High density lipoprotein subclasses inhibit low density lipoprotein oxidation

It has been reported earlier that high density lipoprotein (HDL) is a scavenger of superoxide anions, hydroxyl radicals (OH-) and behaves like superoxide dismutase. In the present investigation, we have studied the effect of HDL subclasses: HDL2 and HDL3 on non enzymatically induced oxidation of low density lipoprotein (LDL) by Fe2+ and sodium ascorbate. Both HDL2 and HDL3 showed protection against the oxidative degradation of LDL-lipids, measured as thiobarbituric acid reactive substance, lipid hydroperoxide and conjugated diene. Oxidized LDL was more electronegative, as evidenced by the increase in relative electrophoretic mobility(REM) on agarose gel. HDL3 significantly protected LDL apoprotein as assessed by reversal of REM after oxidation. HDL2 and HDL3 significantly inhibited the generation of OH- in nonenzymic systems in vitro. However, HDL2 was more active against enzymic formation of OH- as compared to HDL3. Alpha-tocopherol could protect LDL lipids and apoprotein components by Fe2+ mediated oxidation but the effects were lower than HDL subclasses. Our findings suggest that HDL subclasses, the potent scavenger of oxygen derived free radicals, play an important role to prevent the oxidative modifications in LDL.