Inhibitory Effect Of Fluoride Research Articles

Inhibitory Effect of Fluoride on Na+,K+ ATPase Activity in Human Erythrocyte Membrane.

The present study was performed to evaluate the role of long-term consumption of excessive fluoride on electrolyte homeostasis and their transporting mechanisms in erythrocytes of subjects afflicted with dental and skeletal fluorosis. A total of 620 adult (20-50 years) Indian residents participated in this study: 258 men and 242 women exposed to high concentrations of fluoride and 120 age and gender-matched control subjects. Erythrocytes were isolated from blood samples, washed, and used for the estimation of intraerythrocyte sodium and potassium concentrations. Na+,K+ ATPase activity was determined spectrophotometrically from a ghost erythrocyte membrane prepared by osmotic lysis. Erythrocyte analytes were correlated with the water and serum fluoride concentrations by Pearson's bivariate correlation and regression analysis. Results indicated a significant increase in intraerythrocyte sodium (F=14306.265, P<0.0001) in subjects from endemic fluorosis study groups as compared to controls. A significant (P<0.05) positive correlation of intracellular sodium was found with water and serum fluoride concentrations. Mean concentration of intraerythrocytic potassium ions showed significant reduction (F=9136.318, P<0.0001) in subjects exposed to fluoride. A significant (P<0.05) negative correlation of potassium ions was noted with water and serum fluoride concentrations. Na+,K+ ATPase activity was significantly declined (F=1572.763, P<0.0001) in subjects exposed to fluoride. A significant (P<0.05) inverse relationship of Na+,K+ ATPase activity was revealed with water and serum fluoride concentrations.

Effectiveness of sodium fluoride mouthrinses on the prevention of dental caries: A systematic review

Background: Caries inhibitory effect of fluoride has been known for about a century. The use of mouthrinses as a vehicle for applying fluoride in a self-administered preventive program was first proposed by Bibby et al. in 1946. Since then sodium fluoride (NaF) mouthrinses have been used extensively as a caries-preventive measure. Aim: To determine the effectiveness of NaF mouthrinses in the prevention of Dental Caries through a systematic review. Materials and Methods: A search strategy for the review was carried out according to the standard Joanna Briggs Institute systematic review methodology. An electronic search was carried out in PubMed, Medline, Google Scholar, and Cochrane Library from 1970 to 2012. Hand search was conducted through the reference list of articles. The main intention of our investigation was to check the amount of reduction in clinical dental caries. Of 657 articles originally identified, 35 records were considered potentially eligible and sought for further assessment. Results: A total of 28 articles met the inclusion criteria and were assessed independently for methodology and performance. Randomized control study design was followed in 17 studies mainly at evidence level; 2 with a preventive fraction ranging from 16% to 65%. The reported mean annual caries reduction among adolescents was 0.76. Conclusion: Daily or weekly NaF mouthrinses had a significant caries reduction among adolescents. Daily and weekly/fortnightly rinse programs showed an average of 39% fewer decayed-missing-filled-surface. Daily use of NaF had a slightly higher caries reduction rate. Not enough data are available to show the effect of fluoride mouth rinsing programs on deciduous dentition.

Fluoride-induced depletion of polyphosphoinositides in rat brain cortical slices: a rationale for the inhibitory effects on phospholipase C

