IGF-I and TGF-beta 1 incorporated in a poly(D,L-lactide) implant coating stimulates osteoblast differentiation and collagen-1 production but reduces osteoblast proliferation in cell culture

The Role of Growth Factors in Bioactive Coatings

With increasing obesity and an ageing population, health complications are also on the rise, such as the need to replace a joint with an artificial one. In both humans and animals, the integration of the implant is crucial, and bioactive coatings play an important role in bone tissue engineering. Since bone tissue engineering is about designing an implant that maximally mimics natural bone and is accepted by the tissue, the search for optimal materials and therapeutic agents and their concentrations is increasing. The incorporation of growth factors (GFs) in a bioactive coating represents a novel approach in bone tissue engineering, in which osteoinduction is enhanced in order to create the optimal conditions for the bone healing process, which crucially affects implant fixation. For the application of GFs in coatings and their implementation in clinical practice, factors such as the choice of one or more GFs, their concentration, the coating material, the method of incorporation, and the implant material must be considered to achieve the desired controlled release. Therefore, the avoidance of revision surgery also depends on the success of the design of the most appropriate bioactive coating. This overview considers the integration of the most common GFs that have been investigated in in vitro and in vivo studies, as well as in human clinical trials, with the aim of applying them in bioactive coatings. An overview of the main therapeutic agents that can stimulate cells to express the GFs necessary for bone tissue development is also provided. The main objective is to present the advantages and disadvantages of the GFs that have shown promise for inclusion in bioactive coatings according to the results of numerous studies.

Irisin enhances osteogenic differentiation of mouse MC3T3-E1 cells via upregulating osteogenic genes

Osteoporosis affects millions of individuals and remains a clinical challenge in terms of prevention and treatment. The present study aimed to investigate the effect of irisin on osteogenic differentiation by exposing MC3T3-E1 cells to different concentrations of irisin. Treated cells were assayed for osteoblast proliferation and osteogenic differentiation by measuring alkaline phosphatase (ALP) activity, calcium deposition, formation of mineralized nodules and the expression of osteogenic genes using reverse transcription-quantitative PCR. The proliferation of MC3T3-E1 cells was unaffected by irisin at the concentrations tested of up to 100 ng/ml (P>0.05). ALP activity and mineralized nodule formation were significantly enhanced by irisin in a dose- and time-dependent manner, indicating that irisin promotes osteoblast differentiation of MC3T3-E1 cells. The expression of osteogenic genes, including ALP, collagen I, runt-related transcription factor 2, osterix, osteopontin, osteocalcin, osteoprotegerin and estrogen receptor α, increased significantly after irisin treatment. The present study demonstrated that irisin promoted the osteogenic differentiation of MC3T3-E1 cells, possibly by upregulating the expression of osteogenic genes and markers. Therefore, irisin may be worthy of further investigation as a potential therapeutic agent for osteoporosis.

Growth Factors, Carrier Materials, and Bone Repair

This chapter provides an overview of the growth factors active in bone regeneration and healing. Both normal and impaired bone healing are discussed, with a focus on the spatiotemporal activity of the various growth factors known to be involved in the healing response. The review highlights the activities of most important growth factors impacting bone regeneration, with a particular emphasis on those being pursued for clinical translation or which have already been marketed as components of bone regenerative materials. Current approaches the use of bone grafts in clinical settings of bone repair (including bone grafts) are summarized, and carrier systems (scaffolds) for bone tissue engineering via localized growth factor delivery are reviewed. The chapter concludes with a consideration of how bone repair might be improved in the future.

Stammzellen in der Regenerativen Medizin – Translationale Hürden und Möglichkeiten zur Überwindung

Der Einsatz von mesenchymalen Stammzellen in der regenerativen Medizin wird immer populärer. Nichtsdestotrotz ist ihre Anwendung im klinischen Alltag noch immer limitiert. Zahlreiche ethische, rechtliche und translationale Probleme sowie Ungewissheit bzgl. der Sicherheit hemmen noch immer die Entstehung von entsprechenden Therapien aus vielversprechenden wissenschaftlichen Ansätzen.

Diese Arbeit soll die Hauptprobleme bei der Translation von stammzellbasierten Therapien aus der Grundlagenforschung und Präklinik in den klinischen Alltag darstellen, sowie Ansätze aufzeigen, diese zu überwinden.

