Erythropoietin after a century of research: younger than ever

Erythropoietin production in neuroepithelial and neural crest cells during primitive erythropoiesis

Erythropoietin (Epo) supports both primitive erythropoiesis in the yolk sac and definitive erythropoiesis in the fetal liver and bone marrow. Although definitive erythropoiesis requires kidney- and liver-secreted Epo, it is unclear which cells produce Epo for primitive erythropoiesis. Here we find neural Epo-producing (NEP) cells in mid-gestational stage embryos using mouse lines that express green fluorescent protein (GFP) under the Epo gene regulation. In these mice, GFP is expressed exclusively in a subpopulation of neural and neural crest cells at embryonic day 9.0 when Epo-deficient embryos exhibit abnormalities in primitive erythropoiesis. The GFP-positive NEP cells express Epo mRNA and the ex vivo culture of embryonic day 8.5 neural tubes results in the secretion of Epo, which is able to induce the proliferation and differentiation of yolk sac-derived erythroid cells. These results thus suggest that NEP cells secrete Epo and might support the development of primitive erythropoiesis.

Red cell volume expansion at altitude: a meta-analysis and Monte Carlo simulation

INTRODUCTION

Altitude acclimatization is associated with a rapid increase in hematocrit. The time course and the contribution of the red cell volume expansion are not clear. The purpose of the present meta-analysis was to explore how much altitude exposure is required to induce polycythemia in healthy lowlanders.

METHODS

A systematic review was performed of 66 published articles (including 447 volunteers) identified through literature search. We performed a mixed-model random-effects meta-analysis and a Monte Carlo simulation on the extracted data.

RESULTS

The following results were obtained in this study: 1) the red cell volume expansion for a given duration of exposure is dependent on altitude (P < 0.0001), that is, that the increase in red cell volume was accelerated at higher altitudes; and 2) the extent of the erythropoietic response depends on the initial red cell volume (P < 0.0001). It seems that exposure time must exceed 2 wk at an altitude of more than 4000 m to exert a statistically significant effect. At lower altitudes, longer exposure times are needed with altitudes lower than 3000 m not yielding an increase within 4 wk.

CONCLUSIONS

Red cell volume response to hypoxia is generally slow, although it accelerates with increasing altitude. This, in combination with a dependency on initial red cell volume, suggests that, for example, athletes may need to spend more time at altitude to see an effect on red cell volume than commonly recommended.

Tight regulation of a timed nuclear import wave of EKLF by PKCθ and FOE during Pro-E to Baso-E transition

Erythropoiesis is a highly regulated process during which BFU-E are differentiated into RBCs through CFU-E, Pro-E, PolyCh-E, OrthoCh-E, and reticulocyte stages. Uniquely, most erythroid-specific genes are activated during the Pro-E to Baso-E transition. We show that a wave of nuclear import of the erythroid-specific transcription factor EKLF occurs during the Pro-E to Baso-E transition. We further demonstrate that this wave results from a series of finely tuned events, including timed activation of PKCθ, phosphorylation of EKLF at S68 by P-PKCθ(S676), and sumoylation of EKLF at K74. The latter EKLF modifications modulate its interactions with a cytoplasmic ankyrin-repeat-protein FOE and importinβ1, respectively. The role of FOE in the control of EKLF nuclear import is further supported by analysis of the subcellular distribution patterns of EKLF in FOE-knockout mice. This study reveals the regulatory mechanisms of the nuclear import of EKLF, which may also be utilized in the nuclear import of other factors.

Hematological parameters, and hematopoietic growth factors: EPO and IL-3 in response to whole-body cryostimulation (WBC) in military academy students

The effects of extreme cold on the human body are not fully understood, there are also no reports on the effect of cryogenic temperatures on the levels of erythropoietin (EPO) and interleukin 3 (IL-3), two important factors that regulate hematopoiesis. Aim: determination of changes in peripheral blood cell counts and EPO and IL-3 levels induced by a series of 10, 20 and 30 standard whole-body cryostimulation (WBC) treatments. The study involved 45 men, experimental group (EXP, n = 30) subjected to 30 WBC treatments (−130°C, treatment duration: 3 minutes) and a control group (CON, n = 15). Blood samples were collected before the series of treatments and after 10, 20 and 30 treatments. After 10 and 20 treatments we observed lower red blood cell counts and hematocrit and hemoglobin levels compared to baseline (p<0.05) and the control group (p<0.05). Additionally we observed an increase in hemoglobin concentration in plasma (p<0.05), and bilirubin after 10 and 20 treatments, and a decrease in plasma concentration of haptoglobin after 10, 20 and 30 treatments (p<0.05). The number of leukocytes was higher after 10 and 20 WBC treatments compared to baseline and the CON group. EPO concentration in plasma was elevated and the concentration of IL-3 was lower after 10, 20 and 30 WBC treatments. The decrease in indices of the erythrocytic system, plasma hemoglobin and bilirubin, with a simultaneous decrease in haptoglobin concentrations after 10 and 20 WBC treatments, may be due to increased intravascular hemolysis. At the same time there was a small, but statistically significant increase in the concentration of EPO stimulated erythropoiesis which could facilitate a return of erythrocytic system indices to initial levels after 30 WBC treatments. Changes in the white blood cell system showed transient mobilization of this system under the influence of WBC.

Contemporary uses of erythropoietin in pregnancy: a literature review

OBJECTIVE

The objectives of this study were to survey the current research and provide an update on the uses and benefits of erythropoietin (EPO) in pregnancy and the postpartum period.

DATA SOURCES

A review of MEDLINE (1947 to present) was performed. Search terms included "erythropoietin," "pregnan*," with subheadings of "administration & dosage," "pharmacokinetics," "therapeutic use," "fetus," "fertility."

METHOD OF STUDY SELECTION

We reviewed relevant articles published from 2002 to 2012. Case reports, observational studies, case-control studies, randomized controlled trials, retrospective analyses, animal studies, and review articles were included. Articles were selected if they discussed a use of EPO in pregnancy or the immediate postpartum period, as well as use of EPO in the neonate.

TABULATION, INTEGRATION, AND RESULTS

Authors independently reviewed and extracted data. Of the 65 articles reviewed, 45 were included. Erythropoietin was used in the treatment of maternal anemia. Because of the molecule's large size, recombinant EPO does not appear to cross the placenta. No fetal morbidity or mortality was noted. Therefore, this is a safe therapy that can be used in pregnancy. Use of EPO may be especially important for women who decline blood products. Neonatal uses of EPO show benefit in the treatment of anemia due to blood type incompatibility.

CONCLUSIONS

Erythropoietin is gaining popularity as a therapeutic option during pregnancy and the postpartum period. Further investigation is needed to establish a standard dosage and dosing interval. New studies reviewing its use in the neonate for perinatal-hypoxic injury and anemia due to blood type incompatibility provide exciting opportunities for further therapeutic use.

