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

A review on fluoride contamination in groundwater and human health implications and its remediation: A sustainable approaches

Contamination of drinking water due to fluoride (F-) is a major concern worldwide. Although fluoride is an essential trace element required for humans, it has severe human health implications if levels exceed 1.5 mg. L-1 in groundwater. Several treatment technologies have been adopted to remove fluoride and reduce the exposure risk. The present article highlights the source, geochemistry, spatial distribution, and health implications of high fluoride in groundwater. Also, it discusses the underlying mechanisms and controlling factors of fluoride contamination. The problem of fluoride-contaminated water is more severe in India's arid and semiarid regions than in other Asian countries. Treatment technologies like adsorption, ion exchange, precipitation, electrolysis, electrocoagulation, nanofiltration, coagulation-precipitation, and bioremediation have been summarized along with case studies to look for suitable technology for fluoride exposure reduction. Although present technologies are efficient enough to remove fluoride, they have specific limitations regarding cost, labour intensity, and regeneration requirements.

The Footprints of Mitochondrial Fission and Apoptosis in Fluoride-Induced Renal Dysfunction

Fluoride (F) is widely distributed in the environment and poses serious health risks to humans and animals. Although a good body of literature demonstrates a close relationship between F content and renal system performance, there is no satisfactory information on the involved intracellular routes. Hence, this study used histopathology and mitochondrial fission to explore fluorine-induced nephrotoxicity further. For this purpose, mice were exposed to the F ion (0, 25, 50, 100 mg/L) for 90 days. The effects of different F levels on renal pathomorphology and ion metabolism were assessed using hematoxylin and eosin (H&E), periodic acid-Schiff stain (PAS), periodic acid-silver methenamine (PASM), Prussian blue (PB), and alkaline phosphatase (ALP) staining. The results showed that F could lead to glomerular atrophy, tubular degeneration, and vacuolization. Meanwhile, F also could increase glomerular and tubular glycoproteins; made thickening of the renal capsule membrane and thickening of the tubular basement membrane; led to the accumulation of iron ions in the tubules; and increased in glomerular alp and decreased tubular alp. Concomitantly, IHC results showed that F significantly upregulated the expression levels of mitochondrial fission-related proteins, including mitochondrial fission factor (Mff), fission 1 (Fis1), and mitochondrial dynamics proteins of 49 kDa (MiD49) and 51 kDa (MiD51), ultimately caused apoptosis. To sum up, excessive fluorine has a strong nephrotoxicity effect, disrupting the balance of mitochondrial fission and fusion, interfering with the process of mitochondrial fission, and then causing damage to renal tissue structure and apoptosis.

Sodium Glucose Transporter-2 Inhibitors (SGLT2Is)-TLRs Axis Modulates Diabetes

Diabetes affects millions of people worldwide and is mainly associated with impaired insulin function. To date, various oral anti-diabetic drugs have been developed, of which, the sodium glucose transporter-2 inhibitors (SGLT2Is) are of the most recent classes that have been introduced. They differ from other classes in terms of their novel mechanism of actions and unique beneficial effects rather than just lowering glucose levels. SGLT2Is can protect body against cardiovascular events and kidney diseases even in non-diabetic individuals. SGLT2Is participate in immune cell activation, oxidative stress reduction, and inflammation mediation, thereby, moderating diabetic complications. In addition, toll like receptors (TLRs) are the intermediators of the immune system and inflammatory process, thus it's believed to play crucial roles in diabetic complications, particularly the ones that are related to inflammatory reactions. SGLT2Is are also effective against diabetic complications via their anti-inflammatory and oxidative properties. Given the anti-inflammatory properties of TLRs and SGLT2Is, this review investigates how SGLT2Is can affect the TLR pathway, and whether this could be favorable toward diabetes.