Fluoride, which is used commonly as a pharmacological tool to activate phosphoinositide-phospholipase C coupled to the heterotrymeric Gq/11 proteins, inhibited the phosphorylation of phosphatidylinositol (PtdIns) to polyphosphoinositides (PtdIns4P and PtdIns4,5P2) in membranes from rat brain cortex. Fluoride enhanced basal production of 3H-inositol phosphates in membranes prepared from brain cortical slices that had been prelabeled with [3H]inositol, but inhibited the stimulation elicited by carbachol in the presence of GTPγS. However in both cases fluoride depleted [3H]PtdIns4P content by 95%. The inhibitory effects of fluoride on the release of 3H-inositol phosphates in slices were not apparent in a pulse [3H]inositol-labeling strategy, but became dramatic in a continuous labeling protocol, particularly at long incubation times. Prelabeling slices with [3H]inositol in the presence of fluoride precluded polyphosphoinositide labeling, and eliminated phospholipase C responsiveness to carbachol under normal or depolarizing conditions, and to the calcium ionophore ionomycin. The lack of response of 3H-polyphosphoinositide-depleted slices to phospholipase C stimuli was not due to fluoride poisoning, unaccesibility of the [3H]inositol label to phospholipase C or desensitization of Gq/11, as the effect of carbachol and GTPγS was restored, in the presence of ATP, in membranes prepared from slices that had been labeled in the presence of fluoride. In conclusion, our data show that fluoride, at a concentration similar to that used to stimulate directly Gq/11-coupled phospholipase C, effectively blocks the synthesis of phospholipase C substrates from PtdIns.

The inhibitory effect of fluoride on carbachol-induced bovine bronchial contraction

The effect of sodium fluoride (NaF) on the responsiveness of airway smooth muscle was investigated in bovine bronchial segments. NaF (0.5–10 mM) induced a delayed concentration-dependent active pressure (AP) and reduced the lactate concentration in the solution. Pyruvate (10 mM) increased the NaF-induced contraction. There was a 50±7% decrease in carbachol (10 μM)-induced AP when bronchi were pretreated with NaF (5 mM) and a 37±9% decrease when NaF (5 mM) was added during the maintained carbachol-induced contraction. These inhibitory effects were enhanced by KCN and hypoxia. When bronchi were pre-incubated with 10 μM verapamil, a calcium channel inhibitor, the contractile effect of 5 mM NaF was reduced to 8±3% of the control. PKC activity in bronchial smooth muscle was significantly increased by NaF (5 mM). Staurosporine (30 nM) abolished the contractile effect of NaF. These results suggest that: (1) NaF either contracts or relaxes bronchial smooth muscle depending on the experimental conditions; (2) the relaxing effect is related to the inhibitory action of NaF on glycolysis; (3) the contractile effect of NaF is possibly mediated by modulation of a calcium channel via a PKC-dependent pathway; (4) carbachol-induced contraction is glycolysis pathway dependent in the absence of NaF but switches to oxidative dependent in its presence.

Effect of cations on the tyrosine kinase activity of the insulin receptor: inhibition by fluoride is magnesium dependent.

We have recently reported that fluoride interacts directly with the insulin receptor, which causes inhibition of its phosphotransferase activity. The inhibitory effect of fluoride on phosphotransferase activity is not due to the formation of complexes with aluminium and occurs in the absence of alterations to the binding of ATP or insulin. In this report we substantiate that the tyrosine kinase activity of insulin receptors partially purified from rat skeletal muscle shows a strict requirement of Mg2+ ions (Ka near 11 mM). This effect of Mg2+ was inhibited in a competitive manner by Mn2+, which is compatible with competition of both divalent ions for binding sites. The inhibition of tyrosine kinase activity caused by fluoride was dependent on the concentration of Mg2+ in the medium and no inhibitory effect was detected at low concentrations of Mg2+. Moreover, the addition of increasing concentrations of Mn2+ in the presence of a constant high concentration of Mg2+, led to a gradual decrease in the inhibitory effect of fluoride. These results indicate that the Mg-insulin receptor complex is the major fluoride-susceptible form. Based on the characteristics of the inhibition of tyrosine kinase shown by fluoride it might be proposed that its action is exerted by the formation of multi-ionic MgF complexes analogous to Pi, which bind to the insulin receptor kinase.

