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-hydrdxy 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 mu M and 1 mM) and MnCl2 (100 mu M) 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 exogneous SOD (250 u ml(-1)) fully reversed the blockade, suggesting the oxidant stress was extracellular. CuDIPS (0.1-3 mu M), CuSO4 (0.3-3 mu M), MnCl2 (1-100 mu M) and MnTMPyP (100-600 mu M) also reversed blockade powerfully, tempol (30 mu M-1 mM) and tiron (0.3-10 mM) reversed blockade weakly and PTIYO (10-300 mu M) 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.