The role of plant growth promoting rhizobacteria in strengthening plant resistance to fluoride toxicity: a review

A wide variety of bacteria are present in soil but in rhizospheric area, the majority of microbes helps plant in defending diseases and facilitate nutrient uptake. These microorganisms are supported by plants and they are known as plant growth-promoting rhizobacteria (PGPR). The PGPRs have the potential to replace chemical fertilizers in a way that is more advantageous for the environment. Fluoride (F) is one of the highly escalating, naturally present contaminants that can be hazardous for PGPRs because of its antibacterial capacity. The interactions of F with different bacterial species in groundwater systems are still not well understood. However, the interaction of PGPR with plants in the rhizosphere region reduces the detrimental effects of pollutants and increases plants' ability to endure abiotic stress. Many studies reveal that PGPRs have developed F defense mechanisms, which include efflux pumps, Intracellular sequestration, enzyme modifications, enhanced DNA repair mechanism, detoxification enzymes, ion transporter/antiporters, F riboswitches, and genetic mutations. These resistance characteristics are frequently discovered by isolating PGPRs from high F-contaminated areas or by exposing cells to fluoride in laboratory conditions. Numerous studies have identified F-resistant microorganisms that possess additional F transporters and duplicates of the well-known targets of F. Plants are prone to F accumulation despite the soil's low F content, which may negatively affect their growth and development. PGPRs can be used as efficient F bioremediators for the soil environment. Environmental biotechnology focuses on creating genetically modified rhizobacteria that can degrade F contaminants over time. The present review focuses on a thorough systemic analysis of contemporary biotechnological techniques, such as gene editing and manipulation methods, for improving plant-microbe interactions for F remediation and suggests the importance of PGPRs in improving soil health and reducing the detrimental effects of F toxicity. The most recent developments in the realm of microbial assistance in the treatment of F-contaminated environments are also highlighted.

Protective Effect of Quercetin and Ginger (Zingiber officinale) Extract against Dimethoate Potentiated Fluoride-Induced Nephrotoxicity in Rats

This study aimed to determine the potential of quercetin and Zingiber officinale (ZO) Roscoe extract to alleviate the renal damage induced by dimethoate (DM) and fluoride (F^-) alone and by their combined exposure in rats. A total of 54 adult Wistar rats were randomly allocated to nine groups (n = 6). A sub-lethal dose of DM (1/10th of the median lethal dose) was administered by oral gavage alone and along with F^- (4.5 ppm, three-fold the permissible limit) in their drinking water continuously for 28 days. Chromatographical analysis revealed the presence of quercetin, curcumin, and other phytochemicals with strong antioxidant properties in ZO-rhizome extract. Severe changes were observed in the levels of the renal biomarkers and histoarchitecture after co-administration of the toxicants, indicating greater kidney damage. The administration of ZO extract (300 mg/kg) along with either or both toxicants led to a significant restoration of the biochemical markers and renal antioxidant profile and histology.

Effects of burnt tire-ash on Na+/K+, Ca2+-ATPase, serum immunoglobulin and brain acetylcholinesterase activities in clarias gariepinus (Burchell, 1822)

Aquatic pollution may continue to deepen following the emergence of new class of toxicants. The present study investigated the effect of water-soluble fraction of burnt tire-ash on Clarias gariepinus. The fish were exposed to sublethal doses; 0.00 g/L, 2.24 g/L, 1.12 g/L and 0.56 g/L of tire-ash solution, representing ¹/5, ¹/10 and ¹/20 of 11.2 g/L median lethal concentration (96 LC₅₀), for 28 days, followed by 14 days recovery trial. Biological sampling was done on exposure day 1, 14 and 28, and on day14 recovery period for biochemical analysis such as the liver and gill Na⁺/K⁺ and Ca²⁺-ATPase, serum immunoglobulin (IgM) and brain acetylcholinesterase (AChE) of the experimental fish. Also, body biomass and behavior were evaluated. The behavioral responses exhibited by the fish to BTA exposure include reduced feeding, hypoactivity, air gulping and skin discoloration, which was observed to be concentration dependent. The body weight of 2.24 g/L and 1.12 g/L BTA-exposed fish decreased significantly than 0.56 g/L exposed fish and the control. Furthermore, findings revealed evident induction of Na⁺/K⁺ and Ca^{2 +}-ATPase activities in both tissues, elevation of serum immunoglobulin content and inhibition of AChE activity in the brain of the exposed fish relative to the control. However, it was also observed that the biochemical parameters normalized after the recovery period. In conclusion, water-soluble fraction of burnt tire-ash produced toxicological effects in the experimental model, hence the present study provides the ecotoxicological insight of tire ash.

