Abstract 3894: Inhibition of iNOS Uncoupling by Tetrahydrobiopterin Confers Cardioprotection through Protein S-Nitrosylation in Streptozotocin-Induced Diabetic Rat
Although expression of inducible nitric oxide synthase (iNOS) and oxidative stress are increased in diabetic (DM) hearts, the role of iNOS uncoupling in ischemia/reperfusion (IR) injury remains unknown. Because iNOS-derived NO is known to play a crucial role in cardioprotection against IR injury in non-DM hearts, we hypothesized that iNOS uncoupling may compromise tolerance to IR injury in the DM heart by decreasing the bioavailability of NO. The expression and activity of iNOS but not n/eNOS were increased in the streptozotocin-induced DM rat heart. Under Langendorff perfusion, superoxide generation as evaluated by dihydroethidium accumulation in the nucleus was significantly increased in cardiomyocytes of the DM heart, but it was inhibited by treatment with the NOS co-factor tetrahydrobiopterin (BH4; 10 μM) or an iNOS selective inhibitor 1400W (10 μM). BH4 increased NOx, a marker of NO bioavailability, and cGMP in the DM heart. The increase in cGMP by BH4 was abrogated by co-treatment with 1400W or a NO-sensitive guanylyl cyclase inhibitor ODQ (10 μM). BH4 significantly decreased nitrotyrosin formation but increased protein S-nitrosylation in the DM heart. The increase in protein S-nitrosylation by BH4 was abolished by co-treatment with a thiol reducing agent dithiothreitol (DTT; 5 mM). The isolated rat heart was subjected to 30 min global ischemia followed by 120 min reperfusion. Post-ischemic recovery of left ventricular (LV) function and infarct size was comparable between the non-DM and the DM hearts. Pre-ischemic treatment with BH4 significantly improved post-ischemic LV function and reduced infarct size only in the DM heart. Co-treatment with BH4 and 1400W, ODQ, or DTT had no significant effect on post-ischemic LV function and infarct size in the non-DM heart. However, co-treatment with BH4 and 1400W or DTT but not ODQ abolished BH4-induced improvement of post-ischemic LV function and reduction of infarct size in the DM heart. These results suggest that inhibition of iNOS uncoupling by BH4 confers cardioprotection against IR injury in the streptozotocin-induced DM rat heart by increasing the bioavailability of NO and this cardioprotective effect is mediated by protein S-nitrosylation but not cGMP.