What is the pathogenesis of fatty liver disease?

Updated: Apr 12, 2018
  • Author: Emily Tommolino, MD; Chief Editor: BS Anand, MD  more...
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Answer

Answer

Alcoholic fatty liver is an early and reversible consequence of excessive alcohol consumption. Fatty liver develops in every individual who consumes more than 60 g of alcohol per day. Many mechanisms of ethanol-induced fatty liver have been proposed. Increased hepatic levels of glycerol 3-phosphate (3-GP) after ethanol ingestion are related to an increase in the ratio of the oxidized form of nicotinamide adenine dinucleotide (NAD+) to the reduced form (NADH) in the liver. A higher concentration of 3-GP results in enhanced esterification of fatty acids.

An increase in free fatty acids has also been incriminated in the pathogenesis. Large amounts of alcohol enhance lipolysis through direct stimulation of the adrenal-pituitary axis. In addition, chronic ethanol ingestion inhibits oxidation of fatty acids in the liver and the release of VLDL into the blood. All of these mechanisms favor steatosis. Centrilobular localization of steatosis results from decreased energy stores caused by relative hypoxia and a shift in lipid metabolism, along with a shift in the redox reaction as a result of preferential oxidation of alcohol in the central zone.

Advances in the understanding of the pathogenesis of alcoholic steatosis have provided some useful insights, including the role of peroxisome proliferator-activated receptor alpha, which is crucial for the regulation of hepatic fatty acid metabolism. Its blockade, in animal models, along with ethanol consumption, contributes to the development of alcoholic fatty liver. In addition, induction of adiponectin, a hormone secreted by adipocytes, has been implicated in the protective effect of saturated fat against the development of alcoholic fatty liver in mice.

The role of the early growth response-1 (EGr-1) transcription factor is thought to be essential for ethanol-induced fatty liver injury in mice. Hepatocyte death by apoptosis occurs in alcoholic fatty liver and has been demonstrated in rats and mice after ethanol feeding. This may be related to mitochondrial proteins that regulate apoptosis and necrosis and that are shown to be induced in mouse fatty liver models.

Serum leptin, a cytokine-type peptide hormone mainly produced by adipocytes, may play an important role in the pathogenesis of steatosis. Steatosis occurs with decreased leptin action, whether due to leptin deficiency or resistance. In patients with alcoholic liver disease, the serum leptin level appears to be independently correlated with the grade of steatosis.

Data from animal studies and clinical studies support the role of proinflammatory cytokine tumor necrosis factor alpha (TNF-alpha) in the early stages of fatty liver, as well as in alcoholic steatohepatitis.


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