Recombinant human erythropoietin (rHuEPO) increases endothelin-1 release by endothelial cells

Erythropoietin and cancer, a double-edged sword

This editorial is focused on the double controversial action of erythropoietin, acting as anticancer agent and as a promoting cancer agent.

Beyond anemia: the clinical impact of the physiologic effects of erythropoietin

Although we have known that oxygen tension affects erythrocyte production since the 19th century, we have only recently begun to understand many subtleties of erythropoietin (EPO) physiology. EPO administration has allowed hundreds of thousands of patients to avoid transfusions. With the beneficial effects so apparent a detailed understanding of the full clinical physiology of this plasma factor seemed less important. However, the unanticipated increase in mortality found in recent randomized studies is prompting a reassessment of this view. We will review what is known about the physiology of this plasma factor that, it is now clear, is more than just an erythrocyte production factor.

Anemia and anemia correction: surrogate markers or causes of morbidity in chronic kidney disease?

Observational studies have shown a strong positive correlation between the severity of anemia and the risk of poor outcomes in patients with chronic kidney disease (CKD). This observation was initially taken to imply that adverse outcomes in CKD are caused by anemia. However, the assumption of causality ignores the possibility that anemia and adverse outcomes might be unrelated and that both are caused by underlying inflammation, oxidative stress and comorbid conditions. Randomized clinical trials of anemia correction have revealed an increased risk of adverse cardiovascular outcomes in patients assigned to normal, rather than subnormal, hemoglobin targets. As a result, correction of anemia is now considered potentially hazardous in patients with CKD. Notably, individuals who did not reach the target hemoglobin level in the clinical trials, despite receiving high doses of erythropoietin and iron, experienced a disproportionately large share of the adverse outcomes. These observations point to overdose of erythropoietin and iron, rather than anemia correction per se, as the likely culprit. This Review explores the reasons for the apparent contradiction between the findings of observational studies and randomized clinical trials of anemia treatment in CKD. I have focused on data from basic and translational studies, which are often overlooked in the design and interpretation of clinical studies and in the formulation of clinical guidelines.

Human recombinant erythropoietin and the incidence of retinopathy of prematurity: a multiple regression model

BACKGROUND

Recombinant human erythropoietin (rhEPO) is used for the treatment of anemia of prematurity. However, it has also been found to have properties similar to vascular endothelial growth factor (VEGF), the major angiogenic factor implicated in the pathogenesis of retinopathy of prematurity (ROP). We sought to determine whether rhEPO is an independent risk factor for the development of ROP.

METHODS

Data were analyzed from 264 infants admitted to the Loma Linda University Children's Hospital neonatal intensive care unit in 1994 and 2002. The data included demographic characteristics, incidence of major morbidities, rhEPO treatment, number of red blood cell transfusions received, and incidence and severity of ROP. A multiple logistic regression model was used to determine the relation of the studied risk factors to the incidence (any stage) and severity (threshold ROP requiring cryotherapy or laser photocoagulation) of ROP.

RESULTS

The risk of developing ROP increased among infants who received >20 doses of rhEPO was higher compared with those who received < or =20 doses (OR, 3.53; 95% CI, 1.59, 7.85). These infants were also more likely to require laser photocoagulation (OR, 4.31; 95% CI, 1.99, 9.33). The age at which rhEPO was started was also a significant risk factor, with those starting rhEPO after 20 days of age having almost fourfold the risk of ROP compared with those starting it on or before 20 days of age (OR, 3.57; 95% CI, 1.59, 8.03).

CONCLUSIONS

rhEPO was found to be a significant independent risk factor for the development of ROP.

Multiorgan-protective actions of blockers of the renin-angiotensin system, statins and erythropoietin: common pleiotropic effects in reno-, cardio- and neuroprotection

Renal diseases induce nephroprotective measures that may affect the heart, brain and other organs. In addition, many cardiovascular and neurological diseases are accompanied by renal lesions. For these reasons, multiorgan-protective measures, including cardio-, reno- and neuro-protective measures, are necessary to treat these diseases. The drugs used in nephrology are often pleiotropic. Although they usually address a single organ or tissue, many of them have complex actions that may provide multiorgan-protection. The present paper aims to review 3 classes of drugs that are commonly prescribed in nephrological practice: statins, RAS blockers (such as ACEIs and ARBs) and erythropoietin (EPO). This paper highlights the renoprotective actions, as well as those that are protective of the heart, brain and other organs, of these drugs at the cellular and molecular level. Their protective actions are attributable to their main effects and pleiotropic effects. The protective pleiotropic actions of these drugs may be exerted on multiple organs, making them multiorgan-protective. Another objective is to analyse the shared multiorgan-protective pleiotropic effects of RAS blockers (ACEIs and ARBs), statins and erythropoietin. This will allow for the practical association of the main renoprotective drugs with multiorgan protection.

Erythropoietin improves skeletal muscle microcirculation and tissue bioenergetics in a mouse sepsis model

Introduction

The relationship between oxygen delivery and consumption in sepsis is impaired, suggesting a microcirculatory perfusion defect. Recombinant human erythropoietin (rHuEPO) regulates erythropoiesis and also exerts complex actions promoting the maintenance of homeostasis of the organism under stress. The objective of this study was to test the hypothesis that rHuEPO could improve skeletal muscle capillary perfusion and tissue oxygenation in sepsis.

Methods

Septic mice in three experiments received rHu-EPO 400 U/kg subcutaneously 18 hours after cecal ligation and perforation (CLP). The first experiment measured the acute effects of rHuEPO on hemodynamics, blood counts, and arterial lactate level. The next two sets of experiments used intravital microscopy to observe capillary perfusion and nicotinamide adenine dinucleotide (NADH) fluorescence post-CLP after treatment with rHuEPO every 10 minutes for 40 minutes and at 6 hours. Perfused capillary density during a three-minute observation period and NADH fluorescence were measured.

Results

rHuEPO did not have any effects on blood pressure, lactate level, or blood cell numbers. CLP mice demonstrated a 22% decrease in perfused capillary density compared to the sham group (28.5 versus 36.6 capillaries per millimeter; p < 0.001). Treatment of CLP mice with rHuEPO resulted in an immediate and significant increase in perfused capillaries in the CLP group at all time points compared to baseline from 28.5 to 33.6 capillaries per millimeter at 40 minutes; p < 0.001. A significant increase in baseline NADH, suggesting tissue hypoxia, was noted in the CLP mice compared to the sham group (48.3 versus 43.9 fluorescence units [FU]; p = 0.03) and improved with rHuEPO from 48.3 to 44.4 FU at 40 minutes (p = 0.02). Six hours after treatment with rHuEPO, CLP mice demonstrated a higher mean perfused capillary density (39.4 versus 31.7 capillaries per millimeter; p < 0.001) and a lower mean NADH fluorescence as compared to CLP+normal saline mice (49.4 versus 52.7 FU; p = 0.03).

Conclusion

rHuEPO produced an immediate increase in capillary perfusion and decrease in NADH fluorescence in skeletal muscle. Thus, it appears that rHuEPO improves tissue bioenergetics, which is sustained for at least six hours in this murine sepsis model.

Direct cardiac actions of erythropoietin (EPO): effects on cardiac contractility, BNP secretion and ischaemia/reperfusion injury

EPO (erythropoietin) has recently been shown to have protective actions upon the myocardium; however, the direct effects of EPO upon cardiac contractile and secretory functions are unknown and the signalling mechanisms are not well defined. In the present study, we provide the first evidence of direct cardiac contractile actions of EPO. In isolated perfused Sprague-Dawley rat hearts, a 30 min infusion of EPO significantly increased contractility in a dose-dependent fashion (maximal change 18+/-2% with 1 unit/ml EPO; P<0.005 compared with vehicle). Perfusate ET-1 (endothelin-1) increased transiently during EPO infusion, and the ET(A/)ET(B) antagonist bosentan abolished the inotropic response to EPO. BNP (B-type natriuretic peptide) secretion (28+/-8%; P<0.05) and nuclear transcription factor GATA-4 DNA-binding activity (51%; P<0.05) were both significantly increased by EPO and blocked by bosentan. In a model of global ischaemic injury, delivery of 1 unit/ml EPO during reperfusion significantly attenuated creatine kinase release (28+/-12%; P<0.05) and significantly improved contractile recovery (P<0.001), independent of ET(A) blockade. Apoptotic indices [assessed by TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling)/cleaved caspase-3-positive cells] were significantly decreased (P<0.01) by 1 unit/ml EPO during reperfusion alone, coincident with significantly increased phosphorylation of myocardial JAK2 (Janus kinase 2) and STAT3 (signal transducer and activator of transcription 3). Thus EPO directly enhances cardiac contractility and BNP secretion and alleviates ischemia/reperfusion injury via ET-1-dependent and -independent mechanisms respectively.

