Effects of fluoride on DNA damage, S-phase cell-cycle arrest and the expression of NF-κB in primary cultured rat hippocampal neurons

Fluoride Induces Neurocytotoxicity by Disrupting Lysosomal Iron Metabolism and Membrane Permeability

The detrimental effects of fluoride on neurotoxicity have been widely recorded, yet the detailed mechanisms underlying these effects remain unclear. This study explores lysosomal iron metabolism in fluoride-related neurotoxicity, with a focus on the Steap3/TRPML1 axis. Utilizing sodium fluoride (NaF)-treated human neuroblastoma (SH-SY5Y) and mouse hippocampal neuron (HT22) cell lines, our research demonstrates that NaF enhances the accumulation of ferrous ions (Fe2+) in these cells, disrupting lysosomal iron metabolism through the Steap3/TRPML1 axis. Notably, NaF exposure upregulated ACSL4 and downregulated GPX4, accompanied by reduced glutathione (GSH) levels and superoxide dismutase (SOD) activity and increased malondialdehyde (MDA) levels. These changes indicate increased vulnerability to ferroptosis within neuronal cells. The iron chelator deferoxamine (DFO) mitigates this disruption. DFO binds to lysosomal Fe2+ and inhibits the Steap3/TRPML1 axis, restoring normal lysosomal iron metabolism, preventing lysosomal membrane permeabilization (LMP), and reducing neuronal cell ferroptosis. Our findings suggest that interference in lysosomal iron metabolism may mitigate fluoride-induced neurotoxicity, underscoring the critical role of the Steap3/TRPML1 axis in this pathological process.

Is Fluoride Blameless?-The Influence of Fluorine Compounds on the Invasiveness of the Human Glioma-like Cell Line U-87

Glioblastoma remains one of the most treatment-resistant and malignant human cancers. Given the documented harmful effects of fluoride on the developing central nervous system and the rising incidence of brain tumors, especially among children, it is pertinent to explore the role of environmental toxins, including fluoride compounds, in the context of brain cancer. This study represents the first investigation into the influence of fluoride on mechanisms related to the invasiveness of human glioblastoma cells. We examined the effects of sodium fluoride (NaF) exposure on the migratory and invasive abilities of the U-87 human glioblastoma cell line, assessing levels of metalloproteinases MMP-2 and MMP-9 secreted by these cells. Additionally, the activation of metabolic pathways associated with invasiveness, including AKT and NF-κB, was analyzed. Our results suggest that the effects induced by NaF at physiologically high concentrations (0.1-10 µM) in U-87 glioblastoma cells may promote a pro-invasive phenotype.

Inhibitory effects of NaF on mitochondrial energy generation in human platelets in vitro

Background

fluoride is a beneficial ion that has been used in various fields, from industrial products to therapeutics. However, due to its narrow therapeutic index, fluoride sometimes acts as a toxic agent at relatively higher concentrations in the human body. Based on the interest in genetic stability, its cytotoxic effects have been investigated mainly in nucleated, adherent cells, such as fibroblasts. However, the sensitivity of blood cells, especially anucleate platelets, to fluoride is poorly understood. To fill this gap in the literature, we investigated the effects of relatively low levels of fluoride on platelet energy metabolism, function, and viability.

Methods

Platelet-rich plasma (PRP) was prepared from 15 non-smoking healthy male adults (age: 28-63) and treated with NaF (0.5 or 1.0 mM) in microtubes for up to 3 days. Platelet function was evaluated based on aggregation and adhesion activities. Platelet energy metabolism was evaluated based on intracellular ATP levels, extracellular lactate levels, and respiration activities. The mitochondrial membrane potential (Em) and localization of reactive oxygen species (ROS) were visualized using cytochemical methods. Platelet viability was evaluated by cell counting and tetrazolium reduction.

Result

NaF (1 mM) significantly reduced platelet viability and inhibited functions. Behind these phenomena, NaF substantially decreased mitochondrial Em and increased ROS production along with significant decreases in oxygen consumption and ATP levels. Simultaneously, NaF increased the lactate levels. Although not statistically significant, similar effects were observed at 0.5 mM NaF.

Conclusion

At relatively low levels, NaF has the potential to attenuate platelet function probably primarily through the inhibition of mitochondrial energy generation. Cytotoxicity may be directly related to ROS production. These findings suggest that when used topically, for example, for caries prevention in the oral cavity, NaF could interfere with wound healing and tissue regeneration by endogenous and exogenously added platelets in the form of PRP.

Fluoride leaching from tuff breccia and its removal by natural and commercial adsorbents

In Japan, the concentration of fluoride (F-) leached from rocks, such as tuff breccia, excavated in tunnel construction projects often exceeds the Japanese environmental standard of 0.8 mg/L. Because of this, proper disposal methods are necessary for managing F--bearing excavated rocks. One effective solution based on circular economy is the use of an adsorption layer system. This system can simultaneously prevent the migration of F- released from excavated rocks and allow the recycling of this construction waste material. To determine the most suitable material for the disposal of excavated F--bearing tuff breccia from a tunnel construction in Hokkaido, Japan, four types of natural geological materials (S-1, S-2, S-3, and S-4) obtained near the tunnel construction site, as well as three types of commercial adsorbents (calcium (Ca), magnesium (Mg), and CaMg adsorbents) were selected for evaluation. The batch adsorption test results showed that S-1 and S-4 had high adsorption capacities for F-, and the adsorption process followed the Langmuir isotherm. The adsorption of F- to the natural adsorbents was strongly influenced by the pH and the presence of bicarbonate ions (HCO3-), but unaffected by chloride (Cl-) and sulfate (SO42-). There was also a strong positive correlation between the abundance of amorphous aluminum (Al) and iron (Fe) extracted and the adsorption of F-, indicating the importance of ion exchange reactions associated with surface OH- in immobilizing F-. Meanwhile, the Mg-bearing adsorbent exhibited the highest adsorption affinity for F- among the commercial adsorbents. This was attributed to adsorption through electrostatic interactions and coprecipitation with magnesium hydroxide (Mg(OH)2) formed during the hydration of magnesium oxide (MgO). To effectively incorporate these adsorbents into the adsorption layer system, parameters such as permeability and residence time need to be determined in order to maximize the retention of F- through adsorption, ion exchange and coprecipitation reactions.

Cytotoxicity induced by abamectin in hepatopancreas cells of Chinese mitten crab, Eriocheir sinensis: An in vitro assay

Toxic effects of abamectin on non-target aquatic organisms have been well documented due to its extensive use in both agricultural and aquacultural areas. However, knowledge of the abamectin induced cytotoxicity in crustacean hepatopancreas is still incomplete. In this study, we investigated the cytotoxic effects of abamectin on hepatopancreas cells of Chinese mitten crab, Eriocheir sinensis by an in vitro assay. The results showed that abamectin inhibited cell viability with elevated reactive oxygen species (ROS) and malondialdehyde (MDA) levels in a dose-dependent manner. Increased olive tail moment (OTM) values and 8-hydroxy-2'-deoxyguanosine (8-OHdG) contents indicate the DNA damage under abamectin exposure. The up-regulation of the typical apoptosis-related protein BCL2-associated X protein (Bax) and the down-regulation of B cell leukemia/lymphoma 2 (Bcl-2) demonstrate apoptosis in hepatopancreas cells. Meanwhile, the activities of both caspase-3 and caspase-9 were increased, indicating caspase-mediated apoptosis. In addition, qRT-PCR results showed the up-regulation of antioxidant genes superoxide dismutase (SOD) and catalase (CAT). The mRNA expression of Cap 'n' Collar isoform-C (CncC) and c-Jun NH2-terminal kinases (JNK) was also significantly increased, implying the involvement of the Nrf2/MAPK pathway in the antioxidative response. The alteration of innate immune-associated genes Toll-like receptor (TLR) and myeloid differentiation primary response gene 88 (Myd88) also indicates the influence of abamectin on immune status. In summary, the present study reveals the cytotoxicity of abamectin on hepatopancreas cells of E. sinensis and this in vitro cell culture model could be used for further assessment of pesticide toxicity.

Unraveling molecular characteristic of fluoride neurotoxicity on U87 glial-like cells: insights from transcriptomic and proteomic approach

The potential of fluoride (F) as a neurotoxicant in humans is still controversial in the literature. However, recent studies have raised the debate by showing different mechanism of F-induced neurotoxicity, as oxidative stress, energy metabolism and inflammation in the central nervous system (CNS). In the present study, we investigated the mechanistic action of two F concentration (0.095 and 0.22 μg/ml) on gene and protein profile network using a human glial cell in vitro model over 10 days of exposure. A total of 823 genes and 2,084 genes were modulated after exposure to 0.095 and 0.22 μg/ml F, respectively. Among them, 168 were found to be modulated by both concentrations. The number of changes in protein expression induced by F were 20 and 10, respectively. Gene ontology annotations showed that the main terms were related to cellular metabolism, protein modification and cell death regulation pathways, such as the MAP kinase (MAPK) cascade, in a concentration independent manner. Proteomics confirmed the changes in energy metabolism and also provided evidence of F-induced changes in cytoskeleton components of glial cells. Our results not only reveal that F has the potential to modulate gene and protein profiles in human U87 glial-like cells overexposed to F, but also identify a possible role of this ion in cytoskeleton disorganization.

