Adrenomedullin reduces ischemic brain injury after transient middle cerebral artery occlusion in rats

Adrenomedullin Is a Diagnostic and Prognostic Biomarker for Acute Intracerebral Hemorrhage

Hemorrhagic stroke remains an important health challenge. Adrenomedullin (AM) is a vasoactive peptide with an important role in cardiovascular diseases, including stroke. Serum AM and nitrate-nitrite and S-nitroso compounds (NOx) levels were measured and compared between healthy volunteers (n = 50) and acute hemorrhagic stroke patients (n = 64). Blood samples were taken at admission (d0), 24 h later (d1), and after 7 days or at the time of hospital discharge (d7). Neurological severity (NIHSS) and functional prognosis (mRankin) were measured as clinical outcomes. AM levels were higher in stroke patients at all times when compared with healthy controls (p < 0.0001). A receiving operating characteristic curve analysis identified that AM levels at admission > 69.0 pg/mL had a great value as a diagnostic biomarker (area under the curve = 0.89, sensitivity = 80.0%, specificity = 100%). Furthermore, patients with a favorable outcome (NIHSS ≤ 3; mRankin ≤ 2) experienced an increase in AM levels from d0 to d1, and a decrease from d1 to d7, whereas patients with unfavorable outcome had no significant changes over time. NOx levels were lower in patients at d0 (p = 0.04) and d1 (p < 0.001) than in healthy controls. In conclusion, AM levels may constitute a new diagnostic and prognostic biomarker for this disease, and identify AM as a positive mediator for hemorrhagic stroke resolution.

Study Protocol for a Randomized, Double-Blind, Placebo-Controlled, Phase-II Trial: AdrenoMedullin for Ischemic Stroke Study

OBJECTIVES

Adrenomedullin (AM), a vasoactive peptide, has strong anti-inflammatory and angiogenic properties, which have been reported to ameliorate the consequences of ischemic stroke in several animal models. After a phase I study in healthy volunteers, two phase II trials of AM for inflammatory bowel diseases have been recently completed. The current AdrenoMedullin For Ischemic Stroke (AMFIS) study aims to assess the safety and efficacy of AM in patients with acute ischemic stroke.

MATERIALS AND METHODS

The AMFIS study is an investigator-initiated, randomized, double-blind, phase-II trial. AM or placebo will be administered to patients with non-cardioembolic ischemic stroke within 24 h after stroke onset. In the first cohort of the AMFIS study, patients will be randomly allocated to the investigation treatment A (30 μg/kg of AM in total for 7 days, n = 20) or placebo group (n = 10). In the second cohort, patients will be assigned to the investigation treatment B (56 μg/kg of AM in total for 7 days, n = 20) or placebo group (n = 10).

RESULTS

Serious adverse events related to the protocol treatment will be evaluated as the primary outcome. All adverse events will be analyzed as the secondary outcome. Regarding efficacy endpoints, the change in National Institutes of Health Stroke Scale and modified Rankin Scale scores will be compared between investigation treatment and placebo groups.

CONCLUSIONS

AM is expected to be a safe and effective treatment for ischemic stroke.

Adrenomedullin: an important participant in neurological diseases

Adrenomedullin, a peptide with multiple physiological functions in nervous system injury and disease, has aroused the interest of researchers. This review summarizes the role of adrenomedullin in neuropathological disorders, including pathological pain, brain injury and nerve regeneration, and their treatment. As a newly characterized pronociceptive mediator, adrenomedullin has been shown to act as an upstream factor in the transmission of noxious information for various types of pathological pain including acute and chronic inflammatory pain, cancer pain, neuropathic pain induced by spinal nerve injury and diabetic neuropathy. Initiation of glia-neuron signaling networks in the peripheral and central nervous system by adrenomedullin is involved in the formation and maintenance of morphine tolerance. Adrenomedullin has been shown to exert a facilitated or neuroprotective effect against brain injury including hemorrhagic or ischemic stroke and traumatic brain injury. Additionally, adrenomedullin can serve as a regulator to promote nerve regeneration in pathological conditions. Therefore, adrenomedullin is an important participant in nervous system diseases.

Polyethylene glycol-conjugated human adrenomedullin as a possible treatment for vascular dementia

Adrenomedullin (AM) is a multifunctional bioactive peptide. Recent studies have shown that AM has protective effects against ischemic brain damage. We recently prepared a long-acting human AM derivative that was conjugated with a 60 kDa polyethylene glycol (PEG-AM), which had an effect similar to that of native AM. In this study, we examined the effect of PEG-AM on four-vessel occlusion model rats, which exhibit vascular dementia. From day 10 to day 14 after surgery, the learning and memory abilities of the rats were examined using a Morris water maze. The rats were treated with a single subcutaneous injection of 1.0 or 10.0 nmol/kg of PEG-AM. PEG-AM treatment reduced the escape latency in the hidden platform test. Furthermore, the treatment increased the time spent in the platform quadrant in the probe test. The data showed that PEG-AM injection prevented memory loss and learning disorders in dose-dependent manner. On day 14, the immunoreactive AM concentration in plasma was 9.749 ± 2.167 pM in the high-dose group (10.0 nmol/kg) and 0.334 ± 0.073 pM in the low-dose group (1.0 nmol/kg). However, even in the low-dose group, a significant effect was observed in both tests. The present data indicate that PEG-AM is a possible therapeutic agent for the treatment of ischemic brain injury or vascular dementia.

Adrenomedullin, a Novel Target for Neurodegenerative Diseases

Neurodegenerative diseases represent a heterogeneous group of disorders whose common characteristic is the progressive degeneration of neuronal structure and function. Although much knowledge has been accumulated on the pathophysiology of neurodegenerative diseases over the years, more efforts are needed to understand the processes that underlie these diseases and hence to propose new treatments. Adrenomedullin (AM) is a multifunctional peptide involved in vasodilation, hormone secretion, antimicrobial defense, cellular growth, and angiogenesis. In neurons, AM and related peptides are associated with some structural and functional cytoskeletal proteins that interfere with microtubule dynamics. Furthermore, AM may intervene in neuronal dysfunction through other mechanisms such as immune and inflammatory response, apoptosis, or calcium dyshomeostasis. Alterations in AM expression have been described in neurodegenerative processes such as Alzheimer's disease or vascular dementia. This review addresses the current state of knowledge on AM and its possible implication in neurodegenerative diseases.

