The "unexpected role" of vitamin E in free radical-induced hemolysis of human erythrocytes: alpha-tocopherol-mediated peroxidation.

Vitamin E involves a group of tocopherols and tocotrienols, in which alpha-tocopherol with the highest biological activity plays a more efficient role in advanced lesions with aged oxidized tissues. However, the results of the present study reveal that a large amount of endogenous alpha-tocopherol in human low-density lipoprotein (LDL) in the absence of any other antioxidants may initiate additional free radical propagation under low concentration of free radical initiator (i.e., 2,2'-azobis(2-amidinopropane hydrochloride) [AAPH], a water-soluble free radical source) to peroxide polyunsaturated fatty acids in LDL in the manner of alpha-tocopherol-mediated peroxidation (TMP). Whether the addition of high concentration of exogenous alpha-tocopherol to human erythrocytes under low concentration of AAPH can also drive TMP is the concern in this research work. Moreover, the hemolysis extent of human erythrocytes peroxidized by AAPH is followed easily by the determination of the hemoglobin outside the erythrocytes. A series of observations on various concentrations of AAPH-induced hemolysis in the presence of various concentrations of exogenous alpha-tocopherol demonstrates that the high concentration of exogenous alpha-tocopherol, coupled with low concentration of AAPH, can initiate TMP in the free-radical-induced peroxidation of human erythrocytes system as well. This result provides direct evidence to support TMP theory and expands its application into in vitro erythrocyte system.