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Riboswitches regulate downstream gene expression by binding to specific small molecules or ions with multiple mechanisms to transfer the binding information. In the case of the fluoride riboswitch, the transcription termination signal is conveyed through a transient excited state (ES). In this work, we performed conventional molecular dynamics (MD) simulations, totaling 180 μs, to obtain the ES structure and investigate the mechanism underlying information transmission in Mg 2+ /F - binding within the fluoride riboswitch aptamer. The Mg 2+ /F - binding pocket exhibits various conformations in its apo form. A series of ES structures were extracted from the MD trajectories of the apo form. The dynamics of the Mg 2+ /F - binding pocket influenced key pair A40-U48 in ES structures. The pathway connecting the binding pocket to the pair involves interactions between the phosphate groups of U7 and G8 and the nucleobases of G8-C47-U48. Our work presents a structural ensemble of the ES and elucidates a pathway for transferring Mg 2+ /F - binding information, thereby facilitating the understanding of how the holo-like apo state achieves transcriptional repression.

Enzymes facilitating the transfer of phosphate groups constitute the most extensive protein families across all kingdoms of life. They make up approximately 10% of the proteins found in the human genome. Understanding the mechanisms by which enzymes catalyze these reactions is essential in characterizing the processes they regulate. Metal fluorides can be used as multifunctional tools to study these enzymes. These ionic species bear the same charge as phosphate and the transferring phosphoryl group and, in addition, allow the enzyme to be trapped in catalytically important states with spectroscopically sensitive atoms interacting directly with active site residues. The ionic nature of these phosphate surrogates also allows their removal and replacement with other analogs. Here, we describe the best practices to obtain these complexes, their use in NMR, X-ray crystallography, cryo-EM, and SAXS and describe a new metal fluoride, scandium tetrafluoride, which has significant anomalous signal using soft X-rays., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Antarctic krill shell waste (AKSW), a byproduct of Antarctic krill processing, has substantial quantity but low utilization. Utilizing microbial-based cell factories, with Pseudomonas putida as a promising candidate, offers an ecofriendly and sustainable approach to producing valuable bioproducts from renewable sources. However, the high fluoride content in AKSW impedes the cell growth of P. putida. This study aims to investigate the transcriptional response of P. putida to fluoride stress from AKSW and subsequently conduct genetic modification of the strain based on insights gained from transcriptomic analysis. Notably, the engineered strain KT +16840+03100 exhibited a remarkable 33.7-fold increase in cell growth, capable of fermenting AKSW for medium-chain-length-polyhydroxyalkanoates (mcl-PHA) biosynthesis, achieving a 40.3-fold increase in mcl-PHA yield compared to the control strain. This research advances our understanding of how P. putida responds to fluoride stress from AKSW and provides engineered strains that serve as excellent platforms for producing mcl-PHA through AKSW., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

3,3,3-Trifluoro-1,2-propanediol undergoes complete defluorination in two distinct steps: first, the conversion into 3,3,3-trifluoropropionaldehyde catalyzed by adenosylcobalamin (coenzyme B12)-dependent diol dehydratase; second, non-enzymatic elimination of all three fluorides from this aldehyde to afford malonic semialdehyde (3-oxopropanoic acid), which is decarboxylated to acetaldehyde. Diol dehydratase accepts 3,3,3-trifluoro-1,2-propanediol as a relatively poor substrate, albeit without significant mechanism-based inactivation of the enzyme during catalysis. Optical and electron paramagnetic resonance (EPR) spectra revealed the steady-state formation of cob(II)alamin and a substrate-derived intermediate organic radical (3,3,3-trifluoro-1,2-dihydroxyprop-1-yl). The coenzyme undergoes Co-C bond homolysis initiating a sequence of reaction by the generally accepted pathway via intermediate radicals. However, the greater steric size of trifluoromethyl and especially its negative impact on the stability of an adjacent radical centre compared to a methyl group has implications for the mechanism of the diol dehydratase reaction. Nevertheless, 3,3,3-trifluoropropionaldehyde is formed by the normal diol dehydratase pathway, but then undergoes non-enzymatic conversion into acetaldehyde, probably via 3,3-difluoropropenal and malonic semialdehyde., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Japanese Biochemical Society. All rights reserved.)

Enzymatic cleavage of C─F bonds in per- and polyfluoroalkyl substances (PFAS) is largely unknown but avidly sought to promote systems biology for PFAS bioremediation. Here, we report the reductive defluorination of α, β-unsaturated per- and polyfluorocarboxylic acids by Acetobacterium spp. The microbial defluorination products were structurally confirmed and showed regiospecificity and stereospecificity, consistent with their formation by enzymatic reactions. A comparison of defluorination activities among several Acetobacterium species indicated that a functional fluoride exporter was required for the detoxification of the released fluoride. Results from both in vivo inhibition tests and in silico enzyme modeling suggested the involvement of enzymes of the flavin-based electron-bifurcating caffeate reduction pathway [caffeoyl-CoA reductase (CarABCDE)] in the reductive defluorination. This is a report on specific microorganisms carrying out enzymatic reductive defluorination of PFAS, which could be linked to electron-bifurcating reductases that are environmentally widespread.

Fluoride (F) can be absorbed from the environment and hyperaccumulate in leaves of Camellia sinensis without exhibiting any toxic symptoms. Fluoride exporter in C. sinensis (CsFEX) could transport F to extracellular environment to alleviate F accumulation and F toxicity, but its functional mechanism remains unclear. Here, combining with pH condition of C. sinensis growth, the characteristics of CsFEX and mechanism of F detoxification were further explored. The results showed that F accumulation was influenced by various pH, and pH 4.5 and 6.5 had a greater impact on the F accumulation of C. sinensis. Through Non-invasive Micro-test Technology (NMT) detection, it was found that F uptake/accumulation of C. sinensis and Arabidopsis thaliana might be affected by pH through changing the transmembrane electrochemical proton gradient of roots. Furthermore, diverse expression patterns of CsFEX were induced by F treatment under different pH, which was basically up-regulated in response to high F accumulation, indicating that CsFEX was likely to participate in the process of F accumulation in C. sinensis and this process might be regulated by pH. Additionally, CsFEX functioned in the mitigation of F sensitivity and accumulation strengthened by lower pH in Escherichia coli and A. thaliana. Moreover, the changes of H + flux and potential gradient caused by F were relieved as well in transgenic lines, also suggesting that CsFEX might play an important role in the process of F accumulation. Above all, F uptake/accumulation were alleviated in E. coli and A. thaliana by CsFEX through exporting F - , especially at lower pH, implying that CsFEX might regulate F accumulation in C. sinensis., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Targeted radionuclide therapy, in which radiopharmaceuticals deliver potent radionuclides to tumours for localized irradiation, has addressed unmet clinical needs and improved outcomes for patients with cancer 1-4 . A therapeutic radiopharmaceutical must achieve both sustainable tumour targeting and fast clearance from healthy tissue, which remains a major challenge 5,6 . A targeted ligation strategy that selectively fixes the radiopharmaceutical to the target protein in the tumour would be an ideal solution. Here we installed a sulfur (VI) fluoride exchange (SuFEx) chemistry-based linker on radiopharmaceuticals to prevent excessively fast tumour clearance. When the engineered radiopharmaceutical binds to the tumour-specific protein, the system undergoes a binding-to-ligation transition and readily conjugates to the tyrosine residues through the 'click' SuFEx reaction. The application of this strategy to a fibroblast activation protein (FAP) inhibitor (FAPI) triggered more than 80% covalent binding to the protein and almost no dissociation for six days. In mice, SuFEx-engineered FAPI showed 257% greater tumour uptake than did the original FAPI, and increased tumour retention by 13-fold. The uptake in healthy tissues was rapidly cleared. In a pilot imaging study, this strategy identified more tumour lesions in patients with cancer than did other methods. SuFEx-engineered FAPI also successfully achieved targeted β- and α-radionuclide therapy, causing nearly complete tumour regression in mice. Another SuFEx-engineered radioligand that targets prostate-specific membrane antigen (PSMA) also showed enhanced therapeutic efficacy. Considering the broad scope of proteins that can potentially be ligated to SuFEx warheads, it might be possible to adapt this strategy to other cancer targets., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

Fluorinated organic chemicals, such as per- and polyfluorinated alkyl substances (PFAS) and fluorinated pesticides, are both broadly useful and unusually long-lived. To combat problems related to the accumulation of these compounds, microbial PFAS and organofluorine degradation and biosynthesis of less-fluorinated replacement chemicals are under intense study. Both efforts are undermined by the substantial toxicity of fluoride, an anion that powerfully inhibits metabolism. Microorganisms have contended with environmental mineral fluoride over evolutionary time, evolving a suite of detoxification mechanisms. In this perspective, we synthesize emerging ideas on microbial defluorination/fluorination and fluoride resistance mechanisms and identify best approaches for bioengineering new approaches for degrading and making organofluorine compounds., (© 2024. The Author(s).)

