Lack of deleterious effect of slow-release sodium fluoride treatment on cortical bone histology and quality in osteoporotic patients

Insufficient bilateral femoral subtrochanteric fractures in a patient receiving imatinib mesylate

We present a case of insufficient bilateral femoral subtrochanteric fractures in a patient who was treated with imatinib mesylate, an anticancer drug, for 1 year after a diagnosis of chronic myelogenous leukemia (CML). A 60-year-old woman presented with bilateral thigh pain for 6 months. A plain radiograph revealed bilateral progressive insufficient fractures on the subtrochanteric areas of the femurs. MRI of the femurs revealed incomplete stress fractures and no evidence of bone metastasis on either femur. Bone densitometry showed normal T-scores around the hip joint and spine. The patient had normal serum levels of calcium, vitamin D derivatives, and thyroid hormones. Serum phosphate levels were decreased, and parathyroid hormone levels were increased. Serum osteocalcin and urinary N-telopeptide of collagen cross-links (NTx) were both decreased. A bone biopsy demonstrated normocellular marrow without leukemic cells. A histomorphometric evaluation of her bones revealed reduced bone turnover despite secondary hyperparathyroidism. The serum markers for bone metabolism and histomorphometric evaluations in this patient suggest that the drug may have an effect on bone metabolism. These effects could be seen for both bone formation and resorption: this could result in impaired bone mineralization, a severely suppressed bone turnover rate, insufficient fractures, and bone necrosis, which are sometimes seen with long-term use of bisphosphonates. To our knowledge, this is the first case of an insufficient bilateral femoral shaft fracture that is potentially related to the use of imatinib mesylate in a patient with CML. Careful examination of bone metabolism should be performed in patients with CML because imatinib mesylate treatment is a lifelong process.

The effect of fluoride administration on rat serum osteocalcin expression during orthodontic movement

INTRODUCTION

Osteocalcin is a bone protein that has been used to mark bone turnover. The precise role of this protein in bone remodeling has not been fully elucidated; however, it was shown to be instrumental in the activation of osteoclastic bone resorption via its effect on osteoblasts. Fluoride influences bone growth by acting as a mitogenic agent for osteoblasts. In this study, we used a rodent model to determine the effects of fluoride administration on systemic osteocalcin during orthodontic tooth movement.

METHODS

Thirty-two 8-week-old female Wistar rats were divided into 4 groups. The first experimental group (n = 10) was fed a normal laboratory diet and distilled water (MilliQ). The second experimental group (n = 10) had the same diet with the addition of fluoridated water. All animals in both groups had 100-g nickel-titanium coil springs secured to their mandibular incisors and left first molars to instigate orthodontic tooth movement for 14 days. The third (n = 6) and fourth (n = 6) groups were the controls. These animals did not undergo orthodontic tooth movement and were given fluoridated (100 ppm sodium fluoride) and nonfluoridated water ad libitum. Phlebotomy was performed via the lateral tail vein before placement of the orthodontic appliances, and final blood samples were obtained via cardiac puncture after the rats were killed 2 weeks later. Serum was isolated from the samples after centrifuging at each stage of phlebotomy, and an enzyme-linked immunosorbent assay (ELISA) was subsequently performed to determine osteocalcin levels in the various sample groups.

RESULTS

Orthodontic tooth movement with high, continuous forces was found to have a positive, statistically significant correlation with serum osteocalcin expression in the rodent model. The use of fluoride as a variable was found to increase the mean osteocalcin concentration, but this was not statistically significant.

CONCLUSIONS

Further understanding of the biological implications of increased osteocalcin expression requires additional research into the local expression of this protein in the gingival crevice during orthodontic movement.

