Chronic administration of aluminum-fluoride or sodium-fluoride to rats in drinking water: alterations in neuronal and cerebrovascular integrity

Community Water Fluoridation in Focus: A Comprehensive Look at Fluoridation Levels across America

Objective: This study reports on the number and percentage of community water systems (CWSs) meeting fluoride concentration standards set by the U.S. Department of Health and Human Services (DHHS). The study also explored changes in the population exposed to optimally fluoridated water in these systems between 2006 and 2020. Methods: This study analyzed U.S. Centers for Disease Control and Prevention data from 2006 to 2020, tabulating state-specific CWS fluoridation rates, ranking them, and calculating the percent change. Results: In 2020, 72.7% of the US population received CWS water, with 62.9% of those individuals served by a CWS system meeting DHHS fluoridation standards. This compares to 69.2% receiving CWS water in 2006 and 74.6% in 2012. The overall change in those receiving fluoridated water was 1.4%, from 61.5% in 2006 to 62.9% in 2020. State-specific percentages ranged from 8.5% in Hawaii to 100% in Washington DC in 2020 (median: 76.4%). Conclusions: Although endorsed by the American Dental Association, the percentage of individuals receiving fluoridated water did not increase substantially from 2006 to 2020, indicating that there has not been much progress toward meeting the Healthy People 2030 goal that 77.1% of Americans receive water with enough fluoride to prevent tooth decay.

Global Scientific Research Landscape on Aluminum Toxicology

This study aimed to identify the landscape of current aluminum toxicity based on knowledge mapping of the 100 most-cited articles on toxicological aspects of aluminum in biological organisms. The research was searched in the Web of Science Core Collection (WoS-CC) with publications between 1945 and 2022. Data regarding authorship, title, journal, year of publication, citation count, country, keywords, study design, and research hotspots were extracted and all elected articles were analyzed. Our results showed that among the articles selected, literature review and in vivo studies were the most common study designs. The USA and England were found as the countries with most publications. Alzheimer's disease (AD), aluminum, and neurotoxicity were found as the most frequent keywords. The articles most cited in world literature suggested that aluminum exposure is associated with Alzheimer's disease, Parkinson's disease (PD), dialysis encephalopathy, amyotrophic lateral sclerosis, neurodegeneration changes, cognitive impairment, such as bone damage, oxidative alterations, and cytotoxicity.

Effects of chronic fluorosis on the brain

This article reviews the effects of chronic fluorosis on the brain and possible mechanisms. We used PubMed, Medline and Cochraine databases to collect data on fluorosis, brain injury, and pathogenesis. A large number of in vivo and in vitro studies and epidemiological investigations have found that chronic fluorosis can cause brain damage, resulting in abnormal brain structure and brain function.Chronic fluorosis not only causes a decline in concentration, learning, and memory, but also has mental symptoms such as anxiety, tension, and depression. Several possible mechanisms that have been proposed: the oxidative stress and inflammation theory, neural cell apoptosis theory, neurotransmitter imbalance theory, as well as the doctrine of the interaction of fluorine with other elements. However, the specific mechanism of chronic fluorosis on brain damage is still unclear. Thus, a better understanding of the mechanisms via which chronic fluorosis causes brain damage is of great significance to protect the physical and mental health of people in developing countries, especially those living in the endemic areas of fluorosis. In brief, further investigation concerning the influence of fluoride on the brain should be conducted as the neural damage induced by it may bring about a huge problem in public health, especially considering growing environmental pollution.

Assessment of renal and hepatic dysfunction by co-exposure to toxic metals (Cd, Pb) and fluoride in people living nearby an industrial zone

Togo's phosphate processing plant at Kpeme discharges waste, containing Cd, Pb, and fluoride, into the sea and on the soil. Heavy metals toxicity on kidneys and the liver has been studied. However, fluoride toxicity on these organs remains to be investigated. The present study deals with the variation in renal and hepatic functioning parameters due to fluoride, Cd and Pb. Totally, 350 volunteers were recruited from five different localities around this phosphate processing plant for sample collection. Cd and Pb contents in blood samples were determined by spectrophotometry and fluoride by the titanium chloride method. Biochemical parameters were measured using Biolab kits. The pollutant contents were elevated in polluted areas where ASAT, ALAT, creatinine, and urea increased, and total protein decreased. Correlation and multivariate tests showed that fluoride is related to the various pathologies mentioned. PCA revealed that phosphate processing in Togo is a source of renal and hepatic toxicity.

Fluoride-Induced Expression of Neuroinflammatory Markers and Neurophysiological Regulation in the Brain of Wistar Rat Model

Excess fluoride intake has been linked with various pathological conditions. The objective of the present study was to understand the role of fluoride in neurotoxic, neuroinflammatory, and neurodegenerative changes in the brain tissue of Wistar rats. Wistar rats were fed with water containing 20-100 ppm (ppm) sodium fluoride (NaF). An array of neurotransmitters (acetylcholine, dopamine, epinephrine, norepinephrine, serotonin, histamine, and glutamate) expression levels were estimated with respect to different fluoride concentrations. Additionally, its effect on the expression levels of specific neuroinflammatory markers (iNOS, COX-2, TNF-α, PKC, VEGF, and HSP-70) in brain tissues of Wister rats was assessed. An increase in NaF concentration resulted in increased fluoride deposition in the brain which in turn caused increase levels of epinephrine, histamine, serotonin, and glutamate and decreased levels of norepinephrine, acetylcholine, and dopamine in a dose-dependent manner. Tissue fluoride levels of the hippocampus, neocortex, cerebellum, spinal cord, and sciatic nerve increased significantly in fluoride fed rats. Transmission electron microscopy in the experimental animals revealed axon deterioration, myelin sheath degeneration, and dark cells with scanty cytoplasm in the spinal cord and sciatic nerve. Additionally, vacuolated swollen mitochondria were observed in the neocortex, hippocampus, and cerebellum. Results suggest excess fluoride intake modulates a set of biological marker and promote neuroinflammatory and neurodegenerative condition in Wister rats. Therefore, we conclude that the accumulation of NaF alters the neurological function which leads to neurodegenerative disorders.

