Beneficial effects of systemic administration of recombinant human erythropoietin in rabbits subjected to subarachnoid hemorrhage

The effects of systemically administered methylprednisolone and recombinant human erythropoietin after acute spinal cord compressive injury in rats

The study design was to decrease the damage of spinal cord on the experimentally induced acute spinal cord injury in rats. The objective of this study was to evaluate whether recombinant human erythropoietin (rHu-EPO) and methylprednisolone (MPSS) improve neurological function and histopathological changes if systemically administered after traumatic spinal cord injury. This study included 48 rats that underwent experimental SCI. Forty-eight animals were randomly divided into six groups. Animals constituted a moderate compression of 0.6 N that was produced by application of an aneurysm clip at level T3 for 1 min. rHu-EPO (1,000 and 3,000 U (Unit) per kg of body weight i.p.) and MPSS (30 mg/kg) were administered 5 min after injury, and control group was saline treated. (1) Control group (n=8), (2) MPSS group (n=8), (3) rHu-EPO 1,000 U group (n=8), (4) MPSS + rHu-EPO 1,000 U group (n=8), (5) rHu-EPO 3,000 U group (n=8), and (6) MPSS + rHu-EPO 3,000 U group (n=8). The neurological function and histopathology were evaluated at 24 and 72 h. According to the neurological functional test scores significant improvements between the control group and the other groups that had taken medical treatment were observed (P<0.001). Histopathologically severe ischemic findings were observed in the control group. A significant decrease in ischemic damage was detected in MPSS + rHu-EPO 3,000 U group (P<0.001). The most significant neurological functional and histopathological improvements were observed after systemical administration of MPSS + rHu-EPO 3,000 U and rHu-EPO 3,000 U. Furthermore, the MPSS + rHu-EPO 3,000 U group provides the most improved neurological functional and histopathological recovery.

Intrinsic and extrinsic erythropoietin enhances neuroprotection against ischemia and reperfusion injury in vitro

This study was designed to investigate the neuroprotective effect of intrinsic and extrinsic erythropoietin (EPO) against hypoxia/ischemia, and determine the optimal time-window with respect to the EPO-induced neuroprotection. Experiments were conducted using primary mixed neuronal/astrocytic cultures and neuron-rich cultures. Hypoxia (2%) induces hypoxia-inducible factor-1alpha (HIF-1alpha) activity followed by strong EPO expression in mixed cultures and weak expression in neuron-rich cultures as documented by both western blot and RT-PCR. Immunoreactive EPO was strongly detected in astrocytes, whereas EPOR was only detected in neurons. Neurons were significantly damaged in neuron-rich cultures but were distinctly rescued in mixed cultures. Application of recombinant human EPO (rhEPO) (0.1 U/mL) within 6 h before or after hypoxia significantly increased neuronal survival compared with no rhEPO treatment. Application of rhEPO after onset of reoxygenation achieved the maximal neuronal protection against ischemia/reperfusion injury (6 h hypoxia followed 24 h reoxygenation). Our results indicate that HIF-1alpha induces EPO gene released by astrocytes and acts as an essential mediator of neuroprotection, prove the protective role of intrinsic astrocytic-neuronal signaling pathway in hypoxic/ischemic injury and demonstrate an optimal therapeutic time-window of extrinsic rhEPO in ischemia/reperfusion injury in vitro. The results point to the potential beneficial effects of HIF-1alpha and EPO for the possible treatment of stroke.

Cerebral Vasospasm After Aneurysmal Subarachnoid Hemorrhage: An Overview of Pharmacologic Management

Cerebral vasospasm remains one of the leading causes of mortality in patients who experience a subarachnoid hemorrhage but survive the initial 24 hours. Vasospasm generally occurs 3-4 days after the initial subarachnoid hemorrhage and peaks at 5-7 days. The pathophysiology of vasospasm is poorly understood, which directly contributes to the inconsistency of management and creates a formidable challenge in clinical practice. Traditionally, hemodilution, hypervolemia, and induced hypertension (so-called triple H therapy); calcium channel blockers; and endovascular therapy have been used as either prophylactic therapy or treatment. However, management of vasospasm varies among physicians and institutions mainly because of a lack of large clinical trials and inconsistent results. Practice has been based primarily on case reports and the preference of each practitioner. Several experimental therapies have been explored; however, large, prospective, randomized controlled trials are needed to elucidate the role of these therapies.

Controversies in the management of aneurysmal subarachnoid hemorrhage*

BACKGROUND

The care of patients with aneurysmal subarachnoid hemorrhage has evolved significantly with the advent of new diagnostic and therapeutic modalities. Although it is believed that these advances have contributed to improved outcomes, considerable uncertainty persists regarding key areas of management.

OBJECTIVE

To review selected controversies in the management of aneurysmal subarachnoid hemorrhage, with a special emphasis on endovascular vs. surgical techniques for securing aneurysms, the diagnosis and therapy of cerebral vasospasm, neuroprotection, antithrombotic and anticonvulsant agents, cerebral salt wasting, and myocardial dysfunction, and to suggest venues for further clinical investigation.

DATA SOURCE

Search of MEDLINE and Cochrane databases and manual review of article bibliographies.

DATA SYNTHESIS AND CONCLUSIONS

Many aspects of care in patients with aneurysmal subarachnoid hemorrhage remain highly controversial and warrant further resolution with hypothesis-driven clinical or translational research. It is anticipated that the rigorous evaluation and implementation of such data will provide a basis for improvements in short- and long-term outcomes.