Reflection ultrasound velocities and histomorphometric and connectivity analyses: correlations and effect of slow-release sodium fluoride

To better understand how structural and functional bone properties contribute to the changes in bone biomechanical properties revealed by ultrasound critical angle reflectometry (UCR) analysis, we measured both UCR velocities and histomorphometric properties in bone biopsy specimens from 33 osteoporotic patients before and following intermittent slow-release sodium fluoride (SRNaF) and continuous calcium citrate administration. Mean skeletal fluoride exposure was 17 months, and mean skeletal fluoride content was 0.203 +/- 0.088 SD% bone ash. Intermittent SRNaF and continuous calcium citrate promoted significant increases in trabecular thickness (122 +/- 18 SD microm to 131 +/- 20, p = 0.020), mineral apposition rate (0.79 +/- 0.26 to 1.05 +/- 0.40 microm/day, p = 0.014), and a significant decline in eroded surface (3.9 +/- 1.6 to 2.8 +/- 1.4%, p = 0.002). There were also significant increases in node number (0.193 +/- 0.100 to 0.368 +/- 0.245, p < 0.01) and node-to-node strut length (0.076 +/- 0.087 to 0.191 +/- 0.173, p < 0.01) relative to total cancellous area. Cortical UCR velocity did not change but cancellous velocity significantly increased by 97 m/s following therapy (p = 0.0005). When compared against the significant changes in bone histomorphometry and connectivity, the sum of both cancellous and cortical ultrasound velocities was significantly correlated with node number/area (R2 = 0.305, p < 0.0001) and node-to-node strut length/area (R2 = 0.372, p < 0.0001) and to a lesser extent with mineral apposition rate (R2 = 0.106, p = 0.032). Multiple regression analysis demonstrated that 40% of the variance in the sum of the UCR velocities can be accounted for by the variability in these histomorphometric and connectivity parameters. There were no significant correlations between the sum of cortical and cancellous ultrasound velocities and cancellous bone volume (R2 = 0.014, p = 0533), trabecular thickness (R2 = 0.012, p = 0.47), or bone mineral density (R2 = 0.003, p = 0.80). These observations indicate that velocity measurements with the UCR methodology show an improvement in bone elasticity associated, in part, with an improvement in the rate of bone mineralization and an improvement in bone quality at the structural level as shown by microarchitecture.

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.

Phenytoin and fluoride act in concert to stimulate bone formation and to increase bone volume in adult male rats

We have recently demonstrated that phenytoin is an osteogenic agent at low doses. The present paper describes observations that a mitogenic dose (i.e., 20 microM in BGJb medium) of fluoride significantly augments the phenytoin-dependent stimulation of normal human bone cell proliferation and alkaline phosphatase (ALP) activity in cell culture. Additionally, the present study was designed to investigate whether fluoride and phenytoin would interact to increase bone formation in rats in vivo. Four groups of weight-matched adult male rats received daily I.P. injection of (1) vehicle (10% DMSO), (2) 5 mg/kg/day phenytoin, (3) 5 mg/kg/day phenytoin and 50 ppm NaF, and (4) 50 ppm NaF and vehicle, respectively, for 36 days. Sodium fluoride (NaF) was delivered in drinking water. Blood samples were drawn weekly and analyzed for serum osteocalcin, ALP, calcium, phosphorus, and 25(OH)D3. Rats were labeled with tetracycline at day 21 and 30 and histomorphometric analysis was carried out on the tibia at the end of the experiment. Neither agent by itself or together affected the serum calcium, phosphorus, or 25(OH)D3 levels. All measures of bone formation, i.e., serum osteocalcin level and ALP activity, bone ALP specific activity, mineral apposition rate, bone formation rate, and % bone formation surface, were increased by each agent. Fluoride and phenytoin together produced bigger increases in each parameter than did each agent alone. Trabecular bone volume was increased in the tibial metaphysis by fluoride or phenytoin alone; and when administered together, the two agents produced a greater increase.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of slow-release sodium fluoride on cancellous bone histology and connectivity in osteoporosis