Microorganisms resist fluoride toxicity using fluoride export proteins from one of several different molecular families. Cariogenic species Streptococcus mutans and Candida albicans extrude intracellular fluoride using a CLC F F - /H + antiporter and FEX fluoride channel, respectively, whereas oral commensal eubacteria, such as Streptococcus gordonii, export fluoride using a Fluc fluoride channel. In this work, we examine how genetic knockout of fluoride export impacts pathogen fitness in single-species and three-species dental biofilm models. For biofilms generated using S. mutans with the genetic knockout of the CLC F transporter, exposure to low fluoride concentrations decreased S. mutans counts, synergistically reduced the populations of C. albicans , increased the relative proportion of oral commensal S. gordonii , and reduced properties associated with biofilm pathogenicity, including acid production and hydroxyapatite dissolution. Biofilms prepared with C. albicans with genetic knockout of the FEX channel also exhibited reduced fitness in the presence of fluoride but to a lesser degree. Imaging studies indicate that S. mutans is highly sensitive to fluoride, with the knockout strain undergoing complete lysis when exposed to low fluoride for a moderate amount of time. Biochemical purification of the S. mutans CLC F transporter and functional reconstitution establishes that the functional protein is a dimer encoded by a single gene. Together, these findings suggest that fluoride export by oral pathogens can be targeted by specific inhibitors to restore biofilm symbiosis in dental biofilms and that S. mutans is especially susceptible to fluoride toxicity., Importance: Dental caries is a globally prevalent condition that occurs when pathogenic species, including Streptococcus mutans and Candida albicans , outcompete beneficial species, such as Streptococcus gordonii , in the dental biofilm. Fluoride is routinely used in oral hygiene to prevent dental caries. Fluoride also has antimicrobial properties, although most microbes possess fluoride exporters to resist its toxicity. This work shows that sensitization of cariogenic species S. mutans and C. albicans to fluoride by genetic knockout of fluoride exporters alters the microbial composition and pathogenic properties of dental biofilms. These results suggest that the development of drugs that inhibit fluoride exporters could potentiate the anticaries effect of fluoride in over-the-counter products like toothpaste and mouth rinses. This is a novel strategy to treat dental caries., Competing Interests: The authors declare no conflict of interest.

Background: Fluoride-resistant Streptococcus mutans (S. mutans) strains have developed due to the wide use of fluoride in dental caries prevention. However, the metabolomics of fluoride-resistant S. mutans remains unclear., Objective: This study aimed to identify metabolites that discriminate fluoride-resistant from wild-type S. mutans., Materials and Methods: Cell supernatants from fluoride-resistant and wild-type S. mutans were collected and analyzed by liquid chromatography-mass spectrometry. Principal components analysis and partial least-squares discriminant analysis were performed for the statistical analysis by variable influence on projection (VIP > 2.0) and p value (Mann-Whitney test, p < 0.05). Metabolites were assessed qualitatively using the Human Metabolome Database version 2.0 ( http://www.hmdb.ca ), or Kyoto Encyclopedia of Genes and Genomes ( http://www.kegg.jp ), and Metaboanalyst 6.0 ( https://www.metaboanalyst.ca )., Results: Fourteen metabolites differed significantly between fluoride-resistant and wild-type strains in the early log phase. Among these metabolites, 5 were identified. There were 32 differential metabolites between the two strains in the stationary phase, 13 of which were identified. The pyrimidine metabolism for S. mutans FR was matched with the metabolic pathway., Conclusions: The fructose-1,6-bisphosphate concentration increased in fluoride-resistant strains under acidic conditions, suggesting enhanced acidogenicity and acid tolerance. This metabolite may be a promising target for elucidating the cariogenic and fluoride resistant mechanisms of S. mutans., (© 2024. The Author(s).)

Fluoride, a global environmental pollutant, is ubiquitous in aquatic environments and coexists with selenium, which can cause complex effects on exposed organisms. However, data on the interaction of fluoride and selenium remain scarce. In this study, female zebrafish (Danio rerio) were exposed to fluoride (80 mg/L sodium fluoride) and/or dietary selenomethionine (Se-Met) for 30, 60 and 90 days, the effects on the liver of zebrafish were investigated. The results indicated that an increase in fluoride burden, inhibited growth and impaired liver morphology were recorded after fluoride exposure. Furthermore, fluoride alone caused oxidative stress and inflammation in the liver, as reflected by the increase in ROS and MDA contents, the reduction of anti-oxidative enzymes, the altered immune related enzymes (ACP, AKP, LZM and MPO) and the expression of IL-6, IL-1β, TNF-α, IL-10 and TGF-β. In contrast, co-exposure to fluoride and Se-Met decreased fluoride burden and restored growth. Furthermore, dietary Se-Met alleviated oxidative stress, inflammation and impaired morphology in liver trigger by fluoride. However, dietary Se-Met alone increased the activities of SOD and CAT. These results demonstrate that the protective effect of dietary Se-Met against chronic fluoride toxicity at a certain level., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Natural products from Actinomycetota have served as inspiration for many clinically relevant therapeutics. Despite early triumphs in natural product discovery, the rate of unearthing new compounds has decreased, necessitating inventive approaches. One promising strategy is to explore environments where survival is challenging. These harsh environments are hypothesized to lead to bacteria developing chemical adaptations (e.g. natural products) to enable their survival. This investigation focuses on ore-forming environments, particularly fluoride mines, which typically have extreme pH, salinity and nutrient scarcity. Herein, we have utilized metagenomics, metabolomics and evolutionary genome mining to dissect the biodiversity and metabolism in these harsh environments. This work has unveiled the promising biosynthetic potential of these bacteria and has demonstrated their ability to produce bioactive secondary metabolites. This research constitutes a pioneering endeavour in bioprospection within fluoride mining regions, providing insights into uncharted microbial ecosystems and their previously unexplored natural products.

Fluoride is known to induce nephrotoxicity; however, the underlying mechanisms remain incompletely understood. Therefore, this study aims to explore the roles and mechanisms of lysosomal membrane permeabilization (LMP) and the GSDME/HMGB1 axis in fluoride-induced nephrotoxicity and the protective effects of rutin. Rutin, a naturally occurring flavonoid compound known for its antioxidative and anti-inflammatory properties, is primarily mediated by inhibiting oxidative stress and reducing proinflammatory markers. To that end, we established in vivo and in vitro models. In the in vivo study, rats were exposed to sodium fluoride (NaF) throughout pregnancy and up until 2 months after birth. In parallel, we employed in vitro models using HK-2 cells treated with NaF, n-acetyl-L-cysteine (NAC), or rutin. We assessed lysosomal permeability through immunofluorescence and analyzed relevant protein expression via western blotting. Our findings showed that NaF exposure increased ROS levels, resulting in enhanced LMP and increased cathepsin B (CTSB) and D (CTSD) expression. Furthermore, the exposure to NaF resulted in the upregulation of cleaved PARP1, cleaved caspase-3, GSDME-N, and HMGB1 expressions, indicating cell death and inflammation-induced renal damage. Rutin mitigates fluoride-induced nephrotoxicity by suppressing ROS-mediated LMP and the GSDME/HMGB1 axis, ultimately preventing fluoride-induced renal toxicity occurrence and development. In conclusion, our findings suggest that NaF induces renal damage through ROS-mediated activation of LMP and the GSDME/HMGB1 axis, leading to pyroptosis and inflammation. Rutin, a natural antioxidative and anti-inflammatory dietary supplement, offers a novel approach to prevent and treat fluoride-induced nephrotoxicity., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Urinary tract infections (UTIs) are one of the most common bacterial infections in humans, with ~400 million cases across the globe each year. Uropathogenic Escherichia coli (UPEC) is the major cause of UTI and increasingly associated with antibiotic resistance. This scenario has been worsened by the emergence and spread of pandemic UPEC sequence type 131 (ST131), a multidrug-resistant clone associated with extraordinarily high rates of infection. Here, we employed transposon-directed insertion site sequencing in combination with metabolomic profiling to identify genes and biochemical pathways required for growth and survival of the UPEC ST131 reference strain EC958 in human urine (HU). We identified 24 genes required for growth in HU, which mapped to diverse pathways involving small peptide, amino acid and nucleotide metabolism, the stringent response pathway, and lipopolysaccharide biosynthesis. We also discovered a role for UPEC resistance to fluoride during growth in HU, most likely associated with fluoridation of drinking water. Complementary nuclear magnetic resonance (NMR)-based metabolomics identified changes in a range of HU metabolites following UPEC growth, the most pronounced being L-lactate, which was utilized as a carbon source via the L-lactate dehydrogenase LldD. Using a mouse UTI model with mixed competitive infection experiments, we demonstrated a role for nucleotide metabolism and the stringent response in UPEC colonization of the mouse bladder. Together, our application of two omics technologies combined with different infection-relevant settings has uncovered new factors required for UPEC growth in HU, thus enhancing our understanding of this pivotal step in the UPEC infection pathway., Importance: Uropathogenic Escherichia coli (UPEC) cause ~80% of all urinary tract infections (UTIs), with increasing rates of antibiotic resistance presenting an urgent threat to effective treatment. To cause infection, UPEC must grow efficiently in human urine (HU), necessitating a need to understand mechanisms that promote its adaptation and survival in this nutrient-limited environment. Here, we used a combination of functional genomic and metabolomic techniques and identified roles for the metabolism of small peptides, amino acids, nucleotides, and L-lactate, as well as the stringent response pathway, lipopolysaccharide biosynthesis, and fluoride resistance, for UPEC growth in HU. We further demonstrated that pathways involving nucleotide metabolism and the stringent response are required for UPEC colonization of the mouse bladder. The UPEC genes and metabolic pathways identified in this study represent targets for the development of innovative therapeutics to prevent UPEC growth during human UTI, an urgent need given the rapidly rising rates of global antibiotic resistance., Competing Interests: The authors declare no conflict of interest.

