Doses Of Fluoride Research Articles

PI3K/AKT signaling pathway involvement in fluoride-induced apoptosis in C2C12 cells

To investigate the mechanisms of fluoride-induced apoptosis, a fluoride-induced C2C12 skeletal muscle cell (C2C12 cell) model was established in this study, and the viability of the C2C12 cells was measured using an MTT assay. Cell morphological changes were observed via haematoxylin and eosin staining and transmission electron microscopy. Apoptosis was monitored through Hoechst staining. The mRNA and protein expression of PI3K, PDK1, AKT1, BAD, Bcl-2, Bax and caspase-9 were detected through real-time PCR and western blotting, respectively. The results showed that the survival rates of C2C12 cells decreased gradually with an increasing fluoride doses. The C2C12 cell structure was seriously damaged by fluoride, presenting with pyknosis, mitochondrial ridge disruption and swollen endoplasmic reticulum. Furthermore, the expression of mRNA in PI3K, BAD, Bcl-2, Bax and caspase-9 were significantly increased in the fluoride group (P < 0.01), while the expression of PDK1 was markedly decreased (P < 0.01). The expression of protein in BAD, Bcl-2 and Bax were significantly increased in the fluoride group (P < 0.01), while the expression of PDK1 and P-AKT1 was markedly decreased (P < 0.01). In conclusion, fluoride-induced apoptosis in C2C12 cells is related to the PI3K/AKT signaling pathway.

Influence of highly concentrated fluoride dentifrices on remineralization characteristics of enamel in vitro.

The aim of this in vitro study was to evaluate the role of highly fluoridated dentifrice on remineralization characteristics of lowly and highly pre-demineralized enamel artificial caries lesions. Bovine enamel specimens were prepared (pH4.95; 21days) and discriminated in either lowly [L] or highly [H] pre-demineralized artificial caries lesions. Specimens with a mean ΔZbaseline,L (95% CI) of 5120 (4995; 5245) vol.% × μm and a mean ΔZbaseline,H of 8187 (8036; 8339) vol.% × μm were selected and randomly allocated to 12 groups (n = 20). Treatments during pH-cycling (28days; 6 × 60min demineralization/day) were brushing 2×/day with fluoride-free (0ppmF- [L0/H0]), 1100ppmF- [L1100/H1100], 2800ppmF- [L2800/H2800], 5000ppmF- [L5000/H5000], 5000ppmF- + glycerin [L5000 + glycerin/H5000 + glycerin], and 5000ppmF-+ TCP [L5000 + TCP/H5000 + TCP] containing dentifrices. Dentifrice slurries were prepared with deionized water (1:3wt/wt). After cycling specimens presenting lesion surface loss were discarded and for the remaining 202 specimens, transversal microradiographic (TMR) analyses (ΔZpH-cycle/LDpH-cycle) were performed again. Changes in mineral loss (ΔΔZ = ΔZbaseline - ΔZpH-cycle) and lesion depth (ΔLD = LDbaseline - LDpH-cycle) were calculated. Significant differences for ΔΔZ could be found between L0, L1100, and L5000 as well as H0, H1100, and H2800/H5000 (p ≤ 0.01; ANCOVA). Except for 0ppm F-, higher ΔΔZ could be found in highly compared with lowly demineralized specimens (p ≤ 0.004; ANCOVA). After pH-cycling, a second lesion front could only be observed in H5000 and H5000 + TCP. The correlation between ΔΔZ and F- was moderate for lowly and highly demineralized lesions (rL = 0.591; pL < 0.001; rH = 0.746; pH < 0.001), indicating a fluoride dose response for both. For both baseline substrate conditions, a dose response for fluoride could be revealed. Remineralization characteristics of enamel directly depended on baseline mineral loss.

