Increased lengthening rate decreases expression of fibroblast growth factor 2, platelet-derived growth factor, vascular endothelial growth factor, and CD31 in a rat model of distraction osteogenesis

Fabrication of chitosan/PVP/dihydroquercetin nanocomposite film for in vitro and in vivo evaluation of wound healing

The high cost of wound healing treatment, the slow recovery of wounds, and the uncertainty of being affected by the body's physiological activities constitute a serious burden on public health. In this work, we report the preparation and characterization of chitosan (CS), PVP, and dihydroquercetin (DHQ) nanofiber film used as wound excipients, as well as in vivo and in vitro evaluations, and verify that the film is effective in wounds. The results show that the prepared film has good morphology, thermal stability and hydrophilicity. In vitro studies have shown that it has antibacterial activity against S.aureus and E.coli, and the DPPH free radical scavenging rate proves that the fiber film has antioxidant activity. MTT cytotoxicity test proved that the film is non-toxic to Hacat cells. Animal experiments have proved that wounds treated with CS-PVP-DHQ nanofiber film heal faster. This article also studied the composite nanofiber film by inducing autophagy pathway and increasing the expression of pan-keratin, vascular endothelial growth factor VEGF and CD31 to promote wound healing. Therefore, the nanofiber film herein show great potential in wound healing applications.

Cranial Bone Transport Promotes Angiogenesis, Neurogenesis, and Modulates Meningeal Lymphatic Function in Middle Cerebral Artery Occlusion Rats

BACKGROUND

Ischemic stroke is a leading cause of death and disability worldwide. However, the time window for quickly dissolving clots and restoring cerebral blood flow, using tissue plasminogen activator treatment is rather limited, resulting in many patients experiencing long-term functional impairments if not death. This study aims to determine the roles of cranial bone transport (CBT), a novel, effective, and simple surgical technique, in the recovery of ischemic stroke using middle cerebral artery occlusion (MCAO) rat model.

METHODS

CBT was performed by slowly sliding a bone segment in skull with a special frame and a speed of 0.25 mm/12 hours for 10 days following MCAO. Morris water maze, rotarod test, and catwalk gait analysis were used to study the neurological behaviors, and infarct area and cerebral flow were evaluated during CBT process. Immunofluorescence staining of CD31 and Nestin/Sox2 (sex determining region Y box 2) was performed to study the angiogenesis and neurogenesis. OVA-A647 (ovalbumin-Alexa Fluor 647) was intracisterna magna injected to evaluate the meningeal lymphatic drainage function.

RESULTS

CBT treatment has significantly reduced the ischemic lesions areas and improved the neurological deficits in MCAO rats compared with the rats in the control groups. CBT treatment significantly promoted angiogenesis and neurogenesis in the brain of MCAO rats. The drainage function of meningeal lymphatic vessels in MCAO rats was significantly impaired compared with normal rats. Ablation of meningeal lymphatic drainage led to increased neuroinflammation and aggravated neurological deficits and ischemic injury in MCAO rats. CBT treatment significantly improved the meningeal lymphatic drainage function and alleviated T-cell infiltration in MCAO rats.

CONCLUSIONS

This study provided evidence for the possible mechanisms on how CBT attenuates ischemic stroke injury and facilitates rapid neuronal function recovery, suggesting that CBT may be an alternative treatment strategy for managing ischemic stroke.

Enhancing the Efficiency of Distraction Osteogenesis through Rate-Varying Distraction: A Computational Study

Distraction osteogenesis (DO) is a mechanobiological process of producing new bone and overlying soft tissues through the gradual and controlled distraction of surgically separated bone segments. The process of bone regeneration during DO is largely affected by distraction parameters. In the present study, a distraction strategy with varying distraction rates (i.e., "rate-varying distraction") is proposed, with the aim of shortening the distraction time and improving the efficiency of DO. We hypothesized that faster and better healing can be achieved with rate-varying distractions, as compared with constant-rate distractions. A computational model incorporating the viscoelastic behaviors of the callus tissues and the mechano-regulatory tissue differentiation laws was developed and validated to predict the bone regeneration process during DO. The effect of rate-varying distraction on the healing outcomes (bony bridging time and bone formation) was examined. Compared to the constant low-rate distraction, a low-to-high rate-varying distraction provided a favorable mechanical environment for angiogenesis and bone tissue differentiation, throughout the distraction and consolidation phase, leading to an improved healing outcome with a shortened healing time. These results suggest that a rate-varying clinical strategy could reduce the overall treatment time of DO and decrease the risk of complications related to the external fixator.

