Toxicity assessment of sodium fluoride in Drosophila melanogaster after chronic sub-lethal exposure

Focus on cognitive impairment induced by excessive fluoride: An update review

Fluorosis is a global public health concern. Prolonged exposure to excessive fluoride causes fluoride accumulation in the hippocampus, resulting in cognitive dysfunction. Cell death is necessary for maintaining tissue function and morphology, and changes in the external morphology of nerve cells and the function of many internal organelles are typical features of cell death; however, it is also a typical feature of cognitive impairment caused by fluorosis. However, the pathogenesis of cognitive impairment caused by different degrees of fluoride exposure varies. Herein, we provide an overview of cognitive impairment caused by excessive fluoride exposure in different age groups, and the underlying mechanisms for cognitive impairment in various model organisms. The mechanisms underlying these impairments include oxidative stress, synaptic and neurotransmission dysfunction, disruption of mitochondrial and energy metabolism, and calcium channel dysregulation. This study aims to provide potential insights that serve as a reference for subsequent research on the cognitive function caused by excessive fluoride.

In-depth transcriptome and physiological function analysis reveals the toxicology of sodium fluoride in the fall webworm Hyphantria cunea

Fluoride is an environmental pollutant that severely injures various organisms in ecosystems. Herein, the non-target organism, fall webworm (Hyphantria cunea), was used to determine the toxicological mechanism of NaF exposure. In this study, H. cunea exposed to NaF showed significant declines in growth and reproduction. The authors conducted RNA sequencing on adipose bodies and midgut tissues from NaF-exposed H. cunea larvae to uncover the toxicological mechanisms. The results showed that extracellular matrix-receptor interaction, pentose and glucuronate interconversions, fatty acid biosynthesis, and ferroptosis might contribute to NaF stress. NaF significantly decreased the antioxidant level, nitrous oxide synthase activity, and NO content, while significantly increasing lipid peroxidation. NaF induced significant changes in the expression of energy metabolism genes. However, the triglyceride content was significantly decreased and the lipase enzyme activity was significantly increased. Moreover, the expression levels of light and heavy chains of ferritin were inhibited in NaF-exposed H. cunea. NaF caused ferritin Fe2+overload in FerHCH1 and FerLCH knockdown H. cunea larvae, activated reactive oxygen species, and reduced the total iron content, eventually increasing the mortality H. cunea larvae. This study identified the toxicological mechanisms of NaF in lipid synthesis and energy metabolism in H. cunea, providing a basis for understanding the molecular mechanisms of NaF toxicity and developing pollution control strategies.

Chronic sub-lethal exposure to clothianidin triggers organismal and sub-organismal-level health hazards in a non-target organism, Drosophila melanogaster

Neonicotinoids are among the most widely used systemic pesticides across the world. These chemicals have gathered significant attention for their potential adverse impacts on non-target organisms. Clothianidin is a novel neonicotinoid pesticide, employed globally to control sucking and chewing types of pests. In nature, various non-target organisms can be exposed to this chemical through contaminated food, water, and air. Nonetheless, extensive investigations demonstrating the sub-lethal impacts of clothianidin on non-target entities are limited. Hence, the present study was aimed to unravel the chronic sub-lethal impacts (LC50 0.74 μg/mL) of clothianidin on a non-target organism, Drosophila melanogaster. The study parameters involved multiple tiers of life ranging from organismal level to the sub-cellular level. 1st instar larvae were exposed to the six sub-lethal concentrations viz. 0.05, 0.06, 0.07, 0.08, 0.09, and 0.1 μg/mL of clothianidin till their 3rd larval instar. Investigations involving organismal level have revealed clothianidin-induced significant reduction in the developmental duration, life span, phototaxis, and physical activities of the treated individuals. Interestingly, the tested compound has also altered the compound eye morphology of treated flies. Study was extended to the tissue and cellular levels where reduced cell viability in gut, brain, and fat body was apparent. Additionally, increased ROS production, nuclear disorganization, and higher lipid deposition were evident in gut of exposed individuals. Study was further extended to the sub-cellular level where chronic exposure to clothianidin up-regulated the major oxidative stress markers such as lipid peroxidation, protein carbonylation, HSP-70, SOD, catalase, GSH, and thioredoxin reductase. Furthermore, the activities of detoxifying enzymes such as CYP4501A1 and GST were also altered. Chronic exposure to clothianidin also triggered DNA fragmentation in treated larvae. In essence, results of this multi-level study depict the ROS-mediated toxicity of clothianidin on a non-target organism, D. melanogaster.

Breaking boundaries: Artificial intelligence for pesticide detection and eco-friendly degradation

