Effects And Mechanisms Of Gut Microbial Metabolites On Nonalcoholic Fatty Liver Disease

Objective:The aim of the study is to explore the role of gut microbial metabolites in the development and progression of nonalcoholic fatty liver disease(NAFLD)Meanwhile,we aim to identify the targets and molecular mechanisms underlying the effects,which may help to provide with novel therapeutic strategies of NAFLDMethods:The rodent model of steatohepatitis was induced with high-fat diet(HFD)feeding for 16 weeks.At the end of 8th week,the negative control group was gavaged with saline while the experimental groups were gavaged with trimethylamine N-oxide(TMAO),indole-3-propionic acid(IPA)or sodium butyrate(NaB),respectively.The liver tissues were harvested at the end of 16th week and subjected to HE staining.The severity of the disease was evaluated based on the pathological alterations.The stool samples were also collected before the rats/mice were sacrificed and 16s rDNA sequencing was performed to analyzed the profile of gut microbiota.The serum levels of endotoxin,liver enzymes,lipids and lipoproteins were measured Immunohistochemistry(IHC),western blot and quantative real-time PCR(qPCR)were applied to detect the expression levels of genes related to lipid metabolism,inflammation,oxidative stress,fibrosis,and so on.Meanwhile in vitro models were established with LPS-treated macrophages to study the effect of IPA on the activation of inflammation and with high glucose,high insulin-treated hepatocytes to study the effect of NaB on the de novo lipogenesis.Western blot and qPCR were utilized to further investigate the targets and molecular mechanismsResults:The rodent model of steatohepatitis was successfully established with HFD feeding for 16 weeks.Compared with the negative control group which received saline gavage,experimental groups with TMAO or IPA or NaB intervention for 8 weeks exhibited attenuation of NASH with different extents.In TMAO-treated HFD-fed group,the infiltration of inflammatory cells and hepatocytes ballooning were significantly alleviated,hepatic and serum levels of cholesterol were decreased,the endoplasmic reticulum(ER)stress and hepatocytes injuries were attenuated,genes related to intestinal cholesterol absorption were down-regulated,and the diversity of gut microbiota was evelated.In the IPA-treated HFD-fed group,hepatic steatosis,inflammation and fibrosis were all improved.The gut microbiota dysbiosis was partially reversed and intestinal mucosal homeostasis was reconstructed,which resulted in decrease of plasma endotoxin with IPA treatment.Furthermore,IPA could directly inhibits LPS-induced activation of proinflammatory signals and down-regulate the expression of proinflammatory cytokines.In the NaB-treated HFD-fed group,hepatic steatosis was significantly attenuated.Moreover,NaB treatment greatly alleviated lipid accumulation in hepatocytes treated with high glucose and high insulin.Mechanistically,NaB decreases the expression of fatty acid synthase(FAS)and stearoyl-CoA desaturase-1(SCD1)which are key lipogenetic enzymes.This effect may be mediated by the activation of AMPK by NaB and subsequent inhibition of sterol regulatory element-binding protein-1(SREBP1)maturationConclusions:Gut microbial metabolites play important roles in the development and progression of NAFLD.TMAO,IPA and NaB can all attenuate the progression of NASH via different mechanisms.Therapeutic approaches targeting the gut microbial metabolites may provide new strategies for NASH treatment.