Comparison between early and delayed systemic treatment with candesartan of rats after ischaemic stroke

Lower Serum Potassium Levels at Admission are Associated with the Risk of Recurrent Stroke in Patients with Acute Ischemic Stroke or Transient Ischemic Attack

INTRODUCTION

Serum potassium abnormality is a risk factor of incident stroke, but whether it is associated with recurrent stroke in patients with acute ischemic stroke (AIS) or transient ischemic attack (TIA) remains unknown. This study aimed to investigate the association of serum potassium with the risk of recurrent stroke in patients with AIS or TIA.

METHODS

We included 12,425 patients from the China National Stroke Registry III. Patients were classified into 3 groups according to tertiles of potassium. The outcomes were recurrence of stroke and combined vascular events at 1 year. Cox proportional hazards regression was adopted to explore the associations by calculating hazard ratios (HRs) and their 95% confidence intervals (CIs).

RESULTS

Among 12,425 enrolled patients, the median (interquartile range) of potassium was 3.92 (3.68-4.19) mmol/L. Compared with the highest tertile, after adjusted for confounding factors, the lowest tertile potassium was associated with increased risk of recurrent stroke at 1 year. The adjusted HR with 95% CI was 1.21 (1.04-1.41). There was an independent, linear association between serum potassium and stroke recurrence. Per 1 mmol/L decrease of potassium was associated with 19% higher risk of recurrent stroke (HR, 1.19; 95% CI, 1.04-1.37). Similar trends were found in ischemic stroke and combined vascular events.

CONCLUSIONS

Lower serum potassium level was independently associated with elevated risk of recurrent stroke in patients with AIS or TIA. The finding suggested that monitoring serum potassium may help physicians to identify patients at high risk of recurrent stroke and to stratify risk for optimal management.

The Role of Sartans in the Treatment of Stroke and Subarachnoid Hemorrhage: A Narrative Review of Preclinical and Clinical Studies

Background: Delayed cerebral vasospasm (DCVS) due to aneurysmal subarachnoid hemorrhage (aSAH) and its sequela, delayed cerebral ischemia (DCI), are associated with poor functional outcome. Endothelin-1 (ET-1) is known to play a major role in mediating cerebral vasoconstriction. Angiotensin-II-type-1-receptor antagonists such as Sartans may have a beneficial effect after aSAH by reducing DCVS due to crosstalk with the endothelin system. In this review, we discuss the role of Sartans in the treatment of stroke and their potential impact in aSAH. Methods: We conducted a literature research of the MEDLINE PubMed database in accordance with PRISMA criteria on articles published between 1980 to 2019 reviewing: "Sartans AND ischemic stroke". Of 227 studies, 64 preclinical and 19 clinical trials fulfilled the eligibility criteria. Results: There was a positive effect of Sartans on ischemic stroke in both preclinical and clinical settings (attenuating ischemic brain damage, reducing cerebral inflammation and infarct size, increasing cerebral blood flow). In addition, Sartans reduced DCVS after aSAH in animal models by diminishing the effect of ET-1 mediated vasoconstriction (including cerebral inflammation and cerebral epileptogenic activity reduction, cerebral blood flow autoregulation restoration as well as pressure-dependent cerebral vasoconstriction). Conclusion: Thus, Sartans might play a key role in the treatment of patients with aSAH.

Hypertensive Response to Ischemic Stroke in the Normotensive Wistar Rat

Background and Purpose—

Over 80% of ischemic stroke patients show an abrupt increase in arterial blood pressure in the hours and days following ischemic stroke. Whether this poststroke hypertension is beneficial or harmful remains controversial and the underlying physiological basis is unclear.

Methods—

To investigate the dynamic cardiovascular response to stroke, adult Wistar rats (n=5–8 per group, 393±34 g) were instrumented with telemeters to blood pressure, intracranial pressure, renal sympathetic nerve activity, and brain tissue oxygen in the predicted penumbra (P o 2 ). After 2 weeks of recovery, cardiovascular signals were recorded for a 3-day baseline period, then ischemic stroke was induced via transient middle cerebral artery occlusion, or sham surgery. Cardiovascular signals were then recorded for a further 10 days, and the functional sensorimotor recovery assessed using the cylinder and sticky dot tests.

Results—

Baseline values of all variables were similar between groups. Compared to sham, in the 2 days following stroke middle cerebral artery occlusion produced an immediate, transient rise above baseline in mean blood pressure (21±3 versus 2±4 mm Hg; P <0.001), renal sympathetic nerve activity (54±11% versus 7±4%; P =0.006), and cerebral perfusion pressure (12±5 versus 1±4; P ≤0.001). Intracranial pressure increased more slowly, peaking 3 days after middle cerebral artery occlusion (14±6 versus −1±1 mm Hg; P <0.001). Treating with the antihypertensive agent nifedipine after stroke (1.5–0.75 mg/kg per hour SC) ameliorated poststroke hypertension (12±3 mm Hg on day 1; P =0.041), abolished the intracranial pressure increase (3±1; P <0.001) and reduced cerebral perfusion pressure (10±3 mm Hg; P =0.017). Preventing poststroke hypertension affected neither the recovery of sensorimotor function nor infarct size.

Conclusions—

These findings suggest that poststroke hypertension is immediate, temporally matched to an increase in sympathetic outflow, and elevates cerebral perfusion pressure for several days after stroke, which may enhance cerebral perfusion. Preventing poststroke hypertension does not appear to worsen prognosis after stroke in young, normotensive, and otherwise healthy rats.

Visual Overview—

An online visual overview is available for this article.

