Coplanar polychlorinated biphenyls impair glucose homeostasis in lean C57BL/6 mice and mitigate beneficial effects of weight loss on glucose homeostasis in obese mice

Exposure to PCB52 (2,2',5,5'-tetrachlorobiphenyl) blunts induction of the gene for uncoupling protein 1 (UCP1) in white adipose

Polychlorinated biphenyls (PCBs) are linked to cancer, learning disabilities, liver and cardiovascular disease, and diabetes. Older schools often contain high levels of PCBs, and inhalation is a major source of exposure. Technical PCB mixtures, called Aroclors, and individual dioxin-like PCBs impair adipocyte function, which can lead to type II diabetes. To determine how PCB52, a non-dioxin like PCB congener found in school air, affects adipose, adolescent male and female rats were exposed to PCB52 by nose-only inhibition for 4h per day for 28 consecutive days. Transcriptomic analysis of white adipose revealed sex-specific differences in gene expression between PCB52- and sham-exposed males and females. Exposed females showed mitochondrial gene changes, including downregulation of the thermogenic uncoupling gene, Ucp1. Human preadipocytes/adipocytes exposed to PCB52 or its main metabolite, 4-OH-PCB52, also showed reduced norepinephrine-induced UCP1 expression. These findings suggest that PCB52 inhalation disrupts thermogenesis in adipose tissue, potentially contributing to metabolic syndrome.

Volatile organic compounds exposure in relation to glucose homeostasis and type 2 diabetes in older adults from the NHANES

The impact of volatile organic compounds (VOCs) on type 2 diabetes (T2D) among older adults is unknown. The multiple linear regression model and the multiple binary logistic regression were used to evaluate the relationships between mVOCs and glucose homeostasis/T2D, respectively. Among the 19 mVOCs, the higher levels of urinary N-acetyl-S-(2-hydroxypropyl)-L-cysteine (2HPMA, compound CID:44146439) and N-acetyl-S-(2-hydroxypropyl)-L-cysteine (HPMMA, compound CID:107774684) were significantly associated with higher odds of T2D (OR = 1.16, 95% confidence interval [CI]:1.01-1.34 for 2HPMA; and OR = 1.27, 95% CI:1.04-1.54 for HPMMA). In addition, higher concentrations of multiple mVOCs in urine were significantly correlated with glucose homeostasis biomarkers, including 2HPMA and 2-thioxothiazolidine-4-carboxylic acid (TTCA, compound CID:3034757) with fasting glucose, HPMMA and mandelic acid (MA, compound CID:1292) with HbA1c, phenylglyoxylic acid (PGA, compound CID:11915) with serum insulin, HbA1c and HOMA-IR. Our findings suggested that exposure to VOCs were associated with increased odds of T2D in older adults, which might be mediated by impaired glucose homeostasis. Mitigating VOCs should be a necessary component of public health strategies aimed at reducing the burden of type 2 diabetes.

Metabolic consequences of interesterified palm oil and PCB-126 co-exposure in C57BL/6 mice

Metabolic dysfunction-associated steatotic liver disease (MASLD) is defined as morphofunctional changes in the liver. Studies have shown that Westernized eating patterns and environmental pollutants can directly induce the development of MASLD. This study evaluates the effect of co-exposure to interesterified palm oil (IPO) and 3,3',4,4',5-pentachlorobiphenyl (PCB-126) on the progression of MASLD in an animal model. C57BL/6 mice were fed IPO and co-exposed to PCB-126 for ten weeks. The co-exposure led to an imbalance in carbohydrate metabolism, increased systemic inflammation markers, and morphofunctional changes in the liver. These liver changes included the presence of inflammatory cells, fibrosis, alterations in aspartate transaminase (AST) and alanine transaminase (ALT) enzymes, and imbalance in gene expression related to fatty acid β-oxidation, de novo lipogenesis, mitochondrial dynamics, and endoplasmic reticulum stress. Separate exposures to IPO and PCB-126 affected metabolism and MASLD progression. Nutritional and lifestyle factors may potentiate the onset and severity of MASLD.

Long-term exposure to polychlorinated biphenyl 126 induces liver fibrosis and upregulates miR-155 and miR-34a in C57BL/6 mice

Environmental pollutants, including polychlorinated biphenyls (PCBs), act as endocrine disruptors and impair various physiological processes. PCB 126 is associated with steatohepatitis, fibrosis, cirrhosis, and other hepatic injuries. These disorders can be regulated by microRNAs (miRNAs). Therefore, this study aimed to investigate the role of miRNAs in non-alcoholic fatty liver disease associated with exposure to PCB 126. Adult male C57BL/6 mice were exposed to PCB 126 (5 μmol/kg of body weight) for 10 weeks. The PCB group showed lipid accumulation in the liver in the presence of macro- and microvesicular steatosis and fibrosis with increased inflammatory and profibrotic gene expression, consistent with non-alcoholic steatohepatitis (NASH). PCB exposure also upregulated miR-155 and miR-34a, which induce the expression of proinflammatory cytokines and inflammation in the liver and reduce the expression of peroxisome proliferator-activated receptor α, which, in turn, impairs lipid oxidation and hepatic steatosis. Therefore, the present study showed that PCB 126 induced NASH via potential mechanisms involving miR-155 and miR-34a, which may contribute to the development of new diagnostic markers and therapeutic strategies.

A systematic review and meta-analysis of environmental contaminant exposure impacts on weight loss and glucose regulation during calorie-restricted diets in preclinical studies: Persistent organic pollutants may impede glycemic control

Epidemiological evidence links chemical exposure with type 2 diabetes (T2DM) risk and prevalence. Chemical exposure may therefore also limit success of weight loss or restoration of glycemic control during calorie restricted diets. Few human studies examine this hypothesis. This systematic review and clustered meta-analysis examines preclinical evidence that exposure to anthropogenic environmental contaminants impedes weight loss and resumption of glycemic control during calorie restriction. Of five eligible papers from 212 unique citations, four used C57BL/6 mice and one used Sprague Dawley rats. In four the animals received high fat diets to induce obesity and impaired glycemic control. All examined persistent organic pollutants (POPs). Polychlorinated biphenyl (PCB) 77 exposure did not affect final mass (standardised mean difference (SMD) = -0.35 [-1.09, 0.39]; n = 5 (experiments); n = 3 (papers)), or response to insulin in insulin tolerance tests (SMD = -1.54 [-3.25, 0.16] n = 3 (experiments); n = 2 (papers)), but impaired glucose control in glucose tolerance tests (SMD = -1.30 [-1.96, -0.63]; n = 6 (experiments); n = 3 (papers)). The impaired glycemic control following perfluoro-octane sulphonic acid (PFOS) exposure and enhanced mass loss following dichlorodiphenyltrichloroethane (DDT) exposure have not been replicated. Animal studies thus suggest some chemical groups, especially PCB and PFOS, could impair glucose control management during calorie restriction, similar to conclusions from limited existing clinical studies. We discuss the research that is urgently required to inform weight management services that are now the mainstay prevention initiative for T2DM.

Loss of flavin-containing monooxygenase 3 modulates dioxin-like polychlorinated biphenyl 126-induced oxidative stress and hepatotoxicity

Dioxin-like pollutants (DLPs), such as polychlorinated biphenyl 126 (PCB 126), are synthetic chemicals classified as persistent organic pollutants. They accumulate in adipose tissue and have been linked to cardiometabolic disorders, including fatty liver disease. The toxicity of these compounds is associated with activation of the aryl hydrocarbon receptor (Ahr), leading to the induction of phase I metabolizing enzyme cytochrome P4501a1 (Cyp1a1) and the subsequent production of reactive oxygen species (ROS). Recent research has shown that DLPs can also induce the xenobiotic detoxification enzyme flavin-containing monooxygenase 3 (FMO3), which plays a role in metabolic homeostasis. We hypothesized whether genetic deletion of Fmo3 could protect mice, particularly in the liver, where Fmo3 is most inducible, against PCB 126 toxicity. To test this hypothesis, male C57BL/6 wild-type (WT) mice and Fmo3 knockout (Fmo3 KO) mice were exposed to PCB 126 or vehicle (safflower oil) during a 12-week study, at weeks 2 and 4. Various analyses were performed, including hepatic histology, RNA-sequencing, and quantitation of PCB 126 and F2-isoprostane concentrations. The results showed that PCB 126 exposure caused macro and microvesicular fat deposition in WT mice, but this macrovesicular fatty change was absent in Fmo3 KO mice. Moreover, at the pathway level, the hepatic oxidative stress response was significantly different between the two genotypes, with the induction of specific genes observed only in WT mice. Notably, the most abundant F2-isoprostane, 8-iso-15-keto PGE2, increased in WT mice in response to PCB 126 exposure. The study's findings also demonstrated that hepatic tissue concentrations of PCB 126 were higher in WT mice compared to Fmo3 KO mice. In summary, the absence of FMO3 in mice led to a distinctive response to dioxin-like pollutant exposure in the liver, likely due to alterations in lipid metabolism and storage, underscoring the complex interplay of genetic factors in the response to environmental toxins.

