Physiological challenges of bone repair

Hydrogen Sulfide Promotes Osteogenesis by Modulating Macrophage Polarization

Macrophages, a versatile subset of immune cells, are essential for successful bone repair. Hydrogen sulfide (H₂S) is a gasotransmitter associated with tissue development and repair. Emerging evidence demonstrates that H₂S is involved in bone formation under physiology condition and bone regeneration under pathology condition. However, whether hydrogen sulfide mediates osteogenesis by influencing macrophages is unknown. Here, we aimed to investigate the effects of hydrogen sulfide on macrophage polarization and the subsequent impact on bone regeneration. In the present study, we found that the H₂S-donor GYY4137 stimulated M0/M1 macrophages to express high level of CD-206 and IL-10 but decreased the levels of i-NOS and TNF-α in M1 macrophages. Furthermore, coculture of GYY4137-treated M0 macrophages with pro-osteoblastic MC3T3-E1 cells significantly increased the viability of the MC3T3-E1 cells. Importantly, the formation of mineralized particles in MC3T3-E1 cells was significantly promoted following coculture with IL-4-treated and GYY4137-treated M0 macrophages. Collectively, our study demonstrated that hydrogen sulfide increased macrophages M2 polarization and subsequently promoted bone regeneration.

Long noncoding RNA Gm31629 promotes bone regeneration by maintaining bone marrow mesenchymal stem cells activity

Background

Long noncoding RNA Gm31629 can regulate hypothalamic neural stem cells (htNSCs) senescence and the aging process. However, the effect of Gm31629 on the senescence of bone marrow mesenchymal stem cells (BMSCs) and bone regeneration is unclear. In the present study, we investigated the effects of Gm31629 on the senescence of BMSCs and bone regeneration.

Methods

Gm31629 knockout (Gm31629-KO) and wild-type (WT) mice were used to establish a bone regeneration model. The Brdu labelling, CCK8 assay, wound healing assay, β-gal staining and osteogenic differentiation assay were used to assess the effects of Gm31629 on the functions of BMSCs. Micro-computed tomography (CT), histochemical and immunohistochemical staining were used to evaluate the ability of bone regeneration. The mimic of Gm31629, theaflavin 3-gallate, was used to investigate its role on the senescence of BMSCs and bone regeneration.

Results

The expression of Gm31629 reduced in BMSCs of middle-aged mice was compared with that of young mice. The deletion of Gm31629 was sufficient to drive the senescence of BMSCs, resulting in impaired bone regeneration in mice. Mechanistically, Gm31629 could interact with Y-box protein 1(YB-1) and delay its degradation, decreasing the transcription of p16^INK4A of BMSCs. We also found that theaflavin 3-gallate could alleviate the senescence of BMSCs and promote bone regeneration in middle-aged mice.

Conclusion

These results indicated that Gm31629 played an important role on BMSCs senescence and bone regeneration and provided a therapeutic target to promote bone regeneration.

Effects of teriparatide and low-intensity aerobic exercise on osteopenia in type 2 diabetes mellitus rats

INTRODUCTION

In patients with type 2 diabetes mellitus (T2DM), bone fragility increases fracture risk. Teriparatide (TPTD) improves bone strength, and exercise therapy suppresses blood glucose levels in T2DM. In this study, the combined effects of TPTD and exercise therapy on trabecular and cortical bone were examined in advanced T2DM model rats.

MATERIALS AND METHODS

Thirty-week-old Otsuka Long-Evans Tokushima Fatty rats were divided into four groups (n = 9-10 in each group at two time points): Cont group (vehicle-treated control), TPTD group (TPTD 30 μg/kg injected subcutaneously, 3 times/week), Exe group (treadmill exercise, 10 m/min, 60 min/day, 5 times/week), and Comb group (TPTD-treated and treadmill exercise combined). Five and 10 weeks after treatment, bone mineral density (BMD), bone strength, and bone micro-architecture were measured.

