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
Toshihisa Ohta1,2,
Seiichi Nakatsugi1,
Kouji Watanabe1,
Toshihiko Kawamori1,
Fumiyasu Ishikawa2,
Masami Morotomi2,
Shigeyuki Sugie3,
Toshiya Toda4,
Takashi Sugimura1 and
Keiji Wakabayashi1,5
1 Cancer Prevention Division, National Cancer Center Research Institute, 1-1 Tsukiji 5-chome, Chuo-ku, Tokyo 104-0045,
2 Yakult Central Institute for Microbiological Research, 1796 Yaho, Kunitachi-shi, Tokyo 186-8650,
3 Gifu University School of Medicine, 40 Tsukasa-machi, Gifu-shi, Gifu 500-8705,
4 Fujicco Co. Ltd, 6-13-4 Minatojimanakamachi, Chuo-ku, Kobe, Hyogo, 650-8558, Japan
 |
Abstract
|
---|
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 SpragueDawley 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.
Abbreviations: FSM, fermented soy milk; HCAs, heterocyclic amines; PhIP, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine.
 |
Introduction
|
---|
Breast cancer is one of the most common cancers in women. It accounts for almost 30% of all newly diagnosed malignant neoplasms in the USA (1). Several epidemiological studies have demonstrated that a high consumption of meat is associated with an increased risk of breast cancer (2,3). Moreover, the risk of breast cancer was found to be significantly elevated with an increased intake of well-done to very well-done meat (4). On the other hand, Gertig et al. reported that there was no association between meat intake or the cooking method of meat and the risk of breast cancer (5). Of the series of carcinogenic heterocyclic amines (HCAs) that have been identified in cooked meat, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), being the most abundant HCA in cooked foods (6), induces cancers in the mammary glands of female rats at a high incidence (79). Therefore, PhIP may play an important role in the development of breast cancer in humans.
High consumption of soybean and soybean-related products has been suggested to contribute to a reduction in the risk of breast cancer in epidemiological studies (10). The average daily consumption of soybean and its products per person in Japan is much higher than the value for Americans (11,12). Many components, such as isoflavones, protease inhibitors, saponins and inositol hexaphosphate, have been investigated in the search for candidates responsible for the chemopreventive effects (13). Among these, isoflavones, particularly genistein, have been demonstrated to show several kinds of biological activity (14). Genistein inhibits protein tyrosine kinase and topoisomerase II activities (15,16). Genistein also has an inhibitory effect on angiogenesis (17), antioxidative potential (18) and phytoestrogenic activity (19). Among four isoflavones tested (genistein and daidzein and their ß-glucoside conjugates, genistin and daidzin), genistein was reported to most effectively inhibit the growth of LNCaP, a human prostate cancer cell line, while daidzein showed a weak inhibitory effect (20). The ß-glucoside conjugates genistin and daidzin exerted far less influence. Genistein can be absorbed in the upper small intestine (21), whereas the ß-glucoside conjugate genistin needs conversion to an aglycone through the action of a ß-glucosidase produced by intestinal bacteria before being absorbed.
In general, the amounts of genistein and daidzein are much less than genistin and daidzin in soybean and its related products, such as soy milk and tofu (12). Based on biological activities of the isoflavone aglycones and glucoside conjugates and the conversion efficiency of glucoside conjugates to aglycones in vivo, soybean-related products containing higher amounts of aglycones than glucoside conjugates of isoflavones would be preferable for cancer prevention. Glycoside conjugates may be converted to aglycones by microbes during fermentation. Therefore, we produced fermented soy milk (FSM) with Bifidobacterium breve strain Yakult in an attempt to increase the amounts of isoflavone aglycones and also to improve the flavor of soy milk. Using the FSM thus obtained, inhibitory effects on PhIP-induced mammary tumor development in SpragueDawley female rats were examined. To determine the active principles in FSM, the effect of an isoflavone mixture of genistein and daidzein was also tested.
 |
Materials and methods
|
---|
Chemicals
PhIP-HCl was obtained from the Nard Institute Ltd (Osaka, Japan). Flavone, used as an internal standard for the analysis of isoflavones, was obtained from Tokyo Kasei Co. (Tokyo, Japan). Genistein and daidzein, which were also applied as standard substances to estimate isoflavone contents, were purchased from Sigma Chemical Co. (St Louis, MO) and Seikagaku Corp. (Tokyo, Japan), respectively.