Pesticides are extensively used agrochemicals across the world to control pest populations. However, irrational application of pesticides leads to contamination of various components of the environment, like air, soil, water, and vegetation, all of which build up significant levels of pesticide residues. Further, these environmental contaminants fuel objectionable human toxicity and impose a greater risk to the ecosystem. Therefore, search of methodologies having potential to detect and degrade pesticides in different environmental media is currently receiving profound global attention. Beyond the conventional approaches, Artificial Intelligence (AI) coupled with machine learning and artificial neural networks are rapidly growing branches of science that enable quick data analysis and precise detection of pesticides in various environmental components. Interestingly, nanoparticle (NP)-mediated detection and degradation of pesticides could be linked to AI algorithms to achieve superior performance. NP-based sensors stand out for their operational simplicity as well as their high sensitivity and low detection limits when compared to conventional, time-consuming spectrophotometric assays. NPs coated with fluorophores or conjugated with antibody or enzyme-anchored sensors can be used through Surface-Enhanced Raman Spectrometry, fluorescence, or chemiluminescence methodologies for selective and more precise detection of pesticides. Moreover, NPs assist in the photocatalytic breakdown of various organic and inorganic pesticides. Here, AI models are ideal means to identify, classify, characterize, and even predict the data of pesticides obtained through NP sensors. The present study aims to discuss the environmental contamination and negative impacts of pesticides on the ecosystem. The article also elaborates the AI and NP-assisted approaches for detecting and degrading a wide range of pesticide residues in various environmental and agrecultural sources including fruits and vegetables. Finally, the prevailing limitations and future goals of AI-NP-assisted techniques have also been dissected.

In silico study unfolds inhibitory potential of epicatechin gallate against SARS-CoV-2 entry and replication within the host cell

Coronavirus disease-19 (COVID-19) is the ongoing pandemic affecting millions of people worldwide. Several vaccine candidates have been designed and developed for the causative virus, SARS-CoV-2. However high mutation rate in the viral genome and the emergence of new variants have challenged the effectiveness of these vaccines developed for previous strains. Hence, screening and identification of anti-SARS-CoV-2 agents having multi-target potency would be more impactful in the prevention of the disease. Epicatechin gallate (ECG) is a green tea polyphenol having various medicinal properties, including anti-oxidative and anti-inflammatory effects. However its role as anti-SARS-CoV-2 agent is not clear. Hence the present in silico study aims to investigate the binding potential of ECG with several proteins which are critical to SARS-CoV-2 entry and replication within the host cell. Molecular docking analyses have revealed that ECG could potentially block several amino acid residues of entry factors in host cells, spike protein, and many non-structural proteins through Hydrogen bonds and hydrophobic interactions. Such interactions with vital proteins could inhibit SARS-CoV-2 entry and its subsequent replication into the host. Therefore, ECG could be a potential therapeutic agent for the prevention of COVID-19. However, the findings of the present study demand further validation in animal models.

Biocompatible and Oxidation-Resistant Ti3 C2 Tx MXene with Halogen-Free Surface Terminations

Surface chemistry influences not only physicochemical properties but also safety and applications of MXene nanomaterials. Fluorinated Ti3 C2 Tx MXene, synthesized using conventional HF-based etchants, raises concerns regarding harmful effects on electronics and toxicity to living organisms. In this study, well-delaminated halogen-free Ti3 C2 Tx flakes are synthesized using NaOH-based etching solution. The transversal surface plasmon mode of halogen-free Ti3 C2 Tx MXene (833 nm) confirmed red-shift compared to conventional Ti3 C2 Tx (752 nm), and the halogen-free Ti3 C2 Tx MXene has a different density of state by the high proportion of -O and -OH terminations. The synthesized halogen-free Ti3 C2 Tx exhibits a lower water contact angle (34.5°) and work function (3.6 eV) than those of fluorinated Ti3 C2 Tx (49.8° and 4.14 eV, respectively). The synthesized halogen-free Ti3 C2 Tx exhibits high biocompatibility with the living cells, as evidenced by no noticeable cytotoxicity, even at very high concentrations (2000 µg mL⁻1 ), at which fluorinated Ti3 C2 Tx caused ≈50% reduction in cell viability upon its oxidation. Additionally, the oxidation stability of halogen-free Ti3 C2 Tx is enhanced unexpectedly, which cumulatively provides a good rationale for pursuing the halogen-free routes for synthesizing MXene materials for their uses in biomedical and therapeutic applications.

Exposure to cytarabine causes side effects on adult development and physiology and induces intestinal damage via apoptosis in Drosophila

Cytarabine (Ara-C) is a widely used drug in acute myeloid leukemia (AML). However, it faces serious challenges in clinical application due to serious side effects such as gastrointestinal disorders and neurologic toxicities. Until now, the mechanism of Ara-C-induced damage is not clear. Here, we used Drosophila melanogaster (fruit fly) as the in vivo model to explore the side effects and mechanism of Ara-C. Our results showed that Ara-C supplementation delayed larval development, reduced lifespan, impaired locomotor capacity, and increased susceptibility to stress response in adult flies. In addition, Ara-C led to the intestinal morphological damage and ROS accumulation in the guts. Moreover, administration of Ara-C promoted gene expressions of Toll pathway, IMD pathway, and apoptotic pathway in the guts. These findings raise the prospects of using Drosophila as in vivo model to rapidly assess chemotherapy-mediated toxicity and efficiently screen the protective drugs.