RESULTS

TPTD and combined treatment significantly increased BMDs of the lumbar spine and femur compared to the Cont group (p < 0.05 to p < 0.01). In the three-point bending test of the femur, only combined treatment increased the maximum load at 5 weeks compared with the Cont and Exe groups (p < 0.01). In the compression test of the distal femoral metaphysis, both TPTD and combined treatment increased the trabecular bone strength compared with the Cont and Exe groups (p < 0.05 to p < 0.01). Although TPTD and combined treatment improved the micro-architecture of trabecular bone (p < 0.05 to p < 0.01), only combined treatment improved the micro-structures of cortical bone from 5 weeks of treatment (p < 0.05 to p < 0.01).

CONCLUSION

The combination of TPTD and treadmill exercise increased BMD and trabecular and cortical bone strength of the femur with improved micro-architecture in T2DM model rats.

Cyasterone accelerates fracture healing by promoting MSCs migration and osteogenesis

Background

Mesenchymal Stem Cells (MSCs) therapy has become a new coming focus of clinical research in regenerative medicine. However, only a small number of implanted MSCs could successfully reach the injured areas. The previous studies have shown that fracture healing time is inversely proportional to concentration of MSCs in injured tissue.

Methods

The migration and osteogenesis of MSCs were assessed by transwell assay and Alizarin Red S staining. Levels of gene and protein expression were checked by qPCR and Western Blot. On the other hand, the enhanced migration ability of MSCs induced by Cyasterone was retarded by CXCR4 siRNA. In addition, the rat model of femoral fracture was established to evaluate the effect of Cyasterone on fracture healing. What's more, we also checked the effect of Cyasterone on mobilisation of MSCs in vivo.

Results

The results showed that Cyasteron increased the number of MSCs in peripheral blood. The concentrations of SDF-1α in serum at different time points were determined by ELISA assay. Micro-CT and histological analysis were used to evaluate the fractured femurs.Our results showed that Cyasterone could promote the migration and osteogenesis capacities of MSCs. The fractured femurs healed faster with treatment of Cyasterone. Meanwhile, Cyasterone could significantly increase the level of SDF-1α in rats with femur fracture.

Conclusion

Cyasterone could promote migration and osteogenesis of MSCs, and most importantly, it could accelerate bone fracture healing.

Translational Potential statement: These findings provide evidence that Cyasterone could be used as a therapeutic reagent for MSCs mobilisation and osteogenesis. What's more, it could acclerate fracture healing.

Mesenchymal Stromal Cell-Based Bone Regeneration Therapies: From Cell Transplantation and Tissue Engineering to Therapeutic Secretomes and Extracellular Vesicles

Effective regeneration of bone defects often presents significant challenges, particularly in patients with decreased tissue regeneration capacity due to extensive trauma, disease, and/or advanced age. A number of studies have focused on enhancing bone regeneration by applying mesenchymal stromal cells (MSCs) or MSC-based bone tissue engineering strategies. However, translation of these approaches from basic research findings to clinical use has been hampered by the limited understanding of MSC therapeutic actions and complexities, as well as costs related to the manufacturing, regulatory approval, and clinical use of living cells and engineered tissues. More recently, a shift from the view of MSCs directly contributing to tissue regeneration toward appreciating MSCs as "cell factories" that secrete a variety of bioactive molecules and extracellular vesicles with trophic and immunomodulatory activities has steered research into new MSC-based, "cell-free" therapeutic modalities. The current review recapitulates recent developments, challenges, and future perspectives of these various MSC-based bone tissue engineering and regeneration strategies.

Atrophic nonunion stromal cells form bone and recreate the bone marrow environment in vivo

Introduction:

Nonunion is a challenging condition in orthopaedics as its etiology is not fully understood. Clinical interventions currently aim to stimulate both the biological and mechanical aspects of the bone healing process by using bone autografts and surgical fixation. However, recent observations showed that atrophic nonunion tissues contain putative osteoprogenitors, raising the hypothesis that its reactivation could be explored to achieve bone repair.

