Antagonic effect of ghrelin and LEAP-2 on hepatic stellate cell activation and liver fibrosis in obesity-associated nonalcoholic fatty liver disease.

BACKGROUND: Growing evidence suggests the key role of ghrelin in the onset and progression of nonalcoholic fatty liver disease (NAFLD). The potential participation of ghrelin and the ghrelin receptor antagonist, LEAP-2, in the onset of liver fibrosis in patients with severe obesity and NAFLD through the regulation of TGF-ß1-induced hepatic stellate cell (HSC) activation was investigated. METHODS: Circulating (n = 179) and hepatic expression (n = 95) of ghrelin and LEAP-2 were measured in patients with severe obesity and available liver pathology analysis undergoing Roux-en-Y gastric bypass (RYGB). The effect of ghrelin isoforms and LEAP-2 on TGF-ß1-induced HSC activation, fibrogenic response, and contractile properties was evaluated in vitro in human LX-2 cells. RESULTS: Plasma and hepatic ghrelin were negatively associated, while LEAP-2 exhibited a positive association with liver fibrosis in patients with obesity and NAFLD. Six months after RYGB, hepatic function was improved and, although acylated ghrelin and LEAP-2 concentrations remained unchanged, both hormones were inversely related to post-surgical levels of profibrogenic factors TGF-ß1 and TIMP-1. Acylated ghrelin treatment reversed TGF-ß1-induced myofibroblast-like phenotype, collagen contractile properties, and the upregulation of factors involved in HSC activation and fibrogenesis via PI3K/Akt/mTOR pathway. Moreover, acylated ghrelin inhibited the mild HSC activation induced by LEAP-2. CONCLUSIONS: Ghrelin is an anti-fibrogenic factor blocking HSC activation induced by the most potent fibrogenic cytokine, TGF-ß1, and LEAP-2. The imbalance between acylated ghrelin and ghrelin receptor antagonist LEAP-2 might contribute to maintain liver fibrosis in patients with obesity and NAFLD.

Ghrelin Reduces TNF-α-Induced Human Hepatocyte Apoptosis, Autophagy, and Pyroptosis: Role in Obesity-Associated NAFLD.

Context: Human obesity is associated with increased circulating TNF-α, a proinflammatory cytokine that induces hepatocyte cell death. Objective: The potential beneficial effects of acylated and desacyl ghrelin in the progression of nonalcoholic fatty liver disease (NAFLD) to nonalcoholic steatohepatitis in obesity via the inhibition of TNF-α-induced hepatocyte apoptosis, autophagic cell death, and pyroptosis were investigated. Design, Settings, and Participants: Plasma ghrelin isoforms and TNF-α were measured in 158 participants, and hepatocyte cell death was evaluated in liver biopsies from 76 patients with morbid obesity undergoing bariatric surgery with available liver echography and pathology analysis. The effect of acylated and desacyl ghrelin on basal and TNF-α-induced cell death was determined in vitro in human HepG2 hepatocytes. Results: Circulating TNF-α and the acylated/desacyl ghrelin ratio were increased, whereas desacyl ghrelin levels were decreased in patients with obesity and NAFLD. Six months after bariatric surgery, decreased acylated/desacyl ghrelin levels, and improved hepatic function were found. Patients with obesity and type 2 diabetes showed increased hepatic ghrelin O-acyltransferase transcripts as well as an increased hepatic apoptosis, pyroptosis, and compromised autophagy. In HepG2 hepatocytes, acylated and desacyl ghrelin treatment reduced TNF-α-induced apoptosis, evidenced by lower caspase-8 and caspase-3 cleavage, as well as TUNEL-positive cells and pyroptosis, revealed by decreased caspase-1 activation and lower high-mobility group box 1 expression. Moreover, acylated ghrelin suppressed TNF-α-activated hepatocyte autophagy, as evidenced by a decreased LC3B-II/I ratio and increased p62 accumulation via AMPK/mTOR. Conclusions: Ghrelin constitutes a protective factor against hepatocyte cell death. The increased acylated/desacyl ghrelin ratio in patients with obesity and NAFLD might constitute a compensatory mechanism to overcome TNF-α-induced hepatocyte apoptosis, autophagy, and pyroptosis.