Abstract:
Indole-3-carbinol (I3C), the most abundant metabolite of glucobrassicins, is
found in cruciferous vegetables such as broccoli, Brussels sprouts, cabbage and
cauliflower. I3C has been shown to have anticarcinogenic activity against many
chemical carcinogens in multiple target organs in animal models. However, the
anticarcinogenic activity of I3C is considered indirect since I3C is converted
irreversibly to its dimer and other condensation products under the low pH
conditions of the stomach. 3,3'-Diindolylmethane (DIM), a primary breakdown
product of I3C, also shows anticarcinogenic activity in a manner similar to I3C.
Our laboratory has shown that I3C dramatically induces CYP1A (cytochrome
P4501A) and inhibits FMO1 (flavin-containing monooxygenase form 1) expression
in rat liver and intestine. We also showed that I3C induced hepatic CYP1A1/1A2 in
male guinea pig, mouse and rabbit. There was no significant difference in FMO1
protein between control and I3C treated groups in these three species. The
simultaneous induction of CYP and repression of FMO may alter the metabolism,
disposition and toxicity of drugs and/or xenobiotics that are substrates of both
monooxygenases such as N, N-dimethylaniline, nicotine and tamoxifen. In liver
microsomes from rats fed I3C or DIM, the ratio of FMO to CYP metabolites of the
three chosen compounds decreased, mostly due to a reduction of N-oxide FMO-dependent
formation. Major concerns associated with human dietary I3C
supplementation are its estrogenic effect as seen in trout and its ability to induce
cytochrome P450s involved in bioactivation. Evidence presented here also
demonstrated a dose response of vitellogenin induction after 2 weeks of dietary I3C
or DIM in rainbow trout. In immature female rat, I3C and DIM significantly
induced uterine peroxidase, hepatic CYP1A1/1A2 and CYP2B1/2B2. All our
results suggested that I3C and/or DIM, in combination with other drugs that are
substrates for both monooxygenases, could alter the therapeutic effects or toxicity
of drugs. Also the estrogenic activity in rainbow trout and immature female rat
should be considered when assessing risk for the use of I3C and DIM as
chemopreventive agents or dietary supplements.
