title: Prevention of spontaneous prostate-related cancer in Lobund-Wistar rats by a soy protein isolate/isoflavone diet.
abstract: BACKGROUND
  Epidemiological surveys recorded that men in the Orient (Japan and China) consuming diets high in soy food were at low risk of developing clinical prostate cancer, compared to a relatively high risk among men in the West who consumed diets low in soy food. Soybeans contain phytoestrogens (isoflavones) with many recorded anticancer mechanisms. The Lobund-Wistar (L-W) rat is a unique model system: approximately 30% develop metastasizing adenocarcinomas spontaneously in the anterior prostate-seminal vesicle complex (P-SV), from which the tumors expand into the dorsolateral lobes. L-W rats are inherently predisposed, possibly by unusually high levels of circulating testosterone (T), to develop P-SV tumors which are T-dependent in the early stages and T-independent in advanced stages of tumorigenesis.
  
  
  METHODS
  L-W rats were fed two diets from age 2-24 months: 1) natural ingredient diet L-485 (Harlan TekLad Diets, Madison, WI) containing soy meal, or 2) a modified starch-casein diet in which soy protein isolate/isoflavones (SPII) replaced casein as a source of protein.
  
  
  RESULTS
  At age 24 months, 3 of 99 (3%) rats on diet SPII and 30 of 100 (30%) rats on diet L-485 developed spontaneous P-SV cancers. Rats on the SPII diet manifested a significant reduction of circulating T, approaching physiological levels. Failure of the rats on diet L-485 to prevent P-SV cancer development suggests that soy meal contained a factor(s) that blocked the antiandrogenic action of the phytoestrogen.
  
  
  CONCLUSIONS
  The spontaneous development of P-SV cancers was significantly prevented in L-W rats consuming the SPII diet from age 2-24 months, possibly through an agonist effect of the soy-derived phytoestrogens.
authors.affiliation: Lobund Laboratory, University of Notre Dame, Notre Dame, Indiana 46556, USA. Morris.Pollard.3@nd.edu
authors.forename: M
authors.initials: M
authors.lastname: Pollard
authors.forename: W
authors.initials: W
authors.lastname: Wolter
mesh_terms: D000818:Animals; D004968:Estrogens, Non-Steroidal / Q000009:adverse effects / Q000494:pharmacology*; D006128:Growth; D007529:Isoflavones; D008297:Male; D048789:Phytoestrogens; D028321:Plant Preparations; D011471:Prostatic Neoplasms / Q000517:prevention & control*; D051381:Rats; D017208:Rats, Wistar; D030262:Soybean Proteins / Q000009:adverse effects / Q000494:pharmacology*; D013025:Glycine max / Q000378:metabolism; D013739:Testosterone / Q000097:blood
chemical_list: D004968:Estrogens, Non-Steroidal; D007529:Isoflavones; D048789:Phytoestrogens; D028321:Plant Preparations; D030262:Soybean Proteins; D013739:Testosterone