Microbubble Injection Enhances Inhibition of Low-Intensity Pulsed Ultrasound on Debris-Induced Periprosthetic Osteolysis in Rabbit Model

Authors

Bin Hu, Xun-Zi Cai, Zhong-Li Shi, Yun-Lin Chen, Xiang Zhao, Han-Xiao Zhu, Shi-Gui Yan

Abstract

We determined whether the addition of microbubbles enhances the effect of low-intensity pulsed ultrasound (LIPUS) on bone–implant integration in an early-stage osteolysis model. The bone canals were injected with titanium particles before implantation to establish the periprosthetic osteolysis model. Before ultrasonic therapy, the microbubble-enhanced LIPUS group (GTi-Us-Mb) received an intra-articular injection of microbubbles. Biomechanical testing revealed that GTi-Us-Mb had significantly greater fixation strength than the LIPUS group (GTi-Us). Distal periprosthetic bone mineral density was also higher in GTi-Us than in the Ti group (GTi), but no significant increase was detected after administration of microbubbles. Histomorphometric analyses revealed that bone formation around the implant in GTi-Us was enhanced by the addition of microbubbles in GTi-Us-Mb. Taken together, our data indicate that microbubble injection enhances the inhibitory effect of LIPUS on debris-induced osteolysis and further strengthens the mechanical fixation of implants in an early-stage osteolysis model in vivo.

Link To Article

http://dx.doi.org/10.1016/j.ultrasmedbio.2014.08.016

Inhibition of osteoclastogenesis and inflammatory bone resorption by targeting BET proteins and epigenetic regulation

Authors

Kyung-Hyun Park-Min, Elisha Lim, Min Joon Lee, Sung Ho Park, Eugenia Giannopoulou, Anna Yarilina, Marjolein van der Meulen, Baohong Zhao, Nicholas Smithers, Jason Witherington, Kevin Lee, Paul P. Tak, Rab K. Prinjha & Lionel B Ivashkiv

Abstract

Emerging evidence suggests that ANKL-induced changes in chromatin state are important for osteoclastogenesis, but these epigenetic mechanisms are not well understood and have not been therapeutically targeted. In this study, we find that the small molecule -BET151 that targets bromo and extra-terminal (BET) proteins that ‘read’ chromatin states by binding to acetylated histones strongly suppresses osteoclastogenesis. -BET151 suppresses pathologic bone loss in NF-induced inflammatory osteolysis, inflammatory arthritis and post-ovariectomy models. Transcriptome analysis identifies a YC-NFAT axis important for osteoclastogenesis. Mechanistically, -BET151 inhibits expression of the master osteoclast regulator FATC1 by suppressing expression and recruitment of its newly identified upstream regulator YC. YC is elevated in rheumatoid arthritis macrophages and its induction by ANKL is important for osteoclastogenesis and NF-induced bone resorption. These findings highlight the importance of an -BET151-inhibited YC-NFAT axis in osteoclastogenesis, and suggest targeting epigenetic chromatin regulators holds promise for treatment of inflammatory and oestrogen deficiency-mediated pathologic bone resorption.

Link To Article

http://dx.doi.org/10.1038/ncomms6418

Effects of Denosumab, Alendronate, or Denosumab Following Alendronate on Bone Turnover, Calcium Homeostasis, Bone Mass and Bone Strength in Ovariectomized Cynomolgus Monkeys

Authors

Paul J. Kostenuik PhD, Susan Y. Smith PhD, Rana Samadfam PhD, Jacquelin Jolette DVM, Lei Zhou PhD and Michael S. Ominsky PhD

Abstract

Postmenopausal osteoporosis is a chronic disease wherein increased bone remodeling reduces bone mass and bone strength. Antiresorptive agents including bisphosphonates are commonly used to mitigate bone loss and fracture risk. Osteoclast inhibition via denosumab (DMAb), a RANKL inhibitor, is a newer approach for reducing fracture risk in patients at increased risk for fracture. The safety of transitioning from bisphosphonate therapy (alendronate; ALN) to DMAb was examined in mature ovariectomized (OVX) cynomolgus monkeys (cynos). One day after OVX, cynos (7-10/group) were treated with vehicle (VEH, s.c.), ALN (50 µg/kg, i.v., twice monthly) or DMAb (25 mg/kg/month, s.c.) for 12 months. Other animals received VEH or ALN for 6 months and then transitioned to 6 months of DMAb. DMAb caused significantly greater reductions in serum CTx than ALN, and transition from ALN to DMAb caused further reductions relative to continued ALN. DMAb and ALN decreased serum calcium (Ca), and transition from ALN to DMAb resulted in a lesser decline in Ca relative to DMAb or VEH-DMAb transition. Bone histomorphometry indicated significantly reduced trabecular and cortical remodeling with DMAb or ALN. Compared with ALN, DMAb caused greater reductions in osteoclast surface, eroded surface, cortical porosity and fluorochrome labeling, and transition from ALN to DMAb reduced these parameters relative to continued ALN. Bone mineral density increased in all active treatment groups relative to VEH controls. Destructive biomechanical testing revealed significantly greater vertebral strength in all three groups receiving DMAb, including those receiving DMAb after ALN, relative to VEH controls. Bone mass and strength remained highly correlated in all groups at all tested skeletal sites, consistent with normal bone quality. These data indicate that cynos transitioned from ALN to DMAb exhibited reduced bone resorption and cortical porosity, and increased BMD and bone strength, without deleterious effects on Ca homeostasis or bone quality.

