Promises and pitfalls in erythopoietin-mediated tissue protection: are nonerythropoietic derivatives a way forward?

Modeling and biological evaluation of pegmolesatide, a novel and potent erythropoiesis-stimulating agent

Pegmolesatide, a synthetic, polyethylene-glycolylated, peptide-based erythropoiesis-stimulating agent (ESA), has been recently approved in China. Pegmolesatide is derived from the structure of endogenous erythropoietin (EPO), a natural product in mammals. This study compared the in vitro effects and selectivity of pegmolesatide to those of recombinant EPO and carbamylated EPO (CEPO) through computer-aided analyses and biological tests. The findings indicate that pegmolesatide exhibited the same stimulating effect on erythropoiesis as EPO with fewer side effects than EPO and CEPO.

Endothelial progenitor cells in the host defense response

Extensive injury of endothelial cells in blood vasculature, especially in the microcirculatory system, frequently occurs in hosts suffering from sepsis and the accompanied systemic inflammation. Pathological factors, including toxic components derived from invading microbes, oxidative stress associated with tissue ischemia/reperfusion, and vessel active mediators generated during the inflammatory response, are known to play important roles in mediating endothelial injury. Collapse of microcirculation and tissue edema developed from the failure of endothelial barrier function in vital organ systems, including the lung, brain, and kidney, are detrimental, which often predict fatal outcomes. The host body possesses a substantial capacity for maintaining vascular homeostasis and repairing endothelial damage. Bone marrow and vascular wall niches house endothelial progenitor cells (EPCs). In response to septic challenges, EPCs in their niche environment are rapidly activated for proliferation and angiogenic differentiation. In the meantime, release of EPCs from their niches into the blood stream and homing of these vascular precursors to tissue sites of injury are markedly increased. The recruited EPCs actively participate in host defense against endothelial injury and repair of damage in blood vasculature via direct differentiation into endothelial cells for re-endothelialization as well as production of vessel active mediators to exert paracrine and autocrine effects on angiogenesis/vasculogenesis. In recent years, investigations on significance of EPCs in host defense and molecular signaling mechanisms underlying regulation of the EPC response have achieved substantial progress, which promotes exploration of vascular precursor cell-based approaches for effective prevention and treatment of sepsis-induced vascular injury as well as vital organ system failure.

The anti-apoptotic and anti-autophagic effects of EPO through PI3K/Akt/mTOR signaling pathway in MAC-T cells

Lipopolysaccharide (LPS) is an important inflammatory and infected factor of bacterial mastitis, which treated bovine mammary epithelial cells (MAC-T) in our previous studies, as mastitis cells model in vitro. Erythropoietin (EPO) is a well-known hematopoietic hormone with antioxidative, anti-apoptotic, and anti-inflammatory roles. We hypothesized that EPO might regulate the apoptosis and autophagy to attenuate the inflammation of mastitis. Western blot, RT-PCR, transmission electron microscope analysis and Annexin V-FITC/PI were used to evaluate the regulation of EPO on apoptosis and autophagy in inflammatory MAC-T cells. These results demonstrated that EPO promoted the proliferation of MAC-T cells. Meanwhile, EPO had a better anti-inflammatory effect in MAC-T cells with LPS treatment. Certainly, EPO also showed anti-apoptotic and anti-autophagic effects. Interestingly, we found that the beneficial effect of EPO on inflammatory MAC-T cells depended on the PI3K/Akt/mTOR signaling pathway, which was involved in the regulation of apoptosis and autophagy. Generally, this study provides an insight for EPO to inhibit apoptosis and autophagy of inflammatory MAC-T cells via PI3K/Akt/mTOR signaling pathway.

Upregulation of erythropoietin and erythropoietin receptor in castration-resistant progression of prostate cancer

Hypoxia-induced erythropoietin signaling plays an important role in tumor growth and invasion. In the present study, we investigated the contribution of erythropoietin signaling pathway to castration-resistant prostate cancer and the development of a neuroendocrine phenotype. Immunohistochemical staining showed that the erythropoietin and erythropoietin receptor scores in castration-resistant prostate cancer and androgen-dependent prostate cancer were 7.55 versus 4.5 and 7.45 versus 5.9,respectively (P < 0.001). Furthermore, a cell proliferation assay was conducted, and the differential expression of erythropoietin and erythropoietin receptor in LNCaP cells and hypoxia-induced LNCaP cells was evaluated using western blot and quantitative real-time PCR. The proliferation capacity of hypoxia-induced LNCaP cells was similar in cultures of both fetal bovine serum and charcoal-stripped fetal bovine serum, suggesting that LNCaP cells acquired hypoxia-induced androgen-independent growth. After 2 weeks of hypoxic culture, LNCaP cells showed a neuroendocrine cell change and increased expression of neuron-specific enolase, erythropoietin, and erythropoietin receptor; knockdown of erythropoietin receptor reversed the hypoxia-induced upregulation of neuron-specific enolase in the LNCaP cells. In conclusion, the concurrent upregulation of erythropoietin and erythropoietin receptor in castration-resistant prostate cancer suggests that the erythropoietin/erythropoietin receptor autocrine loop plays an important role in the progression of castration resistance and is responsible for the development of a neuroendocrine phenotype.

Pleiotropic effect of erythropoiesis-stimulating agents on circulating endothelial progenitor cells in dialysis patients

BACKGROUND

Recent studies have suggested that erythropoiesis-stimulating agents (ESAs) may accelerate not only angiogenesis but also vasculogenesis, beyond erythropoiesis.