Effects of perinatal fluoride exposure on the expressions of miR-124 and miR-132 in hippocampus of mouse pups

To investigate the effects of perinatal fluoride exposure on learning and memory ability of mouse offspring, ICR female mice were received different doses of sodium fluoride (0, 25, 50, 100 mg/L NaF) from pregnant day 7 to lactational day 21. Pups were exposed to fluoride through the cord blood and breast milk. Open field test showed that compared to the control group, perinatal fluoride exposure significantly decreased the number of entries into the center zone in 100 mg/L NaF group. In the eight-arm maze test, the number of working memory errors, reference memory errors, and the total arm entries were significantly increased in fluoride treatment groups, compared to the control group. Additionally, 100 mg/L NaF significantly elevated the expression levels of miR-124, miR-132, and DiGeorge syndrome chromosomal region 8 (DGCR8) in hippocampus of mouse pups at postnatal day (PND) 21. Contrarily, methyl CpG binding protein 2 (MeCP2) were dramatically reduced in 50 and 100 mg/L NaF groups, while cAMP-response element binding protein (CREB) mRNA level was significantly decreased in all fluoride groups. These findings suggested that the impairment of learning and memory in mouse offspring induced by perinatal fluoride exposure may partly result from the enhanced miR-124 and miR-132 and the alterations of their target genes.

Soil microbial activity, yield and grain quality of rice (Oryza sativa L.) as influenced by graded doses of fluoride in alfisols

A field experiment was conducted at Regional Research and Technology Transfer Station (RRTTS), Chiplima, OUAT, during 2014–15 and 2015–16 to study the impact of graded doses of fluoride on soil microbial activity, yield and grain quality of rice. Six doses of fluoride i.e., No fluoride, 100, 150, 200, 250 and 300 ppm F in form of hydrofluoric acid (HF) were applied as foliar spray. Highest grain (36.73 q/ha) and straw (47.34 q/ha) yield of rice was recorded with T1 (No fluoride) where as lowest grain (32.90 q/ha) and straw (40.09 q/ha) yield was observed with T6 (foliar spray of F @ 300 ppm as HF). The grain yield was decreased significantly with increasing doses of fluoride. The decrease in grain yield was highest (10.42%) with T 6 (foliar spray of F @ 300 ppm as HF) over control (T1 = No fluoride) where a lowest value of 3.02% was observed Significantly highest total chlorophyll content (4.53 mg/g fresh leaf) was observed with T 1 which was decreased to lowest value of 2.26 mg/g fresh leaf (T6) due to increasing doses of fluoride. The lowest value with respect to leaf area index (4.18), grain length (4.38 mm), kernel elongation (6.18 mm), plant height (123.78 cm) and panicle length (22.28 cm) was recorded with T6 (foliar spray of F @ 300 ppm as HF). Howeverhighest F uptake (24.71 kg/ha) was recorded with foliar spray of F @ 300 ppm as HF (T6). The variation in grain quality parameters such as protein content (R2=0.982), amylose content (R2=0.981) and alkali value (R2=0.839) were significant due to increase in F doses. Soil microbial biomass carbon (MBC), soil dehydrogenase activity (DHA) and soil bacterial population were decreased with increased doses of F irrespective of crop growth stages.

The Auditory Working Memory of 13-15-Year-Old Adolescents Using Water with Varying Fluoride Concentrations from Selected Public Primary Schools in North Kajiado Sub County

Water contributes significantly to the physiological functions in the in the human body. However, low fluoride doses have been reported to affect the central nervous system (CNS) without first causing the physical malformations of dental and skeletal fluorosis. Aims and objectives were to determine fluoride concentrations in water used by adolescents who were born and raised in North Kajiado and correlated it with their Auditory Working Memory Index (AWMI). The survey was cross-sectional and descriptive involving 269 school children aged 13-15 years. A purposeful sampling frame was used to select the schools. Fluoride in water was determined using the Fluoride Ion selective electrode. The AWM was assessed using the Wechsler intelligence scale for Children V (WISC-V) subtest. The mean auditory working index for the group was 111.5±22.6 while the boys had a mean AWMI of 111.46±22.37 and the girls 111.56±22.75. A comparison of the AWM of children from low (105.40±23.6) and high (99.52±23.2) fluoride schools and medium with high fluoride school had significant differences. The AWM for the children whose household water had low fluoride had higher AWMI 122.58±19.9 compared to those whose household had high fluoride in the with ANOVA F (2, 266) = 17.968, p≤.0001 and Tukey HSD for low and medium (m=-5.919, se=3.146, p=.145, low and high fluoride, (m=-18.559. se=3.124, p≤.001; medium and high (m=-12.640, se= 3.32, p≤.001 at 95% CL. In conclusion, low fluoride in the water seemed to enhance the AWM. However, the AWM declined with an increased in the fluoride concentration in water.