In Silico Analysis Reveals the Inhibitory Potential of Madecassic Acid against Entry Factors of SARS-CoV-2

Coronavirus disease 19 (COVID-19) is the ongoing global health emergency caused by SARS-CoV-2 infection. The virus is highly contagious, affecting millions of people worldwide. SARS-CoV-2, with its trimeric spike glycoprotein, interacts with the angiotensin-converting enzyme 2 (ACE2) receptor and other co-receptors like basigin to invade the host cell. Moreover, certain host proteases like transmembrane serine proteases, furin, neuropilin 1 (NRP1), and endosomal cathepsins are involved in the priming of spike glycoproteins at the S1/S2 interface. This is critical for the entry of viral genome and its replication in the host cytoplasm. Vaccines and anti-SARS-CoV-2 drugs have been developed to overcome the infection. Nonetheless, the frequent emergence of mutant variants of the virus has imposed serious concerns regarding the efficacy of therapeutic agents, including vaccines that were developed for previous strains. Thus, screening and development of pharmaceutical agents with multi-target potency could be a better choice to restrain SARS-CoV-2 infection. Madecassic acid (MDCA) is a pentacyclic triterpenoid found in Centella asiatica. It has multiple medicinal properties like anti-oxidative, anti-inflammatory, and anti-diabetic potential. However, its implication as an anti- SARS-CoV-2 agent is still obscure. Hence, in the present in silico study, the binding affinities of MDCA for spike proteins, their receptors, and proteases were investigated. Results indicated that MDCA interacts with ligand-binding pockets of the spike receptor binding domain, ACE2, basigin, and host proteases, viz. transmembrane serine proteinase, furin, NRP1, and endosomal cathepsins, with greater affinities. Moreover, the MDCA-protein interface was strengthened by prominent hydrogen bonds and several hydrophobic interactions. Therefore, MDCA could be a promising multi-target therapeutic agent against SARS-CoV-2 infection.

Fluoride exposure causes behavioral, molecular and physiological changes in adult zebrafish (Danio rerio) and their offspring

Fluoride exposure through drinking water, foods, cosmetics, and drugs causes genotoxic effects, oxidative damage, and impaired cognitive abilities. In our study, the effects of fluoride on anxiety caused by the circadian clock and circadian clock changes in a zebrafish model were investigated at the molecular level on parents and the next generations. For this purpose, adult zebrafish were exposed to 1.5 ppm, 5 ppm, and 100 ppm fluoride for 6 weeks. At the end of exposure, anxiety-like behaviors and sleep/wake behaviors of the parent fish were evaluated with the circadian rhythm test and the novel tank test. In addition, antioxidant enzyme activities and melatonin levels in brain tissues were measured. In addition, morphological, physiological, molecular and behavioral analyzes of offspring taken from zebrafish exposed to fluoride were performed. In addition, histopathological analyzes were made in the brain tissues of both adult zebrafish and offspring, and the damage caused by fluoride was determined. The levels of BMAL1, CLOCK, PER2, GNAT2, BDNF and CRH proteins were measured by immunohistochemical analysis and significant changes in their levels were determined in the F- treated groups. The data obtained as a result of behavioral and molecular analyzes showed that parental fluoride exposure disrupts the circadian rhythm, causes anxiety-like behaviors, and decreases the levels of brain antioxidant enzymes and melatonin in parents. In addition, delay in hatching, increase in death and body malformations, and decrease in blood flow velocity, and locomotor activity was observed in parallel with dose increase in offspring. On the other hand, an increase in offspring apoptosis rate, ROS level, and lipid accumulation was detected. As a result, negative effects of fluoride exposure on both parents and next generations have been identified.

Synergistic action of organophosphates and COVID-19 on inflammation, oxidative stress, and renin-angiotensin system can amplify the risk of cardiovascular maladies

Organophosphates (OPs) are ubiquitous environmental contaminants, widely used as pesticides in agricultural fields. In addition, they serve as flame-retardants, plasticizers, antifoaming or antiwear agents in lacquers, hydraulic fluids, and floor polishing agents. Therefore, world-wide and massive application of these compounds have increased the risk of unintentional exposure to non-targets including the human beings. OPs are neurotoxic agents as they inhibit the activity of acetylcholinesterase at synaptic cleft. Moreover, they can fuel cardiovascular issues in the form of myocardities, cardiac oedema, arrhythmia, systolic malfunction, infarction, and altered electrophysiology. Such pathological outcomes might increase the severity of cardiovascular diseases which are the leading cause of mortality in the developing world. Coronavirus disease-19 (COVID-19) is the ongoing global health emergency caused by SARS-CoV-2 infection. Similar to OPs, SARS-CoV-2 disrupts cytokine homeostasis, redox-balance, and angiotensin-II/AT₁R axis to promote cardiovascular injuries. Therefore, during the current pandemic milieu, unintentional exposure to OPs through several environmental sources could escalate cardiac maladies in patients with COVID-19.

Proteotranscriptomic Integration analyses reveals new mechanistic insights regarding Bombyx mori fluorosis

The commercial value of silkworms has been widely explored and the effects of fluoride exposure on silkworms' breeding and silk production cannot be ignored. Bombyx mori is a commonly used model to explore the mechanisms of fluorosis. In the present study, we analyzed the differences in physiological and biochemical indicators after exposing larva to NaF, then evaluated differential genes and proteins. Compared to control, larvae exposed to 600 mg L^-1 NaF presented decreased bodyweight, damaged midgut tissue, and were accompanied by oxidative stress. The RNA-seq showed 1493 differentially expressed genes (574 upregulated and 919 downregulated). Meanwhile, the TMT detected 189 differentially expressed proteins (133 upregulated and 56 downregulated). The integrative analysis led to 4 upregulated and 9 downregulated genes and proteins. Finally, we hypothesized that fluoride exposure might affect the intestinal digestion of silkworms, inhibit the gene expression of detoxification enzymes and stimulate cellular immune responses. Our current findings provided new insights into insect fluorosis.