Mechanisms of disease: the hypoxic tubular hypothesis of diabetic nephropathy

Diabetic nephropathy is traditionally considered to be a primarily glomerular disease, although this contention has recently been challenged. Early tubular injury has been reported in patients with diabetes mellitus whose glomerular function is intact. Chronic hypoxia of the tubulointerstitium has been recognized as a mechanism of progression that is common to many renal diseases. The hypoxic milieu in early-stage diabetic nephropathy is aggravated by manifestations of chronic hyperglycemia-abnormalities of red blood cells, oxidative stress, sympathetic denervation of the kidney due to autonomic neuropathy, and diabetes-mellitus-induced tubular apoptosis; as such, tubulointerstitial hypoxia in diabetes mellitus might be an important early event. Chronic hypoxia could have a dominant pathogenic role in diabetic nephropathy, not only in promoting progression but also during initiation of the condition. Early loss of tubular and peritubular cells reduces production of 1,25-dihydroxyvitamin D3 and erythropoietin, which, together with dysfunction of their receptors caused by the diabetic state, diminishes the local trophic effects of the hormones. This diminution could further compromise the functional and structural integrity of the parenchyma and contribute to the gradual decline of renal function.

New insights into nephrogenic systemic fibrosis

Nephrogenic systemic fibrosis is a new disorder reported almost exclusively in patients who have renal insufficiency and are exposed to contrast media formulated with gadolinium. High morbidity and mortality are associated with this severely disabling and painful condition. The acute phase begins upon exposure to gadolinium contrast media, characterized by a systemic inflammatory response involving iron mobilization, and then as a progressive, chronic phase in which fibrosis develops. Proposed is a unifying model of cumulative risk factors in which the interplay of systemic inflammation and stimulated hematopoietic environment associated with hyperparathyroidism and erythropoietin may tie to a common pathogenic mechanism of fibrogenesis. Because there are no uniformly effective interventions to treat nephrogenic systemic fibrosis other than successful renal transplantation, prevention by avoiding gadolinium contrast media in patients with chronic kidney disease is vital. On the basis of suspected pathogenesis, it is also reasonable to limit erythropoietin and iron therapy to dosages ensuring recommended targets and adequately control hyperparathyroidism. Herein is reviewed what is currently known about this subject.

Nonclassic Endogenous Novel Regulators of Angiogenesis

Angiogenesis, the process through which new blood vessels arise from preexisting ones, is regulated by several "classic" factors, among which the most studied are vascular endothelial growth factor (VEGF) and fibroblast growth factor-2 (FGF-2). In recent years, investigations showed that, in addition to the classic factors, numerous endogenous peptides play a relevant regulatory role in angiogenesis. Such regulatory peptides, each of which exerts well-known specific biological activities, are present, along with their receptors, in the blood vessels and may take part in the control of the "angiogenic switch." An in vivo and in vitro proangiogenic effect has been demonstrated for erythropoietin, angiotensin II (ANG-II), endothelins (ETs), adrenomedullin (AM), proadrenomedullin N-terminal 20 peptide (PAMP), urotensin-II, leptin, adiponectin, resistin, neuropeptide-Y, vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating polypeptide (PACAP), and substance P. There is evidence that the angiogenic action of some of these peptides is at least partly mediated by their stimulating effect on VEGF (ANG-II, ETs, PAMP, resistin, VIP and PACAP) and/or FGF-2 systems (PAMP and leptin). AM raises the expression of VEGF in endothelial cells, but VEGF blockade does not affect the proangiogenic action of AM. Other endogenous peptides have been reported to exert an in vivo and in vitro antiangiogenic action. These include somatostatin and natriuretic peptides, which suppress the VEGF system, and ghrelin, that antagonizes FGF-2 effects. Investigations on "nonclassic" regulators of angiogenesis could open new perspectives in the therapy of diseases coupled to dysregulation of angiogenesis.

Acute haemodynamic effects of erythropoietin alone and in combination with dopamine in a porcine model

BACKGROUND

Previous studies in rodents from different kinds of shock models and isolated vessel models indicate that erythropoietin (EPO) has haemodynamic effects through interaction with sympathetic stimuli. This has relevance to the recently described non-haematopoietic effects of EPO, e.g. tissue protective effects. Studies describing the acute effects on integrated physiological haemodynamic variables in larger animal models are scarce though.

AIM

To examine the acute effects of EPO on standard physiological haemodynamic parameters as well as a possible synergistic effect of a sympathetic agonist (dopamine) and EPO on these parameters. RESULTS AND DESIGN: A porcine model was applied. Invasive haemodynamic variables were recorded at baseline, during 2 h after EPO injection and with addition of dopamine. Significant changes were only seen with addition of dopamine. Thus cardiac output increased only significantly in control group (21% versus 4%, P<0.05), and accordingly a decline in systemic vascular resistance was only seen in the control group (19% versus 5%, P< 0.05) with addition of dopamine. Pulmonary vascular resistance increased in EPO group (42% versus unchanged, P<0.05). There was a trend towards increase in left ventricular contractility as measured by slope of the pressure-volume relation (E(max)) in EPO group with addition of dopamine.

CONCLUSION

Erythropoietin has small but significant haemodynamic effects on the response to a sympathetic agonist in the present minimal invasive porcine model.

Erythropoietin and the cardiorenal syndrome: cellular mechanisms on the cardiorenal connectors

We have recently proposed severe cardiorenal syndrome (SCRS), in which cardiac and renal failure mutually amplify progressive failure of both organs. This frequent pathophysiological condition has an extremely poor prognosis. Interactions between inflammation, the renin-angiotensin system, the balance between the nitric oxide and reactive oxygen species and the sympathetic nervous system form the cardiorenal connectors and are cornerstones in the pathophysiology of SCRS. An absolute deficit of erythropoietin (Epo) and decreased sensitivity to Epo in this syndrome both contribute to the development of anemia, which is more pronounced than renal anemia in the absence of heart failure. Besides expression on erythroid progenitor cells, Epo receptors are present in the heart, kidney, and vascular system, in which activation results in antiapoptosis, proliferation, and possibly antioxidation and anti-inflammation. Interestingly, Epo can improve cardiac and renal function. We have therefore reviewed the literature with respect to Epo and the cardiorenal connectors. Indeed, there are indications that Epo can diminish inflammation, reduce renin-angiotensin system activity, and shift the nitric oxide and reactive oxygen species balance toward nitric oxide. Information about Epo and the sympathetic nervous system is scarce. This analysis underscores the relevance of a further understanding of clinical and cellular mechanisms underlying protective effects of Epo, because this will support better treatment of SCRS.

In vivo stimulatory effect of erythropoietin on endothelial nitric oxide synthase in cerebral arteries

The discovery of tissue protective effects of erythropoietin has stimulated significant interest in erythropoietin (Epo) as a novel therapeutic approach to vascular protection. The present study was designed to determine the cerebral vascular effects of recombinant Epo in vivo. Recombinant adenoviral vectors (10(9) plaque-forming units/animal) encoding genes for human erythropoietin (AdEpo) and beta-galactosidase (AdLacZ) were injected into the cisterna magna of rabbits. After 48 h, basilar arteries were harvested for analysis of vasomotor function, Western blotting, and measurement of cGMP levels. Gene transfer of AdEpo increased the expressions of recombinant Epo and its receptor in the basilar arteries. Arteries exposed to recombinant Epo demonstrated attenuation of contractile responses to histamine (10(-9) to 10(-5) mol/l) (P < 0.05, n = 5). Endothelium-dependent relaxations to acetylcholine (10(-9) to 10(-5) mol/l) were significantly augmented (P < 0.05, n = 5), whereas endothelium-independent relaxations to a nitric oxide (NO) donor 2-(N,N-diethylamino)diazenolate-2-oxide sodium salt remained unchanged in AdEpo-transduced basilar arteries. Transduction with AdEpo increased the protein expression of endothelial NO synthase (eNOS) and phosphorylated the S1177 form of the enzyme. Basal levels of cGMP were significantly elevated in arteries transduced with AdEpo consistent with increased NO production. Our studies suggest that in cerebral circulation, Epo enhances endothelium-dependent vasodilatation mediated by NO. This effect could play an important role in the vascular protective effect of Epo.

Important role of endogenous erythropoietin system in recruitment of endothelial progenitor cells in hypoxia-induced pulmonary hypertension in mice

BACKGROUND

Recent studies have suggested that endogenous erythropoietin (Epo) plays an important role in the mobilization of bone marrow-derived endothelial progenitor cells (EPCs). However, it remains to be elucidated whether the Epo system exerts protective effects on pulmonary hypertension (PH), a fatal disorder encountered in cardiovascular medicine.