Mast Cell Mediators Inhibit Osteoblastic Differentiation and Extracellular Matrix Mineralization

Mast cells are multifunctional immune cells that participate in many important processes such as defense against pathogens, allergic reactions, and tissue repair. These cells perform their functions through the release of a wide variety of mediators. This release occurs mainly through cross-linking IgE (immunoglobulin E) bound to high affinity IgE receptors by multivalent antigens. The abundance of mast cells in connective tissue, surrounding blood vessels, and their involvement in the early stages of bone repair support the possibility of physiological and pathological interactions between mast cells and osteoblasts. However, the participation of mast cell mediators in osteogenesis is not fully understood. Therefore, the objective of this work was to investigate the role of mast cell mediators in the acquisition of the osteogenic phenotype in vitro. The results show that pooled mast cell mediators can affect proliferation, morphology, and cytoskeleton of osteoblastic cells, and impair the activity and expression of alkaline phosphatase as well as the expression of bone sialoprotein. Also, mast cell mediators inhibit the expression of mRNA for those proteins and inhibit the formation and maturation of calcium nodules and consequently inhibit mineralization. Therefore, mast cell mediators can modulate osteogenesis and are potential therapeutic targets for treatments of bone disorders.

Electrospun Polymeric Core-sheath Yarns as Drug Eluting Surgical Sutures

Drug-coated sutures are widely used as delivery depots for antibiotics and anti-inflammatory drugs at surgical wound sites. Although drug-laden coating provides good localized drug concentration, variable loading efficiency and release kinetics limits its use. Alternatively, drug incorporation within suture matrices is hampered by the harsh fabrication conditions required for suture-strength enhancement. To circumvent these limitations, we fabricated mechanically robust electrospun core-sheath yarns as sutures, with a central poly-l-lactic acid core, and a drug-eluting poly-lactic-co-glycolic acid sheath. The electrospun sheath was incorporated with aceclofenac or insulin to demonstrate versatility of the suture in loading both chemical and biological class of drugs. Aceclofenac and insulin incorporated sutures exhibited 15% and 4% loading, and release for 10 and 7 days, respectively. Aceclofenac sutures demonstrated reduced epidermal hyperplasia and cellularity in skin-inflammation animal model, while insulin loaded sutures showed enhanced cellular migration in wound healing assay. In conclusion, we demonstrate an innovative strategy of producing mechanically strong, prolonged drug-release sutures loaded with different classes of drugs.

Transforming growth factor Beta family: insight into the role of growth factors in regulation of fracture healing biology and potential clinical applications

The transforming growth factor beta (TGF-β) family forms a group of three isoforms, TGF-β1, TGF-β2, and TGF-β3, with their structure formed by interrelated dimeric polypeptide chains. Pleiotropic and redundant functions of the TGF-β family concern control of numerous aspects and effects of cell functions, including proliferation, differentiation, and migration, in all tissues of the human body. Amongst many cytokines and growth factors, the TGF-β family is considered a group playing one of numerous key roles in control of physiological phenomena concerning maintenance of metabolic homeostasis in the bone tissue. By breaking the continuity of bone tissue, a spread-over-time and complex bone healing process is initiated, considered a recapitulation of embryonic intracartilaginous ossification. This process is a cascade of local and systemic phenomena spread over time, involving whole cell lineages and various cytokines and growth factors. Numerous in vivo and in vitro studies in various models analysing cytokines and growth factors' involvement have shown that TGF-β has a leading role in the fracture healing process. This paper sums up current knowledge on the basis of available literature concerning the role of the TGF-β family in the fracture healing process.

Analysis of genetic regulation and cytokine expressions of distraction osteogenesis reconstruction for cleft palate

Because cleft palate (CP) is one of the most common congenital deformities, surgeons have tried for longtime to achieve an ideal reconstruction of the palatal bone defects and restoration of muscle attachments. In this study, a new CP model on rhesus was established and corrected by an approach of distraction osteogenesis (DO), and then quantitative studies of regulation of osteogenesis genes and expression of alkaline phosphatase (ALP), insulin-like growth factor-I (IGF-I), osteopontin (OPN), and osteocalcin (OC) in different phases of new bone formation were preformed. The CP models (23 animals) were established surgically. In the experimental group (21 animals), the tissue defects were repaired by means of DO at the rhythm of 0.4 mm twice per day. The specimens were retrieved in 1, 2, 4, 6, 8, 12, and 24 weeks (3 animals each) after completion of distraction. The IGF-I, ALP, OPN, and OC messenger RNA (mRNA) were detected by real-time reverse transcription polymerase chain reaction, and their proteins were then analyzed by enzyme-linked immunosorbent assay tests. The results are compared with those of the experimental control and empty control groups (2 animals each). In the distraction gap, the mRNA and protein expressions levels of IGF-I and ALP were both highly upregulated and reaching apex in the early phase of new bone formation. Otherwise, the mRNA and protein expressions of OPN and OC demonstrated high level during intermediate and later remodeling stages. These results suggest that the reconstruction of CP bone defect by means of DO could get definitely intramembraneous new bone formation and eventually quite normal bone structure via consecutive remodeling in situ.

