Journal Article

Inhibition of azoxymethane-induced colon carcinogenesis in male F344 rats by the citrus limonoids obacunone and limonin

Takuji Tanaka, Masayo Maeda, Hiroyuki Kohno, Manabu Murakami, Seiko Kagami, Masaki Miyake and Keiji Wada

in Carcinogenesis

Volume 22, issue 1, pages 193-198
Published in print January 2001 | ISSN: 0143-3334
Published online January 2001 | e-ISSN: 1460-2180 | DOI: http://dx.doi.org/10.1093/carcin/22.1.193
Inhibition of azoxymethane-induced colon carcinogenesis in male F344 rats by the citrus limonoids obacunone and limonin

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The modifying effects of dietary administration of the citrus limonoids obacunone and limonin on azoxymethane (AOM)-induced colon tumorigenesis were investigated in two experiments in male F344 rats. In a pilot study, we examined the modifying effects of obacunone and limonin on AOM-induced (20 mg/kg body wt, once a week for 2 weeks) formation of aberrant crypt foci (ACF). Dietary feeding of both compounds at dose levels of 200 and 500 p.p.m. during AOM exposure for 4 weeks (`initiation' feeding) or after AOM treatment for 4 weeks (`post-initiation' feeding) significantly inhibited ACF formation (55–65% reduction by `initiation' feeding, P < 0.001; 28–42% reduction by `post-initiation' feeding, P < 0.05–0.002). In a long-term study designed to confirm the protective effects of obacunone and limonin on ACF development, one group was treated with AOM alone and another four groups received the carcinogen treatment plus diets containing 500 p.p.m. test compounds for 3 weeks (initiation phase) or 29 weeks (post-initiation phase). Two groups were treated with obacunone or limonin alone (500 p.p.m. in diet) and one group was maintained on the basal diet. At the termination of the study, dietary exposure to obacunone or limonin during the initiation phase was found to have significantly reduced the incidence of colonic adenocarcinoma (72 versus 25 or 6%, P = 0.004 or 0.00003). Obacunone or limonin feeding during the post-initiation phase also reduced the frequency of colonic adenocarcinoma (72 versus 13%, P = 0.0002). Our results suggest that the citrus limonoids obacunone and limonin might be useful for the prevention of human colon cancers.

Keywords: ACF, aberrant crypt foci; AOM, azoxymethane; GST, glutathione S-transferase; QR, quinone reductase.

Journal Article.  4556 words.  Illustrated.

Subjects: Clinical Cytogenetics and Molecular Genetics

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