Relationship between bone fluoride content and histological evidence of calcification defects in osteoporotic women treated long term with sodium fluoride

Biomechanical and Bone Material Properties of Schnurri-3 Null Mice

Schnurri‐3 (Shn3) is an essential regulator of postnatal skeletal remodeling. Shn3‐deficient mice (Shn3–/–) have high bone mass; however, their bone mechanical and material properties have not been investigated to date. We performed three‐point bending of femora, compression tests of L3 vertebrae. We also measured intrinsic material properties, including bone mineralization density distribution (BMDD) and osteocyte lacunae section (OLS) characteristics by quantitative backscatter electron imaging, as well as collagen cross‐linking by Fourier transform infrared microspectroscopy of femora from Shn3–/– and WT mice at different ages (6 weeks, 4 months, and 18 months). Moreover, computer modeling was performed for the interpretation of the BMDD outcomes. Femora and L3 vertebrae from Shn3–/– aged 6 weeks revealed increased ultimate force (2.2‐ and 3.2‐fold, p < .01, respectively). Mineralized bone volume at the distal femoral metaphysis was about twofold (at 6 weeks) to eightfold (at 4 and 18 months of age) in Shn3–/– (p < .001). Compared with WT, the average degree of trabecular bone mineralization was similar at 6 weeks, but increased at 4 and 18 months of age (+12.6% and +7.7%, p < .01, respectively) in Shn3–/–. The analysis of OLS characteristics revealed a higher OLS area for Shn3–/– versus WT at all ages (+16%, +23%, +21%, respectively, p < .01). The collagen cross‐link ratio was similar between groups. We conclude that femora and vertebrae from Shn3–/– had higher ultimate force in mechanical testing. Computer modeling demonstrated that in cases of highly increased bone volume, the average degree of bone matrix mineralization can be higher than in WT bone, which was actually measured in the older Shn3–/– groups. The area of 2D osteocyte lacunae sections was also increased in Shn3‐deficiency, which could only partly be explained by larger remnant areas of primary cortical bone. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Changes in the degree of mineralization with osteoporosis and its treatment

The diagnosis of osteoporosis is based on low bone mineral density (BMD) and/or the occurrence of fragility fractures. The majority of patients, however, have also abnormally low bone matrix mineralization. The latter is indicative of alterations in bone turnover rates and/or in kinetics of mineral accumulation within the newly formed bone matrix. Osteoporosis therapies can alter the bone matrix mineralization according to their action on bone turnover and/or mineralization kinetics. Antiresorptives, including the most widely used bisphosphonates, reduce the bone turnover rate resulting in a decrease in heterogeneity and an increase in the degree of mineralization toward to or even beyond normal values. Anabolic agents increase the bone volume and the amount of newly formed bone resulting in a likely transient decrease in mean degree and homogeneity of mineralization. Hence, the measurement of bone matrix mineralization is a sensitive tool to evaluate the response to therapy.

Bone quality: what is it and how is it measured?

Bone quality describes aspects of bone composition and structure that contribute to bone strength independently of bone mineral density. These include bone turnover, microarchitecture, mineralisation, microdamage and the composition of bone matrix and mineral. New techniques to assess these components of bone quality are being developed and should produce important insights into determinants of fracture risk in untreated and treated disease.

The Effect of Tamoxifen and Fluoride on Bone Mineral Density, Biomechanical Properties and Blood Lipids in Ovariectomized Rats

The most important aspect of therapy with fluoride and tamoxifen concerns its influence on bone tissue and lipid metabolism. The aim of the study was to evaluate the effect of tamoxifen and natrium fluoride (NaF) on bone metabolism, biochemical properties and blood lipids levels in ovariectomized rats. The study was performed in Wistar rats divided into 5 subgroups: ovariectomized controls, rats treated with NaF 20 mg/kg/24 hr, rats treated with NaF 20 mg/kg/24 hr+tamoxifen 2 mg/kg/24 hr, rats treated with NaF 20 mg/kg/24 hr plus tamoxifen 4 mg/kg/24 hr, and sham-operated controls. In ovariectomized rats the increase of total cholesterol, low-density lipoproteins cholesterol (LDL-cholesterol) as well as the decrease of bone mineral content, bone mineral density and biomechanical properties was observed. The therapy with NaF increased the level of total cholesterol, LDL-cholesterol, triglycerides, bone mineral density, bone mineral content. In this group the decrease of bone strength and stiffness was observed. The administration of tamoxifen reduced the changes in plasma lipid levels, but did not improve the biomechanical properties of bone tissue.

