[New biochemical methods for evaluation of the oxidative-antioxidative potential of low-density lipoproteins].

Today one of the leading theories in the concept of atherogenesis underlines the key role of oxidized low-density lipoproteins (LDL). This paper describes new original and easy-to-use biochemical methods for evaluating the oxidative-antioxidative potential (LDL resistance to oxidation in vitro and the LDL level of alpha-tocopherol and retinol), as well as the results of their development and testing in 2 groups (62 patients with coronary atherosclerosis and 95 healthy individuals). LDL were isolated from their sera via precipitation with heparin and MnCl2. The precipitated LDL were washed in 0.9% NaCl solution and dissolved in 1 M NaCl solution. For evaluation of the resistance of LDL to oxidation in vitro, the precipitated LDL were incubated at 37 degrees C with 50 microM of copper ions; before and 0.5 h, 1.0 h, and 2.0 h after LDL incubation, TBARS products were determined by the fluorimetric technique after Schun J. et al. (1978). For evaluation of the antioxidative potntial of LDL, the concentrations of alpha-tocopheral and retinol in the precipitated LDL were measured by using the fluorimetric technique described by Taylor S. L. et al. (1976). The new methods were found to be highly reproducible. There was a high positive correlation (r = +0.98 +/- 0.04, p < 0.001) between the oxidative resistance of the LDL isolated from sera by ultracentrifugation and that of the precipitated LDL. There was also a high positive correlation (r = +0.79 +/- 0.09, p < 0.01) between the alpha-tocopherol and retinol levels determined by the fluorimetric technique and the LDL levels measured by the authors' method. The new methods were clinically tested with success. The significantly elevated baseline level of lipid perioxidation products in the precipitated LDL, the low oxidative resistance of the precipitated LDL in vitro, and reduced concentrations of alpha-tocopherol and retinol in the precipitated LDL were recorded in the patients with coronary atherosclerosis as compared to the healthy individuals. These results confirm that LDL oxidative-antioxidative disturbances play an important role in the pathogenesis of coronary atherosclerosis.