Different effects of antiresorptive therapies on vertebral and nonvertebral fractures in postmenopausal osteoporosis

Anabolic action of parathyroid hormone regulated by the β2-adrenergic receptor

Parathyroid hormone (PTH), the major calcium-regulating hormone, and norepinephrine (NE), the principal neurotransmitter of sympathetic nerves, regulate bone remodeling by activating distinct cell-surface G protein-coupled receptors in osteoblasts: the parathyroid hormone type 1 receptor (PTHR) and the β(2)-adrenergic receptor (β(2)AR), respectively. These receptors activate a common cAMP/PKA signal transduction pathway mediated through the stimulatory heterotrimeric G protein. Activation of β(2)AR via the sympathetic nervous system decreases bone formation and increases bone resorption. Conversely, daily injection of PTH (1-34), a regimen known as intermittent (i)PTH treatment, increases bone mass through the stimulation of trabecular and cortical bone formation and decreases fracture incidences in severe cases of osteoporosis. Here, we show that iPTH has no osteoanabolic activity in mice lacking the β(2)AR. β(2)AR deficiency suppressed both iPTH-induced increase in bone formation and resorption. We showed that the lack of β(2)AR blocks expression of iPTH-target genes involved in bone formation and resorption that are regulated by the cAMP/PKA pathway. These data implicate an unexpected functional interaction between PTHR and β(2)AR, two G protein-coupled receptors from distinct families, which control bone formation and PTH anabolism.

Bone health-related factors and the use of bisphosphonates in community setting--15-year follow-up study

The present study investigated the bone health related factors that were associated with the use of bisphosphonates (BP) among 2,050 postmenopausal Finnish women. Low BMD + low trauma energy fracture was the strongest determinant of BP use, while other secondary causes of osteoporosis were less strongly related with BP use. BP use was associated with reduced femoral neck (FN) and lumbar spine (LS) bone loss rate.

INTRODUCTION

The aim was to identify bone health related factors associated with the use of BP in a community setting.

METHODS

A population-based sample of 2,050 Finnish postmenopausal women was measured with dual X-ray absorptiometry at the FN and LS in 1989, 1994, 1999 and 2004, and information on osteoporosis risk factors, including low-trauma energy fractures, were collected with postal inquiries. Self-reported use of BP in 2004 was considered as the end point variable.

RESULTS

Among BP users, 12% had T-score > -2.0 SD and no fracture during follow-up (FU). In women without any bone medication, 26% had T-score < -2.0 SD or low-trauma energy fracture or both during the FU. In BP users, a significant reduction in FN and LS bone loss rate, cumulative with duration of use, was observed in ANCOVA (p < 0.001). Among BP users, there was a significantly higher proportion of women with several independent risk factors for osteoporosis and more spine and humerus fractures but less ankle fractures. T-score < -2 SD combined with low-trauma energy fracture was significantly related to the use of BPs (p < 0.001, OR = 15.96) and T-score < -2 SD was a stronger predictor of BP use (p < 0.001, OR = 13.29) than fracture (p > 0.05, OR = 1.35) in multivariate logistic regression. Other factors related with BP use were vitamin D use (p = 0.001, OR = 2.27), high number of medications (p < 0.001, OR = 1.26) and rheumatoid arthritis (p < 0.05, OR 2.55).

CONCLUSIONS

These findings reveal the recent bone health-related indications for BP prescription.

Bisphosphonates do not inhibit periosteal bone formation in estrogen deficient animals and allow enhanced bone modeling in response to mechanical loading