Chemical Aspects of Human and Environmental Overload with Fluorine

Over the last 100-120 years, due to the ever-increasing importance of fluorine-containing compounds in modern technology and daily life, the explosive development of the fluorochemical industry led to an enormous increase of emission of fluoride ions into the biosphere. This made it more and more important to understand the biological activities, metabolism, degradation, and possible environmental hazards of such substances. This comprehensive and critical review focuses on the effects of fluoride ions and organofluorine compounds (mainly pharmaceuticals and agrochemicals) on human health and the environment. To give a better overview, various connected topics are also discussed: reasons and trends of the advance of fluorine-containing pharmaceuticals and agrochemicals, metabolism of fluorinated drugs, withdrawn fluorinated drugs, natural sources of organic and inorganic fluorine compounds in the environment (including the biosphere), sources of fluoride intake, and finally biomarkers of fluoride exposure.

Apoptotic and Degenerative Changes in the Enteric Nervous System Following Exposure to Fluoride During Pre- and Post-natal Periods

Children born in fluorosis endemic areas usually suffer from gastrointestinal complications and are unable to attain normal growth as per their age group. The enteric nervous system (ENS) controls gut movement and functions. It is highly vulnerable to any ingested toxins. Based on observations, it was hypothesized that fluoride exposure during pregnancy and lactation might induce ENS developmental defects. The aim of this study is to investigate the effects of fluoride exposure during pregnancy and lactation on ENS of the first-generation rat pups. After confirmation of pregnancy, female rats were divided into 3 groups and kept on normal water (group 1), 50 ppm of fluoride (group 2), and 100 ppm of fluoride (group 3). The fluoride exposure started at the start of pregnancy and continued until lactation. On the 21st post-natal day, the pups were euthanized and the gut tissue and blood were harvested and subjected to fluoride measurement, oxidative stress estimation, histopathological and ultrastructural analysis, TUNEL, and immunofluorescence. The quantitative expressional analysis of embryonic lethal abnormal vision-like 4 (ELAVL4) (a pan-neuronal marker) and glial fibrillary acidic protein (GFAP) (a glial cell marker) genes was performed by RT-qPCR. An increase in oxidative stress, subcellular and cellular injuries, and apoptosis in enteric neuronal, glial, and epithelial cells was observed in the distal colon of the first-generation pups. Ganglionic degeneration, reduced expression of HuC/D and GFAP, altered colon muscle layer thickness, and tissue edema were observed in the fluoride-treated groups compared with the control. Fluoride exposure during prenatal and lactation period leads to subcellular and cellular injuries due to increased oxidative stress and apoptosis in the ENS. The reduction in the number of neurons and glia due to increased apoptosis may cause alterations in ENS development.

Global Proteomic Profile Integrated to Quantitative and Morphometric Assessment of Enteric Neurons: Investigation of the Mechanisms Involved in the Toxicity Induced by Acute Fluoride Exposure in the Duodenum

The enteric nervous system is responsible for controlling the gastrointestinal tract (GIT) functions. Enteric neuropathies are highly correlated to the development of several intestinal disturbances. Fluoride (F) is extensively applied for dental health improvement and its ingestion can promote systemic toxicity with mild to severe GIT symptomatology and neurotoxicity. Although F harmful effects have been published, there is no information regarding noxiousness of a high acute F exposure (25 mg F/kg) on enteric neurons and levels of expression of intestinal proteins in the duodenum. Quantitative proteomics of the duodenum wall associated to morphometric and quantitative analysis of enteric neurons displayed F effects of a high acute exposure. F-induced myenteric neuroplasticity was characterized by a decrease in the density of nitrergic neurons and morphometric alterations in the general populations of neurons, nitrergic neurons, and substance P varicosities. Proteomics demonstrated F-induced alterations in levels of expression of 356 proteins correlated to striated muscle cell differentiation; generation of precursor metabolites and energy; NADH and glutathione metabolic process and purine ribonucleoside triphosphate biosynthesis. The neurochemical role of several intestinal proteins was discussed specially related to the modulation of enteric neuroplasticity. The results provide a new perspective on cell signaling pathways of gastrointestinal symptomatology promoted by acute F toxicity.

Dual-channel ratiometric recognition of Al3+ and F- ions through an ESIPT-ESICT signalling mechanism

An optical probe 1 has been synthesized comprising naphthalimide unit conjugated with Schiff base, exhibiting excited state intramolecular proton transfer and intramolecular charge transfer as a potential sensor for Al³⁺ and F^- ions using standard spectroscopic techniques. The probe 1 exhibited local and charge-transfer excitation at 340 nm and 460 nm, respectively. On excitation at 460 nm, probe 1 displayed two emission bands at 510 nm and 610 nm, accompanied by Stokes' shift of 50 nm and 150 nm, respectively. The solvatochromic effect and theoretical calculation depicted that the representative emissions resulted from the ESICT/ESIPT phenomenon. Upon addition of Al³⁺ ions, the charge transfer excitation at 460 nm was enhanced ratiometrically to local excitation at 340 nm and showed a color change from orange to yellow. Similarily, probe 1.Al³⁺ displayed emission enhancement at 540 nm in H₂O/CH₃CN (1:9; v/v) and showed a color change from yellow to blue-green emission. Following the detection of Al³⁺ ions, hydrolysis of probe 1 to its reacting precursors was observed. The detection of Al³⁺ ions was also demonstrated in surfactant-containing water. The limit of detection (LOD) of probe 1 (H₂O/CH₃CN (1:9; v/v)) towards Al³⁺ ions was measured to be 3.2 × 10^-8 M. The probe 1 displayed a ratiometric absorption response towards F^- ions with a new peak at 570 nm and showed a color change from orange to purple. The probe 1.F^- displayed a decrease in emission at 635 nm. The LOD of probe 1 (CH₃CN) towards F^- ions was measured to be 7.5 × 10^-7 M.

