Patients with alcoholic liver disease frequently exhibit iron overload in association with increased hepatic fibrosis. Even moderate alcohol consumption elevates body iron stores; however, the underlying molecular mechanisms are unknown. Hepcidin, a circulatory peptide synthesized in the liver, is a key mediator of iron metabolism. Ethanol metabolism significantly down-regulated both in vitro and in vivo hepcidin mRNA and protein expression. 4-Methylpyrazole, a specific inhibitor of the alcohol-metabolizing enzymes, abolished the effects of ethanol on hepcidin. However, ethanol did not alter the expression of transferrin receptor1 and ferritin or the activation of iron regulatory RNA-binding proteins, IRP1 and IRP2. Mice maintained on 10-20% ethanol for 7 days displayed down-regulation of liver hepcidin expression without changes in liver triglycerides or histology. This was accompanied by elevated duodenal divalent metal transporter1 and ferroportin protein expression. Injection of hepcidin peptide negated the effect of ethanol on duodenal iron transporters. Ethanol down-regulated hepcidin promoter activity and the DNA binding activity of CCAAT/enhancer-binding protein α (C/EBPα) but not β. Interestingly, the antioxidants vitamin E and N-acetylcysteine abolished both the alcohol-mediated down-regulation of C/EBPα binding activity and hepcidin expression in the liver and the up-regulation of duodenal divalent metal transporter 1. Collectively, these findings indicate that alcohol metabolism-mediated oxidative stress regulates hepcidin transcription via C/EBPα, which in turn leads to increased duodenal iron transport.

Patients with alcoholic liver disease frequently exhibit increased body iron stores, as reflected by elevated serum iron indices (transferrin saturation, ferritin) and hepatic iron concentration. Even mild to moderate alcohol consumption has been shown to increase the prevalence of iron overload. Moreover, increased hepatic iron content is associated with greater mortality from alcoholic cirrhosis, suggesting a pathogenic role for iron in alcoholic liver disease. Alcohol increases the severity of disease in patients with genetic hemochromatosis, an iron overload disorder common in the Caucasian population. Both iron and alcohol individually cause oxidative stress and lipid peroxidation, which culminates in liver injury. Despite these observations, the underlying mechanisms of iron accumulation and the source of the excess iron observed in alcoholic liver disease remain unclear. Over the last decade, several novel iron-regulatory proteins have been identified and these have greatly enhanced our understanding of iron metabolism. For example, hepcidin, a circulatory antimicrobial peptide synthesized by the hepatocytes of the liver is now known to play a central role in the regulation of iron homeostasis. This review attempts to describe the interaction of alcohol and iron-regulatory molecules. Understanding these molecular mechanisms is of considerable clinical importance because both alcoholic liver disease and genetic hemochromatosis are common diseases, in which alcohol and iron appear to act synergistically to cause liver injury.

Alcohol reduces and iron increases liver hepcidin synthesis. This study investigates the interaction of alcohol and iron in the regulation of hepcidin messenger RNA (mRNA) expression in animal models. Mice were administered 10% ethanol for 7 days after an iron-overloaded diet. Rats were administered regular or ethanol-Lieber De Carli diets for 7 weeks with or without carbonyl iron. Hfe−/− mice were used as a model for genetic iron overload. Hepcidin mRNA expression was determined by real-time polymerase chain reaction (PCR) and northern blotting. Iron elevated and alcohol decreased liver hepcidin expression in mice and rats. Interestingly, despite iron overload, alcohol was capable of suppressing the up-regulation of hepcidin mRNA expression in both models. Liver iron and ferritin protein expression was elevated in alcohol-treated rats, but was not elevated further in rats treated with both iron and alcohol. Duodenal ferroportin protein expression was increased both in alcohol-treated mice and in mice treated with alcohol and iron. Hfe−/− mice treated with ethanol for 7 days exhibited a further decrease in hepcidin mRNA expression. The iron-induced increase in DNA-binding activity of the transcription factor CCAAT/enhancer binding protein alpha (C/EBP alpha) was also suppressed by alcohol. Conclusion: Alcohol abolishes the iron-induced up-regulation of both liver hepcidin transcription and the DNA-binding activity of C/EBP alpha. Of note, hepcidin protects the body from the harmful effects of iron overload. Our findings therefore suggest that alcohol negates the protective effect of hepcidin, which may have implications for the liver injury observed in alcoholic liver disease and genetic hemochromatosis in combination with alcohol. (Hepatology 2007.)

