Study On The Effect Of Melatonin On Oleic Acid And Methylglyoxal Induced Lipid Accumulation In HepG2 Cells

Non-alcoholic fatty liver disease has been a serious global health problem in affluent Western countries,and is steadily rising in incidence in newly industrialized countries like China.The main characteristic of non-alcoholic fatty liver disease is hepatic lipid accumulation.With the development of society,high-fat diet increases the probability of occurrence of non-alcoholic fatty liver disease.Oleic acid is the main composition of fatty acids in people's diet.Excessive oleic acid intake will promote liver lipid generated and lead to lipid accumulation,which has an important influence on the development of non-alcoholic fatty liver disease.Non-alcoholic fatty liver disease as a kind of metabolic disease,it is frequently accompanied by type 2 diabetes.The non-enzymatic glycation reaction always occurs in diabetic patients due to hyperglycemia.Methylglyoxal is the reactant of the non-enzymatic glycation reaction.Methylglyoxal can lead to insulin resistance,promote disturbance of lipid metabolism,and further result in lipid accumulation in the liver.Therefore methylglyoxal is the main causes of diabetic fatty liver.Melatonin exists as an active ingredient in several foods,and has been reported to attenuate fatty acid induced-fatty liver disease in animals,however,its molecular mechanisms are not well elucidated.Herein,we investigated the effects of melatonin on lipid accumulation induced by oleic acid and methylglyoxal in HepG2 cells,and characterized the change of related protein and gene in lipid anabolic pathways and catabolic pathways.The results are as follows:In oleic acid induced lipid accumulation models,pretreatment with melatonin significantly inhibited accumulation of triglyceride and cholesterol induced by incubating HepG2 cells with high concentrations of oleic acid(oleic acid overload).Melatonin pretreatment induced phosphorylation of AMP-activated protein kinase(AMPK)and acetyl-CoA carboxylase(ACC),causing their activation and inactivation,respectively.Expression levels of peroxisome proliferator activated receptor-a(PPARa)and its target gene carnitine palmitoyl-CoA transferase 1(CPT1),which are associated with lipolysis,were upregulated by melatonin,whereas expression of sterol regulatory element binding protein-lc(SREBP-1c),fatty acid synthase(FAS)and stearoyl-CoA desaturase-1(SCD1),which are associated with lipogenesis,were downregulated(p<0.05).In methylglyoxal induced lipid accumulation models,methylglyoxal significantly increase the formation of lipid droplets,reduce the level of phospho-AMPK,upregulated the gene expression of SREBP-1c,FAS,and SCD1,and downregulated the gene expression of PPARa and CPT1(p<0.05).Pretreatment with melatonin significantly ameliorated methylglyoxal induced lipid accumulation by scavenging methylglyoxal in H'epG2 cells(p<0.05).These results suggested melatonin is a potential protective agent against oleic acid and methylglyoxal induced lipid accumulation.The protective role of melatonin depended on activating of AMPK,inactivating lipid anabolic pathways and activating catabolic pathways.