Fluorine-Free Fabrication of MXene via Photo-Fenton Approach for Advanced Lithium-Sulfur Batteries

The mainstream synthesis method for MXene is using aqueous fluorine-containing acidic solutions to eliminate the A-element layers from their MAX phases. However, this strategy is environmentally hazardous and impairs the material performance (e.g., supercapacitor and Li-S batteries) owing to the presence of -F terminations. Herein, we exploit a low-temperature "soft chemistry" approach based on photo-Fenton (P.F.) reaction for the fabrication of F-free Ti₃C₂ (Ff-Ti₃C₂) with high purity of 95%. It is confirmed that the continuous generation of highly reactive oxygen species (HO^• and O₂^•- radicals) during the P.F. reaction weakens the metallic Ti-Al bonds in the MAX phase and promotes the formation of high concentration OH^- anions, which are conducive to the sequential topochemical deintercalation of Al layers. Moreover, the strengthened charge accumulation on the Ff-Ti₃C₂ surface creates rich electron "reservoirs" for actuating the Li-S chemistry, which not only strengthens the host-guest interactions but also propels the kinetics of the polysulfide conversion. Taking advantage of the superior mechanical robustness, better electrolyte wettability, and improved electrocatalytic activity, the resultant Ff-Ti₃C₂ can be used as an ideal sulfur host and Li-S chemistry mediator for advanced flexible Li-S batteries.

Prolonged fluoride exposure alters neurotransmission and oxidative stress in the zebrafish brain

Fluoride is an essential chemical found in dental preparations, pesticides and drinking water. Excessive fluoride exposure is related to toxicological and neurological disruption. Zebrafish are used in translational approaches to understand neurotoxicity in both biomedical and environmental areas. However, there is no complete knowledge about the cumulative effects of fluoride on neurotransmission systems. Therefore, the aim of this study was to evaluate whether prolonged exposure to sodium fluoride (NaF) alters cholinergic and glutamatergic systems and oxidative stress homeostasis in the zebrafish brain. Adult zebrafish were used, divided into four experimental groups, one control group and three groups exposed to NaF at 30, 50 and 100 mg.L^-1 for a period of 30 days. After NaF at 30 mg.L^-1 exposure, there were significant decreases in acetylcholinesterase (29.8%) and glutamate uptake (39.3%). Furthermore, thiobarbituric acid-reactive species were decreased at NaF 50 mg.L^-1 (32.7%), while the group treated with NaF at 30 mg.L^-1 showed an increase in dichlorodihydrofluorescein oxidation (41.4%). NaF at 30 mg.L^-1 decreased both superoxide dismutase (55.3%) and catalase activities (26.1%). The inhibitory effect observed on cholinergic and glutamatergic signalling mechanisms could contribute to the neurodegenerative events promoted by NaF in the zebrafish brain.

Role of cerium oxide nanoparticles in improving oxidative stress and developmental delays in Drosophila melanogaster as an in-vivo model for bisphenol a toxicity

Bisphenol A (BPA) is an endocrine-disrupting chemical used commonly in the manufacture of plastic bottles, beverage cans, consumer products, and medical devices. It has a high risk of disrupting hormone-mediated processes which are critical for the growth and development of an infant. In the present study, the flies are exposed to different concentrations of BPA (0.05 and 0.5 mM), which represented the federally regulated LOAEL (50 mg/kg bw/day) and a higher dose of 1 mM, to study the change in cell death, nuclear instability oxidative stress, and behavioral anomalies leading to complex behavioral disorders like Autism. Effects of BPA doses (0.05, 0.5, 1 mM) were studied and the flies showed deficits in social interaction, locomotion, and enhanced oxidative stress that was found to be deteriorating among the flies. Automated tracking and robust MATLAB analysis of behavioral paradigms like position, movement, velocity, and courtship have given us an insight into a detrimental change in development and behavior when exposed to BPA. The flies were also co-treated with Cerium Oxide nanoparticles (CeO₂ NP), well known for its antioxidant properties due to their antioxidant enzyme biomimetic nature, resulted in low oxidative stress, genotoxicity, and an improvement in behavior. In this work, we have tested our hypothesis of oxidative stress and nuclear instability as a potent cause for improper development in Drosophila when exposed to EDCs like BPA which is a potential hazard for both health and environment and might lead to various developmental disorders in children.

Fluoride-Free 2D Niobium Carbide MXenes as Stable and Biocompatible Nanoplatforms for Electrochemical Biosensors with Ultrahigh Sensitivity

Recently, 2D niobium carbide MXene has drawn vast attention due to its merits of large surface area, good metallic conductivity, and tunable band gap, making it desirable for various applications. However, the usage of highly toxic fluoride-containing etchant and quite long etching time in the conventional synthesis route has greatly hindered further exploration of MXene, especially restricting its biomedical application. Herein, novel fluoride-free Nb2CT x nanosheets are prepared by a facile strategy of electrochemical etching (E-etching) exfoliation. Taking advantage of rapid aluminum clearance, excellent chemical stability, and biocompatibility from the MXene by E-etching, fluoride-free Nb2CT x /acetylcholinesterase-based biosensors are constructed for phosmet detection with the limit of detection down to 0.046 ng mL-1. The fabricated Nb2CT x -based biosensor is superior to the counterpart from hydrofluoric acid-etched Nb2CT x , indicating that fluoride-free MXene can enhance the enzyme activity and electron transfer in the biosensor. The results prove that the fluorine-free MXene shows promise for developing biosensors with high performance of ultrahigh sensitivity and selectivity. It is highly expected that the fluoride-free MXene as a stable and biocompatible nanoplatform has great potential to be expanded to many other biomedical fields.