The suppressive effects of bisphosphonates (BPs) on bone remodeling are clear yet there is conflicting data concerning the effects of BPs on modeling (specifically formation modeling on the periosteal surface). The normal periosteal expansion that occurs during aging has significant benefits to maintaining/improving the bones' mechanical properties and thus it is important to understand whether BPs affect this bone surface. Therefore, the purpose of this study was to determine the effects of BPs on periosteal bone formation modeling induced by ovariectomy (OVX) and mechanical loading. Six-month-old Sprague-Dawley OVX rats (n=60; 12/group) were administered vehicle, risedronate, alendronate, or zoledronate at doses used clinically for treatment of post-menopausal osteoporosis. Three weeks after initiating BP treatment, all animals underwent in vivo ulnar loading of the right limb every other day for 1 week (3 total sessions). Periosteal surface mineral apposition rate, mineralizing surface, and bone formation rate were determined at the mid-diaphysis of both loaded (right) and non-loaded (left) ulnae. There was no significant effect of any of the BPs on periosteal bone formation parameters compared to VEH-treated animals in the non-loaded limb, suggesting that BP treatment does not compromise the normal periosteal expansion associated with estrogen loss. Mechanical loading significantly increased BFR in the loaded limb compared to the non-loaded limb in all BP-treated groups, with no difference in the magnitude of this effect among the various BPs. Collectively, these data show that BP treatment, at doses comparable to those used for treatment of post-menopausal osteoporosis, (1) does not alter the periosteal formation activity that occurs in the absence of estrogen and (2) allows normal stimulation of periosteal bone formation in response to the anabolic stimulation of mechanical loading.

Eel calcitonin (elcatonin) suppressed callus remodeling but did not interfere with fracture healing in the femoral fracture model of cynomolgus monkeys

We investigated the effect of eel calcitonin (elcatonin) on the process of fracture repair in the osteotomized femur of cynomolgus monkeys, since they possess a Haversian remodeling system similar to that of humans. Alendronate was used for comparison. Twenty female cynomolgus monkeys (Macaca fascicularis), aged 18-22 years, were allocated into five groups: control (CNT, n = 4), low-dose elcatonin group (0.5 U/kg; ELL, n = 4), high-dose elcatonin group (5 U/kg; ELH, n = 4), low-dose alendronate group (10 microg/kg; ALL, n = 4) and high-dose alendronate group (100 microg/kg; ALH, n = 4). All animals were given subcutaneous injections twice a week for 3 weeks. Then fracture was produced surgically by transversely cutting the midshaft of the right femur and fixing with stainless steel plate. After fracture, treatments were continued until sacrifice at 26 weeks after surgery. The femora were assessed by micro CT, contact microradiograph, three-point bending mechanical test and histomorphometry. Micro CT showed that callus sizes in elcatonin-treated groups were similar to CNT, whereas alendronate-treated groups had larger calluses than those in the CNT and elcatonin-treated groups. Fracture lines almost disappeared in the CNT and elcatonin-treated groups but remained clear in the alendronate-treated groups. Total area did not differ significantly between the elcatonin-treated groups and the CNT but was significantly greater in the ALH compared to the CNT and elcatonin-treated groups, due to increased callus area in the ALH group. Callus remodeling was less suppressed in the elcatonin-treated groups than in the alendronate-treated groups when compared with callus remodeling in the CNT. Although no significant differences in structural mechanical properties such as ultimate load, stiffness and work to failure were found among all groups, ultimate stress was significantly reduced in the ALH group compared with CNT and ELL groups. In conclusion, mild suppression of callus remodeling by elcatonin did not impair overall fracture healing process. In contrast, alendronate delayed structural fracture healing process by strongly suppressing callus remodeling.

Ibandronate and the risk of non-vertebral and clinical fractures in women with postmenopausal osteoporosis: results of a meta-analysis of phase III studies

OBJECTIVE

The marketed doses of ibandronate, 150 mg once-monthly oral and 3 mg quarterly intravenous (IV) injection, produce greater increases in lumbar spine bone mineral density than treatment with the 2.5 mg oral daily dose. This meta-analysis assessed whether these doses also reduce fracture risk relative to placebo.

STUDY DESIGN AND METHODS

Individual patient data from the intent-to-treat populations of the BONE, IV fracture prevention, MOBILE, and DIVA studies were grouped into three dose levels based on annual cumulative exposure (ACE), defined as the annual dose (mg) x bioavailability (0.6%, oral; 100%, IV) or placebo. Six key non-vertebral fractures (NVFs) (clavicle, humerus, wrist, pelvis, hip, and leg), all NVFs, and all clinical fractures were examined.

