Strontium ranelate phase 2 dose-ranging studies: PREVOS and STRATOS studies

The effects of strontium on bone mineral: A review on current knowledge and microanalytical approaches

The interest in effects of strontium (Sr) on bone has greatly increased in the last decade due to the development of the promising drug strontium ranelate. This drug is used for treating osteoporosis, a major bone disease affecting hundreds of millions of people worldwide, especially postmenopausal women. The novelty of strontium ranelate compared to other treatments for osteoporosis is its unique effect on bone: it simultaneously promotes bone formation by osteoblasts and inhibits bone resorption by osteoclasts. Besides affecting bone cells, treatment with strontium ranelate also has a direct effect on the mineralized bone matrix. Due to the chemical similarities between Sr and Ca, a topic that has long been of particular interest is the incorporation of Sr into bones replacing Ca from the mineral phase, which is composed by carbonated hydroxyapatite nanocrystals. Several groups have analyzed the mineral produced during treatment; however, most analysis were done with relatively large samples containing numerous nanocrystals, resulting thus on data that represents an average of many crystalline domains. The nanoscale analysis of the bone apatite crystals containing Sr has only been described in a few studies. In this study, we review the current knowledge on the effects of Sr on bone mineral and discuss the methodological approaches that have been used in the field. In particular, we focus on the great potential that advanced microscopy and microanalytical techniques may have on the detailed analysis of the nanostructure and composition of bone apatite nanocrystals produced during treatment with strontium ranelate.

Strontium Ranelate: Long-Term Efficacy against Vertebral, Nonvertebral and Hip Fractures in Patients with Postmenopausal Osteoporosis

Osteoporosis treatments need to combine an unequivocally demonstrated reduction of fractures, at various skeletal sites, long-term safety, and a user-friendly profile, optimizing therapeutic adherence. Strontium ranelate is the first compound to simultaneously decrease bone resorption and stimulate bone formation. Its antifracture efficacy, at various skeletal sites, has been established up to 8 years, through studies of the highest methodological standards. Increases in bone mineral density, observed after 1 year of treatment, are predictive of the long-term fracture efficacy, hence suggesting, for the first time in osteoporosis, that bone densitometry can be used as a monitoring tool for both efficacy and compliance. Owing to a positive benefit/risk ratio, strontium ranelate may now be considered as a first-line treatment in the management of osteoporosis.

Preliminary evaluation of therapeutic ion release from Sr-doped zinc-silicate glass ceramics

Bioactive and degradable porous bioceramics play an important role in many clinical situations. Porosity is essential to the performance of a material that is proposed to be used as an implantable osseous scaffold. Scaffolds provide a three dimensional support and template to osseous integration and vascularization. Combining the porosity of a scaffold with the ability of the scaffold material to deliver therapeutic ions to the site of implantation goes some way towards developing an ideal bone graft. A series of strontium-doped zinc silicate (Ca-Sr-Na-Zn-Si) glass ceramics scaffoldswere developed, whose porosity was measured to be between 93% and 96%, which is advantageous in terms of osseous integration and vascularization. The levels of Zn2+ and Sr2+ detected as a result of degradation of the crystalline phases were found to be 1.4–600 parts per million (ppm) and 0–583 ppm, respectively. The levels detected correlate well with the levels of Sr2+ and Zn2+ions typically associated with clinical benefits, including antibacterial efficacy, osteoblastic differentiation and impaired osteoclastic resorption.