METHODS

We conducted a 12-week prospective study in 51 dialysis patients; 13 were treated with recombinant human erythropoietin (EPO, 5290.4 ± 586.9 IU/week), 16 with darbepoetin (DA, 42.9 ± 4.3 µg/week), 12 with epoetin β pegol (CERA, 40.5 ± 4.1 µg/week) and 10 with no ESAs. Vascular mediators comprising endothelial progenitor cells (EPCs), vascular endothelial growth factor (VEGF), matrix metalloproteinase-2 (MMP-2), and high-sensitivity C-reactive protein (hs-CRP) were measured at 0 and 12 weeks. EPCs were measured by flow cytometry as CD45^lowCD34⁺CD133⁺ cells.

RESULTS

The EPC count increased significantly to a greater extent in the EPO group than in the other three group, and increased significantly from 0 to 12 weeks in a EPO dose-dependent manner. In both the DA and CERA groups, the EPC count did not change at 12 weeks. Serum levels of VEGF, MMP-2 and hs-CRP were not affected by ESA treatment in all groups. In the CERA group, serum ferritin decreased significantly compared to the no-ESA group and correlated with CERA dose, although use of iron was permitted if required during the prospective study period of 12 weeks.

CONCLUSIONS

When patients on dialysis were treated with clinical doses of various ESAs, only EPO induced a significant increase of circulating EPCs from bone marrow, whereas, DA and CERA had no effect.

Erythropoietin in Lupus: Unanticipated Immune Modulating Effects of a Kidney Hormone

Systemic lupus erythematosus (SLE) is a multiorgan autoimmune disease with variable clinical presentation, typically characterized by a relapsing-remitting course. SLE has a multifactorial pathogenesis including genetic, environmental, and hormonal factors that lead to loss of tolerance against self-antigens and autoantibody production. Mortality in SLE patients remains significantly higher than in the general population, in part because of the limited efficacy of available treatments and the associated toxicities. Therefore, novel targeted therapies are urgently needed to improve the outcomes of affected individuals. Erythropoietin (EPO), a kidney-produced hormone that promotes red blood cell production in response to hypoxia, has lately been shown to also possess non-erythropoietic properties, including immunomodulatory effects. In various models of autoimmune diseases, EPO limits cell apoptosis and favors cell clearance, while reducing proinflammatory cytokines and promoting the induction of regulatory T cells. Notably, EPO has been shown to reduce autoimmune response and decrease disease severity in mouse models of SLE. Herein, we review EPO's non-erythropoietic effects, with a special focus on immune modulating effects in SLE and its potential clinical utility.

Are all erythropoiesis-stimulating agents created equal?

Erythropoiesis-stimulating agents (ESAs) are effective drugs to correct and maintain haemoglobin (Hb) levels, however, their use at doses to reach high Hb targets has been associated with an increased risk of cardiovascular adverse events, mortality and cancer. Presently used ESAs have a common mechanism of action but different pharmacokinetic and pharmacodynamic characteristics. Accordingly, the mode of activation of the erythropoietin (EPO) receptor can exert marked differences in downstream events. It is unknown whether the various ESA molecules have different efficacy/safety profiles. The relative mortality and morbidity risks associated with the use of different types of ESAs remains poorly evaluated. Recently an observational study and a randomized clinical trial provided conflicting results regarding this matter. However, these two studies displayed several differences in patient characteristics and ESA molecules used. More importantly, by definition, randomized clinical trials avoid bias by indication and suffer less from confounding factors. Therefore they bring a higher degree of evidence. The scenario becomes even more complex when considering the new class of ESAs, called prolyl-hydroxylase domain (PHD) inhibitors. They are oral drugs that mimic exposure to hypoxia and stabilize hypoxia-inducible factor α. They profoundly differ from presently used ESAs, as they have multiple targets of action, including the stimulation of endogenous EPO synthesis, direct mobilization/absorption of iron and a higher reduction of hepcidin. Accordingly, they have the potential to be more effective in inflamed patients with functional iron deficiency, i.e. the setting of patients who are at higher risk of cardiovascular events and mortality in response to present ESA use. As for ESAs, individual PHD inhibitors differ in molecular structure and degree of selectivity for the three main PHD isoforms; their efficacy and safety profiles may therefore be different from that of presently available ESAs.

Recombinant Erythropoietin Provides Protection against Renal Fibrosis in Adenine-Induced Chronic Kidney Disease

Chronic kidney disease (CKD) causes anemia by renal damage. In CKD, the kidney is submitted to hypoxia, persistent inflammation, leading to fibrosis and permanent loss of renal function. Human recombinant erythropoietin (rEPO) has been widely used to treat CKD-associated anemia and is known to possess organ-protective properties that are independent from its well-established hematopoietic effects. Nonhematopoietic effects of EPO are mediated by an alternative receptor that is proposed to consist of a heterocomplex between the erythropoietin receptor (EPOR) and the beta common receptor (βcR). The present study explored the effects of rEPO to prevent renal fibrosis in adenine-induced chronic kidney disease (Ad-CKD) and their association with the expression of the heterodimer EPOR/βcR. Male Wistar rats were randomized to control group (CTL), adenine-fed rats (Ad-CKD), and Ad-CKD with treatment of rEPO (1050 IU/kg, once weekly for 4 weeks). Ad-CKD rats exhibited anemia, uremia, decreased renal function, increased infiltration of inflammatory cells, tubular atrophy, and fibrosis. rEPO treatment not only corrected anemia but reduced uremia and partially improved renal function as well. In addition, we observed that rEPO diminishes tubular injury, prevents fibrosis deposition, and induces the EPOR/βcR heteroreceptor. The findings may explain the extrahematopoietic effects of rEPO in CKD and provide new strategies for the treatment of renal fibrosis in CKD.

