Exposure to a northern contaminant mixture (NCM) alters hepatic energy and lipid metabolism exacerbating hepatic steatosis in obese JCR rats

Update of the risk assessment of polybrominated diphenyl ethers (PBDEs) in food

The European Commission asked EFSA to update its 2011 risk assessment on polybrominated diphenyl ethers (PBDEs) in food, focusing on 10 congeners: BDE-28, -47, -49, -99, -100, -138, -153, -154, -183 and ‑209. The CONTAM Panel concluded that the neurodevelopmental effects on behaviour and reproductive/developmental effects are the critical effects in rodent studies. For four congeners (BDE-47, -99, -153, -209) the Panel derived Reference Points, i.e. benchmark doses and corresponding lower 95% confidence limits (BMDLs), for endpoint-specific benchmark responses. Since repeated exposure to PBDEs results in accumulation of these chemicals in the body, the Panel estimated the body burden at the BMDL in rodents, and the chronic intake that would lead to the same body burden in humans. For the remaining six congeners no studies were available to identify Reference Points. The Panel concluded that there is scientific basis for inclusion of all 10 congeners in a common assessment group and performed a combined risk assessment. The Panel concluded that the combined margin of exposure (MOET) approach was the most appropriate risk metric and applied a tiered approach to the risk characterisation. Over 84,000 analytical results for the 10 congeners in food were used to estimate the exposure across dietary surveys and age groups of the European population. The most important contributors to the chronic dietary Lower Bound exposure to PBDEs were meat and meat products and fish and seafood. Taking into account the uncertainties affecting the assessment, the Panel concluded that it is likely that current dietary exposure to PBDEs in the European population raises a health concern.

Interplay of Obesity, Ethanol, and Contaminant Mixture on Clinical Profiles of Cardiovascular and Metabolic Diseases: Evidence from an Animal Study

Obesity, ethanol, and contaminants are known risk factors of cardiovascular and metabolic diseases (CMD). However, their interplay on clinical profiles of these diseases remains unclear, and thus were investigated in this study. Male lean or obese JCR rats were given water or 10% ethanol and orally treated with or without a contaminant mixture (CM) dissolved in corn oil and loaded on two cookies at 0, 1.6, or 16 mg/kg BW/day dose levels for 4 weeks. The CM consisted 22 environmental contaminants found in human blood or serum of Northern populations. Over 60 parameters related to CMD were examined. The results revealed that obesity in JCR rats resembles the clinical profiles of non-alcoholic fatty liver disease in humans. Obesity was also associated with increased serum and organ retention of mercury, one of the chemical components of CM. Exposure to ethanol lightened hyperlipidemia, increased liver retention of mercury, and increased risk for hypertension in the obese rats. CM lessened hyperlipidemia and hyperenzymemia, worsened systemic inflammation and increased the risk for hypertension in the obese rats. CM markedly increased serum ethanol levels with or without ethanol exposure. Tissue total mercury contents significantly correlated with clinical parameters with altered profiles by both ethanol and obesity. These results suggest that obese individuals may be more prone to contaminant accumulation. Ethanol and CM exposure can alter clinical profiles associated with obesity, which may lead to misdiagnosis of CMD associated with obesity. CM can alter endogenous production and/or metabolism of ethanol, further complicating disease progression, diagnosis, and treatment.

Structure dependence and species sensitivity of in vivo hepatobiliary toxicity with lysophosphatidic acid receptor 1 (LPA1) antagonists

BMS-986020, BMS-986234 and BMS-986278, are three lysophosphatidic acid receptor 1 (LPA₁) antagonists that were or are being investigated for treatment of idiopathic pulmonary fibrosis (IPF). Hepatobiliary toxicity (elevated serum AST, ALT, and ALP, plasma bile acids [BAs], and cholecystitis) was observed in a Phase 2 clinical trial with BMS-986020, and development was discontinued. In dogs and rats, the species used for the pivotal toxicology studies, there was no evidence of hepatobiliary toxicity in the dog while findings in the rat were limited to increased plasma BAs levels (6.1× control), ALT (2.9×) and bilirubin (3.4×) with no histopathologic correlates. Since neither rats nor dogs predicted clinical toxicity, follow-up studies in cynomolgus monkeys revealed hepatobiliary toxicity that included increased ALT (2.0× control) and GLDH (4.9×), bile duct hyperplasia, cholangitis, cholestasis, and cholecystitis at clinically relevant BMS-986020 exposures with no changes in plasma or liver BAs. This confirmed monkey as a relevant species for identifying hepatobiliary toxicity with BMS-986020. In order to assess whether the toxicity was compound-specific or related to LPA₁ antagonism, two structurally distinct LPA₁ antagonists (BMS-986234 and BMS-986278), were evaluated in rat and monkey. There were no clinical or anatomic pathology changes indicative of hepatobiliary toxicity. Mixed effects on plasma bile acids in both rat and monkey has made this biomarker not a useful predictor of the hepatobiliary toxicity. In conclusion, the nonclinical data indicate the hepatobiliary toxicity observed clinically and in monkeys administered BMS-986020 is compound specific and not mediated via antagonism of LPA₁.