Filtration of dermal fibroblast-conditioned culture media is required for the reliable quantitation of cleaved carboxy-terminal peptide of collagen type I (CICP) by ELISA

Cleavage of the collagen type I carboxy-terminal peptide (CICP) from the procollagen molecule is an essential step in collagen biosynthesis. The commercial CICP ELISA (Quidel Corporation, USA), developed for quantifying CICP in serum in clinical monitoring, is often also applied to cellular studies as a measure of collagen synthesis. However, unlike in serum samples, which contain only cleaved CICP, cell-conditioned culture media also contains "uncleaved CICP", namely procollagen, and there is no specific guidance on how to interpret the ELISA data obtained with such samples. Here we attempted to reliably quantify cleaved CICP in human dermal fibroblast-conditioned cell culture media using the CICP ELISA. CICP concentration was determined in the parent and filtered samples of culture media of dermal fibroblasts (CCD-25SK). Gel-separated samples were also subjected to protein staining or analyzed by Western blot using the anti-CICP antibodies supplied in the ELISA kit. The derived concentrations of CICP in the filtered aliquots and the parent unfiltered samples increased over time. The increase in CICP in the unfiltered samples was not proportional to the increase seen in the filtered aliquot. CICP ELISA antibodies recognized both the cleaved CICP trimer and procollagen molecule. The data presented show that (a) the commercial CICP ELISA recognizes both procollagen and cleaved CICP in cell-conditioned culture media and thus attention should be paid in interpreting data from cell culture studies using this ELISA and (b) the filtration method described herein can be used to exclusively and reliably monitor cleaved CICP.

Evaluation of biological activity of bone morphogenetic proteins on exposure to commonly used electrospinning solvents

Bone tissue engineering is one of the emerging strategies for developing functionally viable bone substitutes. The recent trend in bone tissue engineering is to combine the benefits of a three-dimensional nanofibrous scaffold with biologically active molecules and responsive stem cells. Electrospinning is the most versatile of the scaffold fabrication strategies and may involve the use of an organic solvent at one stage or another. In spite of all distinct advantages of electrospinning, valid concerns about potentially denaturing interactions between the organic solvent and the biomolecules exist. Efforts are ongoing to incorporate osteoinductive molecules, such as bone morphogenetic proteins (BMPs), during the electrospinning process. The challenge lies in ensuring that the biological activity of these incorporated molecules survives the process. This study was specifically designed to investigate the effects of exposure to commonly used organic solvents on heterodimeric BMP-2/7 using slot-blot assay quantified by infrared imaging and on embryonic myoblasts stably transfected with BMP-specific response element linked to a luciferase reporter – C2C12BRA. Overall, the biological activity of these molecules significantly decreased when exposed to organic solvents but can be restored to their original values by increasing the polarity of the solvent. It was found that an aqueous buffer can effectively overcome the deleterious effects of organic solvents on BMPs, thus generating osteoinductive bone scaffolds.

Emerging ideas: Interleukin-12 nanocoatings prevent open fracture-associated infections

BACKGROUND

Infection is a major clinical complication of orthopaedic implants and prosthetic devices, and patients with traumatic open fractures have a high risk of infection that may exceed 30%. Surgical trauma, burns, and major injuries such as traumatic open fractures induce immunosuppression, decrease resistance to infection, and decrease production of T helper type 1 (Th1) cytokines.

QUESTIONS/HYPOTHESES

Exogenous interleukin-12 p70 (IL-12p70 or IL-12), a natural cytokine that plays a central role in Th1 response and bridges innate and adaptive immunities, will reduce open fracture-associated infection.

METHOD OF STUDY

We propose using exogenous IL-12 nanocoating to restore or enhance the body's natural defense system to combat pathogens. Rats will have a femur fractured, inoculated with Staphylococcus aureus or injected with phosphate buffered saline, left open for 1 hour, and then fixed with an intramedullary Kirschner wire with or without IL-12 nanocoating. Animals will be euthanized at postoperative Day 21; samples of blood, soft tissue, bone, and draining lymph nodes will be collected. Infection, bone healing, and local and systemic responses will be determined.

SIGNIFICANCE

IL-12 nanocoating is a promising prophylactic means to modulate the host immune response to help prevent open fracture-associated infections and to avoid the problem of antibiotic resistance.

Effect of β-tricalcium phosphate coated with zoledronic acid on human osteoblasts and human osteoclasts in vitro

The combination of a bone graft material with bisphosphonates (BPs) might be advantageous for an optimal balance of material resorption and stimulation of bone formation. This study investigated the effect of β-tricalcium phosphate (β-TCP) bone grafts coated with zoledronic acid (ZOL) on osteoblast-like cells and osteoclast-like cells (OLC). As a drug carrier, the polymer poly(D,L-lactide) was used and three different concentrations of ZOL were tested. β-TCP coated with ZOL stimulated the production of osteocalcin (OC), osteoprotegerin, and sRANKL in osteoblast-like cells. The polymer coating alone caused a significant increase in collagen type 1 and OC production. OLC viability was inhibited and the tartrate-resistant acidic phosphatase isoform-5b was significantly decreased after cultivation on polymer-coated β-TCP for 12 days. The three different concentrations of ZOL decreased cell viability and no TRAPiso-5b was detectable, indicating a strong reduction of the TRAPiso-5b after 12 days in culture. After 21 days in culture, only the higher ZOL concentrations significantly reduced cell viability and TRAPiso-5b. The results of this study show that coating of β-TCP with ZOL has stimulating effects on osteoblast-like cells. Additionally, an inhibition of osteoclasts was seen. The combination of this bone grafting material with BPs might, therefore, be effective in the treatment of large bone defects.