METHODS AND RESULTS

A mouse model of hypoxia-induced PH was used for study. We evaluated right ventricular systolic pressure, right ventricular hypertrophy, and pulmonary vascular remodeling in mice lacking the Epo receptor (EpoR) in nonerythroid lineages (EpoR(-/-) rescued mice) after 3 weeks of exposure to hypoxia. Those mice lack EpoR in the cardiovascular system but not in the hematopoietic system. The development of PH and pulmonary vascular remodeling were accelerated in EpoR(-/-) rescued mice compared with wild-type mice. The mobilization of EPCs and their recruitment to the pulmonary endothelium were significantly impaired in EpoR(-/-) rescued mice. By contrast, reconstitution of the bone marrow with wild-type bone marrow cells ameliorated PH in the EpoR(-/-) rescued mice. Hypoxia enhanced the expression of EpoR on pulmonary endothelial cells in wild-type but not EpoR(-/-) rescued mice. Finally, hypoxia activated endothelial nitric oxide synthase in the lungs in wild-type mice but not in EpoR(-/-) rescued mice.

CONCLUSIONS

These results indicate that the endogenous Epo/EpoR system plays an important role in the recruitment of EPCs and prevents the development of PH during chronic hypoxia in mice in vivo, suggesting the therapeutic importance of the system for the treatment of PH.

Erythropoietin biology in cancer

Erythropoietin (Epo) has long been known to be the principal hematopoietic growth factor that regulates cellular proliferation and differentiation along the erythroid lineage. Recent studies have shown that Epo is a pleiotropic cytokine that is proangiogenic and exerts broad tissue-protective effects in diverse nonhematopoietic organs. Recombinant Epo (rEpo) has been widely used in the clinic to prevent or treat malignancy-associated anemia. A series of clinical trials have documented the efficacy of rEpo in reducing RBC transfusion requirements and improving quality of life in cancer patients, and a recent meta-analysis suggested a positive effect on survival. However, two randomized trials reported negative outcomes with rEpo, as patients in the rEpo arm fared worse than their placebo-treated counterparts with respect to progression-free survival. The expression of Epo receptor (EpoR) in cancer cells has raised the possibility that exogenous rEpo may exert direct effects on tumor cells associated with the potential for stimulation of proliferation, inhibition of apoptosis, or modulation of sensitivity to chemoradiation therapy. The presence of an autocrine-paracrine Epo-EpoR system in tumors and potential effects of Epo on tumor microenvironment and angiogenesis are consistent with a complex biology for Epo-EpoR signaling in cancer that requires further research. This review describes Epo and EpoR biology, focusing on the pleiotropic effects of Epo on nonhematopoietic tissues as well as the expression and function of EpoR in cancer cells.

Erythropoietin -induced proliferation of gastric mucosal cells

AIM: To analyze the localization of erythropoietin receptor on gastric specimens and characterize the effects of erythropoietin on the normal gastric epithelial proliferation using a porcine gastric epithelial cell culture model.

METHODS: Erythropoietin receptor was detected by RT-PCR, Western blotting and immunohistochermistry. Growth stimulation effects of erythropoietin on cultured gastric mucosal cells were determined by ELISA using bromodeoxyuridine (BrdU).

RESULTS: Erythropoietin receptor was detected on cultured porcine gastric mucosal epithelial cells. Erythropoietin receptor was also detected histochemically at the base of gastric mucosal epithelium. BrdU assay demonstrated a dose-dependent increase in growth potential of cultured porcine gastric mucosal epithelial cells by administration of erythropoietin, as well as these effects were inhibited by administration of anti- erythropoietin antibody (P < 0.01).

CONCLUSION: These findings indicate that erythropoietin has a potential to proliferate gastric mucosal epithelium via erythropoietin receptor.

Emerging biological roles for erythropoietin in the nervous system

Erythropoietin mediates an evolutionarily conserved, ancient immune response that limits damage to the heart, the nervous system and other tissues following injury. New evidence indicates that erythropoietin specifically prevents the destruction of viable tissue surrounding the site of an injury by signalling through a non-haematopoietic receptor. Engineered derivatives of erythropoietin that have a high affinity for this receptor have been developed, and these show robust tissue-protective effects in diverse preclinical models without stimulating erythropoiesis. A recent successful proof-of-concept clinical trial that used erythropoietin to treat human patients who had suffered a stroke encourages the evaluation of both this cytokine and non-erythropoietic derivatives as therapeutic agents to limit tissue injury.

Cyclooxygenase inhibition with acetylsalicylic acid unmasks a role for prostacyclin in erythropoietin-induced hypertension in uremic rats

We previously reported that thromboxane (TX)A2synthesis and receptor blockade prevented recombinant human erythropoietin (rhEPO)-induced hypertension in chronic renal failure rats. The present study was designed to investigate the effect of a cyclooxygenase inhibitor, acetylsalicylic acid (ASA), on blood pressure, renal function, and the concentration of eicosanoïds and endothelin-1 (ET-1) in vascular and renal tissues of rhEPO-treated or rhEPO-untreated uremic rats. Renal failure was induced by a 2-stage 5/6 renal mass ablation. Rats were divided into 4 groups: vehicle, rhEPO (100 U/kg, s.c., 3 times per week), ASA (100 mg·kg–1·day–1), and rhEPO + ASA; all animals were administered drugs for 3 weeks. The TXA2- and prostacyclin (PGI2)-stable metabolites (TXB2and 6-keto-PGF1α, respectively), as well as ET-1, were measured in renal cortex and either the thoracic aorta or mesenteric arterial bed. The uremic rats developed anemia, uremia, and hypertension. They also exhibited a significant increase in vascular and renal TXB2(p < 0.01) and 6-keto-PGF1α(p < 0.01) concentrations. rhEPO therapy corrected the anemia but aggravated hypertension (p < 0.05). TXB2and ET-1 tissue levels further increased (p < 0.05) whereas 6-keto-PGF1αwas unchanged in rhEPO-treated rats compared with uremic rats receiving the vehicle. ASA therapy did not prevent the increase in systolic blood pressure nor the progression of renal disease in rhEPO-treated or rhEPO-untreated uremic rats, but suppressed both TXB2and 6-keto-PGF1αtissue concentrations (p < 0.05). ASA had no effect on vascular and renal ET-1 levels. Cyclooxygenase inhibition had no effect on rhEPO-induced hypertension owing, in part, to simultaneous inhibition of both TXA2and its vasodilatory counterpart PGI2synthesis, whereas the vascular ET-1 overproduction was maintained. These results stress the importance of preserving PGI2production when treating rhEPO-induced hypertension under uremic conditions. Key words: hypertension, erythropoietin, renal failure, acetylsalicilic acid, prostacyclin, thromboxane, endothelin-1.

Etiology and management of hypertension in chronic kidney disease

The kidneys are vital in the pathogenesis of hypertension and are also pathologically affected by the presence of hypertension. The prevalence of hypertension in chronic kidney disease (CKD) depends on age, the severity of renal failure, and proteinuria. The intricate and inextricable relationship between CKD and hypertension seems to cause cardiovascular disease that has assumed epidemic proportions. This article discusses the etiology and treatment of hypertension in CKD so that it can be better controlled.

Glomerular Localization of Erythropoietin Receptor mRNA and Protein in Neonatal and Mature Mouse Kidney

BACKGROUND/AIMS

Erythropoietin (EPO) possesses well-established hematopoietic properties as the primary stimulator of red blood cell formation by binding to its receptor (EPO-R). Recent evidence suggests pathophysiological roles of EPO in several non-hematopoietic tissues including kidney. Our aim was to further clarify the glomerular localization of EPO-R in normal kidney, as well as changes in its expression during glomerulogenesis.

METHODS

We analyzed EPO-R mRNA and protein expression in neonatal and adult mouse kidney by in situ hybridization and immunohistochemistry. To confirm the precise localization and developmental changes of EPO-R expression in podocytes in mature and developing glomeruli, we examined co-expression with the podocyte markers WT-1 and synaptopodin.

RESULTS

In addition to tubular expression as reported recently, EPO-R expression was observed in podocytes as well as endocapillary cells in the glomeruli from adult mice. In newborn kidney, EPO-R mRNA and protein expression was first observed in developing podocytes in S-shaped bodies with expression subsequently increasing in glomeruli at the capillary-loop and maturing stages. Immunoelectron microscopy also demonstrated cytoplasmic expression of EPO-R that was prominent at the basal sides of podocytes in glomeruli at the late capillary-loop and maturing stage.

CONCLUSION

EPO-R is expressed in developing and mature podocytes in mouse kidney, suggesting a possible role for EPO in podocyte biology.