Erythropoietin prevents the increase in blood-brain barrier permeability during pentylentetrazol induced seizures

Recombinant human erythropoietin (r-Hu EPO) has been shown to exert neuroprotection in ischemic, excitotoxicity, trauma, convulsions and neurodegenerative disorders. Blood-brain barrier (BBB) leakage plays a role in the pathogenesis of many pathological states of the brain including neurodegenerative disorders. This study aimed to investigate the effects of r-Hu EPO on BBB integrity in pentylentetrazol (PTZ) induced seizures in rats. Seizures were observed and evaluated regard to latency and intensity for an hour. Macroscopical and spectrophotometrical measurement of Evans Blue (EB) leakage were observed for BBB integrity. r-Hu EPO was given intraperitoneally 24 h prior to seizure induction. Total seizure duration of 720+/-50 s after single PTZ administration (80 mg/kg i.p.) was declined to 190+/-40 s in r-Hu EPO pretreatment. A typical BBB breakdown pattern (i.e. staining in cerebellum, cerebral cortex, midbrain, hippocampus, thalamus and corpus striatum) was observed in rat brains with PTZ induced seizures; whereas, EPO pretreatment confined BBB leakage to cerebellum and cortical areas, and lessened the intensity of tonic-clonic seizures observed in PTZ seizures. The protective effect of r-Hu EPO on BBB permeability in seizures is a new and original finding. The protective action of r-Hu EPO in seizures and some of CNS pathologies warrant further investigations.

Methylprednisolone neutralizes the beneficial effects of erythropoietin in experimental spinal cord injury

Inflammation plays a major pathological role in spinal cord injury (SCI). Although antiinflammatory treatment using the glucocorticoid methyprednisolone sodium succinate (MPSS) improved outcomes in several multicenter clinical trials, additional clinical experience suggests that MPSS is only modestly beneficial in SCI and poses a risk for serious complications. Recent work has shown that erythropoietin (EPO) moderates CNS tissue injury, in part by reducing inflammation, limiting neuronal apoptosis, and restoring vascular autoregulation. We determined whether EPO and MPSS act synergistically in SCI. Using a rat model of contusive SCI, we compared the effects of EPO [500-5,000 units/kg of body weight (kg-bw)] with MPSS (30 mg/kg-bw) for proinflammatory cytokine production, histological damage, and motor function at 1 month after a compression injury. Although high-dose EPO and MPSS suppressed proinflammatory cytokines within the injured spinal cord, only EPO was associated with reduced microglial infiltration, attenuated scar formation, and sustained neurological improvement. Unexpectedly, coadministration of MPSS antagonized the protective effects of EPO, even though the EPO receptor was up-regulated normally after injury. These data illustrate that the suppression of proinflammatory cytokines alone does not necessarily prevent secondary injury and suggest that glucocorticoids should not be coadministered in clinical trials evaluating the use of EPO for treatment of SCI.

Role of endothelial NO synthase phosphorylation in cerebrovascular protective effect of recombinant erythropoietin during subarachnoid hemorrhage-induced cerebral vasospasm

BACKGROUND AND PURPOSE

In the present study, the effect of subarachnoid hemorrhage (SAH) on the phosphorylation of endothelial NO synthase (eNOS) and the ability of recombinant erythropoietin (Epo) to augment this vasodilator mechanism in the spastic arteries were studied.

METHODS

Recombinant adenoviral vectors (10(9) plaque-forming units per animal) encoding genes for human Epo (AdEpo), and beta-galactosidase were injected immediately after injection of autologous arterial blood into the cisterna magna (day 0) of rabbits. Cerebral angiography was performed on day 0 and day 2, and basilar arteries were harvested for Western blots, measurement of cGMP levels, and analysis of vasomotor functions.

RESULTS

Injection of autologous arterial blood into cisterna magna resulted in significant vasospasm of the basilar arteries. Despite the narrowing of arterial diameter and reduced expression of eNOS, expressions of phosphorylated protein kinase B (Akt) and phosphorylated eNOS were significantly increased in spastic arteries. Gene transfer of AdEpo reversed the vasospasm. AdEpo-transduced basilar arteries demonstrated significant augmentation of the endothelium-dependent relaxations to acetylcholine, whereas the relaxations to an NO donor, 2-(N,N-diethylamino)diazenolate-2-oxide sodium salt, were not affected. Transduction with AdEpo further increased the expression of phosphorylated Akt and eNOS and elevated basal levels of cGMP in the spastic arteries.

CONCLUSIONS

Phosphorylation of eNOS appears to be an adaptive mechanism activated during development of vasospasm. The vascular protective effect of Epo against cerebral vasospasm induced by SAH may be mediated in part by phosphorylation of Akt/eNOS.

Heat acclimation increases hypoxia-inducible factor 1alpha and erythropoietin receptor expression: implication for neuroprotection after closed head injury in mice

Experimental evidence indicates that long-term exposure to moderately high ambient temperature (heat acclimation, HA) mediates cross-tolerance to various types of subsequently applied stress. The transcriptional activator hypoxia-inducible factor 1 (HIF-1) has been implicated in playing a critical role in HA. It also regulates the expression of Erythropoietin (Epo), whose neuroprotective effects have been shown in a variety of brain injuries. The aim of the present study was to examine whether HA exerts a beneficial effect on the outcome of closed head injury (CHI) in mice and to explore the possible involvement of HIF-1 and Epo in this process. Heat acclimated mice and matched normothermic controls were subjected to CHI or sham surgery. Postinjury motor and cognitive parameters of acclimated mice were compared with those of controls. Mice were killed at various time points after injury or sham surgery and brain levels of HIF-1alpha, the inducible subunit of HIF-1, Epo, and the specific erythropoietin receptor (EpoR) were analyzed by Western immunoblotting. Motor and cognitive functions of acclimated mice were significantly better than those of controls. Heat acclimation was found to induce a significant increase in expression of nuclear HIF-1alpha and EpoR. The EpoR/Epo ratio was also significantly higher in acclimated mice as compared with controls. Nuclear HIF-1alpha and EpoR were higher in the acclimated group at 4 h after injury as well. The improved outcome of acclimated mice taken together with the basal and postinjury upregulation of the examined proteins suggests the involvement of this pathway in HA-induced neuroprotection.

