Silymarin protects against acute ethanol-induced hepatotoxicity in mice.

Although much progress has been made in understanding the pathogenesis of alcoholic liver disease (ALD), there remains no effective therapy for this disease. Accumulated evidence has demonstrated that both oxidative stress and abnormal cytokine production, especially tumor necrosis factor (TNF), play important etiological roles in the pathogenesis of ALD. Therefore, agents that have both antioxidant and anti-inflammatory properties, particularly anti-TNF production, represent promising therapeutic interventions for ALD. There is increasing evidence that oxidative stress plays an important etiologic role in the development of ALD. Alcohol administration causes accumulation of reactive oxygen species (ROS), including superoxide, hydroxyl radical, and hydrogen peroxide (Nordmann et al., 1992). Reactive oxygen species, in turn, cause lipid peroxidation of cellular membranes and protein and DNA oxidation, which result in hepatocyte injury (Kurose et al., 1997; Navasumrit et al., 2000; Rouach et al., 1997). Reduced glutathione (GSH) is one of the most prominent defense molecules in the liver. Besides serving as a substrate for GSH-related enzymes, GSH acts as a free radical scavenger and a regenerator of α-tocopherol and plays an important role in the maintenance of protein sulfhydryl groups (Fernandez-Checa et al., 1998; Kurose et al., 1996). Several studies have reported that acute ethanol (EtOH) administration decreases hepatic GSH content (Masini et al., 1994; Shaw et al., 1983; Song et al., 2003). The decrease in GSH has been related to an enhanced oxidation of GSH to oxidized glutathione (GSSG) as a consequence of increased generation of ROS (Videla and Valenzuela, 1982). Restoration of GSH has been shown to inhibit EtOH-induced liver injury (Fermandez-Checa et al., 1995; Iimuro et al., 2000). It is conveivable that agents with a hepatic antioxidant property would be a potential therapy for ALD. Abnormal cytokine metabolism, especially TNF, is another major feature of ALD (McClain and Cohen, 1989). Previous investigations showed that rats chronically fed alcohol had much higher lipopolysaccharide (LPS)-stimulated plasma levels of TNF than control rats, and liver injury could be attenuated by agents such as prostaglandin analog that down-regulated TNF production (Honchel et al., 1992). Moreover, acute EtOH administration to mice has been found to induce hepatic TNF-α production and mRNA expression and down-regulated TNF production by antioxidants was paralleled by attenuated hepatic lipid peroxidation, steatosis, and liver injury (Zhou et al., 2003). Silymarin is a flavonoid extracted from the milk thistle Silibum marianum. It has been reported to prevent liver injuries induced by various chemicals or toxins including EtOH (Farghali et al., 2000; Halim et al., 1997; Lieber et al., 2003). Although the hepatoprotective properties of silymarin have been reported both from in vitro and in vivo studies, its mechanism of action still has not been established. Two major mechanisms that have been proposed include functioning as an antioxidative scavenger of free radicals (mainly active toward HO and HOCl and less so for H2O2 or O2−) and as a regulator of immune functions by modulating cytokine production (Ferenci et al., 1989; Luper, 1998). The current study was undertaken to determine whether silymarin supplementation could attenuate acute EtOH-induced hepatotoxicity and to explore the possible mechanism (s) involved in this protection.