Erythropoietin potentiates EDHF-mediated dilations in rat middle cerebral arteries

Adverse neural effects of delayed, intermittent treatment with rEPO after asphyxia in preterm fetal sheep

KEY POINTS

We have previously shown that high-dose constant infusion of recombinant human erythropoietin (rEPO) from 30 min to 72 h after asphyxia in preterm fetal sheep reduced histological injury and improved electrophysiological recovery. This study shows that a high-dose infusion of rEPO from 6 to 72 h after asphyxia did not improve EEG recovery, oligodendrocyte and neuronal survival at 1 week post-asphyxia. Of concern, intermittent rEPO boluses started 6 h after asphyxia were associated with impaired EEG recovery and bilateral cystic injury of temporal lobe intragyral white matter. Intermittent boluses of rEPO were associated with significantly increased cerebral vascular resistance and hypoperfusion, particularly after the first dose, but did not affect seizures, suggesting mismatch between perfusion and brain activity.

ABSTRACT

Recombinant human erythropoietin (rEPO) is a promising treatment for hypoxic-ischaemic brain injury. Disappointingly, a large randomized controlled trial in preterm infants found that prophylactic, repeated high-dose rEPO boluses started within 24 h of birth did not improve neurodevelopmental outcomes. We examined whether initiation of a continuous infusion of rEPO at the end of the latent phase after hypoxic-ischaemia (HI) might improve outcomes compared with intermittent bolus injections. Chronically instrumented preterm (0.7 gestation) fetal sheep received sham asphyxia or asphyxia induced by complete umbilical cord occlusion for 25 min. Six hours after asphyxia, fetuses received either a continuous infusion of rEPO (loading dose 2000 IU, infusion at 520 IU/h) from 6 to 72 h post-asphyxia or intravenous saline or 5000 IU rEPO, with repeated doses every 48 h for 5 days. Continuous infusion of rEPO did not improve EEG recovery, oligodendrocyte and neuronal survival at 1 week post-asphyxia. By contrast, intermittent rEPO boluses were associated with impaired EEG recovery and bilateral cystic injury of temporal lobe intragyral white matter in 6/8 fetuses. These studies demonstrate for the first time that initiation of intermittent rEPO boluses 6 h after HI, at a dose comparable with recent clinical trials, exacerbated neural injury. These data reinforce the importance of early initiation of many potential neuroprotective therapies.

Erythropoietin-Associated Posterior Reversible Encephalopathy Syndrome

INTRODUCTION

This case demonstrates an underrecognized cause of posterior reversible encephalopathy syndrome (PRES).

CASE REPORT

We report a 51-year-old male with a history of essential hypertension without preexisting renal impairment who presented with 3 days of occipital headache and convulsive status epilepticus in the setting of refractory hypertension. He had been receiving outpatient human recombinant erythropoietin injections for virally mediated bone marrow suppression, which worsened his baseline hypertension. Magnetic resosnance imaging (MRI) of the brain on admission showed diffuse bilateral, symmetric signal hyperintensities and patchy enhancement involving the cortex and white matter in both cerebral hemispheres. His blood pressure and seizures were successfully treated during hospital admission, with complete resolution of his neurological deficits. MRI brain performed 6 weeks from initial scan showed normalization of his prior findings.

CONCLUSION

Recombinant human erythropoietin (RhEPO) may be an underrecognized cause of PRES and should be considered in patients receiving this treatment regardless of the absence or presence of renal impairment. RhEPO-mediated precipitation/exacerbation of hypertension, alterations in cerebral blood flow, and changes in endothelial integrity may underlie this association. MRI signal changes are reversible and typical for that of PRES, and significant improvement of symptoms can be expected.

Neuroprotective mechanisms of erythropoietin in a rat stroke model

Objective

This study was designed to investigate the indirect neuroprotective properties of recombinant human erythropoietin (rhEPO) pretreatment in a rat model of transient middle cerebral artery occlusion (MCAO).

