TABLE 1
List of endogenous AHR activators derived from indole or tryptophan metabolism
| Origin | Compound | Structure | MW | Confirmed Ligand | Human AHR Selective Agonist | Mouse AHR Selective Agonist | References |
|---|---|---|---|---|---|---|---|
| Exogenous | 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) |  | 321.97 | ✓ | ✓ | Poland and Knutson, 1982 | |
| Dietary | lndole-3-carbinol (I3C) |  | 147.18 | ✓ | Bjeldanes et al., 1991; Ito et al., 2007 | ||
| Dietary | lndole-3-acetonitrile (I3ACN) |  | 156.18 | ✓ | Bjeldanes et al., 1991 | ||
| Dietary | 3,3′-Diindolylmethane (DIM) |  | 246.31 | ✓ | Bjeldanes et al., 1991 | ||
| Dietary | 2-(Indol-3-ylmethyl)-3,3′-diindolylmethane (Ltr-1) |  | 369.47 | ✓ | Bjeldanes et al., 1991 | ||
| Dietary | Indolo[3,2-b]carbazole (ICZ) |  | 254.28 | ✓ | Bjeldanes et al., 1991; Jellinck et al., 1993 | ||
| Dietary | 2-(1′H-indole-3′-carbonyl)-thiazole-4-carboxylic acid methyl ester (ITE) |  | 286.31 | ✓ | Song et al., 2002 | ||
| Microbial | Indole |  | 117.15 | ✓ | ✓ | Miller, 1997; Hubbard, 2015 | |
| Microbial | lndole-3-acetic acid (IAA) |  | 175.18 | ✓ | Miller, 1997; Jin et al., 2014 | ||
| Microbial | lndole-3-aldehyde (IAld) |  | 145.16 | ✓ | Bjeldanes et al., 1991; Zelante et al., 2013 | ||
| Microbial | Tryptamine |  | 160.22 | ✓ | Miller, 1997; Jin et al., 2014 | ||
| Microbial | 3-Methyl-indole (skatole) |  | 131.17 | * | Weems and Yost, 2010; Hubbard, 2015 | ||
| Yeast | Tryptamine |  | 248.24 | * | Schrenk et al., 1999; Vlachos et al., 2012 | ||
| Microbial/host metabolism | Indigo |  | 248.24 | ✓ | ✓ | Adachi et al., 2001; Peter Guengerich et al., 2004; Sugihara et al., 2004 | |
| Microbial/host metabolism | Indirubin |  | 262.27 | ✓ | ✓ | Adachi et al., 2001; Peter Guengerich et al., 2004; Sugihara et al., 2004; Flaveny et al., 2009 | |
| Microbial/host metabolism | lndoxyl-3-sulfate (I3S) |  | 213.21 | ✓ | ✓ | Schroeder et al., 2010 | |
| Host metabolism | Kynurenine (Kyn) |  | 208.21 | ✓ | ✓ | Mezrich et al., 2010; Opitz et al., 2011 | |
| Host metabolism | Kynurenic acid (KA) |  | 189.17 | ✓ | ✓ | DiNatale et al., 2010a | |
| Host metabolism | Xanthurenic acid |  | 205.17 | * | ✓ | DiNatale et al., 2010a | |
| Host metabolism | Cinnabarinic acid (CA) |  | 300.22 | * | Lowe et al., 2014 | ||
| UV-light oxidation | 6-Formylindolo[3,2-b]carbazole (FICZ) |  | 284.31 | ✓ | Rannug et al., 1987, 1995 |
MW, molecular weight.
↵* Molecule is an activator of AHR, but further ligand binding assays are required.