CYP2D6 and CYP2A6 biotransform dietary tyrosol into hydroxytyrosol

[Display omitted] •The mechanism of tyrosol-to-hydroxytyrosol conversion remained unknown.•Tyrosine hydroxylase was not involved in the formation of hydroxytyrosol (HT).•CYP2A6 and CYP2D6 catalyzed the conversion of tyrosol into HT.•Interindividual differences on HT formation were found in human genotyped livers.•Dietary benefits of tyrosol-containing foods remain to be evaluated in light of CYP polymorphisms. The dietary phenol tyrosol has been reported to be endogenously transformed into hydroxytyrosol, a potent antioxidant with multiple health benefits. In this work, we evaluated whether tyrosine hydroxylase (TH) and cytochrome P450s (CYPs) catalyzed this process. To assess TH involvement, Wistar rats were treated with α-methyl-L-tyrosine and tyrosol. Tyrosol was converted into hydroxytyrosol whilst α-methyl-L-tyrosine did not inhibit the biotransformation. The role of CYP was assessed in human liver microsomes (HLM) and tyrosol-to-hydroxytyrosol conversion was observed. Screening with selective enzymatic CYP inhibitors identified CYP2A6 as the major isoform involved in this process. Studies with baculosomes further demonstrated that CYP2D6 and CYP3A4 could transform tyrosol into hydroxytyrosol. Experiments using human genotyped livers showed an interindividual variability in hydroxytyrosol formation and supported findings that CYP2D6 and CYP2A6 mediated this reaction. The dietary health benefits of tyrosol-containing foods remain to be evaluated in light of CYP pharmacogenetics.