RESULTS

This meta-analysis included 8710 patients. Cox proportional-hazards models estimated the adjusted relative risk (RR) for fracture with ibandronate versus placebo, and time to fracture was compared using log-rank tests. The high-dose group (ACE > or = 10.8 mg) showed significant reductions in the adjusted RR of key NVFs (34.4%, p = 0.032), all NVFs (29.9%, p = 0.041), and clinical fractures (28.8%, p = 0.010) relative to placebo. The high-dose group also had significantly longer time to fracture versus placebo for key NVFs (p = 0.031), all NVFs (p = 0.025), and clinical fractures (p = 0.002). Study limitations included: not all studies were placebo-controlled; a limited number of baseline characteristics were available for multivariate analyses.

CONCLUSION

Ibandronate at dose levels of ACE > or = 10.8 mg, which includes the marketed 150 mg once-monthly oral and 3 mg quarterly IV injection regimens, may provide significant non-vertebral and clinical fracture efficacy.

Hip fracture protection by alendronate treatment in postmenopausal women with osteoporosis: a review of the literature

Osteoporosis most commonly affects postmenopausal women, placing them at a significant risk of fractures. In particular, hip fractures are an important cause of mortality and morbidity among postmenopausal women. Anti-resorptive therapies that produce greater decreases in bone turnover markers together with greater increases in bone mineral density (BMD) are associated with greater reductions in fracture risk, especially at sites primarily composed of cortical bone such as the hip. Thus, treatment with potent anti-resorptive drugs like alendronate is a strategy for preventing hip fractures in postmenopausal women with osteoporosis. The purpose of this paper is to discuss the efficacy of alendronate against hip fractures and the mechanism for this anti-fracture efficacy in postmenopausal women with osteoporosis. A meta-analysis of randomized controlled trials has shown that alendronate reduces the risk of hip fractures by 55% in postmenopausal women with osteoporosis. According to the analyses of the Fracture Intervention Trial, each 1 standard deviation reduction in a 1-year change in bone-specific alkaline phosphatase (BSAP) is associated with 39% fewer hip fractures in alendronate-treated postmenopausal women, and those with at least 30% reduction in BSAP have a 74% lower risk of hip fractures relative to those with less than 30%. Alendronate is effective in reducing the risk of hip fractures across a spectrum of ages. The mechanism for this anti-fracture efficacy has been clarified; alendronate strongly suppresses bone turnover and subsequently increases hip BMD, decreases cortical porosity, improves parameters of hip structure geometry (cortical thickness, cross-sectional area, section modulus, and buckling ratio), and produces more uniform mineralization (increases the mean degree of mineralization of bone) in cortical bone. A once-weekly regimen of alendronate administration provides better patient compliance and persistence with the treatment than the once-daily dosing regimen, leading to greater efficacy against hip fractures. Thus, the efficacy of alendronate against hip fractures has been confirmed in postmenopausal women with osteoporosis, especially with a once-weekly dosing regimen.

Osteoporosis: a still increasing prevalence

It is estimated that over 200 million people worldwide have osteoporosis. The prevalence of osteoporosis is continuing to escalate with the increasingly elderly population. The major complication of osteoporosis is an increase in fragility fractures leading to morbidity, mortality, and decreased quality of life. In the European Union, in 2000, the number of osteoporotic fractures was estimated at 3.79 million. A baseline fracture is a very strong predictor of further fractures with 20% of patients experiencing a second fracture within the first year. The costs to health care services are already considerable and, on current trends, are predicted to double by 2050. The direct costs of osteoporotic fractures to the health services in the European Union in the year 2000 were estimated at 32 billion Euros. Guidelines for the diagnosis and treatment of osteoporosis are available in many countries; however, implementation is generally poor despite the availability of treatments with proven efficacy. Programs to increase awareness of osteoporosis and its outcomes are necessary for healthcare specialists and the general public. Earlier diagnosis and intervention prior to the first fracture are highly desirable.