Administration of Erythropoietin Fails to Improve Long-Term Healing or Cardiac Function After Myocardial Infarction in the Rat

Erythropoietin (epo), initially recognized and used clinically to increase erythropoiesis, has been shown to have beneficial effects on various other tissues in the setting of hypoxia and ischemia. Epo has been shown to reduce apoptosis after myocardial infarction, but few studies have evaluated the long-term effects of epo treatment on left ventricular (LV) remodeling, cardiac function, and blood flow after healing of a permanent coronary artery occlusion. The aim of this study was to assess the effects of epo treatment on the healed heart 6 weeks after myocardial infarction. Anesthetized rats underwent coronary artery occlusion and were treated with erythropoietin (5000 units/kg/day, n=21) or saline (n=20) the day before surgery, the day of, then for 5 days. At 6 weeks LV ventriculography to assess LV volumes and ejection fractions and histologic assessment of infarct size and LV cavity and wall dimensions were performed. Overall epo had no effect on LV remodeling or cardiac function. There were no significant differences in infarct morphology, infarct size (44+/-3% of the LV circumference versus 39+/-3%), LV cavity area, scar thickness, LV systolic volume, or ejection fraction (44+/-3% versus 39+/-3%) between the epo and saline groups, respectively. However, for any given size of myocardial infarct, LV ejection fraction was significantly higher in erythropoietin hearts and LV systolic volumes lower. Thus, in our model, treatment with epo had no long-term beneficial effect on LV remodeling after myocardial infarction but may have exerted some positive effect on LV function.

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.

Erythropoietin and Erythropoietin Receptor Expression after Experimental Spinal Cord Injury Encourages Therapy by Exogenous Erythropoietin

OBJECTIVE

Erythropoietin (EPO) is a pleiotropic cytokine originally identified for its role in erythropoiesis. Recent studies have demonstrated that EPO and its receptor (EPO-R) are expressed in the central nervous system, where EPO exerts neuroprotective functions. Because the expression of the EPO and EPO-R network is poorly investigated in the central nervous system, the aim of the present study was to investigate whether the resident EPO and EPO-R network is activated in the injured nervous system.

METHODS

A well-standardized model of compressive spinal cord injury in rats was used. EPO and EPO-R expression was determined by immunohistochemical analysis at 8 hours and at 2, 8, and 14 days in the spinal cord of injured and noninjured rats.

RESULTS

In noninjured spinal cord, weak immunohistochemical expression of EPO and EPO-R was observed in neuronal and glial cells as well as in endothelial and ependymal cells. In injured rats, a marked increase of expression of EPO and EPO-R was observed in neurons, vascular endothelium, and glial cells at 8 hours after injury, peaking at 8 days, after which it gradually decreased. Two weeks after injury, EPO immunoreactivity was scarcely detected in neurons, whereas glial cells and vascular endothelium expressed strong EPO-R immunoreactivity.

CONCLUSION

These observations suggest that the local EPO and EPO-R system is markedly engaged in the early stages after nervous tissue injury. The reduction in EPO immunoexpression and the increase in EPO-R staining strongly support the possible usefulness of a therapeutic approach based on exogenous EPO administration.

The pharmacokinetics of erythropoietin in the cerebrospinal fluid after intravenous administration of recombinant human erythropoietin

OBJECTIVES

Erythropoietin (EPO) was originally described as a regulator of erythropoiesis. Recently, synthesis of EPO and expression of the EPO receptor (EPO-R) have been reported for the central nervous system (CNS). The potential use of EPO to prevent or reduce CNS injury and the paucity of information regarding its entry into the human CNS led us to examine the pharmacokinetics (PK) of recombinant human EPO (r-HuEPO) in the serum and cerebrospinal fluid (CSF).

METHODS

Four patients with Ommaya reservoirs were enrolled to facilitate serial CSF sampling. R-HuEPO was given intravenously (IV) in single doses of 40,000 IU or 1,500 IU/kg and in multiple doses of 40,000 IU daily for 3 days.

RESULTS

The EPO concentrations in the CSF increased after a period of slow equilibration. Linear first-order distribution kinetics were observed for serum and CSF. The concentration of EPO in the CSF was proportional to the serum concentration of EPO and the permeability of the blood-brain barrier (BBB), as determined by the albumin quotient (QA=[albumin] CSF/[albumin] serum). A rise in the CSF concentration was seen as early as 3 h after IV administration. Peak levels (C(max)) were reached between 9 h and 24 h. After a single dose of 1,500 IU/kg, the Cmax in the CSF ranged from 11 mIU/ml to 40 mIU/ml, and the ratios of CSF/serum Cmax ranged from 3.6x10-4 to 10.2x10-4. The terminal half-life (t1/2) values of EPO in serum and CSF were similar. The t(1/2) of r-HuEPO in the CSF ranged from 25.6 h to 35.5 h after a single dose of 1,500 IU/l. Using these parameters a PK model was generated that predicts the concentration-time profile of EPO in the CSF.

CONCLUSIONS

We report that r-HuEPO can cross the human BBB and describe for the first time the PK of EPO in the CSF after IV administration. Our data suggest that the concentration-time profile of EPO in the CSF can be predicted for individual patients if the serum concentration of EPO and the Q(A) are known. This information may be useful in the design of clinical trials to explore the potential therapeutic effects of EPO during CNS injury.

Erythropoietin on a tightrope: balancing neuronal and vascular protection between intrinsic and extrinsic pathways

Enthusiasm for erythropoietin (EPO) as a broad cytoprotective agent continues to increase at an almost exponential rate. The premise that EPO was required only for erythropoiesis was eventually shed by recent work demonstrating the existence of EPO and its receptor in other organs and tissues outside of the liver and the kidney, such as the brain and heart. As a result, EPO has been identified as a possible candidate in the formulation of therapeutic strategies for both cardiac and nervous system diseases. EPO has been shown to mediate an array of vital cellular functions that involve progenitor stem cell development, cellular protection, angiogenesis, DNA repair, and cellular longevity. An important requirement to achieve the goal of preventing or even reducing cellular injury by any cytoprotective agent is the ability to uncover the cellular pathways that ultimately drive a cell to its demise. We present for consideration several critical cellular pathways modulated by EPO that involve Janus kinase 2 (Jak2), the serine-threonine kinase Akt, forkhead transcription factors, glycogen synthase kinase-3beta (GSK-3beta), cellular calcium, protein kinase C, caspases, as well as the control of inflammatory microglial activation. As we continue to gain new insight into these pathways, EPO should emerge as a critical agent for the development, maturation, and survival of cells throughout the body.