Fluoride exposure during pregnancy and lactation triggers oxidative stress and molecular changes in hippocampus of offspring rats

Long-term exposure to high concentrations of fluoride (F) can damage mineralized and soft tissues such as bones, liver, kidney, intestine, and nervous system of adult rats. The high permeability of the blood-brain barrier and placenta to F during pregnancy and lactation may be critical to neurological development. Therefore, this study aimed to investigate the effects of F exposure during pregnancy and lactation on molecular processes and oxidative biochemistry of offspring rats' hippocampus. Pregnant Wistar rats were randomly assigned into 3 groups in accordance with the drinking water received: G1 - deionized water (control); G2 - 10 mg/L of F and G3 - 50 mg/L of F. The exposure to fluoridated water began on the first day of pregnancy and lasted until the 21^st day of breastfeeding (when the offspring rats were weaned). Blood plasma samples of the offspring rats were collected to determine F levels. Hippocampi samples were collected for oxidative biochemistry analyses through antioxidant capacity against peroxyl (ACAP), lipid peroxidation (LPO), and nitrite (NO₂^-) levels. Also, brain-derived neurotrophic factor (BDNF) gene expression (RT-qPCR) and proteomic profile analyses were performed. The results showed that exposure to both F concentrations during pregnancy and lactation increased the F bioavailability, triggered redox imbalance featured by a decrease of ACAP, increase of LPO and NO₂^- levels, BDNF overexpression and changes in the hippocampus proteome. These findings raise novel questions regarding potential repercussions on the hippocampus structure and functioning in the different cognitive domains.

Aluminum-Induced Toxicity in Salivary Glands of Mice After Long-term Exposure: Insights into the Redox State and Morphological Analyses

Several studies indicate aluminum (Al) as a potent toxicant, mainly related to central nervous system disorders. However, investigations about the Al effects over salivary glands are still scarce. In this way, the present study aimed to investigate whether the Al chloride (AlCl₃) is able of triggering oxidative stress in parotid and submandibular glands of mice and also, if any morphological impairment is observed. For this, twenty mice were divided into two groups: Exposed group (EG), which received 18.5 mg/kg of AlCl₃ by intragastric gavage for 60 days and control group (CG), which received distilled water by intragastric gavage during the same period of time. After that, levels of reduced glutathione (GSH) and malonaldehyde (MDA) were analyzed and we performed morphological analyses by evaluating the area of parenchyma, stroma, acini, and ducts in both glands. Statistical analyses were performed by Student's t test and two-way ANOVA, adopting p < 0.05. No abnormal body weight was observed and data indicates that although both major salivary glands are susceptible to Al-induced oxidative stress, by increasing MDA and reducing GSH, only submandibular glands decreased the parenchyma and increased stroma area. Moreover, the submandibular glands showed smaller total area of acini and higher total area of ducts, in comparison with the control group. Notably, AlCl₃ induces oxidative stress in both glands, however, submandibular glands showed to be more susceptible to Al effects than parotid glands. Our study gives evidences about Al toxicity in parotid and submandibular glands and claims for new investigations to understand more mechanisms of Al-induced toxicity.

Water Quality for Cattle: Metalloid and Metal Contamination of Water

Water is the most important nutrient for rangeland livestock. However, competition with municipalities, industry, and other water users often results in grazing livestock being forced to use water supplies that are less than perfect. Surface water in western rangleands are often contaminated by mineral extraction, irrigation runoff and other human activities. Mineral contaminants in drinking water are additive with similar contaminants in feedstuffs. The goal of this article is to provide producers and veterinarians with the basic background to make informed decisions about whether a given water supply is "safe" for livestock.

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

Introduction:

Curcumin, a yellow-pigment, found in the popular Indian spice turmeric (Curcuma longa), poses pharmaceutical applications due to its anti-inflammatory, antioxidant, and chemoprotective properties. Excessive fluoride causes fluorosis leading to neurodegeneration and associated behavioral deficits, particularly in children. This study aimed at investigating the neuroprotective ability of curcumin on sodium fluoride (NaF)-related alterations of acetylcholine, catecholamines, histological changes in hippocampus and behavior of rats exposed to NaF during pre- and post-natal period.

Methods:

Pregnant albino Wistar rats were chosen and divided into four groups. The experimental period lasted 53 days (i.e. the gestational period of 23 days and post-gestational period of 30 days), at which the control group received normal tap water, the experimental group received NaF (20 ppm/kg bw) through drinking water, and the protective groups received curcumin (10 mg and 20mg/kg bw) by gavage and NaF (20 ppm/kg bw) through drinking water. Behavioral study (open field test) was done using postnatal pups aged 21 and 30 days. The brains of postnatal pups aged 1, 7, 14, 21, and 30 days were collected and used for biochemical analysis and those of pups aged 14, 21, and 30 days were used for histopathological analysis.

Results:

NaF-exposed rats showed a significant (P<0.05) decrease in body weight, brain weight, and behavioral activities, which were significantly reversed with curcumin treatment. The levels of epinephrine significantly (P<0.05) increased, whereas norepinephrine, dopamine and acetylcholine levels declined in NaF-treated group compared with the control group, which were significantly (P<0.05) reversed after treatment by curcumin (10 mg/kg bw and 20 mg/kg bw) along with NaF. The histological alterations, including shrinkage of neurons and nissal substances were observed in the hippocampus of NaF-treated pups that the control pups, whereas co-treatment with curcumin and NaF showed ameliorative effects and controlled the histological alterations.

