Magnesium Isoglycyrrhizinate Ameliorate Nonalcoholic Fatty Liver Disease And The Underlying Mechanisms

In recent years,the prevalence of nonalcoholic fatty liver disease(NAFLD)is increasing in the general population.However,NAFLD treatment clinically is still at an exploratory stage,and the lack of effective and low-side-effect drugs for treating NAFLD makes it the second-largest liver disease next to viral hepatitis.Lipotoxicity,which is closely associated with the accumulations of triglyceride and lipid droplets in the liver,often accompanied by the occurrence of NAFLD and may become an important factor for NAFLD to develop to nonalcoholic steatohepatitis(NASH),liver fibrosis and even hepatic carcinoma.Magnesium isoglycyrrhizinate(MgIG),one of the fourth generation of glycyrrhizic acid,is an 18?-glycyrrhizic acid(GA)extracted from Licorice and after isomerization and salification.Clinically,MgIG is mainly utilized for the adjuvant treatment of liver damage caused by chemotherapy and surgery in the form of injections.However,it has not been used for clinical treatment of NAFLD to date.In this study,it was found that MgIG was able to attenuate lipid accumulation,TG level,and reactive oxygen species(ROS)production in hepatocytes(HepG2,LO2,AML-12 and primary hepatocytes)induced by free fatty acids(FFAs),thereby reducing inflammatory response and apoptosis of hepatocytes.High fat diets(HFD)treatment increased body weight of mice,accompanied by large fat accumulation in the liver.Compared with mice treated with HFD,MgIG injection significantly decreased body weight of mice and reduced fat accumulation and TG level in the liver.Collectively,MgIG showed a superior effect for the treatment of NAFLD.To explore the underlying mechanisms of MgIG on NAFLD,it was revealed in our study that autophagy was induced in hepatocytes in vitro and in vivo,and the lipid droplets,autophagosomes and lysosomes colocalized in the cells after the treatment of MgIG.Chloroquine.an inhibitor of autophagy,and ATG5 knock down,which block autophagosomes formation,reduced the protective effects of MgIG on hepatocytes exposed to FFAs.and further promoted inflammatory responses in hepatocytes.suggesting that MgIG exerted its protective effects on NAFLD by enhancing hepatocyte autophagy.Moreover,further studies showed the role of MgIG in regulation of gene expression of adipose lipase such as HSL and ATGL,indicating that MgIG showed the ability to promote lipids degradation through multiple biological mechanisms.mTOR.the target of rapamycin,triggers autophagy by sensing changes in hormones,amino acids or ATPs in cells.In the current study,it was demonstrated that MgIG regulated mTOR signaling negatively by its regulation on AKT.Furthermore,in hepatocytes exposed to FFAs and livers of mice treated with HFD,MgIG treatment still had the ability to inhibit mTOR pathway,suggesting that the induction of autophagy by MgIG was associated with its effect on mTOR inhibition.However,it was not synchronous between the down-regulation of mTOR and the occurrence of autophagy after the administration of MgIG in this study,demonstrating mTOR signaling pathway is not the only pathway that MgIG induce autophagy.The specific molecular mechanisms need further investigationHere are the innovations of this study.Firstly,MgIG was applied to NAFLD treatment,expanding the clinical indication range of MgIG.Secondly,it was found that MgIG was able to trigger autophagy in hepatocytes in NAFLD,and the relationships between autophagy and lipid clearance were clarified.Thirdly,the molecular mechanisms how MgIG induce autophagy in hepatocytes in NAFLD were initially explored.Collectively,this study expands clinical application values of MgIG,providing new theoretical basis for the further development and utilization of MgIG and the clinical treatment of NAFLD.