2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)-induced changes in glucose transporting activity in guinea pigs, mice, and rats in vivo and in vitro

Sex-specific, non-linear and congener-specific association between mixed exposure to polychlorinated biphenyls (PCBs) and diabetes in U.S. adults

BACKGROUND

Whether and to what extent the impact of exposure to various polychlorinated biphenyls (PCBs) congeners on diabetes, as well as the important contributors, have remained unclear.

OBJECTIVE

We aimed to investigate the association patterns between PCBs mixture and diabetes, identify the critical congeners, and explore the potential modifiers.

METHODS

The present study included 5900 U.S. adults from the National Health and Nutrition Examination Survey (NHANES) conducted between 2007 and 2016. Weighted logistic regression, restricted cubic spline regression, weighted quantile sum (WQS) regression and Bayesian kernel machine regression (BKMR) were applied to estimate the linear and non-linear associations of single and mixed PCB exposure with diabetes. Subgroup analyses were also conducted to explore potential sex differences.

RESULTS

In the weighted logistic regression model, total PCBs were positively associated with diabetes (OR = 1.33, P < 0.025), and significant non-linear associations were observed using RCS analyses. The non-linear positive association between PCBs mixed exposure and diabetes was likewise found in the WQS and BKMR results. PCB180, PCB194, PCB196, and PCB167 were with the highest weights in the WQS, and PCB209 and PCB66 were with the highest posterior inclusion probabilities in the BKMR. Additionally, exposure to total PCBs and most of individual PCB congeners were significantly associated with elevated risk of in females (OR = 1.74; P for trend < 0.001), while fewer significant associations were observed in males.

CONCLUSION

The present study highlighted the importance of the long-term surveillance of PCBs and the need to enhance protective measures against them. Notably, these associations were non-linear, congener-specific, and significantly stronger in females than males, especially at relatively high levels of PCBs exposure. Further prospective and mechanistic studies were warranted to ascertain the causal effects between PCBs mixture and diabetes.

Possible effects of agent orange and posttraumatic stress disorder on hyperglycemia in Korean veterans from the US-Vietnam war

This study was conducted to examine whether Korean veterans from the US-Vietnam War who had a diagnosis of type II diabetes mellitus (T2DM) as well as past history of exposure to agent orange (AO) are vulnerable to hyperglycemia when receiving intra-articular corticosteroid injection (IACI) for pain relief.The current study included a total of 49 patients (n = 49) who received an injection of triamcinolone 20 or 40 mg to the shoulder under sonographic guidance or did that of dexamethasone 10 mg or triamcinolone 40 mg combined with dexamethasone 20 mg to the spine under fluoroscopic guidance. Their 7-day fasting blood glucose (FBG) levels were measured and then averaged, serving as baseline levels. This is followed by measurement of FBG levels for 14 days of IACI. Respective measurements were compared with baseline levels. The patients were also evaluated for whether there are increases in FBG levels depending on insulin therapy as well as HbA1c ≥ 7% or HbA1c < 7%.Overall, there were significant increases in FBG levels by 64.7 ± 42.5 mg/dL at 1 day of IACI from baseline (P < .05). HbA1c ≥ 7% and HbA1c < 7% showed increases in FBG levels by 106.1 ± 49.0 mg/dL and 46.5 ± 3.8 mg/dL, respectively, at 1 day of IACI from baseline (P < .05). In the presence and absence of insulin therapy, there were significant increases in them by 122.6 ± 48.7 mg/dL and 48.0 ± 20.4 mg/dL, respectively, at 1 day of IACI from baseline (P < .05). But there were decreases in them to baseline levels at 2 days of IACI.Clinicians should consider the possibility of hyperglycemia when using corticosteroids for relief of musculoskeletal pain in Korean veterans from the US-Vietnam War who had a history of exposure to AO.

Selective beta-cell toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin on isolated pancreatic islets

An association between exposure to environmental pollutants and diabetes risk has been repeatedly shown by epidemiological studies. However, the biological basis of this association still need to be clarified. In this research we explored the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure on isolated pancreatic islets. After 1, 6 and 24 h exposure of isolated islets to different concentrations (1-50 nM) of TCDD we assayed: i) cell survival; ii) ultrastructure; iii) glucose-stimulated insulin secretion (GSIS); iv) expression of selected genes. A significant, dose-related increase of both necrosis and apoptosis was observed isolated rat islets after 24 h exposure to TCDD. The electron microscopic analysis revealed, at the same time point, the presence of several ultrastructural alterations (mitochondrial swelling, increased mitophagy, dilation of the endoplasmic reticulum) that, very interestingly, were exclusively observed in beta cells and not in other endocrine cells. Similar results were obtained in isolated human islets. GSIS was rapidly (1 h) and persistently (6 and 24 h) decreased by TCDD exposure even at the smallest concentration (1 nM). TCDD exposure significantly affected gene expression in isolated islets: Glut2, Gck, Bcl-xL, MafA, Pdx1 FoxO1 and IRE1 gene expression was significantly decreased, whereas Puma, DP5, iNOS and Chop gene expression was significantly increased after 6 h exposure to TCDD. In conclusion, our results clearly indicated that pancreatic beta cells represent not only a sensitive but also a specific target of the toxic action of dioxin.

Associations between the exposure to persistent organic pollutants and type 2 diabetes in East China: A case-control study

Persistent organic pollutants (POPs) have been associated with a high risk of type 2 diabetes in different regions, although few studies from China have been published. We aimed to investigate the associations between POP exposure and type 2 diabetes in Chinese population. A total of 158 participants diagnosed with type 2 diabetes and 158 participants without the disorder from Shandong Province were enrolled in this case-control study during 2016-2017. Nine polychlorinated biphenyl congeners (PCBs) and 2 polybrominated diphenyl ethers with detectable levels in ≥75% of the participants were selected for data analysis. The results showed that POP exposure was significantly and positively associated with the risk of diabetes after adjusting for age, sex, BMI, triglycerides and total cholesterol. However, we did not observe an obvious modified effect of adiposity on the associations between POP exposure and diabetes in the present study, as strong associations between POPs and diabetes were observed in both the higher-BMI (BMI≥25 kg/m²) and the lower-BMI (BMI<25 kg/m²) groups. POPs showed stronger associations with diabetes in males than in females. The odds ratio (OR) for the highest quartile of ∑POPs was 6.97 for males, nearly two times higher than that for females (OR = 3.58). All these findings suggest that POP exposure may impact the risk of diabetes in Chinese population.

Prenatal dioxin exposure and glucose metabolism in the Seveso Second Generation study

BACKGROUND

Exposure to endocrine disrupting compounds such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) during susceptible developmental windows may alter risk of metabolic disease later in life. Animal studies of in utero and lactational TCDD exposure report associations with alterations in insulin sensitivity and energy homeostasis, but epidemiologic evidence is limited. We examined the relationship of prenatal TCDD exposure with markers of glucose homeostasis in the Seveso Second Generation study, a unique cohort of children born to TCDD-exposed women resulting from a 1976 explosion in Seveso, Italy.