Intensive weight loss and cognition: The dynamics of persistent organic pollutants in adipose tissue can explain the unexpected results from the Action for Health in Diabetes (Look AHEAD) study

OBJECTIVE

The aim of this paper is to propose a new hypothesis for the role of lipophilic chemical mixtures stored in adipose tissue in the development of dementia. Specifically, we present how the dynamics of these chemicals can explain the unexpected findings from the Action for Health in Diabetes (Look AHEAD) study, which failed to show long-term benefits of intentional weight loss on cognition, despite substantial improvements in many known risk factors for dementia. Moreover, we discuss how the role of obesity in the risk of dementia can change depending on the dynamics of these chemicals in adipose tissue.

NEW HYPOTHESIS

Human adipose tissue is widely contaminated with various neurotoxic chemicals. Typical examples are persistent organic pollutants (POPs), strong lipophilic chemicals with long half-lives. Both unintentional and intentional weight loss increases the release of POPs from adipocytes into the circulation. As POPs in the blood can easily reach the brain, the intentional weight-loss group of the Look AHEAD study may have experienced an unappreciated and long-term disadvantage on their cognition. Additionally, POPs may be involved in the link between obesity and dementia, as dysfunctional hypertrophic adipocytes enhance the release of POPs from adipocytes to the circulation through uncontrolled lipolysis. In contrast, metabolically healthy obese people may have a low risk of dementia because the safe storage of POPs in adipose tissue would decrease the amount of POPs reaching the brain.

MAJOR CHALLENGES FOR THE HYPOTHESIS

In human studies, there are practical difficulties involved with measuring POPs in the blood, including high costs and complex assays. As the serum concentrations of POPs are continuously affected by weight loss and gain, prospective studies may require serial measurements of POPs. In in-vitro and in-vivo experimental studies, how to simulate the exposure dose, duration, and mixture patterns in humans would be critical.

LINKAGE TO OTHER MAJOR THEORIES

Even though POPs are direct neurotoxins at a high dosage, low-dose POPs are mitochondrial toxins. Therefore, chronic exposure to low-dose POPs is linked to known key interrelated mechanisms in the pathogenesis of dementia, such as mitochondrial dysfunction and neuroinflammation.

Maternal folic acid supplementation does not counteract the deleterious impact of prenatal exposure to environmental pollutants on lipid homeostasis in male rat descendants

Prenatal exposure to persistent organic pollutants (POPs) has been associated with the development of metabolic syndrome-related diseases in offspring. According to epidemiological studies, father’s transmission of environmental effects in addition to mother’s can influence offspring health. Moreover, maternal prenatal dietary folic acid (FA) may beneficially impact offspring health. The objective is to investigate whether prenatal FA supplementation can overcome the deleterious effects of prenatal exposure to POPs on lipid homeostasis and inflammation in three generations of male rat descendants through the paternal lineage. Female Sprague-Dawley rats (F0) were exposed to a POPs mixture (or corn oil) +/− FA supplementation for 9 weeks before and during gestation. F1 and F2 males were mated with untreated females. Plasma and hepatic lipids were measured in F1, F2, and F3 males after 12-h fast. Gene expression of inflammatory cytokines was determined by qPCR in epididymal adipose tissue. In F1 males, prenatal POPs exposure increased plasma lipids at 14 weeks old and hepatic lipids at 28 weeks old and prenatal FA supplementation decreased plasma total cholesterol at 14 weeks old. Prenatal POPs exposure decreased plasma triglycerides at 14 weeks old in F2 males. No change was observed in inflammatory markers. Our results show an impact of the paternal lineage on lipid homeostasis in rats up to the F2 male generation. FA supplementation of the F0 diet, regardless of POPs exposure, lowered plasma cholesterol in F1 males but failed to attenuate the deleterious effects of prenatal POPs exposure on plasma and hepatic lipids in F1 males.

