Erythropoietin (EPO) — EPO-receptor signaling improves early endochondral ossification and mechanical strength in fracture healing

Erythropoietin supplementation induces dysbiosis of the gut microbiota and impacts mucosal immunity in a non-diseased mouse model

A number of drug treatments are known to alter the dialogue between the gut microbiota and the immune system components in the digestive mucosa. Alterations in intestinal homeostasis are now well known to affect peripheral immune responses and favor the occurrence of a number of pathologies such as allergies and cancers. Erythropoietin's known pleiotropic effects might explain the adverse events sometimes observed in anemic patients treated by erythropoiesis-stimulating agents (ESA). However, the impact of this therapeutic cytokine on the homeostasis of the intestinal tract has not previously been investigated in detail. By studying a mouse model of erythropoietin (EPO) supplementation for 28 days, we observed EPO-induced dysbiosis of the fecal microbiota characterized by a greater bacterial load, lower bacterial diversity and taxonomic changes. With regard to the mucosal immune system, an analysis of leukocyte populations in the small intestine and colon treatment revealed low proportions of ileal CD4 lymphocyte subpopulations (Treg, Tr17 and Th17 cells), IgA-secreting plasma cells, and a major macrophage subpopulation, involved in the control of lymphocyte responses. Our results provide for the first time a descriptive analysis of intestinal EPO's regulatory properties and raise questions about the involvement of EPO-induced alterations in the microbiota and the gut immune effectors in the control of intestinal and peripheral immune responses.

Erythropoietin treatment and osteoporotic fracture risk in hemodialysis patients: A nationwide population-based study

Objectives

Concerns about erythropoietin (EPO) therapy for anemia in patients with end-stage renal disease (ESRD) contributing to potential bone loss and increased fracture risks are growing. This study investigated the impact of EPO administration on the risk of common osteoporotic fractures in ESRD patients.

Methods

This population-based retrospective cohort study compared EPO users and non-EPO users among ESRD patients undergoing hemodialysis, diagnosed with ESRD between 2000 and 2014 identified from the National Health Insurance Research Database of Taiwan. The cohorts were matched at a propensity score ratio of 1:1, resulting in equal sample sizes of 2839. Variables related to comorbidities were considered.

Results

EPO users exhibited higher cumulative incidences of major osteoporotic fractures, hip fractures, spine fractures, and wrist fractures compared with the non-EPO user (all P < 0.001). In adjusted Cox regression models, higher adjusted subdistribution hazard ratios (aSHRs) were observed for major osteoporotic fractures (2.41, 95% confidence interval [CI] = 2.01-2.89), osteoporotic hip fractures (2.19, 95% CI = 1.69-2.85), spine fractures (2.50, 95% CI = 1.87-3.34), and wrist fractures (2.34, 95% CI = 1.44-3.78) in EPO users than in non-EPO users. The risk of major osteoporotic fractures significantly increased with increasing EPO doses (P for trend < 0.0001), and a similar trend was observed for the risks of osteoporotic spine and wrist fractures.

Conclusions

Our findings suggest that EPO treatment in patients with ESRD undergoing hemodialysis is associated with an increased risk of osteoporotic fractures.

Osteoblastic erythropoietin is not required for bone mass accrual

Erythropoietin (EPO), primarily produced by interstitial fibroblasts in the kidney during adulthood, and its receptor are well-known for their crucial role in regulating erythropoiesis. Recent research has unveiled an additional function of circulating EPO in the control of bone mass accrual and homeostasis through its receptor, which is expressed in both osteoblasts and osteoclasts. Notably, cells of the osteoblast lineage can produce and secrete functional EPO upon activation of the hypoxia signaling pathway. However, the physiological relevance of osteoblastic EPO remains to be fully elucidated. This study aimed to investigate the potential role of osteoblastic EPO in regulating bone mass accrual and erythropoiesis in young adult mice. To accomplish this, we employed a mutant mouse model lacking EPO specifically in mesenchymal progenitors and their descendants. Our findings indicate that in vivo loss of EPO in the osteoblast lineage does not significantly affect either bone mass accrual or erythropoiesis in young adult mice. Further investigations are necessary to comprehensively understand the potential contribution of EPO produced and secreted by osteoblast cells during aging, repair, and under pathological conditions.

Effects of Erythropoietin-Promoted Fracture Healing on Bone Turnover Markers in Cats

In orthopaedics, erythropoietin (EPO) is applied in the preoperative management of anaemic patients, but also as a stimulating factor to assist bone regeneration due to its angiogenic and osteoinductive potential. Since orthopaedists mainly rely on their clinical experience to assess bone healing, additional and more objective methods such as studying the dynamics of bone markers are needed. Therefore, the aim of this study was to investigate the plasma activity of bone-specific alkaline phosphatase (BALP), the N-terminal propeptide of type I collagen (PINP), the C-terminal telopeptide of type I collagen (CTX), and deoxypyridinoline (DPD) during the first 2 months of healing of comminuted fractures in cats, either non-stimulated or locally stimulated with recombinant human erythropoietin (rhEPO). The study included twelve cats of mixed breeds, aged 7.2 ± 4 months, weighing 2.11 ± 1.1 kg, with comminuted diaphyseal fractures of the femur. Surgical treatment with plate osteosynthesis was performed in all animals. The cats were randomly divided into two groups-a control (n = 6) and an EPO group (n = 6). The locally applied EPO leads to the increased activity of bone formation markers (BALP and PINP) during the second week after the osteosynthesis, preceding the peaks in the control group by two weeks. The studied bone resorption markers (DPD, CTX) varied insignificantly during the studied period. In conclusion, erythropoietin could serve as a promoter of bone healing in comminuted fractures in cats.

A Molecular Troika of Angiogenesis, Coagulopathy and Endothelial Dysfunction in the Pathology of Avascular Necrosis of Femoral Head: A Comprehensive Review

Avascular necrosis of the femoral head (ANFH) is a painful disorder characterized by the cessation of blood supply to the femoral head, leading to its death and subsequent joint collapse. Influenced by several risk factors, including corticosteroid use, excessive alcohol intake, hypercholesterolemia, smoking and some inflammatory disorders, along with cancer, its clinical consequences are thrombus formation due to underlying inflammation and endothelial dysfunction, which collaborates with coagulopathy and impaired angiogenesis. Nonetheless, angiogenesis resolves the obstructed free flow of the blood by providing alternative routes. Clinical manifestations of early stage of ANFH mimic cysts or lesions in subchondral bone, vasculitis and transient osteoporosis of the hip, rendering it difficult to diagnose, complex to understand and complicated to cure. To date, the treatment methods for ANFH are controversial as no foolproof curative strategy is available, and these depend upon different severity levels of the ANFH. From an in-depth understanding of the pathological determinants of ANFH, it is clear that impaired angiogenesis, coagulopathy and endothelial dysfunction contribute significantly. The present review has set two aims, firstly to examine the role and relevance of this molecular triad (impaired angiogenesis, coagulopathy and endothelial dysfunction) in ANFH pathology and secondly to propose some putative therapeutic strategies, delineating the fact that, for the better management of ANFH, a combined strategy to curtail this molecular triangle must be composed rather than focusing on individual contributions.