Iodine Status in Pregnant Women Having Urinary Fluoride in Contaminated Areas: A Case Study of Phayao Province

Fluoride naturally occurs in the Earth's crust and is widely dispersed in groundwater. The high consumption of fluoride can inhibit iodine metabolism in the human body, especially in the thyroid gland. This study assessed iodine knowledge, iodine consumption behavior, urinary iodine (UI), thyroid stimulating hormone (serum TSH), and free triiodothyronine3 (serum FT3) and examined the connection between fluoride exposure and UI and thyroid function as serum concentrations of TSH and FT3 in pregnant women dwelling in an area of endemic fluorosis. This was a cross-sectional study. The population included 152 pregnant women within the 1^st trimester of pregnancy, during which they were provided antenatal care (ANC) in seven public community hospitals in Phayao province, Thailand. The study consisted of two components. First, the study consisted of a questionnaire in which we evaluated the iodine knowledge and iodine consumptive behaviors in subjects. Second, biochemical data were investigated to evaluate thyroid function in the subjects. The gestational age of most subjects was 8-12 weeks. The study population has lived in fluoride-contaminated areas since birth (76.97%). The iodine and iodine consumption levels were moderate (50.00%). Their food iodine consumption was 3-4 days/week, and the top five consumption ranks were iodized salt, cooked pork, eggs, sticky rice, and iodine fish sauce. In terms of biochemical parameters, 63.16% of respondents had UI levels below 150.00 g/L, which is below the normal reference range of 150.00-249.00 g/L. 89.47% of the risk of hypothyroidism was associated with serum TSH levels below 2.50 g/L. In 38.16% of the samples, normal levels of serum FT3 (2.00-4.40 pg/L) were identified in the subjects. In addition, 61.84% of the samples had FT3 concentrations greater than 4.40 pg/L (high intake of iodine). The approved association between positive serum FT3 data and serum TSH was positive (r = 260 and p < 0.05). These studies imply that these elevated levels of TSH and FT3 place pregnant women in their first trimester at risk for hypothyroidism.

Dimethyl phthalate destroys the cell membrane structural integrity of Pseudomonas fluorescens

A Gram-negative bacteria (Pseudomonas fluorescens) was exposed to different concentrations (0, 20, and 40 mg/L) of dimethyl phthalate (DMP) for 8 h, and then Fourier transform infrared spectroscopy (FTIR) analysis, lipopolysaccharide content detection, analysis of fatty acids, calcein release test, proteomics, non-targeted metabolomics, and enzyme activity assays were used to evaluate the toxicological effect of DMP on P. fluorescens. The results showed that DMP exposure caused an increase in the unsaturated fatty acid/saturated fatty acid (UFA/SFA) ratio and in the release of lipopolysaccharides (LPSs) from the cell outer membrane (OM) of P. fluorescens. Moreover, DMP regulated the abundances of phosphatidyl ethanolamine (PE) and phosphatidyl glycerol (PG) of P. fluorescens and induced dye leakage from an artificial membrane. Additionally, excessive reactive oxygen species (ROS), malondialdehyde (MDA), and changes in antioxidant enzymes (i.e., catalase [CAT] and superoxide dismutase [SOD]) activities, as well as the inhibition of Ca²⁺-Mg²⁺-ATPase and Na⁺/K⁺-ATPase activities in P. fluorescens, which were induced by the DMP. In summary, DMP could disrupt the lipid asymmetry of the outer membrane, increase the fluidity of the cell membrane, and destroy the integrity of the cell membrane of P. fluorescens through lipid peroxidation, oxidative stress, and ion imbalance.

