Novel biomarkers of the metabolism of caffeic acid derivatives in vivo

The purpose of this study was to investigate biomarkers of the bioavailabil ity and metabolism of hydroxy cinnamate derivatives through the determinati on of the pharmacokinetics of their urinary elimination and identification of the metabolites excreted. Coffee was used as a rich source of caffeic ac id derivatives and human supplementation was undertaken. The results show a highly significant increase in the excretion of ferulic, isoferulic, dihyd roferulic acid (3-(4-hydroxy-3-methoxyphenyl)-propionic acid), and vanillic acid postsupplementation relative to the levels presupplementation. Thus, ferulic, isoferulic, and dihydroferulic acids are specific biomarkers for t he bioavailability and metabolism of dietary caffeic acid esters. Isoferuli c acid is a unique biomarker as it is not a dietary component, however, dih ydroferulic acid may well derive from other flavonoids with a structurally related B-ring. 3-Hydroxyhippuric acid has also been identified as an indic ator for bioavailability and metabolism of phenolic compounds, and shows a highly significant excretion increase postsupplementation. The results reve al isoferulic acid (and possibly dihydroferulic acid) as novel markers of c affeoyl quinic acid metabolism. (C) 2001 Elsevier Science Inc.