The Erythropoietin Receptor and Its Expression in Tumor Cells and Other Tissues

Erythropoietin (EPO) is the primary regulator of erythropoiesis, stimulating growth, preventing apoptosis, and promoting differentiation of red blood cell progenitors. The EPO receptor belongs to the cytokine receptor superfamily. Although the primary role of EPO is the regulation of red blood cell production, EPO and its receptor have been localized to several nonhematopoietic tissues and cells, including the central nervous system (CNS), endothelial cells, solid tumors, the liver, and the uterus. The presence of EPO receptors and the possibility of EPO signaling in these tissues and cells have led to numerous studies of the effects of EPO at these sites. In particular, expression of EPO and the EPO receptor in cancer cells has generated much interest because of concern that administration of recombinant human erythropoietin (rHuEPO) to patients with breast and other cancer cells expressing the EPO receptor may promote tumor growth via the induction of cell proliferation or angiogenesis. However, evidence supporting a growth-promoting effect has been inconclusive. Moreover, several preclinical studies have shown a beneficial effect of EPO on delaying tumor growth. Further, it is conceivable that increased expression of EPO could reduce tumor hypoxia and ameliorate the deleterious effects of hypoxia on tumor growth, metastasis, and treatment resistance. On the other hand, EPO has also been shown to produce an angiogenic effect in vascular endothelial cells in vitro. However, there is no evidence that these effects occur in vivo to promote tumor growth. EPO and EPO receptors are expressed in neural tissue, and they are upregulated there by hypoxia. Animal studies have shown that administration of epoetin alfa (an rHuEPO) reduces tissue injury due to ischemic stroke, blunt trauma, and experimental autoimmune encephalomyelitis. These findings suggest that epoetin alfa may provide a therapeutic benefit in patients with stroke, trauma, epilepsy, and other CNS-related disorders. Clearly, further study of EPO and the EPO receptor in nonhematopoietic tissue is warranted to determine the potential therapeutic usefulness of rHuEPO as well as to determine the signaling pathway responsible for its effect in vivo.

Anemia as a risk factor and therapeutic target in heart failure

Anemia has recently been recognized as an important comorbid condition and potentially novel therapeutic target in patients with heart failure (HF). Anemia is common in HF patients, with a prevalence ranging from 4% to 55% depending on the population studied. Multiple potential mechanisms of interaction exist between anemia and the clinical syndrome of HF, including hemodilution, inflammatory activation, renal insufficiency, and malnutrition. A growing body of literature from observational databases and clinical trials suggests that anemia is an independent risk factor for adverse outcomes in patients with HF. Although preliminary data suggest that treatment of anemia may result in significant symptomatic improvement in HF, aggressive treatment of anemia may also be associated with increased risk of hypertension or thrombosis. Multiple ongoing studies will provide definitive data on the balance of risks and benefits of anemia treatment in chronic HF.

Beneficial and ominous aspects of the pleiotropic action of erythropoietin

The primary function of the glycoprotein hormone erythropoietin (Epo) is to promote red cell production by inhibiting apoptosis of erythrocytic progenitors in hemopoietic tissues. However, functional Epo receptors (Epo-R) have recently been demonstrated in various nonhemopoietic tissues indicating that Epo is a more pleiotropic viability and growth factor. Herein, in vitro and in vivo effects of Epo in the brain and the cardiovascular system are reviewed. In addition, the therapeutic impact of Epo in oncology is considered, including the question of whether Epo might promote tumor growth. Convincing evidence is available that Epo acts as a neurotrophic and neuroprotective factor in the brain. Epo prevents neuronal cells from hypoxia-induced and glutamate-induced cell death. Epo-R is expressed by neurons and glia cells in specific regions of the brain. Epo supports the survival of neurons in the ischemic brain. The neuroprotective potential of Epo has already been confirmed in a clinical trial on patients with acute stroke. With respect to the vasculature, Epo acts on both endothelial and smooth muscle cells. Epo promotes angiogenesis and stimulates the production of endothelin and other vasoactive mediators. In addition, Epo-R is expressed by cardiomyocytes. The role of Epo as a myocardial protectant is at the focus of present research. Epo therapy in tumor patients is practiced primarily to maintain the hemoglobin concentration above the transfusion trigger and to reduce fatigue. In addition, increased tumor oxygenation may improve the efficacy of chemotherapy and radiotherapy. However, tumor cells often express Epo-R. Therefore, careful studies are required to fully exclude that recombinant human Epo (rHuEpo) promotes tumor growth.

Low-dose therapy with the long-acting erythropoietin analogue darbepoetin alpha persistently activates endothelial Akt and attenuates progressive organ failure

BACKGROUND

The hematopoietic cytokine erythropoietin has cytoprotective effects in endothelial cells in vitro that are mediated through direct activation of the pro-survival Akt tyrosine kinase signaling pathway. We tested the hypothesis that low-dose therapy with the long-acting recombinant human erythropoietin analogue darbepoetin alpha protects vascular endothelium in vivo in a classic remnant kidney rat model characterized by severe endothelial damage, progressive vascular sclerosis, and ischemia-induced tissue fibrosis.

METHODS AND RESULTS

Using a parallel group study design, we randomly assigned animals after 5/6 nephrectomy to treatment with either saline (n=36) or 0.1 microg/kg body wt darbepoetin (n=24) subcutaneously once weekly. We monitored hematocrit, blood pressure, and serum creatinine regularly and obtained renal tissue 6 weeks after nephrectomy for morphological and immunohistochemical analysis. Darbepoetin-treated animals had significantly improved survival compared with saline-treated controls (63% versus 33%; P<0.05), although hematocrit levels were similar in both groups. Darbepoetin treatment ameliorated endothelial damage; attenuated the composite tissue injury score (saline 1.9+/-0.4; darbepoetin 0.4+/-0.2; P<0.001), which included vascular sclerosis, glomerulosclerosis, and tubulointerstitial damage; and preserved renal function. We found persistent activation of the pro-survival Akt signaling pathway in endothelial and epithelial glomerular cells in darbepoetin-treated animals, accompanied by a significant reduction of apoptotic cell death in renal tissue.

CONCLUSIONS

Low-dose darbepoetin treatment confers vascular and tissue protection that is associated with persistent stimulation of the pro-survival Akt signaling pathway. The use of recombinant human erythropoietin or analogues may have utility in preventing ischemia-related progressive vascular injury and organ failure.

Blood pressure response to erythropoietin injection in hemodialysis and predialysis patients

Recombinant human erythropoietin (rHuEPO) has been reported to induce hypertension. We investigated the effect of a single injection of rHuEPO on blood pressure in patients receiving hemodialysis (HD) and in patients with predialysis chronic renal failure (CRF). Forty-one patients receiving HD and 36 patients with predialysis CRF received an intravenous injection of rHuEPO, and blood pressure and plasma endothelin-1 were measured before and 30 min after the injection. Mean blood pressure was increased significantly in HD patients, but not in CRF patients (HD: 103+/-5 to 105+/-6 mmHg, p<0.05; CRF: 103+/-4 to 103+/-6, NS). The percentage of patients with increased mean blood pressure of more than 10 mmHg after rHuEPO injection was significantly larger in the HD than in the CRF group (27.0% vs. 5.5%, p<0.01). A positive correlation was found between changes in endothelin-1 level and mean blood pressure in the HD (r=0.43, p<0.01) but not in predialysis chronic renal failure. In conclusion, a single injection of rHuEPO increased blood pressure with a positive correlation with endothelin-1 release in hemodialysis patients, but not in predialysis chronic renal failure patients.

Endothelial progenitor cell proliferation and differentiation is regulated by erythropoietin Rapid Communication

BACKGROUND

Circulating bone marrow-derived endothelial progenitor cells (EPCs) promote vascular reparative processes. In humans, their number correlate with endothelial function and cardiovascular risk. We tested the hypothesis that darbepoetin alfa [i.e., a recombinant analogue of the cytokine erythropoietin (EPO)] stimulates proliferation and differentiation of EPCs.

METHODS

We assessed CD34+ circulating stem cells (cSCs) in whole blood using flow cytometry and, in addition, proliferation/differentiation of EPCs in an in-vitro assay during 6 weeks of a standard darbepoetin therapy in eight patients with renal anemia.

RESULTS

Darbepoetin treatment caused a significant increase in the number of CD34+ cSCs (week 2, 193%+/- 46%; and week 6, 298%+/- 90%; P < 0.05 vs. baseline). In addition, darbepoetin markedly increased the number of functionally active EPCs (week 2, 256%+/- 48%; and week 6, 299%+/- 59%; both P < 0.01 vs. baseline). The effect of darbepoetin on functional activity of EPCs assessed in a tube formation assay was dose dependent. Administration of darbepoietin caused activation of protein kinase B (Akt) in cultured EPCs.

CONCLUSION

A standard treatment with darbepoetin markedly enhances EPC proliferation and differentiation in renal patients. The use of recombinant EPO analogues may be a novel and safe therapeutic approach in patients with vascular pathology.

