PEROXIDATION OF MODEL LIPOPROTEIN SOLUTIONS SENSITIZED BY PHOTOREDUCTION OF FERRITIN BY 365-NM RADIATION

A mechanistic study involving the 365 nm irradiation of aerated, phosphate-buffered solutions of human high-density lipoproteins (HDL(3) fraction) and ferritin was undertaken. The 365 nm irradiation of phosphate-buffered horse spleen ferritin solutions induces the release of Fe2+ in the medium. The initial quantum yield of Fe2+ release on irradiation is 0.002. This quantum yield is oxygen independent. The 365 nm irradiation of mixtures of HDL and ferritin leads to alterations in apolipoproteins as revealed by tryptophan (Trp) oxidation and electrophoretic pattern modification. In parallel with protein damage, lipid peroxidation is induced as shown by hydroperoxide and thiobarbituric acid reactive substances (TBARS) formation. These peroxidations are strongly reduced in 0.1 M formate solution, which suggests chain initiation by (OH)-O-. radicals or subsequent radicals produced by (OH)-O-.. They are completely inhibited by desferrioxamine, consistent with propagation by Fe2+ ion. By contrast, incubation of HDL in the presence of ferritin and FeSO4 induces only poor auto-oxidation. The biological relevance of this study is discussed.