Adrenomedullin promotes differentiation of oligodendrocyte precursor cells into myelin-basic-protein expressing oligodendrocytes under pathological conditions in vitro

Oligodendrocytes, which are the main cell type in cerebral white matter, are generated from their precursor cells (oligodendrocyte precursor cells: OPCs). However, the differentiation from OPCs to oligodendrocytes is disturbed under stressed conditions. Therefore, drugs that can improve oligodendrocyte regeneration may be effective for white matter-related diseases. Here we show that a vasoactive peptide adrenomedullin (AM) promotes the in vitro differentiation of OPCs under pathological conditions. Primary OPCs were prepared from neonatal rat brains, and differentiated into myelin-basic-protein expressing oligodendrocytes over time. This in vitro OPC differentiation was inhibited by prolonged chemical hypoxic stress induced by non-lethal CoCl(2) treatment. However, AM promoted the OPC differentiation under the hypoxic stress conditions, and the AM receptor antagonist AM(22-52) canceled the AM-induced OPC differentiation. In addition, AM treatment increased the phosphorylation level of Akt in OPC cultures, and correspondingly, the PI3K/Akt inhibitor LY294002 blocked the AM-induced OPC differentiation. Taken together, AM treatment rescued OPC maturation under pathological conditions via an AM-receptor-PI3K/Akt pathway. Oligodendrocytes play critical roles in white matter by forming myelin sheath. Therefore, AM signaling may be a promising therapeutic target to boost oligodendrocyte regeneration in CNS disorders.

Crosstalk between cerebral endothelium and oligodendrocyte

It is now relatively well accepted that the cerebrovascular system does not merely provide inert pipes for blood delivery to the brain. Cerebral endothelial cells may compose an embedded bunker of trophic factors that contribute to brain homeostasis and function. Recent findings suggest that soluble factors from cerebral endothelial cells nourish neighboring cells, such as neurons and astrocytes. Although data are strongest in supporting mechanisms of endothelial-neuron and/or endothelial-astrocyte trophic coupling, it is likely that similar interactions also exist between cerebral endothelial cells and oligodendrocyte lineage cells. In this mini-review, we summarize current advances in the field of endothelial-oligodendrocyte trophic coupling. These endothelial-oligodendrocyte interactions may comprise the oligovascular niche to maintain their cellular functions and sustain ongoing angiogenesis/oligodendrogenesis. Importantly, it should be noted that the cell-cell interactions are not static-the trophic coupling is disturbed under acute phase after brain injury, but would be recovered in the chronic phase to promote brain remodeling and repair. Oligodendrocyte lineage cells play critical roles in white matter function, and under pathological conditions, oligodendrocyte dysfunction lead to white matter damage. Therefore, a deeper understanding of the mechanisms of endothelial-oligodendrocyte trophic coupling may lead to new therapeutic approaches for white matter-related diseases, such as stroke or vascular dementia.

Acute mountain sickness, inflammation, and permeability: new insights from a blood biomarker study

The pathophysiology of acute mountain sickness (AMS) is unknown. One hypothesis is that hypoxia induces biochemical changes that disrupt the blood-brain barrier (BBB) and, subsequently, lead to the development of cerebral edema and the defining symptoms of AMS. This study explores the relationship between AMS and biomarkers thought to protect against or contribute to BBB disruption. Twenty healthy volunteers participated in a series of hypobaric hypoxia trials distinguished by pretreatment with placebo, acetazolamide (250 mg), or dexamethasone (4 mg), administered using a randomized, double-blind, placebo-controlled, crossover design. Each trial included peripheral blood sampling and AMS assessment before (-15 and 0 h) and during (0.5, 4, and 9 h) a 10-h hypoxic exposure (barometric pressure = 425 mmHg). Anti-inflammatory and/or anti-permeability [interleukin (IL)-1 receptor agonist (IL-1RA), heat shock protein (HSP)-70, and adrenomedullin], proinflammatory (IL-6, IL-8, IL-2, IL-1β, and substance P), angiogenic, or chemotactic biomarkers (macrophage inflammatory protein-1β, VEGF, TNF-α, monocyte chemotactic protein-1, and matrix metalloproteinase-9) were assessed. AMS-resistant subjects had higher IL-1RA (4 and 9 h and overall), HSP-70 (0 h and overall), and adrenomedullin (overall) compared with AMS-susceptible subjects. Acetazolamide raised IL-1RA and HSP-70 compared with placebo in AMS-susceptible subjects. Dexamethasone also increased HSP-70 and adrenomedullin in AMS-susceptible subjects. Macrophage inflammatory protein-1β was higher in AMS-susceptible than AMS-resistant subjects after 4 h of hypoxia; dexamethasone minimized this difference. Other biomarkers were unrelated to AMS. Resistance to AMS was accompanied by a marked anti-inflammatory and/or anti-permeability response that may have prevented downstream pathophysiological events leading to AMS. Conversely, AMS susceptibility does not appear to be related to an exaggerated inflammatory response.

Lack of adrenomedullin, but not complement factor H, results in larger infarct size and more extensive brain damage in a focal ischemia model

Adrenomedullin (AM) and its binding protein, complement factor H (FH), are expressed throughout the brain. In this study we used a brain-specific conditional knockout for AM and a complete knockout for FH to investigate the effect of these molecules on the pathophysiology of stroke. Following 48 h of middle cerebral artery permanent occlusion, there was a statistically significant infarct size increase in animals lacking AM when compared to their wild type littermates. In contrast, lack of FH did not affect infarct volume. To investigate some of the mechanisms by which lack of AM may augment brain damage, markers of nitrosative stress, apoptosis, and autophagy were studied at the mRNA and protein levels. There was a significant increase of inducible nitric oxide synthase (iNOS), matrix metalloproteinase-9 (MMP9), fractin, and Beclin-1 in the peri-infarct area of AM-deficient mice when compared to their wild type counterparts and to contralateral and sham-operated controls. These data suggest that AM exerts a neuroprotective action in the brain and that this protection may be mediated by regulation of iNOS, matrix metalloproteases, and inflammatory mediators. In the future, substances that increase AM actions in the central nervous system may be used as potential neuroprotective agents in stroke.

