Regulation of osteogenic proteins by chondrocytes

Harnessing Growth Factor Interactions to Optimize Articular Cartilage Repair

The failure of cartilage healing is a major impediment to recovery from joint disease or trauma. Growth factors play a central role in cell function and have been proposed as potential therapeutic agents to promote cartilage repair. Decades of investigation have identified many growth factors that promote the formation of cartilage in vitro and in vivo. However, very few of these have progressed to human trials. A growth factor that robustly augments articular cartilage healing remains elusive. This is not surprising. Articular cartilage repair involves multiple cellular processes and it is unlikely that any single agent will be able to optimally regulate all of them. It is more likely that multiple regulatory molecules may be required to optimize the maintenance and restoration of articular cartilage. If this is the case, then interactions among growth factors may be expected to play a key role in determining their therapeutic value. This review explores the hypothesis that growth factor interactions could help optimize articular cartilage healing.

The current state of the osteoarthritis drug development pipeline: a comprehensive narrative review of the present challenges and future opportunities

In this narrative review article, we critically assess the current state of the osteoarthritis (OA) drug development pipeline. We discuss the current state-of-the-art in relation to the development and evaluation of candidate disease-modifying OA drugs (DMOADs) and the limitations associated with the tools and methodologies that are used to assess outcomes in OA clinical trials. We focus on the definition of DMOADs, highlight the need for an updated definition in the form of a consensus statement from all the major stakeholders, including academia, industry, regulatory agencies, and patient organizations, and provide a summary of the results of recent clinical trials of novel DMOAD candidates. We propose that DMOADs should be more appropriately targeted and investigated according to the emerging clinical phenotypes and molecular endotypes of OA. Based on the findings from recent clinical trials, we propose key topics and directions for the development of future DMOADs.

Disease-modifying drugs in osteoarthritis: current understanding and future therapeutics

INTRODUCTION

Osteoarthritis (OA) is a leading cause of pain and disability among adults with a current prevalence of around 15% and a predicted prevalence of 35% in 2030 for symptomatic OA. It is increasingly recognized as a heterogeneous multi-faceted joint disease with multi-tissue involvement of varying severity. Current therapeutic regimens for OA are only partially effective and often have significant associated toxicities. There are no disease-modifying drugs approved by the regulatory bodies. Areas covered: We reviewed the opportunities within key OA pathogenetic mechanism: cartilage catabolism/anabolism, pathological remodeling of subchondral bone and synovial inflammation to identify targeted disease-modifying osteoarthritis drugs, based on compounds currently in Phase II and III stages of clinical development in which x-ray and/or MRI was used as the structural outcome with/without symptomatic outcomes according to regulatory requirements. Expert opinion: Given the heterogeneity of the OA disease process and complex overlapping among these phenotypes, a 'one size fits all' approach used in most clinical trials would unlikely be practical and equally effective in all patients, as well as in all anatomical OA sites. On the other hand, it is a challenge to develop a targeted drug with high activity, specificity, potency, and bioavailability in the absence of toxicity for long-term use in this chronic disease of predominantly older adults. Further research and insight into evaluation methods for drug-targeted identification of early OA and specific characterization of phenotypes, improvement of methodological designs, and development/refinement of sensitive imaging and biomarkers will help pave the way to the successful discovery of disease-modifying drugs and the optimal administration strategies in clinical practice.

BMP-7-Loaded PGLA Microspheres as a New Delivery System for the Cultivation of Human Chondrocytes in a Collagen Type I Gel: The Common Nude Mouse Model

Purpose

Bone morphogenic protein 7 (BMP-7) released from polylactide (PLGA) microspheres has proven to be a potent system in cartilage tissue engineering in vitro. However, in vivo data are still lacking. The aim of this study was to investigate this BMP-7 release system utilizing the nude mouse as a small animal model.

Methods

Human osteoarthritic chondrocytes of 10 patients were enzymatically released and transferred into a collagen type-I gel. A concentration of 2×105 cells/mL was used. BMP-7 encapsulated in PGLA microspheres was added at an initial concentration of 500 ng BMP-7/mL gel. Untreated specimens and specimens with empty microspheres served as control. Samples were cultivated subcutaneously in nude mice for 6 weeks.

Results

After recovery, chondrocytes of all groups displayed a spheroid morphology without signs of dedifferentiation. The proteoglycan and collagen type II content of the control groups was restricted to the immediate pericellular region, whereas treatment group samples showed enhanced collagen type II production. Collagen type II and aggrecan gene expression was enhanced in treatment group samples with respect to the two control groups (mean ± SD: 0.268 ± 0.450 to 0.152 ± 0.129 and 0.155 ± 0.216 ng/ng β-actin for collagen type II; 0.535 ± 0.731 to 0.367 ± 0.651 and 0.405 ± 0.326 ng/ng β-actin for aggrecan), whereas collagen type I gene expression decreased by a factor of 10. Relative protein quantification of collagen type II, collagen type I and proteoglycan was in accordance.

Conclusions

Our data suggest that BMP-7 release from PGLA microspheres led to an improved tissue-engineered cartilage analogue in vivo with an increase in hyaline-cartilage-specific components.

A collagen membrane containing osteogenic protein-1 facilitates bone regeneration in a rat mandibular bone defect

OBJECTIVES

Osteogenic protein-1 (OP-1) has shown osteoinductive activities and is useful for clinical treatments, including bone regeneration. Regenerative procedures using a bioabsorbable collagen membrane (BCM) are well established in periodontal and implant dentistry. We evaluated the subsequent effects of the BCM in combination with OP-1 on bone regeneration in a rat mandibular circular critical-sized bone defect in vivo.

DESIGN

We used 8 rats that received surgery in both sides of the mandible, and created the total 16 defects which were divided into 4 groups: Group 1; no treatment, as a control, Group 2; BCM alone, Group 3; BCM containing low dose 0.5μg of OP-1 (L-OP-1), and Group 4; BCM containing high dose 2.0μg of OP-1 (H-OP-1). Newly formed bone was evaluated by micro computed tomography (micro-CT) and histological analyses at 8 weeks postoperatively. In quantitative and qualitative micro-CT analyses of the volume of new bone formation, bone density, and percentage of new bone area was evaluated.

RESULTS

BCM with rhOP-1 significantly increased and accelerated bone volume, bone mineral density, and percentage of new bone area compared to control and BCM alone at 8 weeks after surgery; these enhancements in bone regeneration in the OP-1-treated groups were dose-dependent.

CONCLUSIONS

OP-1 delivered with a BCM may have effective osteoinductive potency and be a good combination for bone regeneration. The use of such a combination device for osteogenesis may result in safer and more predictable bone regenerative outcomes in the future.

Differentiation of hMSC and hPDLSC induced by PGE2 or BMP-7 in 3D models

Regenerative therapies of pathogenic tissue defects are gaining increasing importance in periodontology. Among others, the osteogenic effect of BMP-7 seems to play a major role in the development of teeth and alveolar bone. Human periodontal ligament stem cells (hPDLSC), as well as human mesenchymal stem cells (hMSC), show the ability to differentiate into various types of tissues. Regarding prostaglandin E2, many studies have confirmed that it is involved in the inflammation associated to periodontitis stimulating osteoclasts, which ultimately leads to resorption of tooth supporting bone. Herein, we aimed to investigate how PGE2 influences regenerative processes. The influence of PGE2 and BMP-7 on the osteogenic differentiation of hMSC and hPDLSC was determined in a 3D cell culture model using qRT-PCR, immunocytochemistry and REM. BMP-7 enhanced the expression of osteogenic markers in hMSC and lowered it in hPDLSC-TERT. BMP-7 had a lower osteogenic effect on hPDLSC-hTERT than on hMSC, while PGE2 decreases the osteogenic differentiation in both cell types, thus, inhibiting anabolic processes. Both cell types presented good proliferation and adhesion onto the scaffolds. The well-developed structural morphology and the support of osteogenic differentiation suggest that the scaffolds are potential candidate materials for bone regeneration. The positivity for Cap in hPDLSC and more in hMSC immunostaining samples indicates the initiation of neocementogenesis as part of periodontal regeneration. In conclusion, BMP7, in particular combined with MSC, seems to have a favourable application also in periodontal regeneration. Our results show that inflammation plays an important role in periodontal regeneration. PGE2 is a key mediator, which stimulates bone resorption also via a mechanism involving the inhibition of osteogenic differentiation of MSC as well as PDLSC. Therefore, regenerative approaches should always be conducted in combination with anti-inflammatory measures oriented to control inflammation.

