Metabolic disposition and biological significance of simple phenols of dietary origin: hydroxytyrosol and tyrosol

Hydroxytyrosol and tyrosol are dietary phenolic compounds present in virgin olive oil and wine. Both compounds are also endogenously synthesized in our body as byproducts of dopamine and tyramine metabolisms, respectively. Over the last decades, research into hydroxytyrosol and tyrosol has experienced an increasing interest due to the role that these compounds may play in the prevention of certain pathologies (e.g. cardiovascular, metabolic, neurodegenerative diseases and cancer). The translation of promising in vitro and in vivo biological effects from preclinical studies to the context of human disease prevention initially depends on whether the dose ingested becomes available at the site of action. In this regard, information regarding the bioavailability and metabolic disposition of hydroxytyrosol and tyrosol is of most importance to evaluate the impact they may have on human health. In this review, we discuss and summarize the state of the art of the scientific evidence regarding the processes of absorption, distribution, metabolism and excretion of both hydroxytyrosol and tyrosol. We also examine the impact of these compounds and their metabolites on biological activity in terms of beneficial health effects. Finally, we evaluate the different analytical approaches that have been developed to measure the plasma and urinary levels of hydroxytyrosol, tyrosol and their metabolites.This work was supported by grants from Instituto de Salud Carlos III FEDER, (PI14/00072) and from DIUE de la Generalitat de Catalunya (2014SGR 680). JRM was supported by a FI-DGR2012 predoctoral fellowship from the Generalitat de Catalunya and CPM was supported by a Juan Rodes fellowship (ISCIII, JR, 15/00005). CIBER de Fisiopatologıa de la Obesidad y Nutricion (CIBEROBN) is an initiative of the Instituto de Salud Carlos III, Madrid, Spain