Conclusion:

The results showed the neuroprotective effect of curcumin on behavior, neurotransmitter levels, and histological changes in the hippocampus against NaF-induced neurotoxicity in developing rat pups.

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.

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.

Cardiovascular dysfunction and oxidative stress following human contamination by fluoride along with environmental xenobiotics (Cd & Pb) in the phosphate treatment area of Togo, West Africa

In Togo, the phosphate ore mill discharges waste containing xenobiotics like cadmium, lead and fluoride. If the role of heavy metals in the appearance of pathologies is known, the role of fluoride remains to be studied alongside xenobiotics. This study tested the hypothesis that the toxicity of fluoride contributes, along with heavy metals, to physiological dysfunction. In this process, we have studied the variation in the parameters of cardiovascular functioning, depending on the level of human contamination by fluoride and xenobiotics. The concentration of Cd and Pb in blood samples were determined by AAS and fluoride by titanium-chloride method. Lipid peroxidation, the total antioxidant potential of collected blood samples and the parameters of cardiovascular dysfunction were also measured. Cd, Pb and F contents and lipid peroxidation were found to be significantly elevated in polluted areas than control zone as well as total cholesterol, LDL and triglyceride. HDL and antioxidant potential of blood decreased in the polluted areas. Correlation tests showed that fluoride levels are related to variations in the bio-indicators of high blood pressure and oxidative stress (R varied from 0.354 to 0.907). Togo phosphate treatment leads to human contamination with fluoride, along with Cd and Pb, increasing the risk of cardiovascular dysfunction and oxidative stress.

Fluoride exposure and kidney and liver function among adolescents in the United States: NHANES, 2013-2016

BACKGROUND

Hepato- and nephrotoxicity of fluoride have been demonstrated in animals, but few studies have examined potential effects in humans. This population-based study examines the relationship between chronic low-level fluoride exposure and kidney and liver function among United States (U.S.) adolescents. This study aimed to evaluate whether greater fluoride exposure is associated with altered kidney and liver parameters among U.S. youth.

METHODS

This cross-sectional study utilized data from the National Health and Nutrition Examination Survey (2013-2016). We analyzed data from 1983 and 1742 adolescents who had plasma and water fluoride measures respectively and did not have kidney disease. Fluoride was measured in plasma and household tap water. Kidney parameters included estimated glomerular filtration rate (calculated by the original Schwartz formula), serum uric acid, and the urinary albumin to creatinine ratio. Liver parameters were assessed in serum and included alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, blood urea nitrogen, gamma-glutamyl transferase, and albumin. Survey-weighted linear regression examined relationships between fluoride exposure and kidney and liver parameters after covariate adjustment. A Holm-Bonferroni correction accounted for multiple comparisons.

RESULTS

The average age of adolescents was 15.4 years. Median water and plasma fluoride concentrations were 0.48 mg/L and 0.33 μmol/L respectively. A 1 μmol/L increase in plasma fluoride was associated with a 10.36 mL/min/1.73 m2 lower estimated glomerular filtration rate (95% CI: -17.50, -3.22; p = 0.05), a 0.29 mg/dL higher serum uric acid concentration (95% CI: 0.09, 0.50; p = 0.05), and a 1.29 mg/dL lower blood urea nitrogen concentration (95%CI: -1.87, -0.70; p < 0.001). A 1 mg/L increase in water fluoride was associated with a 0.93 mg/dL lower blood urea nitrogen concentration (95% CI: -1.44, -0.42; p = 0.007).

CONCLUSIONS

Fluoride exposure may contribute to complex changes in kidney and liver related parameters among U.S. adolescents. As the study is cross-sectional, reverse causality cannot be ruled out; therefore, altered kidney and/or liver function may impact bodily fluoride absorption and metabolic processes.

Synergistic oxidative impact of aluminum chloride and sodium fluoride exposure during early stages of brain development in the rat

Aluminum is widely used in industry and in cooking utensils, especially in countries with low economic and social standards. Fluoride is also used in industry, a major component of toothpaste and is added to the drinking water in many countries to fight teeth decay and cavities. Consequently, the coexistence of aluminum and fluoride is highly probable. Growing evidence indicates that environmental pollutants during the early stages of embryonic development may reprogram the offspring's brain capabilities to encounter oxidative stress during the rest of their postnatal life. This study investigated the impact of sodium fluoride (NaF, 0.15 g/L) and aluminum chloride (AlCl₃, 500 mg/L) added, individually or in combination, to the deionized drinking water starting from day 6 of gestation until just after weaning, or until the age of 70 days postnatal life. A significant decline was observed in tissue contents of vitamin C, reduced glutathione, GSH/GSSH ratio, and the total protein, as well as in the activities of Na⁺/K⁺-ATPase and superoxide dismutase (SOD) in almost all cases. On the contrary, lipid peroxidation and NO, as total nitrate, exhibited a significant increase in comparison with the corresponding control. Based on the present results, administration of Al and NaF, alone or in combination abated the quenching effects of the antioxidant system and induced oxidative stress in most brain regions under investigation. In conclusion, aluminum and fluoride are very noxious environmental pollutants that interfere with the proper functions of the brain neurons and their combination together aggravates their hazard.