Preparation of FSM and isoflavone mixture
A seed culture of Bifidobacterium breve strain Yakult was added to soy milk (Shikokukakouki Co. Ltd, Tokushima, Japan) at 10 ml/l and fermentation was allowed to proceed statically at 37°C for 18 h under anerobic conditions. The pH and viable cell counts of the FSM were 4.6 and 4.1x109 colony-forming units/ml, respectively. The FSM obtained was then lyophilized and levels of genistein, genistin, daidzein and daidzin in FSM were analyzed according to the method described by Kikuchi-Hayakawa et al. (22). These amounts were 1318 µg for genistein, 26 µg for genistin, 677 µg for daidzein and 269 µg for daidzin per gram lyophilized material. The crude protein, crude fat and ash content levels in the lyophilized FSM were 44, 24 and 32%, respectively.
The soybean isoflavone mixture was prepared as follows. First, defatted soybeans were extracted with boiled water and the extracted material was applied to a Sepabeads SP207 column (Mitsubishi Kasei Co., Tokyo, Japan) and eluted with methanol. After evaporation the residue was redissolved in 50% (v/v) ethanol and hydrolyzed with 5% (v/v) sulfuric acid to remove glucose from co-existent glucoside-conjugated forms. The soybean isoflavone mixture consisted of ~80% genistein; most of the remainder was daidzein.
Mammary carcinogenesis experiments in rats
Female SpragueDawley rats, 6 weeks old, were purchased from CLEA Japan Inc. (Tokyo, Japan) and housed 3 rats/cage with wood chips in an air-conditioned animal room with a 12 h light/dark cycle. Starting at 7 weeks of age, a total of 204 rats were fed a modified AIN-76A high fat basal diet (23.5% corn oil; CLEA Japan Inc.) and an experimental diet containing 0.02 or 0.04% of the isoflavone mixture or 10% FSM during and after carcinogen exposure. Doses of the isoflavone mixture and FSM were chosen on the basis of the chemopreventive data shown in our previous report (23). The compositions of the diets used in the present study are shown in Table I
. The concentrations of components in diets containing test samples were isocalorically adjusted to those in the basal diet. Diets were stored at 4°C until use. A fresh diet was provided to the rats once a week. Dietary isoflavones were confirmed to be stable under these conditions by HPLC analysis.
All animals except those for vehicle treatment received intragastric intubations of PhIP at a dose of 85 mg/kg body wt four times weekly for 2 weeks, as described previously (24). Body weight and diet intake were measured weekly and animals were monitored daily for their general health and mammary tumor development. At 20 weeks after the first dosing with PhIP, all animals were killed under ether anesthesia and the numbers and sizes of all mammary tumors were recorded. The length (L), width (W) and height (H) of each lesion were measured with calipers and tumor volumes were calculated using the formula V = LxWxHx
/6. Tumor samples and organs demonstrating apparent abnormalities were fixed with 10% buffered formalin and embedded in paraffin. Sections were stained with hematoxylin and eosin for histological examination and pathological diagnosis of mammary tumors was made according to criteria as described previously (25).
Statistical analysis
The significance of differences in incidences of tumors was analyzed by the
2 test. Other data were examined using Welch's t-test. A P value of <0.05 was regarded as significant.
 |
Results
|
---|
Daily dietary intake in the PhIP-treated groups was 21.3 g/day with the control diet, 20.7 g with 10% FSM, 20.9 g with the 0.02% isoflavone mixture and 22.6 g with the 0.04% isoflavone mixture, on average (Table II
). Administration of FSM and isoflavone mixture did not affect the feeding and behavior of rats. The body weights of PhIP-treated rats ranged from 325.3 to 344.6 g and those of vehicle-treated rats were 353.9362.3 g (Table II
). Body weight gain was thus slightly decreased by PhIP treatment, but no significant differences were observed among the PhIP-treated groups. Also, no differences were observed regarding liver weight in each group (Table II
). During the study, five rats in the PhIP-treated groups and one rat in the vehicle-treated group died of acute problems due to intubation, and these were not included in the effective numbers.
