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

Neuroendocrine regulation in stroke

The neuroendocrine system, a crosstalk between the central nervous system and endocrine glands, balances and controls hormone secretion and their functions. Neuroendocrine pathways and mechanisms often get dysregulated following stroke, leading to altered hormone secretion and aberrant receptor expression. Dysregulation of the hypothalamus-pituitary-thyroid (HPT) axis and hypothalamus-pituitary-adrenal (HPA) axis often led to severe stroke outcomes. Post-stroke complications such as cognitive impairment, depression, infection etc. are directly or indirectly influenced by the altered neuroendocrine activity that plays a crucial role in stroke vulnerability and susceptibility. Therefore, it is imperative to explore various neurohormonal inter-relationships in regulating stroke, its outcome, and prognosis. Here, we review the biology of different hormones associated with stroke and explore their regulation with a view towards prospective therapeutics.

Pharmacological Modulations of Nrf2 and Therapeutic Implications in Aneurysmal Subarachnoid Hemorrhage

An aneurysmal subarachnoid hemorrhage (aSAH) is a subtype of stroke with high morbidity and mortality. The main causes of a poor prognosis include early brain injury (EBI) and delayed vasospasm, both of which play a significant role in the pathophysiological process. As an important mechanism of EBI and delayed vasospasm, oxidative stress plays an important role in the pathogenesis of aSAH by producing reactive oxygen species (ROS) through the mitochondria, hemoglobin, or enzymatic pathways in the early stages of aSAH. As a result, antioxidant therapy, which primarily targets the Nrf2-related pathway, can be employed as a potential strategy for treating aSAH. In the early stages of aSAH development, increasing the expression of antioxidant enzymes and detoxifying enzymes can relieve oxidative stress, reduce brain damage, and improve prognosis. Herein, the regulatory mechanisms of Nrf2 and related pharmacological compounds are reviewed, and Nrf2-targeted drugs are proposed as potential treatments for aSAH.

Role of endothelial nitric oxide synthase for early brain injury after subarachnoid hemorrhage in mice

The first few hours and days after subarachnoid hemorrhage (SAH) are characterized by cerebral ischemia, spasms of pial arterioles, and a significant reduction of cerebral microperfusion, however, the mechanisms of this early microcirculatory dysfunction are still unknown. Endothelial nitric oxide production is reduced after SAH and exogenous application of NO reduces post-hemorrhagic microvasospasm. Therefore, we hypothesize that the endothelial NO-synthase (eNOS) may be involved in the formation of microvasospasms, microcirculatory dysfunction, and unfavorable outcome after SAH. SAH was induced in male eNOS deficient (eNOS^-/-) mice by endovascular MCA perforation. Three hours later, the cerebral microcirculation was visualized using in vivo 2-photon-microscopy. eNOS^-/- mice had more severe SAHs, more severe ischemia, three time more rebleedings, and a massively increased mortality (50 vs. 0%) as compared to wild type (WT) littermate controls. Three hours after SAH eNOS^-/- mice had fewer perfused microvessels and 40% more microvasospasms than WT mice. The current study indicates that a proper function of eNOS plays a key role for a favorable outcome after SAH and helps to explain why patients suffering from hypertension or other conditions associated with impaired eNOS function, have a higher risk of unfavorable outcome after SAH.

The calcimimetic R-568 attenuates subarachnoid hemorrhage-induced vasospasm through PI3K/Akt/eNOS signaling pathway in the rat model

Cerebral vasospasm (CVS) causes mortality and morbidity in patients after subarachnoid hemorrhage (SAH). The mechanism and adequate treatment of CVS are still elusive. R-568 is a calcimimetic agent known to exert a vasodilating effect. However, there is no report on its vasodilator effect against SAH-induced vasospasm. In the present study, we investigated the therapeutic effect of R-568 on the SAH-induced CVS model in rats. Seventy-two adult male Sprague-Dawley rats were divided into 8 groups: sham surgery; SAH only; SAH + Vehicle, SAH + R-568; SAH + R-568 + Wortmannin (the PI3K inhibitor); SAH + Wortmannin; SAH + R-568 + Calhex-231 (a calcilytic agent); SAH + Calhex-231. SAH was induced by blood (0.3 mL) given by intracisternal injection. R-568 (20 µM) was administered intracisternal immediately prior to experimental SAH. Basilar arteries (BAs) were obtained to evaluate PI3K/Akt/eNOS pathway (immunoblotting) and morphological changes 48 h after SAH. Perimeters of BAs were decreased by 24.1% in the SAH group compared to the control group and the wall thickness was increased by 75.3%. With R-568 treatment, those percentages were 9.6% and 29.6%, respectively, indicating that vasospasm was considerably improved when compared with the SAH group (P < 0.001 in both). While p-PI3K/PI3K and p-Akt/Akt ratio and eNOS protein expression were markedly decreased in the SAH rats, treatment with R-568 resulted in a significant increase in these levels. The beneficial effects of R-568 were partially blocked in the presence of Calhex-231 and completely blocked in the presence of Wortmannin. Herein, we found that treatment with R-568 would attenuate SAH-induced CVS through the PI3K/Akt/eNOS pathway and demonstrate therapeutic promise in CVS treatment following SAH.

Role of Endothelial Nitric Oxide Synthase in Isoflurane Conditioning-Induced Neurovascular Protection in Subarachnoid Hemorrhage

Background

Delayed cerebral ischemia remains a common and profound risk factor for poor outcome after subarachnoid hemorrhage (SAH). The aim of our current study is to define the role of endothelial nitric oxide synthase (eNOS) in isoflurane conditioning‐induced neurovascular protection after SAH.

Methods and Results

Ten‐ to 14‐week‐old male wild‐type mice (C57BL/6) as controls and eNOS knockout male mice (strain # 002684) were obtained for the study. Animals underwent either sham surgery, SAH surgery, or SAH with isoflurane conditioning. Anesthetic post conditioning was performed with isoflurane 2% for 1 hour, 1 hour after SAH. Normothermia was maintained with the homeothermic blanket. In a separate cohort, nitric oxide synthase was inhibited by a pan nitric oxide synthase inhibitor, L‐nitroarginine methyl ester. Vasospasm measurement was assessed 72 hours after SAH and neurological function was assessed daily. Isoflurane‐induced changes in the eNOS protein expression were measured. eNOS protein expression was significantly increased by isoflurane conditioning in naïve mice as well as mice subjected to SAH. Vasospasm of the middle cerebral artery and neurological deficits were evident following SAH versus sham surgery, both in wild‐type mice and eNOS knockout mice. Isoflurane conditioning attenuated vasospasm and neurological deficits in wild‐type mice. This delayed cerebral ischemia protection was lost in L‐nitroarginine methyl ester ‐administered mice and eNOS knockout mice.

Conclusions

Our data indicate isoflurane conditioning provides robust protection against SAH‐induced vasospasm and neurological deficits, and that this delayed cerebral ischemia protection is critically mediated via isoflurane‐induced augmentation of eNOS.

