Study Of Effects And Molecular Mechanism Of Conjugated Linoleic Acid On Lipid Metabolism In Db/db Mice

BackgroundNonalcoholic fatty liver disease(NAFLD)is a clinical pathological syndrome characterized by excessive deposition of fat in the hepatocytes,which is the main feature of the exclusion of alcohol and other clear liver damage.It is closely related to type 2 diabetes(T2DM),insulin resistance(IR),obesity,metabolic syndrome and so on.It may advance to liver cirrhosis even liver cancer severely.The incidence of non-alcoholic fatty liver disease is increasing worldwide and there is no effective treatment in clinic.Conjugated linoleic acid(CLA)refers to the linoleic acid isomers containing conjugated double bonds,of which the two isomers c9,t11-CLA and t10,c12-CLA are the most important ingredient.Studies have shown that CLA can play a variety of important physiological functions,such as weight-loss,lipid-lowering,anti-oxidation,anti-tumor,and treatment of diabetes.However,its molecular mechanism of action is not completely clear.Peroxisome proliferator-activated receptors(PPARs)are ligand-activated transcription factors,in which PPARa and PPARy are involved in the regulation of expression of various lipid metabolism-related genes,resulting in energy balance.And plays an important regulatory role in metabolic function.ObjectivesTo analyze the therapeutic effects of conjugated linoleic acid on db/db mice and explore the mechanism of conjugated linoleic acid in the regulation of lipid metabolism-related genes such as CD36,ACC,and FASN through nuclear transcription factor pathways such as PPARa,PPARy,and SREBP-lc.MethodsAnimal experiments:c9,t11-conjugated linoleic acid and t10,c12-conjugated linoleic acid were mixed and fed to male diabetic(db/db)mice aged 18 months.The body weight,dietary intake,fasting blood glucose,triglycerides and total cholesterol levels were measured.Hepatic pathological changes and fatty acid content were detected by HE staining and oil red staining.Fluorescent quantitative PCR and western blot were used to detect peroxisome proliferator-activated receptor a(PPARa),peroxisome proliferator-activated receptor y(PPARy),and differentiation antigen cluster 36(CD36).The carbohydrate response original binding protein(CHREBP)and sterols regulate gene expression levels such as the original binding protein 1c(SREBP-1c).Cell experiments:HepG2 cells were treated with 50uM c9,t11-cla or t10,c12-cla respectively.The control group was treated with linoleic acid.Detecting the gene expressions of PPARa,PPARy,CD36,ACC and analysis changes of these gene expressions after knocking down of PPARaor PPARygene.ResultsConjugated linoleic acid can reduce the amount of diet in mice,effectively reduce the weight of obese mice and lower serum triglyceride and cholesterol levels.(2)conjugated linoleic acid can effectively reduce fasting blood glucose and increase glucose tolerance in db/db mice.(3)liver pathology and oil red staining showed that conjugated linoleic acid could reduce the accumulation of lipid droplets in the liver and improve fatty liver effectively.(4)Conjugated linoleic acid increased PPARa protein expression and decreased CD36 and PPARyprotein expression.Conjugated linoleic acid significantly inhibited FANS gene expression,probably by reducing SREBP-1c protein expression.(5)Conjugated linoleic acid can increase the level of phosphorylation of ACC,increase the concentration of acetyl coenzyme A,inhibit the synthesis of fatty acids,and increase the oxidation of fatty acids.ConclusionsTwo conjugated linoleic acid isomers mix can significantly improve fatty liver in db/db mice.The mechanism may be to decrease the expression of CD36 by decreasing the expression of PPARy gene and reduce the absorption of fatty acids by cells;to decrease the expression of SREBP-lc protein.Inhibition of FANS gene expression reduces fatty acid synthesis;increases ACC phosphorylation levels,inhibits ACC activity,and reduces de novo synthesis of fatty acids.In addition,the anti-tumor effects of conjugated linoleic acid may be related to the increased expression of E-cadherin protein and decreased expression of N-cadherin protein.