Methods

One hundred and ten male Wistar rats were randomly assigned to four groups receiving either 5,000 IU/kg rhEPO intravenously or saline 15 minutes prior to MCAO and bilateral craniectomy or sham craniectomy. Bilateral craniectomy aimed at elimination of the space-consuming effect of postischemic edema. Diagnostic workup included neurological examination, assessment of infarct size and cerebral edema by magnetic resonance imaging, wet–dry technique, and quantification of hemispheric and local cerebral blood flow (CBF) by flat-panel volumetric computed tomography.

Results

In the absence of craniectomy, EPO pretreatment led to a significant reduction in infarct volume (34.83 ± 9.84% vs. 25.28 ± 7.03%; p = 0.022) and midline shift (0.114 ± 0.023 cm vs. 0.083 ± 0.027 cm; p = 0.013). We observed a significant increase in regional CBF in cortical areas of the ischemic infarct (72.29 ± 24.00% vs. 105.53 ± 33.10%; p = 0.043) but not the whole hemispheres. Infarct size-independent parameters could not demonstrate a statistically significant reduction in cerebral edema with EPO treatment.

Conclusions

Single-dose pretreatment with rhEPO 5,000 IU/kg significantly reduces ischemic lesion volume and increases local CBF in penumbral areas of ischemia 24 h after transient MCAO in rats. Data suggest indirect neuroprotection from edema and the resultant pressure-reducing and blood flow-increasing effects mediated by EPO.

Erythropoietin mediates brain-vascular-kidney crosstalk and may be a treatment target for pulmonary and resistant essential hypertension

Organ crosstalk pathways represent the next frontier for target-mining in molecular medicine for existing syndromes. Pulmonary hypertension and resistant essential hypertension are syndromes that have been proven elusive in etiology, and frequently refractory to first-line management. Underlying crosstalk mechanisms, not yet considered in these treatments, may hinder outcomes or unlock novel treatments. This review focuses systematically on erythropoietin, a synthesizable molecule, as a mediator of brain-kidney crosstalk. Insights gained from this review will be applied to cardiovascular diseases in a clinician-directed fashion.

A review of the effects of some endocrinological factors on respiratory mechanics

CONTEXT

Endocrinological factors have been recently described to affect respiratory mechanics.

OBJECTIVE

To review recent literature data, most of all obtained by the end-inflation occlusion method, describing the effects of molecules of endocrinological interest such as endothelin, erythropoietin and renin-angiotensin, on respiratory mechanics parameters.

METHODS

The papers considered in this review were found by inserting in Pubmed/Medline the following indexing terms: hormones, endothelin, erythropoietin, angiotensin and respiratory mechanics.

RESULTS

It was found that the above cited molecules, beside their well known physiological main effects, exhibit influences on respiratory mechanics, most of all on the airflow resistance, which was described to be increased by endothelin and angiotensin, and decreased by erythropoietin.

CONCLUSIONS

A number of molecules of biological interest exhibit unexpected influences on respiratory mechanics. The clinical effects depend on the consequences of modified inspiratory pressure values the respiratory muscles have to perform for a given breathing pattern.

Erythropoietin has a restorative effect on the contractility of arteries following experimental hypoxia

INTRODUCTION

The aim of this study was to investigate the effect of erythropoietin on vascular contractility using an in vitro model of hypoxia replicating the hypoxic environment of blood vessels and surrounding adipose tissue in obesity.