Rutin Improves Cardiac and Erythrocyte Membrane-Bound ATPase Activities in Male Rats Exposed to Cadmium Chloride and Lead Acetate

Cardiovascular diseases have been associated with cadmium (Cd) and lead (Pb). Impaired Ca²⁺ and Na⁺/K⁺-ATPase activities have also been linked to hemolytic and cardiovascular disorders. This study investigated the effect of rutin on Cd and/or Pb-induced cardiac and erythrocyte disorders in male rats. Twenty-five (25) male Wistar rats were treated as (n=5): Control, Pb (60 mg/kg, p.o), Cd (5 mg/kg, p.o), Pb + Cd, Rutin + Pb + Cd (50 mg/kg Rt, 60 mg/kg Pb, 5 mg/kg Cd, p.o). Plasma electrolyte and Ca²⁺- and Na⁺/K⁺-ATPase activities in the erythrocyte and heart of the rats were assayed. There was an increased and decreased activity of cardiac and erythrocyte Na⁺/K⁺-ATPase in Pb- (172%) and Cd- (33.7%) treated groups, respectively. However, rutin increased erythrocyte Na⁺/K⁺-ATPase activity in Cd + Pb when compared with Cd and Cd + Pb groups. Erythrocyte Ca²⁺-ATPase activity was decreased in the Pb (68%), Cd (68%) and Cd + Pb (55.3%) groups. Cardiac Na⁺/K⁺-ATPase activity was not altered in Pb and Cd groups while it decreased in Cd + Pb. Rutin increased the activity of the pump in Cd +Pb-treated rats compared to the Cd+Pb group. Therefore, rutin reversed cadmium- and lead-induced impaired cardiac and erythrocyte membrane Ca²⁺- and Na⁺/K⁺-ATPase activities. Graphical Abstract Dotted lines-decrease activity, curved lines-increased activity (created with BioRender.com ).

Potential cellular endocrinology mechanisms underlying the effects of Chinese herbal medicine therapy on asthma

Asthma is a complex syndrome with polygenetic tendency and multiple phenotypes, which has variable expiratory airflow limitation and respiratory symptoms that vary over time and in intensity. In recent years, continuous industrial development has seriously impacted the climate and air quality at a global scale. It has been verified that climate change can induce asthma in predisposed individuals and that atmospheric pollution can exacerbate asthma severity. At present, a subset of patients is resistant to the drug therapy for asthma. Hence, it is urgent to find new ideas for asthma prevention and treatment. In this review, we discuss the prescription, composition, formulation, and mechanism of traditional Chinese medicine monomer, traditional Chinese medicine monomer complex, single herbs, and traditional Chinese patent medicine in the treatment of asthma. We also discuss the effects of Chinese herbal medicine on asthma from the perspective of cellular endocrinology in the past decade, emphasizing on the roles as intracellular and extracellular messengers of three substances-hormones, substances secreted by pulmonary neuroendocrine cells, and neuroendocrine-related signaling protein-which provide the theoretical basis for clinical application and new drug development.

3,4-Dihydroxybenzaldehyde mitigates fluoride-induced cytotoxicity and oxidative damage in human RBC

BACKGROUND

Fluoride is an essential micronutrient that is needed for mineralization of bones and formation of dental enamel. It is a widely dispersed environmental pollutant and chronic exposure to it is toxic, resulting in malignancies and hematological damage in humans. Blood is a major and early target of environmental pollutants and toxicants like fluoride. Fluoride generates reactive oxygen species and free radicals which induce oxidative stress in target cells and mediate its toxic effects. The aim of this study was to determine the mitigating effect of plant antioxidant 3,4-dihydroxybenzaldehyde (DHB) on sodium fluoride (NaF) induced oxidative damage and cytotoxicity in isolated human red blood cells (RBC) METHOD: Isolated human RBC were treated with 0.5 mM NaF, in absence or presence of different concentrations of DHB (0.1-2.5 mM). Several biochemical parameters were analyzed in cell lysates and whole cells.