An Efficient and Reproducible Protocol for Distraction Osteogenesis in a Rat Model Leading to a Functional Regenerated Femur

This protocol describes the use of a newly developed external fixator for distraction osteogenesis in a rat femoral model. Distraction osteogenesis (DO) is a surgical technique leading to bone regeneration after an osteotomy. The osteotomized extremities are moved away from each other by gradual distraction to reach the desired elongation. This procedure is widely used in humans for lower and upper limb lengthening, treatment after a bone nonunion, or the regeneration of a bone defect following surgery for bone tumor excision, as well as in maxillofacial reconstruction. Only a few studies clearly demonstrate the efficiency of their protocol in obtaining a functional regenerated bone, i.e., bone that will support physiological weight-bearing without fracture after removal of the external fixator. Moreover, protocols for DO vary and reproducibility is limited by lack of information, making comparison between studies difficult. The aim of this study was to develop a reproducible protocol comprising an appropriate external fixator design for rat limb lengthening, with a detailed surgical technique that permits physiological weight-bearing by the animal after removal of the external fixator.

The Effect of Bone Marrow Mesenchymal Stem Cells Application on Distracted Bone Quality during Rapid Rate of Distraction Osteogenesis

Distraction osteogenesis (DO) bone regenerate usually suffers from an inferior quality especially with rapid rate. This study was conducted to investigate the effect of mesenchymal stem cells (MSCs) application on different rates of distraction bone quality. Twenty-four goats were divided into group A with standard DO and group B with rapid distraction osteogenesis (RDO) both aided by MSCs. Group C with standard DO and group (D) with RDO were controls. Kruskal-Wallis test and Conover's post hoc analysis was used to evaluate significance ( p  = 0.05). Histomorphometry showed a strongly significant (SS) increase ( p  = 0.00036) in trabecular bone (TB) in group A (TB = 174.7 µm, SD = 33.5) and group B (TB = 166.8 µm, SD = 14) compared with group C (TB = 115.4 µm, SD = 19.6) and group D (TB = 86.1 µm, SD = 9.3). There was SS decrease ( p  = 0.00093) in osteoid percentage (OP) in group A (OP = 13.4%, SD = 2) and group B (OP = 11.5%, SD = 6.5) compared with group C (OP = 27.3, SD = 3.5) and group D (OP = 26.2%, SD = 2.6). Energy dispersive X-ray showed a nonsignificant increase ( p  = 0.11) in calcification (Ca ²⁺ %) in group A (Ca ²⁺ % = 17.6%, SD = 4.9) and group B (Ca ²⁺ % = 17.6%, SD = 4.3) compared with group C (Ca ²⁺ % = 14.2%, SD = 6.7) and group D (Ca ²⁺ % = 11.5%, SD = 2.4). MSCs application improved microscopic bone quality during standard DO and RDO. However, macroscopic bone quality improvement still needs further investigation.

Low intensity pulsed ultrasound in the treatment of long bone nonunions: Evaluation of cytokine expression as a tool for objectifying nonunion therapy

BACKGROUND

Nonunion is one of the most common complications in bone healing. After several clinical studies, the effect of low intensity pulsed ultrasound (LIPUS) in the treatment of nonunions remains unclear because of the difficulty in evaluating its effect on bone healing. In former studies, the analysis of serum cytokine expression patterns over time has proven to be an objective method for showing the bone healing process and evaluating nonunion therapies. This study evaluates LIPUS as a treatment option for patients with nonunions based on the analysis of serum cytokine expression.

