Experimental type 2 diabetes increases the number of insulin-positive cells in rat spleen

Type 2 diabetes (T2D) is a chronic metabolic disease, being one of the leading causes of death and disability worldwide. Immune system disorders play an important role in the T2D pathogenesis, and immune system is exposed to increased stress resulting both of changes in immunometabolic regulation and disruption of tissue homeostasis caused by oxidative stress and chronic inflammation. Opportunities for adaptation of immune organs in T2D are of interest, especially, potential ectopic expression of insulin. Under hyperglycemic conditions, insulin-containing cells were detected in various organs, including the spleen. The aim of the present work was to estimate the number of insulin-positive cells (IPCs) in the spleen of rats with experimental T2D. The disorder was induced in mature male Wistar rats by intraperitoneal administration of 110 mg/kg nicotinamide followed by 65 mg/kg streptozotocin. 30 days later, blood samples and spleens were obtained. The level of glycemia, insulin contents, activity of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) in blood were assessed as well as markers of oxidative stress in the spleen. Biochemical studies revealed an increase in ALT activity in blood, along with increase in malondialdehyde (MDA) levels and decreased levels of reduced glutathione (GSH) in the spleen tissue of rats with experimental T2D. Meanwhile the activity of superoxide dismutase (SOD) and catalase in the spleen did not change. An increase in MDA level associated with unchanged activity of antioxidant enzymes and decreased GSH content suggests the development of oxidative stress in the tissue. Microscopy of spleen tissues was examined by immunohistochemistry using antibodies to proinsulin and insulin, showing an increased number of insulin-positive cells (IPCs) in the spleen tissue of rats with experimental T2D compared with diabetes-free animals. Optical density of the IPC cytoplasm was found to be increased in diabetic rats, thus suggesting increased functional activity of IPCs. Increase of numbers and functional activities of IPCs in the spleen in experimental model of T2D may indicate an adaptive role of extra-pancreatic insulin expression under the conditions of oxidative stress and cytolysis, including those in immunopoietic organs.