Pioglitazone Prevents Acute Liver Injury Induced by Ethanol and Lipopolysaccharide Through the Suppression of Tumor Necrosis Factor-??

Abstract

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma), which is a ligand-dependent transcriptional factor, forms a heterodimer with retinoid X receptor (RXR) and controls many genes that are relevant to the regulation of lipid metabolism and insulin sensitization. Recent studies have shown that stimulation of PPAR-gamma inhibits the production of inflammatory cytokines in monocytes and macrophages. Alcohol and lipopolysaccharide (LPS) have already been shown to induce liver injury through the activation of many inflammatory cytokines. Thus, the activation of PPAR-gamma by its ligand may represent a potential effect causing liver injury. In this study, we investigated the effects of pioglitazone, a ligand for PPAR-gamma, on acute liver injury induced by ethanol and LPS. Female Sprague-Dawley rats that weighed 300 g were given ethanol (5 g/kg body weight) intragastrically and received an intraperitoneal injection of LPS 24 hr later. Subsequently, pioglitazone (1 mg/kg body weight) or vehicle alone was injected intraperitoneally 10 min and 24 hr after ethanol administration. Plasma levels of aspartate transaminase and alanine aminotransferase were measured by spectrophotometer. Plasma levels of tumor necrosis factor-alpha (TNF-alpha) were also determined using an enzyme-linked immunosorbent assay. Plasma and hepatic levels of lipid peroxide were measured, and the histologic findings of the liver were examined. Reverse transcription-polymerase reaction analysis of TNF-alpha, PPAR-gamma, RXR-alpha, and beta-actin mRNA was performed. Western blot analysis using the p65 subunit of NF-kappaB was also performed. Pioglitazone prevented increase in plasma aspartate transaminase, alanine aminotransferase, and TNF-alpha levels but had no effect on plasma and hepatic levels of lipid peroxide. Pioglitazone also prevented hepatic inflammation and necrosis induced by ethanol and LPS. Ethanol and LPS induction of TNF-alpha mRNA in the liver was blunted by pioglitazone; however, RXR-alpha mRNA was not affected. PPAR-gamma mRNA levels were suppressed by ethanol and LPS but recaptured by pioglitazone. Western blot analysis showed that pioglitazone did not inhibit translocation of NF-kappaB to nuclei. These results suggest that pioglitazone may prevent liver injury induced by ethanol and LPS through the suppression of TNF-alpha.