Polychlorinated biphenyls, mercury, and antinuclear antibody positivity, NHANES 2003-2004

Serum antinuclear antibody positivity (ANA) has been associated with elevated serum polychlorinated biphenyls (PCBs) among residents in PCB-polluted areas; however, associations in general populations have not been reported by congener type or with adjustment for mercury. Cross-sectional data on serum PCBs, total blood mercury, ANA, and potential confounders age, race, body mass index, menopausal status, and dietary eicosapentaenoic acid (EPA) were obtained from the 2003-2004 National Health and Nutrition Examination Survey (NHANES) for males and females aged 12-85. PCB congeners were summed separately for dioxin-like and nondioxin-like PCBs; the former were weighted for toxic equivalent factors. Total PCBs by congener type and mercury were analyzed as both continuous log-transformed variables and as categorical quintiles. Logistic regression models were stratified by sex. There were no associations between nondioxin-like PCBs or mercury and ANA among males or females. Among females (n=114 affected and 518 unaffected), adjusting for potential confounders, the prevalence odds for ANA positivity were significantly elevated per incremental increase in log-transformed dioxin-like PCBs (odds ratio {OR}=1.66; 95% confidence interval {CI}=1.24, 2.23); the highest dioxin-like PCB quintile (>0.00425-0.04339ng/g) was significantly associated with 4.04 (95% CI=2.43, 6.70) greater prevalence odds for ANA positivity relative to the lowest quintile (Ptrend<0.001). We present novel findings of an association between low-level dioxin-like PCBs and ANA among women. No associations were observed between mercury and ANA at mercury levels common to the U.S. population.

PNPLA3 rs738409, hepatocellular carcinoma occurrence and risk model prediction in patients with cirrhosis

BACKGROUND & AIMS

Several studies have reported an association between the genetic variant rs738409 (G) in the PNPLA3 gene and the risk of cirrhosis in various liver diseases. Our purpose was to assess the influence of this polymorphism on the risk of hepatocellular carcinoma (HCC) occurrence in two distinct longitudinal cohorts of patients with cirrhosis as well as its possible usefulness in HCC-risk model prediction.

METHODS

PNPLA3 rs738409 genotypes were assessed in 279 patients with alcoholic- and 253 patients with HCV-related cirrhosis. These patients were followed-up and screened for the risk of HCC, and the influence of rs738409 on the occurrence of liver cancer was assessed using the Kaplan-Meier method, then according to the multivariate Cox model.

RESULTS

In patients with HCV-related cirrhosis, rs738409 genotypes did not influence the risk of HCC development (log-rank = 0.7) or death (log-rank = 0.2). Conversely, in patients with alcoholic cirrhosis, the rs738409 (GG) genotype was an independent risk factor for HCC occurrence (HR = 1.72 [1.21-2.45], log-rank = 0.002) as well as older age, male gender, and higher BMI. Combining these features enabled HCC-risk stratification of this population into three groups with the 6-year cumulative incidence ranging from 3.4% (low risk, n = 58), 12.2% (intermediate risk, n = 163), and 51.7% (high risk, n = 58), respectively (HR = 4.3 [2.7-6.4]; log-rank <0.0001).

CONCLUSIONS

This study provides key data that affirm the influence of the rs738409 (GG) genotype on the occurrence of HCC in patients with alcoholic cirrhosis. Its combination with clinical features refines the selection of patients at higher risk of liver cancer development.

Toxicological function of adipose tissue: focus on persistent organic pollutants

BACKGROUND

Adipose tissue (AT) is involved in several physiological functions, including metabolic regulation, energy storage, and endocrine functions.

OBJECTIVES

In this review we examined the evidence that an additional function of AT is to modulate persistent organic pollutant (POP) toxicity through several mechanisms.

METHODS

We reviewed the literature on the interaction of AT with POPs to provide a comprehensive model for this additional function of AT.

DISCUSSION

As a storage compartment for lipophilic POPs, AT plays a critical role in the toxicokinetics of a variety of drugs and pollutants, in particular, POPs. By sequestering POPs, AT can protect other organs and tissues from POPs overload. However, this protective function could prove to be a threat in the long run. The accumulation of lipophilic POPs will increase total body burden. These accumulated POPs are slowly released into the bloodstream, and more so during weight loss. Thus, AT constitutes a continual source of internal exposure to POPs. In addition to its buffering function, AT is also a target of POPs and may mediate part of their metabolic effects. This is particularly relevant because many POPs induce obesogenic effects that may lead to quantitative and qualitative alterations of AT. Some POPs also induce a proinflammatory state in AT, which may lead to detrimental metabolic effects.

CONCLUSION

AT appears to play diverse functions both as a modulator and as a target of POPs toxicity.