Silencing VEGF-B Diminishes the Neuroprotective Effect of Candesartan Treatment After Experimental Focal Cerebral Ischemia

The pro-survival effect of VEGF-B has been documented in different in vivo and in vitro models. We have previously shown an enhanced VEGF-B expression in response to candesartan treatment after focal cerebral ischemia. In this study, we aimed to silence VEGF-B expression to assess its contribution to candesartan's benefit on stroke outcome. Silencing VEGF-B expression was achieved by bilateral intracerebroventricular injections of lentiviral particles containing short hairpin RNA (shRNA) against VEGF-B. Two weeks after lentiviral injections, rats were subjected to either 90 min or 3 h of middle cerebral artery occlusion (MCAO) and randomized to intravenous candesartan (1 mg/kg) or saline at reperfusion. Animals were sacrificed at 24 or 72 h and brains were collected and analyzed for hemoglobin (Hb) excess and infarct size, respectively. Functional outcome at 24, 48 and 72 h was assessed blindly. Candesartan treatment improved neurobehavioral and motor function, and decreased infarct size and Hb. While silencing VEGF-B expression diminished candesartan's neuroprotective effect, candesartan-mediated vascular protection was maintained even in the absence of VEGF-B suggesting that this growth factor is not the mediator of candesartan's vascular protective effects. However, VEGF-B is a mediator of neuroprotection achieved by candesartan and represents a potential drug target to improve stroke outcome. Further studies are needed to elucidate the underlying molecular mechanisms of VEGF-B in neuroprotection and recovery after ischemic stroke.

Cell-based and pharmacological neurorestorative therapies for ischemic stroke

Ischemic stroke remains one of most common causes of death and disability worldwide. Stroke triggers a cascade of events leading to rapid neuronal damage and death. Neuroprotective agents that showed promise in preclinical experiments have failed to translate to the clinic. Even after decades of research, tPA remains the only FDA approved drug for stroke treatment. However, tPA is effective when administered 3-4.5 h after stroke onset and the vast majority of stroke patients do not receive tPA therapy. Therefore, there is a pressing need for novel therapies for ischemic stroke. Since stroke induces rapid cell damage and death, neuroprotective strategies that aim to salvage or replace injured brain tissue are challenged by treatment time frames. To overcome the barriers of neuroprotective therapies, there is an increasing focus on neurorestorative therapies for stroke. In this review article, we provide an update on neurorestorative treatments for stroke using cell therapy such as bone marrow derived mesenchymal stromal cells (BMSCs), human umbilical cord blood cells (HUCBCs) and select pharmacological approaches including Minocycline and Candesartan that have been employed in clinical trials. This review article discusses the present understanding of mechanisms of neurorestorative therapies and summarizes ongoing clinical trials. This article is part of the Special Issue entitled 'Cerebral Ischemia'.

Neuroprotective effects of AT1 receptor antagonists after experimental ischemic stroke: what is important?

The present study conducted in rats defines the requirements for neuroprotective effects of systemically administered AT1 receptor blockers (ARBs) in acute ischaemic stroke. The inhibition of central effects to angiotensin II (ANG II) after intravenous (i.v.) treatment with candesartan (0.3 and 3 mg/kg) or irbesartan and losartan (3 and 30 mg/kg) was employed to study the penetration of these ARBs across the blood-brain barrier. Verapamil and probenecid were used to assess the role of the transporters, P-glycoprotein and the multidrug resistance-related protein 2, in the entry of losartan and irbesartan into the brain. Neuroprotective effects of i.v. treatment with the ARBs were investigated after transient middle cerebral artery occlusion (MCAO) for 90 min. The treatment with the ARBs was initiated 3 h after the onset of MCAO and continued for two consecutive days. Blood pressure was continuously recorded before and during MCAO until 5.5 h after the onset of reperfusion. The higher dose of candesartan completely abolished, and the lower dose of candesartan and higher doses of irbesartan and losartan partially inhibited the drinking response to intracerebroventricular ANG II. Only 0.3 mg/kg candesartan improved the recovery from ischaemic stroke, and 3 mg/kg candesartan did not exert neuroprotective effects due to marked blood pressure reduction during reperfusion. Both doses of irbesartan and losartan had not any effect on the stroke outcome. An effective, long-lasting blockade of brain AT1 receptors after systemic treatment with ARBs without extensive blood pressure reductions is the prerequisite for neuroprotective effects in ischaemic stroke.

Mechanisms of acute neurovascular protection with AT1 blockade after stroke: Effect of prestroke hypertension

Stroke is a leading cause of adult disability worldwide. Improving stroke outcome requires an orchestrated interplay that involves up regulation of pro-survival pathways and a concomitant suppression of pro-apoptotic mediators. In this investigation, we assessed the involvement of eNOS in the AT1 blocker-mediated protective and pro-recovery effects in animals with hypertension. We also evaluated the effect of acute eNOS inhibition in hypertensive animals. To achieve these goals, spontaneously hypertensive rats (SHR) were implanted with blood pressure transmitters, and randomized to receive either an eNOS inhibitor (L-NIO) or saline one hour before cerebral ischemia induction. After 3 hours of ischemia, animals were further randomized to receive either candesartan or saline at the time of reperfusion and sacrificed either 24 hours or 7 days later. Candesartan induced an early protective effect that was independent of eNOS inhibition (50% improvement in motor function). However, the protective effect of candesartan was associated with about five fold up regulation of BDNF expression and about three fold reduction in ER stress markers, in an eNOS dependent manner. The early benefit of a single dose of candesartan, present at 24 hours after stroke, was diminished at 7 days, perhaps due to a failure to induce an angiogenic response in these hypertensive animals. In conclusion, our findings demonstrate an early prorecovery effect of candesartan at both functional and molecular levels. Candesartan induced prorecovery signaling was mediated through eNOS. This effect was not maintained at 7 days after experimental ischemia.