Methods:

Here we characterized atrophic nonunion stromal cells (NUSC) in vitro, using bone marrow stromal cells (BMSC) and osteoblasts as controls cells of the osteoblastic lineage, and evaluated its ability to form bone in vivo.

Results:

NUSC had proliferative and senescence rates comparable to BMSC and osteoblasts, and homogeneously expressed the osteolineage markers CD90 and CD73. Regarding CD105 and CD146 expression, NUSC were closely related to osteoblasts, both with an inferior percentage of CD105⁺/CD146⁺ cells as compared to BMSC. Despite this, NUSC differentiated along the osteogenic and adipogenic lineages in vitro; and when transplanted subcutaneously into immunocompromised mice, new bone formation and hematopoietic marrow were established.

Conclusions:

This study demonstrates that NUSC are osteogenically competent, supporting the hypothesis that their endogenous reactivation could be a strategy to stimulate the bone formation while reducing the amount of bone autograft requirements.

The Impact of Type 2 Diabetes on Bone Fracture Healing

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disease known by the presence of elevated blood glucose levels. Nowadays, it is perceived as a worldwide epidemic, with a very high socioeconomic impact on public health. Many are the complications caused by this chronic disorder, including a negative impact on the cardiovascular system, kidneys, eyes, muscle, blood vessels, and nervous system. Recently, there has been increasing evidence suggesting that T2DM also adversely affects the skeletal system, causing detrimental bone effects such as bone quality deterioration, loss of bone strength, increased fracture risk, and impaired bone healing. Nevertheless, the precise mechanisms by which T2DM causes detrimental effects on bone tissue are still elusive and remain poorly studied. The aim of this review was to synthesize current knowledge on the different factors influencing the impairment of bone fracture healing under T2DM conditions. Here, we discuss new approaches used in recent studies to unveil the mechanisms and fill the existing gaps in the scientific understanding of the relationship between T2DM, bone tissue, and bone fracture healing.

Orthopaedic traumatology: fundamental principles and current controversies for the acute care surgeon

Multiply injured patients with fractures are co-managed by acute care surgeons and orthopaedic surgeons. In most centers, orthopaedic surgeons definitively manage fractures, but preliminary management, including washouts, splinting, reductions, and external fixations, may be performed by selected acute care surgeons. The acute care surgeon should have a working knowledge of orthopaedic terminology to communicate with colleagues effectively. They should have an understanding of the composition of bone, periosteum, and cartilage, and their reaction when there is an injury. Fractures are usually fixed urgently, but some multiply injured patients are better served with a damage control strategy. Extremity compartment syndrome should be suspected in all critically injured patients with or without fractures and a low threshold for compartment pressure measurements or empiric fasciotomy maintained. Acute care surgeons performing rib fracture fixation and other chest wall injury reconstructions should follow the principles of open fracture reduction and stabilization.

Exercise initiated after the onset of insulin resistance improves trabecular microarchitecture and cortical bone biomechanics of the tibia in hyperphagic Otsuka Long Evans Tokushima Fatty rats

