Incidence of fractures of the femur, including subtrochanteric, up to 8 years since initiation of oral bisphosphonate therapy: a register-based cohort study using the US MarketScan claims databases.

UNLABELLED: In a cohort study of users of bisphosphonates, we evaluated the incidence of fragility fractures at all sites on the femur following for up to 8 years of therapy with alendronate or risedronate. We did not find evidence for a reversal of fracture protection with long-term use of bisphosphonates. INTRODUCTION: Few studies have acquired adequate data with prolonged follow-up on bisphosphonate users in the general population to evaluate their long-term effects on the risk of hip fractures including those in the subtrochanteric region. METHODS: This cohort study utilizes a large USA database (January 1, 2000 to June 30, 2009). We compared patients with higher versus lower degrees of compliance [medication possession ratio, MPR <1/3 (the reference), 1/3-<2/3, or ≥ 2/3]. Radiographic adjudication of fracture site and features were not performed. Hazard ratios (HR) for fracture were estimated using time-dependent Cox models. Restricted cubic splines (RCS) were used to plot HRs for fracture against duration of therapy. RESULTS: There were 3,655 incident cases of femoral fracture (764 subtrochanteric/shaft, 2,769 hip) identified during 917,741 person-years of follow-up (median = 3 years) on 287,099 patients (267,374 were women) from the date when they initiated oral bisphosphonate therapy. The corresponding HRs (95% confidence interval, CI) for overall femoral fractures associated with each additional year of therapy were 0.93 (0.86-1.01) within 5 years, and 0.89 (0.77-1.03) beyond 5 years for risedronate and 0.86 (0.81-0.91) and 0.95 (0.84-1.07) for alendronate, respectively. The corresponding estimates for subtrochanteric/shaft fractures were 1.05 (0.87-1.26) and 0.89 (0.60-1.33) for risedronate and 0.99 (0.92-1.05) and 1.05 (0.92-1.20) for alendronate, respectively. The HRs (95% CI) for overall femoral fractures associated with each additional year of alendronate or risedronate therapy within 5 and beyond 5 years were not significantly different. CONCLUSION: Our study showed persistence of overall hip fracture protection with long-term use of alendronate or risedronate.

Risedronate in adults with osteogenesis imperfecta type I: increased bone mineral density and decreased bone turnover, but high fracture rate persists.

UNLABELLED: Bisphosphonates can increase bone mineral density (BMD) in children with osteogenesis imperfecta (OI). In this study of adults with OI type I, risedronate increased BMD at lumbar spine (but not total hip) and decreased bone turnover. However, the fracture rate in these patients remained high. INTRODUCTION: Intravenous bisphosphonates given to children with OI can increase BMD and reduce fracture incidence. Oral and/or intravenous bisphosphonates may have similar effects in adults with OI. We completed an observational study of the effect of risedronate in adults with OI type I. METHODS: Thirty-two adults (mean age, 39 years) with OI type I were treated with risedronate (total dose, 35 mg weekly) for 24 months. Primary outcome measures were BMD changes at lumbar spine (LS) and total hip (TH). Secondary outcome measures were fracture incidence, bone pain, and change in bone turnover markers (serum procollagen type I aminopropeptide (P1NP) and bone ALP). A meta-analysis of published studies of oral bisphosphonates in adults and children with OI was performed. RESULTS: Twenty-seven participants (ten males and seventeen females) completed the study. BMD increased at LS by 3.9% (0.815 vs. 0.846 g/cm(2), p = 0.007; mean Z-score, -1.93 vs. -1.58, p = 0.002), with no significant change at TH. P1NP fell by 37% (p = 0.00041), with no significant change in bone ALP (p = 0.15). Bone pain did not change significantly (p = 0.6). Fracture incidence remained high, with 25 clinical fractures and 10 major fractures in fourteen participants (0.18 major fractures per person per year), with historical data of 0.12 fractures per person per year. The meta-analysis did not demonstrate a significant difference in fracture incidence in patients with OI treated with oral bisphosphonates. CONCLUSIONS: Risedronate in adults with OI type I results in modest but significant increases in BMD at LS, and decreased bone turnover. However, this may be insufficient to make a clinically significant difference to fracture incidence.

Differences between bisphosphonates in binding affinities for hydroxyapatite.

Bisphosphonates (BPs) inhibit bone resorption and are widely used for the treatment of bone diseases, including osteoporosis. BPs are also being studied for their effects on hydroxyapatite (HAP)-containing biomaterials. There is a growing appreciation that there are hitherto unexpected differences among BPs in their mineral binding affinities that affect their pharmacological and biological properties. To study these differences, we have developed a method based on fast performance liquid chromatography using columns of HAP to which BPs and other phosphate-containing compounds can adsorb and be eluted by using phosphate buffer gradients at pH 6.8. The individual compounds emerge as discrete and reproducible peaks for a range of compounds with different affinities. For example, the peak retention times (min; mean +/- SEM) were 22.0 +/- 0.3 for zoledronate, 16.16 +/- 0.44 for risedronate, and 9.0 +/- 0.28 for its phosphonocarboxylate analog, NE10790. These results suggest that there are substantial differences among BPs in their binding to HAP. These differences may be exploited in the development of biomaterials and may also partly explain the extent of their relative skeletal retention and persistence of biological effects observed in both animal and clinical studies.

