The Improvement On Glucose Metabolism Disorders And Molecular Mechanism Of Cichoric Acid

Glucose metabolism,regulated by multiple and complicated signaling pathways,is a primary metabolic pathway to provide energy for the organism.Glucose metabolism disorders closely related to metabolic syndrome development,seriously affect human health and quality of life,leading to systemic chronic complications and a variety of organ damage in the body.In recent years,a variety of natural plant extracts and their derivatives are used as a dietary supplement,which has become a new direction to prevent the development of glucose metabolism disorders.Cichoric acid,is a phenolic acid,with anti-obesity,antioxidant,antiinflammatory,antiviral and immune function.It has been reported that cichoric acid is effective on reducing the blood glucose level.However,there are little evidence on the molecular mechanism of cichoric acid on the regulation of glucose metabolism disorder.Based on the above,the aim of the present research was to evaluate the regulation of cichoric acid on glycogen synthesis,glucose uptake,and glucose homeostasis.Furthermore,the underlying mechanism of the improvement of glucose metabolism and inflammatory response induced by glucose metabolism disorder,was also elucidated in the aspects of AMPK energy regulatory pathway,insulin signaling pathway and oxidative stress.It provided a new research ideas and theoretical basis for the study of the functional activity of chicory acid.The major contents and results are as follows:(1)The C57BL/6J diabetic mice was intraperitoneal injected with the multiple low dose of streptozotocin(MLD-STZ).To investigate the hypoglycemic effect and its mechanism,cichoric acid was supplemented in drinking water as dietary supplement.The results showed that cichoric acid remarkably improved body weight by 26.4%,speed by 1.6 times,locomotor activity by 1.7 times and fasting insulin concentration by 69.3%,decreased the fasting blood glucose by 33.5% and insulin resistance index by 63.5%,as well as regulated the insulin sensitivity and glucose sensitivity.Further analysis of the mechanism,to inhibit apoptosis mitochondrial signal transduction and alleviate the apoptosis of islet tissue induced by MLDSTZ,cichoric acid inhibited c-Jun N-terminal kinase(JNK)expression,regulated the expression of anti-apoptosis protein B-cell lymphoma-2(Bcl-2),down-regulated the expression of apoptosis protein Bcl-2 assaciated X protein,leading to the decrease of mitochondrial cytochrome c release.The insulin secretion was also improved by cichoric acid via the regulation of insulin secretion-related genes.In addition,chronic hyperglycemia leads to glucose toxicity and inflammation in MLD-STZ induced diabetic mice,with the high level of tumor necrosis factor-?(TNF-?)and interleukin(IL-1?),liver function index(Alanine aminotransferase and aspartate aminotransferase),renal function index(creatinine and urea nitrogen),as well as lactic acid in the serum.However,cichoric acid significantly suppressed inflammatory response and adjusted abnormal organ index.These results suggested that cichoric acid regulated blood glucose homeostasis via inhibition of pancreatic tissue apoptosis,the improvement of insulin release and the inhibition of inflammatory response.(2)The liver and muscle tissue samples were selected to investigate the regulation of cichoric acid on glycogen synthesis and inflammatory injury in diabetic mice.The results suggested that cichoric acid increased AMP-activated protein kinase(AMPK)phosphorylation,decreased acetyl CoA carboxylase phosphorylation,and promoted glycogen synthesis by 43.4% and 94.2% in the liver and muscle diabetic mice;cichoric acid activated the insulin signaling pathway,decreased gene expression of its negative regulatory factors,and then increased glucose transport.At the same time,cichoric acid regulated the gene expressions of glycolysis and gluconeogenesis in liver,as well as mitochondrial biogenesis-related gene expressions in muscle.In the study of tissue inflammatory injury in diabetic mice,cichoric acid inhibited the expression of inflammatory mediators(Cyclooxygenase-2(COX-2)and inducible nitric oxide synthase(iNOS))and cytokines(TNF-? and IL-6),activated nuclear factor-E2-related factor 2(Nrf2)-kelch-like ECH-associated protein 1(Keap1)antioxidant defense system and stimulated the gene expression of antioxidant enzymes,leading to the improvement of inflammatory injury.These results suggested that the regulation effect of cichoric acid on glycogen accumulation and inflammatory injury in liver and muscle of diabetic mice.(3)The cocktail method was used to differentiate 3T3-L1 preadipocytes into mature adipocytes.On this basis,insulin resistance model was induced by TNF-? in mature adipocytes to investigate the effect and molecular mechanism of cichoric acid on insulin resistance.The results showed that cichoric acid regulated the insulin signaling pathway,promoted the expression and membrane translocation of glucose transporter(GLUT)4,inhibited the expression of protein tyrosine phosphatase 1B(PTP1B),improved glucose uptake and insulin resistance in adipocytes;cichoric acid inhibited oxidative stress,the gene expressions of inflammatory factors,signal transduction of mitogen-activated protein kinases(MAPKs)and nuclear transcription factor-?B(NF-?B)inflammatory pathways.These results suggested that cichoric acid regulated lipid metabolism of mature adipocytes and inhibited insulin resistance and inflammatory response in TNF-? induced mature adipocytes.(4)To explore the molecular mechanisms for the improvement of glucose metabolism disorders by cichoric acid,high concentration of glucosamine was used to establish the insulin resistance cell model of HepG2 cells.The results indicated that cichoric acid regulated insulin signaling pathway,promoted membrane translocation of GLUT2 and enhanced glucose uptake in glucosamine-induced HepG2 cells.By constructing PTP1 B overexpressing cells,it was confirmed that cichoric acid improved insulin signaling pathway and glucose uptake via the suppression of PTP1 B.Cichoric acid increased AMPK phosphorylation,the expression of sirtuin type 1 and glycogen synthase kinase-3?(GSK-3?)phosphorylation,and inhibited cAMP-response element binding protein phosphorylation.With the addition of AMPK activator or inhibitor,it was confirmed that cichoric acid promoted GSK-3? phosphorylation and GLUT2 membrane translocation,and further respectively regulated of glucose uptake and glycogen synthesis,via AMPK pathway.Moreover,cichoric acid inhibited the expression of inflammatory mediators,the phosphorylation of p38,JNK and I?B,and the nuclear translocation of NF-?B in glucosamineinduced HepG2 cells.With the inhibitors addition of MAPKs or NF-?B,it was detected that cichoric acid inhibited NF-?B pathway via MAPKs pathway,and then inhibit the expression of COX-2 and iNOS as well as the corresponding inflammatory response.Cichoric acid reduced the production of reactive oxygen species,promoted Nrf2 nuclear translocation,suppressed the Keap1 expression,activated Nrf2-Keap1 antioxidant defense system and the activities of antioxidant enzymes.With the inhibitors addition of reactive oxygen species N-acetyl-Lcysteine or MAPKs and NF-?B pathway,it was confirmed that cichoric acid decreased the expression of COX-2 and iNOS,the signal transduction of inflammatory pathway and insulin pathway,and further regulated the glucose uptake via the inhibition of oxidative stress.