Identification and pharmacokinetics of novel alkylresorcinol metabolites in human urine, new candidate biomarkers for whole-grain wheat and rye intake.

Biomarkers of dietary intake are prominent tools in nutritional research. The alkylresorcinol metabolites 3,5-dihydroxybenzoic acid (3,5-DHBA) and 3-(3,5-dihydroxyphenyl)propanoic acid (3,5-DHPPA) have been proposed as exposure biomarkers of whole-grain (WG) wheat and rye intake. However, the profile of alkylresorcinol metabolites is not fully understood. The aim of this study was to investigate the metabolism of alkylresorcinols in mice and in humans, while further determining urinary pharmacokinetics of the novel alkylresorcinol metabolites to explore their potential as biomarkers of WG wheat intake. Utilization of the liquid chromatography-mass spectrometry approach resulted in 10 alkylresorcinol metabolites identified in mice and in humans, including 3 phenolic acids and 7 of their phase II conjugates. Among them, 2 novel metabolites were discovered: 5-(3,5-dihydroxyphenyl)pentanoic acid (3,5-DHPPTA) and 2-(3,5-dihydroxybenzamido)acetic acid (3,5-DHBA glycine). The structures of these 2 metabolites were confirmed by comparing with authentic standards synthesized in-house. In the pharmacokinetic study, a group of 12 volunteers consumed a polyphenolic-restricted diet for 4 d before ingesting WG wheat bread containing 61 mg of alkylresorcinols. Urine samples were collected for 32 h, and alkylresorcinol metabolites were quantified with HPLC-coulometric electrode array detection. The mean urinary excretion rates and mean apparent half-life of 3,5-DHPPTA, 3,5-DHBA glycine, 3,5-DHBA, and 3,5-DHPPA at each time point were determined. Our results suggest that 3,5-DHPPTA and 3,5-DHBA glycine may be used in combination with 3,5-DHBA and 3,5-DHPPA as potential biomarkers to increase the accuracy of recording WG wheat and rye intake in epidemiologic studies. Further validation of 3,5-DHPPTA and 3,5-DHBA glycine as potential biomarkers is warranted.