Polychlorinated biphenyls exposure and type 2 diabetes: Molecular mechanism that causes insulin resistance and islet damage

Polychlorinated biphenyls (PCBs) are typical persistent organic pollutants that have been associated with type 2 diabetes (T2DM) in cohort studies. This review aims to comprehensively assess the molecular mechanisms of PCBs-induced T2DM. Recent progress has been made in the research of PCBs in liver tissue, adipose tissue, and other tissues. By influencing the function of nuclear receptors, such as the aryl hydrocarbon receptor (AhR), pregnancy X receptor (PXR), and peroxisome proliferator activated receptor γ (PPARγ), as well as the inflammatory response, PCBs disrupt the balance of hepatic glucose and lipid metabolism. This is associated with insulin resistance (IR) in the target organ of insulin. Through androgen receptor (AR), estrogen receptor α/β (ERα/β), and pancreato-duodenal-homeobox gene-1 (PDX-1), PCBs affect the secretion of insulin and increase blood glucose. Thus, this review is a discussion on the relationship between PCBs exposure and the pathogenesis of T2DM. It is hoped to provide basic concepts for diabetes research and disease treatment.

Xylazine suppresses fentanyl consumption during self-administration and induces a unique sex-specific withdrawal syndrome that is not altered by naloxone in rats

Prescription and illicit opioid use are a public health crisis, with the landscape shifting to fentanyl use. Since fentanyl is 100-fold more potent than morphine, its use is associated with a higher risk of fatal overdose that can be remediated through naloxone (Narcan) administration. However, recent reports indicate that xylazine, an anesthetic, is increasingly detected in accidental fentanyl overdose deaths. Anecdotal reports suggest that xylazine may prolong the fentanyl "high," alter the onset of fentanyl withdrawal, and increase resistance to naloxone-induced reversal of overdose. To date, no preclinical studies have evaluated the impacts of xylazine on fentanyl self-administration (SA; 2.5 μg/kg/infusion) or withdrawal to our knowledge. We established a rat model of xylazine/fentanyl co-SA and withdrawal and evaluated outcomes as a function of biological sex. When administered alone, chronic xylazine (2.5 mg/kg, intraperitoneal) induced unique sex-specific withdrawal symptomatology, whereby females showed delayed onset of signs and a possible enhancement of sensitivity to the motor-suppressing effects of xylazine. Xylazine reduced fentanyl consumption in both male and female rats regardless of whether it was experimenter-administered or added to the intravenous fentanyl product (0.05, 0.10, and 0.5 mg/kg/infusion) when compared to fentanyl SA alone. Interestingly, this effect was dose-dependent when self-administered intravenously. Naloxone (0.1 mg/kg, subcutaneous injection) did not increase somatic signs of fentanyl withdrawal, regardless of the inclusion of xylazine in the fentanyl infusion in either sex; however, somatic signs of withdrawal were higher across time points in females after xylazine/fentanyl co-SA regardless of naloxone exposure as compared to females following fentanyl SA alone. Together, these results indicate that xylazine/fentanyl co-SA dose-dependently suppressed fentanyl intake in both sexes and induced a unique withdrawal syndrome in females that was not altered by acute naloxone treatment. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Emerging Contaminants: An Emerging Risk Factor for Diabetes Mellitus

Emerging contaminants have been increasingly recognized as critical determinants in global public health outcomes. However, the intricate relationship between these contaminants and glucose metabolism remains to be fully elucidated. The paucity of comprehensive clinical data, coupled with the need for in-depth mechanistic investigations, underscores the urgency to decipher the precise molecular and cellular pathways through which these contaminants potentially mediate the initiation and progression of diabetes mellitus. A profound understanding of the epidemiological impact of these emerging contaminants, as well as the elucidation of the underlying mechanistic pathways, is indispensable for the formulation of evidence-based policy and preventive interventions. This review systematically aggregates contemporary findings from epidemiological investigations and delves into the mechanistic correlates that tether exposure to emerging contaminants, including endocrine disruptors, perfluorinated compounds, microplastics, and antibiotics, to glycemic dysregulation. A nuanced exploration is undertaken focusing on potential dietary sources and the consequential role of the gut microbiome in their toxic effects. This review endeavors to provide a foundational reference for future investigations into the complex interplay between emerging contaminants and diabetes mellitus.

Identification of PCB congeners and their thresholds associated with diabetes using decision tree analysis

Few studies have investigated the potential combined effects of multiple PCB congeners on diabetes. To address this gap, we used data from 1244 adults in the National Health and Nutrition Examination Survey (NHANES) 2003-2004. We used (1) classification trees to identify serum PCB congeners and their thresholds associated with diabetes; and (2) logistic regression to estimate the odds ratios (ORs) and 95% confidence intervals (CIs) of diabetes with combined PCB congeners. Of the 40 PCB congeners examined, PCB 126 has the strongest association with diabetes. The adjusted OR of diabetes comparing PCB 126 > 0.025 to ≤ 0.025 ng/g was 2.14 (95% CI 1.30-3.53). In the subpopulation with PCB 126 > 0.025 ng/g, a lower PCB 101 concentration was associated with an increased risk of diabetes (comparing PCB 101 < 0.72 to ≥ 0.72 ng/g, OR 3.3, 95% CI 1.27-8.55). In the subpopulation with PCB 126 > 0.025 & PCB 101 < 0.72 ng/g, a higher PCB 49 concentration was associated with an increased risk of diabetes (comparing PCB 49 > 0.65 to ≤ 0.65 ng/g, OR 2.79, 95% CI 1.06-7.35). This nationally representative study provided new insights into the combined associations of PCBs with diabetes.

PCB126 exposure during pregnancy alters maternal and fetal gene expression

Polychlorinated biphenyls (PCBs) are organic pollutants that can have lasting impacts on offspring health. Here, we sought to examine maternal and fetal gene expression differences of aryl hydrocarbon receptor (AHR)-regulated genes in a mouse model of prenatal PCB126 exposure. Female mice were bred and gavaged with 1 µmole/kg bodyweight PCB126 or vehicle control on embryonic days 0 and 14, and maternal and fetal tissues were collected on embryonic day 18.5. Total RNAs were isolated, and gene expression levels were analyzed in both maternal and fetal tissues using the NanoString nCounter system. Interestingly, we found that the expression levels of cytochrome P450 (Cyp)1a1 and Cyp1b1 were significantly increased in response to PCB exposure in the tested maternal and fetal tissues. Furthermore, PCB exposure altered the expression of several other genes related to energy balance, oxidative stress, and epigenetic regulation in a manner that was less consistent across tissue types. These results indicate that maternal PCB126 exposure significantly alters gene expression in both developing fetuses and pregnant dams, and such changes vary in intensity and expressivity depending on tissue type. The altered gene expression may provide insights into pathophysiological mechanisms by which in utero PCB exposures contribute to PCB-induced postnatal metabolic diseases.

Deficiency of Adipose Aryl Hydrocarbon Receptor Protects against Diet-Induced Metabolic Dysfunction through Sexually Dimorphic Mechanisms

The molecular mechanisms underlying diet-induced obesity are complex and remain unclear. The activation of the aryl hydrocarbon receptor (AhR), a xenobiotic sensor, by obesogens may contribute to diet-induced obesity through influences on lipid metabolism and insulin resistance acting at various sites, including adipose tissue. Thus, our hypothesis was that conditional AhR depletion, specifically from mature adipose tissue (CadKO), would improve high-fat diet (HFD)-induced metabolic dysfunction. CadKO protects mice from HFD-induced weight gain. CadKO females eat fewer calories, leading to increased energy expenditure (EE) and improved glucose tolerance on HFD. Our exploration of adipose tissue biology suggests that the depletion of AhR from adipocytes provides female mice with an increased capacity for adipogenesis and lipolysis, allowing for the maintenance of a healthy adipocyte phenotype. The HFD-induced leptin rise was reduced in CadKO females, but the hypothalamic leptin receptor (LepR) was increased in the energy regulatory regions of the hypothalamus, suggesting an increased sensitivity to leptin. The estrogen receptor α (ERα) was higher in CadKO female adipose tissue and the hypothalamus. CadKO males displayed a delayed progression of obesity and insulin resistance. In males, CadKO ameliorated proinflammatory adipocytokine secretion (such as TNFα, IL1β, IL6) and displayed reduced inflammatory macrophage infiltration into adipose depots. Overall, CadKO improves weight control and systemic glucose homeostasis under HFD challenge but to a more profound extent in females. CadKO facilitates a lean phenotype in females and mediates healthy adipose-hypothalamic crosstalk. In males, adipose-specific AhR depletion delays the development of obesity and insulin resistance through the maintenance of healthy crosstalk between adipocytes and immune cells.

Gene-environment interaction in long-term effects of polychlorinated biphenyls exposure on glucose homeostasis and type 2 diabetes: The modifying effects of genetic risk and lifestyle

The longitudinal relationships of polychlorinated biphenyls (PCBs) exposure with glucose homeostasis and type 2 diabetes (T2D) risk among Chinese population have not been assessed, and interactions of PCB exposure with genetic susceptibility and lifestyle are unclear. In this prospective cohort study, fasting plasma glucose (FPG) and insulin (FPI) and seven serum indicator-PCBs were measured for each participant. We constructed polygenic risk score (PRS) of T2D and healthy lifestyle score. Each 1-unit increment of ln-transformed PCB-118 was related with a 0.141 mmol/L, 11.410 pmol/L, 0.661, and 74.5% increase in FPG, FPI, homeostasis model assessment of insulin resistance, and incident T2D risk over 6 years, respectively. Each 1-unit increment in T2D-PRS was related with a 0.169 mmol/L elevation of FPG and 65.5% elevation of incident T2D risk during 6 years. Compared with participants who had low T2D-PRS and low PCB-118, participants with high T2D-PRS and high PCB-118 showed a significant increase in FPG (0.162 mmol/L; P for interaction <0.001) and incident T2D risk [hazard ratio (HR)= 2.222]. Participants with low PCB-118, low PRS, and healthy lifestyle had the lowest incident T2D risk (HR=0.232). Our findings highlighted the significance of reducing PCB exposure and improvement in lifestyle for T2D prevention and management, especially for individuals with higher genetic risk of T2D.