Fluoride exposure disrupts the cytoskeletal arrangement and ATP synthesis of HT-22 cell by activating the RhoA/ROCK signaling pathway

BACKGROUND

Fluoride, an environmental contaminant, is ubiquitously present in air, water, and soil. It usually enters the body through drinking water and may cause structural and functional disorders in the central nervous system in humans and animals. Fluoride exposure affects cytoskeleton and neural function, but the mechanism is not clear.

METHODS

The specific neurotoxic mechanism of fluoride was explored in HT-22 cells. Cellular proliferation and toxicity detection were investigated by CCK-8, CCK-F, and cytotoxicity detection kits. The development morphology of HT-22 cells was observed under a light microscope. Cell membrane permeability and neurotransmitter content were determined using lactate dehydrogenase (LDH) and glutamate content determination kits, respectively. The ultrastructural changes were detected by transmission electron microscopy, and actin homeostasis was observed by laser confocal microscopy. ATP enzyme and ATP activity were determined using the ATP content kit and ultramicro-total ATP enzyme content kit, respectively. The expression levels of GLUT1 and 3 were assessed by Western Blot assays and qRT-PCR.

RESULTS

Our results showed that fluoride reduced the proliferation and survival rates of HT-22 cells. Cytomorphology showed that dendritic spines became shorter, cellular bodies became rounder, and adhesion decreased gradually after fluoride exposure. LDH results showed that fluoride exposure increased the membrane permeability of HT-22 cells. Transmission electron microscopy results showed that fluoride caused cells to swell, microvilli content decreased, cellular membrane integrity was damaged, chromatin was sparse, mitochondria ridge gap became wide, and microfilament and microtubule density decreased. Western Blot and qRT-PCR analyses showed that RhoA/ROCK/LIMK/Cofilin signaling pathway was activated by fluoride. F-actin/G-actin fluorescence intensity ratio remarkably increased in 0.125 and 0.5 mM NaF, and the mRNA expression of MAP2 was significantly decreased. Further studies showed that GLUT3 significantly increased in all fluoride groups, while GLUT1 decreased (p < 0.05). ATP contents remarkably increased, and ATP enzyme activity substantially decreased after NaF treatment with the control.

CONCLUSION

Fluoride activates the RhoA/ROCK/LIMK/Cofilin signaling pathway, impairs the ultrastructure, and depresses the connection of synapses in HT-22 cells. Moreover, fluoride exposure affects the expression of glucose transporters (GLUT1 and 3) and ATP synthesis. Sum up fluoride exposure disrupts actin homeostasis, ultimately affecting structure, and function in HT-22 cells. These findings support our previous hypothesis and provide a new perspective on the neurotoxic mechanism of fluorosis.

Fluoride in the Central Nervous System and Its Potential Influence on the Development and Invasiveness of Brain Tumours-A Research Hypothesis

The purpose of this review is to attempt to outline the potential role of fluoride in the pathogenesis of brain tumours, including glioblastoma (GBM). In this paper, we show for the first time that fluoride can potentially affect the generally accepted signalling pathways implicated in the formation and clinical course of GBM. Fluorine compounds easily cross the blood-brain barrier. Enhanced oxidative stress, disruption of multiple cellular pathways, and microglial activation are just a few examples of recent reports on the role of fluoride in the central nervous system (CNS). We sought to present the key mechanisms underlying the development and invasiveness of GBM, as well as evidence on the current state of knowledge about the pleiotropic, direct, or indirect involvement of fluoride in the regulation of these mechanisms in various tissues, including neural and tumour tissue. The effects of fluoride on the human body are still a matter of controversy. However, given the growing incidence of brain tumours, especially in children, and numerous reports on the effects of fluoride on the CNS, it is worth taking a closer look at these mechanisms in the context of brain tumours, including gliomas.

Serum Levels of CXCR4, SDF-1, MCP-1, NF-κB and ERK1/2 in Patients with Skeletal Fluorosis

C-X-C motif chemokine receptor 4 (CXCR4), stromal cell-derived factor-1 (SDF-1), monocyte chemoattractant protein-1 (MCP-1), extracellular signal-regulated kinase 1/2 (ERK1/2) and nuclear factor-κB (NF-κB) affect bone cells and play an important role in bone and joint diseases, but the data on CXCR4, SDF-1, MCP-1, ERK1/2 and NF-κB in the serum of skeletal fluorosis (SF) patients are inconclusive. Thus, according to the "Diagnostic Criteria for Endemic Skeletal Fluorosis" (WS 192-2008), we enrolled patients with SF (n = 60) as the SF group and those without SF as the controls (n = 60). Serum levels of CXCR4, SDF-1, MCP-1, ERK1/2 and NF-κB were detected by enzyme-linked immunosorbent assays (ELISAs). Serum SDF-1, CXCR4, MCP-1 and NF-κB levels were significantly higher in the SF group than in the control group. Within the serum of SF patients, CXCR4 and SDF-1 levels were positively correlated with NF-κB levels. There was no correlation between MCP-1 levels and those of ERK1/2 or NF-κB. SDF-1 and CXCR4 may activate the NF-κB pathway, and MCP-1 affects the occurrence and development of SF by regulating osteocytes through other pathways. The SDF-1/CXCR4 axis and MCP-1 signalling pathway provide a new theoretical basis for the occurrence and development of SF.

Determination of fluoride content in teas and herbal products popular in Poland

PURPOSE

Fluoride level, due to its narrow therapeutical range, must be constantly monitored in beverages, especially in daily-consumed plant infusions. Fluoride is important for prevention of tooth decay and osteoporosis, but its excess leads to fluorosis. Since tea can selectively absorb fluorides from soils, the question arises if a long-term consumption can pose an adverse effect on human health.

METHODS

Infusions of 33 popular teas (black, green, white, earl grey, pu-erh), tea-like products (rooibos, yerba mate) and herbs (chamomile, mint, nettle, purges, yarrow) available in the Polish market were analyzed with respect to a fluoride level by means of a validated ion-selective electrode method, which is proven to be fast and reliable.

RESULTS

Significantly different fluoride concentrations in infusions were observed, with black tea on top, where extraction of fluoride is the highest (average 2.65 mg F^-/L, range 0.718-6.029 mg/L). Two-fold higher fluoride contents were measured in infusions made from black tea bags than from leaves (average 3.398 mg/L and 1.529 mg/L, respectively). Green teas released comparable amounts of fluoride as black teas, while in herbal extracts the fluoride content was negligible.

CONCLUSIONS

The rank with respect to the fluoride concentration in an infusion is as follows: black tea > green tea > earl grey > pu-erh > white tea>>>rooibos, yerba mate, herbal products. Increasing of brewing time results in an increased fluoride content, but the overall content of fluoride in the analyzed infusions of teas and herbs was not high enough to cause a risk of fluorosis, even if left to brew up to 15 min.

Cells Adapt to Resist Fluoride through Metabolic Deactivation and Intracellular Acidification

Fluoride is highly abundant in the environment. Many organisms have adapted specific defense mechanisms against high concentrations of fluoride, including the expression of proteins capable of removing fluoride from cells. However, these fluoride transporters have not been identified in all organisms, and even organisms that express fluoride transporters vary in tolerance capabilities across species, individuals, and even tissue types. This suggests that alternative factors influence fluoride tolerance. We screened for adaptation against fluoride toxicity through an unbiased mutagenesis assay conducted on Saccharomyces cerevisiae lacking the fluoride exporter FEX, the primary mechanism of fluoride resistance. Over 80 independent fluoride-hardened strains were generated, with anywhere from 100- to 1200-fold increased fluoride tolerance compared to the original strain. The whole genome of each mutant strain was sequenced and compared to the wild type. The fluoride-hardened strains utilized a combination of phenotypes that individually conferred fluoride tolerance. These included intracellular acidification, cellular dormancy, nutrient storage, and a communal behavior reminiscent of flocculation. Of particular importance to fluoride resistance was intracellular acidification, which served to reverse the accumulation of fluoride and lead to its excretion from the cell as HF without the activity of a fluoride-specific protein transporter. This transport mechanism was also observed in wild-type yeast through a manual mutation to lower their cytoplasmic pH. The results demonstrate that the yeast developed a protein-free adaptation for removing an intracellular toxicant.