Erythropoietin regulates endothelial progenitor cells

Circulating bone marrow-derived endothelial progenitor cells (EPCs) promote vascular reparative processes and neoangiogenesis, and their number in peripheral blood correlates with endothelial function and cardiovascular risk. We tested the hypothesis that the cytokine erythropoietin (EPO) stimulates EPCs in humans. We studied 11 patients with renal anemia and 4 healthy subjects who received standard doses of recombinant human EPO (rhEPO). Treatment with rhEPO caused a significant mobilization of CD34(+)/CD45(+) circulating progenitor cells in peripheral blood (measured by flow cytometry), and increased the number of functionally active EPCs (measured by in vitro assay) in patients (week 2, 312% +/- 31%; week 8, 308% +/- 40%; both P <.01 versus baseline) as well as in healthy subjects (week 8, 194% +/- 15%; P <.05 versus baseline). The effect on EPCs was already observed with an rhEPO dose of about 30 IU/kg per week. Administration of rhEPO increased the number of functionally active EPCs by differentiation in vitro in a dose-dependent manner, assessed in cell culture and by tube formation assay. Furthermore, rhEPO activates the Akt protein kinase pathway in EPCs. Erythropoietin increases the number of functionally active EPCs in humans. Administration of rhEPO or EPO analogs may open new therapeutic strategies in regenerative cardiovascular medicine.

Plasma angiopoietin-1, angiopoietin-2 and Tie-2 in breast and prostate cancer: a comparison with VEGF and Flt-1

BACKGROUND

Angiogenesis is essential for tumour growth and metastasis, and is coordinated by several classes of growth factors mediating their effect through receptors linked, in turn, to tyrosine kinase. These growth factors include angiopoietin-1 (Ang-1), angiopoietin-2 (Ang-2) and vascular endothelial growth factor (VEGF), which act through receptors Flt-1 and Tie-2.

MATERIALS AND METHODS

In order to further determine abnormalities in levels of Ang-1, Ang-2, Tie-2, sFlt-1 and VEGF in human cancer (and their interrelationships), these molecules were measured in plasma from 30 patients with breast cancer, 30 patients with prostate cancer and 12 healthy controls per cancer group.

RESULTS

In breast cancer, levels of Ang-1 (P=0.0005), Ang-2 (P=0.0173), Tie-2 (P=0.0001), and VEGF (P=0.0001) were all significantly raised, and plasma levels of sFlt-1 (P=0.045) were significantly reduced compared with controls. However, in prostate cancer, only levels of VEGF and Tie-2 were significantly higher (both P=0.001). There were no significant differences between levels of any molecule between the two groups of cancer. The only difference between the healthy control groups was lower Ang-1 in the women compared with men. Significant correlations were found between levels of Ang-1 and Tie-2 both in breast (r=0.498, P=0.005) and prostate cancer (r=0.643, P=<0.001). Angiopoietin-1 was also positively correlated with Ang-2 in both breast (r=0.422, P=0.02) and prostate cancer (r=0.543, P=0.002).

CONCLUSIONS

Abnormal levels of Ang-1, Ang-2 and their receptor, Tie-2, are present in breast and prostate cancer, and their interrelationships may be important in the pathophysiology of these conditions.

Erythropoietin as an angiogenic factor

Erythropoietin (Epo) is produced by the fetal liver and adult kidney and is an essential stimulator of erythropoiesis. It has, however, been shown to modulate host cellular signal transduction pathway to perform many other functions. New sites of Epo production have been found, such as the female reproductive organs and central nervous system. This review summarizes the involvement of Epo in the regulation of angiogenesis in both normal and pathological conditions.

Erythropoietin is a potent physiologic stimulus for endothelial progenitor cell mobilization

Increasing evidence suggests that postnatal neovascularization involves the recruitment of circulating endothelial progenitor cells (EPCs). Hematopoietic and endothelial cell lineages share common progenitors. Cytokines formerly thought to be specific for the hematopoietic system have only recently been shown to affect several functions in endothelial cells. Accordingly, we investigated the stimulatory potential of erythropoietin (Epo) on EPC mobilization and neovascularization. The bone marrow of Epo-treated mice showed a significant increase in number and proliferation of stem and progenitor cells as well as in colony-forming units. The number of isolated EPCs and CD34+/flk-1+ precursor cells was significantly increased in spleen and peripheral blood of Epo-treated mice compared with phosphate-buffered saline-treated mice. In in vivo models of postnatal neovascularization, Epo significantly increased inflammation- and ischemia-induced neovascularization. The physiologic relevance of these findings was investigated in patients with coronary heart disease. In a multivariate regression model, serum levels of Epo and vascular endothelial growth factor were significantly associated with the number of stem and progenitor cells in the bone marrow as well as with the number and function of circulating EPCs. In conclusion, the present study suggests that Epo stimulates postnatal neovascularization at least in part by enhancing EPC mobilization from the bone marrow. Epo appears to physiologically regulate EPC mobilization in patients with ischemic heart disease. Thus, Epo serum levels may help in identifying patients with impaired EPC recruitment capacity.

Increased endothelin: nitric oxide ratio is associated with erythropoietin-induced hypertension in hemodialysis patients

Regular administration of recombinant human erythropoietin (rHuEPO) is frequently associated with a rise in arterial blood pressure in hemodialysis (HD) patients. The aim of this study was to examine the effects of rHuEPO on plasma endothelin (ET)-1 and nitric oxide products (NOx) concentration in HD patients. Fifteen patients on maintenance HD with hematocrit of less than 25% were included in the present study. All patients received 3,000 units of rHuEPO intravenously three times a week at the end of each HD session. Plasma levels of ET-1, NOx, thromboxane B2 (TXB2), prostacyclin (6-keto-PGF1alpha), and cyclic guanosine 3',5'-monophosphate (cGMP) were measured before, 2, and 4 weeks after rHuEPO treatment. Plasma concentrations of ET-1, TXB2, and 6-keto-PGF1alpha were measured by radioimmunoassay. Plasma NOx was measured by high-performance liquid chromatography. An rHuEPO-induced increase in mean arterial blood pressure of over 6 mmHg occurred in 7 patients (hypertensive group), whereas the elevation of mean arterial blood pressure was less than 5 mmHg in 8 patients (nonhypertensive group). Plasma ET-1 levels were elevated in all HD patients. Elevated plasma ET-1 levels remained unchanged after rHuEPO treatment in the hypertensive group, whereas the increase in plasma ET-1 levels was attenuated in the nonhypertensive group. Plasma NOx concentrations were also increased in all HD patients. This increase in plasma NOx levels was lessened in the hypertensive group after rHuEPO administration; however, plasma NOx levels remained increased in the nonhypertensive group. Changes in mean arterial blood pressure were significantly correlated with changes in plasma ET-1/NOx ratio. Plasma levels of TXB2, 6-keto-PGF1alpha, and cGMP were unchanged after rHuEPO administration in the hypertensive and nonhypertensive groups. These results suggest that an increase in ET-1/NOx ratio in blood, probably occurring in vascular endothelial cells, may be associated with rHuEPO-induced hypertension in HD patients.

Endothelin-1 in chronic renal failure and hypertension

Investigation into the role of endothelin-1 (ET-1) in renal function has revealed two major direct actions leading to the control of extracellular volume and blood pressure. These are the regulation of renal hemodynamics and glomerular filtration rate and the modulation of sodium and water excretion. In the rat remnant kidney model of chronic renal failure, ET-1 production is increased in blood vessels and renal tissues. These changes are related to an increase in preproET-1 expression and correlate with the rise in blood pressure, the development of cardiovascular hypertrophy, and the degree of renal insufficiency and injury. Selective ETA receptor blockade prevents the progression of hypertension and the vascular and renal damage, supporting a role for ET-1 in chronic renal failure progression. The increase in ET-1 production can be associated with other local mediators, including angiotensin II, transforming growth factor-beta1 and nitric oxide, the local production of which is also altered in chronic renal failure. In human patients with essential hypertension, atherosclerosis, and nephrosclerosis, plasma ET-1 levels are increased compared with patients with uncomplicated essential hypertension. Similarly, plasma ET-1 concentrations are markedly increased in patients with end-stage renal disease undergoing dialysis, and this correlates with blood pressure, suggesting that ET-1 may contribute to hypertension in these patients. The treatment of anemia in patients with renal failure with human recombinant erythropoietin increases blood pressure by accentuating the underlying endothelial dysfunction and the elevated vascular ET-1 production. Overall, these results support a role for ET-1 in hypertension and the end-organ damage associated with chronic renal failure. ETA receptor blockade may then represent a potential target for the management of hypertension and cardiovascular and renal protection.

