Eugenol Ameliorates Hepatic Steatosis and Fibrosis by Down-Regulating SREBP1 Gene Expression via AMPK-mTOR-p70S6K Signaling Pathway

Abstract

Beneficial effect of eugenol on fatty liver was examined in hepatocytes and liver tissue of high fat diet (HFD)-fed C57BL/6J mice. To induce a fatty liver, palmitic acid or isolated hepatocytes from HFD-fed Sprague-Dawley (SD) rats were used in vitro studies, and C57BL/6J mice were fed HFD for 10 weeks. Lipid contents were markedly decreased when hepatocytes were treated with eugenol for up to 24 h. Gene expressions of sterol regulatory element binding protein 1 (SREBP1) and its target enzymes were suppressed but those of lipolysis-related proteins were increased. As a regulatory kinase for lipogenic transcriptional factors, the AMP-activated protein kinase (AMPK) signaling pathway was examined. Protein expressions of phosphorylated Ca²⁺-calmodulin dependent protein kinase kinase (CAMKK), AMPK and acetyl-CoA carboxylase (ACC) were significantly increased and those of phosphorylated mammalian target of rapamycin (mTOR) and p70S6K were suppressed when the hepatocytes were treated with eugenol at up to 100 µM. These effects were all reversed in the presence of specific inhibitors of CAMKK, AMPK or mTOR. In vivo studies, hepatic triglyceride (TG) levels and steatosis score were decreased by 45% and 72%, respectively, in eugenol-treated mice. Gene expressions of fibrosis marker protein such as α-smooth muscle actin (α-SMA), collagen type I (Col-I) and plasminogen activator inhibitor-1 (PAI-1) were also significantly reduced by 36%, 63% and 40% in eugenol-treated mice. In summary, eugenol may represent a potential intervention in populations at high risk for fatty liver.