[Growth and differentiation factor 5 (GDF-5) composite improves the healing of necrosis of the femoral head in a sheep model. Analysis of an animal model]

BMP-2 (and partially GDF-5) coating significantly accelerates and augments bone formation close to hydroxyapatite/tricalcium-phosphate/brushite implant cylinders for tibial bone defects in senile, osteopenic sheep

Bilateral defects (diameter 8 mm) in the medial tibial head of senile, osteopenic female sheep (n = 48; 9.63 ± 0.10 years; mean ± SEM) were treated with hydroxyapatite (HA)/beta-tricalcium phosphate (β-TCP)/dicalcium phosphate dihydrate (DCPD; brushite) cylinders coated with BMP-2 (25 or 250 micrograms) or growth differentiation factor (GDF)-5 (125 or 1250 micrograms; left side); cylinders without BMP served as controls (right side). Three, 6, and 9 months post-operation (n = 6 each group), bone structure and formation were analyzed in vivo by X-ray and ex vivo by osteodensitometry, histomorphometry, and micro-computed tomography (micro-CT) at 3 and 9 months. Semi-quantitative X-ray evaluation showed significantly increasing bone densities around all implant cylinders over time. High-dose BMP-2-coated cylinders (3 and 9 months) and low-dose GDF-5-coated cylinders (3 and 6 months) demonstrated significantly higher densities than controls (dose-dependent for BMP-2 at 3 months). This was confirmed by osteodensitometry at 9 months for high-dose BMP-2-coated cylinders (and selected GDF-5 groups), and was again dose-dependent for BMP-2. Osteoinduction by BMP-2 was most pronounced in the adjacent bone marrow (dynamic histomorphometry/micro-CT). BMP-2 (and partially GDF-5) significantly increased the bone formation in the vicinity of HA/TCP/DCPD cylinders used to fill tibial bone defects in senile osteopenic sheep and may be suitable for surgical therapy of critical size, non-load-bearing bone defects in cases of failed tibial head fracture or defect healing.

Insulin/IGF-1R, SIRT1, and FOXOs Pathways-An Intriguing Interaction Platform for Bone and Osteosarcoma

Aging is a substantial risk factor for the development of osteoarthritis (OA) and, probably, an essential substrate for the development of neoplastic disease of the bone, such as osteosarcoma, which is the most common malignant mesenchymal primary bone tumor. Genetic studies have established that the insulin/insulin-like growth factor 1 (IGF-1)/phosphatidylinositol-3 kinase (PI3K)/AKT (Protein Kinase B) signal transduction pathway is involved across species, including nematodes, fruit flies, and mammals. SIRT1, a phylogenetically-conserved family of deacetylases, seems to play pleiotropic effects in epithelial malignancies of the liver and interact with the IGF-1/PI3K/AKT signal transduction pathway. Some of the most critical processes in degenerative conditions may indeed include the insulin/IGF1R and SIRT1 signaling pathways as well as some specific transcription factors. The Forkhead box O (FOXO) transcription factors (FOXOs) control diverse cellular functions, such as metabolism, longevity, and cell death. FOXOs play a critical role in the IGF-1/PI3K/AKT signal transduction pathway. FOXOs can indeed be modulated to reduce age-related diseases. FOXOs have advantageous inhibitory effects on fibroblast and myofibroblast activation, which are accompanied by a subsequent excessive production of extracellular matrix. FOXOs can block or decrease the fibrosis levels in numerous organs. Previously, we observed a correlation between nuclear FOXO3 and high caspase-8 expression, which induces cellular apoptosis in response to harmful external stimuli. In this perspective, we emphasize the current advances and interactions involving the insulin/IGF1R, SIRT1, and FOXOs pathways in the bone and osteosarcoma for a better understanding of the mechanisms potentially underpinning tissue degeneration and tumorigenesis.

