Parathyroid hormone added to established hormone therapy: effects on vertebral fracture and maintenance of bone mass after parathyroid hormone withdrawal

Sequential treatment of ovariectomized mice with bFGF and risedronate restored trabecular bone microarchitecture and mineralization

Basic fibroblast growth factor (bFGF), a potent mitogen, has been found to restore trabecular bone mass and connectivity in osteopenic rats. The purpose of this study was to determine how sequential treatment of ovariectomized (OVXed) mice with bFGF followed by risedronate would restore trabecular microarchitecture and improve bone strength through alterations in bone mineralization. Six-month old female Swiss-Webster mice were OVXed or sham-operated and left untreated for 4 weeks to develop osteopenia. At week 5, a group of Sham and OVXed mice were treated with vehicle, and 3 other groups of OVXed mice were treated with bFGF (1 mg/kg daily, s.c., 5x/week) for 3 weeks. At week 8, one group of bFGF-treated mice was sacrificed and the other two bFGF-treated groups were treated with vehicle or risedronate (Ris, 5 microg/kg, s.c., 3x/week) for an additional 6 weeks. Study endpoints included trabecular microarchitecture by microCT, histomorphometry, bone turnover, degree of bone mineralization (DBM), and whole bone strength for the lumbar vertebral body. Compared to sham-operated animals, OVXed mice had significant reductions in trabecular bone volume, connectivity density, DBM, and bone biomechanical properties (P < 0.05). Treatment with bFGF resulted in higher trabecular bone structure and bone strength compared to pre-treatment sham control (P < 0.05). Treatment of OVXed mice with bFGF for 3 weeks followed by 6 weeks Ris maintained the trabecular microarchitecture gained by bFGF treatment, and DBM and bone strength were restored to baseline control levels. Also compared to Sham-operated animals, serum TGF-beta1 was transiently increased after OVX, increased an additional 100% after bFGF withdrawal, and decreased by 30% with risedronate. In addition, DBM was the strongest predictor for bone biomechanical properties (R2 > 0.7, P < 0.001). Serum TGF-beta1 correlated with bone turnover (DPD/Cr, osteocalcin) and was negatively correlated to DBM. Thus, in osteopenic mice, sequential treatment with bFGF followed by risedronate increased trabecular bone microarchitecture, DBM, and bone strength. In addition, suppression of the serum TGF-beta1 with risedronate was associated with increased DBM. Therefore, sequential treatment with bFGF and Ris restores trabecular architecture and allows mineralization of bone to increase, which appears to be beneficial to bone strength.

Combined treatment with a beta-blocker and intermittent PTH improves bone mass and microarchitecture in ovariectomized mice

Intermittent administration of parathyroid hormone (PTH) induces bone remodeling and renewed bone modeling, resulting in net bone gain. beta-blockers improve trabecular bone architecture in young ovariectomized mice by preventing the inhibition of bone formation and stimulation of bone resorption induced by the adrenergic system. To test the hypothesis that PTH and beta-blockers may exert synergistic effects on the skeleton, 15-week-old ovariectomized mice were either given oral propranolol (PRO) or left untreated for 8 weeks, adding daily hPTH(1-34) (80 microg/kg/day) or vehicle (VEH) during the last 4 weeks. The skeletal response was evaluated using pDXA, microCT, histomorphometry and biochemical markers. PRO significantly attenuated loss of bone mineral density (BMD) at whole body (WB) (-0.1% in PRO vs. -2.4% in VEH, P < 0.05), but not at spine or femur 4 weeks after OVX. Thereafter, PTH increased BMD at all sites in both PRO- and VEH-treated mice (+6.7% to +14%, P < 0.05 to P < 0.0001 vs. VEH). Over 8 weeks, sequential-combined treatment of PRO and PTH significantly improved BMD over PTH alone at WB (+9.1% vs. +4.4% over baseline, respectively, P < 0.005) and spine (+9% vs. -1.7%, respectively, P < 0.05). These effects were paralleled by a decrease in TRACP5b with PRO (P < 0.05 vs. VEH) and an increase in osteocalcin with PTH, irrespective of PRO (P < 0.0001 vs. VEH). Trabecular bone microarchitecture, such as BV/TV, trabecular number and ConnD, was significantly improved by sequential-combined treatment of PRO and PTH compared to PTH alone. At midshaft femur, both PRO and PTH significantly increased cross-sectional area (CSA), but the effects of the two drugs on CSA and cortical thickness were not additive. Dynamic histomorphometry indicated that bone formation was increased by PTH at both cortical and trabecular surfaces, whereas PRO increased osteoblast number and surface on trabecular surfaces. The combined treatment further improved the extent of mineralization and BFR over PTH alone (P < 0.05) at endocortical surfaces and recapitulated the effects of PTH and PRO alone on trabecular surfaces. These results indicate that beta-adrenergic blockade may partially improve the bone remodeling balance induced by estrogen deficiency. In turn, PRO exerted synergistic effects with intermittent PTH on bone mass and cancellous bone architecture. As such, combined therapy of beta-blockers and PTH may be of interest in the treatment of postmenopausal osteoporosis.

Primary hyperparathyroidism and malignancy: "studies by nature"

The American Food and Drug Administration approval of parathyroid hormone (PTH) administration for osteoporosis as well as the possibility for its future therapeutic applications requires an examination of the suggested association between PTH and cancer, particularly osteosarcomas. The objective was to evaluate such a connection by collecting observational data from two groups of patients, designated as "studies by nature". Cohort 1: Medical records of all patients with primary hyperparathyroidism that were treated in a referral center during a 12-year period were retrospectively reviewed for malignancy before, at the time or after diagnosis. Cohort 2: Records of patients with osteosarcomas that were treated in referral centers during 15 years were retrospectively reviewed for hyperparathyroidism, as indicated by history or laboratory results. There were 582 patients with primary hyperparathyroidism. While 56 (9.6%) had malignancy, 47 (8%) developed cancer after diagnosis with hyperparathyroidism during 6.1 years of documentation. This rate did not exceed the incidence of developing cancer among the general population. Although thyroid cancer was about 4 times the incidence in the general population, this may be attributed to a high level of detection while work-up, treating and following the parathyroid disease. None had osteosarcoma. None of the 126 patients with osteosarcoma had documentation of primary hyperparathyroidism or had biochemical evidence of hyperparathyroidism. No obvious association was found between primary hyperparathyroidism and cancer. Similarly, there was no demonstrable relationship between osteosarcomas and hyperthyroidism biochemical stigmata. Since PTH may contribute to tumor invasiveness, screening for existing neoplasms, especially prostate and breast, before PTH treatment may be of importance.

Anabolic skeletal therapy for osteoporosis

Antiresorptive agents for osteoporosis are a cornerstone of therapy, but anabolic drugs have recently widened our therapeutic options. By directly stimulating bone formation, anabolic agents reduce fracture incidence by improving bone qualities besides increasing bone mass. In this article, we review the role of anabolic treatment for osteoporosis. The only anabolic agent currently approved in the United States for osteoporosis, teriparatide [recombinant human parathyroid hormone(1-34)], has clearly emerged as a major approach to selected patients with osteoporosis. Teriparatide increases bone density and bone turnover, improves microarchitecture, and changes bone size. The incidence of vertebral and nonvertebral fractures is reduced. Teriparatide is approved for both postmenopausal women and men with osteoporosis who are at high risk for fracture. Other potential anabolic therapies for osteoporosis, including other forms of parathyroid hormone, strontium ranelate, growth hormone, and insulin-like growth factor-1, are also reviewed in this article.

Estrogen therapy for postmenopausal osteoporosis

Osteoporosis is a worldwide problem that results in fractures that lead to disability and high costs to society. Estrogen therapy is frequently utilized for postmenopausal symptoms, but also has proven protective effects on the skeleton. The main action of estrogen at the cellular level is to inhibit the osteoclast by increasing levels of osteoprotegerin (OPG). OPG binds to the receptor activator of NFkB and prevents osteoclast differentiation, activity and survival. Numerous trials have demonstrated the positive effect estrogen has on the improvement of bone mineral density, and lower doses have also proven efficacious with fewer side effects. Both observational and randomized clinical trials have demonstrated the ability of estrogen treatment to prevent fractures. Topics that remain controversial include the appropriate length of estrogen treatment for postmenopausal women and the appropriate follow-up after treatment discontinuation.

Parathyroid hormone for the treatment of osteoporosis: a systematic review

BACKGROUND

Human parathyroid hormone (hPTH)(1-34) was approved in 2004 for the treatment of severe osteoporosis. Members of the Osteoporosis Canada clinical guidelines committee conducted a systematic review of randomized controlled trials (RCTs) to assess the efficacy and safety of hPTH for fracture prevention in postmenopausal women and men with osteoporosis.

