Bone remodelling and aposition onto calcium phosphate coated polymer surfaces in the spine: an in vivo animal model

Authors

T Steffen, BJC Freeman and M Aebi

Abstract

Long term, secondary implant fixation of Total Disc Replacements (TDR) can be enhanced by hydroxyapatite or similar osseo-conductive coatings. These coatings are routinely applied to metal substrates. The objective of this in vivo study was to investigate the early stability and subsequent bone response adjacent to an all polymer TDR implant over a period of six months in an animal model. Six skeletally mature male baboons (Papio annubis) were followed for a period of 6 months. Using a transperitoneal exposure, a custom-sized Cadisc L device was implanted into the disc space one level above the lumbo-sacral junction in all subjects. Radiographs of the lumbar spine were acquired prior to surgery, and post-operatively at intervals up to 6 months to assess implant stability. Flourochrome markers (which contain molecules that bind to mineralization fronts) were injected at specified intervals in order to investigate bone remodeling with time. Animals were humanely euthanized six months after index surgery. Test and control specimens were retrieved, fixed and subjected to histological processing to assess the bone-implant-bone interface. Fluorescence microscopy and confocal scanning laser microscopy were utilized with BioQuant image analysis to determine the bone mineral apposition rates and gross morphology. Radiographic evaluation revealed no loss of disc height at the operative level or adjacent levels. No evidence of subsidence or significant migration of the implant up to 6 months. Heterotopic ossification was observed to varying degrees at the operated level. Histology revealed the implant primary fixation features embedded within the adjacent vertebral endplates. Flourochrome distribution revealed active bone remodeling occurring adjacent to the polymeric end-plate with no evidence of adverse biological responses. Mineral apposition rates of between 0.7 and 1.7 microns / day are in keeping with literature values for hydroxyapatite coated implants in cancellous sites of various species. Radiographic assessment demonstrates that the Cadisc L implant remains stable in vivo with no evidence of subsidence or significant migration. Histological analysis suggests the primary fixation features are engaged, and in close apposition with the adjacent vertebral bone. Flourochrome markers provide evidence of a positive bone remodelling response in the presence of the implant.

Link to Article

http://www.bjjprocs.boneandjoint.org.uk/content/94-B/SUPP_XXXVI/85.short

Quantitative Histologic Evidence of Amifostine Induced Cytoprotection in an Irradiated Murine Model of Mandibular Distraction Osteogenesis

Authors

Tchanque-Fossuo, Catherine N. MD, MS; Donneys, Alexis MD, MS; Razdolsky, Elizabeth R. BS; Monson, Laura; Farberg, Aaron S. BS; Deshpande, Sagar S. BS; Sarhaddi, Deniz BA; Poushanchi, Behdod BS; Goldstein, Steven A. PhD; Buchman, Steven R. MD

Abstract

Head and neck cancer (HNC) management requires adjuvant radiation therapy (XRT). The authors have previously demonstrated the damaging effect of a human equivalent dose of radiation (HEDR) on a murine mandibular model of distraction osteogenesis (DO). Utilizing quantitative histomorphometry (QHM), our specific aim is to objectively measure the radio-protective effects of Amifostine (AMF) on the cellular integrity and tissue quality of an irradiated and distracted regenerate. Sprague Dawley rats were randomly assigned into 2 groups: XRT/DO and AMF/XRT/DO, which received AMF prior to XRT. Both groups were given HEDR in 5 fractionated doses and underwent a left mandibular osteotomy with bilateral fixator placement. Distraction to 5.1mm was followed by a 28-day consolidation period. Left hemimandibles were harvested. QHM was performed for osteocyte count (Oc), empty lacunae (EL), Bone Volume/Tissue Volume (BV/TV) and Osteoid Volume/Tissue Volume (OV/TV) ratios. AMF/XRT/DO exhibited bony bridging as opposed to XRT/DO fibrous unions. QHM analysis revealed statistically significant higher Oc and BV/TV ratio in AMF-treated mandibles compared with irradiated mandibles. There was a corresponding decrease in EL and the ratio of OV/TV between AMF/XRT/DO and XRT/DO. We have successfully established the significant osseous cytoprotective and histoprotective capacity of AMF on DO in the face of XRT. AMF-sparing effect on bone cellularity correlated with an increase in bony union and elimination of fibrous union. We posit that the demonstration of similar efficacy of AMF in the clinic may allow the successful implementation of DO as a viable reconstructive option for HNC in the future.

