Hepatoprotective dibenzylbutyrolactone lignans of Torreya nucifera against CCI₄-induced toxicity in primary cultured rat hepatocytes

Three dibenzylbutyrolactone lignans, (-)-arctigenin, (-)-traxillagenin, and (-)-4′-demethyltraxillagenin, isolated from the bark of Torreya nucifera SIEB. et ZUCC. (Taxaceae) showed significant hepatoprotective activity in primary cultures of rat hepatocytes injured by carbon tetrachloride (CCl ₄). These lignans reduced the release of glutamic pyruvic transaminase into the culture medium from the CCl₄-injured primary cultures of rat hepatocytes. Further investigation revealed that the three lignans significantly preserved the level of glutathione (GSH) and activities of superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase in the CCl₄-injured rat hepatocytes. The lignans also ameliorated lipid peroxidation as demonstrated by a reduction in malondialdehyde-related products. Moreover, these lignans significantly attenuated the GSH reduction caused by diethylmaleate which depletes GSH through the formation of stable conjugates. However, these lignans showed no effect on the GSH synthesis inhibited by buthionine sulfoximine. From these results, it can be concluded that arctigenin, traxillagenin, and 4′- demethyltraxillagenin may protect hepatocytes from CCl₄ injury by maintaining the GSH level.