RESULTS

Treatment of RBC with NaF increased the formation of reactive oxygen and nitrogen species. It oxidized thiols, proteins and lipids and generated their peroxidative products. Methemoglobin level, heme degradation and lipid peroxidation were increased but cellular antioxidant status declined significantly in NaF alone treated RBC, compared to the control. NaF inhibited antioxidant, membrane bound and glycolytic enzymes in RBC. However, prior incubation of RBC with DHB significantly attenuated the NaF-induced alterations in all these parameters in a DHB concentration-dependent manner.

CONCLUSION

These results show that DHB mitigates NaF-induced oxidative damage in human RBC, probably because of its antioxidant character.

Fluoride Exposure through Different Drinking Water Sources in a Contaminated Basin in Guanajuato, Mexico: A Deterministic Human Health Risk Assessment

Water fluoride levels above the World Health Organization’s guideline (1.5 mg/L), common in overexploited aquifers, represent a health hazard. Our objective was to assess the health risks posed by exposure to fluoride in different drinking water sources in a contaminated basin in Mexico. Fluoride was measured in mutual drinking water sources and in the urine of 39 children and women. Risks were estimated through hazard quotient (HQ) by drinking water source. Dental fluorosis was assessed in the children. Mean fluoride water concentrations (mg/L) were: well, 4.2; waterhole, 2.7; bottled, 2.1; rainwater, 0.4. The mean urinary fluoride concentrations (specific gravity adjusted) were 2.1 mg/L and 3.2 mg/L in children and women, respectively. Our multiple linear regression model showed children’s urinary fluoride concentrations increased 0.96 mg/L for every 1 mg/L increase in water fluoride (p < 0.001). Dental fluorosis was diagnosed in 82% of the children, and their HQ according to drinking water source was: well, 1.5; waterhole, 1.1; bottled, 0.8; harvested rainwater, 0.3. The pervasive dental fluorosis indicates a toxic past fluoride exposure; urinary fluoride levels and HQs indicate high exposure and current health risks for most children. Drinking harvested rainwater will likely prevent most of the local fluoride exposure.

Effects of Fluoride on Submandibular Glands of Mice: Changes in Oxidative Biochemistry, Proteomic Profile, and Genotoxicity

Although fluoride (F) is well-known to prevent dental caries, changes in cell processes in different tissues have been associated with its excessive exposure. Thus, this study aimed to evaluate the effects of F exposure on biochemical, proteomic, and genotoxic parameters of submandibular glands. Twenty one old rats (n = 30) were allocated into three groups: 60 days administration of drinking water containing 10 mgF/L, 50 mgF/L, or only deionized water (control). The submandibular glands were collected for oxidative biochemistry, protein expression profile, and genotoxic potential analyses. The results showed that both F concentrations increased the levels of thiobarbituric acid–reactive substances (TBARS) and reduced glutathione (GSH) and changed the proteomic profile, mainly regarding the cytoskeleton and cellular activity. Only the exposure to 50 mgF/L induced significant changes in DNA integrity. These findings reinforce the importance of continuous monitoring of F concentration in drinking water and the need for strategies to minimize F intake from other sources to obtain maximum preventive/therapeutic effects and avoid potential adverse effects.

