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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 studiesSoy Protein Isolates and Genistein: Effects on Initiation, Promotion, and Progression of Colon Cancer
Daniel D. Gallaher*, Cynthia M. Gallaher*, &, Zili An#, and Robert M. Hoffman#, Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN* and AntiCancer, Inc., San Diego, CA#.A series of studies have been conducted in our laboratory examining the effect of soy protein isolate (SPI) and genistein on the initiation and promotion of colonic precancerous lesions (aberrant crypts) in dimethylhydrazine-treated rats. Using a recently processed high genistein SPI or a casein-based diet containing genistein a significant reduction in the number of aberrant crypts was observed compared to a casein-based diet alone when the diets were fed beginning 1 week after carcinogen treatment (initiation phase). In a subsequent study, we fed SPI to rats prior and during carcinogen treatment (initiation phase), during the promotional phase only, or for both the initiation and promotional phases. A casein-based genistein diet was fed during the initiation phase only. Compared to the casein-based diet, none of the regimens significantly reduced the number of aberrant crypts. However, SPI fed during initiation and promotion significantly increased the number of aberrant crypts. We hypothesized this increase was related to changes in protein quality with long term storage, as the SPI used had been stored for >2 years at room temperature. We next compared the effect of feeding an "aged SPI" with feeding recently processed SPI and a casein based diet on the promotional phase of aberrant crypt development. Carcinogen treated rats fed the aged SPI had a significantly greater number of aberrant crypts than the casein-fed control group. However, the number of aberrant crypts did not differ between the recently processed SPI and the casein-based diet. Recently processed SPI was then aged under increased temperature and relative humidity. Alkali extracts of the aged SPI exhibited much greater fluorescence then SPI held frozen, consistent with the formation of Maillard browning products. Finally, to examine the ability of SPI and genistein to inhibit tumor growth and metastases, human colon tumor was surgically transplanted into the cecum of nude mice (MetaMouseTM model). After recovery from surgery, the animals were fed diets that were either casein-based, SPI-based, casein-based containing genistein (0.3mg/kg and 1 mg/kg). There were no significant differences among the groups in either survival rate or tumor size. Thus, SPI and genistein do not appear to affect the progression of colon cancer, and the effect on initiation and promotion is uncertain.
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