Evaluation of Preventive Role of Systemically Applied Erythropoietin after Tooth Extraction in a Bisphosphonate-Induced MRONJ Model

Background and Objectives: In this experimental study, the prophylactic effect of systemically administered erythropoietin (EPO) in medication-related osteonecrosis of the jaw (MRONJ) was evaluated. Materials and Methods: The osteonecrosis model was established using 36 Sprague Dawley rats. EPO was systemically applied before and/or after tooth extraction. Groups were formed based on the application time. All samples were evaluated histologically, histomorphometrically, and immunohistochemically. A statistically significant difference in new bone formation was observed between the groups (p < 0.001). Results: When new bone-formation rates were compared, no significant differences were observed between the control group and the EPO, ZA+PostEPO, and ZA+Pre-PostEPO groups (p = 1, 0.402, and 1, respectively); however, this rate was significantly lower in the ZA+PreEPO group (p = 0.021). No significant differences in new bone formation were observed between the ZA+PostEPO and ZA+PreEPO groups (p = 1); however, this rate was significantly higher in the ZA+Pre-PostEPO group (p = 0.009). The ZA+Pre-PostEPO group demonstrated significantly higher intensity level in VEGF protein expression than the other groups (p < 0.001). Conclusions: Administering EPO two weeks pre-extraction and continuing EPO treatment for three weeks post-extraction in ZA-treated rats optimized the inflammatory reaction, increased angiogenesis by inducing VEGF, and positively affected bone healing. Further studies are needed to determine the exact durations and doses.

Oxygen-Generating Biomaterials for Translational Bone Regenerative Engineering

Successful regeneration of critical-size defects remains one of the significant challenges in regenerative engineering. These large-scale bone defects are difficult to regenerate and are often reconstructed with matrices that do not provide adequate oxygen levels to stem cells involved in the regeneration process. Hypoxia-induced necrosis predominantly occurs in the center of large matrices since the host tissue's local vasculature fails to provide sufficient nutrients and oxygen. Indeed, utilizing oxygen-generating materials can overcome the central hypoxic region, induce tissue in-growth, and increase the quality of life for patients with extensive tissue damage. This article reviews recent advances in oxygen-generating biomaterials for translational bone regenerative engineering. We discussed different oxygen-releasing and delivery methods, fabrication methods for oxygen-releasing matrices, biology, oxygen's role in bone regeneration, and emerging new oxygen delivery methods that could potentially be used for bone regenerative engineering.

Bone Healing of Critical-Sized Femoral Defects in Rats Treated with Erythropoietin Alone or in Combination with Xenograft

Critical-size bone defect models are the standard in studies of the osteogenic potential of biomaterials. The present investigation aimed to evaluate the ability of recombinant human erythropoietin (EPO) to induce trabecular bone healing either alone or combined with a xenograft in a rat femoral critical-size defect model. Five-mm bone defects were created in the femoral diaphysis of fifty-six skeletally mature male Wistar albino rats. The animals were divided into six groups: one control group and five experimental groups. The defects in the control group were left empty, whereas an absorbable collagen cone soaked either with saline or erythropoietin (alone or in combination with xenograft) was placed in locally treated groups. The systemic treatment group received EPO subcutaneously. Bone formation was objectively evaluated through radiography, osteodensitometry and histological examination on post-operative days 30 and 90. The results demonstrate that EPO, locally applied on a collagen scaffold, was capable of inducing bone healing, whereas the single systemically administered high EPO dose had only an insignificant effect on bone formation. The combination of EPO with a bone substitute under the form of cancellous granules resulted in more rapid integration between the xenograft and host bone.

Role of hormones in bone remodeling in the craniofacial complex: A review

Background

Diseases such as periodontitis and osteoporosis are expected to rise tremendously by 2050. Bone formation and remodeling are complex processes that are disturbed in a variety of diseases influenced by various hormones.

Objective

This study aimed to review and present the roles of various hormones that regulate bone remodeling of the craniofacial complex.

Methods

A literature search was conducted on PubMed and Google Scholar for studies related to hormones and jawbone. Search strategies included the combinations ("name of hormone" + "dental term") of the following terms: "hormones", "oxytocin", "estrogen", "adiponectin", "parathyroid hormone", "testosterone", "insulin", "angiotensin", "cortisol", and "erythropoietin", combined with a dental term "jaw bone", "alveolar bone", "dental implant", "jaw + bone regeneration, healing or repair", "dentistry", "periodontitis", "dry socket", "osteoporosis" or "alveolitis". The papers were screened according to the inclusion criteria from January 1, 2000 to March 31, 2021 in English. Publications included reviews, book chapters, and original research papers; in vitro studies, in vivo animal, or human studies, including clinical studies, and meta-analyses.

Results

Bone formation and remodeling is a complex continuous process involving many hormones. Bone volume reduction following tooth extractions and bone diseases, such as periodontitis and osteoporosis, cause serious problems and require a great understanding of the process.

Conclusion

Hormones are with us all the time, shape our development and regulate homeostasis. Newly discovered effects of hormones influencing bone healing open the possibilities of using hormones as therapeutics to combat bone-related diseases.

Silk Fibroin/Collagen/Hydroxyapatite Scaffolds Obtained by 3D Printing Technology and Loaded with Recombinant Human Erythropoietin in the Reconstruction of Alveolar Bone Defects

The fast osteogenesis of the large alveolar fossa and the maintenance of the height of the alveolar ridge after tooth extraction have always been a clinical challenge. Therefore, this work describes the creation of innovative silk fibroin/collagen/hydroxyapatite (SCH) biological scaffolds by 3D printing technology, which are loaded with recombinant human erythropoietin (rh-EPO) for the reconstruction of bone defects. Low-temperature 3D printing can maintain the biological activity of silk fibroin and collagen. The SCH scaffolds showed the ideal water absorption and porosity, being a sustained-release carrier of rh-EPO. The optimized scaffolds had ideal mechanical properties in vitro, and MC3T3-E1 cells could easily adhere and proliferate on it. In vivo experiments in rabbits demonstrated that the composite scaffolds gradually degraded and promoted the accumulation and proliferation of osteoblasts and the formation of collagen fibers, significantly promoting the reconstruction of mandibular defects. In this study, a novel composite biological scaffold was prepared using 3D printing technology, and the scaffold was innovatively combined with the multifunctional growth factor rh-EPO. This provides a new optimized composite material for the reconstruction of irregular mandible defects, and this biomaterial is promising for clinical reconstruction of alveolar bone defects.

Diagnostic Imaging Studies on Local and Systemic Erythropoietin Application for Promoting Bone Regeneration in Rat Calvarial Defects

The purpose of this study was to compare the effects of local and systemic application of recombinant human erythropoietin (rhEPO) on the healing of rat calvarial defects. Twenty-four male skeletally-mature Wistar rats were used. Two bone 5 mm critical size defects were created in calvarial bones of each rat. In rats from experimental group I (n = 12), EPO was applied locally on a collagen cone in left defects, whereas a collagen cone soaked with physiological saline was placed in right defects. The rats from experimental group II were injected once intraperitoneally with 4900 IU/kg EPO; a collagen cone was only placed in left defects, whereas the right defects were left empty. The systemic effect of EPO treatment was monitored by haematological analyses on days 0, 30 and 90. Bone healing was monitored via radiography and computed tomography on the same time intervals. The results demonstrated that local EPO application had no significant effect on haemopoiesis, unlike the systemic application. At the same time, it resulted in new bone formation and therefore, could be successfully used as a means of promoting bone regeneration.

Hypoxia-Inducible Factors Signaling in Osteogenesis and Skeletal Repair

Sufficient oxygen is required to maintain normal cellular and physiological function, such as a creature’s development, breeding, and homeostasis. Lately, some researchers have reported that both pathological hypoxia and environmental hypoxia might affect bone health. Adaptation to hypoxia is a pivotal cellular event in normal cell development and differentiation and in pathological settings such as ischemia. As central mediators of homeostasis, hypoxia-inducible transcription factors (HIFs) can allow cells to survive in a low-oxygen environment and are essential for the regulation of osteogenesis and skeletal repair. From this perspective, we summarized the role of HIF-1 and HIF-2 in signaling pathways implicated in bone development and skeletal repair and outlined the molecular mechanism of regulation of downstream growth factors and protein molecules such as VEGF, EPO, and so on. All of these present an opportunity for developing therapies for bone regeneration.