TARGET AUDIENCE

Obstetricians and gynecologists, family physicians.

LEARNING OBJECTIVES

After completing this CME activity, physicians should be better able to treat anemia in pregnancy, including causes and interventions; assess renal disease in pregnancy, targets of hemoglobin, precautions, and treatment considerations; and evaluate erythropoietin use in neonates and fetuses, including benefits, complications, and areas for upcoming research/uses.

A mouse model of adult-onset anaemia due to erythropoietin deficiency

Erythropoietin regulates erythropoiesis in a hypoxia-inducible manner. Here we generate inherited super-anaemic mice (ISAM) as a mouse model of adult-onset anaemia caused by erythropoietin deficiency. ISAM express erythropoietin in the liver but lack erythropoietin production in the kidney. Around weaning age, when the major erythropoietin-producing organ switches from the liver to the kidney, ISAM develop anaemia due to erythropoietin deficiency, which is curable by administration of recombinant erythropoietin. In ISAM severe chronic anaemia enhances transgenic green fluorescent protein and Cre expression driven by the complete erythropoietin-gene regulatory regions, which facilitates efficient labelling of renal erythropoietin-producing cells. We show that the majority of cortical and outer medullary fibroblasts have the innate potential to produce erythropoietin, and also reveal a new set of erythropoietin target genes. ISAM are a useful tool for the evaluation of erythropoiesis-stimulating agents and to trace the dynamics of erythropoietin-producing cells.

Erythropoietin and the heart: physiological effects and the therapeutic perspective

Erythropoietin (Epo) has been thought to act exclusively on erythroid progenitor cells. The identification of Epo receptor (EpoR) in non-haematopoietic cells and tissues including neurons, astrocytes, microglia, immune cells, cancer cell lines, endothelial cells, bone marrow stromal cells, as well as cells of myocardium, reproductive system, gastrointestinal tract, kidney, pancreas and skeletal muscle indicates that Epo has pleiotropic actions. Epo shows signals through protein kinases, anti-apoptotic proteins and transcription factors. In light of interest of administering recombinant human erythropoietin (rhEpo) and its analogues for limiting infarct size and left ventricular (LV) remodelling after acute myocardial infarction (AMI) in humans, the foremost studies utilising rhEpo are reviewed. The putative mechanisms involved in Epo-induced cardioprotection are related to the antiapoptotic, anti-inflammatory and angiogenic effects of Epo. Thus, cardioprotective potentials of rhEpo are reviewed in this article by focusing on clinical applicability. An overview of non-haematopoietic Epo analogues, which are a reliable alternative to the classic EpoR agonists and may prevent undesired side effects, is also provided.

MCPIP1 deficiency in mice results in severe anemia related to autoimmune mechanisms

Autoimmune gastritis is an organ-specific autoimmune disease of the stomach associated with pernicious anemia. The previous work from us and other groups identified MCPIP1 as an essential factor controlling inflammation and immune homeostasis. MCPIP1^-/- developed severe anemia. However, the mechanisms underlying this phenotype remain unclear. In the present study, we found that MCPIP1 deficiency in mice resulted in severe anemia related to autoimmune mechanisms. Although MCPIP1 deficiency did not affect erythropoiesis per se, the erythropoiesis in MCPIP1^-/- bone marrow erythroblasts was significantly attenuated due to iron and vitamin B₁₂ (VB₁₂) deficiency, which was mainly resulted from autoimmunity-associated gastritis and parietal cell loss. Consistently, exogenous supplement of iron and VB₁₂ greatly improved the anemia phenotype of MCPIP1^-/- mice. Finally, we have evidence suggesting that autoimmune hemolysis may also contribute to anemia phenotype of MCPIP1^-/- mice. Taken together, our study suggests that MCPIP1 deficiency in mice leads to the development of autoimmune gastritis and pernicious anemia. Thus, MCPIP1^-/- mice may be a good mouse model for investigating the pathogenesis of pernicious anemia and testing the efficacy of some potential drugs for treatment of this disease.

Whole body metabolic effects of prolonged endurance training in combination with erythropoietin treatment in humans: a randomized placebo controlled trial

Erythropoietin (Epo) administration improves aerobic exercise capacity and insulin sensitivity in renal patients and also increases resting energy expenditure (REE). Similar effects are observed in response to endurance training. The aim was to compare the effects of endurance training with erythropoiesis-stimulating agent (ESA) treatment in healthy humans. Thirty-six healthy untrained men were randomized to 10 wk of either: 1) placebo (n = 9), 2) ESA (n = 9), 3) endurance training (n = 10), or 4) ESA and endurance training (n = 8). In a single-blinded design, ESA/placebo was injected one time weekly. Training consisted of biking for 1 h at 65% of wattmax three times per week. Measurements performed before and after the intervention were as follows: body composition, maximal oxygen uptake, insulin sensitivity, REE, and palmitate turnover. Uncoupling protein 2 (UCP2) mRNA levels were assessed in skeletal muscle. Fat mass decreased after training (P = 0.003), whereas ESA induced a small but significant increase in intrahepatic fat (P = 0.025). Serum free fatty acid (FFA) levels and palmitate turnover decreased significantly in response to training, whereas the opposite pattern was found after ESA. REE corrected for lean body mass increased in response to ESA and training, and muscle UCP2 mRNA levels increased after ESA (P = 0.035). Insulin sensitivity increased only after training (P = 0.011).

IN CONCLUSION

1) insulin sensitivity is not improved after ESA treatment despite improved exercise capacity, 2) the calorigenic effects of ESA may be related to increased UCP2 gene expression in skeletal muscle, and 3) training and ESA exert opposite effects on lipolysis under basal conditions, increased FFA levels and liver fat fraction was observed after ESA treatment.

Congenital erythrocytosis associated with gain-of-function HIF2A gene mutations and erythropoietin levels in the normal range

Hypoxia-inducible factor 2α (HIF-2α) plays a pivotal role in the balancing of oxygen requirements throughout the body. The protein is a transcription factor that modulates the expression of a wide array of genes and, in turn, controls several key processes including energy metabolism, erythropoiesis and angiogenesis. We describe here the identification of two cases of familial erythrocytosis associated with heterozygous HIF2A missense mutations, namely Ile533Val and Gly537Arg. Ile533Val is a novel mutation and represents the genetic HIF2A change nearest to Pro-531, the primary hydroxyl acceptor residue, so far identified. The Gly537Arg missense mutation has already been described in familial erythrocytosis. However, our patient is the only described case of a de novo HIF2A mutation associated with the development of congenital polycythemia. Functional in vivo studies, based on exogenous expression of hybrid HIF-2α transcription factors, indicated that these genetic alterations lead to the stabilization of HIF-2α protein. All the identified polycythemic subjects with HIF2A mutations show serum erythropoietin in the normal range, independently of the hematocrit values and phlebotomy frequency. The erythroid precursors obtained from the peripheral blood of patients showed an altered phenotype, including an increased rate of growth and a modified expression of some HIF-2α target genes. These results suggest the novel proposal that polycythemia observed in subjects with HIF2A mutations might also be due to primary changes in hematopoietic cells and not only secondary to increased erythropoietin levels.

