Loss of Endothelium-derived Nitric Oxide in Rabbit Aorta by Oxidant Stress: Restoration by Superoxide Dismutase Mimetics

1. Structurally distinct superoxide dismutase (SOD) mimetics were examined for their ability to protect nitric oxide (NO) from destruction by oxidant stress in rabbit aorta. 2. These were the spin traps, PTIYO (4-phenyl-2,2,5,5-tetramethyl imidazolin-1-yloxy-5-oxide), tempol (4-hydroxy 2,2,6,6,-tetramethylpiperidine-1-oxyl) and tiron (4,5-dihydroxy-1,3-benzene-disulphonic acid), the metal salts, CuSO4 and MnCl2, and the metal-based agents CuDIPS (Cu (II)-[diisopropylsalicylate]2) and MnTMPyP (Mn (III) tetrakis [1-methyl-4-pyridyl]porphyrin). 3. Oxidant stress was generated in isolated aortic rings by inactivating endogenous Cu/Zn SOD with diethyldithiocarbamate (DETCA; 60 min) either alone at 3 mM or at 0.3 mM in combination with superoxide generation using xanthine oxidase (XO; 4.8 mu ml(-1)) and hypoxanthine (HX; 0.1 mM). 4. Acetylcholine (ACh)-induced relaxation was inhibited by DETCA (3 mM, 60 min) and was not restored by exogenous SOD (250 u ml(-1)), suggesting the oxidant stress was intracellular. MnTMPyP (600 microM and 1 mM) and MnCl2 (100 microM) were the only agents to reverse the blockade of ACh-induced relaxation. 5. Addition of XO/HX to DETCA (0.3 mM)-treated tissues powerfully impaired ACh-induced relaxation and exogenous SOD (250 u ml(-1)) fully reversed the blockade, suggesting the oxidant stress was extracellular. CuDIPS (0.1-3 microM), CuSO4 (0.3-3 microM), MnCl2 (1-100 microM) and MnTMPyP (100-600 microM) also reversed blockade powerfully, tempol (30 microM-1 mM) and tiron (0.3-10 mM) reversed blockade weakly and PTIYO (10-300 microM) enhanced the blockade. 6. Thus, MnTMPyP was the only SOD mimetic to restore NO-dependent relaxation in conditions of both extracellular and intracellular oxidant stress. This agent may, therefore, provide a lead in the development of SOD mimetics for the treatment of pathologies associated with oxidant stress.