Fourier transform infrared imaging as a tool to chemically and spatially characterize matrix-mineral deposition in osteoblasts.

Mineralizing osteoblasts are regularly used to study osteogenesis and model in vivo bone formation. Thus, it is important to verify that the mineral and matrix being formed in situ are comparable to those found in vivo. However, it has been shown that histochemical techniques alone are not sufficient for identifying calcium phosphate-containing mineral.

Bisphosphonates improve trabecular bone mass and normalize cortical thickness in ovariectomized, osteoblast connexin43 deficient mice.

The gap junction protein, connexin43 (Cx43) controls both bone formation and osteoclastogenesis via osteoblasts and/or osteocytes. Cx43 has also been proposed to mediate an anti-apoptotic effect of bisphosphonates, potent inhibitors of bone resorption. We studied whether bisphosphonates are effective in protecting mice with a conditional Cx43 gene deletion in osteoblasts and osteocytes (cKO) from the consequences of ovariectomy on bone mass and strength.

Effects of alendronate and risedronate on bone material properties in actively forming trabecular bone surfaces.

We used Raman and Fourier transform infrared microspectroscopy (FTIRM) analysis to examine the intrinsic bone material properties at actively bone-forming trabecular surfaces in iliac crest biopsies from women with postmenopausal osteoporosis (PMO) who were treated with either alendronate (ALN) or risedronate (RIS). At eight study sites, women were identified who had postmenopausal osteoporosis (PMO), were at least 5 years postmenopause, and had been on long-term therapy (either 3-5 years or >5 years) with daily or weekly ALN or RIS. Following standard tetracycline labeling, biopsies were collected from 102 women (33 treated with ALN for 3-5 years [ALN-3], 35 with ALN for >5 years [ALN-5], 26 with RIS for 3-5 years [RIS-3], and 8 with RIS for >5 years [RIS-5]) and were analyzed at anatomical areas of similar tissue age in bone-forming areas (within the fluorescent double labels).

Increased strontium uptake in trabecular bone of ovariectomized calcium-deficient rats treated with strontium ranelate or strontium chloride.

Based on clinical trials showing the efficacy to reduce vertebral and non-vertebral fractures, strontium ranelate (SrR) has been approved in several countries for the treatment of postmenopausal osteoporosis. Hence, it is of special clinical interest to elucidate how the Sr uptake is influenced by dietary Ca deficiency as well as by the formula of Sr administration, SrR versus strontium chloride (SrCl(2)). Three-month-old ovariectomized rats were treated for 90 days with doses of 25 mg kg(-1) d(-1) and 150 mg kg(-1) d(-1) of SrR or SrCl(2) at low (0.

Bisphosphonates do not alter the rate of secondary mineralization.

Bisphosphonates function to reduce bone turnover, which consequently increases the mean degree of tissue mineralization at an organ level. However, it is not clear if bisphosphonates alter the length of time required for an individual bone-modeling unit (BMU) to fully mineralize. We have recently demonstrated that it takes ~350 days (d) for normal, untreated cortical bone to fully mineralize.

Greater magnitude of turnover suppression occurs earlier after treatment initiation with risedronate than alendronate.

Clinical data suggest that reductions in fractures associated with osteoporosis may occur sooner in patients treated with risedronate (RIS) compared to those treated with alendronate (ALN). This could be explained by differences in the time course of turnover suppression between these two bisphosphonates. To determine if differences in the onset of turnover suppression exist between RIS and ALN, female New Zealand white rabbits (total n=32) were treated with clinically relevant doses of RIS or ALN and then administered different fluorochrome labels weekly for four weeks in order to allow histological assessment of the time-course of turnover suppression.

MicroRNA-10b regulates tumorigenesis in neurofibromatosis type 1.

MicroRNAs (miRNAs) are frequently deregulated in human tumors, and play important roles in tumor development and progression. The pathological roles of miRNAs in neurofibromatosis type 1 (NF1) tumorigenesis are largely unknown. We demonstrated that miR-10b was up-regulated in primary Schwann cells isolated from NF1 neurofibromas and in cell lines and tumor tissues from malignant peripheral nerve sheath tumors (MPNSTs).

Modulation of sclerostin expression by mechanical loading and bone morphogenetic proteins in osteogenic cells.

The anabolic effect of dynamic mechanical loading on skeletal architecture has been repeatedly demonstrated, but the cellular and molecular events occurring between load and ultimate bone formation remain obscure. The discovery of sclerostin, an antagonist of Wnt/Lrp5 signaling, and the sclerosing bone dysplasias that result from its mutation suggest its pivotal role in modulating bone formation. We examined expression of Sost mRNA across a variety of clonal cell lines spanning the osteogenic phenotype from immature osteoblast to mature osteocyte.

Bisphosphonates do not inhibit periosteal bone formation in estrogen deficient animals and allow enhanced bone modeling in response to mechanical loading.

The suppressive effects of bisphosphonates (BPs) on bone remodeling are clear yet there is conflicting data concerning the effects of BPs on modeling (specifically formation modeling on the periosteal surface). The normal periosteal expansion that occurs during aging has significant benefits to maintaining/improving the bones' mechanical properties and thus it is important to understand whether BPs affect this bone surface. Therefore, the purpose of this study was to determine the effects of BPs on periosteal bone formation modeling induced by ovariectomy (OVX) and mechanical loading.