The vascularization paradox of non-union formation

Despite major research efforts to elucidate mechanisms of non-union formation, failed fracture healing remains a common complication in orthopedic surgery. Adequate vascularization has been recognized as a crucial factor for successful bone regeneration, as newly formed microvessels guarantee the supply of the callus tissue with vital oxygen, nutrients, and growth factors. Accordingly, a vast number of preclinical studies have focused on the development of vascularization strategies to stimulate fracture repair. However, recent evidence suggests that stimulation of blood vessel formation is an oversimplified approach to support bone regeneration. This review discusses the role of vascularization during bone regeneration and delineates a phenomenon, for which we coin the term "the vascularization paradox of non-union-formation". This view is based on the results of a variety of experimental studies that suggest that the callus tissue of non-unions is indeed densely vascularized and that pro-angiogenic mediators, such as vascular endothelial growth factor, are sufficiently expressed at the facture site. By gaining further insights into the molecular and cellular basis of non-union vascularization, it may be possible to develop more optimized treatment approaches or even prevent the non-union formation in the future.

Development of an ischemic fracture healing model in mice

BACKGROUND AND PURPOSE

In fracture healing, ischemia caused by vascular injuries, chronic vascular diseases, and metabolic comorbidities is one of the major risk factors for delayed union and non-union formation. To gain novel insights into the molecular and cellular pathology of ischemic fracture healing, appropriate animal models are needed. Murine models are of particular interest, as they allow to study the molecular aspects of fracture healing due to the availability of both a large number of murine antibodies and gene-targeted animals. Thus, we present the development of an ischemic fracture healing model in mice.

MATERIAL AND METHODS

After inducing a mild ischemia by double ligature of the deep femoral artery in CD-1 mice, the ipsilateral femur was fractured by a 3-point bending device and stabilized by screw osteosynthesis. In control animals, the femur was fractured and stabilized without the induction of ischemia. The femora were analyzed at 2 and 5 weeks after fracture healing by means of radiology, biomechanics, histology, and histomorphometry.

RESULTS

The surgically induced ischemia delayed and impaired the process of fracture healing. This was indicated by a lower Goldberg score, decreased bending stiffness, and reduced bone callus formation in the ischemic animals when compared with the controls.

INTERPRETATION

We introduce a novel ischemic femoral fracture healing model in mice, which is characterized by delayed bone healing. In future, the use of this model may allow both the elucidation of the molecular aspects of ischemic fracture healing and the study of novel treatment strategies.

Local Application of Mineral-Coated Microparticles Loaded With VEGF and BMP-2 Induces the Healing of Murine Atrophic Non-Unions

Deficient angiogenesis and disturbed osteogenesis are key factors for the development of nonunions. Mineral-coated microparticles (MCM) represent a sophisticated carrier system for the delivery of vascular endothelial growth factor (VEGF) and bone morphogenetic protein (BMP)-2. In this study, we investigated whether a combination of VEGF- and BMP-2-loaded MCM (MCM + VB) with a ratio of 1:2 improves bone repair in non-unions. For this purpose, we applied MCM + VB or unloaded MCM in a murine non-union model and studied the process of bone healing by means of radiological, biomechanical, histomorphometric, immunohistochemical and Western blot techniques after 14 and 70 days. MCM-free non-unions served as controls. Bone defects treated with MCM + VB exhibited osseous bridging, an improved biomechanical stiffness, an increased bone volume within the callus including ongoing mineralization, increased vascularization, and a histologically larger total periosteal callus area consisting predominantly of osseous tissue when compared to defects of the other groups. Western blot analyses on day 14 revealed a higher expression of osteoprotegerin (OPG) and vice versa reduced expression of receptor activator of NF-κB ligand (RANKL) in bone defects treated with MCM + VB. On day 70, these defects exhibited an increased expression of erythropoietin (EPO), EPO-receptor and BMP-4. These findings indicate that the use of MCM for spatiotemporal controlled delivery of VEGF and BMP-2 shows great potential to improve bone healing in atrophic non-unions by promoting angiogenesis and osteogenesis as well as reducing early osteoclast activity.

Erythropoietin Non-hematopoietic Tissue Response and Regulation of Metabolism During Diet Induced Obesity

Erythropoietin (EPO) receptor (EPOR) determines EPO response. High level EPOR on erythroid progenitor cells gives rise to EPO regulated production of red blood cells. Animal models provide evidence for EPO activity in non-hematopoietic tissue mediated by EPOR expression. Beyond erythropoiesis, EPO activity includes neuroprotection in brain ischemia and trauma, endothelial nitric oxide production and cardioprotection, skeletal muscle wound healing, and context dependent bone remodeling affecting bone repair or bone loss. This review highlights examples of EPO protective activity in select non-hematopoietic tissue with emphasis on metabolic response mediated by EPOR expression in fat and brain and sex-specific regulation of fat mass and inflammation associated with diet induced obesity. Endogenous EPO maintains glucose and insulin tolerance and protects against fat mass accumulation and inflammation. Accompanying the increase in erythropoiesis with EPO treatment is improved glucose tolerance and insulin response. During high fat diet feeding, EPO also decreases fat mass accumulation in male mice. The increased white adipose tissue inflammation and macrophage infiltration associated with diet induced obesity are also reduced with EPO treatment with a shift toward an anti-inflammatory state and decreased inflammatory cytokine production. In female mice the protective effect of estrogen against obesity supersedes EPO regulation of fat mass and inflammation, and requires estrogen receptor alpha activity. In brain, EPOR expression in the hypothalamus localizes to proopiomelanocortin neurons in the arcuate nucleus that promotes a lean phenotype. EPO stimulation of proopiomelanocortin neurons increases STAT3 signaling and production of proopiomelanocortin. Cerebral EPO contributes to metabolic response, and elevated brain EPO reduces fat mass and hypothalamus inflammation during diet induced obesity in male mice without affecting EPO stimulated erythropoiesis. Ovariectomy abrogates the sex-specific metabolic response of brain EPO. The sex-dimorphic EPO metabolic response associated with fat mass accumulation and inflammation during diet induced obesity provide evidence for crosstalk between estrogen and EPO in their anti-obesity potential in female mice mediated in part via tissue specific response in brain and white adipose tissue. Endogenous and exogenous EPO response in non-hematopoietic tissue demonstrated in animal models suggests additional activity by which EPO treatment may affect human health beyond increased erythropoiesis.

Erythropoietin treatment and the risk of hip fractures in hemodialysis patients

Erythropoietin (EPO) is the primary regulator of bone marrow erythropoiesis. Mouse models have provided evidence that EPO also promotes bone remodeling and that EPO-stimulated erythropoiesis is accompanied by bone loss independent of increased red blood cell production. EPO has been used clinically for three decades to treat anemia in end-stage renal disease, and notably, although the incidence of hip fractures decreased in the United States generally after 1990, it rose among hemodialysis patients coincident with the introduction and subsequent dose escalation of EPO treatment. Given this clinical paradox and findings from studies in mice that elevated EPO affects bone health, we examined EPO treatment as a risk factor for fractures in hemodialysis patients. Relationships between EPO treatment and hip fractures were analyzed using United States Renal Data System (USRDS) datasets from 1997 to 2013 and Consolidated Renal Operations in a Web-enabled Network (CROWNWeb) datasets for 2013. Fracture risks for patients treated with <50 units of EPO/kg/week were compared to those receiving higher doses by multivariable Cox regression. Hip fracture rates for 747,832 patients in USRDS datasets (1997-2013) increased from 12.0 per 1000 patient years in 1997 to 18.9 in 2004, then decreased to 13.1 by 2013. Concomitantly, average EPO doses increased from 11,900 units/week in 1997 to 18,300 in 2004, then decreased to 8,800 by 2013. During this time, adjusted hazard ratios for hip fractures with EPO doses of 50-149, 150-299, and ≥ 300 units/kg/week compared to <50 units/kg/week were 1.08 (95% confidence interval [CI], 1.01-1.15), 1.22 (95% CI, 1.14-1.31), and 1.41 (95% CI, 1.31-1.52), respectively. Multivariable analyses of 128,941 patients in CROWNWeb datasets (2013) replicated these findings. This study implicates EPO treatment as an independent risk factor for hip fractures in hemodialysis patients and supports the conclusion that EPO treatment may have contributed to changing trends in fracture incidence for these patients during recent decades. Published 2021. This article is a U.S. Government work and is in the public domain in the USA. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Preclinical studies on pleiotropic functions of erythropoietin on bone healing