Transient Mild Cerebral Ischemia Significantly Deteriorated Cognitive Impairment in a Mouse Model of Alzheimer's Disease via Angiotensin AT1 Receptor

BACKGROUND

Ischemic stroke is suggested to be potentially associated with cognitive impairment in Alzheimer's disease (AD). We hypothesized that cerebral ischemia deteriorates cognitive impairment in AD, through angiotensin II.

METHODS

We used 5XFAD mouse, a model of AD with vascular and cerebral amyloid-β deposition. Transient cerebral ischemia of mice was induced by bilateral common carotid artery occlusion (BCCAO) for 17 minutes. The posttreatment with olmesartan, an ARB, or vehicle was started at 24 hours after BCCAO and was performed for 5 weeks. Experimental mice consisted of 5 groups: (i) wild-type mice, (ii) wild-type mice with BCCAO, (iii) 5XFAD mice, (iv) 5XFAD mice with BCCAO, (v) 5XFAD mice with BCCAO and olmesartan postadministration.

RESULTS

BCCAO in 5XFAD caused greater escape latency (P < 0.01) on water maze test than that in wild type, indicating that transient brief cerebral ischemia enhanced cognitive decline in 5XFAD mice. Posttreatment with olmesartan significantly reduced escape latency (P < 0.01) on water maze test, retention trial latency (P < 0.05) on passive avoidance test, and retention time of outer zone (P < 0.01) on open-field test in 5XFAD subjected to BCCAO. This protective effect of olmesartan against cognitive impairment in 5XFAD with BCCAO was associated with the protection of neuron and attenuation of oxidative stress in hippocampus and the suppression of blood-brain barrier disruption.

CONCLUSIONS

We obtained the evidence that transient brief cerebral ischemia deteriorated cognitive impairment in AD model through AT1 receptor.

Renin-angiotensin system as a potential therapeutic target in stroke and retinopathy: experimental and clinical evidence

As our knowledge expands, it is now clear that the renin-angiotensin (Ang) system (RAS) mediates functions other than regulating blood pressure (BP). The RAS plays a central role in the pathophysiology of different neurovascular unit disorders including stroke and retinopathy. Moreover, the beneficial actions of RAS modulation in brain and retina have been documented in experimental research, but not yet exploited clinically. The RAS is a complex system with distinct yet interconnected components. Understanding the different RAS components and their functions under brain and retinal pathological conditions is crucial to reap their benefits. The aim of the present review is to provide an experimental and clinical update on the role of RAS in the pathophysiology and treatment of stroke and retinopathy. Combining the evidence from both these disorders allows a unique opportunity to move both fields forward.

Protective Effect of Aliskiren in Experimental Ischemic Stroke: Up-Regulated p-PI3K, p-AKT, Bcl-2 Expression, Attenuated Bax Expression

Aliskiren (ALK), a pharmacological renin inhibitor, is an effective antihypertensive drug and has potent anti-apoptotic activity, but it is currently unknown whether ALK is able to attenuate brain damage caused by acute cerebral ischemia independent of its blood pressure-lowering effects. This study aimed to investigate the role of ALK and its potential mechanism in cerebral ischemia. C57/BL6 mice were subjected to transient middle cerebral artery occlusion (tMCAO) and treated for 5 days with Vehicle or ALK (10 or 25 mg/kg per day via intragastric administration), whereas Sham-operated animals served as controls. Treatment with ALK significantly improved neurological deficits, infarct volume, brain water content and Nissl bodies after stroke (P < 0.05), which did not affect systemic blood pressure. Furthermore, the protection of ALK was also related to decreased levels of apoptosis in mice by enhanced activation of phosphatidylinositol 3-kinase (PI3K)/AKT pathway, increased level of Bcl-2 and reduced Bax expression (P < 0.05). In addition, ALK's effects were reversed by PI3K inhibitors LY294002 (P < 0.05). Our data indicated that ALK protected the brain from reperfusion injuries without affecting blood pressure, and this effect may be through PI3K/AKT signaling pathway.

Artery reopening is required for the neurorestorative effects of angiotensin modulation after experimental stroke

BACKGROUND

Blood flow restoration with fibrinolysis and thrombectomy is recommended to limit injury in stroke patients with proximal artery occlusion. Angiotensin receptor blockers have been shown to be neuroprotective in models of permanent and temporary occlusion, but the benefits on expression of trophic factors have been seen only when the artery is reopened. It is possible that early artery opening with endovascular intervention may increase the likelihood of identifying an effective combination therapy for patients.

METHODS

Normotensive male Wistar rats were subjected to mechanical middle cerebral artery occlusion (either temporary or permanent), followed by randomization to receive candesartan (0.3 mg/kg IV) or saline. Functional outcome, infarct size, and biochemical changes were assessed 24 h after ischemia induction.

RESULTS

Lack of reperfusion blunted candesartan induced neuroprotection (p < 0.05) and reduced the improvement of functional outcome (p < 0.05). With reperfusion, candesartan increased mature BDNF expression in the contralateral hemisphere (p < 0.05) and activated prosurvival (Akt-GSK3-β) signaling (p < 0.05). Without reperfusion, candesartan significantly reduced VEGF expression and MMP activation and increased NOGO A expression, creating an environment hostile to recovery.

CONCLUSION

Candesartan induced pro-recovery effects are dependent on the presence of reperfusion.

Neuroprotective Effect of Scutellarin on Ischemic Cerebral Injury by Down-Regulating the Expression of Angiotensin-Converting Enzyme and AT1 Receptor

Background and Purpose

Previous studies have demonstrated that angiotensin-converting enzyme (ACE) is involved in brain ischemic injury. In the present study, we investigated whether Scutellarin (Scu) exerts neuroprotective effects by down-regulating the Expression of Angiotensin-Converting Enzyme and AT1 receptor in a rat model of permanent focal cerebral ischemia.

