The effect of tyrosol, hydroxytyrosol and oleuropein on the non-enzymatic lipid peroxidation of rat liver microsomes

The effects of the polyphenolic compounds from virgin olive oil: tyrosol, h ydroxytyrosol and oleuropein on the non-enzymatic lipid peroxidation induce d by ascorbate-Fe2+ of rat liver microsomes were examined. The inhibition o f light emission (maximal induced chemiluminescence) by oleuropein was conc entration dependent. Hydroxytyrosol showed a substantial degree of inhibiti on against ascorbate-Fe2+ induced lipid peroxidation in rat liver microsome s that was at least 6 times higher than that observed in the presence of ol europein. Inhibition of lipid peroxidation by tyrosol was not observed. In rat liver microsomes incubated alone or in the presence of tyrosol, the fat ty acid composition was profoundly modified when subjected to in vitro pero xidation mediated by ascorbate-Fe2+, with a considerable decrease of 18:2n6 and 20:4n6; however, changes in fatty acid composition were not observed w hen microsomes were incubated with hydroxytyrosol. When oleuropein was used at low concentration (5, 15 muM) a considerable decrease of 20:4n6 was obs erved, but 18:2n6 was not modified; at higher concentration (30, 60 muM) ch anges in fatty acid composition were not observed. There was a very good co rrelation between the presence of oxidized phospholipids and the changes in polyunsaturated fatty acids previously observed. Thus, hydroxytyrosol show ed the highest protection again oxidized phospholipid formation. The presen ce of oleuropein at low concentration (5, 15 muM) does not prevent the form ation of oxidized phospholipids (8.02 +/- 1.22 and 1.22 +/- 1.22) but conce ntration higher than 30 muM avoids completely the formation of this molecul es whereas tyrosol at any concentration assayed was found to be ineffective and allows the formation not only of oxidized phospholipids but also of ox idized cholesterol.