Acetate, the key modulator of inflammatory responses in acute alcoholic hepatitis

Abstract

Acute alcoholic hepatitis is characterized by disproportionate macrophage inflammatory cytokine responses to bacterial lipopolysaccharide. Lack of knowledge of the underlying mechanism has limited progress toward effective therapy. We postulated a novel mechanism by which ethanol increases histone acetylation, increasing proinflammatory gene transcription and cytokine synthesis. Cytokine responses to lipopolysaccharide in a human macrophage cell line cultured in 86 mM ethanol, 1 mM acetate, and normal media were measured by multiplex immunoassay. Changes in histone acetylation were determined by immunofluorescence microscopy and chromatin immunoprecipitation on presentation. The effect of ethanol and acetate on acetyl-coenzyme A (acetyl-coA) synthetases, which convert acetate to acetyl-coA, the substrate for histone acetylation, was determined by quantitative reverse-transcription polymerase chain reaction and immunoblotting. Knockdown of acetyl-coA synthetases by short hairpin RNA (shRNA) was used to determine their role in ethanol's enhancement of the inflammatory cytokine response. Ethanolexposed macrophages developed enhanced interleukin 6 (IL6), IL8, and tumor necrosis factor alpha responses to lipopolysaccharide with time-dependent increases in histone acetylation that could be prevented by inhibition of ethanol metabolism. Chromatin immunoprecipitation confirmed increased histone acetylation at promoter regions of specific cytokine genes. The effect of ethanol was reproduced by incubation with acetate, the principal hepatic metabolite of ethanol, and both ethanol and acetate reduced histone deacetylase activity and up-regulated acetyl-coA synthetases. Knockdown of the acetyl-coA synthetases abrogated the effect of ethanol on cytokine production. Conclusion: Synthesis of metabolically available acetyl-coA from acetate is critical to the increased acetylation of proinflammatory gene histones and consequent enhancement of the inflammatory response in ethanol-exposed macrophages. This mechanism is a potential therapeutic target in acute alcoholic hepatitis. (HEPATOLOGY 2010; 51:1988-1997 A lcoholic liver disease (ALD) is a significant and growing global health problem. Clinical liver failure in ALD can result from chronic hepatocyte injury producing cirrhosis or from rapid, acute hepatocellular dysfunction secondary to inflammation in acute alcoholic hepatitis. AAH This acute inflammatory form of ALD carries a mortality of up to 35% on first presentation, killing patients before they have the opportunity to reap the benefits of appropriate health education and subsequent abstinence from alcohol. 1

Different Mechanisms for Histone Acetylation by Ethanol and Its Metabolite Acetate in Rat Primary Hepatocytes

“…It is also of interest to note that acetate supplementation inhibited HDAC activity in brain (Soliman and Rosenberger, 2011). Acetate is also a modulator of inflammatory responses (Kendrick et al, 2010). The literature evidence and results presented here support the view that ethanol itself activates histone acetyltransferase, whereas acetate inhibits HDAC.…”

Theophylline improves steroid sensitivity in acute alcoholic hepatitis

“…However, ethanol metabolism is itself a potent source of reactive oxygen species, which may impair the ability of the glucocorticoid receptor to recruit HDACs to ''switch off'' transcription of proinflammatory genes by the same mechanism. Alternatively, we have recently demonstrated that the increased concentrations of free acetate generated by ethanol metabolism favor increased histone acetylation and enhanced proinflammatory gene expression in a cell-line model of AAH, 19 and this mechanism could antagonize the normal glucocorticoid effect.…”

Apoptotic effect of sodium acetate on a human gastric adenocarcinoma epithelial cell line

“…Rodent neutrophils exposed to acetate undergo global inhibition of HDAC activity (Vinolo et al, 2011). Treatment with 1 mM acetate significantly reduces the HDAC activity and increases global histone acetylation in human macrophages, corresponding to a decrease in inflammatory cytokine [interleukin (IL)-6, IL-8, and tumor necrosis factor (TNF)-a] production (Kendrick et al, 2010). Conversely, human gastric adenocarcinoma (AGS) cells treated with sodium acetate for 24 h showed increased mRNA and protein levels of IL-1β, IL-8, and TNF-α.…”