Herbal extracts represent a wide spectrum of biologically active ingredients with potential medical applications. By screening minor constituents of jasmine essential oil towards aryl hydrocarbon receptor (AhR) activity using a gene reporter assay (GRA), we found the antagonist effects of jasmone (3-methyl-2-[(2Z)-pent-2-en-1-yl]cyclopent-2-en-1-one). It inhibited 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-, benzo[a]pyrene (BaP)-, and 6-formylindolo[3,2-b]carbazole (FICZ)-triggered AhR-dependent luciferase activity in a concentration-dependent manner. However, the inhibition differed markedly between TCDD, BaP, and FICZ, with the latter being significantly less inhibited. The dose-response analysis confirmed an allosteric type of AhR antagonism. Furthermore, jasmone efficiently inhibited AhR activation by AhR agonists and microbial catabolites of tryptophan (MICTs). TCDD- and FICZ-inducible CYP1A1 expression in primary human hepatocytes was inhibited by jasmone, whereas in the human HepG2 and LS180 cells, jasmone antagonized only TCDD-activated AhR. Jasmone only partially displaced radiolabeled TCDD from its binding to mouse Ahr, suggesting it is not a typical orthosteric ligand of AhR. TCDD-elicited AhR nuclear translocation was not affected by jasmone, whereas downstream signaling events, including the formation of the AhR:ARNT complex and enrichment of the CYP1A1 promoter, were inhibited by jasmone. In conclusion, we show that jasmone is a potent allosteric antagonist of AhR. Such discovery may help to find and/or clarify the use of jasmone in pharmaco- and phytotherapy for conditions where AhR plays a key role.

• Keywords
• AhR, CYP1A1, ChIP, HepG2, LS180, jasmone,
• MeSH
• Cytochrome P-450 CYP1A1 genetics   metabolism   MeSH
• Humans MeSH
• Ligands MeSH
• Mice MeSH
• Polychlorinated Dibenzodioxins * adverse effects   MeSH
• Receptors, Aryl Hydrocarbon * antagonists & inhibitors   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Cytochrome P-450 CYP1A1 MeSH
• jasmone MeSH Browser
• Ligands MeSH
• Polychlorinated Dibenzodioxins * MeSH
• Receptors, Aryl Hydrocarbon * MeSH

The human aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that is a pivotal regulator of human physiology and pathophysiology. Allosteric inhibition of AhR was previously thought to be untenable. Here, we identify carvones as noncompetitive, insurmountable antagonists of AhR and characterize the structural and functional consequences of their binding. Carvones do not displace radiolabeled ligands from binding to AhR but instead bind allosterically within the bHLH/PAS-A region of AhR. Carvones do not influence the translocation of ligand-activated AhR into the nucleus but inhibit the heterodimerization of AhR with its canonical partner ARNT and subsequent binding of AhR to the promoter of CYP1A1. As a proof of concept, we demonstrate physiologically relevant Ahr-antagonism by carvones in vivo in female mice. These substances establish the molecular basis for selective targeting of AhR regardless of the type of ligand(s) present and provide opportunities for the treatment of disease processes modified by AhR.

• MeSH
• Cytochrome P-450 CYP1A1 genetics   MeSH
• Skin * metabolism   radiation effects   MeSH
• Ligands MeSH
• Mice MeSH
• Promoter Regions, Genetic MeSH
• Aryl Hydrocarbon Receptor Nuclear Translocator * genetics   metabolism   MeSH
• Receptors, Aryl Hydrocarbon * genetics   metabolism   MeSH
• Ultraviolet Rays adverse effects   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Cytochrome P-450 CYP1A1 MeSH
• Ligands MeSH
• Aryl Hydrocarbon Receptor Nuclear Translocator * MeSH
• Receptors, Aryl Hydrocarbon * MeSH

The activation of the aryl hydrocarbon receptor (AhR) by xenobiotic compounds was demonstrated to result in the degradation of the androgen receptor (AR). Since prostate cancer is often dependent on AR, it has become a significant therapeutic target. As a result of the emerging concept of bacterial mimicry, we tested whether compounds with indole scaffolds capable of AhR activation have the potential to restrict AR activity in prostate cancer cells. Altogether, 22 indolic compounds were tested, and all of them activated AhR. However, only eight decreased DHT-induced AR luciferase activity. All indoles, which met the AhR-activating and AR-suppressing criteria, decreased the expression of DHT-inducible AR target genes, specifically KLK3 and FKBP5 mRNAs. The reduced AR binding to the KLK3 promoter was confirmed by a chromatin immunoprecipitation (ChIP) assay. In addition, some indoles significantly decreased AR protein and mRNA level. By using CRISPR/Cas9 AhR knockout technology, no relationship between AhR and AR, measured as target gene expression, was observed. In conclusion, some indoles that activate AhR possess AR-inhibiting activity, which seems to be related to the downregulation of AR expression rather than to AR degradation alone. Moreover, there does not seem to be a clear relationship that would connect AhR activation with AR activity suppression in 22Rv1 cells.

