Biol. Pharm. Bull. 28(1) 53—57 (2005)

neurotoxicity following cerebral ischemia-reperfusion. Accumulation of ROS, particularly superoxide anion (O ) and hydrogen peroxide (H2O2) causes damage to membrane phospholipids, proteins and DNA. Under normal circumstances, these oxidant species can be effectively scavenged by antioxidant enzymes, namely superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPX). In mammalian SOD is able to convert O to H2O2. 2) The H2O2 formed is subsequently removed by the cytosolic catalase and GPX to form water and molecular oxygen. However, the sudden burst of ROS, for example, during cerebral ischemia-reperfusion can overwhelm the antioxidant defense, resulting in lipid peroxidation and hence cerebral infarction. In this regard, transgenic mice over-expressing SOD, catalase, or GPX showed significant reduction of infarct volume and edema formation. Intravenous administration of polyethylene-conjugated SOD or GPX could also reduce the size of brain infarction. In contrast, after transient focal cerebral ischemia, knockout mice without SOD, catalase, or GPX expression showed an increased extent of lipid peroxidation, leading to an exacerbated infarction. In our previous report, the antioxidant activities of Choto-san and its related constituents were investigated employing various established in vitro systems, such as a protective effect on H2O2-induced oxidative damage in NG108-15 cells, lipid peroxidation in mouse brain homogenate induced by Fe /ascorbate system, DPPH, superoxide, nitric oxide and hydroxyl radical scavenging, reducing power, and iron chelation. Choto-san and its related constituents significantly protected NG108-15 cells from injury induced by H2O2 exposure in vitro and also inhibited lipid peroxidation in the brain homogenate. Furthermore, they exhibited a strong concentration-dependent scavenging effect on DPPH radical, superoxide, nitric oxide and hydroxyl radical. The multiple antioxidant activity of Choto-san and its related constituents was evident as it showed strong reducing power, and also ferrous ion chelating potency. The data obtained in the in vitro models clearly establish the antioxidant activity of Chotosan. These in vitro results suggest the possibility that Chotosan could be effectively employed as an antioxidant, to alleviate oxidative stress. Activation of the function of endogenous antioxidant systems in tissue is the characteristic of antioxidant compounds. Many plant extracts or antioxidants have been reported to exert an indirect scavenging effect on free radical-induced tissue injury by activating the function of endogenous antioxidant systems. Thus it is likely that the antioxidant effect of Choto-san is due to not only free radical-scavenging activity but also to the modulation of endogenous antioxidant defense system. Therefore, we investigated the effect of Choto-san and its related constituents on the activities of the antioxidant enzymes such as SOD, catalase and GPX as well as the level of intracellular glutathione in vitro using NG108-15 cell cultures system.