METHODS

We searched MEDLINE, EMBASE, HTA, Current Contents and the Cochrane Controlled Trials Registry for published data from 1966 to February 2005. A systematic literature search for RCTs was conducted using the Cochrane Collaborative approach. We identified 12 trials that randomly assigned patients either to hPTH or placebo or to hPTH or an active comparator and were at least 1 year in duration. Outcomes included change in bone mineral density (BMD), fractures, back pain and adverse events. Two independent reviewers abstracted data on study characteristics and outcomes.

RESULTS

hPTH(1-34) significantly increases lumbar spine BMD, with smaller increases at the femoral neck and total hip. hPTH(1-84) significantly increases lumbar spine BMD. The data show a significant reduction in both vertebral and nonvertebral fractures with hPTH(1-34) in postmenopausal women with previous vertebral fractures. There were no data on fractures comparing the approved dose of hPTH(1-34) with active comparators.

INTERPRETATION

There is Level I evidence that hPTH(1-34) significantly increases BMD at all skeletal sites except the radius and significantly reduces the risk of new vertebral and nonvertebral fractures in postmenopausal women with prior fractures.

Drug combination strategies for osteoporosis

Several medications are effective in reducing the incidence of osteoporotic fractures. Vertebral and nonvertebral fractures can be reduced by 30-65% by administering anticatabolic agents (e.g. raloxifene, alendronate, and risedronate) or anabolic agents (e.g. the active parathyroid hormone fragment teriparatide and strontium ranelate). These medications were investigated in placebo-controlled randomized trials in vast populations. Study extensions provided information on long-term efficacy and safety. However, the best strategy for using these medications in high-risk individuals remains unclear. For instance, the relative merits of starting with an anabolic agent or on an anticatabolic agent have not been compared. The patient's age, severity of the osteoporosis (bone mineral density and risk factor profile), specific characteristics of each medication, and patient preferences regarding drug-dosing modalities should be considered. Compliance must be evaluated regularly. Whereas minimal treatment durations have been determined, optimal durations remain incompletely evaluated and should be determined on a case-by-case basis according to the severity of the bone disease and to the treatment response in terms of clinical features and bone mineral density. Synchronous and t treatment combinations have been evaluated. Disappointing results were obtained with synchronous parathyroid hormone and bisphosphonate therapy. In contrast, the parathyroid hormone-bisphosphonate sequence holds promise for the treatment of severe postmenopausal osteoporosis with at least two vertebral fractures. However, little is known about potential synergies among medications in terms of fracture risk reduction. Synchronous and sequential regimens have not been compared in randomized clinical trials, and such trials would be extraordinarily difficult to design. Nevertheless, available data allow a number of suggestions regarding treatment strategies. The most important step is deciding to start effective treatment (raloxifene, bisphosphonate, teriparatide, or strontium ranelate) in patients at risk for fractures. Patients should be given detailed information on potential benefits and long-term treatment modalities.

The use of parathyroid hormone in the treatment of osteoporosis

Anabolic skeletal agents have recently broadened our therapeutic options for osteoporosis. By directly stimulating bone formation, they reduce fracture incidence by improving bone qualities in addition to increasing bone mass. Teriparatide [recombinant human parathyroid hormone(1-34)], the only anabolic agent currently approved in the United States for osteoporosis, has emerged as a major therapeutic approach to selected patients with osteoporosis. Teriparatide is approved for both postmenopausal women and men with osteoporosis who are at high risk for fracture. With the use of this anabolic agent, bone density and bone turnover increase, microarchitecture improves, and bone size is beneficially altered. The incidence of vertebral and nonvertebral fractures is reduced with teriparatide use. Combination therapy with parathyroid hormone and an antiresorptive does not appear to offer definitive advantages over the use of PTH or an antiresorptive alone, although recent ideas about combining these agents may offer new insights. In order to maintain increases in bone density acquired during PTH therapy, it is important to follow its use with an antiresorptive agent.

Combination of anabolic and antiresorptive agents for the treatment of osteoporosis

Combination therapy strategies for osteoporosis are reviewed in this article. Regimens including two antiresorptives agents increase BMD more than single therapy alone, but they have not proved to reduce fracture risk. The alternative of combining antiresorptives together with anabolics has gained more interest. There are, however, many questions still pending, as which antiresorptive should be used, and the appropriate sequence of the treatments. It seems that bisphosphonates can blunt the anabolic effect of parathyroid hormone (PTH) when given simultaneously. Instead, when PTH follows the antiresorptive treatment the anabolic effect seems not to be blunted. Finally, other possible approach would be to initiate therapy with an anabolic agent and maintain the effect with any antiresorptive if necessary.

Intermittent parathyroid hormone therapy to increase bone formation

Clinical data suggested that parathyroid hormone (PTH) might be effective in improving bone mass in patients with osteoporosis, providing its resorptive effects, which are particularly marked at cortical sites, were kept under control. We reviewed the evidence that intermittent PTH therapy is a valid treatment option whose predominant effect is bone anabolism. In cell culture studies, PTH affected both bone formation and bone resorption, suggesting that the net result of PTH therapy may be either bone gain or bone loss depending on the dosage, mode of administration, bone site, and animal species. Histological studies established that intermittent PTH therapy was associated with an increase in trabecular bone and, importantly, with improvements in trabecular and cortical microarchitectural parameters that have not been reported with antiresorptive drugs. This anabolic effect of intermittent PTH therapy translates into increased biomechanical strength, despite the increase in endocortical porosity seen in humans and nonhuman primates. The biochemical response profile to intermittent PTH therapy in clinical trials indicated a phase of isolated anabolism followed by an overall increase in bone remodeling that predominantly affected bone formation, the result being a large increase in spinal bone mineral density as early as the first treatment year. Thus, intermittent PTH therapy exerts predominantly anabolic effects on bone.

Expression of bone morphogenetic proteins in normal human intramembranous and endochondral bones

Bone morphogenetic proteins (BMPs) are growth and differentiation factors that have been purified and widely accepted to be the most important regulators in the processes of bone formation. The aim of this study was to identify the BMPs that are expressed in normal human bone, and to investigate the specific pattern of BMP2-BMP9 expression in normal human intramembranous and endochondral bone to maintain homeostasis, as well as in ex vivo primary cell culture of human osteoblasts from intramembranous and endochondral bone. Semi-quantitative RT-PCR indicated that 2 types of bone of different embryological origin have distinct patterns of BMP expression. BMP3, 4, 7 and 8 were strongly expressed in normal intramembranous bone compared to endochondral bone, whereas BMP2 and 5 were highly expressed in endochondral bone. The expression of BMP9 and BMP15 in human bone was identified for the first time. From the very similar expression patterns of BMPs in fresh normal bone and ex vivo osteoblastic cell culture, it can be proposed that the different proportions of BMPs in normal human intramembranous and endochondral bone needed to maintain normal homeostasis.

Combination/sequential therapies for anabolic and antiresorptive skeletal agents for osteoporosis

In this paper, we focus upon the use of anabolic skeletal therapy for the treatment of postmenopausal and other forms of osteoporosis. The only anabolic skeletal agent currently available is a recombinant bioactive fragment of parathyroid hormone, PTH(1-34), known as teriparatide. The full length molecule, human PTH(1-84) is being investigated at this time as are other PTH molecules. Teriparatide improves bone quality by actions on bone turnover, bone density, bone size, and microarchitecture. In postmenopausal women with osteoporosis, teriparatide reduces the incidence for vertebral and nonvertebral fractures. In individuals who have been treated previously with an antiresorptive agent, the subsequent actions of teriparatide on bone density are delayed transiently if bone turnover is markedly suppressed. Combination therapy with teriparatide or PTH(1-84) and an antiresorptive does not appear, at this time, to offer advantages over the use of PTH or an antiresorptive alone. To maintain the gains in bone density with PTH, it is important to follow its use with an antiresorptive agent.

Parathyroid hormone as an anabolic skeletal therapy

The quest for effective treatment for osteoporosis merits great attention because of the widespread prevalence of this disease, which is not only associated with fragility fractures, but also with significant morbidity and mortality. The efficacy of the antiresorptive drugs in this disease is achieved by reducing bone turnover, increasing bone density and improving other aspects of bone quality. This article concentrates on another approach to the treatment of osteoporosis, namely the use of anabolic therapy, which has even greater prospects for improving bone quality. Parathyroid hormone (PTH) is currently available only as the recombinant amino-terminal fragment, PTH(1-34), known as teriparatide. The full-length molecule, human PTH(1-84), is currently being investigated, as are other PTH molecules. Teriparatide improves bone quality through actions on bone turnover, bone density, bone size and bone microarchitecture. In postmenopausal women with osteoporosis, teriparatide reduces the incidence of vertebral and nonvertebral fractures. In individuals who have previously been treated with an antiresorptive agent, the subsequent actions of teriparatide on bone density are transiently delayed if bone turnover has been markedly suppressed. Combination therapy with teriparatide or PTH(1-84) and an antiresorptive agent does not appear, at this time, to offer advantages over the use of PTH or an antiresorptive agent alone. However, in order to maintain the densitometric gains in bone density obtained with PTH, it is important to follow its use with that of an antiresorptive agent.