The influence of fluoride on the adsorption of proteoglycans and glycosaminoglycans to hydroxyapatite

Proteoglycans and their spatial arms, the glycosaminoglycans, are known to interact with hydroxyapatite, and are considered to have a role in the regulation of mineralization. This study investigates the interactive mechanisms, with particular attention directed at the influence of fluoride on the adsorption process. Proteoglycans and glycosaminoglycans were adsorbed to hydroxyapatite in the presence of fluoride (1-20 ppm range). The adsorbates included a chondroitin 4-sulfate-rich proteoglycan extracted from rat incisor dentine, hyaluronan, chondroitin 4-sulfate, and dermatan sulfate. The order of glycosaminoglycan in decreasing affinity for hydroxyapatite was chondroitin 4-sulfate, dermatan sulfate, and hyaluronan, and the individual glycosaminoglycans showed different responses to the presence of fluoride. Graded increases in fluoride (1-4 ppm) led to 5-40% reduction of glycosaminoglycan adsorption to hydroxyapatite. The proteoglycan showed less affinity for hydroxyapatite, and demonstrated a reduction in adsorption of up to 22% with 20 ppm fluoride. The inhibitory effect of fluoride indicated an electrostatic mechanism, presumably via the calcium sites in the hydroxyapatite lattice.

Aluminium fluoride and magnesium, activators of heterotrimeric GTP‐binding proteins, affect high‐affinity binding of the fungal toxin fusicoccin to the fusicoccin‐binding protein in oat root plasma membranes

The fusicoccin-binding protein was solubilised from purified oat root plasma membranes. The solubilised protein retained full binding activity, provided that protease inhibitors were included. Sodium fluoride reduced the high-affinity [3H]fusicoccin binding to almost zero in a concentration-dependent way, with an optimum at approximately 20 mM sodium fluoride. The presence of magnesium (> 100 microM) was required for the inhibitory action of fluoride, whereas addition of low amounts of aluminum (25 microM) shifted the fluoride optimum to lower concentrations. Fluoride changes the biochemical properties of the binding protein in a reversible manner, because the inhibition was both prevented and reversed by 1 M ammonium sulphate. The combined effects of aluminium, fluoride and magnesium are reminiscent of the action of activated GTP-binding proteins. Since no functional assay for GTP-binding-protein activity in plants is available yet, GTP-binding-protein activation by fluoride and magnesium was deduced from competition with binding of [gamma-35S]GTP[S] to purified plasma membranes. Indeed, fluoride (20 mM) completely blocked the specific binding of [gamma-35S]GTP[S]. It is concluded that the inhibitory effect of fluoride upon the binding of fusicoccin is indirect and mediated through activated GTP-binding proteins. A hypothesis on the mechanism of fusicoccin action is presented wherein the fusicoccin-binding protein is one component of a signal-transduction chain, two or more steps downstream of a heterotrimeric GTP-binding protein.

Inhibitory effect of fluoride on insulin receptor autophosphorylation and tyrosine kinase activity

Fluoride is a nucleophilic reagent which has been reported to inhibit a variety of different enzymes such as esterases, asymmetrical hydrolases and phosphatases. In this report, we demonstrate that fluoride inhibits tyrosine kinase activity of insulin receptors partially purified from rat skeletal muscle and human placenta. Fluoride inhibited in a similar dose-dependent manner both beta-subunit autophosphorylation and tyrosine kinase activity for exogenous substrates. This inhibitory effect of fluoride was not due to the formation of complexes with aluminum and took place in the absence of modifications of insulin-binding properties of the insulin receptor. Fluoride did not complete with the binding site for ATP or Mn2+. Fluoride also inhibited the autophosphorylation and tyrosine kinase activity of receptors for insulin-like growth factor I from human placenta. Addition of fluoride to the pre-phosphorylated insulin receptor produced a slow (time range of minutes) inhibition of receptor kinase activity. Furthermore, fluoride inhibited tyrosine kinase activity in the absence of changes in the phosphorylation of prephosphorylated insulin receptors, and the sensitivity to fluoride was similar to the sensitivity of the unphosphorylated insulin receptor. The effect of fluoride-on tyrosine kinase activity was markedly decreased when insulin receptors were preincubated with the copolymer of glutamate/tyrosine. Prior exposure of receptors to free tyrosine or phosphotyrosine also prevented the inhibitory effect of fluoride. However, the protective effect of tyrosine or phosphotyrosine was maximal at low concentrations, suggesting the interaction of these compounds with the receptor itself rather than with fluoride. These data suggest: (i) that fluoride interacts directly and slowly with the insulin receptor, which causes inhibition of its phosphotransferase activity; (ii) that the binding site of fluoride is not structurally modified by receptor phosphorylation; and (iii) based on the fact that fluoride inhibits phosphotransferase activity in the absence of alterations in the binding of ATP, Mn2+ or insulin, we speculate that fluoride binding might affect the transfer of phosphate from ATP to the tyrosine residues of the beta-subunit of the insulin receptor and to the tyrosine residues of exogenous substrates.