Moderate exercise relieves fluoride-induced liver and kidney inflammatory responses through the IKKβ/NFκB pathway

With the intensification of environmental pollution, the content of fluoride is increasing in human and animal living environments. Long-term fluoride exposure can cause damage to the liver and kidney, which are the main sites for fluoride metabolism, storage and removal. Moreover, exercise often accompanies the entire process of fluoride exposure in humans and animals. However, the mechanism of exercise on fluoride-induced liver and kidney injury remains unclear. Hence, we established a fluoride exposure and/or exercise mouse model to explore the influence of exercise on fluoride-induced liver and kidney inflammation and the potential mechanism. The results showed that fluoride caused obvious structural and functional damage and the notable recruitment of immunocytes in the liver and kidney. In addition, fluoride increased the levels of IL-1β, IL-2, IL-4, IL-6, IL-10, IL-12, IL-13, IL-21, TNF-α, and TGF-β but decreased the ratio of IFN-γ/IL-4 and IL-2/IL-10, which indicated that fluoride disturbed the inflammatory balance and caused hepatonephritis. In addition, the expression levels of IKKβ and NFκB were increased, and the expression of IκBα was decreased after fluoride exposure, indicating that fluoride activated the IKKβ/NFκB pathway. In summary, long-term moderate treadmill exercise relieved fluoride-induced liver and kidney inflammatory responses through the IKKβ/NFκB pathway, and exercise can be used to prevent fluoride-induced liver and kidney damage.

Fluoride Exposure from Ready-To-Drink Coffee Consumption

Fluoride is present in various foods ingested daily. It has been demonstrated that the intake of high concentrations of fluoride, both in adults and children, can cause pathologies, among which dental fluorosis, osteoporosis and damage to the central nervous system stand out. The objective of this study was to determine the fluoride concentrations in 60 samples of ready-to-drink cold brewed coffee of different brands and types (expresso, cappuccino, macchiato and decaffeinated) by the fluoride ion-selective potentiometric method. A statistical analysis was also performed to discern the existence of differences between these categories. The highest fluoride concentration (1.465 mg/L) was found in espresso coffee followed by Macchiato (1.254 mg/L). Decaffeinated coffee is the one that presented the lowest fluoride concentration with 0.845 mg/L. The risk assessment was conducted considering different consumption scenarios (250, 500 and 750 mL/day). The UL (upper level) established by the EFSA (European Food Safety Authority) at 7 mg/day was used. The consumption of three servings poses no health risk; however, it confers a significant value of fluoride contribution to the diet.

Near-Infrared Turn-On Fluorescent Probe for Aqueous Fluoride Ion Detection and Cell Imaging

Fluoride ions are one of the most essential anions in the human body and have been implicated in various pathological and physiological processes. The detection of fluoride ions in aqueous solution, as well as the imaging of fluoride ions in living cells, remains a challenge. We herein report a BODIPY-based fluorescent probe employing a pinacol borate group as the recognition moiety for the detection of fluoride ions in aqueous solutions. This probe shows high selectivity and sensitivity to fluoride ions with a significant near-infrared fluorescence turn-on response. In addition, this probe was successfully employed in fluorescence bioimaging of fluoride ions in the human cervical cancer cell and mouse mammary cancer cell, demonstrating its good cell permeability and stability under physiological conditions.

A systematic review on fluoride-induced epigenetic toxicity in mammals

Fluoride, one of the global groundwater contaminants, is ubiquitous in our day-to-day life from various natural and anthropogenic sources. Numerous in vitro, in vivo, and epidemiological studies are conducted to understand the effect of fluoride on biological systems. A low concentration of fluoride is reported to increase oral health, whereas chronic exposure to higher concentrations causes fluoride toxicity (fluorosis). It includes dental fluorosis, skeletal fluorosis, and fluoride toxicity in soft tissues. The mechanism of fluoride toxicity has been reviewed extensively. However, epigenetic regulation in fluoride toxicity has not been reviewed. This systematic review summarizes the current knowledge regarding fluoride-induced epigenetic toxicity in the in vitro, in vivo, and epidemiological studies in mammalian systems. We examined four databases for the association between epigenetics and fluoride exposure. Out of 932 articles (as of 31 March 2022), 39 met our inclusion criteria. Most of the studies focused on different genes, and overall, preliminary evidence for epigenetic regulation of fluoride toxicity was identified. We further highlight the need for epigenome studies rather than candidate genes and provide recommendations for future research. Our results indicate a correlation between fluoride exposure and epigenetic processes. Further studies are warranted to elucidate and confirm the mechanism of epigenetic alterations mediated fluoride toxicity.

High concentration of sodium fluoride in drinking water induce hypertrophy versus atrophy in mouse skeletal muscle via modulation of sarcomeric proteins

Fluoride at high doses is a well-known toxic agent for the musculoskeletal system, primarily in bone and cartilage cells. Research on fluoride toxicity concerning particularly on the skeletal muscle is scanty. We hypothesized that during skeletal fluorosis, along with bone, muscle is also affected, so we have evaluated the effects of Sodium fluoride (NaF) on mouse skeletal muscles. Sodium fluoride (80 ppm) was administered to 5-week-old C57BL6 mice drinking water for 15 and 60 days, respectively. We carried out histology, primary culture, molecular and proteomic analysis of fluoride administered mouse skeletal muscles. Results indicated an increase in the muscle mass (hypertrophy) in vivo and myotubes ex vivo by activating the IGF1/PI3/Akt/mTOR signalling pathway due to short term NaF exposure. The long-term exposure of mice to NaF caused loss of muscle proteins leading to muscle atrophy due to activation of the ubiquitin-proteasome pathway. Differentially expressed proteins were characterized and mapped using a proteomic approach. Moreover, the factors responsible for protein synthesis and PI3/Akt/mTOR pathway were upregulated, leading to muscle hypertrophy during the short term NaF exposure. Long term exposure to NaF resulted in down-regulation of metabolic pathways. Elevated myostatin resulted in the up-regulation of the muscle-specific E3 ligases-MuRF1, promoting the ubiquitination and proteasome-mediated degradation of critical sarcomeric proteins.

Amaral S, Buzalaf MAR. Effect of Physical Exercise and Genetic Background on Glucose Homeostasis and Liver/Muscle Proteomes in Mice

We compared the parameters related to glucose homeostasis, and liver and muscle proteomes in fluorosis-susceptible (A/J; S) and fluorosis-resistant (129P3/J; R) mice in response to fluoride (F) exposure and exercise. Ninety male mice (45 R-mice and 45 S-mice) were randomized into three groups: (SI; RI) No-F, No-Exercise, (SII; RII) 50 ppm F, No-Exercise, (SIII; RIII) 50 ppm F, Exercise. Overall, mean F concentrations in the plasma and femur were significantly higher in R-mice compared with S-mice. In R-mice, exercise resulted in an increase in F accumulation in the femur. In S-mice, the mean plasma glucose level was significantly higher in Group II compared with Groups I and III. There was an increase in liver proteins involved in energy flux and antioxidant enzymes in non-exercise groups (I, II) of S-mice in comparison with the corresponding groups of R-mice. The results also showed a decrease in muscle protein expression in Group I S-mice compared with their R-mice counterparts. In conclusion, the findings suggest an increased state of oxidative stress in fluorosis-susceptible mice that might be exacerbated by the treatment with F. In addition, fluorosis-susceptible mice have plasma glucose levels higher than fluorosis-resistant mice on exposure to F, and this is not affected by exercise.

Fluoride induced down-regulation of IKBKG Gene expression inhibits hepatocytes senescence

BACKGROUND

Accumulating evidences have confirmed that liver is one of the more severely damaged organs during chronic fluorosis. However, the detail mechanism is unclear to data. At present, the objective of this study was to investigate the relationship between down-regulation of IKBKG gene expression and hepatocyte senescence induced by sodium fluoride (NaF).

METHODS

Chronic fluorosis rats and NaF-exposure human liver L02 cells were reproduced the model of hepatocyte senescence in vivo and in vitro. The mRNA and protein levels of p16, p21 and IKBKG, the IL-8 level were determined. The role of IKBKG in fluoride-induced senescence of hepatocytes was explored by knock down in hepatocytes in vivo and in vitro.

RESULTS

The number of senescence-positive cells in rat liver tissues was increased as well as the level of IL-8 and the expression levels of p16, p21 and IKBKG in fluoride exposure to rat depending on the fluoride concentration. The similar results were obtained in NaF treated liver L02 cells, and the number of cells that stagnated in the G2 phase increased significantly. Further, our results confirmed that decreasing the expression of IKBKG in hepatocytes could reduce fluoride-induced hepatocyte senescence and the changes of senescence-related indicators both in vivo and in vitro.

CONCLUSION

These results indicated that the elevated expression of IKBKG was positive relation with the fluoride-induced senescence in hepatocytes, suggesting the hepatocyte senescence might have a special relationship with fluoride-caused liver damage. Because of the present results limitation, the mechanism of fluoride induced senescence in hepatocytes should be concentrated in the future in detail, especially the novel targets for fluoride induced liver injury.

