Neuroprotection with angiotensin receptor antagonists: a review of the evidence and potential mechanisms

Duration of Intracranial Pressure Increase after Aneurysmal Subarachnoid Hemorrhage: Prognostic Factors and Association with the Outcome

OBJECTIVE

A rupture of the intracranial aneurysm is frequently complicated, with an increase of intracranial pressure (ICP) requiring conservative and/or surgical treatment. We analyzed the risk factors related to the duration of pathologic ICP increase and the relationship between ICP burden and the outcome of subarachnoid hemorrhage (SAH).

METHODS

Consecutive cases with aneurysmal SAH treated at our institution between 01/2003 and 06/2016 were eligible for this study. Different admission variables were evaluated to predict the duration of ICP increase >20 mmHg in univariate and multivariate analyses. The association of the ICP course with SAH outcome parameters (risk of cerebral infarction, in-hospital mortality, and unfavorable outcome at 6 months defined as modified Rankin scale >3) was adjusted for major outcome-relevant confounders.

RESULTS

Of 820 SAH patients, 378 individuals (46.1%) developed at least one ICP increase requiring conservative and/or surgical management after aneurysm treatment (mean duration: 1.76 days, range: 1 - 14 days). In the multivariable linear regression analysis, patients' age (unstandardized coefficient [UC]=-0.02, p <0.0001), World Federation of Neurosurgical Societies (WFNS) grade 4-5 at admission (UC=0.71, p <0.004), regular medication with the angiotensinconverting enzyme (ACE) inhibitors (UC=-0.61, p =0.01), and presence of intracerebral hemorrhage (UC=0.59, p =0.002) were associated with the duration of ICP increase. In turn, patients with longer ICP elevations were at higher risk for cerebral infarction (adjusted odds ratio [aOR]=1.32 per-day-increase, p <0.0001), in-hospital mortality (aOR=1.30, p <0.0001) and unfavorable outcome (aOR=1.43, p <0.0001). SAH patients who underwent primary decompressive craniectomy (DC) showed shorter periods of ICP increase than patients with a secondary decompression (mean: 2.8 vs 4.9 days, p <0.0001).

CONCLUSION

The duration of ICP increase after aneurysm rupture is a strong outcome predictor and is related to younger age and higher initial severity of SAH. Further analysis of the factors impacting the course of ICP after SAH is essential for the optimization of ICP management and outcome improvement.

Safety and biomarker effects of candesartan in non-hypertensive adults with prodromal Alzheimer's disease

Observational studies suggest that angiotensin receptor blockers in hypertensive adults are associated with lower post-mortem indicators of Alzheimer's disease pathology. Candesartan, an angiotensin receptor blocker, has a positive cognitive effect in mild cognitive impairment with hypertension. However, its safety and effects in non-hypertensive individuals with Alzheimer's disease are unclear. This is the first double-blind randomized placebo-controlled trial aimed to assess safety and effects of 1-year therapy of candesartan on biomarkers and clinical indicators of Alzheimer's disease in non-hypertensive individuals with biomarker-confirmed prodromal Alzheimer's disease. Seventy-seven non-hypertensive participants 50 years or older (mean age: 68.1 years; 62% women; 20% African American) with mild cognitive impairment and biomarker confirmed Alzheimer's disease were randomized to escalating doses of once daily oral candesartan (up to 32 mg) or matched placebo. Main outcomes included safety and tolerability of candesartan, cerebrospinal fluid biomarkers (amyloid-β42, amyloid-β40, total tau and phospho-tau). Additional exploratory outcomes included PET imaging (Pittsburgh Compound-B (11C-PiB) and 18F-flortaucipir), brain MRI (structural and connectivity measures) and cognitive functioning. Analyses used intention-to-treat approach with group comparisons of safety measures using Chi-square test, and repeated measures mixed effects models were used to assess candesartan effects on main and exploratory outcomes (ClinicalTrials.gov, NCT02646982). Candesartan was found to be safe with no significant difference in safety measures: symptoms of hypotension, renal failure or hyperkalemia. Candesartan was also found to be associated with increases in cerebrospinal fluid Aβ40 (between-group mean difference: 1211.95 pg/ml, 95% confidence interval: 313.27, 2110.63) and Aβ42 (49.51 pg/ml, 95% confidence interval: -98.05, -0.98) reflecting lower brain amyloid accumulation. Candesartan was associated with decreased 11C-PiB in the parahippocampal region (-0.1104, 95% confidence interval: -0.19, -0.029) which remained significant after false discovery rate correction, and with an increase in functional network connectivity in the subcortical networks. Candesartan was further associated with improved executive function (Trail Making Test Part B) performance (-11.41 s, 95% confidence interval: -11.94, -10.89) and trended for an improved global cognitive functioning reflected by a composite cognitive score (0.002, 95% confidence interval: -0.0002, 0.005). We did not observe significant effects on tau levels, hippocampal volume or other cognitive measures (memory or clinical dementia rating scale-sum of boxes). In conclusion, among non-hypertensive prodromal Alzheimer's disease, candesartan is safe and likely decreases brain amyloid biomarkers, enhances subcortical brain connectivity and has favourable cognitive effects. These findings suggest that candesartan may have an important therapeutic role in Alzheimer's disease, and warrant further investigation given the lack of clear treatment options for this devastating illness.

