The effect of endothelin receptor A antagonism on basilar artery endothelium-dependent relaxation after ischemic stroke

Maternal high-fat diet programs cerebrovascular remodeling in adult rat offspring

Maternal environmental factors such as diet have consequences on later health of the offspring. We found that maternal high-fat diet (HFD) exposure renders adult offspring brain more susceptible to ischemic injury. The present study was further to investigate whether HFD consumption during rat pregnancy and lactation influences the cerebral vasculature in adult male offspring. Besides the endothelial damage observed in the transmission electron microscopy, the MCAs of offspring from fat-fed dams fed with control diet (HFD/C) also displayed increased wall thickness and media/lumen ratio, suggesting that cerebrovascular hypertrophy or hyperplasia occurs. Moreover, smaller lumen diameter and elevated myogenic tone of the MCAs over a range of intralumenal pressures indicate inward cerebrovascular remodeling in HFD/C rats, with a concomitant increase in vessel stiffness. More importantly, both wire and pressure myography demonstrated that maternal HFD intake also enhanced the MCAs contractility to ET-1, accompanied by increases in ET types A receptor (ET_AR) but not B (ET_BR) density in the arteries. Furthermore, ET_AR antagonism but not ET_BR antagonism restored maternal HFD-induced cerebrovascular dysfunction in adult offspring. Taken together, maternal diet can substantially influence adult offspring cerebrovascular health, through remodeling of both structure and function, at least partially in an ET-1 manner.

Enhancing cerebral perfusion with external counterpulsation after ischaemic stroke: how long does it last?

OBJECTIVE

External counterpulsation (ECP) is a non-invasive method used to augment cerebral perfusion in ischaemic stroke. We aimed to investigate time-course effects on blood pressure elevation and cerebral blood flow augmentation induced by ECP in ischaemic stroke.

METHODS

Patients with acute unilateral ischaemic stroke and large artery occlusive disease were recruited to receive 35 daily 1 h ECP treatment sessions. Serial transcranial Doppler monitoring of bilateral middle cerebral arteries was performed on days 3, 5, 7, 10, 14, 21, 28 and 35 after stroke onset. Flow velocity changes before, during and after ECP and continuous beat-to-beat blood pressure data were recorded. The cerebral augmentation index (CAI) is the increase in the percentage of the middle cerebral artery mean flow velocity during ECP compared with baseline.

RESULTS

The CAI in patients with stroke was significantly higher on the ipsilateral side and on the contralateral side on day 3 (ipsilateral CAI, 9.3%; contralateral CAI, 7.2%), day 5 (7.0%; 6.7%), day 7 (6.8%; 6.0%), day 10 (6.0%; 5.1%), day 14 (4.7%; 2.6%) and day 21 (4.1%; 2.2%) after stroke onset than that in controls (-2.0%) (all p<0.05). There was a significant trend of decreasing CAI on the ipsilateral and contralateral sides over time after a stroke. Differences in the percentage increase in the mean blood pressure did not change significantly over time in patients with stroke.

CONCLUSIONS

Blood pressure elevation persists throughout ECP treatment, which consists of 35 sessions. However, cerebral blood flow augmentation may last at least 3 weeks and then appears to return to baseline 1 month after acute stroke onset.

Key Immune Events of the Pathomechanisms of Early Cardioembolic Stroke: Multi-Database Mining and Systems Biology Approach

While inflammation has generally been regarded as a negative factor in stroke recovery, this viewpoint has recently been challenged by demonstrating that inflammation is a necessary and sufficient factor for regeneration in the zebrafish brain injury model. This close relationship with inflammation suggests that a re-examination of the immune system’s role in strokes is necessary. We used a systems biology approach to investigate the role of immune-related functions via their interactions with other molecular functions in early cardioembolic stroke. Based on protein interaction models and on microarray data from the blood of stroke subjects and healthy controls, networks were constructed to delineate molecular interactions at four early stages (pre-stroke, 3 h, 5 h and 24 h after stroke onset) of cardioembolic stroke. A comparative analysis of functional networks identified interactions of immune-related functions with other molecular functions, including growth factors, neuro/hormone and housekeeping functions. These provide a potential pathomechanism for early stroke pathophysiology. In addition, several potential targets of miRNA and methylation regulations were derived based on basal level changes observed in the core networks and literature. The results provide a more comprehensive understanding of stroke progression mechanisms from an immune perspective and shed light on acute stroke treatments.