Exploring the role of excess fluoride in chronic kidney disease: A review

This review covers nearly 100 years of studies on the toxicity of fluoride on human and animal kidneys. These studies reveal that there are direct adverse effects on the kidneys by excess fluoride, leading to kidney damage and dysfunction. With the exception of the pineal gland, the kidney is exposed to higher concentrations of fluoride than all other soft tissues. Therefore, exposure to higher concentrations of fluoride could contribute to kidney damage, ultimately leading to chronic kidney disease (CKD). Among major adverse effects on the kidneys from excessive consumption of fluoride are immediate effects on the tubular area of the kidneys, inhibiting the tubular reabsorption; changes in urinary ion excretion by the kidneys disruption of collagen biosynthesis in the body, causing damages to the kidneys and other organs; and inhibition of kidney enzymes, affecting the functioning of enzyme pathways. This review proposes that there is a direct correlation between CKD and the consumption of excess amounts of fluoride. Studies particularly show immediate adverse effects on the tubular area of human and animal kidneys leading to CKD due to the consumption of excess fluoride. Therefore, it is very important to conduct more investigations on toxicity studies of excess fluoride on the human kidney, including experiments using human kidney enzymes, to study more in depth the impact of excess fluoride on the human kidney. Further, the interference of excess fluoride on collagen synthesis in human body and its effect on human kidney should also be further investigated.

The Fluoride Debate: The Pros and Cons of Fluoridation

Fluoride is one of the most abundant elements found in nature. Water is the major dietary source of fluoride. The only known association with low fluoride intake is the risk of dental caries. Initially, fluoride was considered beneficial when given systemically during tooth development, but later research has shown the importance and the advantages of its topical effects in the prevention or treatment of dental caries and tooth decay. Water fluoridation was once heralded as one of the best public health achievements in the twentieth century. Since this practice is not feasible or cost effective in many regions, especially rural areas, researchers and policy makers have explored other methods of introducing fluoride to the general population such as adding fluoride to milk and table salt. Lately, major concerns about excessive fluoride intake and related toxicity were raised worldwide, leading several countries to ban fluoridation. Health-care professionals and the public need guidance regarding the debate around fluoridation. This paper reviews the different aspects of fluoridation, their effectiveness in dental caries prevention and their risks. It was performed in the PubMed and the Google Scholar databases in January 2018 without limitation as to the publication period.

Excited state proton transfer (ESIPT) based molecular probe to sense F− and CN− anions through a fluorescence “turn-on” response

Dual anion sensing through an efficient thiazole based phenolic Schiff base containing molecular probe by means of fluorescence “turn-on” response.

Identification of the Al-binding proteins that account for aluminum neurotoxicity and transport in vivo

Studies have shown that aluminum (Al) is the most abundant neurotoxic element on Earth, and is implicated in the pathogenesis of Alzheimer's disease (AD). However, the mechanisms underlying Al-induced neurotoxicity are still largely elusive. Based on affinity analyses with Al and LC-LTQ-MS, we have found that serum albumin, brain CK-B and 14-3-3ζ protein have a high affinity for Al³⁺, and albumin has a much stronger affinity for Al than transferrin. The normal activity of CK-B, and physiological combination of 14-3-3ζ with tau can be severely perturbed by Al. We anticipate that our assay will provide a new focus concerning the mechanism underlying Al-induced neurotoxicity, and aid the design of strategies to prevent AD and other human diseases related to Al overload.

Protective effect of resveratrol against neuronal damage through oxidative stress in cerebral hemisphere of aluminum and fluoride treated rats

Aluminum has no defined biological function and it is potentially involved in the pathogenesis of neurodegenerative disorders. Furthermore, the presence of fluoride causes more aluminum to accumulate in the brain, resulting in increased neuronal damage. In recent years, resveratrol through its ameliorative effects was found to be a neuroprotectant. This study reports the protective effects of resveratrol on combined aluminum and fluoride induced neuronal damage through oxidative stress in rats. Protective effects of resveratrol (30 mg/kg b.w) on markers of oxidative stress were determined in rats exposed to aluminum chloride (100 mg/kg b.w) along with sodium fluoride (10 mg/kg b.w) for 8 weeks. The results showed a statistically significant (p<0.05) increase in lipid peroxidation (LPx) as well as a significant (p<0.05) decrease in superoxide dismutase and catalase activity. Enlarged cells, neurofibrillary tangles, and vacuolar spaces showing oxidative stress in the cerebral cortex were also observed in hematoxylin and eosin stained sections in aluminum and fluoride treated rats. Administration of resveratrol along with aluminum + fluoride showed significant reversal of oxidative stress and neuronal damage in rats. Thus resveratrol potentially acts as a neuroprotectant against aluminum chloride + sodium fluoride induced neuronal damage through its anti-oxidant efficacy.

Sodium fluoride does not affect the working memory and number of pyramidal cells in rat medial prefrontal cortex

Fluoride is a chemical compound known to bring about fluorosis. It is thought to disrupt the central nervous system because of its ability to induce excitotoxicity and oxidative stress. Any damage of pyramidal cells in the prefrontal cortex would result in cognitive function and working memory regulation disorders. The present study aimed at investigating the effects of sodium fluoride (NaF) on the working memory and estimated total number of medial prefrontal cortex pyramidal cells of adult male rats. Thirty-two male Wistar rats were assigned into four groups, namely control and three treated groups receiving 5, 10 and 20 mg/kg BW, respectively, of oral NaF solution for 30 days. The working memory test was carried out using a Y-maze. The number of pyramidal cells in the medial prefrontal cortex was estimated using an unbiased stereological method. There was no significant difference among groups in the working memory and number of pyramidal neurons in the medial prefrontal cortex cells.