Dietary fluoride intake during pregnancy and neurodevelopment in toddlers: A prospective study in the progress cohort

Foods and beverages provide a source of fluoride exposure in Mexico. While high fluoride concentrations are neurotoxic, recent research suggests that exposures within the optimal range may also pose a risk to the developing brain. This prospective study examined whether dietary fluoride intake during pregnancy is associated with toddlers' neurodevelopment in 103 mother-child pairs from the PROGRESS cohort in Mexico City. Food and beverage fluoride intake was assessed in trimesters 2 and 3 using a food frequency questionnaire and Mexican tables of fluoride content. We used the Bayley-III to evaluate cognitive, motor, and language outcomes at 12 and 24 months of age. Adjusted linear regression models were generated for each neurodevelopment assessment time point (12 and 24 months). Mixed-effects models were used to consider a repeated measurement approach. Interactions between maternal fluoride intake and child sex on neurodevelopmental outcomes were tested. Median (IQR) dietary fluoride intake during pregnancy was 1.01 mg/d (0.73, 1.32). Maternal fluoride intake was not associated with cognitive, language, or motor outcomes collapsing across boys and girls. However, child sex modified the association between maternal fluoride intake and cognitive outcome (p interaction term = 0.06). A 0.5 mg/day increase in overall dietary fluoride intake was associated with a 3.50-point lower cognitive outcome in 24-month old boys (95 % CI: -6.58, -0.42); there was no statistical association with girls (β = 0.07, 95 % CI: -2.37, 2.51), nor on the cognitive outcome at 12-months of age. Averaging across the 12- and 24-month cognitive outcomes using mixed-effects models revealed a similar association: a 0.5 mg/day increase in overall dietary fluoride intake was associated with a 3.46-point lower cognitive outcome in boys (95 % CI: -6.23, -0.70). These findings suggest that the development of nonverbal abilities in males may be more vulnerable to prenatal fluoride exposure than language or motor abilities, even at levels within the recommended intake range.

DNA methylation and fluoride exposure in school-age children: Epigenome-wide screening and population-based validation

Excessive fluoride exposure and epigenetic change can induce numerous adverse health outcomes, but the role of epigenetics underneath the harmful health effects induced by fluoride exposure is unclear. In such gap, we evaluated the associations between fluoride exposure and genome-wide DNA methylation, and identified that novel candidate genes associated with fluoride exposure. A total of 931 school-age children (8-12 years) in Tongxu County of Henan Province (China) were recruited in 2017. Urinary fluoride (UF) concentrations were measured using the national standardized ion selective electrode method. Participants were divided into a high fluoride-exposure group (HFG) and control group (CG) according to the UF concentrations. Candidate differentially methylated regions (DMRs) were screened by Infinium-Methylation EPIC BeadChip of DNA samples collected from 16 participants (eight each from each group). Differentially methylated genes (DMGs) containing DMRs associated with skeletal and neuronal development influenced by fluoride exposure were confirmed using MethylTarget™ technology from 100 participants (fifty each from each group). DMGs were verified by quantitative methylation specific PCR from 815 participants. Serum levels of hormones were measured by auto biochemical analyzer. The mediation analysis of methylation in the effect of fluoride exposure on hormone levels was also performed. A total of 237 differentially methylated sites (DMSs) and 212 DMRs were found in different fluoride-exposure groups in the epigenome-wide phase. Methylation of the target sequences of neuronatin (NNAT), calcitonin-related polypeptide alpha (CALCA) and methylenetetrahydrofolate dehydrogenase 1 showed significant difference between the HFG and CG. Each 0.06% (95% CI: -0.11%, -0.01%) decreased in NNAT methylation status correlated with each increase of 1.0 mg/L in UF concentration in 815 school-age children using QMSP. Also, each 1.88% (95% CI: 0.04%, 3.72%) increase in CALCA methylation status correlated with each increase of 1.0 mg/L in UF concentration. The mediating effect of NNAT methylation was found in alterations of ACTH levels influenced by fluoride exposure, with a β value of 11.7% (95% CI: 3.4%, 33.4%). In conclusion, long-term fluoride exposure affected the methylation pattern of genomic DNA. NNAT and CALCA as DMGs might be susceptible to fluoride exposure in school-age children.

Comprehensive and critical appraisal of plant-based defluoridation from environmental matrices

Fluoride is recognized as one of the global environmental threats because of its non-biodegradable nature and long-term persistence in the environment. This has created the dire need to explore various defluoridation techniques (membrane process, adsorption, precipitation, reverse osmosis, ion exchange, and electrocoagulation). Owing to their cost ineffectiveness and high operational costs, these technologies failed to find any practical utility in fluoride remediation. Comparatively, defluoridation techniques involving the use of low-cost plant-derived adsorbents and fluoride phytoremediators are considered better alternatives. Through this review, an attempt has been made to critically synthesize information about various plant-based bioadsorbents and hyperaccumulators from existing literature. Moreover, mechanisms underlying the fluoride adsorption and accumulation by plants have been thoroughly discussed that will invigorate the researchers to develop novel ideas about process/product modifications to further enhance the removal potential of the adsorbents and plants. Literature survey unravels that various low-cost plant-derived adsorbents have shown their efficacy in defluoridation, yet there is an urgent need to explore their pragmatic application on a commercial scale.

Fluoride exposure and children's intelligence: Gene-environment interaction based on SNP-set, gene and pathway analysis, using a case-control design based on a cross-sectional study

BACKGROUND

Excessive fluoride exposure has been associated with intelligence loss, but little is known about gene-fluoride interactions on intelligence at SNP-set, gene and pathway level.

OBJECTIVES

Here we conducted a population-based study in Chinese school-aged children to estimate the associations of fluoride from internal and external exposures with intelligence as well as to explore the gene-fluoride interactions on intelligence at SNP-set, gene and neurodevelopmental pathway level.

METHODS

A total of 952 resident children aged 7 to 13 were included in the current study. The fluoride contents in drinking water, urine, hair and nail were measured using the ion-selective electrode method. LASSO Binomial regression was conducted to screen the intelligence-related SNP-set. The gene-fluoride interactions at gene and pathway levels were detected by the Adaptive Rank Truncated Product method.

RESULTS

The probability of high intelligence was inversely correlated with fluoride contents in water, urine, hair and nail (all P < 0.001). The SNP-set based on rs3788319, rs1879417, rs57377675, rs11556505 and rs7187776 was related to high intelligence (P = 0.001) alone and by interaction with water, urinary and hair fluoride (P = 0.030, 0.040, 0.010), separately. In gene level, CLU and TOMM40 interacted with hair fluoride (both P = 0.017) on intelligence. In pathway level, Alzheimer disease pathway, metabolic pathway, signal transduction pathway, sphingolipid signaling pathway and PI3K-AKT signaling pathway interacted with fluoride on intelligence in men.

CONCLUSIONS

Our study suggests that fluoride is inversely associated with intelligence. Moreover, the interactions of fluoride with mitochondrial function-related SNP-set, genes and pathways may also be involved in high intelligence loss.

Fluoride Alters Signaling Pathways Associated with the Initiation of Dentin Mineralization in Enamel Fluorosis Susceptible Mice

Fluoride can alter the formation of mineralized tissues, including enamel, dentin, and bone. Dentin fluorosis occurs in tandem with enamel fluorosis. However, the pathogenesis of dentin fluorosis and its mechanisms are poorly understood. In this study, we report the effects of fluoride on the initiation of dentin matrix formation and odontoblast function. Mice from two enamel fluorosis susceptible strains (A/J and C57BL/6J) were given either 0 or 50 ppm fluoride in drinking water for 4 weeks. In both mouse strains, there was no overall change in dentin thickness, but fluoride treatment resulted in a significant increase in the thickness of the predentin layer. The lightly mineralized layer (LL), which lies at the border between predentin and fully mineralized dentin and is associated with dentin phosphoprotein (DPP), was absent in fluoride exposed mice. Consistent with a possible reduction of DPP, fluoride-treated mice showed reduced immunostaining for dentin sialoprotein (DSP). Fluoride reduced RUNX2, the transcription regulator of dentin sialophosphoprotein (DSPP), that is cleaved to form both DPP and DSP. In fluoride-treated mouse odontoblasts, the effect of fluoride was further seen in the upstream of RUNX2 as the reduced nuclear translocation of β-catenin and phosphorylated p65/NFκB. In vitro, MD10-F2 pre-odontoblast cells showed inhibition of the Dspp mRNA level in the presence of 10 μM fluoride, and qPCR analysis showed a significantly downregulated level of mRNAs for RUNX2, β-catenin, and Wnt10b. These findings indicate that in mice, systemic exposure to excess fluoride resulted in reduced Wnt/β-catenin signaling in differentiating odontoblasts to downregulate DSPP production via RUNX2.