METHODS

We included 426 children who were 18 years or older with complete follow-up data including a fasting blood draw. Insulin and glucose were measured and the updated homoeostatic model assessment was used to estimate insulin resistance (HOMA2-IR) and beta-cell function (HOMA2-B). Prenatal TCDD exposure was defined in two ways, as initial maternal serum TCDD concentration and TCDD estimated at pregnancy.

RESULTS

The children (222 female, 204 male) averaged 28.6 (±6.0) years. We found a 10-fold increase in TCDD estimated at pregnancy was inversely associated with insulin (adj-β = -1.24 μIU/mL, 95% confidence interval (CI): -2.38, -0.09) and HOMA2-B (adj-β = -10.2% decrease, 95% CI: -17.8, -1.9) among daughters, but not sons (insulin: adj-β = 0.57 μIU/mL, 95% CI: -0.84, 1.98, P for interaction = 0.04; and HOMA2-B: adj-β = 0.8% increase, 95% CI -10.7, 13.9, P for interaction = 0.11). Similar effect modification was observed for TCDD estimated at pregnancy and HOMA2-IR (P for interaction = 0.13). The models for initial maternal serum TCDD showed similar effect modification by child sex. The observed associations in daughters showed evidence of mediation by body mass index, which we have previously found to be associated with prenatal TCDD exposure in female offspring.

CONCLUSION

These results suggest prenatal exposure to TCDD is associated with lower insulin resistance and beta compensation in female offspring, and show evidence of mediation by body mass index.

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.

Persistent organic pollutants and the incidence of type 2 diabetes in the CARLA and KORA cohort studies

BACKGROUND

Associations between several persistent organic pollutants (POPs) and type 2 diabetes have been found in humans, but the relationship has rarely been investigated in the general population. The current nested case-control study examined internal exposure to polychlorinated biphenyls (PCB) and pesticides and the incidence of type 2 diabetes among participants of two population-based German cohort studies.

METHODS

We retrospectively selected 132 incident cases of type 2 diabetes and 264 age- and sex-matched controls from the CARdiovascular Living and Aging in Halle (CARLA) study (2002-2006, East Germany) and the Cooperative Health Research in the Region of Augsburg (KORA) study (1999-2001, South Germany) based on diabetes status at follow-up examinations in 2007-2010 and 2006-08, respectively (60% male, mean age 63 and 54 years). We assessed the association between baseline POP concentrations and incident diabetes by conditional logistic regression adjusted for cohort, BMI, cholesterol, alcohol, smoking, physical activity, and parental diabetes. Additionally, we examined effect modification by sex, obesity, parental diabetes and cohort.

RESULTS

In both cohorts, diabetes cases showed a higher BMI, a higher frequency of parental diabetes, and higher levels of POPs. We observed an increased chance for incident diabetes for PCB-138 and PCB-153 with an odds ratio (OR) of 1.50 (95%CI: 1.07-2.11) and 1.53 (1.15-2.04) per interquartile range increase in the respective POP. In addition, explorative results suggested higher OR for women and non-obese participants.

CONCLUSIONS

Our results add to the evidence on diabetogenic effects of POPs in the general population, and warrant both policies to prevent human exposure to POPs and additional research on the adverse effects of more complex chemical mixtures.

Persistent Organic Pollutant-Mediated Insulin Resistance

Persistent organic pollutants (POPs) such as organochlorine (OC) pesticides, polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) have become wide-spread environmental contaminants as a consequence of their extensive use, long-range transport, and persistence. Because POPs are highly resistant to metabolic degradation, humans bioaccumulate these lipophilic and hydrophobic pollutants in fatty tissues for many years. Previous studies have demonstrated that POPs including PCBs are involved in the development of diabetes mellitus (DM) type 2 and insulin resistance. Numerous epidemiological studies suggest an association between POP burden and DM type 2/metabolic syndrome. In addition, several experimental studies have provided additional evidence supporting the association between POP exposure and DM type 2 or insulin resistance. Epidemiological and experimental studies have provided compelling evidence indicating that exposure to POPs increases the risk of developing insulin resistance and metabolic disorders. However, the detailed molecular mechanism underlying POP-induced insulin resistance is yet to be elucidated. In this article, we review literature that has reported on the association between POP burden and insulin resistance and the mechanism underlying POP-induced insulin resistance, and discuss implications for public health.

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.

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.

Polluted Pathways: Mechanisms of Metabolic Disruption by Endocrine Disrupting Chemicals

PURPOSE OF REVIEW

Environmental toxicants are increasingly implicated in the global decline in metabolic health. Focusing on diabetes, herein, the molecular and cellular mechanisms by which metabolism disrupting chemicals (MDCs) impair energy homeostasis are discussed.

RECENT FINDINGS

Emerging data implicate MDC perturbations in a variety of pathways as contributors to metabolic disease pathogenesis, with effects in diverse tissues regulating fuel utilization. Potentiation of traditional metabolic risk factors, such as caloric excess, and emerging threats to metabolism, such as disruptions in circadian rhythms, are important areas of current and future MDC research. Increasing evidence also implicates deleterious effects of MDCs on metabolic programming that occur during vulnerable developmental windows, such as in utero and early post-natal life as well as pregnancy. Recent insights into the mechanisms by which MDCs alter energy homeostasis will advance the field's ability to predict interactions with classical metabolic disease risk factors and empower studies utilizing targeted therapeutics to treat MDC-mediated diabetes.

Transcriptomic and Functional Analyses on the Effects of Dioxin on Insulin Secretion of Pancreatic Islets and β-Cells

In this study, transcriptomic and Ingenuity Pathway Analysis (IPA) underlined that an ex-vivo TCDD treatment (0.1 nM) stimulated insulin-release in mouse pancreatic islets via the effect on the Akt-mTOR-p70S6K, AMPK and ERK1/2 pathways. Functional studies using both ex-vivo islets and the mouse β-cell-line (Min-6) validated the stimulatory effects of TCDD (0.1 and 1 nM) on basal-insulin secretion. At 0.1 nM TCDD treatment on Min-6, Western blot analysis showed activation of ERK1/2 and decreased expression of pyruvate dehydrogenase kinase (PDK). A reduction of PDK expression is associated with an increase of pyruvate dehydrogenase flux. This observation was supported by the detection of significantly higher cellular ATP levels, an increase of glucose-stimulated-insulin-secretion (GSIS), and an inhibition of the AMPK pathway. At 1 nM TCDD treatment on Min-6, significant inhibitions of the Akt-mTOR pathway, cellular ATP production, and GSIS were evident. The experimental studies in Min-6 supported the IPA of transcriptomic data in pancreatic islets. Collectively, TCDD treatment caused an elevated basal-insulin release in both islets and β-cell cultures. Moreover, our data revealed that the modulation of the Akt-mTOR-p70S6K, AMPK and ERK1/2 pathways might be an important component of the mechanism for the TCDD-perturbing effects on ATP production in β-cells in affecting insulin secretion.