Mechanisms of Environmental Contributions to Fatty Liver Disease

PURPOSE

Fatty liver disease (FLD) affects over 25% of the global population and may lead to liver-related mortality due to cirrhosis and liver cancer. FLD caused by occupational and environmental chemical exposures is termed "toxicant-associated steatohepatitis" (TASH). The current review addresses the scientific progress made in the mechanistic understanding of TASH since its initial description in 2010.

RECENT FINDINGS

Recently discovered modes of actions for volatile organic compounds and persistent organic pollutants include the following: (i) the endocrine-, metabolism-, and signaling-disrupting chemical hypotheses; (ii) chemical-nutrient interactions and the "two-hit" hypothesis. These key hypotheses were then reviewed in the context of the steatosis adverse outcome pathway (AOP) proposed by the US Environmental Protection Agency. The conceptual understanding of the contribution of environmental exposures to FLD has progressed significantly. However, because this is a new research area, more studies including mechanistic human data are required to address current knowledge gaps.

Effects of cross-fostering and developmental exposure to mixtures of environmental contaminants on hepatic gene expression in prepubertal 21 days old and adult male Sprague-Dawley rats

The notion that adverse health effects produced by exposure to environmental contaminants (EC) may be modulated by the presence of non-chemical stressors is gaining attention. Previously, our lab demonstrated that cross-fostering (adoption of a litter at birth) acted as a non-chemical stressor that amplified the influence of developmental exposure to EC on the glucocorticoid stress-response in adult rats. Using liver from the same rats, the aim of the current study was to investigate whether cross-fostering might also modulate EC-induced alterations in hepatic gene expression profiles. During pregnancy and nursing, Sprague-Dawley dams were fed cookies laced with corn oil (control, C) or a chemical mixture (M) composed of polychlorinated biphenyls (PCB), organochlorine pesticides (OCP), and methylmercury (MeHg), at 1 mg/kg/day. This mixture simulated the contaminant profile reported in maternal human blood. At birth, some control and M treated litters were cross-fostered to form two additional groups with different biological/nursing mothers (CC and MM). The hepatic transcriptome was analyzed by DNA microarray in male offspring at postnatal days 21 and 78-86. Mixture exposure altered the expression of detoxification and energy metabolism genes in both age groups, but with different sets of genes affected at day 21 and 78-86. Cross-fostering modulated the effects of M on gene expression pattern (MM vs M), as well as expression of energy metabolism genes between control groups (CC vs C). In conclusion, while describing short and long-term effects of developmental exposure to EC on hepatic transcriptomes, these cross-fostering results further support the consideration of non-chemical stressors in EC risk assessments.

Protein S-glutathionylation: The linchpin for the transmission of regulatory information on redox buffering capacity in mitochondria

Protein S-glutathionylation reactions are a ubiquitous oxidative modification required to control protein function in response to changes in redox buffering capacity. These reactions are rapid and reversible and are, for the most part, enzymatically mediated by glutaredoxins (GRX) and glutathione S-transferases (GST). Protein S-glutathionylation has been found to control a range of cell functions in response to different physiological cues. Although these reactions occur throughout the cell, mitochondrial proteins seem to be highly susceptible to reversible S-glutathionylation, a feature attributed to the unique physical properties of this organelle. Indeed, mitochondria contain a number of S-glutathionylation targets which includes proteins involved in energy metabolism, solute transport, reactive oxygen species (ROS) production, proton leaks, apoptosis, antioxidant defense, and mitochondrial fission and fusion. Moreover, it has been found that conjugation and removal of glutathione from proteins in mitochondria fulfills a number of important physiological roles and defects in these reactions can have some dire pathological consequences. Here, we provide an updated overview on mitochondrial protein S-glutathionylation reactions and their importance in cell functions and physiology.

Persistent Endocrine-Disrupting Chemicals and Fatty Liver Disease

PURPOSE OF REVIEW

Non-alcoholic fatty liver disease (NAFLD) is the most prominent chronic liver disease in Western countries, affecting approximately 25% of the population worldwide. Sex-specific differences in the development of NAFLD are apparent. While obesity and insulin resistance are major contributors to the increasing prevalence of NAFLD, a growing body of literature suggests that exposure to persistent endocrine-disrupting chemicals (pEDCs) may also play a role. This review summarizes recent (2011 and later) scientific literature investigating exposures to pEDCs, specifically persistent organic pollutants (POPs), and NAFLD, with a focus on sex-specific associations.