Human cultured IMR-32 neuronal-like and U87 glial-like cells have different patterns of toxicity under fluoride exposure

BACKGROUND

Fluoride (F) is a naturally exists in nature but several studies have indicated it as an environmental toxicant to all leaving beings. Human F exposure has increased over the years since this ion has been used by industry on foods, beverages, toothpastes and on water supply. Although F is safe at optimal concentrations in water supply, human exposure to high levels could trigger neurofunctional deficits.

MATERIALS AND METHODS

In this study, human glial-like (U87) and neuronal-like (IMR-32) cells lineages were used to access F toxicity and CNS cell sensibility on both cell facing the same protocol. Cells were exposed to F over 3, 5 and 10 days on two different F concentrations. Fluoride exposed cells were evaluated by standard toxicity assays to cell viability, apoptosis, necrosis and general cell metabolism. Oxidative stress parameters were evaluated by ATP and ROS levels, lipid peroxidation, GSH/GSSG ratio and comet assay.

RESULTS

No changes were observed in IMR-32 at any given time while after 10 days of exposure to 0.22μg/mL, U87 glial-like cells showed signs of toxicity such as decreased cell viability by necrosis while general cell metabolism was increased. Oxidative stress parameters were next evaluated only on U87 glial-like cells after 10 days of exposure. F induced a decrease on ATP levels while no changes were observed on reactive oxygen species and lipid peroxidation. GSH/GSSG ratio was decreased followed by DNA damage both on 0.22μg/mL F.

CONCLUSIONS

Our results suggest an important differential behavior of the distinct types of cells exposed to the different fluoride concentrations, pointing that the U87 glial-like cells as more susceptible to damage triggered by this ion.

Human/eukaryotic ribosomal protein L14 (RPL14/eL14) overexpression represses proliferation, migration, invasion and EMT process in nasopharyngeal carcinoma

Although human/eukaryotic ribosomal protein L14 (RPL14/eL14) is known to be associated with a variety of cancers, its role in nasopharyngeal carcinoma (NPC) remains unclear. The aim of this study was to explore the impact of RPL14(eL14) in NPC. The results of quantitative real-time polymerase chain reaction (qRT-PCR), western blot, and immunohistochemical staining revealed that the expression of RPL14(eL14) significantly reduced in NPC tissues and cells. Furthermore, the protein expression of RPL14(eL14) was linked to NPC-related clinical pathological features, including the T and N classification of Tumor Node Metastasis (TNM) staging (all p < 0.05). Cell counting kit-8 (CCK-8) assay and colony formation assay revealed that RPL14(eL14) overexpression repressed NPC cell proliferation. In cell cycle assay, RPL14(eL14) overexpression significantly blocked NPC cells in S phase. Overexpression of RPL14(eL14) repressed cell migration and invasion in NPC as shown by transwell assay and cell scratch healing assay. In addition, RPL14(eL14) was closely correlated with the expression of epithelial–mesenchymal transition (EMT) biomarkers, including E-cadherin, N-cadherin, and vimentin as detected by western blot. In conclusion, our results revealed that RPL14(eL14) may be considered as an antioncogene in NPC, which greatly suppresses cancer progression.

DNA damage, immunotoxicity, and neurotoxicity induced by deltamethrin on the freshwater crayfish, Procambarus clarkii

Pyrethroid pesticides are applied to both agricultural and aquacultural industries for pest control. However, information of their impact on the commercial important freshwater crayfish, Procambarus clarkii is scarce. Therefore, the present study aimed to characterize to effects of a commonly used pyrethroid pesticide, deltamethrin on DNA damage, immune response, and neurotoxicity in P. clarkii. Animals were exposed to 7, 14, and 28 ng/L of deltamethrin, which correspond to 1/8, 1/4, and 1/2 of the LC50 (96 hours) of this pyrethroid to P. clarkii. Significant increase of olive tail moment (OTM) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) was found after deltamethrin exposure in a dose-dependent way. Total hemocyte counts (THC) and activities of immune-related enzymes including acid phosphatase (ACP), lysozyme (LZM), and phenoloxidase (PO) were all decreased and significantly lower than control at concentration of 28 ng/L after 96 hours exposure. Acetylcholinesterase (AChE) activity, an indicator of neurotoxic effect was investigated and it was decreased significantly in muscles at 14 and 28 ng/L after 24 hours exposure. The level of intracellular reactive oxygen species (ROS) in hemocytes was also measured and the significant increase of ROS was found at 14 and 28 ng/L concentrations. The results revealed that deltamethrin induced DNA damage, immunotoxicity, and neurotoxicity in P. clarkii by excessive generation of ROS. Because of the dose-dependent responses of all parameters under exposure of deltamethrin at environmentally realistic concentrations, these parameters could be used as sensitive biomarkers for risk assessment of deltamethrin in aquaculture area.

The effect of vitamin E and selenium combination in repairing fluoride-induced DNA damage to NRK-52E cells

Prolonged and excessive fluoride exposure can lead to fluorosis. The kidney is one of the organs that are injured mostly due to fluoride-induced damage. Fluoride can induce DNA damage at cytotoxic concentrations. This study aims to determine the extent of NaF-induced DNA damage and to investigate the effect of vitamin E and selenium combination (ES) in preventing and repairing this damage. For this purpose, we administered different combinations of NaF and ES to NRK-52E cells and determined the effective concentrations of ES and the NaF IC₅₀ values associated with different incubation times (3, 12, and 24 h) by using the MTT assay. The determined quantities of NaF IC₅₀ in association with time and the NaF IC₅₀ + ES combination were administered to the cells. The extent of DNA damage was determined with the comet assay and the expression levels of the Ku70/80 and PARP-1 genes were determined with the RT-qPCR method. DNA damage significantly increased in all experimental groups compared to the control group (p < 0.05). It was found out that the NaF and ES combination statistically reduced the DNA damage compared to the damage observed in the NaF-treated groups (p < 0.05). Treatment of the ES combination significantly increased the expressions of Ku70 and Ku80 genes involved in DNA repair (p < 0.05). We concluded that vitamin E and selenium can potentially be effective in the repair of fluoride-induced DNA damage based on the results of this in vitro study. Our results may shed light on the prevention of DNA damage associated with fluorosis.

Investigation of the genotoxic effects of fluoride on a bone tissue model

Fluorides are thought to be a major cause of osteocarcinogenesis, due to their widespread industrial use, ability to accumulate in bone tissue, and genotoxic and probable carcinogenic properties. In vitro experiments investigating the genotoxic potential of fluorides in bone tissue models can provide valuable indirect information on their involvement in osteocarcinogenesis. Here, we investigated whether sodium fluoride (NaF) has the ability to induce DNA damage and chromosomal abnormalities in human osteosarcoma cells after 48 and 72 h of exposure. The cell cultures were treated with NaF in concentrations of 0, 20, 100 and 200 μg/ml. The level of DNA damage was assessed by the comet assay, and the frequency of chromosomal abnormalities by a micronucleus test. A significant increase in DNA damage indicators was noted in the samples treated with fluoride concentrations of 100 and 200 µg/ml, after 48 and 72 h of exposure. The micronucleus test revealed a dose-dependent increase in cells with micronuclei, nucleoplasmic bridges and nuclear protrusions. Increasing the concentration of NaF led to an increase in the prevalence of cytogenetic indicators after both treatment durations. This demonstrated ability of fluorine to exert genotoxic effects on bone cells indirectly indicates the possible importance of fluoride in the aetiology of osteosarcoma.

Effects of Fluoride Long-Term Exposure over the Cerebellum: Global Proteomic Profile, Oxidative Biochemistry, Cell Density, and Motor Behavior Evaluation

Although the literature does not provide evidence of health risks from exposure to fluoride (F) in therapeutic doses, questions remain about the effects of long-term and high-dose use on the function of the central nervous system. The objective of this study was to investigate the effect of long-term exposure to F at levels similar to those found in areas of artificial water fluoridation and in areas of endemic fluorosis on biochemical, proteomic, cell density, and functional parameters associated with the cerebellum. For this, mice were exposed to water containing 10 mg F/L or 50 mg F/L (as sodium fluoride) for 60 days. After the exposure period, the animals were submitted to motor tests and the cerebellum was evaluated for fluoride levels, antioxidant capacity against peroxyl radicals (ACAP), lipid peroxidation (MDA), and nitrite levels (NO). The proteomic profile and morphological integrity were also evaluated. The results showed that the 10 mg F/L dose was able to decrease the ACAP levels, and the animals exposed to 50 mg F/L presented lower levels of ACAP and higher levels of MDA and NO. The cerebellar proteomic profile in both groups was modulated, highlighting proteins related to the antioxidant system, energy production, and cell death, however no neuronal density change in cerebellum was observed. Functionally, the horizontal exploratory activity of both exposed groups was impaired, while only the 50 mg F/L group showed significant changes in postural stability. No motor coordination and balance impairments were observed in both groups. Our results suggest that fluoride may impair the cerebellar oxidative biochemistry, which is associated with the proteomic modulation and, although no morphological impairment was observed, only the highest concentration of fluoride was able to impair some cerebellar motor functions.