Anabolic therapy for osteoporosis: Parathyroid hormone

Recombinant human parathyroid hormone (PTH 1-34) is the only anabolic agent currently approved for the treatment of osteoporosis. The term anabolic is based on mechanism of action. PTH stimulates bone formation, in contrast to antiresorptive agents, which reduce bone resorption and formation. Recent investigations involving the PTH(1-34) and PTH(1-84) peptides, alone and in combination or sequential regimens with antiresorptive agents, have provided a greater understanding of the place of PTH in the armamentarium against osteoporosis. These studies indicate that adding a bisphosphonate to PTH in previously untreated individuals does not produce additional bone benefit; however, sequential use of PTH followed-up by an antiresorptive agent is highly effective at increasing bone mineral density. Adding PTH after an antiresorptive agent also produces substantial bone density increments, though the magnitude of bone density increase may differ for different antiresorptive agents. PTH can repair underlying micro-architectural defects in bone, improve bone mass substantially, and perhaps change macro-architecture and geometry of bone. There are still many unanswered questions regarding PTH treatment of osteoporosis, including the optimal duration of treatment, optimal dosing regimen, mechanism of resistance to its effect after 18-24 months, and the effect of subsequent rechallenge.

Anabolic Agents: A New Chapter in the Management of Osteoporosis

Osteoporosis in postmenopausal women has until now been treated with antiresorptive agents, reducing the incidence of fragility fracture by approximately 50%. Clinical research has led to the development of new anabolic therapies capable of increasing the production of bone matrix by osteoblasts and reversing microarchitectural deterioration, resulting in major improvements in both bone quality and bone quantity. Teriparatide, a recombinant human parathyroid hormone consisting of the first 34 of 84 amino acids in human parathyroid hormone, has been shown to reduce significantly the risk of both vertebral and non-vertebral fractures in postmenopausal women. This agent was recently approved for use in Canada. Strontium ranelate is a new oral agent capable of uncoupling bone resorption from bone formation, which results in increases in bone formation with reductions in bone resorption. This agent has also been shown to reduce the risk of both vertebral and non-vertebral fracture while improving bone structure. Anabolic therapies represent a major advance in the management of postmenopausal osteoporosis, and they may provide significant benefit to those patients with severe osteoporosis in whom antiresorptive therapy has proven insufficient. Anabolic therapies should complement the antiresorptive treatments currently available for use in women with postmenopausal osteoporosis.

Effect of teriparatide [rhPTH(1-34)] on BMD when given to postmenopausal women receiving hormone replacement therapy

The effects of teriparatide when given in combination with HRT were studied in postmenopausal women with low bone mass or osteoporosis. The data provide evidence that the adverse event profile for combination therapy with teriparatide + HRT together is consistent with that expected for each treatment alone and that the BMD response is greater than for HRT alone.

INTRODUCTION

Teriparatide [rhPTH(1-34)], given as a once-daily injection, activates new bone formation in patients with osteoporosis. Hormone replacement therapy (HRT) prevents osteoporosis by reducing bone resorption and formation. Combination therapy with these two compounds, in small clinical trials, increased BMD and reduced vertebral fracture burden. The purpose of this study was to determine whether teriparatide provided additional effect on BMD when given in combination with HRT.

MATERIALS AND METHODS

A randomized, double-blind, placebo-controlled study was conducted in postmenopausal women with either low bone mass or osteoporosis. Patients were randomized to placebo subcutaneous plus HRT (n = 125) or teriparatide 40 microg/day (SC) plus HRT (TPTD40 + HRT; n = 122) for a median treatment exposure of 13.8 months. Approximately one-half of the patients in each group were pretreated with HRT for at least 12 months before randomization. Patients received 1000 mg calcium and 400-1200 IU of vitamin D daily as oral supplementation. BMD was measured by DXA.

RESULTS

Compared with HRT alone, TPTD40 + HRT produced significant (p < 0.001) increases in spine BMD (14% versus 3%), total hip (5.2% versus 1.6%), and femoral neck (5.2% versus 2%) at study endpoint. BMD, in whole body and ultradistal radius, was higher, and in the one-third distal radius was lower, in the combination therapy but not in the HRT group. Serum bone-specific alkaline phosphatase and urinary N-telopeptide/Cr were increased significantly (p < 0.01) in the women receiving TPTD40 + HRT compared with HRT. A similar profile of BMD and bone markers was evident in both randomized patients as well as in subgroups of patients not pretreated or pretreated with HRT. Patients tolerated both the treatments well. Nausea and leg cramps were more frequently reported in the TPTD40 + HRT group.

CONCLUSIONS

Adding teriparatide, a bone formation agent, to HRT, an antiresorptive agent, provides additional increases in BMD beyond that provided by HRT alone. The adverse effects of teriparatide when added to HRT were similar to the adverse effects described for teriparatide administered alone. Whether teriparatide was initiated at the same time as HRT or after at least 1 year on HRT, the incremental increases over HRT alone were similar.

Canadian Consensus Conference on osteoporosis, 2006 update

OBJECTIVE

To provide guidelines for the health care provider on the diagnosis and clinical management of postmenopausal osteoporosis.

OUTCOMES

Strategies for identifying and evaluating high-risk individuals, the use of bone mineral density (BMD) and bone turnover markers in assessing diagnosis and response to management, and recommendations regarding nutrition, physical activity, and the selection of pharmacologic therapy to prevent and manage osteoporosis.

EVIDENCE

MEDLINE and the Cochrane database were searched for articles in English on subjects related to osteoporosis diagnosis, prevention, and management from March 2001 to April 2005. The authors critically reviewed the evidence and developed the recommendations according to the Journal of Obstetrics and Gynaecology Canada's methodology and consensus development process.

VALUES

The quality of evidence is rated using the criteria described in the report of the Canadian Task Force on the Periodic Health Examination. Recommendations for practice are ranked according to the method described in this report.

SPONSORS

The development of this consensus guideline was supported by unrestricted educational grants from Berlex Canada Inc., Lilly Canada, Merck Frosst, Novartis, Novogen, Novo Nordisk, Proctor and Gamble, Schering Canada, and Wyeth Canada.

Effects of cyclic versus daily hPTH(1-34) regimens on bone strength in association with BMD, biochemical markers, and bone structure in mice

We developed a cyclic PTH regimen with repeated cycles of 1-week on and off daily PTH injection and explored its effects on bone strength, BMD, bone markers, and bone structure in mice. Cyclic protocols produced 60-85% of the effects achieved by daily protocols with 57% of the total PTH given, indicating more economic use of PTH. The study supports further exploration of cyclic PTH regimens for the treatment of osteoporosis.

INTRODUCTION

To minimize the cost and the catabolic action of hPTH(1-34), a cyclic PTH regimen with repeated 3-month cycles of on-and-off daily injection of hPTH(1-34) was developed in humans and shown to be as effective as a daily regimen in increasing vertebral BMD. However, changes in BMD may not adequately predict changes in bone strength. A murine model was developed to explore the efficacy of a cyclic PTH regimen on bone strength in association with other bone variables.

MATERIALS AND METHODS

Twenty-week-old, intact, female C57BL/J6 mice (n = 7/group) were treated with (1) daily injection with vehicle for 7 weeks (control); (2) daily injection with hPTH(1-34) (40 microg/kg/day) for 7 weeks (daily PTH); and (3) daily injection with hPTH(1-34) and vehicle alternating weekly for 7 weeks (cyclic PTH). BMD was measured weekly by DXA, and serum bone markers, bone structure, and strength were measured at 7 weeks.

RESULTS

Daily and cyclic PTH regimens increased BMD at all sites by 16-17% and 9-12%, respectively (all p < 0.01). The most dramatic effect of cyclic PTH occurred during the second week of treatment when PTH was off, with femoral and tibial BMD continuing to increase to the same extent as that produced by daily PTH. Both daily and cyclic PTH regimens significantly increased osteocalcin (daily, 330%; cyclic, 260%), mTRACP (daily, 145%; cyclic, 70%), femoral cortical width (daily, 23%; cyclic, 13%), periosteal circumference (daily, 5%; cyclic, 3.5%), and bone strength (max load: daily, 48%; cyclic, 28%; energy absorbed: daily, 103%; cyclic, 61%), respectively. Femoral bone strength was positively correlated with BMD, bone markers, and cortical structure. Neither regimen had an effect on vertebral bone strength. Although actual effects of cyclic PTH were 60-85% of those produced by daily PTH, the effects of cyclic PTH per unit amount administered were slightly greater than those of daily PTH for most measures.

