The Role And Mechanism Of Sulforaphane In The Improvement Of Non-alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease(NAFLD)is a metabolic syndrome associated with obesity and type 2 diabetes.In recent years,the incidence of NAFLD has exploded in the world.However,due to the complexity of its mechanism and the difficulty of treatment,there are still great limitations in people's understanding of NAFLD.Currently,there are no approved drugs for NAFLD treatment in the world.The common clinical treatments include lipid-lowering and anti-inflammatory drugs,but their effectiveness and safety are still lacking in clinical research.Regulation of insulin resistance,which is the cause of NAFLD,by plant active substances is a noval strategy to prevent and treat NAFLD.Previous studies have shown that the plant active substance sulforaphane(SFN)can reduce body weight and maintain insulin homeostasis,but the effect and mechanism of SFN on NAFLD is unknown.Therefore,SFN was selected as the research object in this study to explore the potential efficacy of SFN in alleviating NAFLD through the mice NAFLD model.Combined with the cell lipid accumulation model,it was found that the potential molecular mechanism of SFN in alleviating NAFLD was related to fibroblast growth factor 21(FGF21).Finally,the effect of SFN combined with FGF21 protein on NAFLD was explored.The main results are as follows:Male C57BL/6J mice aged 7 weeks were fed a high-fat diet for 12 weeks to establish a NAFLD model.Then,through 6 weeks of SFN dietary intervention,the body weight,food intake,liver lipid accumulation,liver function,liver inflammation,blood lipid and insulin levels of the mice were investigated.The results showed that SFN did not change the body weight and food intake of mice.However,SFN significantly improved liver steatosis and decreased the contents of triglyceride,cholesterol as well as liver weight and liver/body weight ratio.SFN also reduced hepatic function injury,inflammation and lipid disorders and improved insulin resistance.After verifying the effects of SFN on improving NAFLD,the molecular mechanism of the process was preliminarily explored in our research.SFN was found that reduced fat synthesis and increased fat decomposition and fat oxidation after detecting hepatic genes and proteins regulating fatty acid metabolism in mice.Meanwhile,SFN partially reduced hepatic endoplasmic reticulum stress in mice,which was not regulated by nuclear factor-erythroid 2-related factor-2(Nrf2).It was also found that the high-fat diet reduced hepatic fibroblast growth factor receptor-1(FGFR1)and increased FGF21 level in mice,indicating that FGF21 resistance happened in liver.SFN increased the hepatic FGFR1 and FGF21 level and decreased the phosphorylated p38 level in NAFLD mice.In order to further clarify how SFN regulates FGF21/FGFR1 signaling pathway to maintain hepatic lipid accumulation homeostasis,HepG2 cells were treated with free fatty acids(FFAs)(palmitic acid/oleic acid)to establish an in vitro lipid accumulation model.Meanwhile,related signaling pathways were detected after exogenous addition of SFN.Concentration dependent experiment results showed that SFN further increased FGF21 level induced by FFAs and reduced adipogenesis related proteins FAS,PPAR? and inflammatory regulatory protein phosphorylation of p38.Time-dependent experiment results showed that SFN increased FGFR1 level in 1 h,?Klotho level in 2 h and finally enhanced FGF21 level in 4 h.After FGFR1 gene knockdown,the effect of SFN on increasing FGF21 and decreasing p38 phosphorylation was weakened,while the effect of SFN on improving lipid accumulation was weakened in cells.After p38 gene knockdown,the effect of SFN on reducing lipogenic proteins FAS and PPAR?was weakened,while the ability of SFN to relieve lipid deposition decreased in cells.Finally,in order to explore the combined effect of SFN and FGF21 on NAFLD,NAFLD mice were injected intraperitoneally with mice recombinant FGF21 protein after SFN intervention for 3 weeks.The results showed that the liver weight,lipid accumulation and four indexes of blood lipid in the combined group were lower than mice in the FGF21 single treatment group.WB results showed that lipogenic protein PPAR? and phosphorylated p38 in the combined group were lower than FGF21 treatment group.Similiar results were seen in HepG2 cells.These results suggested that SFN dietary intervention effectively alleviated NAFLD by maintaining FGF21 homeostasis.Importantly,FGFR1 played a vital role during this process.SFN significantly reduced hepatic lipid accumulation and inflammatory response as well as improved insulin resistance and maintained hepatic lipid homeostasis by activating FGFR1 to increase the expression of FGF21.Our research provides experimental basis and theoretical support for SFN as a dietary additive and FGFR1 agonist in the later application.