Examining the Relationship Between Bone Mineral Density and Fracture Risk Reduction During Pharmacologic Treatment of Osteoporosis

Osteoporosis is a skeletal disorder characterized by compromised bone strength that predisposes the patient to an increased risk for fracture. Elements of bone strength include bone mineralization, architecture, turnover, size, and bone mineral density (BMD). Measurement of BMD is the most readily available, noninvasive method for assessing osteoporotic fracture risk and is used by the World Health Organization for diagnostic purposes. Because low BMD is predictive of increased fracture risk, it was believed that changes in BMD during pharmacologic therapy for osteoporosis would strongly predict observed fracture risk reductions. We examined the relationship between changes in BMD and reduction in fracture risk during pharmacologic therapy in postmenopausal women with osteoporosis. The correlation between BMD increases and fracture risk reduction during treatment is not consistent; larger increases in BMD do not necessarily correlate with greater reductions in fracture risk. Multiple factors, in addition to BMD, appear to contribute to the increased bone strength and decreased fracture risk achieved with approved drug therapies for osteoporosis. Until the exact relationship of these factors is fully understood, clinicians should continue to evaluate drug efficacy for osteoporosis based on the fracture risk reductions from well-designed clinical trials.

The roles of bone mineral density, bone turnover, and other properties in reducing fracture risk during antiresorptive therapy

Osteoporosis is a skeletal disorder characterized by compromised bone strength and increased risk of fracture. Properties related to bone strength include rate of bone turnover, bone mineral density, geometry, microarchitecture, and mean degree of mineralization. These properties (with or without bone density) are sometimes collectively referred to as bone quality. Antiresorptive agents may reduce fracture risk by several separate but interrelated effects on these individual properties. For example, antiresorptive agents have been reported to reduce bone turnover, stabilize or increase bone density, preserve or improve microarchitecture, reduce the number or size of resorption sites, and improve mineralization. Although changes in bone architecture and mineralization are not currently measurable in clinical practice, bone turnover is assessed easily in vivo and affects the other bone properties. Moreover, antiresorptive therapies that produce larger decreases in bone turnover markers together with larger increases in bone mineral density are associated with greater reductions in fracture risk, especially at sites primarily composed of cortical bone such as the hip. Reductions in fracture risk are the most convincing evidence of good bone quality. Data from well-designed randomized clinical trials with up to 10 years of continuous antiresorptive therapy have shown that certain antiresorptive agents effectively reduce fracture risk and (together with extensive preclinical data) suggest no deleterious effects on bone quality.

Simple Computer Model for Calculating and Reporting 5-Year Osteoporotic Fracture Risk in Postmenopausal Women

PURPOSE

To devise, validate, and test a software model that improves how clinicians calculate individual risk for osteoporotic fracture and expected treatment benefit.

METHODS

We developed a simple model of seven easily ascertained items plus bone mineral density (BMD) that calculates absolute fracture risk and expected absolute risk reduction after treatment. Baseline clinical variables and longitudinal fracture data from two large osteoporosis cohort studies validated the model's accuracy in predicting fracture risk. We then surveyed 298 clinicians to evaluate the likelihood they would prescribe alendronate in three hypothetical cases, first given the clinical data alone and then with model-derived data on fracture risk and expected treatment benefit.

RESULTS

We found a strong linear relationship with the model's predicted fracture risk and observed fracture rates in two large observational cohorts but the model overestimated risk 2-3 fold. The model predicted a 1:200 5-year risk for spinal fracture and a 1:40 risk for nonspinal fracture in an index case of a younger, thin, osteopenic woman. Given this hypothetical history with BMD t-scores, 26% of clinicians were likely to prescribe alendronate; when also given model-calculated 5-year fracture risks with or without treatment, only 13% were likely to prescribe alendronate (p < 0.001). For 2 other osteoporosis patients in whom risk was much higher, further information on fracture risk and expected treatment benefit did not alter prescribing.

CONCLUSIONS

Reporting absolute fracture risk with and without treatment promises to be most useful in women with osteopenia, a common clinical dilemma in younger postmenopausal women.

Effects of doxycycline on mechanical properties of bones in rats with ovariectomy-induced osteopenia

Tetracyclines have been reported to inhibit bone resorption and intensify bone formation. The aim of the present study was to investigate the effects of doxycycline (20 mg/kg PO daily for 28 days) on bone mechanical properties in bilaterally ovariectomized and sham-operated rats. The experiment was carried out on 3-month-old Wistar rats. Mechanical properties of the whole femur (extrinsic stiffness, ultimate and breaking load, deformation caused by applied load) and the femoral neck (load at fracture) as well as bone mass and bone mineral content in the tibia, femur, and L4 vertebra were examined. Bilateral ovariectomy resulted in decreases in bone mineral content/bone mass ratio and worsening of mechanical properties of the femoral neck. The changes were counteracted by doxycycline. Doxycycline reversed the effect of ovariectomy on load at fracture of the femoral neck. Doxycycline did not significantly affect the mechanical properties of bones in the sham-operated rats.

