Temporal expression of proteoglycans in the rat limb during bone healing

The role of chondroitin sulfate to bone healing indicators and compressive strength

OBJECTIVES

The function of bone is to protect the vital organs of the body. Mechanical strength, especially compressive strength, plays an important role in fulfilling its function. Fracture healing depends on several substances, such as collagen, glucosaminoglycane and proteoglycan. Chondroitin sulfate as part of proteoglycane is an important component in the formation of callus in fracture healing. The aim of this study is to prove chondroitin sulfate role in supporting fracture healing.

METHODS

The in vivo experiment has been performed to Rattus novergicus which met the inclusion criteria (age 3 months, 200-300 g weight), 18 males of R. norvegicus, Wistar strain, were divided into three equal groups of six rats each. After being anesthetized, fracturation was performed in a sterile manner to get simple fracture. The area of dissection is in half length of tibial bone and the fracture incision is about 1 cm. Then it followed by immobilization of the lower leg bone on one side with a cast. The first group was given chondroitin sulfate 7 mg in 2 mL distilled water/200 g weight for 2 weeks. The second group was given chondroitin sulfate 7 mg in 2 mL distilled water/200 g weight for 4 weeks. The third group was given distilled water. This research was focused on treatment of cartilage. The callus position is in half length of tibial bone.

RESULTS

There were significant differences in the increase of TGF-β, the number of osteoblasts and callus compressive strength in the groups with chondroitin sulfate treatment for 2 and 4 weeks, compared to the control group (p<0.01).

CONCLUSIONS

Administering chondroitin sulfate in a dose of 7 mg in 2 mL distilled water for 2 and 4 weeks may increase production of TGF-β, the osteoblast numbers and the callus compressive strength in fracture healing.

Preventive Moderate Continuous Running-Exercise Conditioning Improves the Healing of Non-Critical Size Bone Defects in Male Wistar Rats: A Pilot Study Using µCT

Although physical exercise has unquestionable benefits on bone health, its effects on bone healing have been poorly investigated. This study evaluated the effects of preemptive moderate continuous running on the healing of non-critical sized bone defects in rats by µCT. We hypothesized that a preemptive running exercise would quicken bone healing. Twenty 5-week-old, male, Wistar rats were randomly allocated to one of the following groups (n = 10): sedentary control (SED) or continuous running (EX, 45 min/d, 5 d/week at moderate speed, for 8 consecutive weeks). A 2 mm diameter bone defect was then performed in the right tibia and femur. No exercise was performed during a 4 week-convalescence. Healing-tissue trabecular microarchitectural parameters were assessed once a week for 4 weeks using µCT and plasma bone turnover markers measured at the end of the study protocol (time point T12). At T12, bone volume fraction (BV/TV; BV: bone volume, TV: tissue volume) of the healing tissue in tibiae and femurs from EX rats was higher compared to that in SED rats (p = 0.001). BV/TV in EX rats was also higher in tibiae than in femurs (p < 0.01). The bone mineral density of the healing tissue in femurs from EX rats was higher compared to that in femurs from SED rats (p < 0.03). N-terminal telopeptide of collagen type I in EX rats was decreased compared to SED rats (p < 0.05), while no differences were observed for alkaline phosphatase and parathyroid hormone. The study provides evidence that preemptive moderate continuous running improves the healing of non-critical sized bone defects in male Wistar rats.

A biomimetic collagen-bone granule-heparan sulfate combination scaffold for BMP2 delivery

Bone morphogenetic protein 2 (BMP2)-induced bone regeneration is most efficacious when a carrier can deliver the growth factor into the defect site while minimizing off-target effects. The control of BMP2 release by such carriers is proving one of the most critical aspects of BMP2 therapy. Thus, increasing numbers of biomaterials are being developed to satisfy the simultaneous need for sustained release, reduced rates of degradation and enhanced activity of the growth factor. Here we report on a biomimetic scaffold consisting of bovine collagen type I, bone granules (Intergraft™), and heparan sulfate with increased affinity for BMP2 (HS3). The HS3 and collagen were complexed and then crosslinked via a simple dehydrothermal method. When loaded with a clinically relevant amount of BMP2 (1.25 mg/cc), the HS3-functionalised scaffolds were able to retain up to 58% of the initial amount of BMP2 over 27 days, approximately 3-fold higher than scaffolds without HS3. The bioactivity of the retained BMP2 was confirmed by gene expression in myoblast cells (C2C12) cultured on the scaffolds under osteogenic stimulation. Together these data demonstrate the efficacy of HS3 as a material to improve the performance collagen/bone granule-based scaffolds.

