Ghrelin ameliorates transformation of hepatic ischemia-reperfusion injury to liver fibrosis by blocking Smad and ERK signalling pathways, and promoting anti-inflammation and anti-oxidation effects

Background & aims: Ghrelin, a gut hormone with pleiotropic effects, may act as a protective signal in parenchymal cells. Hepatic ischemia-reperfusion injury (HIRI) causes acute-on-chronic liver failure and induces transformation of acute to chronic injury. HIRI model of mice was established by a semi-hepatic blocking method and treated with Ghrelin. This process is involved in inflammation, oxidative stress damage and apoptosis, and is associated with the expansion and activation of fibrotic haematopoietic stem cells (HSCs) which express and secrete high levels of collagen that induces liver fibrosis. Therefore, we investigated the effects of Ghrelin during transformation of HIRI to liver fibrosis, and explored the molecular mechanism of Ghrelin's action based on Smad and ERK pathways. Methods: Hepatic injury was detected by plasma ALT levels. The hepatic histology and collagen were elucidated by HE staining and Masson staining, respectively. Liver inflammation levels and inflammatory cell counts were assessed by MPO and HE staining, respectively. The antioxidant capacity of plasma was evaluated based on the levels of SOD, MDA, and XOD. The mRNA or protein expression levels of genes related to apoptosis, fibrosis, Smad, and ERK pathways were assessed by real-time quantitative PCR (RT-qPCR), ELISA, or western blotting. Results: The HIRI model was established to investigate the effects of the liver injury transformed to liver fibrosis. Ghrelin exhibited good hepatic protection by ameliorating liver histological changes and decreasing plasma ALT levels. Ghrelin significantly decreased the expression of MPO than that in model group, suggesting that Ghrelin blocked the inflammatory response in the HIRI liver tissue; this supports the anti-inflammatory effects of Ghrelin. Ghrelin significantly decreased apoptosis (enhanced Bcl-2 expression, and down-regulated Bax and Caspase 3). Ghrelin exhibited anti-oxidative effects as it inhibited plasma MDA levels, and promoted plasma SOD and XOD levels. Moreover, Ghrelin inhibited activation of hepatic stellate cells, blocked traditional fibrotic Smad and ERK signalling pathways, and reduced hepatic fibrosis by stimulating degradation of extracellular matrices (ECMs; such as collagen I, collagen III, HA, and LN). Conclusions: This study demonstrates that Ghrelin delays the transformation of HIRI to liver fibrosis process which is correlated to its anti-apoptotic, anti-inflammatory, and anti-oxidative effects. Moreover, Ghrelin alleviates HIRI-mediated liver fibrosis, inhibits activation of HSCs, and reduces accumulation of ECM via inhibition of Smad and ERK signalling pathways.