Toxic effects of fluoride in intestinal epithelial cells and the mitigating effect of methanol extract of coconut haustorium by enhancing de novo glutathione biosynthesis

Fluoride ions are an important environmental contaminant and pollutant found in a wide variety of environmental conditions. The fluoride in drinking water is evident to induce toxic effects including neurodegeneration, skeletal and dental fluorosis as well as organ damage. Nutraceuticals and functional foods are emerging as possible preventive agents against fluoride toxicity. Hence, the possible use of an emerging functional food-the coconut haustorium is being evaluated against sodium fluoride-induced toxicity in intestinal cells (IEC-6). The cells exposed to fluoride showed significant cell death mediated through the increased lipid peroxidation and glutathione depletion. The glutathione biosynthetic enzymes were inhibited by the exposure to fluoride and the apoptotic genes (caspases 3/7 and apaf-1) were upregulated. The CHE pre-treatment improved the activity of enzymes involved in the de novo biosynthesis of glutathione and subsequently improved the intracellular GSH pool. The improved antioxidant defense was also evident from the reduced expression of apoptotic genes (p < 0.05). Overall, the study concludes that fluoride ions induce oxidative stress-mediated apoptosis in intestinal epithelial cells, via inhibiting glutathione biosynthesis. Methanol extract of coconut haustorium increased glutathione biosynthesis and subsequently prevented fluoride toxicity in IEC-6 cells by virtue of its antioxidant potentials.

Borassus flabellifer Linn haustorium methanol extract mitigates fluoride-induced apoptosis by enhancing Nrf2/Haeme oxygenase 1 -dependent glutathione metabolism in intestinal epithelial cells

Fluoride is the most common cause of drinking water-associated toxicity and is known to induce various metabolic imbalances and dental/skeletal fluorosis. The present study analyzed the protective effect of Borassus flabellifer Linn. haustorium extract (BHE) against fluoride-induced intestinal redox metabolism and apoptosis. The total polyphenols and total flavonoids present in BHE were estimated to be 39.67 ± 5.14 mg gallic acid equivalent/g extract and 8.59 ± 0.74 mg quercetin equivalent. In cultured intestinal epithelial cells (IEC-6), sodium fluoride exposure-induced apoptosis mediated through antioxidant enzyme inhibition and subsequent oxidative damages. Further, there observed an increased expression of caspase-3, caspase-7, and apoptotic protease activating factor-1 (apaf-1) genes, increased cytochrome C release, and caspase 3/7 activity indicating the apoptosis- mediated cell death (p < 0.05). Upon pretreatment with BHE, the cytotoxic effect of fluoride was reduced by decreasing the expression of apoptotic genes and increased the cytochrome release as well as caspase 3/7 activity (p < 0.01). Providing the mechanistic basis, the expression of nuclear factor erythroid 2-related factor-2 (Nrf2)/haeme oxygenase-1 (HO1) gene was increased in the BHE pretreated cells; corroborating to these, there observed increased activity of glutathione biosynthetic enzymes (p < 0.05) and glutathione reductase. Hence, the protective effect of BHE may be mediated through Nrf2-mediated glutathione biosynthesis, the subsequent establishment of redox balance, and inhibition of apoptosis in intestinal epithelial cells.

Ouabain induces memory impairment and alter the BDNF signaling pathway in an animal model of bipolar disorder: Cognitive and neurochemical alterations in BD model

BACKGROUND

The present study aims to evaluate the effects of ouabain on memory and neurotrophic parameters in the brains of rats.

METHODS

Wistar rats received an intracerebroventricular (ICV) injection of ouabain or artificial cerebrospinal fluid (aCSF). Seven and 14 days after ICV administration, the animals were subjected to the open-field and splash tests. Furthermore, the pro-BDNF, BDNF, TrkB, and CREB were assessed in the frontal cortex and hippocampus of the rats, in both seven and 14 days after ICV injection. The memory of the animals was tested by novel object recognition test (NOR) and inhibitory avoidance task (IA), only 14 days after ICV administration.

RESULTS

Ouabain increased locomotion and exploration in the animals seven days after its administration; however, 14 days after ICV, these behavioral parameters return to the basal level. Seven days after ouabain administration increased grooming behavior in the splash test; on the other hand, seven days after ouabain injection decreased the grooming behavior, which is considered an anhedonic response. Besides, ouabain decreased recognition index in the NOR and decreased aversive memory in the IA, when compared to the control group. The levels of pro-BDNF and BDNF decreased in the frontal cortex seven days after ouabain; but its receptor (TrkB) and CREB decreased seven and 14 days after ouabain, in both cerebral structures evaluated.