Attenuation of interstitial inflammation and fibrosis by recombinant human erythropoietin in chronic cyclosporine nephropathy

BACKGROUND

Evidence suggests that recombinant human erythropoietin (rHuEPO) protects neurons and cardiomyocytes from acute insults. We investigated the protective effect of rHuEPO on cyclosporine (CsA)-induced renal injury.

METHODS

CsA (15 mg/kg/day) was given to rats for 1 or 4 weeks, and rHuEPO was concurrently administered at a dose of 100 units/kg (thrice weekly). Effects of rHuEPO on CsA-induced renal injury were evaluated with tubulointerstitial fibrosis (TIF) score, macrophage infiltration, expression of proinflammatory and profibrotic cytokines, and apoptotic cell death.

RESULTS

Administration of rHuEPO decreased TIF score and the number of macrophages, which increased significantly in CsA-treated rat kidneys. At the molecular level, rHuEPO treatment decreased proinflammatory mediators (osteopontin and C-reactive protein) and profibrotic mediators (transforming growth factor-beta1 and transforming growth factor-beta1-inducible gene-h3). Increased apoptotic cell death in CsA-treated rat kidneys was significantly decreased with rHuEPO cotreatment, and apoptosis-related genes were regulated in favor of cell survival (increased Bcl-2 and suppressed caspase-3).

CONCLUSION

rHuEPO has a renoprotective effect against chronic CsA-induced renal injury.

Have no fear, erythropoietin is here: erythropoietin protects fear conditioning performances after functional inactivation of the amygdala

This study investigated the capacity of erythropoietin (EPO) to protect fear conditioning performances against functional inactivation of the amygdala. We infused an excitotoxic dose of glutamate in the lateral nucleus of the amygdala (LA) of adult rats in order to block the output projections to brainstem areas controlling the expression of conditioned fear responses. Subsequently, animals with excitotoxic lesions in the LA displayed altered short and long-term fear conditioned responses, but the integrity of their general emotional reactivity was preserved, as indicated by their open-field behavior. EPO infused immediately after glutamate succeeded to protect the conditioned fear performances of rats. This effect was reliably represented on both short, and long-term memory tests of conditioned fear. This and other studies have supported the potent neuroprotective activity of EPO, discriminable both morphologically, and behaviorally.

Neurodevelopmental outcome and growth at 18 to 22 months' corrected age in extremely low birth weight infants treated with early erythropoietin and iron

BACKGROUND

Clinical trials evaluating the use of erythropoietin (Epo) have demonstrated a limited reduction in transfusions; however, long-term developmental follow-up data are scarce.

OBJECTIVE

We compared anthropometric measurements, postdischarge events, need for transfusions, and developmental outcomes at 18 to 22 months' corrected age in extremely low birth weight (ELBW) infants treated with early Epo and supplemental iron therapy with that of placebo/control infants treated with supplemental iron alone.

METHODS

The National Institute of Child Health and Human Development Neonatal Research Network completed a randomized, controlled trial of early Epo and iron therapy in preterm infants < or =1250 g. A total of 172 ELBW (< or =1000-g birth weight) infants were enrolled (87 Epo and 85 placebo/control). Of the 72 Epo-treated and 70 placebo/control ELBW infants surviving to discharge, follow-up data (growth, development, rehospitalization, transfusions) at 18 to 22 months' corrected age were collected on 51 of 72 Epo-treated infants (71%) and 51 of 70 placebo/controls (73%) by certified examiners masked to the treatment group. Statistical significance was determined using chi2 analysis.

RESULTS

There were no significant differences between treatment groups in weight or length or in the percentage of infants weighing <10th percentile either at the time of discharge or at follow-up, and no difference was found in the mean head circumference between groups. A similar percentage of infants in each group was rehospitalized (38% Epo and 35% placebo/control) for similar reasons. There were no differences between groups with respect to the percentage of infants with Bayley-II Mental Developmental Index <70 (34% Epo and 36% placebo/control), blindness (0% Epo and 2% placebo/control), deafness or hearing loss requiring amplification (2% Epo and 2% placebo/control), moderate to severe cerebral palsy (16% Epo and 18% placebo/control) or the percentage of infants with any of the above-described neurodevelopmental impairments (42% Epo and 44% placebo/control).

CONCLUSIONS

Treatment of ELBW infants with early Epo and iron does not significantly influence anthropometric measurements, need for rehospitalization, transfusions after discharge, or developmental outcome at 18 to 22 months' corrected age.

Cytoprotection by darbepoetin/epoetin alfa in pig tubular and mouse mesangial cells

BACKGROUND

Erythropoietin has recently been found to have cytoprotective effects in the central nervous system (CNS) and retina. The purpose of this study was to determine if darbepoetin alfa (DA) has cytoprotective properties in renal tissues.

METHODS

DA was studied in LLC/PK1 and mesangial cells. Renal cellular injury was induced in different experiments by prostaglandin D2 synthase (PGDS), camptothecin, hydrogen peroxide, and hypoxia. Cellular proliferation and apoptosis were measured [apoptosis by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate (dUTP) nick end-labeling (TUNEL) assay or by caspase-3 activity]. In a separate experiment, an inactive form of erythropoietin alfa was used to study receptor effects.

RESULTS

DA protected against the antiproliferative effects of PGDS. In both LLC/PK1 (TUNEL and caspase-3) and mesangial cells (TUNEL), DA reduced the apoptotic stimulus of PGDS. Epoetin alfa was also found to reduce apoptosis. In LLC/PK1 cells, DA reduced apoptosis induced by camptothecin, but not hydrogen peroxide. DA reduced LLC/PK1 apoptosis induced by hypoxia when added 24 hours before hypoxia, but not when given concurrent with the hypoxic stimulus. Erythropoietin inactive did not protect against PGDS-induced apoptosis.

