MEASUREMENT OF ANTIOXIDANT ACTIVITY IN LIPOPROTEINS USING ENHANCED CHEMILUMINESCENCE

We describe a new assay for antioxidant activity (AOA) in lipoprotein solutions based upon their potential to quench light emission from a g lowing horseradish peroxidase-catalyzed enhanced chemiluminescent reac tion. By comparison with the quenching activity of the tocopherol-anal ogue trolox the AOA can be quantified. These measurements suggest that all lipoprotein fractions have significant AOA and that this has a no n-linear relationship with lipoprotein concentration increasing signif icantly on a per particle basis at higher concentrations. Mean AOA in very low density, low density and high density lipoprotein fractions w ere 39.9 +/- 5.3, 20.3 +/- 4.0 and 5.3 +/- 1.0 mu mol of trolox equiva lents per litre, respectively, when measured at 1 mg protein/ml. Using known values for the protein content of the lipoprotein fractions, th ese values correspond to 79.8 +/- 10.7, 10.3 +/- 2.0 and 0.84 +/- 0.15 equivalents per particle. Parallel measurements of light emission and conjugated diene formation suggest that the oxidative stress imposed by the peroxidase-catalyzed reaction leads to lipid peroxidation but o nly after all AOA has been exhausted. AOA was significantly correlated with the cr-tocopherol content in 30 lipoprotein samples (r = 0.764). This assay offers a rapid and simple method for investigating the eff ects of diseases, drugs or dietary manipulation on lipoprotein AOA.