Metabolism disrupting chemicals and metabolic disorders

The recent epidemics of metabolic diseases, obesity, type 2 diabetes(T2D), liver lipid disorders and metabolic syndrome have largely been attributed to genetic background and changes in diet, exercise and aging. However, there is now considerable evidence that other environmental factors may contribute to the rapid increase in the incidence of these metabolic diseases. This review will examine changes to the incidence of obesity, T2D and non-alcoholic fatty liver disease (NAFLD), the contribution of genetics to these disorders and describe the role of the endocrine system in these metabolic disorders. It will then specifically focus on the role of endocrine disrupting chemicals (EDCs) in the etiology of obesity, T2D and NAFLD while finally integrating the information on EDCs on multiple metabolic disorders that could lead to metabolic syndrome. We will specifically examine evidence linking EDC exposures during critical periods of development with metabolic diseases that manifest later in life and across generations.

Environmental Risk Factors and Type 1 Diabetes: Past, Present, and Future

Type 1 diabetes is an autoimmune condition that results from the destruction of the insulin-producing beta cells of the pancreas. The excess morbidity and mortality resulting from its complications, coupled with its increasing incidence, emphasize the importance of better understanding the causes of this condition. Over the past several decades, a substantive amount of work has been done and, although many advances have occurred in identifying disease-susceptibility genes, there has been a lag in understanding the environmental triggers. Several putative environmental risk factors have been proposed, including infections, dietary factors, air pollution, vaccines, location of residence, family environment and stress. However, most of these factors have been inconclusive, thus supporting the need for further study into the causes of type 1 diabetes.

Exposure to persistent organochlorine pollutants and type 2 diabetes mellitus

Persistent organochlorine pollutants (POPs), such aspolychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs), dichloro diphenyl trichloroethane (DDT) and its major metabolite 1,1-dichloro-2,2-bis (p-chlorophenyl)-ethylene (p,p' -DDE) have been associated with type 2 diabetes mellitus (T2DM) in recent epidemiological studies. We have analysed 2,2',4,4',5,5' -hexachlorobiphenyl (CB-153) and p,p'-DDE in 544 serum-samples from Swedish women with a median age of 50 years. The participants were asked if they had diabetesand if so, what type of diabetes, years since diagnosis and what kind of treatment they had. Associations between exposure and T2DM were analysed by logistic regression. Moreover, trends of T2DM prevalence were tested with Jonckheere-Terpstra' test. Sixteen of the 544 women (3%) had diabetes, of which15 were classified as T2DM. There was a significant associationwith T2DM for both CB-153 (an increase of 100ng/glipid corresponded to an odds ratio [OR] of 1. 6, 95% confidenceinterval [CI] 1. 0, 2. 7) and p,p9-DDE (OR 1. 3, 95%CI 1. 1, 1. 6). In addition, significant positive trends betweenquartiles of CB-153 and T2DM (P 5 0. 004) and p,p9-DDEand T2DM (P 5 0. 002) were observed. The study showsan association between POP serum concentrations andan increased prevalence of T2DM. Human & Experimental Toxicology (2007) 26, 447—451

Serum aryl hydrocarbon receptor ligand activity is associated with insulin resistance and resulting type 2 diabetes

AIMS

Dioxin or dioxin-like compounds are ligands of the aryl hydrocarbon receptor (AhR), which is a ligand-activated nuclear transcription factor. There are limited studies about the association of serum AhR ligand activities and T2DM. Our objective was to investigate the association of serum AhR ligand activities with T2DM and its related metabolic parameters.

METHODS

This case-control study involved 83 subjects with T2DM as well as age-, sex-, and body mass index (BMI)-matched subjects with impaired glucose tolerance (IGT, n = 130) and normal glucose tolerance (NGT, n = 83). Serum AhR ligand activities were measured using a cell-based AhR ligand assay and standardized as 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TCDDeq, pmol/l).

RESULTS

The T2DM group had the highest AhR ligand activities compared to the IGT and NGT groups [median (interquartile range), 68.1 (53.1, 81.5), 60.2 (45.8, 75.1), and 53.3 (46.1, 63.7) pmol/l, respectively; P = 0.003]. In the multivariate analysis, the log2-transformed TCDDeq levels were significantly associated with the risk of T2DM after adjusting for age, sex, and BMI (odds ratio 2.26, 95 % confidence interval 1.34-3.82; P = 0.002). In nondiabetic subjects, serum AhR ligand activities showed a positive correlation with fasting glucose and insulin concentrations and the homeostasis model assessment of insulin resistance, but showed a negative correlation with adiponectin concentrations.

CONCLUSIONS

Serum AhR ligand activities were higher in the T2DM group and were correlated with the parameters of insulin resistance. Further investigation is required to elucidate the causal relationship between AhR ligand activity and T2DM.

Association of dioxin and other persistent organic pollutants (POPs) with diabetes: epidemiological evidence and new mechanisms of beta cell dysfunction

The worldwide explosion of the rates of diabetes and other metabolic diseases in the last few decades cannot be fully explained only by changes in the prevalence of classical lifestyle-related risk factors, such as physical inactivity and poor diet. For this reason, it has been recently proposed that other "nontraditional" risk factors could contribute to the diabetes epidemics. In particular, an increasing number of reports indicate that chronic exposure to and accumulation of a low concentration of environmental pollutants (especially the so-called persistent organic pollutants (POPs)) within the body might be associated with diabetogenesis. In this review, the epidemiological evidence suggesting a relationship between dioxin and other POPs exposure and diabetes incidence will be summarized, and some recent developments on the possible underlying mechanisms, with particular reference to dioxin, will be presented and discussed.

Persistent organic pollutants and type 2 diabetes: a prospective analysis in the nurses' health study and meta-analysis

BACKGROUND

Prospective data regarding persistent organic pollutants (POPs) and risk of type 2 diabetes (T2D) are limited, and the results for individual POPs are not entirely consistent across studies.

OBJECTIVES

We prospectively examined plasma POP concentrations in relation to incident T2D and summarized existing evidence in a meta-analysis.

METHODS

Plasma polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT), dichlorodiphenyldichloroethylene (DDE), and hexachlorobenzene (HCB) concentrations were measured in 1,095 women who were free of diabetes at blood draw in 1989-1990 and participated in two case-control studies in the Nurses' Health Study. We identified 48 incident T2D cases through 30 June 2008. We conducted a literature search in PubMed and EMBASE through December 2011 to identify prospective studies on POPs in relation to diabetes. We used a fixed-effects model to summarize results.

RESULTS

After multivariable adjustment, plasma HCB concentration was positively associated with incident T2D [pooled odds ratio (OR) 3.59 (95% CI: 1.49, 8.64, ptrend = 0.003) comparing extreme tertiles]. Other POPs were not significantly associated with diabetes. After pooling our results with those of six published prospective studies that included 842 diabetes cases in total, we found that HCB and total PCBs both were associated with diabetes: the pooled ORs were 2.00 (95% CI: 1.13, 3.53; I2 = 21.4%, pheterogeneity = 0.28) and 1.70 (95% CI: 1.28, 2.27; I2 = 16.3%, pheterogeneity = 0.30) for HCB and total PCBs, respectively.

CONCLUSIONS

These findings support an association between POP exposure and the risk of T2D.