Methods

Adult Sprague–Dawley rats were administrated with different dosages of Scu by oral gavage for 7 days and underwent permanent middle cerebral artery occlusion (pMCAO). Blood pressure was measured 7 days after Scu administration and 24 h after pMCAO surgery by using a noninvasive tail cuff method. Cerebral blood flow (CBF) was determined by Laser Doppler perfusion monitor and the neuronal dysfunction was evaluated by analysis of neurological deficits before being sacrificed at 24 h after pMCAO. Histopathological change, cell apoptosis and infarct area were respectively determined by hematoxylin–eosin staining, terminal deoxynucleotidyl transfer-mediated dUTP nick end labeling (TUNEL) analysis and 2,3,5-triphenyltetrazolium chloride staining. Tissue angiotensin II (Ang II) and ACE activity were detected by enzyme-linked immunosorbent assays. The expression levels of ACE, Ang II type 1 receptor (AT1R), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-1β (IL-1β) were measured by Western blot and real-time PCR. ACE inhibitory activity of Scu in vitro was detected by the photometric determination.

Results

Scu treatment dose-dependently decreased neurological deficit score, infarct area, cell apoptosis and morphological changes induced by pMCAO, which were associated with reductions of ACE and AT1R expression and the levels of Ang II, TNF-α, IL-6, and IL-1β in ischemic brains. Scu has a potent ACE inhibiting activity.

Conclusion

Scu protects brain from acute ischemic injury probably through its inhibitory effect on the ACE/Ang II/AT1 axis, CBF preservation and proinflammation inhibition.

Candesartan attenuates ischemic brain edema and protects the blood-brain barrier integrity from ischemia/reperfusion injury in rats

Background: Angiotensin II (Ang II) has an important role on cerebral microcirculation; however, its direct roles in terms of ischemic brain edema need to be clarified. This study evaluated the role of central Ang II by using candesartan, as an AT1 receptor blocker, in the brain edema formation and blood-brain barrier (BBB) disruption caused by ischemia/reperfusion (I/R) injuries in rat. Methods: Rats were exposed to 60-min middle cerebral artery (MCA) occlusion. Vehicle and non-hypotensive doses of candesartan (0.1 mg/kg) were administered one hour before ischemia. Neurological dysfunction scoring was evaluated following 24 h of reperfusion. Animals were then decapitated under deep anesthesia for the assessments of cerebral infarct size, edema formation, and BBB permeability. Results: The outcomes of 24 h reperfusion after 60-min MCA occlusion were severe neurological disability, massive BBB disruption (Evans blue extravasation = 12.5 ± 1.94 µg/g tissue), 4.02% edema, and cerebral infarction (317 ± 21 mm³). Candesartan at a dose of 0.1 mg/kg, without changing arterial blood pressure, improved neurological dysfunction scoring together with significant reductions in BBB disruption (54.9%), edema (59.2%), and cerebral infarction (54.9%). Conclusions: Inactivation of central AT1 receptors, if not accompanied with arterial hypotension, protected cerebral micro-vasculatures from damaging effects of acute stroke.

Sequential Therapy with Minocycline and Candesartan Improves Long-Term Recovery After Experimental Stroke

Minocycline and candesartan have both shown promise as candidate therapeutics in ischemic stroke, with multiple, and somewhat contrasting, molecular mechanisms. Minocycline is an anti-inflammatory, antioxidant, and anti-apoptotic agent and a known inhibitor of matrix metalloproteinases (MMPs). Yet, minocycline exerts antiangiogenic effects both in vivo and in vitro. Candesartan promotes angiogenesis and activates MMPs. Aligning these therapies with the dynamic processes of injury and repair after ischemia is likely to improve success of treatment. In this study, we hypothesize that opposing actions of minocycline and candesartan on angiogenesis, when administered simultaneously, will reduce the benefit of candesartan treatment. Therefore, we propose a sequential combination treatment regimen to yield a better outcome and preserve the proangiogenic potential of candesartan. In vitro angiogenesis was assessed using human brain endothelial cells. In vivo, Wistar rats subjected to 90-min middle cerebral artery occlusion (MCAO) were randomized into four groups: saline, candesartan, minocycline, and sequential combination of minocycline and candesartan. Neurobehavioral tests were performed 1, 3, 7, and 14 days after stroke. Brain tissue was collected on day 14 for assessment of infarct size and vascular density. Minocycline, when added simultaneously, decreased the proangiogenic effect of candesartan treatment in vitro. Sequential treatment, however, preserved the proangiogenic potential of candesartan both in vivo and in vitro, improved neurobehavioral outcome, and reduced infarct size. Sequential combination therapy with minocycline and candesartan improves long-term recovery and maintains candesartan's proangiogenic potential.

The protective arms of the renin-angiontensin system in stroke

It is quite well established that activation of the so-called protective arms of the renin-angiotensin system (RAS), involving both AT2 and Mas receptors, provides a counter-regulatory role to AT1 receptor overactivity that may drive pathological changes in the cardiovascular system. In this brief review, we will focus on recent evidence that identifies at least three different pathways that may be effective in the setting of stroke and may be complementary with AT1 receptor blockade. Such mechanisms include AT2 receptor stimulation, Mas receptor stimulation and insulin-regulated aminopeptidase blockade. This report highlights recent data demonstrating striking neuroprotective effects in preclinical models of stroke targeting each of these pathways, which may pave the way for translational opportunities in this field.

