I3C Use Increases Toxic Estrogen (4-Hydroxy Estrogen [4-OH E])

I3C Use Increases Toxic Estrogen (4-Hydroxy Estrogen [4-OH E])

Differences in the hepatic P450-dependent metabolism of estrogen and tamoxifen in response to treatment of rats with 3,3'-diindolylmethane and its parent compound indole-3-carbinol.

Parkin DR, Malejka-Giganti D.

Veterans Affairs Medical Center, Minneapolis, MN 55417, USA.

Cancer Detect Prev. 2004;28(1):72-9.

Indole-3-carbinol (I3C), present in cruciferous vegetables, and its major in vivo product 3,3'-diindolylmethane (DIM), have been reported to suppress estrogen-responsive cancers. This effect may be mediated through the modification of cytochrome P450 (CYP) complement and activities leading to estrogen detoxification. We examined the effects of a 4-day treatment of female Sprague-Dawley rats with DIM at 8.4 and 42 mg/kg body weight (bwt), on the hepatic CYP protein level, CYP1A1, 1A2, 2B1/2 and 3A1/2 probe activities and CYP-dependent metabolism of 17beta-estradiol (E2) and estrone (E1). At 42 mg/kg bwt, DIM effected a small increase (2.8-fold) in CYP1A1 activity, and at both dose levels it reduced CYP3A1/2 activity by approximately 40%. At the higher dose level, DIM decreased the rates of oxidation of E2 to 4-OH-E2, 4-OH-E1, 6alpha-OH-E2 and 6(alpha+beta)-OH-E1 by 39, 44, 71 and 60%, respectively, and E1 to 6(alpha+beta)-OH-E1 by 39%. These effects were considerably different from those of I3C reported by us previously. We also examined the effects of DIM and I3C on the hepatic microsomal metabolism of tamoxifen (TAM). Whereas metabolism of TAM was unaffected by DIM, formation of N-desmethyl-TAM (and its presumed derivative) was increased approximately 3-fold by I3C at 250 mg/kg bwt. Since N-desmethyl-TAM is transformed to a genotoxic metabolite, dietary exposure to I3C may enhance hepatic carcinogenicity of TAM in the rat. The differences between I3C and DIM in CYP-mediated activities and metabolism indicate that DIM is not a proximate intermediate in the mechanism of action of I3C.

Changes in levels of urinary estrogen metabolites after oral indole-3-carbinol treatment in humans.

Michnovicz JJ, Adlercreutz H, Bradlow HL.

Rockefeller University Hospital and The Institute for Hormone Research, New York, NY 10016, USA.

J Natl Cancer Inst. 1997 May 21;89(10):718-23.

BACKGROUND: The oxidative metabolism of estrogens in humans is mediated primarily by cytochrome P450, many isoenzymes of which are inducible by dietary and pharmacologic agents. One major pathway, 2-hydroxylation, is induced by dietary indole-3-carbinol (I3C), which is present in cruciferous vegetables (e.g., cabbage and broccoli). PURPOSE: Because the pool of available estrogen substrates for all pathways is limited, we hypothesized that increased 2-hydroxylation of estrogens would lead to decreased activity in competing metabolic pathways. METHODS: Urine samples were collected from subjects before and after oral ingestion of I3C (6-7 mg/kg per day). In the first study, seven men received I3C for 1 week; in the second study, 10 women received I3C for 2 months. A profile of 13 estrogens was measured in each sample by gas chromatography-mass spectrometry. RESULTS: In both men and women, I3C significantly increased the urinary excretion of C-2 estrogens. The urinary concentrations of nearly all other estrogen metabolites, including levels of estradiol, estrone, estriol, and 16alpha-hydroxyestrone, were lower after I3C treatment. CONCLUSIONS: These findings support the hypothesis that I3C-induced estrogen 2-hydroxylation results in decreased concentrations of several metabolites known to activate the estrogen receptor. This effect may lower estrogenic stimulation in women. IMPLICATIONS: I3C may have chemopreventive activity against breast cancer in humans, although the long-term effects of higher catechol estrogen levels in women require further investigation.