The evidence for efficacy of osteoporosis treatment in men with primary osteoporosis: a systematic review and meta-analysis of antiresorptive and anabolic treatment in men

Purpose. Fragility fractures in men constitute a major worldwide public health problem with a life-time risk of 13%. It cannot be directly inferred that antiosteoporotic drugs effective in women have the same effect in men. Our aim was to appraise the existing evidence for efficacy of osteoporosis treatment in men. Methods. This study was a systematic review of the published literature on the clinical efficacy of medical osteoporosis therapy in the reduction of fracture risk in men (age > 50 years). Studies included were randomised, placebo-controlled trials of men. Results. Five BMD studies of antiresorptive treatment were included. All studies showed an increase in BMD, but there was only a nonsignificant trend in the reduction of clinical fractures. Three BMD studies of anabolic treatment with teriparatide were also included. These showed a significant mean increase in spine BMD and for vertebral fractures a non-significant trend towards a reduction was seen. Conclusion. The evidence of medical osteoporosis treatment in men is scant and inconclusive due to the lack of prospective RCT studies with fracture prevention as primary end point. So far, all evidence is based on BMD increases in small RCT studies showing BMD increases comparable to those reported in postmenopausal women.

Strontium ranelate: a look back at its use for osteoporosis

IMPORTANCE OF THE FIELD

Osteoporosis is now considered a major health problem in all developed and in most developing (non-African) countries.

AREAS COVERED IN THIS REVIEW

In this review, we provide an extensive literature survey (MEDLINE, PubMed, Cochrane Controlled Register), for articles dealing with osteoporosis management and/or strontium ranelate, from 1920 to 2010.

WHAT THE READER WILL GAIN

The objective is to provide an extensive, unbiased assessment of the available data allowing strontium ranelate to be placed in perspective with other anti-osteoporosis treatments.

TAKE HOME MESSAGE

Owing to a positive benefit-to-risk ratio, strontium ranelate may now be considered a first-line treatment in the management of osteoporosis.

The effect of prior bisphosphonate therapy on the subsequent BMD and bone turnover response to strontium ranelate

Strontium ranelate is an effective treatment for osteoporosis in treatment-naive women. In the United Kingdom, bisphosphonates are often used first line. Prior bisphosphonate use may blunt the bone mineral density (BMD) response to strontium ranelate by reducing strontium uptake into the bone. Sixty bisphosphonate-naive women and 60 women discontinuing bisphosphonates were recruited. All women commenced strontium ranelate and calcium/vitamin D. BMD and bone turnover markers were recorded for 12 months. After 12 months, the bisphosphonate-naive group's BMD increased by 5.6% (p < .001) at the spine, 3.4% (p < .001) at the total hip, and 4.0% (p < .001) at the heel. By comparison, the prior bisphosphonate group had a 2.1% (p = .002) increase at the spine but no change at the hip or heel. At all time points, BMD was significantly greater in the bisphosphonate-naive group. In the prior bisphosphonate group, there was no significant change in BMD during the first 6 months at the spine, but between months 6 and 12 there was a parallel gain in BMD (0.027 versus 0.020 g/cm(2), p = .40). The baseline difference in bone markers was no longer significant by 3 months for bone-specific alkaline phosphatase (BSAP) and 6 months for procollagen type 1 amino-terminal propeptide (P1NP) and carboxy-terminal cross-linking telopeptide of type I collagen (CTX). More women in the prior bisphosphonate group suffered a vertebral fracture (2 versus 8 women, p = .047). After bisphosphonates, bone turnover remains suppressed for up to 6 months, with blunting of the BMD response to strontium ranelate during this time. After 6 months, BMD increases in the spine but not at the hip or heel.

The cost-effectiveness of strontium ranelate in the UK for the management of osteoporosis

The cost-effectiveness of strontium ranelate was compared to no treatment in UK women using the FRAX algorithm for fracture risk assessment. At a willingness-to-pay of pound 30,000 per quality-adjusted life-year (QALY), strontium ranelate was generally cost-effective in women with prior fracture at the threshold of osteoporosis from an age of 65 years.

INTRODUCTION

The objectives of the study were to estimate the cost-effectiveness of strontium ranelate in the UK for the treatment of osteoporosis and to establish intervention thresholds for treatment using the FRAX tool.

METHODS

The cost-effectiveness of strontium ranelate was compared to no treatment in postmenopausal women with clinical risk factors for fracture using a lifetime simulation model based on Markov cohort methodology that incorporated the features of FRAX.