Erythropoietin (ЕPО) is a glycoprotein hormone, mainly known for its haemopoietic function. For orthopaedics, its pleiotropic effects – osteogenic and angiogenic potential, are of primary interest. The exact mechanism of EPO action is still unclear. The effects of EPO on bone healing were investigated through experiments with rats, mice, rabbits and pigs. Each of used models for experimental bone defects (calvarial models, long bone segmental defects, posterolateral spinal fusion and corticosteroid-induced femoral head osteonecrosis) has specific advantages and flaws. Obtaining specific and correct results is largely dependent on the used model. The brief evaluation of models could serve for standardisation of preclinical studies on bone regeneration.

Effects of Erythropoietin in White Adipose Tissue and Bone Microenvironment

Erythropoietin (EPO) is expressed primarily in fetal liver and adult kidney to stimulate red blood cell production. Erythropoietin receptor expression is not restricted to erythroid progenitor cells, and non-erythroid EPO activity includes immune response and bone remodeling. In bone fracture models, EPO administration promotes bone formation and accelerates bone healing. In contrast, in healthy adult mice, exogenous EPO-stimulated erythropoiesis has been concomitant with bone loss, particularly at high EPO, that may be accompanied by increased osteoclast activation. Other EPO-associated responses include reduced inflammation and loss of fat mass with high-fat diet feeding, especially in male mice. While EPO exhibited a sex-dimorphic response in regulation of fat mass and inflammation in obese mice, EPO-stimulated erythropoiesis as well as EPO-associated bone loss was comparable in males and females. EPO administration in young mice and in obese mice resulted in bone loss without increasing osteoclasts, suggesting an osteoclast-independent mechanism, while loss of endogenous EPO decreased bone development and maintenance. Ossicle formation of bone marrow stromal cell transplants showed that EPO directly regulates the balance between osteogenesis and adipogenesis. Therefore, during development, endogenous EPO contributes to normal bone development and in maintaining the balance between osteogenesis and adipogenesis in bone marrow stromal cells, while EPO treatment in mice increased erythropoiesis, promoted bone loss, decreased bone marrow adipogenesis, and increased osteoclast activity. These observations in mouse models suggest that the most prevalent use of EPO to treat anemia associated with chronic kidney disease may compromise bone health and increase fracture risk, especially at a high dose.

Erythropoietin regulates metabolic response in mice via receptor expression in adipose tissue, brain, and bone

Erythropoietin (EPO) acts by binding to erythroid progenitor cells to regulate red blood cell production. While EPO receptor (Epor) expression is highest on erythroid tissue, animal models exhibit EPO activity in nonhematopoietic tissues, mediated, in part, by tissue-specific Epor expression. This review describes the metabolic response in mice to endogenous EPO and EPO treatment associated with glucose metabolism, fat mass accumulation, and inflammation in white adipose tissue and brain during diet-induced obesity and with bone marrow fat and bone remodeling. During high-fat diet-induced obesity, EPO treatment improves glucose tolerance, decreases fat mass accumulation, and shifts white adipose tissue from a pro-inflammatory to an anti-inflammatory state. Fat mass regulation by EPO is sex dimorphic, apparent in males and abrogated by estrogen in females. Cerebral EPO also regulates fat mass and hypothalamus inflammation associated with diet-induced obesity in males and ovariectomized female mice. In bone, EPO contributes to the balance between adipogenesis and osteogenesis in both male and female mice. EPO treatment promotes bone loss mediated via Epor in osteoblasts and reduces bone marrow adipocytes before and independent of change in white adipose tissue fat mass. EPO regulation of bone loss and fat mass is independent of EPO-stimulated erythropoiesis. EPO nonhematopoietic tissue response may relate to the long-term consequences of EPO treatment of anemia in chronic kidney disease and to the alternative treatment of oral hypoxia-inducible factor prolyl hydroxylase inhibitors that increase endogenous EPO production.

Vascularization Strategies in the Prevention of Nonunion Formation

Delayed healing and nonunion formation are major challenges in orthopedic surgery, which require the development of novel treatment strategies. Vascularization is considered one of the major prerequisites for successful bone healing, providing an adequate nutrient supply and allowing the infiltration of progenitor cells to the fracture site. Hence, during the last decade, a considerable number of studies have focused on the evaluation of vascularization strategies to prevent or to treat nonunion formation. These involve (1) biophysical applications, (2) systemic pharmacological interventions, and (3) tissue engineering, including sophisticated scaffold materials, local growth factor delivery systems, cell-based techniques, and surgical vascularization approaches. Accumulating evidence indicates that in nonunions, these strategies are indeed capable of improving the process of bone healing. The major challenge for the future will now be the translation of these strategies into clinical practice to make them accessible for the majority of patients. If this succeeds, these vascularization strategies may markedly reduce the incidence of nonunion formation. Impact statement Delayed healing and nonunion formation are a major clinical problem in orthopedic surgery. This review provides an overview of vascularization strategies for the prevention and treatment of nonunions. The successful translation of these strategies in clinical practice is of major importance to achieve adequate bone healing.

The effect of erythropoietin on rat rotator cuff repair model: An experimental study

OBJECTIVES

The aim of this study was to determine whether erythropoietin (EPO) can enhance rotator cuff healing in rats as measured by histological analysis and biomechanical testing.

METHODS

A total of 72 rats were included in this study. In the control group (n = 24), repair was performed without EPO injection. In the local group (n = 24) EPO was injected in the repair site. In the systemic group (n = 24) EPO was administered as an intraperitoneal injection every day for 10 days after repair. Rats were euthanized on day 10 (n = 12 from each group) and day 28 (n = 12 from each group). Histopathological (n = 6) and biomechanical examinations (n = 6) were done.

RESULTS

Biomechanical results reveal that the maximum load to failure values of the early control group were statistically lower than those of the early systemic group (p = 0.006). Comparing the the total Bonar values histopathologically reveal that the early systemic group was statistically higher than those of the early local group (p = 0.043). The late control group was statistically higher than those of the late local group (p = 0.003) and the late systemic group (p = 0.034). The late systemic group was statistically higher than those of the late local group (p = 0.003).

CONCLUSIONS

EPO application had a positive effect biomechanically in the early euthanized group and histopathologically in the late euthanized group.

Erythropoietin-Induced Changes in Bone and Bone Marrow in Mouse Models of Diet-Induced Obesity

Obesity remodels bone and increases bone marrow adipocytes (BMAT), which negatively regulate hematopoiesis and bone. Reduced BMAT could restore altered hematopoiesis and bone features. We analyzed the potential of erythropoietin (EPO), the cytokine required for erythropoiesis, to inhibit BMAT in C57BL6/J mice fed four weeks of a high-fat diet (HFD). Acute EPO administration markedly decreased BMAT in regular chow diet (RCD) and HFD-fed mice, without affecting whole body fat mass. Micro-CT analysis showed EPO reduced trabecular bone in RCD- and HFD-fed mice, but EPO-treated HFD-fed mice maintained cortical bone mineral density and cortical bone volume, which was reduced on RCD. Despite achieving similar increased hematocrits with BMAT loss in RCD- and HFD-fed mice treated with EPO, decreased bone marrow cellularity was only observed in RCD-fed mice concomitant with an increasing percentage of bone marrow erythroid cells. In contrast, in HFD-fed mice, EPO increased endothelial cells and stromal progenitors with a trend toward the normalization of marrow homeostasis. EPO administration increased c-terminal FGF23 and intact serum FGF23 only in HFD-fed mice. These data demonstrate the distinct EPO responses of bone and marrow in normal and obese states, accompanying EPO-induced loss of BMAT.

