Table 2.

Aryl hydrocarbon receptor (AHR) ligands

Ligand	EC50 (mol/kg)	Metabolized?	References
HAH (TCDD)	10−12	No	116,117
PAH (BaP)	10−5–10−6	Yes	117,118
PCB (pentaCB)	10−7	Yes	104
FICZ	10−10–10−12	Yes	109,119
Indirubin	10−8	Yes	45,120
Lipoxin-4a	10−9	Yes	121
Bilirubin	10−6	Yes	122
ITE	10−9	?	123,124
ICZ	10−8–10−10	Yes	116,125

This table contains some of the best studied AHR ligands. The EC₅₀ is the dose of the ligand that leads to 50% of the maximal cytochrome P450 gene induction. These are estimates and are dependent on many factors, including cell type and AHR allele. Some AHR ligands are metabolized enzymatically and are short-lived. The EC₅₀s of these ligands are sensitive to the timing of induction.

FICZ, 6-formylindolo(3,2-b)carbazole; ICZ, indolo(3,2-b)carbazole; ITE, 2-(1′H-indole-3′-carbonyl)-thiazole-4-carboxylic acid methyl ester; PAH, polycyclic aromatic hydrocarbon; PCB, polychlorinated biphenyl; TCDD, 2,3,7,8 tetrachlorodibenzo-p-dioxin.