Metal-induced oxidative burst in isolated human neutrophils

Experimental evidence have been suggesting that the toxicity of metals may involve inflammatory processes, with subsequent sustained overproduction of pro-oxidant reactive species, leading to indirect toxic effects, namely genotoxicity. Neutrophils, as important mediators of the innate defence systems, may have a hitherto not known role on these metal-induced adverse effects. Thus, the aim of the present study was to evaluate the putative activation of human neutrophils' oxidative burst by two groups of metals, the first group being able to undergo redox-cycling reactions (iron, copper, chromium and cobalt), whilst the primary route for the toxicity of the second group is not dependent on redox reactions (mercury and cadmium). The generation of reactive oxygen species (ROS) by metal-stimulated neutrophils was measured using the chemiluminometric probe luminol. Appropriate scavengers and metabolizing enzymes were subsequently used to identify the reactive species produced. The modulatory effects of metals on phorbol myristate acetate (PMA)-activated neutrophils were also studied. To evaluate the contribution of protein kinase C (PKC) on metal stimulatory effect, we used the specific inhibitor of PKC Gö6983. The obtained results showed that, in the present experimental conditions, only Cd (II) has the ability to stimulate the production of superoxide radical (O₂⁻), hydrogen peroxide (H₂O₂), and hypochlorous acid (HOCl) in isolated human neutrophils. The same metal showed a synergistic effect with PMA. It was also demonstrated that Cd (II) induces neutrophils' oxidative burst mainly via activation of PKC, precluding a significant contribution of other cellular pathways for ROS generation mediated by this metal. These observations indicate that the sustained activation of human neutrophils may contribute for the long term adverse effects on human health mediated by Cd (II).