Cigarette smoking decreases TGF-b1 serum concentrations after long bone fracture

TGF-b1 serum concentrations are considered to be one of the most promising markers of fracture healing. Previously, we demonstrated significant differences in the post-traumatic time courses of patients with timely and delayed fracture healing. The aim of this study was to evaluate possible differences in the serum concentrations of TGF-b1 in cigarette-smoking vs. non-smoking patients with timely and delayed fracture healing in order to understand pathophysiological pathways through which smoking impairs fracture healing.Serum samples were collected from 248 patients undergoing surgical treatment for long bone fractures within 1 year of surgery. Samples from 14 patients with atrophic-type delayed fracture healing were compared with 14 matched patients with normal bone healing. Each group included seven smokers and seven non-smokers. Post-operative serum concentrations were analysed at 1, 2, 4, 8, and 12 weeks as well as 1 year after surgery. The patients were monitored both clinically and radiologically for the entire duration of the study.All patients increased TGF-b1 serum concentrations after surgery. In patients with normal fracture healing, significantly higher TGF-b1 levels were observed in non-smokers (70 ng/ml) than in smokers(50 ng/ml) at the 4th week after surgery (p = 0.007). Also at the 4th week, in patients with delayed healing, significantly lower TGF-b1 levels were observed in smokers than in non-smokers (38 ng/ml vs.47 ng/ml, p = 0.021). However, no significant differences between non-smokers with delayed healing and smokers with normal healing (p = 0.151) were observed at the 4th week after surgery. TGF-b1 serum concentrations reached a plateau in all groups from the 6th to the 12th week after surgery, with a slight decrease observed in the final measurement taken 1 year after surgery.This study demonstrates that, after fracture, TGF-b1 serum concentrations are reduced by smoking,and this reduction is statistically significant during the 4th week after surgery. Our findings may help reveal the mechanism by which smoking impairs fracture healing. Furthermore, these results may help to establish a serological marker that predicts impaired fracture healing soon after the injury. Surgeons will not only be able to monitor the bone healing, but they will also be able to monitor the success of additional treatments such as ultrasound and bone morphologic proteins (BMPs).

Fibroblast and vascular endothelial growth factor coating of decellularized vascular grafts stimulates undesired giant cells and graft encapsulation in a rat model

Replacing an infected prosthesis with a bioimplant provides a hopeful alternative in septic vascular surgery. The objective of this study was to determine the effect of fibroblast endothelial growth factors (FGF) and vascular endothelial growth factors (VEGF) coating on a decellularized vascular graft in a rat model and the possible impact on recellularization processes. Rat aortas were decellularized, crosslinked with genipin, and coated with poly-(D, L) lactide containing either FGF or VEGF. Observation periods were 6 and 12 weeks. Surprisingly, we found moderate accumulation of giant cells around the grafts that contained poly-(D, L) lactide acid. FGF and VEGF grafts showed massive stimulation of giant cells and eosinophils leading to complete graft encapsulation (P < 0.05). Pseudointmal hyperplasia was significantly increased in the FGF group (P < 0.05). Both results can only be interpreted as very negative. We achieved a situation in diametric opposition to that which we had hoped for. These data demonstrate that the use of growth factors may produce harmful side effects.

Polymer coating of porcine decellularized and cross-linked aortic grafts

This article investigates a method of modifying and optimizing the biocompatibility of decellularized vascular bioimplants when treated with a specialized, drug eluting coating. For this purpose, we carried out aortic transplantations using a porcine model. Decellularized, cross-linked aortic grafts were coated with poly(D,L-lactide) (PDLLA). To this coating, we added the anticoagulant drug lepirudin which, following transplantation, would be linearly eluted. These aortic grafts are easily manipulated in surgery. It was shown that, as a result of the lepirudin-eluting coating, the rate of thrombogenesis was reduced and the patency rate was significantly improved. However, lumen-stenosing pseudointima developed in all of the transplants and was not effected by PDLLA coating. Furthermore, no evidence of recellularisation was documented. This trial demonstrates that polymer coating of decellularized tissue is possible. Neointimal hyperplasia and the absence of cellular repopulation mark the negative consequences of this concept.

