Distal tibial fracture repair in a neurofibromatosis type 1-deficient mouse treated with recombinant bone morphogenetic protein and a bisphosphonate

Authors

A. Schindeler, O. Birke, N. Y. C. Yu, A. Morse, A. Ruys, P. A. Baldock, D. G. Little

Abstract

Congenital pseudarthrosis of the tibia is an uncommon manifestation of neurofibromatosis type 1 (NF1), but one that remains difficult to treat due to anabolic deficiency and catabolic excess. Bone grafting and more recently recombinant human bone morphogenetic proteins (rhBMPs) have been identified as pro-anabolic stimuli with the potential to improve the outcome after surgery. As an additional pharmaceutical intervention, we describe the combined use of rhBMP-2 and the bisphosphonate zoledronic acid in a mouse model of NF1-deficient fracture repair. Fractures were generated in the distal tibiae of neurofibromatosis type 1-deficient (Nf1+/–) mice and control mice. Fractures were open and featured periosteal stripping. All mice received 10 µg rhBMP-2 delivered in a carboxymethylcellulose carrier around the fracture as an anabolic stimulus. Bisphosphonate-treated mice also received five doses of 0.02 mg/kg zoledronic acid given by intraperitoneal injection. When only rhBMP but no zoledronic acid was used to promote repair, 75% of fractures in Nf1+/– mice remained ununited at three weeks compared with 7% of controls (p < 0.001). Systemic post-operative administration of zoledronic acid halved the rate of ununited fractures to 37.5% (p < 0.07). These data support the concept that preventing bone loss in combination with anabolic stimulation may improve the outcome following surgical treatment for children with congenital pseudarthoris of the tibia and NF1.

Link to Article

http://dx.doi.org/10.1302/0301-620X.93B8.25940

Mice lacking Nf1 in osteochondroprogenitor cells display skeletal dysplasia similar to patients with neurofibromatosis type I

Authors

Weixi Wang, Jeffrey S. Nyman, Koichiro Ono, David A. Stevenson, Xiangli Yang and Florent Elefteriou

Abstract

Mutations in NF1 cause neurofibromatosis type I (NF1), a disorder characterized, among other clinical manifestations, by generalized and focal bony lesions. Dystrophic scoliosis and tibial pseudoarthrosis are the most severe skeletal manifestations for which treatment is not satisfactory, emphasizing the dearth of knowledge related to the biology of NF1 in bone cells. Using reporter mice, we report here that the mouse Col2α1-Cre promoter is active in chondrocytes but also in adult bone marrow osteoprogenitors giving rise to osteoblasts. Based on this finding, we crossed the Col2α1-Cre transgenic and Nf1flox/flox mice to determine whether loss of Nf1 in axial and appendicular osteochondroprogenitors recapitulates the skeletal abnormalities of NF1 patients. By microtomographic and X-rays studies, we show that Nf1Col2-/- mice display progressive scoliosis and kyphosis, tibial bowing, and abnormalities in skull and anterior chest wall formation. These defects were accompanied by a low bone mass phenotype, high bone cortical porosity, osteoidosis, increased osteoclastogenesis, and decreased osteoblast number, as quantified by histomorphometry and 3D-microtomography. Loss of Nf1 in osteochondroprogenitors also caused severe short stature and intervertebral disc defects. Blockade of the RAS/ERK activation characteristic of Nf1-/- osteoprogenitors by lovastatin during embryonic development could attenuate the increased cortical porosity observed in mutant pups. These data and the skeletal similarities between this mouse model and NF1 patients thus suggest that activation of the RAS/ERK pathway by Nf1 loss-of-function in osteochondroprogenitors is responsible for the vertebral and tibia lesions in NF1 patients, and that this molecular signature may represent a good therapeutic target.

Link to Article

http://dx.doi.org/10.1093/hmg/ddr310

Diabetes mellitus negatively affects peri-implant bone formation in the diabetic domestic pig

Authors

Cornelius von Wilmowsky, Philipp Stockmann, Igor Harsch, Kerstin Amann, Philipp Metzler, Rainer Lutz, Tobias Moest, Friedrich Wilhelm Neukam, Karl Andreas Schlegel

Abstract

Diabetes mellitus is classified as a relative contraindication for implant treatment, and higher failure rates have been seen in diabetic patients. The aim of the present study was to investigate the effect of diabetes on peri-implant bone formation in an animal model of human bone repair. Diabetes was induced by an intravenous application of streptozotocin (90 mg/kg) in 15 domestic pigs. Implants were placed after significant histopathological changes in the hard and soft tissues were verified. The bone–implant contact (BIC), peri-implant bone mineral density (BMD), and expression of collagen type-I and osteocalcin proteins were qualitatively evaluated 4 and 12 weeks after implantation. Fifteen animals served as healthy controls. Diabetes caused pathological changes in the soft and hard tissues. The BIC and BMD were significantly reduced in the diabetic group after 4 and 12 weeks. Collagen type-I was increased in the diabetic group at both time points, whereas osteocalcin was reduced in the diabetic group. Poorly controlled diabetes negatively affects peri-implant bone formation and bone mineralization. These findings have to be taken into consideration for diabetic patients with an indication for implant therapy.

