Improving effect of cordycepin on insulin synthesis and secretion in normal and oxidative-damaged INS-1 cells

Diabetes mellitus (DM) has recently become one of the major diseases that have received attention. Cordycepin (molecular formula: C₁₀H₁₃N₅O₃), is one of the major bioactive components of Cordyceps militaris, decreases blood glucose levels. In this study, the effect and mechanism of cordycepin in normal and oxidative-damaged INS-1 cells were explored by using cell and molecular biology methods. Results showed that cordycepin could enhance insulin synthesis and secretion. The mechanism is possibly related to the elevated ATP content induced membrane depolarisation and increased Ca²⁺ concentration. At the genetic level, cordycepin upregulated the mRNA level of insulin, pancreatic duodenal homeobox factor-1 (PDX-1) and glucose transporter 1 (GLUT1). At the protein level, cordycepin promoted the expression of PDX-1, GLUT1, serine threonine kinase (Akt) and phosphorylated Akt (P-Akt). These effects may also contribute to the enhancement of insulin synthesis and secretion. Further analysis revealed that cordycepin protected against H₂O₂-induced damage on INS-1 cells and improved their viability and insulin synthesis/secretion. This effect should be attributed to the reduced intracellular reactive oxygen species (ROS), enhanced mitochondrial membrane potential (MMP), increased activity of superoxide dismutase (SOD) and upregulated genetic and protein expression of catalase (CAT), PDX-1, GLUT1 and P-Akt. In conclusion, cordycepin promotes insulin synthesis and secretion in normal islet β cells and improves this function in oxidative-damaged islet β cells. Given that islet β cells are vulnerable to oxidative stress, the improving effect of cordycepin on the antioxidant capacity and insulin synthesis/secretion of INS-1 cells may be an important mechanism for its hypoglycaemic effect.