Effects of a soybean isoflavone mixture on carcinogenesis in prostate and seminal vesicles of F344 rats.

Several epidemiological studies have suggested an inverse association between the risk of prostate cancer and intake of soybeans and their products. In vitro data pointing to possible anti-carcinogenic properties of the soybean isoflavone, genistein, led us to investigate the chemopreventive potential of soybean isoflavones in a rat carcinogenesis model induced by 3,2'-dimethyl-4-aminobiphenyl (DMAB) and testosterone propionate (TP). Animals received DMAB s.c. injections at 2-week intervals for the first 20 weeks and implanted silicon tubes containing 40 mg of TP, replaced at 6-week intervals throughout the experiment. The soybean isoflavone mixture consisting of 74% genistein and 21% daidzein was mixed in basal diet (AIN-76A) at concentrations of 100 and 400 ppm and fed to F344 male rats throughout the experiment. Rats treated with carcinogens and administered isoflavone mixture at 100 and 400 ppm developed adenocarcinomas at incidences of 35% and 29%, respectively, in the prostate and seminal vesicles, whereas the figure was 60% for those maintained on control diet. Feeding of the isoflavone mixture at 100 and 400 ppm significantly inhibited the number of argyrophilic nucleolar organizer regions (AgNORs) in adenocarcinomas of the accessory sex glands as compared to those of rats fed control diet. No influence on the development of neoplastic lesions originating in other organs was noted. The results of this study provide evidence that soybean isoflavones may have potential as chemopreventive agents against carcinogenesis in the prostate.     

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

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.     

Beef Tallow, but Not Perilla or Corn Oil, Promotion of Rat Prostate and Intestinal Carcinogenesis by 3,2-Dimethyl-4-aminobiphenyl

The modifying effects of three kinds of fat (corn oil, beef tallow or perilla oil, each at 20% in the diet) on F344 rat prostate carcinogenesis induced by 3,2-dimethyl-4-aminobiphenyl (DMAB) were investigated. Non-invasive carcinomas of the ventral prostate were induced by DMAB alone and invasive carcinomas of the other prostate lobes and seminal vesicles by DMAB and testosterone propionate (TP). Eight groups of F344 rats were initiated with 50 mg/kg body weight of DMAB at 2-week intervals for the first 20 weeks, four also receiving TP, extended until week 60. The animals received basal chow powder diet or one of three high fat diets throughout the experiment (60 weeks). One further group served as a non-carcinogen-treated control maintained on basal chow powder diet. Beef tallow significantly increased the development of ventral prostate carcinomas with DMAB alone (from 15 to 45%, P<0.05), while perilla oil reduced the incidence of prostatic intraepithelial neoplasia (PIN) in the ventral lobe of rats given DMAB + TP (from 70 to 10%, P<0.01), but not in those given DMAB alone. No other effects of high fats were observed regarding PIN or invasive cancers of the dorsolateral and anterior prostate or seminal vesicles. A satellite experiment demonstrated that all high fat diets for 4 weeks increased the 5-bromo-2-deoxyuridine (BrdU) labeling index of prostate epithelial cells, suggesting that a high fat intake, irrespective of the fatty acid composition, may accelerate cell kinetics in the prostate. Of the three high fat diets, beef tallow was also found to increase intestinal carcinogenesis. Thus, the present data revealed carcinogenesis in the prostate and intestine to be promoted by beef tallow.     

Sequential Observation of Rat Prostate Lesion Development Induced by 3,2'-Dimethyl-4-aminobiphenyl and Testosterone

3,2'-Dimethyl-4-aminobiphenyl (DMAB), when combined with high doses of testosterone propionate (TP) induces invasive adenocarcinomas with metastatic potential in the rat prostate. The processes underlying this tumor development, including the involvement of atypical hyperplasias, were sequentially investigated in F344 rats. DMAB was given subcutaneously at a dose of 50 mg/kg body weight 10 times at 2-week intervals. TP was administered chronically (in Silastic tubes) from the beginning of the experiment or after the DMAB administration until termination (week 60). Invasive adenocarcinomas were induced in the lateral and anterior prostate as well as the seminal vesicles. Atypical hyperplasias appeared from an early stage, with the later appearance of cancers being closely associated with such foci of morphological alteration. The findings confirm that combined administration of DMAB and pharmacological doses of TP yields invasive adenocarcinomas in the rat prostate and provide further support for the conclusion that atypical hyperplasias are premalignant lesions.     