RESULTS

At a threshold of pound 30,000 per QALY, strontium ranelate was generally cost-effective in women from an age of 65 years with prior fracture at the threshold of osteoporosis (i.e., a T-score of -2.5 SD) and in women with a prior fracture (and no information on bone mineral density) from the age of 65 years. At a threshold of pound 20,000, strontium ranelate became cost-effective at a 10-year fracture probability of 25.7% and at 16.9% with a threshold of pound 30,000 for a QALY.

CONCLUSIONS

Strontium ranelate is a cost-effective agent for the treatment of established osteoporosis in women over the age of 65 years. Cost-effective scenarios were also found for the prevention and treatment of fractures associated with osteoporosis, in younger women with additional clinical risk factors.

Current and emerging pharmacologic therapies for the management of postmenopausal osteoporosis

Postmenopausal osteoporosis is an asymptomatic skeletal disease that is often underdiagnosed and undertreated. Osteoporotic fractures are associated with substantial morbidity and mortality and impaired quality of life-socially, emotionally, and financially. Considering the growing burden of osteoporotic fractures worldwide, there remains an ongoing need for progress in the diagnosis of osteoporosis, identification of individuals at high fracture risk, and treatment to prevent fractures. Adequate intake of calcium and vitamin D is recommended as baseline therapy for osteoporosis prevention and treatment. Available pharmacological agents for the management of postmenopausal osteoporosis may not be appropriate for all women. Oral bisphosphonates are generally considered first-line therapy for patients with osteoporosis, but their use may be limited by gastrointestinal side effects. Other agents include hormone therapy, the selective estrogen receptor modulator (SERM) raloxifene, salmon calcitonin, teriparatide (human recombinant parathyroid hormone), and strontium ranelate (in some countries). Factors that may contribute to poor compliance and persistence with current osteoporosis therapies include drug intolerance, complexity of dosing regimens, and poor understanding of the relative benefit and risk with treatment. Emerging therapies for postmenopausal osteoporosis include novel SERMs (bazedoxifene, lasofoxifene, ospemifene, arzoxifene) and denosumab. Because SERMs can display mixed functional estrogen receptor agonist or antagonist activity depending on the target tissue, they may confer beneficial effects on bone with limited stimulation of other tissues (e.g., breast, endometrium). Clinical investigation of these promising new agents is ongoing to evaluate efficacy and safety, with the goal of developing effective strategies to maximize long-term tolerance, compliance, and persistence with therapy.

Strontium ranelate: new data on fracture prevention and mechanisms of action

Osteoporosis treatments need to combine an unequivocally demonstrated reduction of fractures, at various skeletal sites, long-term safety, and a user-friendly profile that optimizes therapeutic adherence. Strontium ranelate is the first compound to simultaneously decrease bone resorption and stimulate bone formation. Its anti-fracture efficacy at various skeletal sites has been established for as long as 5 years through studies of the highest methodological standards. Increases in bone mineral density observed after 1 year of treatment are predictive of the long-term fracture efficacy, suggesting for the first time in osteoporosis that bone densitometry can be used as a monitoring tool. Due to a positive risk/benefit ratio, strontium ranelate is now considered as a first-line treatment in the management of osteoporosis.

Bone-forming agents in the management of osteoporosis

Women often consult for the first time after osteoporosis has already become established. Medications have therefore been developed which can stimulate bone formation, with the ultimate goal of restoring bone quantity and quality and reducing spinal and peripheral fractures to a greater extent than can be obtained with inhibitors of bone resorption. Peptides of the parathyroid hormone family, when given intermittently, increase the number and activity of osteoblasts, leading to an increase in bone mass and in an improvement in skeletal architecture. Teriparatide (1-34 parathyroid hormone, PTH) reduces vertebral and non-vertebral fractures at a dose of 20 microg/day given in subcutaneous daily injections. 1-84 PTH reduces vertebral fractures, but results on non-vertebral fractures are lacking. Strontium ranelate, suggested to uncouple bone formation from bone resorption, reduces vertebral, non-vertebral and hip fractures in osteoporotic patients aged >74 years. Reduction of a vertebral fracture has also been shown in osteopenic patients. Long-term (5-year) data are available on vertebral, non-vertebral, major non-vertebral and hip fractures in osteoporotic patients. Combination/sequential treatments using inhibitors of bone resorption and bone-forming agents have been assessed in a variety of regimens. Benefits from the use of bone-forming agents appear to be largely independent of previous treatment with inhibitors of bone resorption. After treatment with an anabolic agent, the use of anti-resorptive medications maintains the benefit of the former treatment. Concomitant use of an inhibitor of bone resorption and a stimulator of bone formation has not, so far, showed any additional benefit compared with each medication given alone.