Low-dose candesartan enhances molecular mediators of neuroplasticity and subsequent functional recovery after ischemic stroke in rats

We have previously reported that angiotensin type 1 receptor (AT1R) blockade with candesartan exerts neurovascular protection after experimental cerebral ischemia. Here, we tested the hypothesis that a low, subhypotensive dose of candesartan enhances neuroplasticity and subsequent functional recovery through enhanced neurotrophic factor expression in rats subjected to ischemia reperfusion injury. Male Wistar rats (290-300 g) underwent 90 min of middle cerebral artery occlusion (MCAO) and received candesartan (0.3 mg/kg) or saline at reperfusion and then once every 24 h for 7 days. Functional deficits were assessed in a blinded manner at 1, 3, 7, and 14 days after MCAO. Animals were sacrificed 14-day post-stroke and the brains perfused for infarct size by cresyl violet. Western blot and immunohistochemistry were used to assess the expression of growth factors and synaptic proteins. Candesartan-treated animals showed a significant reduction in the infarct size [t (13) = -5.5, P = 0.0001] accompanied by functional recovery in Bederson [F (1, 13) = 7.9, P = 0.015], beam walk [F (1, 13) = 6.7, P = 0.023], grip strength [F (1, 13) = 15.2, P = 0.0031], and rotarod performance [F (1, 14) = 29.8, P < 0.0001]. In addition, candesartan-treated animals showed significantly higher expression of active metalloproteinase-3 (MMP-3), laminin, and angiopoietin-1 (Ang-1). The expression of vascular endothelial growth factor (VEGF) and brain-derived neurotrophic factor (BDNF) and its receptor was significantly increased in the animals treated with candesartan. Also, we observed significant increases in neuroplasticity markers, synaptophysin, and PSD-95. These results indicate that low-dose candesartan had a large and enduring effect on measures of plasticity, and this accompanied the functional recovery after ischemic stroke.

Attenuation of focal cerebral ischemic injury following post-ischemic inhibition of angiotensin converting enzyme (ACE) activity in normotensive rat

BACKGROUND

Central renin angiotensin system has an important role on the cerebral microcirculation and metabolism. Our previous work showed that inhibition of angiotensin converting enzyme (ACE) activity prior to induction of ischemia protected the brain from severe ischemia/reperfusion (I/R) injuries. This study evaluated the impacts of post-ischemic inhibition of ACE, enalapril, on brain infarction in normotensive rats.

METHODS

Rats were anesthetized with chloral hydrate (400 mg/kg). Focal cerebral ischemia was induced by 60-min intraluminal occlusion of right middle cerebral artery (MCA). Intraperitoneal injection of enalapril (0.03 or 0.1 mg/kg) was done after MCA reopening (reperfusion). Neurological deficit score (NDS) was evaluated after 24 h and the animals randomly assigned for the assessments of infarction, absolute brain water content (ABWC) and index of brain edema.

RESULTS

Severe impaired motor functions (NDS = 2.78 ± 0.28), massive infarction (cortex = 214 ± 19 mm3, striatum = 86 ± 5 mm3) and edema (ABWC = 83.1 ± 0.46%) were observed in non-treated ischemic rats. Non-hypotensive dose of enalapril (0.03 mg/kg) significantly reduced NDS (1.5 ± 0.22), infarction (cortex = 102 ± 16 mm3, striatum = 38 ± 5 mm3) and edema (ABWC = 80.9 ± 0.81%). Enalapril at dose of 0.1 mg/kg significantly lowered arterial pressure could not improve NDS (2.0 ± 0.45) and reduce infarction (cortex = 166 ± 26 mm3, striatum = 71 ± 11 mm3).

CONCLUSION

Post-ischemic ACE inhibition in the normotensive rats without affecting arterial pressure protects the brain from reperfusion injuries; however, this beneficial action is masked by hypotension.

Elevated blood pressure in the acute phase of stroke and the role of Angiotensin receptor blockers

Raised blood pressure (BP) is common after stroke but its causes, effects, and management still remain uncertain. We performed a systematic review of randomized controlled trials that investigated the effects of the angiotensin receptor blockers (ARBs) administered in the acute phase (≤72 hours) of stroke on death and dependency. Trials were identified from searching three electronic databases (Medline, Cochrane Library and Web of Science Database). Three trials involving 3728 patients were included. Significant difference in BP values between treatment and placebo was found in two studies. No effect of the treatment was seen on dependency, death and vascular events at one, three or six months; the cumulative mortality and the number of vascular events at 12 months differed significantly in favour of treatment in one small trial which stopped prematurely. Evidence raises doubts over the hypothesis of a specific effect of ARBs on short- and medium-term outcomes of stroke. It is not possible to rule out that different drugs might have different effects. Further trials are desirable to clarify whether current findings are generalizable or there are subgroups of patients or different approaches to BP management for which a treatment benefit can be obtained.

A Comparative Study of Neuroprotective Effect of Single and Combined Blockade of AT1 Receptor and PARP-1 in Focal Cerebral Ischaemia in Rat

Background

Cerebral ischaemia results in enhanced expression of type 1 angiotensin receptor and oxidative stress. Free radicals due to oxidative stress lead to excessive DNA damage causing overactivation of poly (ADP-ribose) polymerase-1 resulting in neuronal death. Activation of both type 1 angiotensin receptors and poly (ADP-ribose) polymerase-1 following cerebral ischaemia takes place simultaneously, but until now, no study has explored the effect of combined blockade of both angiotensin type 1 angiotensin receptor and poly (ADP-ribose) polymerase-1 in cerebral ischaemia.

Aim

Our purpose was to compare the effect of single and combined treatment with angiotensin type 1 angiotensin receptor blocker, candesartan, and the poly (ADP-ribose) polymerase-1 inhibitor, 1, 5 isoquinolinediol, on brain damage and oxidative stress in transient focal cerebral ischaemia in rats.