New insights into ToF-SIMS imaging in osteoporotic bone research

The present work focuses on the application of time-of-flight secondary ion mass spectrometry (ToF-SIMS) in osteoporotic bone research. In order to demonstrate the benefit, the authors present concrete application examples of ToF-SIMS in three different areas of bone research. ToF-SIMS as a mass spectrometric imaging technique allows simultaneous visualization of mineralized and nonmineralized bone tissue as well as implanted biomaterials and bone implant interphases. In the first example, the authors show that it is possible to study the incorporation and distribution of different components released from bone filler materials into bone with a single mass spectrometric measurement. This not only enables imaging of nonstained bone cross sections but also provides further insights beyond histologically obtained information. Furthermore, they successfully identified several mass fragments as markers for newly formed cartilage tissue and growth joint in bone. Different modes of ToF-SIMS as well as different SIMS instruments (IONTOF's TOF.SIMS 5 and M6 Hybrid SIMS, Ionoptika's J105) were used to identify these mass signals and highlight the high versatility of this method. In the third part, bone structure of cortical rat bone was investigated from bone sections embedded in technovit (polymethyl methacrylate, PMMA) and compared to cryosections. In cortical bone, they were able to image different morphological features, e.g., concentric arrangement of collagen fibers in so-called osteons as well as Haversian canals and osteocytes. In summary, the study provides examples of application and shows the strength of ToF-SIMS as a promising analytical method in the field of osteoporotic bone research.

Scalable MSC-derived bone tissue modules: In vitro assessment of differentiation, matrix deposition, and compressive load bearing

Enhancements to the mechanical properties of modular designs for bone tissue engineering could increase their clinical applications. In this study, bone marrow mesenchymal stem cells (MSCs) and hydroxyapatite (HAP) microgranules were encapsulated in polyelectrolyte complex membranes composed of chondroitin 4-sulfate (C4S), carboxymethyl cellulose (CMC) and chitosan. Microcapsules were formed with and without HAP microgranules, and cultured in either osteoinduction medium (Osteo) or expansion medium (Exp) to produce four microcapsule conditions: Osteo, Osteo+HAP, Exp, and Exp+HAP. Microcapsules facilitated alkaline phosphatase secretion and deposition of bone specific proteins (osteocalcin and osteopontin) by encapsulated MSCs over 28 days of osteogenic culture. SEM and micro-CT analysis showed cell-deposited mineral covering the surfaces of the HAP microgranules and interior of the microcapsule membrane. The mineralized microcapsules could be combined and fused into cylindrical constructs (4 × 5 mm, W × H), and uniaxial compression tests confirmed that microcapsule mineralization greatly enhanced the yield stresses of Osteo and Osteo+HAP fused constructs (10.4 ± 4.4 MPa and 6.4 ± 2.8 MPa), compared to only HAP microgranules (Exp+HAP, 0.5 ± 0.3 MPa). The C4S/CMC/Chitosan microcapsules provide a platform allowing pre-mineralization of microcapsules in vitro for later assembly of larger load-bearing constructs, or for use as an injectable bone regeneration strategy. STATEMENT OF SIGNIFICANCE: Clinical translation of bone tissue engineering is limited by the difficulty of generating space filling implants that both resist compressive loading, and simultaneously deliver cells throughout the bone defect. Here, we present the design of a microcapsule system containing both stem cells capable of rebuilding bone tissue, and a mechanically tough bone-like mineral, that imparts compression resistance to the microcapsules. The microcapsules support stem cell differentiation to an osteogenic phenotype, that can mineralize the microcapsule membrane and interior. The mineralized microcapsules can be assembled into larger bone constructs, and have mechanical properties on par with trabecular bone.