METHODS

In this prospective, single institution study, venous blood samples from 23 patients were taken from October 2012 to October 2013 before starting LIPUS therapy and at the end of week 1 and 2 and after 1, 2, and 3 months. Patients attended clinical and radiological follow-up examinations at the same intervals. After treating all patients according to the LIPUS therapy protocol, we divided them into two groups: Group 1 consisted of patients with healing at the nonunion site, and Group 2 consisted of patients with failed nonunion therapy. We measured transforming growth factor-β1 (TGF-β1), platelet-derived growth factor (PDGF), and basic fibroblastic growth factor (bFGF) at all time-points.

RESULTS

The TGF-β1 serum concentration increased from the pre-treatment value to 1 week within the unsuccessful group. Otherwise, no significant differences between groups in measured cytokines during LIPUS therapy could be detected.

CONCLUSION

Our findings suggest that LIPUS does not lead to a significant increase in cytokine levels in patients with nonunions. It is likely that "successful" treatment can be attributed to spontaneous healing. Our results suggest that LIPUS is not a proper treatment for long bone nonunions.

Selection of animal models for pre-clinical strategies in evaluating the fracture healing, bone graft substitutes and bone tissue regeneration and engineering

In vitro assays can be useful in determining biological mechanism and optimizing scaffold parameters, however translation of the in vitro results to clinics is generally hard. Animal experimentation is a better approximation than in vitro tests, and usage of animal models is often essential in extrapolating the experimental results and translating the information in a human clinical setting. In addition, usage of animal models to study fracture healing is useful to answer questions related to the most effective method to treat humans. There are several factors that should be considered when selecting an animal model. These include availability of the animal, cost, ease of handling and care, size of the animal, acceptability to society, resistance to surgery, infection and disease, biological properties analogous to humans, bone structure and composition, as well as bone modeling and remodeling characteristics. Animal experiments on bone healing have been conducted on small and large animals, including mice, rats, rabbits, dogs, pigs, goats and sheep. This review also describes the molecular events during various steps of fracture healing and explains different means of fracture healing evaluation including biomechanical, histopathological and radiological assessments.

Gene expression of osteogenic factors following gene therapy in mandibular lengthening

This study investigated the effect of gene therapy on the expression of osteogenic mediators in mandibular distraction osteogenesis rabbits. Bilateral mandibular osteotomies were performed in 45 New-Zealand rabbits. After a latency of 3 days, the mandibles were elongated using distractors with a rate of 0.8 mm/d for 7 days. After the completion of distraction, the rabbits were randomly divided into 5 groups: 2 μg (0.1 μg/μL) of recombinant plasmid pIRES-hVEGF165-hBMP-2, recombinant plasmid pIRES-hBMP2, recombinant plasmid pIRES-hVEGF165, pIRES, and the same volume of normal saline were injected into the distraction gap of groups A, B, C, D, and E, respectively, followed by electroporation. Three animals were killed at the 7th, 14th, and 28th day after gene transfected in different groups, respectively. The lengthened mandibles were harvested and processed for immunohistochemical examinations; the mean optic densities (MODs) and integral optical density of bone morphogenetic protein (BMP-2) and transforming growth factor β1 (TGF-β1)-positive cells were measured by CMIAS-2001A computerized image analyzer. The data were analyzed with SPSS (SPSS Inc, Chicago, IL). Bone morphogenetic protein 2 and TGF-β1 staining was mainly located in inflammatory cells, monocytes, fibroblasts, osteoblasts, osteocytes, and chondrocytes in the distraction zones. Their strongest expression reached to the peak at the seventh day and decreased at the 14th day of consolidation stage; at the 28th day, they expressed weakly. Image analysis results show that, at the seventh day, the expression of BMP-2 in group B (0.26 ± 0.03, 0.36 ± 0.02) was the strongest; there was significant difference among them (P < 0.01), whereas the expression of TGF-β1 in group C (0.38 ± 0.06, 1.05 ± 0.19) is strongest followed by group A (0.34 ± 0.05, 0.95 ± 0.16) and B (0.33 ± 0.07, 0.90 ± 0.19). At every time point, the level of expression of BMP-2 and TGF-β1 in gene therapy groups (groups A, B, and C) was remarkably higher than those in non-gene therapy groups(groups D and E). There were significant differences between gene therapy groups and non-gene therapy groups (P < 0.05 or P < 0.001). These results indicated that local gene transfection can up-regulate the expression of osteogenic mediators (BMP-2 and TGF-β1), which may promote cell differentiation and proliferation and stimulate extracellular matrix synthesis and new bone formation in distraction gap.