Prolyl hydroxylase domain inhibitors: a route to HIF activation and neuroprotection

Abstract Ischemic stroke is a major cause of death worldwide, and current therapeutic options are very limited. Preconditioning with an ischemic or hypoxic insult is beneficial in experimental models of ischemic stroke. Ischemia/hypoxia results in activation of numerous transcription factors, including hypoxia inducible factor (HIF), which is a master regulator of oxygen homeostasis. HIF activation induces a diverse range of target genes, encompassing a wide variety of cellular processes; including angiogenesis, energy metabolism, cell survival, radical production/scavenging, iron metabolism, stem cell homing, and differentiation. Inhibition of HIF prolyl hydroxylase domain (PHD) enzymes results in activation of HIF and is likely to mimic, at least in part, the effects of hypoxia preconditioning. A caveat is that not all consequences of HIF activation will be beneficial and some could even be deleterious. Nevertheless, PHD inhibitors may be therapeutically useful in the treatment of stroke. Prototype PHD inhibitors have shown promising results in preclinical models.

Protein kinase A-dependent suppression of reactive oxygen species in transient focal ischemia in adrenomedullin-deficient mice

This study was designed to examine the effect of adrenomedullin deficiency on cerebral infarction and the relationship between adrenomedullin and cyclic AMP-protein kinase A pathway in regulating reactive oxygen species (ROS). Adrenomedullin heterozygous and wild-type mice were subjected to 60-mins focal ischemia. We used adrenomedullin heterozygous mice because adrenomedullin homozygotes die in utero. Infarct volume, neurologic deficit scores, and immunohistochemical analyses were evaluated at several time points after ischemia. The infarct volume and neurologic deficit scores were significantly worse in adrenomedullin heterozygous mice. Significant accumulation of inducible nitric oxide, oxidative DNA damage, and lipid peroxidation was noted after reperfusion in adrenomedullin heterozygous mice. Treatment of wild-type mice with H89, a protein kinase A inhibitor, resulted in increased infarct size, and worsening of neurologic deficit score and other parameters to levels comparable to those of adrenomedullin heterozygous mice. In contrast, cilostazol, which increases cyclic AMP, rescued neurologic deficit and ROS accumulation in adrenomedullin heterozygous mice. This study showed that adrenomedullin downregulation results in increase in ROS after transient focal ischemia in mice. The results also indicated that adrenomedullin has an important function against ischemic injury through the cyclic AMP-protein kinase A pathway.

Complement factor H, a marker of self protects against experimental autoimmune encephalomyelitis

The CNS innate immune response is a "double-edged sword" representing a fine balance between protective antipathogen responses and detrimental neurocytotoxic effects. Hence, it is important to identify the key regulatory mechanisms involved in the control of CNS innate immunity and which could be harnessed to explore novel therapeutic avenues. In analogy to the newly described neuroimmune regulatory proteins also known as "don't eat me" signals (CD200, CD47, CD22, fractalkine, semaphorins), we herein identify the key role of complement regulator factor H (fH) in controlling neuroinflammation initiated in an acute mouse model of Ab-dependent experimental autoimmune encephalomyelitis. Mouse fH was found to be abundantly expressed by primary cultured neurons and neuronal cell lines (N1E115 and Neuro2a) at a level comparable to BV2 microglia and CLTT astrocytes. Mouse neurons expressed other complement regulators crry and low levels of CD55. In the brain, the expression of fH was localized to neuronal bodies and axons, endothelial cells, microglia but not oligodendrocytes and myelin sheaths and was dramatically reduced in inflammatory experimental autoimmune encephalomyelitis settings. When exogenous human fH was administered to disease Ab-dependent experimental autoimmune encephalomyelitis animals, there was a significant decrease in clinical score, inflammation, and demyelination, as compared with PBS-injected animals. We found that the accumulation of human fH in the brain parenchyma protected neurons from complement opsonization, axonal injury, and leukocyte infiltration. Our data argue for a key regulatory activity of fH in neuroprotection and provide novel therapeutic avenues for CNS chronic inflammatory diseases.

Deferroxamine preconditioning promotes long-lasting retinal ischemic tolerance

OBJECTIVE

"Ischemic tolerance" can be induced in the retina by "preconditioning" with brief periods of non-injurious retinal ischemia or systemic hypoxia. The present study was undertaken to assess whether tolerance can be induced pharmacologically by deferroxamine (DFX), an iron chelator, which promotes the expression of the transcription factor, hypoxia-inducible factor 1-alpha (HIF-1alpha), and to identify potential HIF-1alpha -induced effectors of this endogenous protective response.

METHODS

ND4 Swiss-Webster mice were preconditioned with DFX (200 mg/kg, intraperitoneally) as a single dose (SDP) or as repetitive doses (RDP; 6 doses over 2 weeks) and then subjected to 30 min of retinal ischemia (by intraocular pressure elevation) 1 or 4 weeks later. Retinal layer thicknesses and cell counts were quantified 1 week after ischemia. Retinae of additional mice were obtained at various times after SDP or RDP to examine protein-level expression of HIF-1alpha and adrenomedullin (ADM), a HIF-1alpha gene target, by immunoblotting and immunohistochemistry.

RESULTS

Ischemia-induced injury was significantly attenuated by SDP 1 week earlier, but not when SDP occurred 4 weeks earlier. However, RDP performed 4 weeks earlier was potently neuroprotective. DFX robustly induced HIF-1alpha protein expression throughout the inner retina, and levels of HIF-1alpha protein remained significantly elevated over the 1- and 4-week periods of time between the respective SDP and RDP stimulus and the induction of retinal ischemia. Increases in ADM protein expression were evident throughout the retina following both preconditioning treatments.

CONCLUSIONS

DFX preconditions the retina against ischemic injury and multiple doses promote a long-lasting, ischemia-protective phenotype. The widespread and protracted elevations in HIF-1alpha protein levels and the robust expression of one of its neuroprotective, prosurvival gene targets, ADM, strongly suggest that DFX-induced preconditioning is HIF-1alpha-dependent. The ability to pharmacologically induce ischemic tolerance in the retina by a clinically well-tolerated drug underscores the potential therapeutic utility of preconditioning for retinal protection in various ischemic retinopathies.