CONCLUSIONS

PTH-enhanced femoral bone strength is positively correlated with its effects on femoral BMD, bone markers, and bone structure. Cyclic PTH regimens represent a potential economic use of PTH and warrant further study.

Anabolic Agents for Osteoporosis

Antiresorptive agents for osteoporosis are a cornerstone of therapy, but anabolic drugs have recently widened our therapeutic options. By directly stimulating bone formation, anabolic agents reduce fracture incidence by improving other bone qualities in addition to increasing bone mass. Teriparatide (human parathyroid hormone[1-34]) has clearly emerged as a major approach for selected patients with osteoporosis. Teriparatide increases bone mineral density and bone turnover, improves bone microarchitecture, and changes bone size. The incidence of vertebral and non-vertebral fractures is reduced. Teriparatide is approved in many countries throughout the world for the treatment of both postmenopausal women and men with osteoporosis who are at high risk for fracture. Another anabolic agent, strontium ranelate, may both promote bone formation and inhibit bone resorption. Clinical trials support the use of strontium ranelate as a treatment for postmenopausal osteoporosis and have shown that strontium ranelate reduces the frequency of vertebral and non-vertebral fractures. Other potential anabolic therapies for osteoporosis, including other forms of parathyroid hormone, growth hormone, and insulin-like growth factor-I, have been examined, although less data are currently available on these approaches.

Anabolic therapy for osteoporosis: parathyroid hormone

Recombinant human parathyroid hormone (PTH 1-34) is the only anabolic agent currently approved for the treatment of osteoporosis. The term anabolic is based on mechanism of action. PTH stimulates bone formation, in contrast to antiresorptive agents, which reduce bone resorption and formation. Recent investigations involving the PTH(1-34) and PTH(1-84) peptides, alone and in combination or sequential regimens with antiresorptive agents, have provided a greater understanding of the place of PTH in the armamentarium against osteoporosis. These studies indicate that adding a bisphosphonate to PTH in previously untreated individuals does not produce additional bone benefit; however, sequential use of PTH followed-up by an antiresorptive agent is highly effective at increasing BMD. Adding PTH after an antiresorptive agent also produces substantial bone density increments, though the magnitude of bone density increase may differ for different antiresorptive agents. PTH can repair underlying micro-architectural defects in bone, improve bone mass substantially, and perhaps change macro-architecture and geometry of bone. There are still many unanswered questions regarding PTH treatment of osteoporosis, including the optimal duration of treatment, optimal dosing regimen, mechanism of resistance to its effect after 18-24 months, and the effect of subsequent rechallenge.

Combination therapy for osteoporosis: considerations and controversy

Combination therapy, the simultaneous use of two pharmaceutical agents with the goal being reduction of fracture risk, is an area of substantial clinical interest. This paper summarizes the rationale, existing clinical trials data, and other considerations relevant to combination therapy for osteoporosis. Combinations of antiresorbers (eg, estrogen plus bisphosphonates) produce greater increases in bone mass than either treatment alone. Conversely, combining anabolic agents (parathyroid hormone) with bisphosphonates does not produce additive effects. None of the existing studies are large enough to determine whether combination treatment reduces fracture risk to a greater extent than use of a single agent. However, it is certain that combination treatment will increase cost and likely that it will increase side effects and reduce therapy adherence. Given the absence of demonstrated fracture reduction benefit, increased cost and likely increase in adverse events, combination therapy is not currently recommended.

A rational approach to evidence gaps in the management of osteoporosis

Major advancements in the treatment of osteoporosis have occurred over the last decade. Therapies including the anti-resorptive drugs such as alendronate and risedronate have been shown in randomized placebo-controlled trials to increase bone mineral density and reduce fracture risk. Anabolic therapy in the form of parathyroid hormone has been introduced as the first treatment to build bone mass. However, gaps in our knowledge about specific management issues that arise frequently among primary care providers persist. In this paper, three common clinical scenarios are discussed: a postmenopausal woman with only slightly reduced bone mineral density; an osteoporotic woman on anti-resorptive therapy for more than 5 years; and a woman who continues to fracture despite treatment. Evidence gaps in each treatment scenario are presented, and rational approaches to management are suggested.

Combination teriparatide and raloxifene therapy for postmenopausal osteoporosis: results from a 6-month double-blind placebo-controlled trial

We compared combination treatment with teriparatide plus raloxifene with teriparatide alone in women with postmenopausal osteoporosis in a 6-month double-blind, placebo-controlled trial that measured biochemical markers of bone turnover and BMD. Markers of bone formation and spine BMD increased similarly with teriparatide alone and combination therapy. However, combination therapy induced a significantly smaller increase in bone resorption versus teriparatide alone and significantly increased total hip BMD versus baseline.

INTRODUCTION

The effects of combining two approved treatments for osteoporosis with different modes of action were examined by comparing teriparatide [rhPTH(1-34)] monotherapy with combination teriparatide and raloxifene therapy.

MATERIALS AND METHODS

A 6-month randomized, double-blind trial comparing teriparatide plus raloxifene (n = 69) versus teriparatide plus placebo (n = 68) was conducted in postmenopausal women with osteoporosis.

RESULTS

Bone formation (N-terminal propeptide of type 1 collagen [PINP]) increased similarly in both treatment groups. However, the increase in bone resorption (serum C-terminal telopeptide of type I collagen [CTx]) in the combination group was significantly smaller than in the teriparatide-alone group (p = 0.015). Lumbar spine BMD significantly increased 5.19 +/- 0.67% from baseline in the teriparatide-alone group. In the combination group, lumbar spine (6.19 +/- 0.65%), femoral neck (2.23 +/- 0.64%), and total hip (2.31 +/- 0.56%) BMD significantly increased from baseline to study endpoint, and the increase in total hip BMD was significantly greater than in the teriparatide-alone group (p = 0.04). In the teriparatide-alone group, mean serum calcium levels increased from baseline to endpoint (0.30 +/- 0.06 mg/dl, p < 0.001), whereas mean serum phosphate remained unchanged. In the combination group, mean serum calcium was unchanged, and mean serum phosphate decreased (-0.20 +/- 0.06 mg/dl, p < 0.001) from baseline to endpoint. Changes in serum calcium (p < 0.001) and phosphate (p < 0.004) were significantly different between treatment groups. The safety profile of combination therapy was similar to teriparatide alone.

CONCLUSIONS

Combination therapy increased bone formation to a similar degree as teriparatide alone. However, the increase in bone resorption was significantly less and total hip BMD significantly increased for combination therapy compared with teriparatide alone. Combination treatment with raloxifene may thus enhance the bone forming effects of teriparatide. Further studies over longer treatment duration that include fracture endpoints are necessary to fully ascertain the clinical significance of combination raloxifene plus teriparatide therapy in postmenopausal osteoporosis.

Tratamiento anabólico en la osteoporosis

Pharmacological treatment of osteoporosis is based mainly on antiresorptive agents. However, there have been recently developed a group of drugs whose mechanism of action is the direct stimulation of bone formation: these drugs are named bone anabolic therapies. Among these compounds are fluoride, growth hormone (GH), insulin-like growth factor type I (IGF-I) and statins. Two further agents with major evidences of efficacy include strontium ranelate and parathyroid hormone (PTH) and its fragments. The present work reviews the current evidences of anabolic agents used in the treatment of osteoporosis.

Sustained nonvertebral fragility fracture risk reduction after discontinuation of teriparatide treatment

A follow-up in 1262 women was conducted after the discontinuation of teriparatide. The hazard ratio for combined teriparatide group (20 and 40 microg) for the 50-month period after baseline was 0.57 (p = 0.002), suggesting a sustained effect in reducing the risk of nonvertebral fragility fracture.

INTRODUCTION

Treatment with teriparatide [rhPTH(1-34)] 20 and 40 microg once-daily subcutaneous dosing significantly reduced the risk of nonvertebral fragility fractures over a median exposure of 19 months.

MATERIALS AND METHODS

All participants in the Fracture Prevention Trial were invited to participate in a follow-up study. Prior treatment assignments were revealed, and patients were able to receive osteoporosis treatments without restriction.

