In vivo production and enzyme-inducing activity of indolo[3,2-6]carbazole

Indolo[3,2-6]carbazole (ICZ) is a potent Ah receptor agonist produced during the oligomerization of indole-3-carbinol (I3C), a breakdown product of the glucobrassicin present in food plants of the Brassica genus. Levels of ICZ present in the feces, urine, gastrointestinal tracts, and livers of rats fed on I3C- or cabbage-supplemented basal diet were 16-fold to over 100-fold higher than levels for animals on the basal diet alone. Levels of ICZ significantly lower than the basal levels for conventional rats were present in feces of germfree rats, indicating that gut bacteria are important for the production of ICZ from essential dietary constituents. Low levels of ICZ in extracts of human feces were also detected. The results suggest further that ICZ by itself may not be responsible for the enzyme-inducing activity of orally administered I3C or its precursors.