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To investigate the antioxidant activity of extract from the raw walnut, Juglans sinensis Dode, we prepared five fractions (methanol (MeOH), dichloromethane (CH₂Cl₂), ethyl acetate (EtOAc), n-buthanol (n-BuOH) and dehydrogen monooxide (H₂O) fractions) and examined. The effect of walnut extract on the oxidative stress was investigated in vitro. The DPPH (2,2-Di (4-tert-octylphenyl)-1-picrylhydrazyl) free radical scavenging activity of extract from raw walnut was shown in the following order: EtOAc fraction＞n-BuOH fraction＞MeOH fraction＞CH₂Cl₂fraction＞H₂O layer. The result showed that the highest activity (0.56 ㎍/ml, IC_(50).) was observed in EtOAc fraction, whereas n-BuOH fraction, MeOH fraction, CH₂Cl₂fraction and H₂O layer of IC_(50) were 2.34 ㎍/ml, 3.88 ㎍/ml, 8.06 ㎍/ml, and 8.19 ㎍/ml, respectively. The radical scavenging activity assay of each fraction showed that the antioxidative activity was observed in the following order: EtOAc fraction (74.27±1.56%)＞MeOH fraction (60.76±3.4%)＞n-BuOH fraction (59.32±0.88%)＞H₂O layer (41.69±2.06%). These results revealed that all fractions, except for CH₂Cl₂fraction, showed high antioxidative activity. Furthermore, the peroxynitrite (ONOO-) scavenging activity was assayed in each fraction. The result showed that the ONOO- scavenging activity of EtOAc fraction, MeOH fraction and n-BuOH fraction from raw walnut was 95.14±0.36%, 90.02±1.19% and 89.41±0.81%, respectively. The tert-butylhydroperoxide (t-BHP) treatment in vitro increased lactate dehydrogenase release and lipid peroxidation in renal cortical slices. Such changes were completely prevented by addition of MeOH fraction, EtOAc fraction and n-BuOH fraction of walnut. These results indicate that the walnut extract exerts the benedicial effect against t-BHP-induced cell injury and its effect may be due to antioxidant action. In addition, it is suggested that walnut extract might be developed as the effective scavenger for the prevention of oxidative stress.
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