Induction of invasive carcinomas in the accessory sex organs other than the ventral prostate of rats given 3,2'-dimethyl-4-aminobiphenyl and testosterone propionate

The promotion effects of testosterone propionate (TP) on prostate carcinogenesis were investigated in F344 rats given the prostatic carcinogen, 3,2'-dimethyl-4-aminobiphenyl (DMAB). One group of animals received s.c. DMAB injections at a dose of 50 mg/kg body weight at 2-week intervals for a total of 10 injections along with s.c. implantations of TP-containing Silastic tubes. A second experimental group of rats was given DMAB at the same dose and intervals but each injection of DMAB was combined with 3 prior consecutive daily 100-mg/kg body weight s.c. injections of TP. After cessation of carcinogen administration, animals in these two groups received TP implants from week 21 to the end of the experiment. All surviving animals were killed at week 56 and accessory sex gland tumor incidences were compared to those in DMAB alone and other appropriate control groups. The groups given TP plus DMAB and subsequent long term administration of TP developed lesions of the dorsolateral prostate, seminal vesicles, and coagulating glands which were all invasive adenocarcinomas. Incidences were 84.2% (16 of 19 rats) and 66.7% (12 of 18 rats), respectively. Macroscopic large tumors were induced in 13 animals among which 8 demonstrated metastasis to the abdominal cavity, liver, or lung. None of the control groups except for the group given TP injections plus DMAB had equivalent tumors. Development of carcinomas of the ventral prostate, which were all of in situ type, were not increased by subsequent treatment with TP. These data thus clearly showed that TP can exert strong enhancing effects on tumor development in the dorsolateral prostate, seminal vesicles, and coagulating glands but not in the ventral prostate.     

Suppressive effects of dietary genistin and daidzin on rat prostate carcinogenesis.

High intake of phytoestrogens through soybeans and their products is thought to be associated with low incidences of prostate and / or breast cancer in Asian countries. Possible chemopreventive effects of genistin or daidzin on rat prostate carcinogenesis were therefore investigated. Male F344 rats were given 10 biweekly subcutaneous injections of 3,2'-dimethyl-4-aminobiphenyl (DMAB) and then either genistin or daidzin in the diet at a concentration of 0.1% for 40 weeks. Other groups of rats given DMAB were treated with genistin or daidzin together with a high dose of testosterone propionate (TP). Both genistin and daidzin reduced the numbers of ventral prostate carcinomas (P < 0.05), with a tendency for decrease in incidence. Invasive carcinomas which developed in the anterior prostate and seminal vesicles with TP were, however, not influenced by the two isoflavones. Thus, the present data suggest that genistin and daidzin possess anti-cancer effects at relatively early stages of prostate cancer development, providing experimental support for epidemiological findings.     

Suppressive Effects of Dietary Genistin and Daidzin on Rat Prostate Carcinogenesis

High intake of phytoestrogens through soybeans and their products is thought to be associated with low incidences of prostate and/or breast cancer in Asian countries. Possible chemopreventive effects of genistin or daidzin on rat prostate carcinogenesis were therefore investigated. Male F344 rats were given 10 biweekly subcutaneous injections of 3,2'-dimethyl-4-aminobiphenyl (DMAB) and then either genistin or daidzin in the diet at a concentration of 0.1% for 40 weeks. Other groups of rats given DMAB were treated with genistin or daidzin together with a high dose of testosterone propionate (TP). Both genistin and daidzin reduced the numbers of ventral prostate carcinomas (P<0.05), with a tendency for decrease in incidence. Invasive carcinomas which developed in the anterior prostate and seminal vesicles with TP were, however, not influenced by the two isoflavones. Thus, the present data suggest that genistin and daidzin possess anti-cancer effects at relatively early stages of prostate cancer development, providing experimental support for epide-miological findings.     

Beef tallow, but not perilla or corn oil, promotion of rat prostate and intestinal carcinogenesis by 3,2'-dimethyl-4-aminobiphenyl.