Identification of PCB Congeners and their Thresholds associated with Diabetes using Decision Tree Analysis

Few studies have investigated the potential combined effects of multiple PCB congeners on diabetes. To address this gap, we used data from 1244 adults in the National Health and Nutrition Examination Survey (NHANES) 2003-2004. We used 1) classification trees to identify serum PCB congeners and their thresholds associated with diabetes; and 2) logistic regression to estimate the odds ratios (ORs) and 95% confidence intervals (CIs) of diabetes with combined PCB congeners. Of the 40 PCB congeners examined, PCB 126 has the strongest association with diabetes. The adjusted OR of diabetes comparing PCB 126 > 0.025 to ≤ 0.025 ng/g was 2.14 (95% CI 1.30-3.53). In the subpopulation with PCB 126 > 0.025 ng/g, a lower PCB 101 concentration was associated with an increased risk of diabetes (comparing PCB 101 < 0.72 to ≥ 0.72 ng/g, OR = 3.3, 95% CI: 1.27-8.55). In the subpopulation with PCB 126 > 0.025&PCB 101 < 0.72 ng/g, a higher PCB 49 concentration was associated with an increased risk of diabetes (comparing PCB 49 > 0.65 to ≤ 0.65 ng/g, OR = 2.79, 95% CI: 1.06-7.35). This nationally representative study provided new insights into the combined associations of PCBs with diabetes.

Critical Overview on Endocrine Disruptors in Diabetes Mellitus

Diabetes mellitus is a major public health problem in all countries due to its high human and economic burden. Major metabolic alterations are associated with the chronic hyperglycemia that characterizes diabetes and causes devastating complications, including retinopathy, kidney failure, coronary disease and increased cardiovascular mortality. The most common form is type 2 diabetes (T2D) accounting for 90 to 95% of the cases. These chronic metabolic disorders are heterogeneous to which genetic factors contribute, but so do prenatal and postnatal life environmental factors including a sedentary lifestyle, overweight, and obesity. However, these classical risk factors alone cannot explain the rapid evolution of the prevalence of T2D and the high prevalence of type 1 diabetes in particular areas. Among environmental factors, we are in fact exposed to a growing amount of chemical molecules produced by our industries or by our way of life. In this narrative review, we aim to give a critical overview of the role of these pollutants that can interfere with our endocrine system, the so-called endocrine-disrupting chemicals (EDCs), in the pathophysiology of diabetes and metabolic disorders.

Exposure to PCB126 during the nursing period reversibly impacts early-life glucose tolerance

Polychlorinated biphenyls (PCBs) are persistent environmental organic pollutants known to have detrimental health effects. Using a mouse model, we previously demonstrated that PCB126 exposure before and during pregnancy and throughout the perinatal period adversely affected offspring glucose tolerance and/or body composition profiles. The purpose of this study was to investigate the glucose tolerance and body composition of offspring born to dams exposed to PCB126 during the nursing period only. Female ICR mice were bred, and half of the dams were exposed to either vehicle (safflower oil) or 1 µmole PCB126 per kg of body weight via oral gavage on postnatal days (PND) 3, 10, and 17 (n = 9 per group). Offspring body weight, lean and fat mass, and glucose tolerance were recorded every three weeks. PCB126 treatment did not alter dam nor offspring body weight (p > 0.05). PCB126-exposed male and female offspring displayed normal body composition (p > 0.05) relative to vehicle-exposed offspring. However, both male and female offspring that were exposed to PCB126 during the nursing period had significantly impaired glucose tolerance at 3 and 9 weeks of age (p < 0.05). At 6 and 12 weeks of age, no impairments in glucose tolerance existed in offspring (p > 0.05). Our current study demonstrates that exposure to PCB126 through the mother's milk does not affect short- or long-term body composition but impairs glucose tolerance in the short-term.

Insight into the physiological and pathological roles of the aryl hydrocarbon receptor pathway in glucose homeostasis, insulin resistance, and diabetes development

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcriptional factor that mediates the toxicities of several environmental pollutants. Decades of research have been carried out to understand the role of AhR as a novel mechanism for disease development. Its involvement in the pathogenesis of cancer, cardiovascular diseases, rheumatoid arthritis, and systemic lupus erythematosus have long been known. One of the current hot research topics is investigating the role of AhR activation by environmental pollutants on glucose homeostasis and insulin secretion, and hence the pathogenesis of diabetes mellitus. To date, epidemiological studies have suggested that persistent exposure to environmental contaminants such as dioxins, with subsequent AhR activation increases the risk of specific comorbidities such as obesity and diabetes. The importance of AhR signaling in various molecular pathways highlights that the role of this receptor is far beyond just xenobiotic metabolism. The present review aims at providing significant insight into the physiological and pathological role of AhR and its regulated enzymes, such as cytochrome P450 1A1 (CYP1A1) and CYP1B1 in both types of diabetes. It also provides a comprehensive summary of the current findings of recent research studies investigating the role of the AhR/CYP1A1 pathway in insulin secretion and glucose hemostasis in the pancreas, liver, and adipose tissues. This review further highlights the molecular mechanisms involved, such as gluconeogenesis, hypoxia-inducible factor (HIF), oxidative stress, and inflammation.

Transcriptome sequencing of 3,3',4,4',5-Pentachlorobiphenyl (PCB126)-treated human preadipocytes demonstrates progressive changes in pathways associated with inflammation and diabetes

Polychlorinated biphenyls (PCBs) are persistent organic pollutants that accumulate in adipose tissue and have been associated with cardiometabolic disease. We have previously demonstrated that exposure of human preadipocytes to the dioxin-like PCB126 disrupts adipogenesis via the aryl hydrocarbon receptor (AhR). To further understand how PCB126 disrupts adipose tissue cells, we performed RNAseq analysis of PCB126-treated human preadipocytes over a 3-day time course. The most significant predicted upstream regulator affected by PCB126 exposure at the early time point of 9 h was the AhR. Progressive changes occurred in the number and magnitude of transcript levels of genes associated with inflammation, most closely fitting the pathways of cytokine-cytokine-receptor signaling and the AGE-RAGE diabetic complications pathway. Transcript levels of genes involved in the IL-17A, IL-1β, MAP kinase, and NF-κB signaling pathways were increasingly dysregulated by PCB126 over time. Our results illustrate the progressive time-dependent nature of transcriptional changes caused by toxicants such as PCB126, point to important pathways affected by PCB126 exposure, and provide a rich dataset for further studies to address how PCB126 and other AhR agonists disrupt preadipocyte function. These findings have implications for understanding how dioxin-like PCBs and other dioxin-like compounds are involved in the development of obesity and diabetes.

Dioxin-like polychlorinated biphenyl 126 (PCB126) disrupts gut microbiota-host metabolic dysfunction in mice via aryl hydrocarbon receptor activation

Exposure to environmental pollutants, including dioxin-like pollutants, can cause numerous health issues. A common exposure route to pollutants is through contaminated foods, and thus the gastrointestinal system and gut microbiota are often exposed to high amounts of pollutants. Multiple studies have focused on the imbalance in intestinal microbiota composition caused by dioxin-like pollutants. Here, we examined the effects of polychlorinated biphenyl 126 (PCB126) on the composition and functions of gut microbes through metagenomic sequencing, and explored the correlations between microflora dysbiosis and aryl hydrocarbon receptor (AHR) signaling. Adult male wild-type and Ahr^-/- mice with a C57BL/6 background were weekly exposed to 50 μg/kg body weight of PCB126 for 8 weeks. Results showed that PCB126 had the opposite effect on gut microbiota composition and diversity in the wild-type and Ahr^-/- mice. Functional prediction found that PCB126 exposure mainly altered carbon metabolism and signal regulatory pathways in wild-type mice but impacted DNA replication and lipopolysaccharide biosynthesis in Ahr^-/- mice. In wild-type mice, PCB126 exposure induced liver injury, decreased serum lipid content, and delayed gastrointestinal motility, which were significantly correlated to several specific bacterial taxa, such as Helicobacter. Following AHR knockout, however, the holistic effects of PCB126 on the host were lessened or abolished. These results suggest that PCB126 may disrupt host metabolism and gut microbiota dynamics via AHR activation. Overall, our findings provide new insight into the complex interactions between host metabolism and gut microbiota, which may contribute to grouped assessment of environmental pollutants in the future.

