Molecular mechanism of alcoholic fatty liver

Abstract

Ethanol abuse and chronic ethanol consumption remains a major public health problem and is responsible for a high rate of morbidity. Alcohol-induced fatty liver generally begins as hepatic steatosis, and if the cause persists, this invariably progresses to steatohepatitis and cirrhosis. The original biochemical explanation for an alcoholic fatty liver centered on the ability of ethanol metabolism to shift the redox state of the liver and inhibit fatty acid oxidation. Subsequent studies found repression of fatty acid oxidation and that the induction of lipogenesis can occur in alcoholic conditions. Ethanol activates sterol regulatory element binding protein 1, inducing a battery of lipogenic enzymes. These effects may be due in part to inhibition of AMP-dependent protein kinase, reduction in plasma adiponectin or increased levels of TNF-α the liver. They in turn activate lipogenic pathways and inhibit fatty acid oxidation. Besides the fatty acid synthesis and oxidation, ethanol also alters lipid droplet (LD, the storage form of triglycerides, TG) metabolism in hepatocytes and very low-density lipoprotein (VLDL) secretion from liver. Because steatosis is now regarded as a significant risk factor for advanced liver pathology, an understanding of the molecular mechanisms in its etiology provides new therapeutic targets to reverse the alcoholic fatty liver.

Keywords: Adiponectin; adenosine monophosphate-activated protein kinase; alcohol; lipid droplets; steatosis/fatty liver.

Figure 1

Potential mechanisms underlying the alcoholic fatty liver. In liver, sterol regulatory element binding protein 1 is responsible for fatty acid synthesis and peroxisome proliferator activated receptor-α, AMPdependent protein kinase (AMPK) and adiponectin are responsible for fatty acid oxidation. Ethanol may influence the activity of PPAR-α, SREBP-1, and AMPK directly or through adiponectin and tumor necrosis factor-α. These effects activate the lipogenic pathways and inhibit fatty acid oxidation. Besides the fatty acid synthesis and oxidation, ethanol also alters lipid droplets (LD, the storage form of TG) metabolism in hepatocytes and very low-density lipoproteins secretion from liver. All these alterations contribute to alcohol-induced fatty liver