Quantification of free and protein-bound trans-resveratrol metabolites and identification of trans-resveratrol-C/O-conjugated diglucuronides - two novel resveratrol metabolites in human plasma.

The polyphenol trans-resveratrol (t-RES) is present as t-RES-3-O-beta-D-glycoside, termed piceid, in several plant-derived foods. Although data on the metabolism and on in vivo effects of t-RES have been reported, quantitative data on the metabolites formed after dietary intake of t-RES or piceid are still lacking. In this study, 85.5 mg of piceid per 70 kg of body weight (bw) were administered to healthy volunteers in a bolus dose. t-RES metabolites formed in plasma and urine were identified and quantified by LC-MS/MS, NMR, and HPLC-DAD analysis using chemically synthesized t-RES conjugate standards. In addition, the amount of t-RES metabolites bound noncovalently to plasma proteins was determined for the first time in humans. The metabolites identified and quantified were t-RES-3-sulfate, t-RES-3,4'-disulfate, t-RES-3,5-disulfate, t-RES-3-glucuronide and t-RES-4'-glucuronide, with t-RES-sulfates being the dominant conjugates in plasma and urine. Besides these metabolites, two novel t-RES-C/O-conjugated diglucuronides have been identified and quantified in plasma and urine. Moreover, it could be shown that up to 50% of the plasma t-RES-3-sulfate, t-RES-disulfates, and the novel t-RES-C/O-diglucuronides were bound to proteins. Total recovery of the dietary administered piceid in urine ranged between 13.6 and 35.7%.