We have previously demonstrated that a treatment regimen of slow-release sodium fluoride (SRNaF) and continuous calcium citrate increases lumbar bone mass, improves cancellous bone material quality, and significantly reduces vertebral fracture rate in osteoporotic patients. In order to assess whether such treatment also improves trabecular structure, we quantitated cancellous bone connectivity before and following 2 years of therapy with SRNaF in 23 patients with osteoporosis and vertebral fractures. In addition, we performed bone histomorphometry on the same sections used for connectivity measurements. There was a significant increase in L2-L4 bone mineral density during therapy (0.827 +/- 0.176 g/cm2 SD to 0.872 +/- 0.166, p = 0.0004). Significant histomorphometric changes were represented by increases in mineral apposition rate (0.6 +/- 0.4 microns/d to 1.1 +/- 0.7, p = 0.0078) and adjusted apposition rate (0.4 +/- 0.3 microns/d to 0.6 +/- 0.4, p = 0.016). On the other hand, trabecular spacing significantly declined (from 1375 +/- 878 microns to 1052 +/- 541, p = 0.05). Two-dimensional quantitation of trabecular struts on iliac crest histological sections disclosed significant increases in mean node number per mm2 of cancellous tissue area (0.22 +/- 0.12 vs. 0.39 +/- 0.27, p = 0.0077), the mean node to free-end ratio (0.23 +/- 0.21 vs. 0.41 +/- 0.46, p < 0.05), and in the mean node to node strut length per mm2 of cancellous area (0.098 +/- 0.101 vs. 0.212 +/- 0.183, p < 0.01). There were no significant changes in any of the measurements associated with free-end number or free-end to free-end strut length.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of intrinsic bone quality in vivo by reflection ultrasound: correction of impaired quality with slow-release sodium fluoride and calcium citrate

The intrinsic (material) quality of cancellous and cortical bone was evaluated in vivo from the measurement of reflection ultrasound velocities in the ulna. In cancellous bone, the reflection ultrasound velocity was inversely correlated with age in normal women (r = -0.48, p = 0.001), with a significantly lower mean value in 32 normal postmenopausal women than in 14 premenopausal women (3124 versus 3341 m/s, p < 0.0001). In 32 untreated osteoporotic women the cancellous bone velocity was lower than in normal postmenopausal subjects (2906 versus 3124 m/s, p = 0.0001). Following treatment with slow-release sodium fluoride plus calcium citrate (mean 2.4 years in 33 osteoporotic patients with no fracture during treatment), the cancellous bone velocity was significantly higher than in untreated osteoporotic women (3082 versus 2906 m/s, p = 0.0002) and was not significantly different from that in normal postmenopausal women. The cortical bone velocity displayed similar trends, but the changes did not attain statistical significance. The measurements were repeated approximately 9 months later in 9 untreated and in 20 treated patients; in 5 additional patients, the measurements were made both before and after 9 months of treatment with slow-release sodium fluoride and calcium citrate. The cancellous bone velocity increased significantly (p = 0.046) in these patients, from 3008 m/s before treatment to 3112 m/s after the first 9 months of treatment. The velocity rose significantly from 3037 to 3167 m/s (p = 0.017) in patients treated for a short time (12-30 months at first measurement), but it did not change in untreated patients or those treated for more than 30 months. Thus, the material quality of cancellous bone decreases with normal aging and is reduced further with the osteoporotic process. This impaired quality may be corrected by treatment with slow-release sodium fluoride plus calcium citrate.

Ultrasound study of bone in vitro

Ultrasound has been investigated as a tool for characterizing the biomechanical competence of bone. The rationale for using ultrasound rests on two points. First, its interaction with tissues can be used to measure their density, velocity, and structure, and thus to characterize the elasticity and to infer the strength of bone. Second, ultrasound may be used to characterize tissue properties over a wide range of spatial dimensions and organizational levels, ranging from its constituents (e.g., trabeculae for cancellous bone) to the entire organ. Different ultrasound techniques can be used to investigate diverse bone properties, but two techniques have emerged as having the potential for providing useful information on problems of current biomedical interest. These measure two parameters, density and velocity, which correlate with the elastic and ultimate properties of bone. In particular, the elasticity E is formally related to the product of density and velocity squared, E = rho v2. Moreover, it has been shown by mechanical testing that there is a single linear correlation between elasticity and strength at all orientations, both in cortical and in cancellous bone, materials with a strong intrinsic anisotropy. At the tissue level, it may therefore be expected that the ultrasound parameters will prove to be useful predictors of bone strength and of its dependence on orientation. In vitro ultrasound studies have shown that these properties can be measured specifically and quantitatively, and that they vary under different physiological conditions.