Fluoride is present everywhere in nature. The primary way that individuals are exposed to fluoride is by drinking water. It's interesting to note that while low fluoride levels are good for bone and tooth growth, prolonged fluoride exposure is bad for human health. Additionally, preclinical studies link oxidative stress, inflammation, and programmed cell death to fluoride toxicity. Moreover, mitochondria play a crucial role in the production of reactive oxygen species (ROS). On the other hand, little is known about fluoride's impact on mitophagy, biogenesis, and mitochondrial dynamics. These actions control the growth, composition, and organisation of mitochondria, and the purification of mitochondrial DNA helps to inhibit the production of reactive oxygen species and the release of cytochrome c, which enables cells to survive the effects of fluoride poisoning. In this review, we discuss the different pathways involved in mitochondrial toxicity and dysfunction induced by fluoride. For therapeutic approaches, we discussed different phytochemical and pharmacological agents which reduce the toxicity of fluoride via maintained by imbalanced cellular processes, mitochondrial dynamics, and scavenging the ROS., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Fluoride can be widely ingested from the environment, and its excessive intake could result in adverse effects. Dental fluorosis is an early sign of fluoride toxicity which can cause esthetic and functional problems. Though apoptosis in ameloblasts is one of the potential mechanisms, the specific signal cascade is in-conclusive. High-throughput sequencing and molecular biological techniques were used in this study to explore the underlying pathogenesis of dental fluorosis, for its prevention and treatment. A fluorosis cell model was established. Viability and apoptosis rate of mouse ameloblast-derived cell line (LS8 cells) was measured using cell counting kit-8 (CCK-8) assay and flow cytometry analysis. Cells were harvested with or without 2-mM sodium fluoride (NaF) stimulation for high-throughput sequencing. Based on the sequencing data, subcellular structures, endoplasmic reticulum stress (ERS), and apoptosis related biomarkers were verified using transmission electron microscopy, quantitative real-time polymerase chain reaction, and Western blotting techniques. Expression of ERS markers, apoptosis related proteins, and enamel formation enzymes were detected using Western blotting after addition of 4-phenylbutyrate (4-PBA). NaF-inhibited LS8 cells displayed time- and dose- dependent viability. Additionally, apoptosis and morphological changes were observed. RNA-sequencing data showed that protein processing in endoplasmic reticulum was obviously affected. ERS and apoptosis were induced by excessive NaF. Downregulation of kallikrein-related peptidase 4 (KLK4) was also observed. Inhibition of ERS by 4-PBA rescued the apoptotic and functional protein changes in cells. Excessive fluoride induces apoptosis by activating ERS, which is mediated by GRP-78/PERK/CHOP signaling. Key proteinase is present in maturation-stage enamel; KLK4 was also affected by fluoride, but rescued by 4-PBA. This study presents a possibility for therapeutic strategies for dental fluorosis, while further exploration is required., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Epidemiology has shown that fluoride exposure is associated with the occurrence of diabetes. However, whether fluoride affects diabetic encephalopathy is unclear. Elderly diabetic patients in areas with endemic (n = 169) or no fluorosis (108) and controls (85) underwent Montreal Cognitive Assessment. Sprague-Dawley rats receiving streptozotocin and/or different fluoride doses were examined for spatial learning and memory, brain morphology, blood-brain barrier, fasting blood glucose and insulin. Cultured SH-SY5Y cells were treated with 50 mM glucose and/or low- or high-dose fluoride, and P53-knockdown or poly-ADP-ribose polymerase-1 (PARP-1) inhibition. The levels of PARP-1, P53, poly-ADP-ribose (PAR), apoptosis-inducing factor (AIF), and phosphorylated-histone H2A.X (ser139) were measured by Western blotting. Reactive oxygen species (ROS), 8-hydroxydeguanosine (8-OHdG), PARP-1 activity, acetyl-P53, nicotinamide adenine dinucleotide (NAD + ), activities of mitochondrial hexokinase1 (HK1) and citrate synthase (CS), mitochondrial membrane potential and apoptosis were assessed biochemically. Cognition of diabetic patients in endemic fluorosis areas was poorer than in other regions. In diabetic rats, fasting blood glucose, insulin resistance and blood-brain barrier permeability were elevated, while spatial learning and memory and Nissl body numbers in neurons declined. In these animals, expression and activity of P53 and PARP-1 and levels of NAD + , PAR, ROS, 8-OHdG, p-histone H2A.X (ser139), AIF and apoptosis content increased; whereas mitochondrial HK1 and CS activities and membrane potential decreased. SH-SY5Y cells exposed to glucose exhibited changes identical to diabetic rats. The changes in diabetic rats and cells treated with glucose were aggravated by fluoride. P53-knockout or PARP-1 inhibition mitigated the effects of glucose with/without low-dose fluoride. Elevation of diabetic encephalopathy was induced by exposure to fluoride and the underlying mechanism may involve overactivation of the PARP-1/P53 pathway., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Fluoride is an environmental toxin prevalent in water, soil, and air. A fluoride transporter called Fluoride EXporter (FEX) has been discovered across all domains of life, including bacteria, single cell eukaryotes, and all plants, that is required for fluoride tolerance. How FEX functions to protect multicellular plants is unknown. In order to distinguish between different models, the dynamic movement of fluoride in wildtype (WT) and fex mutant plants was monitored using [ 18 F]fluoride with positron emission tomography. Significant differences were observed in the washout behavior following initial fluoride uptake between plants with and without a functioning FEX. [ 18 F]Fluoride traveled quickly up the floral stem and into terminal tissues in WT plants. In contrast, the fluoride did not move out of the lower regions of the stem in mutant plants resulting in clearance rates near zero. The roots were not the primary locus of FEX action, nor did FEX direct fluoride to a specific tissue. Fluoride efflux by WT plants was saturated at high fluoride concentrations resulting in a pattern like the fex mutant. The kinetics of fluoride movement suggested that FEX mediates a fluoride transport mechanism throughout the plant where each individual cell benefits from FEX expression., (© 2024. The Author(s).)

