The morphology and lattice structure of bone crystal after strontium treatment in goats

Podosome-Driven Defect Development in Lamellar Bone under the Conditions of Senile Osteoporosis Observed at the Nanometer Scale

The degradation mechanism of human trabecular bone harvested from the central part of the femoral head of a patient with a fragility fracture of the femoral neck under conditions of senile osteoporosis was investigated by high-resolution electron microscopy. As evidenced by light microscopy, there is a disturbance of bone metabolism leading to severe and irreparable damages to the bone structure. These defects are evoked by osteoclasts and thus podosome activity. Podosomes create typical pit marks and holes of about 300-400 nm in diameter on the bone surface. Detailed analysis of the stress field caused by the podosomes in the extracellular bone matrix was performed. The calculations yielded maximum stress in the range of few megapascals resulting in formation of microcracks around the podosomes. Disintegration of hydroxyapatite and free lying collagen fibrils were observed at the edges of the plywood structure of the bone lamella. At the ultimate state, the disintegration of the mineralized collagen fibrils to a gelatinous matrix comes along with a delamination of the apatite nanoplatelets resulting in a brittle, porous bone structure. The nanoplatelets aggregate to big hydroxyapatite plates with a size of up to 10 x 20 μm². The enhanced plate growth can be explained by the interaction of two mechanisms in the ruffled border zone: the accumulation of delaminated hydroxyapatite nanoplatelets near clusters of podosomes and the accelerated nucleation and random growth of HAP nanoplatelets due to a nonsufficient concentration of process-directing carboxylated osteocalcin cOC.

Advances in Bone-targeted Drug Delivery Systems for Neoadjuvant Chemotherapy for Osteosarcoma

Targeted therapy for osteosarcoma includes organ, cell and molecular biological targeting; of these, organ targeting is the most mature. Bone-targeted drug delivery systems are used to concentrate chemotherapeutic drugs in bone tissues, thus potentially resolving the problem of reaching the desired foci and minimizing the toxicity and adverse effects of neoadjuvant chemotherapy. Some progress has been made in bone-targeted drug delivery systems for treatment of osteosarcoma; however, most are still at an experimental stage and there is a long transitional period to clinical application. Therefore, determining how to combine new, polymolecular and multi-pathway targets is an important research aspect of designing new bone-targeted drug delivery systems in future studies. The purpose of this article was to review the status of research on targeted therapy for osteosarcoma and to summarize the progress made thus far in developing bone-targeted drug delivery systems for neoadjuvant chemotherapy for osteosarcoma with the aim of providing new ideas for highly effective therapeutic protocols with low toxicity for patients with osteosarcoma.

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.

Effect of strontium ranelate on bone mineral: Analysis of nanoscale compositional changes

Strontium ranelate has been used to prevent bone loss and stimulate bone regeneration. Although strontium may integrate into the bone crystal lattice, the chemical and structural modifications of the bone when strontium interacts with the mineral phase are not completely understood. The objective of this study was to evaluate apatite from the mandibles of rats treated with strontium ranelate in the drinking water and compare its characteristics with those from untreated rats and synthetic apatites with and without strontium. Electron energy loss near edge structures from phosphorus, carbon, calcium and strontium were obtained by electron energy loss spectroscopy in a transmission electron microscope. The strontium signal was detected in the biological and synthetic samples containing strontium. The relative quantification of carbon by analyzing the CK edge at an energy loss of ΔE = 284 eV showed an increase in the number of carbonate groups in the bone mineral of treated rats. A synthetic strontium-containing sample used as control did not exhibit a carbon signal. This study showed physicochemical modifications in the bone mineral at the nanoscale caused by the systemic administration of strontium ranelate.

Insight into biological apatite: physiochemical properties and preparation approaches

Biological apatite is an inorganic calcium phosphate salt in apatite form and nano size with a biological derivation. It is also the main inorganic component of biological hard tissues such as bones and teeth of vertebrates. Consequently, biological apatite has a wide application in dentistry and orthopedics by using as dental fillers and bone substitutes for bone reconstruction and regeneration. Given this, it is of great significance to obtain a comprehensive understanding of its physiochemical and biological properties. However, upon the previous studies, inconsistent and inadequate data of such basic properties as the morphology, crystal size, chemical compositions, and solubility of biological apatite were reported. This may be ascribed to the differences in the source of raw materials that biological apatite are made from, as well as the effect of the preparation approaches. Hence, this paper is to provide some insights rather than a thorough review of the physiochemical properties as well as the advantages and drawbacks of various preparation methods of biological apatite.

Effects of strontium on the quality of bone apatite crystals: a paired biopsy study in postmenopausal osteoporotic women

In paired biopsies of osteoporotic women treated with either strontium ranelate or a placebo for 36 months, characteristics of bone apatite crystals were not influenced by the presence of strontium. The mean rate of substitutions of calcium by strontium ions was 4.5 %.

INTRODUCTION

The potential effect of strontium (Sr) on bone apatite crystals was investigated in paired biopsies of osteoporotic women treated with either strontium ranelate (SrRan) or a placebo for 36 months.

METHODS

In ten paired biopsies, crystallinity, apparent length and width/thickness of crystals, interplanar distances, and lattice parameters of unit cells were assessed by X-ray diffraction and selected area electron diffraction.

RESULTS

All these parameters, reflecting crystal and unit cell characteristics, were not influenced by the presence of Sr and were similar in SrRan and placebo groups after 36 months of treatment. The mean rate of substitutions of calcium by Sr ions was 4.5 %.