Mechanisms of action of bisphosphonates: similarities and differences and their potential influence on clinical efficacy.

UNLABELLED: Bisphosphonates (BPs) are well established as the leading drugs for the treatment of osteoporosis. There is new knowledge about how they work. The differences that exist among individual BPs in terms of mineral binding and biochemical actions may explain differences in their clinical behavior and effectiveness. INTRODUCTION: The classical pharmacological effects of bisphosphonates (BPs) appear to be the result of two key properties: their affinity for bone mineral and their inhibitory effects on osteoclasts. DISCUSSION: There is new information about both properties. Mineral binding affinities differ among the clinically used BPs and may influence their differential distribution within bone, their biological potency, and their duration of action. The antiresorptive effects of the nitrogen-containing BPs (including alendronate, risedronate, ibandronate, and zoledronate) appear to result from their inhibition of the enzyme farnesyl pyrophosphate synthase (FPPS) in osteoclasts. FPPS is a key enzyme in the mevalonate pathway, which generates isoprenoid lipids utilized for the post-translational modification of small GTP-binding proteins that are essential for osteoclast function. Effects on other cellular targets, such as osteocytes, may also be important. BPs share several common properties as a drug class. However, as with other families of drugs, there are obvious chemical, biochemical, and pharmacological differences among the individual BPs. Each BP has a unique profile that may help to explain potential clinical differences among them, in terms of their speed and duration of action, and effects on fracture reduction.

Regulation of bim in glucocorticoid-mediated osteoblast apoptosis.

Osteoblasts undergo apoptosis both in vitro and in vivo in response to high dose glucocorticoid (GC) treatment. However, the molecular mechanisms remain elusive, hindering the prevention and treatment of this side-effect. Apoptosis was induced by dexamethasone (Dex) in murine MBA-15.4 osteoblasts within 24-48 h of treatment. We found dose- and time-dependent upregulation of Bim protein, a pro-apoptotic Bcl-2 family member, with highest levels at 24-48 h for 1 microM Dex. This was also observed in primary human bone marrow stromal cells. Bim is subjected to stringent transcriptional and post-translational regulation in osteoblasts. Bim mRNA was upregulated in response to 1 microM Dex; both cycloheximide and the GC receptor antagonist, RU486, prevented Dex-induction of Bim protein, indicating transcriptional regulation involving the GC receptor. The proteasome inhibitor, MG132, potently increased Bim protein levels. Bim was also upregulated in osteoblasts undergoing apoptosis in response to serum deprivation and matrix detachment. Gene silencing experiments show that short interference RNA (siRNA) specific for Bim or the downstream effector Bax both reduced apoptosis induced by Dex in osteoblastic cells. These findings suggest that Bim is a novel regulator of osteoblast apoptosis and may be a therapeutic target.

Agonists of TRAIL death receptors induce myeloma cell apoptosis that is not prevented by cells of the bone marrow microenvironment.

The growth and survival of myeloma cells is critically regulated by cells of the bone marrow microenvironment, including osteoblasts. Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) is a potent inducer of myeloma cell apoptosis, however, this antimyeloma activity is inhibited by osteoprotegerin (OPG) released from osteoblasts. Therefore, we hypothesized that specific agonists of TRAIL death receptors would not be inhibited by OPG released from osteoblasts and thus may represent a novel therapeutic approach in multiple myeloma. In the present study, TRAIL-induced apoptosis was demonstrated to be mediated through both DR4 and DR5. Specific agonist antibodies to DR4 or DR5 dose-dependently induced myeloma cell apoptosis, which was not prevented by OPG or by medium conditioned by osteoblasts. Co-culture of myeloma cells with osteoblasts protected against TRAIL-induced apoptosis of myeloma cells, and this protective effect was due to OPG. In contrast, the co-culture of myeloma cells with osteoblasts had no protective effect on apoptosis induced by specific agonists of DR4 or DR5. TRAIL has been proposed as a potential antitumour therapy, but within the bone marrow microenvironment OPG may interfere with the action of TRAIL. Specific agonists of TRAIL death receptors would not be subject to this inhibition and thus may provide an alternative specific antimyeloma therapy.

Ibandronate: pharmacology and preclinical studies.

