relevant doses of endocrine disrupting chemicals affect male fertility by interfering with sertoli cell glucose metabolism in mice

The growing global deterioration in several aspects of human health has been partly attributed to hazardous effects of endocrine-disrupting chemicals (EDCs) exposure. Therefore, experts and government regulatory agencies have consistently advocated for studies on the combined effects of EDCs that model human exposure to multiple environmental chemicals in real life. Here, we investigated how low concentrations of bisphenol A (BPA), and phthalates compounds affect the Sertoli cell glucose uptake/lactate production in the testis and male fertility. An EDC mixture containing a detected amount of each chemical compound in humans, called daily exposure (DE), and DE increased in magnitude by 25 (DE25), 250 (DE250), and 2500 (DE2500), and corn oil (control) were administered for six weeks to male mice. We found that DE activated estrogen receptor beta (Erβ) and glucose-regulated protein 78 (Grp 78) and disrupted the estradiol (E2) balance. In addition, DE25, DE250, and DE2500 doses of the EDC mixture via binding with Sertoli cells' estrogen receptors (ERs) inhibited the glucose uptake and lactate production processes by downregulating glucose transporters (GLUTs) and glycolytic enzymes. As a result, endoplasmic reticulum stress (ERS), marked by unfolded protein response (UPR) activation, was induced. The accompanying upregulation of activating transcription factor 4 (ATF4), inositol requiring enzyme-1 (IRE1), C/EBP homologous protein (CHOP), and mitogen-activated protein kinase (MAPK) signaling promoted antioxidant depletion, testicular cell apoptosis, abnormal regulation of the blood-testis barrier, and decreased sperm count. Therefore, these findings suggest that human and wildlife exposure to multiple environmental chemicals can produce a wide range of reproductive health complications in male mammals.

Citrus peel ameliorates mucus barrier damage in HFD-fed mice

Citrus peel is rich in bioactive components, especially polyphenols, which are considered to have great potential in the prevention of intestinal diseases. The intestinal mucus barrier is the first defense against the invasion of foreign substances. In this study, we aimed to explore the possibility and mechanism of citrus peel in alleviating the mucus barrier damage in high-fat-diet (HFD) mice. We found that citrus peel powder (CPP) supplementation effectively reduced body weight, fat weight, intestinal permeability, hyperlipidemia, and systemic inflammation in HFD-fed mice. In particular, CPP increased the number of goblet cells, the protein expression of Mucin-2 (Muc2), and the thickness of the mucus layer, thereby strengthening the colonic mucus barrier function. Moreover, CPP supplementation also reduced the expression of endoplasmic reticulum stress (ERS) proteins (GRP78 and CHOP) and increased the expression of T-synthase (O-glycosylation rate-limiting enzyme) and its chaperone protein (Cosmc) in the colon of HFD-fed mice, which suggested that CPP could improve the abnormal protein folding and O-glycosylation of Muc2 during processing and modification. In summary, our study indicates that CPP plays an effective role in relieving mucus barrier damage by improving the production and properties of Muc2, providing new perspectives on the development of CPP as a dietary supplement for strengthening the intestinal barrier.

In vivo hypoglycemic effects of bisphenol F exposure in high-fat diet mice

Bisphenol F (BPF) is a widely used bisphenol A (BPA) substitute plastic additive that has attracted increasing public concerns due to its potential toxic effects on animal and human health. Although previous studies have indicated that BPF might have harmful effects on metabolic homeostasis, the systematic effects of BPF on glucose disorders remain controversial. In this study, mice fed a normal chow diet (ND) and high-fat diet (HFD) were administered BPF at a dose of 100 μg/kg of body weight, and glucose metabolism was monitored after both short- and long-term treatment. Little change in glucose metabolism was observed in BPF-treated ND mice, but improved glucose metabolism was observed in BPF-treated HFD mice. Consistently, BPF treatment led to increased insulin signalling in the skeletal muscle of HFD mice. Additionally, liver metabolite levels also revealed increased carbohydrate digestion and improved TCA cycle progression in BPF-treated HFD mice. Our results demonstrate that sustained BPF exposure at an environmentally relevant dosage may substantially improve glucose metabolism and enhance insulin sensitivity in mice fed a high-fat diet.

