Scientific Program (Oral Abstracts) | Poster Abstracts | Speaker List
SECOND INTERNATIONAL SYMPOSIUM
ON THE ROLE OF SOY
IN PREVENTING AND TREATING CHRONIC DISEASESeptember 15-18, 1996
Brussells, Belgium
SCIENTIFIC PROGRAM
(Oral Abstracts)Soy and Cancer
Animal studiesDietary soy in the prevention of prostate cancer in animal models
R. Santti, L. Salo and S. Mäkelä: Institute of Biomedicine and Medicity Research Laboratory, University of Turku, FIN 20520, Turku, Finland.
Soy is widely used in Asian countries, with a low incidence of prostate cancer, suggesting the chemopreventive action for soy. The chemopreventive action of soy has been confirmed in animal models for prostate carcinogenesis. The development of dysplastic changes, morphologically similar to prostatic intraepithelial neoplasia (PIN) in human prostate, was delayed in the prostate of Han: NMRI male mice estrogenized with the synthetic nonsteroidal estrogen, diethylstilbestrol (DES; 2mg on days 1-3 after birth), and given soybean-containing feed (7% roasted soybean meal) from fertilization onwards (Mäkelä et al: J.Nutr. 125:437-445,1996). Both the number of the animals showing dysplasia and also the severity of the alterations in dysplastic epithelium were lower in animals given soy-containing feed. Further, in rats transplanted with the androgen-sensitive Dunning R3327 PAP prostatic cancer tissue on soy diet (33% defatted, heated soy flour) the tumors developed later and were smaller after transplantation when compared to the control rats on a fiber-free diet (Adlercreuts, personal communication). The significance of soy could be explained by the ability of soy-derived phytoestrogens (isoflavonoids) to antagonize the action of more potent endogenous estrogens in initiation and/or promotion of tumor formation. This hypothesis was tested in the neoDES mouse model.The growth inhibition of prostatic lobes seen after neonatal estrogenization of the mice was reversed by soy when given from fertilization onwards. The antiestrogenic action of soy was also seen in the mouse uterus bioassay (6mg/kg DES in feed). However, no evidence for antiestrogenicety (capability to antagonize the action of 17 estradiol, 50-100mg/mouse) of soy was found in short-term tests with adult animals when the development of squamous epithelial metaplasia and expression of c-fos protoncogene in prostate were used as endpoints of estrogen action. Estrogen-like effect of genistein on c-fos expression was
evident in adult mice and induced by doses (200mg/mouse) comparable to the amounts ingested by mice in daily soy-based feed. Genistein given neonatally in a dose of 100mg (on days 1-3 a.b.) had no effect on the weight of sex accessory glands and caused only a marginal increase in the expression of c-fos gene. The missing antiestrogenic effects soy in adult males could be interpreted by assuming that the neonatal period may be more critical for antiestrogenic action of soy. Alternatively, the chemopreventive action of soy is not due to its antiestrogenicity.Soy Symposium Home http://soyfoods.com/symposium/
U.S. Soyfoods Directory Home http:soyfoods.com/
© Copyright 1997
Indiana Soybean Board