The presence of p47phox in liver parenchymal cells is a key mediator in the pathogenesis of alcoholic liver steatosis.

Nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase) is a membrane-bound enzyme complex that was originally found in phagocytic cells including neutrophils and macrophages where it plays an important role in host defense by generating superoxide with the secondary production of other reactive oxygen species (ROS; Babior, 2004). Normally, the enzyme complex presents in a latent form and, upon stimulation, it is rapidly activated via assembly of its cytosolic and membrane-bound subunits in the active NADPH complex. It is known that the complex consists of the membrane-bound flavocytochrome b558, composed of 1 gp91phox and 1 p22phox subunits, and 4 regulatory cytosolic components, p47phox, p67phox, p40phox, and the small G protein Rac ½ (Bedard and Krause, 2007; Lambeth, 2004). During the last 2 decades, the use of more sensitive assays revealed the presence of low amounts of ROS in cell types other than phagocytes (Gill and Wilcox, 2006; Hilenski et al., 2004; Infanger et al., 2006; Krause, 2004; Sorce and Krause, 2009). The nonphagocyte NADPH complex is structurally and functionally similar to phagocyte NADPH. However, the nonphagocyte NADPH oxidases are constitutively active, producing relatively low levels of ROS under basal conditions and generating higher levels of oxidants in response to different stimuli (De Minicis et al., 2006). Despite the constant growth in understanding alcohol metabolism and action, the mechanisms by which alcohol causes cell injury are still not clear. Some of the leading hypotheses of alcohol-induced cell injury include redox state changes (Dey and Cederbaum, 2006; Wu et al., 2006). Several differentially localized and expressed enzymatic systems contribute to ROS formation in the liver, including endothelial NO synthases, cytochrome P450 monooxygenases, and NADPH oxidase (Bailey and Cunningham, 1998; Zima and Kalousova, 2005). In the healthy liver, antioxidant systems such as superoxide dismutase and catalase efficiently remove excess ROS to maintain the normal cell homeostasis. However, in chronic liver diseases there is increased ROS production, resulting in oxidative stress (Arteel, 2003; Hentze et al., 2003; Tirmenstein et al., 2000; Videla, 2009; Zhang et al., 2001). Hepatotoxic agents (e.g., bile salts) can activate the NADPH oxidase and stimulate death pathways such as CD95-induced signaling to induce apoptosis in hepatocytes (Reinehr et al., 2005). In addition, nonparenchymal cells in the liver such as Kupffer cells and liver macrophages contain the phagocytic form of NADPH oxidase and are believed to mediate hepatocellular damage in alcohol-induced liver injury (Hasegawa et al., 2002; Thakur et al., 2006). Previous studies showed that treatment of mice with gadolinium chloride (GdCl3) prevents free radical formation and alcohol-induced liver injury in the enteral alcohol feeding model (Adachi et al., 1994). Furthermore, the NADPH oxidase inhibitor, diphenyleneiodonium sulfate, prevented alcohol-induced liver injury almost completely by inhibiting free radical formation in another study (Kono et al., 2001). Finally, hepatic steatosis observed in wild-type (WT) mice was prevented nearly completely in p47phox knockout [KO] mice (Kono et al., 2000). However, the contribution of NADPH oxidase between liver parenchymal cells and immune cells is yet to be determined in the development of alcoholic liver disease (ALD). Here, we investigated the possible mechanism of the protection from alcoholic liver steatosis in total body p47phox- KO mice and found that NADPH oxidase in bone marrow (BM)-derived cells did not prevent alcohol-induced steatosis or liver damage. Results from our study suggest that possibly the p47phox/NADPH oxidase complex in parenchymal cells could have the primary significance in alcoholic liver injury.