Purification, characterization and inhibition by fluoride of enolase from Streptococcus mutans DSM 320523.

Enolase from Streptococcus mutans has been purified to homogeneity by a three-step procedure. As shown by analytical ultracentrifugation and polyacrylamide gel electrophoresis under denaturing conditions, the purified enzyme is an octamer with molecular weight Mr = 360 kDa, composed of eight identical subunits with Mr = 45 kDa. The kinetic parameters of S. mutans enolase in the presence of 1 mM Mg2+ are Aspec = 130 IU x mg-1 and KM = 0.44 mM as determined by steady-state experiments in the D-glycerate 2-phosphate to enolpyruvate phosphate reaction. Enzymatic activity is inhibited noncompetitively by fluoride in the range between 0 and 10 mM NaF yielding Ki = Kii = 1.39 mM, but inhibition characteristics become competitive when tested above 10 mM. In the presence of only small amounts of phosphate (0.5 mM) the inhibitory effect of fluoride is enhanced dramatically yielding Ki = 0.26 mM. Inhibition by NaPO3F is competitive with Ki = 0.9 mM, indicating that free fluoride ions in combination with phosphate are more effective in inhibiting S. mutans enolase. It can be concluded that inhibition of enolase by fluoride in combination with phosphate can influence glycolysis in S. mutans and so reduce acid production or even growth rate, thereby leading to potential anticariogenic effects.

Demineralization of Human Dentine Compared with Enamel in a pH-Cycling Apparatus with a Constant Composition during De- and Remineralization Periods

A comparison was made between the demineralization of enamel and dentine with and without abraded surfaces. This was done in a pH-cycling experiment for different demineralization/remineralization ratios--in the range from 1:1 to 1:4--and for different fluoride additions (up to 2 ppm) in solution. A new automatic pH-cycling system, in which the de- and remineralization solutions have a constant composition during the de- and remineralization cycles, was used to create mineral loss in human dentine and enamel. Changes in mineral content were monitored by means of longitudinal microradiography. A linear correlation was found between the amount of mineral lost and the total demineralization time for both dentine and enamel. The demineralization rates were comparable for abraded enamel and dentine and for polished enamel and dentine, and this rate was roughly doubled by the removal of the outer surface for both tissues. This showed that the presence of the outer surface is equally important to dentine and enamel. Under the pH-cycling conditions used, a logarithmic relation was found between the addition of fluoride and the decrease in demineralization for both enamel and dentine. The inhibitory effect of fluoride on demineralization was most pronounced on abraded enamel, followed by pumice-polished enamel, abraded dentine and pumice-polished dentine. About 2 ppm fluoride was needed under the conditions used to stop enamel demineralization completely; in the case of dentine, however, this amount of added fluoride did not inhibit demineralization.

PH‐dependent fluoride inhibition of catalase activity

The inhibitory effects of fluoride on several catalases were examined over a range of pH conditions. Preparations of bovine-liver catalase were sensitive to fluoride under acidic conditions. Catalase activity associated with whole-cell preparations of Actinomyces viscosus NP 311A remained relatively constant between pH 3.0 and 8.0 and was inhibited by fluoride in a pH-dependent manner. Fluoride was also observed to enhance hydrogen peroxide killing of A. viscosus NP 311A under acidic pH conditions. Results suggest that some catalase enzymes, including those associated with common plaque bacteria, may be inhibited by fluoride in a pH-dependent manner.