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

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

Potential risk of organophosphate exposure in male reproductive system of a non-target insect model Drosophila melanogaster

Based on several adverse reports of pesticides on reproductive efficiency of various organisms, studies on "reproductive toxicity" have gained importance. Fecundity, reflecting reproductive success of any organism, is governed by several factors from female and male reproductive systems. This present study explored morphological and biochemical alterations in the male reproductive system of a non-target model organism, Drosophila melanogaster following chronic sub-lethal exposure (1^st instar larvae differentially exposed to 1-6 μg/mL until adulthood) to the organophosphate (OP) pesticide, acephate (chronic LC₅₀ 8.71 μg/mL). This study demonstrates altered testis structure, decreased germ cell viability and gross body weight, increased activities of oxidative stress marker lipid peroxidase (LPO), and the endogenous antioxidant enzyme catalase (CAT)in addition with altered expression of reproductive marker proteins like vitellogenin and mitoferrin in acephate-exposed flies when compared to control counterparts. Altered reproductive behavior, indicated by a significant decline in the number of mating pairs, validates the adverse effect of chronic acephate exposure on male reproduction in the non-target insect model D. melanogaster.

Toxicological effects of ciprofloxacin exposure to Drosophila melanogaster

The abuse of ciprofloxacin (CIP) may cause serious side effects and the mechanisms underlying these effects remain unclear. Here, we determinate the 48 h, 72 h and 96 h LC₅₀ values of CIP to Drosophila melanogaster and demonstrate a series of adverse effects after D. melanogaster was exposed to CIP at a sublethal concentration (3.2 mg mL^-1). Treated individuals showed shorter lifespan, delayed development and many of the treated larvae failed to pupate or hatch. Smaller body size was observed at every life stage when exposed to CIP and the size of pupae, the weight of third-instar larvae exhibited a perfectly dose-response relationship that the larger concentration exposed to, the smaller body size or lighter weight is. Moreover, reduction in fat body cell viability, elevated oxidative stress markers (SOD and CAT) and down-regulation of diap1, ex, two target genes of Yorkie (Yki), was observed in response to CIP exposure. Most importantly, we found two types of black spot in Drosophila and the proportion of larvae with a black spot was positively related to the treatment dose, which is new in the field. This study provides a scientific basis for the potential harm caused by abuse of quinolones with the goal of urging cautious use of antibiotics.

Protective role of resveratrol, a natural polyphenol, in sodium fluoride-induced toxicity in Drosophila melanogaster

Sodium fluoride (NaF) is used in water fluoridation and dental products such as mouth rinses and toothpastes. Resveratrol is a natural polyphenol with antioxidant and anti-inflammatory properties. The present study was carried out to evaluate the toxicity of NaF and the protective role of resveratrol in Drosophila melanogaster. For longevity assay, Harwich strain of D. melanogaster was treated with NaF (0, 10, 30, 50, 70 and 90 mg/kg diet) throughout the lifespan and daily mortality recorded. Then, flies were again treated with similar doses of NaF for seven days to evaluate survival rate and oxidative stress markers. Thereafter, 60 mg resveratrol/kg diet was selected to determine its ameliorative role in NaF (70 mg/kg)-induced toxicity in flies: Group A (control), Group B (60 mg resveratrol/kg diet), Group C (70 mg NaF/kg diet), and Group D (resveratrol, 60 mg/kg diet) + NaF, 70 mg/kg diet). Thereafter, Glutathione-S-transferase (GST), catalase and acetylcholinesterase (AchE) activities, as well as total thiol (T-SH), nitrites/nitrates and hydrogen peroxide (H2O2) levels were determined. The results showed that resveratrol prevented NaF-induced elevation of H2O2and nitrites/nitrates levels, as well as catalase activity. In addition, resveratrol restored NaF-induced inhibition of GST and AChE activities and depletion of T-SH content ( P < 0.05). Conclusively, resveratrol offered protective benefit against NaF-mediated toxicity in flies due to its antioxidant and anti-inflammatory properties.

Impact statement

D. melanogaster was used to understand the impact of NaF on lifespan and emergence rate as well as the rescue role of resveratrol. These parameters are difficult to carry out in previously used models such as rodents. This further enforces in part, the suitability of D. melanogaster in studying NaF-induced toxicity and the therapeutic effects of drugs. Additionally, we found that resveratrol rescued D. melanogaster from oxidative stress-induced by sodium fluoride (NaF) administration. This study is of public health significance as it indicated that the consumption of fruits rich in resveratrol such as grapes may offer protective role against inadvertent exposure to NaF and related chemicals.

Role of fluoride induced epigenetic alterations in the development of skeletal fluorosis

Fluoride is an essential trace element required for proper bone and tooth development. Systemic high exposure to fluoride through environmental exposure (drinking water and food) may result in toxicity causing a disorder called fluorosis. In the present study, we investigated the alteration in DNA methylation profile with chronic exposure (30 days) to fluoride (8 mg/l) and its relevance in the development of fluorosis. Whole genome bisulfite sequencing (WGBS) was carried out in human osteosarcoma cells (HOS) exposed to fluoride. Whole genome bisulfite sequencing (WGBS) and functional annotation of differentially methylated genes indicate alterations in methylation status of genes involved in biological processes associated with bone development pathways. Combined analysis of promoter DNA hyper methylation, STRING: functional protein association networks and gene expression analysis revealed epigenetic alterations in BMP1, METAP2, MMP11 and BACH1 genes, which plays a role in the extracellular matrix disassembly, collagen catabolic/organization process, skeletal morphogenesis/development, ossification and osteoblast development. The present study shows that fluoride causes promoter DNA hypermethylation in BMP1, METAP2, MMP11 and BACH1 genes with subsequent down-regulation in their expression level (RNA level). The results implies that fluoride induced DNA hypermethylation of these genes may hamper extracellular matrix deposition, cartilage formation, angiogenesis, vascular system development and porosity of bone, thus promote skeletal fluorosis.