RECENT FINDINGS

The overwhelming majority of studies were conducted in single-sex animal models and provide biological evidence that exposures to 2,3,7,8-tetrachlorodibenzo-p-dioxin polychlorinated biphenyls, and other POPs or POP mixtures are negatively associated with liver health. There were four cross-sectional epidemiological studies in humans that reported associations for several POPs, including polychlorinated biphenyls and perfluorinated chemicals, with elevated liver enzymes. Only one of these studies, using a sample of gastric bypass surgery patients, examined sex-specific associations of POPs and liver enzymes, finding adverse associations among women only. The noticeable lack of studies investigating how differences (i.e., biochemical, physiological, and behavioral) between men and women may influence associations of pEDCs and NAFLD represents a large research gap in environmental health. Sexual dimorphism in metabolic processes throughout the body, including the liver, is established but often overlooked in the designs and analyses of studies. Other factors identified in this review that may also act to modulate associations of environmental chemicals and NAFLD are reproductive status and dietary nutrient intakes, which also remain understudied in the literature. Despite knowledge of sexual dimorphism in the actions of pEDCs, as well as in metabolic processes related to NAFLD development, few experimental or epidemiological studies have investigated sex-dependent associations. Future studies, especially those in humans, should be designed to address this research need. Consideration of other factors, such as reproductive status, dietary intakes, and mixtures of chemicals with varying endocrine-disrupting capabilities, should be explored.

DR, Lee DH. Persistent Organic Pollutants and Type 2 Diabetes: A Critical Review of Review Articles

Low dose persistent organic pollutants (POPs) have emerged as a new risk for type 2 diabetes (T2D). Despite substantial evidence from human and experimental studies, there are several critical issues which have not been properly addressed by POPs researchers. First, as POPs exist as mixtures, findings about POPs from human studies should be interpreted from the viewpoint of lipophilic chemical mixtures which include both measured and unmeasured POPs. Second, as POPs can directly reduce insulin secretion of beta cells, the role of POPs may be more prominent in the development of beta-cell dysfunction-dominant T2D rather than insulin resistance-dominant T2D. Third, there are multidimensional interrelationships between POPs and adipose tissue. Even though POPs are now considered as a new risk factor for T2D, independent of obesity, POPs and obesity are mechanistically linked to each other. POPs are involved in key mechanisms linking obesity and T2D, such as chronic inflammation of adipose tissue and lipotoxicity with ectopic fat accumulation. Also, POPs can explain puzzling human findings which suggest benefits of obesity because healthy adipose tissue can be protective by reducing the amount of POPs reaching other organs. Fourth, non-linear dose-response relationships between POPs and T2D are biologically possible. Although POPs are well-known endocrine disrupting chemicals (EDCs), mitochondrial dysfunction may be a more plausible mechanism due to unpredictability of EDC mixtures. As adipose tissue plays a role as an internal exposure source of POPs, how to manage POPs inside us may be essential to protect against harms of POPs.

Association of blood polychlorinated biphenyls and cholesterol levels among Canadian Inuit

BACKGROUND

It has generally been thought that Inuit populations have low risk of cardiovascular disease due to high consumption of omega-3 fatty acids found in traditional marine-based diets. However, results of recent surveys showed that Inuit populations are experiencing increasing rates of cardiovascular disease and related risk factors.

OBJECTIVE

The purpose of this study was to investigate if blood polychlorinated biphenyls (PCBs) are associated with high cholesterol and related parameters in Canadian Inuit, known risk factors for cardiovascular disease.

METHODS

The Adult Inuit Health Survey (IHS, 2007-2008) included 2595 Inuit participants from three regions of the Canadian Arctic, of which 2191 could be classified as with or without high cholesterol. The high cholesterol outcome was defined by LDL-C > 3.36mmol/L or taking medication(s) that reduce cholesterol, and was examined in adjusted logistic regression models with individual blood levels of PCB congeners, sum of dioxin-like PCBs (∑DL-PCBs), or sum of non-dioxin-like PCBs (∑NDL-PCBs). Statistically significant covariates for high cholesterol were ranked in importance according to the proportion of the model log likelihood explained. Continuous clinical parameters of total cholesterol, triglycerides, LDL-C, and HDL-C were examined in multiple linear regression models with ∑DL-PCBs or ∑NDL-PCBs.