HIF-1alpha subunit and vasoactive HIF-1-dependent genes are involved in carbon monoxide-induced cerebral hypoxic stress response

Hypoxia-inducible transcription factor-1 (HIF-1) is the most important component of cellular and molecular adaptive responses to hypoxia. We aimed to analyze effects of systemic hypoxia and CO exposure on the oxygen-regulated alpha-subunit of HIF-1 and HIF-1-dependent vasoactive target genes in rat brain. Brains of adult Sprague-Dawley rats were investigated after incubation for 3 and 12 h under normoxia, hypoxia (8% O(2)) and CO 0.1% (n = 10 per group). Upon 3 h of exposure, hypoxia and CO-induced accumulation of HIF-1alpha protein in brain homogenates assessed by Western blot analysis. In contrast to hypoxia HIF-1alpha signals decreased markedly during 12 h-exposure to CO. By immunohistochemistry, intensive HIF-1alpha-positive staining was found in neurons of the cortex and hippocampus. Cerebral expression of vasoactive target genes adrenomedullin (ADM) and vascular endothelial growth factor (VEGF) showed up-regulation during both hypoxia and CO exposure indicating functional activation of HIF-1. Hypoxia increased ADM (P < 0.05) and VEGF mRNA levels within 3 h (P < 0.01) which persisted up to 12 h of exposure (ADM, P < 0.05; VEGF, P < 0.001). Similarly, CO inhalation led to early up-regulation of VEGF (3 h: P < 0.05; 12 h: P < 0.01), but a more delayed increase of ADM mRNA levels (3 h: n.s., 12 h: P < 0.01). We suggest that CO-induced oxygen deprivation is a potent stimulus to cerebral HIF-1-regulated hypoxic stress responses even though its effects are more transient than exposure to hypoxia.

Adrenomedullin expression is up-regulated by acute hypobaric hypoxia in the cerebral cortex of the adult rat

Hypobaric hypoxia can produce neuropsychological disorders such as insomnia, dizziness, memory deficiencies, headache and nausea. Here we report the changes in adrenomedullin (AM) expression observed in rats exposed to hypobaric hypoxia and different times of reoxygenation. AM immunoreactivity was transiently elevated in the cerebral cortex after 7 h of exposure to a simulated altitude of 8325 m (27 000 ft). This higher expression was seen in all pyramidal cells and in a subset of small interneurons. AM-positive nonpyramidal neurons contained also calbindin and calretinin, but no parvalbumin immunoreactivity, thus identifying them as bipolar and double bouquet cells. Small blood vessels and related astroglia also became immunoreactive following the hypobaric insult. AM up-regulation decreased progressively with the time of reoxygenation, reaching almost control levels after 5 days. Real-time PCR quantification of AM mRNA and Western blotting confirmed the up-regulation of AM expression following hypobaria. In addition, hypobaria modulates alternative splicing of the AM gene resulting in a higher production of AM. Our data show that AM expression regulation constitutes a cortical response to hypobaria, suggesting that AM modulation may provide new therapeutic avenues to prevent and/or treat the symptoms produced by hypobaria.

Effect of nasal continuous positive airway pressure treatment on plasma adrenomedullin levels in patients with obstructive sleep apnea syndrome: roles of nocturnal hypoxia and oxidant stress

Obstructive sleep apnea syndrome (OSAS) is recognized as one of the risk factors of hypertension and cardiovascular disorders. In the current study, we hypothesized that the hypoxic stress and oxidative stress caused by obstructive sleep apnea would increase circulating adrenomedullin (ADM) levels in untreated OSAS patients as compared to an age and body mass index (BMI)-matched control group and an age-matched, but normal-BMI control group. We further hypothesized that nasal continuous positive airway pressure (nCPAP) treatment may decrease OSAS-induced hypoxic stress, oxidative stress and ADM levels. To examine these hypotheses, we measured circulating ADM and reactive oxygen species (ROS) from leukocytes before and after nCPAP therapy in OSAS patients. The circulating levels of ADM and amount of ROS in untreated OSAS patients were significantly greater than those in the controls. No differences in ADM levels were found between the increased-BMI controls and normal-BMI controls. We observed that nCPAP treatment decreased sleep apneas, nocturnal oxyhemoglobin desaturation, the circulating ADM, and ROS production by leukocytes in OSAS patients. The ADM levels were associated with the magnitude of oxyhemoglobin desaturation rather than the number of sleep apneas. These observations suggest that nCPAP therapy could reduce OSAS-induced nocturnal hypoxemia, generation of ROS, and ADM in patients with OSAS.

Corticotropin-releasing factor (CRF)-induced behaviors are modulated by intravenous administration of teneurin C-terminal associated peptide-1 (TCAP-1)

The teneurin C-terminal associated peptides (TCAP) are a recently discovered family of bioactive peptides that can attenuate aspects of the behavioral stress responses of rats. Because TCAP has some structural similarity to the corticotropin-releasing factor (CRF) family of peptides, and modulates elements of the stress response, TCAP may act to modulate CRF actions in vivo. This hypothesis was tested by investigating anxiety-related behaviors in male rats following repeated intravenous (IV) TCAP-1 administration with either an acute intracerebroventricular (ICV) or IV CRF challenge. TCAP-1 alone did not affect behavioral responses significantly, however did significantly affect CRF-regulated behaviors depending on CRF's mode of injection. In both the elevated plus-maze and the open field tests, TCAP-1 had an anxiolytic effect on ICV CRF responses as indicated by decreased stretched-attend postures in the elevated plus maze (p<0.05), and increased center time and center entries in the open field (p<0.05). However, prior TCAP-1 treatment has an anxiogenic effect on the IV CRF-induced behaviors (decreased center entries and total distance in the open field (p<0.05)). TCAP-1's actions are not mediated through acute changes in glucocorticoid levels and may occur via a central action in the brain. A fluorescently (FITC)-labeled TCAP-1 analog was IV-administered to investigate whether IV TCAP-1 has the potential to regulate central mechanisms by crossing the blood-brain barrier. FITC-TCAP-1 was detected in blood vessels and fibers in the brain indicating that uptake into the brain is a possible route for its interaction with CRF and its receptors. Thus, TCAP may modulate CRF-associated behaviors by a direct action in the CNS.