To reveal the molecular mechanism of brain damage induced by chronic fluorosis, expression of PTEN-induced kinase 1 (PINK1)/parkin RBR E3 ubiquitin-protein ligase (Parkin)-mediated mitophagy pathway and activity of mitochondrial superoxide dismutase (SOD) were investigated in rat brains and primary cultured neurons exposed to high level of fluoride. Sprague-Dawley (SD) rats were treated with fluoride (0, 5, 50, and 100 ppm) for 3 and 6 months. The primary neurons were exposed to 0.4 mM (7.6 ppm) fluoride and thereafter treated with 100 nM rapamycin (a stimulator of mitophagy) or 50 μM 3-methyladenine (3-MA, an inhibitor of mitophagy) for 24 h. The expressions of PINK1/Parkin at the protein level and the activity of SOD in mitochondria of rat brains and cultured neurons were determined by Western blotting and biochemical method, respectively. The results showed that the rats exposed to fluoride exhibited different degrees of dental fluorosis. In comparison to controls, the expressions of PINK1 and Parkin were significantly higher in the rat brains and primary neurons exposed to high fluoride. In addition, a declined activity of mitochondrial SOD was determined. Interestingly, rapamycin treatment enhanced but 3-MA inhibited the changes of PINK1/Parkin pathway and SOD activity, and the correlations between the inhibited SOD activity and the elevated PINK1/Parkin proteins were observed. The results suggest that the inhibition of mitochondrial SOD activity induced by fluorosis may stimulate the expressions of mitophagy (PINK1/ Parkin) pathway to maintain the mitochondrial homeostasis., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

To investigate the impact of the ethanoic fractions of Periploca forrestii Schltr. (P. forrestii) in ameliorating the liver injury caused by fluoride ingestion and to explore the potential mechanisms. Initially, an in vitro fluorosis cell model was constructed using the human normal liver cell line (L-02) induced by fluoride. Cell viability was assessed using the CCK-8 assay kit. The lactate dehydrogenase (LDH) assay kit was utilized to measure LDH content in the cell supernatant, while the malonic dialdehyde (MDA) assay kit was employed to determine MDA levels within the cells. Subsequently, a fluorosis rat model was established, and LDH content in the cell supernatant was measured using the LDH assay kit. Various parameters, including MDA, superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), catalase (CAT), and reactive oxygen species (ROS) content within the cells, were detected using appropriate assay kits. Additionally, cell apoptosis rate was determined using the Annexin V-FITC/PI cell apoptosis assay kit. The protein expression levels of B-cell lymphoma-2 (Bcl-2), Bcl-2-associated X protein (Bax), Caspase-3, Cleaved Caspase-3, Caspase-9, and Cleaved Caspase-9 were analyzed through Western blotting. Compared to the model group, the ethanolic fraction D of P.forrestii (Fr.D) increased cell viability (P < 0.01) and decreased LDH and MDA levels (P < 0.01). In the high-dose Fr.D treatment group of fluoride-poisoned rats, serum ALT, AST, LDH and MDA levels significantly decreased (P < 0.01). Results from rat primary cells exhibited that the Fr.D administration group exhibited significantly higher cell survival rates than the fluoride group (P < 0.01). Similarly, primary rat cells treated with Fr.D showed enhanced cell viability (P < 0.05) and reduced apoptosis rate, LDH, MDA, SOD, GSH-Px, CAT, and ROS levels (P < 0.05) compared to the model group. Western blot analysis indicated that the Fr.D treatment group elevated the Bcl-2/Bax protein expression ratio and reduced Caspase-3 and Caspase-9 activation levels (P < 0.01) compared to the model group. The results suggest that components within the Fr.D from Periploca forrestii may alleviate fluoride-induced liver injury by potentially counteracting oxidative stress and cell apoptosis., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Fluoride exerts detrimental effects on germ cells and increases the infertility rate in women. Nevertheless, the precise mechanisms behind the developmental abnormalities caused by fluoride in oocytes remain poorly comprehended. The current study, we established mitochondrial damage model in oocytes via 50 μg/mL sodium fluoride (NaF) supplementation. We then examined the effects of honokiol in preventing mitochondrial deficits caused by NaF and investigated the mechanisms through which honokiol protects oocytes. The findings investigated that NaF increased levels of mitochondrial reactive oxygen species (mtROS) and hindered mitochondrial function, as evidenced by the dissipation of mitochondrial membrane potential, abnormal expression of mitochondrial DNA copy numbers, and mtDNA harm in oocytes. mtROS scavenging using Mito-TEMPO alleviated oxidative damage in mitochondria and restored the oocyte developmental competence. Superoxide dismutase 2 (SOD2) acetylation was significantly increased, whereas sirtuin 3 (SIRT3) expression was decreased in NaF-treated oocytes. The addition of honokiol helped in the deacetylation of SOD2 at K122 through SIRT3, resulting in the removal of excessive mtROS and the recovery of mitochondrial function. Therefore, SIRT3/SOD2 pathway aids honokiol in mitigating fluoride-induced mitochondrial dysfunction. Overall, honokiol improved the mitochondrial harm caused by NaF by controlling mtROS and mitochondrial function, with the SIRT3/SOD2 pathway having an important function. These findings suggest honokiol as a potential therapeutic strategy for NaF-induced oocyte development and mitochondrial deficits., Competing Interests: Declaration of competing interest The authors declare no competing interests., (Copyright © 2023. Published by Elsevier B.V.)

Fluoride (F - ) export proteins, including F - channels and F - transporters, are widespread in biology. They contribute to cellular resistance against fluoride ion, which has relevance as an ancient xenobiotic, and in more modern contexts like organofluorine biosynthesis and degradation or dental medicine. This chapter summarizes quantitative methods to measure fluoride transport across membranes using fluoride-specific lanthanum-fluoride electrodes. Electrode-based measurements can be used to measure unitary fluoride transport rates by membrane proteins that have been purified and reconstituted into lipid vesicles, or to monitor fluoride efflux into living microbial cells. Thus, fluoride electrode-based measurements yield quantitative mechanistic insight into one of the major determinants of fluoride resistance in microorganisms, fungi, yeasts, and plants., (Copyright © 2024. Published by Elsevier Inc.)

The use of molecular dynamics (MD) simulations to study biomolecular systems has proven reliable in elucidating atomic-level details of structure and function. In this chapter, MD simulations were used to uncover new insights into two phylogenetically unrelated bacterial fluoride (F - ) exporters: the CLC F F - /H + antiporter and the Fluc F - channel. The CLC F antiporter, a member of the broader CLC family, has previously revealed unique stoichiometry, anion-coordinating residues, and the absence of an internal glutamate crucial for proton import in the CLCs. Through MD simulations enhanced with umbrella sampling, we provide insights into the energetics and mechanism of the CLC F transport process, including its selectivity for F - over HF. In contrast, the Fluc F - channel presents a novel architecture as a dual topology dimer, featuring two pores for F - export and a central non-transported sodium ion. Using computational electrophysiology, we simulate the electrochemical gradient necessary for F - export in Fluc and reveal details about the coordination and hydration of both F - and the central sodium ion. The procedures described here delineate the specifics of these advanced techniques and can also be adapted to investigate other membrane protein systems., (Copyright © 2024. Published by Elsevier Inc.)

Solid-state nuclear magnetic resonance (NMR) methods can probe the motions of membrane proteins in liposomes at the atomic level, and propel the understanding of biomolecular processes for which static structures cannot provide a satisfactory description. High-resolution crystallography snapshots have provided a structural basis for fluoride channels. NMR is a powerful tool to build upon these snapshots and depict a dynamic picture of fluoride channels in native-like lipid bilayers. In this contribution, we discuss solid-state and solution NMR experiments to detect fluoride binding and transport by fluoride channels. Ongoing developments in membrane protein sample preparation and ssNMR methodology, particularly in using 1 H, 19 F and 13 C-detection schemes, offer additional opportunities to study structure and functional aspects of fluoride channels., (Copyright © 2024. Published by Elsevier Inc.)

The Chloride Channel (CLC) family includes proton-coupled chloride and fluoride transporters. Despite their similar protein architecture, the former exchange two chloride ions for each proton and are inhibited by fluoride, whereas the latter efficiently transport one fluoride in exchange for one proton. The combination of structural, mutagenesis, and functional experiments with molecular simulations has pinpointed several amino acid changes in the permeation pathway that capitalize on the different chemical properties of chloride and fluoride to fine-tune protein function. Here we summarize recent findings on fluoride inhibition and transport in the two prototypical members of the CLC family, the chloride/proton transporter from Escherichia coli (CLC-ec1) and the fluoride/proton transporter from Enterococcus casseliflavus (CLC F -eca)., (© 2022. The Author(s), under exclusive license to Springer Nature Switzerland AG.)

The interactions between communities of microorganisms inhabiting the dental biofilm is a major determinant of oral health. These biofilms are periodically exposed to high concentrations of fluoride, which is present in almost all oral healthcare products. The microbes resist fluoride through the action of membrane export proteins. This chapter describes the culture, growth and harvest conditions of model three-species dental biofilm comprised of cariogenic pathogens Streptococcus mutans and Candida albicans and the commensal bacterium Streptococcus gordonii. In order to examine the role of fluoride export by S. mutans in model biofilms, procedures for generating a strain of S. mutans with a genetic knockout of the fluoride exporter are described. We present a case study examining the effects of this mutant strain on the biofilm mass, acid production and mineral dissolution under exposure to low levels of fluoride. These general approaches can be applied to study the effects of any gene of interest in physiologically realistic multispecies oral biofilms., (Copyright © 2024. Published by Elsevier Inc.)

