Human absorption of a supplement containing purified hydroxytyrosol, a natural antioxidant from olive oil, and evidence for its transient association with low-density lipoproteins

There is growing interest in the health effects of olive oil polyphenols, particularly hydroxytyrosol (HT), for their potential application in the treatment of inflammatory conditions such as cardiovascular disease (CVD). As oxidative modification of low-density lipoproteins (LDL) plays a central role in the development of CVD, natural antioxidants are a main target for the nutraceutical industry. In this study we firstly investigated the absorption of pure hydroxytyrosol (99.5%) administered as a supplement in an aqueous solution (2.5 mg/kg BW) in the plasma and urine of healthy volunteers (n = 10).Plasma Cmax for HT and homovanillic alcohol (HvOH) were detected at 13.0 ± 1.5 and 16.7 ± 2.4 min, respectively. The HT and HvOH levels were undetectable 2-h after the administration. HT, HvOH, homovanillic acid and 3,4-dihydroxyphenylacetic acid were found as free forms (44%) or as glucuronide (34.4%) or sulphate (21.2%) conjugates in the 24-h urine samples of the subjects.In a second phase of the study, the same amounts of HT were administered to the subjects and the presence of HT in purified plasma lipoproteins was investigated in LDL fractions freshly isolated. 10 min after the ingestion of the HT supplement, more than 50% of the total amount detected was present in the LDL-purified fractions and its concentration declined in accordance with its presence in plasma but no changes were found in total antioxidant capacity, malondialdehyde or LDL lag time. These results indicate that pure HT transiently associates with LDL lipoproteins in vivo.