The modifying effects of three kinds of fat (corn oil, beef tallow or perilla oil, each at 20% in the diet) on F344 rat prostate carcinogenesis induced by 3,2'-dimethyl-4-aminobiphenyl (DMAB) were investigated. Non-invasive carcinomas of the ventral prostate were induced by DMAB alone and invasive carcinomas of the other prostate lobes and seminal vesicles by DMAB and testosterone propionate (TP). Eight groups of F344 rats were initiated with 50 mg / kg body weight of DMAB at 2-week intervals for the first 20 weeks, four also receiving TP, extended until week 60. The animals received basal chow powder diet or one of three high fat diets throughout the experiment (60 weeks). One further group served as a non-carcinogen-treated control maintained on basal chow powder diet. Beef tallow significantly increased the development of ventral prostate carcinomas with DMAB alone (from 15 to 45%, P < 0.05), while perilla oil reduced the incidence of prostatic intraepithelial neoplasia (PIN) in the ventral lobe of rats given DMA + TP (from 70 to 10%, P < 0.01), but not in those given DMAB alone. No other effects of high fats were observed regarding PIN or invasive cancers of the dorsolateral and anterior prostate or seminal vesicles. A satellite experiment demonstrated that all high fat diets for 4 weeks increased the 5-bromo-2-deoxyuridine (BrdU) labeling index of prostate epithelial cells, suggesting that a high fat intake, irrespective of the fatty acid composition, may accelerate cell kinetics in the prostate. Of the three high fat diets, beef tallow was also found to increase intestinal carcinogenesis. Thus, the present data revealed carcinogenesis in the prostate and intestine to be promoted by beef tallow.     

Lack of modifying effects of 4-ter t-octylphenol and benzyl butyl phthalate on 3,2-dimethyl-4-aminobiphenyl-induced prostate carcinogenesis in rats

The modifying effects of dietary feeding of two estrogenic compounds, 4-tert-octylphenol (tOP) and benzyl butyl phthalate (BBP), on 3,2-dimethyl-4-aminobiphenol (DMAB)-induced prostatic carcinogenesis were investigated in male F344 rats. We also assessed the effects of the test compounds on the proliferating cell nuclear antigen (PCNA) index in induced neoplasms, prostatic intra-epithelial neoplasm (PIN), and non-lesional glands in the prostate. To induce prostatic neoplasms, rats were given subcutaneous injections of DMAB (25 mg/kg body weight) every other week, 10 times in total. They also received the experimental diet containing 10 or 100 ppm tOP and BBP for 40 weeks, starting 1 week after the last dosing of DMAB. DMAB exposure produced prostatic adenocarcinoma with an incidence of 41.2% at the end of the study (week 60). Dietary administration of tOP and BBP did not affect the incidence of prostatic adenocarcinoma: 43.8% in the DMAB --> 10 ppm tOP group; 25.0% in the DMAB --> 100 ppm tOP group; 43.8% in the DMAB --> 10 ppm BBP group; and 43.8% in the DMAB --> 100 ppm BBP group. The PCNA indices in adenocarcinomas, PIN, and non-lesional glands in rats treated with DMAB and tOP or BBP were slightly lower than that of the DMAB alone group, but the differences were not statistically significant. These results might suggest that dietary feeding of the estrogenic compounds tOP and BBP did not modulate DMAB-induced prostatic carcinogenesis in rats.     

Low-dose dietary phytoestrogen abrogates tamoxifen-associated mammary tumor prevention

Wild-type erbB-2/neu transgenic mice were used to study the interactions between tamoxifen and dietary phytoestrogens (or isoflavones) by dose and form in vivo. Mice were randomized to one of four dietary formulas and implanted with an 8-week continuous-release tamoxifen or placebo pellet at 8 weeks of age. In placebo-treated mice, soy meal diet (but not diets supplemented with low-dose or high-dose isoflavones or a casein diet) resulted in prolongation of tumor latency. In tamoxifen-treated mice fed the soy meal, casein, or high-dose isoflavone enriched diets, the majority (>80%) showed no tumor formation by 60 weeks of age. Of the mice that developed tumors, latency was significantly prolonged. In tamoxifen-treated mice fed the low-dose isoflavone enriched diet, a much higher rate of mammary tumor development (>50%; P < 0.002) and a shorter tumor latency were observed. In vitro studies of human and mouse mammary tumor cell lines confirm that low doses of genistein, co-administered with tamoxifen, promote cell proliferation. This is in contrast to tamoxifen alone or tamoxifen with higher doses of genistein that are growth inhibitory. In summary, low-dose dietary isoflavones abrogated tamoxifen-associated mammary tumor prevention in vivo. These interactions are supported by in vitro data from human and mouse mammary tumor cell lines. These dose-associated interactions likely have relevance to the human use of tamoxifen for prevention or treatment of breast cancer.     