Risedronate preserves bone architecture in postmenopausal women with osteoporosis as measured by three-dimensional microcomputed tomography

The deterioration of trabecular microarchitecture induced by elevated bone turnover is increasingly recognized as a factor in the pathogenesis of osteoporotic fractures. We investigated the effect of the reduction of turnover with risedronate on trabecular architecture in postmenopausal women with osteoporosis. Iliac crest bone biopsy specimens taken before and after 3 years of treatment from patients receiving risedronate 5 mg daily (n = 21) or placebo (n = 17) were analyzed using 3-D microcomputed tomography. We found a significant correlation between baseline bone turnover and bone loss in the placebo group, providing evidence that higher turnover induced higher bone loss leading to a greater degree of architectural degradation. When patients were classified into two groups based on baseline bone turnover (MS/BS less than or greater than the median value for the entire cohort), significant decreases in trabecular bone volume (BV/TV, P = 0.009) and trabecular thickness (Tb.Th*, P = 0.008) and an increase in marrow star volume (Ma.St.V, P = 0.008), a measure of trabecular porosity, were observed in the higher turnover (MS/BS> median) placebo-treated patients. The trabecular structure shifted from plates to rods as shown by an increase in structure model index (SMI, P = 0.028) and bone surface to bone volume ratio (BS/BV, P = 0.006). The changes from baseline in the lower turnover (MS/BS<median) placebo patients were variable and not statistically significant. In the risedronate group, the bone volume and the architectural parameters did not change significantly from baseline values in either the higher or the lower turnover groups. Comparing the pair-wise changes from baseline in the higher turnover group, the placebo group experienced decreases in BV/TV (P = 0.071) and Tb.Th* (P = 0.012), and increase in Ma.St.V (P = 0.043), compared to the risedronate-treated women. Also, in comparison to the risedronate group, the trabecular structures in the placebo group were more rod-like, indicated by higher SMI (P = 0.009) and BS/BV (P = 0.02). The results demonstrated that trabecular architecture deteriorated significantly in the placebo-treated women who had higher bone turnover at baseline, and this deterioration was prevented by 3 years of risedronate treatment, presumably because of the reduction in bone turnover. The preservation of architecture may be a contributory mechanism by which risedronate reduces the risk of vertebral fractures in osteoporotic women.

Changes in bone mineral density explain little of the reduction in vertebral or nonvertebral fracture risk with anti-resorptive therapy

The structural basis for the reduction in vertebral and nonvertebral fracture risk in patients using anti-resorptive therapy is not well understood. As reduced bone mineral density (BMD) increases the risk for fracture and anti-resorptive agents increase BMD, it was commonly held that the increase in BMD explained the fracture risk reduction until several meta-analyses either failed to detect a significant association between vertebral fracture risk reduction and the incremental increase in BMD or reported that only a small proportion of the vertebral fracture risk reduction was explained by changes in BMD. Recently, it was reported that the risk of nonvertebral fractures decreased when an increase in BMD accompanied anti-resorptive treatment [J. Clin. Endrocrinol. Metab. 87 (2002) 1586]. However, a reanalysis of the data, using the same statistical methods after correcting for discrepancies in the reported BMD and person-year data, suggested that the magnitude of reductions in nonvertebral fracture risk was not associated with the magnitude of increases in BMD at the end of the first year or at completion of the studies. We infer that only a small proportion of risk reduction in vertebral and nonvertebral fractures observed with anti-resorptive drug therapy is explained by the increase in BMD. Further studies are needed to define the structural basis of the fracture risk reduction.

Is bone mineral density predictive of fracture risk reduction?

