Fluoride exposure changed the structure and the expressions of Y chromosome related genes in testes of mice

Evaluation of fluoride exposure using disability-adjusted life years and health risk assessment in south-western Iran: A novel Monte Carlo simulation

Consumption of fluoride-contaminated water is a worldwide concern, especially in developing countries, including Iran. However, there are restricted studies of non-single-value health risk assessment and the disease burden regarding fluoride intake nationwide. Prolonged exposure to excessive fluoride has been linked to adverse health effects such as dental and skeletal fluorosis. This can lead to under-mineralization of hard tissues, causing aesthetic concerns for teeth and changes in bone structure, increasing the risk of fractures. As such, we aimed to implement probability-based frameworks using Monte Carlo methods to explore the potential adverse effects of fluoride via the ingestion route. This platform consists of two sectors: 1) health risk assessment of various age categories coupled with a variance decomposition technique to measure the contributions of predictor variables in the outcome of the health risk model, and 2) implementing Monte Carlo methods in dose-response curves to explore the fluoride-induced burden of diseases of dental fluorosis and skeletal fractures in terms of disability-adjusted life years (DALYs). For this purpose, total water samples of 8053 (N=8053) from 57 sites were analyzed in Fars and Bushehr Provinces. The mean fluoride concentrations were 0.75 mg/L and 1.09 mg/L, with maximum fluoride contents of 6.5 mg/L and 3.22 mg/L for the Fars and Bushehr provinces, respectively. The hazard quotient of the 95th percentile (HQ>1) revealed that all infants and children in the study area were potentially vulnerable to over-receiving fluoride. Sobol' sensitivity analysis indices, including first-order, second-order, and total order, disclosed that fluoride concentration (Cw), ingestion rate (IRw), and their mutual interactions were the most influential factors in the health risk model. DALYs rate of dental fluorosis was as high as 981.45 (uncertainty interval: UI 95 % 353.23-1618.40) in Lamerd, and maximum DALYs of skeletal fractures occurred in Mohr 71.61(49.75-92.71), in Fars Province, indicated severe dental fluorosis but mild hazard regarding fractures. Residents of the Tang-e Eram in Bushehr Province with a DALYs rate of 3609.40 (1296.68-5993.73) for dental fluorosis and a DALYs rate of 284.67 (199.11-367.99) for skeletal fractures were the most potentially endangered population. By evaluating the outputs of the DALYs model, the gap in scenarios of central tendency exposure and reasonable maximum exposure highlights the role of food source intake in over-receiving fluoride. This research insists on implementing defluoridation programs in fluoride-endemic zones to combat the undesirable effects of fluoride. The global measures presented in this research aim to address the root causes of contamination and help policymakers and authorities mitigate fluoride's harmful impacts on the environment and public health.

Prolonged fluoride exposure induces spatial-memory deficit and hippocampal dysfunction by inhibiting small heat shock protein 22 in mice

Millions of residents in areas with high-fluoride drinking water supply ingest excessive levels of fluoride for long periods. This study investigated the mechanisms and impacts of lifelong exposure to naturally occurring moderate-high-fluoride drinking water on spatial-memory function by studying mice in controlled experiments. Spatial-memory deficits and disorders of hippocampal neuronal electrical activity were observed in mice exposed to 25-ppm or 50-ppm-fluoride drinking water for 56 weeks, but not in adult or old mice exposed to 50 ppm fluoride for 12 weeks. Ultrastructural analysis showed severely damaged hippocampal mitochondria, evidenced by reduced mitochondrial membrane potential and ATP content. Mitochondrial biogenesis was impaired in fluoride-exposed mice, manifesting as a significantly reduced mtDNA content, mtDNA-encoded subunits mtND6 and mtCO1, and respiratory complex activities. Fluoride reduced expression of Hsp22, a beneficial mediator of mitochondrial homeostasis, and decreased levels of signaling for the PGC-1α/TFAM pathway-which regulates mitochondrial biogenesis-and the NF-κβ/STAT3 pathway-which regulates mitochondrial respiratory chain enzyme activity. Hippocampus-specific Hsp22-overexpression improved fluoride-induced spatial-memory deficits by activating the PGC-1α/TFAM and STAT3 signaling pathways, while Hsp22-silencing aggravated the deficits by inhibiting both pathways. Downregulation of Hsp22 plays a vital role in fluoride-induced spatial-memory deficits by impacting mtDNA-encoding subsets and mitochondrial respiratory chain enzyme activity.