Link to Article

http://dx.doi.org/10.1097/PRS.0b013e31826d2201

Hexa-D-Arginine treatment increases 7B2•PC2 activity in hyp-mouse osteoblasts and rescues the HYP phenotype

Authors

Baozhi Yuan, Jian Q. Feng, Stephen Bowman, Ying Liu, Robert D. Blank, Iris Lindberg, Marc K. Drezner

Abstract

Inactivating mutations of PHEX/Phex underlie disease in patients with X-linked hypophosphatemia (XLH) and the hyp-mouse, a murine homologue of the human disorder. Although increased serum FGF-23 underlies the HYP phenotype, the mechanism(s) by which PHEX mutations inhibit FGF-23 degradation and/or enhance production remains unknown. Here we show that treatment of wild type mice with the proprotein convertase (PC) inhibitor, Decanoyl-Arg-Val-Lys-Arg-chloromethyl ketone, increases serum FGF-23 and produces the HYPphenotype. Since PC2 is uniquely co-localized with PHEX in osteoblasts/bone, we examined if PC2 regulates PHEX-dependent FGF-23 cleavage and production. Transfection of murine osteoblasts with PC2 and its chaperone protein 7B2 cleaved FGF-23, while Signe1 (7B2) RNAi transfection, which limited 7B2 protein production, decreased FGF-23 degradation and increased Fgf-23 mRNA and protein. The mechanism by which decreased 7B2•PC2 activity influences Fgf-23 mRNA was linked to reduced conversion of proBMP1 to active BMP1, which resulted in limited cleavage of DMP1, and consequent increased Fgf-23 mRNA. The significance of decreased 7B2•PC2 activity in XLH was confirmed by studies of hyp-mouse bone, which revealed significantly decreased Sgne1 (7B2) mRNA and 7B2 protein, and limited cleavage of proPC2 to active PC2. The expected downstream effects of these changes included decreased FGF-23 cleavage and increased FGF-23 synthesis, secondary to decreased BMP1-mediated degradation of DMP1. Subsequent Hexa-D-Arginine treatment of hyp-mice enhanced bone 7B2•PC2 activity, normalized FGF-23 degradation and production, and rescued the HYP phenotype. These data suggest decreased PHEX-dependent 7B2•PC2 activity is central to the pathogenesis of XLH.

Link to Article

http://dx.doi.org/10.1002/jbmr.1738

Lack of CCR5 modifies glial phenotypes and population of the nigral dopaminergic neurons, but not MPTP-induced dopaminergic neurodegeneration

Authors

Dong-Young Choi, Myung-Koo Lee, Jin Tae Hong

Abstract

Constitutive expression of C-C chemokine receptor (CCR) 5 has been detected in astrocytes, microglia and neurons, but its physiological roles in the central nervous system are obscure. The bidirectional interactions between neuron and glial cells through CCR5 and its ligands were thought to be crucial for maintaining normal neuronal activities. No study has described function of CCR5 in the dopaminergic neurodegeneration in Parkinson's disease. In order to examine effects of CCR5 on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic neurodegeneration, we employed CCR5 wild type (WT) and knockout (KO) mice. Immunostainings for tyrosine hydroxylase (TH) exhibited that CCR5 KO mice had lower number of TH-positive neurons even in the absence of MPTP. Difference in MPTP (15 mg/kg × 4 times, 2 hr interval)-mediated loss of TH-positive neurons was subtle between CCR5 WT and KO mice, but there was larger dopamine depletion, behavioral impairments and microglial activation in CCR5 deficient mice. Intriguingly, CCR5 KO brains contained higher immunoreactivity for monoamine oxidase (MAO) B which was mainly localized within astrocytes. In agreement with upregulation of MAO B, concentration of MPP + was higher in the substantia nigra and striatum of CCR5 KO mice after MPTP injection. We found remarkable activation of p38 MAPK in CCR5 deficient mice, which positively regulates MAO B expression. These results indicate that CCR5 deficiency modifies the nigrostriatal dopaminergic neuronal system and bidirectional interaction between neurons and glial cells via CCR5 might be important for dopaminergic neuronal survival.