The results of sequential observation of mammary gland tumors by palpation in the PhIP-treated groups are shown in Figure 1
. Palpable tumors in the control diet group first appeared at 12 weeks after the first dosing with PhIP and the incidences (percentage of rats with tumors) reached 55% at 18 weeks and 57% at 20 weeks, with a final multiplicity (no. of tumors/rat) of 1.0 ± 0.2 per rat. Incidences and multiplicities of palpable tumors at 20 weeks were 31% and 0.5 ± 0.1 for the 10% FSM group, 41% and 0.9 ± 0.2 for the 0.02% isoflavone mixture group and 41% and 0.9 ± 0.2 for the 0.04% isoflavone mixture group. Thus, both incidences and multiplicities were lower in the experimental diet groups as compared with the control diet group. All animals were killed at 20 weeks after the first dosing with PhIP. Additional non-palpable tumors were also detected at termination.

View larger version (17K):
[in this window]
[in a new window]
|
Fig. 1. Time course of palpable mammary tumors in rats treated orally with PhIP. (A) Incidence (percent of rats with tumors) and (B) multiplicity (average number of palpable tumors/rat). Open squares, PhIP plus control diet; closed squares, PhIP plus 10% FSM; open circles, PhIP plus 0.02% isoflavones; closed circles, PhIP plus 0.04% isoflavones.
|
|
All the mammary gland tumors in the PhIP-treated control and experimental diet groups were diagnosed histologically as invasive ductal carcinomas, except for two cases of intraductal carcinoma and fibroadenoma. Data for the incidences, multiplicities and volumes of all mammary gland tumors at the end of the experiment are shown in Table III
. The incidences of tumors were 71% in the control diet group, 51% in the FSM group and 68 and 61% in the groups treated with isoflavone mixtures at 0.02 and 0.04%, respectively. Multiplicities of tumors were clearly decreased by the administration of FSM (1.2 ± 0.2), the 0.02% isoflavone mixture (2.2 ± 0.4) and the 0.04% isoflavone mixture (1.5 ± 0.3), as compared with the control diet (2.6 ± 0.5). Furthermore, feeding of FSM and the isoflavone mixtures reduced tumor volume, especially in the FSM diet group, being decreased by 83%. No mammary tumors were detected in the vehicle-treated groups. Moreover, in vehicle-treated animals, chronic administration of 10% FSM or isoflavone mixture did not produce any gross or histological changes in the liver, kidneys, stomach, intestines and lungs. No other tumors than mammary gland tumors were observed in PhIP- and vehicle-treated rats.
 |
Discussion
|
---|
In the present study, the fermented soy product FSM was found to inhibit the development of tumors in the mammary glands of PhIP-treated SpragueDawley female rats. In addition, the isoflavone components genistein and daidzein also showed chemopreventive action against PhIP-induced mammary carcinogenesis. Consistent with these data, soybeans, soy protein isolate and miso, produced from soybeans by fermentation, have been reported to show inhibitory effects on chemically and irradiation induced mammary carcinogenesis in rats (2629).
Quantification analysis revealed FSM to contain 1318 and 677 µg/g genistein and daidzein, respectively, in lyophilized material. This indicates that the isoflavone contents in 10% FSM are 132 p.p.m. for genistein and 68 p.p.m. for daidzein, being almost equivalent to the 0.02% isoflavone mixture in the diet. FSM caused a greater reduction of mammary tumor development than the 0.02% isoflavone mixture; this might be due to the possible presence of several other anticarcinogens such as protease inhibitors, phytosterol, saponins and inositol hexaphosphate, which could act additively or synergistically with isoflavones. The average daily consumption of soybean and their products per person in Japan in 1997 was 68.9 g, being 4.8% of total food intake (30). On the basis of these data, the total intake of genistein and genistin by the Japanese can be calculated to be 0.2 mg/day/kg body wt (12). These levels are almost 60-fold less than those of genistein taken from the FSM diet in rats.