Structure and mineralisation density of antler and pedicle bone in red deer (Cervus elaphus L.) exposed to different levels of environmental fluoride: a quantitative backscattered electron imaging study

The structure and relative degree of mineralisation of antler and pedicle bone of yearling red deer stags exposed either to low or high levels of environmental fluoride were determined by digital quantitative backscattered electron (BSE) imaging. Bone fluoride content (BFC) in antlers (845 +/- 86 mg F-/kg ash, arithmetic mean +/- S.E.M.) and pedicles (1448 +/- 154 mg F-/kg ash) of deer from a highly fluoride polluted area in North Bohemia (Czech Republic) were significantly higher (P < 0.001) than those of controls from uncontaminated regions in West Germany (antlers: 206 +/- 41, pedicles: 322 +/- 52 mg F-/kg ash). Mean (56.5 +/- 4.5%) and maximum (84.9 +/- 2.1%) mineralised bone area of the control antlers significantly (P < 0.05 and P < 0.001, respectively) exceeded the corresponding values for the N. Bohemian deer (43.3 +/- 1.3 and 73.3 +/- 1.9%, respectively), while the pedicles from the 2 groups did not differ significantly. In the pooled antler samples (n = 18), negative correlations existed between BFC and mean (r(s) = -0.62, P < 0.01) as well as maximum (r(s) = -0.69, P < 0.01) mineralised bone area. Morphological imaging revealed a decreased width and an increased porosity of the antler cortex in the N. Bohemian specimens. Mean (148.5 +/- 1.7) and maximum (154.2 +/- 1.7) BSE-signal intensities (= grey levels; range between a monobrominated (grey level 0) and a monoiodinated (grey level 255) dimethacrylate resin standard) of the antlers from the controls were significantly higher than those of the N. Bohemian deer (140.7 +/- 2.1 and 145.7 +/- 2.2, respectively; P < 0.05 for both comparisons). In the pooled antler samples, negative correlations between BFC and mean (r(s) = -0.51, P < 0.05) as well as maximum (r(s) = -0.52, P < 0.05) BSE-signal intensities were observed. No significant differences in mineralisation density parameters were found for the 2 pedicle samples, and BFC and mineralisation density of the pooled pedicles were uncorrelated. Morphological imaging revealed bone mottling (denoting increased remodelling activity) and frequent occurrence of apparently increased osteocyte lacunae in some of the pedicles from the N. Bohemian deer. It is concluded that the reduced amount of mineralised bone in, and the lower mineralisation density of, the N. Bohemian antlers resulted from a fluoride induced disturbance of bone mineralisation. The rapid growth of antlers leads both to a high mineral demand and a high rate of fluoride uptake during antlerogenesis. This, and the limited lifespan of antlers, which does not allow for a compensation of a delay in the onset or progression of the mineralisation process, renders antler bone particularly susceptible to fluoride. Antlers are therefore considered a useful model for studying fluoride effects on bone formation. Furthermore, analysis of cast antlers enables a noninvasive monitoring of environmental pollution by fluorides.