The role of TGFβ receptor 1-smad3 signaling in regulating the osteoclastic mode affected by fluoride

Studies that have focused on the role TGFβ signaling plays in osteoclast activity are gradually increasing; however, literature is rare in terms of fluorosis. The aim of this study is to observe the role the TβR1/Smad3 pathway plays in fluoride regulating cellsosteoclast-like cells that are under the treatment of TGFβ receptor 1 kinase. The RANKL-mediated osteoclast-like cells from RAW264.7 cells were used as osteoclast precursor model. The profile of miRNA expression in fluoride-treated osteoclast-like cells exhibited 303 upregulated miRNAs, 61 downregulated miRNAs, and further drew 37 signaling pathway maps by KEGG and Biocarta pathway enrichment analysis. TGFβ and its downstream effectors were included among them. Osteoclast viability, formation and function were detected via MTT method, bone resorption pit and tartrate-resistant acid phosphatase (TRACP) staining, respectively. Results demonstrated that different doses of fluoride exhibited a biphasic effect on osteoclast cell viability, differentiation, formation and function. It indicated that a low dose of fluoride treatment stimulated them, but high dose inhibited them. SB431542 acted as TβR1 kinase inhibitor and blocked viability, formation and function of osteoclast-like cells regulated by fluoride. The expression of the osteoclast marker, RANK, and TβR1/Smad3 at gene and protein level was analyzed under fluoride with and without SB431542 treatment. Fluoride treatment indicated little effect on the RANK protein expression; however it significantly influenced TRACP expression in osteoclast-like cells. The stimulation of fluoride on the expression of Smad3 gene and phosphorylated Smad3 protein exhibited dose-dependent manner. SB431542 significantly impeded phosphorylation of Smad3 protein and TRACP expression in osteoclast-like cells that were exposed to fluoride. Our work demonstrated that TGFβ signaling played a key role in fluoride regulating osteoclast differentiation, formation and function. It elucidated that TβR1/Smad3 pathway participated in the mechanism of biphasic modulation of osteoclast mode regulated by fluoride.

The effect of fluoride on the structure, function, and proteome of intestinal epithelia.

Fluoride exposure is widespread, with drinking water commonly containing natural and artificially added sources of the ion. Ingested fluoride undergoes absorption across the gastric and intestinal epithelia. Previous studies have reported adverse gastrointestinal effects with high levels of fluoride exposure. Here, we examined the effects of fluoride on the transepithelial ion transport and resistance of three intestinal epithelia. We used the Caco-2 cell line as a model of human intestinal epithelium, and rat and mouse colonic epithelia for purposes of comparison. Fluoride caused a concentration-dependent decline in forskolin-induced Cl- secretion and transepithelial resistance of Caco-2 cell monolayers, with an IC50 for fluoride of about 3 mM for both parameters. In the presence of 5 mM fluoride, transepithelial resistance fell exponentially with time, with a t1/2 of about 7 hours. Subsequent imaging by immunofluorescence and scanning electron microscopy showed structural abnormalities in Caco-2 cell monolayers exposed to fluoride. The Young's modulus of the epithelium was not affected by fluoride, although proteomic analysis revealed changes in expression of a number of proteins, particularly those involved in cell-cell adhesion. In line with its effects on Caco-2 cell monolayers, fluoride, at 5 mM, also had profound effects on Cl- secretion and transepithelial resistance of both rat and mouse colonic epithelia. Our results show that treatment with fluoride has major effects on the structure, function, and proteome of intestinal epithelia, but only at concentrations considerably higher than those likely to be encountered in vivo, when much lower fluoride doses are normally ingested on a chronic basis.

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

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

Fluoride resistance capacity in mammalian cells involves complex global gene expression changes.

