AhR transcriptional activity in serum of Inuits across Greenlandic districts

Dioxin-like activity in environmental and human samples from Greenland and Denmark

A mixture of persistent organic pollutants relevant for human exposure inhibits the transactivation activity of the aryl hydrocarbon receptor in vitro

Modulation of aryl hydrocarbon receptor activity by four and a half LIM domain 2

Xenoestrogenic and dioxin-like activity in blood of East Greenland polar bears (Ursus maritimus)

Persistent organic pollutants (POPs) are lipophilic compounds that travel with lipids and accumulate mainly in adipose tissue. Recent human evidence links low-dose POPs to an increased risk of type 2 diabetes (T2D). Because humans are contaminated by POP mixtures and POPs possibly have nonmonotonic dose-response relations with T2D, critical methodological issues arise in evaluating human findings. This review summarizes epidemiological results on chlorinated POPs and T2D, and relevant experimental evidence. It also discusses how features of POPs can affect inferences in humans. The evidence as a whole suggests that, rather than a few individual POPs, background exposure to POP mixtures-including organochlorine pesticides and polychlorinated biphenyls-can increase T2D risk in humans. Inconsistent statistical significance for individual POPs may arise due to distributional differences in POP mixtures among populations. Differences in the observed shape of the dose-response curves among human studies may reflect an inverted U-shaped association secondary to mitochondrial dysfunction or endocrine disruption. Finally, we examine the relationship between POPs and obesity. There is evidence in animal studies that low-dose POP mixtures are obesogenic. However, relationships between POPs and obesity in humans have been inconsistent. Adipose tissue plays a dual role of promoting T2D and providing a relatively safe place to store POPs. Large prospective studies with serial measurements of a broad range of POPs, adiposity, and clinically relevant biomarkers are needed to disentangle the interrelationships among POPs, obesity, and the development of T2D. Also needed are laboratory experiments that more closely mimic real-world POP doses, mixtures, and exposure duration in humans.

Xenoestrogenic and dioxin-like activity in blood of East Greenland polar bears (Ursus maritimus)

Superfamily of cytochrome P450 enzymes (CYPs), a distinctive enzyme system by which human body defends itself against toxic compounds, is the subject of a complex regulation process involving various mechanisms, on the levels of expression and activity. Apart from physiological factors, several patho-physiological ones such as inflammation, infection, and stress affect CYP expression. The aim of this review is to summarize the current knowledge on the role of microtubules network in the regulation of drug metabolizing CYPs. Experiments on human and animal cell models revealed that microtubules disruption severely impaired basal and inducible expression of human CYP 1A1, 2B6, 2C8, 2C9, 2C19, and 3A4, and rat CYP 1A2, 2B1, 2B2, and 3A23. Inhibition of aryl hydrocarbon receptor (AhR) and glucocorticoid receptor (GR) transcriptional activity by microtubules disarray was found to be responsible for the suppressed CYP enzymes expression. However, the mechanism by which microtubules interfering agents (MIAs) inhibit GR and AhR transcriptional activities is not fully understood yet. Several lines of evidence indicate that: i) the cell cycle, G2/M phase in particular, has an influence on AhR and GR transcriptional activity, and ii) MIAs negatively modulate GR transcriptional activity via the activation of c-Jun-N-terminal kinase. In conclusion, down-regulation of major CYP enzymes by microtubules disarray is intriguing from the mechanistic point of view and in relation to the cell differentiation.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a persistent organic pollutant (POP), an unintentional byproduct of various industrial processes, and a human carcinogen. The expression of the cytochrome P450 1A (cyp1a) gene is upregulated in the presence of TCDD through activating the aryl hydrocarbon receptor pathway in a dose-dependent manner. Several essential response elements, including the 8 potential xenobiotic response elements in the cyp1a promoter region, have been identified to be the main functional parts for the response to TCDD. Thus, we aimed to develop a convenient and sensitive biomonitoring tool to examine the level of POPs in the environment and evaluate its potential human health risks by TCDD. Here, we established a transgenic zebrafish model with a red fluorescent reporter gene ( mCherry) using the truncated cyp1a promoter. Under exposure to TCDD, the expression pattern of mCherry in the reporter zebrafish mirrored that of endogenous cyp1a mRNA, and the primary target tissues for TCDD were the brain vessels, liver, gut, cloaca, and skin. Our results indicated that exposure of the embryos to TCDD at concentrations as low as 0.005 nM for 48 h, which did not elicit morphologic abnormalities in the embryos, markedly increased mCherry expression. In addition, the reporter embryos responded to other POPs, and primary liver cell culture of zebrafish revealed that Cyp1a protein was mainly expressed in the cytoplasm of liver cells. Furthermore, our transgenic fish embryos demonstrated that TCDD exposure can regulate the expression levels of several tumor-related factors, including epidermal growth factor, TNF-α, C-myc, proliferating cell nuclear antigen, TGF-β, serine/threonine kinase (Akt), and phosphorylated Akt, suggesting that our transgenic fish can be used as a sensitive model to evaluate the carcinogenicity induced by TCDD exposure.-Luo, J.-J., Su, D.-S., Xie, S.-L., Liu, Y., Liu, P., Yang, X.-J., Pei D.-S. Hypersensitive assessment of aryl hydrocarbon receptor transcriptional activity using a novel truncated cyp1a promoter in zebrafish.