The effect of altering the mechanical loading environment on the expression of bone regenerating molecules in cases of distraction osteogenesis

Distraction osteogenesis (DO) is a surgical technique where gradual and controlled separation of two bony fragments following an osteotomy leads to the induction of new bone formation in the distracted gap. DO is used for limb lengthening, correction of bony deformities, and the replacement of bone loss secondary to infection, trauma, and tumors. Although DO gives satisfactory results in most cases, one major drawback of this technique is the prolonged period of time the external fixator has to be kept on until the newly formed bone consolidates thus leading to numerous complications. Numerous attempts at accelerating bone formation during DO have been reported. One specific approach is manipulation of the mechanical environment during DO by applying changes in the standard protocol of distraction. Attempts at changing this mechanical environment led to mixed results. Increasing the rate or applying acute distraction, led to poor bone formation in the distracted zone. On the other hand, the addition of compressive forces (such as weight bearing, alternating distraction with compression or by over-lengthening, and then shortening) has been reported to increase bone formation. It still remains unclear why these alterations may lead to changes in bone formation. While the cellular and molecular changes occurring during the standard DO protocol, specifically increased expression of transforming growth factor-β1, platelet-derived growth factor, insulin-like growth factor, basic fibroblast growth factor, vascular endothelial growth factor, and bone morphogenic proteins have been extensively investigated, the literature is sparse on the changes occurring when this protocol is altered. It is the purpose of this article to review the pertinent literature on the changes in the expression of various proteins and molecules as a result of changes in the mechanical loading technique in DO and try to define potential future research directions.

Expression of MMP-1 and TIMP-1 in irradiated mandibles during distraction osteogenesis

OBJECTIVES

The study aimed to evaluate the expression of MMP-1 and TIMP-1 in irradiated mandibles during distraction osteogenesis.

STUDY DESIGN

Rabbits in the experimental group received preoperative radiation of 9 Gy for 5 fractions. After 1 month, all rabbits underwent osteotomy and distraction osteogenesis with 7 days of latency. Three rabbits in the control and experimental groups were killed at days 7, 12, 18, and 25. Specimens were subjected to immunohistochemical examination and real-time polymerase chain reaction analysis.

RESULTS

At day 7, expression of MMP-1 and TIMP-1 was significantly suppressed in the radiotherapy group in contrast to the control group. At day 12, expression of MMP-1 was significantly higher in the control group. At day 18, expression of MMP-1 and TIMP-1 was significantly higher in the control than in the radiotherapy group.

CONCLUSIONS

Radiotherapy changes the expression pattern of MMP-1 and TIMP-1.

Responses of distraction regenerate to high-frequency traction at a rapid rate

BACKGROUND

Continuous traction is capable of creating an optimal biological environment for bone healing which may finally compensate for the rapid distraction rate in distraction osteogenesis. This study was designed to investigate the response of distraction callus to continuous distraction at a rapid rate using a rabbit model of mandibular lengthening.

METHODS

Thirty adult New Zealand white rabbits were randomly assigned to the intermittent (1 step/d) or continuous distraction (8 steps/s) group, with 15 in each. After osteotomy, manual-driven or autodriven distractor was adapted accordingly. The distraction was activated at a rate of 3.0 mm/d for 4 days. Five rabbits in each group were killed at week 2, week 4, and week 12 of consolidation, respectively. Plain radiography, microcomputed tomography, and histology examinations were used to evaluate the bone regeneration status.

RESULTS

Plain radiographs and histologic studies demonstrated more advanced bone healing in continuous distraction group than that in intermittent distraction group at all the examined time points. Quantitative microcomputed tomography analysis showed significantly higher bone volume in continuous distraction group at week 2 (p < 0.01) and week 4 (p < 0.05) of consolidation.

CONCLUSIONS

Continuous traction by autodriven distractor could be a promising clinical alternative to shorten the treatment course of distraction osteogenesis. Further studies to test its clinical potential using large animals that have similar metabolic rate and muscular resistance with human being are necessary.