Enhanced reconstruction of long bone architecture by a growth factor mutant combining positive features of GDF-5 and BMP-2

Non healing bone defects remain a worldwide health problem and still only few osteoinductive growth factors are available for clinical use in bone regeneration. By introducing BMP-2 residues into growth and differentiation factor (GDF)-5 we recently produced a mutant GDF-5 protein BB-1 which enhanced heterotopic bone formation in mice. Designed to combine positive features of GDF-5 and BMP-2, we suspected that this new growth factor variant may improve long bone healing compared to the parent molecules and intended to unravel functional mechanisms behind its action. BB-1 acquired an increased binding affinity to the BMP-IA receptor, mediated enhanced osteogenic induction of human mesenchymal stem cells versus GDF-5 and higher VEGF secretion than BMP-2 in vitro. Rabbit radius defects treated with a BB-1-coated collagen carrier healed earlier and with increased bone volume compared to BMP-2 and GDF-5 according to in vivo micro-CT follow-up. While BMP-2 callus often remained spongy, BB-1 supported earlier corticalis and marrow cavity formation, showing no pseudojoint persistence like with GDF-5. Thus, by combining positive angiogenic and osteogenic features of GDF-5 and BMP-2, only BB-1 restored a natural bone architecture within 12 weeks, rendering this promising growth factor variant especially promising for long bone regeneration.

Stem cell- and growth factor-based regenerative therapies for avascular necrosis of the femoral head

Avascular necrosis (AVN) of the femoral head is a debilitating disease of multifactorial genesis, predominately affects young patients, and often leads to the development of secondary osteoarthritis. The evolving field of regenerative medicine offers promising treatment strategies using cells, biomaterial scaffolds, and bioactive factors, which might improve clinical outcome. Early stages of AVN with preserved structural integrity of the subchondral plate are accessible to retrograde surgical procedures, such as core decompression to reduce the intraosseous pressure and to induce bone remodeling. The additive application of concentrated bone marrow aspirates, ex vivo expanded mesenchymal stem cells, and osteogenic or angiogenic growth factors (or both) holds great potential to improve bone regeneration. In contrast, advanced stages of AVN with collapsed subchondral bone require an osteochondral reconstruction to preserve the physiological joint function. Analogously to strategies for osteochondral reconstruction in the knee, anterograde surgical techniques, such as osteochondral transplantation (mosaicplasty), matrix-based autologous chondrocyte implantation, or the use of acellular scaffolds alone, might preserve joint function and reduce the need for hip replacement. This review summarizes recent experimental accomplishments and initial clinical findings in the field of regenerative medicine which apply cells, growth factors, and matrices to address the clinical problem of AVN.

Thermoresponsive self-assembled elastin-based nanoparticles for delivery of BMPs

Elastin-like polymers are a new type of protein-based polymers that display interesting properties in the biomaterial field. Bone morphogenetic proteins (BMPs) are cytokines with a strong ability to promote new bone formation. In this work, we explored the use of elastin-like nanoparticles (average size 237.5+/-3.0 nm), created by thermoresponsive self-assembly, for the combined release of bone morphogenetic protein-2 (BMP-2) and bone morphogenetic protein-14 (BMP-14). These BMPs could be encapsulated at high efficiency into the elastin-like particles and delivered in a sustained way for 14 days. The activity of the growth factors was retained, as shown by the induction of ALP activity and osteogenic mineralization in C2C12 cells. Increased bioactivity was observed with a combined release of BMP-2 and BMP-14. This approach shows a significant potential for future tissue engineering applications in bone.

A preliminary report on the effect of dimeric rhGDF-5 and its monomeric form rhGDF-5C465A on bone healing of rat cranial defects

INTRODUCTION

The purpose of the study was to compare the efficacy on rat skull defects of two bone growth factors derived from the GDF-5 family.