The present study extends our previous findings that exercise, which prevents the onset of insulin resistance and type 2 diabetes (T2D), also prevents the detrimental effects of T2D on whole-bone and tissue-level strength. Our objective was to determine whether exercise improves bone's structural and material properties if insulin resistance is already present in the Otsuka Long-Evans Tokushima Fatty (OLETF) rat. The OLETF rat is hyperphagic due to a loss-of-function mutation in cholecystokinin-1 receptor (CCK-1 receptor), which leads to progressive obesity, insulin resistance and T2D after the majority of skeletal growth is complete. Because exercise reduces body mass, which is a significant determinant of bone strength, we used a body-mass-matched caloric-restricted control to isolate body-mass-independent effects of exercise on bone. Eight-wk old, male OLETF rats were fed ad libitum until onset of hyperglycemia (20weeks of age), at which time they were randomly assigned to three groups: ad libitum fed, sedentary (O-SED); ad libitum fed, treadmill running (O-EX); or, sedentary, mild caloric restriction to match body mass of O-EX (O-CR). Long-Evans Tokushima Otsuka rats served as the normophagic, normoglycemic controls (L-SED). At 32weeks of age, O-SED rats had T2D as evidenced by hyperglycemia and a significant reduction in fasting insulin compared to OLETFs at 20weeks of age. O-SED rats also had reduced total body bone mineral content (BMC), increased C-terminal telopeptide of type I collagen (CTx)/tartrate resistant acid phosphatase isoform 5b (TRAP5b), decreased N-terminal propeptide of type I procollagen (P1NP), reduced percent cancellous bone volume (BV/TV), trabecular number (Tb.N) and increased trabecular separation (Tb.Sp) and structural model index (SMI) of the proximal tibia compared to L-SED. T2D also adversely affected biomechanical properties of the tibial diaphysis, and serum sclerostin was increased and β-catenin, runt-related transcription factor 2 (Runx2) and insulin-like growth factor-I (IGF-I) protein expression in bone were reduced in O-SED vs. L-SED. O-EX or O-CR had greater total body bone mineral density (BMD) and BMC, and BV/TV, Tb.N, Tb.Sp, and SMI compared to O-SED. O-EX had lower CTx and CR greater P1NP relative to O-SED. O-EX, not O-CR, had greater cortical thickness and area, and improved whole-bone and tissue-level biomechanical properties associated with a 4-fold increase in cortical bone β-catenin protein expression vs. O-SED. In summary, EX or CR initiated after the onset of insulin resistance preserved cancellous bone volume and structure, and EX elicited additional benefits in cortical bone.

Economic Benefit of Calcium and Vitamin D Supplementation: Does It Outweigh the Cost of Nonunions?

OBJECTIVES

The purpose was to evaluate economic benefit of calcium and vitamin D supplementation in orthopaedic trauma patients. We hypothesized that reduced nonunion rates could justify the cost of supplementing every orthopaedic trauma patient.

DESIGN

Retrospective, economic model.

SETTING

Level 1 trauma center.

PATIENTS/PARTICIPANTS

Adult patients over 3 consecutive years presenting with acute fracture.

INTERVENTION

Operative or nonoperative fracture management.

MAIN OUTCOME MEASUREMENTS

Electronic medical records were queried for ICD-9 code for diagnosis of nonunion and for treatment records of nonunion for fractures initially treated within our institution.

RESULTS

In our hospital, a mean of 92 (3.9%) fractures develop nonunion annually. A 5% reduction in nonunion risk from 8 weeks of vitamin D supplementation would result in 4.6 fewer nonunions per year. The mean estimate of cost for nonunion care is $16,941. Thus, the projected reduction in nonunions after supplementation with vitamin D and calcium would save $78,030 in treatment costs per year. The resulting savings outweigh the $12,164 cost of supplementing all fracture patients during the first 8 weeks of fracture healing resulting in a net savings of $65,866 per year.

CONCLUSIONS

Vitamin D and calcium supplementation of orthopaedic trauma patients for 8 weeks after fracture seems to be cost effective. Supplementation may also reduce the number of subsequent fractures, enhance muscular strength, improve balance in the elderly, elevate mood leading to higher functional outcome scores, and diminish hospital tort liability by reducing the number of nonunions.

LEVEL OF EVIDENCE

Economic Level V. See Instructions for Authors for a complete description of levels of evidence.

