Direct Assessment of Cumulative Aryl Hydrocarbon Receptor Agonist Activity in Sera from Experimentally Exposed Mice and Environmentally Exposed Humans

Abstract

BackgroundAryl hydrocarbon receptor (AhR) ligands adversely affect many biological processes. However, assessment of the significance of human exposures is hampered by an incomplete understanding of how complex mixtures affect AhR activation/inactivation.ObjectivesThese studies used biological readouts to provide a broader context for estimating human risk than that obtained with serum extraction and gas chromatography/mass spectroscopy (GC/MS)-based assays alone.MethodsAhR agonist activity was quantified in sera from dioxin-treated mice, commercial human sources, and polychlorinated biphenyl (PCB)–exposed Faroe Islanders using an AhR-driven reporter cell line. To validate relationships between serum AhR agonist levels and biological outcomes, AhR agonist activity in mouse sera correlated with toxic end points. AhR agonist activity in unmanipulated (“neat”) human sera was compared with these biologically relevant doses and with GC/MS-assayed PCB levels.ResultsMouse serum AhR agonist activity correlated with injected dioxin dose, thymic atrophy, and heptomegaly, validating the use of neat serum to assess AhR agonist activity. AhR agonist activity in sera from Faroe Islanders varied widely, was associated with the frequency of recent pilot whale dinners, but did not correlate with levels of PCBs quantified by GC/MS. Surprisingly, significant “baseline” AhR activity was found in commercial human sera.ConclusionsAn AhR reporter assay revealed cumulative levels of AhR activation potential in neat serum, whereas extraction may preclude detection of important non-dioxin-like biological activity. Significant levels of AhR agonist activity in commercial sera and in Faroe Islander sera, compared with that from experimentally exposed mice, suggest human exposures that are biologically relevant in both populations.

Enzyme induction and histopathology elucidate aryl hydrocarbon receptor–mediated versus non–aryl hydrocarbon receptor–mediated effects of Aroclor 1268 in American mink (Neovison vison)

“…Hepatomegaly in Aroclor 1268-treated mink was highly dose-dependent. As a nonspecific pathology frequently documented as a toxicological response to PCB exposure, both ortho-substituted and non-ortho-substituted PCBs can induce hepatomegaly [2,55,56]. However, contrary to these studies [2,55,56], hepatomegaly was absent in positive control mink, suggesting that although mechanisms of hepatomegaly have the potential to be AhR-mediated, the pathway that induced hepatomegaly in Aroclor 1268-exposed mink was not.…”

“…As a nonspecific pathology frequently documented as a toxicological response to PCB exposure, both ortho-substituted and non-ortho-substituted PCBs can induce hepatomegaly [2,55,56]. However, contrary to these studies [2,55,56], hepatomegaly was absent in positive control mink, suggesting that although mechanisms of hepatomegaly have the potential to be AhR-mediated, the pathway that induced hepatomegaly in Aroclor 1268-exposed mink was not. Hepatomegaly of mammals exposed to PCBs is typically attributed to inflammation, hypertrophy of hepatocytes through the proliferation of smooth endoplasmic reticulum, hepatic steatosis, development of lesions, or the accumulation of necrotic hepatocytes, all of which can be confirmed histologically [2,57].…”

Aryl hydrocarbon receptor ligands in cancer: friend and foe

“…However, environmental ligands such as halogenated planar polycyclic hydrocarbons, as well as dietary ligands previously described, could facilitate a significant level of activation through systemic circulation. Indeed, AHR ligands have been detected in serum from cancer-free individuals through the use of reporter assay systems 28, 29 . Several indole-derived potent human AHR ligands, indirubin, indigo and metabolites of 6-formylindolo[3,2- b ]carbazole, have been identified in human urine 30, 31 .…”

The aryl hydrocarbon receptor directs hematopoietic progenitor cell expansion and differentiation

“…To quantify baseline AhR transcriptional activity, presumably enforced by an endogenous AhR ligand, we cloned a human AhRdriven promoter 38,39 into a lentivirus reporter vector that encodes for dsRed and ZsGreen ( Figure 4A). This dual gene AhR-driven reporter construct allowed for the normalization of transduction efficiency, correction for autoflorescence, and the quantification of baseline or FICZ-induced AhR transcriptional activity without bias for specific gene targets.…”