Tissue Morphology and Antigenicity in Mouse and Rat Tibia: Comparing 12 Different Decalcification Conditions

Conventional bone decalcification is a time-consuming process and is therefore unsuitable for clinical applications and time-limited research projects. Consequently, we compared the effect of four different decalcification solutions applied at three different temperatures, and assessed the rate of decalcification and the implications on tissue morphology and antigenicity of mouse and rat tibiae. Bones were decalcified with 10% ethylenediaminetetraacetic acid (EDTA), 10% formic acid, 5% hydrochloric acid, and 5% nitric acid at 4C, 25C, and 37C. Decalcification in both species was fastest in nitric acid at 37C and slowest in EDTA at 4C. Histological and immunohistochemical staining confirmed that the conventional protocols of EDTA at 4C and 25C remain the best option regarding the quality of tissue preservation. Whereas formic acid at 4C is a good alternative saving about 90% of the decalcification time, hydrochloric and nitric acids should be avoided particularly in case of rat tibia. By contrast, due to their smaller size, mouse tibiae had shorter decalcification times and tolerated higher temperatures and exposure to acids much better. In conclusion, this study demonstrated that depending on the specific research question and sample size, alternative decalcification methods could be used to decrease the time of decalcification while maintaining histological accuracy.

A polycaprolactone-β-tricalcium phosphate-heparan sulphate device for cranioplasty

BACKGROUND

Cranioplasty is a surgical procedure used to treat a bone defect or deformity in the skull. To date, there is little consensus on the standard-of-care for graft materials used in such a procedure. Graft materials must have sufficient mechanical strength to protect the underlying brain as well as the ability to integrate and support new bone growth. Also, the ideal graft material should be individually customized to the contours of the defect to ensure a suitable aesthetic outcome for the patient.

PURPOSE

Customized 3D-printed scaffolds comprising of polycaprolactone-β-tricalcium phosphate (PCL-TCP) have been developed with mechanical properties suitable for cranioplasty. Osteostimulation of PCL-TCP was enhanced through the addition of a bone matrix-mimicking heparan sulphate glycosaminoglycan (HS3) with increased affinity for bone morphogenetic protein-2 (BMP-2). Efficacy of this PCL-TCP/HS3 combination device was assessed in a rat critical-sized calvarial defect model.

METHOD

Critical-sized defects (5 mm) were created in both parietal bones of 19 Sprague Dawley rats (Male, 450-550 g). Each cranial defect was randomly assigned to 1 of 4 treatment groups: (1) A control group consisting of PCL-TCP/Fibrin alone (n = 5); (2) PCL-TCP/Fibrin-HSft (30 μg) (n = 6) (HSft is the flow-through during HS3 isolation that has reduced affinity for BMP-2); (3) PCL-TCP/Fibrin-HS3 (5 μg) (n = 6); (4) PCL-TCP/Fibrin-HS3 (30 μg) (n = 6). Scaffold integration and bone formation was evaluated 12-weeks post implantation by μCT and histology.

RESULTS

Treatment with PCL-TCP/Fibrin alone (control) resulted in 23.7% ± 1.55% (BV/TV) of the calvarial defect being filled with new bone, a result similar to treatment with PCL-TCP/Fibrin scaffolds containing either HSft or HS3 (5 μg). At increased amounts of HS3 (30 μg), enhanced bone formation was evident (BV/TV = 38.6% ± 9.38%), a result 1.6-fold higher than control. Further assessment by 2D μCT and histology confirmed the presence of enhanced bone formation and scaffold integration with surrounding host bone only when scaffolds contained sufficient bone matrix-mimicking HS3.

CONCLUSION

Enhancing the biomimicry of devices using a heparan sulphate with increased affinity to BMP-2 can serve to improve the performance of PCL-TCP scaffolds and provides a suitable treatment for cranioplasty.

Fabrication of polycaprolactone-silanated β-tricalcium phosphate-heparan sulfate scaffolds for spinal fusion applications

BACKGROUND CONTEXT

Interbody spinal fusion relies on the use of external fixation and the placement of a fusion cage filled with graft materials (scaffolds) without regard for their mechanical performance. Stability at the fusion site is instead reliant on fixation hardware combined with a selected cage. Ideally, scaffolds placed into the cage should both support the formation of new bone and contribute to the mechanical stability at the fusion site.

