Prostatic soy isoflavone concentrations exceed serum levels after dietary supplementation.

ABSTRACT

BACKGROUND: The effects of soy isoflavones on prostate cancer may be concentration-dependent. The impact of soy supplementation on isoflavone concentrations in prostate tissues and serum remain unclear. OBJECTIVE: To assess and compare concentrations of soy isoflavones in prostate tissue and serum among 19 men with prostate cancer who had elected to undergo radical prostatectomy. METHODS: Participants were randomized to receive either daily soy supplements (82 mg/day aglycone equivalents) or placebos for 2 weeks (14 days) prior to surgery. Serum samples were obtained at the time of the surgery. Isoflavone concentrations were measured by HPLC/ESI-MS-MS. RESULTS: The median (25th, 75th percentile) total isoflavone concentration in the isoflavone-supplemented group was 2.3 micromol/L (1.2, 6.9) in the prostate tissue and 0.7 micromol/L (0.2, 1.2) in the serum. Total isoflavone concentrations in this group were an average of approximately 6-fold higher in prostate tissue compared to serum; the tissue versus serum ratio was significantly lower for genistein than daidzein, 4-fold versus 10-fold, P = 0.003. Tissue and serum levels of isoflavones among the placebo group were negligible with a few exceptions. CONCLUSIONS: The findings from the present study suggest that prostate tissue may have the ability to concentrate dietary soy isoflavones to potentially anti-carcinogenic levels.