Pleiotropic effects of gold(I) mixed-ligand complexes of 9-deazahypoxanthine on transcriptional activity of receptors for steroid hormones, nuclear receptors and xenoreceptors in human hepatocytes and cell lines

Gut Microbial Catabolites of Tryptophan Are Ligands and Agonists of the Aryl Hydrocarbon Receptor: A Detailed Characterization

We examined the effects of gut microbial catabolites of tryptophan on the aryl hydrocarbon receptor (AhR). Using a reporter gene assay, we show that all studied catabolites are low-potency agonists of human AhR. The efficacy of catabolites differed substantially, comprising agonists with no or low (i3-propionate, i3-acetate, i3-lactate, i3-aldehyde), medium (i3-ethanol, i3-acrylate, skatole, tryptamine), and high (indole, i3-acetamide, i3-pyruvate) efficacies. We displayed ligand-selective antagonist activities by i3-pyruvate, i3-aldehyde, indole, skatole, and tryptamine. Ligand binding assay identified low affinity (skatole, i3-pyruvate, and i3-acetamide) and very low affinity (i3-acrylate, i3-ethanol, indole) ligands of the murine AhR. Indole, skatole, tryptamine, i3-pyruvate, i3-acrylate, and i3-acetamide induced CYP1A1 mRNA in intestinal LS180 and HT-29 cells, but not in the AhR-knockout HT-29 variant. We observed a similar CYP1A1 induction pattern in primary human hepatocytes. The most AhR-active catabolites (indole, skatole, tryptamine, i3-pyruvate, i3-acrylate, i3-acetamide) elicited nuclear translocation of the AhR, followed by a formation of AhR-ARNT heterodimer and enhanced binding of the AhR to the CYP1A1 gene promoter. Collectively, we comprehensively characterized the interactions of gut microbial tryptophan catabolites with the AhR, which may expand the current understanding of their potential roles in intestinal health and disease.

Mono-methylindoles induce CYP1A genes and inhibit CYP1A1 enzyme activity in human hepatocytes and HepaRG cells

Mono-methylindoles (MMI) were described as agonists and/or antagonists of the human aryl hydrocarbon receptor (AhR). Here, we investigated the effects of MMI on AhR-CYP1A pathway in human hepatocytes and HepaRG cells derived from human progenitor hepatic cells. All MMI, except of 2-methylindole, strongly induced CYP1A1 and CYP1A2 mRNAs in HepaRG cells. Induction of CYP1A genes was absent in AhR-knock-out HepaRG cells. Consistently, CYP1A1 and CYP1A2 mRNAs and proteins were induced by all MMIs (except 2-methylindole), in human hepatocytes. The enzyme activity of CYP1A1 was inhibited by MMIs in human hepatocytes and LS180 colon cancer cells in a concentration-dependent manner (IC₅₀ values from 1.2 μM to 23.8 μM and from 3.4 μM to 11.4 μM, respectively). Inhibition of CYP1A1 activity by MMI in human liver microsomes was much weaker as compared to that in intact cells. Incubation of parental MMI with human hepatocytes either diminished (4-methylindole, 6-methylindole) or enhanced (7-methylindole) their agonist effects on AhR in AZ-AHR reporter cells. In conclusion, overall effects of MMI on AhR-CYP1A pathway in human cells comprise the induction of CYP1A genes through AhR, the inhibition of CYP1A catalytic activity and possibly the metabolic transformation causing loss or gain of AhR agonist activity of parental compounds.

Assessment of endocrine disruption potential of essential oils of culinary herbs and spices involving glucocorticoid, androgen and vitamin D receptors

Essential oils (EOs) of culinary herbs and spices are consumed on a daily basis. They are multicomponent mixtures of compounds with already demonstrated biological activities. Taking into account regular dietary intake and the chemical composition of EOs, they may be considered as candidates for endocrine-disrupting entities. Therefore, we examined the effects of 31 EOs of culinary herbs and spices on transcriptional activities of glucocorticoid receptor (GR), androgen receptor (AR) and vitamin D receptor (VDR). Using reporter gene assays in stably transfected cell lines, weak anti-androgen and anti-glucocorticoid activity was observed for EO of vanilla and nutmeg, respectively. Moderate augmentation of calcitriol-dependent VDR activity was caused by EOs of ginger, thyme, coriander and lemongrass. Mixed anti-glucocorticoid and VDR-stimulatory activities were displayed by EOs of turmeric, oregano, dill, caraway, verveine and spearmint. The remaining 19 EOs were inactive against all receptors under investigation. Analyses of GR, AR and VDR target genes by means of RT-PCR confirmed the VDR-stimulatory effects, but could not confirm the anti-glucocorticoid and anti-androgen effects of EOs. In conclusion, although we observed minor effects of several EOs on transcriptional activities of GR, AR and VDR, the toxicological significance of these effects is very low. Hence, 31 EOs of culinary herbs and spices may be considered safe, in terms of endocrine disruption involving receptors GR, AR and VDR.