Effect of bone morphogenetic proteins 2 and 7 on septal chondrocytes in alginate

Objective

To determine the effects of bone morphogenetic proteins (BMP)-2 and −7, and serum, on extracellular matrix production by human septal chondrocytes in alginate.

Study Design

Human nasal septal chondrocytes were expanded, suspended in alginate, and cultured in BMP-2 or 7, with and without serum. The optimal concentration of each growth factor was determined based on matrix production. Next, the synergistic effects of BMP-2 and −7 at optimal concentrations were determined on separate beads, based on matrix quantity and histology.

Results

Matrix content was highest with concentrations of BMP-2 and −7 of 100 ng/ml and 20 ng/ml, respectively, with serum. Adding both BMP-2 and −7, with serum, increased matrix content by factors of 5.1 versus serum-only cultures, 2.7 versus only BMP-2 with serum, and 2.4 versus only BMP-7 with serum. All comparisons were statistically significant.

Conclusion

BMP-2 and −7 significantly increase production of extracellular matrix by septal chondrocytes suspended in alginate. The presence of serum improves matrix production.

Significance

BMP-2 and −7 have great potential for use in cartilage tissue engineering.

Tissue engineering a human phalanx

A principal purpose of tissue engineering is the augmentation, repair or replacement of diseased or injured human tissue. This study was undertaken to determine whether human biopsies as a cell source could be utilized for successful engineering of human phalanges consisting of both bone and cartilage. This paper reports the use of cadaveric human chondrocytes and periosteum as a model for the development of phalanx constructs. Two factors, osteogenic protein-1 [OP-1/bone morphogenetic protein-7 (BMP7)], alone or combined with insulin-like growth factor (IGF-1), were examined for their potential enhancement of chondrocytes and their secreted extracellular matrices. Design of the study included culture of chondrocytes and periosteum on biodegradable polyglycolic acid (PGA) and poly-l-lactic acid (PLLA)-poly-ε-caprolactone (PCL) scaffolds and subsequent implantation in athymic nu/nu (nude) mice for 5, 20, 40 and 60 weeks. Engineered constructs retrieved from mice were characterized with regard to genotype and phenotype as a function of developmental (implantation) time. Assessments included gross observation, X-ray radiography or microcomputed tomography, histology and gene expression. The resulting data showed that human cell-scaffold constructs could be successfully developed over 60 weeks, despite variability in donor age. Cartilage formation of the distal phalanx models enhanced with both OP-1 and IGF-1 yielded more cells and extracellular matrix (collagen and proteoglycans) than control chondrocytes without added factors. Summary data demonstrated that human distal phalanx models utilizing cadaveric chondrocytes and periosteum were successfully fabricated and OP-1 and OP-1/IGF-1 accelerated construct development and mineralization. The results suggest that similar engineering and transplantation of human autologous tissues in patients are clinically feasible. Copyright © 2016 John Wiley & Sons, Ltd.

Use of bone morphogenetic proteins in mesenchymal stem cell stimulation of cartilage and bone repair

The extracellular matrix-associated bone morphogenetic proteins (BMPs) govern a plethora of biological processes. The BMPs are members of the transforming growth factor-β protein superfamily, and they actively participate to kidney development, digit and limb formation, angiogenesis, tissue fibrosis and tumor development. Since their discovery, they have attracted attention for their fascinating perspectives in the regenerative medicine and tissue engineering fields. BMPs have been employed in many preclinical and clinical studies exploring their chondrogenic or osteoinductive potential in several animal model defects and in human diseases. During years of research in particular two BMPs, BMP2 and BMP7 have gained the podium for their use in the treatment of various cartilage and bone defects. In particular they have been recently approved for employment in non-union fractures as adjunct therapies. On the other hand, thanks to their potentialities in biomedical applications, there is a growing interest in studying the biology of mesenchymal stem cell (MSC), the rules underneath their differentiation abilities, and to test their true abilities in tissue engineering. In fact, the specific differentiation of MSCs into targeted cell-type lineages for transplantation is a primary goal of the regenerative medicine. This review provides an overview on the current knowledge of BMP roles and signaling in MSC biology and differentiation capacities. In particular the article focuses on the potential clinical use of BMPs and MSCs concomitantly, in cartilage and bone tissue repair.

Multifaceted signaling regulators of chondrogenesis: Implications in cartilage regeneration and tissue engineering

Defects of articular cartilage present a unique clinical challenge due to its poor self-healing capacity and avascular nature. Current surgical treatment options do not ensure consistent regeneration of hyaline cartilage in favor of fibrous tissue. Here, we review the current understanding of the most important biological regulators of chondrogenesis and their interactions, to provide insight into potential applications for cartilage tissue engineering. These include various signaling pathways, including: fibroblast growth factors (FGFs), transforming growth factor β (TGF-β)/bone morphogenic proteins (BMPs), Wnt/β-catenin, Hedgehog, Notch, hypoxia, and angiogenic signaling pathways. Transcriptional and epigenetic regulation of chondrogenesis will also be discussed. Advances in our understanding of these signaling pathways have led to promising advances in cartilage regeneration and tissue engineering.

Photoactivation of TAZ via Akt/GSK3β signaling pathway promotes osteogenic differentiation

Osteogenesis disorder is involved in osteoporosis and other related bone diseases, in which osteogenic differentiation is essential. Osteogenic differentiation is a complicated process regulated by intricate signal transduction networks. It has been reported that low-power laser irradiation (LPLI) has an osteogenic potential by promoting osteoblast differentiation. However, the molecular mechanisms remain to be understood. In this study, we reveal a novel mechanism that Akt/GSK3β/TAZ (transcriptional co-activator with PDZ-binding motif) signaling pathway plays a crucial role in LPLI-enhanced osteoblast differentiation. Photomodulation by LPLI activated Akt/GSK3β pathway which inhibited TAZ phosphorylation, leading to the increase of TAZ protein level and nuclear aggregation. Meanwhile, knockdown of TAZ suppressed osteogenic differentiation promoted by LPLI. Further study showed that LPLI promoted the interaction between TAZ and core-binding factor 1 (Cbfa1), up-regulating the transcription of osteopontin (OPN) and osteocalcin (OCN) and the activity of alkaline phosphatase (ALP). However, inhibition of Akt/GSK3β pathway reversed the effects of TAZ on osteogenic differentiation induced by LPLI. Taken together, for the first time, we report that LPLI promotes osteoblast differentiation via TAZ activation dependent on Akt/GSK3β signaling pathway.

Intradiscal application of rhBMP-7 does not induce regeneration in a canine model of spontaneous intervertebral disc degeneration

INTRODUCTION

Strategies for biological repair and regeneration of the intervertebral disc (IVD) by cell and tissue engineering are promising, but few have made it into a clinical setting. Recombinant human bone morphogenetic protein 7 (rhBMP-7) has been shown to stimulate matrix production by IVD cells in vitro and in vivo in animal models of induced IVD degeneration. The aim of this study was to determine the most effective dose of an intradiscal injection of rhBMP-7 in a spontaneous canine IVD degeneration model for translation into clinical application for patients with low back pain.

