Background: Both C-peptide and nicotinamide are known to reduce blood glucose in type 1 diabetes. In the present study, the effects of C-peptide alone or in combination with nicotinamide on glucose and insulin levels in streptozotocin-nicotinamide-induced type 2 diabetic mice. Methods: The study used 70 adult male NMARI mice, weighing 25–35 g, divided into seven groups: control; type 1 diabetic; type 2 diabetic; type 2 diabetic + C-peptide; type 2 diabetic + nicotinamide; type 2 diabetic + nicotinamide and C-peptide; type 2 diabetic + glyburide. Type 2 diabetes was induced with ip injection of streptozotocin–nicotinamide. Twenty eight days after the onset of diabetes, treatment with C-peptide, nicotinamide, nicotinamide + C-peptide, or glyburide were initiated. Glucose and insulin levels were evaluated. One-way ANOVA and Least Significant Difference (LSD) tests were used to test for significance. Results: Blood glucose significantly increased (P < 0.001) in all diabetic mice compared with control mice. Insulin resistance and blood glucose levels were significantly reduced (P < 0.05) in C-peptide and nicotinamide + C-peptide mice compared with type 2 diabetic mice. Conclusions: The present study supports the anti-diabetic effects of C-peptide, nicotinamide + C-peptide, and suggests that one of the anti-diabetic mechanisms of these compounds is mediated through the reduction of insulin resistance.

Background: Both c-peptide and nicotinamide are known to increase blood insulin in diabetes. In the present study, we examined the effect of c-peptide alone or in combination with nicotinamide on insulin levels in pancreatic islets in mice. Methods: This study was conducted with 60 adult male Naval Medical Research Institute (NMARI) mice weighing 25 to 30 g. Pancreatic islets from normal mice were isolated by the collagenase digestion method. Mice were divided into ten groups of six (n = 6): control, glyburide (1 and 10 μM), C-peptide (50 and 100 nM), nicotinamide (10, 25, and 100 mM), nicotinamide + C-peptide (100 mM and 100 nM), and buffer in different glucose concentrations (2.8, 5.6, and 16.7 mM). Insulin secretion was measured using insulin radioimmunoassay method. Results: Insulin secretion significantly increased at 16.7 mM glucose concentration compared with 2.8 and 5.6 mM glucose concentrations. Incubation of islets at 2.8 and 5.6 mM glucose concentrations and nicotinamide + C-peptide, nicotinamide 25 and 100 mM, and C-peptide 100 nM significantly increased insulin secretion compared with the control group. In addition, incubation of islets at 16.7 mM glucose with nicotinamide + C-peptide significantly increased insulin secretion. Glyburide at 10 μM concentration was more effective than nicotinamide at 10 and 100 mM, C-peptide 50 and 100 nM in the presence of 16.7 mM glucose concentration. However, the combination of nicotinamide + C-peptide was more effective than glyburide at a concentration of 10 μM in the presence of a 16.7 mM glucose concentration. Conclusions: This paper suggests that c-peptide, nicotinamide, and the combination of c-peptide and nicotinamide in-creases insulin secretion from pancreatic islets.
C-Peptide ; Niacinamide