CONCLUSION

DA has renal antiapoptotic effects for both toxic and hypoxic stimuli. The effect may be mediated via the Erythropoietin receptor.

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.

Erythropoietin Attenuates Post-Traumatic Injury in Organotypic Hippocampal Slices

Recent experimental evidence indicates that erythropoietin (Epo), in addition to its hormonal role in regulating red cell production, operates as a neuroprotective agent. So far, the neuroprotective effect of human recombinant Epo (rhEpo) has been mainly demonstrated in models of cerebral ischemia/hypoxia and in selected in vivo studies of traumatic neuronal injury. To further investigate the potential role of this multifunctional trophic factor in post-traumatic cell death, we examined the protective effects of rhEpo in a newly developed model of mechanical trauma in organotypic hippocampal slices. Organotypic rat hippocampal slices were subjected to traumatic injury by allowing a stylus to impact on the CA1 area with an energy of 6 microJ. Hippocampal damage was identified and measured 24 and 48 h later with the fluorescent dye propidium iodide (PI). In untreated slices, the impact induced a significant increase in the mean hippocampal PI fluorescence, co-localized with the area of impact at 24 h (primary post-traumatic injury) and progressively spread to the whole slice between 24 and 48 h (secondary post-traumatic injury). Addition of rhEpo (1-100 UI/mL) or of the NMDA antagonist MK-801 (30 microM) immediately after the traumatic injury reduced hippocampal damage by approximately 30% when observed 24 h later. At 48 h after trauma, the protective effect of rhEpo was greater (by about 47%) and significantly more pronounced than that of MK-801 (28%). Our results suggest that the neuroprotective activity of rhEpo is particularly effective against delayed, secondary post-traumatic damage. This well tolerated agent could provide a therapeutic benefit in pathologies involving post-traumatic neurodegeneration.

Does erythropoietin protect the preterm brain?

There is a high incidence of hypoxic-ischaemic brain injury and intraventricular haemorrhage in newborn infants, particularly those born preterm. Many die during the newborn period or suffer permanent neurodevelopmental handicaps. Hypoxic brain injury develops over several hours and could potentially be influenced by intervention. At present, no drug exists that effectively prevents infant brain injury or ameliorates detrimental neurodevelopmental effects. The hypothesis is put forward that systemic administration of recombinant human erythropoietin positively affects the neurodevelopmental outcome of high risk preterm infants affected by brain injury. A multicentre, randomised, placebo controlled study is proposed to prospectively test this hypothesis.

Erythropoietin (epoetin) as a protective factor for the brain

Erythropoietin (EPO) has been viewed traditionally as a hematopoietic cytokine. Emerging evidence now exists supporting a physiologic role for EPO within the nervous system. EPO is expressed in the developing central nervous system and is capable of regulating the production of neuronal progenitor cells. There are numerous preclinical studies demonstrating a neuroprotective potential for EPO in a variety of disorders of both the central and peripheral nervous systems. A small pilot study in patients with acute ischemic stroke has recently been completed and the results are encouraging. Its mechanism of action is multifactorial but probably related to its ability to act as an antiapoptotic agent. Its widespread use clinically for the treatment of anemias has given us the experience and knowledge of its safety and pharmacokinetics. EPO is thus an ideal compound to study for the potential treatment of a variety of neurologic disorders.

Erythropoietin as a tissue-protective cytokine in brain injury: what do we know and where do we go?

In the 10 years since neurotrophic activity was first reported for erythropoietin (EPO), a broad understanding of its multiple paracrine/autocrine functions has emerged. Recent studies firmly establish EPO as a multifunctional molecule, typical of the pliotrophic cytokine superfamily of which it is a member. The realization that EPO activates neuroprotection by multiple mechanisms has identified a generalized system of local tissue protection with EPO as a critical component. Here, the authors characterize the biology of the local tissue-protective system, review data that support this concept, and suggest why non-hematopoietic analogues of EPO may be better choices as therapeutics.

Asialoerythropoietin is not effective in the R6/2 line of Huntington's disease mice

Background

Huntington's disease (HD) is a hereditary neurodegenerative disorder caused by an expanded CAG repeat in the HD gene. Both excitotoxicity and oxidative stress have been proposed to play important roles in the pathogenesis of HD. Since no effective treatment is available, this study was designed to explore the therapeutic potential of erythropoietin (EPO), a cytokine that has been found to prevent excitotoxicity, and to promote neurogenesis. To avoid the side effects of a raised hematocrit, we used asialoerythropoietin (asialoEPO), a neuroprotective variant of EPO that lacks erythropoietic effects in mice. R6/2 transgenic HD mice were treated with this cytokine from five to twelve weeks of age.

Results

We provide new evidence that cell proliferation in the dentate gyrus of the R6/2 hippocampus is reduced by 50% compared to wild-type littermate controls. However, we found that the asialoEPO treatment did not affect the progression of motor symptoms, weight loss or the neuropathological changes. Furthermore, cell proliferation was not enhanced.

Conclusions

We conclude that the chosen protocol of asialoEPO treatment is ineffective in the R6/2 model of HD. We suggest that reduced hippocampal cell proliferation may be an important and novel neuropathological feature in R6 HD mice that could be assessed when evaluating potential therapies.