The Influence of fluoride on chronic kidney disease of uncertain aetiology (CKDu) in Sri Lanka

Fluoride is an element that is widely distributed in the environment. The involvement of fluoride in pathogenesis of Chronic Kidney Disease of uncertain aetiology (CKDu) in Sri Lanka is a much-debated topic. This study aimed to investigate the fluoride concentration in drinking water in CKDu affected areas in Sri Lanka and to evaluate the possible effect of renal impairment on serum fluoride levels in CKDu patients. Drinking water (n = 60) from the common water sources from two CKDu prevalent areas and serum samples of CKDu patients (n = 311) and healthy controls (n = 276) were collected. Both environmental and biological samples were analysed for the concentration of fluoride. The fluoride concentration in over 95% of drinking water samples was below the WHO guideline of 1.5 mg/L. Serum fluoride concentrations in majority of the unaffected and early-stage CKDu patients (stages 1 and 2, eGFR >60 ml/min/1.73m2) were below the normal upper concentration of 50 μg/l and significantly higher levels were observed in patients in late stages of CKDu compared to the healthy controls. The available guidelines for drinking water are solely based on healthy populations with normal renal function. But, it is evident that once the kidney function is impaired, patients enter a vicious cycle as fluoride gradually accumulates in the body, further damaging the kidney tissue. Thus, close monitoring of serum fluoride levels in CKDu patients and establishing health-based target guidelines for fluoride in drinking water for the CKDu patients are recommended to impede the progression to end stage renal disease.

Mitigative effect of Momordica cymbalaria fruit extract against sodium fluoride induced hepatotoxicity in Wistar male albino rats

OBJECTIVES

The main objective of the present study is to evaluate the mitigative effect of hydroalcoholic extract of Momordica cymbalaria fruits against sodium fluoride (NaF) induced hepatotoxicity.

METHODS

In this study, Wistar male albino rats were randomly divided into five groups of six rats each. Group I and II served as normal and toxic controls. Group III as plant control received extract at a dose of 400 mg/kg b. wt, p.o and Groups IV and V as treatment groups received extract at a dose 200 and 400 mg/kg b. wt, p.o for 30 days. All groups except Groups I and III received 100 ppm of NaF through drinking water. After completion of the study, blood collected for the estimation of liver blood serum biomarkers such as aspartate aminotransferases (AST), alanine aminotransferases (ALT), alkaline Phosphatase (ALP), direct and total bilirubin, total protein and albumin. The liver tissue homogenate was for estimation of lipid peroxidation, catalase, and reduced glutathione levels.

RESULTS

The results showed that NaF intoxication caused elevation of liver blood serum levels and lipid peroxidation; decreased levels of serum total protein, albumin and liver reduced glutathione, and catalase observed. The treatment groups showed decreased elevated serum biomarkers (ALT, AST, and ALP), liver lipid peroxidation and increased serum total protein and albumin, liver reduced glutathione and catalase levels in a dose-dependent manner. Histopathological studies also further strongly supported for mitigative effects of the plant.

CONCLUSIONS

In conclusion, our findings of the study indicated that M. cymbalaria fruits were a potential drug candidate in the treatment of NaF induced hepatotoxicity.

Toxicity of fluoride: critical evaluation of evidence for human developmental neurotoxicity in epidemiological studies, animal experiments and in vitro analyses

Recently, epidemiological studies have suggested that fluoride is a human developmental neurotoxicant that reduces measures of intelligence in children, placing it into the same category as toxic metals (lead, methylmercury, arsenic) and polychlorinated biphenyls. If true, this assessment would be highly relevant considering the widespread fluoridation of drinking water and the worldwide use of fluoride in oral hygiene products such as toothpaste. To gain a deeper understanding of these assertions, we reviewed the levels of human exposure, as well as results from animal experiments, particularly focusing on developmental toxicity, and the molecular mechanisms by which fluoride can cause adverse effects. Moreover, in vitro studies investigating fluoride in neuronal cells and precursor/stem cells were analyzed, and 23 epidemiological studies published since 2012 were considered. The results show that the margin of exposure (MoE) between no observed adverse effect levels (NOAELs) in animal studies and the current adequate intake (AI) of fluoride (50 µg/kg b.w./day) in humans ranges between 50 and 210, depending on the specific animal experiment used as reference. Even for unusually high fluoride exposure levels, an MoE of at least ten was obtained. Furthermore, concentrations of fluoride in human plasma are much lower than fluoride concentrations, causing effects in cell cultures. In contrast, 21 of 23 recent epidemiological studies report an association between high fluoride exposure and reduced intelligence. The discrepancy between experimental and epidemiological evidence may be reconciled with deficiencies inherent in most of these epidemiological studies on a putative association between fluoride and intelligence, especially with respect to adequate consideration of potential confounding factors, e.g., socioeconomic status, residence, breast feeding, low birth weight, maternal intelligence, and exposure to other neurotoxic chemicals. In conclusion, based on the totality of currently available scientific evidence, the present review does not support the presumption that fluoride should be assessed as a human developmental neurotoxicant at the current exposure levels in Europe.

Principles of fluoride toxicity and the cellular response: a review

Fluoride is ubiquitously present throughout the world. It is released from minerals, magmatic gas, and industrial processing, and travels in the atmosphere and water. Exposure to low concentrations of fluoride increases overall oral health. Consequently, many countries add fluoride to their public water supply at 0.7-1.5 ppm. Exposure to high concentrations of fluoride, such as in a laboratory setting often exceeding 100 ppm, results in a wide array of toxicity phenotypes. This includes oxidative stress, organelle damage, and apoptosis in single cells, and skeletal and soft tissue damage in multicellular organisms. The mechanism of fluoride toxicity can be broadly attributed to four mechanisms: inhibition of proteins, organelle disruption, altered pH, and electrolyte imbalance. Recently, there has been renewed concern in the public sector as to whether fluoride is safe at the current exposure levels. In this review, we will focus on the impact of fluoride at the chemical, cellular, and multisystem level, as well as how organisms defend against fluoride. We also address public concerns about fluoride toxicity, including whether fluoride has a significant effect on neurodegeneration, diabetes, and the endocrine system.

Biological approaches of fluoride remediation: potential for environmental clean-up

Fluoride (F), anion of fluorine which is naturally present in soil and water, behaves as toxic inorganic pollutant even at lower concentration and needs immediate attention. Its interaction with flora, fauna and other forms of life, such as microbes, adversely affect various physiochemical parameters by interfering with several metabolic pathways. Conventional methods of F remediation are time-consuming, laborious and cost intensive, which renders them uneconomical for sustainable agriculture. The solution lies in cracking down this environmental contaminant by adopting economic, eco-friendly, cost-effective and modern technologies. Biological processes, viz. bioremediation involving the use of bacteria, fungi, algae and higher plants that holds promising alternative to manage F pollution, recover contaminated soil and improve vegetation. The efficiency of indigenous natural agents may be enhanced, improved and selected over the hazardous chemicals in sustainable agriculture. This review article emphasizes on various biological approaches for the remediation of F-contaminated environment, and exploring their potential applications in environmental clean-up. It further focuses on thorough systemic study of modern biotechnological approaches such as gene editing and gene manipulation techniques for enhancing the plant-microbe interactions for F degradation, drawing attention towards latest progresses in the field of microbial assisted treatment of F-contaminated ecosystems. Future research and understanding of the molecular mechanisms of F bioremediation would add on to the possibilities of the application of more competent strains showing striking results under diverse ecological conditions.

Chronic Exposure to Fluoride Affects GSH Level and NOX4 Expression in Rat Model of This Element of Neurotoxicity

Exposure of neural cells to harmful and toxic factors promotes oxidative stress, resulting in disorders of metabolism, cell differentiation, and maturation. The study examined the brains of rats pre- and postnatally exposed to sodium fluoride (NaF 50 mg/L) and activity of NADPH oxidase 4 (NOX4), catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR), concentration of glutathione (GSH), and total antioxidant capacity (TAC) in the cerebellum, prefrontal cortex, hippocampus, and striatum were measured. Additionally, NOX4 expression was determined by qRT-PCR. Rats exposed to fluorides (F-) showed an increase in NOX4 activity in the cerebellum and hippocampus, a decrease in its activity in the prefrontal cortex and hippocampus, and upregulation of NOX4 expression in hippocampus and its downregulation in other brain structures. Analysis also showed significant changes in the activity of all antioxidant enzymes and a decrease in TAC in brain structures. NOX4 induction and decreased antioxidant activity in central nervous system (CNS) cells may be central mechanisms of fluoride neurotoxicity. NOX4 contributes to blood-brain barrier damage, microglial activation, and neuronal loss, leading to impairment of brain function. Fluoride-induced oxidative stress involves increased reactive oxygen speciaes (ROS) production, which in turn increases the expression of genes encoding pro-inflammatory cytokines.