Recovery of trabecular and cortical bone turnover after discontinuation of risedronate and alendronate therapy in ovariectomized rats.

Alendronate (ALN) and risedronate (RIS) are bisphosphonates effective in reducing bone loss and fractures associated with postmenopausal osteoporosis. However, it is uncertain how long it takes bone turnover to be re-established after treatment withdrawal, and whether this differs between the two drugs. The objective of this study was to determine the time required to re-establish normal bone turnover after the discontinuation of ALN and RIS treatment in an animal model of estrogen-deficiency osteoporosis.

Bisphosphonates: an update on mechanisms of action and how these relate to clinical efficacy.

The bisphosphonates (BPs) are well established as the treatments of choice for disorders of excessive bone resorption, including Paget's disease of bone, myeloma and bone metastases, and osteoporosis. There is considerable new knowledge about how BPs work. Their classical pharmacological effects appear to result from two key properties: their affinity for bone mineral and their inhibitory effects on osteoclasts.

Bisphosphonate binding affinity as assessed by inhibition of carbonated apatite dissolution in vitro.

Bisphosphonates (BPs), which display a high affinity for calcium phosphate surfaces, are able to selectively target bone mineral, where they are potent inhibitors of osteoclast-mediated bone resorption. The dissolution of synthetic hydroxyapatite (HAP) has been used previously as a model for BP effects on natural bone mineral. The present work examines the influence of BPs on carbonated apatite (CAP), which mimics natural bone more closely than does HAP.

In situ examination of the time-course for secondary mineralization of Haversian bone using synchrotron Fourier transform infrared microspectroscopy.

At the tissue level it is well established that the rate of remodeling is related to the degree of mineralization. However, it is unknown how long it takes for an individual bone structural unit (BSU) to become fully mineralized during secondary mineralization. Using synchrotron Fourier transform infrared microspectroscopy (FTIRM) we examined the time required for newly formed bone matrix to reach a physiological mineralization limit.

Risedronate and alendronate suppress osteocyte apoptosis following cyclic fatigue loading.

Purpose: The purpose of this study was to determine whether bisphosphonate treatment can prevent or delay osteocyte apoptosis in a cyclic fatigue animal model and if there are differences between two different bisphosphonates in their effects on osteocyte apoptosis.

Introduction: Fatigue loading induces microdamage in long bones in rats and causes osteocyte apoptosis. In vitro data suggest that the bisphosphonates can prevent osteocyte apoptosis.

Bisphosphonates suppress periosteal osteoblast activity independently of resorption in rat femur and tibia.

Recent studies demonstrate that bisphosphonates suppress bone resorption by leading to apoptosis of the osteoclast and inhibiting the differentiation to mature osteoclasts. The influence of bisphosphonates on bone formation is unknown, although it has been hypothesized that bisphosphonates inhibit osteoblast apoptosis and stimulate osteoblast proliferation and differentiation in vitro, leading to increased bone formation. The purpose of this study was to investigate the effect of bisphosphonates on bone formation.

Inhibition of protein prenylation by bisphosphonates causes sustained activation of Rac, Cdc42, and Rho GTPases.

Unlabelled: N-BPs, which inhibit bone resorption by preventing prenylation of small GTPases, unexpectedly cause the accumulation of GTP-bound, unprenylated Rho family GTPases in macrophages and osteoclasts. In macrophages, this also leads to sustained, Rac-mediated activation of p38. The antiresorptive activity of N-BPs may therefore be caused at least in part, by the accumulation of unprenylated small GTPases, causing inappropriate activation of downstream signaling pathways.

The effect of risedronate on bone mineralization as measured by micro-computed tomography with synchrotron radiation: correlation to histomorphometric indices of turnover.

The primary goal of our study was to determine changes in bone mineralization in postmenopausal osteoporotic women treated for 3 years with risedronate or placebo. A secondary goal was to determine the relationship between mineralization and indices of bone turnover measured on the same biopsies. The degree of mineralization was measured by micro-computed tomography using Synchrotron radiation (Synchrotron microCT) in the trabecular bone of paired transiliac biopsies taken at baseline and after 3 years of treatment from patients receiving risedronate 5 mg daily (n=11) or placebo (n=8).

Regulation of mineral-to-matrix ratio of lumbar trabecular bone in ovariectomized rats treated with risedronate in combination with or without vitamin K2.

The relationship between bone turnover and bone tissue and material properties was examined in ovariectomized (OVX) rats treated with risedronate in combination with or without vitamin K2. Seventy female rats, 18 weeks of age, were assigned to 7 groups (n=10): sham-operated + vehicle control; OVX + vehicle control; OVX + risedronate 0.1, 0.

Risedronate preserves trabecular architecture and increases bone strength in vertebra of ovariectomized minipigs as measured by three-dimensional microcomputed tomography.

Risedronate reduces the risk of new vertebral fractures up to 70% within 1 year of treatment in patients with osteoporosis. Both increases in bone mass and preservation of bone architecture are thought to contribute to antifracture effects. Our objectives were to determine the effects of risedronate on trabecular bone mass and architecture and to determine the relative contributions of mass and architecture to strength in the vertebra of ovariectomized (OVX) minipigs.