• Keywords
• AR, AhR, indoles, prostate cancer, skatole,
• MeSH
• Receptors, Androgen genetics   metabolism   MeSH
• Indoles pharmacology   MeSH
• Humans MeSH
• Cell Line, Tumor MeSH
• Prostatic Neoplasms * genetics   metabolism   MeSH
• Receptors, Aryl Hydrocarbon * genetics   metabolism   MeSH
• Check Tag
• Humans MeSH
• Male MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Receptors, Androgen MeSH
• Indoles MeSH
• Receptors, Aryl Hydrocarbon * MeSH

Aryl hydrocarbon receptor (AHR) plays pivotal roles in intestinal physiology and pathophysiology. Intestinal AHR is activated by numerous dietary, endogenous, and microbial ligands. Whereas the effects of individual compounds on AHR are mostly known, the effects of real physiological mixtures occurring in the intestine have not been studied. Using reporter gene assays and RT-PCR, we evaluated the combinatorial effects (3520 combinations) of 11 microbial catabolites of tryptophan (MICTs) on AHR. We robustly (n = 30) determined the potencies and relative efficacies of single MICTs. Synergistic effects of MICT binary mixtures were observed between low- or medium-efficacy agonists, in particular for combinations of indole-3-propionate and indole-3-lactate. Combinations comprising highly efficacious agonists such as indole-3-pyruvate displayed rather antagonist effects, caused by saturation of the assay response. These synergistic effects were confirmed by RT-PCR as CYP1A1 mRNA expression. We also tested mimic multicomponent and binary mixtures of MICTs, prepared based on the metabolomic analyses of human feces and colonoscopy aspirates, respectively. In this case, AHR responsiveness did not correlate with type of diet or health status, and the indole concentrations in the mixtures were determinative of gross AHR activity. Future systematic research on the synergistic activation of AHR by microbial metabolites and other ligands is needed.

• Keywords
• aryl hydrocarbon receptor, indole derivatives, microbiome, mimic mixtures, tryptophan metabolites,
• MeSH
• Cytochrome P-450 CYP1A1 genetics   metabolism   MeSH
• Indoles metabolism   pharmacology   MeSH
• Humans MeSH
• Ligands MeSH
• RNA, Messenger metabolism   MeSH
• Propionates MeSH
• Pyruvates MeSH
• Receptors, Aryl Hydrocarbon * metabolism   MeSH
• Intestines MeSH
• Tryptophan * metabolism   pharmacology   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Cytochrome P-450 CYP1A1 MeSH
• Indoles MeSH
• Ligands MeSH
• RNA, Messenger MeSH
• Propionates MeSH
• Pyruvates MeSH
• Receptors, Aryl Hydrocarbon * MeSH
• Tryptophan * MeSH

Aryl hydrocarbon receptor (AhR) is a critical player in the crosstalk between the gut microbiota and its host. However, factors regulating AhR within the gut, which is a complex metabolomic environment, are poorly understood. This study investigates the effect of a combination of metabolites on the activation mechanism of AhR. AhR activity was evaluated using both a luciferase reporter system and mRNA levels of AhR target genes on human cell lines and human colonic explants. AhR activation was studied by radioligand-binding assay, nuclear translocation of AhR by immuofluorescence and protein co-immunoprecipitation of AhR with ARNT. Indirect activation of AhR was evaluated using several tests and inhibitors. The promoter of the target gene CYP1A1 was studied both by chromatin immunoprecipitation and by using an histone deacetylase HDAC inhibitor (iHDAC). Short-chain fatty acids, and butyrate in particular, enhance AhR activity mediated by endogenous tryptophan metabolites without binding to the receptor. This effect was confirmed in human intestinal explants and did not rely on activation of receptors targeted by SCFAs, inhibition of AhR degradation or clearance of its ligands. Butyrate acted directly on AhR target gene promoter to reshape chromatin through iHDAC activity. Our findings revealed that butyrate is not an AhR ligand but acts as iHDAC leading to an increase recruitment of AhR to the target gene promoter in the presence of tryptophan-derived AhR agonists. These data contribute to a novel understanding of the complex regulation of AhR activation by gut microbiota-derived metabolites.

• Keywords
• AhR, CYP1A1, FICZ, HDAC, Microbiota, SCFAs, butyrate, metabolites, tryptophan,
• MeSH
• Butyrates pharmacology   MeSH
• Humans MeSH
• Ligands MeSH
• Receptors, Aryl Hydrocarbon * genetics   metabolism   MeSH
• Gastrointestinal Microbiome * MeSH
• Tryptophan MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Butyrates MeSH
• Ligands MeSH
• Receptors, Aryl Hydrocarbon * MeSH
• Tryptophan MeSH

