Effects of Risedronate in Runx2 Overexpressing Mice, an Animal Model for Evaluation of Treatment Effects on Bone Quality and Fractures

Young mice overexpressing Runx2 specifically in cells of the osteoblastic lineage failed to gain bone mass and exhibited a dramatic increase in bone resorption, leading to severe osteopenia and spontaneous vertebral fractures. The objective of the current study was to determine whether treatment with a bisphosphonate (risedronate, Ris), which reduces fractures in postmenopausal as well as in juvenile osteoporosis, was able to improve bone quality and reduce vertebral fractures in mice overexpressing Runx2. Four-week-old female Runx2 mice received Ris at 2 and 10 μg/kg subcutaneously twice a week for 12 weeks. Runx2 and wild-type mice received vehicle (Veh) as control. We measured the number of new fractures by X-ray and bone mineral density (BMD) by DEXA. We evaluated bone quality by histomorphometry, micro-CT, and Fourier transform infrared imaging (FTIRI). Ris at 20 μg/kg weekly significantly reduced the average number of new vertebral fractures compared to controls. This was accompanied by significantly increased BMD, increased trabecular bone volume, and reduced bone remodeling (seen in indices of bone resorption and formation) in the vertebrae and femoral metaphysis compared to Runx2 Veh. At the femur, Ris also increased cortical thickness. Changes in collagen cross-linking seen on FTIRI confirmed that Runx2 mice have accelerated bone turnover and showed that Ris affects the collagen cross-link ratio at both forming and resorbing sites. In conclusion, young mice overexpressing Runx2 have high bone turnover-induced osteopenia and spontaneous fractures. Ris at 20 μg/kg weekly induced an increase in bone mass, changes in bone microarchitecture, and decreased vertebral fractures

Phenotypic spectrum in osteogenesis imperfecta due to mutations in TMEM38B: unravelling a complex cellular defect.

Context: Recessive mutations in TMEM38B cause type XIV osteogenesis imperfecta (OI) by dysregulating intracellular calcium flux. Objectives: Clinical and bone material phenotype description and osteoblast differentiation studies. Design and Setting: Natural history study in paediatric research centres. Patients: Eight patients with type XIV OI. Main Outcome Measures: Clinical examinations included: bone mineral density, radiographs, echocardiography and muscle biopsy. Bone biopsy samples (n=3) were analysed using histomorphometry, quantitative backscattered electron microscopy and Raman microspectroscopy. Cellular differentiation studies were performed on proband and control osteoblasts and normal murine osteoclasts. Results: The clinical phenotype of type XIV OI ranges from asymptomatic to severe. Previously unreported features include vertebral fractures, periosteal cloaking, coxa vara and extraskeletal features (muscular hypotonia, cardiac abnormalities). Proband L1-L4 bone density Z-score was reduced (median -3.3 [range -4.77 to +0.1; n=7]), and increased by +1.7 (1.17 to 3.0; n=3) following bisphosphonate therapy. TMEM38B mutant bone has reduced trabecular bone volume, osteoblast and particularly osteoclast numbers, with >80% reduction in bone resorption. Bone matrix mineralization is normal and nanoporosity low. We demonstrate a complex osteoblast differentiation defect with decreased expression of early markers and increased late and mineralization-related markers. Predominance of TRIC-B over TRIC-A expression in murine osteoclasts supports an intrinsic osteoclast defect underlying low bone turnover. Conclusions: OI type XIV has a bone histology, matrix mineralization and osteoblast differentiation pattern that is distinct from OI with collagen defects. Probands are responsive to bisphosphonates and some show muscular and cardiovascular features possibly related to intracellular calcium flux abnormalities

Differential effects of homocysteine and beta aminopropionitrile on preosteoblastic MC3T3-E1 cells