Non-erythropoietic erythropoietin-derived peptide protects mice from systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease, which results in various organ pathologies. However, current treatment towards SLE is suboptimal. Erythropoietin (EPO) has been shown to promote SLE recovery, but clinical application can be limited by its haematopoiesis-stimulating effects. EPO-derived helix-B peptide (ARA290) is non-erythrogenic but has been reported to retain the anti-inflammatory and tissue-protective functions of EPO. Therefore, here we investigated the effects and potential mechanisms of ARA290 on SLE. The administration of ARA290 to pristane-induced SLE and MRL/lpr mice significantly suppressed the level of serum antinuclear autoantibodies (ANAs) and anti-dsDNA autoantibodies, reduced the deposition of IgG and C3, and ameliorated the nephritis symptoms. Moreover, the serum concentrations of inflammatory cytokine IL-6, MCP-1 and TNF-α in SLE mice were reduced by ARA290. Further, ARA290 decreased the number of apoptotic cells in kidney. In vitro experiment revealed that ARA290 inhibited the inflammatory activation of macrophages and promoted the phagocytotic function of macrophages to apoptotic cells. Finally, ARA290 did not induce haematopoiesis during treatment. In conclusion, ARA290 ameliorated SLE, which at least could be partly due to its anti-inflammatory and apoptotic cell clearance promoting effects, without stimulating haematopoiesis, suggesting that ARA290 could be a hopeful candidate for SLE treatment.

Activation of the β-common receptor by erythropoietin impairs acetylcholine-mediated vasodilation in mouse mesenteric arterioles

Clinically, erythropoietin (EPO) is known to increase systemic vascular resistance and arterial blood pressure. However, EPO stimulates the production of the potent vasodilator, nitric oxide (NO), in culture endothelial cells. The mechanism by which EPO causes vasoconstriction despite stimulating NO production may be dependent on its ability to activate two receptor complexes, the homodimeric EPO (EPOR2 ) and the heterodimeric EPOR/β-common receptor (βCR). The purpose of this study was to investigate the contribution of each receptor to the vasoactive properties of EPO. First-order, mesenteric arteries were isolated from 16-week-old male C57BL/6 mice, and arterial function was studied in pressure arteriographs. To determine the contribution of each receptor complex, EPO-stimulating peptide (ESP), which binds and activates the heterodimeric EPOR/βCR complex, and EPO, which activates both receptors, were added to the arteriograph chamber 20 min prior to evaluation of endothelium-dependent (acetylcholine, bradykinin, A23187) and endothelium-independent (sodium nitroprusside) vasodilator responses. Only ACh-induced vasodilation was impaired in arteries pretreated with EPO or ESP. EPO and ESP pretreatment abolished ACh-induced vasodilation by 100% and 60%, respectively. EPO and ESP did not affect endothelium-independent vasodilation by SNP. Additionally, a novel βCR inhibitory peptide (βIP), which was computationally developed, prevented the impairment of acetylcholine-induced vasodilation by EPO and ESP, further implicating the EPOR/βCR complex. Last, pretreatment with either EPO or ESP did not affect vasoconstriction by phenylephrine and KCl. Taken together, these findings suggest that acute activation of the heterodimeric EPOR/βCR in endothelial cells leads to a selective impairment of ACh-mediated vasodilator response in mouse mesenteric resistance arteries.

Erythropoietin and Nrf2: key factors in the neuroprotection provided by apo-lactoferrin

Among the properties of lactoferrin (LF) are bactericidal, antianemic, immunomodulatory, antitumour, antiphlogistic effects. Previously we demonstrated its capacity to stabilize in vivo HIF-1-alpha and HIF-2-alpha, which are redox-sensitive multiaimed transcription factors. Various tissues of animals receiving recombinant human LF (rhLF) responded by expressing the HIF-1-alpha target genes, hence such proteins as erythropoietin (EPO), ceruloplasmin, etc. were synthesized in noticeable amounts. Among organs in which EPO synthesis occurred were brain, heart, spleen, liver, kidneys and lungs. Other researchers showed that EPO can act as a protectant against severe brain injury and status epilepticus in rats. Therefore, we tried rhLF as a protector against the severe neurologic disorders developed in rats, such as the rotenone-induced model of Parkinson's disease and experimental autoimmune encephalomyelitis as a model of multiple sclerosis, and observed its capacity to mitigate the grave symptoms. Moreover, an intraperitoneal injection of rhLF into mice 1 h after occlusion of the medial cerebral artery significantly diminished the necrosis area measured on the third day in the ischaemic brain. During this period EPO was synthesized in various murine tissues. It was known that EPO induces nuclear translocation of Nrf2, which, like HIF-1-alpha, is a transcription factor. In view that under conditions of hypoxia both factors demonstrate a synergistic protective effect, we suggested that LF activates the Keap1/Nrf2 signaling pathway, an important link in proliferation and differentiation of normal and malignant cells. J774 macrophages were cultured for 3 days without or in the presence of ferric and ferrous ions (RPMI-1640 and DMEM/F12, respectively). Then cells were incubated with rhLF or Deferiprone. Confocal microscopy revealed nuclear translocation of Nrf2 (the key event in Keap1/Nrf2 signaling) induced by apo-rhLF (iron-free, RPMI-1640). The reference compound Deferiprone (iron chelator) had the similar effect. Upon iron binding (in DMEM/F12) rhLF did not activate the Keap1/Nrf2 pathway. Added to J774, apo-rhLF enhanced transcription of Nrf2-dependent genes coding for glutathione S-transferase P and heme oxygenase-1. Western blotting revealed presence of Nrf2 in mice brain after 6 days of oral administration of apo-rhLF, but not Fe-rhLF or equivalent amount of PBS. Hence, apo-LF, but not holo-LF, induces the translocation of Nrf2 from cytoplasm to the nucleus, probably due to its capacity to induce EPO synthesis.