METHODS AND RESULTS

Pharmacological in vitro studies were carried out on small mesenteric arterial segments from male Wistar rats with and without perivascular fat and endothelium. Contractile responses were investigated by wire myography under normoxia, experimental hypoxia ± erythropoietin and l-NNA. Perivascular fat exerted an anticontractile effect which was lost following the induction of experimental hypoxia. Erythropoietin prevented the loss of the anticontractile capacity when vessels were incubated for one hour before the induction of hypoxia or throughout the period of hypoxia; this was found to be independent of the function of perivascular fat, as fat denuded arteries had a similar reduction in contractility (artery no fat + hypoxia vs. artery no fat + hypoxia + erythropoietin). The mechanism by which erythropoietin was exerting its effect was found to be partially endothelium dependent and associated with an increase of nitric oxide bioavailability as nitric oxide synthase inhibition prevented the effect.

CONCLUSIONS

Whilst erythropoietin is working downstream from perivascular fat, it is possible that it may be therapeutically useful in obesity when hypoxia and inflammation reduce the normal activity of perivascular fat.

Erythropoietin acutely decreases airway resistance in the rat

While some experimental data suggest that erythropoietin (EPO) influences respiratory mechanics, reports on scientific trials are lacking. In the present work, respiratory mechanics were measured using the end-inflation occlusion method in control and EPO treated anaesthetised and positive-pressure ventilated rats. Causing an abrupt inspiratory flow arrest, the end-inflation occlusion method makes it possible to measure the ohmic airway resistance and the respiratory system elastance. It was found that EPO induces a significant decrement in the ohmic airway resistance, not noted in control animals, 20 and 30 min after intraperitoneal EPO injection. The elastic characteristics of the respiratory system did not vary. Hypotheses about the mechanism (s) explaining these results were addressed. In particular, additional experiments have indicated that the decrement in airway resistance could be related to an increase in nitric oxide production induced by EPO. Spontaneous increments in plasmatic erythropoietin levels, such as those that take place in association with hypoxia and/or blood loss, appear to be related to the decrement in airway resistance, allowing pulmonary ventilation to increase without altering respiratory mechanics leading to deleterious increments in energy dissipation during breathing.

Isolated human and rat cerebral arteries constrict to increases in flow: role of 20-HETE and TP receptors

Elevation of intraluminal pressure increases vasomotor tone, which thought to have a substantial role in regulation of cerebral blood flow (CBF). Interestingly, responses of cerebral vessels to increases in flow varied and have not been studied in human cerebral arteries. We hypothesized that increases in flow elicit constrictions of isolated human and rat cerebral arteries and aimed to elucidate the underlying mechanisms. Human cerebral arteries and rat middle cerebral arteries constricted to increases in flow (P<0.05). Simultaneous increase in intraluminal flow+pressure further reduced the diameter compared with pressure-induced changes (P<0.05), leading to constant estimated CBF. Flow-induced constrictions were abolished by HET0016 (inhibitor of synthesis of 20-hydroxyeicosatetraenoic acid (20-HETE) or inhibition of COXs or blocking TP (thromboxane A(2)/prostaglandin H(2), receptors and attenuated by scavenging reactive oxygen species (ROS). Flow-enhanced ROS formation was significantly reduced by HET0016. In conclusion, in human and rat cerebral arteries (1) increases in flow elicit constrictions, (2) signaling mechanism of flow-induced constriction of cerebral arteries involves enhanced production of ROS, COX activity, and mediated by 20-HETE via TP receptors, and (3) we propose that simultaneous operation of pressure- and flow-induced constrictions is necessary to provide an effective autoregulation of CBF.

Improved cerebrovascular function and reduced histological damage with darbepoietin alfa administration after cortical impact injury in rats