Adrenomedullin and adrenomedullin binding protein-1 prevent acute lung injury after gut ischemia-reperfusion

BACKGROUND

Ischemic bowel remains a critical problem, resulting in up to 80% mortality. Acute lung injury, a common complication after intestinal ischemia/reperfusion (I/R), might be responsible for such a high mortality rate. Our previous studies have shown that administration of a novel vasoactive peptide adrenomedullin (AM) and its binding protein (AMBP-1) reduces the systemic inflammatory response in rat models of both hemorrhage and sepsis. It remains unknown whether administration of AM/AMBP-1 has any protective effects on intestinal I/R-induced acute lung injury. We hypothesized that administration of AM/AMBP-1 after intestinal I/R prevents acute lung injury through downregulation of proinflammatory cytokines.

STUDY DESIGN

Intestinal I/R was induced by placing a microvascular clip across superior mesenteric artery (SMA) for 90 minutes in adult male Sprague-Dawley rats (275 to 325 g). On release of the SMA clamp, the animals were treated with either AM (12 mug/kg body weight) in combination with AMBP-1 (40 microg/kg body weight) or vehicle (1 mL normal saline) during a period of 30 minutes through a femoral vein catheter. Lung samples were collected at 4 hours after treatment or sham operation. Lung injury was assessed by examining lung water content, morphologic changes, and granulocyte myeloperoxidase activity. Tumor necrosis factor-alpha and interleukin-6 gene expression and their protein levels in the lungs were measured by reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. In additional groups of animals, AM/AMBP-1 or vehicle was administered at 1 hour after onset of reperfusion. Lung histology was examined at 3 hours after treatment.

RESULTS

Intestinal I/R induced considerable lung injury, as characterized by lung edema, histopathologic changes, increased myeloperoxidase activity, and proinflammatory cytokines (tumor necrosis factor-alpha and interleukin-6) levels in the lungs. Administration of AM/AMBP-1 after ischemia mitigated lung injury and dramatically downregulated proinflammatory cytokines. Lung injury was also ameliorated by delayed AM/AMBP-1 treatment as evidenced by improvement in lung histology.

CONCLUSIONS

AM/AMBP-1 can be developed as a novel treatment to attenuate acute lung injury after an episode of gut ischemia. The protective effect of AM/AMBP-1 appears to be mediated through downregulation of proinflammatory cytokines.

Adrenomedullin facilitates reinnervation of phenol-injured perivascular nerves in the rat mesenteric resistance artery

Our previous report showed that innervation of calcitonin gene-related peptide (CGRP)- and neuropeptide Y (NPY)-containing nerves in rat mesenteric resistance arteries was markedly reduced by topical application of phenol, and that nerve growth factor (NGF) facilitates the reinnervation of both nerves. We also demonstrated that a CGRP superfamily peptide, adrenomedullin, is distributed in perivascular nerves of rat mesenteric resistance arteries. In the present study, we investigated the influence of adrenomedullin on the reinnervation of mesenteric perivascular nerves following topical phenol treatment. Under pentobarbital-Na anesthesia, 8-week-old Wistar rats underwent in vivo topical application of phenol (10% phenol in 90% ethanol) to the superior mesenteric artery proximal to the bifurcation of the abdominal aorta. After the treatment, the animals were subjected to immunohistochemistry of the third branch of small arteries proximal to the intestine and to vascular responsiveness testing on day 7. Topical phenol treatment caused marked reduction of the density of NPY-like immunoreactive (LI)- and CGRP-LI nerve fibers in the arteries. Adrenomedullin (360 or 1000 ng/h) or NGF (250 ng/h), which was administered intraperitoneally for 7 days using an osmotic mini-pump immediately after topical phenol treatment, significantly increased the density of CGRP-LI- and NPY-LI nerve fibers compared with saline. Treatment with adrenomedullin (1000 ng/h) or NGF restored adrenergic nerve-mediated vasoconstriction and CGRP nerve-mediated vasodilation in the perfused mesenteric artery treated topically with phenol. These results suggest that adrenomedullin, like NGF, has a facilitatory effect on the reinnervation of perivascular nerves.

The neuroprotective and vasculo-neuro-regenerative roles of adrenomedullin in ischemic brain and its therapeutic potential

Adrenomedullin (AM) is a vasodilating hormone secreted mainly from vascular wall, and its expression is markedly enhanced after stroke. We have revealed that AM promotes not only vasodilation but also vascular regeneration. In this study, we focused on the roles of AM in the ischemic brain and examined its therapeutic potential. We developed novel AM-transgenic (AM-Tg) mice that overproduce AM in the liver and performed middle cerebral artery occlusion for 20 min (20m-MCAO) to examine the effects of AM on degenerative or regenerative processes in ischemic brain. The infarct area and gliosis after 20m-MCAO was reduced in AM-Tg mice in association with suppression of leukocyte infiltration, oxidative stress, and apoptosis in the ischemic core. In addition, vascular regeneration and subsequent neurogenesis were enhanced in AM-Tg mice, preceded by increase in mobilization of CD34(+) mononuclear cells, which can differentiate into endothelial cells. The vasculo-neuro-regenerative actions observed in AM-Tg mice in combination with neuroprotection resulted in improved recovery of motor function. Brain edema was also significantly reduced in AM-Tg mice via suppression of vascular permeability. In vitro, AM exerted direct antiapoptotic and neurogenic actions on neuronal cells. Exogenous administration of AM in mice after 20m-MCAO also reduced the infarct area, and promoted vascular regeneration and functional recovery. In summary, this study suggests the neuroprotective and vasculo-neuro-regenerative roles of AM and provides basis for a new strategy to rescue ischemic brain through its multiple hormonal actions.

