FREE-RADICALS AS POTENTIAL MEDIATORS OF METAL-ALLERGY - NI2-MEDIATED AND CO2+-MEDIATED FREE-RADICAL GENERATION()

The generation of free radicals by Ni2+ and Co2+ was studied at physio logical pH in H2O2-containing solutions in the absence and presence of various radical-mediating ligands and in human peripheral blood monon uclear cell (PBMC) cultures. With ESR spectroscopy, free radical speci es were identified and quantitated by spin trapping with 5,5-dimethyl- 1-pyrroline-N-oxide (DMPO). Co2+ generated hydroxyl radicals from H2O2 in PBS solutions containing glutathione (GSH) or histidine (His). Omi ssion of GSH or His from the reaction mixture significantly reduced th e ESR-signal, indicating the importance of metal-chelation in free rad ical generation. Carnosine did not significantly enhance the reactivit y of Co2+ toward H2O2, whereas cysteine (Cys) and N-acetylcysteine (NA C) suppressed free radical generation. Under identical reaction condit ions, Ni2+ was markedly less reactive toward H2O2 in comparison with C o2+. GSH, His, Cys and NAC did not enhance free radical generation of Ni2+ from H2O2. However, in the presence of carnosine weak but signifi cantly enhanced ESR intensities were found. Incubation of PBMC culture s from healthy subjects with Co2+ (10-50 mu M) yielded the DMPO-(OH)-O -. adduct, suggesting Co2+-mediated hydroxyl radical generation. In co ntrast, incubation of PBMC cultures with Ni2+ (10-50 mu M) did not pro duce a detectable ESR-signal. Ascorbic acid efficiently inhibited Co2-mediated free radical generation in PBS solutions and PBMC cultures. The observed difference in free radical generating capacity between Ni 2+ and Co2+ is of interest with respect to the absence of cross-reacti vity between the two metal-ions in experimental allergic contact derma titis. (C) 1998 Elsevier Science B.V. All rights reserved.