Molecular and immunohistochemical alterations in fluoride-induced neurological impediment in adult rats

Abstract

This study highlights the potential neurotoxic and impaired behavioral effects associated with high fluoride concentrations in drinking water.

Purpose: Fluoride is known to cause neurotoxicity, evinced by lower I.Q. levels in children from high-fluoride regions as compared to those in low-fluoride regions. Thus, the present study was designed to investigate the molecular mechanism behind the neurological and behavioural changes induced by sodium fluoride in Wistar rats.

Material and methods: A total of 24 female Wistar rats, aged six weeks and weighing approximately 150-220 g, were randomly divided into three groups: Group I (control) received reverse osmosis (R.O.) water, Group II received Sodium Fluoride (NaF) at 10 ppm, and Group III received NaF at 50 ppm in their drinking water for 60 days. The animals underwent behavioural tests including the Forced Swim Test (F.S.T.), Open Field Test (OFT), and Novel Object Recognition Test (N.O.R.T.), to assess any alterations in behaviour. After 60 days, the animals were euthanized, and their blood and brain samples were analysed to evaluate biochemical changes by Western Blot/I.H.C. analysis of B.A.X., Bcl2, LC3B, TLR4, PARP1, p53, Caspase, α-Synuclein, PARKIN, NeuN, KI67, DNM-1, and M.F.N. for assessing molecular pathways for toxicity.

Results: Impaired locomotion, memory impairment, and behaviour resembling depression in the animals were evinced by reduced mobility index in the F.S.T., discrimination index in the N.O.R.T., and reduced locomotor activity in the open field test results. Additionally, alterations in antioxidant levels and oxidative stress parameters were observed in the brain. The expression levels of various apoptotic and inflammatory biomarkers (B.A.X., Bcl2, TLR4, PARP1, p53, and Caspase) showed apoptosis in neurons. The confocal studies showed increased expression of inflammatory (α-Synuclein, PARKIN), apoptotic (LC3B, B.A.X., p53, KI67), and mitochondrial dysfunction (NeuN, DNM-1, M.F.N.) markers in fluoride-treated animals. Toxicity was more prominent in 50 ppm of fluoride-treated animals.

Conclusion: Fluoride showed potent neuronal toxicity as evidenced by alterations of various molecular markers.

Keywords: Apoptotic markers; Behavioural changes; Confocal microscopy; Fluoride; Immunohistochemistry; Memory deficits.