Postischemic infusion of adrenomedullin protects against ischemic stroke by inhibiting apoptosis and promoting angiogenesis

Adrenomedullin (AM) is a peptide hormone widely distributed in the central nervous system. Our previous study showed that AM gene delivery immediately after middle cerebral artery occlusion (MCAO) protected against cerebral ischemia/reperfusion (I/R) injury by promoting glial cell survival and migration. In the present study, we investigated the effect of delayed AM peptide infusion on ischemic brain injury at 24 h after MCAO. AM infusion significantly reduced neurological deficit scores at days 2, 4, and 8 after cerebral I/R. AM reduced cerebral infarct size at 8 and 15 days after surgery as determined by quantitative analysis. Double staining showed that AM infusion reduced TUNEL-positive apoptotic cells in both neurons and glial cells, as well as reduced caspase-3 activity in the ischemic area of the brain. In addition, AM treatment increased capillary density in the ischemic region at 15 days after I/R injury. Parallel studies revealed that AM treatment enhanced the proliferation of cultured endothelial cells as measured by both (3)H-thymidine incorporation and in situ BrdU labeling. Both in vitro and in vivo AM effects were blocked by calcitonin gene-related peptide (8-37), an AM receptor antagonist. Moreover, AM's effects were associated with increased cerebral nitric oxide (NO) levels, as well as decreased NAD(P)H oxidase activities and superoxide anion production. These results indicate that a continuous supply of exogenous AM peptide protects against I/R injury by improving the survival of neuronal and glial cells, and promoting angiogenesis through elevated NO formation and suppression of oxidative stress.

Autocrine peptide mediators of cerebral endothelial cells and their role in the regulation of blood-brain barrier

A unique feature of cerebral endothelial cells (CECs) is the formation of the blood-brain barrier (BBB), which contributes to the stability of the brain microenvironment. CECs are capable of producing several substances mediating endothelium-dependent vasorelaxation or vasoconstriction, regulating BBB permeability, and participating in the regulation of cell-cell interactions during inflammatory and immunological processes. The chemical nature of these mediators produced by CECs ranges from gaseous anorganic molecules (e.g. nitric oxide) through lipid mediators (e.g. prostaglandins) to peptides. Peptide mediators are a large and diverse family of bioactive molecules which can elicit multiple effects on cerebral endothelial functions. In this review, we summarize current knowledge of peptide mediators produced by CECs, such as adrenomedullin, angiotensin, endothelin and several others and their role in the regulation of BBB functions.

Adrenomedullin protects rat cerebral endothelial cells from oxidant damage in vitro

Increased permeability and reduced cerebral endothelial cell (CEC) viability induced by oxidative stress are the hallmarks of the blood-brain barrier disruption. In our experiments hydrogen peroxide (H2O2, 0.5 mM) induced a continuous decrease of the transendothelial electrical resistance (TEER) and resulted in intercellular gap formations in cultured rat CECs. Adrenomedullin (AM) increased TEER, enhanced peripheral localization of F-actin bands and attenuated the increased permeability induced by H2O2. Furthermore, AM treatment preserved mitochondrial membrane potential, attenuated cytochrome c release, and consequently improved CEC viability in H2O2 treated cultures. These results suggest that AM treatment protects CECs against oxidative injury.

Adrenomedullin stimulates nitric oxide release from SK-N-SH human neuroblastoma cells by modulating intracellular calcium mobilization

We used SK-N-SH human neuroblastoma cells to test the hypothesis that adrenomedullin (ADM), a multifunctional neuropeptide, stimulates nitric oxide (NO) release by modulating intracellular free calcium concentration ([Ca2+]i) in neuron-like cells. We used a nitrite assay to demonstrate that ADM (10 pM to 100 nM) stimulated NO release from the cells, with a maximal response observed with 1 nM at 30 min. This response was blocked by 1 nM ADM(22-52), an ADM receptor antagonist or 2 microM vinyl-L-NIO, a neuronal NO synthase inhibitor. In addition, 5 microM 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester, an intracellular calcium chelator, eliminated the ADM-induced NO release. Similar results were observed when the cells were incubated in calcium-free medium or when L-type calcium channels were inhibited with 5 microM nifedipine or 10 microM nitrendipine. Depletion of calcium stores in the endoplasmic reticulum (ER) with 1 microM cyclopiazonic acid or 150 nM thapsigargin, or inhibition of ryanodine-sensitive receptors in the ER with 10 microM ryanodine attenuated the ADM-induced NO release. NO responses to ADM were mimicked by 1 mM dibutyryl cAMP, a cAMP analog, and were abrogated by 5 microM H-89, a protein kinase A inhibitor. Furthermore, Fluo-4 fluorescence-activated cell sorter analysis showed that ADM (1 nM) significantly increased [Ca2+]i at 30 min. This response was blocked by nifedipine (5 microM) or H-89 (5 microM) and was reduced by ryanodine (10 microM). These results suggest that ADM stimulates calcium influx through L-type calcium channels and ryanodine-sensitive calcium release from the ER, probably via cAMP-protein kinase A-dependent mechanisms. These elevations in [Ca2+)]i cause activation of neuronal NO synthase and NO release.

Effects of polyhemoglobin-antioxidant enzyme complex on ischemia-reperfusion in kidney

INTRODUCTION

The kidney suffers ischemia-reperfusion (I/R) injury during transplantation. The purpose of the present study was to investigate the therapeutic effect of artificials cells on renal I/R injury through biochemical assays and histological examination.

METHODS

We prepared artificial cells using cross-linked hemoglobin (Hb), superoxide dismutase (SOD), and catalase. Normal male Sprague-Dawley rats were divided into 6 groups: the sham-operated control group, the group treated with polyHb,and the group treated with polyHb-SOD-catalase (PSC) (per groups were subjected to ischemia for 1 hour or 2 hours). After reperfusion for 4 hours, kidney and blood samples were obtained.

RESULTS

The levels of SOD and catalase in the PSC group were 15 and 50 times higher than those of the control group, respectively. In the polyHb group, the levels of blood urea nitrogen (BUN), serum creatinine, renal hydrogen peroxide, and renal malondialdehyde were increased. However, their levels were significantly decreased by PSC administration. Renal SOD activity did not show any significant changes in the polyHb group, but renal catalase activity was decreased by polyHb treatment in comparison with the control group. The activities of renal SOD and catalase were increased using PSC treatment. In the histological findings, the PSC group showed no evidence of acute tubular necrosis in proximal convoluted tubules; their microvilli and cytoplasmic microorganelles were relatively well preserved.

CONCLUSIONS

These results show that PSC effectively reduces renal damage via diminished oxygen free radical-mediated injury after I/R.

Adrenomedullin enhances therapeutic potency of mesenchymal stem cells after experimental stroke in rats

BACKGROUND AND PURPOSE

Adrenomedullin (AM) induces angiogenesis and inhibits cell apoptosis through the phosphatidylinositol 3-kinase/Akt pathway. Transplantation of mesenchymal stem cells (MSCs) has been shown to improve neurological deficits after stroke in rats. We investigated whether AM enhances the therapeutic potency of MSC transplantation.

