Strontium ranelate treatment improves trabecular and cortical intrinsic bone tissue quality, a determinant of bone strength

Strontium ranelate enhances callus strength more than PTH 1-34 in an osteoporotic rat model of fracture healing

Treatment of an underlying disease is often initiated after the occurrence of an osteoporotic fracture. Our aim was to investigate whether teriparatide (PTH 1-34) and strontium ranelate affect fracture healing in ovariectomized (OVX) rats when provided for the first time after the occurrence of an osteoporotic fracture. We combined the model of an OVX rat with a closed diaphyseal fracture. Sixty Sprague Dawley rats were randomly assigned to four groups. Fracture healing in OVX rats after treatment with pharmacological doses of strontium ranelate and PTH 1-34 was compared with OVX and sham-treated control groups. After 28 days, the femur was excised and scanned by micro computed tomography and the callus evaluated, after which biomechanical torsional testing was performed and torque and toughness until reaching the yield point were analyzed. Only treatment with strontium ranelate led to a significant increase in callus resistance compared to the OVX control rats, whereas both PTH 1-34 and strontium ranelate increased the bone volume/tissue volume ratio of the callus. The PTH 1-34-increased trabecular bone volume within the callus was even higher compared to sham. As for the callus tissue volume, the increase induced by strontium ranelate was significant, contrary to the changes induced by PTH. Callus in strontium ranelate-treated animals is more resistant to torsion compared with OVX control rats. To our knowledge, this is the first report of the enhancement of fracture healing by strontium ranelate. Because both treatments enhance bone and tissue volume within the callus, there may be a qualitative difference between the calluses of PTH 1-34- and strontium ranelate-treated OVX rats. The superior results obtained with strontium ranelate compared to PTH in terms of callus resistance could be the consequence of a better quality of the new bone formed within the callus.

Is bone quality associated with collagen age?

The World Health Organization defines osteoporosis as a systemic disease characterized by decreased bone tissue mass and microarchitectural deterioration, resulting in increased fracture risk. Since this statement, a significant amount of data has been generated showing that these two factors do not cover all risks for fracture. Other independent clinical factors, such as age, as well as aspects related to qualitative changes in bone tissue, are believed to play an important role. The term "bone quality" encompasses a variety of parameters, including the extent of mineralization, the number and distribution of microfractures, the extent of osteocyte apoptosis, and changes in collagen properties. The major mechanism controlling these qualitative factors is bone remodeling, which is tightly regulated by the osteoclast/osteoblast activity. We focus on the relationship between bone remodeling and changes in collagen properties, especially the extent of one posttranslational modification. In vivo, measurements of the ratio between native and isomerized C-telopeptides of type I collagen provides an index of bone matrix age. Current preclinical and clinical studies suggests that this urinary ratio provides information about bone strength and fracture risk independent of bone mineral density and that it responds differently according to the type of therapy regulating bone turnover.

Efficacy and safety of 2 g/day of strontium ranelate in Asian women with postmenopausal osteoporosis

Strontium ranelate is a new effective anti-osteoporotic treatment having a unique mode of action, reducing bone resorption while promoting continued bone formation, with a broad range of anti-fracture efficacy at vertebral as well as peripheral sites. In Phase III studies, it has proven its early and sustained efficacy against vertebral fractures in Caucasians along with a significant increase in lumbar bone mineral density (BMD). The aim of this randomized double-blind study was to demonstrate the efficacy of strontium ranelate (2 g/day) on lumbar spine bone mineral density and the clinical and biological safety in Asian postmenopausal osteoporotic patients compared to placebo over 1 year. Three hundred and twenty-nine eligible women from mainland China, Hong Kong and Malaysia were randomized into the study. The baseline characteristics were similar in the treatment and placebo groups: mean age of 66.2+/-6.5 years, time since menopause 17.6+/-7.2 years. In the Full Analysis Set (FAS, N=302), the mean baseline lumbar L2-L4 BMD was 0.715+/-0.106 g/cm(2) in the strontium ranelate group and 0.708 +/- 0.109 g/cm2 in the placebo group. The mean baseline femoral neck BMD was 0.575+/-0.074 g/cm2 and 0.566+/-0.069 g/cm2 respectively and mean total hip BMD was 0.642+/-0.080 g/cm2 and 0.631 +/-0.088 g/cm2 respectively. The overall compliance was 91.4% in the study drug group, and 97.4% in the placebo group. After 1 year of treatment, the lumbar spine, femoral neck and total hip BMD in the treated group was significantly increased by 3-5% as compared to placebo. Strontium ranelate was well tolerated. The most frequently reported emergent adverse events were comparable in both groups (60.4% versus 60.0%), with majority of them being mild gastrointestinal disorders. There were no clinically relevant changes in laboratory tests, such as blood routine, hepatic and renal function. It is thus concluded that the effects of 2 g/day strontium ranelate on BMD and its safety profile in this cohort of postmenopausal osteoporotic Asian women were consistent with results obtained from Caucasian women in which the efficacy on the reduction in risk of fracture has been proven.