Persistent organic pollutants and β-cell toxicity: a comprehensive review

Persistent organic pollutants (POPs) are a diverse family of contaminants that show widespread global dispersion and bioaccumulation. Humans are continuously exposed to POPs through diet, air particles, and household and commercial products; POPs are consistently detected in human tissues, including the pancreas. Epidemiological studies show a modest but consistent correlation between exposure to POPs and increased diabetes risk. The goal of this review is to provide an overview of epidemiological evidence and an in-depth evaluation of the in vivo and in vitro evidence that POPs cause β-cell toxicity. We review evidence for six classes of POPs: dioxins, polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), organophosphate pesticides (OPPs), flame retardants, and per- and polyfluoroalkyl substances (PFAS). The available data provide convincing evidence implicating POPs as a contributing factor driving impaired glucose homeostasis, β-cell dysfunction, and altered metabolic and oxidative stress pathways in islets. These findings support epidemiological data showing that POPs increase diabetes risk and emphasize the need to consider the endocrine pancreas in toxicity assessments. Our review also highlights significant gaps in the literature assessing islet-specific endpoints after both in vivo and in vitro POP exposure. In addition, most rodent studies do not consider the impact of biological sex or secondary metabolic stressors in mediating the effects of POPs on glucose homeostasis and β-cell function. We discuss key gaps and limitations that should be assessed in future studies.

The Role of Persistent Organic Pollutants in Obesity: A Review of Laboratory and Epidemiological Studies

Persistent organic pollutants (POPs) are considered as potential obesogens that may affect adipose tissue development and functioning, thus promoting obesity. However, various POPs may have different mechanisms of action. The objective of the present review is to discuss the key mechanisms linking exposure to POPs to adipose tissue dysfunction and obesity. Laboratory data clearly demonstrate that the mechanisms associated with the interference of exposure to POPs with obesity include: (a) dysregulation of adipogenesis regulators (PPARγ and C/EBPα); (b) affinity and binding to nuclear receptors; (c) epigenetic effects; and/or (d) proinflammatory activity. Although in vivo data are generally corroborative of the in vitro results, studies in living organisms have shown that the impact of POPs on adipogenesis is affected by biological factors such as sex, age, and period of exposure. Epidemiological data demonstrate a significant association between exposure to POPs and obesity and obesity-associated metabolic disturbances (e.g., type 2 diabetes mellitus and metabolic syndrome), although the existing data are considered insufficient. In conclusion, both laboratory and epidemiological data underline the significant role of POPs as environmental obesogens. However, further studies are required to better characterize both the mechanisms and the dose/concentration-response effects of exposure to POPs in the development of obesity and other metabolic diseases.

Lack of Offspring Nrf2 Does Not Exacerbate the Detrimental Metabolic Outcomes Caused by In Utero PCB126 Exposure

Human environmental exposures to toxicants, such as polychlorinated biphenyls (PCBs), increase oxidative stress and disease susceptibility. Such exposures during pregnancy and/or nursing have been demonstrated to adversely affect offspring health outcomes. Nuclear factor erythroid-2-related factor 2 (Nrf2) regulates the antioxidant response and is involved in the detoxification of coplanar PCBs, like PCB126. The purpose of this study was to investigate glucose tolerance and body composition in PCB-exposed offspring expressing or lacking Nrf2. We hypothesized that offspring lacking Nrf2 expression would be more susceptible to the long-term health detriments associated with perinatal PCB exposure. During gestation, whole-body Nrf2 heterozygous (Het) and whole-body Nrf2 knockout (KO) mice were exposed to vehicle or PCB126. Shortly after birth, litters were cross-fostered to unexposed dams to prevent PCB exposure during nursing. Offspring were weaned, and their body weight, body composition, and glucose tolerance were recorded. At two months of age, PCB exposure resulted in a significant reduction in the average body weight of offspring born to Nrf2 Het dams (p < 0.001) that primarily arose from the decrease in average lean body mass in offspring (p < 0.001). There were no differences in average body weight of PCB-exposed offspring born to Nrf2 KO dams (p > 0.05), and this was because offspring of Nrf2 KO dams exposed to PCB126 during pregnancy experienced a significant elevation in fat mass (p = 0.002) that offset the significant reduction in average lean mass (p < 0.001). Regardless, the lack of Nrf2 expression in the offspring themselves did not enhance the differences observed. After an oral glucose challenge, PCB-exposed offspring exhibited significant impairments in glucose disposal and uptake (p < 0.05). Offspring born to Nrf2 Het dams exhibited these impairments at 30 min and 120 min, while offspring born to Nrf2 KO dams exhibited these impairments at zero, 15, 30, 60 and 120 min after the glucose challenge. Again, the interactions between offspring genotype and PCB exposure were not significant. These findings were largely consistent as the offspring reached four months of age and demonstrate that the lack of offspring Nrf2 expression does not worsen the metabolic derangements caused by in utero PCB exposure as we expected. Future directions will focus on understanding how the observed maternal Nrf2 genotypic differences can influence offspring metabolic responses to in utero PCB exposure.

Pharmacological blockage of the AHR-CYP1A1 axis: a call for in vivo evidence

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that can be activated by structurally diverse compounds arising from the environment and the microbiota and host metabolism. Expanding evidence has been shown that the modulation of the canonical pathway of AHR occurs during several chronic diseases and that its abrogation might be of clinical interest for metabolic and inflammatory pathological processes. However, most of the evidence on the pharmacological abrogation of the AHR-CYP1A1 axis has been reported in vitro, and therefore, guidance for in vivo studies is needed. In this review, we cover the state-of-the-art of the pharmacodynamic and pharmacokinetic properties of AHR antagonists and CYP1A1 inhibitors in different in vivo rodent (mouse or rat) models of disease. This review will serve as a road map for those researchers embracing this emerging therapeutic area targeting the AHR. Moreover, it is a timely opportunity as the first AHR antagonists have recently entered the clinical stage of drug development.

Applicability of Scrape Loading-Dye Transfer Assay for Non-Genotoxic Carcinogen Testing

Dysregulation of gap junction intercellular communication (GJIC) is recognized as one of the key hallmarks for identifying non-genotoxic carcinogens (NGTxC). Currently, there is a demand for in vitro assays addressing the gap junction hallmark, which would have the potential to eventually become an integral part of an integrated approach to the testing and assessment (IATA) of NGTxC. The scrape loading-dye transfer (SL-DT) technique is a simple assay for the functional evaluation of GJIC in various in vitro cultured mammalian cells and represents an interesting candidate assay. Out of the various techniques for evaluating GJIC, the SL-DT assay has been used frequently to assess the effects of various chemicals on GJIC in toxicological and tumor promotion research. In this review, we systematically searched the existing literature to gather papers assessing GJIC using the SL-DT assay in a rat liver epithelial cell line, WB-F344, after treating with chemicals, especially environmental and food toxicants, drugs, reproductive-, cardio- and neuro-toxicants and chemical tumor promoters. We discuss findings derived from the SL-DT assay with the known knowledge about the tumor-promoting activity and carcinogenicity of the assessed chemicals to evaluate the predictive capacity of the SL-DT assay in terms of its sensitivity, specificity and accuracy for identifying carcinogens. These data represent important information with respect to the applicability of the SL-DT assay for the testing of NGTxC within the IATA framework.

Predicting consequences of POP-induced disruption of blubber glucose uptake, mass gain rate and thyroid hormone levels for weaning mass in grey seal pups

Persistent organic pollutants (POPs) are endocrine disruptors that alter adipose tissue development, regulation and function. Top marine predators are particularly vulnerable because they possess large fat stores that accumulate POPs. However, links between endocrine or adipose tissue function disruption and whole animal energetics have rarely been investigated. We predicted the impact of alterations to blubber metabolic characteristics and circulating thyroid hormone (TH) levels associated with polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and organochlorine pesticides (OCPs) on suckling mass gain and weaning mass in wild grey seal pups. Glucose uptake by inner blubber was a strong predictor of whole animal mass gain rate, which in turn, resulted in heavier weaning mass. Weaning mass was predicted to increase by 3.7 ± 1.59 (sem) %, through increased mass gain rate, in the absence of the previously reported suppressive effect of dioxin-like PCB (DL-PCBs) on blubber glucose uptake. PBDEs were, conversely, associated with faster mass gain. Alleviation of this effect was predicted to reduce weaning mass by 6.02 ± 1.86% (sem). To better predict POPs effects on energy balance, it is crucial to determine if and how PBDEs promote mass gain in grey seal pups. Weaning mass was negatively related to total T3 (TT3) levels. A 20% (range = 9.3-31.7%) reduction in TT3 by DL-PCBs partially overcame the effect of DL-PCB -mediated reduction in blubber glucose uptake. Overall, DL-PCBs were thus predicted to reduce weaning mass by 1.86 ± 1.60%. Organohalogen impacts on whole-animal energy balance in grey seal pups appear to partially offset each other through opposing effects on different mechanisms. POP effects were generally minor, but the largest POP-induced reductions in weaning mass were predicted to occur in pups that were already small. Since weaning mass is positively related to first-year survival, POPs may disproportionately affect smaller individuals, and could continue to have population-level impacts even when levels are relatively low compared to historical values. Our findings show how in vitro experiments combined with measurements in vivo can help elucidate mechanisms that underpin energy balance regulation and help to quantify the magnitude of disruptive effects by contaminants and other stressors in wildlife.

Reproductive outcomes associated with flame retardants among couples seeking fertility treatment: A paternal perspective

BACKGROUND

Polybrominated diphenyl ethers (PBDEs) have been phased out of production for nearly a decade yet are still frequently detected in serum of U.S. adults. PBDE concentrations have been associated with adverse reproductive outcomes and laboratory studies suggest hydroxylated-BDEs (OH-BDEs) may act as endocrine disruptors. We set out to assess the joint effects of paternal and maternal serum PBDE concentrations on in vitro fertilization (IVF) outcomes and the association between paternal serum OH-BDE concentrations and IVF outcomes.