Obesity II: Establishing causal links between chemical exposures and obesity

Obesity is a multifactorial disease with both genetic and environmental components. The prevailing view is that obesity results from an imbalance between energy intake and expenditure caused by overeating and insufficient exercise. We describe another environmental element that can alter the balance between energy intake and energy expenditure: obesogens. Obesogens are a subset of environmental chemicals that act as endocrine disruptors affecting metabolic endpoints. The obesogen hypothesis posits that exposure to endocrine disruptors and other chemicals can alter the development and function of the adipose tissue, liver, pancreas, gastrointestinal tract, and brain, thus changing the set point for control of metabolism. Obesogens can determine how much food is needed to maintain homeostasis and thereby increase the susceptibility to obesity. The most sensitive time for obesogen action is in utero and early childhood, in part via epigenetic programming that can be transmitted to future generations. This review explores the evidence supporting the obesogen hypothesis and highlights knowledge gaps that have prevented widespread acceptance as a contributor to the obesity pandemic. Critically, the obesogen hypothesis changes the narrative from curing obesity to preventing obesity.

In Vitro Effects of Emerging Bisphenols on Myocyte Differentiation and Insulin Responsiveness

Bisphenols are endocrine disrupting chemicals to which humans are ubiquitously exposed to. Prenatal bisphenol A exposure can lead to insulin resistance. However, the metabolic effects of other emerging bisphenols, such as bisphenol S (BPS) and bisphenol F (BPF), are less understood. Because the skeletal muscle is the largest of the insulin target tissues, the goal of this study was to evaluate the effects of 2 emerging bisphenols (BPS and BPF) on cytotoxicity, proliferation, myogenic differentiation, and insulin responsiveness in skeletal muscle cells. We tested this using a dose-response approach in C2C12 mouse and L6 rat myoblast cell lines. The results showed that C2C12 mouse myoblasts were more susceptible to bisphenols compared with L6 rat myoblasts. In both cell lines, bisphenol A was more cytotoxic, followed by BPF and BPS. C2C12 myoblast proliferation was higher upon BPF exposure at the 10-4 M dose and the fusion index was increased after exposure to either BPF or BPS at doses over 10-10 M. Exposure to BPS and BPF also reduced baseline expression of p-AKT (Thr) and p-GSK-3β, but not downstream effectors such as mTOR and glucose transporter-4. In conclusion, at noncytotoxic doses, BPS and BPF can alter myoblast cell proliferation, differentiation, and partially modulate early effectors of the insulin receptor signaling pathway. However, BPS or BPF short-term exposure evaluated here does not result in impaired insulin responsiveness.

Long-term exposure to low doses of bisphenol S has hypoglycaemic effect in adult male mice by promoting insulin sensitivity and repressing gluconeogenesis

Bisphenol S (BPS), an industrial chemical that is a structural analogue of bisphenol A, has been widely reported to be involved in various biological processes. Epidemiological studies have demonstrated that exposure to BPS is associated with dysglycaemia-related health outcomes. The role of BPS in glucose metabolism, however, remains controversial. In this study, we aimed to investigate the effects of chronic exposure to environmentally relevant concentrations of BPS on glucose metabolism in different nutritionally conditioned mice. Our results revealed that 1-month exposure to a BPS dosage of 100 μg/kg bw slightly increased the insulin sensitivity of normal diet-fed mice, and that this effect was enhanced after 3-month exposure. It was also found that BPS exposure attenuated insulin resistance and reduced gluconeogenesis in high-fat diet-fed mice. Consequently, the concentrations of hepatic metabolites related to glucose metabolism were altered in both groups of mice. Moreover, thyroid hormone signalling was disrupted after BPS administration in both groups of mice. Taken together, our results demonstrated that chronic exposure to environmentally relevant concentrations of BPS exerted an unexpected hypoglycaemic effect in mice of different nutritional statuses, and that this was partly attributable to disrupted thyroid hormone signalling.