New and emerging treatments for osteoporosis

A variety of new treatments for osteoporosis have become available within the last several years, and a number of emerging treatments remain in late clinical stage development. New and emerging treatments include more potent members, or more convenient formulations, of existing classes of therapy, but a number of the emerging treatments are first-generation compounds addressing specific therapeutic targets based on recent advances in understanding of basic bone biology. These new and emerging treatments include agents with anticatabolic effects, compounds with anabolic effects, and one agent possibly containing both anticatabolic and anabolic effects. The increasing variety of new and emerging treatments increases the possibility that effective therapy will be targeted to the specific needs of the individual patient.

Osteoblasts play key roles in the mechanisms of action of strontium ranelate

BACKGROUND AND PURPOSE

Strontium ranelate reduces fracture risk in postmenopausal women with osteoporosis. Evidence from non-clinical studies and analyses of bone markers in phase III trials indicate that this is due to an increase in osteoblast formation and a decrease of osteoclastic resorption. The aim of this work was to investigate, in human cells, the mechanisms by which strontium ranelate is able to influence the activities of osteoblasts and osteoclasts.

EXPERIMENTAL APPROACH

Human primary osteoblasts were used to examine effects of strontium ranelate on replication (thymidine incorporation), differentiation (Runx2 and alkaline phosphatase) and cell survival (cell counts and caspase activity). Osteoprotegerin (OPG) was measured by quantitative reverse transcription PCR (qRT-PCR) and elisa and receptor activator of NFkappaB ligand (RANKL) by qRT-PCR and Western blot. As strontium ranelate has been proposed as an agonist of the calcium-sensing receptor (CaSR), the involvement of CaSR in the effects of strontium ranelate on OPG and RANKL expression, and cell replication was examined using siRNA.

KEY RESULTS

Strontium ranelate increased mRNA and protein levels of OPG and suppressed those of RANKL. Strontium ranelate also stimulated osteoblast replication and differentiation and increased cell survival under stress. Knocking down CaSR suppressed strontium ranelate-induced stimulation of OPG mRNA, reduction of RANKL mRNA, and increase in replication, indicating the involvement of CaSR in these responses.

CONCLUSIONS AND IMPLICATIONS

Our results demonstrate that osteoblasts play a key role in the mechanism of action of the anti-fracture agent, strontium ranelate by mediating both its anabolic and anti-resorptive actions, at least in part, via activation of CaSR.

Strontium ranelate improves bone strength in ovariectomized rat by positively influencing bone resistance determinants

SUMMARY

Treatment of adult ovariectomized (OVX) rats with strontium ranelate prevented vertebral biomechanics degradation as a result of the prevention of bone loss and micro-architecture deterioration associated to an effect on intrinsic bone material quality. Strontium ranelate influenced the determinants of bone strength by prevention of ovariectomy-induced changes which contribute to explain strontium ranelate antifracture efficacy.

INTRODUCTION

Strontium ranelate effects on the determinants of bone strength in OVX rats were evaluated.