It has been reported that administration of genistein prenatally and/or neonatally inhibits dimethylbenz[a]anthracene-induced mammary gland cancer development in rats (3134). In addition, i.p. injection of genistein was demonstrated to reduce N-methyl-N-nitrosourea-induced mammary cancer in rats (35). In the present study, dietary feeding of the genistein and daidzein mixture in adult rats was also shown to be effective in inhibiting development of mammary tumors in PhIP-treated rats. As mentioned in the Introduction, several possible mechanisms, such as inhibition of protein tyrosine kinase and topoisomerase II activities and also antiestrogenic activity, have been proposed as playing a role in the reduction in mammary carcinogenesis by isoflavone compounds, including genistein. Since cyclooxygenase-2 was overexpressed in the mammary gland tumors induced by PhIP used in the present study (data not shown), an influence on expression of this enzyme may be related to the reduction in mammary carcinogenesis by the isoflavone mixture (36,37). An alteration of the metabolism of PhIP by isoflavones is another potential candidate mechanism, although it was found that the mutagenic activity of PhIP in Salmonella strains was not affected by the isoflavone mixture. Due to technical difficulties, it was not possible to study PhIPDNA adducts in the mammary tissue itself, however, the PhIPDNA adduct levels in the heart of rats in each group were measured at week 20 using the 32P-post-labeling method, because it has been reported that HCA treatment causes a linear increase in DNA adducts in the heart with time, with almost no change after discontinuation of exposure in rats (38). No significant differences in the levels of PhIPDNA adducts in the heart were observed in the experimental and control diet groups (data not shown). Clearly, further experiments to elucidate the inhibitory mechanisms of mammary carcinogenesis by FSM and isoflavone compounds in soybean and soybean products are warranted.
In conclusion, administration of FSM inhibited the development of PhIP-induced mammary tumors in female SpragueDawley rats. Since fermentation improves the flavor as well as the isoflavone aglycone content of soy milk, FSM would be a suitable food for prevention of mammary cancer in man.
 |
Acknowledgments
|
---|
This study was supported by a grant from the Organization for Pharmaceutical Safety and Research (OPSR) of Japan, Grants-in-Aid for Cancer Research from the Ministry of Health and Welfare and from the Ministry of Health and Welfare for the Second Term Comprehensive 10 Year Strategy for Cancer Control, Japan, and also a grant from the Yakult Bio-science Foundation.
 |
Notes
|
---|
5 To whom correspondence should be addressed Email: kwakabay{at}gan2.ncc.go.jp 
 |
References
|
---|
-
Henderson,B.E., Pike,M.C., Bernstein,L. and Ross,R.K. (1996) Breast cancer. In Schottenfeld,D. and Fraumeni,J.F.Jr (ed.) Cancer Epidemiology and Prevention, 2nd Edn. Oxford University Press, New York, NY, pp. 10221039.
-
Boyd,N.F., Martin,L.J., Noffel,M., Lockwood,G.A. and Trichler,D.L. (1993) A meta-analysis of studies of dietary fat and breast cancer risk. Br. J. Cancer, 68, 627636.[ISI][Medline]
-
Toniolo,P., Riboli,E., Shore,R.E. and Pasternack,B.S. (1994) Consumption of meat, animal products, protein and fat and risk of breast cancer: a prospective cohort study in New York. Epidemiology, 5, 391397.[ISI][Medline]
-
Zheng,W., Gustafson,D.R., Sinha,R., Cerhan,J.R., Moore,D., Hong,C.P., Anderson,K.E., Kushi,L.H., Sellers,T.A. and Folsom,A.R. (1998) Well-done meat intake and the risk of breast cancer. J. Natl Cancer Inst., 90, 17241729.[Abstract/Free Full Text]
-
Gertig,D.M., Hankinson,S.E., Hough,H., Spiegelman,D., Colditz,G.A., Willett,W.C., Kelsey,K.T. and Hunter,D.J. (1999) N-Acetyl transferase 2 genotypes, meat intake and breast cancer risk. Int. J. Cancer, 80, 1317.[ISI][Medline]
-
Felton,J.S., Knize,M.G., Shen,N.H., Lewis,P.R., Andresen,B.D., Happe,J. and Hatch,F.T. (1986) The isolation and identification of a new mutagen from fried ground beef: 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). Carcinogenesis, 7, 10811086.[Abstract]
-
