Fluoride – influenced presynaptic and MAPK – mediated TrkB signaling alterations, induced neurotoxicity

Abstract

Fluoride (F), an inorganic substance, is everywhere in the environment. Fluoride exposure is caused mainly by geogenic sources, such as drinking wells and deep soil water. Excess fluoride-containing water usage for many years may cause neurotoxic damage. The mechanism underlying the neurotoxicology of endemic fluorosis remains obscure. Fluoride crosses the blood-brain barrier and accumulates within neurons. In our study, chronic exposure to fluoride-induced epileptogenesis in neuroblastoma (SK-N-SH) cells was followed with tools like Brain-derived neurotrophic factor (BDNF) and Synapsin 1 (SYN 1) protein expression. SK-N-SH cells were incubated with fluoride water (1 mg/L and 6 mg/L) for 24 h in-vitro. Prolonged ingestion of fluoride causes chronic fluorosis. Fluoride exposure reduced cell viability gradually from 48 to 96 h. The standard structure of axon spines and dendritic outgrowth in high fluoride water vanished. TrkB activated MAPK/ERK downstream signaling pathway is triggered by increased BDNF protein expression and decreased SYN 1 protein levels observed in fluoride water incubation. Further 96 hours incubation with fluoride-cleared water increased viability of SK-N-SH cells and a normal expression of BDNF and SYN 1 protein levels, suggests that fluoride-blocked BDNF-TrkB pathway might have been replaced by high-levels expression of BDNF protein where incubation medium contains concomitant lowered levels of fluoride. Hypothesis is that scaffold proteins regained normal expression might have influenced conducted normal excitation and transmission could reduce neurotoxic effect or even might control seizures.