Special Review: Accelerating fracture repair in humans: a reading of old experiments and recent clinical trials

β-catenin mRNA encapsulated in SM-102 lipid nanoparticles enhances bone formation in a murine tibia fracture repair model

Fractures continue to be a global economic burden as there are currently no osteoanabolic drugs approved to accelerate fracture healing. In this study, we aimed to develop an osteoanabolic therapy which activates the Wnt/β-catenin pathway, a molecular driver of endochondral ossification. We hypothesize that using an mRNA-based therapeutic encoding β-catenin could promote cartilage to bone transformation formation by activating the canonical Wnt signaling pathway in chondrocytes. To optimize a delivery platform built on recent advancements in liposomal technologies, two FDA-approved ionizable phospholipids, DLin-MC3-DMA (MC3) and SM-102, were used to fabricate unique ionizable lipid nanoparticle (LNP) formulations and then tested for transfection efficacy both in vitro and in a murine tibia fracture model. Using firefly luciferase mRNA as a reporter gene to track and quantify transfection, SM-102 LNPs showed enhanced transfection efficacy in vitro and prolonged transfection, minimal fracture interference and no localized inflammatory response in vivo over MC3 LNPs. The generated β-cateninGOF mRNA encapsulated in SM-102 LNPs (SM-102-β-cateninGOF mRNA) showed bioactivity in vitro through upregulation of downstream canonical Wnt genes, axin2 and runx2. When testing SM-102-β-cateninGOF mRNA therapeutic in a murine tibia fracture model, histomorphometric analysis showed increased bone and decreased cartilage composition with the 45 μg concentration at 2 weeks post-fracture. μCT testing confirmed that SM-102-β-cateninGOF mRNA promoted bone formation in vivo, revealing significantly more bone volume over total volume in the 45 μg group. Thus, we generated a novel mRNA-based therapeutic encoding a β-catenin mRNA and optimized an SM-102-based LNP to maximize transfection efficacy with a localized delivery.

Methods to accelerate fracture healing - a narrative review from a clinical perspective

Bone regeneration is a complex pathophysiological process determined by molecular, cellular, and biomechanical factors, including immune cells and growth factors. Fracture healing usually takes several weeks to months, during which patients are frequently immobilized and unable to work. As immobilization is associated with negative health and socioeconomic effects, it would be desirable if fracture healing could be accelerated and the healing time shortened. However, interventions for this purpose are not yet part of current clinical treatment guidelines, and there has never been a comprehensive review specifically on this topic. Therefore, this narrative review provides an overview of the available clinical evidence on methods that accelerate fracture healing, with a focus on clinical applicability in healthy patients without bone disease. The most promising methods identified are the application of axial micromovement, electromagnetic stimulation with electromagnetic fields and direct electric currents, as well as the administration of growth factors and parathyroid hormone. Some interventions have been shown to reduce the healing time by up to 20 to 30%, potentially equivalent to several weeks. As a combination of methods could decrease the healing time even further than one method alone, especially if their mechanisms of action differ, clinical studies in human patients are needed to assess the individual and combined effects on healing progress. Studies are also necessary to determine the ideal settings for the interventions, i.e., optimal frequencies, intensities, and exposure times throughout the separate healing phases. More clinical research is also desirable to create an evidence base for clinical guidelines. To make it easier to conduct these investigations, the development of new methods that allow better quantification of fracture-healing progress and speed in human patients is needed.

3D Printed Piezoelectric BaTiO3/Polyhydroxybutyrate Nanocomposite Scaffolds for Bone Tissue Engineering

