Abstract LB-188: Isoflavone pharmacokinetics and metabolism after consumption of soy and soy-almond bread in men with asymptomatic prostate cancer.

Abstract

Abstract Background: Soy phytochemicals, particularly isoflavones, are hypothesized to have anti-prostate cancer activity. Soy isoflavones are present predominantly as glucosides but when combined with β-glucosidase activity in almond meal, a greater conversion to aglycones has been observed. We hypothesized that soy bread will serve as an excellent source of soy polyphenols and that an aglycone-rich soy-almond bread (SAB) compared to a glycoside-rich soy bread (SB) will demonstrate greater bioavailability of soy isoflavones. Methods: SB and SAB were fed in a 20 week randomized phase II cross-over trial involving 32 men with asymptomatic metastatic prostate cancer and escalating prostate specific antigen (PSA). Isoflavones were quantitated by HPLC in soy breads and isoflavone metabolites in 24h urine. HPLC-tandem mass spectrometry evaluated isoflavone pharmacokinetics in plasma. Biomarkers were determined by chemiluminescence-based assays. Results: The aglycone composition in the SB and SAB was 18% and 78%, respectively. Compliance was 95±14%, toxicity rare and limited to grade I GI complaints (NIH_NCI criteria). Urinary isoflavone patterns over 24hours revealed that isoflavonoid metabolites were significantly greater with soy bread consumption. Plasma pharmacokinetics following a test meal showed that daidzein (p=0.028) and genistein (p=0.010) absorption was significantly faster from the aglycone-rich SAB. Interestingly, PSA doubling time was prolonged compared to pre-enrollment, in 60% of men (n=30) with soy intervention. Conclusions: Bread is an excellent vehicle for the delivery of soy phytochemicals with outstanding compliance. Modification of soy bread with a source of β-glucosidase may enhance the initial absorption rates of isoflavones. Food products, such as SAB, with consistent and stable composition of phytochemicals can be developed that are appropriate for long-term chemoprevention studies in humans or as an adjunct to therapy. Citation Format: Jennifer H. Ahn-Jarvis, Steven K. Clinton, Elizabeth M. Grainger, Kenneth M. Riedl, Steven J. Schwartz, Yael Vodovotz. Isoflavone pharmacokinetics and metabolism after consumption of soy and soy-almond bread in men with asymptomatic prostate cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-188. doi:10.1158/1538-7445.AM2013-LB-188