Hydroxy-tyrosol

Oleuropein and its metabolites are terpenoids present in all parts of plant and represent the chemotaxonomic markers of O. europaea. Tyrosol, hydroxy-tyrosol and related compounds represent the main characteristic phenolic fraction of O. europaea and are recognised as very powerful anti-oxidising agents. 

In the olive, there are two main compounds, besides that reported in the literature. The first one is oleuropein, the first secoiridoid isolated in 1960 by Panizzi in Roma, as mentioned above. The second one is the comoside that is a hemiquinone glucoside, structurally and biogenetically related to hydroxy-tyrosol that is the principal free phenol in the olive. It should be remembered that, depending on the olive cultivar, the oleuropein can be prevalent against the comoside, or it could be the contrary, until reaching the equality. 

Comoside 11 is a glucoside that could be biogenetically related to hydroxy-tyrosol, the main phenolic component of O. europaea. 

Tyrosol and hydroxy-tyrosol glucosides (Fig.6) constitute the principal part of minor phenolic components of olive. In fact, hydroxy-tyrosol 14 and tyrosol 18 are present in all parts of 0. europaea. It seems that glucose links all hydroxyls of phenol moiety without an evident... 

Hydroxy-tyrosol glucosides were isolated from different olive cultivars, and their relative quantities seem to be in relation with the olive organ considered [14],... 

Structures of compounds 15-17 were determined by spectroscopical method, essentially H- and 13C-NMR spectroscopy. Comparison between t3C-NMR data of glucosides 15-17 and hydroxy-tyrosol allowed to determine the site of glucosylation and therefore the structure of these compounds. 

Compound 22, ligstroside, is very similar to oleuropein from which it differs for the presence of a tyrosol unit instead of hydroxy-tyrosol [24]. 

This usually happens in mild acid conditions. These two rearrangements are the first one is hydroxy tyrosol 14, that arises from a... 

Pharmacological studies were mainly focussed on oleuropein that represents die key phenolic compound in O. europaea, and on related phenolic compounds such as tyrosol and hydroxy-tyrosol. Therefore, the following discussion will be focussed on reported biological activity of these compounds. 

Oleuropein and hydroxy-tyrosol, derived from oleuropein hydrolysis [46], possess several biological properties certainly mediated by their antioxidant and free radical-scavenging ability (antimicrobial, hypotensive, vasodilatator and hypoglycaemic activities) [47],... 

The antioxidative effect of oleuropein and hydroxy-tyrosol (see Fig 20) was investigated by Saija et al. [51], in a model system consisting of dipalmitoyl-phosphatidyl-eholine/Unoleic acid unilamellar vesicles and a water-soluble azo-compound as a free radical generator. 

Oleuropein appears to interfere with some biological processes such as lipoprotein oxidation, platelet aggregation, platelet and leukocyte eicosanoid production and cardiovascular control too. As previously described, oleuropein and hydroxy-tyrosol are characterised by a catechol moiety that appears to be needed for their scavenger and antioxidant activities. In fact, it was demonstrated that these compounds prevent thermally initiated autoxidation of methyl linoleate in homogenous solutions [56], protect LDL from oxidation [57] and inhibit production of... 

The free radical-scavenging capacity of oleuropein and hydroxy-tyrosol was tested, using some radical generators. As a radical initiator, AAPH 2,2 -azobis (2-amidinopropane)-hydrochloride) was used for peroxyl radicals generation, because it is a common free radical found in the body [59] and has often been used in several antioxidant activity assays [60]. It appears to be slightly less reactive than OH-radical [61]. 

Other experimental studies carried out with a different radical, DPPH (7, l-diphenyl-2-picrylhydrazyl radical), revealed that oleuropein and hydroxy-tyrosol elicit a good, concentration-dependent, scavenging effect... 

Incubation of DPPC/LA idipalmitoylphosphatidylcholine/linoleic acid) LUV with AAPH increased the accumulation of LOOH (linoleic peroxy acid) formed from LA peroxidation. When the tested biphenols were added, a reduction in the amount of LOOH formed was observed and thus oleuropein proved more effective than hydroxy-tyrosol [62]. 

The cited works demonstrated that oleuropein and hydroxy-tyrosol are potent antioxidants against lipid peroxidation in phospholipid bilayers, induced by aqueous oxygen radicals. These results may be very interesting, because biphenols could have important applications in human diseases caused by free radical damage. 

The antioxidant effects of natural phenols in olive oils was studied by Papadopoulos [46], adding extracts of a VOQ, having polyphenols, to a sophisticated bleaching oil, washed-out of phenolic antioxidants and evidenced a significant inhibition of auto-oxidation over time in comparison with samples without such an addition. On the other hand, it has revealed that this effect is more pronounced in hydroxy-tyrosol than caffeic acid and protocatechuic acid... 

Reactive oxygen species are associated to xanthine/ipoxanthine system. In fact, the oxidative stress caused by hydrogen peroxide and xanthine oxidase is repressed in the presence of hydroxy-tyrosol, though, unexpectedly, it was inactive in concentrations under 500 pmol/L. The... 

These results showed that oleuropein has a good antioxidative activity. The beneficial health effects of Mediterranean diet are probably related to non-nutrient components present in foods, such as olive oil, as well as wine and others. In fact, oleuropein and hydroxy-tyrosol, both green and black tea components and gallic acid inhibit androstenedione 6-p-hydroxylase activity. 

Some results evidenced that human CYP3A have a very good capacity to generate reactive oxygen species therefore, there were interesting results in examining the effects of dietary phenols, such as oleuropein and hydroxy-tyrosol, known CYP3 A inhibitors [69],... 

However, it is chiefly underlined that olive oil phenols, such as hydroxy-tyrosol, and others food-derived compounds, such as gallic acid, work as free radical scavengers. Recently, free radicals have been correlated to several diseases for human health. 

Hydroxy-tyrosol (DPE 3,4-dihydroxyphenylethanol) is a liposoluble and hydrosoluble compound present in high concentration in extra virgin olive oil, in free or esterified form, such as oleuropein aglycone [42-43]. 

Hydroxy-tyrosol oCoumaric acid Gallic acid... 

Aeschbach, R., Loliger, J., Scott, B.C., Murcia, A., Butler, J., Halliwell, B., and Aruoma, O.I. 1994. Antioxidant actions of thymol, carvacrol, 6-gingerol, zingerone and hydroxy-tyrosol. Food Chem. Toxicol, 32 31-36. 

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