Bone defects are a significant health problem worldwide. Novel treatment approaches in the tissue engineering field rely on the use of biomaterial scaffolds to stimulate and guide the regeneration of damaged tissue that cannot repair or regrow spontaneously. This work aimed at developing and characterizing new piezoelectric scaffolds to provide electric bio-signals naturally present in bone and vascular tissues. Mixing and extrusion were used to obtain nanocomposites made of polyhydroxybutyrate (PHB) as a matrix and barium titanate (BaTiO3) nanoparticles as a filler, at BaTiO3/PHB compositions of 5/95, 10/90, 15/85 and 20/80 (w/w%). The morphological, thermal, mechanical and piezoelectric properties of the nanocomposites were studied. Scanning electron microscopy analysis showed good nanoparticle dispersion within the polymer matrix. Considerable increases in the Young's modulus, compressive strength and the piezoelectric coefficient d31 were observed with increasing BaTiO3 content, with d31 = 37 pm/V in 20/80 (w/w%) BaTiO3/PHB. 3D printing was used to produce porous cubic-shaped scaffolds using a 90° lay-down pattern, with pore size ranging in 0.60-0.77 mm and good mechanical stability. Biodegradation tests conducted for 8 weeks in saline solution at 37 °C showed low mass loss (∼4%) for 3D printed scaffolds. The results obtained in terms of piezoelectric, mechanical and chemical properties of the nanocomposite provide a new promising strategy for vascularized bone tissue engineering.

The molecular pathway triggered by zirconia in endothelial cells involves epigenetic control

The requirement to achieve natural looking restorations is one of the most challenging aspects in dentistry. Although zirconia has provided new opportunities for achieving superior aesthetics and physicochemical outcomes, very little has been achieved for its cellular and molecular performance, especially considering angiogenesis and osteogenesis. As angiogenesis is a secondary event and concomitant to osteogenesis, an indirect effect of dental implant on endothelial cells could be the release of active molecules such as those already reported affecting osteoblasts. To better address this issue, we challenged human endothelial cells (HUVECs) with zirconia-conditioned medium up to 72 h to allow analysis specific gene expression and protein pattern of mediators of epigenetic machinery in full. Our data shows involvement of zirconia in triggering intracellular signaling through MAPK-ERK activation, leading the signal to activate histone deacetylase HDAC6 likely with concomitant well-modulated DNA methylation profile by DNMTs and TETs. These signaling pathways seem to culminate in cytoskeleton rearrangement of endothelial cells, an important prerequisite to cell migration expected in angiogenesis. Collectively, this study demonstrates for the first time epigenetic-related molecular mechanism involved in endothelial cells responding to zirconia, revealing a repertoire of signaling molecules capable of executing the reprogramming process of gene expression, which are necessary to drive cell proliferation, migration, and consequently angiogenesis. This set of data can further studies using gene editing approaches to better elucidate functional roles.

Effect of weekly teriparatide injections on osteoporotic fracture healing: protocol for a double-blind, randomised controlled trial

INTRODUCTION

Both animal studies and clinical trials have shown that daily parathyroid hormone administration promotes bone fracture healing. We previously found that weekly injections of the recombinant human parathyroid hormone teriparatide at a dosage of 20 μg/kg promoted tibial fracture healing to the same extent as daily injections of teriparatide at a dosage of 10 μg/kg in a rodent model. However, the effect of weekly teriparatide administration on human fracture healing is unreported. This protocol describes a randomised controlled clinical trial designed to evaluate whether weekly administration of teriparatide accelerates fracture repair in humans.

METHODS AND ANALYSIS

This single-centre, double-blind, randomised controlled trial will be conducted in Peking University Third Hospital. Eligible patients with Colles' fracture incurred within 48 hours will be randomly divided into two groups (n=40 per group) that will receive 14 weekly subcutaneous injections of either saline or teriparatide (40 μg/week). The primary outcome will be the time taken to achieve radiographic healing, as assessed using the modified radiographic union scale for tibial fractures. The secondary outcomes will be functional assessments, including the self-administered Patient-Rated Wrist Evaluation questionnaire, grip strength and rate of fracture non-union.

ETHICS AND DISSEMINATION

Ethical approval has been obtained from the Peking University Third Hospital Medical Science Research Ethics Committee (M2020207). The findings will be disseminated in peer-reviewed publications.

TRIAL REGISTRATION NUMBER

NCT04473989: protocol version: 1.