RESULTS

A total of 719 participants had high cholesterol (32.8%). PCBs were associated with increased risk of high cholesterol, and higher levels of serum triglycerides, total cholesterol, and LDL-C. No association was observed between PCBs and serum HDL-C. With respect to other statistically significant covariates for high cholesterol, the log likelihood ranking of PCBs generally fell between body mass index (BMI) and age.

CONCLUSION

Further work is needed to corroborate the associations observed with PCBs and lipids in Canadian Inuit and to examine if they are causal in the direction anticipated.

Identification of lipidomic markers of chronic 3,3',4,4',5-pentachlorobiphenyl (PCB 126) exposure in the male rat liver

Exposure to PCB 126, an environmentally relevant aryl hydrocarbon receptor agonist, is an environmental factor causing hepatic steatosis in rodent models; however, the lipidome of PCB 126-exposed rats has not been investigated in-depth. The objective of the present study was therefore to characterize dose-dependent changes in the lipid profile in the liver of male Sprague-Dawley rats exposed to PCB 126. Rats were exposed for three month to intraperitoneal injections of 0.01, 0.05 and 0.2μmol/kg bw PCB 126 in corn oil. Control animals were exposed in parallel and received corn oil alone. Lipids were extracted from whole liver homogenate and levels of polar lipids and fatty acids incorporated into triglycerides (FATAGs) were determined with tandem mass spectrometry using electrospray ionization. PCB 126 exposure increased the hepatic content of polar lipids and FATAGs. Protein adjusted levels of several polar lipid classes, in particular phosphatidylserine levels, decreased, whereas FATAGs levels typically increased with increasing PCB 126 dose. Sensitive, dose-dependent endpoints of PCB 126 exposure included an increase in levels of adrenic acid incorporated into triglycerides and changes in levels of certain ether-linked phospholipid and 1-alkyl/1-alkenyldiacylglycerol species, as determined using partial least square discriminant analysis (PLS-DA) and ANOVA. These changes in the composition of polar lipids and fatty acid in the liver of PCB 126 exposed rats identified several novel markers of PCB 126-mediated fatty liver disease that need to be validated in further studies.

Endocrine-disrupting chemicals and the regulation of energy balance

Energy balance involves the adjustment of food intake, energy expenditure and body fat reserves through homeostatic pathways. These pathways include a multitude of biochemical reactions, as well as hormonal cues. Dysfunction of this homeostatic control system results in common metabolism-related pathologies, which include obesity and type 2 diabetes mellitus. Metabolism-disrupting chemicals (MDCs) are a particular class of endocrine-disrupting chemicals that affect energy homeostasis. MDCs affect multiple endocrine mechanisms and thus different cell types that are implicated in metabolic control. MDCs affect gene expression and the biosynthesis of key enzymes, hormones and adipokines that are essential for controlling energy homeostasis. This multifaceted spectrum of actions precludes compensatory responses and favours metabolic disorders. Herein, we review the main mechanisms used by MDCs to alter energy balance. This work should help to identify new MDCs, as well as novel targets of their action.

Exposure to an environmentally relevant mixture of organochlorine compounds and polychlorinated biphenyls Promotes hepatic steatosis in male Ob/Ob mice

Hepatic steatosis is recognized as an independent risk factor for the development of cardiovascular disease. While obesity and type 2 diabetes are well-established risk factors in the development of hepatic steatosis, recent studies have revealed exposure to mixtures of persistent organic pollutants (POPs), which are environmental contaminants in various fatty foods, can promote steatosis. Thus, the present study was designed to determine if exposure to a defined mixture of prevalent polychlorinated biphenyls (PCBs) and organochlorine (OC) pesticides or their metabolites promote hepatic steatosis in a genetically induced model of type 2 diabetes, the leptin-deficient ob/ob mouse. Male C57BL/6J wild type (WT) or ob/ob mice were administered an environmentally relevant mixture of PCBs and OCs for 7 weeks via oral gavage. Exposure to POPs did not significantly alter fasting serum glucose or insulin levels. However, POPs exposure significantly increased hepatic triglyceride content in ob/ob animals, while decreasing serum triglyceride levels. This POPs-mediated increase in hepatic triglyceride content did not appear to be associated with significantly increased inflammation in either the liver or adipose. Exposure to POPs significantly induced the expression of cytochrome P450 3a11 in WT animals, yet the expression of this cytochrome was significantly downregulated in ob/ob animals regardless of POPs exposure. Taken together, the present data indicate exposure to an environmentally relevant mixture of both PCBs and OC pesticides in ob/ob mice promotes hepatic steatosis while decreasing hypertriglyceridemia, which demonstrates exposure to a defined mixture of POPs alters systemic lipid metabolism in a genetically induced model of obesity and type 2 diabetes. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1399-1411, 2017.