Cancer treatment-related bone loss: a review and synthesis of the literature

Cancer therapy can result in significant bone loss and increased risk of fragility fracture. Chemotherapy, aromatase inhibitors, and gonadotropin-releasing hormone analogues contribute to increases in the rate of bone remodelling and reduce bone mineral density. Patients with prostate cancer on androgen deprivation therapy experience an increase in the risk of fracture. New research has demonstrated the key role played by bisphosphonates in preventing declines in bone density and increases in bone remodelling. Novel antiresorptive agents targeting receptor activator of nuclear factor κB ligand have great potential in skeletal protection and prevention of bone loss related to cancer therapy. Early assessment of skeletal health, followed by initiation of calcium, vitamin D, and an exercise program are valuable in the prevention and treatment of osteoporosis. In addition, individuals at increased risk for fracture should be offered antiresorptive therapy. Early data have demonstrated that bisphosphonates are able to prevent the bone loss and increased bone remodelling associated with cancer therapy, including aromatase inhibition and androgen deprivation therapy. The present paper reviews the new research and advances in the management of bone loss associated with both cancer therapy and estrogen deficiency in the postmenopausal female.

Relationship between bone mineral density changes and fracture risk reduction in patients treated with strontium ranelate

OBJECTIVE

Our objective was to analyze the relationship between bone mineral density (BMD) changes and fracture incidence during 3-yr treatment with strontium ranelate.

PATIENTS

Women from the strontium ranelate arm of the Spinal Osteoporosis Therapeutic Intervention study and the TReatment Of Peripheral OSteoporosis study were evaluated.

OUTCOME MEASURES

The outcome measures included BMD at the lumbar spine, femoral neck, and total proximal femur assessed at baseline and after a follow-up of 1 and 3 yr; semiquantitative visual assessment of vertebral fractures; and nonvertebral fractures based on written documentation.

RESULTS

After 3 yr of strontium ranelate treatment, each percentage point increase in femoral neck and total proximal femur BMD was associated with a 3% (95% adjusted confidence interval, 1-5%) and 2% (1-4%) reduction in risk of a new vertebral fracture, respectively. The 3-yr changes in femoral neck and total proximal femur BMD explained 76% and 74%, respectively, of the reduction in vertebral fractures observed during the treatment. Three-year changes in spine BMD were not statistically associated with the incidence of new vertebral fracture (P = 0.10). No significant associations were found between 3-yr changes in BMD and incidence of new nonvertebral fractures, but a trend was found for femoral neck BMD (P = 0.09) and for total proximal femur BMD (P = 0.07). An increase in femoral neck BMD after 1 yr was significantly associated with the reduction in incidence of new vertebral fractures observed after 3 yr (P = 0.04).

CONCLUSION

During 3-yr strontium ranelate treatment, an increase in femoral neck BMD was associated with a proportional reduction in vertebral fracture incidence.

Effects of parathyroid hormone alone or in combination with antiresorptive therapy on bone mineral density and fracture risk--a meta-analysis

AIM

The effects of parathyroid hormone (PTH) alone or in combination with antiresorptive therapy on changes in bone mineral density (BMD) and fracture risk were studied.

MATERIALS AND METHODS

Randomised placebo controlled trials were retrieved from the PubMed, Web of Science or Embase databases.