Fluorine is a bone‐seeking element ubiquitously present in the environment and widely used in many oral hygiene products. In humans, excessive intake of fluoride may cause dental and skeletal fluorosis. However, endemic fluorosis does not appear to develop in a proportion of individuals exposed to the same levels of fluoride. The mechanisms by which mammalian cells resist fluoride are still unclear. In this study, we developed strains of mouse L‐929 cells resistant to different levels of fluoride. High‐throughput RNA‐sequencing analyses of the fluoride‐resistant L‐929 cells indicated that massive changes in global gene expression occurred, compared with the wild‐type L‐929 cells. The main biological processes and functions changed were associated with the extracellular region and matrix, response to stress, receptor binding, and signal transduction. This indicated that high doses of fluoride not only exerted stress on L‐929 cells but also induced functional pathways that helped them adapt to the presence of fluoride or to expel it. These data should prove useful in identifying cellular processes or transporters/channels that play central roles in adaptation to or expulsion of fluoride in humans.

A Rat Experimental Study of the Relationship Between Fluoride Exposure and Sensitive Biomarkers.

Chronic excessive fluoride exposure impairs human health and damages not only the skeletal system and the teeth but also the soft tissues such as the brain, liver, kidneys, pancreas and spinal cord. However, there is limited research regarding the exposure levels and sensitive biomarkers. This study was aimed to establish the relationship between fluoride exposure and sensitive biomarkers. Ninety-six rats were randomly divided into six groups, with each group exposed to 0, 2, 4, 8, 16 and 32mg NaF/(kg.bw), respectively. Correlation analysis of the exposure levels, the tissue distributions and the effects was done, and the possible mathematical relationship between the exposure and sensitive biomarkers is discussed. Our findings revealed that the level of serum fluoride can serve as one of the sensitive indicators to reflect the ex-exposure levels (in the present article, ex-exposure means the fluoride exposure pathway from the outside, which differs from the burden of the organism). Furthermore, an equation determining the external exposure dose of serum fluoride was obtained by fitting the coefficient 0.901. Simultaneously, enzyme levels were closely compared with the burden of the tissue, which showed that the activities of alkaline phosphatase significantly correlated with serum fluoride levels (R 2=-0.259, p<0.05), as well as with the fluoride levels of the lung (R 2=0.463, ρ<0.01), the thymus (R 2=0.429, ρ<0.05) and the ovary/testicle (R 2=0.685, ρ<0.01). Results suggested that excessive fluoride exposure might affect reproduction by altering the activities of alkaline phosphatase. In addition, some indicators related to immunity and calcium absorption exhibited sensitivity to tissue burden, among which activating transcriptional factor 4 (ATF4), an important indicator involved in bone metabolism, was found sensitive to the ex-exposure level. These findings highlight the gap between health effects in epidemiology research and the total intake amount of fluoride from the environment. This study presents a novel insight into the method of establishing the relationship between fluoride exposure and sensitive biomarkers.

Genotoxic effect and rat hepatocyte death occurred after oxidative stress induction and antioxidant gene downregulation caused by long term fluoride exposure

Studies focusing on possible genotoxic effects of excess fluoride are contradictory and inconclusive. Currently, studies have reported a probable link to oxidative stress, DNA damage and apoptosis induced by fluoride in rat hepatocytes. We developed an in vivo study administering three doses of fluoride by gavage given to rats for 60 day. Micronucleus test was applied to investigate genotoxic potential of fluoride. The TUNEL method determined DNA fragmentation and apoptosis. Biochemical parameters to investigate mitochondrial swelling and oxidative stress. Semi-quantitative RT-PCR and immunostaining to determine mRNA and protein expression of antioxidant enzymes. Analyses of the hepatic function and morphology were performed. Our results revealed the genotoxic potential of fluoride but did not confirm mitochondrial swelling nor an increase of positive TUNEL labelling induced by fluoride, indicating absence of apoptosis. Oxidative stress induction was confirmed and is probably associated to DNA damage. Cell death events such as empty nuclear spaces, cytoplasm degeneration, nuclear pyknosis, karyorrhexis and karyorrhexis followed by karyolysis were observed. Hepatic function did not appear to be significantly modified makes no evidence of necrosis and suggesting other cell death pathway, the autophagic. In conclusion, prolonged fluoride intake at chosen concentrations caused imbalance of the cellular oxidative state, affected DNA and disrupted cellular homeostasis. It is recommended that fluoride supplementation requires a fresh consideration in light of the current study.

Haematological evaluation of sodium fluoride toxicity in oryctolagus cunniculus.