Persistent organic pollutants and diabetes among Inuit in the Canadian Arctic

Type 2 diabetes is a chronic metabolic disease that is of increasing concern in Inuit communities. Behavioural factors such as physical inactivity and poor diet are well-known risk factors. Exposure to persistent organic pollutants (POPs) has emerged as an additional factor in the pathogenesis of diabetes. In this study, association between polychlorinated biphenyls (PCBs) and p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE) with diabetes in Canadian Inuit was examined. Data from the Adult Inuit Health Survey (2007-2008) of Inuit participants from the Canadian Arctic were analyzed. Self-reported diabetes (excluding gestational diabetes) and clinical measurement of fasting glucose were examined as outcomes. Association with individual PCB congeners, sum of dioxin-like PCBs (∑DL-PCB), non-dioxin-like PCBs (∑NDL-PCB), total PCBs (∑PCB), and p,p'-DDE were investigated using multiple regression models adjusted for confounding factors. Using different methods to incorporate serum lipids, highest vs. lowest quartile exposures to PCB-105, PCB-118, PCB-153, PCB-156, PCB-170, PCB-180, PCB-183, ∑PCB, and p,p'-DDE were associated with increased risk of diabetes. For these PCBs, odds ratios (ORs) ranged from 1.9-3.5 (lower 95% CI: 0.8-1.4, upper 95% CI: 4.4-9.0) and for p,p'-DDE the OR was 2.5 (lower 95% CI: 1.1-1.2, upper 95% CI: 5.9-6.0). The highest vs. lowest quartile exposure to most PCBs and p,p'-DDE were associated with an increase of fasting glucose by 3-7%. PCBs and p,p'-DDE were associated with increased risk of diabetes and higher fasting glucose level in a cross-sectional survey of Canadian Inuit. Cause-effect relationships of PCBs and p,p'-DDE with diabetes and diabetes-related outcomes need to be further investigated in a cohort study.

Molecular Pathogenesis of NASH

Nonalcoholic steatohepatitis (NASH) is the main cause of chronic liver disease in the Western world and a major health problem, owing to its close association with obesity, diabetes, and the metabolic syndrome. NASH progression results from numerous events originating within the liver, as well as from signals derived from the adipose tissue and the gastrointestinal tract. In a fraction of NASH patients, disease may progress, eventually leading to advanced fibrosis, cirrhosis and hepatocellular carcinoma. Understanding the mechanisms leading to NASH and its evolution to cirrhosis is critical to identifying effective approaches for the treatment of this condition. In this review, we focus on some of the most recent data reported on the pathogenesis of NASH and its fibrogenic progression, highlighting potential targets for treatment or identification of biomarkers of disease progression.

The Emerging Role of Disturbed CoQ Metabolism in Nonalcoholic Fatty Liver Disease Development and Progression

Although non-alcoholic fatty liver disease (NAFLD), characterised by the accumulation of triacylglycerol in the liver, is the most common liver disorder, the causes of its development and progression to the more serious non-alcoholic steatohepatitis (NASH) remain incompletely understood. Oxidative stress has been implicated as a key factor in both these processes, and mitochondrial dysfunction and inflammation are also believed to play a part. Coenzyme Q (CoQ) is a powerful antioxidant found in all cell membranes which has an essential role in mitochondrial respiration and also has anti-inflammatory properties. NAFLD has been shown to be associated with disturbances in plasma and liver CoQ concentrations, but the relationship between these changes and disease development and progression is not yet clear. Dietary supplementation with CoQ has been found to be hepatoprotective and to reduce oxidative stress and inflammation as well as improving mitochondrial dysfunction, suggesting that it may be beneficial in NAFLD. However, studies using animal models or patients with NAFLD have given inconclusive results. Overall, evidence is now emerging to indicate that disturbances in CoQ metabolism are involved in NAFLD development and progression to NASH, and this highlights the need for further studies with human subjects to fully clarify its role.

