Roles And Underlying Mechanisms Of Vaccarin In Ameliorating Glucose And Lipid Metabolic Disorder

Destructive glucose and lipid metabolism in the liver is a crucial characteristic of type 2 diabetes mellitus(T2DM),eventually leading to insulin resistance and subsequent hyperglycemia and hyperlipidemia.Vaccarin is an active flavonoid glycoside associated with various biological functions.Previous studies have shown that vaccarin has pharmacological effects such as improving endothelial damage,promoting angiogenesis,inhibiting hyperglycemia,hypertension,and hyperlipidemia,but its effects on glucose and lipid metabolic disorder in T2 DM are still unclear.In this study,the HepG2 cells were treated with 18 mM GlcN for 18 h,and then treated with 5 μM vaccarin for 24 h to evaluated the effect of vaccarin on glucose metabolism disorders.GlcN treatment raised glucose production and increased mRNA and protein levels of PEPCK and G6 Pase and phosphorylation levels of FOXO1 in HepG2 cells,which were effectively attenuated by vaccarin.GlcN treatment reduced glycogen levelsand GSK3β phosphorylation,but it increased the phosphorylation expression of GS in HepG2 cells,changes that were prevented by treatment of cells with vaccarin.Meanwhile,vaccarin restored the GlcN-induced inhibition of AMPK phosphorylation.However,AMPK inhibitor Compound C abolished the effects of vaccarin in regulating glucose production,glycogen synthesis,and expression of related factors in GlcN-incubated HepG2 cells.AMPK activator AICAR mimics the effects of vaccarin on gluconeogenesis as well as glycogen synthesis and storage in GlcN-challenged HepG2 cells.These results suggest that vaccarin attenuates gluconeogenesis by promoting AMPK-mediated FOXO1 phosphorylation and promotes glycogen synthesis by activating AMPK/GSK3β signaling pathway to improve glucose metabolism disorder in HepG2 cells.To further investigate the effects of vaccarin on lipid metabolism derangements,we used free fatty acids to induce a model of hepatic steatosis.FFAs exposure promoted steatosis by upregulating mRNA and protein levels of SREBP1 and FAS,but downregulating mRNA and protein levels of CPT1 and ACC phosphorylation levels in HepG2 cells,effects that were essentially normalized by vaccarin.The lower levels of AMPK phosphorylation were restored to near baseline in FFAs-exposed HepG2 cells incubated with vaccarin.Pre-incubation with Compound C completely blocked the inhibitory effect of vaccarin on related factors of de novo lipogenesis and lipidolysis in HepG2 cell response to FFAs.Of note,both vaccarin and the AMPK activator AICAR rectified the detrimental effects of FFAs on lipid metabolism derangements in HepG2 cells.Our data revealed that vaccarin inhibits de novo lipogenesis by promoting AMPK/SREBP1 signaling pathway and promotes lipidolysis by activating AMPK/ACC signaling pathway to improve steatosis in HepG2 cells.Finally,we used STZ/HFD induced mouse model of T2 DM to evaluate the effects of vaccarin on hepatic glucose and lipid metabolic disorder in T2 DM mice.Vaccarin treatment effectively reduced the fasting blood glucose,improved glucose tolerance and insulin sensitivity,and promoted glycogen synthesis in the liver of T2 DM mice.The increase of lipid level in serum and liver were inhibited by vaccarin in T2 DM mice.Vaccarin administration normalized hepatic dysfunction and reduced the accompanying impressive lipid diffusion in T2 DM mice.Meanwhile,vaccarin effectively regulated related factors of hepatic gluconeogenesis,glycogen synthesis,de novo lipogenesis,lipidolysis and AMPK,significantly improved hepatic glucose and lipid metabolic disorder in liver of T2 DM mice.These results suggest that vaccarin maybe a new and effective therapeutic agent for treatment of T2DM.