RESULTS

Approximately 60% of the 1262 patients received an osteoporosis treatment at some time during follow-up, with greater use in the former placebo group than in the combined former teriparatide group (p < 0.05). The hazard ratios for nonvertebral fragility fractures in each teriparatide group relative to placebo were statistically significant for the 50-month period including treatment and follow-up (p < 0.03). In the follow-up period, the hazard ratio was significantly different between the 40 mug and combined groups versus placebo but not for the 20 microg group versus placebo. However, the 20 and 40 microg groups were not different from each other. Kaplan-Meier analysis of time to fracture showed that the fracture incidence in the former placebo and teriparatide groups diverged during the 50-month period including teriparatide treatment and follow-up (p = 0.009). Total hip and femoral neck BMD decreased in teriparatide-treated patients who had no follow-up treatment; BMD remained stable or further increased in patients who received a bisphosphonate after teriparatide treatment.

CONCLUSIONS

While the study design is observational, the results support a sustained effect of teriparatide in reducing the risk of nonvertebral fragility fractures up to 30 months after discontinuation of treatment.

Daily and cyclic parathyroid hormone in women receiving alendronate

BACKGROUND

We evaluated whether patients with osteoporosis treated with long-term alendronate have a response to parathyroid hormone treatment and whether short, three-month cycles of parathyroid hormone therapy could be as effective as daily administration.

METHODS

We randomly assigned 126 women with osteoporosis who had been taking alendronate for at least 1 year to continued alendronate plus parathyroid hormone (1-34) subcutaneously daily, continued alendronate plus parathyroid hormone (1-34) subcutaneously daily for three 3-month cycles alternating with 3-month periods without parathyroid hormone, or alendronate alone for 15 months.

RESULTS

In both parathyroid hormone groups, bone formation indexes rose swiftly. Among the women who were receiving cyclic parathyroid hormone, bone formation declined during cycles without parathyroid hormone and increased again during cycles with parathyroid hormone. Bone resorption increased in both parathyroid hormone groups but increased progressively more in the daily-treatment group than in the cyclic-therapy group. Spinal bone mineral density rose 6.1 percent in the daily-treatment group and 5.4 percent in the cyclic-therapy group (P<0.001 for each parathyroid hormone group as compared with the alendronate group and no significant difference between parathyroid hormone groups). One woman in the daily-treatment group, two in the cyclic-therapy group, and four in the alendronate group had new or worsening vertebral deformities.

CONCLUSIONS

This study suggests that a regimen of three-month cycles of parathyroid hormone alternating with three-month cycles without parathyroid hormone causes the early phase of action of parathyroid hormone (characterized by pure stimulation of bone formation) to be dissociated from the later phase (activation of bone remodeling). The early phase may be more important to the increase in spinal bone mineral density. In patients with persistent osteoporosis after prior alendronate treatment, both daily treatment and cyclic treatment with parathyroid hormone increase spinal bone mineral density.

Parathyroid hormone and teriparatide for the treatment of osteoporosis: a review of the evidence and suggested guidelines for its use

All therapies currently recommended for the management of osteoporosis act mainly to inhibit bone resorption and reduce bone remodeling. PTH and its analog, teriparatide [recombinant human PTH(1-34)], represent a new class of anabolic therapies for the treatment of severe osteoporosis, having the potential to improve skeletal microarchitecture. Significant reductions in both vertebral and appendicular fracture rates have been demonstrated in the phase III trial of teriparatide, involving elderly women with at least one prevalent vertebral fracture before the onset of therapy. However, there is as yet no evidence that the antifracture efficacy of PTH will be superior to the bisphosphonates, whereas cost-utility estimates suggest that teriparatide is significantly more expensive. Teriparatide should be considered as treatment for postmenopausal women and men with severe osteoporosis, as well as for patients with established glucocorticoid-induced osteoporosis who require long-term steroid treatment. Teriparatide should also be considered for the management of individuals at particularly high risk for fractures, including subjects who are younger than age 65 and who have particularly low bone mineral density measurements (T scores < or = 3.5). Teriparatide therapy is not recommended for more than 2 yr, based, in part, on the induction of osteosarcoma in a rat model of carcinogenicity. Total daily calcium intake from both supplements and dietary sources should be limited to 1500 mg together with adequate vitamin D intake (< or =1000 U/d). Monitoring of serum calcium may be safely limited to measurement after 1 month of treatment; mild hypercalcemia may be treated by withdrawing dietary calcium supplements, reducing the dosing frequency of PTH, or both. At present, concurrent therapy with antiresorptive therapy, particularly bisphosphonates, should be avoided, although sequential therapy with such agents may consolidate the beneficial effects upon the skeleton after PTH is discontinued.

Combination therapy for osteoporosis: considerations and controversy

Combination therapy, the simultaneous use of two pharmaceutical agents with the goal being reduction of fracture risk, is an area of substantial clinical interest. This paper summarizes the rationale, existing clinical trials data, and other considerations relevant to combination therapy for osteoporosis. Combinations of antiresorbers (eg, estrogen plus bisphosphonates) produce greater increases in bone mass than either treatment alone. Conversely, combining anabolic agents (parathyroid hormone) with bisphosphonates does not produce additive effects. None of the existing studies are large enough to determine whether combination treatment reduces fracture risk to a greater extent than use of a single agent. However, it is certain that combination treatment will increase cost and likely that it will increase side effects and reduce therapy adherence. Given the absence of demonstrated fracture reduction benefit, increased cost and likely increase in adverse events, combination therapy is not currently recommended.

New perspectives on parathyroid hormone therapy

PURPOSE OF REVIEW

The prevention and treatment of osteoporosis has traditionally involved the use of antiresorptive therapies. The introduction of parathyroid hormone, an anabolic agent that enhances bone formation, has been accompanied by new treatment strategies. This article reviews combination and sequential therapy approaches with parathyroid hormone and antiresorptive agents to optimize efficacy outcomes.

RECENT FINDINGS

The distinguishing features of the anabolic and antiresorptive therapies for the treatment of osteoporosis has led to the hypothesis that the appropriate use of both agents, either in sequence or in combination, may result in superior fracture protection compared with either anabolic or antiresorptive treatment alone. This enthusiasm has been tempered by the observations that the transition from daily bisphosphonate therapy may blunt the efficacy of teriparatide. By contrast, more recent studies suggest that once-weekly bisphosphonate therapy may provide a better option with parathyroid hormone either in combination or in sequence. These considerations are critical to understanding the benefits of sequential treatment (parathyroid hormone followed by an antiresorptive agent), which aims to maintain or build on the large gains in efficacy from short-term therapy with parathyroid hormone. Because patients may require an additional treatment course of parathyroid hormone in the future, the choice of antiresorptive agent should be carefully considered. In addition, more recent evidence suggests that the forms of parathyroid hormone may have important differences in action that influence combination and sequence outcomes.

SUMMARY

Combination and sequential therapy with parathyroid hormone offers new options to maximize efficacy in patients at risk for osteoporotic fracture.

Enhancement of experimental fracture-healing by systemic administration of recombinant human parathyroid hormone (PTH 1-34)

BACKGROUND

Recombinant human parathyroid hormone (PTH [1-34]; teriparatide) is a new treatment for postmenopausal osteoporosis that can be systemically administered for the primary purpose of increasing bone formation. Because several studies have described the enhancement of fracture-healing and osteointegration in animals after use of PTH, we sought to critically analyze this skeletal effect.

METHODS

Two hundred and seventy male Sprague-Dawley rats underwent standard, closed femoral fractures and were divided into three groups that were administered daily subcutaneous injections of 5 or 30 mug/kg of PTH (1-34) or vehicle (control). The dosing was administered for up to thirty-five days. Groups were further divided into three subgroups and were killed on day 21, 35, or 84 after the fracture. The bones were subjected to mechanical torsion testing, histomorphometric analysis, or microquantitative computed tomography.

RESULTS

By day 21, calluses from the group treated with 30 mug of PTH showed significant increases over the controls with respect to torsional strength, stiffness, bone mineral content, bone mineral density, and cartilage volume. By day 35, both groups treated with PTH showed significant increases in bone mineral content and density and total osseous tissue volume, and they demonstrated significant decreases in void space and cartilage volume (p < 0.05). Torsional strength was significantly increased at this time-point in the group treated with 30 mug of PTH (p < 0.05). While dosing was discontinued on day 35, analyses performed after eighty-four days in the group treated with 30 mug of PTH showed sustained increases over the controls with respect to torsional strength and bone mineral density. No change was noted in osteoclast density at the time-points measured, suggesting that treatment with PTH enhanced bone formation but did not induce bone resorption.

CONCLUSIONS

These data show that daily systemic administration of PTH (1-34) enhances fracture-healing by increasing bone mineral content and density and strength, and it produces a sustained anabolic effect throughout the remodeling phase of fracture-healing.

