RESISTANCE OF LIPOPROTEIN(A) TO LIPID-PEROXIDATION INDUCED BY OXYGENATED FREE-RADICALS PRODUCED BY GAMMA-RADIOLYSIS - A COMPARISON WITH LOW-DENSITY-LIPOPROTEIN

Lipid peroxidation of lipoprotein(a) [Lp(a)] by defined oxygen-centred free radicals (O-2(-.)/OH., O-2(-.), O-2(-.)/HO2.) produced by gamma radiolysis was compared with that of paired samples of low-density lip oprotein (LDL). Lp(a) appeared to be more resistant to oxidation than LDL, as indicated by the kinetic study of four markers of lipid peroxi dation: decrease in vitamin E, formation of conjugated dienes and alde hydic products, and modification of electrophoretic mobility. In contr ast, similar kinetics of lipid peroxidation were obtained for LDL and Lp(a-), which is the lipoparticle issued following the reductive cleav age of apolipoprotein(a) from Lp(a), thus suggesting that the greater resistance of Lp(a) to lipid peroxidation was due to the presence of a polipoprotein(a). Lipid peroxidation of Lp(a) and LDL induced by perox yl radicals, which were produced by an azo compound [2,2'-azobis-(2-am idinopropane)dihydrochloride], confirmed both the resistance of Lp(a) to lipid peroxidation and the propensity of Lp(a-) to exhibit a greate r susceptibility to oxidation than intact Lp(a). Our findings also ind icated that the high content of apolipoprotein(a) in N-acetylneuramini c acid residues was only partly responsible for the resistance of Lp(a ) to oxidation.