Free radicals as potential mediators of metal-allergy: Ni 2+- and Co 2+-mediated free radical generation

• Published in: European journal of pharmaceutical sciences Vol. 6; no. 4; pp. 279 - 286
• Main Authors: Van den Broeke, Leon T, Gräslund, Astrid, Nilsson, J.Lars G, E. Wahlberg, Jan, Scheynius, Annika, Karlberg, Ann-Therese
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 1998
• Subjects: Co 2; Contact allergy; ESR spectroscopy; Free radicals; Human; Ni 2; Human; Contact allergy; Free radicals; His: histidine; DMPO: 5,5-dimethyl-1-pyrroline-N-oxide; NAC: N-acetylcysteine; Ni 2; ESR spectroscopy; GSH: glutathione; ACD: allergic contact dermatitis; Cys: cysteine; PBMC: peripheral blood mononuclear cell; PBS: phosphate buffered saline (pH=7.4, 10 mM); Co 2
• ISSN: 0928-0987; 1879-0720
• DOI: 10.1016/S0928-0987(97)10024-0

The generation of free radicals by Ni 2+ and Co 2+ was studied at physiological pH in H 2O 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 2O 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 2O 2, whereas cysteine (Cys) and N-acetylcysteine (NAC) suppressed free radical generation. Under identical reaction conditions, Ni 2+ was markedly less reactive toward H 2O 2 in comparison with Co 2+. GSH, His, Cys and NAC did not enhance free radical generation of Ni 2+ from H 2O 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 μM) yielded the DMPO- ⋅OH adduct, suggesting Co 2+-mediated hydroxyl radical generation. In contrast, incubation of PBMC cultures with Ni 2+ (10–50 μM) 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.