Superoxide anion radical (O2(-)) degrades methylmercury to inorganic mercury in human astrocytoma cell line (CCF-STTG1)

Methylmercury (MeHg) is a global pollutant that is affecting the health of millions of people worldwide. However, the mechanism of MeHg toxicity still remains somewhat elusive and there is no treatment. It has been known for some time that MeHg can be progressively converted to inorganic mercury (iHg) in various tissues including the brain. Recent work has suggested that cleavage of the carbon-metal bond in MeHg in a biological environment is facilitated by reactive oxygen species (ROS). However, the oxyradical species that actually mediates this process has not been identified. Here, we provide evidence that superoxide anion radical (O2(-)) can convert MeHg to iHg. The calculated second-order rate constant for the degradation of 1μM MeHg by O2(-) generated by xanthine/xanthine oxidase was calculated to be 2×10(5)M(-1)s(-1). We were also able to show that this bioconversion can proceed in intact CCF-STTG1 human astrocytoma cells exposed to paraquat (PQ), a O2(-) generating viologen. Notably, exposure of cells to increasing amounts of PQ led to a dose dependent increase in both MeHg and iHg. Indeed, a 24h exposure to 500μM PQ induced a ∼13-fold and ∼18-fold increase in intracellular MeHg and iHg respectively. These effects were inhibited by superoxide dismutase mimetic MnTBAP. In addition, we also observed that a 24h exposure to a biologically relevant concentration of MeHg (1μM) did not induce cell death, oxidative stress, or even changes in cellular O2(-) and H2O2. However, co-exposure to PQ enhanced MeHg toxicity which was associated with a robust increase in cell death and oxidative stress. Collectively our results show that O2(-) can bioconvert MeHg to iHg in vitro and in intact cells exposed to conditions that simulate high intracellular O2(-) production. In addition, we show for the first time that O2(-) mediated degradation of MeHg to iHg enhances the toxicity of MeHg by facilitating an accumulation of both MeHg and iHg in the intracellular environment.

Alcoholic, Nonalcoholic, and Toxicant-Associated Steatohepatitis: Mechanistic Similarities and Differences

Hepatic steatosis and steatohepatitis are common histologic findings that can be caused by multiple etiologies. The three most frequent causes for steatosis/steatohepatitis are alcohol (alcoholic steatohepatitis, ASH), obesity/metabolic syndrome (nonalcoholic steatohepatitis, NASH), and environmental toxicants (toxicant-associated steatohepatitis, TASH). Hepatic steatosis is an early occurrence in all three forms of liver disease, and they often share common pathways to disease progression/severity. Disease progression is a result of both direct effects on the liver as well as indirect alterations in other organs/tissues such as intestine, adipose tissue, and the immune system. Although the three liver diseases (ASH, NASH, and TASH) share many common pathogenic mechanisms, they also exhibit distinct differences. Both shared and divergent mechanisms can be potential therapeutic targets. This review provides an overview of selected important mechanistic similarities and differences in ASH, NASH, and TASH.

Impact of methylmercury exposure on mitochondrial energetics in AC16 and H9C2 cardiomyocytes

It has been reported that chronic low dose exposures of methylmercury (MeHg) is associated with cardiovascular diseases in many populations worldwide. The toxic mechanisms through which these adverse effects occur are currently unknown. The objective of this study was to determine the bioenergetic and cytotoxic effects of MeHg on AC16 and H9C2 cardiomyocyte cell lines. Both cell lines exhibit significantly decreased mitochondrial function, cell viability and increased reactive oxygen species (ROS) production. Decreases in maximal respiration and reserve capacity was observed in both cell lines at 1μM. Bioenergetic profile experiments were also performed in tandem with cells exposed to diamide or menadione, compounds which accumulate in mitochondria and disrupt oxidative phosphorylation. AC16 cells show MeHg dose dependant sensitivities with Stateapparent and ATP production values, but H9C2 cells do not show these trends. H9C2 cells may be more resistant to MeHg toxicity than AC16 cells as reflected in the increases of proton leak and Stateapparent. No changes in expression of respiratory complexes were observed. Results suggest that MeHg has the potential to induce cytotoxicity. Furthermore, MeHg may have differential effects on AC16 and H9C2 cells, derived from human and rat cardiac tissue respectively, suggesting that differences in MeHg toxicity may be species-dependent.