Comparison of gene expression of tissue inhibitor of matrix metalloproteinase-1 between continuous and intermittent distraction osteogenesis: a quantitative study on rabbits

BACKGROUND

Distraction osteogenesis is a controlled surgical procedure that initiates a regenerative process and uses mechanical strain to enhance the biological responses of the injured tissues to create new bone. To explore the effect of high-frequency mechanical traction on the expression of tissue inhibitor of matrix metalloproteinase-1 (TIMP-1), we compared the gene expression of TIMP-1 between continuous and intermittent distraction osteogenesis using a rabbit model of mandibular lengthening.

MATERIALS AND METHODS

Forty adult New Zealand white rabbits were randomly assigned to the intermittent and continuous distraction groups. A unilateral mandibular osteotomy was performed and a custom-designed manual-driven or auto-driven distractor was bridged over the osteotomy segments. Animals were sacrificed at day-6, day-10, day-14 and day-21 after osteotomy. Samples were examined with real-time polymerase chain reaction (PCR).

RESULTS

Real-time PCR examination showed significantly higher mRNA levels of TIMP-1 under continuous distraction than that under intermittent distraction at day-6 and day-10. No significant differences were found at day-14 and day-21.

CONCLUSION

High-frequency traction provides a good mechanical environment for accelerating bone formation by up-regulating TIMP-1.

Effect of intermittent administration of adiponectin on bone regeneration following mandibular osteodistraction in rabbits

Adiponectin, a protein hormone produced and secreted exclusively by adipocytes, was reported to increase bone mass and stimulate angiogenesis. However, the effect of adiponectin on bone regeneration following distraction osteogenesis has not yet been reported. In this study, rapid unilateral mandibular osteodistraction (distraction rate = 2 mm/day) was applied in 24 New Zealand white rabbits. The animals were then randomly divided into groups A and B (n=12 for each group). At the 1st, 3rd, and 5th day of the distraction, 200 µl PBS and 200 µl PBS contained 2 µg rh-adiponectin was intermittently injected into the distraction gap in groups A and B, respectively. At 6 weeks after the end of distraction, the rabbits were sacrificed, and the distracted mandibles were harvested and processed for radiography, dual energy X-ray absorptiometry (DXA), micro-CT, histology, and three-point bend testing. Under a rapid distraction, immature bone formation was seen in the distracted callus from group A. However, much greater bone formation and higher bone mineral density (BMD) and bone mineral content (BMC) of the distracted callus were observed in group B. Such finding was confirmed by histological, micro-CT examinations, and mechanical strength test. The results of this study suggest that intermittent administration of adiponectin can promote bone regeneration following rapid mandibular osteodistraction in rabbits.

NELL1 promotes high-quality bone regeneration in rat femoral distraction osteogenesis model