Inorganic fluoride and functions of brain

Although actively disputed and questioned, it has been proposed that chronic exposure to inorganic fluoride (F^-) is toxic for brain. The major question for this review was whether an excessive F^- intake is causally related to adverse neurological and cognitive health conditions in human beings and animals. The paper systematically and critically summarizes the findings of the studies showing positive associations between F^- intoxication and various intellectual defects, as well as of those which attempted to clarify the nature of F^- neurotoxicity. Many works provide support for a link between pre- and postnatal F^- exposure and structural and functional changes in the central nervous system responsible for neurological and cognitive disorders. The mechanisms suggested to underlie F^- neurotoxicity include the disturbances in synaptic transmission and synaptic plasticity, premature death of neurons, altered activities of components of intracellular signaling cascades, impaired protein synthesis, deficit of neurotrophic and transcriptional factors, oxidative stress, metabolic changes, inflammatory processes. However, the majority of works have been performed on laboratory rodents using such F^- doses which are never exist in the nature even in the regions of endemic fluorosis. Thus, this kind of treatment is hardly comparable with human exposure even taking into account the higher rate of F^- clearance in animals. Of special importance are the data collected on humans chronically consuming excessive F^- doses in the regions of endemic fluorosis or contacting with toxic F^- compounds at industrial sites, but those works are scarce and often criticized due to low quality. New, expertly performed studies with repeated exposure assessment in independent populations are needed to prove an ability of F^- to impair neurological and intellectual development of human beings and to understand the molecular mechanisms implicated in F^--induced neurotoxicity.

Clofibrate, a PPAR-α agonist, abrogates sodium fluoride-induced neuroinflammation, oxidative stress, and motor incoordination via modulation of GFAP/Iba-1/anti-calbindin signaling pathways

Fluoride is an environmental contaminant that is ubiquitously present in air, water, and soil. It is commonly added in minute quantity to drinking water, toothpaste, and mouth rinses to prevent tooth decay. Epidemiological findings have demonstrated that exposure to fluoride induced neurodevelopmental toxicity, developmental neurotoxicity, and motor disorders. The neuroprotective effect of clofibrate, a peroxisome proliferator-activated receptor alpha agonist, was investigated in the present study. Forty male Wistar rats were used for this study and randomly grouped into 10 rats per group as control, sodium fluoride (NaF) alone (300 ppm), NaF plus clofibrate (250 mg/kg), and NaF plus lisinopril (10 mg/kg), respectively, for 7 days. NaF was administered in drinking water while clofibrate and lisinopril were administered by oral gavage. Markers of neuronal inflammation and oxidative stress, acetylcholinesterase activity, and neurobehavioral (hanging wire and open field) tests were performed. Immunohistochemistry was performed on brain tissues, and they were probed with glial fibrillary acidic protein, ionized calcium-binding adaptor molecule 1, and cerebellar Ca²⁺ -binding protein calbindin-D28k. The results showed that NaF significantly increased of oxidative stress and neuroinflammation and inhibited AChE activity. Immunostaining showed reactive astrocytes, microgliosis, loss of dendritic spines, and arborization in Purkinje cells in rats administered only NaF. Neurobehavioral results showed that cotreatment of NaF with clofibrate improved muscular strength and locomotion, reduced anxiety, and significantly reduced astrocytic count. Overall, cotreatment of NaF with either clofibrate or lisinopril showed neuroprotective effects by mitigating neuronal inflammation and oxidative and motor incoordination. Hence, clofibrate could be seen as a novel drug candidate against neurodegeneration and motor disorders.

Cytotoxic and genotoxic potential of respirable fraction of composite dust on human bronchial cells

OBJECTIVE

To determine the cytotoxic and genotoxic potential of the respirable fraction of composite dust (<4 μm) on human bronchial epithelial cells.

METHODS

Composite sticks of three commercial dental composites (Filtek Supreme XTE, Grandio, Transbond XT) were ground in an enclosed plexiglass chamber with a rough dental bur (grain-size 100 μm) and the generated airborne respirable dust was collected in a personal cyclone on a teflon filter (pore size 5 μm). Immediately after particle collection, the dust was quantified gravimetrically and the particles were suspended in cell culturing medium. Next, human bronchial epithelial cells (16HBE14o-) were exposed to the suspensions (3 μg/ml-400 μg/ml). After 24 h, cell viability (WST-1 assay) and membrane integrity (LDH assay) were evaluated. Furthermore, the genotoxic effect of a sub-cytotoxic concentration (50 μg/ml) of composite dust was evaluated by the comet assay after 3 h exposure and cell cycle disturbances were analyzed by flow cytometry. Cellular uptake of particles was evaluated by transmission electronic microscope (TEM).

RESULTS

For all three tested composite materials, a decrease in metabolic activity of 10-35% was observed when the cells were exposed to the highest concentrations (100 μg/ml-400 μg/ml). Toxicity was partially linked to membrane disruption especially after 72 h exposure. All tested composites provoked a mild genotoxic effect after short-term exposure compared to the control groups. TEM revealed that respirable particles of all tested composites were taken up by the cells.

SIGNIFICANCE

The respirable fraction of composite dust only showed cytotoxic effects at the highest concentrations, whereas mild genotoxicity was observed after exposure to a sub-cytotoxic concentration.

Nitrate and Phosphate Transporters Rescue Fluoride Toxicity in Yeast

Organisms are exposed to fluoride in the air, water, and soil. Yeast and other microbes utilize fluoride channels as a method to prevent intracellular fluoride accumulation and mediate fluoride toxicity. Consequently, deletion of fluoride exporter genes (FEX) in S. cerevisiae resulted in over 1000-fold increased fluoride sensitivity. We used this FEX knockout strain to identify genes, that when overexpressed, are able to partially relieve the toxicity of fluoride exposure. Overexpression of five genes, SSU1, YHB1, IPP1, PHO87, and PHO90, increase fluoride tolerance by 2- to 10-fold. Overexpression of these genes did not provide improved fluoride resistance in wild-type yeast, suggesting that the mechanism is specific to low fluoride toxicity in yeast. Ssu1p and Yhb1p both function in nitrosative stress response, which is induced upon fluoride exposure along with metal influx. Ipp1p, Pho87p, and Pho90p increase intracellular orthophosphate. Consistent with this observation, fluoride toxicity is also partially mitigated by the addition of high levels of phosphate to the growth media. Fluoride inhibits phosphate import upon stress induction and causes nutrient starvation and organelle disruption, as supported by gene induction monitored through RNA-Seq. The combination of observations suggests that transmembrane nutrient transporters are among the most sensitized proteins during fluoride-instigated stress.

GSTO1 acts as a mediator in sodium fluoride-induced alterations of learning and memory related factors expressions in the hippocampus cell line

The mechanism of GSTO1, as a high-risk factor for neurological damage, in sodium fluoride (NaF)-induced learning and memory impairment remained still unclear. Hence, in this study, we used the siRNA-GSTO1 HT22 model to explore the effect of NaF and siRNA-GSTO1 on the viability, and proliferation rate of HT22 cells, as well as the mRNA and protein expression levels of cyclic adenosine monophosphate (cAMP) response element binding protein (CREB), neural cell adhesion molecule (NCAM), stem cell factor (SCF) and brain-derived neurotrophic factor (BDNF). The results of MTT showed that 10^-3, 10^-4, and 10^-5 moL/L sodium fluoride (NaF) exposure could significantly promote the proliferation of HT22 cells at 24 h, 36 h, and 48 h, respectively. In addition, our results showed that exposure to 10^-3, 10^-4, and 10^-5 moL/l NaF increased GSTO1 mRNA and protein expression, but decreased CREB and BDNF expression levels in a dose and time-dependent manner. The mRNA and protein expressions of GSTO1, CREB and BDNF were significantly decreased in the siRNA-GSTO1 and NaF + siRNA-GSTO1 group (P < 0.05). We have shown that various NaF doses affected the learning and memory ability by down-regulation the expressions of CREB, BDNF, NCAM and SCF. In summary, we concluded that GSTO1 plays a mediator role in NaF-induced neurological damage.

