Modulation of oxidative damage by natural products

Abstract

Using rat liver membrane as a model system, modulation of oxidative damage induced by pathophysiological agents such as photosensitization and radiation was examined with two medicinal plant extracts, namely Andrographis paniculata (Ap) and Swertia chirata (Sc). Results showed that simultaneous addition of both the extracts (50 μg/ml) in independent experiments during generation of reactive oxygen species (ROS) could significantly prevent increased levels of products of lipid peroxidation, such as conjugated dienes, lipid hydroperoxide, TBARS and 4-hydroxylnonenals. The oxidative damage observed with depletion of major endogenous antioxidants, such as GSH, as well as enhanced formation of protein oxidation, was effectively reduced by these extracts. Similarly, degradation of mitochondrial proteins by ROS, induced during photosensitization, was effectively prevented by both the extracts (SDS–PAGE experiments). The antioxidative property of these extracts could be attributed to their scavenging ability with superoxide, hydroxyl radicals and singlet oxygen species, the major species generated during photosensitization and γ-radiation. The high scavenging ability of the extracts may be due to high phenolic contents, flavonoid constituents and considerable reducing equivalents. The pulse radiolysis studies showed high reactivity with ABTS −. The reaction of the extracts of Ap and Sc with dimethyl p-phenylene diamine dihydrochloride (DMPD), one of the important stable synthetic radicals gave >30% inhibition at 50 μg/ml. In view of these observations, termination of the free radical reaction, and quenching of reactive oxygen are suggested to be, in part, responsible for the antioxidant activity of Andrographis paniculata and Swertia chirata extracts. Therefore, Andrographis paniculata and Swertia chirata extracts may emerge as effective antioxidative agents, protecting cells from pathophysiological oxidants, generated during UV–vis photosensitization/radiation-induced injury, and may be useful in the food industry as effective synthetic antioxidants.