Inducible nitric oxide synthase and cyclooxgenase-2 mediate protection of hydrogen peroxide preconditioning against apoptosis induced by oxidative stress in PC12 cells.

The induction of inducible nitric oxide synthase (iNOS) in response to different stress is associated with simultaneous induction of cyclooxygenase-2 (COX-2) in various cell types. Both iNOS and COX-2 have been reported to mediate the late phase of cardioprotection induced by different preconditioning. However, whether both iNOS and COX-2 are mediators in the neuroprotection induced by preconditioning with hydrogen peroxide (H(2)O(2)) at low concentration is unknown. In this study, using the neurosecretory cell line-PC12 cells to set up the model of neuroprotection of preconditioning with H(2)O(2) against apoptosis, we first investigate what changes in expression of iNOS and COX-2 appear during H(2)O(2) preconditioning, then determine if both iNOS inhibitor and COX-2 inhibitor interfere with the neuroprotection elicited by preconditioning with H(2)O(2). We found that preconditioning with H(2)O(2) at 10 microM significantly protected PC12 cells against apoptosis induced by lethal H(2)O(2) (50 microM) and increased the expression of iNOS and COX-2 and that selective iNOS inhibitor, aminoguanidine (AG) and COX-2 inhibitor, NS-398 obviously blocked the protective effects induced by preconditioning with 10 microM H(2)O(2). The results of this study suggest that both iNOS and COX-2 are mediators of the neuroprotection induced by preconditioning with oxidative stress (H(2)O(2) at low concentration) in PC12 cells.

Hydrogen peroxide preconditioning protects PC12 cells against apoptosis induced by oxidative stress.

Oxidative stress can induce significant cell death by apoptosis. We explore whether prior exposure to H2O2 (H2O2 preconditioning) protects PC12 cells against the apoptotic consequences of subsequent oxidative damages and what role the ATP-sensitive potassium (K(ATP)) channels play in the preconditioning protection. PC12 cells were preconditioned with 90 min exposure to H2O2 at 10 micromol/L, followed by 24-h recovery and subsequent exposures to different concentrations (20, 30, 50 and 100 micromol/L) of H2O2 for 24 h respectively. We used PI staining flow cytometry (FCM) to observe the apoptosis of PC12 cells. It was shown that 24-h exposures to H2O2 at 20, 30, 50 and 100 micromol/L respectively induced substantial cell apoptosis, which was greatly prevented in the preconditioning cells, indicating that H2O2 preconditioning protected PC12 cells against apoptosis induced by H2O2. Administration of pinacidil (10 micromol/L), an K(ATP) channel activator, significantly attenuated the apoptosis of PC12 cells induced by H2O2 at 30 and 50 micromol/L for 24 h respectively. Glybenclamide (10 micromol/L), a K(ATP) channel inhibitor, significantly suppressed or abolished the protective effects caused by the pinacidil but not by H2O2 preconditioning. However, when both H2O2 preconditioning and pinacidil were co-applied, their protection against the apoptosis of PC12 cells was much stronger than that of the individual one of them. These results suggest that H2O2 preconditioning protects PC12 cells against apoptosis and that the activation of K(ATP) channels is not involved in, but synergetically enhances adaptive protection of H2O2 preconditioning.