The Many Facets of Erythropoietin Physiologic and Metabolic Response

In mammals, erythropoietin (EPO), produced in the kidney, is essential for bone marrow erythropoiesis, and hypoxia induction of EPO production provides for the important erythropoietic response to ischemic stress, such as during blood loss and at high altitude. Erythropoietin acts by binding to its cell surface receptor which is expressed at the highest level on erythroid progenitor cells to promote cell survival, proliferation, and differentiation in production of mature red blood cells. In addition to bone marrow erythropoiesis, EPO causes multi-tissue responses associated with erythropoietin receptor (EPOR) expression in non-erythroid cells such neural cells, endothelial cells, and skeletal muscle myoblasts. Animal and cell models of ischemic stress have been useful in elucidating the potential benefit of EPO affecting maintenance and repair of several non-hematopoietic organs including brain, heart and skeletal muscle. Metabolic and glucose homeostasis are affected by endogenous EPO and erythropoietin administration affect, in part via EPOR expression in white adipose tissue. In diet-induced obese mice, EPO is protective for white adipose tissue inflammation and gives rise to a gender specific response in weight control associated with white fat mass accumulation. Erythropoietin regulation of fat mass is masked in female mice due to estrogen production. EPOR is also expressed in bone marrow stromal cells (BMSC) and EPO administration in mice results in reduced bone independent of the increase in hematocrit. Concomitant reduction in bone marrow adipocytes and bone morphogenic protein suggests that high EPO inhibits adipogenesis and osteogenesis. These multi-tissue responses underscore the pleiotropic potential of the EPO response and may contribute to various physiological manifestations accompanying anemia or ischemic response and pharmacological uses of EPO.

Recombinant Human Erythropoietin Proteins Synthesized in Escherichia coli Cells: Effects of Additional Domains on the in vitro and in vivo Activities

The aim of this work was to compare biological activities of three variants of bacterially expressed human recombinant erythropoietin (EPO) with additional protein domains: 6His-s-tag-EPO protein carrying the s-tag (15-a.a. oligopeptide from bovine pancreatic ribonuclease A) at the N-terminus and HBD-EPO and EPO-HBD proteins containing heparin-binding protein domains (HBD) of the bone morphogenetic protein 2 from Danio rerio at the N- and C-termini, respectively. The commercial preparation Epostim (LLC Pharmapark, Russia) produced by synthesis in Chinese hamster ovary cells was used for comparison. The EPO variant with the C-terminal HBD domain connected by a rigid linker (EPO-HBD) possesses the best properties as compared to HBD-EPO with the reverse domain arrangement. It was ~13 times more active in vitro (i.e., promoted proliferation of human erythroleukemia TF-1 cells) and demonstrated a higher rate of association with the erythropoietin receptor. EPO-HBD also exhibited the greatest binding to the demineralized bone matrix (DBM) and more prolonged release from the DBM among the four proteins studied. Subcutaneous administration of EPO-HBD immobilized on DBM resulted in significantly more pronounced vascularization of surrounding tissues in comparison with the other proteins and DBM alone. Therefore, EPO-HBD displayed better performance with regard to all the investigated parameters than other examined EPO variants, and it seems promising to study the possibility of its medical use.

Pleiotropic effects of Erythropoietin. Influence of Erythropoietin on processes of mesenchymal stem cells differentiation

Structure and synthesis of Erythropoietin: Erythropoietin (EPO) is a glycoprotein hormone.

Recombinant Erythropoietin (Epoetin): Human recombinant erythropoietin is characterised as a factor which stimulates differentiation and proliferation of erythroid precursor cells, and as a tissue protective factor.

Anti-ischemic effects of recombinant Erythropoietin: Erythropoietin is one of the most perspective humoral agents which are involved in the preconditioning phenomenon.

Erythropoietin receptors and signal transduction pathways: Erythropoietin effects on cells through their interconnection with erythropoietin receptors, which triggers complex intracellular signal cascades, such as JAK2/STAT signaling pathway, phosphatidylinositol 3-kinase (PI3K), protein kinase C, mitogen-activated protein kinase (MAPK), and nuclear factor (NF)-κB signaling pathways.

Mechanisms of the effect of Erythropoietin on hematopoietic and non-hematopoietic cells and tissues: In addition to regulation of haemopoiesis, erythropoietin mediates bone formation as it has an effect on hematopoietic stem cells and osteoblastic niche, and this illustrates connection between the processes of haematopoiesis and osteopoiesis which take place in the red bone marrow.

The effect of Erythropoietin on mesenchymal stem cells and process of bone tissue formation: Erythropoietin promotes mesenchymal stem cells proliferation, migration and differentiation in osteogenic direction. The evidence of which is expression of bone phenotype by cells under the influence of EPO, including activation of bone specific transcription factors Runx2, osteocalcin and bone sialoprotein.

Conclusion: Erythropoietin has a pleiotropic effect on various types of cells and tissues. But the mechanisms which are involved in the process of bone tissue restoration via erythropoietin are still poorly understood.

Synthesis in Escherichia coli and Characterization of Human Recombinant Erythropoietin with Additional Heparin-Binding Domain

Recombinant human erythropoietin (EPO) with additional N-terminal heparin-binding protein domain (HBD) from bone morphogenetic protein 2 was synthesized in Escherichia coli cells. A procedure for HBD-EPO purification and refolding was developed for obtaining highly-purified HBD-EPO. The structure of recombinant HBD-EPO was close to that of the native EPO protein. HBD-EPO contained two disulfide bonds, as shown by MALDI-TOF mass spectrometry. The protein demonstrated in vitro biological activity in the proliferation of human erythroleukemia TF-1 cell test and in vivo activity in animal models. HBD-EPO increased the number of reticulocytes in the blood after subcutaneous injection and displayed local angiogenic activity after subcutaneous implantation of demineralized bone matrix (DBM) discs with immobilized HBD-EPO. We developed a quantitative sandwich ELISA method for measuring HBD-EPO concentration in solution using rabbit polyclonal serum and commercial monoclonal anti-EPO antibodies. Pharmacokinetic properties of HBD-EPO were typical for bacterially produced EPO. Under physiological conditions, HBD-EPO can reversibly bind to DBM, which is often used as an osteoplastic material for treatment of bone pathologies. The data on HBD-EPO binding to DBM and local angiogenic activity of this protein give hope for successful application of HBD-EPO immobilized on DBM in experiments on bone regeneration.

Effects of erythropoietin for precaution of steroid-induced femoral head necrosis in rats

BACKGROUND

Steroids such as glucocorticoid have been widely used for their excellent anti-inflammatory, anti-immune, and anti-shock properties. However, the long-term use in high doses has been found to cause necrosis of femoral head and other serious adverse reactions. Thus, it is of great importance to safely use these medications on patients without inducing bone necrosis.

METHODS

In this preclinical study, we examined the effects of erythropoietin (EPO) to attenuate the induction of steroid-induced femoral bone necrosis using rats to build up the in-vivo models. Rats were randomly divided into three groups: negative control group (group A), disease group (group B), and EPO group (group C). 20 mg/kg methylprednisolone was administrated into group B and group C for 6 weeks with two intramuscular injections per week per rat. Group C was further given daily intraperitoneal injections of rHuEPO during this period. Group A received only injection of saline at the same schedule. 12 weeks after the initial drug administration, the rats' femoral tissues were harvested for HE staining, immunohistochemistry studies for PECAM-1(also CD31) expression and Western Blotting for VEGF expression.