Exposure to Fluoride From in Utero to Puberty Alters Gonadal Structure and Steroid Hormone Expression in Offspring Rats

The reproductive toxicity of fluoride has been proven by a large number of studies. While the underlying mechanism of reproductive toxicity during pregnancy is still unclear. Hence, in this study, we investigated the effects of fluoride exposure on ovarian and testicular steroid hormone synthesis in young and adult rat offspring. We established a model of fluoride-exposed rat pups from in utero to puberty to explore the mechanisms of fluoride impacts on reproductive toxicity in the offspring. The results showed that NaF exposure did not affect the 3 weeks of age offspring. Whereas the body weight in both sexes significantly decreased, and the ovarian and testicular tissue structures were damaged at 11 weeks of age. In females, the total number of secondary follicles and mature follicles were significantly reduced after NaF exposure. Moreover, estradiol (E2) and follicle-stimulating hormone (FSH) levels in the females were significantly reduced in the 100 mg/L NaF exposure group. In males, the sperm viability and testosterone (T) were significantly decreased in the NaF exposure groups. Additionally, during steroidogenesis in ovaries and testes, fluoride remarkably decreased the expression levels of genes and proteins, including acute regulatory protein (StAR), 3β-hydroxysteroid dehydrogenase (3β-HSD), cytochrome P450 17a-hydroxylase (CYP17A1), and cholesterol side-chain cleavage enzyme (CYP11A1), while the mRNA levels of 17β-hydroxysteroid dehydrogenase (17β-HSD) decreased only in the testes. These results indicated that fluoride exposure disrupted the steroid hormone balance by changing several important steroidogenic-related genes associated with the development of the gonads, and damage the normal structure of the gonads in rat offspring.

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

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

Fluoride subacute testicular toxicity in Wistar rats: Benchmark dose analysis for the redox parameters, essential elements and DNA damage

Excessive fluoride (F^-) levels in the environment could induce different pathological changes, including comorbidities in reproductive functions. Hence, the aim of the present in vivo study was to explore F^- subacute toxicity mechanisms via Benchmark dose (BMD) methodology on rat's testicles. The experiment was conducted on thirty male Wistar rats for 28 days, divided into six groups (n = 5): 1) Control (tap water); 2) 10 mg/L F^-; 3) 25 mg/L F^-; 4) 50 mg/L F^-; 5) 100 mg/L F^-; 6) 150 mg/L F^-. Testicles were dissected out and processed for the determination of F^- tissue concentrations, redox status parameters, essential elements level, and DNA damage. PROASTweb 70.1 software was used for determination of external and internal dose-response relationship. The results confirmed a significant increase in superoxide anion (O₂^.-), total oxidative status (TOS), copper (Cu), zinc (Zn), iron (Fe), DNA damage levels, and decrease in superoxide dismutase activity (SOD1) and total thiol (SH) groups. The dose-dependent changes were confirmed for SOD1 activity and DNA damage. The most sensitive parameters were SOD1 activity and DNA damage with the lowest BMDLs 0.1 μg F^-/kg b. w. Since human and animal populations are daily and frequently unconsciously exposed to F^-, this dose-response study is valuable for further research regarding the F^- health risk assessment.

Gestational exposure to fluoride impairs cognition in C57 BL/6 J male offspring mice via the p-Creb1-BDNF-TrkB signaling pathway

Fluoride exposure has a detrimental effect on neurodevelopment, while the underlying processes remain unknown. The goal of this study was to investigate how fluoride impacts synaptogenesis, with a focus on the phosphorylation of Creb1 (p-Creb1)-brain-derived neurotrophic factor (BDNF)-tyrosine kinase B (TrkB) pathway. We generated a sodium fluoride (NaF) model using C57 BL/6 J mice exposed to 100 mg/L NaF from gestation day 1 (GD1) to GD20. It was identified that NaF treatment impaired the learning and memory abilities of the male offspring, reduced dendritic spine density, lowered postsynaptic density protein-95 (PSD95) and synaptophysin (SYN) expression in the male offspring's hippocampus, indicating that synaptic dysfunction may contribute to the cognitive impairment in the NaF model. In addition, in vivo experiment demonstrated that the protein abundance of BDNF and the ratio of p-Creb1 to Creb1 were increased in the hippocampus of NaF offspring, while the level of TrkB was reduced. Similarly, PC12 cells treated with NaF also showed increased expression of BDNF and decreased levels of TrkB. Notably, fluoride treatment increased p-Creb1 in vitro, while inhibiting p-Creb1 by 66615 significantly alleviated the effects of NaF exposure, indicating that p-Creb1 exerts a regulatory function in the BDNF-TrkB pathway. Altogether, these results demonstrated prenatal fluoride exposure triggered neurotoxicity in the male offspring hippocampus was linked to synaptogenesis damage caused by activating p-Creb1, which disrupted the BDNF-TrkB pathway.

Vitamin C and E supplementation can ameliorate NaF mediated testicular and spermatozoal DNA damages in adult Wistar rats

OBJECTIVE

Present study was designed to explore the efficacy of vitamin C and E (VC&VE) against fluoride mediated testicular, epididymal and spermatozoal anomalies.

MATERIALS AND METHODS

Thirty two adult Wistar rats were divided into four groups. Group-I was control; Group-II received sodium fluoride (NaF) at 15 mg/kg/day dose; Group-III was provided with VC (200 mg/kg/day) and VE (400 mg/kg/day) plus NaF; Group-IV received only VC&VE. Structural integrity and oxidative stress markers (superoxide dismutase, catalase, malondialdehyde and protein carbonyl) of testis and epididymis were assessed. Spermatozoal parameters (count, motility, viability and hypo-osmotic swelling) were evaluated. Testicular functional maker enzymes (acid phosphatase, alkaline phosphatase and lactate dehydrogenase) were also assessed. Integrity of testicular and spermatozoal DNA were evaluated. Testicular fluoride content was measured.