METHODS

This analysis included 189 couples (contributing 285 IVF cycles) recruited between 2006 and 2016 from a longitudinal cohort based at Massachusetts General Hospital Fertility Center who completed at least one IVF cycle and had an available blood sample at study entry. Congeners (47, 99, 100, 153, and 154) and OH-BDEs (3-OH-BDE47, 5-OH-BDE47, 6-OH-BDE47 and 4-OH-BDE49) were quantified in serum. Log-transformed PBDEs and OH-BDEs were modeled in quartiles for associations with IVF outcomes using multivariable generalized mixed models and cluster weighted generalized estimating equations.

RESULTS

Lipid-adjusted concentrations of PBDEs and OH-BDEs were higher in females than in male partners. There were no clear patterns of increases in risk of adverse IVF outcomes associated with PBDEs and OH-BDEs. However, some decreases in associations with IVF outcomes were observed in isolated quartiles.

CONCLUSIONS

Our assessment of couple level exposure is unique and highlights the importance of including male and female exposures in the assessment of the influence of environmental toxicants on pregnancy outcomes.

Toxic Effects of Polychlorinated Biphenyl Congeners and Aroclors on Embryonic Growth and Development

Polychlorinated biphenyls (PCBs) cause significant health and reproductive problems in many vertebrates. Exposure during embryogenesis likely leads to defects in organ development, compromising survival and growth through adulthood. The present study identifies the impact of PCBs on the embryonic development of key organs and resulting consequences on survival and growth. Zebrafish embryos were treated with individual PCB congeners (126 or 104) or one of 4 Aroclor mixtures (1016, 1242, 1254, or 1260) and analyzed for changes in gross embryonic morphology. Specific organs were assessed for defects during embryonic development, using a variety of transgenic zebrafish to improve organ visualization. Resulting larvae were grown to adulthood while survival and growth were assayed. Embryonic gross development on PCB treatment was abnormal, with defects presenting in a concentration-dependent manner in the liver, pancreas, heart, and blood vessel organization. Polychlorinated biphenyl 126 treatment resulted in the most consistently severe and fatal phenotypes, whereas treatments with PCB 104 and Aroclors resulted in a range of more subtle organ defects. Survival of fish was highly variable although the growth rates of surviving fish were relatively normal, suggesting that maturing PCB-treated fish that survive develop compensatory strategies needed to reach adulthood. Life span analyses of fish from embryogenesis through adulthood, as in the present study, are scarce but important for the field because they help identify foci for further studies. Environ Toxicol Chem 2021;40:187-201. © 2020 SETAC.

A polyphenol-rich cranberry extract protects against endogenous exposure to persistent organic pollutants during weight loss in mice

The dramatic rise in the global occurrence of obesity and associated diseases calls for new strategies to promote weight loss. However, while the beneficial effects of weight loss are well known, rapid loss of fat mass can also lead to the endogenous release of liposoluble molecules with potential harmful effects, such as persistent organic pollutants (POP). The aim of this study was to evaluate the impact of a polyphenol-rich cranberry extract (CE) on POP release and their potential deleterious effects during weight loss of obese mice. C57BL/6 J mice were fed an obesogenic diet with or without a mixture of POP for 12 weeks and then changed to a low-fat diet to induce weight loss and endogenous POP release. The POP-exposed mice were then separated in two groups during weight loss, receiving either CE or the vehicle. Unexpectedly, despite the higher fat loss in the CE-treated group, the circulating levels of POP were not enhanced in these mice. Moreover, glucose homeostasis was further improved during CE-induced weight loss, as revealed by lower fasting glycemia and improved glucose tolerance as compared to vehicle-treated mice. Interestingly, the CE extract also induced changes in the gut microbiota after weight loss in POP-exposed mice, including blooming of Parvibacter, a member of the Coriobacteriaceae family which has been predicted to play a role in xenobiotic metabolism. Our data thus suggests that the gut microbiota can be targeted by polyphenol-rich extracts to protect from increased POP exposure and their detrimental metabolic effects during rapid weight loss.

Exposure to Low Doses of Dechlorane Plus Promotes Adipose Tissue Dysfunction and Glucose Intolerance in Male Mice

The prevalence of type 2 diabetes (T2D) continues to increase worldwide. It is well established that genetic susceptibility, obesity, overnutrition and a sedentary life style are risk factors for the development of T2D. However, more recently, studies have also proposed links between exposure to endocrine-disrupting chemicals (EDCs) and altered glucose metabolism. Human exposure to environmental pollutants that are suspected to have endocrine disruptor activity is ubiquitous. One such chemical is Dechlorane Plus (DP), a flame retardant, that is now detected in humans and the environment. Here we show that exposure of mice to low, environmentally relevant doses of DP promoted glucose intolerance in mice fed a high-fat diet independent of weight gain. Furthermore, DP had pronounced effects on the adipose tissue, where it induced the development of hypertrophied white adipose tissue (WAT), and increased serum levels of resistin, leptin, and plasminogen activator inhibitor-1. In addition, DP exposure induced "whitening" of brown adipose tissue (BAT), and reduced BAT uncoupling protein 1 expression. Importantly, some of these effects occurred even when the mice were fed a regular, low-fat, diet. Finally, WAT adipogenic markers were reduced with DP treatment in the WAT. We also show that DP directly inhibited insulin signaling in murine adipocytes and human primary subcutaneous adipocytes in vitro. Taken together, our results show that the exposure to low and environmentally relevant levels of DP may contribute to the development of T2D.

Exposure to 2,3,3',4,4',5-hexachlorobiphenyl promotes nonalcoholic fatty liver disease development in C57BL/6 mice

Previous in vitro studies have indicated that 2,3,3',4,4',5-hexachlorobiphenyl (PCB 156) may be a new contributor to metabolic disruption and may further cause the occurrence of nonalcoholic fatty liver disease (NAFLD). However, no study has clarified the specific contributions of PCB 156 to NAFLD progression by constructing an in vivo model. Herein, we evaluated the effects of PCB 156 treatment (55 mg/kg, i.p.) on the livers of C57BL/6 mice fed a control diet (CD) or a high-fat diet (HFD). The results showed that PCB 156 administration increased intra-abdominal fat mass, hepatic lipid levels and dyslipidemia in the CD-fed group and aggravated NAFLD in HFD-fed group. By using transcriptomics studies and biological methods, we found that the genes expression involved in lipid metabolism pathways, such as lipogenesis, lipid accumulation and lipid β-oxidation, was greatly altered in liver tissues exposed to PCB 156. In addition, the cytochrome P450 pathway, peroxisome proliferator-activated receptors (PPARs) and the glutathione metabolism pathway were significantly activated following exposure to PCB 156. Furthermore, PCB 156 exposure increased serum transaminase levels and lipid peroxidation, and the redox-related genes were significantly dysregulated in liver tissue. In conclusion, our data suggested that PCB 156 could promote NAFLD development by altering the expression of genes related to lipid metabolism and inducing oxidative stress.

Prebiotic inulin consumption reduces dioxin-like PCB 126-mediated hepatotoxicity and gut dysbiosis in hyperlipidemic Ldlr deficient mice

Exposure to some environmental pollutants increases the risk of developing inflammatory disorders such as steatosis and cardiometabolic diseases. Diets high in fermentable fibers such as inulin can modulate the gut microbiota and lessen the severity of pro-inflammatory diseases, especially in individuals with elevated circulating cholesterol. Thus, we aimed to test the hypothesis that hyperlipidemic mice fed a diet enriched with 8% inulin would be protected from the pro-inflammatory toxic effects of PCB 126. Four groups of male Ldlr^-/- mice were fed a high cholesterol diet containing 8% inulin or 8% cellulose (control) for 12 weeks. At weeks 2 and 4, mice were exposed to PCB 126 or vehicle (control). PCB 126 exposure induced wasting and impaired glucose tolerance, which were attenuated by inulin consumption. PCB 126 exposure induced hepatic lipid accumulation and increased inflammatory gene expression, which were both decreased by inulin consumption. In addition, inulin feeding decreased atherosclerotic lesion development in the aortic root and modulated the expression of enzymes related to glycolysis. Finally, 16S rRNA sequencing of gut microbial populations showed that PCB 126 modulated multiple microbiota genera (e.g., 3-fold decrease in Allobaculum and 3-fold increase in Coprococcus) which were normalized in inulin fed mice. Overall our data support the hypothesis that a dietary intervention that targets the gut microbiota may be an effective means of attenuating dioxin-like pollutant-mediated diseases.

Perinatal exposure to 2-Ethylhexyl Diphenyl Phosphate (EHDPHP) affected the metabolic homeostasis of male mouse offspring: Unexpected findings help to explain dose- and diet- specific phenomena

The environmental health risks of a new type of organophosphate flame retardant, 2-ethylhexyl diphenyl phosphate (EHDPHP), which is present in large quantities in various Nordic foods, have attracted the attention of scientists recently. In this study, the metabolic homeostasis of low-fat diet (LFD) and high-fat diet (HFD) fed male mice offspring was assessed after perinatal exposure to two doses (30 μg/kg bw/day and 300 μg/kg bw/day) of EHDPHP. Perinatal exposure to EHDPHP resulted in weight changes in male mice offspring, altered glucose tolerance and induced liver damage, and surprisingly these changes were dose- and diet- specific. Then the ¹H NMR-based metabolomics, 16S rRNA sequencing, and qRT-PCR techniques were used to explore the mechanisms of these specific changes. The results indicate that the increase in short-chain fatty acids and the increase in Clostridium in the high-dose group may be responsible for the dose-specificity, while the attenuation of the purine metabolic pathway and the decrease in glutamine levels in the HFD group are accountable for the diet-specificity. In addition, down-regulation of PPARG (peroxisome proliferator-activated receptor gamma) gene expression levels might have caused the decrease in body weight in the H + HFD (high dose exposure with HFD feeding) group. Over all, these results elucidated the effects of dosage and diet on the toxicology of EHDPHP.

