Absence of Exposed Bone Following Dental Extraction in Beagle Dogs Treated With 9 Months of High-Dose Zoledronic Acid Combined With Dexamethasone

Authors

Matthew R. Allen, Tien-Min Gabriel Chu, Salvatore L. Ruggiero

Abstract

Factors contributing to osteonecrosis of the jaw with anti-remodeling drug treatment are unclear. Epidemiologic and experimental studies have suggested the combination of bisphosphonates and dexamethasone results in osteonecrosis of the jaw more often than either agent alone. The goal of this study was to assess the combination of these 2 drugs in a large animal model previously shown to be susceptible to exposed bone in the oral cavity when treated with bisphosphonates. Skeletally mature beagle dogs were untreated controls or treated with zoledronic acid (ZOL), dexamethasone (DEX), or ZOL plus DEX. ZOL and DEX were given at doses based on those used in humans. All animals underwent single molar extraction at 7 and 8 months after the start of the study. Extraction sites were obtained at month 9 for assessment of osseous healing using micro–computed tomography and histology. No animals were observed to have exposed bone after dental extraction, yet 1 animal treated with ZOL and 1 treated with ZOL plus DEX had severely disrupted extraction sites as viewed by computed tomography and histology. These 2 animals had an intense periosteal reaction that was less obvious but still present in all ZOL-treated animals and absent from untreated animals. There was no significant difference in bone volume within the socket among groups at 4 or 8 weeks after healing, yet the ratio of surface to volume was significantly higher in animals treated with ZOL plus DEX at 8 weeks compared with control animals. These findings suggest a more complex pathophysiology to osteonecrosis of the jaw than is implied by previous epidemiologic studies and those in rodents and raise questions about the potential role of DEX in its etiology.

Link to Article

http://dx.doi.org/10.1016/j.joms.2012.11.016

Inactivation of Lrp5 in osteocytes reduces Young's modulus and responsiveness to the mechanical loading

Authors

Liming Zhao, Joon W. Shim, Todd R. Dodge, Alexander G. Robling, Hiroki Yokota

Abstract

Low-density-lipoprotein receptor-related protein 5 (Lrp5) is a co-receptor in Wnt signaling, which plays a critical role in development and maintenance of bone. Osteoporosis-pseudoglioma syndrome, for instance, arises from loss-of-function mutations in Lrp5, and global deletion of Lrp5 in mice results in significantly lower bone mineral density. Since osteocytes are proposed to act as a mechanosensor in the bone, we addressed a question whether a conditional loss-of-function mutation of Lrp5 selective to osteocytes (Dmp1-Cre;Lrp5f/f) would alter responses to ulna loading. Loading was applied to the right ulna for 3min (360cycles at 2Hz) at a peak force of 2.65N for 3 consecutive days, and the contralateral ulna was used as a non-loaded control. Young's modulus was determined using a midshaft section of the femur. The results showed that compared to age-matched littermate controls, mice lacking Lrp5 in osteocytes exhibited smaller skeletal size with reduced bone mineral density and content. Compared to controls, Lrp5 deletion in osteocytes also led to a 4.6-fold reduction in Young's modulus. In response to ulna loading, mineralizing surface, mineral apposition rate, and bone formation rate were diminished in mice lacking Lrp5 in osteocytes by 52%, 85%, and 69%, respectively. Collectively, the results support the notion that the loss-of-function mutation of Lrp5 in osteocytes causes suppression of mechanoresponsiveness and reduces bone mass and Young's modulus. In summary, Lrp5-mediated Wnt signaling significantly contributes to maintenance of mechanical properties and bone mass.

Link to Article

http://dx.doi.org/10.1016/j.bone.2013.01.033

Fabrication of crosslinked carboxymethylchitosan microspheres and their incorporation into composite scaffolds for enhanced bone regeneration

Authors

Benjamin T. Reves, Joel D. Bumgardner, Warren O. Haggard

Abstract

Carboxymethylchitosan (CMCS) microspheres were prepared by the carboxymethylation of chitosan (CS) beads using monochloroacetic acid. The CMCS microspheres were crosslinked using two different methods: the amine-amine crosslinker genipin and carbodiimide chemistry, yielding Gen-X CMCS and X-CMCS beads, respectively. The Gen-X CMCS beads were found to have poor degradation and drug release profiles. The X-CMCS microspheres displayed good potential for use in tissue engineering applications in which degradation and local drug delivery are desired. The X-CMCS beads displayed enzymatic degradation of 82.7 ± 1.2% in 100 μg/mL lysozyme after 1 month. An extended release of rhBMP-2 for at least 45 days was also observed with the X-CMCS microspheres. Scaffolds were formed by fusing beads together, and the X-CMCS beads were successfully incorporated into composite X-CMCS/CS scaffolds. The composite scaffolds had increased degradation of 14.5 ± 6.6% compared to 0.5 ± 0.4% for CS-only scaffolds, and the X-CMCS/CS scaffolds released more rhBMP-2 at all timepoints. The composite scaffolds also supported the attachment and proliferation of SAOS-2 cells. The addition of X-CMCS beads resulted in fabrication of scaffolds with improved properties for use in bone tissue engineering.