Soy isoflavones enhance radiotherapy in a metastatic prostate cancer model

We previously reported that genistein, the bioactive isoflavone of soybeans, acts as a radiosensitizer for prostate cancer. Pretreatment of tumor cells with genistein potentiated radiation-induced killing in vitro and in orthotopic models in vivo. However, pure genistein promoted increased lymph node metastasis, when administered alone in vivo. We investigated in vitro and in vivo the effects of soy isoflavones (genistein, daidzein and glycitein) as soy pills of similar composition are used in human interventions but not pure genistein. Soy isoflavones inhibited cell survival and potentiated radiation cell killing in PC-3 tumor cells, in vitro. Increased cell killing correlated with inhibition of antiapoptotic molecules Bcl-xL and survivin, upregulation of proapoptotic Bax molecule and PARP cleavage, suggesting activation of apoptotic pathways. In vivo, using the PC-3 orthotopic metastatic mouse model, soy isoflavones and prostate tumor irradiation led to enhanced control of primary tumor growth and metastasis, as observed with pure genistein and radiation. Interestingly, treatment with soy isoflavones did not increase metastasis to para-aortic lymph nodes in contrast to the consistent increase caused by pure genistein. Histologically prostate tumors, treated with soy isoflavones and radiation, showed tumor destruction and in situ tissue alterations, comparable with genistein and radiation effects. However, genistein, but not soy isoflavones, caused induction of HIF1-alpha in prostate tumors, suggesting that induction of hypoxia by pure genistein could contribute to increased metastasis. Our studies demonstrate the safety and potential role of soy isoflavones for enhancing the therapeutic effect of radiotherapy in prostate cancer.     

Decrease of Prostaglandin E2 and 5–Bromo–2'–deoxyuridine Labeling but Not Prostate Tumor Development by Indomethacin Treatment of Rats Given 3,2'–Dimethyl-4-aminobiphenyl and Testosterone Propionate

The modifying effects of indomethacin (IM) on rat prostate carcinogenesis induced by 3,2'–dimethyl–4–aminobiphenyl (DMAB) were investigated. F344 rats were given 50 mg/kg body weight of DMAB at 2–week intervals for 20 weeks and then received IM at a dose of 20 ppm in the drinking water for 37 weeks. Separate groups additionally received testosterone propionate (TP) in Silastic tubes throughout the experiment. DMAB alone induced carcinomas in situ in the ventral lobe and in combination with TP caused invasive carcinomas of the dorso–lateral and anterior lobes and seminal vesicles. No clear suppression by IM of development of in situ carcinomas or in vasive carcinomas was observed. In a short–term satellite experiment, it was revealed that prostaglandin E₂ (PGE₂) levels in the dorso–lateral prostate and seminal vesicles, but not the ventral prostate, were significantly reduced by IM and that TP itself also suppressed PGE₂ levels. The 5–bromo–2'–deoxyuridine labeling index in the ventral prostate was significantly decreased by IM administration. These results indicate that while IM can efficiently suppress tissue PGE₂ levels, it does not inhibit tumor development in the prostate or seminal vesicles of rats in the present model.     