PCB126 blocks the thermogenic beiging response of adipocytes

Subcutaneous white adipose tissue is capable of becoming thermogenic in a process that is referred to as "beiging." Beiging is associated with activation of the uncoupling protein, UCP1, and is known to be important for preventing adipose hypertrophy and development of insulin resistance. Polychlorinated biphenyls (PCBs) accumulate in fat, and it is hypothesized that disruption of adipogenesis and adipocyte function by PCBs may be causative in the development of obesity and diabetes. We developed immortal human subcutaneous preadipocytes that, when differentiated, are capable of beiging. Preadipocytes that were treated with polychlorinated biphenyl congener 126 (PCB126), followed by differentiation, were suppressed for their ability to activate UCP1 upon β-adrenergic stimulation with norepinephrine (NE), demonstrating a block in the beiging response. Treatment of preadipocytes with another known endogenous AhR agonist, indoxyl sulfate (IS), followed by differentiation also blocked the NE-stimulated upregulation of UCP1. Knockdown of the aryl hydrocarbon receptor (AhR) caused the preadipocytes to be refractory to PCB126 and IS effects. The chemical AhR antagonist, CH223191, was effective at preventing the effects of PCB126 but not IS, indicating AhR ligand specificity of CH223191. Repression of NE-induced UCP1 upregulation was also observed when already-differentiated mature adipocytes were treated with PCB126 but not IS. These results indicate that exposure of preadipocytes to endogenous (IS) or exogenous (PCB126) AhR agonists is effective at blocking them from becoming functional adipocytes that are capable of the beiging response. Mature adipocytes may have differential responses. This finding suggests a mechanism by which dioxin-like PCBs such as PCB126 could lead to disruption in energy homeostasis, potentially leading to obesity and diabetes.

Exposure to Aroclor 1254 differentially affects the survival of pancreatic β-cells and α-cells in the male mice and the potential reason

Previous works showed that chronic exposure to Aroclor 1254 disrupted glucose homeostasis and induced insulin resistance in male mice. To further observe the different effects of Aroclor 1254 exposure on the pancreatic α-cells and β-cells, male mice were exposed to Aroclor 1254 (0, 0.5, 5, 50, 500 μg/kg) for 60 days, the pancreas was performed a histological examination. The results showed that the percentage of apoptosis cell (indicated by TUNEL assay) was increased in both α-cells and β-cells, as the Aroclor 1254 dose was increased; the proliferation (indicated by PCNA expression) rate of β-cells was elevated while that of α-cells was not affected, resulting in an increased β-cell mass and a decreased α-cell mass in a dose-depend manner. The number of Pdx-1 positive β-cells was significantly increased whereas that of Arx positive α-cells was markedly decreased, indicating an enhanced β-cell neogenesis and a weakened α-cell neogenesis. The drastically reduction of serum testosterone levels in all the treatments suggested an anti-androgenic potency of Aroclor 1254. The up-regulation of estrogen receptors (ERα and ERβ) and androgen receptor in β-cells might be responsible for the increased β-cell mass and neogenesis.

Environmental neglect: endocrine disruptors as underappreciated but potentially modifiable diabetes risk factors

Type 2 diabetes prevalence is increasing dramatically across the globe, imposing a tremendous toll on individuals and healthcare systems. Reversing these trends requires comprehensive approaches to address both classical and emerging diabetes risk factors. Recently, environmental toxicants acting as endocrine-disrupting chemicals (EDCs) have emerged as novel metabolic disease risk factors. EDCs implicated in diabetes pathogenesis include various inorganic and organic molecules of both natural and synthetic origin, including arsenic, bisphenol A, phthalates, polychlorinated biphenyls and organochlorine pesticides. Indeed, evidence implicates EDC exposures across the lifespan in metabolic dysfunction; moreover, specific developmental windows exhibit enhanced sensitivity to EDC-induced metabolic disruption, with potential impacts across generations. Importantly, differential exposures to diabetogenic EDCs likely also contribute to racial/ethnic and economic disparities. Despite these emerging links, clinical practice guidelines fail to address this underappreciated diabetes risk factor. Comprehensive approaches to stem the tide of diabetes must include efforts to address its environmental drivers.

Effects of Aryl Hydrocarbon Receptor Deficiency on PCB-77-Induced Impairment of Glucose Homeostasis during Weight Loss in Male and Female Obese Mice

BACKGROUND

Lipophilic polychlorinated biphenyls (PCBs) accumulate with obesity, but during weight loss, liberated PCBs act as ligands of the aryl hydrocarbon receptor (AhR) to negatively influence health. Previous studies demonstrated that PCB-77 administration to obese male mice impaired glucose tolerance during weight loss. Recent studies indicate higher toxic equivalencies of dioxin-like PCBs in exposed females than males.

OBJECTIVES

We compared effects of PCB-77 on weight gain or loss and glucose homeostasis in male vs. female mice. We defined effects of AhR deficiency during weight gain or loss in male and female mice exposed to PCB-77.

METHODS

Study design was vehicle (VEH) or PCB-77 administration while fed a high-fat (HF) diet for 12 wk, followed by weight loss for 4 wk. The following groups were examined: male and female C57BL/6 mice administered VEH or PCB-77, female [Formula: see text] and [Formula: see text] mice administered VEH or PCB-77, and male [Formula: see text] and [Formula: see text] mice administered PCB-77. Glucose tolerance was quantified during weight gain (week 11) and loss (week 15); liver and adipose AhR and IRS2 (insulin receptor substrate 2) mRNA abundance, and PCB-77 concentrations were quantified at week 16.

RESULTS

PCB-77 attenuated development of obesity in females but not males. During weight loss, PCB-77 impaired glucose tolerance of males. AhR-deficient females (VEH) were resistant to diet-induced obesity. Compared with VEH-treated mice, HF-fed [Formula: see text] females treated with PCB-77 has less weight gain, and [Formula: see text] females had greater weight gain. During weight loss, [Formula: see text] females but not [Formula: see text] males treated with PCB-77 exhibited impaired glucose tolerance. In [Formula: see text] females administered PCB-77, IRS2 mRNA abundance was lower in adipose tissue compared with VEH-treated mice.

CONCLUSION

Male and female mice responded differently to PCB-77 and AhR deficiency in body weight (BW) regulation and glucose homeostasis. AhR deficiency reversed PCB-77-induced glucose impairment of obese males losing weight but augmented glucose intolerance of females. These results demonstrate sex differences in PCB-77-induced regulation of glucose homeostasis of mice. https://doi.org/10.1289/EHP4133.

Exposure to Aroclor 1254 persistently suppresses the functions of pancreatic β-cells and deteriorates glucose homeostasis in male mice

Polychlorinated biphenyls (PCBs) are a class of persistent organic pollutants that have been shown to be related to the occurrence of type 2 diabetes mellitus (T2DM). Nevertheless, it is necessary to further explore the development of T2DM caused by PCBs and its underlying mechanisms. In the present study, 21-day-old C57BL/6 male mice were orally treated with Aroclor 1254 (0.5, 5, 50 or 500 μg kg^-1) once every three days. After exposure for 66 d, the mice showed impaired glucose tolerance, 13% and 14% increased fasting serum insulin levels (FSIL), and 63% and 69% increases of the pancreatic β-cell mass in the 50 and 500 μg kg^-1 groups, respectively. After stopping exposure for 90 d, treated mice returned to normoglycemia and normal FSIL. After re-exposure of these recovered mice to Aroclor 1254 for 30 d, fasting plasma glucose showed 15%, 28% and 16% increase in the 5, 50 and 500 μg kg^-1 treatments, FSIL exhibited 35%, 27%, 30% and 32% decrease in the 0.5, 5, 50 or 500 μg kg^-1 groups respectively, and there was no change in pancreatic β-cell mass. Transcription of the pancreatic insulin gene (Ins2) was significantly down-regulated in the 50 and 500 μg kg^-1 groups, while DNA-methylation levels were simultaneously increased in the Ins2 promoter during the course of exposure, recovery and re-exposure. Reduced insulin levels were initially rescued by a compensative increase in β-cell mass. However, β-cell mass eventually failed to make sufficient levels of insulin, resulting in significant increases in fasting blood glucose, and indicating the development of T2DM.