Plant-Produced Asialo-Erythropoietin Restores Pancreatic Beta-Cell Function by Suppressing Mammalian Sterile-20-like Kinase (MST1) and Caspase-3 Activation

Pancreatic beta-cell death adversely contributes to the progression of both type I and II diabetes by undermining beta-cell mass and subsequently diminishing endogenous insulin production. Therapeutics to impede or even reverse the apoptosis and dysfunction of beta-cells are urgently needed. Asialo-rhuEPO, an enzymatically desialylated form of recombinant human erythropoietin (rhuEPO), has been shown to have cardioprotective and neuroprotective functions but with no adverse effects like that of sialylated rhuEPO. Heretofore, the anti-apoptotic effect of asialo-rhuEPO on pancreatic beta-cells has not been reported. In the current study, we investigated the cytoprotective properties of plant-produced asialo-rhuEPO (asialo-rhuEPO^P) against staurosporine-induced cell death in the pancreatic beta-cell line RIN-m5F. Our results showed that 60 IU/ml asialo-rhuEPO^P provided 41% cytoprotection while 60 IU/ml rhuEPO yielded no effect. Western blotting results showed that asialo-rhuEPO^P treatment inhibited both MST1 and caspase-3 activation with the retention of PDX1 and insulin levels close to untreated control cells. Our study provides the first evidence indicating that asialo-rhuEPO^P-mediated protection involves the reduction of MST1 activation, which is considered a key mediator of apoptotic signaling in beta-cells. Considering the many advantages its plant-based expression, asialo-rhuEPO^P could be potentially developed as a novel and inexpensive agent to treat or prevent diabetes after further performing studies in cell-based and animal models of diabetes.

Elevated hematocrit enhances platelet accumulation following vascular injury

Red blood cells (RBCs) demonstrate procoagulant properties in vitro, and elevated hematocrit is associated with reduced bleeding and increased thrombosis risk in humans. These observations suggest RBCs contribute to thrombus formation. However, effects of RBCs on thrombosis are difficult to assess because humans and mice with elevated hematocrit typically have coexisting pathologies. Using an experimental model of elevated hematocrit in healthy mice, we measured effects of hematocrit in 2 in vivo clot formation models. We also assessed thrombin generation, platelet-thrombus interactions, and platelet accumulation in thrombi ex vivo, in vitro, and in silico. Compared with controls, mice with elevated hematocrit (RBC^HIGH) formed thrombi at a faster rate and had a shortened vessel occlusion time. Thrombi in control and RBC^HIGH mice did not differ in size or fibrin content, and there was no difference in levels of circulating thrombin-antithrombin complexes. In vitro, increasing the hematocrit increased thrombin generation in the absence of platelets; however, this effect was reduced in the presence of platelets. In silico, direct numerical simulations of whole blood predicted elevated hematocrit increases the frequency and duration of interactions between platelets and a thrombus. When human whole blood was perfused over collagen at arterial shear rates, elevating the hematocrit increased the rate of platelet deposition and thrombus growth. These data suggest RBCs promote arterial thrombosis by enhancing platelet accumulation at the site of vessel injury. Maintaining a normal hematocrit may reduce arterial thrombosis risk in humans.

Low-dose erythropoietin treatment is not associated with clinical benefits in severely anaemic Jehovah's Witnesses: a plea for a change

BACKGROUND

Jehovah's Witnesses who refuse blood transfusion have high mortality. Erythropoietin (EPO) has been used as an alternative to blood transfusion. The optimal dosing of EPO in anaemic Jehovah's Witnesses is unknown. The aim of our study was to evaluate the clinical benefits of treatment with a low dose (<600 IU/kg/week) of epoietin beta (EPO-β).

MATERIALS AND METHODS

This was an observational study, retrospectively considering a 10-year period during which 3,529 adult Jehovah's Witnesses with a total of 10,786 hospital admissions were identified from databases of four major public hospitals in New Zealand. Patients with severe symptomatic anaemia (haemoglobin <80 g/L) who were unable to tolerate physical activity were included in the study. Patients treated without EPO were assigned to the conventional therapy group and those treated with EPO to the EPO treatment group.

RESULTS

Ninety-one Jehovah's Witnesses met the eligibility criteria. Propensity score matching yielded a total of 57 patients. Patients treated with conventional therapy and those treated with EPO had similar durations of severe anaemia (average difference 6.25 days, 95% confidence interval [CI]: -3.77-16.27 days; p=0.221). The mortality rate among Jehovah's Witnesses treated with conventional therapy was 4.68 per year (95% CI: 2.23-9.82), while that in those treated with EPO was 2.77 per year (95% CI: 0.89-8.60). Treatment with EPO was associated with a mortality ratio of 0.59 (95% CI: 0.1-2.6; p=0.236). Both groups of patients had similar in-hospital survival (p=0.703).

DISCUSSION

Treatment with low-dose EPO-β was not associated with either shorter duration of severe anaemia or a reduction in mortality.

Isoforms of the Erythropoietin receptor in dopaminergic neurons of the Substantia Nigra

Erythropoietin receptor (EpoR) regulates erythrocytes differentiation in blood. In the brain, EpoR has been shown to protect several neuronal cell types from cell death, including the A9 dopaminergic neurons (DA) of the Substantia Nigra (SN). These cells form the nigrostriatal pathway and are devoted to the control of postural reflexes and voluntary movements. Selective degeneration of A9 DA neurons leads to Parkinson's disease. By the use of nanoCAGE, a technology that allows the identification of Transcription Start Sites (TSSs) at a genome-wide level, we have described the promoter-level expression atlas of mouse A9 DA neurons purified with Laser Capture Microdissection (LCM). Here, we identify mRNA variants of the Erythropoietin Receptor (DA-EpoR) transcribed from alternative TSSs. Experimental validation and full-length cDNA cloning is integrated with gene expression analysis in the FANTOM5 database. In DA neurons, the EpoR gene encodes for a N-terminal truncated receptor. Based on STAT5 phosphorylation assays, we show that the new variant of N-terminally truncated EpoR acts as decoy when co-expressed with the full-length form. A similar isoform is also found in human. This work highlights new complexities in the regulation of Erythropoietin (EPO) signaling in the brain.

