Effect of Nickel on HaCat and U2OS Proliferation

OBJECTIVE: Studies reported that dental cast alloys may release metal ions. Nickel is a component of biomedical appliances and it can be released during corrosion causing adverse effects in oral environment. Purpose of this study was to evaluate the effect of nickel on cells proliferation. METHODS: Human osteosarcoma (U2OS) and human keratinocytes (HaCat) were growth respectively in McCoy's medium and DMEM. Both cell lines were exposed to different nickel chloride (NiCl2) concentrations (0-7.5mM). Cells viability was quantified by propidium iodide and flow cytometry. The effect of NiCl2 on cell proliferation was evaluated by flow cytometry using carboxyfluorescein diacetate succinimidyl ester (CFDA-SE). CFDA-SE is a non-fluorescent compound that diffuses passively into cells. Within the cells, esterases remove the acetyl moieties, leaving carboxyfluorescein succinimidyl ester (CFSE) that binds to proteins and is well retained within the cells. CFSE is partitioned equally among daughter cells with each division, so the reduction of fluorescence intensity in the time meant cells proliferation. Optical microscopy were also used to assess cells growth after 24-48-72h. Statistical analysis was performed with Tukey ANOVA (p < 0.05). RESULTS: NiCl2 induced a dose and time-dependent reduction of viability. After 24h, 1mM NiCl2 caused a reduction of viability in U2OS, while 2.5mM showed a toxic effect in HaCat compared to untreated cells (p<0.05). A 1.5-fold inhibition of cell proliferation has been show in U2OS treated with 1mM NiCl2 for 24h compared to untreated cells. After 48h and 72h a significant inhibition of proliferation has been show in U2OS treated with 0.25mM (1.7-fold) with a maximum inhibition caused by 0.75mM NiCl2 (2.5-fold). NiCl2 induced a similar time dependent proliferation inhibition in HaCat. The inhibition of cells growth caused by NiCl2 was confirmed by optical microscopy. CONCLUSION: Our results suggest that release of Nickel from dental biomaterials may inhibits normal cells proliferation.