RESULTS

PTH alone or in combination with antiresorptive drugs reduced vertebral [relative risk (RR)=0.36, 95% confidence interval (CI): 0.28-0.47, 2p<0.01] and non-vertebral (RR=0.62, 95% CI: 0.48-0.82, 2p<0.01) fracture risk and increased spine BMD by 6.6% (95% CI: 5.2-8.1%, 2p<0.01) and hip BMD non-significantly by 1.0% (95% CI: -0.1 to 2.1%, 2p=0.08) during 11-36 months of follow-up (13 trials). The gain in spine and hip BMD tended to increase with the length of the PTH treatment. No significant effect of study duration on fracture risk could be demonstrated. The major adverse events were hypercalcaemia, nausea and discomfort at the injection sites. Only limited data are currently available on fracture risk reduction with PTH plus antiresorptive therapies.

CONCLUSION

Although the number of studies on non-vertebral fractures is limited, our pooled analysis revealed that PTH alone or in combination with antiresorptive drugs would appear to be able to reduce the risk of vertebral and non-vertebral fractures and to increase spine and perhaps hip BMD. However, these analyses were based on cross-sectional data--i.e. based on indirect comparisons--and further studies with a direct comparison of study duration are necessary. No studies comparing PTH, PTH plus antiresorptive drugs and antiresorptive drug versus placebo in a factorial design are available; consequently, we were unable to draw any conclusions on the superiority of PTH plus antiresorptive drug versus antiresorptive drug or PTH alone with respect to BMD or fractures.

An economic evaluation of strontium ranelate in the treatment of osteoporosis in a Swedish setting: based on the results of the SOTI and TROPOS trials

INTRODUCTION

Strontium ranelate is a new therapy for the treatment and prevention of osteoporosis that has been shown in two phase III clinical trials (the Spinal Osteoporosis Therapeutic Intervention [SOTI] and the Treatment Of Peripheral OSteoporosis Study [TROPOS] trials) to reduce the risk of osteoporotic fractures at the vertebral, non-vertebral and hip level in postmenopausal women. The aim of this study was to estimate the potential cost-effectiveness of strontium ranelate in the treatment of osteoporosis in postmenopausal Swedish patients.

METHODS

A Markov cohort model was adapted to fit patients corresponding to the patients in the SOTI and TROPOS clinical trials. The model was populated with Swedish cost and epidemiological data. In the base case, the cost-effectiveness was estimated for 69-year old women with low bone mineral density (BMD) and prevalent vertebral fractures (SOTI) and for 77-year old women with low BMD (TROPOS). The cost-effectiveness analysis had a societal perspective.

RESULTS

In the base case analysis, the cost per quality-adjusted life years (QALY) gained of strontium ranelate patients compared to no treatment patients was estimated at SEK 472,586 and SEK 259,643, including costs in added life years, based on the SOTI and the TROPOS trials, respectively. Excluding cost in added life years, the cost per QALY gained was estimated at SEK 336,420 (SOTI) and SEK 165,680 (TROPOS). In subgroup analyses, in patients 74 years and older with a T-score lower than -2.4 and patients older than 80 years of age, strontium ranelate was found to be cost saving compared to no treatment.

CONCLUSIONS

The results in the base case analyses and the sensitivity analyses of this study indicate that, compared to no treatment, strontium ranelate is cost-effective in the treatment of postmenopausal women with low BMD.

Strontium ranelate for preventing and treating postmenopausal osteoporosis

BACKGROUND

Strontium ranelate is a new treatment for osteoporosis therefore, its benefits and harms need to be known.

OBJECTIVES

To determine the efficacy and safety of strontium ranelate for the treatment and prevention of postmenopausal osteoporosis.

SEARCH STRATEGY

We searched MEDLINE (1996 to March 2005), EMBASE (1996 to week 9 2005), the Cochrane Library (1996 to Issue 1 2005), reference lists of relevant articles and conference proceedings from the last two years. Additional data was sought from authors.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) of at least one year duration comparing strontium ranelate versus placebo reporting fracture incidence, bone mineral density (BMD), health related quality of life or safety in postmenopausal women. Treatment (versus prevention) population was defined as women with prevalent vertebral fractures and/or lumbar spine BMD T score < -2.5 SD.

