The effect of isolated soy protein on plasma biomarkers in elderly men with elevated serum prostate specific antigen.
OBJECTIVE
We performed a randomized double-blind crossover pilot study in elderly men with elevated prostate specific antigen (PSA) on the effects of the daily consumption of 2 soy beverages, each containing 20 gm. of isolated soy protein, on the isoflavone concentration in blood and urine, and on the 3 serum biomarkers cholesterol, PSA and the soluble p105 component of the p185erbB-2 proto-oncogene.


METHODS
A total of 34 men supplemented their diet by consuming 1 of 2 soy protein beverages assigned randomly twice daily for a 6-week period. In a second 6-week period they consumed the other soy protein beverage. The beverage ISP+ provided 42 mg. of genistein and 27 mg. of daidzein daily, whereas the other beverage, ISP-, provided only 2.1 and 1.3 mg. of these isoflavones daily, respectively. Blood and 24-hour urine samples were obtained before the study, at 2-week intervals during the study and 2 weeks after study completion.


RESULTS
ISP+ and to a lesser extent ISP- substantially increased the serum concentration and urinary output of the isoflavones and their metabolites. Serum cholesterol was significantly decreased by ISP+ irrespective of the order in which the 2 soy beverages were administered and in apparent correlation with the total isoflavone concentration. There was no significant effect of the soy beverages on serum PSA and p105erbB-2 values.


CONCLUSIONS
This study reveals that short-term exposure of elderly men with elevated serum PSA values to soy protein containing isoflavones decreases serum cholesterol but not the serum biomarkers PSA and p105erbB-2.
Urban
D
D
Division of Urology, Departments of Surgery, Pathology and Pharmacology and Toxicology, and Biostatistics Unit and Mass Spectrometry Shared Facility, Comprehensive Cancer Center, University of Alabama at Birmingham, USA.
Irwin
W
W
Kirk
M
M
Markiewicz
M A
MA
Myers
R
R
Smith
M
M
Weiss
H
H
Grizzle
W E
WE
Barnes
S
S
D000368:Aged; D015415:Biomarkers / Q000097:blood; D002784:Cholesterol / Q000097:blood; D018592:Cross-Over Studies; D004311:Double-Blind Method; D006801:Humans; D007529:Isoflavones / Q000378:metabolism / Q000494:pharmacology; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D017430:Prostate-Specific Antigen / Q000097:blood*; D000090063:Proto-Oncogene Mas; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000097:blood; D030262:Soybean Proteins / Q000494:pharmacology*; D013997:Time Factors
D015415:Biomarkers; D002784:Cholesterol; D007529:Isoflavones; D017430:Prostate-Specific Antigen; D000090063:Proto-Oncogene Mas; D018719:Erb-b2 Receptor Tyrosine Kinases; D030262:Soybean Proteins; C000715470:MAS1 protein, human