Altered lipid homeostasis in a PCB-resistant Atlantic killifish (Fundulus heteroclitus) population from New Bedford Harbor, MA, U.S.A

Sentinel species such as the Atlantic killifish (Fundulus heteroclitus) living in urban waterways can be used as toxicological models to understand impacts of environmental metabolism disrupting compound (MDC) exposure on both wildlife and humans. Exposure to MDCs is associated with increased risk of metabolic syndrome, including impaired lipid and glucose homeostasis, adipogenesis, appetite control, and basal metabolism. MDCs are ubiquitous in the environment, including in aquatic environments. New Bedford Harbor (NBH), Massachusetts is polluted with polychlorinated biphenyls (PCBs), and, as we show for the first time, tin (Sn). PCBs and organotins are ligands for two receptor systems known to regulate lipid homeostasis, the aryl hydrocarbon receptor (AHR) and the peroxisome proliferator-activated receptors (PPARs), respectively. In the current study, we compared lipid homeostasis in laboratory-reared killifish from NBH (F2) and a reference location (Scorton Creek, Massachusetts; F1 and F2) to evaluate how adaptation to local conditions may influence responses to MDCs. Adult killifish from each population were exposed to 3,3',4,4',5-pentachlorobiphenyl (PCB126, dioxin-like), 2,2',4,4',5,5'-hexachlorobiphenyl (PCB153, non-dioxin-like), or tributyltin (TBT, a PPARγ ligand) by a single intraperitoneal injection and analyzed after 3 days. AHR activation was assessed by measuring cyp1a mRNA expression. Lipid homeostasis was evaluated phenotypically by measuring liver triglycerides and organosomatic indices, and at the molecular level by measuring the mRNA expression of pparg and ppara and a target gene for each receptor. Acute MDC exposure did not affect phenotypic outcomes. However, overall NBH killifish had higher liver triglycerides and adiposomatic indices than SC killifish. Both season and population were significant predictors of the lipid phenotype. Acute MDC exposure altered hepatic gene expression only in male killifish from SC. PCB126 exposure induced cyp1a and pparg, whereas PCB153 exposure induced ppara. TBT exposure did not induce ppar-dependent pathways. Comparison of lipid homeostasis in two killifish populations extends our understanding of how MDCs act on fish and provides a basis to infer adaptive benefits of these differences in the wild.

Dioxin-like PCB 126 Increases Systemic Inflammation and Accelerates Atherosclerosis in Lean LDL Receptor-Deficient Mice

Exposure to dioxins and related persistent organic pollutants likely contributes to cardiovascular disease (CVD) risk through multiple mechanisms including the induction of chronic inflammation. Epidemiological studies have shown that leaner individuals may be more susceptible to the detrimental effects of lipophilic toxicants because they lack large adipose tissue depots that can accumulate and sequester these pollutants. This phenomenon complicates efforts to study mechanisms of pollutant-accelerated atherosclerosis in experimental animal models where high-fat feeding and adipose expansion limit the bioavailability of lipophilic pollutants. Here, we investigated whether a model dioxin-like pollutant, PCB 126, could increase inflammation and accelerate atherosclerosis in Ldlr-/- mice fed a low-fat atherogenic diet. We fed Ldlr-/- mice the Clinton/Cybulsky diet (10% kcal fat, 0.15% cholesterol) and sacrificed mice at 8, 10, or 12 weeks postPCB (2 doses of 1 μmol/kg) or vehicle gavage. To characterize this novel model, we examined the effects of PCB 126 on markers of systemic inflammation, hematological indices, fatty livers, and atherosclerotic lesion size. Mice exposed to PCB 126 exhibited significantly increased plasma inflammatory cytokine levels, increased circulating biomarkers of CVD, altered platelet, and red blood cell counts, increased accumulation of hepatic fatty acids, and accelerated atherosclerotic lesion formation in the aortic root. PCB 126 also increased circulating neutrophils, monocytes, and macrophages as determined by flow cytometry analysis. Exposure to dioxin-like PCB 126 increases inflammation and accelerates atherosclerosis in mice. This low-fat atherogenic diet may provide a useful tool to study the mechanisms linking exposure to lipophilic pollutants to increased risk of CVD.

Persistent Organic Pollutant Burden, Experimental POP Exposure, and Tissue Properties Affect Metabolic Profiles of Blubber from Gray Seal Pups

Persistent organic pollutants (POPs) are toxic, ubiquitous, resist breakdown, bioaccumulate in living tissue, and biomagnify in food webs. POPs can also alter energy balance in humans and wildlife. Marine mammals experience high POP concentrations, but consequences for their tissue metabolic characteristics are unknown. We used blubber explants from wild, gray seal ( Halichoerus grypus) pups to examine impacts of intrinsic tissue POP burden and acute experimental POP exposure on adipose metabolic characteristics. Glucose use, lactate production, and lipolytic rate differed between matched inner and outer blubber explants from the same individuals and between feeding and natural fasting. Glucose use decreased with blubber dioxin-like PCBs (DL-PCB) and increased with acute experimental POP exposure. Lactate production increased with DL-PCBs during feeding, but decreased with DL-PCBs during fasting. Lipolytic rate increased with blubber dichlorodiphenyltrichloroethane and its metabolites (DDX) in fasting animals, but declined with DDX when animals were feeding. Our data show that POP burdens are high enough in seal pups to alter adipose function early in life, when fat deposition and mobilization are vital. Such POP-induced alterations to adipose metabolic properties may significantly alter energy balance regulation in marine top predators, with the potential for long-term impacts on fitness and survival.

Environmental pollutant-mediated disruption of gut microbial metabolism of the prebiotic inulin

Exposure to environmental pollutants is associated with a greater risk for metabolic diseases including cardiovascular disease. Pollutant exposure can also alter gut microbial populations that may contribute to metabolic effects and progression of inflammatory diseases. Short-chain fatty acids (SCFAs), produced from gut fermentation of dietary carbohydrates, such as inulin, exert numerous effects on host energy metabolism and are linked to a reduced risk of diseases. The hypothesis was that exposure to dioxin-like pollutants modulate gut microbial viability and/or fermentation processes. An inulin-utilizing isolate was collected from murine feces, characterized and used in subsequent experiments. Exposure to polychlorinated biphenyl, PCB 126 impeded bacterial viability of the isolate at concentrations of 20 and 200 μM. PCB 126 exposure also resulted in a significant loss of intracellular potassium following exposure, indicating cell membrane disruption of the isolate. Furthermore, total fecal microbe samples from mice were harvested, resuspended and incubated for 24 h in anaerobic media containing inulin with or without PCB 126. HPLC analysis of supernatants revealed that PCB 126 exposure reduced succinic acid production, but increased propionate production, both of which can influence host glucose and lipid metabolism. Overall, the presented evidence supports the idea that pollutant exposure may contribute to alterations in host metabolism through gut microbiota-dependent mechanisms, specifically through bacterial fermentation processes or membrane disruption.

Mitochondria as target of endocrine-disrupting chemicals: implications for type 2 diabetes

Type 2 diabetes is a chronic, heterogeneous syndrome characterized by insulin resistance and pancreatic β-cell dysfunction or death. Among several environmental factors contributing to type 2 diabetes development, endocrine-disrupting chemicals (EDCs) have been receiving special attention. These chemicals include a wide variety of pollutants, from components of plastic to pesticides, with the ability to modulate endocrine system function. EDCs can affect multiple cellular processes, including some related to energy production and utilization, leading to alterations in energy homeostasis. Mitochondria are primarily implicated in cellular energy conversion, although they also participate in other processes, such as hormone secretion and apoptosis. In fact, mitochondrial dysfunction due to reduced oxidative capacity, impaired lipid oxidation and increased oxidative stress has been linked to insulin resistance and type 2 diabetes. Herein, we review the main mechanisms whereby metabolism-disrupting chemical (MDC), a subclass of EDCs that disturbs energy homeostasis, cause mitochondrial dysfunction, thus contributing to the establishment of insulin resistance and type 2 diabetes. We conclude that MDC-induced mitochondrial dysfunction, which is mainly characterized by perturbations in mitochondrial bioenergetics, biogenesis and dynamics, excessive reactive oxygen species production and activation of the mitochondrial pathway of apoptosis, seems to be a relevant mechanism linking MDCs to type 2 diabetes development.

Polychlorinated biphenyls (PCBs) exposure and cardiovascular, endocrine and metabolic diseases: A population-based cohort study in a North Italian highly polluted area

BACKGROUND AND AIMS

Exposure to polychlorinated biphenyls (PCBs) has been linked to the onset of cardiovascular, endocrine, and metabolic diseases, but no conclusive evidence has been provided so far. A chemical factory produced PCBs from 1938 to 1984 in Brescia (North Italy) resulting in environmental contamination and human exposure. We aimed to evaluate the association between PCB serum levels and subsequent incidence of chronic diseases through a prospective cohort study design.

METHODS

Based on surveys conducted in Brescia province between 2001 and 2013, a cohort of 1331 subjects with at least one measure of PCB serum levels during the period was selected and followed longitudinally. Serum concentration of total PCBs was computed summing up the levels of 24 PCB congeners determined by gas chromatography. The data on incidence of hypertension, cardiovascular diseases, and endocrine and metabolic chronic diseases were retrieved from the Brescia Health Protection Agency database. Poisson regression models adjusted for age, level of education, BMI, cholesterol level, tobacco smoking and alcohol drinking were employed to calculate rate ratios (RRs).

RESULTS

1331 subjects were enrolled (45.7% males, mean age 50.6 years) contributing to 10,006 person-years of follow-up. A dose-response relationship was observed between PCB serum levels and the onset of hypertension (RR for 2nd and 3rd tertiles of serum PCB distribution: 2.07, 95% CI 1.18-3.63, and 2.41, 1.30-4.47, respectively). A possible, though not statistically significant, increase of the risk of cardiovascular disease was also found (RR for 2nd and 3rd tertiles of serum PCB distribution: 1.61, 0.72-3.64, and 1.96, 0.86-4.48, respectively). The results based on lipid-standardized PCBs were slightly attenuated. No association was found between PCB serum levels and occurrence of diabetes and endocrine disorders. Stratified analysis by body mass index showed an increased risk of hypertension in subjects at 2nd and 3rd tertile of serum PCB distribution in overweight/obese subjects only.