Soy extract inhibits mammary adenocarcinoma growth in a syngeneic mouse model

The effects of the soybean isoflavone genistein and a commercially-available isoflavone-containing soy extract on the growth of F3II mouse mammary adenocarcinoma cells were investigated. Female Balb/c mice injected (s.c.) with F3II cells and fed diets supplemented with 0.6% soy extract (containing genistein at 750 ppm) exhibited a significant 90% reduction in tumor weight compared to controls, whereas female mice fed diets supplemented with 750 ppm genistein alone exhibited a significant 40% reduction in tumor weight compared to controls. Tumor samples from animals fed the 0.6% soy extract, but not from those animals fed the 750 ppm genistein diet alone, exhibited significantly higher protein levels of the cyclin-dependent kinase inhibitor p21(waf1/cip1) compared to controls. Neither of the two experimental diets altered tumor estrogen receptor-alpha or progesterone receptor protein levels. In vitro, genistein significantly inhibited F3II cell proliferation (IC(50) approximately 2-3 microM) and caused a G2/M block in cell cycle progression at concentrations as low as 5 microM. This genistein-induced G2/M arrest in vitro was associated with a significant increase in the protein expression of phosphorylated p34(cdc2) and of cyclin B1. These results indicate that genistein is an inhibitor of F3II mouse mammary adenocarcinoma cell growth in vivo and in vitro, in part due to its effect on specific cell cycle regulatory proteins. In addition, genistein fed to mice as part of the soy extract resulted in a greater magnitude of inhibition of mouse mammary adenocarcinoma tumor growth, compared to tumor growth of animals fed an equivalent amount of genistein alone. This suggests that genistein along with other constituent(s) in the soy extract may also contribute to suppression of F3II tumor growth.     

Lack of modification by naturally occurring antioxidants of 3,2'-dimethyl-4-aminobiphenyl-initiated rat prostate carcinogenesis

The modifying effects of 6 naturally occurring antioxidants on 3,2'-dimethyl-4-aminobiphenyl (DMAB)-initiated rat prostate carcinogenesis were investigated in male F344 rats. Animals were pretreated with DMAB in a 20-week initiation protocol and then administered basal diet containing 0.8% catechol, 0.8% resorcinol, 0.8% hydroquinone, 2 ppm selenium, 2% gamma-orysanol or 1% alpha-tocopherol for 40 weeks. The experiment was terminated at week 60 for histopathological assessment of lesion development. Atypical hyperplasias and carcinomas of the prostate were observed in the ventral lobe in all groups treated with DMAB. However, the incidences of these lesions were not significantly different between carcinogen control and antioxidant-treated groups. There were also no significant increases or decreases in the incidences of tumors in any other organs.     

Dietary supplementation with silymarin inhibits 3,2'-dimethyl-4-aminobiphenyl-induced prostate carcinogenesis in male F344 rats.

PURPOSE: Silymarin has been shown to be a potent anticarcinogenic agent. Here, we investigated the modifying effects of dietary feeding with a naturally occurring polyphenolic antioxidant flavonoid silymarin on 3,2'-dimethyl-4-aminobiphenyl (DMAB)-induced prostatic carcinogenesis in male F344 rats. EXPERIMENTAL DESIGN: Male F344 rats were given s.c. injections of DMAB (25 mg/kg body weight) every other week for 20 weeks. They also received the experimental diet containing 100 or 500 ppm silymarin for 40 weeks, starting 1 week after the last dosing of DMAB. All of the rats were sacrificed 60 weeks after the start of the experiment. Histopathology and immunohistochemistry for proliferative cell nuclear antigen, cyclin D1, and apoptotic indices were done in the prostatic lesions, including invasive adenocarcinomas, intraepithelial neoplasms, and nonlesional glands. RESULTS: Dietary feeding with 500 ppm silymarin significantly inhibited the incidence of prostatic adenocarcinoma when compared with the DMAB-alone group (17.6% versus 50.0%, P < 0.05). The proliferative cell nuclear antigen- and cyclin D1-positive indices in adenocarcinomas, prostatic intraepithelial neoplasm, and nonlesional glands in rats treated with DMAB and silymarin were slightly lower than that of the DMAB-alone group. Also, dietary administration of silymarin increased apoptotic index in prostatic adenocarcinoma by measuring immunohistochemically positive nuclei for ssDNA. CONCLUSIONS: Our results indicate that silymarin exerts chemopreventive ability against chemically induced prostatic carcinogenesis through apoptosis induction and modification of cell proliferation.     

