Hepatocyte cell death via apoptosis and necrosis are major hallmarks of ethanol-induced liver injury. However, inhibition of apoptosis is not sufficient to prevent ethanol-induced hepatocyte injury or inflammation. Since receptor interacting protein kinase (RIP) 3-mediated necroptosis, a non-apoptotic cell death pathway, is implicated in a variety of pathological conditions, here we tested the hypothesis that ethanol-induced liver injury is RIP3-dependent and RIP1-independent. Increased expression of RIP3 was detected in livers of mice after chronic ethanol feeding, as well as in liver biopsies from patients with alcoholic liver disease. Chronic ethanol feeding failed to induce RIP3 in the livers of cytochrome P450 2E1 (CYP2E1)-deficient mice, indicating CYP2E1-mediated ethanol metabolism is critical for RIP3 expression in response to ethanol feeding. Mice lacking RIP3 were protected from ethanol-induced steatosis, hepatocyte injury and expression of pro-inflammatory cytokines. In contrast, RIP1 expression in mouse liver remained unchanged following ethanol feeding and inhibition of RIP1 kinase by necrostatin-1 did not attenuate ethanol-induced hepatocyte injury. Ethanol-induced apoptosis, assessed by TUNEL-positive nuclei and accumulation of cytokeratin-18 fragments in the liver, was independent of RIP3. Conclusion These data demonstrate that CYP2E1-dependent RIP3 expression induces hepatocyte necroptosis during ethanol feeding. Ethanol-induced hepatocyte injury is RIP3-dependent, but independent of RIP1 kinase activity; intervention of this pathway could be targeted as a potential therapeutic strategy.

The effect of moderate alcohol consumption on liver fibrosis is not well understood, but evidence suggests that adenosine may play a role in mediating the effects of moderate ethanol on tissue injury. Ethanol increases the concentration of adenosine in the liver. Adenosine 2A receptor (A2AR) activation is known to enhance hepatic stellate cell (HSC) activation and A2AR deficient mice are protected from fibrosis in mice. Making use of a novel mouse model of moderate ethanol consumption in which female C57BL/6J mice were allowed continued access to 2% (vol/vol) ethanol (11% calories) or pair-fed control diets for 2 days, 2 weeks or 5 weeks and superimposed with exposure to CCl4, we tested the hypothesis that moderate ethanol consumption increases fibrosis in response to carbon tetrachloride (CCl4) and that treatment of mice with an A2AR antagonist prevents and/or reverses this ethanol-induced increase in liver fibrosis. Neither the expression or activity of CYP2E1, required for bio-activation of CCl4, nor AST and ALT activity in the plasma were affected by ethanol, indicating that moderate ethanol did not increase the direct hepatotoxicity of CCl4. However, ethanol feeding enhanced HSC activation and exacerbated liver fibrosis upon exposure to CCl4. This was associated with an increased sinusoidal angiogenic response in the liver. Treatment with A2AR antagonist both prevented and reversed the ability of ethanol to exacerbate liver fibrosis.ConclusionModerate ethanol consumption exacerbates hepatic fibrosis upon exposure to CCl4. A2AR antagonism may be a potential pharmaceutical intervention to decrease hepatic fibrosis in response to ethanol.

MIF, a multi-potent protein that exhibits both cytokine and chemotactic properties, is expressed by many cell types, including hepatocytes and non-parenchymal cells. We hypothesized that MIF is a key contributor to liver injury after ethanol exposure. Female C57BL/6 or MIF−/− mice were fed an ethanol-containing liquid diet or pair-fed control diet for 4 (11% total kcal; early response) or 25 (32% kcal; chronic response) days. Expression of MIF mRNA was induced at both 4d and 25d of ethanol feeding. After chronic ethanol, hepatic triglycerides and plasma ALT and AST were increased in wild-type, but not MIF−/−, mice. In order to understand the role of MIF in chronic ethanol-induced liver injury, we investigated the early response of wild-type and MIF−/− to ethanol. Ethanol feeding for 4d increased apoptosis of hepatic macrophages and activated complement in both wild-type and MIF−/− mice. However, TNFα expression was increased only in wild-type mice. This attenuation of TNF-α expression was associated with fewer F4/80+ macrophages in liver of MIF−/− mice. After 25d of ethanol feeding, chemokine expression was increased in wild-type mice, but not MIF−/− mice. Again, this protection was associated with decreased F4/80+ cells in MIF−/− mice after ethanol feeding. Chronic ethanol feeding also sensitized wild-type, but not MIF−/−, mice to lipopolysaccharide, increasing chemokine expression and monocyte recruitment into the liver. Conclusion Taken together, these data indicate that MIF is an important mediator in the regulation of chemokine production and immune cell infiltration in the liver during ethanol feeding and promotes ethanol-induced steatosis and hepatocyte damage.

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Obesity is associated with increased susceptibility to dyslipidemia, insulin resistance, and hypertension, a combination of traits that comprise the traditional definition of the metabolic syndrome. Recent evidence suggests that obesity is also associated with the development of nonalcoholic fatty liver disease (NAFLD). Despite the high prevalence of obesity and its related conditions, their etiologies and pathophysiology remains unknown. Both genetic and environmental factors contribute to the development of obesity and NAFLD. Previous genetic analysis of high-fat, diet-induced obesity in C57BL/6J (B6) and A/J male mice using a panel of B6-ChrA/J/NaJ chromosome substitution strains (CSSs) demonstrated that 17 CSSs conferred resistance to high-fat, diet-induced obesity. One of these CSS strains, CSS-17, which is homosomic for A/J-derived chromosome 17, was analyzed further and found to be resistant to diet-induced steatosis. In the current study we generated seven congenic strains derived from CCS-17, fed them either a high-fat, simple-carbohydrate (HFSC) or low-fat, simple-carbohydrate (LFSC) diet for 16 weeks and then analyzed body weight and related traits. From this study we identified several quantitative trait loci (QTLs). On a HFSC diet, Obrq13 protects against diet-induced obesity, steatosis, and elevated fasting insulin and glucose levels. On the LFSC diet, Obrq13 confers lower hepatic triglycerides, suggesting that this QTL regulates liver triglycerides regardless of diet. Obrq15 protects against diet-induced obesity and steatosis on the HFSC diet, and Obrq14 confers increased final body weight and results in steatosis and insulin resistance on the HFSC diet. In addition, on the LFSC diet, Obrq 16 confers decreased hepatic triglycerides and Obrq17 confers lower plasma triglycerides on the LFSC diet. These congenic strains provide mouse models to identify genes and metabolic pathways that are involved in the development of NAFLD and aspects of diet-induced metabolic syndrome.