New bone formation by murine osteoprogenitor cells cultured on corticocancellous allograft bone

Albumin-impregnated bone granules modulate the interactions between mesenchymal stem cells and monocytes under in vitro inflammatory conditions

Bone regeneration around newly implanted biomaterials is a complex process, which in its early phases involves the interactions between Mesenchymal Stem Cells (MSCs) and immune cells. The response of these cells to the biomaterial depends both on the local microenvironment and on the characteristics of the inserted bone substitute. In this work, bone allografts impregnated with albumin are loaded with a co-culture of human MSCs and monocytes; bone granules without albumin are used for comparison. Co-cultures are contextually treated with pro-inflammatory cytokines to simulate the inflammatory milieu naturally present during the bone regeneration process. As revealed by microscopic images, albumin-impregnated bone granules promote adhesion and interactions between cells populations. Compared to control granules, albumin coating diminishes reactive species production by cells. This reduced oxidative stress may be attributable to antioxidant properties of albumin, and it is also reflected in the mitigated gene expression of mitochondrial electron transport chain complexes, where most intracellular reactive molecules are generated. MSCs-monocytes co-cultured onto albumin-impregnated bone granules additionally release higher amounts of immunomodulatory cytokines and growth factors. In summary, this work demonstrates that impregnation of bone granules with albumin positively modulates the interactions between MSCs and immune cells, consequently influencing their mutual activities and immunomodulatory functions.

Non-unions treated with bone morphogenic protein 7: introducing the quantitative measurement of human serum cytokine levels as promising tool in evaluation of adjunct non-union therapy

BACKGROUND

In this study we sought to determine if application of bone morphogenic protein 7 (BMP-7) promotes physiological bone healing of non-unions and to investigate if serum cytokine analysis may serve as a promising tool in the analysis of adjunct non-union therapy. Therefore we analyzed the influence of BMP-7 application on the serum cytokine expression patterns on patients with impaired bone healing compared to patients that showed proper bone healing.

METHODS

Our study involved analyzing blood samples from 208 patients with long bone fractures together with patients that subsequently developed non-unions. From this large pool, 15 patients with atrophic non-union were matched to 15 patients with atrophic non-union treated with local application of BMP-7 as well as normal bone healing. Changes in the cytokine expression patterns were monitored during the 1st, 2nd, 4th, 8th, 12th and 52nd week. The patients were followed both clinically and radiologically for the entire duration of the study. Serum cytokine expression levels of transforming growth factor beta (TGF-β), platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF) were analyzed and compared.

RESULTS

Serum expression of TGF-β were nearly parallel in all three groups, however serum concentrations were significantly higher in patients with proper bone healing and those treated with BMP-7 than in patients with non-unions (p < 0.05). bFGF serum concentrations increased initially in patients with proper bone healing and in those treated with BMP-7. Afterwards, values decreased; bFGF serum concentrations in the BMP-7 group were significantly higher than in the other groups (p < 0.05). PDGF serum concentration levels were nearly parallel in all groups, serum concentrations were significantly higher in patients with proper bone healing and those treated with BMP-7 than in patients with non-unions (p < 0.05).

CONCLUSION

Treatment with BMP-7 in patients with former non-unions led to similar cytokine expression patterns after treatment as those found in patients with proper bone healing. Our results suggest that treatment with BMP-7 promote healing of non-unions. Furthermore, quantitative measurement of serum cytokine expression is a promising tool for evaluating the effectiveness of additional non-union therapies such as adjunct application of growth factors.

Enhancing allograft bone healing through gene therapy

STUDY DESIGN

A review and synopsis of recent literature pertinent to allograft bone healing.

OBJECTIVE

To review the basic principles and primary issues regarding the healing of allograft bone. To review progress made in understanding the molecular mechanisms of healing, and efforts being made to manipulate these processes to enhance healing.

SUMMARY OF BACKGROUND DATA

Bone grafting with both autografts and allografts is a common reconstructive procedure. Failure to heal and catastrophic failure of seemingly healed structural grafts occur. There is currently a great deal of excitement about the potential of bone marrow-derived cells to enhance healing. Gene transfer techniques have been developed which allow the insertion of desired deoxyribonucleic acid-encoded messages into cells. Such messages can result in the production of therapeutic proteins. Gene therapy has been used to enhance the healing of allografts in a murine model.

METHODS

Literature review.

