Background: There has been increasing interest in the concept that exposures to environmental chemicals may be contributing factors to the epidemics of diabetes and obesity. On 11–13 January 2011, the National Institute of Environmental Health Sciences (NIEHS) Division of the National Toxicology Program (NTP) organized a workshop to evaluate the current state of the science on these topics of increasing public health concern.Objective: The main objective of the workshop was to develop recommendations for a research agenda after completing a critical analysis of the literature for humans and experimental animals exposed to certain environmental chemicals. The environmental exposures considered at the workshop were arsenic, persistent organic pollutants, maternal smoking/nicotine, organotins, phthalates, bisphenol A, and pesticides. High-throughput screening data from Toxicology in the 21st Century (Tox21) were also considered as a way to evaluate potential cellular pathways and generate -hypotheses for testing which and how certain chemicals might perturb biological processes related to diabetes and obesity.Conclusions: Overall, the review of the existing literature identified linkages between several of the environmental exposures and type 2 diabetes. There was also support for the “developmental obesogen” hypothesis, which suggests that chemical exposures may increase the risk of obesity by altering the differentiation of adipocytes or the development of neural circuits that regulate feeding behavior. The effects may be most apparent when the developmental exposure is combined with consumption of a high-calorie, high-carbohydrate, or high-fat diet later in life. Research on environmental chemical exposures and type 1 diabetes was very limited. This lack of research was considered a critical data gap. In this workshop review, we outline the major themes that emerged from the workshop and discuss activities that NIEHS/NTP is undertaking to address research recommendations. This review also serves as an introduction to an upcoming series of articles that review the literature regarding specific exposures and outcomes in more detail.

The Ah receptor (AhR) mediates many of the toxic responses induced by polyhalogenated and polycyclic hydrocarbons (PAHs) which are ubiquitous environmental contaminants causing toxic responses in human and wildlife. NF-B is a pleiotropic transcription factor controlling many physiological functions adversely affected by PAHs, including immune suppression, thymus involution, hyperkeratosis, and carcinogenesis. Here, we show physical interaction and mutual functional repression between AhR and NF-B. This mutual repression may provide an underlying mechanism for many hitherto poorly understood PAH-induced toxic responses, and may also provide a mechanistic explanation for alteration of xenobiotic metabolism by cytokines and compounds that regulate NF-B.

At the request of the U.S. Environmental Protection Agency (U.S. EPA), the National Toxicology Program organized an independent and open peer review to evaluate the scientific evidence on low-dose effects and nonmonotonic dose-response relationships for endocrine-disrupting chemicals in mammalian species. For this peer review, "low-dose effects" referred to biologic changes that occur in the range of human exposures or at doses lower than those typically used in the standard testing paradigm of the U.S. EPA for evaluating reproductive and developmental toxicity. The demonstration that an effect is adverse was not required because in many cases the long-term health consequences of altered endocrine function during development have not been fully characterized. A unique aspect of this peer review was the willing submission of individual animal data by principal investigators of primary research groups active in this field and the independent statistical reanalyses of selected parameters prior to the peer review meeting by a subpanel of statisticians. The expert peer-review panel (the panel) also considered mechanistic data that might influence the plausibility of low-dose effects and identified study design issues or other biologic factors that might account for differences in reported outcomes among studies. The panel found that low-dose effects, as defined for this review, have been demonstrated in laboratory animals exposed to certain endocrine-active agents. In some cases where low-dose effects have been reported, the findings have not been replicated. The shape of the dose-response curves for reported effects varied with the end point and dosing regimen and were low-dose linear, threshold-appearing, or nonmonotonic. The findings of the panel indicate that the current testing paradigm used for assessments of reproductive and developmental toxicity should be revisited to see whether changes are needed regarding dose selection, animal-model selection, age when animals are evaluated, and the end points being measured following exposure to endocrine-active agents.

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Proinflammatory cytokines, such as tumor necrosis factor (TNF)-␣, interleukin-1␤, and lipopolysaccharides (LPS), suppress the gene expression of cytochrome P-450 1A1 (cyp1a1). The mechanism of the suppression is not well understood. In present study, we show that activation of nuclear factor-B (NF-B) is a critical event leading to the suppression of cyp1a1 gene expression, thus providing an underlying mechanism for the TNF-␣-and LPS-induced cyp1a1 suppression. We demonstrated that: (i) inducible RelA expression down-regulated aryl hydrocarbon receptor (AhR) activated reporter gene; (ii) the suppressive effects of LPS and TNF-␣ on the AhR-activated reporter gene could be blocked by pyrrolidine dithiocarbamate, which is known to inhibit NF-B action; and (iii) TNF-␣ and LPSimposed repression could be reversed by the NF-B super repressor (SRIB␣), thus demonstrating the specific involvement of NF-B. Furthermore, nuclear receptor coactivators p300/CBP and steroid receptor coactivator-1 act individually as well as cooperatively to reverse the suppressive effects by NF-B on the AhR-activated reporter gene, suggesting that these transcriptional coactivators serve as the common integrators for the two pathways, thereby mediating the cross-interactions between AhR and NF-B. Finally, using the chromatin immunoprecipitation assay, we demonstrated that AhR ligand induces histone H4 acetylation at the cyp1a1 promoter region containing the TATA box, whereas TNF-␣ inhibits this acetylation, suggesting that AhR/NF-B interaction converges at level of transcription involving chromatin remodeling.