Blood is promptly affected by environmental pollutants and toxicants that can cause many metabolic disorders. The high level of fluoride acts as a potential pollutant, insecticide and rodenticide with very high toxicity, associated with the hematological damage. This study aimed to determine the toxicity of Sodium Fluoride on hematological parameters in Oryctolagus cunniculus. Twenty rabbits were acclimatized and divided in to control group and three experimental groups.Experimental group-I, II and III were treated with 10, 30 and 50 mg/kg body weight doses of Sodium Fluoride orally. Various blood parameters such as TEC, Hb, HCT, MCV, MCH, MCHC, TLC and PLT count were investigated. Result findings showed that values of blood indices in experimental groups were significantly lower than the control group. Oneway ANOVA was applied for statistical analysis. The outcomes of the current studies indicated the reduction in RBC counts (anemia), leukocyte count (leukocytopenia), monocytosis, eosinopenia, neutrophilia and thrombocytosis on fluoride intoxication. Hematological disruptions like microcytic hypochromic anemia and decreased leukocyte count may be linked to the inflammatory effects of Sodium Fluoride on lymphatic organs.

Skeletal fluorosis: a rare cause of diffuse bone condensation

A 69-year-old man, native of metlaoui in Tunisia, presented to the Department of Rheumatology at our institution with 10 years of non-inflammatory rachialgia with polyarthralgia. On examination, the patient had no fever or joint swelling, his teeth had brown strains and rough, there was diffuse tenderness at the cervical and lumbar spine and neurological examination was normal. Standard radiographs revealed diffuse bone condensation involving all vertebrae of the cervical, dorsal (A) and lumbar (B) spine, the skull (C), the pelvis (D) and the limbs. The origin of the patient, the brownish color of the teeth and the radiological appearance led to suspicion of fluoride poisoning, which was confirmed by the very high blood fluoride and urine dosage. Skeletal fluorosis is a rare toxic osteopathy characterized by massive bone fixation of fluoride. Its origin is dominated in the countries of North Africa by hydro-telluric poisoning. Its severity lies in the development of skeletal deformities and neurological complications. Management of fluorosis generally focuses on symptom treatment.

Dental fluorosis, unguided flouride dosing and oral health advocacy practitioners perception of the emerging paradigm

BackgroundOral health day is an international day to highlight the benefits of a healthy mouth and to promote worldwide awareness of issues around oral health. In Nigeria oral health policy was developed by the Federal Ministry of Health, approved by the National Council on Health and launched in November 2012.&#x0D; ObjectivesFluoride is a topical issue world over. Knowledge of sources of fluoride is a pre-condition to adjusting of the existing natural occurring fluoride level in drinking water.Materials and methods 259 questionnaires were administered to oral health practitioners in University of Benin Teaching Hospital, Consultants through Senior Registrars to Dental students. 182 (70.27%) were returned. Aggregate percentage response was 42.88%.&#x0D; Conclusion:We therefore conclude that a deliberate policy on fluoride dosing through regulation of quality of fluoride sources from Dental products to sea food is very necessary and timely.

Dental Fluorosis and Catalase Immunoreactivity of the Brain Tissues in Rats Exposed to High Fluoride Pre- and Postnatally

This study evaluated dental fluorosis of the incisors and immunoreactivity in the brain tissues of rats given chronic fluoride doses pre- and postnatally. Female rats were given drinking water with 0, 30 or 100ppm fluoride ad libitum throughout gestation and the nursing period. In addition, 63 male offspring were treated with the same water regimens as the mothers after weaning and were followed for 1, 3 or 5months. The upper and lower incisors were collected, and all teeth were examined under a stereomicroscope and scored by two blinded examiners using a modified rodent enamel fluorosis index. Cortical, hippocampal and cerebellar brain samples were evaluated morphologically and immunohistochemically. All fluoride-treated pups were born with low body weight (p=0.001). All animals from the fluoride groups had enamel fluorosis with defects of various degrees. The increase in the dental fluorosis scores in the fluoride treatment groups was significant (p<0.01). The catalase immunoreactivity in the 30- and 100-ppm fluoride groups was significantly higher than that in the controls after 1, 3 and 5months (p<0.001). In conclusion, this study showed that rats with dental fluorosis had catalase immunoreactivity in the brain tissues, which may reflect the neurobehavioral toxicity of fluoride.