Link to Article

http://dx.doi.org/10.1002/jbm.b.32865

Strontium ranelate reduces cartilage degeneration and subchondral bone remodeling in rat osteoarthritis model

Authors

De-gang Yu, Hui-feng Ding, Yuan-qing Mao, Ming Liu, Bo Yu, Xin Zhao,Xiao-qing Wang, Yang Li, Guang-wang Liu, Shao-bo Nie, Shen Liu andZhen-an Zhu

Abstract

Medial meniscal tear (MMT) operation was performed in adult SD rats to induce OA. SR (625 or 1800 mg·kg−1·d−1) was administered via gavage for 3 or 6 weeks. After the animals were sacrificed, articular cartilage degeneration was evaluated using toluidine blue O staining, SOX9 immunohistochemistry and TUNEL assay. The changes in microarchitecture indices and tissue mineral density (TMD), chemical composition (mineral-to-collagen ratio), and intrinsic mechanical properties of the subchondral bones were measured using micro-CT scanning, confocal Raman microspectroscopy and nanoindentation testing, respectively. The high-dose SR significantly attenuated cartilage matrix and chondrocyte loss at 6 weeks, and decreased chondrocyte apoptosis, improved the expression of SOX9, a critical transcription factor responsible for the expression of anabolic genes type II collagen and aggrecan, at both 3 and 6 weeks. Meanwhile, the high-dose SR also significantly attenuated the subchondral bone remodeling at both 3 and 6 weeks, as shown by the improved microarchitecture indices, TMD, mineral-to-collagen ratio and intrinsic mechanical properties. In contrast, the low-dose SR did not significantly change all the detection indices of cartilage and bone at both 3 and 6 weeks. The high-dose SR treatment can reduce articular cartilage degeneration and subchondral bone remodeling in the rat MMT model of OA.

Link to Article

http://dx.doi.org/10.1038/aps.2012.167

Indentation properties and glycosaminoglycan content of human menisci in the deep zone

Authors

John T. Moyer, Ryan Priest, Troy Bouman, Adam C. Abraham, Tammy L. Haut Donahue

Abstract

Menisci are two crescent shaped fibrocartilaginous structures that provide fundamental load distribution and support within the knee joint. Their unique shape transmits axial stresses (i.e. “body force”) into hoop or radial stresses. The menisci are primarily an inhomogeneous aggregate of glycosaminoglycans (GAGs) supporting bulk compression and type I collagen fibrils sustaining tension. It has been shown that the superficial meniscal layers are functionally homogeneous throughout the three distinct regions (anterior, central and posterior) using a 300 μm diameter spherical indenter tip, but the deep zone of the meniscus has yet to be mechanically characterized at this scale. Furthermore, the distribution and content of GAG throughout the human meniscal cross-section have not been examined. This study investigated the mechanical properties, via indentation, of the human deep zone meniscus among three regions of the lateral and medial menisci. The distribution of GAGs through the cross-section was also documented. Results for the deep zone of the meniscus showed the medial posterior region to have a significantly greater instantaneous elastic modulus than the central region. No significant differences in the equilibrium modulus were seen when comparing regions or the hemijoint. Histological results revealed that GAGs are not present until at least ∼600 μm from the meniscal surface. Understanding the role and distribution of GAG within the human meniscus in conjunction with the material properties of the meniscus will aid in the design of tissue engineered meniscal replacements.

Link to Article

http://dx.doi.org/10.1016/j.actbio.2012.12.033

Type I Phosphotidylinosotol 4-Phosphate 5-Kinase γ Regulates Osteoclasts in a Bifunctional Manner

Authors

Tingting Zhu, Jean C. Chappel, Fong-Fu Hsu, John Turk, Rajeev Aurora, Krzysztof Hyrc, Pietro De Camilli, Thomas J. Broekelmann, Robert P. Mecham, Steven L. Teitelbaum, and Wei Zou

Abstract

Type 1 phosphotidylinosotol-4 phosphate 5 kinase γ (PIP5KIγ) is central to generation of phosphotidylinosotol (4,5)P2 (PI(4,5)P2). PIP5KIγ also participates in cytoskeletal organization by delivering talin to integrins, thereby enhancing their ligand binding capacity. As the cytoskeleton is pivotal to osteoclast function, we hypothesized that absence of PIP5KIγ would compromise their resorptive capacity. Absence of the kinase diminishes PI(4,5) abundance and desensitizes precursors to RANK ligand-stimulated differentiation. Thus, PIP5KIγ−/− osteoclasts are reduced in number in vitro and confirm physiological relevance in vivo. Despite reduced numbers, PIP5KIγ−/− osteoclasts surprisingly have normal cytoskeletons and effectively resorb bone. PIP5KIγ overexpression, which increases PI(4,5)P2, also delays osteoclast differentiation and reduces cell number but in contrast to cells lacking the kinase, its excess disrupts the cytoskeleton. The cytoskeleton-disruptive effects of excess PIP5KIγ reflect its kinase activity and are independent of talin recognition. The combined arrested differentiation and disorganized cytoskeleton of PIP5KIγ-transduced osteoclasts compromises bone resorption. Thus, optimal PIP5KIγ and PI(4,5)P2 expression, by osteoclasts, are essential for skeletal homeostasis.

Link to Article

http://dx.doi.org/10.1074/jbc.M112.446054