Effects of chronic ingestion of sodium fluoride on myocardium in a second generation of rats

Possible effects of long term exposure (6 months) to sodium fluoride (NaF) through drinking water on the morphology and biochemistry of myocardial tissue in second generation adult male rats were investigated. Wistar strain female and male rats were reared until the second generation of rats obtained, during which they were given 1, 10, 50 and 100 mg/L NaF in drinking water. Of the second generation, 28 male rats were divided into four groups and had the same treatment. All the second generation rats were sacrificed and autopsied at the end of the 6 months. In the samples of myocardial tissues, the levels of serum fluoride and the activities of principal antioxidant enzymes were determined, and a histopathological examination was conducted. Significant histopathological changes were found in the myocardial tissue of rats treated with 50 and 100 mg/L NaF. These were myocardial cell necrosis, extensive cytoplasmic vacuole formation, nucleus dissolution in myosits, swollen and clumped myocardial fibers, fibrillolysis, interstitial oedema, small hemorrhagic areas and hyperaemic vessels. Additionally, the increased activities of superoxide dismutase (SOD), glutathione peroxidase (GSH–Px), catalase (CAT) and thiobarbituric acid–reactive substance (TBARS) levels were observed in the myocardial tissues of rats treated with 10 and 50 mg/L NaF. On the other hand, the activities of SOD, GSH–Px, and CAT decreased, but the TBARS levels increased in the myocardial tissues of rats treated with 100 mg/L. The present results revealed that prolonged ingestion of fluoride through drinking water, particularly with high doses, induced significant histopathological and biochemical changes leading to myocardial tissue damage.

Drinking water quality and chronic kidney disease of unknown etiology (CKDu): synergic effects of fluoride, cadmium and hardness of water

High prevalence of chronic kidney disease of unknown etiology (CKDu) in some regions of the world is suspected mainly due to a toxin-mediated renal failure. We examined the incidence of CKDu and potable chemical water quality in a CKDu-affected region. This region has been identified as a high-risk zone for CKDu (location: latitude: 8.3500°-9.0000°, longitude: 80.3833°-81.3000°, North Central Province, NCP, Sri Lanka) by the World Health Organization (WHO). However, within this macro-region, small pockets of CKDu non-prevalence zones do exist; notably, the residents in those pockets consume spring water. Therefore, the drinking water quality of four areas, namely high-CKDu-prevalence areas (zone I), low-CKDu-prevalence area (zone II), the CKDu-free isolated pockets (zone III) and control areas (controls) were examined for F, Al, Cd, and As, and hardness and the statistical analysis were carried out to probe possible correlations among these parameters. The fluoride and hardness concentrations of water in zone III and control areas are much lower compared to zones I and II, and the water hardness is ~61 mg/L CaCO3. In zones I and II, the harness of drinking water is ~121-180 mg/L CaCO3; however, Al, Cd and As concentrations are almost comparable and below WHO recommendations. In most of the locations in zones I and II, the F concentration in drinking water is higher than the WHO recommendations. The peculiar distribution patterns of CKDu point to a synergic effect of trace elements in water for etiology of the disease.

Relationship Between Dental Fluorosis and Intelligence Quotient of School Going Children In and Around Lucknow District: A Cross-Sectional Study

BACKGROUND

Fluoridation of drinking water, despite being regarded as one of the top ten public health achievements of the twentieth century, has remained a much debated concept. Various studies on animals and aborted human fetuses have confirmed that excessive fluoride intake during infancy and early childhood, causes a number of irreversible structural and functional changes in the CNS leading to memory, learning and intellectual deficits.

AIM

To compare the IQ levels of school children of two different locations, having different fluoride levels in water, and to establish a relationship between fluoride levels, prevalence of fluorosis and its effect on IQ levels.

MATERIALS AND METHODS

A cross-sectional study was conducted among 429 children aged 6 - 12 years, selected by stratified random sampling from two different areas with different levels of fluoride in drinking water in and around Lucknow district. Dental fluorosis was measured using Dean's Fluorosis Index. Intelligence Quotient was measured using Raven's Coloured Progressive Matrices (1998 edition).

RESULTS

Majority of the fluorosis free children (76.3%) had an IQ grade 2 (definitely above the average). Majority of the children suffering from very mild and mild dental fluorosis were found to have IQ grade 3 (Intellectually average). Children with moderate cases of dental fluorosis were found to have IQ grade 4 (Definitely below average). Only 5 children with severe fluorosis were included in the study and they all were found to have an IQ grade 5. Hence, a trend of increase in the IQ grade (decrease in intellectual capacity) was observed indicating a strong correlation between fluorosis grade and IQ grade.

CONCLUSION

Findings of this study suggest that the overall IQ of the children exposed to high fluoride levels in drinking water and hence suffering from dental fluorosis were significantly lower than those of the low fluoride area.

The impact of aluminum, fluoride, and aluminum-fluoride complexes in drinking water on chronic kidney disease

It is suspected that drinking water containing fluoride and aluminum results in negative health effects especially on brain, liver, and kidney. In this investigation, the effect of F, Al, and AlFx complex on chronic kidney disease (CKD) was investigated. Mice were treated either with WHO recommended or slightly higher F and Al levels in drinking water. Treatment solutions contained 0.05-10.0 mg/L of F, 0.08-10.0 mg/L of Al, or 0.07-15 mg/L of AlFx, and the treatment period was 42 weeks. Blood urea level and creatinine levels were investigated as a measure of malfunction of kidneys. Histopathological evaluations of kidney tissues were carried out to assess the extent of damage that F, Al, and AlFx complex could cause. It was demonstrated that the treated drinking water containing F and Al with par with WHO or moderately above the WHO levels or AlFx in low level (0.07-15 mg/L) does not lead to CKD in mice.