The efforts for therapeutic targeting of the aryl hydrocarbon receptor (AhR) have emerged in recent years. We investigated the effects of available antimigraine triptan drugs, having an indole core in their structure, on AhR signaling in human hepatic and intestinal cells. Activation of AhR in reporter gene assays was observed for Avitriptan and to a lesser extent for Donitriptan, while other triptans were very weak or no activators of AhR. Using competitive binding assay and by homology docking, we identified Avitriptan as a low-affinity ligand of AhR. Avitriptan triggered nuclear translocation of AhR and increased binding of AhR in CYP1A1 promotor DNA, as revealed by immune-fluorescence microscopy and chromatin immune-precipitation assay, respectively. Strong induction of CYP1A1 mRNA was achieved by Avitriptan in wild type but not in AhR-knockout, immortalized human hepatocytes, implying that induction of CYP1A1 is AhR-dependent. Increased levels of CYP1A1 mRNA by Avitriptan were observed in human colon carcinoma cells LS180 but not in primary cultures of human hepatocytes. Collectively, we show that Avitriptan is a weak ligand and activator of human AhR, which induces the expression of CYP1A1 in a cell-type specific manner. Our data warrant the potential off-label therapeutic application of Avitriptan as an AhR-agonist drug.

• Keywords
• Antimigraine drugs, Aryl Hydrocarbon Receptor, Triptans, repurposing,
• MeSH
• Enzyme Activation drug effects   MeSH
• Cytochrome P-450 CYP1A1 genetics   MeSH
• Hepatocytes metabolism   MeSH
• Cells, Cultured MeSH
• Humans MeSH
• Ligands MeSH
• Models, Molecular MeSH
• Organ Specificity MeSH
• Drug Repositioning MeSH
• Promoter Regions, Genetic drug effects   MeSH
• Receptors, Aryl Hydrocarbon agonists   chemistry   metabolism   MeSH
• Molecular Docking Simulation MeSH
• Intestinal Mucosa metabolism   MeSH
• Sulfonamides pharmacology   MeSH
• Basic Helix-Loop-Helix Transcription Factors agonists   chemistry   metabolism   MeSH
• Tryptamines pharmacology   MeSH
• Up-Regulation MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• AHR protein, human MeSH Browser
• avitriptan MeSH Browser
• CYP1A1 protein, human MeSH Browser
• Cytochrome P-450 CYP1A1 MeSH
• Ligands MeSH
• Receptors, Aryl Hydrocarbon MeSH
• Sulfonamides MeSH
• Basic Helix-Loop-Helix Transcription Factors MeSH
• Tryptamines MeSH

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.

• Keywords
• aryl hydrocarbon receptor, indoles, microbiome, tryptophan,
• MeSH
• Cytochrome P-450 CYP1A1 genetics   MeSH
• Gene Expression MeSH
• Indoles MeSH
• Humans MeSH
• Ligands MeSH
• Metabolic Networks and Pathways MeSH
• Protein Multimerization MeSH
• Mice MeSH
• Cell Line, Tumor MeSH
• Promoter Regions, Genetic MeSH
• Receptors, Aryl Hydrocarbon agonists   metabolism   MeSH
• Genes, Reporter MeSH
• Gastrointestinal Microbiome * drug effects   MeSH
• Basic Helix-Loop-Helix Transcription Factors agonists   metabolism   MeSH
• Tryptophan metabolism   MeSH
• Protein Binding MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• AHR protein, human MeSH Browser
• CYP1A1 protein, human MeSH Browser
• Cytochrome P-450 CYP1A1 MeSH
• indole MeSH Browser
• Indoles MeSH
• Ligands MeSH
• Receptors, Aryl Hydrocarbon MeSH
• Basic Helix-Loop-Helix Transcription Factors MeSH
• Tryptophan MeSH

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.

• Keywords
• Aryl hydrocarbon receptor, Entero-hepatic axis, Methylindoles, Microbial catabolites, Tryptophan,
• MeSH
• Cytochrome P-450 CYP1A1 antagonists & inhibitors   biosynthesis   genetics   MeSH
• Enzyme Induction MeSH
• Hepatocytes drug effects   enzymology   MeSH
• Indoles pharmacology   MeSH
• Cytochrome P-450 Enzyme Inducers pharmacology   MeSH
• Cytochrome P-450 Enzyme Inhibitors pharmacology   MeSH
• Microsomes, Liver drug effects   enzymology   MeSH
• Middle Aged MeSH
• Humans MeSH
• Young Adult MeSH
• Cell Line, Tumor MeSH
• Colonic Neoplasms enzymology   MeSH
• Receptors, Aryl Hydrocarbon agonists   genetics   metabolism   MeSH
• Aged MeSH
• Basic Helix-Loop-Helix Transcription Factors agonists   genetics   metabolism   MeSH
• Dose-Response Relationship, Drug MeSH
• Check Tag
• Middle Aged MeSH
• Humans MeSH
• Young Adult MeSH
• Male MeSH
• Aged MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• AHR protein, human MeSH Browser
• CYP1A1 protein, human MeSH Browser
• Cytochrome P-450 CYP1A1 MeSH
• Indoles MeSH
• Cytochrome P-450 Enzyme Inducers MeSH
• Cytochrome P-450 Enzyme Inhibitors MeSH
• Receptors, Aryl Hydrocarbon MeSH
• Basic Helix-Loop-Helix Transcription Factors MeSH