DATA COLLECTION AND ANALYSIS

Two reviewers independently determined study eligibility, assessed trial quality and extracted the relevant data. Disagreements were resolved by consensus. RCTs were grouped by dose of strontium ranelate and treatment duration. Where possible, meta-analysis was conducted using the random effects model.

MAIN RESULTS

Four trials met the inclusion criteria. Three included a treatment population (0.5 to 2 g of strontium ranelate daily) and one a prevention population (0.125 g, 0.5 g and 1 g daily). A 37% reduction in vertebral fractures (RR 0.63, 95% CI 0.56, 0.71) and a 14% reduction in non-vertebral fractures (RR 0.86, 95% CI 0.75, 0.98) were demonstrated over three years with 2 g of strontium ranelate daily in a treatment population. An increase in BMD was shown at all BMD sites after two to three years in both populations. Lower doses of strontium ranelate were superior to placebo and the highest dose demonstrated the greatest reduction in vertebral fractures and increase in BMD. An increased risk of diarrhea with 2 g of strontium ranelate was found; however, adverse events did not affect the risk of discontinuing treatment nor did it increase the risk of serious side effects, gastritis or death. Additional data suggests that the risk of vascular and nervous system side-effects is slightly increased with taking 2 g of strontium ranelate daily over three to four years.

AUTHORS' CONCLUSIONS

There is silver level evidence (www.cochranemsk.org) to support the efficacy of strontium ranelate for the reduction of fractures (vertebral and to a lesser extent non-vertebral) in postmenopausal osteoporotic women and an increase in BMD in postmenopausal women with/without osteoporosis. Diarrhea may occur however, adverse events leading to study withdrawal were not significantly increased with taking 2 g of strontium ranelate daily. Potential vascular and neurological side-effects need to be further explored.

Strontium ranelate for preventing and treating postmenopausal osteoporosis

BACKGROUND

Strontium ranelate is a new anti-osteoporosis therapy therefore, its benefits and harms need to be known.

OBJECTIVES

To determine the efficacy and safety of strontium ranelate for the treatment and prevention of postmenopausal osteoporosis.

SEARCH STRATEGY

We searched MEDLINE (1996 to March 2005), EMBASE (1996 to week 9 2005), the Cochrane Library (1996 to Issue 1 2005), reference lists of relevant articles and conference proceedings from the last two years. Additional data was sought from authors and industry sponsors.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) of at least one year duration comparing strontium ranelate versus placebo reporting fracture incidence, bone mineral density (BMD), health related quality of life and/or safety outcomes in postmenopausal women. Treatment (versus prevention) population was defined as women with prevalent vertebral fractures and/or lumbar spine BMD T score < -2.5 SD.

DATA COLLECTION AND ANALYSIS

Two reviewers independently determined study eligibility, assessed trial quality and extracted the relevant data. Disagreements were resolved by consensus. RCTs were grouped by dose of strontium ranelate and treatment duration. Where possible, meta-analysis was conducted using the random effects model.

