Comparative study on toxicity of methylmercury chloride and methylmercury hydroxide to the human neuroblastoma cell line SH-SY5Y

Toxicities of methylmercury chloride (CH₃HgCl) and methylmercury hydroxide (CH₃HgOH) to cultured neuroblastoma cell line SH-SY5Y in vitro are evaluated. This is the comparative study between two methylmercury compounds to find out the extent of toxicity of these compounds are toxic to SH-SY5Y cell line. Both cytotoxicity and genotoxicity experiments were carried out to find out the more toxic compound. For cytotoxicity study, four staining assay methods independently with trypan blue (TB), acridine orange/ethidium bromide (AO/EB), 3-(4,5-dimethylthiazol-2-yl) 2,5-diphenyl tetrazolium bromide (MTT), and neutral red (NR) were used and the comet assay method was done for genotoxicity study. The obtained toxicity data were used for probit analysis. In cytotoxicity, CH₃HgCl had minimum inhibitory concentration (MIC) value in each assay method as 3 mg/L invariably; LC₂₅ values were in the range 7.41 to 10.23 mg/L, and LC₅₀ values were 14.79 to 15.48 mg/L; while LC₇₅ values were 20.89 to 26.91 mg/L. Moreover, LC₁₀₀ value was 30 mg/L, known from comet assay experiments for CH₃HgCl. Similarly for CH₃HgOH, the MIC value in each assay method was invariably 3 mg/L, the LC₂₅ values were in the range 12.58 to 16.59 mg/L, and LC₅₀ values were 19.49 to 23.44 mg/L; LC₇₅ values were 27.54 to 30.90 mg/L and LC₁₀₀ value was 42 mg/L in each assay done for cytotoxicity and genotoxicity studies. Computed DNA fragmentation indices in comet assays were 98.6 ± 0.57 30 mg/L with CH₃HgCl and 76 ± 5.29 30 mg/L with CH₃HgOH. This study clearly indicated that methylmercury chloride is more toxic than methylmercury hydroxide to SH-SY5Y cell line. Toxicity of Hg had been quantified with in vitro cultured human neuroblastoma cell line; since it has neurotoxic effects, its neural evaluation has implications in environmental health issues.