Influence of the fluoride ion in the stability of bone hydroxyapatite achieved in patients after the fluo-calcic therapy

It has been proposed that fluoride ion might actively enter into the basic structural framework of the bone, within its main constituent, the hydroxyapatite (HA), by substituting systematically the OH- ion in the crystal chemical formula Ca5[(PO4)3OH]. Accurate compositional studies have become necessary in order to explain an eventual stabilizing effect. Loss in weight (TG) and chemical reaction (DTG) while varying the temperature have been carried out for the first time on specimens under normal conditions and after fluo-calcic treatment, in parallel with accurate chemical compositional determinations by atomic absorption analysis. Our investigation shows that the new structure present after treatment is mechanically stable and proves more resistant to osteolytic processes.     

Influence of dietary lead on fluoride bioavailability in the rat

A factorial experiment was conducted with weanling rats fed a purified diet to determine the influence of dietary lead (0 or 100 ppm) as either lead acetate or lead carbonate on fluoride bioavailability (2 or 10 ppm as sodium fluoride). During the 6-wk study, both forms of lead depressed weight gain, regardless of the fluoride level, despite the fact that food intake was similar for all treatment groups. Both forms of lead produced a small, but significant, reduction in femur and second molar fluoride. This effect, however, could only be demonstrated in rats fed diets containing 10 ppm fluoride, indicating a significant interaction between lead and fluoride for these indices of fluoride bioavailability. This interactive effect between fluoride and lead was also demonstrated for apparent fluoride absorption. Both forms of dietary lead significantly increased the lead concentration of plasma, femur, liver, and kidney, and both forms of lead significantly increased the urinary excretion of delta-aminolevulinic acid. The level of dietary fluoride failed to influence these measurements. We therefore conclude that, although small amounts of dietary lead reduce fluoride bioavailability, small amounts of dietary fluoride do not appear to significantly influence the utilization of dietary lead.     

Influence of excessive fluoride consumption on the severity of dystrophic cardiac calcification in DBA/2 mice

Soft tissue calcifications in inbred laboratory mice are frequently observed and are often associated with dystrophic cardiac calcinosis (DCC). We tested the hypothesis that an excessive intake of fluoride would inhibit pathological calcifications in DCC-susceptible mice. A diet containing either a high (200 mg F/kg added to the diet) or low fluoride content (no F added) was fed to both weanling and retired breeder DBA/2 mice. The high-fluoride diet reduced feed intake and body weight gain when given after weaning. It was found that a high fluoride intake effectively reduces soft tissue calcifications in young mice, but not in retired breeders. Because DCC in mice is a pathological finding that could interfere with certain experimental procedures, it is suggested that the optimum fluoride concentration in the diet for mice of susceptible strains should be established.     

The effects of short-term fluoride ingestion on bone formation and resorption in the rat femur

Summary The femurs from rats given 120 ppm fluoride in their drinking water for 4 weeks were examined with histological, histochemical, and radiographic methods. Blood removed from the rats prior to sacrifice was analyzed for calcium, phosphorus, and alkaline phosphatase. Results of this study indicated that the ingestion of fluoride produced wide osteoid seams on the periosteal surface of the femoral diaphysis within 4 weeks. The increase in osteoid appeared to be due to an increase in the number of osteoid-producing cells (osteoblasts) along with a subsequent delay in the mineralization of this tissue. The metabolic activity of osteoblasts did not appear to be affected since the intracellular production of acid and alkaline phosphatase was not inhibited. However, due to the high concentration of fluoride ingested, abnormal collagen deposition and a change in bone mineral may have combined to cause a delay in osteoid mineralization. Mineralization was also delayed in the distal femoral epiphyseal plate resulting in an increase in the number of hypertrophied cells. Resorption of metaphyseal trabecular bone, presumably formed prior to fluoride administration, was increased causing a reduction in the amount of trabeculae extending into the shaft of the femur. Concurrent with these changes in bone, the serum levels of calcium, phosphorus, and alkaline phosphatase remained within normal ranges.     

Influence of the freezing process upon fluoride binding to hemeproteins.