Local application of zoledronic acid incorporated in a poly(D,L-lactide)-coated implant accelerates fracture healing in rats

BACKGROUND AND PURPOSE

Zoledronic acid (ZOL) has been shown in vitro and in vivo to inhibit osteoclastic activity and to regulate osteoblasts. Its antiresorptive effect is used clinically in the treatment of bone-consuming pathologies to prevent skeletal complications. Because of its effect on bone cells, there might be a possible benefit in treatment of fractures by local application from a biodegradable poly(D,L-lactide) (PDLLA) coating of osteosynthetic implants. We analyzed the effect of locally applied ZOL from a PDLLA coating of intramedullary implants on fracture healing.

MATERIAL AND METHODS

Standardized midshaft fractures of the right tibia of 5-month-old rats were stabilized either with uncoated, PDLLA-coated, or ZOL-coated implants. Animals were killed 42 or 84 days after fracture. Tibiae were dissected and mechanically tested. Results Radiographs taken 42 days after fracture showed at least unilateral bridging in all groups. Maximum load and torsional stiffness were highest in the group treated with ZOL. 84 days after fracture, the torsional stiffness of the ZOL-treated group remained higher than that of the uncoated group whereas the maximum load for the control groups reached the results for the ZOL-coated group.

INTERPRETATION

Local application of ZOL from PDLLA coating appears to accelerate the achievement of mechanical stability in fractures.

Carrier systems and application of growth factors in orthopaedics

With optimal surgical treatment within an appropriate time frame, bony tissue has the potential to regenerate defects without the formation of scar tissue. However, even under optimal mechanical circumstances and appropriate operative treatment, healing can fail and delayed or non-union occur. In Europe delayed bone healing leads to socio-economic costs of up to 14.7 billion euros per year. In addition to the optimal clinical treatment, the success of bone regeneration depends on the following main aspects: (1) adequate mechanical stabilization and biological competence of the organism, (2) osteogenic cells, (3) osteoconductive structures or scaffolds, and (4) growth factors (Diamond Concept)(1). Further, (5) a sufficient vascularisation is essential for the nutritive supply. Within the last years two growth factors, BMP-2 and BMP-7, were approved for clinical use in orthopaedic and trauma surgery for different indications.(2,3) The establishment of carrier systems and application techniques for growths factors is the focus of current research. The combination of a well established stabilization system and local drug delivery system for bioactive factors could be a therapeutical strategy to optimize bone healing and reduce the complication rate, in the future.

Bisphosphonates incorporated in a poly(D,L-lactide) implant coating inhibit osteoclast like cells in vitro

Nitrogen containing bisphosphonates such as zoledronic acid (ZOL) are clinically used to prevent osteoclast induced bone loss. Previous studies indicated that bisphosphonates prevent osteoclast formation, decreases their resorption activity and lead to osteoclast apoptosis. Aim of the study was to investigate the effect of ZOL on fusion and resorption activity of osteoclast like cells (OLC) derived from human peripheral blood mononuclear cells (PBMNC) in vitro. For application of ZOL a local drug delivery system based on a coating for medical devices was used. ZOL was incorporated in the coating based on Poly(D,L-Lactide) (PDLLA) in different concentrations (10-50 microM). Control groups were treated without ZOL or ZOL pure substance in corresponding concentrations. Human PBMNCs were isolated and stimulated to form OLCs. After an experimental period of 144 h, TRAP staining of polynucleated cells was performed and TRAP positive cells were counted. A pit formation assay was performed and resorption lacunas on dentin chips were counted. Results showed a significant dose dependent decrease in the number of TRAP positive cells after exposure to ZOL incorporated in the drug delivery system or applied as pure substance. The amount of resorption lacunas was also dose dependent decreased using both application methods. In conclusion, exposure to specific concentrations of ZOL incorporated in a drug delivery system showed a significant decrease in OLC formation and activity comparable to the effect of pure substance. The effect on osteoclasts might be of clinical benefit to reduce orthopedic implant loosening and to support fracture healing.

Effects of a mixture of growth factors and proteins on the development of the osteogenic phenotype in human alveolar bone cell cultures

Strategies to promote bone repair have included exposure of cells to growth factor (GF) preparations from blood that generally include proteins as part of a complex mixture. This study aimed to evaluate the effects of such a mixture on different parameters of the development of the osteogenic phenotype in vitro. Osteoblastic cells were obtained by enzymatic digestion of human alveolar bone and cultured under standard osteogenic conditions until subconfluence. They were subcultured on Thermanox coverslips up to 14 days. Treated cultures were exposed during the first 7 days to osteogenic medium supplemented with a GFs + proteins mixture containing the major components found in platelet extracts [platelet-derived growth factor-BB, transforming growth factor (TGF)-beta1, TGF-beta2, albumin, fibronectin, and thrombospondin] and to osteogenic medium alone thereafter. Control cultures were exposed only to the osteogenic medium. Treated cultures exhibited a significantly higher number of adherent cells from day 4 onward and of cycling cells at days 1 and 4, weak alkaline phosphatase (ALP) labeling, and significantly decreased levels of ALP activity and mRNA expression. At day 14, no Alizarin red-stained nodular areas were detected in cultures treated with GFs + proteins. Results were confirmed in the rat calvaria-derived osteogenic cell culture model. The addition of bone morphogenetic protein 7 or growth and differentiation factor 5 to treated cultures upregulated Runx2 and ALP mRNA expression, but surprisingly, ALP activity was not restored. These results showed that a mixture of GFs + proteins affects the development of the osteogenic phenotype both in human and rat cultures, leading to an increase in the number of cells, but expressed a less differentiated state.