PURPOSE

We recently developed a scaffold consisting of silane-modified PCL-TCP (PCL-siTCP) with mechanical properties that can withstand the higher loads generated in the spine. To ensure the scaffold more closely mimicked the bone matrix, we incorporated collagen (Col) and a heparan sulfate glycosaminoglycan sugar (HS3) with increased affinity for heparin-binding proteins such as bone morphogenetic protein-2 (BMP-2). The osteostimulatory characteristic of this novel device delivering exogenous BMP2 was assessed in vitro and in vivo as a prelude to future spinal fusion studies with this device.

STUDY DESIGN/SETTING

A combination of cell-free assays (BMP2 release), progenitor cell-based assays (BMP2 bioactivity, cell proliferation and differentiation), and rodent ectopic bone formation assays was used to assess the osteostimulatory characteristics of the PCL-siTCP-based scaffolds.

MATERIALS AND METHODS

Freshly prepared rat mesenchymal stem cells were used to determine reparative cell proliferation and differentiation on the PCL-siTCP-based scaffolds over a 28-day period in vitro. The bioactivity of BMP2 released from the scaffolds was assessed on progenitor cells over a 28-day period using ALP activity assays and release kinetics as determined by enzyme-linked immunosorbent assay. For ectopic bone formation, intramuscular placement of scaffolds into Sprague Dawley rats (female, 4 weeks old, 120-150 g) was achieved in five animals, each receiving four treatments randomized for location along the limb. The four groups tested were (1) PCL-siTCP/Col (5-mm diameter×1-mm thickness), PCL-siTCP/Col/BMP2 (5 µg), (3) PCL-siTCP/Col/HS3 (25 µg), and (4) PCL-siTCP/Col/HS3/BMP2 (25 and 5 µg, respectively). Bone formation was evaluated at 8 weeks post implantation by microcomputed tomography (µCT) and histology.

RESULTS

Progenitor cell-based assays (proliferation, mRNA transcripts, and ALP activity) confirmed that BMP2 released from PCL-siTCP/Col/HS3 scaffolds increased ALP expression and mRNA levels of the osteogenic biomarkers Runx2, Col1a2, ALP, and bone gla protein-osteocalcin compared with devices without HS3. When the PCL-siTCP/Col/HS3/BMP2 scaffolds were implanted into rat hamstring muscle, increased bone formation (as determined by two-dimensional and three-dimensional µCTs and histologic analyses) was observed compared with scaffolds lacking BMP2. More consistent increases in the amount of ectopic bone were observed for the PCL-siTCP/Col/HS3/BMP2 implants compared with PCL-siTCP/Col/BMP2. Also, increased mineralizing tissue within the pores of the scaffold was seen with modified-tetrachrome histology, a result confirmed by µCT, and a modest but detectable increase in both the number and the thickness of ectopic bone structures were observed with the PCL-siTCP/Col/HS3/BMP2 implants.

CONCLUSIONS

The combination of PCL-siTCP/Col/HS3/BMP2 thus represents a promising avenue for further development as a bone graft alternative for spinal fusion surgery.

[Research progress in osteogenesis and osteogenic mechanism of heparan sulfate]

Objective

To discuss the role of heparan sulfate (HS) in bone formation and bone remodeling and summarize the research progress in the osteogenic mechanism of HS.

Methods

The domestic and abroad related literature about HS acting on osteoblast cell line in vitro, HS and HS composite scaffold materials acting on the ani-mal bone defect models, and the effect of HS proteoglycans on bone development were summarized and analyzed.

Results

Many growth factors involved in fracture healing especially heparin-binding growth factors, such as fibroblast growth factors, bone morphogenetic protein, and transforming growth factor β, are connected noncovalently with long HS chains. HS proteoglycans protect these proteins from protease degradation and are directly involved in the regulation of growth factors signaling and bone cell function. HS can promote the differentiation of stem cells into osteoblasts and enhance the differentiation of osteoblasts. In bone matrix, HS plays a significant role in promoting the formation, maintaining the stability, and accelerating the mineralization.

