INS and diabetes mellitus: Insulin levels in the blood are increased during the early stages of T2DM; however, long-term glucose stimulation can cause toxicity to the pancreatic β-cell, leading to ER stress and cell apoptosis in the later stages of diabetes, which results in a decline in the ability of the β-cell to synthesize and secrete insulin, thus leading to a decrease in insulin levels in the blood plasma [34].