CNTO 530 increases expression of HbA and HbF in murine models of β-thalassemia and sickle cell anemia

CNTO 530 is an erythropoietin receptor agonist MIMETIBODY^TM construct. CNTO 530 has been shown to be active in a number of rodent models of acquired anemia (e.g. renal insufficiency and chemotherapy induced anemia). We investigated the efficacy of CNTO 530 in murine models of β-thalassemia and sickle cell anemia (Berkeley mice). β- thalassemic mice are deficient in expression of α-globin chain and heterozygous mice are characterized by a clinical syndrome similar to the human β-thalassemia intermedia. Berkeley mice are knocked out for murine alpha and beta globin and are transgenic for human alpha, beta (sickle) and gamma globin genes. Berkeley mice thus express human sickle hemoglobin A (HbS) and can also express human fetal hemoglobin. These mice express a severe compensated hypochromic microcytic anemia and display the sickle cell phenotype. To test the effectiveness of CNTO 530, mice from both genotypes received a single subcutaneous (s.c.) dose of CNTO 530 or darbepoetin-α (as a comparator) at 10,000 U/kg, a dose shown to cause a similar increase in reticulocytes and hemoglobin in normal mice. Hematologic parameters were evaluated over time. CNTO 530, but not darbepoetin-α, increased reticulocytes, red blood cells and total hemoglobin in β- thalassemic mice. In Berkeley mice CNTO 530 showed an increase in reticulocytes, red blood cells, F-cells, total hemoglobin and fetal hemoglobin. In conclusion, CNTO 530 is effective in murine models of β-thalassemia and sickle cell anemia. These data suggest that CNTO 530 may have beneficial effects in patients with genetically mediated hemoglobinopathies.

Erythropoietin administration partially prevents adipose tissue loss in experimental cancer cachexia models

Cancer-associated cachexia is characterized, among other symptoms, by a dramatic loss of both muscle and fat. In addition, the cachectic syndrome is often associated with anemia. The object of the present investigation was to assess the effects of erythropoietin (EPO) treatment on experimental cancer cachexia models. The results clearly show that, in addition to the improvement of the hematocrit, EPO treatment promoted a partial preservation of adipose tissue while exerting negligible effects on muscle loss. Administration of EPO to tumor-bearing animals resulted in a significant increase of lipoprotein lipase (LPL) activity in adipose tissue, suggesting that the treatment favored triacylglycerol (TAG) accumulation in the adipose tissue. In vitro experiments using both adipose tissue slices and 3T3-L1 adipocytes suggests that EPO is able to increase the lipogenic rate through the activation of its specific receptor (EPOR). This metabolic pathway, in addition to TAG uptake by LPL, may contribute to the beneficial effects of EPO on fat preservation in cancer cachexia.

Suppression of coronary atherosclerosis by helix B surface Peptide, a nonerythropoietic, tissue-protective compound derived from erythropoietin

Erythropoietin (EPO), a type I cytokine originally identified for its critical role in hematopoiesis, has been shown to have nonhematopoietic, tissue-protective effects, including suppression of atherosclerosis. However, prothrombotic effects of EPO hinder its potential clinical use in nonanemic patients. In the present study, we investigated the antiatherosclerotic effects of helix B surface peptide (HBSP), a nonerythropoietic, tissue-protective compound derived from EPO, by using human umbilical vein endothelial cells (HUVECs) and human monocytic THP-1 cells in vitro and Watanabe heritable hyperlipidemic spontaneous myocardial infarction (WHHLMI) rabbits in vivo. In HUVECs, HBSP inhibited apoptosis (≈70%) induced by C-reactive protein (CRP), a direct mediator of atherosclerosis. By using a small interfering RNA approach, Akt was shown to be a key molecule in HBSP-mediated prevention of apoptosis. HBSP also attenuated CRP-induced production of tumor necrosis factor (TNF)-α and matrix metalloproteinase-9 in THP-1 cells. In the WHHLMI rabbit, HBSP significantly suppressed progression of coronary atherosclerotic lesions as assessed by mean cross-sectional stenosis (HBSP 21.3 ± 2.2% versus control peptide 38.0 ± 2.7%) and inhibited coronary artery endothelial cell apoptosis with increased activation of Akt. Furthermore, TNF-α expression and the number of M1 macrophages and M1/M2 macrophage ratio in coronary atherosclerotic lesions were markedly reduced in HBSP-treated animals. In conclusion, these data demonstrate that HBSP suppresses coronary atherosclerosis, in part by inhibiting endothelial cell apoptosis through activation of Akt and in association with decreased TNF-α production and modified macrophage polarization in coronary atherosclerotic lesions. Because HBSP does not have the prothrombotic effects of EPO, our study may provide a novel therapeutic strategy that prevents progression of coronary artery disease.

The role and regulation of erythropoietin (EPO) and its receptor in skeletal muscle: how much do we really know?

Erythropoietin (EPO) primarily activates erythroid cell proliferation and growth and is active in several types of non-hematopoietic cells via its interaction with the EPO-receptor (EPO-R). This review focuses on the role of EPO in skeletal muscle. The EPO-R is expressed in skeletal muscle cells and EPO may promote myoblast differentiation and survival via the activation of the same signaling cascades as in hematopoietic cells, such as STAT5, MAPK and Akt. Inconsistent results exist with respect to the detection of the EPO-R mRNA and protein in muscle cells, tissue and across species and the use of non-specific EPO-R antibodies contributes to this problem. Additionally, the inability to reproducibly detect an activation of the known EPO-induced signaling pathways in skeletal muscle questions the functionality of the EPO-R in muscle in vivo. These equivocal findings make it difficult to distinguish between a direct effect of EPO on skeletal muscle, via the activation of its receptor, and an indirect effect resulting from a better oxygen supply to the muscle. Consequently, the precise role of EPO in skeletal muscle and its regulatory mechanism/s remain to be elucidated. Further studies are required to comprehensively establish the importance of EPO and its function in skeletal muscle health.

A multi-center study on the regenerative effects of erythropoietin in burn and scalding injuries: study protocol for a randomized controlled trial

Background

Although it was initially assumed that erythropoietin (EPO) was a hormone that only affected erythropoiesis, it has now been proposed that EPO plays an additional key role in the regulation of acute and chronic tissue damage.

Via the inhibition of inflammatory reactions and of apoptosis, stem cell recruitment, advancement of angiogenesis and growth factor release, EPO enhances healing and thus restitutio ad integrum after trauma. Human skin contains EPO receptors and is able to synthesize EPO. We therefore hypothesize that EPO is able to optimize wound healing in thermally injured patients.