EPO's alter ego: erythropoietin has multiple actions

Many cancer patients suffer from anemia, which has a major detrimental effect on their quality of life. Recombinant human erythropoietin (rHuEPO) is now widely used in cancer patients, as it improves hematocrit, lowers blood transfusion requirements, and improves quality of life. Recent research indicates that EPO has pleiotropic effects on the body well beyond the maintenance of red cell mass, but the mechanisms involved in relieving fatigue and improving quality of life in cancer patients are poorly understood. EPO receptors (EPO-Rs) have been detected in many different cells and tissues, providing evidence for autocrine, paracrine, and endocrine functions of EPO. Apart from its endocrine function, EPO may have a generalized role as an antiapoptotic agent that is associated with enhancement of muscle tone, mucosal status, and gonadal and cognitive function. The recent discovery of EPO-Rs in breast tumor vasculature, while raising important questions about the possible effects of pharmacological doses of rHuEPO on tumor cells, also suggests that the receptors could provide a useful target for drugs attached to EPO.

Potential neuroprotective benefits of erythropoietin during experimental hypothermic circulatory arrest

OBJECTIVE

Recent studies have shown that erythropoietin protects neurons from glutamate toxicity and ischemia. This study was performed to evaluate the potential neuroprotective effect of erythropoietin during experimental hypothermic circulatory arrest.

METHODS

Twenty pigs were randomized to receive intravenously either 500 IU/kg recombinant human erythropoietin or saline before a 75-minute period of hypothermic circulatory arrest at an intracerebral temperature of 18 degrees C.

RESULTS

After the administration of erythropoietin, its concentration in the cerebrospinal fluid increased 4.5-fold 8 hours after the start of rewarming, whereas it did not increase in control animals. The 7-day survival rate was 60% in the erythropoietin group and 70% in the control group (P = 1.0). No significant differences were observed between the study groups in terms of electroencephalography, behavioral score, and histopathologic score. The erythropoietin group had higher vascular resistance and mean arterial pressure values, lower intracerebral concentrations of glutamate and glycerol, higher brain tissue oxygen tension, and lower apoptotic index.

CONCLUSIONS

Administration of 500 IU/kg erythropoietin intravenously before hypothermic circulatory arrest was followed by an increased erythropoietin concentration in the cerebrospinal fluid. Although previous studies have demonstrated neuroprotective effects of erythropoietin during brain ischemia, the present study, using a chronic porcine model, failed to show any significant benefit after administration of erythropoietin in terms of mortality or brain histopathology. Lower intracerebral concentrations of glutamate and glycerol, higher brain tissue oxygen tension, and lower apoptotic index observed in the erythropoietin group, however, suggest that a distinct neuroprotective effect of erythropoietin might be achieved at different dosages and timing of administration.

Endothelin receptors in the aetiology and pathophysiology of varicose veins

INTRODUCTION

varicose veins are tortuous and poorly contractile. Their aetiology remains unclear. Neovascularisation has been suggested as a possible explanation. Endothelins are mitogenic, promoting proliferation and migration of endothelial cells via endothelin-B receptors. We hypothesise that endothelial cells and endothelin receptor density and distribution may play a role in the development of varicosis.

METHODS

saphenous vein segments from nine patients with varicose veins were compared to six controls. Slide-mounted sections were incubated in radioactive labelled endothelin-1 and receptor subtype-selective ligands and binding sites assessed using autoradiography. Endothelin-1 and endothelial cells were identified by immunohistochemistry and CD31-positive staining cells counted.

RESULTS

radioactive labelled endothelin-1 and endothelin-B receptor binding was reduced in varicose compared to control veins (p=0.04). Endothelin-A receptor binding was diffuse, with no difference in density in both groups (p=0.58). Endothelin-B receptor binding was diffuse with superimposed clusters. Although the density of medial endothelin-B receptor binding was reduced in the varicose group, more clusters were identified in this group compared to controls (p=0.005). CD-31 staining identified these clusters as endothelial cells.

CONCLUSION

the reduced endothelin-1 binding and endothelin-B receptor density may be partially responsible for the reduced vasocontractility in varicose veins. We speculate that the increase in endothelin-B receptor binding CD31-positive endothelial cells in varicose veins may potentially stimulate mitogenesis and migration, leading to new vessel formation.

Effects of recombinant erythropoietin therapy on circulating endothelial markers in hemodialysis patients

Effects of a 4-week course of recombinant human erythropoietin (rHuEpo) therapy on four circulating endothelium-derived cardiovascular risk markers were studied in 20 patients receiving maintenance hemodialysis in relation to surrogates of chronic inflammation, liver function, and arterial blood pressure. Soluble intercellular adhesion molecule-1 (sICAM-1), antigens of plasminogen activator inhibitor-1 (PAI-1:Ag) and von Willebrand factor (vWF:Ag), and soluble thrombomodulin (sTM) were determined by immunoenzymatic assays. C-reactive protein; alpha1 acid-glycoprotein; alpha1-antitrypsin; immunoglobulin M, A, and G; interleukin-6; lipoprotein(a); fibrinogen; total protein; albumin; total cholesterol; hepatitis B and C markers; liver enzymes; prothrombin time; and phosphorus were measured by routine methods. The rHuEpo treatment resulted in a 25% increase in sICAM-1 (Wilcoxon's p = 0.001), a 50% increase in PAI-1:Ag (p = 0.004), a 15% increase in sTM (p = 0.002), and did not change vWF:Ag levels. The increase in sICAM-1 concentration directly correlated with that of PAI-1:Ag (Spearman's rho = 0.483, p = 0.031). The rHuEpo-induced increases in hemoglobin, platelets, and pre-dialysis diastolic blood pressure levels did not correlate with the increments in the endothelial markers studied. In conclusion, short-term rHuEpo therapy activates vascular endothelium in patients receiving maintenance hemodialysis. This specific effect may influence cardiovascular risk.

Determinants of mean arterial pressure and pulse pressure in chronic haemodialysis patients

Hypertension is highly prevalent in the dialysis population, and has been implicated in the pathogenesis of the observed excess of cardiovascular morbidity and mortality in these patients. Nevertheless, there are no reports on the clinical and biochemical determinants of both pulse pressure (PP) and mean arterial pressure (MAP) in dialysis populations. A total of 541 haemodialysed patients from 11 dialysis centres were included in the study. The demographic, clinical, and biological characteristics were recorded. Both pre- and post- dialytic blood pressures (systolic and diastolic) were measured. PP and MAP were calculated. Mean predialytic PP was 67 +/- 17 mm Hg and significantly decreased after dialysis (60 +/- 18 mm Hg; P < 0.0001). In multivariate analysis, a 10 mm Hg increase in PP was positively associated with age (RR, 2.01; 95% CI, 1.35-5.01, for a 10-year increase in age), diabetes mellitus (RR, 1.08; 95% CI, 1.04-1.14), interdialytic weight gain (IWG) (RR, 1.84; 95% CI, 1.07-3.18, for 1% increase in IWG), and current smoking (RR, 2.59; 95% CI, 1.13-5.92) and negatively with Hb concentration (RR, 0.92; 95% CI, 0.84-0.99, for a 1 g/100 ml in Hb). Mean predialytic MAP was 98 +/- 15 mm Hg and significantly decreased after dialysis (91 +/- 16 mm Hg; P < 0.0001). In multivariate analysis, a 10 mm Hg increase in MAP was positively associated with parathyroid hormone (PTH) (RR, 1.32; 95% CI, 1.15-1.6, for 50 ng/ml in PTH), erythropoietin (EPO) treatment (RR, 1.09; 95% CI, 1.03-1.16), and current smoking (RR, 1.87; 95% CI, 1.39-2.41). PP and MAP are associated with different clinical parameters. Most of these factors are potentially reversible. Smoking cessation, correction of anaemia and limitation of IWG should be important challenges for physicians in care of dialysis patients.

Cardiovascular effects of erythropoietin and anemia correction

Although recombinant erythropoietin has no short-acting pressor effect in vivo, its long-term administration frequently raises arterial pressure in humans and animals, with renal insufficiency. Contrary to the original view, erythropoietin-induced hypertension is not due to amelioration of anemia, because a similar rise in blood pressure occurs, despite persistent anemia, in erythropoietin-treated iron-deficient animals and humans. Moreover, multiple small blood transfusions administered to simulate the action of erythropoietin fail to increase blood pressure. Finally, iron repletion in severely anemic iron-deficient patients maintained on constant erythropoietin dosages does not raise blood pressure, despite a dramatic increase in hematocrit. Thus, chronic erythropoietin administration results in a hematocrit-independent, vasoconstriction-dependent hypertension that is marked by, and largely due to, elevated resting and agonist-stimulated cytoplasmic calcium concentration, leading to resistance to the vasodilatory action of nitric oxide. In addition, increased endothelin production, upregulation of tissue (but not circulating) renin and angiotensinogen expression, and a possible change in vascular tissue prostaglandin production have been variably demonstrated with erythropoietin administration in humans, intact animals and cultured endothelial cells. Erythropoietin has been shown to promote angiogenesis and stimulate endothelial and vascular smooth muscle cell proliferation. Finally, partial correction of anemia with erythropoietin therapy may partly prevent or reverse left ventricular hypertrophy in dialysis-dependent and dialysis-independent patients with chronic renal insufficiency. However, data on the risks and benefits of complete correction of anemia in this population are limited and inconclusive, and await future investigation.