An overview of new pharmacological treatments for cerebrovascular dysfunction after experimental subarachnoid hemorrhage

Cerebral vasospasm and the resulting cerebral ischemia occurring after subarachnoid hemorrhage (SAH) are still responsible for the considerable morbidity and mortality in patients affected by cerebral aneurysms. Mechanisms contributing to the development of vasospasm, abnormal reactivity of cerebral arteries and cerebral ischemia after SAH have been intensively investigated in recent years. It has been suggested that the pathogenesis of vasospasm is related to a number of pathological processes, including endothelial damage, smooth muscle cell contraction resulting from spasmogenic substances generated during lyses of subarachnoid blood clots, changes in vascular responsiveness and inflammatory or immunological reactions of the vascular wall. A great deal of experimental and clinical research has been conducted in an effort to find ways to prevent these complications. However, to date, the main therapeutic interventions remain elusive and are limited to the manipulation of systemic blood pressure, alteration of blood volume or viscosity, and control of arterial dioxide tension. Even though no single pharmacological agent or treatment protocol has been identified which could prevent or reverse these deadly complications, a number of promising drugs have been investigated. Among these is the hormone erythropoietin (EPO), the main regulator of erythropoiesis. It has recently been found that EPO produces a neuroprotective action during experimental SAH when its recombinant form (rHuEPO) is systemically administered. This topic review collects the relevant literature on the main investigative therapies for cerebrovascular dysfunction after aneurysmal SAH. In addition, it points out rHuEPO, which may hold promise in future clinical trials to prevent the occurrence of vasospasm and cerebral ischemia after SAH.

Long-acting erythropoietin: clinical studies and potential uses in neonates

Aranesp (darbepoietin alfa) is a biologically modified form of recombinant human erythropoietin (rHuEpo). Two additional carbohydrate-binding sites give Aranesp a half-life about three times that of rHuEpo. Extensive studies in adults and early studies in children indicate that Aranesp can be administered far less frequently than rHuEpo with an equivalent erythropoietic effect. This article reviews these studies and reports on the in vitro effects of Aranesp on human fetal and neonatal erythroid progenitors.

Erythropoietin and the nervous system

Erythropoietin (Epo) is a hematopoietic growth factor and cytokine which stimulates erythropoiesis. In recent years, Epo has been shown to have important nonhematopoietic functions in the nervous system. Nonerythropoietic actions of Epo include a critical role in the development, maintenance, protection and repair of the nervous system. A wide variety of experimental studies have shown that Epo and its receptor are expressed in the nervous system and Epo exerts remarkable neuroprotection in cell culture and animal models of nervous system disorders. In this review, we summarize the current knowledge on the neurotrophic and neuroprotective properties of Epo, the mechanisms by which Epo produces neuroprotection and the signal transduction systems regulated by Epo in the nervous system.

Recombinant erythropoietin as a neuroprotective treatment: in vitro and in vivo models

The biologic effects of erythropoietin in the central and peripheral nervous system involve the activation of its specific cell surface receptor and corresponding signal transduction pathways. This article reviews the neuroprotective effects of erythropoietin in brain, emphasizing the progress made using in vitro and in vivo research models.

Erythropoietin both protects from and reverses experimental diabetic neuropathy

Erythropoietin (EPO) possesses generalized neuroprotective and neurotrophic actions. We tested the efficacy of recombinant human EPO (rhEPO) in preventing and reversing nerve dysfunction in streptozotocin (STZ)-induced diabetes in rats. Two days after STZ [60 mg/kg of body weight (b.w.), i.p.], diabetic animals were administered rhEPO (40 microg/kg of b.w.) three times weekly for 5 weeks either immediately (preventive) before or after a 5-week delay (therapeutic) after induction of hyperglycemia or at a lower dose (8 microg/kg of b.w. once per week) for 8 weeks (prolonged). Tail-nerve conduction velocities (NCV) was assessed at 5 and 11 weeks for the preventive and therapeutic schedule, respectively. Compared to nondiabetic rats, NCV was 20% lower after 5 weeks in the STZ group, and this decrease was attenuated 50% by rhEPO. Furthermore, the reduction of Na(+),K(+)-ATPase activity of diabetic nerves (by 55%) was limited to 24% in the rhEPO-treated group. In the therapeutic schedule, NCV was reduced by 50% after 11 weeks but by only 23% in the rhEPO-treated group. rhEPO treatment attenuated the decrease in compound muscle action potential in diabetic rats. In addition, rhEPO treatment was associated with a preservation of footpad cutaneous innervation, as assessed by protein gene product 9.5 immunostaining. Diabetic rats developed alterations in mechanical and thermal nociception, which were partially reversed by rhEPO given either in a preventative or therapeutic manner. These observations suggest that administration of rhEPO or its analogues may be useful in the treatment of diabetic neuropathy.

Erythropoietin protects the in vitro blood-brain barrier against VEGF-induced permeability

The blood-brain barrier (BBB) ensures the homeostasis of the brain microenvironment, mostly through complex tight junctions between brain endothelial cells that prevent the passage of hydrophilic molecules from blood to brain and vice versa. A recent study has shown in vivo that systemic administration of erythropoietin (Epo) protects against brain injury. Using an in vitro model of the bovine BBB, we observed that the expression of the Epo receptor is modulated by its ligand and hypoxic stimuli such as vascular endothelial growth factor (VEGF) treatment. In addition, Epo protects against the VEGF-induced permeability of the BBB, decreases the levels of endothelial nitric oxide synthase and restores junction proteins. The kinetic transport experiments revealed the capacity of Epo to cross the in vitro BBB in a saturable and specific way. Our results suggest a new mechanism for Epo-induced neuroprotection, in which circulating Epo controls and maintains the BBB through an Epo receptor signalling pathway and the re-establishment of cell junctions.

Erythropoietin in the cerebrospinal fluid of patients with aneurysmal subarachnoid haemorrhage originates from the brain

Recent years' research has revealed a specific, neuroprotective erythropoietin (EPO) system in the central nervous system (CNS) that is upregulated by hypoxia. The presence and dynamics of EPO in the cerebrospinal fluid (CSF) of patients with subarachnoid haemorrhage (SAH) has not been investigated. We collected a total of 83 corresponding serum and CSF samples from 18 patients with aneurysmal SAH and compared the concentrations of EPO with those of blood-derived markers of blood-brain barrier function (albumin, transferrin, alpha(2)-macroglobulin) and with those of proteins with well-known CNS synthesis (prealbumin, apolipoprotein E). The EPO concentration in CSF was 0.93 (0.82) mU/ml (median and inter-quartile range). Nine patients presented CSF-EPO values above 1 mU/ml. CSF levels did not correlate with serum concentrations and were independent of blood-brain barrier integrity suggesting a synthesis in CNS rather than a blood-derived origin. Furthermore, the median CSF:serum ratio (Q(protein)) of EPO was similar to those of prealbumin and apolipoprotein E, and much higher than those of albumin, transferrin and alpha(2)-macroglobulin. When the Q(protein) of all proteins were plotted against Q(albumin), EPO showed dynamics similar to CNS-derived proteins. Our data indicate that EPO in the CSF of patients with aneurysmal SAH originates mainly from the CNS.