Methods/Design

This is a large, prospective, randomized, double-blind, multi-center study, funded by the German Federal Ministry of Education and Research, and fully approved by the designated ethics committee. The trial, which is to investigate the effects of EPO in severely burned patients, is in its recruitment phase and is being carried out in 13 German burn care centers. A total of 150 patients are to be enrolled to receive study medication every other day for 21 days (EPO 150 IU/kg body weight or placebo). A follow-up of one year is planned. The primary endpoint of this study is the time until complete re-epithelialization of a defined skin graft donor site is reached. Furthermore, clinical parameters such as wound healing, scar formation (using the Vancouver scar scale), laboratory values, quality of life (SF-36), angiogenic effects, and gene- and protein-expression patterns are to be determined. The results will be carefully evaluated for gender differences.

Discussion

We are seeking new insights into the mechanisms of wound healing in thermally injured patients and more detailed information about the role EPO plays, specifically in these complex interactions. We additionally expect that the biomimetic effects of EPO will be useful in the treatment of acute thermal dermal injuries.

Trial registration

EudraCT Number: 2006-002886-38, Protocol Number: 0506, ISRCT Number: http://controlled-trials.com/ISRCTN95777824/ISRCTN95777824.

Erythrocytosis and pulmonary hypertension in a mouse model of human HIF2A gain of function mutation

The central pathway for oxygen-dependent control of red cell mass is the prolyl hydroxylase domain protein (PHD):hypoxia inducible factor (HIF) pathway. PHD site specifically prolyl hydroxylates the transcription factor HIF-α, thereby targeting the latter for degradation. Under hypoxia, this modification is attenuated, allowing stabilized HIF-α to activate target genes, including that for erythropoietin (EPO). Studies employing genetically modified mice point to Hif-2α, one of two main Hif-α isoforms, as being the critical regulator of Epo in the adult mouse. More recently, erythrocytosis patients with heterozygous point mutations in the HIF2A gene have been identified; whether these mutations were polymorphisms unrelated to the phenotype could not be ruled out. In the present report, we characterize a mouse line bearing a G536W missense mutation in the Hif2a gene that corresponds to the first such human mutation identified (G537W). We obtained mice bearing both heterozygous and homozygous mutations at this locus. We find that these mice display, in a mutation dose-dependent manner, erythrocytosis and pulmonary hypertension with a high degree of penetrance. These findings firmly establish missense mutations in HIF-2α as a cause of erythrocytosis, highlight the importance of this HIF-α isoform in erythropoiesis, and point to physiologic consequences of HIF-2α dysregulation.

Erythropoietin receptor (EpoR) agonism is used to treat a wide range of disease

The erythropoietin receptor (EpoR) was discovered and described in red blood cells (RBCs), stimulating its proliferation and survival. The target in humans for EpoR agonists drugs appears clear-to treat anemia. However, there is evidence of the pleitropic actions of erythropoietin (Epo). For that reason, rhEpo therapy was suggested as a reliable approach for treating a broad range of pathologies, including heart and cardiovascular diseases, neurodegenerative disorders (Parkinson's and Alzheimer's disease), spinal cord injury, stroke, diabetic retinopathy and rare diseases (Friedreich ataxia). Unfortunately, the side effects of rhEpo are also evident. A new generation of nonhematopoietic EpoR agonists drugs (asialoEpo, Cepo and ARA 290) have been investigated and further developed. These EpoR agonists, without the erythropoietic activity of Epo, while preserving its tissue-protective properties, will provide better outcomes in ongoing clinical trials. Nonhematopoietic EpoR agonists represent safer and more effective surrogates for the treatment of several diseases such as brain and peripheral nerve injury, diabetic complications, renal ischemia, rare diseases, myocardial infarction, chronic heart disease and others.

Erythropoietin administration suppresses human monocyte function in vitro and during therapy-induced anemia in HCV patients

Erythropoietin (EPO) is a hormone that controls red blood cell production. Binding of EPO to the EPO-receptor results in increased numbers of red blood cells in the circulation, which makes EPO a potent molecule to treat anemia in various groups of patients. Although numerous studies have examined the clinical effects of EPO, its immunological effects have received less attention. In this study, we examined the immunological effects of EPO on human monocytes. We show that human monocytes express EPO receptor mRNA, and are responsive to EPO in cell culture. In vitro exposure of PBMC from individuals to EPO and the TLR4 ligand LPS showed a significant reduction of monocytes producing IL-6 and TNF, while the frequencies of IL-12p40, IL-10, MIP-1β and IL-8-producing cells did not change upon incubation with EPO. In addition, EPO did increase the phagocytic activity but did not affect the ability to produce ROS by monocytes. Moreover, we studied eight chronic HCV patients undergoing treatment with peg-IFN and ribavirin, who were administered EPO for treatment-induced anemia. Blood was collected before and 7 days after EPO injection. In 7 patients, we observed a significant decline at day 7 after EPO administration of the frequency of monocytes producing various pro-inflammatory cytokines following stimulation with the TLR4 ligand LPS and the TLR7/8 ligand R848, which is in line with our in vitro findings. Our findings demonstrate an inhibitory effect of EPO on the secretion of effector molecules by monocytes and a stimulatory effect on the phagocytic activity by monocytes.

Regulation of erythropoiesis by hypoxia-inducible factors

A classic physiologic response to systemic hypoxia is the increase in red blood cell production. Hypoxia-inducible factors (HIFs) orchestrate this response by inducing cell-type specific gene expression changes that result in increased erythropoietin (EPO) production in kidney and liver, in enhanced iron uptake and utilization and in adjustments of the bone marrow microenvironment that facilitate erythroid progenitor maturation and proliferation. In particular HIF-2 has emerged as the transcription factor that regulates EPO synthesis in the kidney and liver and plays a critical role in the regulation of intestinal iron uptake. Its key function in the hypoxic regulation of erythropoiesis is underscored by genetic studies in human populations that live at high-altitude and by mutational analysis of patients with familial erythrocytosis. This review provides a perspective on recent insights into HIF-controlled erythropoiesis and iron metabolism, and examines cell types that have EPO-producing capability. Furthermore, the review summarizes clinical syndromes associated with mutations in the O(2)-sensing pathway and the genetic changes that occur in high altitude natives. The therapeutic potential of pharmacologic HIF activation for the treatment of anemia is discussed.

Regulation of Bone Marrow Angiogenesis by Osteoblasts during Bone Development and Homeostasis

Bone marrow is a highly heterogeneous and vascularized tissue. The various cell types populating the bone marrow extensively communicate with each other, and cell-to-cell cross talk is likely to be essential for proper bone development and homeostasis. In particular, the existence of osteogenesis and angiogenesis coupling has been recently proposed. Despite its high degree of vascularization, a gradient of oxygenation is present in the bone marrow, and the endosteal surface of cortical bone appears to be among the most hypoxic areas in the body. Oxygen (O2) is both an essential metabolic substrate and a regulatory signal that is in charge of a specific genetic program. An important component of this program is the family of transcription factors known as hypoxia-inducible factors (HIFs). In this Perspective, we will summarize our current knowledge about the role of the HIF signaling pathway in controlling bone development and homeostasis, and especially in regulating the crosstalk between osteoblasts, progenitor cells, and bone marrow blood vessels.