The present research work approaches the accumulation of fluoride ions from contaminated water using an aquatic plant Monochoria hastate L. in hydroponic culture. A design of experiment (DOE) has been adopted and an analysis of variance has been conducted to establish the statistical significance of various process parameters. The different experimental factors are root and shoot (Factor A), fluoride concentration (Factor B), and experimental days (Factor C) largely influence the output response. Plants treated with 5 mg/L of fluoride solutions accumulated the highest concentration in root biomass 1.23 mg/gm, and shoot biomass 0.820 mg/gm, dry weight after 21 days' experimentation. The accumulation mechanism and potentiality of treated plants depend on root cells of the plasma membrane and energy-capturing molecules of adenosine triphosphate. Monochoria hastate L. root biomass was characterized to confirm the accumulation of fluoride ions in the experimented plants using scanning electron micrographs-energy dispersive spectrum (SEM-EDS), and Fourier transforms infrared analysis (FTIR) analysis.

There is intense interest in removing fluorinated compounds from the environment, environments are most efficiently remediated by microbial enzymes, and defluorinating enzymes are readily monitored by fluoride determination. Fluorine is the most electronegative element. Consequently, all mechanisms of enzymatic C-F bond cleavage produce fluoride anion, F - . Therefore, methods for the determination of fluoride are critical for C-F enzymology and apply to any fluorinated organic compounds, including PFAS, or per- and polyfluorinated alkyl substances. The biodegradation of most PFAS chemicals is rare or unknown. Accordingly, identifying new enzymes, or re-engineering the known defluorinases, will require rapid and sensitive methods for measuring fluoride in aqueous media. Most studies currently use ion chromatography or fluoride specific electrodes which are relatively sensitive but low throughput. The methods here describe refashioning a drinking water test to efficiently determine fluoride in enzyme and cell culture reaction mixtures. The method is based on lanthanum alizarin complexone binding of fluoride. Reworking the method to a microtiter well plate format allows detection of as little as 4 nmol of fluoride in 200 μL of assay buffer. The method is amenable to color imaging, spectrophotometric plate reading and automated liquid handling to expedite assays with thousands of enzymes and/or substrates for discovering and improving enzymatic defluorination., (Copyright © 2024. Published by Elsevier Inc.)

In the process of tooth development, the interaction between genetic information, epigenetic inheritance, and environment jointly affects the teeth formation. At present, the mechanism of dental fluorosis is rarely studied from transcriptomics, and there is no report on epigenetic perspective. In the study, SD rats were randomly divided into dental fluorosis group and control group fed with NaF (150 mg/L) or distilled water for 8 weeks. After 3.5 days of birth, the RNAs or DNA of rat mandibular molars were detected by RNA-seq or MethylTarget, respectively. The results demonstrated that a total of 1723 differentially expressed genes (DEGs) and 2511 differential expression lncRNAs (DE-lncRNAs) were mainly involved in the ion channels, calcium ion transport, and immunomodulatory signaling pathways. ATP2C1 and Nr1d1, which were related to Ca 2+ transport, cellular calcium homeostasis, endoplasmic reticulum stress and immunity, may be the key genes in the formation of dental fluorosis. Notably, we also found that the immune response plays an important role in the formation of dental fluorosis, and a large amount of DEGs was enriched in immune regulation and NF-κB signaling pathways. Furthermore, the methylation levels of 13 sites were increased in Ago4, Atf3, Atp2c1, Dusp1, Habp4, and Mycl, while methylation levels of 5 CpG sites decreased in Ago4, Atp2c1, Habp4, and Traf6, and conformably, the expression of these genes have been significantly changed. This study comprehensively analyzed the occurrence mechanism of dental fluorosis from transcriptomics and epigenetics, so as to provide theoretical reference for further research., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Hepatotoxicity induced by excessive fluoride (F) exposure has been extensively studied in both humans and animals. Chronic fluorosis can result in liver apoptosis. Meanwhile, moderate exercise alleviates apoptosis caused by pathological factors. However, the effect of moderate exercise on F-induced liver apoptosis remains unclear. In this research, sixty-four three-week-old Institute of Cancer Research (ICR) mice, half male and half female, were randomly divided into four groups: control group (distilled water); exercise group (distilled water and treadmill exercise); F group [100 mg/L sodium fluoride (NaF)]; and exercise plus F group (100 mg/L NaF and treadmill exercise). The liver tissues of mice were taken at 3 months and 6 months, respectively. Hematoxylin-eosin (HE) staining and situ terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) results showed that nuclear condensation and apoptotic hepatocytes occurred in the F group. However, this phenomenon could be reversed with the intervention of treadmill exercise. The results of QRT-PCR and western blot displayed NaF- induced apoptosis via tumor necrosis factor recpter 1 (TNFR1) signaling pathway, while treadmill exercise could restore the molecular changes caused by excessive NaF exposure., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Fluorine is a halogen element widely distributed in nature, but due to excessive emissions from industrial manufacturing and agricultural production, etc., the soil is over-enriched with fluoride and the normal growth of plants is under stress, and it also poses a great threat to human health. In this review, we summarized the sources of fluoride in soil, and then analyzed the potential mechanisms of fluoride uptake in soil-plant systems. In addition, the main influences of soil ecosystems on plant fluoride uptake were discussed, soil management options to mitigate fluoride accumulation in plants were also summarized. The bioremediation techniques were found to be a developmental direction to improve fluoride pollution. Finally, we proposed other research directions, including fluoride uptake mechanisms in soil-plant systems at the molecular expression levels, development of visualization techniques for fluoride transport in plants, interactions mechanisms between soil microhabitats and plant metabolism affecting fluoride uptake, as well as combining abiotic additives, nanotechnology and biotechnology to remediate fluoride contamination problems., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Ltd.)

Biochemical and/or molecular mechanisms of arsenic or fluoride toxicity in experimental animals have been widely investigated in the recent past. However, their combined effects on target cells/organelle are poorly understood. The present study was executed to delineate their combined effects on mitochondrial function in the liver of rat. Female Wistar rats (140 ± 20 g) were force fed individually or in combination with sodium arsenate (4 mg/kg body weight) and sodium fluoride (4 mg/kg body weight) for 90 days. Thereafter, established markers of mitochondrial function viz. mitochondrial lipid peroxidation, oxidative phosphorylation, ATPase, succinic dehydrogenase, and caspase-3 activity were determined. Cytochrome C release and oxidative DNA damage were also estimated in the liver of respective groups of rats. The study showed significant differences in these results amongst the three groups. Observations on parameters viz. LPO, cytochrome-C, caspase-3, and 8-OHdG suggested an antagonistic relationship between these two elements. Results on ATPase, SDH, and ADP:O ratio indicated synergism. It is concluded that As III + F in combination may express differential effects on signalling pathways and proapoptotic/antiapoptotic proteins/genes that contribute to liver cell death. Interaction of As and F with mitochondria., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

This study was carried out to investigate the protective properties of royal jelly on the testicular tissue of rats with testicular damage by giving fluoride. Sperm motility, epididymal sperm density and abnormal sperm ratios were examined and visualized with a light microscope. Expression levels of Caspase-3, Bcl-2, Nrf-2, NF-κB, COX-2, TNF-α and IL1-α proteins in testis tissue were determined by western blot technique. As a result of the study, MDA level, expression level of Bcl-2, NFҡB, COX-2, TNF-α and IL1-α proteins, abnormal sperm rates were found higher in Fluoride-50 and Fluoride100 groups compared to other groups. In addition GSH, Catalase enzyme levels, expression levels of Caspase-3 and Nrf-2 proteins were found to be higher in Fluoride + Royal Jelly groups compared to Fluoride-50 and Fluoride-100 groups. In addition, lower degeneration of testicular tissue was found in the histological evaluation in the Fluoride + Royal Jelly groups compared to the other groups. When the data are evaluated royal jelly provides effective protection against testicular damage. From this point of view, we hope that similar results will be obtained when royal jelly is tested on humans., (© 2023. The Author(s), under exclusive licence to Society for Reproductive Investigation.)

