Pro-Oxidative Interactions of Cobalt with Human Neutrophils

Abstract

The primary objectives of this study were to investigate the effects of cobalt(II) chloride (Co, 1.5–25 μ M) on the reactivity of hydrogen peroxide (H₂O₂, 100 μ M) or oxidants generated by activated human neutrophils. The prooxidative interactions of Co with H₂O₂ or cells were measured by luminol-enhanced chemiluminescence (LECL), and according to the extent of oxidative inactivation of added alpha-1-proteinase inhibitor (API). Cobalt dramatically potentiated the oxidation of luminol and API by both H₂O₂ and neutrophils activated with phorbol 12-myristate 13-acetate (5 ng/ml), without affecting the assembly of NADPH oxidase or the magnitude of oxygen consumption by the cells. Using 5,5-dimethyl-pyrolline 1-oxide-based electron spin resonance spectroscopy we were unable to detect hydroxyl radical formation by Co in the presence of either H₂O₂ or activated neutrophils, while the corresponding LECL responses were unaffected by the hydroxyl radical scavengers benzoate and mannitol (50 mM). These observations indicate that Co potentiates the reactivity of neutrophil-derived oxidants, primarily H₂O₂, which if operative in vivo during exposure to the heavy metal may pose the risk of oxidant- and protease-mediated tissue injury.