Myeloperoxidase/nitrite-mediated lipid peroxidation of low-density lipoprotein as modulated by flavonoids

In the presence of a H2O2-generating system, myeloperoxidase (MPO) caused conjugated diene formation in low-density lipoprotein (LDL), indicating lipid peroxidation which was dependent on nitrite but not on chloride. The oxidation of LDL was inhibited by micromolar concentrations of flavonoids such as (-)-epicatechin, quercetin, rutin, taxifolin and luteolin, presumably via scavenging of the MPO-derived NO2 radical. The flavonoids served as substrates of MPO leading to products with distinct absorbance spectra. The MPO-catalyzed oxidation of flavonoids was accelerated in the presence of nitrite. (C) 2003 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.