Fluoride association with ferric myoglobins and hemoglobins in aqueous buffers above freezing has been well studied. We chose this reaction to investigate the feasibility of observing titration intermediates and estimating dissociation constants at the freezing temperature by electron paramagnetic resonance spectroscopy at cryogenic temperatures. Dependence of apparent dissociation constant upon protein concentration was observed, a factor of four decrease in protein accompanied by about a fourfold increase in the apparent tightness of binding in the range of protein concentration studied. Binding was also found to depend upon cooling rate and concentration of additives (serum albumin, sucrose, glycerol). These effects appear to be associated with freezing-induced concentration of ligand, a process described in the literature. Bands of high concentration of electrolyte accompany solute rejection during ice growth, sweeping by slowing moving macromolecules. Thus, just before being trapped in the solid, the protein can experience a greater concentration of salt than in the original liquid. A mathematical model of this process, based upon simplifying assumptions about nucleation and ice-crystal growth rates in super-cooled solution, shows how the average concentration of mobile solute species can depend upon the concentration of all species present. Semiquantitative computer simulations of the actual, more complex, freezing are also presented and lead to estimates of ice particle size which are then compared with estimates from the former model.     

Influence of lifelong soy isoflavones consumption on bone mass in the rat

Soy isoflavones (IFs) have shown a bone-sparing effect through epidemiological studies in the Asian population. However, there is no evidence as to whether such protection would result from a lifelong exposure. We investigated the impact of an early exposure to IFs on bone status. Sixty female Wistar rats were fed either a standard diet (n=30) or the same food enriched with IFs (0.87 mg/g of diet) (n=30). After 1 month, they were allowed to mate, and were kept on the same regimen during the whole gestation and lactation periods. At weaning, female pups were each assigned to one of four nutritional groups; within each experimental group, animals were split into two groups, fed either the standard or the IF-rich diet. At 2, 3, 6, 12, 18, and 24 months after birth, 10 animals in each group were sacrificed. Femurs were collected for mechanical testing and bone mineral density (BMD) measurement. The rats perinatally or lifelong exposed to the IF-rich diet exhibited higher body weight and fat mass at 24 months of age. Peak bone mass was achieved between 6 and 12 months and did not differ between groups. In animals perinatally exposed to IF, BMD continued to increase. Thus, at 24 months, femoral total BMD (P<0.05), metaphyseal BMD (P<0.01), and failure load (P<0.05) were higher in the offspring born from mothers provided IF during pregnancy. Postnatal exposure alone did not improve bone parameters. This experiment provides evidence that perinatal exposure to phytoestrogens leads to a higher BMD later in life. It is suggested that these changes may have occurred as a consequence of programming effects, as has been shown for the endocrine and immune systems.     

Effect of manganese on calcification of bone

1. Young mice were maintained on a basal diet composed of meat, which is poor in both manganese and calcium. 2. The addition of small amounts (2·5–5·0mg./kg. of meat) of manganese improved weight gain and calcification of bone and decreased incorporation of injected radiocalcium into bone. 3. Prolonged treatment with larger amounts (10·0–25·0mg./kg. of meat) of manganese depressed growth, induced defective calcification of bone and increased incorporation of radiocalcium into bone.     

Two-stage mechanism of the fluoride inhibition of inorganic pyrophosphatase using the fluoride ion

Some kinetic and spectral approaches have been used to study the interactions in the enzyme-Mg2+-F--pyrophosphate (or imidodiphosphate, a non-hydrolyzeable pyrophosphate analog) system underlying the mechanism of yeast inorganic pyrophosphatase inhibition by fluoride. The continuous curves of the enzymatic reaction were obtained with an automatic phosphate analyzer operating on the time scale of seconds. Increasing concentrations of NaF caused an increase in the inactivation rate constant to a constant level of 5.3 min-1 for PPi (pH 6.2-7.2) and 3.9 min-1 for imidodiphosphate, (pH 7.2). At a saturating fluoride concentration, the initial rate of PPi hydrolysis dropped to 10%. NaF and imidodiphosphate changed the protein spectrum at 270-310 nm and strengthened the binding of each other to the protein. The binding of F- required a Mg2+-binding site with Kd = 0.15 mM being filled in. The free enzyme and its Ca2+ complex did not bind F-. The experimental results indicate that pyrophosphatase inhibition by fluoride occurs in two steps. The inhibitor adds first to the Mg2+ ion on the enzyme in a readily reversible reaction causing a 90% decrease of the catalytic activity. Thereafter, a slow isomerization of the enzymesubstrate complex takes place, resulting in a complete loss of activity.     