Conclusion

The osteogenesis of HS is pronounced. HS is likely to become the clinical treatment measures of fracture nonunion or delayed union, and is expected to provide more choices for bone tissue engineering with identification of its long-term safety.

Alterations in mandibular morphology associated with glypican 1 and glypican 3 gene mutations

OBJECTIVES

Glypican 1 (GPC1) and glypican 3 (GPC3) are bone co-regulators that act downstream in many of the signalling pathways associated with craniosynostosis. Morphometric data from GPC-knockout mice were analysed to determine whether elimination of GPC1 and GPC3 genes would alter mandibular morphology.

SETTING AND SAMPLE POPULATION

The murine model included five male and five female mandibles in each of GPC1-knockout, GPC1/GPC3-knockout and wild-type (control) groups. Female GPC3-knockout mice had a very high rate of perinatal lethality, and therefore, only five males were included in this group.

METHODS

The mandibular morphology of GPC1-knockout (n=10), GPC3-knockout (n=5), GPC1/GPC3-knockout (n=10) and wild-type (n=10) mice was compared by analysing five landmark-based linear dimensions: anterior and posterior lengths, as well as ascending, descending and posterior heights. Measurements were recorded on three-dimensional micro-CT reconstructions.

RESULTS

GPC3-knockout mandibles were larger than wild-type mandibles for all dimensions (P<.05). Mandibular heights were more affected than lengths. A decreasing trend of mandibular dimensions across the mouse groups (GPC3-knockout>GPC1/GPC3-knockout>GPC1-knockout=wild-type) (P<.05) indicated that an increase in mandibular size was associated with increased GPC3 expression, but not GPC1.

CONCLUSIONS

Alterations in GPC3 expression are likely to mediate changes to mandibular size in craniosynostosis. These findings have potential future applications in the prevention and treatment of craniosynostosis and associated craniofacial dysmorphology.

Repair of segmental ulna defects using a β-TCP implant in combination with a heparan sulfate glycosaminoglycan variant

Given the wide spread clinical use of ceramic-based bone void fillers, we sought to determine the efficacy of an FDA-approved β-tricalcium phosphate bone graft substitute (JAX™) in combination with a carboxymethyl cellulose (CMC) handling agent that included a particular heparan glycosaminoglycan (GAG) variant, herein referred to as HS3. Having recently demonstrated efficacy of a combination collagen/HS3 device, we further aimed to determine the support that HS3 could offer a handling agent used to administer a more tissue-relevant bone void filler. This study evaluated the JAX™-HS3 combination device in 1.5 cm critical-sized defects in the ulna bones of 27 male New Zealand White rabbits. Treatment groups consisted of JAX™ applied with CMC alone, or JAX™ with CMC containing either 30 μg or 100 μg of the HS3 GAG. Data based on radiographic, μCT, mechanical, and histological analyses at 4 and 8 weeks post-surgery, clearly demonstrate enhanced new bone formation in the JAX™-HS3 combination treated defects compared to treatment with JAX™ alone. The efficacy of such a combination advocates for inclusion of HS3 in handling agents used in the preparation of various bone void fillers being used in orthopaedic surgery.

STATEMENT OF SIGNIFICANCE

Synthetic bone grafts and demineralized bone matrices are gaining prominence as alternatives to autologous and allogeneic bone grafts and are frequently administered in granular form, necessitating their combination with a handling agent. Typical handling agents include glycerol, gelatin, cellulose, hyaluronic acid and lecithin, formulated as hydrogels, which can be further enhanced by the addition of heparan sulfate (HS) glycosaminoglycans that augment the osteostimulatory properties of the graft. Here we assessed the efficacy of β-TCP granules combined with a hydrogel consisting of carboxymethyl cellulose and the HS variant (HS3) previously shown to enhance osteogenic healing. The data advocates for HS3 to be included during the formulation of hydrogel-based carriers that support the various bone void fillers being used in orthopaedic surgery.