MAIN RESULTS

A total of four trials met our inclusion criteria, three of which investigated the effects of strontium ranelate compared to placebo in a treatment population (doses ranged from 0.5 to 2 g daily) and one, in a prevention population (doses 0.125, 0.5 and 1 g daily). In osteoporotic, postmenopausal women a 37% reduction in vertebral fractures (two trials, n = 5082, RR 0.63, 95% CI 0.56 to 0.71) and a 14% reduction in non-vertebral fractures (two trials, n = 6572, RR 0.86, 95% CI 0.75 to 0.98) was demonstrated over a three year period with 2 g of strontium ranelate daily. An increase in BMD at all sites was shown with the same dose: lumbar spine BMD (two trials, n = 1614, WMD adjusted for strontium content 5.44, 95% CI 3.41 to 7.46 and WMD not adjusted 11.29, 95% CI 10.22 to 12.37 over two years), femoral neck and total hip (two trials, n = 4230, WMD 8.25, 95% CI 7.84 to 8.66 and WMD 9.83, 95% CI 9.39 to 10.26 respectively over three years). One gram of strontium ranelate daily in postmenopausal women without osteoporosis increased BMD at all sites over a two year period: lumbar spine (one trial, n = 59, WMD adjusted for strontium content 2.39, 95% CI 0.15 to 4.63 and WMD not adjusted 6.68, 95% CI 5.16 to 8.20), femoral neck (one trial, n= 60, WMD 2.52, 95%CI 0.96 to 4.09) and total hip (one trial, n = 60, WMD 1.02, 95% CI 0.48 to 1.56). In both the treatment and prevention populations, lower doses of strontium ranelate were superior to placebo with the highest dose of strontium ranelate demonstrating the greatest reduction in vertebral fractures and increase in BMD. There is some evidence to suggest that 2 g of strontium ranelate daily compared to placebo may have a beneficial effect on health related quality of life in postmenopausal women after three years of treatment. Two grams of strontium ranelate daily increased the risk of diarrhea (RR 1.38%, 95% CI 1.02 to 1.87); however, adverse events did not affect the risk of discontinuing strontium ranelate nor did it increase the risk of serious side effects, gastritis or death. Additional data obtained suggests that the risk of vascular system disorders including venous thromboembolism (two trials, n = 6669, 2.2% versus 1.5%, OR 1.5, 95% CI 1.1 to 2.1) and pulmonary embolism (two trials, n = 6669, 0.8% versus 0.4%, OR 1.7, 95% CI 1.0 to 3.1) as well as nervous system disorders such as headaches (3.9% versus 2.9%), seizures (0.3% versus 0.1%), memory loss (2.4% versus 1.9%) and disturbance in consciousness (2.5% versus 2.0%) is slightly increased with taking 2 g of strontium ranelate daily over a 3 to 4 year period.

AUTHORS' CONCLUSIONS

There is silver level evidence to support the efficacy of strontium ranelate for the reduction of vertebral fractures (and to a lesser extent non-vertebral fractures) in postmenopausal osteoporotic women and an increase in BMD (all sites) in postmenopausal women with and without osteoporosis. Diarrhea may occur however, adverse events leading to study withdrawal were not significantly increased in the strontium ranelate group. Potential risks to the vascular and neurological system associated with taking 2 g of strontium ranelate daily need to be further explored and quantified.

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.

Epilepsy, osteoporosis and fracture risk - a meta-analysis

This meta-analysis assesses the effects of epilepsy on fracture risk and changes in bone mineral density (BMD) in patients with epilepsy. A search of PubMed was conducted using the key words epilepsy, fracture, and bone mineral. A weighted estimate of relative risk of fractures and changes in BMD (Z-score) was calculated. From the changes in BMD, expected increase in relative fracture risk was calculated. A total of 11 studies on fracture risk and 12 studies on BMD were retrieved. The relative risk of any fracture was increased (2.2, 95% CI: 1.9-2.5, five studies), as was the risk of hip (5.3, 3.2-8.8, six studies), forearm (1.7, 1.2-2.3, six studies), and spine fractures (6.2, 2.5-15.5, three studies). A large proportion of fractures (35%) seemed related to seizures. Spine (mean +/- SEM: -0.38 +/- 0.06) and hip (-0.56 +/- 0.06) BMD Z-scores were significantly decreased, hip more than spine (2P < 0.05). The expected increases in relative risk of any fracture from BMD Z-scores were 1.2-1.3, and significantly lower than observed (2P < 0.05). The deficit in BMD in patients with epilepsy is too small to explain the observed increase in fracture risk. The remainder of the increase in fracture risk may be linked to seizures.