[Associations of exposure to dioxins and polychlorinated biphenyls with diabetes: based on epidemiological findings]

Persistent organic pollutants (POPs) are a group of chemical substances that have the common properties of resistance to biodegradation, wide-range transportation, high lipophilicity, bioaccumulation in fat, and biomagnification in the food chain. POPs are persistent in the environment worldwide and have potential adverse impacts on human health and the environment. Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs) are well known chemicals that are considered as POPs. The association between high-level exposure to dioxins and type 2 diabetes among U.S. Air Force veterans who had been exposed to Agent Orange contaminated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) during the Vietnam War was reported in the late 1990s. This association has been supported by similar epidemiologic studies, whose subjects were exposed to high doses of dioxins in their places of work involving phenoxyacid herbicide production and spraying, and in the industrial accident in Seveso, Italy. Recently, low-level exposure to dioxins and PCBs has been reported to be linked to type 2 diabetes. Cross-sectional studies in the U.S. general population and Japanese general population showed that body burden levels of some dioxins and PCBs were strongly associated with the prevalence of type 2 diabetes. Very recently, following these cross-sectional studies, several prospective studies have suggested that low-level exposure to some PCBs predicted the future risk of type 2 diabetes in the general population. Environmental exposure to some dioxins and PCBs, which mainly accumulate in adipose tissue, may play a role in the development of type 2 diabetes.

Relationship of polychlorinated biphenyls with type 2 diabetes and hypertension

Diabetes and hypertension are important contributors to morbidity and mortality worldwide. Both of these conditions are caused by some combination of genetic and environmental factors which may include exposure to persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs). Studies have shown an association between elevated serum PCBs and the metabolic syndrome, insulin sensitivity and insulin secretion. Cross-sectional studies have shown associations between diabetes or hypertension and certain PCB congeners or classes, while those same studies show no association between diabetes or hypertension and several other PCB congeners. In animal and human cell studies, various PCBs and dioxins appear to alter glucose and insulin metabolism. These studies specifically show effects on the glucose transporter (GLUT-4) gene and protein; insulin-like growth factor binding protein-1 (IGFBP-1); nuclear transcription factor kappa B (NFκB); tumor necrosis factor alpha (TNF-α); and insulin production. There are a few longitudinal studies examining the association of diabetes or hypertension and PCBs with no consensus conclusion. Some longitudinal studies have found there to be an association, others have not and a gender difference has also been noted. Prospective studies are needed to determine if PCBs and other POPs contribute to development of diabetes and hypertension.

Increased hospitalizations for ischemic stroke with comorbid diabetes and residential proximity to sources of organic pollutants: a 12-year population-based study

BACKGROUND

Evidence is emerging that exposure to persistent organic pollutants (POP) is a risk factor for atherosclerosis-related diseases and for diabetes mellitus (DM). We hypothesized that residential proximity to sources of POP will be associated with an increase in hospitalization rates for ischemic stroke (IS) with comorbid DM (IS-DM).

METHODS

We examined IS-DM hospitalization rates in the New York State (exclusive of New York City) during a 12-year period. POP exposure status was assessed based on residency in a zip code containing or abutting environmental sources of POP. Adjusted relative risks (RR) of IS-DM hospitalization were estimated by multivariate Poisson regression.

RESULTS

A statistically significant 10% increase in IS-DM hospitalization rates was observed in populations environmentally exposed to POP (adjusted RR 1.10, 95% confidence interval, CI, 1.01-1.20; p = 0.031). IS-DM hospitalization rates were also higher in males (adjusted RR 1.34, 95% CI 1.30-1.39; p < 0.001), in blacks (adjusted RR 4.54, 95% CI 4.16-4.94; p < 0.001) and in older age groups (p for trend <0.001).

CONCLUSIONS

Residential proximity to sources of POP is associated with an increase in RR of IS-DM hospitalization. Our findings support the hypothesis of POP being a risk factor for IS. Further studies are warranted.

A nested case-control study of intrauterine exposure to persistent organochlorine pollutants in relation to risk of type 1 diabetes

BACKGROUND

The incidence of type 1 diabetes in Europe is increasing at a rate of about 3% per year and there is also an increasing incidence throughout the world. Type 1 diabetes is a complex disease caused by multiple genetic and environmental factors. Persistent organochlorine pollutants (POPs) have been suggested as a triggering factor for developing childhood type 1 diabetes. The aim of this case-control study was to assess possible impacts of in utero exposure to POPs on type 1 diabetes.

METHODOLOGY/ PRINCIPAL FINDINGS

The study was performed as a case-control study within a biobank in Malmö, a city located in the Southern part of Sweden. The study included 150 cases (children who had their diagnosis mostly before 18 years of age) and 150 controls, matched for gender and day of birth. 2,2',4,4',5,5'-hexachlorobiphenyl (PCB-153) and the major DDT metabolite 1,1-dichloro-2,2-bis (p-chlorophenyl)-ethylene (p,p'-DDE) were used as a biomarkers for POP exposure. When comparing the quartile with the highest maternal serum concentrations of PCB-153 with the other quartiles, an odds ratio (OR) of 0.73 (95% confidence interval [CI] 0.42, 1.27) was obtained. Similar results was obtained for p,p'-DDE (OR 0.56, 95% CI 0.29, 1.08).

CONCLUSIONS

The hypothesis that in utero exposure to POPs will trigger the risk for developing type 1 diabetes was not supported by the results. The risk estimates did, although not statistically significant, go in the opposite direction. However, it is not reasonable to believe that exposure to POPs should protect against type 1 diabetes.

Exposure to p,p'-DDE: a risk factor for type 2 diabetes

BACKGROUND

Persistent organic pollutants (POPs), such as PCBs, DDT and dioxins have in several cross-sectional studies shown strong associations with type 2 diabetes mellitus. Reversed causality can however not be excluded. The aim of this case-control study was to evaluate whether POPs concentration is a risk factor for type 2 diabetes.

METHODOLOGY/PRINCIPAL FINDINGS

A case-control study was performed within a well-defined cohort of women, age 50-59 years, from the Southern part of Sweden. Biomarkers for POP exposure, 2,2',4,4',5,5'-hexachlorobiphenyl (CB-153) and 1,1-dichloro-2,2-bis (p-chlorophenyl)-ethylene (p,p'-DDE) were analyzed in stored serum samples, which were collected at the baseline examination when the cohort was established. For 107 out of the 371 cases, serum samples were stored at least three years before their type 2 diabetes was diagnosed. In this data set, CB-153 and p,p'-DDE were not associated with an increased risk to develop type 2 diabetes. However, when only the cases (n = 39) that were diagnosed more than six years after the baseline examination and their controls were studied, the women in the highest exposed quartile showed an increased risk to develop type 2 diabetes (OR of 1.6 [95% 0.61, 4.0] for CB-153 and 5.5 [95% CI 1.2, 25] for p,p'-DDE).

CONCLUSIONS/SIGNIFICANCE

The results from the present case-control study, including a follow-up design, confirms that p,p'-DDE exposure can be a risk factor for type 2 diabetes.

Metabolically favorable remodeling of human adipose tissue by human adenovirus type 36

OBJECTIVE

Experimental infection of rats with human adenovirus type 36 (Ad-36) promotes adipogenesis and improves insulin sensitivity in a manner reminiscent of the pharmacologic effect of thiozolinediones. To exploit the potential of the viral proteins as a therapeutic target for treating insulin resistance, this study investigated the ability of Ad-36 to induce metabolically favorable changes in human adipose tissue.