Parathyroid hormone for the treatment of osteoporosis

Imbalances in bone metabolism result in bone mass loss and skeletal fragility in postmenopausal women and older men. Most osteoporosis treatments decrease bone metabolism and prevent the progression of bone loss and architectural damage to the skeleton. Analogs of parathyroid hormone stimulate the formation of new bone and offer new options for managing osteoporosis. This review highlights the effects of parathyroid hormone on bone density and fracture risk in patients with osteoporosis and addresses several of the important issues pertaining to the use of these new agents in daily clinical practice.

TARGET AUDIENCE

Obstetricians and Gynecologists, Family Physicians.

LEARNING OBJECTIVES

After completion of this article, the reader should be able to summarize the different mechanisms of action between parathyroid hormone analogues and antiresorptive drugs, to outline the effects of teriparatide treatment of patients with osteoporosis, and list the indications of teriparatide therapy.

A review of teriparatide and its clinical efficacy in the treatment of osteoporosis

Until recently, antiresorptive medications such as bisphosphonates and raloxifene represented the main pharmacological treatment options for patients with osteoporosis. With the introduction of teriparatide (rhPTH (1-34) ), a recombinant formulation of parathyroid hormone (PTH) consisting of the first 34 amino acids of the N -terminal region, bone-forming therapy has now become possible. Preclinical, as well as human studies, have shown increases in trabecular as well as cortical bone mass with subsequent improvements in bone microstructure and cortical thickness. The subcutaneous daily dose of teriparatide 20 microg has been shown to decrease the occurrence of new vertebral fractures in caucasian women (70 years of age) by 65%, in a large randomised, double-blind placebo-controlled trial. Moderate-to-severe fractures or multiple vertebral fractures could be reduced by 90 and 77%, respectively. There was also a significant beneficial effect on new nonvertebral fractures (-35%) by the end of the 21-month treatment period. The reduction in nonvertebral fractures became evident after approximately 8 - 12 months of treatment. Smaller studies in men with low bone mass showed similar effects on bone mineral density and changes in bone turnover markers when compared to the results obtained in postmenopausal women. Recent data suggest that teriparatide is best given as monotherapy and not in combination with a bisphosphonate. Previous bisphosphonate treatment is also likely to diminish the bone anabolic potential of teriparatide. In order to preserve bone mass gained during the recommended 18- to 24-month treatment period, antiresorptive medication should be prescribed following teriparatide treatment. Studies so far have not shown serious PTH-related side effects. Hypercalcaemia is usually mild and transient and the osteosarcoma risk reported in rat toxicology studies is very unlikely to be predictive of a similar risk in humans. As teriparatide is expensive, its use at the moment should be limited to patients with more severe forms of osteoporosis, usually with the presence or history of one or more fractures because of those patients' high risk for subsequent fractures.

Does early PTH treatment compromise bone strength? The balance between remodeling, porosity, bone mineral, and bone size

The treatment of osteoporotic women with recombinant human parathyroid hormone (rhPTH) increases bone mineral density and reduces fracture risk. However, there has been concern that the initiation of therapy in women with low bone mass may cause an early and transient increased fracture risk because PTH stimulates bone remodeling, which in its first phase is associated with bone resorption. Animal and human studies suggest, however, that the stimulation of remodeling caused by rhPTH(1-34) does not lead to a deterioration of bone's mechanical properties or to an increased fracture risk even early in the treatment. There are several reasons for this. Bone biomarkers associated with formation rise earlier than those associated with resorption, suggesting that there is an initial period prior to the stimulation of remodeling during which bone formation occurs on surfaces without prior resorption. This initial period of formation may protect the patient from the later small and transient losses that occur through remodeling. Moreover, the increased remodeling occurs on cancellous surfaces or close to the endosteal surface of bone, where its mechanical effect is minimal. Additionally, these transient losses may be compensated by periosteal apposition that maintains the overall strength of the bone. Thus, the early stimulation of bone formation without prior resorption, and the redistribution of bone from cancellous and endocortical surfaces to the periosteal surface combine to prevent the mechanical deterioration that could otherwise occur with a transient acceleration of bone remodeling in a patient with low bone mass.

Statin lipid-lowering drugs and bone mineral density

BACKGROUND

HMG Co-A reductase inhibitors (statin lipid-lowering drugs) have been associated with a reduced rate of fractures in some studies, but not in others. We examined the relationship between statin use and bone density among postmenopausal women.

METHODS

We conducted a cross-sectional survey at one academic medical center. Postmenopausal women who underwent bone densitometry and agreed to a telephone interview were surveyed about osteoporosis risk factors, use of hormone replacement therapy and osteoporosis medications and statin exposure. We then developed linear regression models adjusting for known counfounders to assess the relationship between statin use and bone mineral density (BMD).

RESULTS

Of 339 women studied, 162 were current or past users of statins, and 177 were not. Statin users and non-users were similar with respect to age, race, prior fracture history, the presence of medical conditions associated with osteoporosis, use of medications for osteoporosis, use of tobacco and use of oral glucocorticoids. Statin users had significantly higher body mass index (BMI) and rates of thiazide use, and were more likely to abstain from alcohol. After adjusting for important confounders, we found that statin use was associated with a significantly higher t-score at the total hip (-0.53 +/- 0.17) compared with non-users (-0.83 +/- 0.18; p = 0.02). At the lumbar spine, there was a trend toward higher t-scores in statin users (-0.91 +/- 0.24) compared with non-users (-1.21 +/- 0.23; p = 0.08).

CONCLUSIONS

These results support the hypothesis that statin use is associated with higher BMD. While it is unclear whether their relationship is causal, further controlled studies examining bone formation and resorption would help determine the clinical implications of these findings.

Effects of combined elcatonin and alendronate treatment on the architecture and strength of bone in ovariectomized rats

We examined the combined effects of elcatonin (ECT) and alendronate (ALN) on bone mass, architecture, and strength in ovariectomized (OVX) rats. Fifty female Sprague Dawley rats, aged 13 weeks, were divided into Sham, OVX, OVX+ECT, OVX+ALN, and OVX+ECT+ALN groups (n = 10). Immediately after ovariectomy, ECT was administered at a dose of 15 units (U)/kg three times a week, and ALN was administered daily at a dose of 2.0 microg/kg, subcutaneously for 12 weeks. The three-dimensional architecture of the bone in the distal femoral metaphysis was analyzed using a microfocus X-ray computed tomography system (microCT), and bone strength was measured using a material-testing machine. Trabecular bone volume (BV/TV) and number (Tb.N) were significantly greater in the OVX+ECT and OVX+ALN groups than in the OVX group. In the OVX+ECT+ALN group, BV/TV and Tb.N were significantly greater when compared with those in the OVX+ECT and OVX+ALN groups. Trabecular thickness (Tb.Th) was significantly greater in the OVX+ECT+ALN group than in the OVX+ALN group. With regard to bone strength, the compression strength in the femoral metaphysis was significantly lower in the OVX group than in the Sham group. The reduction of compression strength was slightly lower in the OVX+ECT and OVX+ALN groups. In the OVX+ECT+ALN group, the compression strength in the femoral metaphysis significantly increased when compared with the OVX and OVX+ECT groups. These results suggest that the combined treatment of ECT and ALN does not alter the individual effects of each drug and that it exerts an additive effect on trabecular architecture and bone strength in OVX rats.

The importance of bisphosphonate therapy in maintaining bone mass in men after therapy with teriparatide [human parathyroid hormone(1-34)]

Teriparatide, the active fragment of human parathyroid hormone (hPTH 1-34), is an anabolic agent for the treatment of osteoporosis. Important questions remain regarding management strategy beyond the recommended 18- to 24-month course of teriparatide treatment. We followed 21 men for up to 2 years after discontinuing teriparatide. Twelve men (57%) chose treatment with bisphosphonate immediately after teriparatide withdrawal, while 9 (43%) opted for no pharmacologic agent. At the end of 1 year lumbar spine bone density increased an additional 5.1+/-1.0% in the bisphosphonate group, while it declined by 3.7+/-1.7% in those on no medication (P<0.002). In six men who delayed initiation of bisphosphonate until 1 year after teriparatide withdrawal, their subsequent gains in the second year, 2.6+/-1.7%, still placed them below the peak gains they achieved on teriparatide. In contrast, the 12 men who began bisphosphonates immediately and continued treatment for the entire 2-year post-PTH period had continued gains at the lumbar spine, 8.9+/-1.5% above their post-PTH values (P=0.002). For the 4-year period, including 2 years of teriparatide and 2 years of bisphosphonate, the total gains at the lumbar spine were 23.6+/-2.9%. Men, who received bisphosphonate in only the 2nd year post-teriparatide, had cumulative gains of 11.1+/-3.4%. Three men who did not receive any bisphosphonate at any time during the post-PTH period had cumulative gains of only 5.5+/-3.7%. These findings suggest that the use of bisphosphonates following teriparatide is an important component of any strategy utilizing this anabolic drug for osteoporosis in men. The immediate use of bisphosphonates after teriparatide withdrawal may help to optimize gains in bone density at the lumbar spine.