Haplotypes in BMP4 and FGF Genes Increase the Risk of Peri-Implantitis

Abstract Despite the success of osseointegrated implants, failures have increased significantly, associated with development of peri-implantitis. Multiple factors influence the peri-implant bone loss, including environmental and genetic causes. BMPs (Bone morphogenetic proteins) are growth factors that induce bone formation. FGF (fibroblast growth factors) and their receptors (FGFRs) play important roles by controlling the levels of cell proliferation, differentiation and migration. BMP/FGF relationship is responsible for promoting bone regeneration and bone loss. The aim of this study was to analyze the correlation between BMP4, FGF3, FGF10 and FGFR1 genes and peri-implant bone loss. Two hundred and fifteen volunteers, with 754 dental implants, were submitted to oral examination and divided in healthy group (n=129) and peri-implantitis group (n=86). Thirteen polymorphisms in BMP4, FGF3, FGF10 and FGFR1 genes were analyzed individually and in haplotype. The chi-square test correlated genotypes, allelic and haplotype frequencies. Values of p<0.05 were considered significant. Volunteers with peri-implantitis demonstrated high incidence of total edentulism (p<0.0001) and thin peri-implant phenotype (p<0.04). Higher incidence of spontaneous bleeding, plaque and implant mobility was observed in peri-implantitis group (p<0.0001 for all). The TT polymorphic genotype for BMP4 rs2761884 was associated with healthy peri-implant (p=0.01). FGF3 rs4631909 (TT+CT genotype) also showed association with the control group (p=0.04). The frequency of C allele for FGF3 rs4631909 showed a tendency for association with peri-implantitis (p=0.08). FGF10 CCTG (p=0.03), BMP4 GAAA (p=0.05) and GGGA (p=0.02) haplotypes were associated with peri-implantitis (p=0.03). Therefore, it may be concluded that BMP4 and FGF10 haplotypes are associated with peri-implantitis.

Inflammation, Bone Healing, and Anti-Inflammatory Drugs: An Update

Fracture healing is a unique multifaceted process requiring the presence of cells, molecular mediators, and angiogenic factors. The state of inflammation dominates the initial phase, but the ideal magnitude and duration of the process for an optimal outcome remains obscure. Biological response modifiers, such as platelet-rich plasma (PRP) preparations, have been used to reconstitute the desirable early inflammatory state, but the results obtained remain inconclusive. Ongoing research to characterize and quantify the inflammatory response after bone fracture is essential in order to better understand the molecular insights of this localized reaction and to expand our armamentarium in the management of patients with an impaired fracture healing response. Non-steroidal anti-inflammatory drugs frequently administered for analgesia after trauma procedures continue to be a cause of concern for a successful bone repair response.

Bone's responses to mechanical loading are impaired in type 1 diabetes

Diabetes adversely impacts many organ systems including the skeleton. Clinical trials have revealed a startling elevation in fracture risk in diabetic patients. Bone fractures can be life threatening: nearly 1 in 6 hip fracture patients die within one year. Because physical exercise is proven to improve bone properties and reduce fracture risk in non-diabetic subjects, we tested its efficacy in type 1 diabetes. We hypothesized that diabetic bone's response to anabolic mechanical loading would be attenuated, partially due to impaired mechanosensing of osteocytes under hyperglycemia. Heterozygous C57BL/6-Ins2(Akita)/J (Akita) male and female diabetic mice and their age- and gender-matched wild-type (WT) C57BL/6J controls (7-month-old, N=5-7 mice/group) were subjected to unilateral axial ulnar loading with a peak strain of 3500 με at 2 Hz and 3 min/day for 5 days. The Akita female mice, which exhibited a relatively normal body weight and a mild 40% elevation of blood glucose level, responded with increased bone formation (+6.5% in Ct.B.Ar, and 4 to 36-fold increase in Ec.BFR/BS and Ps.BFR/BS), and the loading effects, in terms of changes of static and dynamic indices, did not differ between Akita and WT females (p ≥ 0.1). However, loading-induced anabolic effects were greatly diminished in Akita males, which exhibited reduced body weight, severe hyperglycemia (+230%), diminished bone formation (ΔCt.B.Ar: 0.003 vs. 0.030 mm(2), p=0.005), and suppressed periosteal bone appositions (ΔPs.BFR/BS, p=0.02). Hyperglycemia (25 mM glucose) was further found to impair the flow-induced intracellular calcium signaling in MLO-Y4 osteocytes, and significantly inhibited the flow-induced downstream responses including reduction in apoptosis and sRANKL secretion and PGE2 release. These results, along with previous findings showing adverse effects of hyperglycemia on osteoblasts and mesenchymal stem cells, suggest that failure to maintain normal glucose levels may impair bone's responses to mechanical loading in diabetics.

