Kinetic study of low density lipoprotein oxidation by copper

Oxidation of Low Density Lipoprotein (LDL) is regarded as a key event in the development of atherosclerosis. The aim of this study was to investigate effect of various copper concentrations on LDL oxidation kinetic profile as a mechanism in atherosclerosis process. LDL was isolated from plasma and its oxidation with copper was investigated by monitoring the formation of conjugated dienes. Based on time course of the formation of conjugated diene was observed at concentrations of 0.5 to 10 µM copper, represented the conventional kinetics of LDL oxidation with an inhibition period followed by a propagation phase. In contrast, at concentrations of 20 to 50 µM copper, LDL oxidation proceeded after a negligibly short lag-time followed by a distinct propagation phase. At lower copper concentrations of about 0.5 µM, LDL oxidation can be combined in 4 consecutive oxidation phase. The increasing copper concentration (to 10 µM) lowered the first propagation and shortened the seconded inhibition period until they melted into one apparent kinetic phase. But in copper concentrations of about 20 to 50 µM, increasing copper concentration increased the first propagation and the second inhibition but lowered the second propagation phase. The results of this investigation on the copper dependence of the oxidation kinetics suggest that LDL contains two different copper binding sites. Copper bound to the low affinity binding sites with molar ratio of 200 to 500 of copper / LDL. These ions bound to the high affinity binding sites with molar ratio of copper / LDL of 5 to 100.