Journal Article

Effects of Indole-3-Carbinol and phenethyl isothiocyanate on colon carcinogenesis induced by azoxymethane in rats

Andrea Y.A. Plate and Daniel D. Gallaher

in Carcinogenesis

Volume 27, issue 2, pages 287-292
Published in print February 2006 | ISSN: 0143-3334
Published online August 2005 | e-ISSN: 1460-2180 | DOI: http://dx.doi.org/10.1093/carcin/bgi210
Effects of Indole-3-Carbinol and phenethyl isothiocyanate on colon carcinogenesis induced by azoxymethane in rats

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Indole-3-carbinol (I3C) and phenethyl isothiocyanate (PEITC) are breakdown products of the glucosinolates glucobrassicin and gluconasturtiin, respectively, and are thought to reduce carcinogen activation by P450 enzymes. To assess the effects of these compounds on colon cancer risk, rats were divided into five groups and fed the following diets: control diet (AIN-93G), or diets with PEITC or I3C added to the control diet: high-PEITC (3.37 mmols/kg diet—high level of PEITC), low-PEITC (0.67 mmols/kg—low level of PEITC), high-I3C (6.8 mmols/kg—high level of I3C) and low-I3C (1.36 mmols/kg—low level of I3C). Diets were fed for 2 weeks before and 10 weeks after administration of the colon carcinogen azoxymethane. Precancerous lesion (aberrant crypt foci, ACF) number in the distal colon was significantly lower in both high-I3C and low-I3C groups (6.9 ± 0.8 and 5.9 ± 0.59 per cm2, respectively) when compared with the control group (10.4 ± 0.9). No significant difference in ACF number was found between the PEITC group and the control group. ACF expressing sialomucin, thought to indicate ACF more likely to progress to tumors, were greater in the high-PEITC group (13 ± 3) than the control (5.6 ± 2). Mucin-depleted ACF, suggested to have the greatest tumorigenic potential, tended to be lower in the low-I3C group (P < 0.06) compared with the control group. Mucosal apoptotic and cell proliferation labeling indices did not differ among groups, suggesting that reduction in the ACF number by I3C does not involve alterations in mucosal cell kinetics. No significant differences were found among the groups in hepatic cytochrome P450 2E1 (CYP2E1) activity, the first enzyme involved in activation of azoxymethane. However, there was increased activity of NADPH- and NADH reductases with high-I3C, which are the enzymes involved in the transfer of reducing equivalents to cytochrome P450. These results suggest that I3C lowers colon cancer risk through a mechanism not involving reduction of carcinogen activation by CYP2E1.

Keywords: AC, aberrant crypt; ACF, aberrant crypt foci; ALI, apoptotic labeling index; AOM, azoxymethane; CPLI, cell proliferation labeling index; CYP2E1, cytochrome P450 2E1; I3C, indole-3-carbinol; MDF, mucin-depleted foci; PEITC, phenethyl isothiocyanate; SOF, foci producing sialomucin only; SPF, sialomucin-producing foci

Journal Article.  5455 words.  Illustrated.

Subjects: Clinical Cytogenetics and Molecular Genetics

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