Ito,N., Hasegawa,R., Sano,M., Tamano,S., Esumi,H., Takayama,S. and Sugimura,T. (1991) A new colon and mammary carcinogen in cooked food, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). Carcinogenesis, 12, 15031506.[Abstract]
-
Hasegawa,R., Sano,M., Tamano,S., Imaida,K., Shirai,T., Nagao,M., Sugimura,T. and Ito,N. (1993) Dose-dependence of 2-amino-1-methyl-6-phenylimidazo[4,5-b]-pyridine (PhIP) carcinogenicity in rats. Carcinogenesis, 14, 25532557.[Abstract]
-
Ghoshal,A., Preisegger,K.H., Takayama,S., Thorgeirsson,S.S. and Snyderwine,E.G. (1994) Induction of mammary tumors in female SpragueDawley rats by the food-derived carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and effect of dietary fat. Carcinogenesis, 15, 24292433.[Abstract]
-
Messina,M.J., Persky,V., Setchell,K.D. and Barnes,S. (1994) Soy intake and cancer risk: a review of the in vitro and in vivo data. Nutr. Cancer, 21, 113131.[ISI][Medline]
-
Coward,L., Barnes,N.C., Setchell,K.D.R. and Barnes,S. (1993) Genistein, daidzein and their ß-glycoside conjugates: antitumor isoflavones in soybean foods from american and asian diets. J. Agric. Food Chem., 41, 19611967.[ISI]
-
Fukutake,M., Takahashi,M., Ishida,K., Kawamura,H., Sugimura,T. and Wakabayashi,K. (1996) Quantification of genistein and genistin in soybeans and soybean products. Food. Chem. Toxicol., 34, 457461.[ISI][Medline]
-
Messina,M. and Barnes,S. (1991) The role of soy products in reducing risk of cancer. J. Natl Cancer Inst., 83, 541546.[ISI][Medline]
-
Adlercreutz,H. (1995) Phytoestrogens: epidemiology and a possible role in cancer protection. Environ. Health Perspect., 103, 103112.[ISI][Medline]
-
Akiyama,T., Ishida,J., Nakagawa,S., Ogawara,H., Watanabe,S., Itoh,N., Shibuya,M. and Fukami,Y. (1987) Genistein, a specific inhibitor of tyrosine-specific protein kinases. J. Biol. Chem., 262, 55925595.[Abstract/Free Full Text]
-
Markovits,J., Linassier,C.P.F., Couprie,J., Pierre,J., Jacquemin-Sablon,A., Saucier,J.M., Le Pecq,J.B. and Larsen,A.K. (1989) Inhibitory effects of the tyrosine kinase inhibitor genistein on mammalian DNA topoisomerase II. Cancer Res., 49, 51115117.[Abstract]
-
Fotsis,T., Pepper,M., Adlercreutz,H., Fleischmann,G., Hase,T., Montesano,R. and Schweigerer,L. (1993) Genistein, a dietary-derived inhibitor of in vitro angiogenesis. Proc. Natl Acad. Sci. USA, 90, 26902694.[Abstract]
-
Wei,H., Wei,L., Frenkel,K., Bowen,R. and Barnes,S. (1993) Inhibition of tumor promoter-induced hydrogen peroxide formation in vitro and in vivo by genistein. Nutr. Cancer, 20, 112.[ISI][Medline]
-
Molteni,A., Brizio-Molteni,L. and Persky,V. (1995) In vitro hormonal effects of soybean isoflavones. J. Nutr., 125, 751S756S.[Medline]
-
Onozawa,M., Fukuda,K., Ohtani,M., Akaza,H., Sugimura,T. and Wakabayashi,K. (1998) Effects of soybean isoflavones on cell growth and apoptosis of the human prostatic cancer cell line LNCaP. Jpn. J. Clin. Oncol., 28, 360363.[Abstract/Free Full Text]
-
Sfakianos,J., Coward,L., Kirk,M. and Barnes,S. (1997) Intestinal uptake and biliary excretion of the isoflavone genistein in rats. J. Nutr., 127, 12601268.[Abstract/Free Full Text]
-
Kikuchi-Hayakawa,H., Onodera,N., Matsubara,S., Yasuda,E., Shimakawa,Y. and Ishikawa,F. (1998) Effects of soya milk and Bifidobacterium-fermented soya milk on plasma and liver lipids and faecal steroids in hamsters fed on a cholesterol-free or cholesterol-enriched diet. Br. J. Nutr., 79, 97105.[ISI][Medline]
-
Onozawa,M., Kawamori,T., Baba,M., Fukuda,K., Toda,T., Sato,H., Ohtani,M., Akaza,H., Sugimura,T. and Wakabayashi,K. (1999) Effects of a soybean isoflavone mixture on carcinogenesis in prostate and seminal vesicles of F344 rats. Jpn. J. Cancer Res., 90, 393398.[ISI][Medline]
-
Suzui,N., Sugie,S., Rahman,K.M., Ohnishi,M., Yoshimi,N., Wakabayashi,K. and Mori,H. (1997) Inhibitory effects of diallyl disulfide or aspirin on 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine-induced mammary carcinogenesis in rats. Jpn. J. Cancer Res., 88, 705711.[ISI][Medline]
-
Russo,J., Russo,I.H., Rogers,A.E., Vanzwieteu,M.J. and Gusterson,B. (1990) Tumours of the mammary gland. In Turusov,V. and Mohr,U. (eds) Pathology of Tumours in Laboratory Animals, IARC Scientific Publications no. 99. IARC, Lyon, Vol. 1, pp. 4778.
