Plasmalogen phospholipids as potential protectors against lipid peroxidation of low density lipoproteins.

A phospholipid subgroup with potential antioxidant properties, the plasmalogen (1-alkenyl, 2-acyl-) fraction, was determined to constitute about 4.5% of total LDL phospholipids. In vitro oxidation of LDL by 2,2'-azobis-(2-amidinopropane hydrochloride) (AAPH, 0.5-10mM) or 5 microM copper induced a selective reduction of plasmalogen subgroups in phosphatidylcholine and phosphatidylethanolamine by 15%-35% within 30 min. Under the same experimental conditions alpha tocopherol (vitamin E) levels were lowered by 5%-40%, indicating a comparable sensitivity of plasmalogen phospholipids and alpha tocopherol towards oxidative attack by AAPH and copper. In vitro enrichment of LDL with 1-alkenyl, 2-lyso-phosphatidylcholine increased the lag phase of formation of conjugated double bonds induced by oxidation of the particles with copper. Incorporation of the lyso plasmalogen did not affect the maximal contents of conjugated dienes in copper oxidized LDL. Due to their relatively high concentration in LDL, their pronounced sensitivity towards oxidation and their capacity to increase the oxidative resistance of the particles, plasmalogen phospholipids may play a significant role in the defense of LDL particles against oxidative stress.