Protective Effect of Curcumin on Hippocampal and Behavior Changes in Rats Exposed to Fluoride During Pre- and Post-natal Period

Esculin, a Coumarin Glucoside Prevents Fluoride-Induced Oxidative Stress and Cardiotoxicity in Zebrafish Larvae

Fluoride (F-) is a major groundwater contaminant spread across the world. In excess concentrations, F- can be detrimental to living beings. F- exposure is linked to cellular redox dyshomeostasis, leading to oxidative stress-mediated pathologies including heart dysfunction. Due to its potent antioxidant properties, various phytochemicals are found to alleviate the symptoms of F- toxicity. Hence, we explore the protective effect of esculin (Esc), a coumarin glucoside on F--induced oxidative stress and cardiotoxicity in zebrafish larvae. The experimental groups consisted of NaF (50 ppm) and Esc (100 μM) groups treated alone and in combination with a control group for 6 h. The groups were maintained till 78 hpf after which the level of oxidants (ROS, LPO, and PCC) and antioxidants (GST, GSH, GPx, SOD, and CAT) were assessed. The results revealed that Esc pretreatment restored the depleted antioxidant markers and reduced the levels of oxidant in the Esc+NaF group, exhibiting its antioxidant potential. In addition, analyses of the heartbeat rate and hemoglobin integrity using o-Dianisidine staining were conducted in the control and experimental groups. Esc treatment prevents F- induced cardiac changes including tachycardia and altered blood flow. Further, the mRNA expression level of antioxidant genes (nrf2, gstp1, hmox1a, prdx1, and nqo1) and cardiac developmental genes (bmp2b, nkx2.5, myh6, and myl7) confirmed that Esc acts as a potent free radical scavenger and antioxidant defense enhancer, protecting zebrafish larvae from NaF-induced oxidative stress and heart dysfunction.

Exploring the protective role of metformin and dehydrozingerone in sodium fluoride-induced neurotoxicity: evidence from prenatal rat models

This study is aimed at evaluating the neurotoxic effects of chronic exposure of sodium fluoride (NaF) in developmental stages in rat using prenatal models. NaF (100 ppm, orally) dosing via drinking water was given to pregnant rats in disease group. In the treatment groups, Metformin & Dehydrozingerone (DHZ) (200 mg/kg) were administered orally along with NaF, and the dosing was continued throughout the gestation and lactation periods to the pups until the end of experiment. Behavioural studies like Novel Object Recognition Test (NORT), Open Field & Actophotometer test and biochemical estimations like Acetylcholinesterase (AchE), Glutathione (GSH), Malondialdehyde (MDA) were conducted on animals followed by histopathological image analysis. It was observed that NaF exposure significantly decreased learning, memory and locomotor ability (at p < 0.05, p ≤ 0.01) in rat pups and was also able to induce anxiety like behavior. Levels of AchE (p ≤ 0.001) and MDA (p ≤ 0.01, p ≤ 0.001) was found to be significantly elevated and GSH levels were significantly decreased (p ≤ 0.01, p ≤ 0.001) in hippocampus and frontal cortex in the disease group. Histopathological image analysis showed presence of degenerated neurons in hippocampus of disease group. From this study, it was observed that treatment with Metformin and DHZ, was able to significantly ameliorate the cognitive impairments, improve the condition of oxidative stress and decrease neuronal degeneration in NaF fed rat pups. These results established the protective role of Metformin and DHZ in NaF induced neurodevelopmental toxicity with particular emphasis on their antioxidant properties.

Metabolic shift as a compensatory response to impaired hippocampal neurogenesis after developmental exposure to sodium fluoride in rats

Fluoride affects neurodevelopment in children. In this study, we examined the effects of developmental exposure to sodium fluoride (NaF) on hippocampal neurogenesis in rats. Dams were given drinking water containing NaF at 0 (untreated controls), 30 or 100 ppm from gestational day 6 to day 21 post-delivery upon weaning, and offspring were reared until postnatal day (PND) 77. On PND 21, NaF at 100 ppm altered the numbers in subpopulations of granule cell lineages, including a decrease in type-3 neural progenitor cells (NPCs), as well as a compensatory increase in type-1 neural stem cells (NSCs) and type-2a NPCs. NaF exposure tended to increase GluR2+ mossy cells in the hilus of the dentate gyrus (DG) in a dose-dependent manner, suggesting that NaF exposure induces a compensatory neurogenic response. NaF also caused a dose-dependent increase in ARC+ granule cells, and it upregulated Ptgs2 in the DG at 100 ppm, suggesting that NaF exposure increases synaptic plasticity in granule cells. NaF at 100 ppm upregulated granule cell lineage marker genes (Nes, Eomes and Rbfox3) and an anti-apoptotic gene (Bcl2), suggesting ameliorating responses against the impaired neurogenesis during NaF exposure. Moreover, NaF at 100 ppm downregulated oxidative phosphorylation-related genes (Atp5f1b and Sdhd) and upregulated a glycolysis-related gene (Hk3), suggesting a metabolic shift in cells undergoing neurogenesis. By PND 77, the changes in granule cell lineages were no longer detected, and GABAergic interneuron marker genes (Calb2 and Reln) were upregulated, suggesting a persistent protective response in granule cell lineages. Together, these findings suggest that developmental NaF exposure causes transient disruption of hippocampal neurogenesis, which in turn induces a metabolic shift as a compensatory response.

Fluoride Induced Neurobehavioral Impairments in Experimental Animals: a Brief Review

Fluoride is one of the major toxicants in the environment and is often found in drinking water at higher concentrations. Living organisms including humans exposed to high fluoride levels are found to develop mild-to-severe detrimental pathological conditions called fluorosis. Fluoride can cross the hematoencephalic barrier and settle in various brain regions. This accumulation affects the structure and function of both the central and peripheral nervous systems. The neural ultrastructure damages are reflected in metabolic and cognitive activities. Hindrances in synaptic plasticity and signal transmission, early neuronal apoptosis, functional alterations of the intercellular signaling pathway components, improper protein synthesis, dyshomeostasis of the transcriptional and neurotrophic factors, oxidative stress, and inflammatory responses are accounted for the fluoride neurotoxicity. Fluoride causes a decline in brain functions that directly influence the overall quality of life in both humans and animals. Animal studies are widely used to explore the etiology of fluoride-induced neurotoxicity. A good number of these studies support a positive correlation between fluoride intake and toxicity phenotypes closely associated with neurotoxicity. However, the experimental dosages highly surpass the normal environmental concentrations and are difficult to compare with human exposures. The treatment procedures are highly dependent on the dosage, duration of exposure, sex, and age of specimens among other factors which make it difficult to arrive at general conclusions. Our review aims to explore fluoride-induced neuronal damage along with associated histopathological, behavioral, and cognitive effects in experimental models. Furthermore, the correlation of various molecular mechanisms upon fluoride intoxication and associated neurobehavioral deficits has been discussed. Since there is no well-established mechanism to prevent fluorosis, phytochemical-based alleviation of its characteristic indications has been proposed as a possible remedial measure.