Method

Transient focal cerebral ischaemia was induced in Sprague-Dawley rats by an intraluminal technique for two-hours following 48 h of reperfusion. Candesartan (0·05 mg/kg) was administered just after initiation of ischaemia followed by a repeat administration at 24 h while 1, 5 isoquinolinediol (0·1 mg/kg) was given one-hour after of ischaemia. After 24 h of reperfusion, neurological deficit was evaluated in the different treatment groups. After 48 h of reperfusion, the rats were sacrificed and the brain was isolated. Ischaemic brain damage by 2,3,5 triphenyl tetrazolium chloride staining, oxidative stress markers, and levels of reactive oxygen species were determined biochemically.

Result

Single treatment with candesartan and 1, 5 isoquinolinediol significantly reduced neurological deficit, infarct, and oedema volume as compared to ischaemic control and different vehicle groups for each of the drugs. However, treatment with candesartan + 1, 5 isoquinolinediol offered greater reduction in neurological deficit, cerebral infarct volume, and oedema as compared to single-drug treatments. Furthermore, treatment with candesartan + 1, 5 isoquinolinediol significantly decreased oxidative stress as compared to single treatments with each drug.

Conclusion

The study suggests that blockade of either type 1 angiotensin receptor or poly (ADP-ribose) polymerase-1 alone provides neuroprotection, but the better result was achieved when both type 1 angiotensin receptor and poly (ADP-ribose) polymerase-1 were blocked together by the combined use of their pharmacological inhibitor in transient cerebral ischaemia in rat.

Treatment of rats with pioglitazone in the reperfusion phase of focal cerebral ischemia: a preclinical stroke trial

Thiazolidinediones (TZDs), pioglitazone, rosiglitazone and troglitazone, the synthetic agonists for the PPARγ, administered prior or during ischemic insult improve stroke outcome in rodents, post-occlusion treatments yielded inconsistent results. In the present experiments carried out according to the Stroke Therapy Academic Industry Roundtable (STAIR) guidelines, we studied the effects of post-ischemic pioglitazone treatment on the outcome of focal cerebral ischemia, inflammatory and apoptotic processes, neuronal degeneration and regeneration, blood pressure, heart rate and physiological variables in blood. Male Wistar rats were subjected to a 90 min middle cerebral artery occlusion (MCAO). Subcutaneous (SC) treatment with vehicle or pioglitazone was initiated 90 min after MCAO, i.e. in the post-ischemic, reperfusion phase and continued on 2 (2 day-experiment, protocol 1) or 5 (5-day experiment, protocol 2) consecutive days. In the 2-day experiment, pioglitazone at a dose of 2.5 mg/kg body weight (bw) reduced infarct volume by 31% and oedema by 43% on day 2 after MCAO and attenuated the infiltration of ischemic cortical tissue with activated microglia and macrophages. The slight reduction in infarct volume by approximately 18%, detected in rats treated with 10 mg/kg bw pioglitazone did not reach statistical significance. The neurological scores of sham-operated rats treated with vehicle or 10 mg/kg bw pioglitazone were not significantly different. In rats subjected to cerebral ischemia, post-ischemic treatment with either dose of pioglitazone alleviated particular motor deficits and sensory impairments on day 2 after MCAO. A single injection of 10 mg/kg bw pioglitazone in the reperfusion phase (90 min after the onset of reperfusion) did not modify systolic and diastolic blood pressure, heart rate and physiological variables compared to vehicle-treated rats at any time point after MCAO. In the 5-day experiment, continuous post-occlusion treatment with 2.5 mg/kg body weight pioglitazone significantly reduced cerebral infarction by 29% and improved the partial paralysis of the forelimb and alleviated sensory deficits. In the peri-infarct cortex, pioglitazone effectively suppressed the accumulation of activated microglia/macrophages, inhibited neuronal degeneration and promoted neuroregeneration and formation of neuronal networks. The current results provide evidence that pioglitazone treatment in the post-ischemic, reperfusion phase improves the recovery from ischemic stroke. Neuroprotective effects of pioglitazone are mediated by inhibition of post-ischemic inflammation and neuronal degeneration, protection of neurones against ischemic injury and by promoting of neuronal regeneration. Our data together with previous findings favour the view that pioglitazone is a promising candidate for clinical stroke trials.

Neuroprotective effect of an angiotensin receptor type 2 agonist following cerebral ischemia in vitro and in vivo

Background

Intracerebral administration of the angiotensin II type 2 receptor (AT₂R) agonist, CGP42112, is neuroprotective in a rat model of ischemic stroke. To explore further its possible cellular target(s) and therapeutic utility, we firstly examined whether CGP42112 may exert direct protective effects on primary neurons following glucose deprivation in vitro. Secondly, we tested whether CGP42112 is effective when administered systemically in a mouse model of cerebral ischemia.

Methods

Primary cortical neurons were cultured from E17 C57Bl6 mouse embryos for 9 d, exposed to glucose deprivation for 24 h alone or with drug treatments, and percent cell survival assessed using trypan blue exclusion. Ischemic stroke was induced in adult male C57Bl6 mice by middle cerebral artery occlusion for 30 min, followed by reperfusion for 23.5 h. Neurological assessment was performed and then mice were euthanized and infarct and edema volume were analysed.

Results

During glucose deprivation, CGP42112 (1x10^-8 M and 1x10^-7 M) reduced cell death by ~30%, an effect that was prevented by the AT₂R antagonist, PD123319 (1x10^-6 M). Neuroprotection by CGP42112 was lost at a higher concentration (1x10^-6 M) but was unmasked by co-application with the AT₁R antagonist, candesartan (1x10^-7 M). By contrast, Compound 21 (1x10^-8 M to 1x10^-6 M), a second AT₂R agonist, had no effect on neuronal survival. Mice treated with CGP42112 (1 mg/kg i.p.) after cerebral ischemia had improved functional outcomes over vehicle-treated mice as well as reduced total and cortical infarct volumes.