METHODS

Canine nucleus pulposus cells (NPCs) were cultured with rhBMP-7 to assess the anabolic effect of rhBMP-7 in vitro, and samples were evaluated for glycosaminoglycan (GAG) and DNA content, histology, and matrix-related gene expression. Three different dosages of rhBMP-7 (2.5 μg, 25 μg, and 250 μg) were injected in vivo into early degenerated IVDs of canines, which were followed up for six months by magnetic resonance imaging (T2-weighted images, T1rho and T2 maps). Post-mortem, the effects of rhBMP-7 were determined by radiography, computed tomography, and macroscopy, and by histological, biochemical (GAG, DNA, and collagen), and biomolecular analyses of IVD tissue.

RESULTS

In vitro, rhBMP-7 stimulated matrix production of canine NPCs as GAG deposition was enhanced, DNA content was maintained, and gene expression levels of ACAN and COL2A1 were significantly upregulated. Despite the wide dose range of rhBMP-7 (2.5 to 250 μg) administered in vivo, no regenerative effects were observed at the IVD level. Instead, extensive extradiscal bone formation was noticed after intradiscal injection of 25 μg and 250 μg of rhBMP-7.

CONCLUSIONS

An intradiscal bolus injection of 2.5 μg, 25 μg, and 250 μg rhBMP-7 showed no regenerative effects in a spontaneous canine IVD degeneration model. In contrast, intradiscal injection of 250 μg rhBMP-7, and to a lesser extent 25 μg rhBMP-7, resulted in extensive extradiscal bone formation, indicating that a bolus injection of rhBMP-7 alone cannot be used for treatment of IVD degeneration in human or canine patients.

Telomerase Activity in Articular Chondrocytes Is Lost after Puberty

OBJECTIVE

Telomere length and telomerase activity are important indicators of cellular senescence and replicative ability. Loss of telomerase is associated with ageing and the development of osteoarthritis. Implantation of telomerase-positive cells, chondrocytes, or stem cells expressing a normal chondrocyte phenotype is desired for cartilage repair procedures. The objective of this study was to identify at what age chondrocytes and at what passage bone marrow-derived mesenchymal stem cells (MSCs) become senescent based on telomerase activity. The effect of osteogenic protein-1 (OP-1) or interleukin-1α (IL-1α) treatment on telomerase activity in chondrocytes was also measured to determine the response to anabolic or catabolic stimuli.

METHODS

Articular cartilage was collected from horses (n = 12) aged 1 month to 18 years. Chondrocytes from prepubescent horses (<15 months) were treated with OP-1 or IL-1α. Bone marrow aspirate from adult horses was collected and cultured for up to 10 days to isolate MSCs. Telomerase activity was measured using the TeloTAGGG Telomerase PCR ELISA kit.

RESULTS

Chondrocytes from prepubescent horses were positive for telomerase activity. Treatment with IL-1α resulted in a decrease in chondrocyte telomerase activity; however, treatment with OP-1 did not change telomerase activity. One MSC culture sample was positive for telomerase activity on day 2; all samples were negative for telomerase activity on day 10.

CONCLUSIONS

These results suggest that chondrocytes from prepubescent donors are potentially more suitable for cartilage repair procedures and that telomerase activity is diminished by anabolic and catabolic cytokine stimulation. If MSCs are utilized in cartilage repair, minimal passaging should be performed prior to implantation.

Meniscal repair possibilities using bone morphogenetic protein-7

This study analysed the influence of bone morphogenetic protein-7 (BMP-7) on cells and meniscal structure. The effect of treatment with BMP-7 was assessed in vitro and in vivo in lesions in the avascular area of the meniscus. Cells were extracted from the outer and inner part of eight menisci of four 2-year-old merino sheep. The menisci were digested with a collagenase mix, and meniscus cells of the synovium, vascular area and avascular area were extracted. The expression of genes for collagen (Col1 and Col2A), matrix metalloproteinases (MMP-2 and MMP-13) and aggrecan was analysed by real time quantitative polymerase chain reaction (qPCR) at baseline and after incubation with BMP-7. Eight sheep aged 2 years and weighing 35-40 kg were used for the in vivo study. Surgery was performed in both knees of every animal. Two holes were made in the avascular area of the medial meniscus of both knees and filled using Putty(®) (control groups) or OP-1 Putty(®), which comprises BMP-7 mixed with a cellulose putty carrier (experimental groups). Animals were sacrificed at 6, 12 and 25 weeks. Adding BMP-7 to vascular cells of the meniscus was associated with a 15-fold increase in Col2A expression and a 78-fold increase in BMP-7 expression. BMP-7 inhibited MMP-2 and MMP-13 expression. Adding BMP-7 to synovial cells inhibited the expression of Col1, doubled the expression of Col2A and reduced the expression of BMP-7; the expression of MMP-2 was inhibited, while that of MMP-13 was increased three-fold. Incubation of cells from the avascular region with BMP-7 was associated with a 2.4-fold increase in Col1 expression, and a 4.4-fold increase in Col2A expression compared with the control. The expression of MMP-2 and BMP-7 was inhibited. In the in vivo study, treatment of the holes in the avascular area of the meniscus with BMP-7 was associated with an important cell presence inside the holes and the appearance of fibrous tissue after 12 weeks; these features were not seen in the control groups. BMP-7 may be a suitable growth factor for stimulation of meniscal cell and collagen formation.

Aging and oxidative stress reduce the response of human articular chondrocytes to insulin-like growth factor 1 and osteogenic protein 1

OBJECTIVE

To determine the effects of aging and oxidative stress on the response of human articular chondrocytes to insulin-like growth factor 1 (IGF-1) and osteogenic protein 1 (OP-1).

METHODS

Chondrocytes isolated from normal articular cartilage obtained from tissue donors were cultured in alginate beads or monolayer. Cells were stimulated with 50-100 ng/ml of IGF-1, OP-1, or both. Oxidative stress was induced using tert-butyl hydroperoxide. Sulfate incorporation was used to measure proteoglycan synthesis, and immunoblotting of cell lysates was performed to analyze cell signaling. Confocal microscopy was performed to measure nuclear translocation of Smad4.

RESULTS

Chondrocytes isolated from the articular cartilage of tissue donors ranging in age from 24 years to 81 years demonstrated an age-related decline in proteoglycan synthesis stimulated by IGF-1 and IGF-1 plus OP-1. Induction of oxidative stress inhibited both IGF-1- and OP-1-stimulated proteoglycan synthesis. Signaling studies showed that oxidative stress inhibited IGF-1-stimulated Akt phosphorylation while increasing phosphorylation of ERK, and that these effects were greater in cells from older donors. Oxidative stress also increased p38 phosphorylation, which resulted in phosphorylation of Smad1 at the Ser(206) inhibitory site and reduced nuclear accumulation of Smad1. Oxidative stress also modestly reduced OP-1-stimulated nuclear translocation of Smad4.

CONCLUSION

These results demonstrate an age-related reduction in the response of human chondrocytes to IGF-1 and OP-1, which are 2 important anabolic factors in cartilage, and suggest that oxidative stress may be a contributing factor by altering IGF-1 and OP-1 signaling.

Cellular and molecular mechanisms of cartilage damage and repair

Cartilage breakdown is the disabling outcome of rheumatic diseases, whether prevalently inflammatory such as rheumatoid arthritis or prevalently mechanical such as osteoarthritis (OA). Despite the differences between immune-mediated arthritides and OA, common mechanisms drive cartilage breakdown. Inflammation, chondrocyte phenotype and homeostatic mechanisms have recently been the focus of research and will be summarised in this review.

The hallmarks of osteoarthritis and the potential to develop personalised disease-modifying pharmacological therapeutics

Osteoarthritis (OA) is an age-related condition and the leading cause of pain, disability and shortening of adult working life in the UK. The incidence of OA increases with age, with 25% of the over 50s population having OA of the knee. Despite promising preclinical data covering various molecule classes, there is regrettably at present no approved disease-modifying OA drugs (DMOADs). With the advent of next generation sequencing technologies, other therapeutic areas, in particular oncology, have experienced a paradigm shift towards defining disease by its molecular composition. This paradigm shift has enabled high resolution patient stratification and supported the emergence of personalised or precision medicines. In this review we evaluate the potential for the development of OA therapeutics to undergo a similar paradigm shift given that OA is increasingly being recognised as a heterogeneous disease affecting multiple joint tissues. We highlight the evidence for the role of these tissues in OA pathology as different "hallmarks" of OA biology and review the opportunities to identify and develop targeted disease-modifying pharmacological therapeutics. Finally, we consider whether it is feasible to expect the emergence of personalised disease-modifying medicines for patients with OA and how this might be achieved.