Compounds, like beta-aminopropionitrile (bAPN) and homocysteine (hcys), are known to inhibit a stable matrix formation. Osteoblast-synthesized collagen matrix regulates the differentiation of precursor cells into mature osteoblasts. They express lysyl oxidase, an enzyme involved in the collagen cross-linking process. Lately, plasma hcys levels have recently been strongly correlated with fracture in humans. We have previously shown that bAPN not only disturbs collagen cross-links but also affects osteoblastic differentiation in a cell culture system.The aim of the present study was to investigate the effects of bAPN and hcys on collagen cross-links and gene expression at the mRNA level by FTIR and quantitative RT-PCR, respectively. We found that bAPN and hcys down-regulated cell multiplication. While bAPN also down-regulated the metabolic activity of MC3T3-E1 cells, hcys down-regulated it by lower concentrations but up-regulated it by higher; both substances up-regulated alkaline phosphatase activity. The substances increased the ratio of pyr/divalent cross-links of collagen, and down-regulated mRNA expression of lysyl hydroxylase (Plod2) and lysyl oxidase (Lox), genes which play an important role in the formation of a stable matrix. Furthermore, we demonstrate that both substances stimulated the expression of Runx2, an indispensable regulator of osteoblastic differentiation. However, analysis of genome wide mRNA expression suggests that hcys and bAPN have differential effects on genes involved in osteoblastic differentiation and phenotype regulation.The results indicate that although both bAPN and hcys affect collagen cross-link post-translational modifications in a similar manner as far as pyr and divalent cross-links are concerned, they have differential effects on the monitored genes expression at the mRNA level, with hcys exerting a broader effect on the genome wide mRNA expression. © 2009 Elsevier Inc

Bone material properties in actively bone-forming trabeculae in postmenopausal women with osteoporosis after three years of treatment with once-yearly Zoledronic acid

Zoledronic acid (ZOL), a third-generation aminobisphosphonate, showed pronounced antifracture efficacy in a phase III clinical trial [Health Outcomes and Reduced Incidence with Zoledronic Acid Once YearlyâPivotal Fracture Trial (HORIZON-PFT)] when administered yearly (5-mg infusions of ZOL), producing significant reductions in morphometric vertebral, clinical vertebral, hip, and nonvertebral fractures by 70%, 77%, 41%, and 25%, respectively, over a 3-year period. The purpose of this study was to analyze the biopsies obtained during the HORIZON clinical trial (152 patients, 82 ZOL and 70 placebo) by means of Raman microspectroscopy (a vibrational spectroscopic technique capable of analyzing undecalcified bone tissue with a spatial resolution of approximately 0.6 Âμm) to determine the effect of ZOL therapy on bone material properties (in particular mineral/matrix ratio, lamellar organization, carbonate and proteoglycan (based on spectral identification of glycosaminoglycan) content, and mineral maturity/crystallinity) at similar tissue age (based on the presence of tetracycline double labels). The results indicated that while ZOL administration increased the mineral/matrix ratio compared with placebo, it also resulted in mineral crystallites with a quality profile (based on carbonate content and maturity/crystallinity characteristics) of younger (with respect to tissue age) bone. Since the comparisons between ZOL- and placebo-treated patients were performed at similar tissue age at actively forming bone surfaces, these results suggest that ZOL may be exerting an effect on bone matrix formation in addition to its well-established antiresorptive effect, thereby contributing to its antifracture efficacy. © 2011 American Society for Bone and Mineral Research

Impact Microindentation Assesses Periosteal Bone Matrix Quality in Humans

Bone and mineral researc

Sclerosteosis patients have altered intrinsic bone material properties as assessed by Raman spectroscopy

Bone and mineral researc

Sclerostin Deficiency Is Linked to Altered Bone Composition

Bone and mineral researc

Lathyrism-induced alterations in collagen cross-links influence the mechanical properties of bone material without affecting the mineral

In the present study a rat animal model of lathyrism was employed to decipher whether anatomically confined alterations in collagen cross-links are sufficient to influence the mechanical properties of whole bone

T3 affects expression of collagen I and collagen cross-linking in bone cell cultures

Thyroid hormones (T3, T4) have a broad range of effects on bone, however, its role in determining the quality of bone matrix is poorly understood. In-vitro, the immortalized mouse osteoblast-like cell line MC3T3-E1 forms a tissue like structure, consisting of several cell layers, whose formation is affected by T3 significantly. In this culture system, we investigated the effects of T3 on cell multiplication, collagen synthesis, expression of genes related to the collagen cross-linking process and on the formation of cross-links