Neurotoxicity of mancozeb-based commercial fungicide in human neuroblastoma SH-SY5Y cells

Mancozeb, a polymeric dithiocarbamate complex fungicide with zinc and manganese salts, has the potential to be neurotoxic to humans. Unfortunately, the parent molecule maneb has attracted far too much attention, limiting the available evidence on mancozeb neurotoxicity to preclinical research and non-human cells. We sought to evaluate mancozeb cytotoxicity in neuroblastoma SH-SY5Y cells at lower concentrations than those used for maneb in in vitro investigations in order to quantify its risk for humans. Commercial mancozeb showed concentration- and time-dependent neurotoxicity in the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction test (EC50= 5.9 µM and 1.7 µM at 24 h and 72 h respectively). Using the trypan blue exclusion dye, cell death toll reached around 100% after 24- and 72-hour exposure to mancozeb 1 µM and 0.5 µM respectively. Reactive oxygen species generated by mancozeb, which peaked at 4 µM, could be the cause of cell death. The number and length of neurites were concentration-dependently reduced by mancozeb at sub-µM concentrations, and this was accompanied by changes in cell biomechanical characteristics (stiffness) as determined by atomic force microscopy. The uncertainty factor obtained from our cytotoxic studies, when performing risk assessment of mancozeb, varied from 200 to 2000, which may result in detectable neurotoxicity in humans in accordance with international regulatory agencies recommendations.