PROTECTION OF POLYUNSATURATED FATTY-ACIDS AGAINST IRON-DEPENDENT LIPID-PEROXIDATION BY A GINKGO-BILOBA EXTRACT (EGB-761)

Iron can induce a peroxidative degradation of the membrane polyunsatur ated fatty acids by the well-known Fenton reaction. Chelated iron can also form a complex with oxygen, called perferryl ion, which is able t o induce lipoperoxidation without a detectable production of hydroxyl radicals. The antioxidant properties of a titrated and standardized ex tract of Ginkgo biloba leaves (EGb 761) against iron-dependent peroxid ative degradation of the membrane polyunsaturated fatty acids were stu died. Rat liver microsomes were exposed to a mixture of NADPH, ADP and FeCl3 hypothesized to produce iron-oxygen complexes. The results of t he analysis of the microsomal polyunsaturated fatty acids by gas chrom atography show that the susceptibility to peroxidation of the differen t polyunsaturated fatty acids increases with their unsaturation level, and that EGb 761 protects these membrane polyunsaturated fatty acids regardless of their susceptibility to peroxidation. This protective ef fect is correlated with the decrease in the thiobarbituric acid-reacti ve substances concentration, bur the calculation of the antioxidant po tency of EGb 761 as an IC50 value using results of the the thiobarbitu ric acid reaction leads to an underestimated evaluation when the react ion is carried out in the presence of iron ions.