Journal Article

Inhibitory effects of <i>Bifidobacterium</i>-fermented soy milk on 2-amino-1-methyl-6-phenylimidazo[4,5-<i>b</i>]pyridine-induced rat mammary carcinogenesis, with a partial contribution of its component isoflavones

Toshihisa Ohta, Seiichi Nakatsugi, Kouji Watanabe, Toshihiko Kawamori, Fumiyasu Ishikawa, Masami Morotomi, Shigeyuki Sugie, Toshiya Toda, Takashi Sugimura and Keiji Wakabayashi

in Carcinogenesis

Volume 21, issue 5, pages 937-941
Published in print May 2000 | ISSN: 0143-3334
Published online May 2000 | e-ISSN: 1460-2180 | DOI: http://dx.doi.org/10.1093/carcin/21.5.937
Inhibitory effects of Bifidobacterium-fermented soy milk on 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine-induced rat mammary carcinogenesis, with a partial contribution of its component isoflavones

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High consumption of soybean and soybean-related products is hypothesized to contribute to protection against breast cancer. Soybean is a rich source of genistein, a putative cancer chemopreventive agent. Fermented soy milk (FSM), which is made of soy milk fermented with the Bifidobacterium breve strain Yakult, contains larger amounts of the isoflavone aglycones genistein and daidzein than unfermented soy milk. In the present study, we examined the effects of FSM and its component isoflavone mixture (genistein:daidzein 4:1) on 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-induced mammary carcinogenesis in rats. Starting at 7 weeks of age, female Sprague–Dawley rats were given PhIP at a dose of 85 mg/kg body wt by intragastric administration four times a week for 2 weeks. They were fed control high fat basal diet or experimental high fat diet containing 10% FSM or 0.02 or 0.04% isoflavone mixture during and after carcinogen exposure. The incidences (percentage of rats with tumors) of mammary gland tumors were 71% in the control diet group, 51% in the FSM group and 68 and 61% in the groups treated with isoflavone mixture at 0.02 and 0.04%, respectively. Mammary tumor multiplicities (number of tumors per rat) were 1.2 ± 0.2 for 10% FSM, 2.2 ± 0.4 for 0.02% isoflavone mixture and 1.5 ± 0.3 for 0.04% isoflavone mixture, being clearly smaller than the control diet value (2.6 ± 0.5). Furthermore, feeding of FSM and the isoflavone mixture at both doses reduced the sizes of mammary tumors. Since the amounts of isoflavones in 10% FSM are approximately equivalent to those in the 0.02% isoflavone mixture, the chemopreventive activity of FSM could be partly attributable to the presence of isoflavones such as genistein and daidzein.

Keywords: FSM, fermented soy milk; HCAs, heterocyclic amines; PhIP, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine.

Journal Article.  3645 words.  Illustrated.

Subjects: Clinical Cytogenetics and Molecular Genetics

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