Bisphenol A disturbs metabolism of primary rat adipocytes without affecting adipokine secretion

Bisphenol A (BPA) is an ubiquitous synthetic chemical exerting numerous adverse effects. Results of rodent studies show that BPA negatively affects adipose tissue. However, the short-term influence of this compound addressing adipocyte metabolism and adipokine secretion is unknown. In the present study, isolated rat adipocytes were exposed for 2 h to 1 and 10 nM BPA. Insulin-induced glucose conversion to lipids along with glucose transport was significantly increased in the presence of BPA. However, basal glucose conversion to lipids, glucose oxidation, and formation of lipids from acetate were unchanged in adipocytes incubated with BPA. It was also shown that BPA significantly increases lipolytic response of adipocytes to epinephrine. However, lipolysis stimulated by dibutyryl-cAMP (a direct activator of protein kinase A) and the antilipolytic action of insulin were not affected by BPA. Moreover, BPA did not influence leptin and adiponectin secretion from adipocytes. Our new results show that BPA is capable of disturbing processes related to lipid accumulation in isolated rat adipocytes. This is associated with the potentiation of insulin and epinephrine action. The effects of BPA appear already after short-term exposure to low doses of this compound. However, BPA fails to change adipokine secretion.

Bisphenols and the Development of Type 2 Diabetes: The Role of the Skeletal Muscle and Adipose Tissue

Bisphenol A (BPA) and bisphenol S (BPS) are environmental contaminants that have been associated with the development of insulin resistance and type 2 diabetes (T2D). Two organs that are often implicated in the development of insulin resistance are the skeletal muscle and the adipose tissue, however, seldom studies have investigated the effects of bisphenols on their metabolism. In this review we discuss metabolic perturbations that occur in both the skeletal muscle and adipose tissue affected with insulin resistance, and how exposure to BPA or BPS has been linked to these changes. Furthermore, we highlight the possible effects of BPA on the cross-talk between the skeletal muscle and adipose tissue.

Metabolically healthy obese vs. Metabolic syndrome - The crosslink between nutritional exposure to bisphenols and physical exercise

Obesity has become a worldwide pandemic as well as a major contributing factor to the increasing rate of type 2 diabetes (T2D). However, there is an intriguing variance demonstrated by a subset of obesity defined as metabolically healthy obesity (MHO). MHO individuals are less prone to develop obesity-related metabolic complications, such as metabolic syndrome (MetS) and further T2D. The exact reason why an MHO person does not present the cluster of risk factors associated with insulin resistance is unknown due to the challenge to mimic MHO in experimental settings. However, MHO individuals present lower sedentary behaviors in comparison to individuals with MetS, which might indicate that an adaptation to skeletal muscle, such as increased insulin sensitivity and glucose transporter (GLUT4), could play a major role in their healthy characteristics. The hypothesis invoked in this paper is that lower exposure to bisphenol together with increased levels of physical exercise underlie the physiological aspects behind MHO characteristics. Evidence suggests that exposure to "obseogens," such as bisphenol A (BPA), appears to impair insulin secretion and insulin response in cells containing GLUT4. Epidemiological studies have associated higher levels of BPA, as well as bisphenol S and F, in children with a risk for MetS development. Therefore, the combination between low bisphenol exposure and increased physical exercise may not necessarily affect body weight, but it could modify several metabolic pathways inhibiting insulin resistance, which characterize the heathy status of the MHO. If confirmed, this hypothesis could lead to therapeutic approaches to reverse MetS and inhibit T2D onset.