Marrow stromal stem cell autologous transplantation in denervated fracture healing: an experimental study in rats

OBJECTIVE

To investigate the influence of bone marrow stromal stem cell (BMSCs) transplantation on healing of fractures combined with central nerve injuries in rats.

METHODS

Forty-eight healthy adult SD male rats were randomly divided into the following three groups (16 rats in each group): group A, simple (left) tibial fracture; group B, tibial fracture combined with T10 spinal cord transection (SCT); group C, tibial fracture combined with T10 SCT and BMSCs transplantation. The tibial fractures were stabilized with modular intramedullary nails and all operated hind limbs were further immobilized in plaster casts to prevent unequal load bearing. BMSCs were labeled with bromodeoxyuridine and implanted into the fractures of C group rats 2 days after creation of the model. The animals in B and C groups were evaluated by postoperative Tarlov scores. The fractured tibiae were evaluated separately radiographically (X-ray and CT) and immunohistochemically 1, 2, 3 and 4 weeks after injury to assess fracture healing. In addition, the wet weights of the left tibias were measured.

RESULTS

All Tarlov score of the B and C group animals reached the requirements of the experiment. One, 2 and 3 weeks after surgery, the tibial callus widths in B and C group animals were significantly greater than those of group A rats (P < 0.05). At 4 weeks the tibial callus width in group C animals had decreased, but still differed significantly from that in group A rats (P < 0.05). One, 2, 3 and 4 weeks after surgery, the wet weights of B and C group tibias were significantly greater than those of group A (P < 0.05). Hematoxylin-eosin-stained sections showed bony union and increased bone trabecula in B and C groups and areas with particles positive for alkaline phosphatase staining were more abundant in groups B and C, especially in group C.

CONCLUSION

Neural regulation plays an important role in fracture healing. Treatment with BMSCs has a positive effect on defective callus in rats that have been subjected to SCT.

Polymorphisms in BMP4 and FGFR1 genes are associated with fracture non-union

Fracture healing is a complex process influenced by a multitude of factors and expression of several thousand genes. Polymorphisms in these genes can lead to an extended healing process and explain why certain patients are more susceptible to develop non-union. A total of 16 SNPs within five genes involved in bone repair pathogenesis (FAM5C, BMP4, FGF3, FGF10, and FGFR1) were investigated in 167 patients with long bone fractures, 101 with uneventful healing, and 66 presenting aseptic non-unions. Exclusion criteria were patients presenting pathological fractures, osteoporosis, hypertrophic and infected non-unions, pregnancy, and children. All genetic markers were genotyped using TaqMan real-time PCR. Chi-square test was used to compare genotypes, allele frequencies, and haplotype differences between groups. Binary logistic regression analyzed the significance of many covariates and the incidence of non-union. Statistical analysis revealed open fracture to be a risk factor for non-union development (p < 0.001, OR 3.6 [1.70-7.67]). A significant association of haplotype GTAA in BMP4 (p = 0.01) and FGFR1 rs13317 (p = 0.005) with NU could be observed. Also, uneventful healing showed association with FAM5C rs1342913 (p = 0.04). Our work supported the role of BMP4 and FGFR1 in NU fracture independently of the presence of previously described risk factors.

The osteoporotic acetabular fracture

Fractures of the acetabulum are some of the most challenging fractures that face orthopedic surgeons. In geriatric patients, these challenges are enhanced by the complexity of fracture patterns, the poor biomechanical characteristics of osteoporotic bone, and the comorbidities present in this population. Nonsurgical management is preferable when the fracture is stable enough to allow mobilization, and healing in a functional position can be expected. When significant displacement and/or hip instability are present, operative management is preferred in most patients, which may include open reduction and internal fixation with or without total hip arthroplasty.