RESEARCH DESIGN AND METHODS

We determined whether Ad-36 increases glucose uptake in human adipose tissue explants. Cell-signaling pathways targeted by Ad-36 to increase glucose uptake were determined in the explants and human adipose-derived stem cells. Ad-2, a nonadipogenic human adenovirus, was used as a negative control. As a proof of concept, nondiabetic and diabetic subjects were screened for the presence of Ad-36 antibodies to ascertain if natural Ad-36 infection predicted improved glycemic control.

RESULTS

Ad-36 increased glucose uptake by adipose tissue explants obtained from nondiabetic and diabetic subjects. Without insulin stimulation, Ad-36 upregulated expressions of several proadipogenic genes, adiponectin, and fatty acid synthase and reduced the expression of inflammatory cytokine macrophage chemoattractant protein-1 in a phosphotidylinositol 3-kinase (PI3K)-dependent manner. In turn, the activation of PI3K by Ad-36 was independent of insulin receptor signaling but dependent on Ras signaling recruited by Ad-36. Ad-2 was nonadipogenic and did not increase glucose uptake. Natural Ad-36 infection in nondiabetic and diabetic subjects was associated with significantly lower fasting glucose levels and A1C, respectively.

CONCLUSIONS

Ad-36 proteins may provide novel therapeutic targets that remodel human adipose tissue to a more metabolically favorable profile.

Associations of environmental exposure to dioxins with prevalent diabetes among general inhabitants in Japan

The aim of this study was to evaluate the associations of environmental exposure to dioxins with diabetes among general inhabitants in Japan. A cross-sectional study was performed on 1374 participants, who were not occupationally exposed to dioxins, aged 15-73 years, living widely in 75 different residential areas of 25 prefectures in Japan through 2002-2006. Seven polychlorinated dibenzo-p-dioxins (PCDDs), 10 polychlorinated dibenzofurans (PCDFs), 12 dioxin-like polychlorinated biphenyls (PCBs), which are assigned a toxic equivalency factor, and biochemical factors were determined in fasting blood. A questionnaire survey on life-style including past history of diseases and treatments was also performed. We examined the associations of the accumulated toxic equivalents (TEQs) of PCDDs+PCDFs, dioxin-like PCBs and total dioxins with prevalent diabetes. Simple and partial correlation analyses revealed that HbA1c correlated with the accumulated TEQs of PCDDs+PCDFs, dioxin-like PCBs and total dioxins. In logistic regression analyses, the third and the highest quartiles of dioxin-like PCBs had adjusted odds ratios (ORs) of 3.07 (95% CI 1.16-8.81) and 6.82 (95% CI 2.59-20.1) compared to the reference (first plus second quartiles). On the other hand, the highest but not the third quartiles of PCDDs+PCDFs and total dioxins had significantly higher adjusted ORs compared to the respective references. These associations persisted when the subjects with poor liver or poor renal function were removed from the analysis. This recent representative data from general inhabitants in Japan showed associations of environmental exposure to dioxins, especially dioxin-like PCBs, with diabetes.

Prevalence of self-reported diabetes and exposure to organochlorine pesticides among Mexican Americans: Hispanic health and nutrition examination survey, 1982-1984

BACKGROUND

The prevalence of diabetes is higher among Mexican Americans than among non-Hispanic whites. Higher serum levels of organochlorine pesticides in Mexican Americans have been reported. Few studies have explored the association between pesticide exposure and diabetes.

OBJECTIVES

We set out to examine the association between self-reported diabetes and serum concentrations of organochlorine pesticides among Mexican Americans residing in the southwestern United States from 1982 to 1984.

METHODS

This study was conducted among a sample of 1,303 Mexican Americans 20-74 years of age from the Hispanic Health and Nutrition Examination Survey. Serum concentrations were available for seven pesticides or pesticide metabolites at quantifiable levels in at least 1% of the study population: p,p'-DDT (dichlorodiphenyltrichloroethane), p,p'-DDE (dichlorodiphenyldichloro-ethylene), dieldrin, oxychlordane, beta-hexachlorocyclohexane, hexachlorobenzene, and trans-nonachlor. We used logistic regression to evaluate the association of self-reported diabetes with exposure to organochlorine pesticides, with and without adjustment for total serum lipids. Nonfasting serum glucose values were compared among exposure groups.

RESULTS

Self-reported diabetes was significantly associated with serum levels above the detectable limit for trans-nonachlor, oxychlordane, and beta-hexachlorocyclohexane and among those with the highest level of exposure to p,p'-DDT and p,p'-DDE. On adjustment for total serum lipids, the association with p,p'-DDT remained significant. Serum glucose levels were elevated among those exposed to trans-nonachlor and beta-hexachlorocyclohexane.

CONCLUSION

This study suggests that higher serum levels of certain organochlorine pesticides may be associated with increased prevalence of diabetes. Additional studies with more extensive clinical assessment are needed to confirm this association.

Association of a polychlorinated dibenzo-p-dioxin, a polychlorinated biphenyl, and DDT with diabetes in the 1999-2002 National Health and Nutrition Examination Survey

The association of a polychlorinated dibenzo-p-dioxin, a polychlorinated biphenyl, and p,p'-DDT with diabetes was evaluated using the 1999-2002 National Health and Nutrition Examination Survey. Persons 20 years old and older were included. Relationships with diagnosed diabetes, undiagnosed diabetes (glycohemoglobin (HbA1c) >6.1%), and total diabetes (diagnosed plus undiagnosed) were tested. When all three chemicals were evaluated together for total diabetes, the unweighted number of participants was 1830. All three compounds were significantly associated with diagnosed diabetes. PCB 126 and p,p'-DDT were significantly associated with undiagnosed diabetes. 1,2,3,6,7,8-hexachlorodibenzo-p-dioxin (HxCDD) was not associated with undiagnosed diabetes. When the three chemicals were included in a combined model for total diabetes, PCB 126>83.8pg/g lipid adjusted had an odds ratio of 2.57 (95% CI 1.33-4.95) compared to PCB 126 < or = 31.2pg/g lipid adjusted. Also significant in a combined model for total diabetes was p,p'-DDT 20.8-26.6ng/g lipid adjusted with an odds ratio of 2.52 (95% CI 1.26-5.02) and p,p'-DDT >26.6ng/g lipid adjusted with an odds ratio of 2.74 (95% CI 1.44-5.23) both compared to p,p'-DDT < or = 20.7ng/g lipid adjusted. HxCDD was not associated with total diabetes in a combined model. When participants with poor liver function and poor kidney function were removed from the analysis, the combined model for total diabetes produced similar results with PCB 126 and p,p'-DDT having been significantly associated, and HxCDD not having been associated. These findings add to the list of chemicals found to be associated with diabetes in the 1999-2002 National Health and Nutrition Examination Survey.