RESULT

Fluoride induced structural changes and alterations of oxidative stress markers were observed in testis and epididymis. Spermatozoal potentials were altered and reduced activities of testicular functional marker enzymes were observed. Fluoride caused testicular and spermatozoal DNA damages. VC&VE supplementation resulted in protectionfrom all fluoride mediated alterations and helped in attenuating testicular fluoride accumulation.

CONCLUSION

Antioxidant properties of VC&VE ameliorated fluoride mediated reproductive damages but only supplementation did not exhibit any notable effect compared to control rats.

Exploring a variance decomposition approach integrated with the Monte Carlo method to evaluate groundwater fluoride exposure on the residents of a typical fluorosis endemic semi-arid tract of India

This study appraised the groundwater fluoride (F^-) endemicity and the exposure levels under the Central Tendency Exposure (CTE) condition and the Reasonable Maximum Exposure (RME) condition on the residents of the semi-arid parts of the Birbhum district of Peninsular India using a Variance Decomposition (Sobol Sensitivity Indices) approach combined with Monte Carlo Simulations. The study finds the national scale drinking water standard limit for F^- (1.5 mg L^-1) is inappropriate for the present survey area where F^- concentration in groundwater varied between 0.26 and 11.82 mg L^-1 and ~54.5% of the samples (N = 400) exceeded this limit. Therefore, estimated the optimum F^- concentration of 0.733 mg L^-1 for the region using the method recommended by the World Health Organization (WHO) to calculate the optimum F^- limit at a regional scale. The average value of F^- concentrations for this region (1.71 mg L^-1) is considerably higher than the estimated optimum concentration or even the maximum permissible limits recommended for the subtropical regions (0.5-0.7 mg L^-1). The exposure analysis revealed the infants and children as potentially vulnerable populations compared to adolescents and adults of the study area for CTE and RME scenarios. The multi-exposure pathways indicated oral intake as the main exposure pathway whereas exposure through dermal contact was insignificant for the residents of all age groups of this region. Based on the first, second and total order Sobol Sensitivity Indices, F^- concentration (C) in groundwater, the groundwater ingestion rate and their combined interaction are the greatest significant parameters for the oral exposure model whereas C and its interaction effects with the proportion of the skin surface area in contact with groundwater as the utmost sensitive variables for the dermal health risks assessment model. The present study insists the inhabitants to intake defluoridated groundwater.

Folic acid Ameliorates the Declining Quality of Sodium Fluoride-Exposed Mouse Oocytes through the Sirt1/Sod2 Pathway

Excessive sodium fluoride (NaF) intake interferes with reproductive function in humans and animals; however, strategies to prevent these effects are still underexplored. Here, we showed that in vivo and in vitro supplementation of folic acid (FA) efficaciously improved the quality of NaF-exposed oocytes. FA supplementation not only increased ovulation of oocytes from NaF-treated mice but also enhanced oocyte meiotic competency and fertilization ability by restoring the spindle/chromosome structure. Moreover, FA supplementation could exert a beneficial effect on NaF- exposed oocytes by restoring mitochondrial function, eliminating reactive oxygen species accumulation to suppress apoptosis. We also found that FA supplementation restored the defective phenotypes in oocytes through a Sirt1/Sod2-dependent mechanism. Inhibition of Sirt1 with EX527 abolished the FA-mediated improvement in NaF-exposed oocyte quality. Collectively, our data indicated that FA supplementation is a feasible approach to protect oocytes from NaF-related deterioration.

Co-exposure to fluoride and arsenic disrupts intestinal flora balance and induces testicular autophagy in offspring rats

While numerous studies have shown that fluoride or arsenic exposure may damage the reproductive system, there are few reports of co-exposure to fluoride and arsenic. In addition, the literature on autophagy and intestinal flora composition in reproductive toxicity studies of co-exposure to fluoride and arsenic is insufficient. In this study, we developed a rat model of fluoride and arsenic exposure via drinking water from pre-pregnancy to 90 days postnatal. Sprague-Dawley rats were randomly divided into sterile water control group, fluoride group (100 mg/L NaF), arsenic group (50 mg/L NaAsO₂) and combined exposure group (100 mg/L NaF+50 mg/L NaAsO₂). Our results showed that fluoride and arsenic exposure caused a reduction in testicular weight and significant pathological damage to tissue. We found that the levels of follicle-stimulating hormone, luteinizing hormone, and testosterone were reduced to varying degrees. Meanwhile experiments showed that fluoride and arsenic exposure can modulate autophagic flux, causing increased levels of Beclin1 and LC3 expression and decreased p62 expression. Analogously, by performing 16S sequencing of rat feces, we found 24 enterobacterial genera that differed significantly among the groups. Furthermore, the flora associated with testicular injury were identified by correlation analysis of hormonal indices and autophagy alterations with intestinal flora composition at the genus level, respectively. In summary, our study shows that fluoride and arsenic co-exposure alters autophagic flux in the testis, causes testicular injury, and reveals an association between altered intestinal flora composition and testicular injury.