Negative Allosteric Modulator of mGluR1 Improves Long-Term Neurologic Deficits after Experimental Subarachnoid Hemorrhage

Aneurysmal subarachnoid hemorrhage (SAH) causes permanent neurological sequelae, but the underlying mechanism needs to be further clarified. Here, we show that inhibition of metabotropic glutamate receptor 1 (mGluR1) with negative allosteric modulator JNJ16259685 improves long-term neurobehavioral outcomes in an endovascular perforation model of SAH. JNJ16259685 improves cerebrovascular dysfunction through attenuation of cerebral blood flow (CBF) reduction, cerebral vasoconstrictio, and microthrombosis formation in a rat SAH model. Moreover, JNJ16259685 reduces experimental SAH-induced long-term neuronal damage through alleviation of neuronal death and degeneration. Mechanically, JNJ16259685 maintains phosphorylation of endothelial NO synthase (eNOS) and vasodilator-stimulated phosphoprotein (VASP) and decreases apoptosis-related factors Bax, active caspase-9, and active caspase-3 following experimental SAH. Altogether, our results suggest JNJ16259685 improves long-term functional impairment through neurovascular protection.

Scutellarin attenuates vasospasm through the Erk5-KLF2-eNOS pathway after subarachnoid hemorrhage in rats

Angiographic vasospasm, especially in the early phases (<72h) of subarachnoid hemorrhage (SAH), is one of the major complications after an aneurysm rupture and is often the cause of delayed neurological deterioration. Scutellarin (SCU), a flavonoid extracted from the traditional Chinese herb Erigeron breviscapus, has been widely accepted as an antioxidant, but the effect of SCU on vasospasm after SAH remains elusive. Endovascular perforation was conducted to induce SAH in Sprague-Dawley rats. Then, the underlying mechanism of the anti-vasospasm effect of SCU was investigated using a modified Garcia scale, India ink angiography, cross-sectional area analysis, immunohistochemistry staining and western blot. SCU (50μM, 100mg/kg) alleviated angiographic vasospasm and improved neurological function 48h after SAH and enhanced the expression of endothelial nitric oxide synthase (eNOS) at the intima of cerebral arteries. In addition, SCU upregulated the expression of phosphorylated extracellular-regulated kinase 5 (p-Erk5) and Kruppel-like factor 2 (KLF2) at 48h after SAH. However, the effects of SCU were reversed by the Erk5 inhibitor XMD8-92. Our results indicate that SCU could attenuate vasospasm and neurological deficits via modulating the Erk5-KLF2-eNOS pathway after SAH, which may provide an experimental basis for the clinical use of SCU treatment in SAH patients.

Signaling Pathway in Cerebral Vasospasm After Subarachnoid Hemorrhage: News Update

Subarachnoid hemorrhage (SAH) caused by ruptured intracranial aneurysms is a serious threat to human health and life. Although advances in surgical and anesthetic techniques have improved the prognosis of patients with aneurysms, the rate of death and disability caused by SAH remains high, predominantly due to cerebral vasospasm (CVS) after SAH and early brain damage. In particular, CVS is a common complication after SAH. However, its pathogenesis has not yet been fully elucidated, and clinically effective prevention and treatment measures are still lacking. Spasm of blood vessels can decrease cerebral blood flow, leading to ischemia and hypoxia in brain tissues and ultimately severe neurological dysfunction. Currently, there is no comprehensive theory that can fully explain the mechanisms underlying SAH-caused CVS. However, studies on signal transduction, apoptosis, and glial cell-mediated mechanisms in recent years have shed new light on the treatment of CVS.

Erythropoietin for the Treatment of Subarachnoid Hemorrhage: A Feasible Ingredient for a Successful Medical Recipe

Subarachnoid hemorrhage (SAH) following aneurysm bleeding accounts for 6% to 8% of all cerebrovascular accidents. Although an aneurysm can be effectively managed by surgery or endovascular therapy, delayed cerebral ischemia is diagnosed in a high percentage of patients resulting in significant morbidity and mortality. Cerebral vasospasm occurs in more than half of all patients after aneurysm rupture and is recognized as the leading cause of delayed cerebral ischemia after SAH. Hemodynamic strategies and endovascular procedures may be considered for the treatment of cerebral vasospasm. In recent years, the mechanisms contributing to the development of vasospasm, abnormal reactivity of cerebral arteries and cerebral ischemia following SAH, have been investigated intensively. A number of pathological processes have been identified in the pathogenesis of vasospasm, including endothelial injury, smooth muscle cell contraction from spasmogenic substances produced by the subarachnoid blood clots, changes in vascular responsiveness and inflammatory response of the vascular endothelium. To date, the current therapeutic interventions remain ineffective as they are limited to the manipulation of systemic blood pressure, variation of blood volume and viscosity and control of arterial carbon dioxide tension. In this scenario, the hormone erythropoietin (EPO) has been found to exert neuroprotective action during experimental SAH when its recombinant form (rHuEPO) is administered systemically. However, recent translation of experimental data into clinical trials has suggested an unclear role of recombinant human EPO in the setting of SAH. In this context, the aim of the current review is to present current evidence on the potential role of EPO in cerebrovascular dysfunction following aneurysmal subarachnoid hemorrhage.

Cerebral Vasospasm: A Review

Cerebral vasospasm is a prolonged but reversible narrowing of cerebral arteries beginning days after subarachnoid hemorrhage. Progression to cerebral ischemia is tied mostly to vasospasm severity, and its pathogenesis lies in artery encasement by blood clot, although the complex interactions between hematoma and surrounding structures are not fully understood. The delayed onset of vasospasm provides a potential opportunity for its prevention. It is disappointing that recent randomized, controlled trials did not demonstrate that the endothelin antagonist clazosentan, the cholesterol-lowering agent simvastatin, and the vasodilator magnesium sulfate improve patient outcome. Minimizing ischemia by avoiding inadequate blood volume and pressure, administering the calcium antagonist nimodipine, and intervention with balloon angioplasty, when necessary, constitutes current best management. Over the past two decades, our ability to manage vasospasm has led to a significant decline in patient morbidity and mortality from vasospasm, yet it still remains an important determinant of outcome after aneurysm rupture.

Memantine Attenuates Delayed Vasospasm after Experimental Subarachnoid Hemorrhage via Modulating Endothelial Nitric Oxide Synthase

Delayed cerebral vasospasm is an important pathological feature of subarachnoid hemorrhage (SAH). The cause of vasospasm is multifactorial. Impairs nitric oxide availability and endothelial nitric oxide synthase (eNOS) dysfunction has been reported to underlie vasospasm. Memantine, a low-affinity uncompetitive N-methyl-d-aspartate (NMDA) blocker has been proven to reduce early brain injury after SAH. This study investigated the effect of memantine on attenuation of vasospasm and restoring eNOS functionality. Male Sprague-Dawley rats weighing 350–450 g were randomly divided into three weight-matched groups, sham surgery, SAH + vehicle, and SAH + memantine groups. The effects of memantine on SAH were evaluated by assessing the severity of vasospasm and the expression of eNOS. Memantine effectively ameliorated cerebral vasospasm by restoring eNOS functionality. Memantine can prevent vasospasm in experimental SAH. Treatment strategies may help combat SAH-induced vasospasm in the future.

