Species-specific relative AHR1 binding affinities of 2,3,4,7,8-pentachlorodibenzofuran explain avian species differences in its relative potency

Xanthohumol Effect on 2,3,7,8-Tetrachlorodibenzo-p-dioxin-Treated Japanese Quails in Terms of Serum Lipids, Liver Enzymes, Estradiol, and Thyroid Hormones

Dioxins are compounds classified as persistent organic pollutants, from which 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is the most toxic to living organisms. TCDD is considered a carcinogen and has proinflammatory influence on animals and humans, promoting free radicals' formation, and binding with the aryl hydrocarbon receptor (AhR) leads to expression of cytochrome p-450 genes that in turn predisposes to mutations. Natural flavonoids, in this case xanthohumol (XN), have been reported to attenuate TCDD toxicity through inhibition of the transformation of the AhR. Moreover, XN shows antioxidant properties. The aim of the study was to compare the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin and XN on lipid, liver enzyme, estradiol, and thyroid enzyme levels in the serum of Japanese quails. Adult, six-month-old, Japanese quails were divided into eight groups according to treatment procedures. Serum levels of total cholesterol (TCh), high-density lipoproteins (HDLs), triglycerides (TGs), estradiol, triiodothyronine, and thyroxine, and activities of alkaline phosphatase, aspartate aminotransferase, and alanine aminotransferase were measured. In comparison with the control group, 2,3,7,8-tetrachlorodibenzo-p-dioxin significantly decreased concentrations of serum HDLs and thyroid hormones and significantly increased the serum TCh level. Levels of serum TGs, liver enzymes, and estradiol were not changed after 2,3,7,8-tetrachlorodibenzo-p-dioxin treatment. Based on our data, XN treatment may also increase the levels of thyroid hormones. Moreover, the tested dioxin disrupts the liver function, especially changing lipids' metabolism. Therefore, more studies are needed for better understanding the mechanism of toxic influence of 2,3,7,8-tetrachlorodibenzo-p-dioxin on key metabolic pathways and organs in living organisms.

Building and Applying Quantitative Adverse Outcome Pathway Models for Chemical Hazard and Risk Assessment

An important goal in toxicology is the development of new ways to increase the speed, accuracy, and applicability of chemical hazard and risk assessment approaches. A promising route is the integration of in vitro assays with biological pathway information. We examined how the adverse outcome pathway (AOP) framework can be used to develop pathway-based quantitative models useful for regulatory chemical safety assessment. By using AOPs as initial conceptual models and the AOP knowledge base as a source of data on key event relationships, different methods can be applied to develop computational quantitative AOP models (qAOPs) relevant for decision making. A qAOP model may not necessarily have the same structure as the AOP it is based on. Useful AOP modeling methods range from statistical, Bayesian networks, regression, and ordinary differential equations to individual-based models and should be chosen according to the questions being asked and the data available. We discuss the need for toxicokinetic models to provide linkages between exposure and qAOPs, to extrapolate from in vitro to in vivo, and to extrapolate across species. Finally, we identify best practices for modeling and model building and the necessity for transparent and comprehensive documentation to gain confidence in the use of qAOP models and ultimately their use in regulatory applications. Environ Toxicol Chem 2019;38:1850-1865. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Relative Effect Potency Estimates for Dioxin-Like Compounds in Pregnant Women with Gestational Diabetes Mellitus and Blood Glucose Outcomes Based on a Nested Case-control Study

To improve the applicability of the toxic equivalents principle for human health risk assessment, systemic relative effect potencies (REPs) for dioxin-like compounds (DLCs) deriving from human in vivo data are required. A prospective nested case-control study was performed to determine REPs from the human serum concentration of DLCs using gestational diabetes mellitus (GDM) and fasting blood glucose (FBG) as the end points of concern. Serum concentration of 29 DLCs from 77 cases and 154 controls were measured. Logistic and linear regression were used to estimate the effects of individual congeners on GDM and FBG, respectively. The REPs based on GDM and FBG were calculated from the ratios of regression coefficients, β_i (DLCs)/β_TCDD. Two sets of consistent human serum-based REPs, that is, GDM-REP and FBG-REP, were established and largely agree with REPs from other human studies. These human-serum REPs show much smaller variation compared to the 4 to 5 orders of magnitude span in REPs database for the present WHO-TEF determination. Moreover, the established REPs fitted well with WHO-TEFs, especially for polychlorinated dibenzo- p-dioxins, furans. These REPs reflecting real human exposure scenarios exhibited validity and could be used to improve health risk assessment of human body burden of DLCs.

Embryonic effects of an environmentally relevant PCB mixture in the domestic chicken

Studies were conducted to develop methods to assess the effects of a complex mixture of polychlorinated biphenyls (PCBs) in the domestic chicken (Gallus domesticus). Treatments were administered by egg injection to compare embryonic effects of an environmentally relevant PCB congener mixture in the domestic chicken over a range of doses. Chicken eggs were injected with the PCB mixture with a profile similar to that found in avian eggs collected on the upper Hudson River, New York, USA, at doses that spanned 0 to 98 μg/g egg. Eggs were hatched in the laboratory to ascertain hatching success. In the domestic chicken, the median lethal dose was 0.3 μg/g. These data demonstrate adverse effects of an environmentally relevant PCB mixture and provide the basis for further work using in vitro and other models to characterize the potential risk to avian populations. Environ Toxicol Chem 2018;37:2513-2522. © 2018 SETAC.

Integrating Monitoring and Genetic Methods To Infer Historical Risks of PCBs and DDE to Common and Roseate Terns Nesting Near the New Bedford Harbor Superfund Site (Massachusetts, USA)

Common and roseate terns are migratory piscivorous seabirds with major breeding colonies within feeding range of the polychlorinated biphenyl (PCB)-contaminated New Bedford Harbor (NBH, MA, USA) Superfund site. Our longitudinal study shows that before PCB discharges into NBH ceased (late 1970s), tern eggs had very high but variable PCB concentrations. However, egg concentrations of PCBs as well as DDE (1,1-bis(p-chlorophenyl)-2,2-dichloroethene), the degradation product of the ubiquitous global contaminant DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane), have since declined. Rate constants for temporal decline of PCB congeners in tern eggs varied inversely with log10KOW (n-octanol-water partition coefficient), shifting egg congener patterns away from those characterizing NBH sediment. To estimate the toxic effects on tern eggs of PCB dioxin-like congener (DLC) exposures, we extrapolated published laboratory data on common terns to roseate terns by characterizing genetic and functional similarities in species aryl hydrocarbon receptors (AHRs), which mediate DLC sensitivity. Our assessment of contaminant risks suggests that terns breeding near NBH were exposed historically to toxic levels of PCBs and DDE; however, acute effects on tern egg development have become less likely since the 1970s. Our approach demonstrates how comparative genetics at target loci can effectively increase the range of inference for chemical risk assessments from tested to untested and untestable species.