Little is known about the combined effect of fluoride (F) and arsenic (As) on bone metabolism. This study aims to explore the effect of co-exposure to F and As on the expressions of TNF receptor-associated factor 6 (TRAF-6), nuclear factor-kappa B (NF-κB), and the related factors in cell and animal experiments. With the rats exposed to different doses of F, As, and combined F-As, we found that F exposure doses were positively correlated with the protein expression of receptor activator of nuclear factor-kappa B ligand (RANKL), receptor activator of nuclear factor-kappa B (RANK), TRAF-6, NF-κB, and nuclear factor of activated T cells (NFAT-c1) (P < 0.001). As exposure doses were negatively correlated with RANK, TRAF-6, NF-κB, and NFAT-c1 (P < 0.001). The effect of F and As interaction on the protein expression of RANKL, TRAF-6, NF-κB, and NFAT-c1 was significant in bone tissue (P < 0.05). In the cellular experiment, F could promote the mRNA expression of RANK, TRAF-6, and NFAT-c1. A higher concentration of As could inhibit the mRNA expression of Tartrate-resistant acid phosphatase (TRAP), RANK, TRAF-6, and NFAT-c1. The effect of F and As interaction on the mRNA expression of TRAP, RANK, TRAF-6, and NFATc1 in osteoclasts was significant (P < 0.001). In conclusion, the expression of TRAF-6 and NF-κB pathway was affected by F and As co-exposure in osteogenic differentiation, and As could antagonize the promoting effect of F on the expression of TRAF-6, TRAP, RANKL, RANK, NF-κB, and NFAT-c1 in these exposure levels. These results could provide a scientific basis for understanding the interaction of F and As in bone formation., (© 2022. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Objective: The purpose of this study was to understand mouse osteoblast ferroptosis under high fluoride environment by stimulating fluoride levels to corresponding levels. In order to define the underlying mechanism of fluoride resistance in mammals and provide a theoretical basis for fluorosis treatment, high-throughput sequencing was applied to map the genetic changes of fluoride-resistant mouse osteoblasts and analyze the role of ferroptosis-related genes., Methods: Cell Counting Kit-8, Reactive Oxygen Species Assay Kit and C11 BODIPY 581/591 were used to monitor proliferation and ferroptosis of mouse osteoblasts MC3T3-E1 under high fluoride environment. Fluoride-tolerant MC3T3-E1 cells were developed by gradient fluoride exposure. The differentially expressed genes of fluorine-resistant MC3T3-E1 cells were identified by high-throughput sequencing., Results: MC3T3-E1 cells cultured in medium containing 20, 30, 60, 90 ppm F - exhibited decreased viability and increased reactive oxygen species and lipid peroxidation levels in correlation with F - concentrations. High-throughput RNA sequencing identified 2702 differentially expressed genes (DEGs) showed more than 2-fold difference in 30 ppm FR MC3T3-E1 cells, of which 17 DEGs were associated with ferroptosis., Conclusion: High fluoride environment affected the content of lipid peroxides in the body and increased the level of ferroptosis, further, ferroptosis-related genes played specific roles in the fluoride resistance of mouse osteoblasts., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Fluoride is a persistent environmental pollutant, and its excessive intake causes skeletal and dental fluorosis. However, few studies focused on the effects of fluoride on osteocytes, making up over 95% of all bone cells. This study aimed to investigate the effect of fluoride on osteocytes in vitro, as well as explore the underlying mechanisms. CCK-8, LDH assay, fluorescent probes, flow cytometry, and western blotting were performed to examine cell viability, apoptosis, mitochondria changes, reactive oxygen species (ROS) and mitochondrial ROS (mtROS), and protein expressions. Results showed that sodium fluoride (NaF) exposure (4, 8 mmol/L) for 24 h inhibited the cell viability of osteocytes MLO-Y4 and promoted G0/G1 phase arrest and increased cell apoptosis. NaF treatment remarkably caused mitochondria damage, loss of MMP, ATP decrease, Cyto c release, and Bax/Bcl-2 ratio increase and elevated the activity of caspase-9 and caspase-3. Furthermore, NaF significantly upregulated the expressions of LC-3II, PINK1, and Parkin and increased autophagy flux and the accumulation of acidic vacuoles, while the p62 level was downregulated. In addition, NaF exposure triggered the production of intracellular ROS and mtROS and increased malondialdehyde (MDA); but superoxide dismutase (SOD) activity and glutathione (GSH) content were decreased. The scavenger N-acetyl-L-cysteine (NAC) significantly reversed NaF-induced apoptosis and mitophagy, suggesting that ROS is responsible for the mitochondrial-mediated apoptosis and mitophagy induced by NaF exposure. These findings provide in vitro evidence that apoptosis and mitophagy are cellular mechanisms for the toxic effect of fluoride on osteocytes, thereby suggesting the potential role of osteocytes in skeletal and dental fluorosis., (© 2022. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Three peptides comprising mono-, di-, and tri-fluoroethylglycine (MfeGly, DfeGly, and TfeGly) residues alternating with lysine were digested by readily available proteases (elastase, bromelain, trypsin, and proteinase K). The degree of degradation depended on the enzyme employed and the extent of fluorination. Incubation of the peptides with a microbial consortium from garden soil resulted in degradation, yielding fluoride ions. Further biodegradation studies conducted with the individual fluorinated amino acids demonstrated that the degree of defluorination followed the sequence MfeGly > DfeGly > TfeGly. Enrichment of the soil bacteria employing MfeGly as a sole carbon and energy source resulted in the isolation of a bacterium, which was identified as Serratia liquefaciens . Cell-free extracts of this bacterium enzymatically defluorinated MfeGly, yielding fluoride ion and homoserine. In silico analysis of the genome revealed the presence of a gene that putatively codes for a dehalogenase. However, the low overall homology to known enzymes suggests a potentially new hydrolase that can degrade monofluorinated compounds. 19 F NMR analysis of aqueous soil extracts revealed the unexpected presence of trifluoroacetate, fluoride ion, and fluoroacetate. Growth of the soil consortium in tryptone soya broth supplemented with fluoride ions resulted in fluoroacetate production; thus, bacteria in the soil produce and degrade organofluorine compounds.