Erythropoietin Pathway: A Potential Target for the Treatment of Depression

During the past decade, accumulating evidence from both clinical and experimental studies has indicated that erythropoietin may have antidepressant effects. In addition to the kidney and liver, many organs have been identified as secretory tissues for erythropoietin, including the brain. Its receptor is expressed in cerebral and spinal cord neurons, the hypothalamus, hippocampus, neocortex, dorsal root ganglia, nerve axons, and Schwann cells. These findings may highlight new functions for erythropoietin, which was originally considered to play a crucial role in the progress of erythroid differentiation. Erythropoietin and its receptor signaling through JAK2 activate multiple downstream signaling pathways including STAT5, PI3K/Akt, NF-κB, and MAPK. These factors may play an important role in inflammation and neuroprogression in the nervous system. This is particularly true for the hippocampus, which is possibly related to learning, memory, neurocognitive deficits and mood alterations. Thus, the influence of erythropoietin on the downstream pathways known to be involved in the treatment of depression makes the erythropoietin-related pathway an attractive target for the development of new therapeutic approaches. Focusing on erythropoietin may help us understand the pathogenic mechanisms of depression and the molecular basis of its treatment.

Carbamylated Erythropoietin Outperforms Erythropoietin in the Treatment of AKI-on-CKD and Other AKI Models

Erythropoietin (EPO) may be a beneficial tissue-protective cytokine. However, high doses of EPO are associate with adverse effects, including thrombosis, tumor growth, and hypertension. Carbamylated erythropoietin (CEPO) lacks both erythropoietic and vasoconstrictive actions. In this study, we compared the renoprotective, hemodynamic, and hematologic activities and survival effects of identical EPO and CEPO doses in rat models of clinically relevant AKI presentations, including ischemia-reperfusion-induced AKI superimposed on CKD (5000 U/kg EPO or CEPO; three subcutaneous injections) and ischemia-reperfusion-induced AKI in old versus young animals and male versus female animals (1000 U/kg EPO or CEPO; three subcutaneous injections). Compared with EPO therapy, CEPO therapy induced greater improvements in renal function and body weight in AKI on CKD animals, with smaller increases in hematocrit levels and similarly improved survival. Compared with EPO therapy in the other AKI groups, CEPO therapy induced greater improvements in protection and recovery of renal function and survival, with smaller increases in systolic BP and hematocrit levels. Overall, old or male animals had more severe loss in kidney function and higher mortality rates than young or female animals, respectively. Notably, mRNA and protein expression analyses confirmed the renal expression of the heterodimeric EPO receptor/CD131 complex, which is required for the tissue-protective effects of CEPO signaling. In conclusion, CEPO improves renal function, body and kidney weight, and survival in AKI models without raising hematocrit levels and BP as substantially as EPO. Thus, CEPO therapy may be superior to EPO in improving outcomes in common forms of clinical AKI.

Effects of erythropoietin combined with tissue plasminogen activator on the rats following cerebral ischemia and reperfusion

OBJECTIVES:

Exogenously administered recombinant human erythropoietin (rhEPO) has been reported to exhibit neuroprotective effects in animal models. However, there are still have some controversies that combination of EPO and tissue plasminogen activator (tPA) in acute ischemic stroke. In the present study, we investigated the effects of local intra-arterial infusion of low-dose EPO in combination with tPA on focal cerebral ischemic stroke.

MATERIALS AND METHODS:

Sixty adult male Sprague–Dawley rats were randomly divided into five groups, including sham, vehicle, EPO, tPA, and EPO+tPA groups. Rats were subjected to middle cerebral artery occlusion (MCAO) and administrated with EPO (800 U/kg, middle cerebral artery injection), tPA (10 mg/kg, tail vein injection), EPO+tPA, or saline (vehicle) onset of reperfusion. Neurobehavioral deficits, infarct volume, brain edema, the expression of tight junction proteins (Claudin-5, Occludin), and AQP4 were assessed following 2 h ischemia and 24 h reperfusion. The number of apoptotic cells in the periinfarct region was detected by the terminal deoxyribonucleotide transferase dUTP nick end labeling (TUNEL) staining.

RESULTS:

The neurobehavioral deficits, brain infarct volume, edema volume, TUNEL-positive cells and downregulation of Claudin-5 and Occludin were alleviated by EPO or EPO plus tPA, following the ischemia/reperfusion (I/R) in rats. The EPO and EPO plus tPA both reduced the upregulation of AQP4 in the ischemic brain tissue.

CONCLUSION:

Our data demonstrate local intra-arterial infusion of low-dose EPO in combination with tPA protected against focal cerebral ischemia in rats manifested by a decrease in brain edema and blood-brain barrier (BBB) disruption after 2 h ischemia and 24 h reperfusion.

Nonerythropoietic Erythropoietin-Derived Peptide Suppresses Adipogenesis, Inflammation, Obesity and Insulin Resistance

Erythropoietin (EPO) has been identified as being crucial for obesity modulation; however, its erythropoietic activity may limit its clinical application. EPO-derived Helix B-surface peptide (pHBSP) is nonerythrogenic but has been reported to retain other functions of EPO. The current study aimed to evaluate the effects and potential mechanisms of pHBSP in obesity modulation. We found that pHBSP suppressed adipogenesis, adipokine expression and peroxisome proliferator-activated receptor γ (PPARγ) levels during 3T3-L1 preadipocyte maturation through the EPO receptor (EPOR). In addition, also through EPOR, pHBSP attenuated macrophage inflammatory activation and promoted PPARγ expression. Furthermore, PPARγ deficiency partly ablated the anti-inflammatory activity of pHBSP in macrophages. Correspondingly, pHBSP administration to high-fat diet (HFD)-fed mice significantly improved obesity, insulin resistance (IR) and adipose tissue inflammation without stimulating hematopoiesis. Therefore, pHBSP can significantly protect against obesity and IR partly by inhibiting adipogenesis and inflammation. These findings have therapeutic implications for metabolic disorders, such as obesity and diabetes.