Darbepoetin alfa (darbEpo) is an erythropoietic glycoprotein that activates the erythropoietin receptor. The aim of our study was to determine whether darbEpo is neuroprotective in a cortical impact injury (CII) model and to determine the characteristics of dose response and time window. To better understand the vascular mechanism of darbEpo neuroprotection, the reactivity of cerebral blood flow (CBF) to l-arginine administration was also studied. Rats were given saline or darbEpo from 2.5 to 50 μg/kg at 5 min after CII or a dose of 25 μg/kg darbEpo at times ranging from 5 min to 24 h after CII. Histological assessment was determined 2 weeks after a severe CII. Other rats were given either darbEpo (25 μg/kg) or saline daily for 3 days before injury. Five minutes after severe CII, they were given either l-arginine or d-arginine. Hemodynamic variables were monitored for 2 h after injury. In the dose-response study, darbEpo in doses of 25 and 50 μg/kg significantly reduced contusion volume from 39.1 ± 6.7 to 8.1 ± 3.1 and 11.2 ± 6.0 mm(3), respectively. In the time window study, darbEpo reduced contusion volume when given in a dose of 25 μg/kg at 5 min to 6 h after the impact injury. In animals pretreated with darbEpo, the CBF response to l-arginine was significantly greater than in the animals pretreated with saline. These data demonstrate that darbEpo has neuroprotective effects in traumatic brain injury in a dose- and time-dependent manner and that vascular effects of darbEpo may have a role in neuroprotection.

Erythropoietin enhances hydrogen peroxide-mediated dilatation of canine coronary collateral arterioles during myocardial ischemia in dogs in vivo

We have previously demonstrated that endothelium-derived hydrogen peroxide (H2O2) plays an important role in the canine coronary microcirculation as an endothelium-derived hyperpolarizing factor in vivo. However, it remains to be examined whether endogenous H2O2 is involved in the dilatation of coronary collaterals during myocardial ischemia in vivo and, if so, whether erythropoietin (EPO) enhances the responses. Canine subepicardial native collateral small arteries (CSA; ≥ 100 μm) and arterioles (CA; <100 μm) were observed using an intravital microscope. Experiments were performed after left anterior descending coronary artery ischemia (90 min) under the following eight conditions ( n = 5 each): control, EPO, EPO+catalase, EPO+ N-monomethyl-l-arginine (l-NMMA), EPO+l-NMMA+catalase, EPO+l-NMMA+iberiotoxin [Ca2+-activated K+ (KCa) channel blocker], EPO+l-NMMA+apamin+charybdotoxin (KCa channel blocker), and EPO+wortmannin (phosphatidylinositol 3-kinase inhibitor). Myocardial ischemia caused significant vasodilatation in CA but not in CSA under control conditions, which was significantly decreased by catalase in CA. After EPO, the vasodilatation was significantly increased in both sizes of arteries and was significantly decreased by catalase. The enhancing effect of EPO was reduced by l-NMMA but not by catalase in CSA and was reduced by l-NMMA+catalase in CA, where the greater inhibitory effects were noted with l-NMMA+catalase, l-NMMA+iberiotoxin, L-NMMA+apamin+charybdotoxin, or wortmannin. EPO significantly ameliorated ischemia-induced impairment of myocardial Akt phosphorylation, which was abolished by l-NMMA+catalase or wortmannin. EPO also ameliorated oxidative stress and myocardial injury, as assessed by plasma 8-hydroxydeoxyguanosine and troponin-T, respectively. These results indicate that EPO enhances H2O2-mediated dilatation of coronary collateral arterioles during myocardial ischemia in dogs in vivo.

Preventing negative effects of smoking on microarterial anastomosis

Although microsurgery has rapid expanded, problems related to microarterial anastomosis continue. Cigarette smoking is one of the major risks for anastomosis by increasing platelet adhesion, and its effects on endothelial cells. Aim of this article is to study the negative effects of cigarettes on microarterial anastomosis line, and to investigate the protective effects of recombinant human erythropoietin (rHuEPO).Ninety-six Sprague-Dawley male rats were divided into 3 groups: group 1 was the control. Rats in groups 2 and 3 were exposed to cigarette smoke starting 21 days prior to surgery for 3 times a day. In group 3, additional 150 IU/kg rHuEPO was given via subcutaneously every 48 hours after microvascular anastomosis, femoral arterial samples, and blood samples were taken for assessment at 1st, 3rd, 5th, and 7th day. Intimae/media ratios were calculated for morphologic analyses.On morphologic analysis of femoral arteries there were statistically significant differences for all 3 groups at 1st, 3rd, 5th, and 7th days (P < 0, 05). The group that made differences was group 2, according to one-way analysis of variance within 3 groups in all days.Smoking decreases endothelial cells healing and causes more thromboses. rHuEPO can prevent these negative effects of smoking.