Erythropoietin increases bioavailability of tetrahydrobiopterin and protects cerebral microvasculature against oxidative stress induced by eNOS uncoupling

This study was designed to determine whether treatment with erythropoietin (EPO) could protect cerebral microvasculature against the pathological consequences of endothelial nitric oxide (NO) synthase uncoupling. Wild-type and GTP cyclohydrolase I (GTPCH-I)-deficient hph1 mice were administered EPO (1000 U/kg/day, s.c., 3 days). Cerebral microvessels of hph1 mice demonstrated reduced tetrahydrobiopterin (BH4) bioavailability, increased production of superoxide anions and impaired endothelial NO signaling. Treatment of hph1 mice with EPO attenuated the levels of 7,8-dihydrobiopterin, the oxidized product of BH4, and significantly increased the ratio of BH4 to 7,8-dihydrobiopterin. Moreover, EPO decreased the levels of superoxide anions and increased NO bioavailability in cerebral microvessels of hph1 mice. Attenuated oxidation of BH4 and inhibition of endothelial NO synthase uncoupling were explained by the increased expression of antioxidant proteins, manganese superoxide dismutase, and catalase. The protective effects of EPO observed in cerebral microvessels of hph1 mice were also observed in GTPCH-I siRNA-treated human brain microvascular endothelial cells exposed to EPO (1 U/mL or 10 U/mL; 3 days). Our results suggest that EPO might protect the neurovascular unit against oxidative stress by restoring bioavailability of BH4 and endothelial NO in the cerebral microvascular endothelium. We demonstrate that treatment with erythropoietin (EPO) could protect cerebral microvasculature against the pathological consequences of endothelial nitric oxide (NO) synthase uncoupling. Our results suggest that EPO might protect the neurovascular unit against oxidative stress by restoring bioavailability of tetrahydrobiopterin (BH4) and endothelial nitric oxide.

The comparative effects of recombinant human erythropoietin and darbepoetin-alpha on cerebral vasospasm following experimental subarachnoid hemorrhage in the rabbit

BACKGROUND

Darbepoetin alpha is a hypersialylated analogue of erythropoietin effective for activating erythropoietin-receptors. This study investigated the vasodilator and neuroprotective effects of darbepoetin alpha on an experimental subarachnoid hemorrhage model and compared it with erythropoietin.

METHODS

Forty adult male New Zealand white rabbits were randomly divided into four groups of ten rabbits each: group 1 (control), group 2 (subarachnoid hemorrhage), group 3 (erythropoietin), and group 4 (darbepoetin alpha). Recombinant human erythropoietin was administered at a dose of 1,000 U/kg intraperitoneally after the induction of subarachnoid hemorrhage and continued every 8 h up to 72 h. Darbepoetin alpha was administered at a single intraperitoneal dose of 30 μg/kg. Animals were killed 72 h after subarachnoid hemorrhage. Basilar artery cross-sectional areas, arterial wall thicknesses, hippocampal degeneration scores and biochemical analyses were measured in all groups.

RESULTS

Both erythropoietin and darbepoetin alpha treatments were found to attenuate cerebral vasospasm and provide neuroprotection after subarachnoid hemorrhage in rabbits. Darbepoetin alpha revealed better morphometric and histopathological results than erythropoietin among experimental subarachnoid hemorrhage-induced vasospasm.

CONCLUSIONS

Our findings, for the first time, showed that darbepoetin alpha can prevent vasospasm and provides neuroprotection following experimental subarachnoid hemorrhage. Moreover, darbepoetin alpha showed better results when compared with erythropoietin.

Role of Akt signaling pathway in delayed cerebral vasospasm after subarachnoid hemorrhage in rats

BACKGROUND

Akt plays an important role in cell survival, proliferation, apoptosis and other activities. It also has been involved in maintaining smooth muscle cell contraction phenotypes in vitro and in vivo. Recent studies have focused on the inhibition of Akt in acute vasospasm and neuronal apoptosis after subarachnoid hemorrhage (SAH). However, its role in delayed cerebral vasospasm (DCVS) has not been reported.

METHODS

In this study, using a "two-hemorrhage" rat model of SAH, we examined the expression of p-Akt and the formation of vasospasm in the basilar arteries. To investigate the possible role of Akt in phenotypic switching, we performed immunohistochemical staining to examine expressions of SMα-actin and proliferating cell nuclear antigen (PCNA), markers of smooth muscle phenotypic switching.

RESULTS

We found that the basilar arteries exhibited vasospasm after SAH and that vasospasm became most severe on day 7 after SAH. Elevated protein expression of p-Akt was detected 4 days after SAH induction, peaked on day 7, and recovered on day 21, which was in a parallel time course to the development of DCVS. Moreover, results of immunohistochemical staining revealed enhanced expression of PCNA but gradual reduction in expression of SMα-actin from day 1 to day 7 after SAH; then, the expressions of PCNA and SMα-actin gradually recovered until day 21.

CONCLUSIONS

These results support a novel mechanism in which the Akt signaling pathway plays an important role in the proliferation of smooth muscle cells (SMCs) rather than inducing phenotype switching in basilar arteries, which promotes the development of DCVS after SAH.

Nitric oxide in cerebral vasospasm: theories, measurement, and treatment

In recent decades, a large body of research has focused on the role of nitric oxide (NO) in the development of cerebral vasospasm (CV) following subarachnoid hemorrhage (SAH). Literature searches were therefore conducted regarding the role of NO in cerebral vasospasm, specifically focusing on NO donors, reactive nitrogen species, and peroxynitrite in manifestation of vasospasm. Based off the assessment of available evidence, two competing theories are reviewed regarding the role of NO in vasospasm. One school of thought describes a deficiency in NO due to scavenging by hemoglobin in the cisternal space, leading to an NO signaling deficit and vasospastic collapse. A second hypothesis focuses on the dysfunction of nitric oxide synthase, an enzyme that synthesizes NO, and subsequent generation of reactive nitrogen species. Both theories have strong experimental evidence behind them and hold promise for translation into clinical practice. Furthermore, NO donors show definitive promise for preventing vasospasm at the angiographic and clinical level. However, NO augmentation may also cause systemic hypotension and worsen vasospasm due to oxidative distress. Recent evidence indicates that targeting NOS dysfunction, for example, through erythropoietin or statin administration, also shows promise at preventing vasospasm and neurotoxicity. Ultimately, the role of NO in neurovascular disease is complex. Neither of these theories is mutually exclusive, and both should be considered for future research directions and treatment strategies.

Genetics of cerebral vasospasm

Cerebral vasospasm (CV) is a major source of morbidity and mortality in aneurysmal subarachnoid hemorrhage (aSAH). It is thought that an inflammatory cascade initiated by extravasated blood products precipitates CV, disrupting vascular smooth muscle cell function of major cerebral arteries, leading to vasoconstriction. Mechanisms of CV and modes of therapy are an active area of research. Understanding the genetic basis of CV holds promise for the recognition and treatment for this devastating neurovascular event. In our review, we summarize the most recent research involving key areas within the genetics and vasospasm discussion: (1) Prognostic role of genetics—risk stratification based on gene sequencing, biomarkers, and polymorphisms; (2) Signaling pathways—pinpointing key inflammatory molecules responsible for downstream cellular signaling and altering these mediators to provide therapeutic benefit; and (3) Gene therapy and gene delivery—using viral vectors or novel protein delivery methods to overexpress protective genes in the vasospasm cascade.