Current status of percutaneous vertebroplasty and percutaneous kyphoplasty--a review

Percutaneous vertebroplasty (PV) and kyphoplasty (PK) are the 2vertebral augmentation procedures that have emerged as minimally invasive surgical options to treat painful vertebral compression fractures (VCF) during the last 2 decades. VCF may either be osteoporotic or tumor-associated. Two hundred million women are affected by osteoporosis globally. Vertebral fracture may result in acute pain around the fracture site, loss of vertebral height due to vertebral collapse, spinal instability, and kyphotic deformity. The main goal of the PV and PK procedures is to give immediate pain relief to patients and restore the vertebral height lost due to fracture. In percutaneous vertebroplasty, bone cement is injected through a minimal incision into the fractured site. Kyphoplasty involves insertion of a balloon into the fractured site, followed by inflation-deflation to create a cavity into which the filler material is injected, and the balloon is taken out prior to cement injection. This literature review presents a qualitative overview on the current status of vertebral augmentation procedures,especially PV and PK, and compares the efficacy and safety of these 2 procedures. The review consists of a brief history of the development of these 2 techniques, a discussion on the current research on the bone cement, clinical outcome of the 2 procedures, and it also sheds light on ongoing and future research to maximize the efficacy and safety of vertebral augmentation procedures.

Role of insulin-like growth factors (IGFs), their receptors and genetic regulation in the chondrogenesis and growth of the mandibular condylar cartilage

Growth of the mandibular condylar cartilage (MCC) is reviewed as a function of genetic and epigenetic factors. The growth centers around the differential spatial concentration of the chondrocytes, influence of growth factors like TGF-β and heterogeneity in the number of IGF receptors, control the action of IGF. Besides these factors, growth of the mandibular condyle is influenced by differential response of chondrocytes as a function of their source/ageing, which in turn is regulated by TGF-β, BMPs and IGFs. While IGF-1 promotes proteoglycan synthesis and survival of the chondrocytes to maintain cartilage homeostasis, TGF-β synergistically catalysed the effect of IGF-1, while BMPs catalysed proteolysis as and when physiologically needed. To understand these processes, role of IGF-1 and its six receptors is at the center to a number of physiological processes being regulated by its mode of application for the growth and differentiation. Probing deeper, biological functions of IGFs seemed to depend on their level of free status rather than bound status to respective IGF-binding proteins (IGF-BPs), considered prerequisite to modulate their biological functions. Genetic regulation of their secretion has thrown light on their insulin-like structural homology, level and response in osteo-arthritis (OA), rheumatic arthritis (RA) and diabetes type-II. Biochemistry and spatial distribution of IGF receptors in different domains exerts control on IGF-1 activities. In ultimate analysis, IGF-axis conserved during the evolution to regulate cell growth and proliferation affect nearly every organ in the body as judged from the techniques determining skeletal maturity and decision making dependent on it for orthodontic, orthognathic/orthopedic and dental implant applications.

Modulation of matrix mineralization by Vwc2-like protein and its novel splicing isoforms

In search of new cysteine knot protein (CKP) family members, we found a novel gene called von Willebrand factor C domain-containing protein 2-like (Vwc2l, also known as Brorin-like) and its transcript variants (Vwc2l-1, Vwc2l-2 and Vwc2l-3). Based on the deduced amino acid sequence, Vwc2l-1 has a signal peptide and 2 cysteine-rich (CR) domains, while Vwc2l-2 lacks a part of 2nd CR domain and Vwc2l-3 both CR domains. Although it has been reported that the expression of Brorin-like was predominantly observed in brain, we found that Vwc2l transcript variants were detected in more ubiquitous tissues. In osteoblasts, the induction of Vwc2l expression was observed at matrix mineralization stage. When Vwc2l was stably transfected into osteoblasts, the matrix mineralization was markedly accelerated in Vwc2l-expressing clones compared to that in the control, indicating the modulatory effect of Vwc2l protein on osteoblastic cell function. The mechanistic insight of Vwc2l-modulation was further investigated and we found that the expression of Osterix, one of the key osteogenic markers, was significantly increased by addition of all Vwc2l isoform proteins. Taken together, Vwc2l is a novel secreted protein that promotes matrix mineralization by modulating Osterix expression likely through TGF-β superfamily growth factor signaling pathway. Our data may provide mechanistic insights into the biological functions of this novel CKP member in bone and further suggest a novel approach to enhance osteoblast function, which enables to accerelate bone formation, regeneration and healing.

The optimal dose of recombinant human osteogenic protein-1 enhances differentiation of mouse osteoblast-like cells: an in vitro study

OBJECTIVE

There is no certain conclusion on the effect of recombinant human Osteogenic Protein-1 (OP-1, BMP-7) on the proliferation of the osteoblast-like cell line, MC3T3-E1. Furthermore, the optimal dose of rhOP-1 on cell differentiation still needs to be elucidated. This investigation aims to delineate the biofunctional characteristics of rhOP-1 in inducing osteoblastogenesis of MC3T3-E1 through in vitro time-course and dose-response studies.

DESIGN

MC3T3-E1 cells were cultured for 1, 4, 7 days with the addition of different rhOP-1 concentrations (0, 10, 20, 50, 100, 200, 400 ng/ml), and cell proliferation and cell differentiation were examined.

RESULTS

MC3T3-E1 cell proliferation was stimulated by rhOP-1 in a dose-dependent manner (0-400 ng/ml) on day 1, whereas on day 4 and 7, it was still stimulated at low concentrations (10, 20, 50 ng/ml) but inhibited at high ones (200, 400 ng/ml). The alkaline phosphatase (ALP) activity, osteocalcin (OC) production, collagen deposition and extracellular matrix mineralization were dramatically elevated by rhOP-1 treatment, as a function of culture time and rhOP-1 concentration, and all of them reached a plateau at the concentration of 200 ng/ml. Real-time quantitative RT-PCR results showed Runx2, AKP-2, OC and Nog mRNA expressions increased in a dose- and time-dependent manner, and their expressions were significantly higher at high rhOP-1 concentrations than that of low ones. No significant differences were found between the effects of 200 ng/ml rhOP-1 and 400 ng/ml rhOP-1 on the differentiation of MC3T3-E1 cells, except the expression of Nog mRNA, whose expression level was much higher at 400 ng/ml than that at 200 ng/ml.

CONCLUSIONS

These results suggest that cell proliferation of MC3T3-E1 is depended on culture time and rhOP-1 concentration, rhOP-1 could stimulate the differentiation of MC3T3-E1 cells and the optimal concentration could be 200 ng/ml.

NELL-1 promotes cartilage regeneration in an in vivo rabbit model

Repair of cartilage due to joint trauma remains challenging due to the poor healing capacity of cartilage and adverse effects related to current growth factor-based strategies. NELL-1 (Nel-like molecule-1; Nel [a protein strongly expressed in neural tissue encoding epidermal growth factor like domain]), a protein first characterized in the context of premature cranial suture fusion, is believed to accelerate differentiation along the osteochondral lineage. We previously demonstrated the ability of NELL-1 protein to maintain the cartilaginous phenotype of explanted rabbit chondrocytes in vitro. Our objective in the current study is to determine whether NELL-1 can affect endogenous chondrocytes in an in vivo cartilage defect model. To generate the implant, NELL-1 was incorporated into chitosan nanoparticles and embedded into alginate hydrogels. These implants were press fit into 3-mm circular osteochondral defects created in the femoral condylar cartilage of 3-month-old New Zealand White rabbits (n=10). Controls included unfilled defects (n=8) and defects filled with phosphate-buffered saline-loaded chitosan nanoparticles embedded in alginate hydrogels (n=8). Rabbits were sacrificed 3 months postimplantation for histological analysis. Defects filled with alginate containing NELL-1 demonstrated significantly improved cartilage regeneration. Remarkably, histology of NELL-1-treated defects closely resembled that of native cartilage, including stronger Alcian blue and Safranin-O staining and increased deposition of type II collagen and absence of the bone markers type I collagen and Runt-related transcription factor 2 (Runx2) as demonstrated by immunohistochemistry. Our results suggest that NELL-1 may produce functional cartilage with properties similar to native cartilage, and is an exciting candidate for tissue engineering-based approaches for treating diverse pathologies of cartilage defects and degeneration.

