title: Free radicals as potential mediators of metal-allergy: Ni2+- and Co2+-mediated free radical generation.
abstract: The generation of free radicals by Ni(2+) and Co(2+) was studied at physiological pH in H(2)O(2)-containing solutions in the absence and presence of various radical-mediating ligands and in human peripheral blood mononuclear cell (PBMC) cultures. With ESR spectroscopy, free radical species were identified and quantitated by spin trapping with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). Co(2+) generated hydroxyl radicals from H(2)O(2) in PBS solutions containing glutathione (GSH) or histidine (His). Omission of GSH or His from the reaction mixture significantly reduced the ESR-signal, indicating the importance of metal-chelation in free radical generation. Carnosine did not significantly enhance the reactivity of Co(2+) toward H(2)O(2), whereas cysteine (Cys) and N-acetylcysteine (NAC) suppressed free radical generation. Under identical reaction conditions, Ni(2+) was markedly less reactive toward H(2)O(2) in comparison with Co(2+). GSH, His, Cys and NAC did not enhance free radical generation of Ni(2+) from H(2)O(2). However, in the presence of carnosine weak but significantly enhanced ESR intensities were found. Incubation of PBMC cultures from healthy subjects with Co(2+) (10-50 microM) yielded the DMPO-.OH adduct, suggesting Co(2+)-mediated hydroxyl radical generation. In contrast, incubation of PBMC cultures with Ni(2+) (10-50 microM) did not produce a detectable ESR-signal. Ascorbic acid efficiently inhibited Co(2+)-mediated free radical generation in PBS solutions and PBMC cultures. The observed difference in free radical generating capacity between Ni(2+) and Co(2+) is of interest with respect to the absence of cross-reactivity between the two metal-ions in experimental allergic contact dermatitis.
authors.affiliation: Dept. of Occupational Health, Occupational Dermatology, National Institute for Working Life, S-171 84 Solna, Sweden. Leon.van.den.Broeke@niwl.se
authors.forename: L T
authors.initials: LT
authors.lastname: Van den Broeke
authors.forename: A
authors.initials: A
authors.lastname: Gräslund
authors.forename: J L
authors.initials: JL
authors.lastname: Nilsson
authors.forename: J E
authors.initials: JE
authors.lastname: Wahlberg
authors.forename: A
authors.initials: A
authors.lastname: Scheynius
authors.forename: A T
authors.initials: AT
authors.lastname: Karlberg
mesh_terms: D000111:Acetylcysteine / Q000494:pharmacology; D000328:Adult; D001205:Ascorbic Acid / Q000378:metabolism; D002336:Carnosine / Q000494:pharmacology; D002478:Cells, Cultured; D003035:Cobalt / Q000633:toxicity*; D003545:Cysteine / Q000494:pharmacology; D017449:Dermatitis, Allergic Contact / Q000503:physiopathology*; D004578:Electron Spin Resonance Spectroscopy; D005260:Female; D016166:Free Radical Scavengers / Q000494:pharmacology; D005609:Free Radicals / Q000032:analysis; D005978:Glutathione / Q000494:pharmacology; D006639:Histidine / Q000494:pharmacology; D006801:Humans; D006861:Hydrogen Peroxide / Q000737:chemistry; D008875:Middle Aged; D009000:Monocytes / Q000187:drug effects / Q000378:metabolism; D009532:Nickel / Q000633:toxicity*
chemical_list: D016166:Free Radical Scavengers; D005609:Free Radicals; D003035:Cobalt; D006639:Histidine; D009532:Nickel; D002336:Carnosine; D006861:Hydrogen Peroxide; D005978:Glutathione; D003545:Cysteine; D001205:Ascorbic Acid; D000111:Acetylcysteine