Protection of endogenous vitamin E and beta-carotene by aminoguanidine upon oxidation of human low-density lipoproteins by *OH/O(2)*-.

ABSTRACT

This study was designed to evaluate the antioxidant effect of aminoguanidine toward human low-density lipoproteins (LDLs) initiated by oxygenated free radicals (*OH/O(2)*-) generated by gamma radiolysis. Initial radiolytic yields related to the markers of lipid peroxidation [i.e. decrease in endogenous alpha-tocopherol and beta-carotene, formation of thiobarbituric acid-reactive substances (TBARS) and conjugated dienes] were determined in 3 g liter(-1) LDLs (expressed as total LDL concentration) in the absence and presence of 10 different concentrations of aminoguanidine (from 0.04 to 5 mmol liter(-1)). Fluorescence and relative electrophoretic mobility of oxidized LDLs were also studied as markers that indirectly reflect the attack of the protein moiety of LDLs (namely apolipoprotein B). Our data clearly showed the inhibitory effect of aminoguanidine on lipid peroxidation induced in LDLs by *OH/O(2)*- in a concentration-dependent manner. This effect probably resulted from a scavenging activity of aminoguanidine toward *OH. In contrast, aminoguanidine did not appear to react significantly with O(2)*-, which resulted in a poor residual lipid peroxidation. Our data led us to determine an optimum [aminoguanidine]/[LDL] ratio ranging from 250 to 500 to obtain the best in vitro protection of LDLs under our experimental conditions. It is also of great interest that aminoguanidine was able to protect endogenous alpha-tocopherol and beta-carotene of LDLs upon *OH/O(2)*(-)-induced oxidation.