INS and diabetes mellitus: To test this hypothesis, we used streptozotocin (STZ), a β-cell specific toxin, to induce diabetes in a mouse model of insulin-deficient diabetes and to assess the efficiency of the GPR119 agonist, PSN632408, and the DPP-IV inhibitor, sitagliptin, alone and in combination on improving pancreatic β-cell function, stimulating β-cell regeneration, and reversing diabetes.