Erythropoietin and engineered innate repair activators

Erythropoietin (EPO) is a pleiotropic type I cytokine that has been identified as a major endogenous tissue protective molecule. In response to injury, EPO and a distinct receptor are expressed with a characteristic temporal and spatial expression pattern. Together, these serve to limit injury and to initiate repair. Administration of EPO in the setting of injury has been shown to be beneficial in a multitude of preclinical models. However, translation into the clinic has been hampered by EPO's adverse effects, including promotion of thrombosis. Recently, engineered molecules based on EPO's structure-activity relationships have been developed that are devoid of hematopoietic effects. These compounds are promising candidates for treatment of a wide variety of acute and chronic diseases.

Erythropoietin receptor expression and its relationship with trastuzumab response and resistance in HER2-positive breast cancer cells

Resistance to trastuzumab is a major issue in the treatment of human epidermal growth factor receptor 2 (HER2)-positive breast cancer. Several potential resistance mechanisms have been investigated, but the results are controversial and no conclusion has been reached. Erythropoietin receptor (EPOR) may function in cell growth, and expressed in various cancer cells. Because the downstream signaling pathways for EPOR and HER2 partially overlapped, we hypothesized that EPOR may play a role in the inhibition effect of trastuzumab and resistance to trastuzumab. Here, we detected the expression of EPOR mRNA and protein in HER2-positive breast cancer cell lines and tissues. EPOR expressed in SKBR3, MDA-MB-453, and UACC-812 cell lines, but not in BT474. Of the 55 HER2-positive cancer tissues, EPOR was positive in 42 samples and highly expressed (H-score ≥ 25) in 24 by immunohistochemistry. The difference between EPOR expression and Ki67 index was significant (P = 0.033), and EPOR expression also positively correlated with higher pathological stage (Spearman correlation coefficient = 0.359; P = 0.007). Exogenous EPO antagonized trastuzumab-induced inhibition of cell proliferation in HER2/EPOR dual-positive breast cancer cells. We then exposed SKBR3 cells to trastuzumab for 4 months to obtain trastuzumab-resistant SKBR3 cell line, which demonstrated higher phosphorylated EPOR level, higher EPO expression and more extracellular secretion than non-resistant parental SKBR3 cells. Downregulation EPOR expression using short hairpin RNA resensitized trastuzumab-resistant cells to this drug, and SKBR3 cells with EPOR downregulation demonstrated attenuated trastuzumab resistance after the same resistance induction. EPOR downregulation plus trastuzumab produced a synergetic action in the inhibition of cell proliferation and invasion in SKBR3 and MDA-MB-453 cell lines. Therefore, EPOR expression may be involved in tumor progression and proliferation in HER2-positive breast cancer. EPO/EPOR contributes to the mechanism of trastuzumab resistance in SKBR3 cell lines, and EPOR downregulation can reverse the resistance to trastuzumab and increase the inhibition effect of this drug.

Hypoxia-inducible factor regulates hepcidin via erythropoietin-induced erythropoiesis

Iron demand in bone marrow increases when erythropoiesis is stimulated by hypoxia via increased erythropoietin (EPO) synthesis in kidney and liver. Hepcidin, a small polypeptide produced by hepatocytes, plays a central role in regulating iron uptake by promoting internalization and degradation of ferroportin, the only known cellular iron exporter. Hypoxia suppresses hepcidin, thereby enhancing intestinal iron uptake and release from internal stores. While HIF, a central mediator of cellular adaptation to hypoxia, directly regulates renal and hepatic EPO synthesis under hypoxia, the molecular basis of hypoxia/HIF-mediated hepcidin suppression in the liver remains unclear. Here, we used a genetic approach to disengage HIF activation from EPO synthesis and found that HIF-mediated suppression of the hepcidin gene (Hamp1) required EPO induction. EPO induction was associated with increased erythropoietic activity and elevated serum levels of growth differentiation factor 15. When erythropoiesis was inhibited pharmacologically, Hamp1 was no longer suppressed despite profound elevations in serum EPO, indicating that EPO by itself is not directly involved in Hamp1 regulation. Taken together, we provide in vivo evidence that Hamp1 suppression by the HIF pathway occurs indirectly through stimulation of EPO-induced erythropoiesis.

Erythropoietin modulates the structure of bone morphogenetic protein 2-engineered cranial bone

The ideally engineered bone should have similar structural and functional properties to the native tissue. Although structural integrity is critical for functional bone regeneration, we know less about modulating the structural properties of the engineered bone elicited by bone morphogenetic protein (BMP) than efficacy and safety. Erythropoietin (Epo), a primary erythropoietic hormone, has been used to augment blood transfusion in orthopedic surgery. However, the effects of Epo on bone regeneration are not well known. Here, we determined the role of Epo in BMP2-induced bone regeneration using a cranial defect model. Epo administration improved the quality of BMP2-induced bone and more closely resembled natural cranial bone with a higher bone volume (BV) fraction and lower marrow fraction when compared with BMP2 treatment alone. Epo increased red blood cells (RBCs) in peripheral blood and also increased hematopoietic and mesenchymal stem cell (MSC) populations in bone marrow. Consistent with our previous work, Epo increased osteoclastogenesis both in vitro and in vivo. Results from a metatarsal organ culture assay suggested that Epo-promoted osteoclastogenesis contributed to angiogenesis because angiogenesis was blunted when osteoclastogenesis was blocked by alendronate (ALN) or osteoprotegerin (OPG). Earlier calcification of BMP2-induced temporary chondroid tissue was observed in the Epo+BMP group compared to BMP2 alone. We conclude that Epo significantly enhanced the outcomes of BMP2-induced cranial bone regeneration in part through its actions on osteoclastogenesis and angiogenesis.

Biologically active, magnICON®-expressed EPO-Fc from stably transformed Nicotiana benthamiana plants presenting tetra-antennary N-glycan structures

In the past two decades plants have emerged as a valuable alternative for the production of pharmaceutical proteins. Since N-glycosylation influences functionality and stability of therapeutic proteins, the plant N-glycosylation pathway should be humanized. Here, we report the transient magnICON(®) expression of the erythropoietin fusion protein (EPO-Fc) in Nicotiana benthamiana plants that produce multi-antennary N-glycans without the plant-specific β1,2-xylose and α1,3-fucose residues in a stable manner (Nagels et al., 2011). The EPO-Fc fusion protein consists of EPO with a C-terminal-linked IgG-Fc domain and is used for pulmonary delivery of recombinant EPO to patients (Bitonti et al., 2004). Plant expressed EPO-Fc was quantified using a paramagnetic-particle chemiluminescent immunoassay and shown to be active in vitro via receptor binding experiments in HEK293T cells. Mass spectrometry-based N-glycan analysis confirmed the presence of multi-antennary N-glycans on plant-expressed EPO-Fc. The described research is the next step towards the development of a production platform for pharmaceutical proteins in plants.