RESULTS

Histology studies showed that compared with the disease group, EPO group had significant improvement and bone morphology being much closer to the negative control group. Immunohistochemical studies revealed that EPO group had statistically much more expression of PECAM-1 than the other groups did. Western Blot demonstrated that the EPO group had significantly higher VEGF expression than the disease group.

CONCLUSION

Results suggested that simultaneous injection of EPO could partially prevent steroid-induced ANFH.

Context-Dependent Skeletal Effects of Erythropoietin

Erythropoietin (Epo) is the main hormone that regulates the production of red blood cells (hematopoiesis), by stimulating their progenitors. Beyond this vital function, several emerging roles have been noted for Epo in other tissues, including neurons, heart, and retina. The skeletal system is also affected by Epo; however, its actions on bone are, as yet, controversial. Here, we review the seemingly contradicting evidence regarding Epo effects on bone remodeling. We also discuss the evidence pointing to a direct vs indirect effect of Epo on the osteoblastic and osteoclastic cell lineages. The current controversy may derive from a context-dependent mode of function of Epo, namely, opposite skeletal actions during bone regeneration and steady-state bone remodeling. Differences in conclusions deriving from the published in vitro studies may thus relate to the different experimental conditions. Taken together, the current state-of-the-art indicates definite Epo effects on bone cells and points to the complexity of the mode of function.

Increased bone formation in a rabbit long-bone defect model after single local and single systemic application of erythropoietin

Background and purpose - Delayed bone healing with non-union is a common problem. Further options to increase bone healing together with surgery are needed. We therefore evaluated a 1-dose single application of erythropoietin (EPO), applied either locally to the defect or systemically during surgery, in a critical-size rabbit long-bone defect. Material and methods - 19 New Zealand White rabbits received a 15-mm defect in the radius diaphysis. An absorbable gelatin sponge was soaked with saline (control group and systemic treatment group) or EPO (local treatment group) and implanted into the gap. The systemic treatment group received EPO subcutaneously. In vivo micro-CT analysis was performed 4, 8, and 12 weeks postoperatively. Vascularization was evaluated histologically. Results - Semiquantitative histomorphometric and radiological evaluation showed increased bone formation (2.3- to 2.5-fold) in both treatment groups after 12 weeks compared to the controls. Quantitative determination of bone volume and tissue volume showed superior bone healing after EPO treatment at all follow-up time points, with the highest values after 12 weeks in locally treated animals (3.0- to 3.4-fold). More vascularization was found in both EPO treatment groups. Interpretation - Initial single dosing with EPO was sufficient to increase bone healing substantially after 12 weeks of follow-up. Local application inside the defect was most effective, and it can be administered directly during surgery. Apart from effects on ossification, systemic and local EPO treatment leads to increased callus vascularization.

Ovariectomy-Induced Osteopenia Influences the Middle and Late Periods of Bone Healing in a Mouse Femoral Osteotomy Model

OBJECTIVE

It is known that bone healing is delayed in the presence of osteoporosis in humans. However, due to the complexities of the healing of osteoporotic fractures, animal models may be more appropriate for studying the effects of osteoporosis in more detail and for testing drugs on the fracture repair process. The purpose of this study was to investigate the influence of ovariectomy-induced osteopenia in bone healing in an open femoral osteotomy model, and to test the feasibility of this model for evaluating the healing process under osteopenic conditions.

METHODS

Ovariectomized (OVX) mouse models were employed to assess the effects of osteopenia on fracture healing, A mid-shaft femur osteotomy model was also established 3 weeks after ovariectomy as an osteopenic fracture group (OVX group). Femurs were then harvested at 2 weeks and 6 weeks after fracture for X-ray radiography, micro-computed tomography (micro-CT), histology, and biomechanical analysis. A sham-operated group (sham group) was used for comparison.

RESULTS

The OVX mice had significantly lower bone volume density (BVF), volumetric bone mineral density (vBMD), and tissue mineral density (TMD) in the fracture calluses at 6 weeks (p<0.05), and similar trend was observed in 2 weeks. Additionally, larger calluses in OVX animals were observed via micro-CT and X-ray, but these did not result in better healing outcomes, as determined by biomechanical test at 6 weeks. Histological images of the healing fractures in the OVX mice found hastening of broken end resorption and delay of hard callus remodeling. The impaired biomechanical measurements in the OVX group (p<0.05) were consistent with micro-CT measurements and radiographic scoring, which also indicated delay in fracture healing of the OVX group.

CONCLUSIONS

This study provided evidence that ovariectomy-induced osteopenia impair the middle and late bone healing process. These data also supported the validity of the mouse femoral osteotomy model in evaluating the process of bone healing under osteopenic conditions.

Evaluation of the osteogenesis and angiogenesis effects of erythropoietin and the efficacy of deproteinized bovine bone/recombinant human erythropoietin scaffold on bone defect repair

Erythropoietin (EPO) could promote the angiogenesis and may also play a role in bone regeneration. This study was conducted to evaluate the osteogenesis and angiogenesis effects of EPO and the efficacy of deproteinized bovine bone/recombinant human EPO scaffold on bone defect repair. Twenty-four healthy adult goats were chosen to build goat defects model and randomly divided into four groups. The goats were treated with DBB/rhEPO scaffolds (group A), porous DBB scaffolds (group B), autogenous cancellous bone graft (group C), and nothing (group D). Animals were evaluated with radiological and histological methods at 4, 8 and 12 weeks after surgery. The grey value of radiographs was used to evaluate the healing of the defects and the outcome revealed that the group A had a better outcome of defect healing compared with group B (P < 0.05). However, the grey values in group A were lower than group C at week 4 and week 8 (P < 0.05), but at week 12 their difference had no statistical significance (P > 0.05). The newly formed bone area was calculated from histological sections and the results demonstrated that the amount of new bone in group A increased significantly compared with that in group B (P < 0.05) but was inferior to that in group C (P > 0.05) at 4, 8, 12 weeks respectively. In addition, the expression of vascular endothelial growth factor (VEGF) by immunohistochemical testing and real-time polymerase chain reaction at 12 weeks in group A was significantly higher than that in group B (P < 0.05), and also better than that in group C at week 4 and week 8 (P < 0.05), but at week 12 their difference had no statistical significance (P > 0.05). Therefore, EPO has significant effects on bone formation and angiogenesis, and has capacity to promote the repair of bone defects. It is worthy of being recommended to further studies.

The effect of erythropoietin on biomechanical properties of the Achilles tendon during the healing process: an experimental study

Background

The aim of this study was to examine the potential biomechanical and histological benefits of systemic erythropoietin administration during the healing of Achilles tendon injury in a rat experimental model.

Methods

Eighty Sprague-Dawley female rats were included in this study. Animals were randomly assigned into two groups with 40 animals in each: erythropoietin group and control group. Then each group was further divided into four subgroups corresponding to four time points with 10 animals in each. A full-thickness cut was made on the Achilles tendon of each animal and then the tendon was sutured with modified Kessler method. Erythropoietin groups received intraperitoneal erythropoietin (500 IU/kg/day) every day at same time throughout the study period, and the control groups received saline in a similar manner. Animals were sacrificed at four time points, and tensile test was performed on each tendon sample to assess maximum load for each sample. In addition, histopathological examination and scoring was done.

Results

Both groups had improvement on tensile test (maximum load) over time. However, groups did not differ with regard to maximum load in any of the time points. Similarly, groups did not differ with regard to any of the histopathological scores over time.

Conclusions

The findings of this study do not support the benefit of systemic erythropoietin administration in Achilles tendon healing process. Further evidence from larger experimental studies is required to justify any such potential benefit.