CONCLUSION

Ouabain-induced animal model of BD is an excellent model to assess memory alteration, observed in bipolar patients. Besides, the memory impairment induced by ouabain seems to be related to BDNF signaling pathway alterations.

Fluoride enhances generation of reactive oxygen and nitrogen species, oxidizes hemoglobin, lowers antioxidant power and inhibits transmembrane electron transport in isolated human red blood cells

Fluoride is a widespread environmental pollutant that at high levels exerts numerous deleterious effects on human health. The toxic effects of fluoride are a matter of serious concern since many countries have regions of endemic fluorosis. The main source of fluoride exposure for humans is intake of contaminated groundwater. Fluoride is absorbed from the gastrointestinal tract and enters the circulating blood, where the abundant red blood cells (RBC) are an early and major target of fluoride toxicity. Chronic fluoride exposure generates free radicals, reactive species which leads to redox imbalance, cytotoxicity and hematological damage. This study aimed to determine the effect of sodium fluoride (NaF) on human RBC under in vitro conditions. Isolated RBC were incubated with different concentrations of NaF (10-500 µM) for 8 h at 37 °C. Several biochemical parameters were determined in hemolysates or whole cells. Treatment of RBC with NaF enhanced the generation of reactive oxygen and nitrogen species. This increased the oxidation of hemoglobin to yield methemoglobin and oxoferrylhemoglobin, which are inactive in oxygen transport. NaF treatment increased the degradation of heme causing release of free iron from its porphyrin ring. Cellular antioxidant power was significantly decreased in NaF-treated RBC, lowering the metal reducing and free radical quenching ability of cells. The two pathways of glucose metabolism in RBC i.e. glycolysis and hexose monophosphate shunt, were inhibited. NaF also inhibited the plasma membrane redox system, and its associated ascorbate free radical reductase, to disrupt transmembrane electron transport. These results suggest that fluoride generates reactive species that cause extensive oxidative modifications in human RBC.

Astaxanthin Decreases Spatial Memory and Glutamate Transport Impairment Induced by Fluoride

Excessive exposure to the sources of fluoride in drinking water, oral care products, and food is a widespread problem. Fluoride is associated with impairment in child intelligence development. It causes DNA damage, oxidative stress, and mitochondrial dysfunction, mainly due to the production of reactive oxygen species (ROS). It has been postulated that the use of antioxidants such as astaxanthin, may alleviate fluoride's adverse effects. This study assessed the effects of fluoride on cellular ROS content and rat's learning and memory ability and investigated the protective potency of astaxanthin with emphasis on the role of glutamate using the Morris Water Maze test, glutamate concentration determination, and western blot techniques. The fluoride treatment of cells results in an increment of cellular ROS, whereas astaxanthin inhibits lipid peroxidation. Fluoride significantly decreases the cellular glutamate uptake and glutamate transporter, protein level, possibly due to the disruption of mitochondrial energy metabolism and defect of the transporter recycle, respectively. The in-vivo study indicated that the treatment of rats with fluoride led to a loss of learning, while astaxanthin improved memory dysfunction. Measurement of ROS and glutamate levels of rat brain hippocampus showed that fluoride increased the ROS but decreased the glutamate. On the other hand, the utilization of astaxanthin decreased the brain ROS content and increased the glutamate level. It seems that fluoride disrupts the normal function of neurons via increment of ROS production and decrement of glutamate level, whereas astaxanthin has neuroprotective potency due to the ROS scavenging ability.