17β-Estradiol attenuates secondary injury through activation of Akt signaling via estrogen receptor alpha in rat brain following subarachnoid hemorrhage

BACKGROUND

Apoptosis is implicated in vasospasm and the long-term sequelae of subarachnoid hemorrhage (SAH). This study tested the hypothesis that attenuation of SAH-induced apoptosis after 17β-estradiol (E2) treatment is associated with an increase in phosphorylation of Akt via estrogen receptor-α (ER-α) in rats.

MATERIALS AND METHODS

We examined the expression of phospho-Akt, ERα and ERβ, and apoptosis in cerebral cortex, hippocampus, and dentate gyrus in a two-hemorrhage SAH model in rats. We subcutaneously implanted other rats with a silicone rubber tube containing E2; they received daily injections of nonselective estrogen receptor antagonist (ICI 182,780), selective ERα-selective antagonist (methyl-piperidino-pyrazole), or ERβ-selective antagonist (R,R-tetrahydrochrysene) after the first hemorrhage.

RESULTS

At 7 d after the first SAH, protein levels of phospho-Akt and ERα were significantly decreased and caspase-3 was significantly increased in the dentate gyrus. The cell death assay revealed that DNA fragmentation was significantly increased in the dentate gyrus. Those actions were reversed by E2 and blocked by ICI 182,780 and methyl-piperidino-pyrazole, but not R,R-tetrahydrochrysene. However, there were no significant changes in the expression of the protein levels of phospho-Akt, ERα, ERβ, and caspase-3, and DNA fragmentation after SAH.

CONCLUSIONS

The present study shows that a beneficial effect of E2 in attenuating SAH-induced apoptosis is associated with activation of the expression of phospho-Akt and ERα, and alteration in caspase-3 protein expression via an ERα-dependent mechanism in the dentate gyrus. These data support further the investigation of E2 in the treatment of SAH in humans.

Statins and anti-inflammatory therapies for subarachnoid hemorrhage

OPINION STATEMENT

Aneurysmal subarachnoid hemorrhage (SAH) induces a potent inflammatory cascade that contributes to endothelial dysfunction, imbalance of vasoactive substances (excess endothelin, depletion of nitric oxide), and arterial vasospasm. This process results in delayed cerebral ischemia, a major cause of neurologic disability in those surviving the initial hemorrhage. The only therapy shown to be effective in improving neurologic outcomes after SAH is a calcium-channel antagonist, nimodipine (although it achieved this result without reducing vasospasm). A number of novel therapies have been explored to inhibit the development of vasospasm and reduce the burden of ischemia and cerebral infarction. Statins are promising candidates, as they block multiple aspects of the inflammatory pathway that contributes to ischemic brain injury. Early clinical trials have produced conflicting results, however, and the adoption of statins in clinical practice should await the results of larger, more definitive studies. Though endothelin-receptor antagonists showed promise in significantly reducing vasospasm in preliminary trials, their failure to improve clinical outcomes in phase 3 studies has been disappointing, highlighting the complex link between vasospasm and ischemia. Future directions in the quest to improve outcomes of patients with SAH may need to approach ischemia as a multifactorial process with inflammatory, vasoactive, and ionic/metabolic components.

Pharmacologic reduction of angiographic vasospasm in experimental subarachnoid hemorrhage: systematic review and meta-analysis

Animal models have been developed to simulate angiographic vasospasm secondary to subarachnoid hemorrhage (SAH) and to test pharmacologic treatments. Our aim was to evaluate the effect of pharmacologic treatments that have been tested in humans and in preclinical studies to determine if animal models inform results reported in humans. A systematic review and meta-analysis of SAH studies was performed. We investigated predictors of translation from animals to humans with multivariate logistic regression. Pharmacologic reduction of vasospasm was effective in mice, rats, rabbits, dogs, nonhuman primates (standard mean difference of -1.74; 95% confidence interval -2.04 to -1.44) and humans. Animal studies were generally of poor methodologic quality and there was evidence of publication bias. Subgroup analysis by drug and species showed that statins, tissue plasminogen activator, erythropoietin, endothelin receptor antagonists, calcium channel antagonists, fasudil, and tirilazad were effective whereas magnesium was not. Only evaluation of vasospasm >3 days after SAH was independently associated with successful translation. We conclude that reduction of vasospasm is effective in animals and humans and that evaluation of vasospasm >3 days after SAH may be preferable for preclinical models.

High dose erythropoietin increases brain tissue oxygen tension in severe vasospasm after subarachnoid hemorrhage

Background

Vasospasm-related delayed cerebral ischemia (DCI) significantly impacts on outcome after aneurysmal subarachnoid hemorrhage (SAH). Erythropoietin (EPO) may reduce the severity of cerebral vasospasm and improve outcome, however, underlying mechanisms are incompletely understood. In this study, the authors aimed to investigate the effect of EPO on cerebral metabolism and brain tissue oxygen tension (P_btO₂).

Methods

Seven consecutive poor grade SAH patients with multimodal neuromonitoring (MM) received systemic EPO therapy (30.000 IU per day for 3 consecutive days) for severe cerebral vasospasm. Cerebral perfusion pressure (CPP), mean arterial blood pressure (MAP), intracranial pressure (ICP), P_btO₂ and brain metabolic changes were analyzed during the next 24 hours after each dose given. Statistical analysis was performed with a mixed effects model.

Results

A total of 22 interventions were analyzed. Median age was 47 years (32–68) and 86 % were female. Three patients (38 %) developed DCI. MAP decreased 2 hours after intervention (P < 0.04) without significantly affecting CPP and ICP. P_btO₂ significantly increased over time (P < 0.05) to a maximum of 7 ± 4 mmHg increase 16 hours after infusion. Brain metabolic parameters did not change over time.

Conclusions

EPO increases P_btO₂ in poor grade SAH patients with severe cerebral vasospasm. The effect on outcome needs further investigation.

Erythropoietin prevents sepsis-related acute kidney injury in rats by inhibiting NF-κB and upregulating endothelial nitric oxide synthase

The pathophysiology of sepsis involves complex cytokine and inflammatory mediator networks, a mechanism to which NF-κB activation is central. Downregulation of endothelial nitric oxide synthase (eNOS) contributes to sepsis-induced endothelial dysfunction. Erythropoietin (EPO) has emerged as a major tissue-protective cytokine in the setting of stress. We investigated the role of EPO in sepsis-related acute kidney injury using a cecal ligation and puncture (CLP) model. Wistar rats were divided into three primary groups: control (sham-operated); CLP; and CLP+EPO. EPO (4,000 IU/kg body wt ip) was administered 24 and 1 h before CLP. Another group of rats received N-nitro-l-arginine methyl ester (l-NAME) simultaneously with EPO administration (CLP+EPO+l-NAME). A fifth group (CLP+EPOtreat) received EPO at 1 and 4 h after CLP. At 48 h postprocedure, CLP+EPO rats presented significantly higher inulin clearance than did CLP and CLP+EPO+l-NAME rats; hematocrit levels, mean arterial pressure, and metabolic balance remained unchanged in the CLP+EPO rats; and inulin clearance was significantly higher in CLP+EPOtreat rats than in CLP rats. At 48 h after CLP, creatinine clearance was significantly higher in the CLP+EPO rats than in the CLP rats. In renal tissue, pre-CLP EPO administration prevented the sepsis-induced increase in macrophage infiltration, as well as preserving eNOS expression, EPO receptor (EpoR) expression, IKK-α activation, NF-κB activation, and inflammatory cytokine levels, thereby increasing survival. We conclude that this protection, which appears to be dependent on EpoR activation and on eNOS expression, is attributable, in part, to inhibition of the inflammatory response via NF-κB downregulation.