A sulfated nanofibrous mesh supporting the osteogenic differentiation of periosteum-derived cells

The periosteum is a thin fibrous membrane covering the surface of long bone and is known to play a critical role in bone development and adult bone fracture healing. Loss or damage of the periosteum tissue during traumatic long bone injuries can lead to retarded healing of bone graft-mediated repair. The regenerative potential of periosteum-derived progenitor cells (PDCs) has inspired their use as an alternative to bone marrow-derived mesenchymal stromal cells (MSCs) to augment scaffold-assisted bone repair. In this study, we first demonstrated that PDCs isolated from adult rat long bone exhibited innate advantages over bone marrow-derived MSCs in terms of faster proliferation and more potent osteogenic differentiation upon induction in plastic-adherent culture. Further, we examined the potential of two electrospun nanofibrous meshes, an uncharged regenerated cellulose mesh and a sulfated mesh, to support the attachment and osteogenic differentiation of PDCs. We showed that both nanofibrous meshes were able to support the attachment and proliferation of PDCs and MSCs alike, with the sulfated mesh enabling significantly higher seeding efficiency than the cellulose mesh. Both meshes were also able to support the osteogenic differentiation of adherent PDCs upon induction by osteogenic media, with the sulfated mesh facilitating more potent mineral deposition by adherent PDCs. Our study supports the sulfated nanofibrous mesh as a promising synthetic periosteal membrane for the delivery of exogenous PDCs to augment bone healing.

Affinity-selected heparan sulfate for bone repair

Bone morphogenetic protein (BMP)-2 is a potent bone healing compound produced at sites of bone trauma. Here we present a therapeutic strategy to harness the activity of endogenously produced BMP-2 by delivery of an affinity-matched heparan sulfate (HS) glycos aminoglycan biomaterial that increases the bioavailability, bioactivity and half-life of this growth factor. We have developed a robust, cost effective, peptide-based affinity platform to isolate a unique BMP-2 binding HS variant from commercially available preparations of HS, so removing the manufacturing bottleneck for their translation into the clinic. This affinity-matched HS enhanced BMP-2-induced osteogenesis through improved BMP-2 kinetics and receptor modulation, prolonged pSMAD signaling and reduced interactions with its antagonist noggin. When co-delivered with a collagen implant, the HS was as potent as exogenous BMP-2 for the healing of critical-sized bone defects in rabbits. This affinity platform can be readily tuned to isolate HS variants targeted ata range of clinically-relevant growth and adhesive factors.

Effects of single and cyclical local injections of basic fibroblast growth factor on cancellous bone defects in rabbits

BACKGROUND

Local administration of basic fibroblast growth factor (bFGF) has anabolic effects on bone formation. A delivery system for local treatment is required to increase efficacy because of its short half-life. However, little is known about the effects of cyclical local injection of bFGF. We evaluated the effects of single and cyclical local injection of bFGF at a cancellous bone defect in the femoral condyle in rabbits.

METHODS

Using the "vehicle only" as a control, a single low dose (40 microg), single high dose (120 microg), or cyclical low dose (40 microg, three times) of bFGF was injected percutaneously into a bone defect implanted with a gelatin sponge. The rabbits were killed at 4 weeks after surgery and the femurs were harvested for evaluation.

RESULTS

Both single and cyclical administration of bFGF dose-dependently increased the amount of new bone formation in the bone defect using radiographs (P < 0.01) and bone mineral density (BMD) measurements (P < 0.01) compared to controls. However, only high-dose bFGF injection significantly increased the cancellous bone volume at the bone defect (P < 0.05) compared to controls, using bone histomorphometry. Cyclical injection of bFGF significantly increased the number of runt-related transcription factor-2 (Runx2)-positive cells compared to single low- and high-dose bFGF administration (P < 0.01 and P < 0.05, respectively), and single high-dose and cyclical administration significantly increased the number of osteopontin-positive cells compared to controls (P < 0.01), based on immunohistochemical analysis.

CONCLUSIONS

These results suggest that high-dose injection of bFGF, at the very early stage of cancellous bone healing, is more effective in increasing cancellous bone volume, and cyclical injection of bFGF may stimulate osteoprogenitor cells.