Bone mineral density (BMD) measurement is a widely available noninvasive means of identifying individuals with osteoporosis and, possibly, those at high risk for fracture. This nonsystematic review examines the relationship between BMD increase and fracture risk reduction in clinical trials evaluating osteoporosis therapy. The trials examined here are predominantly in postmenopausal women. BMD increase correlates poorly with fracture risk reduction in clinical trials of osteoporosis therapy conducted in postmenopausal women. Although BMD may increase with therapy, the increase is not measurable until later, and the overall increase is too small to account for the timing and magnitude of fracture risk reduction. BMD is only one of many contributors to bone strength and fracture risk reduction. Bone strength is derived from bone quantity, which consists of density and size, and bone quality, which, in turn, consists of structure (micro- and macroarchitecture), material properties, and turnover. Data are beginning to accrue suggesting that changes in bone turnover markers may be an accurate predictor of fracture risk reduction. Future research will elucidate the link between changes in bone turnover markers and bone architecture as a measure of osteoporosis treatment efficacy. Until then, physicians will continue to rely on fracture risk reduction data from well-designed clinical trials when judging the efficacy of different treatments for osteoporosis.

Relationship between changes in bone mineral density and fracture risk reduction with antiresorptive drugs: some issues with meta-analyses

Published meta-analyses have investigated the relationship between changes in BMD and fracture risk reduction observed with antiresorptive agents, with inconsistent results. Many factors may affect the outcome of such analyses. Our work explores some of these factors and illustrates the need for caution in interpreting the results of meta-analyses.

INTRODUCTION

The role of the increase in bone mineral density (BMD) in fracture risk reduction observed in osteoporotic patients treated with antiresorptive drugs is unclear. We examined the effects of study selection, the use of summary statistics or individual patient data (IPD) as the basis for the analyses, and the choice of BMD values used on the outcome of meta-analyses.

MATERIALS AND METHODS

To evaluate the effects of study selection, we performed Poisson regression analyses using the results from a number of published studies. To evaluate the effects of using individual patient data instead of summary statistics, we simulated the IPD for vertebral fracture to match the summary statistics for published trials and compared these results with those based on meta-regression using summary statistics. We also evaluated the effect of varying the BMD increase with treatment (3-8%) used in predicting the fracture risk reductions in these simulations.

RESULTS

The Poisson regression, which found a statistically significant relationship between nonvertebral fracture risk and spinal BMD when 18 trials of varying designs, duration, and sample size were included in the analysis (p = 0.02), was no longer significant when the analysis was based on the 7 large studies that were placebo-controlled, at least 3 years in duration (at least 1000 patient-years). Meta-analyses of simulated IPD from 12 trials of six antiresorptive agents gave accurate results regardless of the proportion of vertebral risk reduction assumed to be related to BMD change, whereas meta-regression based on summary statistics always produced an estimate around 50%. When the actual data from two risedronate studies were analyzed, the meta-regression based on summary statistics demonstrated a stronger correlation between BMD change and fracture risk reduction than the results based on the IPD analysis. In predicting the fracture risk reduction, the use of the average BMD gain (3%) observed in all studies in the calculations produced an overall fracture risk reduction very similar to the one observed clinically. In contrast, the use of a large BMD gain (8%) produced a substantially higher estimated fracture risk reduction and resulted in a high proportion of fracture risk reduction being attributed to BMD change.

CONCLUSIONS

Many factors may influence the outcome of meta-analyses, and caution should be used in interpreting the results of such analyses when exploring the relationship between BMD changes and fracture risk reduction with antiresorptive therapy of osteoporosis.

Statins prevent bisphosphonate-induced gamma,delta-T-cell proliferation and activation in vitro

The acute phase response is the major adverse effect of intravenously administered N-BPs. In this study we show that N-BPs cause gamma,delta-T-cell activation and proliferation in vitro by an indirect mechanism through inhibition of FPP synthase, an effect that can be overcome by inhibiting HMG-CoA reductase with a statin. These studies clarify the probable initial cause of the acute phase response to N-BP drugs and suggest a possible way of preventing this phenomenon.

INTRODUCTION

The acute phase response is the major adverse effect of intravenously administered nitrogen-containing bisphosphonate drugs (N-BPs), used in the treatment of metabolic bone diseases. This effect has recently been attributed to their action as non-peptide antigens and direct stimulation of gamma,delta-T-cells. However, because N-BPs are potent inhibitors of farnesyl diphosphate (FPP) synthase, they could cause indirect activation of gamma,delta-T-cells owing to the accumulation of intermediates upstream of FPP synthase in the mevalonate pathway, such as isopentenyl diphosphate/dimethylallyl diphosphate, which are known gamma,delta-T-cell agonists.

