Surgically‑induced mouse models in the study of bone regeneration: Current models and future directions (Review)

Clinical potential of plasma-functionalized graphene oxide ultrathin sheets for bone and blood vessel regeneration: Insights from cellular and animal models

Graphene and graphene oxide (GO), due to their unique chemical and physical properties, possess biochemical characteristics that can trigger intercellular signals promoting tissue regeneration. Clinical applications of thin GO-derived sheets have inspired the development of various tissue regeneration and repair approaches. In this study, we demonstrate that ultrathin sheets of plasma-functionalized and reduced GO, with the oxygen content ranging from 3.2 % to 22 % and the nitrogen content from 0 % to 8.3 %, retain their essential mechanical and molecular integrity, and exhibit robust potential for regenerating bone tissue and blood vessels across multiple cellular and animal models. Initially, we observed the growth of blood vessels and bone tissue in vitro using these functionalized GO sheets on human adipose-derived mesenchymal stem cells and umbilical vein endothelial cells. Remarkably, our study indicates a 2.5-fold increase in mineralization and two-fold increase in tubule formation even in media lacking osteogenic and angiogenic supplements. Subsequently, we observed the initiation, conduction, and formation of bone and blood vessels in a rat tibial osteotomy model, evident from a marked 4-fold increase in the volume of low radio-opacity bone tissue and a significant elevation in connectivity density, all without the use of stem cells or growth factors. Finally, we validated these findings in a mouse critical-size calvarial defect model (33 % higher healing rate) and a rat skin lesion model (up to 2.5-fold increase in the number of blood vessels, and 35 % increase in blood vessels diameter). This study elucidates the pro-osteogenic and pro-angiogenic properties of both pristine and plasma-treated GO ultrathin films. These properties suggest their significant potential for clinical applications, and as valuable biomaterials for investigating fundamental aspects of bone and blood vessel regeneration.

The Nanotheranostic Researcher’s Guide for Use of Animal Models of Traumatic Brain Injury

Traumatic brain injury (TBI) is currently the leading cause of injury-related morbidity and mortality worldwide, with an estimated global cost of USD 400 billion annually. Both clinical and preclinical behavioral outcomes associated with TBI are heterogeneous in nature and influenced by the mechanism and frequency of injury. Previous literature has investigated this relationship through the development of animal models and behavioral tasks. However, recent advancements in these methods may provide insight into the translation of therapeutics into a clinical setting. In this review, we characterize various animal models and behavioral tasks to provide guidelines for evaluating the therapeutic efficacy of treatment options in TBI. We provide a brief review into the systems utilized in TBI classification and provide comparisons to the animal models that have been developed. In addition, we discuss the role of behavioral tasks in evaluating outcomes associated with TBI. Our goal is to provide those in the nanotheranostic field a guide for selecting an adequate TBI animal model and behavioral task for assessment of outcomes to increase research in this field.

Effect of Urolithin A on Bone Repair in Mice with Bone Defects

BACKGROUND

Bone defect difficult to manage clinically and it is a big challenge to repair it. Secondary metabolites source from herb has shown potential for the treatment of bone defect.

METHODS

Mesenchymal stem cells (MSCs) were isolated from mice and incubated with urolithin A (UA) (10, 25, and 50 µg/mL). 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay was performed to estimate apoptosis and mineralisation was evaluated by alkaline phosphatase assay and alizarin red S staining. A middle femoral defect was induced in mice and bone tissue was prepared for endochondral ossification by treating with UA. The effect of UA was estimated by determining markers of osteoblast proliferation in serum and micro-computed tomography to analyse bone defects.

RESULTS

UA enhanced mineralisation of MSCs and osteogenic gene markers in MSCs in vitro. Also, the bone defect score and bone mineral density were improved by UA. Moreover, UA ameliorated the altered Wnt3a protein and histopathological changes in bone defect mice.

CONCLUSION

Presented report conclude that UA enhances osteoblast proliferation in bone-defect mice by activating the Wnt pathway.

The effects of VEGF-centered biomimetic delivery of growth factors on bone regeneration

It is accepted that biomimetic supply of signaling molecules during bone regeneration can provide an appropriate environment for accelerated new bone formation. In this study, we developed a growth factor delivery system based on porous particles and a thermosensitive hydrogel that allowed fast, continuous, and delayed/continuous release of growth factors to mimic their biological production during bone regeneration. It was observed that the Continuous group (continuous release of growth factors) provides a better environment for the osteogenic differentiation of hPDCs than the Biomimetic group (biomimetic release of growth factors), and thus is anticipated to promote bone regeneration. However, contrary to expectation, the Biomimetic group promoted significant new bone formation compared to the Continuous group. From the systematic cell culture experiments, the initial supply of VEGF was considered to have more favorable effects on the osteoclastogenesis than osteogenesis, which may hinder bone regeneration. Our results indicated that the continuous supply of VEGF (in particular, at early stage) from VEGF-loaded biomaterial might not be conducive to new bone formation. Therefore, we suggest that a biomimetic supply of growth factors is a more pivotal parameter for sufficient tissue regeneration. Its use as a molecular delivery system may also serve as a useful tool for the investigation of biological processes and molecules during tissue regeneration processes.