NELL1 (NEL-like molecule-1; NEL [a protein strongly expressed in neural tissue encoding epidermal growth factor like domain]) is a cranisynostosis-associated molecule directly regulated by Runx2, the master molecule in controlling osteoblastic differentiation. NELL1 has exhibited potent osteoinductive activity for bone regeneration in several animal models. However, its capacity for promoting repair of long-bone defects remains unknown. In this study, we investigated the osteogenic effects of NELL1 on femoral distraction osteogenesis using adenoviral gene delivery and multiple approaches of in vivo analysis. Thirty Sprague-Dawley (SD) rats were randomly assigned to 3 groups for treatment (n=10 each): adenovirus-green fluorescent protein (Ad-GFP)-NELL1 or Ad-GFP at 1×10⁹ plaque-forming units/ml diluted in saline, or saline alone. The femoral distraction was at a speed of 0.25 mm every 12h for 14 days, and a single injection of Ad-GFP-NELL1 or Ad-GFP was given at the mid-distraction period. The effective NELL1 delivery in vivo after Ad-GFP-NELL1 injection was evaluated by optical imaging. The bone regeneration was assessed quantitatively at days 21, 28, 42, and 56 by live 3-D micro-computed tomography (micro-CT), and animals were sacrificed at day 56 for biomechanical testing and histological analysis. Exogenous NELL1 was expressed in the distracted gap for at least 14 days after Ad-GFP-NELL1 transfection. The bone union rate in the distracted gap was significantly higher with Ad-GFP-NELL1 than with Ad-GFP (9/9 vs. 4/9 rats) or saline alone (5/9 rats) at day 56. The serial 3-D micro-CT images and quantitation obtained with the development and application of radiolucent external fixators showed less callus but more mature cortical bones formed with Ad-GFP-NELL1 than with Ad-GFP transfection and saline administration during distraction osteogenesis. The biomechanical properties of femur samples with Ad-GFP-NELL1 transfection were better than samples with Ad-GFP transfection or saline treatment, and were similar with unoperated femurs. Histology revealed cartilaginous tissues in the middle of distraction gaps with Ad-GFP transfection and saline treatment but only bony bridges with Ad-GFP-NELL1 transfection at the final time point (day 56). Coincidently, the expression of Runx2, BMP2, and BMP7 did not differ among groups at day 56, whereas the expression of osteocalcin and osteopontin was slightly higher with Ad-GFP-NELL1 transfection. Thus, sustained Ad-NELL1 protein delivery into a local area of a rat femoral distraction osteogenesis model remarkably improved regeneration of good-quality bones and accelerated bone union at a high rate. Acquiring serial micro-CT data during rat femoral distraction osteogenesis and regional adenovirus delivery of NELL1 may facilitate future in vivo studies.

Insufficient bone regenerate after intramedullary femoral lengthening: risk factors and classification system

BACKGROUND

Control of distraction rate with an intramedullary skeletal kinetic distractor (ISKD) may be problematic and a high distraction rate may result in insufficient bone regenerate.

QUESTIONS/PURPOSES

Are distraction problems preventable when using the ISKD, and what are the risk factors for and radiologic types of insufficient bone regenerate during ISKD lengthening?

PATIENTS AND METHODS

We analyzed 37 consecutive ISKD femoral lengthening procedures in 35 patients with a mean age 33 ± 11 years and minimum followup of 12 months (average, 27 ± 9 months; range, 12-55 months). The average length gain was 42.8 ± 12.9 mm.

RESULTS

Eight patients had problems during distraction: seven had "runaway nails" and one had a nondistracting nail. Insufficient bone regenerate developed in eight patients. Important risk factors were a distraction rate greater than 1.5 mm/day (9.1 times higher risk), age 30 years or older, smoking, and lengthening greater than 4 cm. Less important risk factors identified were creation of the osteotomy at the site of previous trauma or surgery and acute correction of associated deformities. We proposed a radiologic classification for failure of bone regeneration: partial regenerate failure (Type I) or complete failure resulting in a segmental defect subdivided according to a length of 3 cm or less (Type IIa) or greater than 3 cm (Type IIb).

CONCLUSIONS

Distraction problems with the ISKD were related mostly to internal malfunction of the lengthening mechanism. A distraction rate greater than 1.5 mm/day should be avoided in femoral intramedullary lengthening. Smoking should be a contraindication for femoral lengthening.

LEVEL OF EVIDENCE

Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.

Comparison of gene expression of osteogenic factors between continuous and intermittent distraction osteogenesis in rabbit mandibular lengthening

OBJECTIVES

This study aimed to evaluate the effect of distraction frequency on the gene expression of osteogenic mediators in mandibular distraction osteogenesis.

STUDY DESIGN

Forty adult New Zealand white rabbits were randomly assigned to the continuous and intermittent distraction groups. Unilateral mandibular osteotomy was performed and custom-designed manual-driven or autodriven distractor was bridged over the osteotomy segments. Animals were humanely killed at day 6, day 10, day 14, and day 21 after osteotomy. mRNA expression of the osteogenic mediators in the distraction regenerate was examined by real-time polymerase chain reaction.

RESULTS

The expression of transforming growth factor-beta(1) was significantly higher at day 6, and the expression of the bone morphogenetic protein-2 was significantly higher from day 6 to day 14, in the continuous distraction group.

CONCLUSION

High-frequency traction up-regulates the expression of osteogenic mediators contributing to the enhanced bone formation.