Cell death and impairment of glucose-stimulated insulin secretion induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the beta-cell line INS-1E

The aim of this research was to characterize 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxicity on the insulin-secreting beta-cell line INS-1E. A sharp decline of cell survival (below 20%) was observed after 1 h exposure to TCDD concentrations between 12.5 and 25 nM. Ultrastructurally, beta-cell death was characterized by extensive degranulation, appearance of autophagic vacuoles, and peripheral nuclear condensation. Cytotoxic concentrations of TCDD rapidly induced a dose-dependent increase in intracellular calcium concentration. Blocking calcium entry by EGTA significantly decreased TCDD cytotoxicity. TCDD was also able to rapidly induce mitochondrial depolarization. Interestingly, 1 h exposition of INS-1E cells to very low TCDD concentrations (0.05-1 nM) dramatically impaired glucose-stimulated but not KCl-stimulated insulin secretion. In conclusion, our results clearly show that TCDD exerts a direct beta-cell cytotoxic effect at concentrations of 15-25 nM, but also markedly impairs glucose-stimulated insulin secretion at concentrations 20 times lower than these. On the basis of this latter observation we suggest that pancreatic beta-cells could be considered a specific and sensitive target for dioxin toxicity.

Carcinogenicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin in experimental models

The contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a prototype compound of a whole class of halogenated aromatic hydrocarbons termed 'dioxinlike' contaminants present in food, human tissue, mothers milk, and environmental samples. Among the various adverse effects caused by TCDD in animal experiments, its carcinogenic effects caused particular concern. In rodents, long-term TCDD treatment leads to the development of tumors of the liver, thyroid, lung, skin, oral cavity and other sites. The occurrence of liver tumors mainly observed in female rats has been used as a basis for quantitative cancer risk assessment for TCDD. TCDD does not behave like a 'complete carcinogen', i. e. no DNA binding of the parent compound or metabolites thereof could be detected. However, enhanced oxidative damage of hepatic DNA was observed, probably resulting from a dramatic induction of cytochrome P450 enzymes, which are under the regulatory, transcriptional control of the TCDD-activated aryl hydrocarbon receptor. The marked enhancement of TCDD-related oxidative liver DNA damage in rats by estrogens warrants further mechanistic investigation. Furthermore, TCDD acts as a tumor promoter, i. e. it facilitates the growth of putative preneoplastic hepatic lesions after initiation with a complete carcinogen. The mechanisms underlying this effect may be related to altered intracellular signaling involving pronounced changes in the phosphorylation pattern of proteins regulating growth and apoptosis. These effects are thought to result in an enhanced survival of preneoplastic cells, some of which can undergo further steps on the way to malignancy. In summary, a better understanding of the mechanisms of the carcinogenicity of TCDD is mandatory to provide a rational basis for a better inter-species extrapolation. The final aim of these efforts is a more reliable risk assessment for the carcinogenic potency of the class of dioxinlike contaminants in humans.

A strong dose-response relation between serum concentrations of persistent organic pollutants and diabetes: results from the National Health and Examination Survey 1999-2002

OBJECTIVE

Low-level exposure to some persistent organic pollutants (POPs) has recently become a focus because of their possible link with the risk of diabetes.

RESEARCH DESIGN AND METHODS

Cross-sectional associations of the serum concentrations of POPs with diabetes prevalence were investigated in 2,016 adult participants in the National Health and Nutrition Examination Survey 1999-2002. Six POPs (2,2',4,4',5,5'-hexachlorobiphenyl, 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin, 1,2,3,4,6,7,8,9-octachlorodibenzo-p-dioxin, oxychlordane, p,p'-dichlorodiphenyltrichloroethane, and trans-nonachlor) were selected, because they were detectable in >or=80% of participants.

RESULTS

Compared with subjects with serum concentrations below the limit of detection, after adjustment for age, sex, race and ethnicity, poverty income ratio, BMI, and waist circumference, diabetes prevalence was strongly positively associated with lipid-adjusted serum concentrations of all six POPs. When the participants were classified according to the sum of category numbers of the six POPs, adjusted odds ratios were 1.0, 14.0, 14.7, 38.3, and 37.7 (P for trend < 0.001). The association was consistent in stratified analyses and stronger in younger participants, Mexican Americans, and obese individuals.

CONCLUSIONS

There were striking dose-response relations between serum concentrations of six selected POPs and the prevalence of diabetes. The strong graded association could offer a compelling challenge to future epidemiologic and toxicological research.

A cross-sectional study of the association between persistent organochlorine pollutants and diabetes

BACKGROUND

Experimental evidence supports the hypothesis that persistent organochlorine pollutants (POPs) may cause type 2 diabetes mellitus, whereas there is no fully convincing epidemiological evidence for such an association. In Sweden the most important source of POP exposure is fatty fish. We have assessed the association between serum levels of POPs and prevalence of diabetes in Swedish fishermen and their wives, with high consumption of fatty fish from the Baltic Sea.

METHODS

In 196 men (median age 60 years) and 184 women (median age 64 years), we analyzed 2,2',4,4',5,5'-hexachlorobiphenyl (CB-153) and 1,1-dichloro-2,2-bis(p-chlorophenyl)-ethylene (p,p'-DDE) in serum using gas chromatography-mass spectrometry. The participants were asked if they had diabetes and, if so, since which year and about medication and diet. The Odds Ratios (OR) for diabetes with respect to continuous exposure variables were analyzed with logistic regression, adjusting for potential confounders. Moreover trends of diabetes prevalence with respect to trichotomized exposure variables were tested with Jonckheere-Terpstra's test.

RESULTS

Six percent of the men and 5% of the women had diabetes. After confounder adjustment CB-153 was significantly associated with diabetes prevalence using both categorized and continuous exposure data (an increase of 100 ng/g lipid corresponded to an OR of 1.16, 95% confidence interval [CI] 1.03, 1.32, p = 0.03). Similar associations were observed for p,p'-DDE (an increase of 100 ng/g lipid corresponded to an OR of 1.05, 95% CI 1.01, 1.09, p = 0.006). Gender stratified analyses showed among men consistent positive associations with CB-153, but a more ambiguous pattern with respect to DDE. In contrast, among the women the associations with p,p'-DDE were stronger than with CB-153.

CONCLUSION

The study provides support that POP exposure might contribute to type 2 diabetes mellitus.

2,3,7,8-Tetrachlorodibenzo-p-dioxin-induced impairment of glucose-stimulated insulin secretion in isolated rat pancreatic islets

We have explored the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) administration on the secretory function of isolated rat pancreatic islets. Twenty-four hours after TCDD administration (1 microg/kg b.w., i.p.), rats showed no significant differences in plasma glucose, insulin, triglycerides and leptin levels whereas plasma-free fatty acids were significantly increased with respect to untreated controls. In isolated islets, DNA and protein content were unchanged, whereas insulin content was significantly decreased in TCDD-treated rats. Incubation with different concentrations of glucose demonstrated a significant impairment of glucose-stimulated insulin secretion in islets isolated from TCDD-treated rats, whereas insulin release was better preserved upon alpha-ketoisocaproate stimulation. A significant reduction of [3H]-2-deoxy-glucose uptake was observed in pancreatic tissue of TCDD-treated rats, whereas no significant reduction in GLUT-2 protein levels was detectable by immunoblotting in islets from TCDD-treated rats. We concluded that low-dose TCDD could rapidly induce significant alterations of the pancreatic endocrine function in the rat.