Systematic Review of the Preclinical Technology Readiness of Orthopedic Gene Therapy and Outlook for Clinical Translation

Bone defects and improper healing of fractures are an increasing public health burden, and there is an unmet clinical need in their successful repair. Gene therapy has been proposed as a possible approach to improve or augment bone healing with the potential to provide true functional regeneration. While large numbers of studies have been performed in vitro or in vivo in small animal models that support the use of gene therapy for bone repair, these systems do not recapitulate several key features of a critical or complex fracture environment. Larger animal models are therefore a key step on the path to clinical translation of the technology. Herein, the current state of orthopedic gene therapy research in preclinical large animal models was investigated based on performed large animal studies. A summary and an outlook regarding current clinical studies in this sector are provided. It was found that the results found in the current research literature were generally positive but highly methodologically inconsistent, rendering a comparison difficult. Additionally, factors vital for translation have not been thoroughly addressed in these model systems, and the risk of bias was high in all reviewed publications. These limitations directly impact clinical translation of gene therapeutic approaches due to lack of comparability, inability to demonstrate non-inferiority or equivalence compared with current clinical standards, and lack of safety data. This review therefore aims to provide a current overview of ongoing preclinical and clinical work, potential bottlenecks in preclinical studies and for translation, and recommendations to overcome these to enable future deployment of this promising technology to the clinical setting.

BMP-2 and VEGF-A modRNAs in collagen scaffold synergistically drive bone repair through osteogenic and angiogenic pathways

Bone has a remarkable potential for self-healing and repair, yet several injury types are non-healing even after surgical or non-surgical treatment. Regenerative therapies that induce bone repair or improve the rate of recovery are being intensely investigated. Here, we probed the potential of bone marrow stem cells (BMSCs) engineered with chemically modified mRNAs (modRNA) encoding the hBMP-2 and VEGF-A gene to therapeutically heal bone. Induction of osteogenesis from modRNA-treated BMSCs was confirmed by expression profiles of osteogenic related markers and the presence of mineralization deposits. To test for therapeutic efficacy, a collagen scaffold inoculated with modRNA-treated BMSCs was explored in an in vivo skull defect model. We show that hBMP-2 and VEGF-A modRNAs synergistically drive osteogenic and angiogenic programs resulting in superior healing properties. This study exploits chemically modified mRNAs, together with biomaterials, as a potential approach for the clinical treatment of bone injury and defects.

Single injection of PTH improves osteoclastic parameters of remodeling at a stress fracture site in rats

Stress fractures (SFx) result from repetitive cyclical loading of bone. They are frequent athletic injuries and underlie atypical femoral fractures following long-term bisphosphonate (BP) therapy. We investigated the effect of a single PTH injection on the healing of SFx in the rat ulna. SFx was induced in 120 female Wistar rats (300 ± 15 g) during a single loading session. A single PTH (8 µg.100g^-1 ) or vehicle (VEH) saline injection was administered 24 h after loading. Rats were divided into four groups (n = 15) and ulnae were examined 1, 2, 6, or 10 weeks following SFx. Two Toluidine Blue and TRAP-stained sections of the SFx were examined for histomorphometric analysis using Osteomeasure™ software. An increase in osteoclast number (N.Oc) and perimeter (Oc.Pm) was observed two weeks following PTH treatment (p < 0.01). At 6 weeks, bone formation was the main activity in BMUs. At 10 weeks, the proportion of healing along the SFx line remained 50% greater in PTH groups (p = 0.839), leading to a 43% reduction in the porosity area of BMU (p = 0.703). The main effect of time was a significant variable along the entire SFx remodeling cycle, with significant interactions between time and treatment type affecting (N.Oc) (p = 0.047) and (Oc.Pm) (p = 0.002). We conclude that a single PTH injection increases osteoclastogenesis by the second week of the remodeling cycle in a SFx in vivo. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Utilization Pattern of Traditional Chinese Medicine among Fracture Patients: A Taiwan Hospital-Based Cross-Sectional Study