Effects of Fluoride Exposure on Primary Human Melanocytes from Dark and Light Skin

Fluoride exposure has adverse effects on human health that have been studied in vitro in cell culture systems. Melanocytes are the melanin pigment-producing cells that have a significant role in the regulation of the process of melanogenesis, which provides several health benefits. Melanocytes are present in the oral cavity, skin, brain, lungs, hair, and eyes. However, to date, there has been no study on the effects of fluoride exposure on melanocytes. Hence, in the current study, we have studied the effects of sodium fluoride (NaF) exposure on neonatal human epidermal melanocytes (HEMn) derived from two different skin phototypes, lightly pigmented (LP) and darkly pigmented (DP). We have assessed the impact of a 24 h and 72 h NaF exposure on metabolic activity and membrane integrity of these cells. In addition, we have evaluated whether NaF exposure might have any impact on the physiological functions of melanocytes associated with the production of melanin, which is regulated by activity of the enzyme tyrosinase. We have also assessed if NaF exposure might induce any oxidative stress in LP and DP melanocytes, by evaluation of production of reactive oxygen species (ROS) and measurement of mitochondrial membrane potential (MMP) levels. Our results showed that HEMn-LP cells showed a higher sensitivity to NaF cytotoxicity than HEMn-DP cells, with significant cytotoxicity at concentrations >1 mM, while concentration range 0.25–1 mM were nontoxic and did not lead to oxidative stress, and also did not alter the levels of intracellular melanin or cellular tyrosinase activity, indicating that treatment up to 1 mM NaF is generally safe to melanocytes from both pigmentation phototypes.

Mechanisms of Fluoride Toxicity: From Enzymes to Underlying Integrative Networks

Fluoride has been employed in laboratory investigations since the early 20th century. These studies opened the understanding of fluoride interventions to fundamental biological processes. Millions of people living in endemic fluorosis areas suffer from various pathological disturbances. The practice of community water fluoridation used prophylactically against dental caries increased concern of adverse fluoride effects. We assessed the publications on fluoride toxicity until June 2020. We present evidence that fluoride is an enzymatic poison, inducing oxidative stress, hormonal disruptions, and neurotoxicity. Fluoride in synergy with aluminum acts as a false signal in G protein cascades of hormonal and neuronal regulations in much lower concentrations than fluoride acting alone. Our review shows the impact of fluoride on human health. We suggest focusing the research on fluoride toxicity to the underlying integrative networks. Ignorance of the pluripotent toxic effects of fluoride might contribute to unexpected epidemics in the future.

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.

Fluoride Exposure Induces Inhibition of Sodium/Iodide Symporter (NIS) Contributing to Impaired Iodine Absorption and Iodine Deficiency: Molecular Mechanisms of Inhibition and Implications for Public Health

The sodium iodide symporter (NIS) is the plasma membrane glycoprotein that mediates active iodide transport in the thyroid and other tissues, such as the salivary, gastric mucosa, rectal mucosa, bronchial mucosa, placenta and mammary glands. In the thyroid, NIS mediates the uptake and accumulation of iodine and its activity is crucial for the development of the central nervous system and disease prevention. Since the discovery of NIS in 1996, research has further shown that NIS functionality and iodine transport is dependent on the activity of the sodium potassium activated adenosine 5'-triphosphatase pump (Na+, K+-ATPase). In this article, I review the molecular mechanisms by which F inhibits NIS expression and functionality which in turn contributes to impaired iodide absorption, diminished iodide-concentrating ability and iodine deficiency disorders. I discuss how NIS expression and activity is inhibited by thyroglobulin (Tg), tumour necrosis factor alpha (TNF-α), transforming growth factor beta 1 (TGF-β1), interleukin 6 (IL-6) and Interleukin 1 beta (IL-1β), interferon-γ (IFN-γ), insulin like growth factor 1 (IGF-1) and phosphoinositide 3-kinase (PI3K) and how fluoride upregulates expression and activity of these biomarkers. I further describe the crucial role of prolactin and megalin in regulation of NIS expression and iodine homeostasis and the effect of fluoride in down regulating prolactin and megalin expression. Among many other issues, I discuss the potential conflict between public health policies such as water fluoridation and its contribution to iodine deficiency, neurodevelopmental and pathological disorders. Further studies are warranted to examine these associations.

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.