Conclusions

These results indicate that CGP42112 can directly protect neurons from ischemia-like injury in vitro via activation of AT₂Rs, an effect opposed by AT₁R activation at high concentrations. Furthermore, systemic administration of CGP42112 can reduce functional deficits and infarct volume following cerebral ischemia in vivo.

Therapeutic effects of postischemic treatment with hypotensive doses of an angiotensin II receptor blocker on transient focal cerebral ischemia

BACKGROUND

Neurovascular protection against cerebral ischemia is not consistently observed with a postischemia hypotensive dose of candesartan. The aim of this study was to determine the levels of brain angiotensin II after reperfusion and the efficacy and therapeutic time window of postischemic treatments with hypotensive doses of candesartan for the treatment of cerebral ischemia.

METHOD

Occlusions of the right middle cerebral artery (60 min) followed by reperfusion were performed using the thread method under halothane anesthesia in Sprague-Dawley (SD) rats. Protein levels of brain angiotensin II and mRNA levels of renin-angiotensin system components were evaluated following reperfusion (n=184 in total). Low-dose or high-dose treatments with candesartan cilexetil (1 or 10 mg/kg per day, respectively) were administered orally immediately following reperfusion once daily for 4 or 7 days (n = 119 in total). An additional group was treated with low-dose candesartan cilexetil after a 12-h delay based on the brain angiotensin II levels (n = 14).

RESULTS

Levels of brain angiotensin II transiently increased 4-12 h after reperfusion, which followed an increase in angiotensinogen mRNA. Candesartan cilexetil treatments significantly reduced blood pressure (BP) in rats administered the high dose and moderately in rats receiving the low dose. A low dose of candesartan cilexetil reduced the infarct size, cerebral edema, and neurological deficits, whereas the high-dose treatments showed limited reductions. Furthermore, oxidative stress following reperfusion was reduced with the low-dose treatments. The therapeutic time window was open for at least 12 h after reperfusion when brain angiotensin II levels had peaked.

CONCLUSION

Postischemic treatments using low hypotensive doses of candesartan cilexetil provided protection against cerebral ischemic injury and may have a clinically relevant therapeutic time window.

The promyelocytic leukemia zinc finger (PLZF) protein exerts neuroprotective effects in neuronal cells and is dysregulated in experimental stroke

Stroke is one of the major medical burdens in industrialized countries. Animal experiments indicate that blockade of the angiotensin AT1 receptor (AT1R) improves neurological outcome after cerebral ischemia. These protective effects are partially mediated by the angiotensin AT2 receptor (AT2R). The transcription factor promyelocytic leukemia zinc finger (PLZF) was identified as a direct adapter protein of the AT2R. Furthermore, our group was able to demonstrate that PLZF also directly binds and mediates the effects of the human (pro)renin receptor [(P)RR] which is involved in brain development. Therefore, we hypothesized that PLZF is involved in neuroprotection. Here we show that PLZF and its receptors (P)RR and AT2R exhibited an ubiquitous expression pattern in different brain regions. Furthermore, stable PLZF overexpression in human neuronal cells was able to mediate neuroprotection in a glutamate toxicity model in vitro. Consistently, PLZF mRNA and protein were downregulated on the ipsilateral side in a stroke model in vivo, whereas the neurodetrimental PLZF target genes cyclin A2 and BID were upregulated under this condition. Further analyses indicated that the neuroprotective AT2R is upregulated upon stable PLZF overexpression in cultured neuronal cells. Finally, reporter gene assays demonstrated the functionality of (P)RR promoter polymorphisms regarding basal and PLZF-induced activity.

A sartan derivative with a very low angiotensin II receptor affinity ameliorates ischemic cerebral damage

Angiotensin II receptor blockers (ARBs) have a potent ability to inhibit oxidative stress and advanced glycation, in addition to their protective effects originated from blood pressure lowering and angiotensin II type 1 receptor (AT(1))-blockade. To obtain a pharmacological tool to dissect the mechanisms of ARBs' protective benefits in experimental stroke, we synthesized a novel ARB-derivative, R-147176, which is 6,700 times less potent than olmesartan in AT(1)-binding inhibition and therefore has a minimal antihypertensive effect, but retains marked inhibitory effects on oxidative stress and advanced glycation. We evaluated the effect of R-147176 (10-30 mg/kg per day), administered orally or intravenously, on brain infarct volume in transient thread occlusion and photothrombotic models in rats. The antioxidative and antiinflammatory properties were also investigated. R-147176 significantly reduced infarct volume, without influence on blood pressure, in both models. R-147176 significantly reduced the numbers of ED-1-positive cells and of TUNEL-positive cells, and protein carbonyl formation in the damaged brain. This ARB derivative, despite its significantly lower AT1 affinity and virtually no antihypertensive effect, ameliorated ischemic cerebral damage through antioxidative and antiinflammatory properties. These findings suggest potential usefulness of R-147176 as a pharmacological tool to investigate the ARBs' protective effect in experimental stroke and open new therapeutic avenues.

Peripheral administration of carbenoxolone reduces ischemic reperfusion injury in transient model of cerebral ischemia

Carbenoxolone (CBX) has a neuroprotective effect in experimental models of brain ischemia and trauma. However, systemic effect of CBX on ischemic reperfusion injuries has not been investigated in a temporary model of focal cerebral ischemia. Male Wistar rats (n = 32) were divided into control and CBX-treated (100, 200, or 400 mg/kg, intraperitoneally) groups. Transient focal cerebral ischemia was induced by 60-minute middle cerebral artery occlusion by filament method, followed by 23-hour reperfusion. At the end of 24-hour ischemia, neurologic deficit score was tested and infarct volumes were determined using triphenyltetrazolium chloride staining. Administration of CBX (100, 200, or 400 mg/kg) at the beginning of ischemia significantly reduced cortical infarct volumes by 48%, 58%, and 63%, and striatal infarct volumes by 34%, 63%, and 63%, respectively. Nevertheless, CBX has no effect on neurologic dysfunction. Our findings indicated that peripheral administration of CBX has a neuroprotective effect on postischemic damage in a temporary model of focal cerebral ischemia in rat.