Effects and mechanism of recombinant human erythropoietin on the growth of human breast cancer MDA-MB-231 cells in nude mice

This study aimed to explore the effects of recombinant human erythropoietin (rhEPO) on the growth of human breast cancer MDA-MB-231 cells in nude mice, and investigate its functions in regulating tumor growth, angiogenesis and apoptosis. A tumor-bearing nude mice model was established by subcutaneous injection of human breast cancer MDA-MB-231 cells. Two weeks later, the mice were randomly divided into four groups (n=6 for each group): negative control group, rhEPO group, EPO antibody group and EPO+EPO antibody group. Drugs were administered to the corresponding mice once every 3 days for five times. The size and weight of tumors were measured after the mice were sacrificed by cervical dislocation. The expression levels of EPO/EPOR, TNF-α, IL-10, and Bcl-2 in the tumor tissues were determined using RT-PCR and Western blot. The microvessel density (MVD) and expression of VEGF in the tumors were detected using immunohistochemistry. TUNEL assay was used to determine apoptosis in tumors. Results show that rhEPO significantly promoted the growth of MDA-MB-231 cells in nude mice (P<0.05). Compared with the negative control group, the expression levels of EPO, EPOR, TNF-α, IL-10, and VEGF, as well as the MVD values, were significantly elevated in the rhEPO group. However, the apoptotic index was significantly reduced (P<0.05). The ability of rhEPO to promote tumor growth may be associated with its functions in promoting microvessel formation and inhibiting tumor cell apoptosis.

Erythropoietin and protection of renal function in cardiac surgery (the EPRICS Trial)

BACKGROUND

To date, there are no known methods for preventing acute kidney injury after cardiac surgery. Increasing evidence suggests that erythropoietin has renal antiapoptotic and tissue protective effects. However, recent human studies have shown conflicting results. The authors aimed to study the effect of a single high-dose erythropoietin preoperatively on renal function after coronary artery bypass grafting in patients with preoperative impaired renal function.

METHODS

This single-center, randomized, double-blind, placebo-controlled study included 75 patients scheduled for coronary artery bypass grafting with preexisting renal impairment estimated glomerular filtration rate based on p-cystatin C (<60 and >15 ml/min). The patients either received a single high-dose erythropoietin (400 IU/kg) or placebo preoperatively. The primary endpoint was renal protection evaluated by p-cystatin C at the third postoperative day compared to the preoperative values. Incidence of acute kidney injury and other renal biomarker changes were among secondary endpoints.

RESULTS

There was no statistically significant difference on the third postoperative day for relative p-cystatin C level changes from baseline between the groups, 131 ± 31% (mean ± SD) for the study group and 125 ± 24% for the control group (P = 0.31; 95% CI, -0.6 to 20% for the difference). There were no statistically significant differences in other renal biomarkers or measures between the groups (p-neutrophil gelatinase-associated lipocalin, p-creatinine, p-urea, and estimated glomerular filtration rate). There were no other differences in outcome variables between the groups.

CONCLUSION

Intravenous administration of a single high-dose (400 IU/kg) erythropoietin did not have a renal protective effect on patients with reduced kidney function undergoing coronary artery bypass surgery.

On the antioxidant properties of erythropoietin and its association with the oxidative-nitrosative stress response to hypoxia in humans

AIM

The aim of this study was to examine if erythropoietin (EPO) has the potential to act as a biological antioxidant and determine the underlying mechanisms.

METHODS

The rate at which its recombinant form (rHuEPO) reacts with hydroxyl (HO˙), 2,2-diphenyl-1-picrylhydrazyl (DPPH˙) and peroxyl (ROO˙) radicals was evaluated in-vitro. The relationship between the erythopoietic and oxidative-nitrosative stress response to poikilocapneic hypoxia was determined separately in-vivo by sampling arterial blood from eleven males in normoxia and following 12 h exposure to 13% oxygen. Electron paramagnetic resonance spectroscopy, ELISA and ozone-based chemiluminescence were employed for direct detection of ascorbate (A(˙-) ) and N-tert-butyl-α-phenylnitrone spin-trapped alkoxyl (PBN-OR) radicals, 3-nitrotyrosine (3-NT) and nitrite (NO2-).

RESULTS

We found rHuEPO to be a potent scavenger of HO˙ (kr = 1.03-1.66 × 10(11) m(-1) s(-1) ) with the capacity to inhibit Fenton chemistry through catalytic iron chelation. Its ability to scavenge DPPH˙ and ROO˙ was also superior compared to other more conventional antioxidants. Hypoxia was associated with a rise in arterial EPO and free radical-mediated reduction in nitric oxide, indicative of oxidative-nitrosative stress. The latter was confirmed by an increased systemic formation of A˙(-) , PBN-OR, 3-NT and corresponding loss of NO2- (P < 0.05 vs. normoxia). The erythropoietic and oxidative-nitrosative stress responses were consistently related (r = -0.52 to 0.68, P < 0.05).

CONCLUSION

These findings demonstrate that EPO has the capacity to act as a biological antioxidant and provide a mechanistic basis for its reported cytoprotective benefits within the clinical setting.

