Chemopreventive Effects of Soy Protein and Purified Soy Isoflavones on DMBA-Induced Mammary Tumors in Female Sprague-Dawley Rats

Abstract

There are conflicting reports on the effect of soy and its components on mammary carcinogenesis in adult female rats, mainly because of different rodent models that are used in chemoprevention studies. The present study was undertaken to compare the tumor-preventative effects of soy protein isolate (SPI) and two of its isoflavones in a "standard" model that had been used for the identification of many chemopreventive agents. Six groups of female Sprague-Dawley rats were provided with modified cornstarch AIN-76A diets supplemented as follows: no additional agents (control), purified genistein (200 mg/kg diet), purified daidzein (200 mg/kg diet), genistein + daidzein (100 mg/kg diet each), SPI containing normal levels of isoflavones (SPI-n), or SPI depleted of isoflavones (SPI-d). Mammary carcinomas were induced by 7,12-dimethylbenz[a]anthracene (DMBA) introduced 1 wk after the animals began consuming the experimental diets. At the end of the study (120 days after DMBA treatment), no significant differences were found among the six groups with respect to tumor incidence or survival, nor was there a significant reduction in tumor multiplicity in the genistein or genistein + daidzein group. However, there was a 32% reduction in tumor multiplicity in the daidzein and SPI-n groups relative to the control group (P < 0.05). The most effective diet was SPI-d, which produced a 50% reduction in tumor multiplicity relative to the control (P < 0.01). The difference between the SPI-d group and the daidzein or SPI-n group was not significant. Median tumor latency was increased from 53 days in the control group to 68 days in the daidzein group and to 72 days in the SPI-d group, but these differences were not statistically significant. These results show that daidzein and SPI (with normal or low levels of isoflavones) are effective inhibitors of DMBA-induced mammary tumors in adult rats.

Soy, isoflavones, and prevalence of allergic rhinitis in Japanese women: The Osaka Maternal and Child Health Study

“…However, 1 study showed that soy protein isolate depleted of isoflavones, as well as purified isoflavones, was an effective inhibitor of 7,12-dimethylbenzanthraceneinduced mammary tumors in adult rats. 35 Alternatively, uncontrolled dietary or nondietary factors may have confounded the relationship between total soy product and isoflavone intake and the prevalence of allergic rhinitis. Japanese persons who have a quite high intake of soy products are likely to follow traditional Japanese diet or behaviors that may be preventive against allergic disorders.…”

Phytoestrogens oestrogen synthesis and breast cancer

“…In vivo genistein and soy protein has been reported to stimulate the growth of implanted MCF-7 xenografts [79,6] whilst other studies have reported anti-tumour effects in such xenografts and in chemically induced mammary cancers [80][81][82]. A review of the literature concluded that in vivo low concentrations of genistein stimulated cell growth but at high concentrations inhibited growth, thus reflecting studies in vitro [67].…”

Evaluation of synthetic isoflavones on cell proliferation, estrogen receptor binding affinity, and apoptosis in human breast cancer cells

“…The development of drug resistance has encouraged the development and testing of new antiestrogens for the treatment of breast cancer. Because of its tissue-specific antiestrogenic/estrogenic properties, genistein has been considered a natural selective estrogen receptor modulator [13][14][15].…”