Over the past three decades, changes to the chemical structures of the bisphosphonates have resulted in progressive improvements in their antiresorptive potencies. Ibandronate is a potent, nitrogen-containing bisphosphonate that possesses a tertiary nitrogen group on its R2 side chain and a hydroxyl group on its R1 side chain, which together confer one of the highest antiresorptive potencies of all bisphosphonates. In common with other nitrogen-containing bisphosphonates, ibandronate is a strong inhibitor of farnesyl pyrophosphate synthase, which probably accounts for its major effects on osteoclast activity. In addition, it binds strongly to hydroxyapatite. The pharmacological efficacy and safety of various continuous and intermittent regimens of ibandronate have been extensively investigated in experimental models of osteoporosis in several animal species, including rats, dogs, and monkeys. In ovariectomized (OVX) rats, intermittent (dosing interval 2, 4, and 6 weeks) and continuous ibandronate regimens provided equivalent results per total dose irrespective of the dosing regimen. Similar results were obtained in OVX dogs and monkeys. High doses of ibandronate many times those used therapeutically were well tolerated and did not impair bone quality or mineralization in rats. Moreover, bone mass, architecture, and strength were maintained or improved, and bone healing was not adversely affected in animal models, regardless of whether ibandronate was administered intermittently or daily. The findings from all these studies demonstrate the efficacy and safety of intermittent ibandronate regimens and support the development of such regimens for the clinical management of postmenopausal osteoporosis.

Novel insights into actions of bisphosphonates on bone: differences in interactions with hydroxyapatite.

Bisphosphonates are now the most widely used drugs for diseases associated with increased bone resorption, such as osteoporosis. Although bisphosphonates act directly on osteoclasts, and interfere with specific biochemical processes such as protein prenylation, their ability to adsorb to bone mineral also contributes to their potency and duration of action. The aim of the present study was to compare the binding affinities for hydroxyapatite (HAP) of 6 bisphosphonates currently used clinically and to determine the effects of these bisphosphonates on other mineral surface properties including zeta potential and interfacial tension. Affinity constants (K(L)) for the adsorption of bisphosphonates were calculated from kinetic studies on HAP crystal growth using a constant composition method at 37 degrees C and at physiological ionic strength (0.15 M). Under conditions likely to simulate bisphosphonate binding onto bone, there were significant differences in K(L) among the bisphosphonates for HAP growth (pH 7.4) with a rank order of zoledronate > alendronate > ibandronate > risedronate > etidronate > clodronate. The measurements of zeta potential show that the crystal surface is modified by the adsorption of bisphosphonates in a manner best explained by molecular charges related to the protonation of their side-chain moieties, with risedronate showing substantial differences from alendronate, ibandronate, and zoledronate. The studies of the solid/liquid interfacial properties show additional differences among the bisphosphonates that may influence their mechanisms for binding and inhibiting crystal growth and dissolution. The observed differences in kinetic binding affinities, HAP zeta potentials, and interfacial tension are likely to contribute to the biological properties of the various bisphosphonates. In particular, these binding properties may contribute to differences in uptake and persistence in bone and the reversibility of effects. These properties, therefore, have potential clinical implications that may be important in understanding differences among potent bisphosphonates, such as the apparently more prolonged duration of action of alendronate and zoledronate compared with the more readily reversible effects of etidronate and risedronate.

Teriparatide (rhPTH 1-34) for the treatment of osteoporosis.

Osteoporosis is a skeletal disorder characterised by compromised bone strength predisposing a person to an increased risk of fracture. Osteoporosis develops through an imbalance between bone resorption by osteoclasts and bone formation by osteoblasts resulting in increased bone loss. Numerous agents used for the prevention and treatment of osteoporosis slow bone loss by decreasing both bone resorption and formation. These include bisphosphonates, hormone replacement therapy, selective oestrogen receptor modulators and calcitonins. All reduce vertebral fracture risk and some reduce non-vertebral fracture risk, but none routinely increases bone mass and strength or restores lost bone architecture. In many respects, antiresorptive therapies halt the progression of osteoporosis. However, for patients who have osteoporosis, particularly those who have sustained their first fracture and are at high risk for subsequent fractures, there is a need to develop agents that stimulate bone formation and, thus, reverse osteoporosis. Teriparatide is the recombinant human 1-34 amino acid sequence of parathyroid hormone recently approved in the US for the treatment of men and postmenopausal women at high risk for osteoporotic fracture and in Europe for the treatment of postmenopausal women with osteoporosis. When given by once-daily injection, teriparatide increases bone mass by stimulating formation of new bone, resulting in the restoration of bone architecture.

Osteoporosis: pathogenesis and clinical intervention.

Osteoporosis is a very common disorder and much has been learnt in recent years about the many pathogenic processes that contribute to bone loss and fragility. Drug treatments are now available to prevent bone loss and reduce fracture, and there are prospects for modifying some of the pathogenic processes themselves. In common with other structures, the tissues of the musculoskeletal system undergo many changes with aging, and some of the commonest skeletal disorders are seen in the elderly. The changes in bone lead to osteoporosis and fractures, whereas muscle changes (sarcopenia) contribute to frailty, and changes in cartilage lead to osteoarthritis.