Immunosuppressive effects of erythropoietin on human alloreactive T cells

Correction of anemia with erythropoietin (EPO) is associated with improved kidney transplant outcomes. Emerging evidence, predominantly from animal models, indicates that these observations may be erythropoiesis-independent and that EPO exhibits immunosuppressive properties. We examined the effects of EPO on human T-cell alloimmunity by first documenting that CD4(+) and CD8(+) T cells express EPO receptor (EPO-R) on their surfaces. In mixed lymphocyte reactions, EPO induced a dose-dependent decrease in allogeneic CD4(+) T-cell proliferation (EPO 1000 U/ml: 44.6%±22.9% of vehicle, P<0.05; 2000 U/ml: 11.1%±4% of vehicle, P<0.001) without inducing cell death. The effects required signals transmitted directly through the EPO-R expressed on T cells, resulting in diminished Th1 differentiation without effects on regulatory T-cell induction. Mechanistic studies revealed that EPO prevented IL-2-induced proliferation by uncoupling IL-2 receptor signaling, inhibiting phosphorylation of the intracellular intermediaries AKT and extracellular signal-regulated kinase that are known to mediate T-cell expansion. EPO treatment reduced expansion of human naïve CD4(+) T cells after adoptive transfer into NOD scid γc(null) mouse recipients, verifying the effects in vivo. Although activated T cells expressed CD131, an alternative EPO receptor, addition of a specific CD131 agonist peptide, ARA290, did not alter T-cell proliferation or cytokine production. Our findings link EPO-R signaling on T cells to inhibition of T-cell immunity, providing one mechanism that could explain the observed protective effects of EPO in kidney transplant recipients.

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.

Erythropoiesis suppression is associated with anthrax lethal toxin-mediated pathogenic progression

Anthrax is a disease caused by the bacterium Bacillus anthracis, which results in high mortality in animals and humans. Although some of the mechanisms are already known such as asphyxia, extensive knowledge of molecular pathogenesis of this disease is deficient and remains to be further investigated. Lethal toxin (LT) is a major virulence factor of B. anthracis and a specific inhibitor/protease of mitogen-activated protein kinase kinases (MAPKKs). Anthrax LT causes lethality and induces certain anthrax-like symptoms, such as anemia and hypoxia, in experimental mice. Mitogen-activated protein kinases (MAPKs) are the downstream pathways of MAPKKs, and are important for erythropoiesis. This prompted us to hypothesize that anemia and hypoxia may in part be exacerbated by erythropoietic dysfunction. As revealed by colony-forming cell assays in this study, LT challenges significantly reduced mouse erythroid progenitor cells. In addition, in a proteolytic activity-dependent manner, LT suppressed cell survival and differentiation of cord blood CD34⁺-derived erythroblasts in vitro. Suppression of cell numbers and the percentage of erythroblasts in the bone marrow were detected in LT-challenged C57BL/6J mice. In contrast, erythropoiesis was provoked through treatments of erythropoietin, significantly ameliorating the anemia and reducing the mortality of LT-treated mice. These data suggested that suppressed erythropoiesis is part of the pathophysiology of LT-mediated intoxication. Because specific treatments to overcome LT-mediated pathogenesis are still lacking, these efforts may help the development of effective treatments against anthrax.

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: multiple targets, actions, and modifying influences for biological and clinical consideration

Hal Broxmeyer highlights the multitude of erythropoietin’s biological functions, including a novel EPO–EPOR signaling cascade involving a serpin–lysosome–cathepsin axis.

Erythropoietin (EPO), a humoral regulator of erythropoiesis and replacement therapy for selected red blood cell disorders in EPO-deficient patients, has been implicated in a wide range of activities on diverse cell, tissue, and organ types. EPO signals via two receptors, one comprising EPO receptor (EPOR) homodimers and the other a heterodimer of EPOR and CD131—the common β chain component of the GM-CSF, interleukin (IL)-3, and IL-5 receptors. Ligation of EPORs triggers various signaling pathways, including the JAK2–STAT5 and MAPK–NF-κB pathways, depending both on the receptor and the target cell type. A new study in this issue reveals a novel EPO-triggered pathway involving a Spi2A serpin–lysosome–cathepsin cascade that is initiated through the homodimeric EPOR complex and is required for the survival of erythroid progenitors. A full understanding of EPO’s effects on various cell types and their potential clinical relevance requires more work on the signaling events initiated through both EPORs, the effects of other cytokines and growth factors that modulate EPO’s actions, and a comparison of the effects of full-length versus truncated forms of EPO.

Tumor necrosis factor-induced cerebral insulin resistance in Alzheimer's disease links numerous treatment rationales

The evident limitations of the amyloid theory of the pathogenesis of Alzheimer's disease are increasingly putting alternatives in the spotlight. We argue here that a number of independently developing approaches to therapy-including specific and nonspecific anti-tumor necrosis factor (TNF) agents, apolipoprotein E mimetics, leptin, intranasal insulin, the glucagon-like peptide-1 mimetics and glycogen synthase kinase-3 (GSK-3) antagonists-are all part of an interlocking chain of events. All these approaches inform us that inflammation and thence cerebral insulin resistance constitute the pathway on which to focus for a successful clinical outcome in treating this disease. The key link in this chain presently absent is a recognition by Alzheimer's research community of the long-neglected history of TNF induction of insulin resistance. When this is incorporated into the bigger picture, it becomes evident that the interventions we discuss are not competing alternatives but equally valid approaches to correcting different parts of the same pathway to Alzheimer's disease. These treatments can be expected to be at least additive, and conceivably synergistic, in effect. Thus the inflammation, insulin resistance, GSK-3, and mitochondrial dysfunction hypotheses are not opposing ideas but stages of the same fundamental, overarching, pathway of Alzheimer's disease pathogenesis. The insight this provides into progenitor cells, including those involved in adult neurogenesis, is a key part of this approach. This pathway also has therapeutic implications for other circumstances in which brain TNF is pathologically increased, such as stroke, traumatic brain injury, and the infectious disease encephalopathies.

