4. Discussion
CSimilar, watery, HT
OXIDATIVE STRESS
The two food supplements studied here are based on ingredients of vegetable origin, mainly olive concentrate resulting from the aqueous by-product generated during olive oil production, and thus contain HT as the main bioactive component. In addition, they contain lemon juice (IP-1) or grape juice (IP-2) concentrates. Despite olive phenolics being a promising functional ingredient, the bioavailability of HT and its derivates could be modulated by the matrix with which they are administered [In line with other studies conducted with olive oil and pure HT [HT metabolites, which were undetected in plasma in the fasting state, were rapidly cleared from plasma in the postprandial phase (CSimilar to previous studies reporting a dose-dependent absorption of HT contained in administered oil [The absolute amount of HT in urine (as the sum of all quantifiable metabolites in 12 h) correlated with the dose administered. This degree of correlation for the three different intervention products was fortified EVOO < IP-1 < IP-2. However, the excreted percentage of the total ingested HT was as follows: fortified EVOO < IP-2 < IP-1. Overall the excretion ranged from 28 to 60%, which is consistent with previously published data [The highest average concentrations of HT metabolites in plasma (as the sum of all the metabolites) were found 30 min after intake of the food supplements, being significantly different to the intake of EVOO, which only rarely showed levels above the quantification limit. HT is highly metabolized mainly to HVA, HT-3-S, and DOPAC; these metabolites (free forms) could often be detected in plasma samples from the food supplement groups and especially immediately after ingestion, but only very rarely in the fortified-EVOO group. Moreover, after ingestion both DOPAC and HVA, reach the maximum plasma concentration at 30 min for both supplements. DOPAC concentration was lower and its elimination faster than that of HVA; this is likely due to DOPAC’s enzymatic transformation into HVA via catecholmethyltransferase [Our findings indicate that regardless of the food matrix (i.e., watery or oily), the free forms of HVA and DOPAC, which result from the oxidation and/or methylation of dietary HT, contribute to a greater extent to the metabolization of HT in the human body. To date, few human studies have looked for the free forms of these metabolites after HT ingestion. Earlier studies conducted with olive oil observed an increase in total HVA (after hydrolysis) in 24 h pooled urine [Among the phase II conjugates, sulphated metabolites (particularly HT-3-S) are preferred over glucuronidated ones. These results are in line with previous studies showing that sulphation at position 3 is preferred to position 4 [Overall, our results show that after ingestion of both aqueous dietary supplements, HT is indeed absorbed and highly metabolized into phase I and phase II metabolites. Moreover, the absence of free HT in the biological samples suggests that its metabolites, especially HVA, DOPAC, and HT-3-S, are more likely to define the positive effects of olive phenolics reported in vivo. These results promise a good potential of both food supplements for the protection against oxidative stress in vivo. Further, the outcomes of this trial let us expect that potential health benefits of both food supplements can be shown in the postprandial phase with the help of lipoxidation markers, as bioavailable HT is expected to counteract lipoxidation.