Free radical lipid oxidation affects cholesterol transfer between lipoproteins and erythrocytes

Human erythrocytes were incubated for 5 h at 37 degrees C with lipoproteins (LP), preliminary oxidized to different extent, as assessed by thiobarbituric acid (TBA) test. Cholesterol content in the cells was increased by 12-14% after incubation with low-density lipoproteins (LDL) along with augmentation of order parameter and rotational correlation time of spin-labeled stearic acids incorporated into membranes. If erythrocytes were incubated with oxidized LDL, containing 2.5-4 times more TBA-reactive material than native ones, cellular content of cholesterol was increased by 24-28%. In contrast, high-density lipoproteins (HDL2 and HDL3) removed cholesterol from cell membranes, when incubated with erythrocytes. This was followed by increased fluidity of membrane lipid phase as detected by the spin probe method. Oxidation of HDL2 and HDL3 decreased their ability to accept cholesterol from cell membranes. No detectable accumulation of TBA-reactive material was observed in the samples during the incubation. The antioxidant, butylated hydroxytoluene (BHT), in the concentration of 10(-5) M did not influence the cholesterol transfer between LP and erythrocytes. Hence, the effects of lipid peroxidation (LPO) on the cholesterol transfer seem to result from LP alterations by oxidation rather than from free radical reactions occurring during the incubation. By increasing cholesterol-donating ability of LDL and inhibition of cholesterol-accepting capacity of HDL lipid peroxidation in LP may activate cholesterol accumulation in blood vessel cells and thus contribute to atherosclerosis.