Effect of 1-week treatment with erythropoietin on the vascular endothelial function in anaesthetized rabbits

Chronic administration of erythropoietin (EPO) is often associated with hypertension in animals and humans. The aim of this study was to estimate whether 1-week treatment with EPO can affect the vascular endothelial function. Rabbits were given with EPO (400 iu kg(-1) s.c.) or saline each other day for 1 week. Hypotensive responses to intravenously given acetylcholine (ACh), endothelium-independent nitric oxide donors (NOC7, nitroprusside and nitroglycerin) and prostaglandin I2 were tested before and after administration of N(G)-nitro-L-arginine methyl ester (L-NAME), a specific nitric oxide synthase inhibitor, under pentobarbitone anaesthesia. Blood haemoglobin concentration in EPO group was significantly higher than that in control group, whereas baseline values of aortic pressure, heart rate and femoral vascular resistance were similar. The dose of ACh (172 ng kg(-1)) requiring for a 15 mmHg hypotension from the baseline in EPO group was apparently higher than that (55 ng kg(-1)) in control group. On the contrary, hypotensive responses to NOC7, nitroprusside, nitroglycerin and prostaglandin I2 were comparable between two groups. The extent of ACh-induced hypotension did not correlate with haemoglobin concentration. L-NAME significantly inhibited the ACh-induced vasodilating response in control group but did not in EPO group. In another set of rabbits, the same treatment with EPO also decreased vasodilating responses to carbachol, bradykinin and substance P besides ACh as compared with control group. These results indicate that 1-week treatment with EPO selectively attenuates depressor responses to endothelium-dependent vasodilators in anaesthetized rabbits, most likely due to inhibition of endothelial nitric oxide synthase.

Erythropoietin in monochorionic twin pregnancies in relation to twin--twin transfusion syndrome

Fetal erythropoietin (Epo) concentrations were studied in monochorionic (MC) twin pregnancies in relation to twin-twin transfusion syndrome (TTTS). Matched maternal and fetal blood samples in utero were obtained from MC twins with TTTS (n = 15) and without TTTS (n = 6). In a second group of five sets of twin pairs with or without TTTS, immunolocalization of Epo was performed in archived paraffin wax sections of liver and kidney collected at autopsy. Epo was measured using a chemiluminescence assay and expressed as gestation independent Z-scores and given as mean +/- 95% confidence intervals (CI). Fetal Epo concentrations in utero were higher in MC twins with TTTS than the non-TTTS as a group (P < 0.001). There was no difference in Epo concentrations between TTTS and non-TTTS twin pairs. Fetal Epo concentrations were correlated with pO(2) in the recipient (r = 0.64; P < 0.01), donor (r = 0.64; P < 0.01) and control twins (r = 0.76; P < 0.01). Immunostaining of the fetal kidney localized Epo primarily to the cytoplasm of the proximal convoluted tubules. The intensity of staining in the kidney and liver was comparable between TTTS and non-TTTS twin pairs. Fetal Epo concentrations were higher in the TTTS than non-TTTS twin pairs and were correlated with the degree of hypoxaemia. However, Epo concentrations were comparable between donor and recipient twins, perhaps due to similar production rather than inter-twin transfusion of blood.

Endothelin-1 induces an angiogenic phenotype in cultured endothelial cells and stimulates neovascularization in vivo

The endothelial cell-derived endothelin-1 (ET-1) is a potent mitogen for endothelial cells, vascular smooth muscle cells, and tumor cells. In this study, we analyzed the role of ET-1 on human umbilical vein endothelial cell (HUVEC) phenotype related to different stages of angiogenesis. ET-1 promoted HUVEC proliferation, migration, and invasion in a dose-dependent manner. The ET(B) receptor (ET(B)R) antagonist, BQ 788, blocked the angiogenic effects induced by ET-1, whereas the ET(A)R antagonist was less effective. ET-1 stimulated matrix metalloproteinase-2 mRNA expression and metalloproteinase-2 production, as determined by reverse transcriptase-polymerase chain reaction and gelatin zymography. Furthermore ET-1 was able to enhance HUVEC differentiation into cord vascular-like structures on Matrigel. When tested in combination with vascular endothelial growth factor (VEGF), ET-1 enhanced VEGF-induced angiogenic-related effects on endothelial cells in vitro. Finally, using the Matrigel plug neovascularization assay in vivo, ET-1 in combination with VEGF stimulated an angiogenic response comparable to that elicited by basic fibroblast growth factor. These findings demonstrated that ET-1 induces angiogenic responses in cultured endothelial cells through ET(B)R and that stimulates neovascularization in vivo in concert with VEGF. ET-1 and its receptors acting as angiogenic regulators might represent new targets for anti-angiogenic therapy.

Chronic nitric oxide inhibition aggravates hypertension in erythropoietin-treated renal failure rats

Alterations in nitric oxide (NO) and endothelin-1 (ET-1) production have recently been reported in erythropoietin (r-HuEPO)-induced hypertension in renal failure rats. The present study was designed to evaluate the effect of NO synthase inhibition with the L-arginine analog NG-nitro-L-arginine methyl ester (L-NAME) on blood pressure (BP) and ET-1 production in control and in uremic rats treated or not treated with r-HuEPO. Renal failure was induced by a two-stage 5/6 nephrectomy. Control and uremic rats were studied separately and subdivided into four groups: vehicle, r-HuEPO, L-NAME + vehicle and L-NAME + r-HuEPO. L-NAME (100 mg/kg/day), r-HuEPO (100 U/kg, subcutaneously, three times per week), the vehicle or both were administered during 4 weeks in control rats and during 2 weeks in uremic rats. Systolic BP was recorded before and after the onset of treatment at weeks 2 and 4 in control rats and at weeks 1 and 2 in uremic rats. Hematocrit, serum creatinine, plasma, blood vessel (thoracic aorta and mesenteric artery bed) and renal cortex immunoreactive (ir) ET-1 concentrations were measured at the end of the protocol. L-NAME enhanced BP in control and uremic rats and the increase was significantly higher in uremic rats under r-HuEPO therapy (222 +/- 7 mmHg vs 198 +/- 6 mmHg, p<0.05). L-NAME induced an increase in thoracic aorta ir-ET-1 concentrations in control and uremic rats. In contrast, ir-ET-1 concentrations were unchanged in the mesenteric arterial bed and the renal cortex of control and uremic animals. R-HuEPO increased thoracic aorta ir-ET-1 contents in L-NAME treated control and uremic rats. These results underline the important role of NO release in opposing the action of vasopressors on blood vessel tone which appears more important in uremic rats treated with r-HuEPO. L-NAME treatment increased large vessel, but not small resistance artery ir-ET-1 concentrations, suggesting differential regulation of ET-1 production in different vascular beds under chronic NO synthase inhibition.

Nonerythropoietic roles of erythropoietin in the fetus and neonate

Epo was once regarded as a cytokine with only hematopoietic effects. It is now clear that the distributions of Epo and Epo-R are more widespread in the developing human. Epo-R is widely distributed during early fetal development, leading to speculation that Epo acts in concert with other growth factors to optimize growth and development. Areas in which Epo has important recognized effects are on endothelial cells, and in the developing heart, gastrointestinal tract, and brain. It may also be important in the regulation of vascular growth during the menstrual cycle, and in the stimulation of testosterone production in men. Epo and Epo-R are prominent in the brain during fetal development, leading to speculation that they play an important role in neurodevelopment. There are also promising data regarding rEpo as a possible neuroprotective agent in such conditions as hypoxia, because it decreases programmed cell death induced during such adverse conditions. It is unlikely, however, that rEpo crosses the blood-brain barrier in normal premature infants, and it is not clear whether the CNS effects of rEpo, should it cross the blood-brain barrier, are harmful or beneficial in the setting of a developing brain.

Capillary/myocyte mismatch in the heart in renal failure--a role for erythropoietin?

BACKGROUND

Chronic renal failure is characterized by remodeling of the heart with left ventricular hypertrophy (increasing oxygen demand) and capillary deficit leading to capillary/myocyte mismatch (decreasing oxygen supply). Erythropoietin (Epo) has known angiogenic properties causing endothelial cell activation, migration and sprouting, mediated at least in part via the JAK/STAT (Janus kinase/signal transducers and activators of transcription) pathway. In uraemic cardiac hypertrophy the presence of diminished capillary supply implies that capillary growth does not keep pace with development of hypertrophy. To investigate whether this was due to a deficit of the angiogenic hormone Epo we examined whether Epo levels are altered and whether an increase in haematocrit by administration of rhEpo influences capillary supply, i.e. capillary/myocyte mismatch in experimental renal failure.