Stat5 signaling specifies basal versus stress erythropoietic responses through distinct binary and graded dynamic modalities

Stat5 signaling in erythroblasts can assume either a binary, low-intensity form, essential for basal erythropoiesis, or a graded, high-intensity response, restricted to early erythroblasts and to erythropoietic stress.

Erythropoietin (Epo)-induced Stat5 phosphorylation (p-Stat5) is essential for both basal erythropoiesis and for its acceleration during hypoxic stress. A key challenge lies in understanding how Stat5 signaling elicits distinct functions during basal and stress erythropoiesis. Here we asked whether these distinct functions might be specified by the dynamic behavior of the Stat5 signal. We used flow cytometry to analyze Stat5 phosphorylation dynamics in primary erythropoietic tissue in vivo and in vitro, identifying two signaling modalities. In later (basophilic) erythroblasts, Epo stimulation triggers a low intensity but decisive, binary (digital) p-Stat5 signal. In early erythroblasts the binary signal is superseded by a high-intensity graded (analog) p-Stat5 response. We elucidated the biological functions of binary and graded Stat5 signaling using the EpoR-HM mice, which express a “knocked-in” EpoR mutant lacking cytoplasmic phosphotyrosines. Strikingly, EpoR-HM mice are restricted to the binary signaling mode, which rescues these mice from fatal perinatal anemia by promoting binary survival decisions in erythroblasts. However, the absence of the graded p-Stat5 response in the EpoR-HM mice prevents them from accelerating red cell production in response to stress, including a failure to upregulate the transferrin receptor, which we show is a novel stress target. We found that Stat5 protein levels decline with erythroblast differentiation, governing the transition from high-intensity graded signaling in early erythroblasts to low-intensity binary signaling in later erythroblasts. Thus, using exogenous Stat5, we converted later erythroblasts into high-intensity graded signal transducers capable of eliciting a downstream stress response. Unlike the Stat5 protein, EpoR expression in erythroblasts does not limit the Stat5 signaling response, a non-Michaelian paradigm with therapeutic implications in myeloproliferative disease. Our findings show how the binary and graded modalities combine to generate high-fidelity Stat5 signaling over the entire basal and stress Epo range. They suggest that dynamic behavior may encode information during STAT signal transduction.

Hormone signaling through the erythropoietin (Epo) pathway is required both for the continuous replacement of red blood cells (RBCs) that are lost through aging (a process known as "basal erythropoiesis") and to boost tissue oxygen when bleeding, in anemia or at high altitude ("stress erythropoiesis"). A key challenge lies in understanding how extracellular Epo concentration is translated into different intracellular signals that promote transcription of proteins that are specific to basal versus stress erythropoiesis. Binding of Epo to its receptor EpoR on the surface of an erythroblast (the precursors of RBCs) triggers the addition of phosphates to a target protein Stat5; the phosphorylated Stat5 becomes activated and induces transcription. We show that the dynamic properties of the Stat5 activation signal convey additional information that specifies either basal or stress responses. During basal conditions, the Stat5 signal is low and binary in nature—an on/off switch-like response. Stress, on the other hand, triggers a distinct Stat5 response consisting of a highintensity signal that increases in a graded fashion with rising Epo concentration. We found that a mouse bearing a truncated EpoR is restricted to the low-intensity binary Stat5 signal and correspondingly fails to initiate stress erythropoiesis. Ultimately, it is the Stat5 protein level in erythroblasts that determines their ability to generate the high-intensity graded Stat5 signal in response to high Epo. These findings have therapeutic potential: targeting Stat5's high-intensity graded signal may inhibit its aberrant function in blood cell cancers without affecting its important binary response in normal cells.

Cobalt metabolism and toxicology--a brief update

Cobalt metabolism and toxicology are summarized. The biological functions of cobalt are updated in the light of recent understanding of cobalt interference with the sensing in almost all animal cells of oxygen deficiency (hypoxia). Cobalt (Co(2+)) stabilizes the transcriptional activator hypoxia-inducible factor (HIF) and thus mimics hypoxia and stimulates erythropoietin (Epo) production, but probably also by the same mechanism induces a coordinated up-regulation of a number of adaptive responses to hypoxia, many with potential carcinogenic effects. This means on the other hand that cobalt (Co(2+)) also may have beneficial effects under conditions of tissue hypoxia, and possibly can represent an alternative to hypoxic preconditioning. Cobalt is acutely toxic in larger doses, and in mammalian in vitro test systems cobalt ions and cobalt metal are cytotoxic and induce apoptosis and at higher concentrations necrosis with inflammatory response. Cobalt metal and salts are also genotoxic, mainly caused by oxidative DNA damage by reactive oxygen species, perhaps combined with inhibition of DNA repair. Of note, the evidence for carcinogenicity of cobalt metal and cobalt sulfate is considered sufficient in experimental animals, but is as yet considered inadequate in humans. Interestingly, some of the toxic effects of cobalt (Co(2+)) have recently been proposed to be due to putative inhibition of Ca(2+) entry and Ca(2+)-signaling and competition with Ca(2+) for intracellular Ca(2+)-binding proteins. The tissue partitioning of cobalt (Co(2+)) and its time-dependence after administration of a single dose have been studied in man, but mainly in laboratory animals. Cobalt is accumulated primarily in liver, kidney, pancreas, and heart, with the relative content in skeleton and skeletal muscle increasing with time after cobalt administration. In man the renal excretion is initially rapid but decreasing over the first days, followed by a second, slow phase lasting several weeks, and with a significant long-term retention in tissues for several years. In serum cobalt (Co(2+)) binds to albumin, and the concentration of free, ionized Co(2+) is estimated at 5-12% of the total cobalt concentration. In human red cells the membrane transport pathway for cobalt (Co(2+)) uptake appears to be shared with calcium (Ca(2+)), but with the uptake being essentially irreversible as cobalt is effectively bound in the cytosol and is not itself extruded by the Ca-pump. It is tempting to speculate that this could perhaps also be the case in other animal cells. If this were actually the case, the tissue partitioning and biokinetics of cobalt in cells and tissues would be closely related to the uptake of calcium, with cobalt partitioning primarily into tissues with a high calcium turn-over, and with cobalt accumulation and retention in tissues with a slow turn-over of the cells. The occupational cobalt exposure, e.g. in cobalt processing plants and hard-metal industry is well known and has probably been somewhat reduced in more recent years due to improved work place hygiene. Of note, however, adverse reactions to heart and lung have recently been demonstrated following cobalt exposure near or slightly under the current occupational exposure limit. Over the last decades the use of cobalt-chromium hard-metal alloys in orthopedic joint replacements, in particular in metal-on-metal bearings in hip joint arthroplasty, has created an entirely new source of internal cobalt exposure. Corrosion and wear produce soluble metal ions and metal debris in the form of huge numbers of wear particles in nanometric size, with systemic dissemination through lymph and systemic vascular system. This may cause adverse local reactions in peri-prosthetic soft-tissues, and in addition systemic toxicity. Of note, the metal nanoparticles have been demonstrated to be clearly more toxic than larger, micrometer-sized particles, and this has made the concept of nanotoxicology a crucial, new discipline. As another new potential source of cobalt exposure, suspicion has been raised that cobalt salts may be misused by athletes as an attractive alternative to Epo doping for enhancing aerobic performance. The cobalt toxicity in vitro seems to reside mainly with ionized cobalt. It is tempting to speculate that ionized cobalt is also the primary toxic form for systemic toxicity in vivo. Under this assumption, the relevant parameter for risk assessment would be the time-averaged value for systemic cobalt ion exposure that from a theoretical point of view might be obtained by measuring the cobalt content in red cells, since their cobalt uptake reflects uptake only of free ionized cobalt (Co(2+)), and since the uptake during their 120 days life span is practically irreversible. This clearly calls for future clinical studies in exposed individuals with a systematic comparison of concurrent measurements of cobalt concentration in red cells and in serum.