Delayed administration of pyroglutamate helix B surface peptide (pHBSP), a novel nonerythropoietic analog of erythropoietin, attenuates acute kidney injury

In preclinical studies, erythropoietin (EPO) reduces ischemia-reperfusion-associated tissue injury (for example, stroke, myocardial infarction, acute kidney injury, hemorrhagic shock and liver ischemia). It has been proposed that the erythropoietic effects of EPO are mediated by the classic EPO receptor homodimer, whereas the tissue-protective effects are mediated by a hetero-complex between the EPO receptor monomer and the β-common receptor (termed "tissue-protective receptor"). Here, we investigate the effects of a novel, selective-ligand of the tissue-protective receptor (pyroglutamate helix B surface peptide [pHBSP]) in a rodent model of acute kidney injury/dysfunction. Administration of pHBSP (10 μg/kg intraperitoneally [i.p.] 6 h into reperfusion) or EPO (1,000 IU/kg i.p. 4 h into reperfusion) to rats subjected to 30 min ischemia and 48 h reperfusion resulted in significant attenuation of renal and tubular dysfunction. Both pHBSP and EPO enhanced the phosphorylation of Akt (activation) and glycogen synthase kinase 3β (inhibition) in the rat kidney after ischemia-reperfusion, resulting in prevention of the activation of nuclear factor-κB (reduction in nuclear translocation of p65). Interestingly, the phosphorylation of endothelial nitric oxide synthase was enhanced by EPO and, to a much lesser extent, by pHBSP, suggesting that the signaling pathways activated by EPO and pHBSP may not be identical.

Systemic VHL gene functions and the VHL disease

The von Hippel-Lindau tumor suppressor gene (VHL) is best known as an E3 ubiquitin ligase that negatively regulates the hypoxia inducible factor (HIF). VHL mutations are the genetic defects underlying several human diseases including polycythemia, familial VHL tumor syndrome and sporadic renal cell carcinoma. VHL mutations can lead to cell-autonomous phenotypes in the tumor cells. However, non-tumor cell-autonomous functions of VHL have also been noted. VHL tumor-derived cytokines can promote inflammation and induce mobilization of endothelial progenitor cells. Up-regulation of HIF caused by VHL loss-of-function mutants, including heterozygotes, has been shown to increase the activities of hematopoietic stem cells, endothelial cells and myeloid cells. As such, systemic functions of VHL likely play important roles in the development of VHL disease.

Giving anemia a boost with inhibitors of prolyl hydroxylase

There is much current interest in the development of inhibitors of the prolyl hydroxylase (PHD) enzymes that regulate the hypoxia-inducible transcription factor (HIF), which in turn stimulates the production of erythropoietin and ultimately red blood cells, as a treatment for anemia. A recent paper reports the synthesis and evaluation of a novel class of potent spirohydantoin-based pan-PHD inhibitors for this purpose. The paper is an exemplar of drug development from high-throughput screen to clinical candidate.

Effect of insulin and an erythropoietin-derived peptide (ARA290) on established neuritic dystrophy and neuronopathy in Akita (Ins2 Akita) diabetic mouse sympathetic ganglia

The Akita mouse is a robust model of diabetic autonomic neuropathy which develops severe diabetes following beta cell death, which occurs reproducibly at 3-4 weeks of age, and maintains the diabetic state without therapy for as long as 11 additional months. Neuritic dystrophy and neuronopathy involving prevertebral sympathetic superior mesenteric and celiac ganglia begin to develop within the first two months of onset of diabetes and are progressive with time. We have examined the effect of insulin implants resulting in normoglycemia and injections of ARA290, a small erythropoietin peptide which has no effect on glycemic parameters, on the reversal of established neuritic dystrophy and neuronopathy. We have found that 4 weeks of insulin therapy beginning at 2 months of diabetes resulted in normalization of blood glucose, body weight and HbA1c. Insulin therapy successfully reversed established neuritic dystrophy and neuronopathy to control levels. Numbers of sympathetic neurons were not significantly changed in either 3 month diabetic or insulin-treated Akita mice. Treatment with ARA290 for 7 weeks beginning at 4 months of diabetes did not result in altered metabolic severity of diabetes as measured by blood glucose, body weight or HbA1c levels. ARA290 treatment was able to decrease neuritic dystrophy by 55-74% compared to untreated diabetics or in comparison to a separate group of diabetic animals representing the 4 month treatment onset point. Surprisingly, there was no effect of ARA290 on ganglionic neuron number or ongoing neuronopathy (pale/degenerating neurons) in diabetic Akita mice during this time period. The development of neuroprotective EPO-like peptides may provide a possible future therapy for this debilitating complication of diabetes; however, it appears that discrete elements may be differentially targeted by the diabetic state and may require selective therapy.

Erythropoietin in the intensive care unit: beyond treatment of anemia

Erythropoietin (EPO) is the major hormone stimulating the production and differentiation of red blood cells. EPO is used widely for treating anemia of critical illness or anemia induced by chemotherapy. EPO at pharmacological doses is used in this setting to raise hemoglobin levels (by preventing the apoptosis of erythroid progenitor cells) and is designed to reduce patient exposure to allogenic blood through transfusions. Stroke, heart failure, and acute kidney injury are a frequently encountered clinical problem. Unfortunately, in the intensive care unit advances in supportive interventions have done little to reduce the high mortality associated with these conditions. Tissue protection with EPO at high, nonpharmacological doses after injury has been found in the brain, heart, and kidney of several animal models. It is now well known that EPO has anti-apoptotic effects in cells other than erythroid progenitor cells, which is considered to be independent of EPOs erythropoietic activities. This review article summarizes what is known in preclinical models of critical illness and discusses why this does not correlate with randomized, controlled clinical trials.