BMP-7 inhibits cartilage degeneration through suppression of inflammation in rat zymosan-induced arthritis

Bone morphogenetic protein-7 (BMP-7) regulates cartilage metabolism and promotes matrix synthesis. However, the effect of BMP-7 on inflammatory arthritis remains unknown. We investigated the effect and mechanism of exogenous BMP-7 on cartilage and synovium in vivo in rat zymosan-induced arthritis. Zymosan was injected into the left knees of Wistar rats. Phosphate-buffered saline or BMP-7 at 10, 100, or 1000 ng per joint was injected into the left knee every 2 days. Normal joints acted as normal controls. The knee joints were analyzed histologically and immunohistologically at 14 days. Joint swelling was evaluated by measuring the transverse diameter of the knee joints. Synovial lysates were collected, and the concentrations of interleukin-1β (IL-1β), IL-6, and IL-10 were measured by enzyme-linked immunosorbent assay. Intra-articular injection of zymosan resulted in acute inflammation and was followed by cartilage degeneration. Local administrations of BMP-7 inhibited this loss of cartilage matrix in a dose-dependent manner. Immunohistochemical analysis demonstrated enhanced type II collagen levels in cartilage and enhanced BMP-7 levels in cartilage and synovium after exogenous BMP-7 treatment. Joint swelling and cell infiltration into synovium were significantly reduced by BMP-7 injections. Administration of BMP-7 decreased IL-1β production significantly and increased IL-10 production in the synovium. Thus, intra-articular injections of BMP-7 had a protective effect on cartilage degeneration in the inflammatory arthritis model by enhancing levels of BMP-7 in cartilage and suppressing the production of IL-1β in synovium.

Regulation of chondrocyte gene expression by osteogenic protein-1

INTRODUCTION

The objective of this study was to investigate which genes are regulated by osteogenic protein-1 (OP-1) in human articular chondrocytes using Affimetrix gene array, in order to understand the role of OP-1 in cartilage homeostasis.

METHODS

Chondrocytes enzymatically isolated from 12 normal ankle cartilage samples were cultured in high-density monolayers and either transfected with OP-1 antisense oligonucleotide in the presence of lipofectin or treated with recombinant OP-1 (100 ng/ml) for 48 hours followed by RNA isolation. Gene expression profiles were analyzed by HG-U133A gene chips from Affimetrix. A cut-off was chosen at 1.5-fold difference from controls. Selected gene array results were verified by real-time PCR and by in vitro measures of proteoglycan synthesis and signal transduction.

RESULTS

OP-1 controls cartilage homeostasis on multiple levels including regulation of genes responsible for chondrocyte cytoskeleton (cyclin D, Talin1, and Cyclin M1), matrix production, and other anabolic pathways (transforming growth factor-beta (TGF-β)/ bone morphogenetic protein (BMP), insulin-like growth factor (IGF), vascular endothelial growth factor (VEGF), genes responsible for bone formation, and so on) as well as regulation of cytokines, neuromediators, and various catabolic pathways responsible for matrix degradation and cell death. In many of these cases, OP-1 modulated the expression of not only the ligands, but also their receptors, mediators of downstream signaling, kinases responsible for an activation of the pathways, binding proteins responsible for the inhibition of the pathways, and transcription factors that induce transcriptional responses.

CONCLUSIONS

Gene array data strongly suggest a critical role of OP-1 in human cartilage homeostasis. OP-1 regulates numerous metabolic pathways that are not only limited to its well-documented anabolic function, but also to its anti-catabolic activity. An understanding of OP-1 function in cartilage will provide strong justification for the application of OP-1 protein as a therapeutic treatment for cartilage regeneration and repair.

Effects of Low Concentration BMP-7 on Human Osteoarthritic Chondrocytes: Comparison of Different Applications

While BMP-7 (OP-1) is one of the most potent growth factors in cartilage tissue engineering, the effects of exogenous low concentration BMP-7 on osteoarthritic chondrocytes are still unknown. Human osteoarthritic chondrocytes obtained from the femoral condyles of 10 patients were grown either in monolayer or in 3D collagen type-I gel culture in vitro. The growth factor was either given as a single dose of 50 ng/mL, a repeated dose, or continuously released from PGLA microspheres. Matrix formation was monitored by immunohistochemical staining and real-time PCR. In contrast to monolayer culture, the differentiated phenotype was prevailed in 3D culture. Collagen type-II protein production in the 3D group with a continuous BMP-7 release was enhanced in comparison to all other groups. Gene expression of collagen type-II and aggrecan was elevated in all treatment groups, with the highest extent in the BMP-7 microsphere group. In summary, treatment of articular chondrocytes with a low dose of BMP-7 leads to an elevated production of extracellular matrix components. This effect is further increased when BMP-7 is given repeatedly or continuously, which proved to be the most effective form of application.

Cartilage biology, pathology, and repair

Osteoarthritis is one of the most common forms of musculoskeletal disease and the most prominent type of arthritis encountered in all countries. Although great efforts have been made to investigate cartilage biology and osteoarthritis pathology, the treatment has lagged behind that of other arthritides, as there is a lack of effective disease-modifying therapies. Numerous approaches for dealing with cartilage degradation have been tried, but enjoyed very little success to develop approved OA treatments with not only symptomatic improvement but also structure-modifying effect. In this review we discuss the most recent findings regarding the regulation of cartilage biology and pathology and highlight their potential therapeutic values.

The role of BMP-7 in chondrogenic and osteogenic differentiation of human bone marrow multipotent mesenchymal stromal cells in vitro

This study addresses the role of bone morphogenetic protein-7 (BMP-7) in chondrogenic and osteogenic differentiation of human bone marrow multipotent mesenchymal stromal cells (BM MSCs) in vitro. BM MSCs were expanded and differentiated in the presence or absence of BMP-7 in monolayer and three-dimensional cultures. After 3 days of stimulation, BMP-7 significantly inhibited MSC growth in expansion cultures. When supplemented in commonly used induction media for 7-21 days, BMP-7 facilitated both chondrogenic and osteogenic differentiation of MSCs. This was evident by specific gene and protein expression analyses using real-time PCR, Western blot, histological, and immunohistochemical staining. BMP-7 supplementation appeared to enhance upregulation of lineage-specific markers, such as type II and type IX collagens (COL2A1, COL9A1) in chondrogenic and secreted phosphoprotein 1 (SPP1), osteocalcin (BGLAP), and osterix (SP7) in osteogenic differentiation. BMP-7 in the presence of TGF-beta3 induced superior chondrocytic proteoglycan accumulation, type II collagen, and SOX9 protein expression in alginate and pellet cultures compared to either factor alone. BMP-7 increased alkaline phosphatase activity and dose-dependently accelerated calcium mineralization of osteogenic differentiated MSCs. The potential of BMP-7 to promote adipogenesis of MSCs was restricted under osteogenic conditions, despite upregulation of adipocyte gene expression. These data suggest that BMP-7 is not a singular lineage determinant, rather it promotes both chondrogenic and osteogenic differentiation of MSCs by co-ordinating with initial lineage-specific signals to accelerate cell fate determination. BMP-7 may be a useful enhancer of in vitro differentiation of BM MSCs for cell-based tissue repair.

