The nitroxide antioxidant Tempol affects metal-induced cyto- and genotoxicity in human lymphocytes in vitro

Stable, membrane-permeating nitroxide radicals have been reported to possess antioxidant activity in various experimental systems while, in parallel, they have been considered to be evidently harmful oxidants. The aim of this study was to evaluate the role of the piperidine nitroxide 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (Tempol) in the modulation of cyto- and genotoxicity in human lymphocytes in vitro by cadmium and chromium, which depend, at least in part, on formation of reactive oxygen species. The cytokinesis-block micronucleus (CBMN) assay to measure micronucleus (MN) formation, the nuclear division index (NDI) and the percentage of apoptotic and necrotic cells were assessed after exposure human lymphocytes to Cd(II), Cr(III) and Cr(VI) or co-incubation with these metals and Tempol. We found a significant ability of 5–50 μM Tempol to diminish toxic effects of the agents tested. In every system studied, Tempol decreased the micronucleus frequency and the percentage of apoptotic and necrotic cells, while it increased the nuclear division index (p < 0.05). We observed adverse effects when 0.1–1 mM Tempol alone was used: inhibition of cell growth, induction of apoptotic and necrotic cell death and chromosomal damage (p < 0.05). Collectively, we demonstrated that Tempol can be considered as a potent anti-apoptotic and antigenotoxic agent, but also as a cytotoxic and clastogenic chemical, depending on the concentration applied.