Biologically active metal-independent superoxide dismutase mimics
Superoxide dismutase (SOD) is an enzyme that detoxifies superoxide (02'-), a potentially toxic oxygen-derived species. Attempts to increase intracellular concentrations of SOD by direct application are complicated because SOD, being a relatively large molecule, does not readily cross cell membranes. We have identified a set of stable nitroxides that possess SOD-like activity, have the advantage of being low molecular weight, membrane permeable, and metal independent, and at pH 7.0 have reaction
... rate constants with 02'ranging from 1.1 X IO3 to 1.3 X IO6 M-' s-l. These S O D mimics protect mammalian cells from damage induced by hypoxanthine/xanthine oxidase and H202, although they exhibit no catalase-like activity. In addition, the nitroxide SOD mimics rapidly oxidize DNA-Fe" and thus may interrupt the Fenton reaction and prevent formation of deleterious OH radicals and/or higher oxidation states of metal ions. Whether by SOD-like activity and/or interception of an electron from redox-active metal ions they protect cells from oxidative stress and may have use in basic and applied biological studies. EXPERIMENTAL PROCEDURES Chemicals. Desferrioxamine (DF) was a gift from Ciba Geigy; hypoxanthine (HX) was purchased from Calbiochem-Boehringer Co.; 2,2,6,6-tetramethylpiperidine-1 -oxy1 (TEM-PO), 4-hydroxy-2,2,6,6-tetramethylpiperidine-I-oxy1 (TEM-POL), 4-hydroxypyrazolo[3,4,-d]pyrimidine (allopurinol), p-toluenesulfonic acid, 2-amino-2-methyl-1 -propanol, 2-butanone, and cyclohexanone were purchased from Aldrich Chemical Co.; tris(oxalato)chromate ( III) [K3[Cr(C2O4)J-202'-+ 2H+ -0, + H 2 0 2 I Abbreviations: EPR, electron paramagnetic resonance; CHD, spiro [cyclohexane-1,2'-doxyl] [spiro[cyclohexane-1,2'-(4',4'-dimethyloxazolidine-3'-oxyl)] 1; DTPA, diethylenetriaminepentaacetate; OXANO, 2-ethyl-2,4,4-trimethyloxazolidine-3-oxyl; TEMPOL, 4-hydroxy-2,2,6,6tetramethylpiperidine-1 -0xyl; TEMPO, 2,2,6,6-tetramethylpiperidine-1oxyl; SOD, superoxide dismutase; DF, desferrioxamine; XO, xanthine oxidase; HX, hypoxanthine.