Fluoride induced testicular toxicities in adult Wistar rats

Fluoride is essential for the development of teeth and bone but its excessive exposure causes reprotoxic effects. We have studied the graded effects of different doses of sodium fluoride (NaF) on 24 adult Wistar rats which were randomly divided into four groups (n = 6). All the rats were given normal diet prepared in our laboratory. Control (group I) rats were received vehicle only and treated rats (group II, III, and IV) were administered NaF orally at 10, 15, and 20 mg/kg/d doses, respectively, for 30 consecutive days. Gravimetric index of testis was decreased significantly in group III and IV rats but such changes were not observed in the accessory reproductive organs. Marked alterations in number, motility, viability, and plasma membrane functional integrity of caudal spermatozoa were noted in most of the treated groups. Noticeable alterations in testicular histoarchitecture were observed in group III and IV rats. Graded Changes of testicular redox homeostasis were noted by assessment of enzymatic (superoxide dismutase [SOD], catalase, glutathione s-transferase [GST], and glutathione peroxidase [GPx]) and nonenzymatic (malondialdehyde [MDA] and protein carbonyl [PC]) markers. Changes of testicular functional markers (acid phosphatase [ACP], alkaline phosphatase [ALP], and lactate dehydrogenase (LDH) activity) were noted in group III and IV rats. DNA fragmentation assay proved the possibility of DNA damage caused by oxidative stress, as evidenced by prominent trailing pattern of fragmented testicular genomic DNA from group III and IV rats. The study concludes that fluoride-mediated oxidative stress not only impedes the structural and functional facets of testis but also results in testicular DNA damage.

Interleukin 17A deficiency alleviates fluoride-induced testicular injury by inhibiting the immune response and apoptosis

The reproductive toxicity of fluoride (F) has been verified by various epidemiological and experimental studies. Our previous work suggested that the interleukin 17A (IL-17A) is involved in the testicular damage induced by excessive F exposure. In this study, we further investigated the role of IL-17A in F-induced testicular injury. Wild type (WT) and IL-17A knockout (IL-17A^-/-) mice were exposed to 0, 25, 50, or 100 mg/L sodium fluoride (NaF) for 90 days. We found that exposure to excessive F levels caused testicular damage, decreased semen quality, negatively affected testicular morphology, and increased the inflammatory response. Specifically, excessive F intake increased the expression levels of IL-17A in the testis and increased the protein levels of Act1, NF-κB, IL-17R, C/EBP-α, and TRAF6 in the IL-17A signaling pathway. The increase in IL-17A expression corresponded to increases expression of IL-17R, IL-6, IL-23, IL-1β, TGF-β and TNF-α as assessed by RT-PCR and ELISA assays. Remarkably, IL-17A knockout in mice ameliorated the effects of F on testicular damage, semen quality, testicular morphology, and the immune response. Additionally, we found the in vitro exposure of Leydig cells to NaF and recombinant IL-17A led to abnormal apoptosis and a decrease in testosterone secretion. Our findings prove that IL-17A plays a key role in the exacerbation of testicular injuries in F-exposed mice, and that IL-17A deficiency can alleviate F-induced injury by inhibiting the immune response and apoptosis in the testis. These data suggest that targeting IL-17A may be a useful therapeutic strategy for treating F-mediated toxicity in the testis.

Hydrogeochemical characterisation and health hazards of fluoride enriched groundwater in diverse aquifer types

High concentration of fluoride (up to 20.9 mg/L) in groundwater with significant variation (p = 5.9E-128) among samples was reported from Birbhum district, an acknowledged fluoride endemic region in India. The groundwater samples (N = 368) were grouped based on their hydrochemical properties and aquifer geology for hydro-geochemical characterization. Friedman's test showed p < 0.0001 confidence level which indicates that fluoride concentration among geological groups and water groups are independent. Bland-Altman plot was used to study the inter-relationships among the groups through bias value (∂) and limit of agreement (LoA). Among the geological groups, laterites and granite-gneiss groups exhibited statistically significantly difference in fluoride geochemistry; whereas the younger and older alluvium groups displayed similar characteristics. The fluoride concentration was found to be in the order Lateritic > Granite-gneiss > Older alluvium ≥ Younger alluvium. Dissolution of minerals (such as fluorite, biotite) in laterite sheeted basalt, and granite-gneiss is the main source of groundwater fluoride in the region. Fluoride concentration is also influenced by depth of water table. Hydrochemical study indicated that fluoride concentration was higher in Na-HCO₃ than in Ca-SO₄ and Ca-HCO₃ type of groundwater. The fluoride concentration were positively correlated with Na⁺ and pH and negatively correlated with the Ca²⁺ and Mg²⁺ signifying linkage with halite dissolution and calcite, dolomite precipitation. Geostatistical mapping of WQI through empirical bayesian kriging (EBK) with respect to regional optimal guideline value (0.73 mg/L) classified that groundwater in some parts of the district are unfit for drinking purpose. Health survey (N = 1767) based on Dean's criteria for dental fluorosis indicated presence of slight to moderate dental hazard. Besides, providing baseline data for management of groundwater quality in the study area, the study demonstrated the applicability of Bland-Altman analysis and empirical bayesian kriging (EBK) in delineation and interpolation of fluoride contaminated region.