Erythropoietin augments bone formation in a rabbit posterolateral spinal fusion model

We tested the hypothesis that erythropoietin (EPO) enhances bone formation after posterolateral spinal fusion (PLF) in a rabbit model. Thirty-four adult rabbits underwent posterolateral intertransverse arthrodesis at the L5-L6 level using 2.0 g autograft per side. The animals were randomly divided into two groups receiving subcutaneous daily injections of either EPO or saline for 20 days. Treatment commenced 2 days preoperatively. Hemoglobin was monitored at baseline and 2, 4, and 6 weeks after fusion surgery. After euthanasia 6 weeks postoperatively, manual palpation, radiographic, and histomorphometric examinations were performed. Bone volume of the fusion mass was estimated by CT after 6 weeks. EPO increased bone fusion volume to 3.85 ccm (3.66-4.05) compared with 3.26 ccm (2.97-3.55) in the control group (p<0.01). EPO treatment improved vascularization of the fusion mass and increased hemoglobin levels (p<0.01). Fusion rate tended to be higher in the EPO group based on manual palpation, CT, and radiographic examinations. For the first time EPO has shown to augment bone formation after autograft PLF in a rabbit model. Increased vascularization provides a partial explanation for the efficacy of EPO as a bone autograft enhancer.

Erythropoietin and its antagonist regulate hypoxic fictive breathing in newborn mice

Clinical use of erythropoietin in adult and newborn patients has revealed its involvement in neuroprotection, neurogenesis, and angiogenesis. More recently, we showed in adult mouse, that brain erythropoietin interacts with the major brainstem centers associated with respiration to enhance the ventilatory response to acute and chronic conditions of physiological hypoxia (e.g., as occurring at high altitude). However, whether brain erythropoietin is involved in breathing regulation in newborns remains unknown. In this study, en bloc brainstem-spinal cord preparations were obtained from mice at postnatal day 4. After various periods (30, 60, or 90 min) of incubation with 0, 25, or 250 U of erythropoietin, preparations were superfused with artificial cerebrospinal fluid bubbled with normoxic or hypoxic gas mixtures. The electrophysiological fictive breathing produced by axons at the C4 ventral root was next recorded. Our results show that erythropoietin attenuates the hypoxia-mediated decrease of the central respiratory activity and improves post-hypoxic recovery. Additional analysis revealed that the soluble erythropoietin receptor (the endogenous erythropoietin antagonist) dramatically decreases neural hypoxic respiratory activity, confirming the specific erythropoietin effect on respiratory drive. These results imply that erythropoietin exerts main modulation and maintenance of respiratory motor output during hypoxic and post-hypoxic challenges in 4-days old mice.

Biosimilar recombinant human erythropoietins ("epoetins") and future erythropoiesis-stimulating treatments

INTRODUCTION

Recombinant human erythropoietin (rhEPO, epoetin) has prospered in the treatment of renal and chemotherapy-associated anemias. Since the patents of the original epoetins expired, biosimilars have been launched. Because these are not fully identical to the original products, non-clinical and clinical studies are necessary to show similarity with respect to quality, safety, and efficacy.

AREAS COVERED

The article summarizes experiences with EU-approved biosimilar epoetins. In particular, the issue of immunogenicity is considered. Neutralizing anti-EPO antibodies can cause pure red cell aplasia (PRCA). Further, a first view is offered on future erythropoiesis-stimulating therapies.

EXPERT OPINION

The term "biosimilar" should only be used for follow-on biopharmaceuticals approved under a defined regulatory pathway. The primary rationale for the therapy with biosimilars is cost saving. Two biosimilar epoetins are available in the EU that are used at the same dose(s) and dosing regimen(s) for indications of the reference product. Their advent has stimulated innovator companies to develop second-generation products with improved pharmacokinetic properties. EPO-mimicking peptides are a new therapeutic option. Other strategies focus on orally active chemical drugs that induce endogenous EPO production ("HIF stabilizers"). Epo gene transfer is also possible, but needs to be further explored with respect to efficacy and safety.

Erythropoietin produced by the retina: its role in physiology and diabetic retinopathy

Erythropoietin (Epo) is the principal regulator of erythropoiesis by inhibiting apoptosis and by stimulating the proliferation and differentiation of erythroid precursor cells. However, Epo also performs extra-erythropoietic actions of which the neuroprotective effects are among the most relevant. Apart from kidney and liver, Epo is also produced by the brain and the retina. In addition, Epo receptor (Epo-R) expression has also been found in the brain and in the retina, thus suggesting an autocrine/paracrine action which seems essential for the physiological homeostasis of both brain and retina. In this review, we will give an overview of the current concepts of the physiology of Epo and will focus on its role in the retina in both normal conditions and in the setting of diabetic retinopathy. Finally, the reasons as to why Epo could be contemplated as a potential new treatment for the early stages of diabetic retinopathy will be given.