Electronic supplementary material

The online version of this article (doi:10.1186/s13018-016-0390-1) contains supplementary material, which is available to authorized users.

Erythropoietin in bone - Controversies and consensus

Erythropoietin (Epo) is the main hormone that regulates the production of red blood cells (hematopoiesis), by stimulating their progenitors. Beyond this vital function, several emerging roles have been noted for Epo in other tissues, including neurons, heart and retina. The skeletal system is also affected by Epo, however, its actions on bone are, as yet, controversial. Here, we review the seemingly contradicting evidence regarding Epo effects on bone remodeling. We also discuss the evidence pointing to a direct versus indirect effect of Epo on the osteoblastic and osteoclastic cell lineages. The current controversy may derive from a context-dependent mode of action of Epo, namely opposite skeletal actions during bone regeneration and steady-state bone remodeling. Differences in conclusions from the published in-vitro studies may thus relate to the different experimental conditions. Taken together, these studies indicate a complexity of Epo functions in bone cells.

Dual Delivery of EPO and BMP2 from a Novel Modular Poly-ɛ-Caprolactone Construct to Increase the Bone Formation in Prefabricated Bone Flaps

Poly-ɛ-caprolactone (PCL) is a biocompatible polymer that has mechanical properties suitable for bone tissue engineering; however, it must be integrated with biologics to stimulate bone formation. Bone morphogenetic protein-2 (BMP2) delivered from PCL produces bone when implanted subcutaneously, and erythropoietin (EPO) works synergistically with BMP2. In this study, EPO and BMP2 are adsorbed separately on two 3D-printed PCL scaffold modules that are assembled for codelivery on a single scaffold structure. This assembled modular PCL scaffold with dual BMP2 and EPO delivery was shown to increase bone growth in an ectopic location when compared with BMP2 delivery along a replicate scaffold structure. EPO (200 IU/mL) and BMP2 (65 μg/mL) were adsorbed onto the outer and inner portions of a modular scaffold, respectively. Protein binding and release studies were first quantified. Subsequently, EPO+BMP2 and BMP2 scaffolds were implanted subcutaneously in mice for 4 and 8 weeks, and the regenerated bone was analyzed with microcomputed tomography and histology; 8.6±1.4 μg BMP2 (22%) and 140±29 IU EPO (69.8%) bound to the scaffold and <1% BMP2 and 83% EPO was released in 7 days. Increased endothelial cell proliferation on EPO-adsorbed PCL discs indicated protein bioactivity. At 4 and 8 weeks, dual BMP2 and EPO delivery regenerated more bone (5.1±1.1 and 5.5±1.6 mm(3)) than BMP2 alone (3.8±1.1 and 4.3±1.7 mm(3)). BMP2 and EPO scaffolds had more ingrowth (1.4%±0.6%) in the outer module when compared with BMP2 (0.8%±0.3%) at 4 weeks. Dual delivery produced more dense cellular marrow, while BMP2 had more fatty marrow. Dual EPO and BMP2 delivery is a potential method to regenerate bone faster for prefabricated flaps.

Erythropoietin directly stimulates osteoclast precursors and induces bone loss

Erythropoietin (EPO) primarily regulates red blood cell formation, and EPO serum levels are increased on hypoxic stress (e.g., anemia and altitude). In addition to anemia, recent discoveries suggest new therapeutic indications for EPO, unrelated to erythropoiesis. We investigated the skeletal role of EPO using several models of overexpression (Tg6 mice) and EPO administration (intermittent/continuous, high/low doses) in adult C57Bl6 female mice. Using microcomputed tomography, histology, and serum markers, we found that EPO induced a 32%-61% trabecular bone loss caused by increased bone resorption (+60%-88% osteoclast number) and reduced bone formation rate (-19 to -74%; P < 0.05 throughout). EPO targeted the monocytic lineage by increasing the number of bone monocytes/macrophages, preosteoclasts, and mature osteoclasts. In contrast to the attenuated bone formation in vivo, EPO treatment in vitro did not inhibit osteoblast differentiation and activity, suggesting an indirect effect of EPO on osteoblasts. However, EPO had a direct effect on preosteoclasts by stimulating osteoclastogenesis in isolated cultures (+60%) via the Jak2 and PI3K pathways. In summary, our findings demonstrate that EPO negatively regulates bone mass and thus bears significant clinical implications for the potential management of patients with endogenously or therapeutically elevated EPO levels.

The osteogenic effect of erythropoietin on human mesenchymal stromal cells is dose-dependent and involves non-hematopoietic receptors and multiple intracellular signaling pathways

Erythropoietin (EPO) is a pleiotropic growth factor. Of interest for skeletal tissue engineering, the non-hematopoietic capabilities of EPO include its osteogenic and angiogenic potencies. The main aim of this study was to investigate the dose-response relationship and determine the lowest effective dose of EPO that reliably increases the osteogenic differentiation of human mesenchymal stromal cells (hMSCs). Additional aims were to elucidate the surface receptors and to investigate the role of the intracellular signaling pathways by blocking the mammalian target of rapamycin (mTOR), Jak-2 protein tyrosine kinase (JAK2), and phosphoinositide 3-kinases (PI3K). The primary outcome measures were two mineralization assays, Arsenazo III and alizarin red, applied after 10, 14, and 21 days. Moreover, alkaline phosphatase activity, cell number, and cell viability were determined after 2 and 7 days. A proportional dose-response relationship was observed. In vivo, the lowest effective dose of 20 IU/ml should be used for further research to accommodate safety concerns about adverse effects. Ex vivo, the most effective dose of 100 IU/ml could facilitate vascularization and bone ingrowth in cell-based scaffolds. The expression of non-hematopoietic receptors EPOR and CD131 was documented, and EPO triggered all three examined intracellular pathways. Future studies of the efficacy of EPO in cell-based tissue engineering can benefit from our findings.

Erythropoietin promotes bone formation through EphrinB2/EphB4 signaling

Recent studies have demonstrated that erythropoietin (EPO) has extensive nonhematopoietic biological functions. However, little is known about how EPO regulates bone formation, although several studies suggested that EPO can affect bone homeostasis. In this study, we investigated the effects of EPO on the communication between osteoclasts and osteoblasts through the ephrinB2/EphB4 signaling pathway. We found that EPO slightly promotes osteoblastic differentiation with the increased expression of EphB4 in ST2 cells. However, EPO increased the expression of Nfatc1 and ephrinB2 but decreased the expression of Mmp9 in RAW264.7 cells, resulting in an increase of ephrinB2-expressing osteoclasts and a decrease in resorption activity. The stimulation of ephrinB2/EphB4 signaling via ephrinB2-Fc significantly promoted EPO-mediated osteoblastic differentiation in ST2 cells. EphB4 knockdown through EphB4 shRNA inhibited EPO-mediated osteoblastic phenotypes. Furthermore, in vivo assays clearly demonstrated that EPO efficiently induces new bone formation in the alveolar bone regeneration model. Taken together, these results suggest that ephrinB2/EphB4 signaling may play an important role in EPO-mediated bone formation.