Effect of dietary genistein on cell replication indices in C57BL6 mice

The phytoestrogen and isoflavone, genistein, inhibited the activity of the DNA synthesis-related enzyme, topoisomerase-II (topo-II), altered cell-cycle traverse and produced cell death in cell culture models. In order to examine the potential effects of genistein on cell replication and cell death in an animal model, 8-week-old C57BL6 mice were fed either a control diet or one containing one of five doses (100-2000 ppm) of genistein for 28 days. At the end of the feeding period, both male and female mice were sacrificed and the serum isoflavone and aglycone levels determined by liquid chromatography with electrospray tandem mass spectrometry (LC-ES/MS/MS). Immunohistochemistry was utilized to measure the cell replication and cell death rates in the small intestine. Total isoflavone concentration increased from below the limits of detection (0.001 microM) in control animals to 0.28 microM in male and 0.54 microM in female mice fed the 2000 ppm diet. A decrease in the percentage of cells in G(0) and an increase in the percentage of cells in S-phase, consistent with topo-II-induced S-phase arrest, was found in the duodenum and jejunum of the small intestine. Thus, genistein appears to accumulate to a sufficient level to affect topo-II activity in the small intestine.     

Effects of soybean isoflavones on cell growth and apoptosis of the human prostatic cancer cell line LNCaP

BACKGROUND: Epidemiological studies have suggested that soybean isoflavones are associated with a lower risk of prostate cancer. However, the mechanisms of prostate cancer prevention by soybean isoflavones have yet to be fully clarified. METHODS: Two soybean isoflavones (genistein and daidzein) and their glucosides (genistin and daidzin) were tested for their effects on cell growth and apoptosis of the LNCaP human prostatic cancer cell line. RESULTS: Among these isoflavones, genistein was found to inhibit the growth of LNCaP most effectively, with an IC50 value of 40 microM. The inhibition of cell growth by genistein was accompanied by the suppression of DNA synthesis and the induction of apoptosis. Expression of prostate-specific antigen (PSA) in LNCaP was also significantly reduced by the treatment with genistein. CONCLUSIONS: The results suggest that genistein might primarily influence human prostate cancer development by reducing tumor growth.      

Synergistic effects of thearubigin and genistein on human prostate tumor cell (PC-3) growth via cell cycle arrest

There is evidence that habitual consumption of green tea by Japanese men is correlated with a reduction in cancers, including prostate; soybean isoflavones are also associated with increased protection. The present study compared the anti-proliferative effect of black tea (Camellia sinensis) polyphenol, thearubigin (TR), alone or combined with the isoflavone genistein, on human prostate (PC-3) carcinoma cells. TR administered alone did not result in any alteration of cell growth. When combined with genistein, however, TR significantly inhibited cell growth and induced a G2/M phase cell cycle arrest in a dose dependent manner. These findings indicate the potential use of combined phytochemicals to provide protection against prostate cancer.     

Dietary effects of soy isoflavones daidzein and genistein on 7,12-dimethylbenz[a]anthracene-induced mammary mutagenesis and carcinogenesis in ovariectomized Big Blue transgenic rats

The major constituents of isoflavones daidzein (DZ) and genistein (GE) interact with the and estrogen receptors in several tissues including mammary tissues. In this study, we used ovariectomy (OVX) to model menopause and determined the effects of DZ, GE or 17beta-estradiol (E(2)) exposures on chemically induced mutagenesis and carcinogenesis in the mammary glands of female Big Blue transgenic rats. The rats were fed control diet containing the isoflavones and E(2) and treated with a single oral dose of 7,12-dimethylbenz[a]anthracene (DMBA) at PND50. Animals were euthanized at 16 or 20 weeks post-carcinogen treatment to assess mutant frequencies (MFs) and histopathological parameters, respectively. The isoflavones or E(2) supplementation alone resulted in the lac I MFs that were not significantly different from the MFs measured in rats fed the control diet alone. DMBA exposure, however, induced significant increases in the lac I MFs in the mammary tissues of both OVX and INT rats and Hprt MFs in spleen lymphocytes (P < 0.01). In general, feeding the isoflavones or E(2) did not cause any significant changes in DMBA-induced mutagenicity in the mammary tissues. However, feeding the isoflavone mixture (daidzein + genistein; DZG) resulted in a significant reduction in the DMBA-induced lac I MFs (P < 0.05). Cell proliferation as measured by PCNA immunohistochemistry was increased in both OVX and INT rats exposed to DMBA as compared with rats fed control diet (P < 0.05). Mammary histology indicated that hyperplasia was induced in most of the treatment groups including control. Although DMBA did not induce mammary tumors in the OVX rats, adenoma and adenocarcinoma were detected in the mammary glands of INT rats.