In vitro studies have shown phenolics in olive oil to be strong radical scavengers. The absorption and elimination of two radiolabeled phenolic constituents of olive oil, hydroxytyrosol and tyrosol were studied in vivo using rats. Compounds were administered intravenously (in saline) and orally (in oil-and water-based solutions). For both compounds, the intravenously and orally administered oil-based dosings resulted in significantly greater elimination of the phenolics in urine within 24 h than the oral, aqueous dosing method. There was no significant difference in the amount of phenolic compounds eliminated in urine between the intravenous dosing method and the oral oil-based dosing method for either tyrosol or hydroxytyrosol. Oral bioavailability estimates of hydroxytyrosol when administered in an olive oil solution and when dosed as an aqueous solution were 99% and 75%, respectively. Oral bioavailability estimates of tyrosol, when orally administered in an olive oil solution and when dosed as an aqueous solution were 98% and 71%, respectively. This is the first study that has used a radiolabeled compound to study the in vivo biological fates of hydroxytyrosol and tyrosol.

Epidemiological studies have shown that the incidence of heart disease and certain cancers is lower in the Mediterranean region. This has been attributed to the high consumption of olive oil in the Mediterranean diet, which contains polyphenolic compounds with antioxidant activity. Although many in vitro studies have been performed to elucidate mechanisms by which these compounds may act, there are virtually no data relating to their fate after ingestion. Therefore, we decided to investigate the intestinal absorption of one of the major olive oil polyphenolics, oleuropein. To do this, a novel in situ intestinal perfusion technique was developed, and the absorption of oleuropein was studied under both iso-osmotic and hypotonic luminal conditions. Oleuropein was absorbed, with an apparent permeability coefficient (P:(app)) of 1.47 +/- 0.13 x 10(-6) cm/s (+/-SE) observed under iso-osmotic conditions. The mechanism of absorption is unclear but may involve transcellular transport (SGLT1) or paracellular movement. Under hypotonic conditions, the permeability of oleuropein was significantly greater (5.92 +/- 0.49 x 10(-6) cm/s, P: < 0.001). This increase is thought to be due to an increase in paracellular movement facilitated by the opening of paracellular junctions in response to hypotonicity. Overall, we determined that the olive oil polyphenolic oleuropein can be absorbed, albeit poorly, from isolated perfused rat intestine. Therefore, it is possible that it or its metabolites may confer a positive health benefit after the consumption of olive oil, most likely via an antioxidant mechanism.

We have examined the inhibition of human hepatic microsomal androstenedione 6beta-hydroxylation and both reductive and oxidative 17beta-hydroxysteroid dehydrogenase (17beta-HSD) activity by complex phenols found in olive oil. Structurally similar compounds were also examined for comparison. Androstenedione 6beta-hydroxylase activity was inhibited by oleuropein glycoside, hydroxytyrosol and gallic acid. Oleuropein glycoside, hydroxytyrosol, gallic acid and dihydroxybenzoic acid also inhibited reductive 17beta-HSD activity. Oxidative 17beta-HSD activity was not inhibited by any of the compounds tested; however gallic acid stimulated activity by approximately 30%. Androstenedione 6beta-hydroxylase activity showed atypical kinetics. For oleuropein glycoside, hydroxytyrosol and gallic acid the apparent K(i) values were determined to be 80, 77 and 70 micromol/L, respectively. Analysis of structural features of inhibitory compounds established that a 3,4-dihydroxyphenyl ethanol structure was required for inhibition of androstenedione 6beta-hydroxylase for this group of compounds.

In patients with ulcerative colitis receiving maintenance 5-ASA therapy there was greater absorption and less acetylation of 5-ASA from mesalazine (Asacol) compared with sulphasalazine or olsalazine, but no evidence from this study that this resulted in increased nephrotoxicity.

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