A rapid method for measurement of the susceptibility to oxidation of low-density lipoprotein.

Oxidation of low-density lipoprotein (LDL) may be important in the pathogenesis of atherosclerosis. We describe a method which measures the oxidation resistance of LDL isolated by a rapid procedure without added antioxidants. LDL was isolated from heparinized plasma by density gradient ultracentrifugation and desalted by gel filtration. The protein concentration was standardized to 50 mg/L and oxidation was promoted by copper (2 mumol/L) at 37 degrees C. The total sample preparation time was 2.5 h. Conjugated diene production was monitored at lambda = 234 nm with computation of the lag time. LDL oxidation was inhibited by EDTA but not heparin. Albumin inhibited LDL oxidation but only in concentrations greater than 50 mg/L. LDL was stable in frozen plasma (-70 degrees C) for 10 weeks, but unstable in the isolated and desalted state. The lag time for LDL from patients treated with the antioxidant probucol was markedly prolonged compared to normal subjects.