Tannoid principles of Emblica officinalis renovate cognitive deficits and attenuate amyloid pathologies against aluminum chloride induced rat model of Alzheimer's disease

BACKGROUND/AIMS

Emblica officinalis is mentioned as a maharasayana in many Ayurvedic texts and promotes intelligence, memory, freedom from disease, longevity, and strength of the senses. The present study has been designed to explore the memory-enhancing effect of the tannoid principles of E. officinalis (EoT) at the biochemical, anatomical, behavioral, and molecular levels against aluminum chloride (AlCl3) induced Alzheimer's disease (AD) in rats. Aluminum is reported to have an important role in the etiology, pathogenesis, and development of AD.

METHODS

Male Wistar rats were divided into control, AlCl3 treated, AlCl3 and EoT (50, 100, and 200 mg/kg bw) co-treated, and EoT (200 mg/kg bw) alone treated groups. In control and experimental rats, behavior tests including water maze and open field test, estimation of aluminum, assay of acetylcholinesterase (AChE) activity, and expression of amyloidogenic proteins were performed.

RESULTS

Intraperitonial injection of AlCl3 (100 mg/kg bw) for 60 days significantly elevated the concentration of aluminum (Al), activity of AChE and protein expressions of amyloid precursor protein, A-beta1-42, beta-, and gamma-secretases as compared to control group in hippocampus and cortex. Co-administration of EoT orally to AlCl3 rats for 60 days significantly revert back the Al concentration, AChE activity, and A-beta synthesis-related molecules in the studied brain regions. The spatial learning, memory, and locomotor impairments observed in AlCl3 treated rats were significantly attenuated by EoT.

CONCLUSION

Therefore, EoT may be a promising therapy in ameliorating neurotoxicity of aluminum, however further studies are warranted to elucidate the exact mechanism of action of EoT.

Fluoride and aluminium disturb neuronal morphology, transport functions, cholinesterase, lysosomal and cell cycle activities

Fluoride and aluminium have been reported to cause severe alterations in the brain. However, their exact mechanisms of neurotoxic activities remain unknown.

AIM

This study was designed to investigate the role of fluoride and aluminium in neuronal transport, lysosomal, cell cycle protein and acetylcholinesterase activities.

METHOD

Adult Wistar rats were given low and high doses of fluoride, aluminium and a combination of both with the control group receiving distilled water for 30 days. Blood sera and brain homogenates were quantified for alkaline phosphatase (biomarker for neuronal transport) activities. Brain sections were stained with cresyl fast violet to detect neuronal cell damage. Histochemical demonstration of acetylcholinesterase (AChE) activity and the immunohistochemical detection of cell cycle protein (anti-cyclin D) and lysosomal protein (anti-cathepsin D) were done using the antigen retrieval method.

RESULT

Results showed severe histomorphologic alterations, dysregulation of membrane transport activities, inhibition of AChE activities and increased expression of lysosomal and cell cycle proteins.

CONCLUSION

These findings confirm that excessive fluoride and aluminium intake induces the progression of cell death which inhibit AChE activities and trigger the release of lysosomal and cell cycle proteins.

Novel indole based dual responsive "turn-on" chemosensor for fluoride ion detection

An efficient new dual channel chemosensor 2,3-bis((E)-(1H-indole-3-yl)methyleneamino)maleonitrile (DN) which exhibits selective sensing of F(-) ions in DMSO, was synthesized by a facile one step condensation reaction of indole-3-carboxaldehyde with diaminomaleonitrile. The probe DN was characterized by elemental analysis, (1)H, (13)C-NMR, ESI-MS and IR spectral techniques. Upon addition of F(-), DN induces remarkable changes in both absorption and fluorescence spectra on the basis of charge transfer mechanism. The receptor DN serves for highly selective, sensitive detection of F(-) without the interference of other relevant anions. The Job's plot analysis indicates the binding stoichiometry to be 1:1 (host/guest).

Fluoride concentrations in the pineal gland, brain and bone of goosander (Mergus merganser) and its prey in Odra River estuary in Poland

The aim of the study was to investigate fluoride concentrations in bone, brain and pineal gland of goosander Mergus merganser wintering in the Odra estuary (Poland) as well as in fish originating from its digestive tract. The fluoride concentrations were determined with potentiometric method. Medians of concentrations in goosander had the highest and the lowest values in pineal gland and brain (>760 and <190 mg/kg, respectively). Fluoride concentration in the pineal gland was significantly greater than in the bone and the brain of the duck. In fish, the fluoride concentration ranged from 37 to 640 mg/kg and significant correlation was revealed between the fluoride concentration and fish weight and length. Based on own results and data of other authors, a daily fluoride intake by the goosander in the Odra estuary was estimated at 15 mg. So high fluoride concentrations like in the duck have not been found in mammal brains.

A histological study of toxic effects of aluminium sulfate on rat hippocampus

Aluminium has toxic effects on many organ systems of the human body. Aluminium toxicity also is a factor in many neurodegenerative diseases. We investigated changes in numbers of hippocampal neurons in rats exposed to aluminium using an optical fractionator and we investigated aluminium-induced apoptosis using the transferase mediated dUTP nick end labeling (TUNEL) assay. Twenty-four female rats were divided equally into control, sham and aluminium-exposed groups. The control group received no treatment. The two treatment groups were injected intraperitoneally with 1 ml 0.9% saline without (sham) and with 3 mg/ml aluminium sulfate every day for two weeks. Following the treatments, the brains were removed, the left hemisphere was used for hippocampal neuron counting using an optical fractionator and the right hemisphere was investigated using hippocampal TUNEL assay to determine the apoptotic index. The number of neurons in the stratum pyramidale of the hippocampus was significantly less in the aluminium group than in the control and sham groups; there was no significant difference between the control and sham groups. The apoptotic index also was significantly higher in the aluminium group than in the other two groups. We quantified the toxic effects of aluminium on the rat hippocampus and determined that apoptosis was the mechanism of aluminium-induced neuron death in the hippocampus.