Gestational Exposure to Bisphenol A and Bisphenol S Leads to Fetal Skeletal Muscle Hypertrophy Independent of Sex

Gestational exposure to bisphenol A (BPA) can lead to offspring insulin resistance. However, despite the role that the skeletal muscle plays in glucose homeostasis, it remains unknown whether gestational exposure to BPA, or its analog bisphenol S (BPS), impairs skeletal muscle development. We hypothesized that gestational exposure to BPA or BPS will impair fetal muscle development and lead to muscle-specific insulin resistance. To test this, pregnant sheep (n = 7-8/group) were exposed to BPA or BPS from gestational day (GD) 30 to 100. At GD120, fetal skeletal muscle was harvested to evaluate fiber size, fiber type, and gene and protein expression related to myogenesis, fiber size, fiber type, and inflammation. Fetal primary myoblasts were isolated to evaluate proliferation and differentiation. In fetal skeletal muscle, myofibers were larger in BPA and BPS groups in both females and males. BPA females had higher MYH1 (reflective of type-IIX fast glycolytic fibers), whereas BPS females had higher MYH2 and MYH7, and higher myogenic regulatory factors (Myf5, MyoG, MyoD, and MRF4) mRNA expression. No differences were observed in males. Myoblast proliferation was not altered in gestationally BPA- or BPS-exposed myoblasts, but upon differentiation, area and diameter of myotubes were larger independent of sex. Females had larger myofibers and myotubes than males in all treatment groups. In conclusion, gestational exposure to BPA or BPS does not result in insulin resistance in fetal myoblasts but leads to fetal fiber hypertrophy in skeletal muscle independent of sex and alters fiber type distribution in a sex-specific manner.

The effect of BPA exposure on insulin resistance and type 2 diabetes - The impact of muscle contraction

Type 2 diabetes (T2D) is considered one of the leading causes of death worldwide. In addition to physical inactivity and obesity, established risk factors for T2D, chemical contaminants consumed in industrialized food such as BPA might also be a contributor to the development of T2D. Epidemiological studies have shown that BPA concentrations are higher in human specimens of T2D when compared to healthy subjects, while experimental studies suggested that bisphenol A (BPA) impairs the pathway by which insulin stimulates glucose uptake. In skeletal muscle and adipocytes, insulin resistance is developed by the impairment of the insulin pathway to stimulate the translocation of glucose transporter, GLUT4, to the cell membrane. Recent results demonstrated that BPA impairs several components of insulin-induced glucose uptake pathway and affect the expression of GLUT4. Regular physical exercise delays or inhibits the development of T2D due to the physiologic processes taking place during muscle contraction, and the fact that skeletal muscle is the site for almost 80% of the glucose transported under insulin stimulation. In fact, the mechanism by which contraction induces glucose uptake in skeletal muscle is partially independent of the insulin pathway, therefore, the effect of BPA on this mechanism is unknown. We hypothesize that during the development of insulin resistance, BPA contributes to the impairment of the molecular pathway by which insulin induces glucose uptake while contraction-induced glucose uptake is not impaired. At the late stages of T2D, BPA may affect GLUT4 expression that will decrease the ability of muscle contraction to induce glucose uptake.

Bisphenol A exposure under metabolic stress induces accelerated cellular senescence in vivo in a p53 independent manner

Senescence is an irreversible process that is a characteristic of age-associated disease like Type 2 diabetes (T2D). Bisphenol-A (BPA), one of the most common endocrine disruptor chemicals, received special attention in the development of insulin resistance and T2D. To understand the role played by BPA in cellular senescence under metabolic stress, zebrafish embryos were exposed to BPA in the absence and presence of hyperglycaemia. Transcriptional levels of the senescence markers p15, p53, Rb1 and β-galactosidase were increased when BPA was combined with metabolic stress. In addition, zebrafish embryos that were exposed to combination of hyperglycaemia and BPA exhibited increased levels of apoptosis. However, cellular senescence remained induced by a combination of hyperglycaemia and BPA exposure even in the absence of a translated p53 protein suggesting that senescence is primarily independent of it but dependent on the p15-Rb1 pathway under our experimental conditions. To confirm that our results hold true in adult mammalian tissues, we validated our embryonic experiments in an adult mammalian metabolic model of skeletal muscle cells. Our work reveals a novel and unique converging role of senescence and apoptosis axis contributing to glucose dyshomeostasis. Thus, we conclude that BPA exposure can exacerbate existing metabolic stress to increase cellular senescence that leads to aggravation of disease phenotype in age-associated diseases like type 2 diabetes.