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

BACKGROUND

Previous studies demonstrated that coplanar polychlorinated biphenyls (PCBs) promote proinflammatory gene expression in adipocytes. PCBs are highly lipophilic and accumulate in adipose tissue, a site of insulin resistance in persons with type 2 diabetes.

OBJECTIVES

We investigated the in vitro and in vivo effects of coplanar PCBs on adipose expression of tumor necrosis factor α (TNF-α) and on glucose and insulin homeostasis in lean and obese mice.

METHODS

We quantified glucose and insulin tolerance, as well as TNF-α levels, in liver, muscle, and adipose tissue of male C57BL/6 mice administered vehicle, PCB-77, or PCB-126 and fed a low fat (LF) diet. Another group of mice administered vehicle or PCB-77 were fed a high fat (HF) diet for 12 weeks; the diet was then switched from HF to LF for 4 weeks to induce weight loss. We quantified glucose and insulin tolerance and adipose TNF-α expression in these mice. In addition, we used in vitro and in vivo studies to quantify aryl hydrocarbon receptor (AhR)-dependent effects of PCB-77 on parameters of glucose homeostasis.

RESULTS

Treatment with coplanar PCBs resulted in sustained impairment of glucose and insulin tolerance in mice fed the LF diet. In PCB-77-treated mice, TNF-α expression was increased in adipose tissue but not in liver or muscle. PCB-77 levels were strikingly higher in adipose tissue than in liver or serum. Antagonism of AhR abolished both in vitro and in vivo effects of PCB-77. In obese mice, PCB-77 had no effect on glucose homeostasis, but glucose homeostasis was impaired after weight loss.

CONCLUSIONS

Coplanar PCBs impaired glucose homeostasis in lean mice and in obese mice following weight loss. Adipose-specific elevations in TNF-α expression by PCBs may contribute to impaired glucose homeostasis.

Chronic exposure to PCBs (Aroclor 1254) exacerbates obesity-induced insulin resistance and hyperinsulinemia in mice

Evidence from recent epidemiological studies has emerged implicating exposure to environmental toxicants as a novel risk factor for the development of type 2 diabetes (T2D) and the metabolic syndrome in the general population. Humans and other organisms in high trophic levels of the food chain consume persistent organic pollutants (POP) through their diet. Few experimental studies demonstrating cause and effect are available and evidence for a direct association between accumulation of POP and T2D is preliminary; however, the possibility exists that lipophilic chemicals that accumulate in fatty tissue may disrupt cellular function and metabolic homeostasis. Chronic exposure of diabetes-prone C57B/6 mice to a polychlorinated biphenyl (PCB) mixture (Aroclor 1254, 36 mg/kg/wk, 20 wk) alone or in combination with high-fat diet impairs carbohydrate metabolism was compared to vehicle-treated control animals. Specifically, PBC exposure was found to produce hyperinsulinemia in both lean and diet-induced obese mice and exacerbated whole-body insulin resistance in obese mice. These changes in carbohydrate metabolism in response to Aroclor 1254 occurred without marked effect on body weight in both lean and obese mice. Our results demonstrate a causative association between PCB exposure and obesity-induced insulin resistance and hyperinsulinemia independent of body weight changes, an observation that contributes to a growing body of evidence suggesting that exposure to environmental pollutants represents a novel risk factor contributing to the diabetes epidemic.

Cytokines as molecular targets for aryl hydrocarbon receptor ligands: implications for toxicity and xenobiotic detoxification

INTRODUCTION

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor historically known for regulating expression of several important drug-detoxifying proteins. Besides drug metabolism pathways, cytokines have been recently recognized as targeted by the AhR signaling cascade, which may contribute to toxicity and changes in xenobiotic detoxification caused by AhR agonists.

AREAS COVERED

This article summarizes the nature of the main cytokines regulated by AhR ligands and reviews their involvement in toxic effects of AhR ligands, especially in relation with inflammation. The article also discusses the potential implications for drug detoxification pathways.

EXPERT OPINION

Even if various cytokines, including inflammatory ones, have already been demonstrated to constitute robust targets for AhR, the exact role played by AhR with respect to inflammation remains to be determined. Further studies are also required to better characterize the molecular mechanisms implicated in regulation of cytokines by AhR ligands and to determine the role that may play AhR-targeted cytokines in alteration of xenobiotic detoxification. Finally, changes in cytokine receptor expression triggered by AhR ligands have additionally to be taken into account to better and more extensively comprehend the role played by AhR in the cytokine/inflammation area.

Does fructose consumption contribute to non-alcoholic fatty liver disease?