MATERIALS AND METHODS

Peripheral blood mononuclear cells (PBMCs) were isolated from healthy volunteers and treated with N-BP, statin, or intermediates/inhibitors of the mevalonate pathway for 7 days in the presence of interleukin (IL)-2. Flow cytometric analysis of the T-cell-gated population was used to quantify the proportion of gamma,delta-T-cells in the CD3+ population.

RESULTS AND CONCLUSIONS

The ability of N-BPs to stimulate proliferation of CD3+ gamma,delta-T-cells in human PBMC cultures matched the ability to inhibit FPP synthase. Gamma,delta-T-cell proliferation and activation (interferon gamma [IFNgamma] and TNFalpha release) was prevented by mevastatin or lovastatin, which inhibit HMG-CoA reductase upstream of FPP synthase and prevent the synthesis of isopentenyl diphosphate/dimethylallyl diphosphate. Desoxolovastatin, an analog of lovastatin incapable of inhibiting HMG-CoA reductase, did not overcome the stimulatory effect of N-BP. Furthermore, statins did not prevent the activation of gamma,delta-T-cells by a synthetic gamma,delta-T-cell agonist or by anti-CD3 antibody. Together, these observations show that N-BPs indirectly stimulate the proliferation and activation of gamma,delta-T-cells caused by inhibition of FPP synthase and intracellular accumulation of isopentenyl diphosphate/ dimethylallyl diphosphate in PBMCs. Because activation of gamma,delta-T-cells could be the initiating event in the acute phase response to bisphosphonate therapy, co-administration of a statin could be an effective approach to prevent this adverse effect.

Severity of prevalent vertebral fractures and the risk of subsequent vertebral and nonvertebral fractures: results from the MORE trial

Prevalent vertebral fractures and baseline bone mineral density (BMD) predict subsequent fracture risk. The objective of this analysis is to examine whether baseline vertebral fracture severity can predict new vertebral and nonvertebral fracture risk. In the randomized, double-blind 3-year Multiple Outcomes of Raloxifene Evaluation (MORE) trial, 7705 postmenopausal women with osteoporosis (low BMD or prevalent vertebral fractures) were randomly assigned to placebo, raloxifene 60 mg/day, or raloxifene 120 mg/day. Post hoc analyses studied the association between baseline fracture severity and new fracture risk in the placebo group and the effects of placebo, raloxifene 60 mg/day, and raloxifene 120 mg/day on new fracture risk in women with the most severe prevalent vertebral fractures (n = 614). Vertebral fracture severity was visually assessed using semiquantitative analysis of radiographs and categorized by estimated decreases in vertebral heights. Reported new nonvertebral fractures were radiographically confirmed. Baseline vertebral fracture severity predicted vertebral and nonvertebral fracture risk at 3 years. In women without prevalent vertebral fractures, 4.3 and 5.5% had new vertebral and nonvertebral fractures, respectively. In women with mild, moderate, and severe prevalent vertebral fractures, 10.5, 23.6, and 38.1% respectively had new vertebral fractures, whereas 7.2, 7.7, and 13.8% respectively experienced new nonvertebral fractures. Number of prevalent vertebral fractures and baseline BMD also predicted vertebral fracture risk, but the severity of prevalent vertebral fractures was the only predictor of nonvertebral fracture risk and remained a significant predictor after adjustment for baseline characteristics, including baseline BMD. In patients with severe baseline vertebral fractures, raloxifene 60 mg/day decreased the risks of new vertebral [RR 0.74 (95% Cl 0.54, 0.99); P = 0.048] and nonvertebral (clavicle, humerus, wrist, pelvis, hip, and leg) fractures [RH 0.53 (95% CI 0.29, 0.99); P = 0.046] at 3 years. To prevent one new fracture at 3 years in women with severe baseline vertebral fractures with raloxifene 60 mg/day, the number needed to treat (NNT) was 10 for vertebral and 18 for nonvertebral fractures. Similar results were observed in women receiving raloxifene 120 mg/day. In summary, baseline vertebral fracture severity was the best independent predictor for new vertebral and nonvertebral fracture risk. Raloxifene decreased new vertebral and nonvertebral fracture risk in the subgroup of women with severe vertebral fractures at baseline. These fractures may reflect architectural deterioration, independent of BMD, leading to increased skeletal fragility.