Traditional Chinese medicine (TCM) divides fracture treatment into three stages. Many TCM herbs and formulas have been used to treat fractures for thousands of years. However, research regarding the Chinese herbal products (CHPs) that should be used at different periods of treatment is still lacking. This study aims to identify the CHPs that should be used at different periods of treatment as well as confirm the TCM theory of fracture periods medicine. We used prescriptions of TCM outpatients with fracture diagnoses analyzed using the Chang Gung Research Database (CGRD) from 2000 to 2015. According to the number of days between the date of the fracture and the clinic visit date, all patients were assigned to one of three groups. Patients with a date gap of 0-13 days were assigned to the early period group; those with a date gap of 14-82 days were assigned to the middle period group; and those with a date gap of 83-182 days were assigned to the late period group. We observed the average number of herbal formulas prescribed by the TCM doctor at each visit was 2.78, and the average number of single herbs prescribed was 6.47. The top three prescriptions in the early fracture period were Zheng-gu-zi-jin-dang, Shu-jing-huo-xue-tang, and Wu-ling-san. In the middle fracture period, the top three formulas were Zheng-gu-zi-jin-dang, Shu-jing-huo-xue-tang, and Zhi-bai-di-huang-wan. In the late fracture period, the top three formulas were Shu-jing-huo-xue-tang, Gui-lu-er-xian-jiao, and Du-huo-ji-sheng-tang. The main single herbs used in the early fracture period were Yan-hu-suo, Gu-sui-bu, and Dan-shen. From the middle to the late period, the most prescribed single herbs were Xu-duan, Gu-sui-bu, and Yan-hu-suo. We concluded that the results showed that the CGRD utilization pattern roughly meets the TCM theory at different fracture periods.

Use of Nonvascularized Autologous Fibular Strut Graft in the Treatment of Major Bone Defect after Periprosthetic Knee Fracture

We present the case of a patient who suffered a comminuted supracondylar periprosthetic femur fracture. The patient was an 86-year-old lady who suffered a minor fall at home and presented at our hospital with a right comminuted distal femur fracture around a total knee arthroplasty. The patient was submitted to a cruciate-sacrificing total knee replacement 6 years before at the same institution. Despite severe metaphyseal fragmentation and short distal fragment, the prosthesis was stable; thus, open fracture reduction and stabilization with internal fixation were performed. The surgical technique included the use of a nonvascularized autologous fibular strut graft as an augmentation technique in conjunction with double plating fixation. Clinically, patient presented a painless aligned knee 12 months after femur fixation, although she was not able to return to an independent level of activity. No pain involving the donor graft site was reported at the time of the most recent follow-up examination. This case study demonstrates the use of free nonvascularized autogenous fibular strut bone graft as an option to bridge major bone defects. This proved to be a relatively simple, not expensive procedure that can be done percutaneously and does not need high-quality training.

No effect of teriparatide on migration in total knee replacement

Background and purpose - Aseptic loosening is a main cause of late revision in total knee replacement (TKR). Teriparatide, a recombinant parathyroid hormone (PTH), stimulates osteoblasts and has been suggested to improve cancellous bone healing in humans. This might also be relevant for prosthesis fixation. We used radiostereometric analysis (RSA) to investigate whether teriparatide influences prosthesis fixation. Early migration as measured by RSA can predict future loosening. Patients and methods - In a randomized controlled trial with blind evaluation, 50 patients with osteoarthritis of the knee were allocated to a teriparatide treatment group (Forsteo, 20 μg daily for 2 months postoperatively) or to an untreated control group. RSA was performed postoperatively and at 6 months, 12 months, and 24 months. The primary effect variable was maximal total point motion (MTPM) from 12 to 24 months. Results - Median maximal total point motion from 12 to 24 months was similar in the 2 groups (teriparatide: 0.14 mm, 10% and 90% percentiles: 0.08 and 0.24; control: 0.13 mm, 10% and 90% percentiles: 0.09 and 0.21). [Authors: this is perhaps better than using "10th" and "90th", which looks ugly in print./language editor] The 95% confidence interval for the difference between group means was -0.03 to 0.04 mm, indicating that no difference occurred. Interpretation - We found no effect of teriparatide on migration in total knee replacement. Other trials using the same dosing have suggested a positive effect of teriparatide on human cancellous fracture healing. Thus, the lack of effect on migration may have been due to something other than the dose. In a similar study in this issue of Acta Orthopaedica, we found that migration could be reduced with denosumab (Ledin et al. 2017 ). The difference in response between the anabolic substance teriparatide and the antiresorptive denosumab suggests that resorption has a more important role during the postoperative course than any deficit in bone formation.