Environmental remediation of heavy metal ions by novel-nanomaterials: A review

Recently, novel-nanomaterials with excellent sorption capacities, mild stability, and environmental-friendly performance, have enabled massive developments in capturing heavy metal ions. This review firstly introduces the preparation and modification of novel-nanomaterials (e.g., MOFs, nZVI, MXenes, and g-C₃N₄). Then, the heavy metal ions' sorption properties and the impact of environmental conditions have been discussed. Subsequently, the sorption mechanisms are verified through batch experiments, spectral analysis, surface complexation models, and theoretical calculations. Finally, the applications prospects of novel-nanomaterials in removing heavy metal ion polluted water have also been discussed, which provide perspective for future in-depth research and practical applications.

Separation and recovery of NaF from fluorine containing solution by the common ion effect of Na. Heliyon 2018;4:e01029. [PMID: 30582047 PMCID: PMC6299105 DOI: 10.1016/j.heliyon.2018.e01029]

The separation and recovery of NaF from fluorine containing solution by the common ion effect of Na⁺ was studied. The solubility of NaF in the solutions of NaCl, NaNO₃, Na₂CO₃, Na₂SO₄ and NaOH at 30 °C was determined. It was found that when the compound containing sodium, such as Na₂CO₃ or Na₂SO₄ was added into NaF saturated solution to product the common ion effect of Na⁺, most of the NaF can be crystallized without evaporating concentration, and the added Na₂CO₃ or Na₂SO₄ can be recovered by cooling crystallization. Combining cooling crystallization with the common ion effect of Na⁺, different processes can be designed to recover NaF from different fluorine containing solutions. This will have a significant impact on the treatment of fluorine containing wastewater and the recycling of fluorine resources.

Effects of sodium fluoride on the reproductive development of Bombyx mori

Bombyx mori was used as a model to evaluate the reproductive toxicity of NaF in insects. Significant reduction in cocoon quality, survival rate, fecundity, and hatchability were observed upon NaF treatment groups. Fluoride determination indicated that F^- has a cumulative effect on the gonad of silkworm. High-performance liquid chromatography revealed that the testosterone content of males was decreased in NaF-treated groups, and enzyme-linked immunosorbent assay showed that the estradiol content was decreased in NaF-treated females. Ultrastructural observation of testicles of silkworm larvae revealed mitochondrial turgescence, endoplasmic reticulum destruction, the appearance of vacuoles and lysosomes, and apoptosis and necrosis of cells in NaF-treated groups. Altered tail length and tail DNA content in Comet assays further confirmed DNA damage in NaF-treated larvae. We demonstrated reproductive toxicity of fluoride toward silkworm at physiological and biochemical levels, and the results provide a theoretical basis for revealing the reproductive toxicity of fluoride in terrestrial insects.

Interplay of ROS and behavioral pattern in fluoride exposed Drosophila melanogaster

Reactive oxygen species (ROS) is known to be associated with the process of aging and other health hazards. Organisms are compelled to compromise with body homeostasis when exposed to toxic substances. In the present study sodium fluoride (NaF) exposure (10-100 μgmL^-1) to Drosophila melanogaster in the parental (P) generation leads to increase in adult mortality and alteration in male-female ratio in the P and F1 (1st Filial) generation. Post-treatment alterations in selected behavioral traits (crawling, embedding and climbing) were observed in larvae and adults. Altered behavioral pattern was found to be associated with reduced mitochondrial activity and decreased number of viable brain cells in treated individuals. Interestingly, higher cholinesterase activities in treated males in comparison to females demonstrate a definite sex bias in NaF-induced response. Hyper-activation of antioxidant enzyme like catalase and reduced superoxide dismutase (SOD) and glutathione-s-transferase (GST) activity indicate a shift in the oxidative status after fluoride exposure. Additionally, increase in lipid peroxidation suggests enhancement in ROS which is further validated through increment in protein carbonyl content. Hence, the observations of the present study propose behavioral alterations resulting from increased ROS after chronic exposure to sub-lethal concentrations of NaF in D. melanogaster.

The toxic effect of sodium fluoride on Spodoptera frugiperda 9 cells and differential protein analysis following NaF treatment of cells

Accumulation of excess fluoride has a destructive effect on the environment, endangering human health, affecting organism growth and development, and leading to damage to the biological chain, thereby affecting ecological environment balance. In recent years, numerous studies focused on the molecular mechanisms associated with fluoride toxicity; however, fluoride-toxicity mechanisms in insect cells remain unclear. This study explored the toxic impact of sodium fluoride (NaF) on Spodoptera frugiperda 9 (Sf9) insect cells. High concentrations of NaF (10^-4 M, 10^-3 M and 10^-2 M) resulted in cell enlargement, cell membrane blurring and breakage, and release of cellular contents. Dose-response curves indicated that NaF-specific inhibition rates on Sf9-cell activity increased along with increases in NaF concentration, with a half-inhibitory concentration (IC₅₀) for NaF of 5.919 × 10^-3 M at 72 h. Compared with controls, the percentages of early and late apoptotic and necrotic cells clearly increased based on observed increases in NaF concentrations. Two-dimensional gel electrophoresis combined with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was used to detect differentially expressed proteins in Sf9 cells treated with IC₅₀ NaF, identifying 17 proteins, seven of which were upregulated and 10 downregulated. These results demonstrated that Sf9 cells showed signs of NaF-mediated toxicity through alterations in cell morphology, apoptosis rates, and protein expression.