Effects of continuous erythropoietin receptor activator in sepsis-induced acute kidney injury and multi-organ dysfunction

BACKGROUND

Despite advances in supportive care, sepsis-related mortality remains high, especially in patients with acute kidney injury (AKI). Erythropoietin can protect organs against ischemia and sepsis. This effect has been linked to activation of intracellular survival pathways, although the mechanism remains unclear. Continuous erythropoietin receptor activator (CERA) is an erythropoietin with a unique pharmacologic profile and long half-life. We hypothesized that pretreatment with CERA would be renoprotective in the cecal ligation and puncture (CLP) model of sepsis-induced AKI.

METHODS

RATS WERE RANDOMIZED INTO THREE GROUPS: control; CLP; and CLP+CERA (5 µg/kg body weight, i.p. administered 24 h before CLP). At 24 hours after CLP, we measured creatinine clearance, biochemical variables, and hemodynamic parameters. In kidney tissue, we performed immunoblotting--to quantify expression of the Na-K-2Cl cotransporter (NKCC2), aquaporin 2 (AQP2), Toll-like receptor 4 (TLR4), erythropoietin receptor (EpoR), and nuclear factor kappa B (NF-κB)--and immunohistochemical staining for CD68 (macrophage infiltration). Plasma interleukin (IL)-2, IL-1β, IL-6, IL-10, interferon gamma, and tumor necrosis factor alpha were measured by multiplex detection.

RESULTS

Pretreatment with CERA preserved creatinine clearance and tubular function, as well as the expression of NKCC2 and AQP2. In addition, CERA maintained plasma lactate at normal levels, as well as preserving plasma levels of transaminases and lactate dehydrogenase. Renal expression of TLR4 and NF-κB was lower in CLP+CERA rats than in CLP rats (p<0.05 and p<0.01, respectively), as were CD68-positive cell counts (p<0.01), whereas renal EpoR expression was higher (p<0.05). Plasma levels of all measured cytokines were lower in CLP+CERA rats than in CLP rats.

CONCLUSION

CERA protects against sepsis-induced AKI. This protective effect is, in part, attributable to suppression of the inflammatory response.

Role of calcitonin gene-related peptide in cerebral vasospasm, and as a therapeutic approach to subarachnoid hemorrhage

Calcitonin gene-related peptide (CGRP) is one of the most potent microvascular vasodilators identified to date. Vascular relaxation and vasodilation is mediated via activation of the CGRP receptor. This atypical receptor is made up of a G protein-coupled receptor called calcitonin receptor-like receptor (CLR), a single transmembrane protein called receptor activity-modifying protein (RAMP), and an additional protein that is required for Ga(s) coupling, known as receptor component protein (RCP). Several mechanisms involved in CGRP-mediated relaxation have been identified. These include nitric oxide (NO)-dependent endothelium-dependent mechanisms or cAMP-mediated endothelium-independent pathways; the latter being more common. Subarachnoid hemorrhage (SAH) is associated with cerebral vasoconstriction that occurs several days after the hemorrhage and is often fatal. The vasospasm occurs in 30-40% of patients and is the major cause of death from this condition. The vasoconstriction is associated with a decrease in CGRP levels in nerves and an increase in CGRP levels in draining blood, suggesting that CGRP is released from nerves to oppose the vasoconstriction. This evidence has led to the concept that exogenous CGRP may be beneficial in a condition that has proven hard to treat. The present article reviews: (a) the pathophysiology of delayed ischemic neurologic deficit after SAH (b) the basics of the CGRP receptor structure, signal transduction, and vasodilatation mechanisms and (c) the studies that have been conducted so far using CGRP in both animals and humans with SAH.

Erythropoietin and hypoxia increase erythropoietin receptor and nitric oxide levels in lung microvascular endothelial cells

Acute lung exposure to low oxygen results in pulmonary vasoconstriction and redistribution of blood flow. We used human microvascular endothelial cells from lung (HMVEC-L) to study the acute response to oxygen stress. We observed that hypoxia and erythropoietin (EPO) increased erythropoietin receptor (EPOR) gene expression and protein level in HMVEC-L. In addition, EPO dose- and time-dependently stimulated nitric oxide (NO) production. This NO stimulation was evident despite hypoxia induced reduction of endothelial NO synthase (eNOS) gene expression. Western blot of phospho-eNOS (serine1177) and eNOS and was significantly induced by hypoxia but not after EPO treatment. However, iNOS increased at hypoxia and with EPO stimulation compared to normal oxygen tension. In accordance with our previous results of NO induction by EPO at low oxygen tension in human umbilical vein endothelial cells and bone marrow endothelial cells, these results provide further evidence in HMVEC-L for EPO regulation of NO production to modify the effects of hypoxia and cause compensatory vasoconstriction.

Endothelial nitric oxide synthase mediates endogenous protection against subarachnoid hemorrhage-induced cerebral vasospasm

BACKGROUND AND PURPOSE

Vasospasm-induced delayed cerebral ischemia remains a major source of morbidity in patients with aneurysmal subarachnoid hemorrhage (SAH). We hypothesized that activating innate neurovascular protective mechanisms by preconditioning (PC) may represent a novel therapeutic approach against SAH-induced vasospasm and neurological deficits and, secondarily, that the neurovascular protection it provides is mediated by endothelial nitric oxide synthase (eNOS).

METHODS

Wild-type mice were subjected to hypoxic PC or normoxia followed 24 hours later by SAH. Neurological function was analyzed daily; vasospasm was assessed on post-surgery Day 2. Nitric oxide availability, eNOS expression, and eNOS activity were also assessed. In a separate experiment, wild-type and eNOS-null mice were subjected to hypoxic PC or normoxia followed by SAH and assessed for vasospasm and neurological deficits.

RESULTS

PC nearly completely prevented SAH-induced vasospasm and neurological deficits. It also prevented SAH-induced reduction in nitric oxide availability and increased eNOS activity in mice with and without SAH. PC-induced protection against vasospasm and neurological deficits was lost in wild-type mice treated with the nitric oxide synthase inhibitor N(G)-nitro-l-arginine methyl ester and in eNOS-null mice.

CONCLUSIONS

Endogenous protective mechanisms against vasospasm exist, are powerful, and can be induced by PC. eNOS-derived nitric oxide is a critical mediator of PC-induced neurovascular protection. These data provide strong "proof-of-principle" evidence that PC represents a promising new strategy to reduce vasospasm and delayed cerebral ischemia after SAH.

Advances in experimental subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) remains to be a devastating disease with high mortality and morbidity. Two major areas are becoming the focus of the research interest of SAH: these are cerebral vasospasm (CVS) and early brain injury (EBI). This mini review will provide a broad summary of the major advances in experimental SAH during the last 3 years. Treatments interfering with nitric oxide (NO)- or endothelin-pathways continue to show antispasmotic effects in experimental SAH. HIF 1 may play both a detrimental and beneficial role in the setting of SAH, depending on its activation stage. Inflammation and oxidative stress contribute to the pathophysiology of both CVS and EBI. Apoptosis, a major component of EBI after SAH, also underlie the etiology of CVS. Since we recognize now that CVS and EBI are the two major contributors to the significant mortality and morbidity associated with SAH, ongoing research will continue to elucidate the underlying pathophysiological pathways and treatment strategies targeting both CVS and EBI may be more successful and improve outcome of patients with SAH.