Fluoride Induces Autoimmune Orchitis Involved with Enhanced IL-17A Secretion in Mice Testis

Fluoride (F) widely exists in the water and food. Recent studies reported that F induced testicular toxicity via inflammation reaction. This study was aimed to explore the mechanism of F-induced inflammation in testis. 100 healthy male mice (BALB/cJ strain) were randomly divided into five groups including: control, experimental autoimmune orchitis (EAO), and three F groups (25, 50, and 100 mg/L sodium fluoride (NaF)). After 150 d, the results showed a significant increase in testicular cytokines levels including of IL-17A, IL-6, IFN-γ, and TNF-α in NaF and EAO groups compared with control group. Interestingly, the presence of specific antisperm autoantibodies in antitesticular autoantibodies and the notable recruitment of immunocyte (T cells and dendritic cells) were also observed in NaF and EAO groups. In addition, findings showed that in NaF and EAO groups macrophages and T cells both significantly secreted IL-17A, and the protein and mRNA levels of cytokines (IL-6 and TGF-β) were significantly increased. From these results, it can be concluded that autoimmune orchitis and IL-17A are implicated in F-induced testicular inflammation.

Exposure of Fluoride with Streptozotocin-Induced Diabetes Aggravates Testicular Damage and Spermatozoa Parameters in Mice

Diabetes mellitus is the most common chronic disease worldwide that causes numerous complications, including male infertility. The prevalence of DM is 451 million people and estimated that would increase to 693 million in 2045. Fluorosis caused by drinking water contaminated with inorganic fluoride is a public health problem in many areas around the world. Previous studies have shown that fluoride exposure damages the male reproductive function. This study aimed to evaluate the fluoride sub-chronic exposure on the spermatozoa function in streptozotocin (STZ)-induced diabetic mice. After confirming diabetes by measuring blood glucose levels, the male mice received 45.2 ppm of fluoride added or deionized water. We evaluated several parameters in diabetic mice exposed to fluoride: standard quality analysis, the mitochondrial transmembrane potential (ψm), the caspase activity in spermatozoa, urinary fluoride excretion, and histological evaluation in the testes. After 60 days of fluoride-exposure, diabetic mice, significantly decreased sperm quality (motility, viability, and concentration). Spermatozoa from fluoride-exposure in diabetic mice presented a significant decrease in ψm and a significant increase in activity caspase 3/7. Urinary fluoride excretion was decreased in diabetic mice exposed to fluoride. Subchronic fluoride exposure of mice with STZ-induced diabetes aggravated testicular damage and the spermatozoa function.

Exploring a multi-exposure-pathway approach to assess human health risk associated with groundwater fluoride exposure in the semi-arid region of east India

Human health risks associated with groundwater fluoride have been assessed using USEPA method in few parts of India, but those assessments were conducted based on a single value for each parameter, which may lead to certain inaccuracy and uncertainties in results. In this study, a higher degree of accuracy in health risk assessment was achieved through Monte Carlo simulations, sensitivity analysis and uncertainty analysis. As fluoride hazards to human health are chronic, a total of 4560 water samples (N = 4560) were collected during consecutive four seasons (2 pre-monsoon and 2 post-monsoon seasons; 1140 samples/season) from the entire Birbhum district, covering all the blocks and geological settings to obtain the spatiotemporal variation of fluoride level. The Empirical Bayesian Kriging geostatistical model was employed to determine fluoride endemic areas. Amongst all blocks, Nalhati-1 had exhibited the highest fluoride level (18.25 mg/L). The study revealed that most of the blocks are vulnerable to groundwater fluoride due to its occurrences in excess level. The average and 95th percentile values of total hazard index indicate that the infants and children populations of the district are more susceptible than the adults and teens. The sensitivity analysis revealed that water ingestion rate and fluoride concentration are the most influential parameters for higher risk of fluoride-related health hazards. Health risks were evaluated through ingestion and dermal exposure routes for infants, children, teens, and adult residents. The exposure was much higher through ingestion than dermal contacts. Ingestion of defluoridated water will reduce the health risks associated with groundwater fluoride exposure.

