Can we enhance fracture vascularity: What is the evidence?

Effects of electric charge on fracture healing

Fracture nonunion is a common and challenging complication. Although direct current stimulation has been suggested to promote fracture healing, differences in cell density near the positive and negative electrodes have been reported during direct current stimulation. This study aimed to explore the effects of these differences on osteoblast proliferation and fracture healing. MC3T3-E1 cells were stimulated by positive and negative charges to observe cell proliferation, apoptosis, and osteogenic factor expression in vitro, while positive and negative charges were connected to the Kirschner wires of the fractures in an in vivo double-toe fracture model in New Zealand white rabbits and fracture healing was assessed in digital radiography (DR) examinations performed on days 1, 15, 30. Bone tissue samples of all rabbits were analysed histologically after the last examination. The results showed that in comparison with the control group, after DC stimulation, the number of cells near the positive electrode decreased significantly (P < 0.05), apoptosis increased (P < 0.05), the expression of osteocalcin, osteoblast-specific genes, and osteonectin decreased significantly near the positive electrode (P < 0.05) and increased significantly at the negative electrode (P < 0.05). The fracture at the positive electrode junction of New Zealand white rabbits did not heal. Histomorphological analysis showed more bone trabeculae and calcified bone in the bone tissue sections of the control group and the negative electrode group than in the positive electrode group. The bone trabeculae were thick and showed good connections. However, positive charge inhibited osteoblast proliferation and a positive charge at fracture sites did not favour fracture healing. Thus, a positive charge near the fracture site may be a reason for fracture nonunion.

Alcohol-induced inhibition of bone formation and neovascularization contributes to the failure of fracture healing via the miR-19a-3p/FOXF2 axis

Aims

Alcoholism is a well-known detrimental factor in fracture healing. However, the underlying mechanism of alcohol-inhibited fracture healing remains poorly understood.

Methods

MicroRNA (miR) sequencing was performed on bone mesenchymal stem cells (BMSCs). The effects of alcohol and miR-19a-3p on vascularization and osteogenic differentiation were analyzed in vitro using BMSCs and human umbilical vein endothelial cells (HUVECs). An in vivo alcohol-fed mouse model of femur fracture healing was also established, and radiological and histomorphometric analyses were used to evaluate the role of miR-19a-3p. The binding of miR-19a-3p to forkhead box F2 (FOXF2) was analyzed using a luciferase reporter assay.

Results

miR-19a-3p was identified as one of the key regulators in the osteogenic differentiation of BMSCs, and was found to be downregulated in the alcohol-fed mouse model of fracture healing. In vitro, miR-19a-3p expression was downregulated after ethanol administration in both BMSCs and HUVECs. Vascularization and osteogenic differentiation were independently suppressed by ethanol and reversed by miR-19a-3p. In addition, the luciferase reporter assay showed that FOXF2 is the direct binding target of miR-19a-3p. In vivo, miR-19a-3p agomir stimulated callus transformation and improved the alcohol-impaired fracture healing.

Conclusion

This study is the first to demonstrate that the miR-19a-3p/FOXF2 axis has a pivotal role in alcohol-impaired fracture healing, and may be a potential therapeutic target.

Cite this article: Bone Joint Res 2022;11(6):386–397.

Topical cutaneous application of carbon dioxide via a hydrogel for improved fracture repair: results of phase I clinical safety trial

Background

Clinicians have very limited options to improve fracture repair. Therefore, it is critical to develop a new clinically available therapeutic option to assist fracture repair biologically. We previously reported that the topical cutaneous application of carbon dioxide (CO₂) via a CO₂ absorption-enhancing hydrogel accelerates fracture repair in rats by increasing blood flow and angiogenesis and promoting endochondral ossification. The aim of this study was to assess the safety and efficacy of CO₂ therapy in patients with fractures.

Methods

Patients with fractures of the femur and tibia were prospectively enrolled into this study with ethical approval and informed consent. The CO₂ absorption-enhancing hydrogel was applied to the fractured lower limbs of patients, and then 100% CO₂ was administered daily into a sealed space for 20 min over 4 weeks postoperatively. Safety was assessed based on vital signs, blood parameters, adverse events, and arterial and expired gas analyses. As the efficacy outcome, blood flow at the level of the fracture site and at a site 5 cm from the fracture in the affected limb was measured using a laser Doppler blood flow meter.

Results

Nineteen patients were subjected to complete analysis. No adverse events were observed. Arterial and expired gas analyses revealed no adverse systemic effects including hypercapnia. The mean ratio of blood flow 20 min after CO₂ therapy compared with the pre-treatment level increased by approximately 2-fold in a time-dependent manner.