The regulation of iron metabolism involves multiple organs including the duodenum, liver and bone marrow. The recent discoveries of novel iron-regulatory proteins have brought the liver to the forefront of iron homeostasis. The iron overload disorder, genetic hemochromatosis, is one of the most prevalent genetic diseases in individuals of Caucasian origin. Furthermore, patients with non-hemochromatotic liver diseases, such as alcoholic liver disease, chronic hepatitis C or nonalcoholic steatohepatitis, often exhibit elevated serum iron indices (ferritin, transferrin saturation) and mild to moderate hepatic iron overload. Clinical data indicate significant differences between men and women regarding liver injury in patients with alcoholic liver disease, chronic hepatitis C or nonalcoholic steatohepatitis. The penetrance of genetic hemochromatosis also varies between men and women. Hepcidin has been suggested to act as a modifier gene in genetic hemochromatosis. Hepcidin is a circulatory antimicrobial peptide synthesized by the liver. It plays a pivotal role in the regulation of iron homeostasis. Hepcidin has been shown to be regulated by iron, inflammation, oxidative stress, hypoxia, alcohol, hepatitis C and obesity. Sex and genetic background have also been shown to modulate hepcidin expression in mice. The role of gender in the regulation of human hepcidin gene expression in the liver is unknown. However, hepcidin may play a role in gender-based differences in iron metabolism and liver diseases. Better understanding of the mechanisms associated with gender-related differences in iron metabolism and chronic liver diseases may enable the development of new treatment strategies.

Hepcidin, a key regulator of iron metabolism, is activated by bone morphogenetic proteins (BMPs). Mice pair-fed with regular and ethanol-containing L. De Carli diets were employed to study the effect of alcohol on BMP signaling and hepcidin transcription in the liver. Alcohol induced steatosis and TGF-beta expression. Liver BMP2, but not BMP4 or BMP6, expression was significantly elevated. Despite increased BMP expression, the BMP receptor, and transcription factors, Smad1 and Smad5, were not activated. In contrast, alcohol stimulated Smad2 phosphorylation. However, Smad4 DNA-binding activity and the binding of Smad4 to hepcidin promoter were attenuated. In summary, alcohol stimulates TGF-beta and BMP2 expression, and Smad2 phosphorylation but inhibits BMP receptor, and Smad1 and Smad5 activation. Smad signaling pathway in the liver may therefore be involved in the regulation of hepcidin transcription and iron metabolism by alcohol. These findings may help to further understand the mechanisms of alcohol and iron-induced liver injury.

Despite heavy consumption over a long period of time, only a small number of alcoholics develop alcoholic liver disease. This alludes to the possibility that other factors, besides alcohol, may be involved in the progression of the disease. Over the years, many such factors have indeed been identified, including iron. Despite being crucial for various important biological processes, iron can also be harmful due to its ability to catalyze Fenton chemistry. Alcohol and iron have been shown to interact synergistically to cause liver injury. Iron-mediated cell signaling has been reported to be involved in the pathogenesis of experimental alcoholic liver disease. Hepcidin is an iron-regulatory hormone synthesized by the liver, which plays a pivotal role in iron homeostasis. Both acute and chronic alcohol exposure suppress hepcidin expression in the liver. The sera of patients with alcoholic liver disease, particularly those exhibiting higher serum iron indices, have also been reported to display reduced prohepcidin levels. Alcohol-mediated oxidative stress is involved in the inhibition of hepcidin promoter activity and transcription in the liver. This in turn leads to an increase in intestinal iron transport and liver iron storage. Hepcidin is expressed primarily in hepatocytes. It is noteworthy that both hepatocytes and Kupffer cells are involved in the progression of alcoholic liver disease. However, the activation of Kupffer cells and TNF-alpha signaling has been reported not to be involved in the down-regulation of hepcidin expression by alcohol in the liver. Alcohol acts within the parenchymal cells of the liver to suppress the synthesis of hepcidin. Due to its crucial role in the regulation of body iron stores, hepcidin may act as a secondary risk factor in the progression of alcoholic liver disease. The clarification of the mechanisms by which alcohol disrupts iron homeostasis will allow for further understanding of the pathogenesis of alcoholic liver disease.