Chemically modified RNA induces osteogenesis of stem cells and human tissue explants as well as accelerates bone healing in rats

Limitations associated to the use of growth factors represent a major hurdle to musculoskeletal regeneration. On the one hand, they are needed to induce neo-tissue formation for the substitution of a necrotic or missing tissue. On the other hand, these factors are used in supraphysiological concentrations, are short lived and expensive and result in many side effects. Here we develop a gene transfer strategy based on the use of chemically modified mRNA (cmRNA) coding for human bone morphogenetic protein 2 (hBMP-2) that is non-immunogenic and highly stable when compared to unmodified mRNA. Transfected stem cells secrete hBMP-2, show elevated alkaline phosphatase levels and upregulated expression of RunX2, ALP, Osterix, Osteocalcin, Osteopontin and Collagen Type I genes. Mineralization was induced as seen by positive Alizarin red staining. hBMP-2 cmRNA transfected human fat tissue also yielded an osteogenic response in vitro as indicated by expression of hBMP-2, RunX2, ALP and Collagen Type I. Delivering hBMP-2 cmRNA to a femur defect in a rat model results in new bone tissue formation as early as 2 weeks after application of very low doses. Overall, our studies demonstrate the feasibility and therapeutic potential of a new cmRNA-based gene therapy strategy that is safe and efficient. When applied clinically, this approach could overcome BMP-2 growth factor associated limitations in bone regeneration.

PTH 1-34 (teriparatide) may not improve healing in proximal humerus fractures. A randomized, controlled study of 40 patients

BACKGROUND AND PURPOSE

There is solid evidence from animal experiments that parathyroid hormone (PTH) improves fracture healing. So far, only 3 papers on PTH and fracture repair in humans have been published. They suggest that PTH may enhance fracture healing, but the results do not appear to justify specific clinical recommendations. This study was carried out to determine whether teriparatide enhances fracture healing of proximal humerus fractures.

PATIENTS AND METHODS

40 post-menopausal women with a proximal humerus fracture were randomized to either daily injections with 20 µg teriparatide (PTH 1-34 (Forteo)) for 4 weeks or control treatment. At randomization, the patients were asked to assess how their pain at rest and during activity (visual analog scale (VAS)) and also function (DASH score) had been prior to the fracture. At 7 weeks and again at 3 months, their current state was assessed and the tests were repeated, including radiographs. 2 radiologists performed a blind qualitative scoring of the callus at 7 weeks. Callus formation was arbitrarily classified as "normal" or "better".

RESULTS

39 patients completed the follow-up. The radiographic assessment showed a correct correlation, "better" in the teriparatide group and "normal" in the control group, in 21 of the 39 cases. There were no statistically significant differences in pain, in use of strong analgesics, or in function between the groups at the follow-up examinations.

INTERPRETATION

There were no radiographic signs of enhanced healing or improved clinical results in the group treated with teriparatide.

Local delivery of zoledronate from a poly (D,L-lactide)-Coating increases fixation of press-fit implants

Early secure fixation of total joint replacements is crucial for long-term survival. Antiresorptive agents such as bisphosphonates have been shown to increase implant fixation. We investigated whether local delivery of zoledronate from poly-D, L-lactide (PDLLA)-coated implants could improve implant fixation and osseointegration. Experimental titanium implants were bilaterally inserted press-fit into the proximal tibiae of 10 dogs. On one side the implant was coated with PDLLA containing zoledronate. The contralateral implant was uncoated and used as control. Observation period was 12 weeks. Implant fixation was evaluated with histomorphometry and biomechanical push-out test. We found an approximately twofold increase in all biomechanical parameters when comparing data from the zoledronate group with their respective controls. Histomorphometry showed increased amount of preserved bone and increased bone formation around the zoledronate implants. This study indicates that local delivery of zoledronate from a PDDLA coating has the potential to increase implant fixation.