Conclusions

The findings of the present study revealed that CO₂ therapy is safe to apply to human patients and that it can enhance blood flow in the fractured limbs.

Trial registration

This study has been registered in the UMIN Clinical Trials Registry (Registration number: UMIN000013641, Date of registration: July 1, 2014).

NF‑κB‑miR15a‑bFGF/VEGFA axis contributes to the impaired angiogenic capacity of BM‑MSCs in high fat diet‑fed mice

Potent paracrine properties, such as secretion of angiogenic cytokines and growth factors, have been considered essential for the function of mesenchymal stem cells (MSCs) in tissue regeneration and repair. The present study determined that bone marrow‑derived mesenchymal stem cells from mice fed a high fat diet (HFD) had reduced pro‑angiogenic capacity, as evident from the reduced expression of vascular endothelial growth factor A (VEGFA) and basic fibroblast growth factor (bFGF); therefore, a reduced number of branches was induced in the angiogenesis assay. Additionally, the present study determined that miR‑15a, a putative microRNA targeting both VEGFA and bFGF, may simultaneously downregulate bFGF and VEGFA expression levels through the 3'‑untranslated region. Inhibition of miR‑15a using an antagonist restored the expression of VEGFA and bFGF under fatty acid treatment and thus the angiogenic capacity. Furthermore, the HFD and fatty acids treatments transcriptionally activated the expression of miR‑15a via nuclear factor‑κB. In conclusion, the findings of the present study revealed that inhibition of miR‑15a may restore the therapeutic efficacy of mesenchymal stem cells in patients suffering from obesity.

Is there a role of coral bone substitutes in bone repair?

Xenogeneic bone graft materials are an alternative to autologous bone grafting. Among such implants, coralline-derived bone grafts substitutes have a long track record as safe, biocompatible and osteoconductive graft materials. In this review, we present the available literature surrounding their use with special focus on the commercially available graft materials. Corals thanks to their chemical and structural characteristics similar to those of the human cancellous bone have shown great potential but clinical data presented to date is ambiguous with both positive and negative outcomes reported. Correct formulation and design of the graft to ensure adequate osteo-activity and resorption appear intrinsic to a successful outcome.

The role of peptides in bone healing and regeneration: a systematic review

BACKGROUND

Bone tissue engineering and the research surrounding peptides has expanded significantly over the last few decades. Several peptides have been shown to support and stimulate the bone healing response and have been proposed as therapeutic vehicles for clinical use. The aim of this comprehensive review is to present the clinical and experimental studies analysing the potential role of peptides for bone healing and bone regeneration.

METHODS

A systematic review according to PRISMA guidelines was conducted. Articles presenting peptides capable of exerting an upregulatory effect on osteoprogenitor cells and bone healing were included in the study.

RESULTS

Based on the available literature, a significant amount of experimental in vitro and in vivo evidence exists. Several peptides were found to upregulate the bone healing response in experimental models and could act as potential candidates for future clinical applications. However, from the available peptides that reached the level of clinical trials, the presented results are limited.

CONCLUSION

Further research is desirable to shed more light into the processes governing the osteoprogenitor cellular responses. With further advances in the field of biomimetic materials and scaffolds, new treatment modalities for bone repair will emerge.

Bmp2 conditional knockout in osteoblasts and endothelial cells does not impair bone formation after injury or mechanical loading in adult mice

Post-natal osteogenesis after mechanical trauma or stimulus occurs through either endochondral healing, intramembranous healing or lamellar bone formation. Bone morphogenetic protein 2 (BMP2) is up-regulated in each of these osteogenic processes and is expressed by a variety of cells including osteoblasts and vascular cells. It is known that genetic knockout of Bmp2 in all cells or in osteo-chondroprogenitor cells completely abrogates endochondral healing after full fracture. However, the importance of BMP2 from differentiated osteoblasts and endothelial cells is not known. Moreover, the importance of BMP2 in non-endochondral bone formation such as intramembranous healing or lamellar bone formation is not known. Using inducible and tissue-specific Cre-lox mediated targeting of Bmp2 in adult (10-24 week old) mice, we assessed the role of BMP2 expression globally, by osteoblasts, and by vascular endothelial cells in endochondral healing, intramembranous healing and lamellar bone formation. These three osteogenic processes were modeled using full femur fracture, ulnar stress fracture, and ulnar non-damaging cyclic loading, respectively. Our results confirmed the requirement of BMP2 for endochondral fracture healing, as mice in which Bmp2 was knocked out in all cells prior to fracture failed to form a callus. Targeted deletion of Bmp2 in osteoblasts (osterix-expressing) or vascular endothelial cells (vascular endothelial cadherin-expressing) did not impact fracture healing in any way. Regarding non-endochondral bone formation, we found that BMP2 is largely dispensable for intramembranous bone formation after stress fracture and also not required for lamellar bone formation induced by mechanical loading. Taken together our results indicate that osteoblasts and endothelial cells are not a critical source of BMP2 in endochondral fracture healing, and that non-endochondral bone formation in the adult mouse is not as critically dependent on BMP2.