[Pharmacotherapy of osteoporosis]

Osteoporosis with increased risk of bone fracture is a disabling syndrome that naturally occurs as long as one ages and moves on two legs. Recent progress in bone cell biology has shed light on the mechanisms underlying the anti-osteoporotic properties of drugs that have been in use for a long time, providing a fresh stage for novel pharmacotherapies. In addition, large scale clinical trials developed in the past decade appear not only to rationalize the clinical utilities of these drugs but also to provide new concepts for the development of new therapeutic modalities. Progress in the fields of basic and clinical research field is briefly reviewed herein.

What is the role of serial bone mineral density measurements in patient management?

The ability of dual X-ray absorptiometry (DXA) to monitor bone mineral density (BMD) has been well documented in epidemiologic and pharmaceutical trials. However, its application to monitoring of patients in clinical practice has been subject to recent controversies. Despite these controversies, most clinical centers rely on DXA for monitoring of patients, and therefore guidance is needed. In this article, we report the positions developed by an expert panel of the International Society for Clinical Densitometry on the use of densitometry for the serial measurement of bone mass for monitoring change in BMD. The panel found DXA to be a precise method of measuring change in BMD if used with an appropriate level of least significant change (LSC), at anatomic sites with good precision and response to therapy, and at 1- to 2-yr time intervals. Monitoring is acceptable for determining when therapy is indicated, and if an agent is not therapeutically effective (i.e., when bone loss occurs despite treatment). Each densitometry center should perform an in vivo precision study on individuals similar to the patient population at the center and determine LSC at a 95% confidence level. If such a precision study cannot be performed, benchmark precision might be used, although there was no agreement on what values should be used. The PA spine is the preferred anatomic site for monitoring. The total hip can be used when the spine study is technically invalid. We conclude with recommendations for further research.

Parathyroid Hormone, Its Fragments and Their Analogs for the Treatment of Osteoporosis

The susceptibility to traumatic fracturing of osteopenic bones, and the spontaneous fracturing of osteoporotic bones by normal body movements caused by the microstructural deterioration and loss of bone, are currently treated with antiresorptive drugs, such as the bisphosphonates, calcitonin, estrogens, and selective estrogen receptor modulators. These antiresorptive agents target osteoclasts and, as their name indicates, reduce or stop bone resorption. They cannot directly stimulate bone formation, increase bone mass above normal values in ovariectomized rat models, or improve microstructure. However, there is a family of agents - the parathyroid hormone (PTH) and some of its fragments and their analogs - which directly stimulate bone growth and improve microstructure independently from impairing osteoclasts. These drugs are about to make their clinical debut in treating patients with osteoporosis and, probably not too far in the future, for accelerating fracture healing. They stimulate osteoblast accumulation and bone formation in three ways via signals from the type 1 PTH/PTH-related protein (PTHR1) receptors on proliferatively inactive preosteoblasts, osteoblasts, osteocytes and bone-lining cells. The receptor signals shut down the proliferative machinery in preosteoblasts and push their maturation to osteoblasts, cause the osteoblastic cells to make and secrete several factors that stimulate the extensive proliferation of osteoprogenitors without PTHRI receptors, stimulate the reversion of bone-lining cells to osteoblasts, and extend osteoblast lifespan and productivity by preventing them from suicidally initiating apoptosis. The first of the PTHs to reach the clinic will be teriparatide [recombinant human (h)PTH-(1-34)], which was recommended for approval in 2001 by the US Food and Drug Administration Endocrinology and Metabolic Drugs Advisory Committee for the treatment of postmenopausal osteoporosis. Teriparatide has been shown to considerably increase cancellous and cortical bone mass, improve bone microstructure, prevent fractures and thus provide benefits that cannot be provided by current antiresorptive drugs, when administered subcutaneously at a daily dose of 20 microg for no longer than 2 years to patients with osteoporosis.