Nitric oxide generation and poly(ADP ribose) polymerase activation precede beta-cell death in rats with a single high-dose injection of streptozotocin.

Streptozotocin (STZ) is widely used for the induction of diabetes in animals by causing destruction of pancreatic beta cells. This experiment was designed to elucidate the sequential process of beta-cell destruction in rats with a single high-dose injection of STZ. At 0, 2, 5, 8 and 24 h after injection, rats were perfused with Krebs-Ringer buffer with dichlorofluorescein diacetate (DCF-DA), a marker for free radicals, and the pancreata were pathologically analyzed. Injection of STZ rapidly elicited an increase in fluorescence of DCF-DA in beta cells at 2 h after the injection. The fluorescence was diminished by carboxy-PTIO, a specific scavenger of nitric oxide (NO), but not by L-NAME, an inhibitor of NO synthase. During this process, an inducible form of NO synthase was not detected. Thereafter, upregulated expression of poly(ADP ribose) polymerase (PARP) and massive beta-cell death were detected at 5-8 h after injection. Migration of macrophages into the islet was conspicuous at 24 h, clearing up the debris of destroyed beta cells. Nicotinamide, a PARP inhibitor, significantly inhibited beta-cell death without apparent suppression of NO generation at 2 h. The current study documented serial processes of STZ-induced beta-cell death, starting with NO generation and PARP activation followed by a clearance with macrophages, where the activation of PARP plays a central role in beta-cell death.