Oral Administration of Resveratrol-Loaded Solid Lipid Nanoparticle Improves Insulin Resistance Through Targeting Expression of SNARE Proteins in Adipose and Muscle Tissue in Rats with Type 2 Diabetes

In the current study, we developed resveratrol (RES)-loaded solid lipid nanoparticle (SLN-RES) in order to improve insulin resistance through the upregulation of SNARE protein complex in rats with type 2 diabetes. The SLN-RES characteristics include the following: the average size of 248 nm, the zeta potential of - 16.5 mV, and 79.9% RES entrapment efficiency. The release profile of SLN-RES showed an initial burst followed by a sustained release in natural condition. Infrared spectroscopy results revealed good incorporation of RES into core SLN. Spherical nanoparticle with less aggregation was observed under electronic microscopic examination. Oral administration of SLN-RES prevented weight loss and showed better hypoglycemic effect than RES. Serum oxidative stress status was restored to the normal level by SLN-RES. Furthermore, expression of synaptosomal-associated protein 23 (Snap23), syntaxin-4 (Stx4), and vesicle-associated membrane protein 2 (Vamp2) as the major elements of SNARE protein complex were reduced by SLN-RES more significantly than RES treatment in muscle tissue. However, SLN-RES has a similar effect to RES treatment in adipose tissue. Taken together, our results revealed SLN-RES could be a modern and interestingly therapeutic approach for the improvement of insulin resistance through targeting the expression of Snap23, Stx4, and Vamp2 in adipose and muscle tissues.

Impact of polyvinyl chloride, polystyrene, and polyethylene on the organism of mice

Goods of plastic, due to their durability, universality and economical properties are broadly used in all spheres of life. On the whole, polymers are inert and nontoxic, but in the process of their production, various additives are used, which on contact or introduction into an organism has a negative effect on it. In our study, we determined the impact of some types of plastic (polyvinyl chloride, polysterene and polyethylene) on the organism of laboratory animals according to changes in their body weight, indices of mass of the internal organs, and blood parameters. For the experiment, we formed four groups of white male mice at the age of 3 weeks and average body weight of 50 g. For each group, we used different litter. For group I, the litter was sawdust; and for the other groups we added plastic products in different volumes to the sawdust; for group II finely cut polyvinyl chloride, for group III cut polyethylene, and for group IV granules of polystyrene. Every 3 days, we determined the body weight of the animals, and 32 days later we determined mass of the organs, clinical and biochemical parameters of the blood. Addition of polyvinyl chloride, polyethylene, and polystyrene into the substrate for mice did not have a significant effect on tempi of growth of body weight, and also relative mass of heart and lungs. Polyvinyl chloride and polystyrene have an immune-suppressive effect, and polyvinyl chloride affects both central and peripheral organs, and polystyrene mostly harms the peripheral organs. All used types of plastic cause leukocytopenia, following which neutrophilia of band neutrophils and monocytosis takes place as a result of damage to the biological barriers. We determined the systemic toxic effect of the studied types of plastic on the internal organs, which manifested in increase in their mass (liver, kidneys), steep increase in the activity of liver enzymes (AST, ALT), simultaneous decrease in activity of alkaline phosphatase and content of cholysterol and glucose in the blood serum of the mice. Also polyvinyl chlorine, polyethylene and polystyrene cause degeneration of the epithelium of the uriniferous tubule, which is manifested in reduction of globulins and creatinine in the blood of animals from the experimental groups following increase in relative mass of the kidneys. The results of our research allow us to state that different types of plastic can cause toxic effect on animals, as well as people who are in frequent contact with them.