Monofluorophosphate combined with hormone replacement therapy induces a synergistic effect on bone mass by dissociating bone formation and resorption in postmenopausal women: a randomized study

Sodium fluoride stimulates bone formation and has been used to treat osteoporosis for decades despite debate about the antifracture efficacy. Hormone replacement therapy (HRT) results in only modest increases in bone mineral density (BMD). However, for women with low bone mass, the ideal therapy should not only inhibit bone resorption but simultaneously stimulate bone formation to increase bone mass above the fracture threshold. We thus performed a randomized, double-blind, placebo-controlled intervention study to prospectively investigate the effect of a low dose of fluoride, in combination with HRT, on BMD and biochemical markers of bone turnover. One hundred healthy postmenopausal women (60-70 yr old) were thus randomly assigned to: 1) HRT [transdermal 17beta-estradiol, releasing 50 microg/day; plus oral norethisterone acetate (NETA), 1 mg/day]; or 2) oral monofluorophosphate (MFP; equivalent to fluoride, 20 mg/day); or 3) HRT+MFP; or 4) placebo, for 96 weeks. All participants received a calcium supplement of 1000 mg/day. Sixty-eight women completed the study. We found a pronounced, linear increase in spinal BMD during treatment with HRT+MFP [11.8% (1.7% SEM)], which was significantly greater than the increase in the HRT group [4.0% (0.5% per yr); P < 0.05]. MFP produced a smaller increase [2.4% (0.6% per yr)], whereas there was no change in the placebo group [0.0% (0.5% SEM)]. Similar changes were found at the other skeletal sites (distal forearm, hip, and total body). Markers of bone formation showed a fall in the HRT group, which was significantly more pronounced than in the combined HRT+MFP group. A nonsignificant increase was found in the MFP group, whereas the placebo group showed a decrease caused by calcium treatment. The marker of bone resorption decreased significantly more in the HRT and the HRT+MFP groups than in the placebo group but tended to increase in the MFP group. In conclusion, this study shows, by use of biochemical markers of bone turnover, that bone resorption and formation may be dissociated, as a result of actions of two compounds with diverging effects on bone turnover. Furthermore, the synergistic effects of relatively low doses of the compounds suggested statistically and clinically significant increases in trabecular and probably also cortical bone. Adverse effects were relatively rare and mild.

Hydroxyapatite and fluorapatite coatings for fixation of weight loaded implants

Survivor analysis of total hip replacement recently has shown disappointing results in younger patients. To improve this, ceramic coatings have been applied to prostheses for cementless use. A new fluorine containing coating, fluorapatite, has been shown to increase bone ingrowth compared with hydroxyapatite in unloaded models. In a weight loaded model, the effects of hydroxyapatite and fluorapatite coated implants on implant fixation and bone ingrowth were evaluated. Eight hydroxyapatite and fluorapatite coated implants with porous surface were inserted into the medial femoral condyles of 8 mature dogs in a paired design. The implants initially were surrounded by a gap communicating with the joint space and were loaded during each gait cycle. After 25 weeks, no differences in pushout data or bone ingrowth between hydroxyapatite and fluorapatite coated implants were found. An important finding was the absence of foreign body reaction in the bone. Neither hydroxyapatite nor fluorapatite coatings delaminated during implantation or as a result of the pushout test. Bone repair activity remained in the initial gap zone, but most of the bone was of the lamellar type. No difference in bone remodeling between the hydroxyapatite and fluorapatite coated implants was found in the initial gap zone. Microprobe analysis showed no increase in fluorine content around the fluorapatite coated implants. The hydroxyapatite and fluorapatite coatings seem efficacious after a 25-week implantation period under weight loaded conditions.

Fewer bone histomorphometric abnormalities with intermittent than with continuous slow-release sodium fluoride therapy

