The Toxic Effect Of Long-term High Insulin Exposure On Pancreatic β-cells

Object: The incidence and prevalence of type 2 diabetes are increasing worldwide.Early insulin therapy has been recommended for utilization in patients with newly diagnosed type 2 diabetes because of β-cell function improving and extended glycemic remissions.However,the potential risks of insulin therapy still require our attention.In vitro experiments show that reduced insulin mRNA level in islet beta cells,glucose stimulated insulin secretion function abate,and appear even islet beta cell death after treated with insulin.However,it is still lack of a powerful in vivo experiments and clinical data for the toxic effects of insulin to islet beta cells.Aimed to define the effects of long-term insulin exposure on the pancreatic β-cells,we collected five insulinoma patients with exogenous hyperinsulinemia who had pancreatic tissues.Meanwhile,we inoculated insulin capsule and MIN6 insulinoma cells for C57BL/6 mice to induce sustained exogenous hyperinsulinemia to further explore the molecular mechanism of insulin-induced islet cell toxicity.Methods: 1.Serological indicators and blood glucose monitoring data of insulinoma people,as well as adjacent pancreatic tissues were collected,and data of pancreatic cancer people and adjacent normal pancreatic tissues were collected as the control group;2.C57BL/6 male mice were subcutaneously inoculated with insulinoma cell MIN6 for long-term high-insulin exposure,while sham group was subcutaneously injected with normal saline as control group.3.C57BL/6 male mice were subcutaneously inoculated with insulin capsules for long-term high-insulin exposure,and Sham operation group was subcutaneously injected with normal saline as control group.4.Blood samples and pancreatic tissues of mice were collected;5.H&E staining of pathological sections was used to observe the changes in the size,number and frequency distribution of pancreatic islets in mice treated with high insulin;6.Immunohistochemical staining of pathological sections was used to observe the synthesis of insulin and glucagon in the pancreatic islets of mice treated with high insulin;7.Immunofluorescence staining of pathological sections was used to observe the changes in the number of adult and adult cells in the pancreatic islets of mice treated with high insulin;8.Immunohistochemical staining and TUNEL staining were used to observe the apoptosis in the pancreatic islets of mice treated with high insulin.Results: 1.Endogenous islet parenchyma injury in insulinoma patients: compared with pancreatic cancer patients,insulin patients experienced long-term exogenous hyperinsulinemia;After the resection of the tumor,there was a significant dysglycemia.At the same time,compared with normal pancreatic tissue adjacent to pancreatic cancer in people with insulinoma,islet cells in pancreatic tissue adjacent to pancreatic cancer in people with insulinoma showed significant dysfunction and decreased number;2.Dysregulation of glucose metabolism in mice caused by insulinoma cells MIN6.After tumor cells were excised,the mice showed significant hyperglycemia rebound,and GTT and ITT results suggested endogenous islet dysfunction in the mice;3.Insulinoma cells MIN6 caused islet damage in the pancreas of mice.The H&E staining results of pathological sections indicated that the total mass of islets in the treated group decreased and the number of islets in the same section decreased;4.Insulinoma cells,MIN6,caused damage to cells in mouse islets.Immunohistochemical staining and immunofluorescence staining results of pathological sections indicated that insulin synthesis dysfunction and decreased number of insulin-producing cells in the treated group;5.Insulinoma cell MIN6 induced apoptosis of intracellular cells in mouse islets.Immunohistochemical staining and TUNEL staining of the pathological sections suggested apoptosis in the islet of mice in the treatment group;6.Long-term treatment with high insulin resulted in cell damage in the pancreatic islet of mice.Immunohistochemical staining and immunofluorescence staining of the pathological sections indicated that insulin synthesis dysfunction,decreased number and apoptosis occurred in the cells in the islet of mice in the treatment group.Conclusion: 1.Population data: after long-term hyperinsulinemia in insulinoma patients,insulin synthesis function and relative quantity of insulin-producing cells in non-tumor parts of the pancreas were weakened and decreased,which led to dysregulation of blood glucose in patients after tumor resection,that is,postoperative hyperglycemia rebound;2.Animal experiments: after long-term high insulin exposure,the number of pancreatic islets in the endogenous pancreatic tissues of mice decreased and atrophic.Insulin synthesis in mouse islet trunk cells decreased and the quantity decreased.In contrast,glucagon synthesis in islet cells increased but the amount did not change significantly.At the same time,apoptosis occurred in the islet of mice,which increased with the increase of insulin treatment time.In summary,long-term high insulin treatment can lead to dysfunction and even death of endogenous islet cells.