METHOD

Male Spraque-Dawley rats were either subjected to partial renal ablation or sham operation. Only modest amounts of renal tissue were removed so that the rats were not anemic. Subgroups of rats received either human (rh)Epo alone or in combination with unspecific antihypertensive treatment (dihydralazine plus furosemide) in order to control the Epo induced rise in blood pressure. Capillary supply was measured stereologically as capillary length per volume myocardium using the orientator method.

RESULTS

Capillary length density was reduced by approximately 25% after partial renal ablation (3237+/-601 vs 4293+/-501 mm/mm(3) in controls). It was not statistically different in animals with partial renal ablation+rhEpo+antihypertensive treatment (3620+/-828 mm/mm(3)) compared to partial ablation alone.

CONCLUSION

The study shows that lack of Epo does not cause, or contribute to, the deficit of capillary growth in the hypertrophied left ventricle of rats with renal failure. In addition, a rise in haematocrit is not accompanied by beneficial effects on alterations of cardiovascular structure in experimental renal failure.

Exposure of endothelial cells to recombinant human erythropoietin induces nitric oxide synthase activity

BACKGROUND

Anemic patients with chronic renal failure receiving recombinant human erythropoietin (rHuEPO) therapy frequently develop hypertension through an unknown mechanism. We hypothesize that EPO receptors (EPORs) on endothelial cells (ECs) in various sites of vasculature may mediate the activities of nitric oxide synthase (NOS) and/or the release of endothelin-1 (ET-1), contributing to blood pressure changes. We tested this hypothesis using primary cultures of ECs obtained from human coronary artery (HCAEC), pulmonary artery (HPAEC), dermis (HDEC), and umbilical vein (HUVEC).

METHODS

EPORs were measured by 125I-EPO binding. The effect of EPO on EPOR, ET-1, and NOS mRNA levels was assessed by quantitative reverse transcription-polymerase chain reaction. Cellular NOS activity and ET-1 release into the medium was measured by the NOSdetect assay and by radioimmunoassay kits.

RESULTS

Short-term (4 h) treatment with EPO (4 U/mL) did not change the number or affinity of EPOR per cell. Neither were there any changes in the amount of EPOR, ET-1, and NOS transcripts (cDNA/microg of mRNA) nor in ET-1 release and NOS activity. In HUVEC only, 24-hour exposure to EPO caused a threefold increase in NOS transcript. In other cells, EPO treatment for six days increased NOS activity by twofold to fourfold.

CONCLUSIONS

We show that upon extended exposure, EPO induces NOS activity but does not affect ET-1 release. These findings indicate that the hypertensive effect of EPO is not likely to be caused by a direct effect on ECs.

Stimulation of tumour necrosis factor-alpha production by recombinant human erythropoietin may contribute to failure of therapy

Although the mechanism of unresponsiveness to recombinant human erythropoietin therapy in dialysis patients has been studied extensively in recent years, many aspects remain unclear. We previously found that administration of erythropoietin induces interleukin-1beta, a cytokine that inhibits erythropoiesis. The present study investigated the involvement of tumour necrosis factor-alpha, another cytokine which inhibits erythropoiesis. Peripheral blood mononuclear cells were obtained from 18 patients on continuous ambulatory peritoneal dialysis, who were being treated with erythropoietin for renal anaemia, and were cultured with various concentrations of erythropoietin (0, 1, 5, 10, and 50 U/ml). Then the tumour necrosis factor-alpha level in the culture supernatant was assayed. The 18 patients were divided into four groups on the basis of the haematocrit after treatment: group A (n = 3), <23.0%; group B (n = 5), 23.0-24.9%; group C (n = 7), 25.0-26.9%; and group D (n = 3), > or =27.0%. In group A, the tumour necrosis factor-alpha level in the culture supernatant was increased by incubation with erythropoietin, while it was not increased in other groups. The tumour necrosis factor-alpha level was significantly higher in group A than in the other groups at erythropoietin concentrations of 5 U/ml. These results suggested that induction of tumour necrosis factor-alpha is one of the reasons for unresponsiveness to recombinant human erythropoietin.

Differential effects of endothelin-1 antagonists on erythropoietin-induced hypertension in renal failure

Recently, it was reported that blood vessel immunoreactive endothelin-1 (irET-1) content is increased in hypertensive uremic rats treated with recombinant human erythropoietin (rhEPO). The present study was designed to evaluate whether ET-1 receptor blockade can prevent the progression of hypertension in renal failure rats receiving rhEPO and, if so, whether selective ET(A) and nonselective ET(A)/ET(B) receptor antagonists are equally effective. Renal failure was induced by a two-stage 5/6 nephrectomy; the animals developed uremia, anemia, and hypertension. After a 4-wk stabilization period, the animals received either rhEPO (100 U/kg, subcutaneously, three times per week) or the vehicle for 4 wk. In protocol A, half of the rats in each group were simultaneously treated with the ET(A)/ET(B) receptor antagonist bosentan (100 mg/kg per d). In protocol B, half of the rats in each group received the selective ET(A) receptor antagonist LU 135252 (50 mg/kg per d). Systolic BP was recorded before and at 2 and 4 wk after the onset of treatment. Serum creatinine levels and hematocrit were measured before treatment and at the end of the study. Creatinine clearance rates and plasma irET-1 concentrations were determined at the end of the study. rhEPO corrected the anemia, but aggravated the hypertension. There was a slight and similar increase in serum creatinine throughout the treatment period in all groups of rats. Both ET-1 receptor antagonists bosentan and LU135252 were effective in attenuating the progression of hypertension in uremic rats receiving the vehicle (P < 0.05). Treatment with LU135252 corrected the increase in BP in rhEPO-treated rats (160+/-7 mmHg versus 187+/-9 mmHg, P < 0.05). In contrast, bosentan did not attenuate the progression of hypertension in rhEPO-treated rats (172+/-10 mmHg versus 168+/-9 mmHg, NS). In summary, selective ET(A) but not ET(A)/ET(B) receptor blockade can prevent the aggravation of hypertension in renal failure rats treated with rhEPO. These results suggest that the endothelin system may be involved in the pathogenesis of rhEPO-induced hypertension in uremic rats with a differential role for ET(A) and ET(B) receptors.

Effects of normal hematocrit on ambulatory blood pressure in epoetin-treated hemodialysis patients with cardiac disease

BACKGROUND

Hypertension is a recognized complication of partial correction of anemia with recombinant human erythropoietin (epoetin) in hemodialysis patients. We used interdialytic ambulatory blood pressure (ABP) monitoring to study the effects of partially corrected anemia versus normal hematocrit (hct) on BP in hemodialysis patients.

METHODS

Repeated interdialytic ABP monitoring was performed for up to one year in 28 chronic hemodialysis patients with cardiac disease who were randomized to achieve and maintain normal hct levels (42 +/- 3%, group A) or anemic hct levels (30 +/- 3%, group B) with epoetin. Routine BP measurements obtained at dialysis treatments were also evaluated.

RESULTS

Mean hct levels were 30.7 +/- 0.7% in group A and 30.6 +/- 0.7% in group B at baseline, then 39.3 +/- 1.2% (group A) and 33.5 +/- 0.6% (group B) at four months, and 42.0 +/- 1.1% (group A) and 30.4 +/- 1.0% (group B) at 12 months. Baseline ABP and routine dialysis unit BP levels were not different between the groups. At 2, 4, 8, and 12 months of follow-up, there were no statistically significant differences in any BP parameters between groups or increases in any BP parameters in either group A or group B patients compared with baseline. At 12 months, the mean nighttime diastolic BP (DBP) in group A patients was slightly but significantly lower than the mean daytime DBP (daytime DBP 76.6 +/- 1.9 mm Hg vs. nighttime DBP 72.9 +/- 2.1 mm Hg, P < 0.05). The mean daytime and nighttime BPs were not different from each other at two, four, and eight months in group A or at any time in group B, and in both groups, most patients had little diurnal change in BP.

CONCLUSION

Correction of hct to normal with epoetin in chronic hemodialysis patients with cardiac disease did not cause increased BP as assessed by interdialytic ABP monitoring or by the measurement of routine predialysis and postdialysis BP. There was little diurnal change in systolic or diastolic BP at baseline or after correction of anemia to normal levels, and although mean nighttime DBP was lower than mean daytime DBP at 12 months in group A, the maintenance of normal hct levels did not affect the abnormal diurnal BP pattern seen at moderately anemic hct levels in most patients.