Combination/sequential therapy in osteoporosis

Combination therapy includes the concomitant or sequential use of compounds sharing the same mode of action (eg, two or more inhibitors of bone resorption) or with distinct pathways of activity (eg, an inhibitor of resorption plus an anabolic agent). Combination use of antiresorptive agents may generate concerns, because of the risk of inducing oversuppression of bone turnover. However, if low doses of estrogen, used for the management of climacteric symptoms, are insufficient to normalize bone turnover, the addition of a bisphosphonate to hormone therapy may prove to be useful to achieve this objective. Patients pretreated with inhibitors of resorption, who have not achieved a full therapeutic response, are good candidates for treatment with anabolic agents. The increase in bone turnover that comes after the introduction of parathyroid hormone (PTH) in patients treated with an antiresorptive agent is similar to that observed in treatment-naïve patients and the pattern of bone mineral density (BMD) increase is also identical, with the exception of a 6 month delay in the spine and hip BMD changes observed in prior alendronate-treated subjects. Current data discourage the concomitant use of alendronate and PTH since the bisphosphonate appears to blunt (in men and women) the anabolic action of PTH. Whether this applies to other bisphosphonates or inhibitors of resorption, remains unknown. The use of an inhibitor of bone resorption after completion of PTH treatment seems an appropriate way to maintain the skeletal benefits gained during therapy. Long-term clinical studies, using fractures as an endpoint should be initiated to better understand the clinical and pharmaco-economic interest of combination therapies in the management of osteoporosis.

Parathyroid hormone: evolving therapeutic concepts

PURPOSE OF REVIEW

Osteoporosis results from a loss of bone mass and structure such that bones break with very little trauma. To reduce bone loss and improve strength, antiresorptive agents have been instituted. Just more than a year ago, a 34-amino acid fragment of parathyroid hormone (recombinant human parathyroid hormone 1-34) was approved for the treatment of osteoporosis. The parathyroid hormone treatment works by stimulating bone formation on all bone surfaces and is referred to as an osteoanabolic agent. The purpose of this article is to review initial phase 2 and phase 3 studies that establish the effectiveness of this agent to treat osteoporosis.

RECENT FINDINGS

In addition, studies that use parathyroid hormone in combination with antiresorptive agents and sequentially are reviewed. Last, unresolved issues related to the duration of use of parathyroid hormone are discussed.

SUMMARY

In summary, parathyroid hormone compounds are a major advance in the treatment of osteoporosis. Additional research will enlighten clinicians on the most efficacious way to use them.

Differential transcriptional effects of PTH and estrogen during anabolic bone formation

The aim of this study was to compare transcriptional regulation in vivo during anabolic bone formation induced by either estradiol (E2) treatment or intermittent parathyroid hormone[1-34] (PTH) therapy. We utilized an ovariectomized (OVX) mouse model of osteoporosis and transcriptional profiling to identify genes upregulated by either high-dose E2 or PTH. Five weeks post-OVX, the mice were administered either E2 and/or PTH, or vehicle for 4 weeks. Femoral bones were analyzed by microCT and histomorphometry to confirm the anabolic effect of each treatment. OVX vehicle-treated control mice lost metaphyseal trabecular bone, with significant decrease in trabecular number, thickness, and connectivity. Both E2 and PTH treatments increased trabecular and cortical bone indices above the level of the sham operated controls, fully restoring both bone volume and bone mineral density (BMD). Moreover, PTH/E2 combination treatment led to significantly greater increase in cancellous bone and BMD than would be expected from the additive effects of the separate treatments. To determine whether PTH and E2 treatments were stimulating similar bone anabolic mechanisms, or were activating distinct signaling pathways, we compared patterns of gene expression using transcriptional profiling after either E2 or PTH treatment. After 4, 11, and 24 days of treatment, total RNA was collected from both the distal femoral metaphysis and diaphysis. Transcriptional profiling was performed using Affymetrix GeneChip probe arrays, comprised of approximately 36,000 full-length mouse genes and EST clusters from the UniGene database. Several markers of osteoblast activity, including c-fos, RANKL, PHEX, and PTHR1, were consistently upregulated by PTH in both skeletal sites. PTH treatment also increased expression of Cathespin K, consistent with the predicted increase in osteoclast activity. E2 treatment upregulated a largely distinct set of genes, including TGFbeta3, and BMP1, as well as several genes critical for cell cycle control, including Cyclin D1 and CDK inhibitor 1A. Overall, comparison of transcriptional profiles suggest that anabolic responses in bone to PTH and high-dose E2 treatment after OVX-induced osteoporosis involve largely distinct patterns of gene regulation, each resulting in restoration of bone mass.

Engineering principles of clinical cell-based tissue engineering

Tissue engineering is a rapidly evolving discipline that seeks to repair, replace, or regenerate specific tissues or organs by translating fundamental knowledge in physics, chemistry, and biology into practical and effective materials, devices, systems, and clinical strategies. Stem cells and progenitors that are capable of forming new tissue with one or more connective tissue phenotypes are available from many adult tissues and are defined as connective tissue progenitors. There are four major cell-based tissue-engineering strategies: (1) targeting local connective tissue progenitors where new tissue is desired, (2) transplanting autogenous connective tissue progenitors, (3) transplanting culture-expanded or modified connective tissue progenitors, and (4) transplanting fully formed tissue generated in vitro or in vivo. Stem cell function is controlled by changes in stem cell activation and self-renewal or by changes in the proliferation, migration, differentiation, or survival of the progeny of stem cell activation, the downstream progenitor cells. Three-dimensional porous scaffolds promote new tissue formation by providing a surface and void volume that promotes the attachment, migration, proliferation, and desired differentiation of connective tissue progenitors throughout the region where new tissue is needed. Critical variables in scaffold design and function include the bulk material or materials from which it is made, the three-dimensional architecture, the surface chemistry, the mechanical properties, the initial environment in the area of the scaffold, and the late scaffold environment, which is often determined by degradation characteristics. Local presentation or delivery of bioactive molecules can change the function of connective tissue progenitors (activation, proliferation, migration, differentiation, or survival) in a manner that results in new or enhanced local tissue formation. All cells require access to substrate molecules (oxygen, glucose, and amino acids). A balance between consumption and local delivery of these substrates is needed if cells are to survive. Transplanted cells are particularly vulnerable. Theoretical calculations can be used to explore the relationships among cell density, diffusion distance, and cell viability within a graft and to design improved strategies for transplantation of connective tissue progenitors. Rational strategies for tissue engineering seek to optimize new tissue formation through the logical selection of conditions that modulate the performance of connective tissue progenitors in a graft site to produce a desired tissue. This increasingly involves strategies that combine cells, matrices, inductive stimuli, and techniques that enhance the survival and performance of local or transplanted connective tissue progenitors.

Teriparatide (Biosynthetic Human Parathyroid Hormone 1-34): A New Paradigm in the Treatment of Osteoporosis

The ideal treatment of osteoporosis should preferably prevent fractures through normalization of bone mass and bone micro-architecture. Biosynthetic human parathyroid hormone 1-34 (teriparatide) was recently approved in the EU and the USA as the first anabolic treatment of osteoporosis. The effects of teriparatide are mediated by the G-protein-dependent, parathyroid hormone receptor-1 in the cell membrane. The binding of the ligand to the receptor activates adenylate cyclase and a number of phospholipases (A, C, and D) and increases intracellular levels of cAMP and calcium. Intermittent teriparatide increases the number of osteoblasts and bone formation by activation of pre-existing osteoblasts, increased differentiation of lining cells, and reduced osteoblast apoptosis. Anabolic effects of teriparatide on bone have been demonstrated in several species. It increases bone mass, structural integrity, bone diameter, and bone strength. Clinical efficacy was demonstrated in a randomized study comprising 1637 post-menopausal women with osteoporosis showing a 65% and 35% reduction of the relative risk of vertebral and appendicular fractures, respectively, during 18 months of treatment. Moreover, bone mineral density in the lumbar spine and hip increased by 9.7% and 2.6%, respectively. Similar effects on bone mineral density have been reported in men with osteoporosis and in glucocorticoid-induced osteoporosis, however, fracture data are limited in these groups. Direct comparison with alendronate revealed that teriparatide has a more pronounced effect on bone mineral density. Teriparatide should be used in combination with calcium plus vitamin D, and may be combined with hormonal replacement therapy. In contrast, alendronate attenuates the effect of teriparatide. The efficacy of other combinations remains uncertain. After termination of teriparatide, bone mineral density of the lumbar spine is reduced by approximately 2-3% after 2 1/2 years. This decrease is prevented by treatment with bisphosphonates. The most frequent adverse effects with teriparatide are nausea, headache, dizziness, and leg cramps, however, only the latter two differed significantly between the groups receiving teriparatide 20 microg/day and placebo. In the pivotal clinical study, reduced dosage or termination of therapy due to hypercalcaemia was necessary in 3% and 0.2%, respectively. In a rat toxicology study, in which teriparatide was administered in high dosages for an extended period of time, osteosarcoma was seen in a significant number of animals. However, none of the approximately 2800 patients in clinical trials has developed osteosarcoma. Teriparatide constitutes a break-through in the treatment of severe osteoporosis, although a number of issues about the optimal use of teriparatide remains unsettled. The published data provide proof of concept on anabolic therapy which changes several paradigms of bone physiology. Other parathyroid hormone analogues are being investigated in clinical trials and the development of non-peptide, small molecules targeted at the parathyroid hormone receptor may be envisaged.