METHODS

Adult female Sprague-Dawley rats were OVX, then treated daily for 52 weeks with 125, 250, or 625 mg strontium ranelate/kg. Bone strength, mass, micro-architecture, turnover, and intrinsic quality were assessed.

RESULTS

Strontium ranelate prevented ovariectomy-induced deterioration in mechanical properties with energy necessary for fracture completely maintained vs. SHAM at 625 mg/kg/day, which corresponds to the clinical dose. This was related to a dose-dependent effect on bone volume, higher trabeculae number, and lower trabecular separation in strontium ranelate vs. OVX. Load and energy required to induce lamella deformation were higher with strontium ranelate than in OVX and in SHAM, indicating that the bone formed with strontium ranelate is able to withstand greater damage before fracture. Bone formation was maintained high or even increased in strontium ranelate as shown by mineralizing surfaces and alkaline phosphatase while strontium ranelate led to reductions in deoxypyridinoline.

CONCLUSION

Strontium ranelate administered at 625 mg/kg/day for 52 weeks prevented OVX-induced biomechanical properties deterioration by influencing the determinants of bone strength: it prevented bone loss and micro-architecture degradation in association with an effect on intrinsic bone quality. These beneficial effects on bone contribute to explain strontium ranelate antifracture efficacy.

No difference between strontium ranelate (SR) and calcium/vitamin D on bone turnover markers in women with established osteoporosis previously treated with teriparatide: a randomized controlled trial

Objective To evaluate the effect of strontium ranelate (SR) on bone turnover markers in women with established osteoporosis previously treated with teriparatide (TPTD--recombinant human PTH 1-34). DESIGN PATIENTS: Twenty-two postmenopausal Caucasian women (aged 65.7 +/- 1.7 years) with established osteoporosis previously treated with TPTD 20 microg daily for 18 months were randomly assigned to receive either SR (SR group, n = 11) or calcium and vitamin D (control group, n = 11).

MEASUREMENTS

Blood samples for serum N-terminal propeptide of type 1 collagen (P1NP), C-terminal telopeptide of type 1 collagen (CTx) and total alkaline phosphatase (ALP) were obtained from all women before (pre-TPTD) and after (post-TPTD) TPTD administration, as well as 6 months after SR or calcium/vitamin D administration (post-SR/Ca).

RESULTS

Serum P1NP, CTx and total ALP increased significantly after TPTD treatment and decreased at the end of the study in both SR and control groups, with no difference between them.

CONCLUSIONS

SR following TPTD administration acts predominantly as an antiresorptive agent with no evidence of additional osteoanabolic action. In this setting, SR is not more effective than Ca/vitamin D as far as bone turnover markers are concerned.

Strontium ranelate treatment of human primary osteoblasts promotes an osteocyte-like phenotype while eliciting an osteoprotegerin response

SUMMARY

The effect of strontium ranelate (SR) on human osteoblast differentiation was tested. SR induced osteoblastic proliferation, in vitro mineralization, and increased the expression of osteocyte markers. SR also elicited an osteoprotegerin (OPG) secretory response. We conclude that SR promotes the osteoblast maturation and osteocyte differentiation while promoting an additional antiresorptive effect.

INTRODUCTION

SR is a new treatment for osteoporosis that reduces the risk of hip and vertebral fractures in postmenopausal women. This study sought to investigate the extent, to which SR modulates human osteoblast differentiation.

METHODS

Adult human primary osteoblasts (NHBC) were exposed to SR under mineralizing conditions in long-term cultures. Osteoblast differentiation status was investigated by cell-surface phenotypic analysis. Expression of genes associated with osteoblast/osteocyte differentiation was examined using real-time RT-PCR. Secreted OPG was assayed by enzyme-linked immunosorbent assay.

RESULTS

SR significantly increased osteoblast replication. SR time- and dose-dependently induced an osteocyte-like phenotype, as determined by cell surface alkaline phosphatase and STRO-1 expression. SR at 5 mM or greater dramatically increased in vitro mineralization. In parallel, mRNA levels of dentin matrix protein (DMP)-1 and sclerostin were higher under SR treatment, strongly suggestive of the presence of osteocytes. SR also increased the OPG/RANKL ratio throughout the culture period, consistent with an effect to inhibit osteoblast-induced osteoclastogenesis.

