We have shown that zebrafish (Danio rerio) are an excellent model for evaluating the link between early life stage exposure to environmental chemicals and disease in adulthood and subsequent unexposed generations. Previously, we used this model to identify transgenerational effects of dioxin (2,3,7,) on skeletal development, sex ratio, and reproductive capacity. Transgenerational inheritance of TCDD toxicity, notably decreased reproductive capacity, appears to be mediated through the male germ line. Thus, we examine testicular tissue for structural and gene expression changes using histology, microarray, and quantitative reverse transcription polymerase chain reaction (qRT-PCR). Histological analysis revealed decreased spermatozoa with concurrent increase in spermatogonia, and decreased germinal epithelium thickness in TCDD-exposed males compared with controls. We also identified altered expression of genes associated with testis development, steroidogenesis, spermatogenesis, hormone metabolism, and xenobiotic response. Altered genes are in pathways involving lipid metabolism, molecular transport, small molecule biochemistry, cell morphology, and metabolism of vitamins and minerals. These data will inform future investigations to elucidate the mechanism of adult-onset and transgenerational infertility due to TCDD exposure in zebrafish.

Findings suggest that obesity alters human sensitivity to smoke exposures through several biological pathways by modifying gene expression. Additional studies are needed to fully understand the clinical impact of these effects, but risk assessments should consider underlying phenotypes, such as obesity, that may modulate sensitivity of vulnerable populations to environmental exposures.

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The aryl hydrocarbon receptor (AHR) is a ligand activated transcription factor and a member of the PER-ARNT-SIM (PAS) superfamily of environmental sensors. The AHR is involved in a series of biological processes including adaptive metabolism of xenobiotics, toxicity of certain environmental pollutants, vascular development, fertility, and immune function. Mouse models, including the Ahr null and Ahr conditional null mice, are widely used for the study of AHR-mediated biology and toxicity. The Ahr conditional null mouse harbors the low affinity Ahrd allele that exhibits approximately a 10-fold lower binding affinity for AHR ligands than the widely used C57BL/6 mouse that harbors the higher affinity Ahrb1 allele. Here, we report a novel mouse model that introduces a V375A polymorphism that converts the low affinity allele into a high-affinity allele, offering a more sensitive conditional model. In the generation of this novel conditional allele, two additional mutants arose, including a three base pair deletion in the PAS-B domain (AhrNG367R) and an early termination codon in the PAS-B domain (AhrTer383). The AhrNG367R allele presents as a phenocopy of the null and the AhrTer383 allele presents as an antimorph when assessing for the ductus venosus endpoint. These new models represent a series of tools that will be useful in further characterizing AHR biology.

The lymphocyte toxicity assay (LTA) is a proposed surrogate marker of sulfonamide antibiotic hypersensitivity. In the LTA, peripheral blood mononuclear cells (PBMCs) undergo apoptosis more readily in hypersensitive versus tolerant patients when exposed to drug‐hydroxylamine metabolites in vitro. The purpose of this study was to identify key gene transcripts associated with increased cytotoxicity from sulfamethoxazole‐hydroxylamine in human PBMCs in the LTA. The LTA was performed on PBMCs of 10 patients hypersensitive to trimethoprim‐sulfamethoxazole (HS) and 10 drug‐tolerant controls (TOL), using two cytotoxicity assays: YO‐PRO (n = 20) and MTT (n = 12). mRNA expression profiles of PBMCs, enriched for CD8+ T cells, were compared between HS and TOL patients. Transcript expression was interrogated for correlation with % cytotoxicity from YO‐PRO and MTT assays. Correlated transcripts of interest were validated by qPCR. LTA results were not significantly different between HS and TOL patients, and no transcripts were found to be differentially expressed between the two groups. 96 transcripts were correlated with cytotoxicity by YO‐PRO (r = ±.63‐.75, FDR 0.188). Transcripts were selected for validation based on mechanistic plausibility and three were significantly over‐expressed by qPCR in high cytotoxicity patients: multi‐specific organic anion transporter C (ABCC5), mitoferrin‐1 (SLC25A37), and Porimin (TMEM123). These data identify novel transcripts that could contribute to sulfonamide‐hydroxylamine induced cytotoxicity. These include SLC25A37, encoding a mitochondrial iron transporter, ABCC5, encoding an arylamine drug transporter, and TMEM123, encoding a transmembrane protein that mediates cell death.

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