Non-insulin Determinant Pathways Maintain Glucose Homeostasis Upon Metabolic Surgery

Background and objectives: The escalating epidemic of obesity,metabolic syndrome and type 2 diabetes represents one of the most pressing biomedical challenges confronting modern society,however,much about the pathogenesis of these disorders remains unknown.Diabetes mellitus is a group of metabolic diseases characterized by hyperglycemia caused by deficiency of insulin secretion,action or both.Long-term hyperglycemia and hyperinsulinemia are associated with chronic injury,dysfunction and failure of multiple organs,especially eyes,kidneys,nerves,heart and blood vessels.At present,clinical treatment programs for diabetes mainly focus on promoting insulin secretion and improving insulin resistance,supplemented by lifestyle intervention.Nevertheless,the therapeutic interventions that work through the insulin pathway mostly lead to weight gain,with a risk of hypoglycemia,and have little if any impact on disease progression.Importantly,the harm of hyperinsulinemia should not be underestimated.Therefore,the study of non-insulin dependent hypoglycemic pathway is of great significance for understanding the pathogenesis of diabetes and the prevention and treatment of diabetes.Non-insulin dependent hypoglycemic pathways are objective and effective.On the basis of his observation in 1854 that diabetes could be induced in rabbits by puncturing the floor of the fourth-cerebral ventricle,the physiologist Claude Bernard proposed a role for the brain in both glucose homeostasis and diabetes pathogenesis.Until the discovery of insulin in 1921,and the subsequent identification of liver,muscle and adipose tissue as principal targets of the powerful effects of insulin on glucose metabolism.Combined with evidence linking diabetes pathogenesis to defective insulin secretion and action,insulin has attracted almost all the focus of diabetes research.Until recent years,research on non-insulin dependent hypoglycemia has been revived.Among them,the study of intervening energy intake and consumption to improve the energy metabolism balance and maintain the glucose homeostasis has attracted more attention.A large number of reports have confirmed that intensive lifestyle interventions,metformin,GLP-1 analogues and their receptor agonists,α glycosidase inhibitors and SGLT2 inhibitors can alleviate diabetes by directly interfering with energy metabolism and by non-insulin dependent way.In addition,animal experiments have reported that infusion of very small doses of drug intervention into the hypothalamus region of energy balance regulation can significantly inhibit hepatic glucose output and control blood glucose at normal levels without dependence on the peripheral insulin system.Metabolic surgery,also known as bariatric surgery,aims at limiting energy intake through gastrointestinal volume reduction and food bypass,and RYGB surgery is an ideal choice in clinical practice.After metabolic surgery,the body weight and glucose homeostasis can be maintained for a long time,and the comprehensive benefits are far greater than those of conventional medicine.Moreover,metabolic surgery can significantly improve diabetic complications such as hypertension,diabetic kidney damage,cognitive impairment and so on.Interestingly,improvements in blood glucose in type 2 diabetes occur within days after surgery,suggesting that post-operative benefits do not depend on increased insulin sensitivity induced by weight loss.Moreover,metabolic surgery has a significant therapeutic effect on obese patients with type I diabetes mellitus,and can reduce or even completely discontinue insulin after surgery.However,the above subjects are often accompanied by the interference of pathological factors such as hyperinsulinemia and insulin resistance,which makes the effect of metabolic surgery on insulin pathway unclear.Therefore,this study used healthy animals as experimental models to avoid the interference of various pathological factors,in order to verify the relationship between metabolic surgery regulation of blood sugar homeostasis and insulin pathway.This study is divided into three parts.1.To determine whether RYGB can maintain glucose homeostasis under the condition of insufficient insulin and reduced insulin sensitivity.2.To explore the possible molecular mechanism of RYGB in regulating glucose homeostasis through non-insulin dependent pathway.3.By collecting and analyzing the clinical data of patients,to clarify the role of non-insulin dependent pathway initiated after RYGB in human.Materials and methods:This study consists of animal experiments and population studies.Animal experiments were conducted on healthy SD rats and C57BL/6J mice.To observe the changes of plasma insulin and blood glucose before and after metabolic surgery,and clarify the mechanism of non-insulin dependent regulation of glucose homeostasis after metabolic surgery.Population studies mainly collect the data of patients undergoing metabolic surgery in recent years,observe plasma insulin,blood glucose,HbA1 c and other indicators,and make statistical analysis.1.To observe the effects of RYGB and Sham surgery on body weight,plasma insulin level and 24-hour dynamic blood glucose in healthy SD rats,and to clarify the changes of islet structure by pathological section.The effect of metabolic surgery on insulin synthesis and secretion was analyzed by western blotting.2.Evaluated insulin sensitivity,hepatic glucose production and glucose uptake in various tissues by using hyperinsulinemic-euglycemic clamp test.The protein expressions related with hepatic glucose production and insulin pathway were analyzed by western blotting.Gradient dose was used to detect the difference of insulin sensitivity of rats.3.Comparing the effects of different metabolic interventions on fasting insulin level,blood glucose,body weight and energy intake,to identify the initiating factors of regulating glucose homeostasis by RYGB.4.To detect the effect of RYGB intervention on fatty acid oxidation in rat liver and muscle tissue.RYGB intervention was performed on C57BL/6J mice to detect the changes of overall metabolic level.5.To explore the effects of RYGB intervention on major glycolipid metabolism related genes and metabolic pathways through gene chip screening.6.The effect of RYGB intervention on the expression of major glycolipid metabolic related proteins and the activity of metabolic pathways was analyzed by western blotting,and the mechanism of maintaining glucose homeostasis after RYGB was explored.7.To verify the therapeutic effect of RYGB on STZ-induced diabetes mellitus model,and observe the effects on insulin level,fasting blood glucose and body weight.The 24-hour dynamic blood glucose of rats was monitored before and after the intervention of metabolic surgery.8.Collect clinical data and analyze the effects of metabolic surgery on dynamic blood glucose,glucose tolerance,BMI,HbA1 c,insulin and C-peptide level.Results:1.RYGB reduces insulin synthesis and secretion,but maintains euglycemia.2.The RYGB-mediated improvement in glucose homeostasis is independent of insulin sensitivity.3.Eliminating the stomach and duodenum by RYGB reduces insulin production and restricts energy uptake.4.RYGB shifts the metabolic profile to maintain glucose homeostasis.5.RYGB alters glucose-and fatty acid-related metabolic targets,in which the increased activity of AMPK may be involved.6.The effect of RYGB on glucose homeostasis has been validated in islet-disrupted rats7.The ability of RYGB to remit hyperglycemia is independent of islet state in patients with type 2 diabetes.Conclusion:1.Gastrointestinal tract rearrangement by RYGB reduces both insulin production and action but persistently maintains euglycemia in healthy rats.2.Excluding the stomach and duodenum by RYGB in rats largely reduces energy intake,which decreases insulin production and triggers insulin-independent metabolic pathways.3.RYGB predominately shifts the metabolic profile to fatty acid oxidation,enhances energy expenditure and triggers multiple metabolic pathways,in which the increased activity of AMPK may be involved.4.Non-insulin dependent glucose homeostasis effect of RYGB can be extended to patients with type 2 diabetes.