Postischemic administration of angiotensin II type 1 receptor blocker reduces cerebral infarction size in hypertensive rats

Lowering the blood pressure (BP) during the acute period following ischemic stroke is still a controversial treatment. In this study, we investigated the effect of postischemic treatment using the angiotensin II type 1 receptor blocker, candesartan, on brain damage in focal cerebral ischemia. Spontaneously hypertensive rats underwent transient occlusion of the middle cerebral artery for 1 h. Candesartan (0.1, 1 and 10 mg kg(-1)) or vehicle was administered orally 3 and 24 h after ischemia. Blood pressure and neurological function were monitored, and infarct volume was evaluated 48 h after occlusion. Cerebral blood flow was measured using laser Doppler flowmetry before and after treatment with candesartan. Activation of Rho-kinase in cerebral microvessels was evaluated by immunohistochemistry. Systolic blood pressure was markedly lowered with both moderate and high doses, but it did not fall with a low dose of candesartan. The infarct volume was reduced in rats treated with the low dose of candesartan but not in those treated with the moderate or high doses. Cerebral blood flow decreased in parallel with the reduction in BP 3 h after treatment using the moderate dose, but it did not change after treatment with the low dose of candesartan, compared with vehicle. Rho-kinase was activated in the brain vessels of the ischemic cortex, but treatment with candesartan suppressed it. Our results show that oral administration of candesartan after transient focal ischemia reduced infarct volume at doses that showed little effect on BP. The neurovascular protective effects of candesartan may be caused by the inhibition of Rho-kinase in brain microvessels.

Candesartan augments ischemia-induced proangiogenic state and results in sustained improvement after stroke

BACKGROUND AND PURPOSE

We have shown that acute treatment with candesartan in an experimental model of stroke resulted in vascular protection and improved outcomes at 24 hours poststroke, but the mechanisms are unknown. We now examine effects of candesartan on proangiogenic factors and 7-day outcomes using the same treatment paradigm.

METHODS

Male Wistar rats underwent 3 hours of middle cerebral artery occlusion followed by reperfusion. A single dose of 1 mg/kg candesartan intravenously was given at reperfusion. Animals received neurobehavioral testing before middle cerebral artery occlusion, at 24 hours after middle cerebral artery occlusion, and at 7 days. Blood pressure was measured by telemetry. Animals euthanized at 24 hours had brain tissue and cerebrospinal fluid collected for matrix metalloproteinase activity, vascular endothelial growth factor expression, and tube formation assay. Neurobehavioral testing included elevated body swing test, Bederson, beam walk, and paw grasp. Cerebrovascular density was quantified using immunohistochemistry at 24 hours and 7 days.

RESULTS

Matrix metalloproteinase-2 activity and vascular endothelial growth factor expression were higher (P=0.035, P=0.042, respectively) and cerebrospinal fluid was significantly more proangiogenic (5x tube formation; P=0.002) in the candesartan group at 24 hours. Although no difference was seen in infarct size at 7 days, treatment improved Bederson scores (2.1 versus 2.9, P=0.0083), elevated body swing test (22.9 versus 39.4, P=0.021), and paw grasp (1.29 versus 2.88, P=0.0001) at 7 days. Candesartan treatment resulted in increased vascular density in the striatum at 7 days (P=0.037).

CONCLUSIONS

Candesartan after reperfusion augments ischemia-induced angiogenic state and provides long-term benefits. The beneficial effects may involve vascular protection and enhancement of early angiogenic remodeling.

Protective mechanisms of the angiotensin II type 1 receptor blocker candesartan against cerebral ischemia: in-vivo and in-vitro studies

BACKGROUND

Angiotensin II type 1 (AT1) receptor blockers decrease ischemia by mechanisms dependent on and independent of arterial blood pressure in hypertensive rats and AT1-R knockout mice, respectively. However, the detailed mechanisms underlying the effects of AT1 receptor blockers remain unclear.

AIMS

To elucidate the systemic and focal effects of AT1 receptor blockers against cerebral ischemia in in-vivo and in-vitro studies.

METHODS

Normotensive Wistar rats were treated for 2 weeks with 0.5 or 1 mg/kg candesartan cilexetil and then subjected to 2-h middle cerebral artery occlusion-reperfusion. Human umbilical endothelial cells were stimulated with the active form of candesartan and angiotensin II in the absence and presence of an angiotensin II type 2 (AT2) receptor antagonist.

RESULTS

In candesartan-pretreated hypotensive and nonhypotensive rats, blood pressure was moderately increased during middle cerebral artery occlusion and fell gradually to the baseline after the reperfusion; it remained elevated in the control even after the reperfusion occlusion. Candesartan treatment resulted in a decrease in the cortical infarct volume and oxidative damage, the hypoxic status was improved, and the expression of repair-associated and growth-associated proteins in the cortical penumbra was augmented. Candesartan also increased the eNOS mRNA level and the lumen size of the middle cerebral artery. In human umbilical endothelial cells, candesartan increased the eNOS protein level AT2-R dependently, inhibited the expression of nicotinamide adenine dinucleotide phosphate oxidase subunits and angiotensin II-induced intracellular reactive oxygen species and nitric oxide, and promoted the extracellular release of nitric oxide, suggesting that it augmented the bioavailability of nitric oxide.

CONCLUSION

Among the mechanisms candesartan exerts in its protection against cerebral ischemia, restoration of endothelial function may represent an attractive therapeutic goal to address cerebral ischemia.