Hypoxic regulation of osteoclast differentiation and bone resorption activity

Bone integrity is maintained throughout life via the homeostatic actions of bone cells, namely, osteoclasts, which resorb bone, and osteoblasts, which produce bone. Disruption of this balance in favor of osteoclast activation results in pathological bone loss, which occurs in conditions including osteoporosis, rheumatoid arthritis, primary bone cancer, and cancer metastasis to bone. Hypoxia also plays a major role in these conditions, where it is associated with disease progression and poor prognosis. In recent years, considerable interest has arisen in the mechanisms whereby hypoxia and the hypoxia-inducible transcription factors, HIF-1α and HIF-2α, affect bone remodeling and bone pathologies. This review summarizes the current evidence for hypoxia-mediated regulation of osteoclast differentiation and bone resorption activity. Role(s) of HIF and HIF target genes in the formation of multinucleated osteoclasts from cells of the monocyte-macrophage lineage and in the activation of bone resorption by mature osteoclasts will be discussed. Specific attention will be paid to hypoxic metabolism and generation of ATP by osteoclasts. Hypoxia-driven increases in both glycolytic flux and mitochondrial metabolic activity, along with consequent generation of mitochondrial reactive oxygen species, have been found to be essential for osteoclast formation and resorption activity. Finally, evidence for the use of HIF inhibitors as potential therapeutic agents targeting bone resorption in osteolytic disease will be discussed.

Shock wave therapy of fracture nonunion

We have used the principles of extracorporeal shock wave therapy (ESWT) in the treatment of nonunion of fractures in 44 patients (49 bones).There were 35 males and 9 females with a mean age of 34 years(range14-70). Clinical and radiological assessment was performed at regular time intervals with a minimum follow up of 18 months. Most common sites involved were the femur and tibia. The average time from initial fracture treatment to intervention with ESWT was 11.9 months (6 months to 5 years). Thirty eight non-union sites had one session of treatment and the rest (11) had more than one session. Union was successful in 75.5% of cases at a mean time of 10.2 months (range 3-19). Failure in the remaining cases was due to more than 5mm gap, instability, compromised vascularity (type of bone) and deep low grade infection; which was discovered at the time of surgical intervention when no signs of radiological healing occurred after 6 months from treatment. Failing sites were shaft of femur, scaphoid, neck of humerus and neck of femur. No local complications were observed.

Biological and molecular profile of fracture non-union tissue: current insights

Delayed bone healing and non-union occur in approximately 10% of long bone fractures. Despite intense investigations and progress in understanding the processes governing bone healing, the specific pathophysiological characteristics of the local microenvironment leading to non-union remain obscure. The clinical findings and radiographic features remain the two important landmarks of diagnosing non-unions and even when the diagnosis is established there is debate on the ideal timing and mode of intervention. In an attempt to understand better the pathophysiological processes involved in the development of fracture non-union, a number of studies have endeavoured to investigate the biological profile of tissue obtained from the non-union site and analyse any differences or similarities of tissue obtained from different types of non-unions. In the herein study, we present the existing evidence of the biological and molecular profile of fracture non-union tissue.

The role of pleiotrophin in bone repair

Bone has an enormous capacity for growth, regeneration, and remodelling, largely due to induction of osteoblasts that are recruited to the site of bone formation. Although the pathways involved have not been fully elucidated, it is well accepted that the immediate environment of the cells is likely to play a role via cell–matrix interactions, mediated by several growth factors. Formation of new blood vessels is also significant and interdependent to bone formation, suggesting that enhancement of angiogenesis could be beneficial during the process of bone repair. Pleiotrophin (PTN), also called osteoblast-specific factor 1, is a heparin-binding angiogenic growth factor, with a well-defined and significant role in both physiological and pathological angiogenesis. In this review we summarise the existing evidence on the role of PTN in bone repair.