RESULTS

Autografts heal by endochondral ossification at the graft-host interface and by intramembranous bone formation over the surface of the graft. Allografts heal predominately by endochondral ossification at the graft-host interface. The living periosteum of a graft contains progenitor cells that have an important role in graft healing. The addition of bone marrow-derived cells to an allograft does not improve healing unless they are genetically modified to express bone morphogenetic protein 2. Gene therapy to induce expression of several other proteins (VEGF and RANKL, caALK2) can also result in markedly improved allograft healing.

CONCLUSION

Gene therapy techniques can create revitalized allografts in a mouse model. These revitalized grafts heal faster, more completely, more durably, and stronger than allografts.

Comparison of six bone-graft substitutes regarding to cell seeding efficiency, metabolism and growth behaviour of human mesenchymal stem cells (MSC) in vitro

INTRODUCTION

Various synthetic bone-graft substitutes are used commercially as osteoconductive scaffolds in the treatment of bone defects and fractures. The role of bone-graft substitutes is changing from osteoconductive conduits for growth to an delivery system for biologic fracture treatments. Achieving optimal bone regeneration requires biologics (e.g. MSC) and using the correct scaffold incorporated into a local environment for bone regeneration. The need for an unlimited supply with high quality bone-graft substitutes continue to find alternatives for bone replacement surgery.

MATERIALS AND METHODS

This in vitro study investigates cell seeding efficiency, metabolism, gene expression and growth behaviour of MSC sown on six commercially clinical available bone-graft substitutes in order to define their biological properties: synthetic silicate-substituted porous hydroxyapatite (Actifuse ABX), synthetic alpha-TCP (Biobase), synthetic beta-TCP (Vitoss), synthetic beta-TCP (Chronos), processed human cancellous allograft (Tutoplast) and processed bovines hydroxyapatite ceramic (Cerabone). 250,000 MSC derived from human bone marrow (n=4) were seeded onto the scaffolds, respectively. On days 2, 6 and 10 the adherence of MSC (fluorescence microscopy) and cellular activity (MTT assay) were analysed. Osteogenic gene expression (cbfa-1) was analysed by RT-PCR and scanning electron microscopy was performed.

RESULTS

The highest number of adhering cells was found on Tutoplast (e.g. day 6: 110.0+/-24.0 cells/microscopic field; p<0.05) followed by Chronos (47.5+/-19.5, p<0.05), Actifuse ABX (19.1+/-4.4), Biobase (15.7+/-9.9), Vitoss (8.8+/-8.7) and Cerabone (8.1+/-2.2). MSC seeded onto Tutoplast showed highest metabolic activity and gene expression of cbfa-1. These data are confirmed by scanning electron microscopy. The cell shapes varied from round-shaped cells to wide spread cells and cell clusters, depending on the bone-graft substitutes. Processed human cancellous allograft is a well-structured and biocompatible scaffold for ingrowing MSC in vitro. Of all other synthetical scaffolds, beta-tricalcium phosphate (Chronos) have shown the best growth behaviour for MSC.

DISCUSSION

Our results indicate that various bone-graft substitutes influence cell seeding efficiency, metabolic activity and growth behaviour of MSC in different manners. We detected a high variety of cellular integration of MSC in vitro, which may be important for bony integration in the clinical setting.

Controlled release of growth factors on allograft bone in vitro

Allografts are important alternatives to autografts for treating defects after major bone loss. Bone growth factors have both local autocrine and paracrine effects and regulate the growth, proliferation, and differentiation of osteoprogenitor cells. To study the effects of prolonged, continuous, local delivery of growth factors on bone growth, we developed a new microelectromechanical system (MEMS) drug delivery device. Bone marrow cells from mice were seeded on mouse allograft discs and cultured in osteogenic media with osteogenic protein 1 (OP-1) and/or basic fibroblast growth factor (FGF-2) delivered from MEMS devices for 6 weeks. We monitored bone formation by changes of bone volume using micro-CT scanning and release of osteocalcin using ELISA. The data suggest the MEMS devices delivered constant concentrations of OP-1 and FGF-2 to the media. Bone marrow cells grew on the allografts and increased bone volume. Addition of OP-1 increased bone formation whereas FGF-2 decreased bone formation. Local delivery of growth factors over a prolonged period modulated the differentiation of osteoprogenitor cells on allograft bone.