CONCLUSION

Overall, the quality of bone apatite crystals was maintained after 36 months of treatment with SrRan.

Strontium is incorporated in different levels into bones and teeth of rats treated with strontium ranelate

The aim of this study was to evaluate the strontium incorporation into specific bones and teeth of rats treated with strontium ranelate. The relative strontium levels [Sr/(Ca + Sr) ratio] were obtained by synchrotron radiation micro X-ray fluorescence. The incisor teeth were further examined by energy dispersive X-ray spectroscopy (EDS) in a scanning electron microscope. The isolated mineral phase was investigated by EDS in a transmission electron microscope and X-ray diffraction. The strontium content was markedly increased in animals treated with strontium ranelate, with different incorporation levels found among specific bones, regions within the same bone and teeth. The highest strontium levels were observed in the iliac crest, mandible and calvaria, while the lowest were observed in the femoral diaphysis, lumbar vertebrae, rib and alveolar bone. The strontium content was higher in the femoral neck than in the diaphysis. The strontium levels also varied within the alveolar bone. High levels of strontium were found in the incisor tooth, with values similar to those in the iliac crest. Strontium was observed in both enamel and dentin. The strontium content of the molar tooth was negligible. Strontium was incorporated into the mineral substance, with up to one strontium replacing one out of 10 calcium ions within the apatite crystal lattice. The mineral from treated animals presented increased lattice parameters, which might be associated to their bone strontium contents. In conclusion, the incorporation of strontium occurred in different levels into distinct bones, regions within the same bone and teeth of rats treated with strontium ranelate.

Distribution of strontium and mineralization in iliac bone biopsies from osteoporotic women treated long-term with strontium ranelate

OBJECTIVE

To investigate interactions between strontium (Sr) and bone mineral and its effects on mineralization in osteoporotic women treated long-term with Sr ranelate (SrRan).

DESIGN

In this study, 34 iliac bone biopsies were analyzed after 2, 12, 24, 36, 48, and 60 months of treatment with SrRan.

METHODS

Sr global distribution was analyzed by X-ray cartography and the percentage of bone area containing Sr was calculated in the bone samples. The focal distribution of Sr in all bone samples was investigated by X-ray microanalysis. The degree of mineralization was assessed by quantitative microradiography.

RESULTS

Absent from old bone formed before the beginning of treatment, Sr was exclusively present in bone formed during this treatment with a much higher focal Sr content in new bone structural units than in old ones. A progressive increase in the extent of areas containing Sr was observed during treatment. The focal bone Sr content in recently formed bone was constant over treatment. Secondary mineralization was maintained at a normal level during treatment.

CONCLUSION

Thus, the quality of bone mineralization (density and heterogeneity at tissue level) was preserved after a long-term treatment with SrRan.

Osteoprotegerin deficiency attenuates strontium-mediated inhibition of osteoclastogenesis and bone resorption

Strontium (Sr) exerts an anabolic and antiresorptive effect on bone, but the mechanism remains unknown. Osteoprotegerin (OPG) expressed by osteoblasts plays an important role in regulating bone homeostasis by inhibiting osteoclastogenesis and bone resorption. This study aims at evaluating the role of OPG in Sr-mediated inhibition of osteoclastogenesis and bone resorption. Six-week-old Opg knockout (KO) male mice and their wild-type (WT) littermates were treated orally with vehicle (Veh) or Sr compound (4 mmol/kg) daily for 8 weeks. Bone mass and microstructure in the lumbar spine (L(4)) and proximal tibia were analyzed with micro-computed tomography (µCT). Bone remodeling was evaluated with serum biochemical analysis and static and dynamic bone histomorphometry. Osteoclast differentiation potential and gene expression were analyzed in bone marrow cells. The findings demonstrate that Sr compound treatment results in greater bone volume and trabecular number than Veh treatment in WT mice. The anabolic response of trabecular bone to Sr treatment is attenuated in KO mice. Although Sr treatment significantly decreases in vitro osteoclastogenesis and bone resorption in WT mice, these effects are attenuated in KO mice. Furthermore, Sr treatment profoundly increases Opg gene expression in the tibias and OPG protein levels in the sera of WT mice. This study concludes that the inhibition of osteoclastogenesis and bone resorption is possibly associated with OPG upregulation by Sr treatment.

In vivo anabolic effect of strontium on trabecular bone was associated with increased osteoblastogenesis of bone marrow stromal cells

In vitro studies have demonstrated that strontium (Sr) could increase osteogenic differentiation of bone marrow stromal cells (BMSCs). We investigated the in vivo effect of Sr on BMSCs. Thirty-six female rats were randomly divided into the following groups: sham operated and treated with either vehicle (Sham + Veh) or Sr compound (Sham + Sr) and ovariectomized and treated with either vehicle (OVX + Veh) or Sr compound (OVX + Sr). Vehicle and Sr were orally administrated daily starting immediately after the surgery and continuing for 12 weeks. The anabolic effect of Sr on trabecular bone was determined at the structural and tissue level by microCT and histomorphometry, respectively. Colony formation assays demonstrated that BMSCs exhibited higher osteogenic colony but lower adipogenic colony in Sr-treated versus Veh-treated OVX rats. The mRNA level of osteogenic genes was higher, while the mRNA level of adipogenic genes was lower in BMSCs from Sr-treated versus Veh-treated Sham and OVX rats. The effect of Sr on rat BMSCs was reproducible in human BMSCs. Taken together, this study suggests that the anabolic effect of Sr on normal or osteoporotic bones is associated with increased osteoblastic differentiation of BMSCs.