This study explores scICP-MS technique as an analytical tool to study the protective effect of different selenium species (Se(IV), SeMeSeCys, SeMet and SeNPs) against mercury-induced toxicity (Hg(II) and MeHg+), using the human neuroblastoma cell line SH-SY5Y as a cell model.

The first step consisted in estimating the cytotoxicity of different concentrations of Hg and Se over SH-SY5Y through MTT assay with the aim of elucidating the protective effect of Se against Hg toxicity. Thus, cells were incubated with Hg (II) and MeHg+ (1.5-70 µM) alone or in presence of Se(IV), SeMeSeCys, SeMet and SeNPs (3 – 70 µM) during 24 or 48 h at 37oC with a humidified atmosphere of 5% CO2. The results showed that cell viability dropped below 60% when cultures were exposed to 25 μM of Hg(II) and 3 μM of MeHg+. However, only co-incubation of MeHg+ with SeMeSeCys and SeMet resulted in a noticeable increase in cell viability.

Furthermore, scICP-MS was employed to determine the amount of mercury, as Hg (II) or MeHg+, accumulated before and after co-exposition to different selenium species at single cell levels. Nevertheless, prior to scICP-MS analysis, sample preparation procedure based on cell fixation using paraformaldehyde (PFA) and optimization of sample introduction system was carried out by varying carrier and make up flows. In particular, results revealed a decrease in the maximum amount of Hg accumulated per individual cell up to the half (from 60 fg Hg cell-1 to 30 fg Hg cell -1) when SeMet (50 μM) was added together with MeHg+ (1.5 μM), as well as when Se(IV) (25 μM) was incubated with Hg(II) (25 μM) (from 500.2 fg Hg cell-1 to 232.4 fg Hg cell -1). In addition, a decrease in the amount of percentage of cell which accumulate the highest amount of Hg were also observed in both cases. In parallel, total selenium and mercury content was determined after acid digestion by ICP-MS, with no significant differences in the levels of Hg accumulated in the presence or absence of different Se species. It is important to highlight the low levels of Hg accumulated by SH-SY5Y cell populations which can be explained due to the interactions of Se with Hg in the culture medium, which leads to a more difficult internalization of Hg by cells. Thus, pretreatment of cell cultures with Se prior to Hg addition were also considered in this study and results were compared with those obtained after co-exposure of the neuroprotective and neurotoxicant agents.

The results included in this work highlight the importance of incorporating scICP-MS in neurotoxicity research.