Tumor necrosis factor-α inhibition attenuates middle cerebral artery remodeling but increases cerebral ischemic damage in hypertensive rats

Hypertension causes vascular inflammation evidenced by an increase in perivascular macrophages and proinflammatory cytokines in the arterial wall. Perivascular macrophage depletion reduced tumor necrosis factor (TNF)-α expression in cerebral arteries of hypertensive rats and attenuated inward remodeling, suggesting that TNF-α might play a role in the remodeling process. We hypothesized that TNF-α inhibition would improve middle cerebral artery (MCA) structure and reduce damage after cerebral ischemia in hypertensive rats. Six-week-old male stroke-prone spontaneously hypertensive rats (SHRSP) were treated with the TNF-α inhibitor etanercept (ETN; 1.25 mg·kg(-1)·day(-1) ip daily) or PBS (equivolume) for 6 wk. The myogenic tone generation, postischemic dilation, and passive structure of MCAs were assessed by pressure myography. Cerebral ischemia was induced by MCA occlusion (MCAO). Myogenic tone was unchanged, but MCAs from SHRSP + ETN had larger passive lumen diameter and reduced wall thickness and wall-to-lumen ratio. Cerebral infarct size was increased in SHRSP + ETN after transient MCAO, despite an improvement in dilation of nonischemic MCA. The increase in infarct size was linked to a reduction in the number of microglia in the infarct core and upregulation of markers of classical macrophage/microglia polarization. There was no difference in infarct size after permanent MCAO or when untreated SHRSP subjected to transient MCAO were given ETN at reperfusion. Our data suggests that TNF-α inhibition attenuates hypertensive MCA remodeling but exacerbates cerebral damage following ischemia/reperfusion injury likely due to inhibition of the innate immune response of the brain.

Mechanisms of action of hyperbaric oxygenation in stroke: a review

This article outlines the therapeutic mechanisms of hyperbaric oxygenation in acute stroke, based on information obtained from peer-reviewed medical literature. Hyperbaric oxygen is an approved treatment modality for ischemia-reperfusion injury in several conditions. It maintains the viability of the marginal tissue, reduces the mitochondrial dysfunction, metabolic penumbra, and blocks inflammatory cascades observed in acute stroke. Basic and clinical data suggest that hyperbaric oxygen could be a safe and effective treatment option in the management of acute stroke. Further work is needed to clarify its clinical utility when applied within the treatment window of "gold standard" treatments (<3-5 hours).

New insights into the mechanism of action of endothelin-1 on cerebral microcirculation

EVALUATION OF: Faraco G, Moraga A, Moore J, Anrather J, Pickel VM, Iadecola C. Circulating endothelin-1 alters critical mechanisms regulating cerebral microcirculation. Hypertension 62(4), 759–766 (2013). This article reviews a study by Faraco and colleagues that attempts to elucidate the mechanism of modulation of the cerebral blood flow by endothelin (ET) 1. ET1 is one of the most powerful vasoconstrictors and plays an important role in cerebrovascular disease and traumatic brain injury. However, the details of the mechanism of action of ET1 are still unknown. The study used a mouse model with a skull window through which the cortical cerebral blood flow was measured with a laser Doppler probe while various agents were applied. The role of reactive oxygen species and integrity of the blood–brain barrier were also assessed. In addition, the location of the ET receptor was determined by incubation of cortex samples with specific antibodies. ET1 increased mean arterial pressure and attenuated the cerebral blood flow increase stimulated by neuronal activity or the endothelium-dependent acethylcholine but not by A23187. ET1 suppresses the endothelial production of nitric oxide by modulating the endothelial nitric oxide synthase phosphorylation through Rho-associated protein kinase. This effect was mediated by an ETA receptor coupled to phospholipase C via GTP-binding protein and was not related to oxidative stress. The ETA receptor was found in the smooth muscle cells of the pial arterioles and cerebral endothelial cells. The resultant vascular dysfunction may increase the risk of brain ischemia by attenuating the cerebrovascular reserve. Improved understanding of the mechanism of action of ET1 on cerebral microcirculation is likely to stimulate the development of new and promising pharmacological targets.