Uncoupling of endothelial nitric oxide synthase after experimental subarachnoid hemorrhage

We studied whether endothelial nitric oxide synthase (eNOS) is upregulated and uncoupled in large cerebral arteries after subarachnoid hemorrhage (SAH) and also whether this causes cerebral vasospasm in a mouse model of anterior circulation SAH. Control animals underwent injection of saline instead of blood (n=16 SAH and n=16 controls). There was significant vasospasm of the middle cerebral artery 2 days after SAH (lumen radius/wall thickness ratio 4.3 ± 1.3 for SAH, 23.2 ± 2.1 for saline, P<0.001). Subarachnoid hemorrhage was associated with terminal deoxynucleotidyl transferase dUTP nick-end labeling, cleaved caspase-3, and Fluoro-Jade-positive neurons in the cortex and with CA1 and dentate regions in the hippocampus. There were multiple fibrinogen-positive microthromboemboli in the cortex and hippocampus after SAH. Transgenic mice expressing lacZ under control of the eNOS promoter had increased X-gal staining in large arteries after SAH, and this was confirmed by the increased eNOS protein on western blotting. Evidence that eNOS was uncoupled was found in that nitric oxide availability was decreased, and superoxide and peroxynitrite concentrations were increased in the brains of mice with SAH. This study suggests that artery constriction by SAH upregulates eNOS but that it is uncoupled and produces peroxynitrite that may generate microemboli that travel distally and contribute to brain injury.

Dose-dependent ultrastructural and morphometric alterations after erythropoietin treatment in rat femoral artery vasospasm model

PURPOSE

Cerebral vasospasm is the common cause of poor outcome after aneurysmal subarachnoid hemorrhage (aSAH). Although many agents are experimentally and clinicaly used to protect or recover from vasospasm, an effective neurotherapeutic drug is still missing. Erythropoietin (EPO) is recently a promising candidate. The aim of this study is to investigate the dose-dependent effects of recombinant human EPO (rhEPO) on arterial wall in a rat femoral artery vasospasm model.

METHODS

Thirty two animals were divided into four groups: vasospasm without any treatment (group A), vasospasm +250 IU/kg rhEPO group (group B), vasospasm +500 IU/kg rhEPO group (group C), and control group (group D). Rat femoral artery vasospasm model was used. For groups B and C, 7 days of 250 IU/kg and 500 IU/kg intraperitoneal rhEPO in 0.3 ml saline were administered respectively; and for groups A and D, 0.3 ml saline were administered intraperitoneally without any treatment. After 7 days, histological and morphometric analyses were carried out.

RESULTS

Vasospasm alone group demonstrated the highest vessel wall thicknesses, comparing to other groups (p < 0.001). While for groups B and C, vessel wall thickness values were significantly higher than the control group (p < 0.001), between these two groups, there was no significant difference achieved (p > 0.05).

CONCLUSION

In our study, there was no significant difference between the two rhEPO treatment groups, but rhEPO treatment was shown to be histologically and morphometrically effective in vasospasm. However, if dosage of EPO treatment is augmented, successful results may be achieved.

Erythropoietin as neuroprotective and neuroregenerative treatment strategy: comprehensive overview of 12 years of preclinical and clinical research

Erythropoietin (EPO), originally discovered as hematopoietic growth factor, has direct effects on cells of the nervous system that make it a highly attractive candidate drug for neuroprotection/neuroregeneration. Hardly any other compound has led to so much preclinical work in the field of translational neuroscience than EPO. Almost all of the >180 preclinical studies performed by many independent research groups from all over the world in the last 12 years have yielded positive results on EPO as a neuroprotective drug. The fact that EPO was approved for the treatment of anemia >20 years ago and found to be well tolerated and safe, facilitated the first steps of translation from preclinical findings to the clinic. On the other hand, the same fact, naturally associated with loss of patent protection, hindered to develop EPO as a highly promising therapeutic strategy for application in human brain disease. Therefore, only few clinical neuroprotection studies have been concluded, all with essentially positive and stimulating results, but no further development towards the clinic has occurred thus far. This article reviews the preclinical and clinical work on EPO for the indications neuroprotection/neuroregeneration and cognition, and hopefully will stimulate new endeavours promoting development of EPO for the treatment of human brain diseases.

Modification of endothelial nitric oxide synthase through AMPK after experimental subarachnoid hemorrhage

Severe subarachnoid hemorrhage (SAH) induces dysfunction of endothelial nitric oxide synthase (eNOS), resulting in severe vasospasm. Clinically, however, some portions of cerebral arteries may show only mild vasospasm. Although severe vasospastic arteries after SAH have been intensively studied, activity of eNOS associated with the mild form of the disease has received less attention. The purpose of the present study was to clarify molecular mechanisms underlying the regulation of eNOS activity in mild vasospastic arteries after SAH. In a rat single-hemorrhage model, basilar arteries were obtained up to 7 days after SAH. Western blot analysis was used to study the temporal profiles of eNOS, phosphorylated (p)-eNOS at Ser(1177) or Thr(495), inducible NOS (iNOS), AMP-activated protein kinase alpha (AMPK alpha, p-AMPK alpha at Thr(172)Akt, p-Akt at Ser(473), cyclic AMP-dependent protein kinase (PKA), and p-PKA at Thr(197) in basilar arteries. Immunohistochemical studies were performed to examine the spatial expression patterns of p-eNOS at Ser(1177) and p-AMPK alpha at Thr(172). Western blot analysis showed eNOS to be significantly phosphorylated at Ser(1177) from 1 to 2 days after SAH, accompanied by upregulation of iNOS and AMPK, while activation states of Akt and PKA did not show significant change. Immunohistochemistry revealed phosphorylation of eNOS and AMPK alpha in endothelial cells of the basilar artery. SAH might thus induce temporary activation of AMPK alpha, which phosphorylates eNOS at Ser(1177) in endothelial cells of mild vasospastic basilar arteries. This signal transduction may play an important role in controlling cerebral blood flow after SAH.

Erythropoietin 2nd cerebral protection after acute injuries: a double-edged sword?

Over the past 15 years, a large body of evidence has revealed that the cytokine erythropoietin exhibits non-erythropoietic functions, especially tissue-protective effects. The discovery of EPO and its receptors in the central nervous system and the evidence that EPO is made locally in response to injury as a protective factor in the brain have raised the possibility that recombinant human EPO (rhEPO) could be administered as a cytoprotective agent after acute brain injuries. This review highlights the potential applications of rhEPO as a neuroprotectant in experimental and clinical settings such as ischemia, traumatic brain injury, and subarachnoid and intracerebral hemorrhage. In preclinical studies, EPO prevented apoptosis, inflammation, and oxidative stress induced by injury and exhibited strong neuroprotective and neurorestorative properties. EPO stimulates vascular repair by facilitating endothelial progenitor cell migration into the brain and neovascularisation, and it promotes neurogenesis. In humans, small clinical trials have shown promising results but large prospective randomized studies failed to demonstrate a benefit of EPO for brain protection and showed unwanted side effects, especially thrombotic complications. Recently, regions have been identified within the EPO molecule that mediate tissue protection, allowing the development of non-erythropoietic EPO variants for neuroprotection conceptually devoid of side effects. The efficacy and the safety profile of these new compounds are still to be demonstrated to obtain, in patients, the benefits observed in experimental studies.