Interaction of neurovascular protection of erythropoietin with age, sepsis, and statin therapy following aneurysmal subarachnoid hemorrhage

Object

In a previous randomized controlled trial, the authors demonstrated that acute erythropoietin (EPO) therapy reduced severe vasospasm and delayed ischemic deficits (DIDs) following aneurysmal subarachnoid hemorrhage. In this study, the authors aimed to investigate the potential interaction of neurovascular protection by EPO with age, sepsis, and concurrent statin therapy.

Methods

The clinical events of 80 adults older than 18 years and with < 72 hours of aneurysmal subarachnoid hemorrhage, who were randomized to receive 30,000 U of intravenous EPO-β or placebo every 48 hours for a total of 3 doses, were analyzed by stratification according to age (< or ≥ 60 years), sepsis, or concomitant statin therapy. End points in the trial included cerebral vasospasm and impaired autoregulation on transcranial Doppler ultrasonography, DIDs, and unfavorable outcome at discharge and at 6 months measured with the modified Rankin Scale and Glasgow Outcome Scale. Analyses were performed using the t-test and/or ANOVA for repeated measurements.

Results

Younger patients (< 60 years old) or those without sepsis obtained benefits from EPO by a reduction in vasospasm, impaired autoregulation, and unfavorable outcome at discharge. Compared with nonseptic patients taking EPO, those with sepsis taking EPO had a lower absolute reticulocyte count (nonsepsis vs sepsis, 143.5 vs. 105.8 × 109/L on Day 6; p = 0.01), suggesting sepsis impaired both hematopoiesis and neurovascular protection by EPO. In the EPO group, none of the statin users suffered DIDs (p = 0.078), implying statins may potentiate neuroprotection by EPO.

Conclusions

Erythropoietin-related neurovascular protection appears to be attenuated by old age and sepsis and enhanced by statins, an important finding for designing Phase III trials.

Erythropoietin improves histological and functional outcomes after traumatic brain injury in mice in the absence of the neural erythropoietin receptor

Erythropoietin (EPO), essential for erythropoiesis, provides neuroprotection. The EPO receptor (EPOR) is expressed in both neural and non-neural cells in the brain. This study was designed to test the hypothesis that EPO provides beneficial therapeutic effects, even in the absence of the neural EPOR. In this study, EPOR-null mice were rescued with selective EpoR expression driven by the endogenous EpoR promoter in hematopoietic tissue, but not in the neural cells. Anesthetized young adult female EPOR-null and wild-type mice were subjected to traumatic brain injury (TBI) induced by controlled cortical impact. EPO (5000 U/kg) or saline was intraperitoneally administered at 6 h and 3 and 7 days post-injury. Sensorimotor and spatial learning functions were assessed. Expression of EPOR and its downstream signal proteins were evaluated by Western blot analysis. Our data demonstrated that EPO treatment significantly reduced cortical tissue damage and hippocampal cell loss, and improved spatial learning following TBI in both the wild-type and EPOR-null mice. EPO treatment significantly improved sensorimotor functional recovery, with better outcomes in the wild-type mice. EPO treatment upregulated anti-apoptotic proteins (p-Akt and Bcl-XL) in the ipsilateral hippocampus and cortex of the injured wild-type and EPOR-null mice. These data demonstrate that EPO significantly provides neuroprotection following TBI, even in the absence of EPOR in the neural cells, suggesting that its therapeutic benefits may be mediated through vascular protection.