Dioxin and diabetes mellitus: an analysis of the combined NIOSH and Ranch Hand data

OBJECTIVES

To reanalyze in a similar manner the two principal studies of TCDD (tetrachlorodibenzo-p-dioxin) and diabetes in an attempt to reconcile disparate results.

METHODS

Data from 990 United States Air Force veterans (Ranch Hand) and 1275 referents were reanalyzed, and a NIOSH population of 267 chemical workers and 227 referents. The Ranch Hand veterans had lower concentrations of lipid adjusted serum TCDD (median 12 parts per trillion (ppt)) than the NIOSH workers (median 75 ppt) when examined in the late 1980s. An analysis was conducted of the combined data sets, adopting a uniform approach to outcome definition, data analysis, and covariate control.

RESULTS

The combined exposed groups did not differ markedly from the combined non-exposed groups for prevalence of diabetes (odds ratio (OR) 1.17, 95% confidence interval (95% CI) 0.92 to 1.48), with no evidence of heterogeneity of exposure effect between studies. Also virtually no difference was found between combined exposed and non-exposed groups in mean fasting serum glucose (difference in log serum glucose 0.002, 95% CI -0.006 to 0.010), and there was little evidence in either study of a dose-response trend for fasting serum glucose. An increasing trend was found (p=0.0001) in prevalence of diabetes with increased TCDD (at the time of examination or at time of last exposure) among the Ranch Hand population, with excess risk largely confined to the highest 8% of the exposed group (>78 ppt serum TCDD), which had an OR of 3.21 (95% CI 1.81 to 5.72) versus those with <10 ppt TCDD. However, no such positive dose-response was found in the NIOSH population.

CONCLUSIONS

There was little overall evidence that the exposed workers were at higher risk than the non-exposed workers of diabetes or abnormal fasting glucose. However, the Ranch Hand subjects showed a positive dose-response for diabetes, whereas the more highly exposed NIOSH subjects did not. The reason for the difference in diabetes dose-response trends between the two studies is unknown.

Toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin and related compounds

Dioxin-type chemicals produce a variety of toxic and biochemical changes, some of which occur at very low doses and last for long periods of time. The most consistent toxin effect is body weight loss. In animals, the histopathologic changes, which are hyperplastic and hypertrophic, affect the gastrointestinal mucosa and the urinary track epithelium. In contrast, atrophic responses are seen in the thymus. Both hyperplasia and necrosis are observed in the liver. The administration of 2,3,7,8-tetrachlorodibenzo-p-dioxin also produces endocrine effects and changes in carbohydrate and lipid metabolism. The most serious toxic effects and the biochemical background of the lesions are reviewed.

Biochemical and toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin in immature male and female chickens

It has been reported that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced body wasting in mammals is associated with decreased adipose tissue lipoprotein lipase (LPL) and glucose transporting (GT) activity with differential sensitivity between genders. This study extends those findings to chickens as an avian model. A significant decrease in body weight gain was demonstrated in immature male and female chickens 10 days after treatment with a single intraperitoneal (i.p.) dose of 10 and 100 microg TCDD/kg. Body weight gain decrease was associated with hepatomegaly and induction of hepatic CYP1A enzymes in both genders. The increase in liver/body weight ratio (48%) and the decreased LPL activity (28%) were significant only in females at 10 microg TCDD/kg. However, the increase in liver/body weight ratio (31%) and the decrease in LPL activity (26%) were significantly demonstrated in males at 100 microg TCDD/kg. Levels of GT were significantly decreased in females (46%) and in males (48%) following treatment with 10 microg TCDD/kg and 100 microg TCDD/kg, respectively. Therefore, in chickens, as in mammals, the TCDD-induced body wasting is accompanied with decreased LPL activity and decreased GT activity and the magnitude of these changes is gender dependent. In contrast to mammals, this study suggests that female chickens are equally, if not more responsive to TCDD toxicity than males.

Serum dioxin level in relation to diabetes mellitus among Air Force veterans with background levels of exposure

Data from several epidemiologic studies suggest that exposure to unusually high amounts of dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin) increases the risk of diabetes mellitus, and experimental data suggest that the mechanism for this is decreased cellular glucose uptake. To investigate the dose-response relation more closely, we examined the association of serum dioxin level with prevalence of diabetes mellitus and with levels of serum insulin and glucose among 1,197 veterans in the Air Force Health Study who never had contact with dioxin-contaminated herbicides and whose serum dioxin level was within the range of background exposure typically seen in the United States (< or =10 ng/kg lipid). Compared with those whose serum dioxin level was in the first quartile (<2.8 ng/kg lipid), the multivariate-adjusted odds of diabetes among those in the highest quartile (> or =5.2 ng/kg lipid) was 1.71 (95% confidence interval = 1.00-2.91). The association was slightly attenuated after adjustment for serum triglycerides. Whether adjustment for serum triglycerides was appropriate, however, cannot be determined with available data. The association of background-level dioxin exposure with the prevalence of diabetes in these data may well be due to reasons other than causality, although a causal contribution cannot be wholly dismissed.

Treatment of rats during pubertal development with 2,3,7,8-tetrachlorodibenzo-p-dioxin alters both signaling kinase activities and epidermal growth factor receptor binding in the testis and the motility and acrosomal reaction of sperm

Different doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (0.1, 1, 5, and 10 micrograms/kg body wt) were administered i.p. to 21-day-old male Sprague-Dawley rats. Control animals received the same volume of the vehicle (acetone:corn oil, 1:19). Body weight and daily food intake were recorded during the 90-day time course of the study. Random samples of five rats were sacrificed at 34, 49, 62, and 90 days of age. Epidermal growth factor receptor (EGFR) in whole testis was measured, as were the activities of c-Src kinase, protein tyrosine kinase (PTK), mitogen-activated protein 2 kinase (MAP2K also termed as Erk2), protein kinase A (PKA), and protein kinase C (PKC). Testicular tissue from 90-day-old rats was evaluated for histopathology, and sperm numbers in whole testis were counted to estimate daily sperm production. The motility of sperm in the vas deferens and caudal segments of the epididymis of 90-day-old rats was measured by computer assisted sperm analysis (CASA) and the function of the sperm was tested by assessment of acrosome reactions. A dose of 10 micrograms/kg resulted in testicular atrophy and histopathologic examination revealed a decrease in the diameter of the seminiferous tubules. Sertoli cell nuclei were clearly seen, but the spermatogonial population was totally absent. Lower doses of TCDD did not affect testicular histology, but doses as low as 1 microgram/kg significantly decreased testicular sperm numbers and affected some sperm functions (motility parameters and acrosome reactions) in 90-day-old rats. Significant decreases in EGFR were found in 34-day-old rats and this effect on EGFR was sustained until the end of the experiment (90 days). Although TCDD significantly increased c-Src kinase activity in immature and mature rats, opposite effects of TCDD on activities of PTK, PKA, and PKC were found in 34-day-old rats vs 49-, 62-, and 90-day-old rats. When 10 micrograms TCDD/kg was administered to 21-day-old rat, 24-h after c-Src kinase inhibitor geldanamycin, there was no testicular atrophy and no change in the daily sperm production was found. These findings provide evidence for involvement of Src kinase signaling and EGFR in the mechanism by which TCDD disrupts testicular development and subsequently affects testis function.