Effects of strontium on the physicochemical characteristics of hydroxyapatite

In a previous experimental study using a chronic renal failure rat model, a dose-related multiphasic effect of strontium (Sr) on bone formation was found that could be reproduced in an in vitro set-up using primary rat osteoblasts. The results from the latter study allowed us to distinguish between a reduced nodule formation in the presence of an intact mineralization at low Sr-doses (1 microg/ml) and an interference of the element with the hydroxyapatite (HA) formation at high doses (20-100 microg/ml). To further investigate the latter effect of Sr on physicochemical bone mineral properties, an in vitro study was set up in which the UMR-106 rat osteosarcoma cell line was exposed to Sr, added to the cell culture medium in a concentration range varying between 0-100 microg/ml. Temporal growth and functionality of the culture was investigated by measurement of the alkaline phosphatase activity and calcium (Ca) concentration in the culture medium (used as an index of Ca-incorporation, i.e., HA formation) at various time points. At the end of the culture period (14 days post-confluence), samples of the mineralized cultures were taken for further analysis using X-ray diffraction (XRD) and Fourier Transform Infra-Red Spectroscopy (FTIR). Synthetic HA doped with various Sr concentrations (based on the cell culture and previous experimental studies and yielding Sr/(Sr + Ca) ratios ranging from 0-60%), was prepared and examined for crystal growth and solubility. Crystal size was assessed using scanning electron microscopy (SEM). Ca incorporation indicated a reduced mineralization in the 20 and 100 microg/ml Sr groups vs. controls. Sr-doped synthetic HA showed a significant dose-dependent reduction in crystal growth, as assessed by SEM, and an increase in solubility, apparent from 12.7% Sr/(Sr + Ca) on. Moreover, in both mineralized cultures and synthetic HA, XRD and FTIR analysis showed a reduced crystallinity and altered crystal lattice at similar concentrations. These new data support our previous in vivo and in vitro findings and point to a potential physicochemical interference of Sr with HA formation and crystal properties in vivo.

A novel cation-sensing mechanism in osteoblasts is a molecular target for strontium

Defining the molecular target for strontium in osteoblasts is important for understanding the anabolic effects of this cation on bone. The current studies demonstrate that a G-protein-mediated response to strontium persists in osteoblasts that lack CASR, suggesting a predominant role for a novel cation-sensing receptor in mediating the osseous response to strontium.

INTRODUCTION

Strontium has anabolic effects on bone and is currently being developed for the treatment of osteoporosis. The molecular target for strontium in osteoblasts has not been determined, but the existence of CASR, a G-protein-coupled receptor calcium-sensing receptor, raises the possibility that strontium actions on bone are mediated through this or a related receptor.

MATERIALS AND METHODS

We used activation of a transfected serum response element (SRE)-luciferase reporter in HEK-293 cells to determine if CASR is activated by strontium. In addition, we examined strontium-mediated responses in MC3T3-E1 osteoblasts and osteoblasts derived from wild-type and CASR null mice to determine if other cation-sensing mechanisms are present in osteoblasts.

RESULTS AND CONCLUSIONS

We found that strontium stimulated SRE-luc activity in HEK-293 cells transfected with full-length CASR but not in cells expressing the alternatively spliced CASR construct lacking exon 5. In contrast, we found that MC3T3-E1 osteoblasts that lack CASR as well as osteoblasts derived from CASR null mice respond to millimolar concentrations of strontium. The response to strontium in osteoblasts was nonadditive to a panel of extracellular cations, including aluminum, gadolinium, and calcium, suggesting a common mechanism of action. In contrast, neither the CASR agonist magnesium nor the calcimimetic NPS-R568 activated SRE activity in osteoblasts, but the response to these agonists was imparted by transfection of CASR into these osteoblasts, consistent with the presence of distinct cation-sensing mechanisms. Co-expression of the dominant negative Galphaq(305-359) minigene also inhibited cation-stimulated SRE activity in osteoblasts lacking known CASR. These findings are consistent with strontium activation of a novel Galphaq-coupled extracellular cation-sensing receptor in osteoblasts with distinct cation specificity.