Purpose: The goals of this study were (1) to compare the injury at the basement membrane zone (BMZ) of rabbit corneal organ cultures exposed to half mustard (2 chloroethyl ethyl sulfide, CEES) and nitrogen mustard with that of in vivo rabbit eyes exposed to sulfur mustard (SM); (2) to test the efficacy of 4 tetracycline derivatives in attenuating vesicant-induced BMZ disruption in the 24-h period postexposure; and (3) to use the most effective tetracycline derivative to compare the improvement of injury when the drug is delivered as drops or hydrogels to eyes exposed in vivo to SM. Methods: Histological analysis of hematoxylin and eosin-stained sections was performed; the ultrastructure of the corneal BMZ was evaluated by transmission electron microscopy; matrix metalloproteinase-9 was assessed by immunofluorescence; doxycycline as drops or a hydrogel was applied daily for 28 days to eyes exposed in vivo to SM. Corneal edema was assessed by pachymetry and the extent of neovascularization was graded by length of longest vessel in each quadrant. Results: Injury to the BMZ was highly similar with all vesicants, but varied in degree of severity. The effectiveness of the 4 drugs in retaining BMZ integrity did not correlate with their ability to attenuate matrix metalloproteinase-9 expression at the epithelial-stromal border. Doxycycline was most effective on organ cultures; therefore, it was applied as drops or a hydrogel to rabbit corneas exposed in vivo to SM. Eyes were examined at 1, 3, 7, and 28 days after exposure. At 7 and 28 days after SM exposure, eyes treated with doxycycline were greatly improved over those that received no therapy. Corneal thickness decreased somewhat faster using doxycycline drops, whereas the hydrogel formulation decreased the incidence of neovascularization. Conclusions: Corneal cultures exposed to 2-chloroethyl ethyl sulfide and nitrogen mustard were effective models to simulate in vivo SM exposures. Doxycycline as drops and hydrogels ameliorated vesicant injury. With in vivo exposed animals, the drops reduced edema faster than the hydrogels, but use of the hydrogels significantly reduced neovascularization. The data provide proof of principle that a hydrogel formulation of doxycycline as a daily therapy for ocular vesicant injury should be further investigated.

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It is a long-standing observation that inflammatory responses and infections decrease drug metabolism capacity in human and experimental animals. Cytochrome P-450 3A4 cyp304 is responsible for the metabolism of over 50% of current prescription drugs, and cyp3a4 expression is transcriptionally regulated by pregnane X receptor (PXR), which is a ligand-dependent transcription factor. In this study, we report that NF-B activation by lipopolysaccharide and tumor necrosis factor-␣ plays a pivotal role in the suppression of cyp3a4 through interactions of NF-B with the PXR⅐retinoid X receptor (RXR) complex. Inhibition of NF-B by NF-B-specific suppressor SRIB␣ reversed the suppressive effects of lipopolysaccharide and tumor necrosis factor-␣. Furthermore, we showed that NF-B p65 disrupted the association of the PXR⅐RXR␣ complex with DNA sequences as determined by electrophoretic mobility shift assay and chromatin immunoprecipitation assays. NF-B p65 directly interacted with the DNA-binding domain of RXR␣ and may prevent its binding to the consensus DNA sequences, thus inhibiting the transactivation by the PXR⅐RXR␣ complex. This mechanism of suppression by NF-B activation may be extended to other nuclear receptor-regulated systems where RXR␣ is a dimerization partner.Inflammatory responses and infections suppress the biotransformation of drugs and decrease the hepatointestinal capacity of drug clearance. This results in alterations of therapeutic indices and increases the toxicity of certain administered drugs. Inflammatory responses also play important roles in liver pathological conditions such as drug-induced hepatitis and cholestatic diseases (1, 2). The mechanisms of these clinically important effects have not been well understood.In human liver, the first pass of biotransformation is mainly carried out by cytochrome P-450 (CYP) 2 3A4, which is the predominant isoform of monooxygenases that are expressed in the adult hepatointestinal system. It is estimated that CYP3A4 is responsible for the metabolism of over 50% of drugs in use today, many of which are either metabolically activated and/or metabolically broken down (detoxified) through this enzyme. Therefore, transcriptional and post-transcriptional alterations of CYP3A4 activity have direct effects on the efficacy of drugs and detoxification of xenobiotics (reviewed in Refs. 3 and 4). Recent molecular and pharmacological studies have demonstrated that transcriptional activation of cyp3a4 is mediated by the nuclear receptor PXR (pregnane X receptor). The rodent PXR (5) and its human homolog hPXR (6), also known as steroid and xenobiotic receptor (7) or hPAR (8), were identified as xenobiotic receptors that can be activated by certain xenobiotics and endobiotics. PXR regulates the expression of cyp3a4 by associating with its obligate partner RXR, and the heterodimer binds to the nuclear receptor response elements found in the regulatory regions of these genes. Genes that are regulated by PXR include multiple drug-resistant genes such as MDR1 (9) and MRP2 (10) as wel...