Mechanisms of gender-specific TCDD-induced toxicity in guinea pig adipose tissue

After treatment with TCDD, the activities of cytosolic AhR-associated c-Src kinase, microsomal protein kinase C (nPKC epsilon), microsomal c-Src kinase, nuclear p44/42 MAPK, c-Jun N terminus kinase, and the amount of microsomal pan-Ras protein were different in males and females. TCDD did not decrease body or adipose tissue weights in transgenic src-deficient male mice as compared to their wild-type littermates, and the activity of AhR-associated c-Src kinase was not increased by TCDD in src-deficient male mice. Similar results were obtained when TCDD was given to male guinea pigs treated with the Src-kinase inhibitor, geldanamycin. Treatment with estradiol protected male guinea pigs from TCDD-induced wasting. TCDD induced similar changes in protein tyrosine kinase activity in adipose tissues of castrated male and intact female guinea pigs. The gender-specific mechanisms of TCDD-induced toxicity appear to involve c-Src kinase, nPKC epsilon, and pan-Ras, as well as overlap in the cytosolic signal transduction pathways of TCDD and sex steroids.

Interruption of estradiol signal transduction by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) through disruption of the protein phosphorylation pathway in adipose tissues from immature and mature female rats

At doses of 10-115 microg/kg, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) decreased body and adipose tissue weights of mature female rats. Doses below 10 microg TCDD/kg decreased body and adipose tissue weights of immature, but not mature females. Doses of 2 and 10 microg TCDD/kg decreased adipose tissue epidermal growth factor receptor (EGFR) binding activity 5 and 7 days later in immature and mature females, respectively. At these times, there was a decrease in the activities of tyrosine kinase (TK), mitogen-activated protein kinase (MAP2K), and protein kinase A (PKA). In mature females, estradiol (E2, 15 microg/kg) increased TK and PKA activities and decreased MAP2K activity. In immature females, E2 decreased TK and PKA activities but not MAP2K activity. TCDD abolished the stimulatory effect of E2 on TK and PKA in mature females, and in immature females TCDD potentiated the negative effect of E2 on all three kinases. TCDD decreased binding of [3H]E2 to cytosolic and nuclear estrogen receptors (ERs) of mature and immature females, and antagonized the stimulatory effect of E2 on ER binding activity. E2 increased DNA binding activity of the estrogen response element (ERE) and activator protein-1, and TCDD antagonized this effect. Geldanamycin, an inhibitor of Src tyrosine kinase, reduced the effects of TCDD on body and adipose tissue weights. Geldanamycin antagonized the effects of TCDD on EGFR binding activity and TK activity. In cell-free preparations, TCDD antagonized E2 action on TK activity in mature females, as well as E2 action on PKA activity in immature females. We hypothesize that TCDD antagonizes E2 action in female adipose tissues through disruption of common cytosolic signal transduction pathways.

Gender differences in the mechanism of dioxin toxicity in rodents and in nonhuman primates

This study examined the differences in mechanisms of toxicity when adipose cells from males and females were exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Glucose uptake by adipose tissue in vitro was decreased significantly in male guinea pigs within 1 d of intraperitoneal injection of TCDD, but there was no significant effect in females, even at 28 d after treatment. A similar difference between male and female guinea pigs was detected in the effect of TCDD on lipoprotein lipase (LPL) activity, except that a significant decrease in LPL activity was observed 28 d after treatment. Experiments with adipose tissue explants from untreated guinea pigs and macaques revealed similar gender differences in the effect of TCDD in vitro on glucose uptake and LPL activity. Both time-course studies and dose-response studies with TCDD in vitro confirmed the greater sensitivity of male tissues to TCDD toxicity. TCDD induced lipid peroxidation in the adipose tissues of male guinea pigs, while it had no effect in females. 3H-TCDD binding affinity studies in adipose explant tissues showed that tissues from male guinea pigs and monkeys had a higher binding capacity for TCDD than female tissues. TCDD induced a significant reduction in nuclear protein phosphorylation and an increase in cytosolic protein phosphorylation in adipose tissue from male guinea pigs; the effects in female tissues were opposite: nuclear protein phosphorylation increased and cytosolic protein phosphorylation decreased. In a cell-free system in the absence of the nucleus, adipose tissues from male guinea pigs and monkeys responded to TCDD with a rapid stimulation of tyrosine kinase activity but female tissues from both species had a significantly lower and slower response. TCDD induced the DNA binding of AP-1 in adipose tissues of male guinea pigs, but in female tissues TCDD reduced the DNA binding of AP-1. In summary, the results of this study demonstrate gender differences in the response of nonreproductive cells to TCDD. Some of these differences involve different mechanisms of toxicity in both the cytoplasmic and nuclear compartments of the cell.

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) modulates function of human luteinizing granulosa cells via cAMP signaling and early reduction of glucose transporting activity

This study examined the changes in cellular glucose uptake, cAMP-dependent protein kinase (PKA), and progesterone production induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in human luteinizing granulosa cells (LGCs) in culture. The role of Ah receptor on TCDD-mediated toxicity in human LGCs was investigated. Treatment of human LGCs with TCDD produced a time- and dose-dependent decrease in the cellular uptake of glucose. The Vmax and the K(m) of glucose transport were decreased by TCDD treatment. Furthermore, cytochalasin B, a specific inhibitor of facilitative glucose transporter proteins, totally abolished the portion of glucose transport activity that is sensitive to TCDD. Pretreatment of the cells with the Ah receptor blockers 4,7-phenanthroline and alpha-naphthoflavone antagonised the effect of TCDD on 3H-Me-glucose uptake. Structure-activity relationship studies with TCDD and three dioxin congeners revealed a rank order for their potency in the inhibition of glucose transport as follows: TCDD > 1,2,3,7,8-PCDD > 1,2,4,7,8-PCDD > 2,7-DCDD. Such a rank order is consistent with the previously determined biological activity of TCDD and the other dioxin congeners. Treatment of cells for 48 h with 10 nM TCDD substantially reduced PKA and progesterone production. The inhibitory effect of TCDD on progesterone production was more pronounced in the presence of insulin (10 micrograms/mL) and D-glucose (13.3 mM). However, cytochalasin B abolished the effect of TCDD on progesterone production. Forskolin (adenylate cyclase activator) abolished the effect of TCDD on glucose uptake and progesterone production but it did not affect the action of TCDD on PKA activity. A relationship between glucose transporting activity and progesterone production in human LGCs treated with TCDD is indicated by several lines of evidence: a) cytochalasin B downregulated glucose transporting activity and progesterone production, b) insulin plus D-glucose downregulated glucose uptake and amplified the negative effect of TCDD on progesterone production, and c) forskolin abolished the negative effect of TCDD on glucose transporting activity and on progesterone production. From the present data we conclude that glucose transporting activity can be used as a sensitive biomarker to detect the very early response to TCDD in human steroid-producing cells and that effect of TCDD on steroid production is mediated through the cAMP-dependent protein kinase.