Polybrominated diphenyl ethers (PBDEs), used as flame retardants, are ubiquitous environmental contaminants. PBDEs act as endocrine disruptors via alterations in thyroid hormone homeostasis. We examined thyroid hormone concentrations and hepatic enzyme activity in weanling rats exposed to three commercial PBDE mixtures: DE-71, DE-79, and DE-83R. Female Long-Evans rats, 28 days old, were orally administered various doses of DE-71, DE-79, or DE-83R for 4 days. Serum and liver samples were collected 24 h after the last dose and analyzed for serum total thyroxine (T(4)), triiodothyronine (T(3)), thyroid-stimulating hormone (TSH), hepatic microsomal ethoxy- and pentoxy-resorufin-O-deethylase (EROD and PROD), and uridinediphosphate-glucuronosyltransferase (UDPGT) activities. The PBDE-treated groups did not exhibit significant changes in body weight; however, increased liver weights, as well as 10- to 20-fold induction in EROD and 30- to 40-fold induction in PROD were found in the DE-71-- and DE-79--treated animals. DE-71 and DE-79 caused dose-dependent depletion of T(4), accompanied by up to 3- to 4-fold induction in UDPGT activities. Serum total T(4) was decreased a maximum of 80% for DE-71 and 70% for DE-79 in the highest dose, with benchmark doses (BMDs) of approximately 12.74 mg/kg/day for DE-71 and 9.25 mg/kg/day for DE-79. Dose-related effects in serum T(3) levels were less apparent, with maximal reductions of 25-30% at the highest dose for both DE-71 and DE-79. The two mixtures showed no effect on serum TSH levels. Benchmark dose analysis revealed that the two mixtures were comparable in altering thyroid hormone levels and hepatic enzyme activity. DE-83R was not effective in altering any of the measured parameters. The present study suggests that short-term exposure to some commercial PBDE mixtures interferes with the thyroid hormone system via upregulation of UDPGTS:

Based on existing data and previous work, a series of studies is proposed as a basis toward a pragmatic early step in transforming toxicity testing. These studies were assembled into a data-driven framework that invokes successive tiers of testing with margin of exposure (MOE) as the primary metric. The first tier of the framework integrates data from high-throughput in vitro assays, in vitro-to-in vivo extrapolation (IVIVE) pharmacokinetic modeling, and exposure modeling. The in vitro assays are used to separate chemicals based on their relative selectivity in interacting with biological targets and identify the concentration at which these interactions occur. The IVIVE modeling converts in vitro concentrations into external dose for calculation of the point of departure (POD) and comparisons to human exposure estimates to yield a MOE. The second tier involves short-term in vivo studies, expanded pharmacokinetic evaluations, and refined human exposure estimates. The results from the second tier studies provide more accurate estimates of the POD and the MOE. The third tier contains the traditional animal studies currently used to assess chemical safety. In each tier, the POD for selective chemicals is based primarily on endpoints associated with a proposed mode of action, whereas the POD for nonselective chemicals is based on potential biological perturbation. Based on the MOE, a significant percentage of chemicals evaluated in the first 2 tiers could be eliminated from further testing. The framework provides a risk-based and animal-sparing approach to evaluate chemical safety, drawing broadly from previous experience but incorporating technological advances to increase efficiency.

Background: Diabetes is a major threat to public health in the United States and worldwide. Understanding the role of environmental chemicals in the development or progression of diabetes is an emerging issue in environmental health.Objective: We assessed the epidemiologic literature for evidence of associations between persistent organic pollutants (POPs) and type 2 diabetes.Methods: Using a PubMed search and reference lists from relevant studies or review articles, we identified 72 epidemiological studies that investigated associations of persistent organic pollutants (POPs) with diabetes. We evaluated these studies for consistency, strengths and weaknesses of study design (including power and statistical methods), clinical diagnosis, exposure assessment, study population characteristics, and identification of data gaps and areas for future research.Conclusions: Heterogeneity of the studies precluded conducting a meta-analysis, but the overall evidence is sufficient for a positive association of some organochlorine POPs with type 2 diabetes. Collectively, these data are not sufficient to establish causality. Initial data mining revealed that the strongest positive correlation of diabetes with POPs occurred with organochlorine compounds, such as trans-nonachlor, dichlorodiphenyldichloroethylene (DDE), polychlorinated biphenyls (PCBs), and dioxins and dioxin-like chemicals. There is less indication of an association between other nonorganochlorine POPs, such as perfluoroalkyl acids and brominated compounds, and type 2 diabetes. Experimental data are needed to confirm the causality of these POPs, which will shed new light on the pathogenesis of diabetes. This new information should be considered by governmental bodies involved in the regulation of environmental contaminants.