Antioxidant effect of ethanol toward in vitro peroxidation of human low-density lipoproteins initiated by oxygen free radicals

This study was designed to evaluate the effect of ethanol on the peroxidati on of human low-density lipoprotein (LDL) initiated by oxygen free radicals (O-2(-) and (OH)-O-. in the absence of ethanol; O-2(-) and ethanol-derived peroxyl radicals, RO2', in the presence of ethanol) generated by gamma rad iolysis. Initial radiolytic yields as determined by several markers of lipi d peroxidation [i.e, decrease in endogenous antioxidants alpha -tocopherol and beta -carotene, formation of conjugated dienes and of thiobarbituric ac id-reactive substances (TEARS)] were determined in 3 g liter(-1) LDLs (expr essed as total LDL concentration) in the absence of ethanol or its presence at six different concentrations (0.42-17 x 10(-2) mol liter(-1)). Ethanol acted as an antiorridant by decreasing the rate of consumption of LDL endog enous antioxidants and the yields of formation of lipid peroxidation produc ts, and by delaying the onset of the propagation phase for conjugated diene s and TEARS. With regard to the different markers studied, except for ar-to copherol and beta -carotene consumption, the effect of ethanol did not appe ar to be dependent on its concentration. Indeed,(OH)-O-. were scavenged by ethanol at the lowest ethanol concentration (0.42 x 10(-2) mol liter(-1)), leading to RO2.. These RO2. resulted in lower radiation-induced yields rela ted to endogenous antioxidant consumption or to formation of lipid peroxida tion products (for example, approximately 10% of RO2. oxidized LDLs from TE ARS). Thus, under our in vitro conditions, ethanol behaved as an antioxidan t when added to the LDL solutions. This should be taken into account in the reported antioxidant activity of wine, This is also of interest when lipop hilic compounds have to be added as ethanolic solutions to LDLs to evaluate in vitro their antioxidant activity toward LDL peroxidation. (C) 2001 by R adiation Research Society.