CONCLUSIONS

This study suggests that SR can promote osteoblast maturation and an osteocyte-like phenotype. Coupled with its effect on the OPG/RANKL system, these findings are consistent with in vivo effects in patients receiving SR for the treatment of osteoporosis.

The use of nanoindentation for characterizing the properties of mineralized hard tissues: state-of-the art review

The use of nanoindentation to determine nanomechanical properties of mineralized tissues has been investigated extensively. A detailed, critical, and comprehensive review of this literature is the subject of the present work. After stating the motivation for the review, a succinct presentation of the challenges, advantages, and disadvantages of the various quasi-static nanoindentation test methods (to obtain elastic modulus, E, and hardness, H) and dynamic test methods (to obtain storage and loss moduli and/or loss/damping factor) is given in the form of a primer. Explicative summaries of literature reports on various intrinsic and extrinsic factors that significantly influence E and H, followed by 15 suggested topics for future research, are included additionally. This review is designed to present a compact guide to the principles of the nanoindentation technique and to emphasize considerations when determining material properties of mineralized tissues.

Rebalancing bone turnover in favour of formation with strontium ranelate: implications for bone strength

This review updates our current knowledge on the mechanism of action of strontium ranelate and analyses the way it rebalances bone turnover and how it influences bone biomechanics. Strontium ranelate is able to increase pre-osteoblast replication, osteoblast differentiation, collagen type I synthesis and bone matrix mineralization probably through a calcium-sensing receptor (CaR)-dependent mechanism. Paralleling this anabolic effect there is inhibition of osteoclast differentiation and activity mediated by an increase in osteoprotegerin (OPG) and a decrease in RANK ligand (RANKL). The overall effect is a rebalanced bone turnover in favour of improved bone geometry, cortical thickness, trabecular bone morphology and intrinsic bone tissue quality, which translates into enhanced bone strength.

Strontium ranelate promotes osteoblastic cell replication through at least two different mechanisms

The cellular and molecular mechanisms involved in osteoblastic cell replication induced by strontium ranelate are presently under investigation. The calcium-sensing receptor is a suggested target but other potential mechanisms have not been investigated. Signaling pathways involved in strontium ranelate-induced replication were investigated in preosteoblastic MC3T3-E1 and pluripotent mesenchymal C3H10T1/2 cells. Strontium ranelate effects were compared with those of calcium chloride as Ca(2+). In MC3T3-E1 cells, strontium ranelate but not CaCl(2) dose-dependently increased cell number whereas similar effects were observed for both cations in C3H10T1/2 cells. Immunoblot analysis indicated that activation of ERK, PKC and PKD by strontium ranelate in MC3T3-E1 cells was delayed compared with CaCl(2). Indeed, onset of signaling by strontium ranelate was detected after one or several hours whereas CaCl(2) had a maximal effect already after 5 min exposure. In C3H10T1/2 cells, strontium ranelate induced two types of signaling, a rapid effect and a delayed response. In addition to activation of ERK, PKC and PKD, strontium ranelate and CaCl(2) also transiently activated p38 in C3H10T1/2 cells. Functional analysis with specific inhibitors indicated that cell replication induced by strontium ranelate involves a PKC/PKD pathway in MC3T3-E1 cells and p38 in C3H10T1/2 cells. In both cell types, inhibition of the ERK pathway decreased basal cell replication but not the strontium ranelate response. In conclusion, strontium ranelate increases the replication of cells of the osteoblastic lineage by two distinct cellular mechanisms. Strontium ranelate may directly interact with the CaSR and trigger mitogenic signals such as p38 in C3H10T1/2 cells. The delayed activation of several signaling pathways in both cell lines, however, suggests the release of an autocrine growth factor by strontium ranelate that represents another potential mechanism for inducing osteoblastic cell replication.