Proliferating and differentiating effects of three different growth factors on pluripotent mesenchymal cells and osteoblast like cells

Growth factors are in clinical use to stimulate bone growth and regeneration. BMP-2 is used in long bone and spinal surgery, PDGFbb for the treatment of periodontal defects and children with growth hormone receptor deficiency are treated with IGF-I.

Aim of the present study was the comparative analysis of the effect of these growth factors released from a local drug delivery system on cells of the osteogenic lineage at differing differentiation stages.

The experiments with the mesenchymal cell line C2C12 revealed a proliferating effect of all three growth factors and a differentiating effect of BMP-2 with a dramatic increase in alkaline phosphatase activity. None of the growth factors stimulated cell migration.

Human osteoblast like cells showed similar results with an increase in proliferation after stimulation with IGF-I or PDGFbb. The enzymatic activity of alkaline phosphatase was enhanced only in the cells stimulated with BMP-2. This group showed also more mineralized matrix compared to the other groups.

In conclusion, the growth factors IGF-I and PDGFbb delivered with a local drug delivery system stimulated cell proliferation, whereas BMP-2 showed a dramatic effect on differentiation on osteoblast precursor cells and osteoblast like cells.

[TGF-beta1 as a pathophysiological factor in fracture healing]

AIM

TGF-beta1 is an important local and systemic regulatory molecule during fracture healing. Various authors have shown differences in the systemic levels of TGF-beta1 over the time taken for bone healing in distraction osteogenesis and osteotomies. Previous studies have shown characteristic differences in the physiological levels of growth factors between normal fracture healing and delayed fracture union. The aim of the present study was to evaluate possible differences in sera levels of patients with normal and delayed union fracture healing.

METHODS

Patients with long bone shaft fractures were recruited prospectively. Peripheral blood samples were collected over a period of 1 year using a standardized time schedule. At the end of the individual's investigation period, TGF-beta1 levels were determined. To achieve a homogeneous collective of patients, only those with a maximum of two fractures were included in the study. After matching for four criteria, we compared patients with normal fracture healing to patients with delayed unions. The fact of delayed union was accepted in case of failed consolidation 4 months after trauma.

RESULTS

During a prospective study period of 1 year, 15 patients with normal fracture healing could be compared to 15 patients suffering from delayed union. By determining the absolute sera levels we found a typical increase of TGF-beta1 up to 2 weeks after fracture in both groups, with a subsequent decrease up to the sixth week after fracture. However, a decline in serum concentration occurred earlier in patients with delayed union, causing significantly lower TGF-beta1 levels in the non-union group 4 weeks after trauma (P=0.00006).

CONCLUSION

Even with a relatively small number of patients, we could show a significant difference in serum concentrations of TGF-beta1 between the investigated groups. If these results can be verified within a larger collective, TGF-beta1 could be used as a predictive cytokine for delayed fracture healing.

Use of bone morphogenetic proteins for treatment of non-unions and future perspectives

Still a major problem in orthopedic and trauma surgery is the delayed healing or the non-union of long bone fractures. Demographic data reveal that due to the steadily rising age of the population, complications with the musculoskeletal system will increase during the next years. Bone morphogenetic proteins (BMPs) have successfully been applied in clinic for the treatment of delayed healing and non-unions. The broad difference concerning the indication, timing of treatment, dosage and application technique of BMPs calls for the need to perform further prospective studies in order to standardize the treatment and furthermore optimize the procedures or even develop new therapeutic strategies. For example, the application technique may be improved and in some cases injectable BMP preparations could be of use. Also the coating of implants with growth factors might be valuable in order to stimulate bone healing and to prevent delayed healing or non-union. This article tries to discuss some of the open questions, however can and will not reflect the absolute standard of care. To make the BMP treatment a standard of care, more clinical data and long time experiences are necessary. The intramedullary application of BMP in combination with autologous or allogenic bone grafts or bone substitutes after debridement and stabilization with implants seems to be an adequate procedure for treatment of atrophic non-unions. However, the total number of patients is too small to draw final conclusions. Further clinical studies need to be performed in the future.