To help resolve the uncertainty whether sodium fluoride (NaF) therapy should be given intermittently or continuously, we examined iliac crest bone biopsies (before and after treatment) and fragility fracture rates in 35 intermittently treated (group I) and 69 continuously treated (group C) patients; all received calcium. The following statistically significant results were obtained. Reduction in vertebral fracture rate was similar in the two groups. Trabecular thickness and the structurally more important mineralized thickness increased only in group I. Group I also accumulated less excess osteoid (surface, volume). Mean osteoid thickness did not change in either group because of a bimodal distribution of wide seams with osteoblasts and double tetracycline labels, and thin seams without osteoblasts or labels. Osteoid was lamellar. Osteoid in abnormal sites (within bone marrow or bone, or around osteocytes) was found less frequently in group I. Adjusted apposition rate declined and mineralization lag time increased in both groups because of extended unlabelled osteoid seams. Erosion surface increased only in group C. Hook and/or tunnel erosion was seen less frequently in group I; it was closely associated with osteoid in abnormal sites and correlated with osteoid surface. Extended osteoid surface may have forced osteoclasts to hollow out trabeculae, leaving the empty osteoid shell in marrow. Excess osteoid volume and eroded surface and osteoid and erosion in abnormal sites correlated with bone fragility in group C. We conclude that intermittent therapy is to be preferred because it (1) increased mineralized trabecular thickness, (2) did not cause excessive osteoid accumulation and erosion, (3) showed less osteoid and erosion in abnormal sites and (4) led to a similar reduction in the vertebral fracture rate as did continuous treatment. The question of whether intermittency of therapy has some other effect independent of the cumulative dose of fluoride administered cannot be answered by this study.

Reductions in bone strength after fluoride treatment are not reflected in tissue-level acoustic measurements

Acoustic velocity measurements are used to estimate tissue-level bone strength after fluoride therapy for osteoporosis. However, acoustic measurements provide information about elasticity, not strength, and bone elasticity does not necessarily correlate with bone strength at a tissue level. The current study was undertaken to evaluate the effects of fluoride treatment on tissue-level acoustic velocities, and to determine the relationship between acoustic velocity and bone strength measured in the femur, femoral neck, and spine. Young adult rabbits were treated with either 0 or 100 parts per million of fluoride in their drinking water for six months. After treatment, the bones were harvested for measurement of tissue fluoride, bone strength, and acoustic properties. Acoustic velocities were measured in the femoral midshaft using an acoustic microscope with a 50 MHz transducer. Both longitudinal and transverse velocities were measured. After the initial acoustic measurements the bone specimens were treated to remove either the organic matrix or mineral, and the acoustic measurements were repeated. Fluoride treatment increased bone fluoride levels 7-8 fold and reduced all biomechanical parameters. Most notably the fracture force of the femoral neck was reduced by 25% (p < 0.005), and the fracture stress of the L-5 vertebra was reduced by 19% (p < 0.05). Fluoride treatment had no significant effect on any of the measured acoustic velocities. The elastic anisotropy of the bone was decreased by demineralization (p < 0.0001) and increased by removal of the organic matrix (p < 0.0001), but unaffected by fluoride treatment. Acoustic measurements were not correlated with bone strength in the femoral neck or femoral midshaft. There was a positive correlation between the longitudinal velocity measured in the femur and the vertebral fracture stress, but this was the only positive association between acoustic velocities and strength measurements. These data cast doubt on the utility of high frequency (>2 MHz) acoustic measurements for evaluating the efficacy of fluoride therapy, especially in the hip.

Comparison of alendronate and sodium fluoride effects on cancellous and cortical bone in minipigs. A one-year study

Fluoride stimulates trabecular bone formation, whereas bisphosphonates reduce bone resorption and turnover. Fracture prevention has not been convincingly demonstrated for either treatment so far. We compared the effects of 1-yr treatment of 9-mo-old minipigs with sodium fluoride (NaF, 2 mg/kg/d p.o.) or alendronate (ALN, 4 amino-1-hydroxybutylidene bisphosphonate monosodium, 1 mg/kg/d p.o.) on the biomechanical and histomorphometric properties of pig bones. As expected, NaF increased and ALN decreased bone turnover, but in these normal animals neither changed mean bone volume. NaF reduced the strength of cancellous bone from the L4 vertebra, relative to control animals, and the stiffness (resistance to deformation) of the femora, relative to the ALN group. In the ALN-treated animals, there was a strong positive correlation between bone strength and L5 cancellous bone volume, but no such correlation was observed in the NaF group. Furthermore, the modulus (resistance to deformation of the tissue) was inversely related to NaF content and there was a relative decrease in bone strength above 0.25 mg NaF/g bone. Moreover, within the range of changes measured in this study, there was an inverse correlation between bone turnover, estimated as the percentage of osteoid surface, and modulus. These findings have relevant implications regarding the use of these agents for osteoporosis therapy.