-
Barnes,S., Grubbs,C., Setchell,K.D. and Carlson,J. (1990) Soybeans inhibit mammary tumors in models of breast cancer. Prog. Clin. Biol. Res., 347, 239253.[Medline]
-
Baggott,J.E., Ha,T., Vaughn,W.H., Juliana,M.M., Hardin,J.M. and Grubbs,C.J. (1990) Effect of miso (Japanese soybean paste) and NaCl on DMBA-induced rat mammary tumors. Nutr. Cancer, 14, 103109.[ISI][Medline]
-
Hawrylewicz,E.J., Huang,H.H. and Blair,W.H. (1991) Dietary soybean isolate and methionine supplementation affect mammary tumor progression in rats. J. Nutr., 121, 16931698.[ISI][Medline]
-
Gotoh,T., Yamada,K., Yin,H., Ito,A., Kataoka,T. and Dohi,K. (1998) Chemoprevention of N-nitroso-N-methylurea-induced rat mammary carcinogenesis by soy foods or biochanin A. Jpn. J. Cancer Res., 89, 137142.[ISI][Medline]
-
Ministry of Health and Welfare (1999) Report of the National Nutrition Survey in 1997. Daiichi-Shuppan, Tokyo, Japan.
-
Lamartiniere,C.A., Moore,J.B., Brown,N.M., Thompson,R., Hardin,M.J. and Barnes,S. (1995) Genistein suppresses mammary cancer in rats. Carcinogenesis, 16, 28332840.[Abstract]
-
Lamartiniere,C.A., Moore,J., Holland,M. and Barnes,S. (1995) Neonatal genistein chemoprevents mammary cancer. Proc. Soc. Exp. Biol. Med., 208, 120123.[Abstract]
-
Murrill,W.B., Brown,N.M., Zhang,J.X., Manzolillo,P.A., Barnes,S. and Lamartiniere,C.A. (1996) Prepubertal genistein exposure suppresses mammary cancer and enhances gland differentiation in rats. Carcinogenesis, 17, 14511457.[Abstract]
-
Fritz,W.A., Coward,L., Wang,J. and Lamartiniere,C.A. (1998) Dietary genistein: perinatal mammary cancer prevention, bioavailability and toxicity testing in the rat. Carcinogenesis, 19, 21512158.[Abstract]
-
Constantinou,A.I., Mehta,R.G. and Vaughan,A. (1996) Inhibition of N-methyl-N-nitrosourea-induced mammary tumors in rats by the soybean isoflavones. Anticancer Res., 16, 32933298.[ISI][Medline]
-
Blanco,A., Habib,A., Levy-Toledano,S. and Maclouf,J. (1995) Involvement of tyrosine kinases in the induction of cyclo-oxygenase-2 in human endothelial cells. Biochem. J., 312, 419423.[ISI][Medline]
-
Akarasereenont,P., Mitchell,J.A., Appleton,I., Thiemermann,C. and Vane,J.R. (1994) Involvement of tyrosine kinase in the induction of cyclo-oxygenase and nitric oxide synthase by endotoxin in cultured cells. Br. J. Pharmacol., 113, 15221528.[Abstract]
-
Övervik,E., Ochiai,M. Hirose,M., Sugimura,T. and Nagao,M. (1991) The formation of heart DNA adducts in F344 rats folllowing dietary administration of heterocyclic amines. Mutat. Res., 256, 3743.[ISI][Medline]
Received July 7, 1999;
revised January 5, 2000;
accepted January 6, 2000.