The effect of swimming on oral health status: competitive versus non-competitive athletes.

ABSTRACTYoung swimmers are particularly susceptible to the onset of oral diseases. Objective To evaluate the oral health status in young competitive and non-competitive swimmers, involving an assessment of salivary cariogenic bacteria and secretory IgA (S-IgA) concentration.Material and Methods Before training sessions (T1), 54 competitive and 69 non-competitive swimmers had the following parameters assessed: decayed, missing, and filled teeth (DMFT), Plaque Index (PlI), and Gingival Index (GI). At T1 and after training sessions (T2), stimulated saliva was collected and microbiological and immunological analyses were performed.Results Competitive swimmers trained 2.02±0.09 hours 5 times a week, while non-competitive swimmers trained 2.03±0.18 hours a week. A total of 14.7% of competitive swimmers suffered dental trauma related to sports. Only 11.76% of the competitive swimmers took a daily dose of fluoride, against 32.65% of non-competitive swimmers (p=0.029). Neither group followed an established diet or presented statistically significant differences in terms of nutritional supplement drink and chocolate intake. There were statistically significant differences in terms of oral hygiene. No significant difference in clinical indexes (DMFT, PlI, and GI) was present. S. mutans was harbored by 18.6% of competitive and the 32.2% of non-competitive swimmers. S. sobrinus was detected in 22.03% of competitive and 91.6% of non-competitive swimmers (p<0.05). S. sanguinis was found only in the saliva of competitive swimmers. The average S-IgA of competitive swimmers decreased significantly at T2 (p<0.05). The pool water had a daily average pH of 7.22.Conclusions Microbial markers, immune status and sporting characteristics are important for establishing guidelines for management of training load in order to minimize physical stress and the risk of oral infection.

FLUORIDE: A REVIEW OF USE AND EFFECTS ON HEALTH.

Introduction:Appropriate oral health care is fundamental for any individual’s health. Dental caries is still one of the major public health problems. The most effective way of caries prevention is the use of fluoride.Aim:The aim of our research was to review the literature about fluoride toxicity and to inform physicians, dentists and public health specialists whether fluoride use is expedient and safe.Methods:Data we used in our review were systematically searched and collected from web pages and documents published from different international institutions.Results:Fluoride occurs naturally in our environment but we consume it in small amounts. Exposure can occur through dietary intake, respiration and fluoride supplements. The most important factor for fluoride presence in alimentation is fluoridated water. Methods, which led to greater fluoride exposure and lowered caries prevalence, are considered to be one of the greatest accomplishments in the 20th century`s public dental health. During pregnancy, the placenta acts as a barrier. The fluoride, therefore, crosses the placenta in low concentrations. Fluoride can be transmitted through the plasma into the mother’s milk; however, the concentration is low. The most important action of fluoride is topical, when it is present in the saliva in the appropriate concentration. The most important effect of fluoride on caries incidence is through its role in the process of remineralization and demineralization of tooth enamel. Acute toxicity can occur after ingesting one or more doses of fluoride over a short time period which then leads to poisoning. Today, poisoning is mainly due to unsupervised ingestion of products for dental and oral hygiene and over-fluoridated water.Conclusion:Even though fluoride can be toxic in extremely high concentrations, it`s topical use is safe. The European Academy of Paediatric Dentistry (EAPD) recommends a preventive topical use of fluoride supplements because of their cariostatic effect.

Analysis of the Role of Insulin Signaling in Bone Turnover Induced by Fluoride.