Protein nitration impairs the myogenic tone of rat middle cerebral arteries in both ischemic and nonischemic hemispheres after ischemic stroke

The myogenic response is crucial for maintaining vascular resistance to achieve constant perfusion during pressure fluctuations. Reduced cerebral blood flow has been reported in ischemic and nonischemic hemispheres after stroke. Ischemia-reperfusion injury and the resulting oxidative stress impair myogenic responses in the ischemic hemisphere. Yet, the mechanism by which ischemia-reperfusion affects the nonischemic side is still undetermined. The goal of the present study was to determine the effect of ischemia-reperfusion injury on the myogenic reactivity of cerebral vessels from both hemispheres and whether protein nitration due to excess peroxynitrite production is the underlying mechanism of loss of tone. Male Wistar rats were subjected to sham operation or 30-min middle cerebral artery occlusion/45-min reperfusion. Rats were administered saline, the peroxynitrite decomposition catalyst 5,10,15,20-tetrakis(4-sulfonatophenyl)prophyrinato iron (III), or the nitration inhibitor epicatechin at reperfusion. Middle cerebral arteries isolated from another set of control rats were exposed to ex vivo oxygen-glucose deprivation with and without glycoprotein 91 tat (NADPH oxidase inhibitor) or N(ω)-nitro-l-arginine methyl ester. Myogenic tone and nitrotyrosine levels were determined. Ischemia-reperfusion injury impaired the myogenic tone of vessels in both hemispheres compared with the sham group (P < 0.001). Vessels exposed to ex vivo oxygen-glucose deprivation experienced a similar loss of myogenic tone. Inhibition of peroxynitrite parent radicals significantly improved the myogenic tone. Peroxynitrite scavenging or inhibition of nitration improved the myogenic tone of vessels from ischemic (P < 0.001 and P < 0.05, respectively) and nonischemic (P < 0.01 and P < 0.05, respectively) hemispheres. Nitration was significantly increased in both hemispheres versus the sham group and was normalized with epicatechin treatment. In conclusion, ischemia-reperfusion injury impairs vessel reactivity in both hemispheres via nitration. We suggest that sham operation rather than the nonischemic side should be used as a control in preclinical stroke studies.

Mechanisms of enhanced basal tone of brain parenchymal arterioles during early postischemic reperfusion: role of ET-1-induced peroxynitrite generation

The contributions of vasoconstrictors (endothelin-1 (ET-1), peroxynitrite) and endothelium-dependent vasodilatory mechanisms to basal tone were investigated in parenchymal arterioles (PAs) after early postischemic reperfusion. Transient middle cerebral artery occlusion (tMCAO) was induced for 2 hours with 30 minutes reperfusion in male Wistar rats and compared with ischemia alone (permanent MCAO (pMCAO); 2.5 hours) or sham controls. Changes in lumen diameter of isolated and pressurized PAs were compared. Quantitative PCR was used to measure endothelin type B (ETB) receptors. Constriction to intravascular pressure ('basal tone') was not affected by tMCAO or pMCAO. However, constriction to inhibitors of endothelial cell, small- (SK) and intermediate- (IK) conductance, Ca(2+)-sensitive K(+) channels (apamin and TRAM-34, respectively) were significantly enhanced in PAs from tMCAO compared with pMCAO or sham. Addition of the ETB agonist sarafotoxin caused constriction in PAs from tMCAO but not from sham animals (21 ± 4% versus 3 ± 3% at 1 nmol/L; P<0.01) that was inhibited by the peroxynitrite scavenger FeTMPyP (5,10,15,20-tetrakis (N-methyl-4'-pyridyl) porphinato iron (III) chloride) (100 μmol/L). Expression of ETB receptors was not found on PA smooth muscle, suggesting that constriction to sarafotoxin after tMCAO was due to peroxynitrite and not ETB receptor expression. The maintenance of basal tone in PAs after tMCAO may restrict flow to the ischemic region and contribute to infarct expansion.

