Eugenol Ameliorates Hepatic Steatosis and Fibrosis by Down-Regulating SREBP1 Gene Expression <i>via</i> 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 Ca 2 -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 eugenoltreated 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.Key words eugenol; fatty liver; fibrosis; AMP-activated protein kinase; sterol regulatory element binding protein Non-alcoholic fatty liver disease (NAFLD) is one of the most common liver ailment worldwide.1) While hepatic steatosis is often asymptomatic, it can progress to non-alcoholic steatohepatitis (NASH). If untreated, NASH can progress to cirrhosis and increased risk of early mortality.2) Obesity and insulin resistance, as seen in type 2 diabetes mellitus (T2DM), and hypertriglyceridemia are well-documented risk factors for NAFLD.3) These factors are key targets for prevention and therapy of NAFLD tends to focus on addressing the obesity or insulin resistance rather than NAFLD itself. NAFLD in the hepatic steatosis (HS) phase can be reversed by lifestyle modification, while NASH is more difficult to treat. Thus, preventing the progression of HS to NASH is of primary importance. Lifestyle recommendations for NAFLD are generally limited to losing weight through energy restriction and/or increasing physical activity, which is often to fail to hold on to them. With this notion, phytochemicals obtained from medicinal plants or foods are attracting alternative options for the treatment of NAFLD and prevention to progress to NASH.

Eugenol Attenuates Cerebral Ischemia-Reperfusion Injury by Enhancing Autophagy via AMPK-mTOR-P70S6K Pathway

“…In addition, suppressing the activation of P70S6K, a key downstream kinase of mTOR, can promote autophagy (Sun et al, 2018a). It has been shown that eugenol activates AMPK phosphorylation, but suppresses mTOR and P70S6K phosphorylation, which attenuates hepatic steatosis and fibrosis (Jo et al, 2014). In the present study, the ratio of p-AMPKa/ AMPKa was increased, while p-mTOR/mTOR and p-P70S6K/ P70S6K ratios were reduced by MCAO or OGD/R, which was further strengthened by eugenol.…”

Sex differences in the effects of high-fat diet on mouse sciatic nerves

“…SREBP1 binds to the sterol regulatory element in the nucleus, and activates the transcription of target genes, such as Fasn, Elvol6 and Scd1, associated with fatty acid synthesis (Xu et al, 2016). Several studies indicated that the lipid accumulation was caused by modulating the activation of SREBP1 signaling in hepatocytes isolated from HFD-fed rodent (Jung et al, 2012;Jo et al, 2014;Kim et al, 2019). Therefore, suggesting that HFD feeding might induce de novo lipogenesis via the activation of SREBP1 signaling in the sciatic nerves similar to the liver.…”

AMPK-Mediated Regulation of Lipid Metabolism by Phosphorylation

“…AMPK was shown to phosphorylate SREBP1c at Ser372, suppressing the proteolytic cleavage of precursor SREBP1c into mature SREBP1c, leading to the suppression of hepatic steatosis in diet-induced insulin-resistant mice. 56) In addition to direct regulation, AMPK can further reduce hepatic lipid contents by suppressing SREBP1c expression through decreasing the activity of mammalian target of rapamycin complex (mTORC), 57,58) an important mediator for the regulation of cellular metabolism and growth that may also promote SREBP-dependent fatty acid synthesis. mTORC1-dependent activation of SREBP1c is thought to accelerate fatty acid synthesis by cleavage of the SREBP1c molecule.…”