Trans-generational transmission of altered phenotype resulting from flubendiamide-induced changes in apoptosis in larval imaginal discs of Drosophila melanogaster

The eye and wing morphology of Drosophila melanogaster maintain unique, stable pattern of genesis from larval eye and wing imaginal discs. Increased apoptosis in cells of eye and wing discs was found to be associated with flubendiamide (fluoride containing insecticide) exposure (at the range 0.25-10μg/mL) in D. melanogaster larvae. The chemical fed larvae on attaining adulthood revealed alterations in morphology and symmetry of their compound eyes and wings through scanning electron microscopy. Nearly 40% and 30% of flies (P generation) demonstrated alterations in eyes and wings respectively. Transmission electron microscopic study (at the range 1-20μg/mL) also established variation in the rhabdomere and pigment cell orientation as well as in the shape of the ommatidium. Subsequent SEM study with F₁ and F₂ generation flies also revealed structural variation in eye and wing. Decrease in percentage of altered eye and wing phenotype was noted in subsequent generations (P> F₁>F₂). Thus, the diamide insecticide, flubendiamide, expected to be environmentally safe at sub-lethal concentrations was found to increase apoptosis in larvae and thereby cause morphological alteration in the adult D. melanogaster. This study further demonstrated trans-generational transmission of altered phenotype in three subsequent generations of a non-target insect model, D. melanogaster.

Sirt1 overexpression suppresses fluoride-induced p53 acetylation to alleviate fluoride toxicity in ameloblasts responsible for enamel formation

Low-dose fluoride is an effective caries prophylactic, but high-dose fluoride is an environmental health hazard that causes skeletal and dental fluorosis. Treatments to prevent fluorosis and the molecular pathways responsive to fluoride exposure remain to be elucidated. Previously we showed that fluoride activates SIRT1 as an adaptive response to protect cells. Here, we demonstrate that fluoride induced p53 acetylation (Ac-p53) [Lys379], which is a SIRT1 deacetylation target, in ameloblast-derived LS8 cells in vitro and in enamel organ in vivo. Here we assessed SIRT1 function on fluoride-induced Ac-p53 formation using CRISPR/Cas9-mediated Sirt1 knockout (LS8^Sirt/KO) cells or CRISPR/dCas9/SAM-mediated Sirt1 overexpressing (LS8^Sirt1/over) cells. NaF (5 mM) induced Ac-p53 formation and increased cell cycle arrest via Cdkn1a/p21 expression in Wild-type (WT) cells. However, fluoride-induced Ac-p53 was suppressed by the SIRT1 activator resveratrol (50 µM). Without fluoride, Ac-p53 persisted in LS8^Sirt/KO cells, whereas it decreased in LS8^Sirt1/over. Fluoride-induced Ac-p53 formation was also suppressed in LS8^Sirt1/over cells. Compared to WT cells, fluoride-induced Cdkn1a/p21 expression was elevated in LS8^Sirt/KO and these cells were more susceptible to fluoride-induced growth inhibition. In contrast, LS8^Sirt1/over cells were significantly more resistant. In addition, fluoride-induced cytochrome-c release and caspase-3 activation were suppressed in LS8^Sirt1/over cells. Fluoride induced expression of the DNA double strand break marker γH2AX in WT cells and this was augmented in LS8^Sirt1/KO cells, but was attenuated in LS8^Sirt1/over cells. Our results suggest that SIRT1 deacetylates Ac-p53 to mitigate fluoride-induced cell growth inhibition, mitochondrial damage, DNA damage and apoptosis. This is the first report implicating Ac-p53 in fluoride toxicity.

Fluorine-free preparation of titanium carbide MXene quantum dots with high near-infrared photothermal performances for cancer therapy

Titanium carbide MXene quantum dots (QDs) were synthesized using an effective fluorine-free method as a biocompatible and highly efficient nanoagent for photothermal therapy (PTT) applications. In contrast to the traditional, hazardous and time-consuming process of HF pretreatment, our fluorine-free method is safe and simple. More importantly, abundant Al oxoanions were found to be modified on the MXene QD surface by the fluorine-free method, which endowed the QDs with strong and broad absorption in the NIR region. As a result, the as-prepared MXene QDs exhibited an extinction coefficient as large as 52.8 Lg^-1 cm^-1 at 808 nm and a photothermal conversion efficiency as high as 52.2%. Both the values are among the best reported so far. The as-prepared MXene QDs achieved simultaneous photoacoustic (PA) imaging and the remarkable PTT effect of tumors. Moreover, MXene QDs showed great biocompatibility without causing noticeable toxicity in vitro and in vivo, indicating their high potential for clinical applications.