Teriparatide: A review

BACKGROUND

Traditionally, the management of osteoporosis in men and women has included the use of antiresorptive agents in combination with calcium and vitamin D supplementation. The mechanism of action of teriparatide is unique in that it possesses anabolic properties and therefore builds bone. Since the approval of teriparatide in the United States in 2002, a great deal of interest regarding its use in osteoporosis has developed.

OBJECTIVES

This article reviews the information available on the new recombinant human parathyroid hormone teriparatide (hPTH [1-34]), including its clinical pharmacology, mechanism of action, pharmacokinetic properties, clinical efficacy, safety profile, potential drug interactions, contraindications and warnings, dosage and administration, and pharmacoeconomics.

METHODS

The articles included in this review were identified through searches of PubMed and MEDLINE (1966-December 2003) and International Pharmaceutical Abstracts (1970-December 2003). Search terms included teriparatide, Forteo, recombinant human parathyroid hormone (1-34), and osteoporosis. The references of the identified articles were reviewed for additional publications. Specific product information was also obtained from the manufacturer of teriparatide.

RESULTS

Teriparatide has been studied in postmenopausal women with osteoporosis, drug-induced osteoporosis (specifically, corticosteroid-induced osteoporosis), and men with osteoporosis. The data available from various clinical trials have shown an increase in both bone mineral density (BMD) and bone mineral content (BMC) with the use of teriparatide compared with placebo. One study found that women treated with the 20-microg dose and the 40-microg dose were 35% and 40%, respectively, less likely to have one or more new nonvertebral fractures compared with placebo (P = 0.02). Another study compared the use of daily teriparatide 40-microg injections versus oral daily alendronate. Results showed that the incidence of nonvertebral fractures was significantly lower in the teriparatide group than the alendronate group (P < 0.05). A study using 20- and 40-microg daily injections of teriparatide was performed in men with osteoporosis. There was a statistically significant increase in lumbar spine BMD of 5.9% in the 20-microg group and 9.0% in the 40-microg group (both, P < 0.001). In the femoral neck, a 1.5% increase in BMD occurred in the 20-microg group (P = 0.021) and a 0.9% increase in the 40-microg group (P < 0.001). A limited number of studies are available assessing the combination of antiresorptive medications and teriparatide; however, the available data suggest that the effects of teriperatide do not require prior stimulation of bone resorption.

CONCLUSIONS

Teriparatide has been shown clinically to improve BMD and BMC in postmenopausal women and in men. Because of its anabolic capabilities, teriparatide can be used as an alternative to the traditional therapies that are currently available for the treatment of osteoporosis, with scheduled monitoring for adverse effects such as hypercalcemia and urinary calcium excretion. In 1 study, mild hypercalcemia was seen most often 4 to 6 hours after SC injection of teriparatide before returning to normal. Urinary calcium was observed to increase by 30 mg/d (0.75 mmol/d) with teriparatide.

Efficacy data on teriparatide (parathyroid hormone) in patients with postmenopausal osteoporosis

Until recently, the only therapeutic agents available for postmenopausal osteoporosis acted by inhibiting bone resorption and decreased the fracture risk by no more than 50%. Teriparatide, the recombinant 1-34 fragment of human parathyroid hormone, is a bone formation enhancer that has recently been licensed for use in established postmenopausal osteoporosis. Intermittent parathyroid hormone administration preferentially stimulates bone formation. The resultant increase in bone mass and improvement in bone architecture translate into a large decrease in the fracture risk that constitutes a major advance in the treatment of postmenopausal osteoporosis. Further work is needed to define the role for teriparatide in the therapeutic strategy for postmenopausal osteoporosis and to determine whether this agent is best used alone or in synchronous or sequential combination with bone resorption inhibitors.

Differential effects of teriparatide on BMD after treatment with raloxifene or alendronate

We investigated the effects of 18 months of treatment with teriparatide in patients previously treated with long-term antiresorptive therapy using bone turnover markers and bone densitometry. Previous raloxifene treatment allowed for teriparatide-induced early bone marker and BMD increases comparable with previously published results for treatment-näive patients. Conversely, previous alendronate treatment reduced the bone marker and BMD response.

INTRODUCTION

Teriparatide [rhPTH(1-34)] has been shown to increase BMD and reduce the risk of fracture in postmenopausal women with osteoporosis. Our objective was to investigate the skeletal effects of 18 months of treatment with teriparatide in women whose osteoporosis was previously treated with either alendronate or raloxifene.

MATERIALS AND METHODS

Daily subcutaneous injections of 20 microg teriparatide were administered for 18 months to 59 postmenopausal women, 60-87 years of age, with BMD T-scores </= -2.0 who had previously received either alendronate (ALN) or raloxifene (RLX) therapy for 18-36 months. All patients received daily calcium (1000 mg) and vitamin D (400 IU) supplementation. The primary study outcome was change in lumbar spine BMD measured by DXA. Secondary outcomes included changes in bone turnover markers, total hip BMD, and safety.

RESULTS

Median baseline bone turnover marker levels in prior ALN patients were about one-half those of prior RLX patients. During teriparatide treatment, bone markers in prior ALN patients increased later and peaked at about one-third lower levels compared with prior RLX patients. During the first 6 months, there were statistically significant (p < 0.05) group differences in BMD change at the hip (prior ALN -1.8% versus prior RLX +0.5%) and at the spine (prior ALN +0.5% versus prior RLX +5.2%). The positive slopes in hip and lumbar spine BMD were similar in both groups between 6 and 18 months. After 18 months, mean lumbar spine BMD increased 10.2% in prior RLX compared with 4.1% in prior ALN (p < 0.05) patients. Furthermore, at 18 months, mean total hip BMD had significantly increased (1.8%, p < 0.05) in prior RLX patients but was not different from baseline in prior ALN patients.

CONCLUSIONS

Teriparatide treatment stimulates bone turnover in patients pretreated with both RLX and ALN. Prior treatment with RLX allows for the expected teriparatide-induced BMD increases comparable with those previously reported for treatment-näive patients. In contrast, prior treatment with ALN prevents increases in BMD, particularly in the first 6 months.

Ion channels in osteoblasts: A story of two intracellular organelles

Recent advances have highlighted a synchronous coordination of osteoblast and osteoclast activity, whereby, the osteoblast collates all signals applied to the bone and activates osteoclastic resorption. The resorption of the bone and its matrix then releases growth factors held within the matrix (bone morphogenetic proteins, insulin-like growth factors and transforming growth factors) which then stimulate the osteoblast to lay down new osteoid. In healthy adults there is a balance between bone deposition and bone loss and there is no net gain or loss, and the amount of calcium (Ca2+) ingested in the diet is equal to that which is excreted. In the early stages of life, the emphasis is on bone building and more Ca2+ is retained from the diet and more bone deposited as the skeleton matures. As we age, and, in particular in postmenopausal women, the osteoclastic activity outweighs the bone deposition and the patient loses bone becoming osteoporotic. The focus of the work reported here was to identify and dissect the various cytosolic intracellular signalling pathways within osteoblasts and establish the importance of each under different physiological conditions. In brief, two basic signalling pathways exist; one is linked with a seven transmembrane spanning protein and specific receptors for ligands (the G protein linked pathways) and one pathway is linked with protein phosphorylation especially of the tyrosine kinases. In general, G protein activity is associated with endocrine ligands such as parathyroid hormone (PTH) and (calcitonin has been linked with tyrosine kinase activity) tyrosine kinase activity is linked with adhesion of osteoblasts and recognition of the substrate to which they are attached. Our specific areas of interest are the ways in which Ca2+ activity within the cell is modified and used as a signal for further activation and possibly differential gene activation.