MECHANISM OF HIGH-DENSITY-LIPOPROTEIN SUBFRACTIONS INHIBITING COPPER-CATALYZED OXIDATION OF LOW-DENSITY-LIPOPROTEIN

Objective: To investigate the role of HDL subfractions, HDL2 and HDL3, on the oxidation of LDL catalyzed by 5 mu M Cu2+ ion, and to illustra te the mechanism of the generation of conjugated diene and thiobarbitu ric acid reactive substances (TBARS) during LDL oxidation. Methods: LD L was incubated for 8 h with 5 mu M Cu2+ ion in phosphate-buffered sal ine (PBS) alone, or in the presence of HDL2, HDL3, HSA, BSA, or transf errin. Meantime, LDL was incubated for 24 h with 10 mu M Ni2+ ions in PES. The amount of conjugated diene and TEARS in each sample of LDL we re measured. Results: (a) HDL2 and HDL3 could inhibit the generation o f conjugated diene, but could not inhibit the generation of TBARS; (b) the transferrin containing HDL, shows the ability of inhibiting the g eneration of both conjugated diene and TBARS; (c) the transferrin pres ented in blood exhibits the inhibitory effect on the generation of con jugated diene and TBARS, however, when the transferrin is saturated wi th Fe3+ ion, it could not inhibit the generation of TBARS; (d) HSA and BSA could prevent the generation of conjugated diene and TBARS; (e) N i2+ ion could induce the generation of conjugated diene, but the amoun t of TEARS was much smaller than that induced by Cu2+ ion. Conclusion: HDL, and HDL, play important role in the copper-catalyzed oxidation o f LDL; it is absolutely necessary to require chelation of Cu2+ ion for inhibiting generation of TBARS; whereas, inhibition of conjugated die ne can be fulfilled either by chelating Cu2+ ion, or the free radicals scavenger. Copyright (C) 1998 The Canadian Society of Clinical Chemis ts.