CONCLUSIONS

These results suggest that PCBs might play a role in the development of hypertension and possibly cardiovascular disease, though alternative explanations are to be considered too.

Alterations in cellular lipid metabolism produce neutral lipid accumulation following exposure to the organochlorine compound trans-nonachlor in rat primary hepatocytes

Recent epidemiological studies have revealed significant positive associations between exposure to organochlorine (OC) pesticides and occurrence of the metabolic syndrome and there are a growing number of animal-based studies to support causality. However, the cellular mechanisms linking OC compound exposure and metabolic dysfunction remain elusive. Therefore, the present study was designed to determine if direct exposure to three highly implicated OC compounds promoted hepatic steatosis, the hepatic ramification of the metabolic syndrome. First, the steatotic effect of p,p'-dichlorodiphenyldichloroethylene (DDE), oxychlordane, and trans-nonachlor was determined in freshly isolated rat primary hepatocytes. Exposure to trans-nonachlor significantly increased neutral lipid accumulation as opposed to DDE and oxychlordane. To determine possible mechanisms governing increased fatty acid availability, the effects of trans-nonachlor exposure on fatty acid uptake, de novo lipogenesis, triglyceride secretion, and fatty acid oxidation were explored. Trans-nonachlor did not significantly alter fatty acid uptake. However, insulin-stimulated de novo lipogenesis as well as basal expression of fatty acid synthase, a major regulator of lipogenesis were significantly increased following trans-nonachlor exposure. Interestingly, there was a significant decrease in fatty acid oxidation following trans-nonachlor exposure. This decrease in fatty acid oxidation was accompanied by a slight, but significant increase in oleic acid-induced cellular triglyceride secretion. Therefore, taken together, the present data indicate direct exposure to trans-nonachlor has a more potent pro-steatotic effect than exposure to DDE or oxychlordane. This pro-steatotic effect of trans-nonachlor appears to be predominately mediated via increased de novo lipogenesis and decreased fatty acid oxidation.

Flux, Impact, and Fate of Halogenated Xenobiotic Compounds in the Gut

Humans and their associated microbiomes are exposed to numerous xenobiotics through drugs, dietary components, personal care products as well as environmental chemicals. Most of the reciprocal interactions between the microbiota and xenobiotics, such as halogenated compounds, occur within the human gut harboring diverse and dense microbial communities. Here, we provide an overview of the flux of halogenated compounds in the environment, and diverse exposure routes of human microbiota to these compounds. Subsequently, we review the impact of halogenated compounds in perturbing the structure and function of gut microbiota and host cells. In turn, cultivation-dependent and metagenomic surveys of dehalogenating genes revealed the potential of the gut microbiota to chemically alter halogenated xenobiotics and impact their fate. Finally, we provide an outlook for future research to draw attention and attract interest to study the bidirectional impact of halogenated and other xenobiotic compounds and the gut microbiota.

Endocrine-disrupting chemicals and risk of diabetes: an evidence-based review

The purpose of this study was to review the epidemiological and experimental evidence linking background exposure to a selection of environmental endocrine-disrupting chemicals (EDCs) with diabetes and impaired glucose metabolism. The review summarises the literature on both cross-sectional and prospective studies in humans, as well as experimental in vivo and in vitro studies. The findings were subjected to evidence grading according to the Grading of Recommendations Assessment, Development and Evaluation (GRADE) classification. We found >40 cross-sectional and seven prospective studies regarding EDCs and risk of diabetes. Taken together, there is moderate evidence for a relationship between exposure to dichlorodiphenyldichloroethylene (p,p'-DDE), a metabolite of the pesticide dichlorodiphenyltrichloroethane, and diabetes development. Regarding polychlorinated biphenyls (PCBs), it is likely that the rodent models used are not appropriate, and therefore the evidence is poorer than for p,p'-DDE. For other EDCs, such as bisphenol A, phthalates and perfluorinated chemicals, the evidence is scarce, since very few prospective studies exist. Brominated flame retardants do not seem to be associated with a disturbed glucose tolerance. Thus, evidence is accumulating that EDCs might be involved in diabetes development. Best evidence exists for p,p'-DDE. For other chemicals, both prospective studies and supporting animal data are still lacking.

A delayed proinflammatory response of human preadipocytes to PCB126 is dependent on the aryl hydrocarbon receptor

Inflammation in adipose tissue is recognized as a causative factor in the development of type II diabetes. Adipocyte hypertrophy as well as bacterial and environmental factors have been implicated in causing inflammation in mature adipocytes. Exposure to persistent organic pollutants such as polychlorinated biphenyls (PCBs) has been associated with the development of type II diabetes. We show here that PCB126, a dioxin-like PCB, activates a robust proinflammatory state in fat cell precursors (preadipocytes). The response was found to be dependent on aryl hydrocarbon receptor (AhR) activation, although induction of the response was delayed compared to upregulation of CYP1A1, a classic AhR-responsive gene. Treatment of preadipocytes with a nuclear factor kappa-light-chain-enhancer of activated B cell (NF-κB) inhibitor partially attenuated the PCB126-induced inflammatory response and partly, but not completely, ameliorated disruption of adipogenesis caused by PCB126. Our results indicate a role for PCB126 in mediating an inflammatory response through AhR in preadipocytes that interferes with adipogenesis.

Air pollution, weight loss and metabolic benefits of bariatric surgery: a potential model for study of metabolic effects of environmental exposures

BACKGROUND

Emerging experimental evidence suggests that air pollution may contribute to development of obesity and diabetes, but studies of children are limited.

OBJECTIVES

We hypothesized that pollution effects would be magnified after bariatric surgery for treatment of obesity, reducing benefits of surgery.

METHODS

In 75 obese adolescents, excess weight loss (EWL), high-density lipoprotein (HDL) cholesterol, triglycerides, alkaline phosphatase (ALP) and hemoglobin A1c (HbA_1c ) were measured prospectively at baseline and following laparoscopic adjustable gastric banding (LAGB). Residential distances to major roads and the average two-year follow-up exposure to particulate matter <2.5 μm (PM_2.5 ), nitrogen dioxide (NO₂ ) and ozone were estimated. Associations of exposure with change in outcome and with attained outcome two years post-surgery were examined.

RESULTS

Major-roadway proximity was associated with reduced EWL and less improvement in lipid profile and ALP after surgery. NO₂ was associated with less improvement in HbA_1c and lower attained HDL levels and change in triglycerides over two years post-surgery. PM_2.5 was associated with reduced EWL and reduced beneficial change or attained levels for all outcomes except HbA_1c .

CONCLUSIONS

Near-roadway, PM_2.5 and NO₂ exposures at levels common in developed countries were associated with reduced EWL and metabolic benefits of LAGB. This novel approach provides a model for investigating metabolic effects of other exposures.

Persistent organic pollutants and risk of type 2 diabetes: A prospective investigation among middle-aged women in Nurses' Health Study II

BACKGROUND

Exposure to persistent organic pollutants (POPs) may predispose to the development of type 2 diabetes (T2D), but prospective human evidence is scarce.

OBJECTIVES

We investigated the association between plasma-POP concentrations in the late 1990s and incident T2D over 11 years of follow-up in the Nurses' Health Study II.

DISCUSSION

Three organochlorine pesticides and 20 polychlorinated biphenyls (PCBs) were measured in banked plasma from 793 case-control pairs of T2D. In a multiviarate-adjusted model, T2D ORs (95%CIs) comparing extreme POP tertiles (high vs. low) were 1.67 (1.24, 2.23; Ptrend < 0.001) for hexachlorobenzene (HCB), 3.62 (2.57, 5.11; Ptrend < 0.001) for β-hexachlorocyclohexane (β-HCH), 1.55 (1.13, 2.13; Ptrend = 0.05) for p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE), and 1.95 (1.42, 2.69; Ptrend < 0.001) for total dioxin-like PCBs (DL-PCBs) which included 5 mono-ortho congeners, PCB-105, 118, 156, 157, and 167. Adjustment for previous weight change and body mass index (BMI) at blood draw attenuated these associations, but that for DL-PCBs remained (OR[95% CI] = 1.78[1.14, 2.76]; Ptrend = 0.006). Age, breastfeeding history, previous weight change and BMI at blood draw were significant predictors of plasma POP concentrations. In addition, we found significant interactions of POPs and weight change before blood draw on T2D risk. ORs (95%CIs) of T2D comparing extreme (high vs. low) POP groups were 2.00 (1.02, 3.92; Ptrend = 0.01) for HCB, 2.69 (1.34, 5.40; Ptrend < 0.001) for β-HCH, and 2.41 (1.22, 4.77; Ptrend < 0.001) for DL-PCBs in the lowest weight gain group, whereas these values were 1.29 (0.73, 2.28; Ptrend = 0.46; Pinteraction = 0.04) for HCB, 1.41 (0.77, 2.60; Ptrend = 0.24; Pinteraction = 0.003) for β-HCH, and 0.90 (0.50, 1.63; Ptrend = 0.61; Pinteraction = 0.01) for DL-PCBs in the highest weight-gain group.

CONCLUSIONS

Our findings suggest that elevated POP exposure may have diabetogenic potential. These data also highlight the impact of lifestyle factors, especially history of weight gain, on circulating POP concentrations and their associations with subsequent T2D risk.