Effect of Nell-1 delivery on chondrocyte proliferation and cartilaginous extracellular matrix deposition

Cartilage tissue engineering using chondrogenic growth factors is an attractive strategy to promote cartilage repair. Bone morphogenetic proteins have been widely studied for their application in cartilage repair. However, functional heterogeneity of bone morphogenetic proteins and unpredictable effects such as cyst formation may limit their therapeutic use. Thus, the use of alternative growth factors with greater osteochondral specificity may be advantageous for cartilage regeneration. Nel-like molecule-1 (Nell-1; Nel is a protein strongly expressed in neural tissue encoding epidermal growth factor-like domain) is a novel growth factor believed to specifically target cells committed to the osteochondral lineage. Mutation of the Nell-1 gene has been shown to disrupt normal cartilage growth and development in rodents. This study investigates the chondrogenic potential of recombinant human Nell-1 protein in a three-dimensional alginate hydrogel microenvironment containing rabbit chondrocytes. To provide controlled delivery and maximize biological efficiency, Nell-1 was incorporated in chitosan microparticles. Over 42 days of culture, chondrocyte proliferation and cluster formation was significantly enhanced by Nell-1 in a dose-dependent manner. Further, the clusters formed in the presence of Nell-1 contained more type II collagen and glycosaminoglycans than clusters formed within Nell-free control gels. These findings demonstrate the ability of Nell-1 to promote chondrocyte proliferation and deposition of cartilage-specific extracellular matrix materials.

Effects of Low Concentrated BMP-7 Administered by co-Cultivation or Plasmid Transfection on Human Osteoarthritic Chondrocytes

Introduction

While BMP-7 has proven to be one of the most potent growth factors in cartilage tissue engineering, protein concentration and route of administration remain a matter of debate. Here we investigated the effects of a low concentration of BMP-7 on human osteoarthritic chondrocytes administered by protein co-cultivation and plasmid transfection.

Methods

Freshly released (P0) or in vitro propagated chondrocytes (P2) were cultivated in a collagen type-I gel for 3 weeks in vitro or in nude mice. Seeded chondrocytes were treated with 50 ng/mL BMP-7 directly added to the medium or were subject to transient BMP-7 plasmid transfection prior to gel cultivation. Untreated specimens served as a control. After recovery, samples were investigated by histological and immunohistochemical staining and real-time PCR.

Results

In vitro, collagen type-II protein production was enhanced, and it was stored mainly pericellularly. Collagen type-II and aggrecan gene expression were enhanced in both treatment groups. After nude mouse cultivation, col-II protein production was further enhanced, but specimens of the BMP-7 transfection group revealed a clustering of col-II positive cells. Gene expression was strongly up-regulated, chondrocyte number was increased and the differentiated phenotype prevailed. In general, freshly released chondrocytes (P0) proved to be superior to chondrocytes pre-amplified in vitro (P2).

Conclusions

Both BMP-7 co-cultivation and plasmid transfection of human osteoarthritic chondrocytes led to improved cartilage repair tissue. Nevertheless, the col-II distribution following BMP-7 co-cultivation was homogeneous, while samples produced by transient transfection revealed a col-II clustering.

Use of bone morphogenic protein-7 as a treatment for osteoarthritis

Osteoarthritis is a degenerative disorder resulting from breakdown of articular cartilage. Previous work has shown bone morphogenic protein-7 has a potential protective effect on cartilage during the development of osteoarthritis. The purpose of this study was to determine whether bone morphogenic protein-7 could decrease the amount of cartilage degradation in preexisting osteoarthritis. The rabbit ACLT model was used as a model of osteoarthritis. Bone morphogenic protein-7 was delivered via Alzet osmotic pump to the joint 4 weeks after anterior cruciate ligament transection; thus cartilage injury was preexisting. The experimental group showed less cartilage degradation than the controls, with an average Outerbridge score of 1.9 versus 2.6 for the controls. Histomorphometry showed a trend toward less cartilage degradation in the bone morphogenic protein-7 group when compared with controls. Semiquantitative real-time polymerase chain reaction showed a considerably greater expression of aggrecan in the bone morphogenic protein-7-treated cartilage when compared with controls and less expression of matrix metalloproteinase-3 and matrix metalloproteinase-13, important catabolic mediators. The synovial tissue of the experimental group also showed considerably less expression of matrix metalloproteinase-3, matrix metalloproteinase-13, and aggrecanase. These results indicate bone morphogenic protein-7 may reduce degradation of articular cartilage in osteoarthritis.

Bone morphogenetic proteins in soft-tissue reconstruction

Different options are reviewed in the field of musculoskeletal tissue reconstruction, from the addition of biological actors (cells, growth factors, biological or artificial scaffolds) to the application of gene therapy or tissue engineering. Growth factors can enable innovative solutions to treat such disease if we can extrapolate to soft tissue the promising results obtained in bone reconstruction with bone morphogenetic proteins. However, as in bone reconstruction, soft-tissue regeneration will depend on the drug delivery carrier, the scaffold for the newly formed tissue, the dose of growth factor and the animal model, which must all be explored before extrapolation to clinical problems.

Chondrogenesis, joint formation, and articular cartilage regeneration

The repair of joint surface defects remains a clinical challenge, as articular cartilage has a limited healing response. Despite this, articular cartilage does have the capacity to grow and remodel extensively during pre- and post-natal development. As such, the elucidation of developmental mechanisms, particularly those in post-natal animals, may shed valuable light on processes that could be harnessed to develop novel approaches for articular cartilage tissue engineering and/or regeneration to treat injuries or degeneration in adult joints. Much has been learned through mouse genetics regarding the embryonic development of joints. This knowledge, as well as the less extensive available information regarding post-natal joint development is reviewed here and discussed in relation to their possible relevance to future directions in cartilage tissue repair and regeneration.

Hyaluronan promotes the chondrocyte response to BMP-7

OBJECTIVE

Chondrocytes exhibit specific responses to bone morphogenetic proteins (BMPs) and transforming growth factor-betas (TGF-betas). The bioactivity of these growth factors is regulated by numerous mediators. In our previous study, Smad1 was found to interact with the cytoplasmic domain of the hyaluronan receptor CD44. The purpose of this study was to determine the ability of hyaluronan in the pericellular matrix to modulate the chondrocyte responses to BMP-7 or TGF-beta1.

EXPERIMENTAL DESIGN

Nuclear translocation of Smad1, Smad2 and Smad4 was studied in bovine articular chondrocytes in response to BMP-7 and TGF-beta1. The effects of matrix disruption by hyaluronidase treatment and the initiation of matrix repair by the addition of hyaluronan on the nuclear translocation of Smad proteins, Smad1 phosphorylation and luciferase expression by a CD44 reporter construct in response to BMP-7 were also studied.

RESULTS

The disruption of the hyaluronan-dependent pericellular matrix of chondrocytes resulted in diminished nuclear translocation of endogenous Smad1 and Smad4 in response to BMP-7; however, the nuclear translocation of Smad2 and Smad4 in these matrix-depleted chondrocytes in response to TGF-beta1 was not diminished. Incubation of the matrix-depleted chondrocytes with exogenous hyaluronan restored Smad1 and Smad4 nuclear translocation and increased pCD44(499)-Luc luciferase expression in response to BMP-7. Both exogenous hyaluronan and matrix re-growth enhanced by hyaluronan synthase-2 (HAS2) transfection restored Smad1 phosphorylation.

CONCLUSIONS

Disruption of hyaluronan-CD44 interactions has little effect on the TGF-beta responses; however, re-establishing CD44-hyaluronan ligation promotes a robust cellular response to BMP-7 by articular chondrocytes. Thus, changes in cell-hyaluronan interactions may serve as a mechanism to modulate cellular responsiveness to BMP-7.

A stable isotope method for the simultaneous measurement of matrix synthesis and cell proliferation in articular cartilage in vivo

OBJECTIVE

Measurements of cell proliferation and matrix synthesis in cartilage explants have identified regulatory factors [e.g., interleukin-1 (IL-1)] that contribute to osteoarthritis and anabolic mediators [e.g., bone morphogenic protein-7 (BMP-7)] that may have therapeutic potential. The objective of this study was to develop a robust method for measuring cell proliferation and glycosaminoglycan synthesis in articular cartilage that could be applied in vivo.