Anemia management and the delay of chronic renal failure progression

Interstitial fibrosis plays a key role in the progression of chronic kidney diseases. Analysis of the biologic effects of erythropoietin and of the pathophysiology of interstitial fibrosis suggest that treatment with epoetin may slow the progression of chronic kidney disease, both by decreasing interstitial fibrosis and by protecting against its consequences. The results of two small prospective studies and of a retrospective one also suggest that treatment with epoetin may have such protective effects.

Asialoerythropoietin is a nonerythropoietic cytokine with broad neuroprotective activity in vivo

Erythropoietin (EPO) is a tissue-protective cytokine preventing vascular spasm, apoptosis, and inflammatory responses. Although best known for its role in hematopoietic lineages, EPO also affects other tissues, including those of the nervous system. Enthusiasm for recombinant human erythropoietin (rhEPO) as a potential neuroprotective therapeutic must be tempered, however, by the knowledge it also enlarges circulating red cell mass and increases platelet aggregability. Here we examined whether erythropoietic and tissue-protective activities of rhEPO might be dissociated by a variation of the molecule. We demonstrate that asialoerythropoietin (asialoEPO), generated by total enzymatic desialylation of rhEPO, possesses a very short plasma half-life and is fully neuroprotective. In marked contrast with rhEPO, this molecule at doses and frequencies at which rhEPO exhibited erythropoiesis, did not increase the hematocrit of mice or rats. AsialoEPO appeared promptly within the cerebrospinal fluid after i.v. administration; intravenously administered radioiodine-labeled asialoEPO bound to neurons within the hippocampus and cortex in a pattern corresponding to the distribution of the EPO receptor. Most importantly, asialoEPO exhibits a broad spectrum of neuroprotective activities, as demonstrated in models of cerebral ischemia, spinal cord compression, and sciatic nerve crush. These data suggest that nonerythropoietic variants of rhEPO can cross the blood-brain barrier and provide neuroprotection.

Recombinant human erythropoietin protects the myocardium from ischemia-reperfusion injury and promotes beneficial remodeling

Erythropoietin (EPO), originally identified for its critical hormonal role in promoting erythrocyte survival and differentiation, is a member of the large and diverse cytokine superfamily. Recent studies have identified multiple paracrineautocrine functions of EPO that coordinate local responses to injury by maintaining vascular autoregulation and attenuating both primary (apoptotic) and secondary (inflammatory) causes of cell death. Experimental evidence also supports a role for EPO in repair and regeneration after brain and spinal cord injury, including the recruitment of stem cells into the region of damage. Tissue expression of the EPO receptor is widespread, especially during development, and includes the heart. However, it is currently unknown as to whether EPO plays a physiological function in adult myocardial tissue. We have assessed the potential protective role of EPO in vitro with adult rat cardiomyocytes, and in vivo in a rat model of myocardial infarction with reperfusion. The results show that EPO markedly prevents the apoptosis of cultured adult rat myocardiocytes subjected to 28 h of hypoxia (approximately 3% normal oxygen). Additional studies employing a rat model of coronary ischemia-reperfusion showed that the administration of recombinant human EPO (5,000 units/kg of body weight; i.p. daily for 7 days) reduces cardiomyocyte loss by approximately 50%, an extent sufficient to normalize hemodynamic function within 1 week after reperfusion. These observations not only suggest a potential therapeutic role for recombinant human EPO in the treatment of myocardial ischemia and infarction by preventing apoptosis and attenuating postinfarct deterioration in hemodynamic function, but also predict that EPO is likely a tissue-protective cytokine in other organs as well.

Cerebral vasospasm after subarachnoid hemorrhage

PURPOSE OF REVIEW

To summarize new pathophysiologic insights and recent advances in the diagnosis and treatment of cerebral vasospasm after aneurysmal subarachnoid hemorrhage.

RECENT FINDINGS

Important, newly recognized mediators of cerebral arterial spasm after subarachnoid hemorrhage include superoxide free radicals, ferrous hemoglobin (which acts as a nitric oxide scavenger), endothelins, protein kinase C, and rho kinase. Microvascular dysfunction and autoregulatory failure also has been an area of increasing research focus in recent years. New diagnostic modalities include measures of cerebral blood flow such as single-photon emission computed tomography and perfusion computed tomography, magnetic resonance imaging, intracranial brain oxygen tension probes, and jugular venous oxygen saturation monitors. Proton magnetic resonance spectroscopy and microdialysis can detect tissue biochemical abnormalities, but these techniques have not found their way into routine clinical practice as of yet. In addition to nimodipine and hypertensive hypervolemic therapy, promising new treatments for vasospasm or its ischemic complications include magnesium sulfate, fasudil hydrochloride, tirilazad mesylate, erythropoietin, and induced hypothermia. Balloon angioplasty has emerged as the primary weapon for treating medically refractory ischemia from vasospasm and in many centers is being used as a first-line treatment or even prophylactically.

SUMMARY

The neurointensive care management of vasospasm after subarachnoid hemorrhage has evolved significantly over the past 10 years, with many new diagnostic modalities and promising treatments now available. Clinical trials are needed to evaluate the efficacy of these new techniques and to further define the optimal management of this often devastating complication.

