Abstract
Better knowledge of the bioavailability and metabolism of isoflavones in prostate tissue is needed to further investigate their mechanisms of action in the context of prostate cancer prevention. A total of 12 men with benign prostatic hyperplasia received soy extract supplementation (3 Evestrel® capsules, providing a total of 112.5 mg isoflavones aglycone eq/day) for 3 days before prostate surgery. Blood and prostate tissues were sampled and metabolites were identified using electrospray ionization liquid chromatography tandem mass spectrometry (LC-ESI-MS/MS) and chemically synthesized standards of glucuronidated isoflavones. The main metabolites were the same in prostate tissue and in plasma, namely, 2 monoglucuronides of daidzein and 2 monoglucuronides of genistein. Concentrations of total isoflavones measured in prostate reached 1.05 ± 0.62 nmol/g tissue (range 0.30–2.23) at the time of sampling, 12 h after the last isoflavone supplementation. At that time point, prostate concentrations were lower than plasma concentrations in all volunteers: 0.47 nmol/g vs. 0.66 μ M for daidzein and 0.58 nmol/g vs. 0.78 μ M for genistein. Isoflavone mechanisms of action should thus be investigated in in vitro cell studies using physiological conditions, intracellular concentrations below 5 nmol/g and no intracellular deconjugation of the monoglucuronide metabolites.
ACKNOWLEDGMENTS
M. Urpi-Sarda thanks the FPI fellowship and AGL2004-08378-C02-01/02 project from Spanish Ministry of Education and Science. A. Gil-Izquierdo is grateful to the Spanish Ministry of Education and Science for his postdoctoral fellowship.
Notes
a Abbreviations are as follows: MRM, multiple reaction monitoring; Nd, not detected; tr, trace; +/−, present in some but not all samples.