The role of small leucine zipper protein in osteoclastogenesis and its involvement in bone remodeling

Bone remodeling is critical to maintain the quality of bone tissues and to heal bone tissue injury. Osteoclasts and osteoblasts are special types of cells involved in this event. In particular, the resorption activity of mature osteoclasts is required for the formation of new bones. Human small leucine zipper protein (sLZIP) is known to induce the osteoblast differentiation of mesenchymal stem cells. However, the roles of sLZIP in osteoclast differentiation and bone remodeling have not been explored. In this study, we investigated the roles of sLZIP in regulating osteoclast formation and in the bone remodeling process using sLZIP transgenic (TG) mice. Tibiae from sLZIP TG mice contained more osteoclasts than those from wild type (WT) mice. Bone marrow-derived macrophages (BMM) from sLZIP TG mice showed increased differentiation into osteoclasts compared with BMM from WT mice. sLZIP bound to the promotor and induced the expression of nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1) and its target osteoclastogenic genes. To understand the role of sLZIP in bone remodeling, a bone-defect model was generated. Results of micro-CT scanning and histologic analysis demonstrated that sLZIP TG mice have faster bone formation during healing compared with WT mice. Notably, the soft callus around the defect area was replaced faster by hard callus in sLZIP TG mice than in WT mice. These findings suggest that sLZIP promotes osteoclast differentiation and plays an important role in bone remodeling.

Characterization of a reproducible model of fracture healing in mice using an open femoral osteotomy

Purpose

The classic fracture model, described by Bonnarens and Einhorn in 1984, enlists a blunt guillotine to generate a closed fracture in a pre-stabilized rodent femur. However, in less experienced hands, this technique yields considerable variability in fracture pattern and requires highly-specialized equipment. This study describes a reproducible and low-cost model of mouse fracture healing using an open femoral osteotomy.

Methods

Femur fractures were produced in skeletally mature male and female mice using an open femoral osteotomy after intramedullary stabilization. Mice were recovered for up to 28 days prior to analysis with microradiographs, histomorphometry, a novel μCT methodology, and biomechanical torsion testing at weekly intervals.

Results

Eight mice were excluded due to complications (8/193, 4.1%), including unacceptable fracture pattern (2/193, 1.0%). Microradiographs showed progression of the fracture site to mineralized callus by 14 days and remodelling 28 days after surgery. Histomorphometry from 14 to 28 days revealed decreased cartilage area and maintained bone area. μCT analysis demonstrated a reduction in mineral surface from 14 to 28 days, stable mineral volume, decreased strut number, and increased strut thickness. Torsion testing at 21 days showed that fractured femurs had 61% of the ultimate torque, 63% of the stiffness, and similar twist to failure when compared to unfractured contralateral femurs.

Conclusions

The fracture model described herein, an open femoral osteotomy, demonstrated healing comparable to that reported using closed techniques. This simple model could be used in future research with improved reliability and reduced costs compared to the current options.

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This study characterized a simple and reproducible model of fracture healing in mice using an open femoral osteotomy.

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Analysis by x-ray, histomorphometry, µCT, and biomechanical testing demonstrated healing comparable to current models.

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This simple model could be used to increase investigation into fracture healing, delayed union, and non-union.

Acceleration of Bone Fracture Healing through the Use of Natural Bovine Hydroxyapatite Implant on Bone Defect Animal Model

Bone is an important organ for supports the body that stores reserve of calcium, phosphorus, and other minerals. In fracture conditions where bleeding, soft tissue edema, nerve damage, and blood vessels around the bone damage happen, they can cause the mobilization of these minerals in the surrounding tissue. One of the efforts made in the treatment of these fractures is reconnection, in which it works by filling of bone defect with a matrix and administration of anti-infection. Biomaterial filling in defective bone is thought to accelerate the healing process of bone fracture and prevent osteomyelitis. For this reason, this study evaluates the acceleration of bone fracture healing using natural hydroxyapatite (NHA) bone filler in rabbits with bone defect model. Fracture modeling was performed by surgical technique and drilling of bones with a 4.2 mm diameter to form a defect in the rabbit femur. Bone implant contained bovine hydroxyapatite-gelatin-glutaraldehyde (BHA implant) or bovine hydroxyapatite-gelatin-glutaraldehyde-gentamicin (BHA-GEN implant) that was inserted in bone defects. 27 rabbits were divided into 3 groups: the control group who had bone defect, the bone defect group was given BHA implant and the bone defect group was given BHA-GEN implant. Observation of osteoclast, osteoblast, osteocyte, BALP level, and bone morphological integrity was carried out on the 14th, 28th, and 42nd days after surgery. Histological observation of rabbit femur showed a significant difference on the number of osteoclast, osteoblast and osteocyte in all three groups. The BALP level also showed a significant difference in the group given the natural BHA bone implant compared to the control group on day 14 (p = 0.0361). Based on the result of the X-ray, there was also a better integration of rabbit femur bone in groups with the use of BHA or BHA-GEN bone implant. Thus, it can be concluded that the use of a natural BHA implant can accelerate the process of bone repair in the fracture of rabbit femur. In addition, BHA implants were compatible as a matrix for supporting the bone cell growth.