Aluminum-induced entropy in biological systems: implications for neurological disease

Over the last 200 years, mining, smelting, and refining of aluminum (Al) in various forms have increasingly exposed living species to this naturally abundant metal. Because of its prevalence in the earth's crust, prior to its recent uses it was regarded as inert and therefore harmless. However, Al is invariably toxic to living systems and has no known beneficial role in any biological systems. Humans are increasingly exposed to Al from food, water, medicinals, vaccines, and cosmetics, as well as from industrial occupational exposure. Al disrupts biological self-ordering, energy transduction, and signaling systems, thus increasing biosemiotic entropy. Beginning with the biophysics of water, disruption progresses through the macromolecules that are crucial to living processes (DNAs, RNAs, proteoglycans, and proteins). It injures cells, circuits, and subsystems and can cause catastrophic failures ending in death. Al forms toxic complexes with other elements, such as fluorine, and interacts negatively with mercury, lead, and glyphosate. Al negatively impacts the central nervous system in all species that have been studied, including humans. Because of the global impacts of Al on water dynamics and biosemiotic systems, CNS disorders in humans are sensitive indicators of the Al toxicants to which we are being exposed.

Zinc modulates aluminium-induced oxidative stress and cellular injury in rat brain

Dysregulation of metal homeostasis has been perceived as one of the key factors in the progression of neurodegeneration. Aluminium (Al) has been considered as a major risk factor, which is linked to several neurodegenerative diseases, especially Alzheimer's disease, whereas zinc (Zn) has been reported as a vital dietary element, which regulates a number of physiological processes in central nervous system. The present study was conducted to explore the protective potential of zinc, if any, in ameliorating neurotoxicity induced by aluminium. Male Sprague Dawley rats received either aluminium chloride (AlCl3) orally (100 mg kg(-1) b.wt. per day), zinc sulphate (ZnSO4) at a dose level of 227 mg L(-1) in drinking water or combined treatment of aluminium and zinc for 8 weeks. Aluminium treatment significantly elevated the levels of lipid peroxidation and reactive oxygen species as well as the activities of catalase, superoxide dismutase and glutathione reductase, which however were decreased following Zn co-treatment of Al-treated rats. In contrast, Al treatment decreased the activities of glutathione-S-transferase as well as the levels of reduced glutathione, oxidised glutathione and total glutathione, but co-administration of Zn to Al-treated animals increased these levels. Furthermore, Al treatment caused a significant increase in the levels of Fe and Mn as well as of Al but decreased the Zn and metallothionein levels. In the Zn-supplemented animals, the levels of Al, Fe, Mn were found to be significantly decreased, whereas the levels of metallothionein as well as Zn were increased. Moreover, histopathological alterations such as vacuolization and loss of Purkinje cells were also evident following Al treatment, which showed improvement upon Zn supplementation. Therefore, zinc has the potential to alleviate aluminium-induced neurodegeneration.

A new perspective on metals and other contaminants in fluoridation chemicals

BACKGROUND

Fluoride additives contain metal contaminants that must be diluted to meet drinking water regulations. However, each raw additive batch supplied to water facilities does not come labeled with concentrations per contaminant. This omission distorts exposure profiles and the risks associated with accidents and routine use.

OBJECTIVES

This study provides an independent determination of the metal content of raw fluoride products.

METHODS

Metal concentrations were analyzed in three hydrofluorosilicic acid (HFS) and four sodium fluoride (NaF) samples using inductively coupled plasma-atomic emission spectrometry. Arsenic levels were confirmed using graphite furnace atomic absorption analysis.

RESULTS

Results show that metal content varies with batch, and all HFS samples contained arsenic (4·9-56·0 ppm) or arsenic in addition to lead (10·3 ppm). Two NaF samples contained barium (13·3-18·0 ppm) instead. All HFS (212-415 ppm) and NaF (3312-3630 ppm) additives contained a surprising amount of aluminum.

CONCLUSIONS

Such contaminant content creates a regulatory blind spot that jeopardizes any safe use of fluoride additives.

Developmental fluoride neurotoxicity: a systematic review and meta-analysis

BACKGROUND

Although fluoride may cause neurotoxicity in animal models and acute fluoride poisoning causes neurotoxicity in adults, very little is known of its effects on children's neurodevelopment.

OBJECTIVE

We performed a systematic review and meta-analysis of published studies to investigate the effects of increased fluoride exposure and delayed neurobehavioral development.

METHODS

We searched the MEDLINE, EMBASE, Water Resources Abstracts, and TOXNET databases through 2011 for eligible studies. We also searched the China National Knowledge Infrastructure (CNKI) database, because many studies on fluoride neurotoxicity have been published in Chinese journals only. In total, we identified 27 eligible epidemiological studies with high and reference exposures, end points of IQ scores, or related cognitive function measures with means and variances for the two exposure groups. Using random-effects models, we estimated the standardized mean difference between exposed and reference groups across all studies. We conducted sensitivity analyses restricted to studies using the same outcome assessment and having drinking-water fluoride as the only exposure. We performed the Cochran test for heterogeneity between studies, Begg's funnel plot, and Egger test to assess publication bias, and conducted meta-regressions to explore sources of variation in mean differences among the studies.

RESULTS

The standardized weighted mean difference in IQ score between exposed and reference populations was -0.45 (95% confidence interval: -0.56, -0.35) using a random-effects model. Thus, children in high-fluoride areas had significantly lower IQ scores than those who lived in low-fluoride areas. Subgroup and sensitivity analyses also indicated inverse associations, although the substantial heterogeneity did not appear to decrease.

CONCLUSIONS

The results support the possibility of an adverse effect of high fluoride exposure on children's neurodevelopment. Future research should include detailed individual-level information on prenatal exposure, neurobehavioral performance, and covariates for adjustment.