Excessive exposure of fluoride not only leads to damage on bone, but also has an adverse effect on soft tissues. Oxidative DNA damage induced by fluoride is thought to be one of the toxic mechanisms of fluoride effect. However, the dose-response of fluoride on oxidative DNA damage is barely studied in organisms. This study investigated the concentration of fluoride in rat blood, kidney, liver, and brain as well as the dose-time effect of fluoride on the expression of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in the above tissues. Rats were exposed to 0 mg/L, 25 mg/L, 50 mg/L, and 100 mg/L of fluorine ion and treated for one and three months. The results showed that the accumulation of fluoride in soft tissues was very different. At the first month, blood fluoride was increased, liver and brain fluoride showed a U-shaped change, and kidney fluoride was not significant. At the third month, blood fluoride was altered with an inverted U-shaped change, kidney and brain fluoride increased, but liver fluoride decreased. Both the exposure concentration and the time of exposure had a significant effect on the expression of 8-OHdG in the above tissues. However, the effect patterns of fluoride on these tissues were notably different at different times. At the first month of fluoride treatment, blood, kidney, and liver 8-OHdG decreased with the increasing fluoride concentration. At the third month, blood 8-OHdG showed a U-shaped change, but kidney 8-OHdG altered with an inverted U-shaped change. Liver 8-OHdG increased, while brain 8-OHdG decreased at the third month. Correlation analysis showed that only blood 8-OHdG was significantly inversely correlated with blood fluoride and dental fluorosis grade in both the first and third months. Liver 8-OHdG was negatively and significantly correlated with liver fluoride. There was a weak but nonsignificant correlation between kidney and brain 8-OHdG and fluoride in both tissues. Additionally, blood 8-OHdG was positively correlated with kidney and liver 8-OHdG at the first month and positively correlated with brain 8-OHdG at the third month. Taken together, our data suggests that concentration and time of fluoride exposure had a significant effect on 8-OHdG, but the effect patterns of fluoride on 8-OHdG were different in the tissues, which suggests that the impact of fluoride on 8-OHdG may be a tissue-specific, as well as a non-monotonic positive correlation., (© 2022. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Fluoride is a common contaminant of groundwater and agricultural commodity, which poses challenges to animal and human health. A wealth of research has demonstrated its detrimental effects on intestinal mucosal integrity; however, the underlying mechanisms remain obscure. This study aimed to investigate the role of the cytoskeleton in fluoride-induced barrier dysfunction. After sodium fluoride (NaF) treatment of the cultured Caco-2 cells, both cytotoxicity and cytomorphological changes (internal vacuoles or massive ablation) were observed. NaF lowered transepithelial electrical resistance (TEER) and enhanced paracellular permeation of fluorescein isothiocyanate dextran 4 (FD-4), indicating Caco-2 monolayers hyperpermeability. In the meantime, NaF treatment altered both the expression and distribution of the tight junction protein ZO-1. Fluoride exposure increased myosin light chain II (MLC2) phosphorylation and triggered actin filament (F-actin) remodeling. While inhibition of myosin II by Blebbistatin blocked NaF-induced barrier failure and ZO-1 discontinuity, the corresponding agonist Ionomycin had effects comparable to those of fluoride, suggesting that MLC2 serves as an effector. Given the mechanisms upstream of p-MLC2 regulation, further studies demonstrated that NaF activated RhoA/ROCK signaling pathway and myosin light chain kinase (MLCK), strikingly increasing the expression of both. Pharmacological inhibitors (Rhosin, Y-27632 and ML-7) reversed NaF-induced barrier breakdown and stress fiber formation. The role of intracellular calcium ions ([Ca 2+ ] i ) in NaF effects on Rho/ROCK pathway and MLCK was investigated. We found that NaF elevated [Ca 2+ ] i , whereas chelator BAPTA-AM attenuated increased RhoA and MLCK expression as well as ZO-1 rupture, thus, restoring barrier function. Collectively, abovementioned results suggest that NaF induces barrier impairment via Ca 2+ -dependent RhoA/ROCK pathway and MLCK, which in turn triggers MLC2 phosphorylation and rearrangement of ZO-1 and F-actin. These results provide potential therapeutic targets for fluoride-induced intestinal injury., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Evidence suggests that fluoride-induced neurodevelopment damage is linked to mitochondrial disorder, yet the detailed mechanism remains unclear. A cohort of Sprague-Dawley rats developmentally exposed to sodium fluoride (NaF) was established to simulate actual exposure of human beings. Using high-input proteomics and small RNA sequencing technology in rat hippocampus, we found mitochondrial translation as the most striking enriched biological process after NaF treatment, which involves the differentially expressed Required Meiotic Nuclear Division 1 homolog (RMND1) and neural-specific miR-221-3p. Further experiments in vivo and in vitro neuroendocrine pheochromocytoma (PC12) cells demonstrated that NaF impaired mitochondrial translation and function, as shown by declined mitochondrial membrane potential and inhibited expression of mitochondrial translation factors, mitochondrial translation products, and OXPHOS complexes, which was concomitant with decreased RMND1 and transcription factor c-Fos in mRNA and proteins as well as elevated miR-221-3p. Notably, RMND1 overexpression alleviated the NaF-elicited mitochondrial translation impairment by up-regulating translation factors, but not vice versa. Interestingly, ChIP-qPCR confirmed that c-Fos specifically controls the RMND1 transcription through direct binding with Rmnd1 promotor. Interference of gene expression verified c-Fos as an upstream positive regulator of RMND1, implicating in fluoride-caused mitochondrial translation impairment. Furthermore, dual-luciferase reporter assay evidenced that miR-221-3p targets c-Fos by binding its 3' untranslated region. By modulating the miR-221-3p expression, we identified miR-221-3p as a critical negative regulator of c-Fos. More importantly, we proved that miR-221-3p inhibitor improved mitochondrial translation and mitochondrial function to combat NaF neurotoxicity via activating the c-Fos/RMND1 axis, whereas miR-221-3p mimic tended towards opposite effects. Collectively, our data suggest fluoride impairs mitochondrial translation by dysregulating the miR-221-3p/c-Fos/RMND1 axis to trigger mitochondrial dysfunction, leading to neuronal death and neurodevelopment defects., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Chronic fluoride exposure can cause developmental neurotoxicity, however the precise mechanisms remain unclear. To explore the mechanism of mitophagy in fluoride-induced developmental neurotoxicity, specifically focusing on PRKAA1 in regulating the PINK1/Parkin pathway, we established a Sprage Dawley rat model with continuous sodium fluoride (NaF) exposure and an NaF-treated SH-SY5Y cell model. We found that NaF exposure increased the levels of LC3-Ⅱ and p62, impaired autophagic degradation, and subsequently blocked autophagic flux. Additionally, NaF exposure increased the expression of PINK1, Parkin, TOMM-20, and Cyt C and cleaved PARP in vivo and in vitro, indicating NaF promotes mitophagy and neuronal apoptosis. Meanwhile, phosphoproteomics and western blot analysis showed that NaF treatment enhanced PRKAA1 phosphorylation. Remarkably, the application of both 3-methyladenosine (3-MA; autophagy inhibitor) and dorsomorphin (DM; AMPK inhibitor) suppressed NaF-induced neuronal apoptosis by restoring aberrant mitophagy. In addition, 3-MA attenuated an increase in p62 protein levels and NaF-induced autophagic degradation. Collectively, our findings indicated that NaF causes aberrant mitophagy via PRKAA1 in a PINK1/Parkin-dependent manner, which triggers neuronal apoptosis. Thus, regulating PRKAA1-activated PINK1/Parkin-dependent mitophagy may be a potential treatment for NaF-induced developmental neurotoxicity., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: Fluoride, an environmental contaminant, is ubiquitously present in air, water, and soil. It usually enters the body through drinking water and may cause structural and functional disorders in the central nervous system in humans and animals. Fluoride exposure affects cytoskeleton and neural function, but the mechanism is not clear., Methods: The specific neurotoxic mechanism of fluoride was explored in HT-22 cells. Cellular proliferation and toxicity detection were investigated by CCK-8, CCK-F, and cytotoxicity detection kits. The development morphology of HT-22 cells was observed under a light microscope. Cell membrane permeability and neurotransmitter content were determined using lactate dehydrogenase (LDH) and glutamate content determination kits, respectively. The ultrastructural changes were detected by transmission electron microscopy, and actin homeostasis was observed by laser confocal microscopy. ATP enzyme and ATP activity were determined using the ATP content kit and ultramicro-total ATP enzyme content kit, respectively. The expression levels of GLUT1 and 3 were assessed by Western Blot assays and qRT-PCR., Results: Our results showed that fluoride reduced the proliferation and survival rates of HT-22 cells. Cytomorphology showed that dendritic spines became shorter, cellular bodies became rounder, and adhesion decreased gradually after fluoride exposure. LDH results showed that fluoride exposure increased the membrane permeability of HT-22 cells. Transmission electron microscopy results showed that fluoride caused cells to swell, microvilli content decreased, cellular membrane integrity was damaged, chromatin was sparse, mitochondria ridge gap became wide, and microfilament and microtubule density decreased. Western Blot and qRT-PCR analyses showed that RhoA/ROCK/LIMK/Cofilin signaling pathway was activated by fluoride. F-actin/G-actin fluorescence intensity ratio remarkably increased in 0.125 and 0.5 mM NaF, and the mRNA expression of MAP2 was significantly decreased. Further studies showed that GLUT3 significantly increased in all fluoride groups, while GLUT1 decreased (p < 0.05). ATP contents remarkably increased, and ATP enzyme activity substantially decreased after NaF treatment with the control., Conclusion: Fluoride activates the RhoA/ROCK/LIMK/Cofilin signaling pathway, impairs the ultrastructure, and depresses the connection of synapses in HT-22 cells. Moreover, fluoride exposure affects the expression of glucose transporters (GLUT1 and 3) and ATP synthesis. Sum up fluoride exposure disrupts actin homeostasis, ultimately affecting structure, and function in HT-22 cells. These findings support our previous hypothesis and provide a new perspective on the neurotoxic mechanism of fluorosis., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Fluoride compounds are abundant and widely distributed in the environment at various concentrations, which can seriously injure the human body. In this study, we aim to evaluate the effects of excessive fluoride exposure on the liver, kidney, and heart tissues of healthy female Xenopus laevis by administering NaF (0, 100, and 200 mg/L) in drinking water for 90 days. The expression level of procaspase-8, cleaved-caspase-8, and procaspase-3 proteins were determined by Western blot. Compared with the control group, the group exposed to NaF exhibited expression levels of procaspase-8, cleaved-caspase-8, and procaspase-3 proteins that were considerably upregulated at a concentration of 200 mg/L in the liver and kidney. The cleaved-caspase-8 protein expression in the group exposed to a high concentration of NaF was lower than that in the control group in heart. Histopathological results by hematoxylin and eosin staining showed that excessive NaF exposure caused necrosis of hepatocytes and vacuolization degeneration. Granular degeneration and necrosis in renal tubular epithelial cells were also observed. Moreover, hypertrophy of myocardial cells, atrophy of myocardial fibers and disorder of myocardial fibers were detected. These results demonstrated that NaF-induced apoptosis and the mediated death receptor pathway activation ultimately damaged the liver and kidney tissues. This finding offers a fresh perspective on the effects of F-induced apoptosis in X. laevis., Competing Interests: Conflict of interests The authors declared that there is no conflict of interest., (Copyright © 2023 Elsevier GmbH. All rights reserved.)