Differential modulation of angiogenesis by erythropoiesis-stimulating agents in a mouse model of ischaemic retinopathy

BACKGROUND

Erythropoiesis stimulating agents (ESAs) are widely used to treat anaemia but concerns exist about their potential to promote pathological angiogenesis in some clinical scenarios. In the current study we have assessed the angiogenic potential of three ESAs; epoetin delta, darbepoetin alfa and epoetin beta using in vitro and in vivo models.

METHODOLOGY/PRINCIPAL FINDINGS

The epoetins induced angiogenesis in human microvascular endothelial cells at high doses, although darbepoetin alfa was pro-angiogenic at low-doses (1-20 IU/ml). ESA-induced angiogenesis was VEGF-mediated. In a mouse model of ischaemia-induced retinopathy, all ESAs induced generation of reticulocytes but only epoetin beta exacerbated pathological (pre-retinal) neovascularisation in comparison to controls (p<0.05). Only epoetin delta induced a significant revascularisation response which enhanced normality of the vasculature (p<0.05). This was associated with mobilisation of haematopoietic stem cells and their localisation to the retinal vasculature. Darbepoetin alfa also increased the number of active microglia in the ischaemic retina relative to other ESAs (p<0.05). Darbepoetin alfa induced retinal TNFalpha and VEGF mRNA expression which were up to 4 fold higher than with epoetin delta (p<0.001).

CONCLUSIONS

This study has implications for treatment of patients as there are clear differences in the angiogenic potential of the different ESAs.

Erythropoietin in combination of tissue plasminogen activator exacerbates brain hemorrhage when treatment is initiated 6 hours after stroke

BACKGROUND AND PURPOSE

Erythropoietin (EPO), a hematopoietic cytokine, exerts neuroprotective effects in experimental stroke. In the present study, we investigated the effect of recombinant human EPO (rhEPO) in combination with tissue plasminogen activator (tPA) on embolic stroke.

METHODS

Rats subjected to embolic middle cerebral artery occlusion (MCAO) were treated with rhEPO (5000 U/kg) in combination with tPA (10 mg/kg) at 2 or 6 hours after MCAO. Control groups consisted of ischemic rats treated with rhEPO (5000 U/kg) alone, tPA (10 mg/kg) alone, or saline at 2 or 6 hours after MCAO.

RESULTS

The combination therapy of rhEPO and tPA initiated 6 hours after MCAO did not reduce the ischemic lesion volume and significantly (P<0.05) increased the incidence of brain hemorrhage measured by frequency of gross hemorrhage and a quantitative spectrophotometric hemoglobin assay compared with rats treated with rhEPO alone and tPA alone. However, when the combination therapy was initiated 2 hours after MCAO, the treatment significantly (P<0.05) reduced the lesion volume and did not substantially increase the incidence of hemorrhagic transformation compared with saline-treated rats. Immunostaining analysis revealed that the combination therapy of rhEPO and tPA at 6 hours significantly (P<0.05) increased matrix metalloproteinase-9, NF-kappaB, and interleukin-1 receptor-associated kinase-1 immunoreactive cerebral vessels compared with rats treated with rhEPO alone and saline.

CONCLUSIONS

EPO exacerbates tPA-induced brain hemorrhage without reduction of ischemic brain damage when administered 6 hours after stroke in a rat model of embolic MCAO and that matrix metalloproteinase-9, NF-kappaB, and interleukin-1 receptor-associated kinase-1 upregulated by the delayed combination therapy may contribute to augmentation of brain hemorrhage.

Erythropoietin increases expression and function of vascular copper- and zinc-containing superoxide dismutase

Previous studies have shown that treatment with erythropoietin (EPO) exerts vascular protective effects. The exact mechanisms responsible for these effects are not completely understood. In the present study, we hypothesized that EPO stimulates expression and activity of copper- and zinc-containing superoxide dismutase (SOD1), thus protecting vascular tissue from oxidative stress induced by excessive concentrations of superoxide anions. EPO treatment of wild-type mice for 2 weeks (1000 U/kg, SC, biweekly) significantly increased aortic expression of SOD1. This effect resulted in a significant reduction of superoxide anion concentrations in aorta of treated mice. The ability of EPO to reduce vascular production of superoxide anions was abolished in SOD1-deficient mice. In a mouse model of wire-induced injury of the common carotid artery, treatment of wild-type mice with EPO prevented pathological remodeling, whereas the vascular effect of EPO was absent in SOD1-deficient mice. Our findings demonstrate that treatment with EPO increases vascular expression of SOD1. This effect appears to be an important molecular mechanism underlying vascular protection by EPO.

Cardiovascular effects of erythropoietin an update

Erythropoietin (EPO) is a therapeutic product of recombinant DNA technology and it has been in clinical use as stimulator of erythropoiesis over the last two decades. Identification of EPO and its receptor (EPOR) in the cardiovascular system expanded understanding of physiological and pathophysiological role of EPO. In experimental models of cardiovascular and cerebrovascular disorders, EPO exerts protection either by preventing apoptosis of cardiac myocytes, smooth muscle cells, and endothelial cells, or by increasing endothelial production of nitric oxide. In addition, EPO stimulates mobilization of progenitor cells from bone marrow thereby accelerating repair of injured endothelium and neovascularization. A novel signal transduction pathway involving EPOR--β-common heteroreceptor is postulated to enhance EPO-mediated tissue protection. A better understanding of the role of β-common receptor signaling as well as development of novel analogs of EPO with enhanced nonhematopoietic protective effects may expand clinical application of EPO in prevention and treatment of cardiovascular and cerebrovascular disorders.

Brain-derived neurotrophic factor stimulates production of prostacyclin in cerebral arteries

BACKGROUND AND PURPOSE

The role of brain-derived neurotrophic factor (BDNF) and its receptor, tropomyosin receptor kinase B, in control of cerebral circulation is poorly understood. The present study was designed to investigate the cerebral vascular effects of BDNF in vivo.

METHODS

Replication incompetent adenovirus encoding either rat BDNF (AdBDNF) or green fluorescent protein was injected intracisternally into rabbits. Forty-eight hours later, animals were euthanized. Plasma and cerebrospinal fluid levels of BDNF were measured by enzyme-linked immunosorbent assay, vasomotor function of isolated basilar arteries was studied in organ chambers, protein expression in the basilar arteries was studied by Western blotting, prostanoid levels were measured by enzyme-linked immunosorbent assay, and cyclic adenosine 3',5'-monophosphate levels were measured by radioimmunoassay.

