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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
Soy Consumption and Cancer Risk : Human StudiesA double-blind, clinical trial of the effects of soy protein on risk parameters for prostate cancer
S. Barnes, D. Urban, W. E. Grizzle, L. Coward, M. Kirk, H. Weiss and W. Irwin
Departments of Pathology and Pharmacology & Toxicology, Division of Urology, Department of Surgery, and Biostatistics Unit and Mass Spectrometry Shared Facility, Comprehensive Cancer Center, University of Alabama at Birmingham, AL 35294, USA.Epidemiological studies have suggested that consumption of soy foods is associated with a reduced risk of prostate cancer. The soy isoflavone genistein (GEN) inhibits the proliferation of human prostate cancer cell lines and freshly isolated prostatic tissue in tissue culture (Geller et. al.., 10th International Congress of Endocrinology, 1996). To determine whether soy protein can alter serum biomarkers of prostate cancer, a pilot clinical trial is being carried out on elderly men who have prostate specific antigen (PSA) values 4 ng/ml, but no prostate cancer, as determined by digital rectal examination and prostate tissue biopsy. A crossover design for the study is used, each patient serving as his own control. The subjects in the study consume one of two soy protein beverages (20g of protein) in each of two six-week periods - each subject consumes the other soy protein beverage in a second 6-week period. Both soy beverages are made using isolated soy protein; one is extracted with ethanol (ISP-) and the other is unextracted (ISP+) and contains 1 mg/g genistein. This study design allowed for a better control of any effect of ISP- on serum biomarkers (PSA and pp105erbB-2, and cholesterol) than using milk proteins. ISP- contained ten-fold lower concentrations of isoflavones compared to ISP+. At this time 17 patients have been recruited into the study, six of whom have completed both arms. Analysis in fasting plasma of the soy isoflavones GEN and daidzein (DZN) and their metabolites, dihydrodaidzein (DHD), O-desmethylangolensin (oDMA) and equol (EQ) by HPLC-multiple reaction ion-mass spectrometry (Clin Chim Acta 247: 121-142, 1996) revealed that (1) EQ appeared in one of the six subjects on ISP+, but not on ISP-, (2) in most patients, DZN metabolites exceeded DZN itself, and (3) GEN and DZN were detectable in plasma in patients on ISP-. This study when complete will determine the short term effects of isolated soy protein on serum biomarkers and on isoflavone metabolism.
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