Fructose is mainly consumed with added sugars (sucrose and high fructose corn syrup), and represents up to 10% of total energy intake in the US and in several European countries. This hexose is essentially metabolized in splanchnic tissues, where it is converted into glucose, glycogen, lactate, and, to a minor extent, fatty acids. In animal models, high fructose diets cause the development of obesity, insulin resistance, diabetes mellitus, and dyslipidemia. Ectopic lipid deposition in the liver is an early occurrence upon fructose exposure, and is tightly linked to hepatic insulin resistance. In humans, there is strong evidence, based on several intervention trials, that fructose overfeeding increases fasting and postprandial plasma triglyceride concentrations, which are related to stimulation of hepatic de novo lipogenesis and VLDL-TG secretion, together with decreased VLDL-TG clearance. However, in contrast to animal models, fructose intakes as high as 200 g/day in humans only modestly decreases hepatic insulin sensitivity, and has no effect on no whole body (muscle) insulin sensitivity. A possible explanation may be that insulin resistance and dysglycemia develop mostly in presence of sustained fructose exposures associated with changes in body composition. Such effects are observed with high daily fructose intakes, and there is no solid evidence that fructose, when consumed in moderate amounts, has deleterious effects. There is only limited information regarding the effects of fructose on intrahepatic lipid concentrations. In animal models, high fructose diets clearly stimulate hepatic de novo lipogenesis and cause hepatic steatosis. In addition, some observations suggest that fructose may trigger hepatic inflammation and stimulate the development of hepatic fibrosis. This raises the possibility that fructose may promote the progression of non-alcoholic fatty liver disease to its more severe forms, i.e. non-alcoholic steatohepatitis and cirrhosis. In humans, a short-term fructose overfeeding stimulates de novo lipogenesis and significantly increases intrahepatic fat concentration, without however reaching the proportion encountered in non-alcoholic fatty liver diseases. Whether consumption of lower amounts of fructose over prolonged periods may contribute to the pathogenesis of NAFLD has not been convincingly documented in epidemiological studies and remains to be further assessed.

PNPLA3 I148M (rs738409) genetic variant is associated with hepatocellular carcinoma in obese individuals

BACKGROUND

Obesity is a risk factor for cancer, including hepatocellular carcinoma. Patatin-like phospholipase domain-containing 3 (PNPLA3) I148M (rs738409) genetic variant has been associated with hepatocellular carcinoma (HCC) in individuals with chronic alcohol abuse or hepatic viral infection. In the present study we examined the association between the PNPLA3 I148M genetic variant and hepatocellular carcinoma in obese individuals from the Swedish Obese Subjects cohort (n = 4047).

METHODS

We performed a matched, prospective, controlled, interventional trial, investigating the effect of bariatric surgery (surgery group) compared to conventional treatment (control group) for obesity.

RESULTS

A total of 9 events were observed in the 15-year median follow up (5 in the control group and 4 in the surgery group). A significantly higher incidence of hepatocellular carcinoma in PNPLA3 148M allele carriers was found in obese individuals in the control group (log-rank P-value = 0.001), but not in the surgery group (log-rank P-value = 0.783). Consistently, an increased risk (for each PNPLA3 148M allele, hazard ratio: 5.9; 95% confidence interval 1.5-23.8; P-value = 0.013) of developing hepatocellular carcinoma was observed only in the control group.

CONCLUSION

The current study is the first prospective report showing the association of the PNPLA3 I148M genetic variant and hepatocellular carcinoma in severely obese individuals.

Accumulation capacity of primary cultures of adipocytes for PCB-126: influence of cell differentiation stage and triglyceride levels

Polychlorinated biphenyls (PCBs) are lipophilic persistent organic chemicals that accumulate at high concentrations in the adipose tissue. Recent studies correlate the presence of such contaminants in fat cells to possible alterations in the regulation of energy homeostasis in adipocytes. As the adipose tissue is composed of adipocytes at several stages of differentiation, it is possible that PCBs already accumulate in cells at an early stage, and thereby impair their development. The exact driving force enabling the massive accumulation of PCBs in fat cells remains unclear. The present study investigated the time-course incorporation of (3)H-PCB-126 in primary cultures of rat adipocytes at both early and late differentiation stages and showed that the accumulation of this congener was already significant at an early stage of differentiation. In addition, triglyceride levels in cells were an important parameter governing (3)H-PCB-126's entry. The extent of adipocyte ability to store this pollutant in vitro was also evaluated and revealed that fat cells were able to accumulate (3)H-PCB-126 at extremely high concentrations. A linear relationship was observed between the amount of (3)H-PCB-126 added to the medium and the one accumulated in the cells, which favors a passive diffusion mechanism for the entry of this pollutant into fat cells.