DPP IV inhibitor suppresses STZ-induced islets injury dependent on activation of the IGFR/Akt/mTOR signaling pathways by GLP-1 in monkeys.

Background: To evaluate the protective effect of the DPP IV inhibitor in STZ-induced islet injury and to identify the molecular events that protect islet against apoptosis.

Methods: 4 diabetic monkeys were treated with streptozotocin (70 mg/kg) in the presence or absence of the DPP IV inhibitor (Sitagliptin), continuing administered for 4 weeks after STZ. The monkeys were evaluated by plasma DPP IV activity, serum active GLP-1 response, blood glucose, insulin and C-P levels, the insulin resistance index (HOMA-IR), and the expression of insulin, caspase-3, IGF receptor (IGFR), p-Akt and p-mTOR in pancreas islets tissues. To test that DPP IV inhibitors might against islets apoptosis via IGFR/Akt/mTOR signaling pathways, the isolated islets from the normal monkeys were pre-treated with or without 10mM STZ for 1h, followed by GLP-1 (10 μM) in the presence or absence of NVP-AEW541 or Wortmannin for 24h, to determined islets function and islet apoptosis.

Results: DPP IV inhibitors treatment showed depressing the degradation of GLP-1 and significantly increased serum GLP-1 levels in DM monkeys. Moreover, treatment of diabetic monkeys with the DPP IV inhibitor or treatment of isolated islets with GLP-1 can decrease islet apoptosis, and enhanced islet function and survival, and the expression of IGF receptor, p-Akt and p-mTOR in islets. When the IGFR/Akt/mTOR signaling pathways was blocked by NVP-AEW541 or Wortmannin, the protective effects of GLP1 on STZ-induced islets injury were inhibited in vitro.

Conclusions: Our data provides evidence that DPP IV inhibitors confer resistance to STZ-induced islet injury. The protective effects of DPP IV inhibitor on STZ-induced islets injury were dependent on activation of the IGFR/Akt/mTOR signaling pathways by GLP-1 in islets of monkeys.