Sodium fluoride induces apoptosis and autophagy via the endoplasmic reticulum stress pathway in MC3T3-E1 osteoblastic cells

Fluorosis and bone pathologies can be caused by chronic and/or excessive fluoride intake. Despite this, few studies have been conducted on the cellular mechanisms underlying osteoblast toxicity in the presence of NaF. Here, we investigated the effects of fluoride on MC3T3-E1 cells. We showed that the proliferation of MC3T3-E1 cells was inhibited by exposure to NaF. In addition, apoptosis was induced by NaF, as caspase-associated proteins showed a higher level of expression and apoptotic bodies were formed. Furthermore, endoplasmic reticulum (ER) stress induced by NaF activated the unfolded protein response (UPR) and upregulated the expression of the glucose-regulated proteins 94 (GRP94) and 78 (BiP). Therefore, ER stress plays a vital role in NaF-induced autophagy and apoptosis. Furthermore, apoptosis is promoted following the inhibition of NaF-induced autophagy. In conclusion, under NaF treatment, the ER stress-signaling pathway is activated, leading to apoptosis and autophagy and affecting the proliferation and survival of MC3T3-E1 cells.

Positive PCNA and Ki-67 Expression in the Testis Correlates with Spermatogenesis Dysfunction in Fluoride-Treated Rats

The present study aimed to evaluate the effect of fluoride (F) on spermatogenesis in male rats. F^- at 50 and 100 mg/L was administered for 70 days, after which the testicular and epididymis tissues were collected to observe the histopathological structure under a light microscope. The ultrastructure of the testis and sperm was also examined via transmission electron microscopy. The apoptosis of spermatogenic cells was measured through terminal deoxynucleotidyl transferase dUTP nick end labeling staining. The expression of proliferation factors, namely, proliferating cell nuclear antigen (PCNA) and Ki-67, in the testicular and epididymis tissues, were assayed through immunohistochemistry. F^- at 50 and 100 mg/L significantly damaged the structure of the testis and epididymis, and the testis and sperm ultrastructure exhibited various changes, including mitochondrial swelling and vacuolization, and apsilated and raised sperm membrane. F treatment significantly increased spermatogenic cell apoptosis in the testis. PCNA (P < 0.01) and Ki-67 (P < 0.01) also presented positive expression in the testis. By comparison, no significant changes occurred in the epididymis. In summary, excessive F intake results in spermatogenesis dysfunction by damaging the testicular structure and inducing spermatogenic cell apoptosis in male rats. The positive expression level of PCNA and Ki-67 was a good response to spermatogenesis dysfunction.

Sodium fluoride disrupts testosterone biosynthesis by affecting the steroidogenic pathway in TM3 Leydig cells

Fluorine is an essential trace element to which humans and animals are exposed through water, food, air and products used for dental health. Numerous studies have reported the detrimental effects of fluoride on testicular function and fertility; however, the underlying mechanisms of testosterone biosynthesis remain unclear. In this study, Leydig cells, the primary cells responsible for the production and regulation of steroid hormones in the testis, were used to elicit effects of sodium fluoride on the steroidogenic pathway. Leydig cells were treated with 0, 0.1, 1, 10 and 100 mg/L sodium fluoride for 24 h, respectively. The result of the study showed that sodium fluoride significantly decreased cell viability and cell proliferation, increased cell cytotoxicity and decreased the amounts of testosterone and 3',5'-cyclic adenosine monophosphate levels in a concentration-dependent manner. Also, these results indicated that NaF suppressed the expression of steroidogenic genes (steroidogenic acute regulatory protein, cholesterol side-chain cleavage enzyme, 3β-hydroxy dehydrogenase type I and 17β-hydroxy dehydrogenase type III) and proteins (luteinizing hormone receptor, cholesterol side-chain cleavage enzyme, 3β-hydroxy dehydrogenase), by changing the mRNA expression levels of the transcription factors (steroidogenic factor-1, GATA binding protein-4, nerve growth factor IB and nuclear receptor subfamily 0 group B member 1).

JNK/STAT signalling pathway is involved in fluoride-induced follicular developmental dysplasia in female mice

Excessive fluoride (F) intake decreases the development of potential oocytes by inducing oxidative stress and apoptosis in female mice in our previous study. This study aims to investigate the underlying mechanisms of F-induced follicular developmental dysplasia. Pathomorphological changes in the ovary tissues were observed under light and transmission electron microscopes. DNA damage and proliferation in granulosa cells were analysed by TUNEL staining and BrdU measurement. The protein expression of cell proliferation related regulatory factors including JNK, STAT3, STAT5, CDK2, CDK4, PCNA and Ki67 in the ovary tissues was measured by immunohistochemistry and Western blot analyses. Results indicated that the structure of granulosa cells in the ovary was seriously damaged by excessive F, evident by the swollen endoplasmic reticulum, mitochondria with vacuoles and nucleus shrinkage. F treatment also considerably enhanced the apoptosis and inhibited the proliferation of granulosa cells. The number of granulosa cells around the oocyte decreased after F treatment. The expression levels of STAT3, CDK2, CDK4 and Ki67 in the ovary tissues were up-regulated, and STAT5 and PCNA did not change significantly after F treatment, whereas JNK expression was down-regulated with increasing F dose. In summary, changes in the expression levels of JNK, STAT3, STAT5, CDK2, CDK4, PCNA and Ki67 in the JNK/STAT signalling pathway are involved in F-induced follicular dysplasia in the ovary.