The nonhematopoietic effects of erythropoietin in skin regeneration and repair: from basic research to clinical use

Erythropoietin (EPO) is the main regulator of red blood cell production but there exists also a variety of nonhematopoietic properties. More recent data show that EPO is also associated with the protection of tissues suffering from ischemia and reperfusion injury as well as with improved regeneration in various organ systems, in particular the skin. This review highlights the mechanisms of EPO in the different stages of wound healing and the reparative processes in the skin emphasizing pathophysiological mechanisms and potential clinical applications. There is clear evidence that EPO effectively influences all wound-healing phases in a dose-dependent manner. This includes inflammation, tissue, and blood vessel formation as well as the remodeling of the wound. The molecular mechanism is predominantly based on an increased expression of the endothelial and inducible nitric oxide (NO) synthase with a consecutive rapid supply of NO as well as an increased content of vascular endothelial growth factor (VEGF) in the wound. The improved understanding of the functions and regulatory mechanisms of EPO in the context of wound-healing problems and ischemia/reperfusion injury, especially during flap surgery, may lead to new considerations of this growth hormone for its regular clinical application in patients.

Erythropoietin use and abuse

Recombinant human erythropoietin (rhEPO) is arguably the most successful therapeutic application of recombinant DNA technology till date. It was isolated in 1977 and the gene decoded in 1985. Since then, it has found varied applications, especially in stimulating erythropoiesis in anemia due to chronic conditions like renal failure, myelodysplasia, infections like HIV, in prematurity, and in reducing peri-operative blood transfusions. The discovery of erythropoietin receptor (EPO-R) and its presence in non-erythroid cells has led to several areas of research. Various types of rhEPO are commercially available today with different dosage schedules and modes of delivery. Their efficacy in stimulating erythropoiesis is dose dependent and differs according to the patient's disease and nutritional status. EPO should be used carefully according to guidelines as unsolicited use can result in serious adverse effects. Because of its capacity to improve oxygenation, it has been abused by athletes participating in endurance sports and detecting this has proved to be a challenge.

Reno-endocrinal disorders: A basic understanding of the molecular genetics

The successful management of endocrine diseases is greatly helped by the complete understanding of the underlying pathology. The knowledge about the molecular genetics contributes immensely in the appropriate identification of the causative factors of the diseases and their subsequent management. The fields of nephrology and endocrinology are also interrelated to a large extent. Besides performing the secretory functions, the renal tissue also acts as target organ for many hormones such as antidiuretic hormone (ADH), atrial natriuretic peptides (ANP), and aldosterone. Understanding the molecular genetics of these hormones is important because the therapeutic interventions in many of these conditions is related to shared renal and endocrine functions, including the anemia of renal disease, chronic kidney disease, mineral bone disorders, and hypertension related to chronic kidney disease. Their understanding and in-depth knowledge is very essential in designing and formulating the therapeutic plans and innovating new management strategies. However, we still have to go a long way in order to completely understand the various confounding causative relationships between the pathology and disease of these reno-endocrinal manifestations.

Detection of EPO doping and blood doping: the haematological module of the Athlete Biological Passport

The increase of the body's capacity to transport oxygen is a prime target for doping athletes in all endurance sports. For this pupose, blood transfusions or erythropoiesis stimulating agents (ESA), such as erythropoietin, NESP, and CERA are used. As direct detection of such manipulations is difficult, biomarkers that are connected to the haematopoietic system (haemoglobin concentration, reticulocytes) are monitored over time (Athlete Biological Passport (ABP)) and analyzed using mathematical models to identify patterns suspicious of doping. With this information, athletes can either be sanctioned directly based on their profile or targeted with conventional doping tests. Key issues for the appropriate use of the ABP are correct targeting and use of all available information (e.g. whereabouts, cross sectional population data) in a forensic manner. Future developments of the passport include the correction of all concentration-based variables for shifts in plasma volume, which might considerably increase sensitivity. New passport markers from the genomic, proteomic, and metabolomic level might add further information, but need to be validated before integration into the passport procedure. A first assessment of blood data of federations that have implemented the passport show encouraging signs of a decreased blood-doping prevalence in their athletes, which adds scientific credibility to this innovative concept in the fight against ESA- and blood doping.

Evaluation of functional erythropoietin receptor status in skeletal muscle in vivo: acute and prolonged studies in healthy human subjects

BACKGROUND

Erythropoietin receptors have been identified in human skeletal muscle tissue, but downstream signal transduction has not been investigated. We therefore studied in vivo effects of systemic erythropoietin exposure in human skeletal muscle.

METHODOLOGY/PRINCIPAL FINDINGS

The protocols involved 1) acute effects of a single bolus injection of erythropoietin followed by consecutive muscle biopsies for 1-10 hours, and 2) a separate study with prolonged administration for 16 days with biopsies obtained before and after. The presence of erythropoietin receptors in muscle tissue as well as activation of Epo signalling pathways (STAT5, MAPK, Akt, IKK) were analysed by western blotting. Changes in muscle protein profiles after prolonged erythropoietin treatment were evaluated by 2D gel-electrophoresis and mass spectrometry. The presence of the erythropoietin receptor in skeletal muscle was confirmed, by the M20 but not the C20 antibody. However, no significant changes in phosphorylation of the Epo-R, STAT5, MAPK, Akt, Lyn, IKK, and p70S6K after erythropoietin administration were detected. The level of 8 protein spots were significantly altered after 16 days of rHuEpo treatment; one isoform of myosin light chain 3 and one of desmin/actin were decreased, while three isoforms of creatine kinase and two of glyceraldehyd-3-phosphate dehydrogenase were increased.

CONCLUSIONS/SIGNIFICANCE

Acute exposure to recombinant human erythropoietin is not associated by detectable activation of the Epo-R or downstream signalling targets in human skeletal muscle in the resting situation, whereas more prolonged exposure induces significant changes in the skeletal muscle proteome. The absence of functional Epo receptor activity in human skeletal muscle indicates that the long-term effects are indirect and probably related to an increased oxidative capacity in this tissue.

Effects of erythropoietin on frataxin levels and mitochondrial function in Friedreich ataxia--a dose-response trial

Friedreich ataxia (FRDA) is an autosomal recessive inherited neurodegenerative disorder leading to reduced expression of the mitochondrial protein frataxin. Previous studies showed frataxin upregulation in FRDA following treatment with recombinant human erythropoietin (rhuEPO). Dose-response interactions between frataxin and rhuEPO have not been studied until to date. We administered escalating rhuEPO single doses (5,000, 10,000 and 30,000 IU) in monthly intervals to five adult FRDA patients. Measurements of frataxin, serum erythropoietin levels, iron metabolism and mitochondrial function were carried out. Clinical outcome was assessed using the "Scale for the assessment and rating of ataxia". We found maximal erythropoietin serum concentrations 24 h after rhuEPO application which is comparable to healthy subjects. Frataxin levels increased significantly over 3 months, while ataxia rating did not reveal clinical improvement. All FRDA patients had considerable ferritin decrease. NADH/NAD ratio, an indicator of mitochondrial function, increased following rhuEPO treatment. In addition to frataxin upregulation in response to continuous low-dose rhuEPO application shown in previous studies, our results indicate for a long-lasting frataxin increase after single high-dose rhuEPO administration. To detect frataxin-derived neuroprotective effects resulting in clinically relevant improvement, well-designed studies with extended time frame are required.