METHODS

A stable isotope-mass spectrometry approach was validated by measuring the metabolic effects of IL-1 and BMP-7 in cultures of mature and immature bovine cartilage explants. The method was also applied in vivo to quantify physiologic turnover rates of matrix and cells in the articular cartilage of normal rats. Heavy water was administered to explants in the culture medium and to rats via drinking water, and cartilage was analyzed for labeling of chondroitin sulfate (CS), hyaluronic acid (HA) and DNA.

RESULTS

As expected, IL-1 inhibited the synthesis of DNA and CS in cartilage explants. However, IL-1 inhibited HA synthesis only in immature cartilage. Furthermore, BMP-7 was generally stimulatory, but immature cartilage was significantly more responsive than mature cartilage, particularly in terms of HA and DNA synthesis. In vivo, labeling of CS and DNA in normal rats for up to a year indicated half-lives of 22 and 862 days, respectively, in the joint.

CONCLUSIONS

We describe a method by which deuterium from heavy water is traced into multiple metabolites from a single cartilage specimen to profile its metabolic activity. This method was demonstrated in tissue culture and rodents but may have significant clinical applications.

Articular cartilage increases transition zone regeneration in bone-tendon junction healing

The fibrocartilage transition zone in the direct bone-tendon junction reduces stress concentration and protects the junction from failure. Unfortunately, bone-tendon junctions often heal without fibrocartilage transition zone regeneration. We hypothesized articular cartilage grafts could increase fibrocartilage transition zone regeneration. Using a goat partial patellectomy repair model, autologous articular cartilage was harvested from the excised distal third patella and interposed between the residual proximal two-thirds bone fragment and tendon during repair in 36 knees. We evaluated fibrocartilage transition zone regeneration, bone formation, and mechanical strength after repair at 6, 12, and 24 weeks and compared them with direct repair. Autologous articular cartilage interposition resulted in more fibrocartilage transition zone regeneration (69.10% +/- 14.11% [mean +/- standard deviation] versus 8.67% +/- 7.01% at 24 weeks) than direct repair at all times. There was no difference in the amount of bone formation and mechanical strength achieved. Autologous articular cartilage interposition increases fibrocartilage transition zone regeneration in bone-tendon junction healing, but additional research is required to ascertain the mechanism of stimulation and to establish the clinical applicability.

Relationship of plasma and synovial fluid BMP-7 with disease severity in knee osteoarthritis patients: a pilot study

The objective of this study was to investigate bone morphogenetic protein-7 (BMP-7) levels in both plasma and synovial fluid of patients with primary knee osteoarthritis (OA) and to determine their relationship to disease severity. Thirty-two patients with knee OA and 15 healthy subjects were enrolled in the study. Anteroposterior knee radiographs were taken to determine the disease severity of the affected knee. The radiographic grading of OA in the knee was performed using the Kellgren-Lawrence criteria. BMP-7 levels in the plasma and synovial fluid were measured using enzyme-linked immunosorbent assay. The mean plasma BMP-7 concentration of the knee OA patients was significantly higher compared with that of healthy controls (12.1 +/- 1.6 vs 3.5 +/- 0.9 pg/ml, P = 0.001). Although BMP-7 levels in plasma were higher with respect to paired synovial fluid samples, the difference was not statistically significant (12.1 +/- 1.6 vs 10.5 +/- 2.2 pg/ml, P = 0.3). Subsequent analysis showed that plasma BMP-7 levels significantly correlated with disease severity (r = 0.77, P < 0.001). Furthermore, the synovial fluid levels of BMP-7 also correlated with disease severity (r = 0.60, P < 0.001). In addition, plasma BMP-7 levels showed a positive correlation with synovial fluid BMP-7 levels (r = 0.71, P < 0.001). Overexpression of BMP-7 in plasma and synovial fluid is related to progressive joint damage in knee OA. These findings suggest that BMP-7 might serve as a biochemical parameter for determining disease severity in primary knee OA and could play a potential role in cartilage protection and repair of OA.

The protective effect of OP-1 on articular cartilage in the development of osteoarthritis

OBJECTIVE

The purpose of this study was to determine whether osteogenic protein 1 (OP-1) would protect articular cartilage from degeneration during the development of osteoarthritis (OA) in the rabbit anterior cruciate ligament transection (ACLT) model. Previous studies have shown that OP-1 is vital to cartilage matrix integrity and repair, stimulates synthesis of cartilage matrix components, proteoglycans, and collagen, and has a protective effect against catabolic mediators like matrix metalloproteinases and interleukin-1.

METHODS

The rabbit ACLT model was used in which the anterior cruciate ligament was transected leading to OA. OP-1 was delivered to the joint surgically for approximately 6 weeks by implantation of an Alzet osmotic pump into the medial thigh with a catheter threaded from the pump into the knee joint. Forty rabbits (20 control and 20 experimental) had the ACLT surgery and implantation of the pump performed simultaneously. They were sacrificed after 9 weeks for analysis. The OA was graded using the Outerbridge classification with India Ink staining. Histological staining and histomorphometry with Hematoxylin & Eosin and Safranin O were performed to analyze OA progression and semi-quantitative polymerase chain reaction (PCR) was performed for anabolic and catabolic genes.

RESULTS

The experimental group had an average Outerbridge score of 1.8 vs 2.5 for the controls (P<0.05). Histomorphometry showed 10.9% surface deterioration or an average depression of 0.05mm vs 22.3% and 0.1mm for the controls (P<0.05). Semi-quantitative PCR showed a significantly greater expression of aggrecan and collagen type II in the OP-1 treated cartilage when compared to controls and less expression of aggrecanase, a catabolic mediator.

CONCLUSIONS

OP-1 may have a potential benefit in protecting articular cartilage during the development of OA.

Induction of chondrogenesis and superficial zone protein accumulation in synovial side population cells by BMP-7 and TGF-beta1

Synovial cells are known to contain a sub-population of cells with multipotent differentiating capacity including chondrocytes. However, the stem/progenitor cells in synovial cells have not been well characterized. Stem/progenitor cells can exclude Hoechst 33342 dye, and the cell fraction with this property is called "side population (SP)." SP cells are present in many adult tissues. The aim of this investigation was to identify, isolate, and characterize SP cells from bovine synovium. Hoechst dye efflux and fluorescence activated cell sorting showed that synovial cells contained 0.60% SP cells. In the presence of verapamil, an inhibitor of ABC transporters critical for the dye efflux property, the SP cell fraction was not observed, indicating the critical role of ABC transporters. Isoforms of ABC transporters (ABCG2 and ABCB1 mRNA) were highly expressed in SP cells derived from the synovial cells by real-time RT-PCR analysis. Bone morphogenetic protein-7 (BMP-7) induced type II collagen mRNA expression characteristic of chondrogenesis in articular cartilage with both SP and non-SP cells. In addition, expression of SZP mRNA, a marker of the surface layer of articular cartilage, was significantly up-regulated by BMP-7, and the protein accumulation of SZP was stimulated by both BMP-7 and TGF-beta1. Thus, synovial cells contain ABC transporter-dependent SP cells. These findings demonstrate that side population cells of synovium differentiate toward an articular chondrocyte phenotype of the surface layer and have direct implications for tissue engineering and regeneration of articular cartilage.

Chondrocyte signaling and artificial matrices for articular cartilage engineering

Chondrocytes depend on their environment to aid in their expression of appropriate proteins. It has been found that the interaction of integrin receptors with chondrocytes effects the production of extracellular molecules such as type II collagen and aggrecan. Additionally, the presence of growth factors such as IGF-1, TGF-beta1 and BMP-7 induce various signaling pathways that also aid in transducing phenotypic expressions by chondrocytes. Natural and synthetic polymers have been used to act as a scaffold for chondrocytes. The production of extracellular matrix proteins by chondrocytes has been studied. As tissue engineers, it is advantageous to explore the possibility of how altering biomaterial properties affect the signaling cascades by activation of receptors and transduction through the cytoplasm. This vital information will be able to aid in the future of engineering an appropriate biomaterial that can incorporate chondrocytes to act as a scaffold for articular cartilage.