Sodium fluoride adversely affects ovarian development and reproduction in Drosophila melanogaster

The study demonstrates the effects of chronic sub-lethal exposure of sodium fluoride (NaF) on reproductive structure and function of female Drosophila melanogaster. As a part of treatment, flies were maintained in food supplemented with sub-lethal concentrations of NaF (10-100 μg/mL). Fecundity, ovarian morphology, presence and profusion of viable cells from ovary and fat body were taken into consideration for evaluating changes in reproductive homeostasis. Wing length (a factor demonstrating body size and reproductive fitness) was also monitored after NaF exposure. Significant reduction in fecundity, alteration in ovarian morphology along with an increase in apoptosis was observed in treated females. Simultaneous decline in viable cell number and larval weight validates the result of MTT assay. Furthermore, altered ovarian Glucose-6-phosphate dehydrogenase and catalase activities together with increased rate of lipid peroxidation after 20 and 40 μg/mL NaF exposure confirmed the changes in reproduction related metabolism. Enhanced lipid peroxidation known for ROS generation might have induced genotoxicity which is confirmed through Comet assay. The enzyme activities were not dose dependent, rather manifested a bimodal response, which suggests a well-knit interaction among the players inducing stress and the ones that help establish physiological homeostasis.

Monitoring the effects of a lepidopteran insecticide, Flubendiamide, on the biology of a non-target dipteran insect, Drosophila melanogaster

Various organisms are adversely affected when subjected to chronic fluoride exposure. This highly electronegative ion present in several insecticide formulations is found to be lethal to target pests. In the present study, Drosophila melanogaster is treated with sub-lethal concentrations of a diamide insecticide formulation, Flubendiamide. Chronic exposure to the diamide (0.5-100 μg/mL) was found to be responsible for increase in fluoride ion concentration in larval as well as adult body fluid. Interestingly, 100 μg/mL Flubendiamide exposure resulted in 107 and 298% increase in fluoride ion concentration whereas only 23 and 52% of Flubendiamide concentration increase in larval and adult body fluid, respectively. Further, in this study, selected life cycle parameters like larval duration, pupal duration and emergence time showed minimal changes, whereas percentage of emergence and fecundity revealed significant treatment-associated variation. It can be noted that nearly 79% reduction in fecundity was observed with 100 μg/mL Flubendiamide exposure. The variations in these parameters indicate probable involvement of fluoride ion in detectable alterations in the biology of the non-target model insect, D. melanogaster. Furthermore, the outcomes of life cycle study suggest change in resource allocation pattern in the treated flies. The altered resource allocation might have been sufficient to resist changes in selective life cycle parameters, but it could not defend the changes in fecundity. The significant alterations indicate a definite trade-off pattern, where the treated individuals happen to compromise. Thus, survival is apparently taking an upper hand in comparison to reproductive ability in response to Flubendiamide exposure. Graphical abstract The figure demonstrates increase in Fluoride and Flubendiamide concentrations in Drosophila melanogaster after chronic sub-lethal exposure to Flubendiamide. Treatment-induced alterations in larval and pupal duration, reduction in fecundity and alteration in male-female ratio is also observed.

The effects of fluoride on neuronal function occurs via cytoskeleton damage and decreased signal transmission

It has been reported that fluoride exposure may cause serious public health problems, particularly neurotoxicity. However, the underlying mechanisms remain unclear. This study used Neuro-2A cells to investigate the effects of fluoride on the cytoskeleton. The Neuro-2A cells were exposed to 0, 1, 2, 4 and 6 mM sodium fluoride (NaF) for 24 h. Cell viability and lactate dehydrogenase (LDH) release were examined. It was observed that exposure to NaF reduced cell viability, disrupted cellular membrane integrity, and high levels of LDH were released. The observed changes occurred in a dose response manner. Morphologic observations showed that cell became rounded and were loosely adherent following exposure to NaF. Axon spines and normal features disappeared with high dose NaF treatment. The expression of MAP2 and synaptophysin decreased, particularly at 4 mM and 6 mM (P < 0.05) for MAP2. These results corroborate the morphologic observations. The content of glutamate and NMDAR (glutamate receptor) protein were assessed to help understand the relationship between synapses and neurotransmitter release using ELISA and Western-blot. Compared with the control, glutamate and NMDAR expression declined significantly at 4 mM and 6 mM (P < 0.05) group. Finally, the ultrastructural changes observed with increasing doses of NaF were: disappearance of synapses, mitochondrial agglutination, vacuole formation, and cellular edema. Taken together, NaF exposure disrupted cellular integrity and suppressed the release of neurotransmitters, thus effecting neuronal function. These findings provide deeper insights into roles of NaF in neuron damage, which could contribute to a better understanding of fluoride-induced neurotoxicity.

Putative mechanisms of genotoxicity induced by fluoride: a comprehensive review

Genotoxicity is the ability of an agent to produce damage on the DNA molecule. Considering the strong evidence for a relationship between genetic damage and carcinogenesis, to elucidate the putative mechanisms of genotoxicity induced by fluoride are important to measure the degree of risk involved to human populations. The purpose of this article is to provide a comprehensive review on genotoxicity induced by fluoride on the basis of its mechanisms of action. In the last 10 years, all published data showed some evidence related to genotoxicity, which is due to mitochondrial disruption, oxidative stress, and cell cycle disturbances. However, this is an area that still requires a lot of investigation since the published data are not sufficient for clarifying the genotoxicity induced by fluoride. Certainly, the new information will be added to those already established for regulatory purposes as a safe way to promote oral healthcare and prevent oral carcinogenesis.