Histomorphometric analysis of iliac crest bone biopsies in placebo-treated versus fluoride-treated subjects

In a 4-year controlled, prospective trial, histomorphometric analysis was used to compare the tissue-level skeletal effects of fluoride therapy in 43 postmenopausal women (75 mg NaF/day) with those of 35 matching placebo subjects; all subjects received 1500 mg/day elemental calcium supplement. In addition to an initial, baseline biopsy, a second biopsy was obtained after 6, 18, 30 or 48 months. Measurements were made on a third biopsy obtained from 8 subjects following at least 72 months of fluoride therapy. The change in cancellous bone volume or trabecular thickness in fluoride-treated subjects was not different from a change in placebo-treated subjects. However, paired analysis in the fluoride-treated subjects indicated that bone volume was increased between the first and second biopsies (p < 0.005). Both osteoid length and width were significantly increased in fluoride compared with placebo subjects; however, only the osteoid surface increased linearly (r = 0.63, p < 0.001). The mineral apposition rate and relative tetracycline-covered bone surface were not different between fluoride and placebo treatment, although they were decreased in both groups in the second biopsy. The tetracycline-covered bone surface returned to normal in the third biopsy. Definitive evidence for osteomalacia is a prolonged mineralization lag time, which following fluoride treatment was found to be increased 9-fold in the second biopsy and 4-fold in the third biopsy. Further evidence for osteomalacia was increased osteoid thickness by 6 months, evidence of focal areas of interstitial mineralization defects, and broad tetracycline labels of low fluorescence intensity. In the third biopsies, osteoclastic resorption was observed beneath osteoid seams. Fluoride therapy increased the cortical width compared with placebo treatment (p < 0.02), and increased the osteoid surface in Haversian canals, but did not change the osteoid width, resorption surface or cortical porosity. After an initial rise, serum fluoride levels remained constant, and the urine values fell slightly. The bone fluoride concentration rose throughout the treatment period, and was correlated with the change in osteoid-covered bone surface (r = 0.56, p < 0.001). Although we found definitive evidence for osteomalacia, the cause of the osteomalacia was not determined in this study. On the other hand, the presence of bone resorption beneath unmineralized osteoid and of osteocyte halos is suggestive of hyperparathyroidism. Thus, it is possible that the strong stimulus for bone formation brought about by fluoride therapy resulted in relative calcium deficiency.

Marked decrease in trabecular bone quality after five years of sodium fluoride therapy--assessed by biomechanical testing of iliac crest bone biopsies in osteoporotic patients

Sodium fluoride has for more than 2 decades been a commonly used therapeutic agent for established osteoporosis because of a repeatedly documented anabolic effect on trabecular bone mass. Recently, however, three controlled trials have failed to demonstrate any therapeutic advantage of NaF over placebo with respect to vertebral fracture rate. Also, there have been several reports of an increased incidence of nonvertebral fractures during fluoride administration. Thus, the efficacy of fluoride therapy remains a controversial issue. The aim of this longitudinal study was to investigate the effect of sodium fluoride (40-60 mg per day), calcium (45 mmol), and vitamin D2 (18,000 IU) on trabecular bone strength, assessed before and after 1 or 5 years of treatment for osteoporosis. Iliac crest biopsies were taken before and after 1 year of treatment in 12 patients, and before and after 5 years of treatment in 14 patients. Measurements were made of biomechanical competence, ash content, and bone fluoride content, and bone strength parameters were normalized for ash content, thereby obtaining a measure of trabecular bone quality. Bone fluoride content was significantly increased after both 1 and 5 years of treatment, indicating that the administered fluoride had been ingested. After 1 year of treatment, no difference was observed in iliac crest trabecular bone ash content. A general trend for decreased bone strength and bone quality was observed, but this was insignificant. After 5 years of fluoride treatment, an insignificant decrease in iliac crest trabecular bone ash content was observed.(ABSTRACT TRUNCATED AT 250 WORDS)