Apaf-1, Bcl-xL, cytochrome c, and caspase-9 form the critical elements for cerebral vascular protection by erythropoietin

Erythropoietin (EPO) plays a prominent role in the regulation of the hematopoietic system, but the potential function of this trophic factor as a cytoprotectant in the cerebral vascular system is not known. The authors examined the ability of EPO to modulate a series of death-related cellular pathways during free radical-induced injury in cerebral microvascular endothelial cells (ECs). Endothelial cell injury was evaluated by trypan blue, DNA fragmentation, membrane phosphatidylserine exposure, apoptotic protease-activating factor-1 (Apaf-1), and Bcl-XL expression, mitochondrial membrane potential, cytochrome c release, and cysteine protease activity. They show that constitutive EPO is present in ECs but is insufficient to prevent cellular injury. Signaling through the EPO receptor, however, remains biologically responsive to exogenous EPO administration to offer significant protection against nitric oxide-induced injury. Exogenous EPO maintains both genomic DNA integrity and cellular membrane asymmetry through parallel pathways that prevent the induction of Apaf-1 and preserve mitochondrial membrane potential in conjunction with enhanced Bcl-XL expression. Consistent with the modulation of Apaf-1 and the release of cytochrome c, EPO also inhibits the activation of caspase-9 and caspase-3-like activities. Identification of novel cytoprotective pathways used by EPO may serve as therapeutic targets for cerebral vascular disease.

Erythropoietin prevents early and late neuronal demise through modulation of Akt1 and induction of caspase 1, 3, and 8

Erythropoietin (EPO) modulates primarily the proliferation of immature erythroid precursors, but little is known of the potential protective mechanisms of EPO in the central nervous system. We therefore examined the ability of EPO to modulate a series of death-related cellular pathways during anoxia and free radical induced neuronal degeneration. Neuronal injury was evaluated by trypan blue, DNA fragmentation, membrane phosphatidylserine exposure, protein kinase B phosphorylation, cysteine protease activity, mitochondrial membrane potential, and mitogen-activated protein (MAP) kinase phosphorylation. We demonstrate that constitutive neuronal EPO is insufficient to prevent cellular injury, but that signaling through the EPO receptor remains biologically responsive to exogenous EPO administration. Exogenous EPO is both necessary and sufficient to prevent acute genomic DNA destruction and subsequent phagocytosis through membrane PS exposure, because neuronal protection by EPO is completely abolished by co-treatment with an anti-EPO neutralizing antibody. Through pathways that involve the initial activation of protein kinase B, EPO maintains mitochondrial membrane potential. Subsequently, EPO inhibits caspase 8-, caspase 1-, and caspase 3-like activities linked to cytochrome c release through mechanisms that are independent from the MAP kinase systems of p38 and JNK. Elucidating some of the novel neuroprotective pathways employed by EPO may further the development of new therapeutic strategies for neurodegenerative disorders.

Erythropoietin fosters both intrinsic and extrinsic neuronal protection through modulation of microglia, Akt1, Bad, and caspase-mediated pathways

1. Erythropoietin (EPO) plays a significant role in the hematopoietic system, but the function of EPO as a neuroprotectant and anti-inflammatory mediator requires further definition. We therefore examined the cellular mechanisms that mediate protection by EPO during free radical injury in primary neurons and cerebral microglia. 2. Neuronal injury was evaluated by trypan blue, DNA fragmentation, phosphatidylserine (PS) exposure, Akt1 phosphorylation, Bad phosphorylation, mitochondrial membrane potential, and cysteine protease activity. Microglial activation was assessed through proliferating cell nuclear antigen and PS receptor expression. 3. EPO provides intrinsic neuronal protection that is both necessary and sufficient to prevent acute genomic DNA destruction and subsequent membrane PS exposure, since protection by EPO is completely abolished by cotreatment with an anti-EPO neutralizing antibody. 4. Extrinsic protection by EPO is offered through the inhibition of cerebral microglial activation and the suppression of microglial PS receptor expression for the prevention of neuronal phagocytosis. In regards to microglial chemotaxis, EPO modulates neuronal poptotic membrane PS exposure necessary for microglial activation primarily through the regulation of caspase 1. 5. EPO increases Akt1 activity, phosphorylates Bad, and maintains neuronal nuclear DNA integrity through the downstream modulation of mitochrondrial membrane potential, cytochrome c release, and caspase 1, 3, and 8-like activities. 6. Elucidating the intrinsic and extrinsic protective pathways of EPO that mediate both neuronal integrity and inflammatory microglial activation may enhance the development of future therapies directed against acute neuronal injury.

Recombinant human erythropoietin counteracts secondary injury and markedly enhances neurological recovery from experimental spinal cord trauma

Erythropoietin (EPO) functions as a tissue-protective cytokine in addition to its crucial hormonal role in red cell production. In the brain, for example, EPO and its receptor are locally produced, are modulated by metabolic stressors, and provide neuroprotective and antiinflammatory functions. We have previously shown that recombinant human EPO (rhEPO) administered within the systemic circulation enters the brain and is neuroprotective. At present, it is unknown whether rhEPO can also improve recovery after traumatic injury of the spinal cord. To evaluate whether rhEPO improves functional outcome if administered after cord injury, two rodent models were evaluated. First, a moderate compression of 0.6 N was produced by application of an aneurysm clip at level T3 for 1 min. RhEPO (1,000 units per kg of body weight i.p.) administered immediately after release of compression was associated with partial recovery of motor function within 12 h after injury, which was nearly complete by 28 days. In contrast, saline-treated animals exhibited only poor recovery. In the second model used, rhEPO administration (5,000 units per kg of body weight i.p. given once 1 h after injury) also produced a superior recovery of function compared with saline-treated controls after a contusion of 1 N at level T9. In this model of more severe spinal cord injury, secondary inflammation was also markedly attenuated by rhEPO administration and associated with reduced cavitation within the cord. These observations suggest that rhEPO provides early recovery of function, especially after spinal cord compression, as well as longer-latency neuroprotective, antiinflammatory and antiapoptotic functions.