EPO promotes bone repair through enhanced cartilaginous callus formation and angiogenesis

Erythropoietin (EPO)/erythropoietin receptor (EPOR) signaling is involved in the development and regeneration of several non-hematopoietic tissues including the skeleton. EPO is identified as a downstream target of the hypoxia inducible factor-α (HIF-α) pathway. It is shown that EPO exerts a positive role in bone repair, however, the underlying cellular and molecular mechanisms remain unclear. In the present study we show that EPO and EPOR are expressed in the proliferating, pre-hypertrophic and hypertrophic zone of the developing mouse growth plates as well as in the cartilaginous callus of the healing bone. The proliferation rate of chondrocytes is increased under EPO treatment, while this effect is decreased following siRNA mediated knockdown of EPOR in chondrocytes. EPO treatment increases biosynthesis of proteoglycan, accompanied by up-regulation of chondrogenic marker genes including SOX9, SOX5, SOX6, collagen type 2, and aggrecan. The effects are inhibited by knockdown of EPOR. Blockage of the endogenous EPO in chondrocytes also impaired the chondrogenic differentiation. In addition, EPO promotes metatarsal endothelial sprouting in vitro. This coincides with the in vivo data that local delivery of EPO increases vascularity at the mid-stage of bone healing (day 14). In a mouse femoral fracture model, EPO promotes cartilaginous callus formation at days 7 and 14, and enhances bone healing at day 28 indexed by improved X-ray score and micro-CT analysis of microstructure of new bone regenerates, which results in improved biomechanical properties. Our results indicate that EPO enhances chondrogenic and angiogenic responses during bone repair. EPO's function on chondrocyte proliferation and differentiation is at least partially mediated by its receptor EPOR. EPO may serve as a therapeutic agent to facilitate skeletal regeneration.

Can we enhance fracture vascularity: What is the evidence?

Angiogenesis is a vital component of bone healing. The formation of the new blood vessels at the fracture site restores the hypoxia and nutrient deprivation found at the early stages after fracture whilst at a later stage facilitates osteogenesis by the activity of the osteoprogenitor cells. Emerging evidence suggests that there are certain molecules and gene therapies that could promote new blood vessel formation and as a consequence enhance the local bone healing response. This article summarizes the current in vivo evidence on therapeutic approaches aiming at the augmentation of the angiogenic signalling during bone repair.

A single topical dose of erythropoietin applied on a collagen carrier enhances calvarial bone healing in pigs

BACKGROUND AND PURPOSE

The osteogenic potency of erythropoietin (EPO) has been documented. However, its efficacy in a large-animal model has not yet been investigated; nor has a clinically safe dosage. The purpose of this study was to overcome such limitations of previous studies and thereby pave the way for possible clinical application. Our hypothesis was that EPO increases calvarial bone healing compared to a saline control in the same subject.

METHODS

We used a porcine calvarial defect model. In each of 18 pigs, 6 cylindrical defects (diameter: 1 cm; height: 1 cm) were drilled, allowing 3 pairwise comparisons. Treatment consisted of either 900 IU/mL EPO or an equal volume of saline in combination with either autograft, a collagen carrier, or a polycaprolactone (PCL) scaffold. After an observation time of 5 weeks, the primary outcome (bone volume fraction (BV/TV)) was assessed with high-resolution quantitative computed tomography. Secondary outcome measures were histomorphometry and blood samples.

RESULTS

The median BV/TV ratio of the EPO-treated collagen group was 1.06 (CI: 1.02-1.11) relative to the saline-treated collagen group. Histomorphometry showed a similar median effect size, but it did not reach statistical significance. Autograft treatment had excellent healing potential and was able to completely regenerate the bone defect independently of EPO treatment. Bony ingrowth into the PCL scaffold was sparse, both with and without EPO. Neither a substantial systemic effect nor adverse events were observed. The number of blood vessels was similar in EPO-treated defects and saline-treated defects.

INTERPRETATION

Topical administration of EPO on a collagen carrier moderately increased bone healing. The dosing regime was safe, and could have possible application in the clinical setting. However, in order to increase the clinical relevance, a more potent but still clinically safe dose should be investigated.

The role of erythropoietin and bone marrow concentrate in the treatment of osteochondral defects in mini-pigs

Background

All available treatment options for osteochondral and chondral defects do not restore hyaline cartilage and are limited to decreasing associated pain, and maintaining or improving joint function. The purpose of this study was to evaluate the potential of erythropoietin (EPO) in combination with bone marrow aspiration concentrate (BMAC) in the treatment of osteochondral defects of mini-pigs.

Methods

14 Goettinger mini-pigs, in which a 6×10 mm osteochondral defect in the medial femoral condyle of both knee joints was created, were randomized into four groups: biphasic scaffold alone, scaffold with EPO, scaffold with BMAC and scaffold in combination with EPO and BMAC. After 26 weeks all animals were euthanized and histological slides were evaluated using a modified ÓDriscoll Score.

Results

In the therapy groups, areas of chondrogenic tissue that contained collagen II were present. Adding EPO (p = 0.245) or BMAC (p = 0.099) alone to the scaffold led to a non-significant increase in the score compared to the control group. However, the combination of EPO and BMAC in the implanted scaffold showed a significant improvement (p = 0.02) in the histological score.

Conclusion

The results of our study show that in mini-pigs, the combination of EPO and BMAC leads to an enhanced osteochondral healing. However, additional research is necessary to further improve the repair tissue and to define the role of MSCs and EPO in cartilage repair.

Differences of bone healing in metaphyseal defect fractures between osteoporotic and physiological bone in rats

Discrepancies in bone healing between osteoporotic and non-osteoporotic bone remain uncertain. The focus of the current work is to evaluate potential healing discrepancies in a metaphyseal defect model in rat femora. Female Sprague-Dawley rats were either ovariectomized (OVX, n=14) and combined with a calcium-, phosphorus- and vitamin D3-, soy- and phytoestrogen-free diet or received SHAM operation with standard diet rat (SHAM, n=14). Three months post-ovariectomy, DEXA measurement showed a reduction of bone mineral density reflecting an osteoporotic bone status in OVX rats. Rats then underwent a 3 mm wedge-shaped osteotomy at the distal metaphyseal area of the left femur stabilized with a T-shaped mini-plate and allowed to heal for 6 weeks. Biomechanical competence by means of a non-destructive three-point bending test showed significant lower flexural rigidity in the OVX rats at 3 mm lever span compared to SHAM animals (p=0.048) but no differences at 10 mm lever span. Microcomputer tomography (μCT) showed bridging cortices and consolidation of the defect in both groups, however, no measurable differences were found in either total ossified tissue or vascular volume fraction. Furthermore, histology showed healing discrepancies that were characterized by cartilaginous remnant and more unmineralized tissue presence in the OVX rats compared to more mature consolidation appearance in the SHAM group. In summary, bone defect healing in metaphyseal bone slightly differs between osteoporotic and non-osteoporotic bone in the current 3 mm defect model in both 3mm lever span biomechanical testing and histology.

The Roles of Mechanical Stresses in the Pathogenesis of Osteoarthritis: Implications for Treatment of Joint Injuries

Excessive joint surface loadings, either single (acute impact event) or repetitive (cumulative contact stress), can cause the clinical syndrome of osteoarthritis (OA). Despite advances in treatment of injured joints, the risk of OA following joint injuries has not decreased in the last 50 years. Cumulative excessive articular surface contact stress that leads to OA results from post-traumatic joint incongruity and instability, and joint dysplasia, but also may cause OA in patients without known joint abnormalities. In vitro investigations show that excessive articular cartilage loading triggers release of reactive oxygen species (ROS) from mitochondria, and that these ROS cause chondrocyte death and matrix degradation. Preventing release of ROS or inhibiting their effects preserves chondrocytes and their matrix. Fibronectin fragments released from articular cartilage subjected to excessive loads also stimulate matrix degradation; inhibition of molecular pathways initiated by these fragments prevents this effect. Additionally, injured chondrocytes release alarmins that activate chondroprogentior cells in vitro that propogate and migrate to regions of damaged cartilage. These cells also release chemokines and cytokines that may contribute to inflammation that causes progressive cartilage loss. Distraction and motion of osteoarthritic human ankles can promote joint remodeling, decrease pain and improve joint function in patients with end-stage post-traumatic OA. These advances in understanding of how altering mechanical stresses can lead to remodeling of osteoarthritic joints and how excessive stress causes loss of articular cartilage, including identification of mechanically induced mediators of cartilage loss, provide the basis for new biologic and mechanical approaches to the prevention and treatment of OA.