Biologically active metalindependent superoxide dismutase mimics. Biochemistry.

ABSTRACT: 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. I n an oxygen-containing environment, cellular metabolism results in the production of several potentially harmful oxygen-derived species. The first in this cascade of active oxygen metabolites is the one-electron reduction product, superoxide (02*-). The function of the superoxide-detoxifying metalloenzyme superoxide dismutase (SOD)' in protecting against oxygen-mediated biological damage is well documented EXPERIMENTAL PROCEDURES Chemicals. Desferrioxamine (DF) was a gift from Ciba Geigy; hypoxanthine (HX) was purchased from CalbiochemBoehringer 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)chromat