L- and T-type calcium channel blockers protect against the inhibitory effects of mipafox on neurite outgrowth and plasticity-related proteins in SH-SY5Y cells

ABSTRACT

Some organophosphorus compounds (OP), including the pesticide mipafox, produce late onset distal axonal degeneration, known as organophosphorus-induced delayed neuropathy (OPIDN). The underlying mechanism involves irreversible inhibition of neuropathy target esterase (NTE) activity, elevated intracellular calcium levels, increased activity of calcium-activated proteases and impaired neuritogenesis. Voltage-gated calcium channels (VGCC) appear to play a role in several neurologic disorders, including OPIDN. Therefore, this study aimed to examine and compare the neuroprotective effects of T-type (amiloride) and L-type (nimodipine) VGCC blockers induced by the inhibitory actions of mipafox on neurite outgrowth and axonal proteins of retinoic-acid-stimulated SH-SY5Y human neuroblastoma cells, a neuronal model widely employed to determine the neurotoxicity attributed to OP. Both nimodipine and amiloride significantly blocked augmentation of intracellular calcium levels and activity of calpains, as well as decreased neurite length, number of differentiated cells, and lowered concentrations of growth-associated protein 43 (GAP-43) and synapsin induced by mipafox. Only nimodipine inhibited reduction of synaptophysin levels produced by mipafox. These findings demonstrate a role for calcium and VGCC in the impairment of neuronal plasticity mediated by mipafox. Data also demonstrated the neuroprotective potential of T-type and L-type VGCC blockers to inhibit OP-mediated actions, which may be beneficial to counteract cases of pesticide poisoning.

Acknowledgments

The authors are deeply grateful to Dr. Cristoforo Scavone and Dr. Lidia Mitiko Yshii (Department of Pharmacology, Universidade de São Paulo—USP, SP, Brazil) for providing SH-SY5Y cells. This work was supported by: CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico, grants number 140105/2015 and 471626/2013-9) and FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo, grants number 2013/26906-6 and 2012/16319-3).

Conflict of Interest Statement

The authors declare that there are no conflicts of interest.