Inhibitory effect of fluoride on the secretion of insulin

The oral administration of sodium fluoride (NaF) (40 mumol/100 body weight [bw]) to fasting rats produced an immediate fall in insulin levels and the consequent increase in glycemia. These phenomena were observed with plasma fluoride concentrations 5-15 microM. Glycemia and insulin returned to normal levels within 4-5 hours, together with the washing out of fluoride from plasma and soft tissues. The insulin secretion of isolated Langerhans islets, perifused with solutions containing 5, 10, or 20 microM fluoride, was found to be significantly inhibited as a function of fluoride levels, both with basal and stimulatory concentrations of glucose. One hour after the intake of 60 mg of NaF, fasting human volunteers showed increased fluoride (5-15 microM) together with a significant fall of plasma insulin levels.

The effect of sodium fluoride on cereal seed germination and seedling growth

Abstract. Fluoride has been shown to inhibit germination and seedling establishment in barley cv. Natasha, wheat cv. Axona and rice cv. Ishikari. The concentrations of fluoride were selected so as to give a satisfactory dose‐response relationship and also to relate to levels of fluoride present under natural conditions. Concentrations used were zero, 0.5, 1.0, 10 and 40 mol m−3 sodium fluoride. In germination studies, barley was found to be least tolerant and rice most tolerant of fluoride. The inhibition was found to be a response to fluoride itself and the observed effects were not due to pH, sodium or an unspecific effect of halide ion. Phosphate, applied at two concentration levels, was unable to overcome the inhibition. Fluoride was also shown to inhibit seedling growth. The inhibitory effects of fluoride may be accounted for by a wide range of metabolic effects including inhibition of gibberellic acid–triggered alpha amylase activity during germination, and later on to inhibition of chlorophyll synthesis in the developing leaves.

Effects of NaF on amylase in mung bean seedlings

Extracts obtained from mung bean ( Vigna radiata ) seedlings treated with NaF at 0, 0.1, 1.0, and 5.0 mM for 48 and 72 hours have been studied for amylase activity. NaF at concentrations as low as 1.0 mM was found to inhibit the enzyme. The inhibitory effect of fluoride was markedly diminished in the presence of added CaCl 2. These data suggest that the F --induced inhibition of amylase in mung bean seedlings may be due to the interaction of F - with Ca 2+, which is required for enzyme activity.

Relationship between the extent of the initial lesion and the inhibitory effect of APF on the progression of caries-like lesions in vitro.

The aim of this study was to determine whether the extent of an initial artificial caries-like lesion was related to its rate of progress after two applications of APF (1.23% F) and exposure to artificial saliva during lesion formation in vitro. Treatment of small lesions (mean depth 65.7 μm) resulted in their reversal or arrest while the same treatment of larger ones (mean depth 127.4 μm) did not prevent their progress despite evidence of some remineralisation. This suggests that the caries inhibitory effect of fluoride is optimal in the small, early lesion.

Effect of Fluoride on the Absorption of Dietary Fat in Rats

The inhibition of lipid absorption by sodium fluoride in adult male rats was investigated following intraduodenal infusion of labeled lipid and cannulation of the intestinal lymphatics. A striking delay in both the appearance and total amount of lymph radioactivity was observed when 26 mm fluoride was included in the infusate. Effective inhibition of lipid absorption was observed over a 15-fold wide range of fluoride concentration (3.3–56 mm). The inhibitory effect of fluoride was not due to an inhibition of lipolysis since the absorption of free palmitic acid was inhibited to the same extent as that of tripalmitoyl glycerol. Studies on the uptake and distribution of infused lipid in the upper small intestine and experiments examining the extent of fluoride-induced absorptive inhibition of different fatty acids suggest that the effect of fluoride may be on the mucosal reesterification of dietary lipid.fluoride lipid absorption mucosal reesterification