In vitro profiling of toxic effects of prominent environmental lower-chlorinated PCB congeners linked with endocrine disruption and tumor promotion

The mechanisms contributing to toxic effects of airborne lower-chlorinated PCB congeners (LC-PCBs) remain poorly characterized. We evaluated in vitro toxicities of environmental LC-PCBs found in both indoor and outdoor air (PCB 4, 8, 11, 18, 28 and 31), and selected hydroxylated metabolites of PCB 8, 11 and 18, using reporter gene assays, as well as other functional cellular bioassays. We focused on processes linked with endocrine disruption, tumor promotion and/or regulation of transcription factors controlling metabolism of both endogenous compounds and xenobiotics. The tested LC-PCBs were found to be mostly efficient anti-androgenic (within nanomolar - micromolar range) and estrogenic (at micromolar concentrations) compounds, as well as inhibitors of gap junctional intercellular communication (GJIC) at micromolar concentrations. PCB 8, 28 and 31 were found to partially inhibit the aryl hydrocarbon receptor (AhR)-mediated activity. The tested LC-PCBs were also partial constitutive androstane receptor (CAR) and pregnane X receptor (PXR) agonists, with PCB 4, 8 and 18 being the most active compounds. They were inactive towards other nuclear receptors, such as vitamin D receptor, thyroid receptor α, glucocorticoid receptor or peroxisome proliferator-activated receptor γ. We found that only PCB 8 contributed to generation of oxidative stress, while all tested LC-PCBs induced arachidonic acid release (albeit without further modulations of arachidonic acid metabolism) in human lung epithelial cells. Importantly, estrogenic effects of hydroxylated (OH-PCB) metabolites of LC-PCBs (4-OH-PCB 8, 4-OH-PCB 11 and 4'-OH-PCB 18) were higher than those of the parent PCBs, while their other toxic effects were only slightly altered or suppressed. This suggested that metabolism may alter toxicity profiles of LC-PCBs in a receptor-specific manner. In summary, anti-androgenic and estrogenic activities, acute inhibition of GJIC and suppression of the AhR-mediated activity were found to be the most relevant modes of action of airborne LC-PCBs, although they partially affected also additional cellular targets.

Itraconazole cis-diastereoisomers activate aryl hydrocarbon receptor AhR and pregnane X receptor PXR and induce CYP1A1 in human cell lines and human hepatocytes

Triazole antimycotic itraconazole contains in its structure three chiral centres; therefore, it forms eight stereoisomers. Commercial preparations of itraconazole are a mixture of four cis-diastereoisomers. There is much evidence that efficacy, adverse effects, and toxicity of chiral drugs may be stereospecific. Therefore, we have prepared 4 pure cis-diastereoisomers of itraconazole and investigated their effects on transcriptional activities of xenoreceptors aryl hydrocarbon receptor AhR and pregnane X receptor PXR. Gene reporter assays showed that itraconazole dose-dependently activated both AhR and PXR, and the activation of AhR but not of PXR was enantiospecific. Itraconazole diastereoisomers transformed AhR and PXR into their DNA-binding forms, as demonstrated by electromobility shift assays. Cytochrome P450 CYP1A1 mRNA and protein were induced by itraconazole diastereoisomers in human hepatoma cells HepG2, human skin cells HaCaT, and in primary human hepatocytes. The expression of CYP3A4 in human intestinal LS180 cells was not influenced by itraconazole, but we observed downregulation of CYP3A4 in human hepatocytes. Collectively, we show that itraconazole is a dual activator of AhR and PXR, with differential effects on the target genes for xenoreceptors. The enantiospecific pattern was observed only in gene reporter assays for AhR. The data presented here might be of toxicological and clinical importance.