Susceptibility of serum lipids to copper-induced peroxidation correlates with the level of high density lipoprotein cholesterol

As a first step in evaluating the significance of our recently developed method of monitoring the kinetics of copper-induced oxidation in unfractionated serum, we recorded the kinetics of lipid oxidation in the sera of 62 hyperlipidemic patients and analyzed the correlation between oxidation and lipid composition of the sera [high density lipoprotein (HDL) cholesterol, low density lipoprotein (LDL) cholesterol, and triglycerides]. We used six factors to characterize the kinetics of oxidation, namely, the maximal absorbance of oxidation products (ODmax), the maximal rate of their production (V-max), and the time at which the rate was maximal (t(max)) at two wavelengths (245 nm, where 7-ketocholesterol and conjugated dienic hydroperoxides absorb intensely, and 268 nm, where the absorbance is mostly due to dienals). The major conclusions of our analyses are that: (i) Both ODmax and V-max correlate positively with the sum of concentrations of the major oxidizable lipids, cholesterol, and cholesteryl esters. (ii). The value of t(max), which is a measure of the lag preceding oxidation and therefore reflects the resistance of the serum lipids to copper-induced oxidation, exhibits a negative correlation with HDL cholesterol. Although this finding accords with the observation of shorter lags for HDL than for LDL, it is apparently inconsistent with the role of HDL as an antirisk factor in coronary heart diseases.