Sodium Fluoride (NaF) Induces Inflammatory Responses Via Activating MAPKs/NF-κB Signaling Pathway and Reducing Anti-inflammatory Cytokine Expression in the Mouse Liver

At present, no reports are focused on fluoride-induced hepatic inflammatory responses in human beings and animals. This study aimed to investigate the mRNA and protein levels of inflammatory cytokines and signaling molecules for evaluating the effect of different doses (0, 12, 24, and 48 mg/kg) of sodium fluoride (NaF) on inflammatory reaction in the mouse liver by using methods of experimental pathology, quantitative real-time polymerase chain reaction (qRT-PCR), and western blot analysis. We found that NaF in excess of 12 mg/kg caused the hepatic inflammatory responses, and the results showed that NaF activated the mitogen-activated protein kinases (MAPKs) signaling pathway by markedly increasing (p < 0.01 or p < 0.05) mRNA and protein levels of apoptosis signal-regulating kinase 1 (ASK1), mitogen-activated protein kinase kinases 1/2 (MEK1/2), extracellular signal-regulated protein kinases 1/2 (Erk1/2), mitogen-activated protein kinase kinases 4/7 (MEK4/7), c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase (p38) and mitogen-activated protein kinase kinases 3/6 (MEK3/6), and the nuclear factor-kappa B (NF-κB) signaling pathway by increasing (p < 0.01 or p < 0.05) the production of NF-κB and inhibitor of nuclear factor kappa-B kinase subunit beta (IKK-β) and reducing (p < 0.01 or p < 0.05) the production of the inhibitory kappa B (IκB). Thus, NaF that caused the hepatic inflammatory responses was characterized by increasing (p < 0.01 or p < 0.05) the production of pro-inflammatory mediators such as interleukin-1β (IL-1β), interleukin-6 (IL-6), interleukin-8 (IL-8), monocyte chemotactic protein 1 (MCP-1), and cyclooxygenase-2 (COX-2) via the activation of MAPKs and NF-κB pathways, and by significantly inhibiting (p < 0.01 or p < 0.05) the production of anti-inflammatory mediators including interleukin-4 (IL-4) and transforming growth factor beta (TGF-β).

Fluoride Exposure Induces Inhibition of Sodium-and Potassium-Activated Adenosine Triphosphatase (Na+, K+-ATPase) Enzyme Activity: Molecular Mechanisms and Implications for Public Health

In this study, several lines of evidence are provided to show that Na + , K + -ATPase activity exerts vital roles in normal brain development and function and that loss of enzyme activity is implicated in neurodevelopmental, neuropsychiatric and neurodegenerative disorders, as well as increased risk of cancer, metabolic, pulmonary and cardiovascular disease. Evidence is presented to show that fluoride (F) inhibits Na + , K + -ATPase activity by altering biological pathways through modifying the expression of genes and the activity of glycolytic enzymes, metalloenzymes, hormones, proteins, neuropeptides and cytokines, as well as biological interface interactions that rely on the bioavailability of chemical elements magnesium and manganese to modulate ATP and Na + , K + -ATPase enzyme activity. Taken together, the findings of this study provide unprecedented insights into the molecular mechanisms and biological pathways by which F inhibits Na + , K + -ATPase activity and contributes to the etiology and pathophysiology of diseases associated with impairment of this essential enzyme. Moreover, the findings of this study further suggest that there are windows of susceptibility over the life course where chronic F exposure in pregnancy and early infancy may impair Na + , K + -ATPase activity with both short- and long-term implications for disease and inequalities in health. These findings would warrant considerable attention and potential intervention, not to mention additional research on the potential effects of F intake in contributing to chronic disease.

Histone Deacetylation in the Promoter of p16 Is Involved in Fluoride-Induced Human Osteoblast Activation via the Inhibition of Sp1 Binding

Chronic fluorosis is a systemic condition which principally manifests as defects in the skeleton and teeth. Skeletal fluorosis is characterized by aberrant proliferation and activation of osteoblasts, however, the underlying mechanisms of osteoblast activation induced by fluoride are not fully understood. Therefore, we investigated the pathogenic mechanism of human primary osteoblast proliferation and activation in relation to histone acetylation of the promoter p16, a well-known cell cycle regulation-related gene. The results showed that sodium fluoride (NaF) induced deacetylation and decreased expression of the p16 gene via inhibition of specificity protein 1 (Sp1) binding to its response element, which accounts for NaF increasing cell viability and promoting proliferation in human primary osteoblasts. These results reveal the regulatory mechanism of histone acetylation of the p16 gene on osteoblast activation in skeletal fluorosis.

The Contribution of Fluoride to the Pathogenesis of Eye Diseases: Molecular Mechanisms and Implications for Public Health

This study provides diverse lines of evidence demonstrating that fluoride (F) exposure contributes to degenerative eye diseases by stimulating or inhibiting biological pathways associated with the pathogenesis of cataract, age-related macular degeneration and glaucoma. As elucidated in this study, F exerts this effect by inhibiting enolase, τ-crystallin, Hsp40, Na⁺, K⁺-ATPase, Nrf2, γ -GCS, HO-1 Bcl-2, FoxO1, SOD, PON-1 and glutathione activity, and upregulating NF-κB, IL-6, AGEs, HsP27 and Hsp70 expression. Moreover, F exposure leads to enhanced oxidative stress and impaired antioxidant activity. Based on the evidence presented in this study, it can be concluded that F exposure may be added to the list of identifiable risk factors associated with pathogenesis of degenerative eye diseases. The broader impact of these findings suggests that reducing F intake may lead to an overall reduction in the modifiable risk factors associated with degenerative eye diseases. Further studies are required to examine this association and determine differences in prevalence rates amongst fluoridated and non-fluoridated communities, taking into consideration other dietary sources of F such as tea. Finally, the findings of this study elucidate molecular pathways associated with F exposure that may suggest a possible association between F exposure and other inflammatory diseases. Further studies are also warranted to examine these associations.

SIRT1 suppresses p53-dependent apoptosis by modulation of p21 in osteoblast-like MC3T3-E1 cells exposed to fluoride

Fluoride is very crucial for development of teeth and bones. Excessive fluoride, however, causes damage to teeth and bones resulting in serious public health problem. SIRT1 regulates physiological and pathological processes such as apoptosis and cell cycle. Although SIRT1 inhibits p53-mediated transactivation, how SIRT1 regulates p53 in fluorosis remains unclear. This study aims to investigate the involvement of SIRT1 in fluoride-induced cell cycle arrest and apoptosis in MC3T3-E1 cells and the underlying mechanism. Cell apoptosis was determined using Annexin V-FITC/PI dual staining, cell cycle detected with PI staining, intracellular ROS levels measured with DCFH-DA probe, and apoptosis-related protein expressions determined using Western blotting. Results showed that there was a promotion in apoptosis rate, intracellular ROS levels, the ratio of Bax/Bcl-2, protein expression (Cyt c, Caspase-3, p53, Ac-p53 and p21) and blockage of S phase after cells were exposed to NaF. Afterwards, the influence of SIRT1 on apoptosis was explored after SRT1720 (SIRT1 activator) and Ex-527 (SIRT1 inhibitor) was introduced. Results indicated that SRT1720 in combination with fluoride significantly decreased the intracellular ROS levels, the protein expression of Caspase-3, Ac-p53 and p21 and alleviated apoptosis, while it was reversed by Ex-527. Collectively, SIRT1 plays an essential role in protection against fluoride-induced oxidative stress and mitochondria-dependent apoptosis in MC3T3-E1 cells. The SIRT1/p53/p21 pathway may be a potential therapeutic target for fluorosis.

Sodium fluoride induced skeletal muscle changes: Degradation of proteins and signaling mechanism

Fluoride is a well-known compound for its usefulness in healing dental caries. Similarly, fluoride is also known for its toxicity to various tissues in animals and humans. It causes skeletal fluorosis leading to osteoporosis of the bones. We hypothesized that when bones are affected by fluoride, the skeletal muscles are also likely to be affected by underlying molecular events involving myogenic differentiation. Murine myoblasts C2C12 were cultured in differentiation media with or without NaF (1 ppm-5 ppm) for four days. The effects of NaF on myoblasts and myotubes when exposed to low (1.5 ppm) and high concentration (5 ppm) were assessed based on the proliferation, alteration in gene expression, ROS production, and production of inflammatory cytokines. Changes based on morphology, multinucleated myotube formation, expression of MyHC1 and signaling pathways were also investigated. Concentrations of NaF tested had no effects on cell viability. NaF at low concentration (1.5 ppm) caused myoblast proliferation and when subjected to myogenic differentiation it induced hypertrophy of the myotubes by activating the IGF-1/AKT pathway. NaF at higher concentration (5 ppm), significantly inhibited myotube formation, increased skeletal muscle catabolism, generated reactive oxygen species (ROS) and inflammatory cytokines (TNF-α and IL-6) in C2C12 cells. NaF also enhanced the production of muscle atrophy-related genes, myostatin, and atrogin-1. The data suggest that NaF at low concentration can be used as muscle enhancing factor (hypertrophy), and at higher concentration, it accelerates skeletal muscle atrophy by activating the ubiquitin-proteosome pathway.