Single-cell ICP-MS for evaluating the Se-protective effect against MeHg⁺-induced neurotoxicity in human neuroblastoma...

The protective effect of selenium (Se) against Hg-induced neurotoxicity has been widely investigated; however, the mechanisms behind this interaction have not been fully elucidated yet. In the current work, the role of Se against MeHg⁺-induced cytotoxicity in the human neuroblastoma cell line (SH-SY5Y) is reported for the first time by tracking Hg uptake and accumulation at the single-cell level by inductively coupled plasma-mass spectrometry in single-cell mode (SC-ICP-MS). The influence of different Se species (SeMet, SeMeSeCys, citrate-SeNPs, and chitosan-SeNPs) on MeHg⁺ cytotoxicity was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. SeMet and SeMeSeCys exhibited protective effects against MeHg⁺-induced cell death, particularly at high MeHg⁺ concentrations (LC₅₀). In addition, chitosan-SeNPs showed greater protection compared to citrate-SeNPs when co-exposed with MeHg⁺. Interestingly, SC-ICP-MS unveiled the heterogeneous distribution of Hg uptake by SH-SY5Y cells. Co-exposure of SeMet and SeMeSeCys with MeHg⁺ led to a reduction of the amount of Hg accumulated per individual cell, which decreased the maximum level of Hg per cell by half (from 60 fg Hg cell^-1 to 30 fg Hg cell^-1) when SeMet was present, along with a decrease in the percentage of cells that accumulated the highest quantity of MeHg⁺. All these data corroborate the protective role of Se against Hg toxicity at the cellular level.