METHODS

Male Lewis rats (n=100) were subjected to 2-hour middle cerebral artery occlusion. Immediately after reperfusion, rats were assigned randomly to receive intravenous transplantation of MSCs plus subcutaneous infusion of AM for 7 days (MSC+AM group), AM infusion alone (AM group), MSC transplantation alone (MSC group), or vehicle infusion (control group). Neurological and immunohistological assessments were performed to examine the effects of these treatments.

RESULTS

Some engrafted MSCs were positive for neuronal and endothelial cell markers, although the number of differentiated MSCs did not differ significantly between the MSC and MSC+AM groups. The neurological score significantly improved in the MSC, AM, and MSC+AM groups compared with the control group. Importantly, improvement in the MSC+AM group was significantly greater than that in the MSC and AM groups. There was marked induction of angiogenesis in the ischemic penumbra in the MSC+AM group, followed by the AM, MSC, and control groups. AM infusion significantly inhibited apoptosis of transplanted MSCs. As a result, the number of engrafted MSCs in the MSC+AM group was significantly higher than that in the MSC group.

CONCLUSIONS

AM enhanced the therapeutic potency of MSCs, including neurological improvement, possibly through inhibition of MSC apoptosis and induction of angiogenesis.

Adrenomedullin Gene Delivery Protects Against Cerebral Ischemic Injury by Promoting Astrocyte Migration and Survival

Adrenomedullin (AM) has been shown to protect against ischemia/reperfusion-induced myocardial infarction and apoptosis. In the present study, we examined the potential neuroprotective action of delayed AM gene transfer in cerebral ischemia. Three days after a 1-hr occlusion of the middle cerebral artery (MCAO), rats were injected intravenously with adenovirus harboring human AM cDNA. The experiment was terminated 7 days after MCAO. AM gene transfer significantly reduced cerebral infarct size compared with that of rats before virus injection and compared with that of rats injected with control virus. The expression of recombinant human AM was identified in ischemic brain by immunostaining. Morphological analyses showed that AM gene transfer enhanced the survival and migration of astrocytes into the ischemic core. Cerebral ischemia markedly increased astrocyte apoptosis, and AM gene delivery significantly reduced apoptosis to near normal levels as seen in sham control rats. Similarly, in primary cultured astrocytes, AM stimulated cell migration and inhibited hypoxia/reoxygenation-induced apoptosis. The effects of AM on both migration and apoptosis were abolished by calcitonin gene-related peptide [CGRP(8-37)], an AM receptor antagonist. Enhanced cell survival after AM gene transfer was accompanied by markedly increased cerebral nitric oxide and Bcl-2 levels, as well as Akt and GSK-3beta phosphorylation, but reduced NADPH oxidase activity and superoxide production. Inactivation of GSK-3beta by phosphorylation led to reduced GSK-3beta activity and caspase- 3 activation. These results indicate that exogenous AM provides neuroprotection against cerebral ischemia injury by enhancing astrocyte survival and migration and inhibiting apoptosis through suppression of oxidative stress-mediated signaling events.

Plasma adrenomedullin and carotid atherosclerosis in atherothrombotic ischemic stroke

OBJECTIVE

Adrenomedullin is known to exert anti-atherosclerotic actions by inhibiting proliferation and migration of smooth muscle cells in vitro. Here we examine the relationship between the plasma concentration of adrenomedullin and ultrasonographic characteristics of carotid arteries both in ischemic stroke and in the absence of cerebrovascular disease.

METHODS

We studied 61 patients with atherothrombotic ischemic stroke in the chronic phase and 50 patients without any cerebrovascular disease. Intima-media thickness and vascular lumen diameters were evaluated by carotid ultrasonography. Plasma mature-adrenomedullin was determined by radioimmunoassay.

RESULTS

Plasma mature-adrenomedullin in the patients with atherothrombotic ischemic stroke in the chronic phase (2.01 +/- 0.58 fmol/ml) was significantly higher than that in the patients without any cerebrovascular disease (1.24 +/- 0.18 fmol/ml, P < 0.001). With multiple regression analysis, plasma mature-adrenomedullin was found to be predicted by: stroke status (atherothrombotic ischemic stroke versus no cerebrovascular disease), diabetes status (yes/no), left ventricular ejection fraction, internal carotid artery intima-media thickness, and common carotid artery pressure strain elastic modulus (R = 0.79; F5,105 = 85.39, P < 0.0001).

CONCLUSION

Plasma mature-adrenomedullin showed significantly positive associations with carotid atherosclerosis and atherothrombotic ischemic stroke, independent of systolic blood pressure.

Restriction-mediated differential display (RMDD) identifies pip92 as a pro-apoptotic gene product induced during focal cerebral ischemia

Studies of gene expression changes after cerebral ischemia can provide novel insight into ischemic pathophysiology. Here we describe application of restriction-mediated differential display to screening for differentially expressed genes after focal cerebral ischemia. This method combines the nonredundant generation of biotin-labeled fragment sets with the excellent resolution of direct blotting electrophoresis, reliable fragment recovery, and a novel clone selection strategy. Using the filament model in mouse with 90 minutes MCA occlusion followed by 2, 6, and 20 hours reperfusion, we have compared gene expression in sham-operated animals to both the ipsi- and contralateral forebrain hemisphere of ischemic mice. Our screening method has resulted in the identification of 70 genes differentially regulated after transient middle cerebral artery occlusion (MCAO), several of which represent unknown clones. We have identified many of the previously published regulated genes, lending high credibility to our method. Surprisingly, we detected a high degree of correspondent regulation of genes in the nonischemic hemisphere. A high percentage of genes coding for proteins in the respiratory chain was found to be up-regulated after ischemia, potentially representing a new mechanism involved in counteracting energy failure or radical generation in cerebral ischemia. One particularly interesting gene, whose upregulation by ischemia has not been described before, is pip92; this gene shows a rapid and long-lasting induction after cerebral ischemia. Here we demonstrate that pip92 induces cell death in primary neurons and displays several hallmarks of pro-apoptotic activity upon overexpression, supporting the notion that we have identified a novel pathophysiological player in cerebral ischemia. In summary, restriction-mediated differential display has proven its suitability for screening complex samples such as brain to reliably identify regulated genes, which can uncover novel pathophysiological mechanisms.