The effect of zoledronic acid incorporated in a poly(D,L-lactide) implant coating on osteoblasts in vitro

Bisphosphonates such as zoledronic acid (ZOL) are used in diseases associated with osteoclast-mediated bone loss. However, their antiresorptive activity is partly due to their effect on osteoblasts. Local application might increase the therapeutical fence and their local efficiency and reduce systemic side effects. Aim of the study was to investigate the effect of ZOL on human osteoblasts like cells in vitro with special focus on the synthesis of factors mediating osteoclast differentiation (RANKL, OPG). ZOL was incorporated in an implant coating based on poly(D,L-lactide) (PDLLA) in different concentrations (10-150 microM). Control groups were treated with uncoated implants, PDLLA-coated implants, and ZOL pure substance in corresponding concentrations. After an experimental period of 144 h, primary human osteoblasts were stained with alamar blue and cell viability was measured. Procollagen I synthesis, osteoprotegerin (OPG) secretion, and soluble receptor activator of nuclear factor-kappaB ligand (sRANKL) were analyzed. Results showed that cell viability was not affected when treated with doses equivalent up to 100 microM ZOL-coated implants (ZOL-CI). Procollagen I synthesis was highest when treated with 50 microM ZOL-CI. OPG increased significantly in the 10 microM ZOL-CI group, whereas sRANKL decreased significantly with different concentrations of ZOL-CI. Higher concentrations or exposure to the pure substance showed a decrease in cell viability, collagen I, OPG, and sRANKL synthesis. In conclusion, exposure to specific concentrations of ZOL-CI showed a beneficial effect on osteoblast differentiation and protein synthesis without influencing their proliferation. Changes in sRANKL and OPG production may contribute to the inhibition of osteoclastic bone resorption. This local antiresorptive effect might be clinically useful in osseous implant integration and fracture healing.

Short term in vivo biocompatibility testing of biodegradable poly(D,L-lactide)—growth factor coating for orthopaedic implants

Fracture healing can be stimulated by exogenous application of growth factors. Using porcine and rat models the efficacy of locally delivered IGF-I and TGF-beta1 from an implant coating has been demonstrated. A thin and biomechanical stable biodegradable poly(D,L-lactide) was used to coat implants and serve as a drug carrier. Due to reports of possible foreign body reactions caused by polymer materials in orthopedic surgery, this study investigated the biocompatibility of the polylactide implant coating and the locally released growth factors during the time course of rat tibial fracture healing (days 5, 10, 15, and 28 after fracture). Monocytes/macrophages and osteoclast were detected using an monoclonal antibody against ED1 (comparable to CD68 in mice and human). The antibody ED1 stains monocytes, macrophages and osteoclast in the bone marrow and in the newly formed fracture callus. A moderate density of the monocytes/macrophages was seen in the proximal part of the medullary canal, but almost no cells were detectable in the region distal to the fracture. The amount of stained cells increased during the observation time with a maximum at days 10 and 15 followed by a decrease at day 28. No differences were detectable between the investigated groups from day 5 to 15 post fracture indicating, that the used poly(D,L-lactide) or the incorporated growth factors do not evoke an elevated immunological response compared to the uncoated titanium implant at the investigated time points. A significantly higher amount of ED1 positive cells was measured 28 days after fracture in the control group compared to the groups with the coated implants. In conclusion, no indication of a foreign body reaction due to the use of the polylactide or the growth factors was found indicating a good short-term biocompatibility of this bioactive coating.

Differences in the fusion and resorption activity of human osteoclasts after stimulation with different growth factors released from a polylactide carrier

Previous in vivo studies were able to demonstrate the efficacy of locally released growth factors IGF-I, TGF-beta1, and BMP-2 from a poly(D,L-lactide) (PDLLA) implant coating on fracture healing. In vitro studies using human osteoblast-like cells showed an enhanced collagen-1 production due to growth factor application without an effect of the PDLLA on the investigated parameter. Both bone-forming osteoblasts and bone-resorbing osteoclasts are important during bone formation and fracture healing. The aim of this study was to investigate the influence of different growth factors and the polylactide coating into which they were incorporated on isolated osteoclasts. In vitro studies using human osteoclast-like cells derived from peripheral blood mononuclear cells (PBMNCs) were performed. Titanium K-wires coated with the lactide loaded with IGF-I and TGF-beta1 (alone and in combination) or BMP-2 were added to the culture in a non-contact manner and the fusion, resorption activity (pit formation assay), and TRAP 5b synthesis of the cells were analyzed. Differences in the effect of the growth factors were seen depending on the differentiation state of the cells. The fusion of the monocytes to multinuclear osteoclasts was significantly enhanced by the application of TGF-beta1 both alone and in combination with IGF-I. No effect was seen after application of IGF-I alone or BMP-2. The resorption activity of the osteoclasts analyzed on dentine chips was significantly enhanced after application of TGF-beta1 or BMP-2. These results indicate a differentiation-dependent effect of growth factors on osteoclasts. TGF-beta1 affects both the osteoclastogenesis and the activity of osteoclasts, whereas BMP-2 had an effect only on the activity of mature osteoclasts but not on the fusion of the PBMNCs.