RESULTS

The levels of BDNF in the cerebrospinal fluid were significantly elevated in AdBDNF-treated rabbits as compared with adenovirus encoding green fluorescent protein-treated rabbits (37+/-5 ng/mL versus 0.006+/-0.003 ng/mL, respectively; P<0.05; n=14). Western blotting studies revealed that in basilar arteries, AdBDNF increased protein expression of prostacyclin synthase, whereas expression of endothelial nitric oxide synthase and phosphorylated (Ser 1177) endothelial nitric oxide synthase remained unchanged. During incubation with arachidonic acid (1 micromol/L), PGI(2) production and levels of cyclic adenosine 3',5'-monophosphate were significantly elevated only in AdBDNF-treated rabbit basilar arteries (P<0.05, n=6). Relaxations to acetylcholine (10(-9) to 10(-5) mol/L) and arachidonic acid (10(-9) to 10(-5) mol/L) were significantly potentiated in basilar arteries from rabbits injected with AdBDNF. Potentiation of relaxations to acetylcholine in AdBDNF-treated basilar arteries was inhibited by the nonselective cyclooxygenase inhibitor, indomethacin (10(-5) mol/L, P<0.05, n=6) and constitutive phospholipase A(2) inhibitor, AACOCF3 (2x10(-5) mol/L, P<0.05, n=5).

CONCLUSIONS

Our results demonstrate that in cerebral arteries, BDNF-induced activation of tropomyosin receptor kinase B receptor signaling in vivo promotes prostacyclin biosynthesis. These findings provide novel mechanistic insight into the vascular protective effect of BDNF in cerebral circulation.

Erythropoietin: a multimodal neuroprotective agent

The tissue protective functions of the hematopoietic growth factor erythropoietin (EPO) are independent of its action on erythropoiesis. EPO and its receptors (EPOR) are expressed in multiple brain cells during brain development and upregulated in the adult brain after injury. Peripherally administered EPO crosses the blood-brain barrier and activates in the brain anti-apoptotic, anti-oxidant and anti-inflammatory signaling in neurons, glial and cerebrovascular endothelial cells and stimulates angiogenesis and neurogenesis. These mechanisms underlie its potent tissue protective effects in experimental models of stroke, cerebral hemorrhage, traumatic brain injury, neuroinflammatory and neurodegenerative disease. The preclinical data in support of the use of EPO in brain disease have already been translated to first clinical pilot studies with encouraging results with the use of EPO as a neuroprotective agent.

Erythropoietin attenuates hypertrophy of neonatal rat cardiac myocytes induced by angiotensin-II in vitro

OBJECTIVE

Erythropoietin (EPO) is a haematopoietic hormone that has been confirmed as a novel cardioprotective agent. In this study, we test the hypothesis that EPO inhibits angiotensin-II (Ang-II)-induced hypertrophy in cultured neonatal rat cardiomyocytes.

MATERIAL AND METHODS

Cultured neonatal rat cardiomyocytes were used to evaluate the effects of EPO on Ang-II-induced hypertrophy in vitro. The surface area and mRNA expression of atrial natriuretic (ANF) myocytes were employed to detect cardiac hypertrophy. A phosphatidylinositol 3'-kinase (PI3K) inhibitor LY294002 and an endothelial nitric oxide synthase (eNOS) inhibitor L-NAME were also employed to detect the underlying mechanism of EPO. Intracellular signal molecules, such as Akt (PKB), phosphorylated Akt, eNOS and transforming growth factor-beta1 (TGF-beta1) protein expression were determined by Western blot. Nitric oxide (NO) levels in the supernatant of cultured cardiomyocytes were assayed using an NO assay kit.

RESULTS

The results indicate that EPO significantly attenuates Ang-II-induced hypertrophy shown as inhibition of increases in cell surface area and ANF mRNA levels. NO production was also increased proportionally in the EPO-treated group. EPO enhanced Akt activation and eNOS protein expression, whereas LY294002 or L-NAME partially abolished the anti-hypertrophic effect of EPO, accompanied by a decrease in Akt activation, eNOS protein expression and/or a reduction of NO production. EPO also down-regulated the protein expression of TGF-beta1.

CONCLUSION

We conclude that EPO attenuates cardiac hypertrophy via activation of the PI3K-Akt-eNOS-NO pathway and the down-regulation of TGF-beta1.

Simvastatin attenuates cerebral vasospasm and improves outcomes by upregulation of PI3K/Akt pathway in a rat model of subarachnoid hemorrhage

BACKGROUND

Cerebral vasospasm is a common sequelae of subarachonoid hemorrhage (SAH), however, the mechanism of cerebral vasospasm is still unclear. Recently, statins have been shown to have efficacy in ameliorating cerebral vasospasm. The present study investigates whether simvastatin attenuates cerebral vasospasm after subarachnoid hemorrhage (SAH) via upregulation of the PI3K/Akt pathway.

METHODS

47 adult male Sprague-Dawley rats were divided into 6 groups: sham-operated, SAH treated with vehicle, SAH treated with low dose simvastatin (1 mg/kg), high dose simvastatin (20 mg/kg), SAH treated with simvastatin plus the PI3K inhibitor (wortmannin), and sham-operated plus wortmannin. Simvastatin was administered intraperitoneally 30 minutes after SAH created by the standard endovascular perforation model. Histological parameters of the ipsilateral internal carotid artery (ICA-diameter, perimeter, and wall thickness) and neurological score were assessed at 24 hours.

FINDINGS

Mortality was reduced to zero in both the treated groups as compared to 20% in the vehicle-treated and 36% in the simvastatin plus wortmannin-treated groups. The decrease in ICA diameter and perimeter observed in vehicle-treated group (203.2 +/- 10.3 microm, 652.7 +/- 29.0 microm) as compared to sham (259.7 +/- 10.6, 865.4 +/- 39.5) were significantly attenuated by high-dose simvastatin (267.4 +/- 8.0, 882.4 +/- 30.0). The increase in wall thickness (vehicle 29.50 +/- 2.42 microm v/s sham 9.52 +/- 0.56 microm) was significantly attenuated by both high and low dose simvastatin (11.87 +/- 1.56, 19.75 +/- 1.40). These effects of simvastatin were blocked with the addition of wortmannin (162.7 +/- 20.6, 528.9 +/- 65.9, 29.19 +/- 1.97). High dose simvastatin improved the neurological deficits after SAH, but this was also blocked by wortmannin.

CONCLUSIONS

The beneficial effects of high dose simvastatin in ameliorating cerebral vasospasm are likely mediated by upregulation of the PI3K/Akt pathway.

Hypertension induced by erythropoietin has a correlation with truncated erythropoietin receptor mRNA in endothelial progenitor cells of hemodialysis patients

Endothelial nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) contribute to erythropoietin (EPO)-induced hypertension, a major adverse reaction associated with EPO therapy. To investigate the mechanism of EPO-induced hypertension, we examined circulating endothelial progenitor cells (EPCs) taken from 56 hemodialysis (HD) patients. Among these EPCs (which reflect the condition of the endothelium), we looked for EPO receptor (EPOR) mRNAs. A truncated form of EPOR acts as a dominant negative regulator of EPO signaling, leading to hypertension. We found that the ratio of truncated EPOR mRNA in EPCs has a correlation with EPO-induced increase in blood pressure (r = 0.36, P = 0.02). The ratio of truncated to total EPOR mRNA in EPCs had an inverse correlation with EPO-induced cGMP production in vitro (r = -0.31, P = 0.02). A similar correlation was observed in cultured human endothelial cells after transfection of the full-length or truncated forms of EPOR (r = -0.92, P < 0.001). It follows, therefore, that evaluation of EPOR isoform mRNA in EPCs can predict EPO-induced hypertension. The termination of the EPO signal by truncated EPORs may decrease NO/cGMP production after EPO exposure, thereby raising blood pressure.