Effect of sodium fluoride on concentrating and diluting ability in the rat

Mechanisms for the concentrating defect produced by fluoride were examined in the rat. Free-water clearance at all levels of delivery was normal after 5 days of chronic fluoride administration in the hereditary hypothalamic diabetes insipidus rat. In the Sprague-Dawley rats, during moderate fluoride administration (120 micronmol/kg per day), urine osmolality and cyclic AMP excretion decreased and urine volume increased, but after exogenous vasopressin, volume decreased and osmolality and cyclic AMP increased appropriately. During larger daily doses of fluoride (240 micronmol/kg per day) urinary osmolality and cyclic AMP decreased and volume increased, which was similar to the changes seen during lower fluoride dosages, but these parameters did not change after exogenous vasopressin. These data suggest that ascending limb chloride reabsorption is unaltered by fluoride administration; in the presence of sufficient fluoride, collecting tubular cells apparently do not generate cyclic AMP or increase permeability appropriately in response to vasopressin. The postulated defect is felt to be due to either a decrease in ATP availability or to a direct inhibitory effect of fluoride on the vasopressin-dependent cyclic AMP generating system.

Inhibitory Effect of Fluoride on Glucose Tests with Glucose Oxidase Strips

Sodium fluoride was inadvertently added as a preservative to the urine of an eight-year-old boy with diabetes mellitus before urinary glucose was measured. On preliminary screening of the urine, the test by glucose oxidase paper reagent strip gave a negative reading for glucose, whereas quantitative urinary glucose assay by the coupled enzyme reaction (hexokinase-glucose 6-phosphate dehydrogenase) gave a glucose concentration of 81.5 g/liter. Inadvertent use of sodium fluoride as a urine preservative may cause a falsely negative result with the glucose tests involving oxidase.

Fluoride Concentrations of Surface Enamel before and after Topical Application of Stannous Fluoride in Naval Recruits

AbstractThe inhibitory effect of fluoride on dental caries is well established, but the exact mechanism of caries prevention is unknown. It has been hypothesised that the effectiveness of topically applied fluoride depends upon its ability to incorporate fluoride into tooth enamel. The purpose of this study was to determine the extent of fluoride uptake in enamel achieved by the topical application of stannous fluoride on Naval Recruits.The 112 Naval Recruits were randomly divided into two equal groups for the study. The experimental group underwent supervised toothbrushing with an 8.9 per cent stannous fluoride prophylaxis paste followed by a 15 second application of a 10 per cent stannous fluoride solution. The control group received no fluoride. Enamel samples were taken from one maxillary central inc;sor of each group initially and again 18 hours after fluoride treatment from the opposite central incisor.The in vivo enamel biopsy technique devised by Brudevold and modified by IVIellberg for measuring fluoride concentrations in enamel was used. The samples were obtained by abrading a limited area of enamel, on the labial surface of the maxillary central incisor teeth, with a rotary felt cone and silicone carbide. The slurry was then collected and analysed for calcium and fluoride content, using an atomic absorption spectrophotometer and a fluoride specific electrode, respectively.An increase in fluoride content of 5 per cent for the group with fluoride witheld, and 13 per cent for the group with fluoride applied were not s:gnificant.The average mean depth for enamel samples was 4.7µm ± 0.7. The differences between depths of the various groups was not significant.Although no significant fluoride uptake was found, it was concluded, because of consistent results obtained with the biopsy technique, that it is a useful tool for further studies of his nature.

Effect of 2, 4-dinitrophenol (DNP) on oxidative phosphorylation in rat liver mitochondria

The effects of a range of DNP concentrations on ADP/O ratio, respiratory control index (RCI), and stimulation of latent ATPase activity of mitochondria have been studied using various substrates. The first and third sites of phosphorylation were found to be more sensitive to DNP action as compared to the second site. No correlation could be seen between any of the three parameters studied. Fluoride was inhibitory to the stimulation of ATPase by DNP only in presence of high concentrations of DNP, but had no inhibitory effect at low DNP concentrations. The inhibitory effects of fluoride and substrates were not additive.