Effects of Fluoride on Surface Structure of Primary Culture Leydig Cells in Mouse

Fluoride (F) is known to induce reproduction toxicity, and the elucidation of its underlying mechanisms is an ongoing research. These findings aim to provide deeper insights into roles of soduim fluoride (NaF) in testis damage, which could contribute to a better understanding of fluoride-induced male reproductive toxicity. The Leydig cells were administrated by 0, 5, 10, and 20 mg/L NaF for 24 h, respectively. Scanning electron microscope was used to identify the change of surface structure in the Leydig cells. The results showed that fluoride exposure of high-dose induced bulged balloon in the membrane of the Leydig cell. We speculated that high doses of NaF inhibited cell proliferation and induced cell apoptosis in Leydig cells. This is the first time that we have reported that fluoride impaired cytomembrane and cytoskeleton of the Leydig cells in vitro treated with different doses of fluoride for 24 h by using a scanning electron microscope. Damage to the cytoskeleton and cytomembrane may be one of the reasons of male reproductive toxicity induced by fluoride.

Effects of different Ca2+ level on fluoride-induced apoptosis pathway of endoplasmic reticulum in the rabbit osteoblast in vitro

In reviewing the literature, the cellular mechanism of fluoride F-induced osteoblast OB cells apoptosis is diverse and perplexing, but detailed regulatory pathway, targets and role of extracellular Ca²⁺ remains still unclear. Hence, in the present study, we investigated the effects of F (9 mg/L F ion) and different Ca²⁺ (0.5, 1, 2, 4, 8 mmol/L) levels treatment on the proliferation rate of osteoblast cells, intracellular free Ca²⁺ ([Ca²⁺]i) and endoplasmic reticulum (ER) stress apoptosis pathway related gene levels of rabbit OB cells. Our results demonstrated that F exposure had a pronounced negative effect on osteoblast survival, further different Ca²⁺ levels treatment suggested that low concentration of Ca²⁺ (0.5-1 mmol/L) relieved the damaged effect, on the contrary, high concentration of Ca²⁺ (2-8 mmol/L) enhanced the effect. In addition, F significantly increased [Ca²⁺]i levels and the expression of ER stress-induced cell apoptosis pathway related genes. Treatment with 0.5-1 mmol/L Ca²⁺ markedly reversed the F-induced harmful effects, but high dose Ca²⁺ (2-8 mmol/L) enhanced these effects. In summary, 0.5-1 mmol/L Ca²⁺ can alleviate F-induced OB cells injure through ER stress apoptosis pathway, which provided a dose basis for the future study on the treatment of skeletal fluorosis with Ca²⁺.

Sodium fluoride disturbs DNA methylation of NNAT and declines oocyte quality by impairing glucose transport in porcine oocytes

Sodium fluoride (NaF) is used as a medicine to prevent tooth decay; however, excessive NaF could cause a pathological damage to the health. Recent studies showed that NaF impaired mouse oocyte maturation, included of abnormal spindle configuration, actin cap formation, cortical granule-free domain formation, and the following development after fertilization. However, few studies used large animals as models to study the toxicology of NaF on oocytes maturation. We proposed a hypothesis that NaF would affect the nuclear and cytoplasmic maturation of porcine oocytes and DNA methylation pattern of imprinted genes in oocytes. Our results showed that NaF affected cumulus expansion, polar body emission, spindle morphology, cortical granule distribution, early apoptosis, and the following development after parthenogenetic activation during porcine oocyte maturation. Moreover, NaF increased the DNA methylation of NNAT and decreased its expression, which disturbed the glucose transport in oocytes. These results suggest that NaF impairs the porcine oocytes maturation epigenetically, which provides a new toxicological mechanism of NaF on the oocyte maturation. Environ. Mol. Mutagen. 59:223-233, 2018. © 2017 Wiley Periodicals, Inc.

Abnormal spermatogenesis following sodium fluoride exposure is associated with the downregulation of CREM and ACT in the mouse testis

cAMP response element modulator (CREM) is involved in regulating gene expression in normal spermatogenesis. The transcriptional activity of CREM is partly regulated by activator of CREM in the testis (ACT). To investigate the effects of different concentrations of sodium fluoride (NaF) on the gene and protein expression of CREM and ACT in the mouse testis, sexually mature male Kunming mice were exposed to 50, 100, or 150 mg/L NaF in their drinking water for 90 days. NaF reduced the sperm count and viability and increased the percentage of malformed sperm in a dose-dependent manner. The mRNA expression of CREM and ACT was markedly downregulated in the NaF-treated groups. Furthermore, immunohistochemistry revealed that CREM and ACT proteins were decreased significantly in the 50, 100, and 150 mg/L NaF-treated groups compared to the control group. These findings indicate that the decreased gene and protein expression of CREM and ACT in the testis is associated with an impairment of reproductive functions by NaF.