Adrenomedullin and cancer

Adrenomedullin (AM) is a pluripotent hormone with structural similarities to calcitonin gene-related peptide (CGRP), which is expressed by many tissues in the body and shows a remarkable range of effects mediated by paracrine/autocrine and possibly endocrine mechanisms. AM has been implicated as a mediator of several pathologies such as cardiovascular and renal disorders, sepsis, inflammation, diabetes and cancer, among others. AM is expressed in a variety of tumors where it aggravates several of the molecular and physiological features of malignant cells. AM has been shown to be a mitogenic factor stimulating growth in several cancer types and to encourage a more aggressive tumor phenotype. In addition, AM is an apoptosis survival factor for cancer cells and an indirect suppressor of the immune response through its binding protein, complement factor H, and regulation in expression of cytokines. AM plays an important role in environments subjected to low oxygen tensions, which is a typical feature in the proximity of solid tumors. Under these conditions, AM is upregulated through a hypoxia-inducible factor 1 (HIF-1)-dependent pathway and acts as a potent angiogenic factor promoting neovascularization. The collective findings brought together over the last years place AM as a major regulator of carcinogenesis-tumor progression and identifies its autocrine loop as a putative target for developing new strategies against human cancers.

Neuroglobin protects the brain from experimental stroke in vivo

Neuroglobin (Ngb) is an O(2)-binding protein localized to cerebral neurons of vertebrates, including humans. Its physiological role is unknown but, like hemoglobin, myoglobin, and cytoglobin/histoglobin, it may transport O(2), detoxify reactive oxygen species, or serve as a hypoxia sensor. We reported recently that hypoxia stimulates transcriptional activation of Ngb in cultured cortical neurons and that antisense inhibition of Ngb expression increases hypoxic neuronal injury, whereas overexpression of Ngb confers resistance to hypoxia. These findings are consistent with a role for Ngb in promoting neuronal survival after hypoxic insults in vitro. Here we report that in rats, intracerebroventricular administration of an Ngb antisense, but not sense, oligodeoxynucleotide increases infarct volume and worsens functional neurological outcome, whereas intracerebral administration of a Ngb-expressing adeno-associated virus vector reduces infarct size and improves functional outcome, after focal cerebral ischemia induced by occlusion of the middle cerebral artery. We conclude that Ngb acts as an endogenous neuroprotective factor in focal cerebral ischemia and may therefore represent a target for the development of new treatments for stroke.

Adrenomedullin, an autocrine mediator of blood-brain barrier function

Since the discovery that adrenomedullin gene expression is 20- to 40-fold higher in endothelial cells than even in the adrenal medulla, this peptide has been regarded as an important secretory product of the vascular endothelium, together with nitric oxide, eicosanoids, endothelin-1, and other vasoactive metabolites. Cerebral endothelial cells secrete an exceptionally large amount of adrenomedullin, and the adrenomedullin concentration is about 50% higher in the cerebral circulation than in the peripheral vasculature. The adrenomedullin production of cerebral endothelial cells is induced by astrocyte-derived factors. Adrenomedullin causes vasodilation in the cerebral circulation, may participate in the maintenance of the resting cerebral blood flow, and may be protective against ischemic brain injury. Recent data from our laboratory indicate that adrenomedullin, as an endothelium-derived autocrine/paracrine hormone, plays an important role in the regulation of specific blood-brain barrier properties. Adrenomedullin is suggested to be one of the physiological links between astrocyte-derived factors, cyclic adenosine 3'5'-monophosphate (cAMP), and the induction and maintenance of the blood-brain barrier. Moreover, the role of adrenomedullin in the differentiation and proliferation of endothelial cells and in angiogenesis suggests a more complex function for adrenomedullin in the cerebral circulation and in the development of the blood-brain barrier.

Brain genomic response following hypoxia and re-oxygenation in the neonatal rat. Identification of genes that might contribute to hypoxia-induced ischemic tolerance

Hypoxic preconditioning (8% O2, 3 h) produces tolerance 24 h after hypoxic-ischemic brain injury in neonatal rats. To better understand the ischemic tolerance mechanisms induced by hypoxia, we used oligonucleotide microarrays to examine genomic responses in neonatal rat brain following 3 h of hypoxia (8% O2) and either 0, 6, 18, or 24 h of re-oxygenation. The results showed that hypoxia-inducible factor (HIF)-1- but not HIF-2-mediated gene expression may be involved in brain hypoxia-induced tolerance. Among the genes regulated by hypoxia, 12 genes were confirmed by real time reverse transcriptase-PCR as follows: VEGF, EPO, GLUT-1, adrenomedullin, propyl 4-hydroxylase alpha, MT-1, MKP-1, CELF, 12-lipoxygenase, t-PA, CAR-1, and an expressed sequence tag. Some genes, for example GLUT-1, MT-1, CELF, MKP-1, and t-PA did not show any hypoxic regulation in either astrocytes or neurons, suggesting that other cells are responsible for the up-regulation of these genes in the hypoxic brain. These genes were expressed in normal and hypoxic brain, heart, kidney, liver, and lung, with adrenomedullin, MT-1, and VEGF being prominently induced in brain by hypoxia. These results suggest that a number of endogenous molecular mechanisms may explain how hypoxic preconditioning protects against subsequent ischemia, and may provide novel therapeutic targets for treatment of cerebral ischemia.

Adrenomedullin over-expression in the caudate-putamen of the adult rat brain after ischaemia-reperfusion injury

The expression of adrenomedullin (AM) was studied in the caudate-putamen of the adult rat brain using a global cerebral ischaemia model. The animals were subjected to 30 min of glucose and oxygen deprivation, and the brains were collected after 0, 2, 4, 6, 8 and 10 h of reperfusion. Coronal sections of the caudate-putamen were studied by immunocytochemistry using a specific polyclonal antibody against AM and examined by light microscopy. Under these experimental conditions AM immunoreactivity increased in the wall of the blood vessels and in three different types of neurons distributed throughout the caudate-putamen. Our findings suggest that the over-expression of AM and its changes in its intracellular location might be involved in the neuronal responses to brain ischaemia with a possible neuroprotector role.