We constructed stably transfected gene reporter cell line AZ-AHR, allowing measurement of aryl hydrocarbon receptor (AhR) transcriptional activity. Human hepatoma HepG2 cells were transfected with a construct containing several AhR binding sites upstream of luciferase reporter gene. We prepared 12 clones and we characterized the best five in responsiveness to TCDD. Dose-response analyses were performed for various AhR ligands, including TCDD, 3-methylcholanthrene, indirubin, resveratrol, omeprazole, and SP600125. The EC(50) values were similar in all tested clones. Induction of luciferase was time-dependent, and treatment for 6 h with 5 nM TCDD was sufficient to evaluate AhR transcriptional activity in 96-well plate format (8-24 fold induction). Response to AhR ligands of cryopreserved cells after thawing was not significantly different from that of fresh cells. Cell line remained fully responsive to AhR ligands over 15 passages and 30 days in culture without significant alterations. Overall, we have developed novel human luciferase reporter cell line AZ-AHR for monitoring AhR transcriptional activity. The sensitivity of the assay allows high throughput format (96-well plate) and evaluation of luciferase activity as soon as after 6 h of incubation, which has potential implication for studies of cytotoxic compounds.

BackgroundSemen quality in humans may be influenced by exposure to endocrine-disrupting compounds.ObjectivesWe analyzed associations between semen characteristics and serum xenoestrogen receptor (XER), xenoandrogen receptor (XAR), and aryl hydrocarbon receptor (AhR) transactivity. XER and XAR activity were measured in serum samples cleared for endogenous steroid hormones and AhR activity in raw lipophilic serum extracts free of proteins.ResultsAll together, 319 men from Warsaw (Poland), Greenland, Kharkiv (Ukraine), and Sweden provided semen and blood samples. No strong and consistent associations between xenobiotic activity and semen quality measures were observed in the four populations. However, when the data were combined across populations sperm concentration increased 40% per unit increase in XER activity [95% confidence interval (CI), 1–79%] in the subgroup with XER activity below the reference level. Among subjects with XER activity above the reference level an increase of 14% (95% CI, 2–28%) was found. Furthermore, an increase of 10% motile sperm per unit increase in XER activity below reference level (95% CI, 0.2–20) was found. We are unable to exclude that the associations are chance findings.ConclusionAlteration of XER, XAR, or AhR transactivity within the range found in serum from the general European and Inuit population seems not to markedly deteriorate sperm cell concentration, motility, or morphology in adult men.

Since 1997 the Arctic Monitoring and Assessment Programme (AMAP) has produced integrated assessment reports on the status of and trends in environmental persistent organic pollutants (POPs) in the Arctic ecosystem. Three reports on biomonitoring POPs and their health risks for Arctic populations were published in 1998, 2002, and 2009. The present review summarizes data from Greenland on human monitoring of biomarkers of POP exposure and bioaccumulation and the determination of biomarkers for POP effects. The review focuses on hormone disruptive potentials and some genetic sensitivity biomarkers. The overview covers Greenlandic studies from 2000 to 2006. The Greenland biomonitoring studies showed general geographical and gender differences of bioaccumulated serum POP levels, which were primarily related to diet and lifestyle. A high intake of traditional Greenlandic diet (eg seal, whale, polar bear, and seabirds) together with smoking caused higher blood concentrations of POPs. The highest POP values were found on the east coast of Greenland. The receptor effect studies showed a general inverse relationship between high serum POP concentration and estrogen receptor (ER) and Ah-receptor (AhR) transactivity; in addition for men in the two West Greenlandic districts, Nuuk and Sisimiut, a trend towards increased induced AR activity was found. An observed trend to an opposite direction between the dioxin-like AhR and ER activity supports the perception of that dioxins exert an antiestrogen effect. In conclusion, the actual mixtures of serum POPs in Greenlandic Inuit have an endocrine disrupting potential. Comparisons between European and Greenlandic male serum POP levels showed significantly higher levels in Inuit; however, in the same study Inuit had significantly lower sperm DNA damage. Further studies are required to elucidate whether the serum POP related effects on hormone receptors and/or AhR are explanatory factors. 'The Arctic dilemma' is that along with the intake of the Greenlandic traditional diet that contains POPs, there are also a number of important nutrients, such as trace elements/antioxidants and marine unsaturated fatty acids which have favorable effects on health. However, a number of studies suggest that an increase in Western food items in the diet can lead to other health risks, such as the metabolic syndrome and its sequels increase in weight, hypertension, diabetes type 2, cardiovascular disease, and cancer, including breast cancer. To elucidate these aspects further studies are required, including those into biomarkers for exposure and effects, epigenetic contexts and the determination of relevant genetic polymorphisms, case-control as well as generation studies. Finally, there is a need for the development of new biomarkers to study the potential POP effects that inhibit the immune system and affect the development of the central nervous system.