Effects of 17beta-estradiol, tamoxifen and raloxifene on the protein and mRNA expression of interleukin-6, transforming growth factor-beta1 and insulin-like growth factor-1 in primary human osteoblast cultures

We investigated the effects of 17betaestradiol and two selective estrogen receptor modulators, tamoxifen and raloxifene, on the expression and release of constitutive and interleukin-1-stimulated interleukin (IL)-6, transforming growth factor-beta1 (TGF-beta1) and insulin-like growth factor-1 by osteoblasts in primary culture from trabecular bone of healthy post-menopausal women. After 24 h incubation with 10(-8) M concentration of these compounds, there was no decrease in: a) the constitutive or IL-1beta-induced levels of IL-6 protein released to culture medium; b) the constitutive IL-6 mRNA expression after incubation of osteoblasts with 10(-8) M 17betaestradiol or 10(-8) M tamoxifen for 1, 3, 6, 24 or 30 h. Although a decrease after 30 h of treatment with 10(-8) M, raloxifene was found in mRNA IL-6 expression, and this fact was not reflected by a decrease in the release of IL-6 protein to the culture medium after 48 h of incubation with 10(-8) M or 10(-7) M raloxifene. Tumoral growth factorTGF-betal expression was not influenced by incubation with these compounds. Gene expression of IGF-I increased following 24 or 30 h incubation with 10(-8) M 17beta-estradiol and 30 h incubation with raloxifene. Tamoxifen did not affect IGF-I expression. In conclusion, the effects of estradiol or tamoxifen on bone metabolism do not appear to be mediated through the regulation of osteoblast IL-6 release or synthesis, but raloxifene produces a decrease in mRNA IL-6 expression. The actions of estradiol, tamoxifen and raloxifene do not appear to be mediated by tumoral growth factor TGF-beta1. On the other hand, an increase in IGF-I synthesis induced by raloxifene and estradiol could mediate, in part, the effects of these compounds on bone.

IGF-I and TGF-beta 1 incorporated in a poly(d,l-lactide) implant coating maintain their activity over long-term storage—cell culture studies on primary human osteoblast-like cells

Biodegradable coating of osteosynthetic materials with poly(D,L-lactide) (PDLLA) and incorporated growth factors has been used successfully as drug carrier to stimulate fracture healing in several rat and porcine models. A cold coating technique was used to incorporate growth factors without loss of activity during the coating process. The aim of this study was to investigate the activity of incorporated insulin like growth factor-I and transforming growth factor-beta 1 (TGF-beta1) after long-time storage (5 and 14 months at -20 degrees C). Primary human osteoblast-like cells (HOB) were cultured in a non-contact manner with titanium wires coated with PDLLA and IGF-I (33 microg) and TGF-beta1 (6 microg) for 0, 5, 10 and 15 days. Osteoblast culture without wires, with titanium wires or wires with the PDLLA coating served as control ( n=3 each time point and group). Cell vitality, cell proliferation and the production of procollagen 1 were measured. No differences in cell count and vitality were accessed in the two growth factor treated groups compared to the control groups at the same time point. Independently from the storage duration, the incorporated growth factors significantly stimulated the production of osteoblast specific type I collagen (CICP) compared to the controls. The results indicate, that the growth factors stimulated osteoblast to an enhanced collagen 1 production and that the coating method meets a major requirement for clinical use of growth factor-coated implants: biological activity of the incorporated growth factors for at least 14 months.

Local delivery of growth factors from coated titanium plates increases osteotomy healing in rats

Different methods for the stabilization of long bone fractures are used in clinic. Besides the development of further stabilization devices, the use of new materials, the modification of the surfaces, and the local application of stimulating factors for enhancement of healing are from great interest. Previous studies successfully used a biodegradable poly(d,l-lactide) coating as a local drug delivery system of growth factors from intramedullary (IM) implants to enhance fracture healing. In this study, we developed a new rat model (n = 60) for plate osteosynthesis and used a plate for stabilization and as a local drug delivery system for the growth factors IGF-I and TGF-beta1. A four-hole titanium plate was used for stabilization of a 0.6-mm osteotomy gap of the femur. The space between the inner holes was coated with 50 microg IGF-I and 10 microg TGF-beta1 incorporated in the poly(d,l-lactide) coating or with the coating alone. After 42 days, biomechanical tests and histomorphological analyses were performed to investigate osteotomy healing. Radiologically small differences were detectable between the groups. The biomechanical torsional testing revealed a significantly higher maximum load of the osteotomized femura after treatment with growth factors compared to the uncoated group. In the histomorphometric analyses measuring the callus composition, a significantly higher percentage of mineralized tissue in the osteotomy callus was assessed in the growth factor treated group compared to the uncoated. In conclusion, the local application of IGF-I and TGF-beta1 from a biodegradable coating enhances the osteotomy healing as shown in the biomechanical testing and the histomorphometry. Bioactive plates could be used in clinic for fracture stabilization and for local and controlled application of growth factors to stimulate bone healing.