Molecular mechanisms underlaying fluoride-induced neurotoxicity: interplay of antioxidants and endoplasmic reticulum stress-mediated apoptotic pathways in rats.

Fluoride is a naturally occurring compound widely present in soil, water, rocks and is essential to maintain the physiological function and structure of bones and teeth. However, chronic exposure to elevated fluoride levels has been linked to adverse neurological effects. Despite its widespread environmental presence, the molecular mechanisms underlying fluoride-induced neurotoxicity remain incompletely understood. This study aimed to elucidate the effects of fluoride on oxidative stress, endoplasmic reticulum (ER) stress, apoptosis, and associated histopathological alterations in brain tissue. Forty Sprague-Dawley rats were randomly assigned to four groups (n = 10 per group; 5 male + 5 female) and administered sodium fluoride (NaF) in drinking water at concentrations of < 0.5 ppm (control), 50 ppm, 150 ppm, and 300 ppm for 90 consecutive days. The expression of antioxidant genes (SOD1 and GCLC), ER stress, and apoptosis-related genes (XBP1, GRP78, BCL-2, and BAX) was quantified using real-time quantitative PCR (RT-qPCR), and histopathological analysis of the brain tissues was performed. Fluoride exposure caused a dose-dependent downregulation of antioxidant and ER stress-related genes and concurrent upregulation of the pro-apoptotic genes. Histopathological analysis revealed structural damage in hippocampus and cerebral cortex, including neuronal shrinkage, vacuolization, and apoptotic features. These findings indicate that prolonged NaF exposure impairs antioxidant defenses, induces ER stress, and activates apoptotic pathways, thereby contributing to neuronal damage. This study provides mechanistic insights into fluoride-induced neurotoxicity and highlights the need for further research on potential therapeutic strategies targeting oxidative and ER stress pathways.