Link to Article

http://dx.doi.org/10.1016/j.nbd.2012.08.001

Microcrack Density and Nanomechanical Properties in the Subchondral Region of the Immature Piglet Femoral Head following Ischemic Osteonecrosis

Authors

Olumide O. Aruwajoye, Mihir K. Patel, Matthew R. Allen, David B. Burr, Pranesh B. Aswath, Harry K.W. Kim

Abstract

Development of a subchondral fracture is one of the earliest signs of structural failure of the immature femoral head following ischemic osteonecrosis, and this eventually leads to a flattening deformity of the femoral head. The mechanical and mineralization changes in the femoral head preceding subchondral fracture have not been elucidated. We hypothesized that ischemic osteonecrosis leads to early material and mechanical alterations in the bone of the subchondral region. The purpose of this investigation was to assess the bone of the subchondral region for changes in the histology of bone cells, microcrack density, mineral content, and nanoindentation properties at an early stage of ischemic osteonecrosis in a piglet model. This large animal model has been shown to develop a subchondral fracture and femoral head deformity resembling juvenile femoral head osteonecrosis. The unoperated, left femoral head of each piglet (n = 8) was used as a normal control, while the right side had a surgical ischemia induced by disrupting the femoral neck vessels with a ligature. Hematoxylin and eosin (H&E) staining and TUNEL assay were performed on femoral heads from 3 piglets. Quantitative backscattered electron imaging, nanoindentation, and microcrack assessments were performed on the subchondral region of both control and ischemic femoral heads from 5 piglets. H&E staining and TUNEL assay showed extensive cell death and an absence of osteoblasts in the ischemic side compared to the normal control. Microcrack density in the ischemic side (3.2 ± 0.79 cracks/mm2) was significantly higher compared to the normal side (0.27 ± 0.27 cracks/mm2) in the subchondral region (p < 0.05). The weighted mean of the weight percent distribution of calcium (CaMean) also was significantly higher in the ischemic subchondral region (p < 0.05). Furthermore, the nanoindentation modulus within localized areas of subchondral bone was significantly increased in the ischemic side (16.8 ± 2.7 GPa) compared to the normal control (13.3 ± 3.2 GPa) (p < 0.05). Taken together, these results support the hypothesis that the nanoindentation modulus of the subchondral trabecular bone is increased in the early stage of ischemic osteonecrosis of the immature femoral head and makes it more susceptible to microcrack formation. We postulate that continued loading of the hip joint when there is a lack of bone cells to repair the microcracks due to ischemic osteonecrosis leads to microcrack accumulation and subsequent subchondral fracture.

Link to Article

http://dx.doi.org/10.1016/j.bone.2012.07.028

Protective Roles of DMP1 in High Phosphate Homeostasis

Authors

Afsaneh Rangiani, Zhengguo Cao, Yao Sun, Yongbo Lu, Tian Gao, Baozhi Yuan, Anika Rodgers, Chunlin Qin, Makoto Kuro-o, Jian Q. Feng

Abstract

Dmp1 (dentin matrix protein1) null mice (Dmp1−/−) display hypophosphatemic rickets with a sharp increase in fibroblast growth factor 23 (FGF23). Disruption of Klotho (the obligatory co-receptor of FGF23) results in hyperphosphatemia with ectopic calcifications formed in blood vessels and kidneys. To determine the role of DMP1 in both a hyperphosphatemic environment and within the ectopic calcifications, we created Dmp1/Klothocompound deficient (Dmp1−/−kl/kl) mice. A combination of TUNEL, immunohistochemistry, TRAP, von Kossa, micro CT, bone histomorphometry, serum biochemistry and Scanning Electron Microscopy techniques were used to analyze the changes in blood vessels, kidney and bone for wild type control, Dmp1−/−,Klothodeficient (kl/kl) and Dmp1−/−kl/kl animals. Interestingly, Dmp1−/−kl/kl mice show a dramatic improvement of rickets and an identical serum biochemical phenotype to kl/kl mice (extremely high FGF23, hyperphosphatemia and reduced parathyroid hormone (PTH) levels). Unexpectedly, Dmp1−/−kl/kl mice presented elevated levels of apoptosis in osteocytes, endothelial and vascular smooth muscle cells in small and large blood vessels, and within the kidney as well as dramatic increase in ectopic calcification in all these tissues, as compared tokl/kl. These findings suggest that DMP1 has an anti-apoptotic role in hyperphosphatemia. Discovering this novel protective role of DMP1 may have clinical relevance in protecting the cells from apoptosis in high-phosphate environments as observed in chronic kidney disease (CKD).

Link to Article

http://dx.doi.org/10.1371/journal.pone.0042329