Function Of Lycium Barbarum Polysaccharide In Regulating Hepatic Glucose Production And Anti-diabetic Nephritis

Diabetes is a systemic chronic metabolic disease that seriously threatens global public health.Epidemiological studies have shown that diabetic patients have reached12.4% of the population in China in 2018,and the global prevalence of adult diabetes has reached 10.5% in 2021.Due to the long-term use of hypoglycemic drugs accompanied by many side effects,it makes sense to develop a hypoglycemic drug or adjuvant from natural products.Lycium barbarum polysaccharide(LBP)is one of the main bioactive components of Lycium barbarum fruit.It is reported in the literature that LBP shows hypoglycemic effect.However,the underlying mechanism has not yet been elucidated.This study aimed to elucidate the effects of LBP on alleviating hepatic insulin resistance,regulating hepatic glucose production and anti-inflammation in diabetic nephropathy.1.Hypoglycemic and improving insulin resistance effects of LBP:(1)HFD-STZ induced diabetic mouse model.The diabetic mice model was successfully established with a fasting blood glucose level of 11.4～23.8 mM and random blood glucose level of13.3～33.3 mM.Then the diabetic mice were subdivided into diabetic group(Fed with HFD and equal amount of saline),MET group(positive group,fed with HFD and metformin,the effective dose of 400mg/kg body weight,oral gavage)and LBP groups(Low-40,Medium-80,High-160mg/kg body weight,dissolved in saline,oral gavage).After 8 weeks of administration,the fasting and random blood glucose,and fasting insulin of mice were assayed.A homeostasis model assessment-insulin resistance(HOMA-IR)was used to evaluate the insulin resistance.The results showed that LBP reduced the blood glucose level significantly and alleviated the insulin resistance.(2)IR-HepG2 model.The results of the CCK8 cell proliferation experiment showed that30 mM glucose inhibited the proliferation of HepG2 cells significantly,and LBP is nontoxic and the dose of 100 μg/m L promoted the proliferation of HepG2.The insulin resistant HepG2(IR-HepG2)was induced by DMEM containing 30 mM glucose for24 h as the occurring of inhibited phosphorylation of AKT(Ser 473)and GSK3α/β(Ser21/9).Additionally,it is insensitive to response the phosphorylation induced by insulin,confirming that insulin resistance occurred in HepG2.The intracellular reactive oxygen species was elevated in IR-HepG2.However,LBP had the effects of insulin sensitization and scavenging reactive oxygen species.2.The effect of LBP on regulating hepatic glucose production:(1)Glucose uptake.Compared to the control group,the expression of GLUT2 in the diabetic group was reduced significantly,suggesting that the glucose uptake in diabetic mice is inhibited.However,LBP intervention can up-regulated the expression of GLUT2 significantly,promoting glucose entrance into hepatocytes.Additionally,the ability of glucose uptake in HepG2 was determined by testing the glucose consumption in the culture medium.Compared with 5.55 mM,30 mM(high)glucose inhibited the glucose consumption of HepG2 significantly.However,LBP significantly promoted the glucose consumption of HepG2 in a dose-dependent manner.These data show that LBP has the effect of enhancing hepatic glucose uptake in both DM mice and HepG2.(2)Glycogen synthesis.Compared to the control group,glycogen synthesis in diabetic group dropped greatly,but LBP greatly increased the expression of GYS2 and glycogen content,indicating the increase storage of glucose in liver.(3)Gluconeogenesis.Compared to the control group,the expressions of glucose-6-phosphatase(G6Pase)and phosphoenolpyruvate carboxykinase(PEPCK)greatly increased in diabetic mice,together with the inhibited phosphorylation of AMPKα(α1 Thr-183 +α2 Thr172),suggesting that the gluconeogenesis was active.LBP inhibited the expression of these two enzymes and stimulated the phosphorylation of AMPKα significantly.These data indicates that LBP inhibits gluconeogenesis via activating AMPK.(4)Glycolysis.Compared to the control group,the expressions of glucokinase(GK),phosphofructokinase 1(PFK1)and pyruvate kinase(PK)was obviously reduced,and pyruvate is more but lactic acid is less in diabetic mice.To a great extent LBP reverted these three enzymes,reduced pyruvate but increased the level of lactic acid,regulating the metabolite flux towards to glycolysis.3.The anti-inflammatory effect of LBP on diabetic nephropathy: Compared to the control group,the serum creatinine,blood urea nitrogen and microalbumin levels were significantly increased in diabetic mice.It exhibited glomerular hypertrophy,enlarged capsule,edema and vacuolar degeneration of renal tubule accompanying with intense inflammatory cell infiltration.The circling serum amyloid A3(SAA3)is elevated and the expressions of pro-inflammatory cytokines are higher in kidney cortex,including tumor necrosis factor α(TNFα),interleukin 1β(IL 1β),interleukin 6(IL6)and SAA3.The degradation of inhibitory κB-α(IκBα)and activating nuclear factor-κB(NF-κB)signaling occurred during the progress of inflammation.LBP greatly ameliorated the renal injury mentioned above and showed the anti-inflammatory effect via inhibiting NF-κB activation.