Consumption of olive products has been established as a health-promoting dietary pattern due to their high content in compounds with eminent pharmacological properties and well-described bioactivities. However, their metabolism has not yet been fully described. The present critical review aimed to gather all scientific data of the past two decades regarding the absorption and metabolism of the foremost olive compounds, specifically of the phenylalcohols hydroxytyrosol (HTyr) and tyrosol (Tyr) and the secoiridoids oleacein (Olea), oleocanthal (Oleo) and oleuropein (Oleu). A meticulous record of the in vitro assays and in vivo (animals and humans) studies of the characteristic olive compounds was cited, and a critical discussion on their bioavailability and metabolism was performed taking into account data from their gut microbial metabolism. The existing critical review summarizes the existing knowledge regarding the bioavailability and metabolism of olive-characteristic phenylalchohols and secoiridoids and spotlights the lack of data for specific chemical groups and compounds. Critical observations and conclusions were derived from correlating structure with bioavailability data, while results from in vitro, animal and human studies were compared and discussed, giving significant insight to the future design of research approaches for the total bioavailability and metabolism exploration thereof.

Hydroxytyrosol (HT) is amongst the most potent natural scavengers of olive products found also in a plethora of foodstuffs, nutraceuticals and supplements. Critical factor for HT potency is its metabolisation fate in human system. Usually, the interpretation of the biochemical pathway that determines the bioavailability and activity is mainly based on plasma and urine analysis via LC–MS. However, the lack of appropriate standards, poses the risk of vague or imprecise identification and systematic quantification inaccuracies. Thus, the goal of the present study is the isolation of HT metabolites from urine and unambiguous identification thereof with NMR. For this purpose, urine samples from women after HT supplementation for a six-month period were used [1]. Urine is a matrix easily obtained in large volumes, providing information about individuals dietary exposure. Urine samples after solid phase extraction-(SPE) treatment were subjected to fractionation using Centrifugal Partition Chromatography-(CPC). CPC lacks solid support, which makes it an excellent choise for biological substrates analysis. After several trials, the best separation was achieved with the biphasic solvent system methyl-t-butyl ether/n-butanol/acetonitrile/water (2:3:1:4, with 8% AA), in ascending mode. For further purification of metabolites semi-preparative RP-HPLC was employed in certain fractions. For the identification both LC-HRMS and NMR were employed. So far, several HT metabolites together with endogenous ones have been identified, in high amount and purity. The unabiguous identification of metabolites and their correlation offer a better insight in HT bioavailability and mechanism of action. Publication Date: 13 December 2021 (online) © 2021. Thieme. All rights reserved. Georg Thieme Verlag Rüdigerstraße 14, 70469 Stuttgart, Germany

Hydroxytyrosol (HT) is one of the most characteristic compound of olive products and a highly potent compound with proven positive impact to human health [1]. Moreover, HT is also an endogenous metabolite produced from dopamine. The release of many HT-based products in the market directed the current research efford to the exploration of HT effect in obesity and investigation of its ADMET properties based on a human intervation study. Therefore, HT was administered as a soft capsule to 28 obese/overweight women in different doses to investigate its anti-obesity effect and the impact on urine metabolome. Towards this purpose, urine samples were collected in three time points (T=0, T=3 months, T=6 months) and analyzed via UPLC-Orbitrap MS using untargeted metabolomics aiming to biomarkers discovery. The three different groups (control, high and low dose) were discriminated according to the administered capsule and dose and 30 statistically significant metabolites were uncovered. Among them, hippuric acid (HA) and phenylacetylglutamine (PAG), two endogenous urine metabolites were distinguished. Additionally, UHPLC-TQ MS methodology using multipole reaction monitoring (MRM) method was used for HA and PAG quantitation in urine samples. HT and homovanillic acid, the most common metabolic derivative of HT, were also quantified. The proposed biomarkers levels verified our initial findings. HA and PAG were associated for the first time with HT consumption and could be utilised as biomarkers. Publication Date: 13 December 2021 (online) © 2021. Thieme. All rights reserved. Georg Thieme Verlag Rüdigerstraße 14, 70469 Stuttgart, Germany