Oxidized frying oil and its polar fraction fed to pregnant mice are teratogenic and alter mRNA expressions of vitamin A metabolism genes in the liver of dams and their fetuses

Persistent Organic Pollutants

Animal studies indicate some persistent organic pollutants (POPs) may be endocrine disruptors and suggest similar health risks for humans. Recent studies have further suggested an association between exposure to POPs and the prevalence of type 2 diabetes. Now an experimental animal study reports evidence of a causal link between POP exposure and insulin resistance syndrome, a cluster of metabolic disorders—including type 2 diabetes—that are marked by sustained high blood sugar [EHP 118:465–471; Ruzzin et al.]. POPs accumulate in fatty tissue, where they can remain for years because they are not easily broken down. Fatty fish are a potential source of POP exposure in many human populations. However, n-3 polyunsaturated fatty acids in fish oil may have beneficial health effects, possibly including protective effects on insulin resistance, that could counterbalance any adverse effects of POPs in fatty fish. In the current study, rats were exposed for 28 days to high-fat diets that contained either crude fish oil (from farmed Atlantic salmon) or fish oil that was refined to remove POPs. As expected, the crude fish oil contained much higher levels of POPs than the refined oil. Gene expression profile comparisons of the livers of the 2 treatment groups showed that POP exposure disrupted lipid homeostasis. Rats on the unrefined fish oil diet gained more weight overall and had increased triacylglycerol, diacylglycerol, and total cholesterol levels compared with rats fed refined fish oil. They also showed impaired insulin action in response to the high-fat diet, whereas the high-fat diet did not seem to cause insulin resistance in the rats fed refined fish oil. Further analysis revealed a reduction in the ability of insulin to stimulate glucose uptake in adipocytes treated with a mixture of POPs that was comparable to the mixture of chemicals in crude fish oil. Adipocyte responses to insulin varied with exposures to different mixtures of individual POPs. The authors conclude that dietary exposure to POPs may be a risk factor for insulin resistance and associated metabolic disorders. Furthermore, the metabolic effects of POP exposures exacerbated deleterious effects of a high-fat diet on rats and appeared to negate protective effects of n-3 polyunsaturated fatty acids on insulin resistance.

ObjectivesTo investigate the effects of excessive tryptophan intake on the body and the effects of tryptophan metabolism-related aryl hydrocarbon receptor (AhR) pathway in healthy rats and chronic kidney disease rats, to study the adverse effects of excess tryptophan.DesignIn Part I Experiment, the healthy rats were fed with diet containing 0.6, 1.2 and 1.8% tryptophan for 12 weeks. After the intervention, the blood and kidney tissues were collected. Serum creatinine and blood urea nitrogen were detected. Hematoxylin–eosin (H&E) staining was used to observe renal pathological changes. Enzyme-linked immunosorbent assay was used to detect serum kynurenic acid and AhR levels. The kidney levels of AhR, CyP1A1 and CyP1B1 were detected by western-blot. In Part II Experiment, the chronic kidney disease (CKD) model was induced by intra-gastric gavage with adenine for 4 weeks. Then the CKD rats were given tryptophan at a dose of 100 mg/kg or 500 mg/kg for eight weeks. Rat survival curve, renal function, renal tissue pathology and serum AhR were detected. Tryptophan-targeted ultra-high-performance liquid chromatography coupled with multiple reaction monitoring mass spectrometry (UHPLC-MRM-MS) was employed to quantitatively access the tryptophan-targeted metabolites in two parts experiments.ResultsIn part I experiment, high tryptophan diet can increase the level of blood urea nitrogen (BUN) in healthy rats and induce focal renal tubulointerstitial injury. Tryptophan-targeted analyzes showed that high tryptophan diet feeding can significantly increase the concentration of kynurenine and indole metabolites. The serum AhR level and kidney AhR, CyP1A1 and CyP1B1 were also significantly increased in high tryptophan diet rats. In part II experiment, high tryptophan intervention induced a significant increase in mortality, serum creatinine, urea nitrogen levels, and renal pathological damage in CKD rats. The levels of tryptophan-targeted metabolites, kynurenine, xanthurenate, picolinic acid, 5-hydroxyindole-3-acetic acid, indole-3-lactic acid, indoleacetate and indoxyl sulfate, showed an upward trend in the high-dose tryptophan group (Ade + Trp-H) compared with the adenine group. The serum AhR of Ade + Trp-H rats was significantly higher than those of adenine rats.ConclusionModerate tryptophan intake may be beneficial, but excessive tryptophan can lead to accumulation of kynurenine and indole metabolites, activate AhR pathway and induce kidney injury.