Quantification of the mandibular defect healing by micro-CT morphometric analysis in rats

PURPOSE

The goal of this study was the evaluation of the bone tissue structural characteristics over the time course of mandibular defect healing using micro-CT technique, as well as determination of the inter-relationships between different micro-CT parameters used for assessment of the bone regeneration process and the patterns of their dynamic changes.

MATERIALS AND METHODS

The body and ramus of the mandible was exposed in 24 Wistar rats. A 2-mm full thickness bony defect was created. Animals were randomized into four groups, which were ended 3, 6, 12 and 24 weeks after operation. The mandible was excised and underwent micro-CT analysis. For statistical evaluation, the Mann-Whitney U test, polynomial or exponential regression and Spearman analysis were applied.

RESULTS

The absolute volume of the bone regenerate increased from 1.69 ± 0.53 mm3 (3 weeks) to 3.36 mm3 ± 0.56 (6 months), as well as percentage of bone volume, increased significantly from 12.5 ± 2.3% at the 3-week term to 26.4 ± 8.7% at the 3-month term or 23.1 ± 8.7% at the 6-month term. Structural (trabecular) thickness gradually increased from 0.13 ± 0.007 mm at the 3-week term to 0.3 ± 0.11 mm at the 6-month term. The structural model index was 0.79 ± 0.46 in the early phase after trauma and then decreased to negative values.

CONCLUSION

The bone regeneration process was characterized by a significant increase (p < 0.05) in bone volume, percentage of bone volume, structural thickness and bone mineral density, and a decrease in bone surface-to-volume ratio and volume of pore space from the 3-week term to the 6-month term. These changes can be mathematically described by nonlinear exponential regression models.

The Effects of Systemic Therapy of PEGylated NEL-Like Protein 1 (NELL-1) on Fracture Healing in Mice

Fractures are common, with an incidence of 13.7 per 1000 adults annually. Systemic agents have been widely used for enhancing bone regeneration; however, the efficacy of these therapeutics for the management and prevention of fracture remains unclear. NEL-like protein 1 (NELL-1) is a potent pro-osteogenic cytokine that has been modified with polyethylene glycol (PEG)ylation [PEGylated NELL-1 (NELL-PEG)] to enhance its pharmacokinetics for systemic therapy. Our aim was to investigate the effects of systemic administration of NELL-PEG on fracture healing in mice and on overall bone properties in uninjured bones. Ten-week-old CD-1 mice were subjected to an open osteotomy of bilateral radii and treated with weekly injections of NELL-PEG or PEG phosphate-buffered saline as control. Systemic injection of NELL-PEG resulted in improved bone mineral density of the fracture site and accelerated callus union. After 4 weeks of treatment, mice treated with NELL-PEG exhibited substantially enhanced callus volume, callus mineralization, and biomechanical properties. NELL-PEG injection significantly augmented bone regeneration, as confirmed by high expression of bone turnover rate, bone formation rate, and mineral apposition rate. Consistently, the immunohistochemistry results also confirmed a high bone remodeling activity in the NELL-PEG-treated group. Our findings suggest that weekly injection of NELL-PEG may have the clinical potential to accelerate fracture union and enhance overall bone properties, which may help prevent subsequent fractures.

A Mouse Model of Orthopedic Surgery to Study Postoperative Cognitive Dysfunction and Tissue Regeneration

Surgery is commonly used to improve and maintain quality of life. Unfortunately, in vulnerable patients such as the elderly, complications may occur and significantly diminish the outcome. Indeed, after routine orthopedic surgery to repair a fracture, as many as 50% of elderly patients suffer from neurologic complications like delirium. Also, the capacity to heal and regenerate tissue after surgery decreases with age, and can impact the quality of fracture repair and even osseous integration of implants. Thus, a better understanding of mechanisms that drive these age-dependent changes could provide strategic targets to minimize risk for such complications and optimize outcomes. Here, we introduce a clinically relevant mouse model of tibial fracture. The postoperative changes in these mice mimic some of the cognitive impairments commonly observed after routine orthopedic surgery in humans. Briefly, an incision is performed in the right hind limb under strictly aseptic conditions. Muscles are disassociated, and a 0.38-mm stainless steel pin is inserted into the upper crest of the tibia, inside the intramedullary canal. Osteotomy is then performed, and the wound is stapled. We have used this model to investigate the effects of surgical trauma on postoperative neuroinflammation and behavioral changes. By applying this fracture model in combination with parabiosis, a surgical model in which 2 mice are anastomosed, we have studied cells and secreted factors that systemically rejuvenate organ function and tissue regeneration after injury. By following our step-by-step protocol, these models can be reproduced with high fidelity, and can be adapted to interrogate many biologic pathways that are altered by surgical trauma.