Excess fluoride (F) exposure can cause oxidative stress in the kidney. As an antioxidant, selenium (Se) can potentially protect the kidney from F-induced injury in rats. Hence, the histopathological, renal biochemical, oxidative stress, and apoptotic-related indices upon exposure to 100 mg/L sodium fluoride (NaF) and various doses of sodium selenite (Na 2 SeO 3 ; 0.5, 1, and 2 mg/L) were assessed. Our results demonstrated that F-mediated renal structural damage and apoptosis elevated the content of serum creatinine (SCr), inhibited the activity of catalase (CAT) in serum, and increased the production of reactive oxygen species (ROS) in kidney and malondialdehyde (MDA) in serum. Interestingly, 1 mg/L dietary supplementation of Se tangibly mitigated these injuries. Furthermore, F could also change the gene and protein expression of the nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1), and NAD(P)H quinone oxidoreductase1 (NQO1). Concomitantly, the different concentrations of Se notably alleviated their expression. Taken together, 1-2 mg/L Se ameliorated F-induced renal injury through oxidative stress and apoptosis-related routes. The recorded ameliorative effects might be related to the activation of the Nrf2/HO-1/NQO1 signaling pathway., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Excessive fluoride exposure can cause liver injury, but the specific mechanisms need further investigation. We aimed to explore the role of impaired lysosomal biogenesis and defective autophagy in fluoride-induced hepatotoxicity and its potential mechanisms, focusing on the role of transcription factor E3 (TFE3) in regulating hepatocyte lysosomal biogenesis. To this end, we established a Sprague-Dawley (SD) rat model exposed to sodium fluoride (NaF) and a rat liver cell line (BRL3A) model exposed to NaF. The results showed that NaF exposure diminished liver function and led to apoptosis as well as autophagosome accumulation and impaired autophagic degradation. In addition, NaF exposure caused compromised lysosome biogenesis and decreased lysosomal degradation, and inhibited TFE3 nuclear translocation. Notably, the mTOR inhibitors rapamycin (RAPA) and Ad-TFE3 promoted lysosomal biogenesis and enhanced lysosomal degradation function. Furthermore, RAPA and Ad-TFE3 reduced NaF-induced apoptosis by alleviating impaired autophagic degradation. In conclusion, NaF impairs lysosomal biogenesis by inhibiting TFE3 nuclear translocation, decreasing lysosomal degradation function, resulting in impaired autophagic degradation, and ultimately inducing apoptosis. Therefore, TFE3 may be a promising therapeutic target for fluoride-induced hepatotoxicity., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Fluoride is a common environmental contaminant that has harmful effects on human health when it is present in high concentrations. Fluoride enters the bloodstream after being absorbed by the gastrointestinal system when fluoride-contaminated groundwater is consumed by people. The aim of the present study was to determine whether polyphenol-rich nano Moringa oleifera (NMO) could protect rat testicles from sodium fluoride (NaF) damage by evaluating sperm quality, sex hormones, testicular oxidative status, histopathology, and StAR gene expression. Twenty-eight adult Wistar rats were divided equally and randomly into four groups: group one received distilled water; group two received NMO at a dosage of 250 mg/kg/body weight; group three received NaF at a dosage of 10 mg/kg/body weight; and group four received NaF and NMO. The rats were orally administrated daily for a duration of eight weeks. The study's findings demonstrated that, in comparison to rats exposed to NaF alone, co-administration of NMO and NaF enhanced sperm motility and viability, decreased sperm morphological changes, restored the balance between oxidant and antioxidant status, improved testosterone and dehydroepiandrosterone, improved testicular histology, raised the Johnson score, and upregulated the StAR gene in testicular tissue. These findings show that NMO is promise as a prophylactic medication against sodium fluoride-induced testicular damage because administration of NMO had no adverse effects and enhanced reproductive health., Competing Interests: Competing interests The authors say they have no competing interests., (Copyright © 2022 Society for Biology of Reproduction & the Institute of Animal Reproduction and Food Research of Polish Academy of Sciences in Olsztyn. Published by Elsevier B.V. All rights reserved.)

Tea plants have adapted to grow in tropical acidic soils containing high concentrations of aluminum (Al) and fluoride (F) (as Al/F hyperaccumulators) and use secret organic acids (OAs) to acidify the rhizosphere for acquiring phosphorous and element nutrients. The self-enhanced rhizosphere acidification under Al/F stress and acid rain also render tea plants prone to accumulate more heavy metals and F, which raises significant food safety and health concerns. However, the mechanism behind this is not fully understood. Here, we report that tea plants responded to Al and F stresses by synthesizing and secreting OAs and altering profiles of amino acids, catechins, and caffeine in their roots. These organic compounds could form tea-plant mechanisms to tolerate lower pH and higher Al and F concentrations. Furthermore, high concentrations of Al and F stresses negatively affected the accumulation of tea secondary metabolites in young leaves, and thereby tea nutrient value. The young leaves of tea seedlings under Al and F stresses also tended to increase Al and F accumulation in young leaves but lower essential tea secondary metabolites, which challenged tea quality and safety. Comparisons of transcriptome data combined with metabolite profiling revealed that the corresponding metabolic gene expression supported and explained the metabolism changes in tea roots and young leaves via stresses from high concentrations of Al and F. The study provides new insight into Al- and F-stressed tea plants with regard to responsive metabolism changes and tolerance strategy establishment in tea plants and the impacts of Al/F stresses on metabolite compositions in young leaves used for making teas, which could influence tea nutritional value and food safety.

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.

It is critical to determine the mechanism underlying fluoride (F)-induced damage of the testes to develop appropriate strategies for monitoring and intervention. In the present study, exposure to 50 mg/L sodium fluoride (NaF) for 90 days damaged the normal structure of the testes and quality of the sperm, particularly the spermatocytes, and triggered overexpression of human antigen R (Elavl1/HuR) according to western blotting and immunofluorescence. Furthermore, 0.5 mM NaF exposure for 24 h exposure increased the proportion of apoptosis and expression of caspase-3 and caspase-9 in mouse spermatocytes (GC-2spd cell line), whereas inhibition of HuR reduced apoptosis and the expression of caspase-3 and caspase-9. Additionally, inhibition of HuR alleviated F-induced autophagy based on observation of the autophagy bodies, detection of autophagy activity, and analysis of the expression of the LC3II/LC3I and p62 proteins. These results reveal that excessive F can lead to overexpression of HuR, resulting in high levels of apoptosis and autophagy in spermatocytes. These findings improve the understanding of the mechanisms underlying F-induced male reproductive toxicity, and HuR may be explored as a treatment target for certain conditions. Excessive fluoride can induce overexpression of HuR in testis and result in excessive apoptosis and autophagy in spermatocytes as well as male reproductive damage, such as a decreased sperm count, decreased sperm motility, and increased deformity rate., (© 2022. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

The study was designed to determine the fluoride distribution after its oral exposure in drinking water and its associated impact on biochemical, antioxidant markers and histology in the liver, kidney, and heart of male Wistar rats. On 100 ppm exposure, the highest accretion of fluoride occurred in the liver followed by the kidney and heart. Fluoride exposure significantly (p˂0.05) increased the plasma levels of dehydrogenase, aminotransferases, kidney injury molecule-1 (KIM-1), and other plasma renal biomarkers but decreased the levels of total plasma proteins and albumin in a dose-dependent manner. Reduction (p˂0.05) in the activities of antioxidant enzymes viz. acetylcholinesterase, arylesterase, superoxide dismutase, catalase, glutathione peroxidase, and reductase with increased levels of protein and lipid peroxidation was recorded in the liver, kidney, and heart of fluoride-administered rats. Fluoride exposure (100 ppm) induced lipid peroxidation was highest in kidney (4.4 times) followed by liver (2.6 times) and heart (2.5 times) and as compared to their respective control. The percent rise in protein oxidation at 30% was almost equal in the kidney and liver but was 21.5% in the heart as compared to control. The histopathological alterations observed included congestion and hemorrhage along with degeneration and necrosis of parenchymal cells in hepato-renal tissues and myocardium, severity of which varied in a dose-dependent manner. Taken together, fluoride distribution in the liver, heart, and kidney after chronic fluoride intake correlated well with fluoride-induced hepatic and cardio-renal toxicity in a concentration-dependent manner. These results draw attention that chronic fluoride intake pose a significant health risk for human and animal residents of fluoride endemic areas., (© 2022. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)