The role of insulin signaling on the mechanism underlying fluoride induced osteopathology was studied. We analyzed the expression of genes related with bone turnover and insulin signaling in rats treated by varying dose of fluoride with or without streptozotocin (STZ) in vivo. Furthermore, insulin receptor (InR) expression in MC3T3-E1 cells (pre-osteoblast cell line) was interfered with small interfering RNA (siRNA), and genes related with osteoblastic and osteoclastic differentiation were investigated in cells exposed to fluoride in vitro for 2days. The in vivo study indicated the possible role of insulin in bone lesion induced by excessive amount of fluoride. Fluoride activated the InR and Insulin-like growth factor 1 (IGF1) signaling, which were involved in the mechanism underlying fluoride induced bone turnover. The TGFβ1 and Wnt10/β-catenin pathway took part in the mechanism of bone lesion induced by fluoride, and insulin probably modulated the TGFβ1 and β-catenin to exert action on bone turnover during the development of bone lesion. The in vitro study showed the concomitant decrease of OPG, osterix and OCN with inhibition of InR expression in osteoblast, and three genes still was low in cells co-treated with fluoride and InR siRNA, which suggested that fluoride probably stimulated the expression of OPG, osterix and OCN through InR signaling. In conclusion, insulin played the important role in bone lesion induced by excessive amount of fluoride through mediating InR receptor signaling, and IGF1 signaling probably exerted action on bone turnover caused by overdose of fluoride.

Changes in the microbial activity and thermal properties of soil treated with sodium fluoride

The presence of sodium fluoride in soil can determine its physicochemical and thermal properties as well as microbial activity. In this study, sodium fluoride was introduced to soil in six doses: 1105, 2210, 4420, 6631, 8841 and 11051mgkg−1 DM soil. Changes in pH, electrolytic conductivity, soil microbial biomass (SIR-SMB) and glucose biodegradation parameters were determined in soil samples containing different doses of sodium fluoride. Soil microbial activity was investigated by the modified SIR3 (AA) method and isothermal microcalorimetry. Soil samples containing higher doses of sodium fluoride were characterized by elevated pH and increased electrolytic conductivity. Our results revealed that soil microbial activity and the kinetics of glucose decomposition were determined by sodium fluoride concentrations in soil. Sodium fluoride doses of 1105–6631mgkg−1 DM soil increased the content of microbial biomass and stimulated glucose degradation in soil samples relative to the control (without sodium fluoride). The two highest doses of sodium fluoride (8841 and 11051mgkg−1 DM soil) reduced SIR-SMB and inhibited degradation of organic matter.

Fluoride induces oxidative damage and SIRT1/autophagy through ROS-mediated JNK signaling

Fluoride is an effective caries prophylactic, but at high doses can also be an environmental health hazard. Acute or chronic exposure to high fluoride doses can result in dental enamel and skeletal and soft tissue fluorosis. Dental fluorosis is manifested as mottled, discolored, porous enamel that is susceptible to dental caries. Fluoride induces cell stress, including endoplasmic reticulum stress and oxidative stress, which leads to impairment of ameloblasts responsible for dental enamel formation. Recently we reported that fluoride activates SIRT1 and autophagy as an adaptive response to protect cells from stress. However, it still remains unclear how SIRT1/autophagy is regulated in dental fluorosis. In this study, we demonstrate that fluoride exposure generates reactive oxygen species (ROS) and the resulting oxidative damage is counteracted by SIRT1/autophagy induction through c-Jun N-terminal kinase (JNK) signaling in ameloblasts. In the mouse-ameloblast-derived cell line LS8, fluoride induced ROS, mitochondrial damage including cytochrome-c release, up-regulation of UCP2, attenuation of ATP synthesis, and H2AX phosphorylation (γH2AX), which is a marker of DNA damage. We evaluated the effects of the ROS inhibitor N-acetylcysteine (NAC) and the JNK inhibitor SP600125 on fluoride-induced SIRT1/autophagy activation. NAC decreased fluoride-induced ROS generation and attenuated JNK and c-Jun phosphorylation. NAC decreased SIRT1 phosphorylation and formation of the autophagy marker LC3II, which resulted in an increase in the apoptosis mediators γH2AX and cleaved/activated caspase-3. SP600125 attenuated fluoride-induced SIRT1 phosphorylation, indicating that fluoride activates SIRT1/autophagy via the ROS-mediated JNK pathway. In enamel organs from rats or mice treated with 50, 100, or 125ppm fluoride for 6 weeks, cytochrome-c release and the DNA damage markers 8-oxoguanine, p-ATM, and γH2AX were increased compared to those in controls (0ppm fluoride). These results suggest that fluoride-induced ROS generation causes mitochondrial damage and DNA damage, which may lead to impairment of ameloblast function. To counteract this impairment, SIRT1/autophagy is induced via JNK signaling to protect cells/ameloblasts from fluoride-induced oxidative damage that may cause dental fluorosis.