The effects of hypertension on the cerebral circulation

Maintenance of brain function depends on a constant blood supply. Deficits in cerebral blood flow are linked to cognitive decline, and they have detrimental effects on the outcome of ischemia. Hypertension causes alterations in cerebral artery structure and function that can impair blood flow, particularly during an ischemic insult or during periods of low arterial pressure. This review will focus on the historical discoveries, novel developments, and knowledge gaps in 1) hypertensive cerebral artery remodeling, 2) vascular function with emphasis on myogenic reactivity and endothelium-dependent dilation, and 3) blood-brain barrier function. Hypertensive artery remodeling results in reduction in the lumen diameter and an increase in the wall-to-lumen ratio in most cerebral arteries; this is linked to reduced blood flow postischemia and increased ischemic damage. Many factors that are increased in hypertension stimulate remodeling; these include the renin-angiotensin-aldosterone system and reactive oxygen species levels. Endothelial function, vital for endothelium-mediated dilation and regulation of myogenic reactivity, is impaired in hypertension. This is a consequence of alterations in vasodilator mechanisms involving nitric oxide, epoxyeicosatrienoic acids, and ion channels, including calcium-activated potassium channels and transient receptor potential vanilloid channel 4. Hypertension causes blood-brain barrier breakdown by mechanisms involving inflammation, oxidative stress, and vasoactive circulating molecules. This exposes neurons to cytotoxic molecules, leading to neuronal loss, cognitive decline, and impaired recovery from ischemia. As the population ages and the incidence of hypertension, stroke, and dementia increases, it is imperative that we gain a better understanding of the control of cerebral artery function in health and disease.

Early effects of high-fat diet on neurovascular function and focal ischemic brain injury

Obesity is a risk factor for stroke, but the early effects of high-fat diet (HFD) on neurovascular function and ischemic stroke outcomes remain unclear. The goal of this study was to test the hypotheses that HFD beginning early in life 1) impairs neurovascular coupling, 2) causes cerebrovascular dysfunction, and 3) worsens short-term outcomes after cerebral ischemia. Functional hyperemia and parenchymal arteriole (PA) reactivity were measured in rats after 8 wk of HFD. The effect of HFD on basilar artery function after middle cerebral artery occlusion (MCAO) and associated O-GlcNAcylation were assessed. Neuronal cell death, infarct size, hemorrhagic transformation (HT) frequency/severity, and neurological deficit were evaluated after global ischemia and transient MCAO. HFD caused a 10% increase in body weight and doubled adiposity without a change in lipid profile, blood glucose, and blood pressure. Functional hyperemia and PA relaxation were decreased with HFD. Basilar arteries from stroked HFD rats were more sensitive to contractile factors, and acetylcholine-mediated relaxation was impaired. Vascular O-GlcNAcylated protein content was increased with HFD. This group also showed greater mortality rate, infarct volume, HT occurrence rate, and HT severity and poor functional outcome compared with the control diet group. These results indicate that HFD negatively affects neurovascular coupling and cerebrovascular function even in the absence of dyslipidemia. These early cerebrovascular changes may be the cause of greater cerebral injury and poor outcomes of stroke in these animals.