Novel mutation and polymorphisms of the HMBS gene detected by denaturing HPLC.

Direct methanolic water extracts without any further treatment or extracts submitted to an acidic treatment yielded similar amounts of tyrosol present in olive oil: 216 ␮g (in 50 mL). From this value, urinary recoveries of tyrosol were unrealistic because they were 131.5–327.8% of the dose administered. When the tyrosol content was estimated after NaOH digestion and sonication of olive oil, the total tyrosol content was 1650 ␮g (in 50 mL). From this value, recoveries of tyrosol in the 24-h urine were 17– 43%, with a mean recovery of 24.7% Ϯ 8.5% (mean Ϯ SD). These values are likely to be a better estimate of the real bioavailability of this compound. The differences in recoveries between the extraction procedures probably reflect differences in the extent to which HCl and NaOH hydrolyze esterified forms of tyrosol present in olive oil (15). The results from the present study clearly show for the first time that urinary tyrosol concentrations are responsive to dietary intake of virgin olive oil. The method developed for urinary tyrosol determination has the sensitivity and accuracy to detect tyrosol in amounts typically present in the urine of nonsupplemented individuals. These results also underline the relevance of adequate estimation of administered phenolic doses in studies linking them to biological effects. In a recent report, recoveries of ϳ20% in urine from tyrosol-enriched olive oil were described (18). These recoveries were obtained after urine samples were submitted to enzymatic hydrolysis by ␤-glucuronidase. Taking into account the similar recoveries of tyrosol when different hydro-lytic procedures (enzymatic vs acidic) were used, it is very likely that tyrosol is excreted in the urine mainly as the glucuronoconjugate. From a theoretical perspective, studies after the administration of pure phenolic compounds or enriched foods have some interest. However, studies in which phenolic ingestion is closer to typical dietary patterns may be more appropriate for estimating bioavailability. Slight details in our study design may have some relevance in experimental results. As an example, subjects who in-gested olive oil with bread had a tyrosol recovery (20% Ϯ 3%; n ϭ 6) lower than that observed in those who directly drank the olive oil (37.5% Ϯ 5.5%; n ϭ 2). The present work is the first description of the bioavail-ability in humans of a phenolic compound present in olive oil administered in its natural form. We found that tyrosol was absorbed from virgin olive oil administered and that one part of …