Link to Article

http://dx.doi.org/10.1111/j.1600-051X.2011.01746.x

Cancellous Bone Osseointegration Is Enhanced by In Vivo Loading

Authors

Xu Yang, Natalie H. Kelly, Jane Han, Turya Nair, Timothy M. Wright, Marjolein C.H. van der Meulen, and Mathias P.G. Bostrom

Abstract

Biophysical stimuli may be an effective therapy to counteract age-related changes in bone structure that affect the primary stability of implants used in joint replacement or fracture fixation. The influence of controlled mechanical loading on osseointegration was investigated using an in vivo device implanted in the distal lateral femur of 12 male rabbits. Compressive loads (1 MPa, 1 Hz, 50 cycles/day, 4 weeks) were applied to a porous titanium foam implant and the underlying cancellous bone. The contralateral limbs served as nonloaded controls. Backscattered electron imaging indicated that the amount of bone ingrowth was significantly greater in the loaded limb than in the nonloaded control limb, whereas the amount of underlying cancellous periprosthetic bone was similar. No significant difference in the mineral apposition rate of the bone ingrowth or periprosthetic bone was measured in the loaded compared to the control limb. Histological analysis demonstrated newly formed woven bone in direct apposition to the implant coating, with a lack of fibrous tissue at the implant–periprosthetic bone interface in both loaded and nonloaded implants. The lack of fibrous tissue demonstrates that mechanical stimulation using this model significantly enhanced cancellous bone ingrowth without the detrimental effects of micromotion. These results suggest that biophysical therapy should be further investigated to augment current treatments to enhance long-term fixation of orthopedic devices. Additionally, this novel in vivo loading model can be used to further investigate the influence of biophysical stimulation on other tissue engineering approaches requiring bone ingrowth into both metallic and nonmetallic cell-seeded scaffolds.

Link to Article

http://dx.doi.org/10.1089/ten.tec.2009.0776

Bone Growth, Maintenance and Loss in the Neolithic Community of Çatalhöyük, Turkey: Preliminary Results

Authors

Sabrina C. Agarwal, Bonnie Glencross, and Patrick Beauchesne

Abstract

Bioarchaeologists have long been interested in the health and the quality of life of early complex societies, particularly with increased sedentism in the context of the adoption of agriculture (Cohen and Armelagos 1984, Cohen and Crane-Kramer 2007, Larsen 1995, Roberts and Cox 2003, Steckel et al. 2002). While studies of health and disease patterns based on skeletal remains for the ancient Near East are numerous (e.g., Smith et al. 1984, Molleson 1994, Horwitz and Smith 2000, Smith and Horwitz 2005, Eshed et al. 2004, 2006, Schultz et al. 2007, Roberts and Buikstra 2007), few sites have yielded large collections of human skeletons in conjunction with detailed archaeological evidence of settlement, lifestyle, diet, and living conditions. The site of Çatalhöyük in the Konya Basin of south-central Turkey is a rare exception, with remarkable archaeological and paleoenvironmental context, revealing changes in community size and structure, shifts in mobility, and the use of plant and animal resources across time. Bioarchaeological evidence from Çatalhöyük provides a unique perspective on early population aggregation, resource use, and consequences of early farming and urbanization on health and lifestyle.

Link to Article

http://escholarship.org/uc/item/9m13784c

Corticosterone selectively targets endo-cortical surfaces by an osteoblast-dependent mechanism

Authors

Holger Henneicke, Markus Herrmann, Robert Kalak, Tara C. Brennan-Speranza, Uta Heinevetter, Nicky Bertollo, Robert E. Day, Dörte Huscher, Frank Buttgereit, Colin R. Dunstan, Markus J. Seibel, and Hong Zhou

Abstract

The pathogenesis of glucocorticoid-induced osteoporosis remains ill defined. In this study, we examined the role of the osteoblast in mediating the effects of exogenous glucocorticoids on cortical and trabecular bone, employing the Col2.3-11βHSD2 transgenic mouse model of osteoblast-targeted disruption of glucocorticoid signalling. Eight week-old male transgenic (tg) and wild-type (WT) mice (n = 20–23/group) were treated with either 1.5 mg corticosterone (CS) or placebo for 4 weeks. Serum tartrate-resistant acid phosphatase 5b (TRAP5b) and osteocalcin (OCN) were measured throughout the study. Tibiae and lumbar vertebrae were analysed by micro-CT and histomorphometry at endpoint. CS suppressed serum OCN levels in WT and tg mice, although they remained higher in tg animals at all time points (p < 0.05). Serum TRAP5b levels increased in WT mice only. The effect of CS on cortical bone differed by site: At the endosteal surface, exposure to CS significantly increased bone resorption and reduced bone formation, resulting in a larger bone marrow cavity cross-sectional area (p < 0.01). In contrast, at the pericortical surface bone resorption was significantly decreased accompanied with a significant increase in pericortical cross-sectional area (p < 0.05) while bone formation remained unaffected. Vertebral cortical thickness and area were reduced in CS treatment mice. Tg mice were partially protected from the effects of exogenous CS, both on a cellular and structural level. At the CS doses used in this study, trabecular bone remained largely unaffected. Endocortical osteoblasts appear to be particularly sensitive to the detrimental actions of exogenous glucocorticoids. The increase in tibial pericortical cross-sectional area and the according changes in pericortical circumference suggest an anabolic bone response to GC treatment at this site. The protection of tg mice from these effects indicates that both catabolic and anabolic action of glucocorticoids are, at least in part, mediated by osteoblasts.

Link to Article

http://dx.doi.org/10.1016/j.bone.2011.06.013