BMP-7 loaded microspheres as a new delivery system for the cultivation of human chondrocytes in a collagen type-I gel

In recent years, interest in chondrocyte cultures for transplantation has gained increasing attention. We investigated the use of PGLA microspheres as a new delivery system for BMP-7 and the effects on human chondrocytes cultivated in a 3D collagen gel culture. In an in vitro study, human chondrocytes obtained from osteoarthritic knee joints were released, transferred into a collagen type-I gel, and cultivated up to 14 days. In the treatment group PGLA microspheres loaded with human recombinant BMP-7 protein were added to the matrix. After the cultivation period, histological and immunohistochemical investigations were performed. In addition, the aggrecan core protein and type-II collagen mRNA concentrations were measured by real-time PCR. Histological staining for proteoglycan and collagen type-II protein and quantification via digital image processing revealed a significantly higher content in the samples cultivated with BMP-7 loaded microspheres in comparison to the control samples. Moreover, the collagen gel scaffold was partially remodeled by the chondrocytes and replaced by newly synthesized extracellular matrix. Cellular proliferation as well as apoptosis were low. In conclusion, we consider the PGLA microsphere system to be a functional device for the delivery of growth factors during the cultivation of articular chondrocytes leading to an increased content of type-II collagen and proteoglycan in the extracellular matrix.

Safety of epidural administration of Osteogenic Protein-1 (OP-1/BMP-7): behavioral and macroscopic observation

STUDY DESIGN

To assess the safety of epidural administration of Osteogenic Protein-1 (OP-1).

OBJECTIVES

To examine if epidural administration of OP-1 or administration into the nucleus pulposus (NP) resulted in ectopic bone formation and/or pain-related behavior.

SUMMARY OF BACKGROUND DATA

OP-1 has the potential for treatment of degenerative disc disease. However, OP-1's safety, when it is applied into the epidural space or herniated nucleus pulposus, is not well established.

METHODS

Forty rats were divided into 5 groups. Sham group: Left L4 and L5 nerve roots were exposed. NP group: The NP obtained from the tail was relocated onto the exposed nerve roots. NP+OP group: The NP obtained from the tail and injected with 0.2 microg of OP-1 in 1 microL of 5% lactose-buffered solution was placed on the nerve roots. GS group: A gelatin sponge was applied on the nerve roots. GS+OP group: A gelatin sponge soaked with 0.2 microg of OP-1 in 1 microL of 5% lactose-buffered solution was placed onto the nerve roots. Motor function and reflex responses to mechanical noxious stimuli were measured in all rats up to 3 weeks after surgery. Three weeks after surgery, all rats were killed for analysis of ectopic bone formation and magnitude of neural compression.

RESULTS

Motor paresis was not observed in any groups. Only rats in the NP group showed evidence of irreversible mechanical hyperalgesia after surgery. There were no differences in the mechanical stimuli response among all groups except the NP group. Macroscopic examination revealed no ectopic bone formation or differences in neural compression among the groups.

CONCLUSION

OP-1 application in the epidural space is safe based on behavioral measures and macroscopic observation on ectopic bone formation at 21 days after surgery.

Differences in matrix accumulation and hypertrophy in superficial and deep zone chondrocytes are controlled by bone morphogenetic protein

Despite the knowledge that superficial zone chondrocytes (SZC, located within 100 mum of the articular surface) and deep zone chondrocytes (DZC, located near the calcified zone) have distinct phenotypes, previous studies on bone morphogenetic proteins (BMPs) have not differentiated its effects on SZC versus DZC. Using a pellet culture model we have compared phenotype, morphology and matrix accumulation in SZC and DZC with or without adenovirus-mediated overexpression of BMP2 or -7 or the BMP antagonist Noggin. Greater accumulation of proteoglycan (PG)-rich matrix in the untreated DZC was associated with a hypertrophic phenotype with large cell diameters and high gene expression levels of runt-related transcription factor-2 (Runx2) as well as higher endogenous BMP activity. Noggin overexpression decreased matrix accumulation and cell diameters in SZC and DZC, confirming a role for endogenous BMP in both processes. In DZC, overexpression of either BMP2 or -7 increased cell diameter without increasing PG-rich matrix accumulation. In contrast, in SZC, BMP overexpression increased matrix accumulation and type II collagen gene expression without increasing cell diameter. These data indicate that differences in endogenous BMP activity level and responsiveness to BMPs define, in part, the differences between the SZC and DZC phenotype. They also suggest that SZC may be a more appropriate target for BMP therapy than DZC.

Anti-catabolic effect of OP-1 in chronically compressed intervertebral discs

Experimental animal models of disc degeneration have been used to assess the biomechanical behavior, biochemical composition, and biological changes in the intervertebral discs. The objective of our study was to evaluate the anabolic and anti-catabolic effects of intradiscal injection of Osteogenic Protein-1 (OP-1) by histology and immunohistochemistry in disc degeneration model. Thirty-four rats were divided into five groups: intact control; sham control; compressed nucleus pulposus (NP) injected with saline; and two OP-1 groups: COP-1 group (compression was continued after intradiscal OP-1 injection) and ROP-1 group (compression was released at the time of OP-1 injection). Anabolic and anti-catabolic effects of OP-1 were evaluated by histology and immunohistochemistry with the following antibodies: anti-pro- and anti-mature OP-1, anti-MMP-13, anti-aggrecanase, anti-substance P, anti-tumor necrosis factor-alpha (TNF-alpha), and anti-interleukin-1beta (IL-1beta). The OP-1 injection to the degenerative disc stimulated an anabolic response characterized by the restoration of the normal morphology of the disc, increased Safranin O staining in the NP, extention of the extracellular matrix, and stimulation of endogenous OP-1 synthesis in the NP, annulus fibrosis (AF), and end-plate. The anti-catabolic effect of OP-1 was documented by reduced immunostaining for aggrecanase, MMP-13, substance P, TNF-alpha, and IL-1beta. This study confirmed the anti-catabolic activity of OP-1 as demonstrated previously in human articular cartilage and provided critical evidence for the potential of OP-1 therapy in the treatment of disc degeneration. Because substance P is a neuropeptide linked with inflammation and pain, a reduction in the level of this protein may support our previously reported results on the effect of OP-1 on pain-related behavior.

A capsular incision leads to a fast osteoarthritic response, but also elevated levels of activated osteogenic protein-1 in rabbit knee joint cartilage

We studied whether a small capsular incision alone, or combined with meniscectomy could induce early osteoarthritic changes in the rabbit knee. Thirty-one rabbits were operated on with a capsular incision in the left knee and meniscectomy in the right knee. Another 12 rabbits were used as controls. The rabbits were killed 3, 6 and 12 weeks after surgery. Osteoarthritic changes in the articular cartilage were evaluated by the modified Mankin score. The subchondral bone was evaluated by scintimetry ((99m)Tc-HDP) and semiquantitative grading of histological changes. Osteogenic protein (OP-1) in its mature and pro-form was examined by immunohistochemistry. Both a capsular incision and meniscectomy induced articular cartilage fibrillation and increased bone metabolic activity during the initial weeks after surgery. Capsular incision led to lesser changes than meniscectomy. Mature OP-1 was elevated, and its pro-form reduced, in meniscectomized knees. A similar pattern was observed in knees with capsular incision. Already 3 weeks after surgery, the articular cartilage and subchondral bone showed typical signs of early osteoarthritis (OA), and a reparative response was suggested by increased intensity of OP-1 staining. As these signs were also found in knees with capsular incision only, it appears that trauma-related factors such as increased bleeding and inflammation are critical for the development of OA.