INS and diabetes mellitus: We previously confirmed that OLETF rats showed a progressive course of type 2 diabetes: mild hyperglycemia and normal plasma insulin level at 8 weeks old, indicating the prediabetic stage; hyperglycemia and hyperinsulinemia at 20 weeks old, indicating the early stage of type 2 diabetes; and severe hyperglycemia and a mixture of hyperinsulinemia and hypoinsulinemia at 30 weeks old, indicating the progressive stage of type 2 diabetes from non-insulin-dependent diabetes mellitus to insulin-dependent diabetes mellitus [9,10].