Phophate-induced renal calcification in the rat.

Studies were done to investigate nephrocalcinosis produced in weanling female Wistar rats fed pelleted, semisynthetic diets. The rats were fed diets varying in concentrations of Ca and P supplied as inorganic salts for periods of 4--6 weeks and results compared with control rats fed laboratory rodent chow for the same period of time. Measurement of renal Ca and P concentrations showed that nephrocalcinosis was produced by semisynthetic diets with inorganic phosphate concentrations as low as 0.5% on a weight basis; in contrast, rats fed regular laboratory chow (P = 0.72%) showed no evidence of nephrocalcinosis. The severity of the lesion was proportional to dietary phosphate concentrations from 0.5 to 1.0% but other dietary factors modified the severity of the lesion. With the lower dietary phosphate of 0.5%, increasing dietary Ca from 0.5 to 1.0% decreased the severity of the renal calcification. Decreasing protein concentrations from 25 to 15% casein increased the severity of the renal lesions. Other dietary factors also appear to modify the phosphate-induced nephrocalcinosis since no lesions occurred in rats on laboratory chow. It is suggested that the availability of dietary phosphate may be a factor. The phosphate in the semisynthetic diets was totally inorganic while the natural foods of laboratory chow contain, at least in part, organic phosphate.     

Effect of dietary fluoride on selenite toxicity in the rat

Three factorial experiments were conducted to determine if high dietary fluoride (F) would inhibit selenite toxicity in rats. Initially, three levels of selenite (0.05, 3, and 5 mg/kg diet) were matched against three levels of F (2, 75, and 150 mg/kg diet). Fluoride failed to prevent the depressive effect of selenite on 8-wk food intake and body wt gain. Selenium (Se) concentration of plasma and kidney and enzymatic activity of whole blood glutathione peroxidase (GSH-Px) were also unaffected by F. Liver Se concentration, however, was slightly (12%) but significantly (p<0.025) reduced when the highest F and Se levels were combined. Fluoride (150 mg/kg) appeared to reduce liver selenite toxicity (5 mg/kg). Therefore, further study focused on liver histology with treatments that eliminated the middle levels of selenite and F. Fluoride prevented the hepatic necrosis seen in selenite-toxic rats. Similar histological lesions were not observed for kidney or heart. Fluoride partially (26%) but significantly (p<0.025) reduced thiobarbituric-reactive substances in selenite-toxic rats, but there was no F effect on intracellular distribution of liver Se, glutathione levels in liver and kidney, or on liver xanthine oxidase activity. Overall, the protective effect of F on selenite toxicity appears to be confined to liver pathology. The exact mechanism for this effect, however, remains unclear. Oregon Agricultural Experiment Station Technical Paper No. 9728.     

Influence of dietary Ca, Mg, and P on cyclic-AMP excretion and kidney calcification in the rat.

A series of five experiments was conducted with young male albino rats to investigate effects of various levels of dietary Ca, P and Mg on urinary cAMP excretion and kidney calcification. Urinary cAMP excretion was shown to be directly correlated with injected parathyroid (PT) hormone dose level and to be inversely associated with dietary Ca intake. Thus, cAMP excretion may be presumed to reflect PT activity in the young rat. Magnesium deficiency tended to reduce cAMP excretion, while P excess did not affect it. Each treatment induced kidney calcification. Calcium deficiency increased cAMP excretion irrespective of Mg status, although nephrocalcinosis appeared only in the Mg-deficient animals. These data support the view that nephrocalcinosis of dietary origin in the rat is not mediated by increased PT activity.