Link To Article

http://dx.doi.org/10.1002/jbmr.2401

Endochondral fracture healing with external fixation in the Sost knockout mouse results in earlier fibrocartilage callus removal and increased bone volume fraction and strength

Authors

A. Morse, N.Y.C. Yu, L. Peacock, K. Mikulec, I. Kramer, M. Kneissel, M.M. McDonald, D.G. Little

Abstract

Sclerostin deficiency, via genetic knockout or anti-Sclerostin antibody treatment, has been shown to cause increased bone volume, density and strength of calluses following endochondral bone healing. However, there is limited data on the effect of Sclerostin deficiency on the formative early stage of fibrocartilage (non-bony tissue) formation and removal. In this study we extensively investigate the early fibrocartilage callus. Closed tibial fractures were performed on Sost−/− mice and age-matched wild type (C57Bl/6J) controls and assessed at multiple early time points (7, 10 and 14 days), as well as at 28 days post-fracture after bony union. External fixation was utilized, avoiding internal pinning and minimizing differences in stability stiffness, a variable that has confounded previous research in this area.

Normal endochondral ossification progressed in wild type and Sost−/− mice with equivalent volumes of fibrocartilage formed at early day 7 and day 10 time points, and bony union in both genotypes by day 28. There were no significant differences in rate of bony union; however there were significant increases in fibrocartilage removal from the Sost−/− fracture calluses at day 14 suggesting earlier progression of endochondral healing. Earlier bone formation was seen in Sost−/− calluses over wild type with greater bone volume at day 10 (221%, p < 0.01). The resultant Sost−/− united bony calluses at day 28 had increased bone volume fraction compared to wild type calluses (24%, p < 0.05), and the strength of the fractured Sost−/− tibiae was greater than that that of wild type fractured tibiae.

In summary, bony union was not altered by Sclerostin deficiency in externally-fixed closed tibial fractures, but fibrocartilage removal was enhanced and the resultant united bony calluses had increased bone fraction and increased strength.

Link To Article

http://dx.doi.org/10.1016/j.bone.2014.10.018

T Cell Expressed CD40L Potentiates the Bone Anabolic Activity of Intermittent PTH Treatment

Authors

Jerid W. Robinson, Jau-Yi Li, Lindsey D. Walker, Abdul Malik Tiyagi, Michael Reott, Mingcan Yu, Jonathan Adams, M. Neale Weitzmann, and Roberto Pacifici

Abstract

T cells are known to potentiate the bone anabolic activity of intermittent parathyroid hormone (iPTH) treatment. One of the involved mechanisms is increased T cell secretion of Wnt10b, a potent osteogenic Wnt ligand that activates Wnt signaling in stromal cells (SCs). However, additional mechanisms might play a role, including direct interactions between surface receptors expressed by T cells and SCs. Here we show that iPTH failed to promote SC proliferation and differentiation into osteoblasts (OBs) and activate Wnt signaling in SCs of mice with a global or T cell-specific deletion of the T cell costimulatory molecule CD40 ligand (CD40L). Attesting to the relevance of T cell expressed CD40L, iPTH induced a blunted increase in bone formation and failed to increase trabecular bone volume in CD40L-/- mice and mice with a T cell-specific deletion of CD40L. CD40L null mice exhibited a blunted increase in T cell production of Wnt10b and abrogated CD40 signaling in SCs in response to iPTH treatment. Therefore, expression of the T cell surface receptor CD40L enables iPTH to exert its bone anabolic activity by activating CD40 signaling in SCs and maximally stimulating T cell production of Wnt10b.

Link To Article

http://dx.doi.org/10.1002/jbmr.2394

Core Binding Factor β of Osteoblasts Maintains Cortical Bone Mass Via Stabilization of Runx2 in Mice

Authors

Kyung-Eun Lim PhD, Na-Rae Park BS, Xiangguo Che MD, Min-Su Han PhD, Jae-Hwan Jeong PhD, Shin-Yoon Kim MD, PhD, Clara Yongjoo Park PhD, Haruhiko Akiyama PhD, Jung-Eun Kim PhD, Hyun-Mo Ryoo PhD, Janet L. Stein PhD, Jane B. Lian PhD, Gary S. Stein PhD and Je-Yong Choi DDS, PhD

Abstract

Core binding factor beta (Cbfβ), the partner protein of Runx family transcription factors, enhances Runx function by increasing the binding of Runx to DNA. Null mutations of Cbfb result in embryonic death, which can be rescued by restoring fetal hematopoiesis but only until birth where bone formation is still nearly absent. Here we address a direct role of Cbfβ in skeletal homeostasis by generating osteoblast-specific Cbfβ-deficient mice (CbfbΔob/Δob) from Cbfb-floxed mice crossed with mice expressing Cre from the Col1a1 promoter. CbfbΔob/Δob mice showed normal growth and development, but exhibited reduced bone mass, particularly of cortical bone. The reduction of bone mass in CbfbΔob/Δob mice is similar to the phenotype of mice with haploinsufficiency of Runx2. Although the number of osteoblasts remained unchanged, the number of active osteoblasts decreased in CbfbΔob/Δob mice and resulted in lower mineral apposition rate. Immunohistochemical and quantitative real-time PCR analyses showed that the expression of osteogenic markers, including Runx2, osterix, osteocalcin and osteopontin, was significantly repressed in CbfbΔob/Δob mice compared to wild type mice. Cbfβ deficiency also reduced Runx2 protein levels in osteoblasts. The mechanism was revealed by forced expression of Cbfβ which increased Runx2 protein levels in vitro by inhibiting polyubiquitination-mediated proteosomal degradation. Collectively, these findings indicate that Cbfβ stabilizes Runx2 in osteoblasts by forming a complex, and thus facilitates the proper maintenance of bone mass, particularly cortical bone.

Link To Article

http://dx.doi.org/10.1039/C4TB01498G