MATERIAL AND METHODS

The study was conducted on 17 adult Wistar rats. On each animal, two symmetrical 6-mm wide, full-thickness, skull defects were carried out in the parietal regions. In 15 out of 17 animals, both experimental defects were filled by the implants. In the group I (n=2), both defects were left empty for control. The 15 other rats were divided into 3 groups: In group II (n=5), a collagen sponge was implanted. In group III (n=5), a collagen sponge impregnated with rhGDF-5 (the genuine dimeric form) was implanted. In group IV (n=5), a collagen sponge impregnated with rhGDF-5C465A (a monomeric form of GDF-5) was implanted. All animals were sacrificed at 8 weeks. The harvested specimens were processed for contact radiography and standard histological examination. The quantitative results were assessed with a semi-quantitative histological scoring system.

RESULTS

One animal in the group II was excluded because it died of unknown reasons. In group I, no bone healing was observed in the defects. In group II, no bone healing was observed in 4 out of 10 defects, and partial bone healing was observed in 5 out of 10 defects. In group III, partial bone healing was also observed in 3 out of 8 defects and complete bone healing in 4 out of 8 defects. In group IV, partial bone healing was observed in 8 out of 10 defects and complete bone healing in 2 out of 10 defects.

CONCLUSION

Bone healing was improved in all treated groups. Further studies are necessary to determine the optimal formulation of these composite implants.

Superior Effect of MD05, Beta-Tricalcium Phosphate Coated With Recombinant Human Growth/Differentiation Factor-5, Compared to Conventional Bone Substitutes in the Rat Calvarial Defect Model

BACKGROUND

MD05 consists of beta-tricalcium phosphate (beta-TCP) coated with recombinant human growth/differentiation factor-5 (rhGDF-5) and is under evaluation as an osteoinductive and osteoconductive bone graft material for use in dental and maxillofacial applications. The objective of this study was to compare the bone regenerative properties of MD05 with those of conventional commercially available bone substitutes.

METHODS

Full-thickness, 6-mm diameter, calvarial critical-size defects (two per animal) were created in adult Sprague-Dawley rats. Groups of rats were implanted with the following: 1) MD05; 2) bovine bone mineral; 3) bovine bone mineral with collagen; 4) bovine bone mineral with synthetic peptide, 5) beta-TCP (from two different manufacturers); or 6) no filling material (sham controls). Blinded macroscopic analysis, histopathologic analysis, and histomorphometric analysis were carried out 6 weeks after implantation.

RESULTS

New bone formation assessed histomorphometrically was about five times greater with MD05 than with the other bone substitutes tested, and bone repair was well advanced in MD05-filled defects after 6 weeks. The extent of fibrous tissue and residual implant were significantly lower in the MD05 group. In contrast to the other materials, the use of MD05 was associated with the complete osseous bridging of the defect and with the presence of normal bone marrow. The osteoinductive effect of rhGDF-5 was apparent from the more pronounced bone ingrowth observed with MD05 compared to the beta-TCP carrier alone. All implants showed good biocompatibility.

CONCLUSION

MD05 achieved superior bone regeneration compared to conventional materials and is a promising new bone substitute for dental and maxillofacial applications.

[Pain management in non-juvenile, aseptic osteonecrosis]

BACKGROUND

Adult aseptic osteonecrosis (ON) represents a clinical picture with unexplained etiology. Since curative treatment of this disease often succeeds only in the early stage, pain therapy plays an important role in the treatment process.

METHOD

We compared established and novel treatment options for ON as well as our own results after i.v. administration of the prostacyclin analogue iloprost with corresponding studies in the literature.

RESULTS

In addition to treatment with nonsteroidal antirheumatic agents and opioids, surgical "core decompression," vasoactive medications, and hyperbaric oxygenation are effective. Treatment with iloprost for 5 days resulted in highly significant pain reduction.

CONCLUSION

Symptomatic treatment is indicated in all stages of ON and curative treatment in stage I and early stage II. In cases of disease progression in the large joints, early endoprosthetic replacement is indicated to avoid secondary damage. In addition to employing vasoactive substances, a further curative treatment approach could be the use of mesenchymal stem cells.