Oleuropein antioxidant activity

Oleuropein antioxidant activity was evaluated "ex vivo", in rats treated with 100 mg/kg of the compound [96]. Plasma and bile were collected and assayed for chemiluminescence reaction. The addition of a solution of antioxidant to a glowing steady-state chemiluminescent reaction temporarily interrupts the light output. The light emission is restored after a time interval that is related to the amount of anti-oxidant added [97]. Bile was collected at 30 min interval for 2 hrs plasma was collected before sacrifice. No difference of light emission was measured with plasma from controls and treated animals. Bile samples of treated animals showed a significant inhibition (90%) of the light emission compared with bile samples from control animals (60%). 

The olives themselves contain many phenolic compounds with antioxidant properties. Bouaziz et al. (2005) investigated the olive cultivar Chemlali from Tunisia. Oleuropein (7.14), a bitter glycoside esterified with a phenolic acid, was the major compound present. Phenolic monomers and twelve flavonoids were also identified. The antioxidant activity of the extract was evaluated. Acid hydrolysis of the extract enhanced its antioxidant activity. / -Hydroxyphenyl-cthanol (7.12) and quercetin (1.43) showed antioxidant activities similar to that of 2,6-di-fert-butyl-4-methyl phenol (7.15), a reference compound with known antioxidant properties. It was suggested that a hydroxyl group at the ortho-position on the flavonoid B ring could contribute to the antioxidant activity of the flavonoids. 

During malaxation, when water is added to olive paste to wash it, tons of waste water (800.000 in Italy only) are produced from the oil industry and discarded. Water soluble compounds are then transfered from olives into waste waters and could be recovered. HPLC analysis of the waste water extract showed the presence of hydroxytyrosol, tyrosol, p-OH benzoic acid, vanillic acid, caffeic acid, oleuropein, verbascoside and other oleuropein derivatives. The extract had powerful antioxidant activity and could represent a cheap source of natural antioxidants to be used to preserve food and cosmetics from fat oxidation and rancidity [51]. 

Rat hepatocytes were treated with Fe-NTA (nitriloacetic acid) [49]. In this model, all the tested compounds, including tyrosol, were able to inhibit lipoperoxidation in the same concentration range 20-100 pM (hydroxytyrosol, caffeic acid and oleuropein). The antioxidant activity of caffeic acid has been already described in erythrocytes, rat isolated... 

The occurrence in the olive pomace of unique oleuropein oligomers (14) with a degree of polymerization of up to five oleuropein monomers was reported by Cardoso et al. [27]. Their bioactivities have, however, not yet been studied. In fact, besides the evidence that olive phenolic compounds can have antioxidant, cardioprotective, antimicrobial, antihypertensive, anti-inflammatory, and chemo-preventive properties [26], the majority of the studies have focused on hydroxytyrosol (15). This compound has revealed remarkable pharmacological and antioxidant activities and thus has been further studied for its bioavaUability and metabolism in humans in order to establish its health-beneficial effects [29-31]. 

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]. 

Using BHT (butylated hydroxytoluene), ascorbic acid and a-tocopherol as standards for comparison, Amro el al. [67] carried out some experimental tests to identify the olive compounds responsible for antioxidant and radical scavenging activities. After a testing period, fraction containing oleuropein showed a significant antioxidant activity, even if the auto-oxidation of the representative fraction of material cake of tested olive was less than those treated with BHT [67]. 

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. 

Ma et al. [132] evaluated the antiviral activity in vitro of five glucoside secoiridoids, lucidumoside C (91), oleoside (78), oleuropein (81), ligustroside (82), and lucidumoside A (93) of Ligustrum lucidum to see if there were any correlation with the antioxidant activity above cited [53],Four strains of pathogenic viruses were used, simple herpes type 1 virus (HSV-1), influence type A virus (FluA), respiratory syncytial virus... 

As summarized in the previous paragraph, LDL cholesterol is oxidized to various oxysterols due with high cytotoxicity and promoting vascular injury [63]. Oleuropein and a mixture of phenols extracted from virgin oil inhibited dose-dependently the formation of oxysterols and prevented apoprotein modification in UV irradiated LDL. IC50 are shown in table 4 results indicate that the mixture is more potent than the single compounds and probucol, a hypocholesterolemic drug with well-known antioxidant activity. As expected the contribution of tyrosol to the antioxidant effect was minimal [71]. 

In diphenols with antioxidant activity (hydroxytyrosol, oleuropein, and caffeic acid), the rates of reactions (ii) and (iv) greatly exceed the rates of reactions (iii) and (v). However, for monopherols including tyrosol, reactions (iii) and (v) are relatively rapid and consequently the molecule lacks effective antioxidant activity. " ... 

Jemai H et al (2008) Hypolipidimic and antioxidant activities of oleuropein and its hydrolysis derivative-rich extracts fiorn Chemlali olive leaves. Chem Biol Interact... 

The characteristics of laboratory-scale extraction methods (e.g., time, extraction efficiency, extractant namre, working temperature) are poorly documented as researchers in this field have so far focussed on the determination of oleuropein and its derivatives [256,257], and the antioxidant activity of the phenolics extracted [231], but not on optimizing the extraction process itself. The extraction methods reported so far are complex and take hours or even days to complete. Sequential extraction of powdered leaves with 1 1 methanol-water, chloroform, and ethyl acetate was attempted by Savoumin et al. [256]. In any case, such toxic extractants should be avoided if the products are ultimately aimed at human use. 

The comparison of the antioxidant potency of hydroxytyrosol, tyrosol, oleuropein with respect to vitamin E and BHT and the synergistic effect with vitamin E were studied in thermal initiated oxidation of methyl linoleate in the presence of azo-compounds, in heptanol or propanohwater. The activity of the phenols was expressed as increase of induction period and extent of reaction inhibition [47]. The azo compounds initiated oxidation is a free radical chain process. Confirming the results from a previous study [43], this study showed that hydroxytyrosol and oleuropein were much more effective than BHT and vitamin E in extending the induction period. Tyrosol was devoid of activity and no synergistic effect on the preservation of methyl linoleate was foxmd when vitamin E was used together with tyrosol. 

Evaluation of olive- and grape-based natural extracts as potential preservatives for food was carried out by Serra et al. (2008). The antimicrobial activities of two waste-derived extracts, from olive oil and wine production, both rich in polyphenols, and three standard well recognized antioxidants (quercetin, hydroxytyrosol, and oleuropein) were investigated against five microbial species (Escherichia coli, Salmonella poona, Bacillus... 

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],... 

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