Fluoride exposure changed the structure and the expressions of HSP related genes in testes of pubertal rats

Previous studies have indicated that fluoride exposure damaged the male reproductive function; however, the cellular mechanism of fluoride-induced testicular toxicity is still unclear. In this study, twenty-two female pregnant Wistar rats were allotted randomly to two groups: control (deionized water) and sodium fluoride (NaF, contain F^-: 67.86 mg/L) groups. After delivery, the dosage was continued for 15 weeks for puppies. Twelve rats in each group were tested at 6 and 9 (pubertal); 12 and 15 (mature) weeks of age. Our results suggested that organ coefficient of epididymis was significantly decreased in the mature (12 and 15 week-old) rats. Epididymal sperm abnormality and femur fluoride concentration were increased with the concomitant decrease in sperm motility and concentration in these experimental periods. Compared to the control, in the NaF group, the seminiferous tubules of each age were reduced in terms of diameter and thickness. The sperm cells were lost and shedding and finally disappeared after 9 weeks. mRNA and protein levels of HSP27 and 90 were decreased with a concomitant increase in HSP70 and HSF mRNA and protein levels in NaF exposed rats. The mRNA and protein levels of HSP27 and HSF (only mRNA) were significantly increased in NaF treated rats at 9 and 15 weeks of age, respectively. In summary, these results emphasize that NaF induces testicular and sperm abnormalities through the involvement of HSPs especially during the pubertal period.

Toxic metabolites, Sertoli cells and Y chromosome related genes are potentially linked to the reproductive toxicity induced by mequindox

Mequindox (MEQ) is a relatively new synthetic antibacterial agent widely applied in China since the 1980s. However, its reproductive toxicity has not been adequately performed. In the present study, four groups of male Kunming mice (10 mice/group) were fed diets containing MEQ (0, 25, 55 and 110 mg/kg in the diet) for up to 18 months. The results show that M4 could pass through the blood-testis barrier (BTB), and demonstrate that Sertoli cells (SCs) are the main toxic target for MEQ to induce spermatogenesis deficiency. Furthermore, adrenal toxicity, adverse effects on the hypothalamic-pituitary-testicular axis (HPTA) and Leydig cells, as well as the expression of genes related to steroid biosynthesis and cholesterol transport, were responsible for the alterations in sex hormones in the serum of male mice after exposure to MEQ. Additionally, the changed levels of Y chromosome microdeletion related genes, such as DDX3Y, HSF2, Sly and Ssty2 in the testis might be a mechanism for the inhibition of spermatogenesis induced by MEQ. The present study illustrates for the first time the toxic metabolites of MEQ in testis of mice, and suggests that SCs, sex hormones and Y chromosome microdeletion genes are involved in reproductive toxicity mediated by MEQ in vivo.

Fluoride induces apoptosis in H9c2 cardiomyocytes via the mitochondrial pathway

Numerous studies have shown that chronic excessive fluoride intake can adversely affect different organ systems. In particular, the cardiovascular system is susceptible to disruption by a high concentration of fluoride. The objectives of this study were to explore the mechanism of apoptosis by detecting the toxic effects of different concentrations of sodium fluoride (NaF) in H9c2 cells exposed for up to 96 h. NaF not only inhibited H9c2 cell proliferation but also induced apoptosis and morphological damage. With increasing NaF concentrations, early apoptosis of H9c2 cells was increased while the mitochondrial membrane potential was decreased. Compared with the control group, the mRNA levels of caspase-3, caspase-9, and cytochrome c all increased with increasing concentrations of NaF. In summary, these data suggest that apoptosis is involved in NaF-induced H9c2 cell toxicity and that activation of the mitochondrial pathway may occur.

The MMP-9/TIMP-1 System is Involved in Fluoride-Induced Reproductive Dysfunctions in Female Mice

A total of 84 healthy female mice were kept with various concentrations of sodium fluoride (F) (0, 50, 100, 150 mg F^-/L in drinking water for 90 days) and were then mated with healthy male mice for 1 week to study the effect of excessive fluoride on female reproductive function, particularly in embryo implantation. The rate of pregnancy, litter size, and the birth weight of female mice were evaluated. Ultrastructural changes of uteri tissues were observed by transmission electron microscopy (TEM). The mRNA expression levels of MMP-9 and TIMP-1 were determined by quantitative real-time PCR. The protein expression levels of MMP-9 and TIMP-1 were analyzed by western blotting. Results showed a significant decrease of litter size in mice exposed to fluoride. TEM images of uteri tissue of mice that underwent a 150 mg/L F^- treatment for 90 days showed a vague nucleus, reduced microvilli, increased lysosomes, a dilated endoplasmic reticulum, and a vacuolization mitochondrion when compared with the control group. Following the damage of the structure, the expression levels of MMP-9 and TIMP-1 in uteri tissues were significantly unregulated in the F 150 group. These results show that MMP-9/TIMP-1 system disturbance and changes of histological structure in uteri tissue are involved in fluoride-induced reproductive dysfunctions.