Targeted delivery as key for the success of small osteoinductive molecules

Molecules such as growth factors, peptides and small molecules can guide cellular behavior and are thus important for tissue engineering. They are rapidly emerging as promising compounds for the regeneration of tissues of the musculoskeletal system. Growth factors have disadvantages such as high cost, short half-life, supraphysiological amounts needed, etc. Therefore, small molecules may be an alternative. These molecules have been discovered using high throughput screening. Small osteoinductive molecules exhibit several advantages over growth factors owing to their small sizes, such as high stability and non-immunogenicity. These molecules may stimulate directly signaling pathways that are important for osteogenesis. However, systemic application doesn't induce osteogenesis in most cases. Therefore, local administration is needed. This may be achieved by using a bone graft material providing additional osteoconductive properties. These graft materials can also act by themselves as a delivery matrix for targeted and local delivery. Furthermore, vascularization is necessary in the process of osteogenesis. Many of the small molecules are also capable of promoting vascularization of the tissue to be regenerated. Thus, in this review, special attention is given to molecules that are capable of inducing both angiogenesis and osteogenesis simultaneously. Finally, more recent preclinical and clinical uses in bone regeneration of those molecules are described, highlighting the needs for the clinical translation of these promising compounds.

Fourier Transform Infrared Spectroscopic Imaging of Fracture Healing in the Normal Mouse

Fourier transform infrared spectroscopic imaging (FTIRI) was used to study bone healing with spatial analysis of various callus tissues in wild type mice. Femoral fractures were produced in 28 male C57BL mice by osteotomy. Animals were sacrificed at 1, 2, 4, and 8 weeks to obtain callus tissue at well-defined healing stages. Following microcomputerized tomography, bone samples were cut in consecutive sections for FTIRI and histology, allowing for spatial correlation of both imaging methods in different callus areas (early calcified cartilage, woven bone, areas of intramembranous and endochondral bone formation). Based on FTIRI, mineral/matrix ratio increased significantly during the first 4 weeks of fracture healing in all callus areas and correlated with bone mineral density measured by micro-CT. Carbonate/phosphate ratio was elevated in newly formed calcified tissue and at week 2 attained values comparable to cortical bone. Collagen maturity and mineral crystallinity increased during weeks 1-8 in most tissues while acid phosphate substitution decreased. Temporal and callus area dependent changes were detected throughout the healing period. These data assert the usefulness of FTIRI for evaluation of fracture healing in the mouse and its potential to evaluate pathologic fracture healing and the effects of therapeutic interventions.

Cranial vault reconstruction with bone morphogenetic protein, calcium phosphate, acellular dermal matrix, and calcium alginate in mice

PURPOSE

To evaluate experimental cranial vault reconstructions, by combining bone morphogenetic protein type 2 (BMP-2) and different matrices.

METHODS

Fourty-nine animals were initially included (seven per group). We designed an experimental, open, prospective and comparative study, divided in seven groups: 1 - BMP-2+calcium phosphate (BT); 2 - BMP-2+acellular dermal matrix (BM); 3 - BMP-2+calcium alginate (BA); 4 - TCP; 5 - MDM; 6 - ALG; 7 - Bone autograft (BAG). A bone failure was created in left parietal bone of adult male mice. At the same procedure reconstruction was performed. After five weeks, animals were sacrificed, and reconstruction area was removed to histological analysis. After exclusion due to death or infection, thirty-eight animals were evaluated (BT=5; BM=6; BA=6; TCP=7; MDM=3; ALG=6; BAG=5).

RESULTS

A higher incidence of infection has occurred in MDM group (57%, P=0.037). In cortical fusion, groups BAG, TCP, and BMP-2+TCP (BT) obtained the best scores, comparing to the others (P=0.00846). In new bone formation, groups BT, BAG, and TCP have presented the best scores (P=0.00835). When neovascularization was considered, best groups were BMP-2+MDM (BM), BMP-2+ALG (BA), TCP, and MDM (P=0.001695). BAG group was the best in bone marrow formation, followed by groups BT and TCP (P=0.008317).

CONCLUSIONS

Bone morphogenetic protein type 2 increased bone regeneration in experimental skull reconstruction, especially when combined to calcium phosphate. Such association was even comparable to bone autograft, the gold-standard treatment, in some histological criteria.