Neuroprotection in Stroke-Focus on the Renin-Angiotensin System: A Systematic Review

Stroke is the primary cause of disability in the adult population. Hypertension represents the leading risk factor being present in almost half the patients. The renin-angiotensin system is involved in the physiopathology of stroke and has an essential impact on hypertension as a risk factor. This article targeted the role of the renin-angiotensin system in stroke neuroprotection by reviewing the current literature available. The mechanism of action of the renin-angiotensin system was observed through the effects on AT1, AT2, and Mas receptors. The neuroprotective properties ascertained by angiotensin in stroke seem to be independent of the blood pressure reduction mechanism, and include neuroregeneration, angiogenesis, and increased neuronal resistance to hypoxia. The future relationship of stroke and the renin-angiotensin system is full of possibilities, as new agonist molecules emerge as potential candidates to restrict the impairment caused by stroke.

Multiple Aspects of Inappropriate Action of Renin-Angiotensin, Vasopressin, and Oxytocin Systems in Neuropsychiatric and Neurodegenerative Diseases

The cardiovascular system and the central nervous system (CNS) closely cooperate in the regulation of primary vital functions. The autonomic nervous system and several compounds known as cardiovascular factors, especially those targeting the renin-angiotensin system (RAS), the vasopressin system (VPS), and the oxytocin system (OTS), are also efficient modulators of several other processes in the CNS. The components of the RAS, VPS, and OTS, regulating pain, emotions, learning, memory, and other cognitive processes, are present in the neurons, glial cells, and blood vessels of the CNS. Increasing evidence shows that the combined function of the RAS, VPS, and OTS is altered in neuropsychiatric/neurodegenerative diseases, and in particular in patients with depression, Alzheimer's disease, Parkinson's disease, autism, and schizophrenia. The altered function of the RAS may also contribute to CNS disorders in COVID-19. In this review, we present evidence that there are multiple causes for altered combined function of the RAS, VPS, and OTS in psychiatric and neurodegenerative disorders, such as genetic predispositions and the engagement of the RAS, VAS, and OTS in the processes underlying emotions, memory, and cognition. The neuroactive pharmaceuticals interfering with the synthesis or the action of angiotensins, vasopressin, and oxytocin can improve or worsen the effectiveness of treatment for neuropsychiatric/neurodegenerative diseases. Better knowledge of the multiple actions of the RAS, VPS, and OTS may facilitate programming the most efficient treatment for patients suffering from the comorbidity of neuropsychiatric/neurodegenerative and cardiovascular diseases.

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.

Central sympathetic nerve activation in subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is a life-threatening condition, and although its two main complications-cerebral vasospasm (CVS)/delayed cerebral ischemia (DCI) and early brain injury (EBI)-have been widely studied, prognosis has not improved over time. The sympathetic nerve (SN) system is important for the regulation of cardiovascular function and is closely associated with cerebral vessels and the regulation of cerebral blood flow and cerebrovascular function; thus, excessive SN activation leads to a rapid breakdown of homeostasis in the brain. In the hyperacute phase, patients with SAH can experience possibly lethal conditions that are thought to be associated with SN activation (catecholamine surge)-related arrhythmia, neurogenic pulmonary edema, and irreversible injury to the hypothalamus and brainstem. Although the role of the SN system in SAH has long been investigated and considerable evidence has been collected, the exact pathophysiology remains undetermined, mainly because the relationships between the SN system and SAH are complicated, and many SN-modulating factors are involved. Thus, research concerning these relationships needs to explore novel findings that correlate with the relevant concepts based on past reliable evidence. Here, we explore the role of the central SN (CSN) system in SAH pathophysiology and provide a comprehensive review of the functional CSN network; brain injury in hyperacute phase involving the CSN system; pathophysiological overlap between the CSN system and the two major SAH complications, CVS/DCI and EBI; CSN-modulating factors; and SAH-related extracerebral organ injury. Further studies are warranted to determine the specific roles of the CSN system in the brain injuries associated with SAH.

Mechanisms and Treatment of Late-Life Depression

(Appeared originally in Translational Psychiatry 2019; 9:188).

Clinical perspectives on ischemic stroke

Treatments for acute stroke have improved over the past years, but have largely been limited to revascularization strategies. The topic of neuroprotection, or strategies to limit brain tissue damage or even reverse it, has remained elusive. Thus, the clinical mainstays for stroke management have focused on prevention. The lack of clinical translation of neuroprotective therapies which have shown promise in the laboratory may, in part, be due to a historic inattention to comorbidities suffered by a majority of stroke patients. With the advent of more stroke models that include one or more relevant comorbidities, it may be possible to identify effective treatments that may translate into new treatments at the clinical level. In the meantime, we review comorbidities in stroke patients, modification of stroke risk factors and available acute stroke treatments in the clinic.

The Angiotensin II Type 2 Receptor, a Target for Protection and Regeneration of the Peripheral Nervous System?

Preclinical evidence, accumulated over the past decade, indicates that the angiotensin II type 2 receptor (AT2R) stimulation exerts significant neuroprotective effects in various animal models of neuronal injury, notably in the central nervous system. While the atypical G protein-coupled receptor superfamily nature of AT2R and its related signaling are still under investigation, pharmacological studies have shown that stimulation of AT2R leads to neuritogenesis in vitro and in vivo. In this review, we focus on the potential neuroprotective and neuroregenerative roles of AT2R specifically in the peripheral nervous system (PNS). The first section describes the evidence for AT2R expression in the PNS and highlights current controversies concerning the cellular distribution of the receptor. The second section focuses on AT2R signaling implicated in neuronal survival and in neurite outgrowth. The following sections review the relatively few preclinical studies highlighting the putative neuroprotective and neuroregenerative effects of AT2R stimulation in the context of peripheral neuropathy.

Roles of vascular risk factors in the pathogenesis of dementia

The number of people with dementia is rapidly growing along with the aging of society and is becoming a social issue worldwide. The results of recent clinical and basic studies have suggested that vascular risk factors, such as hypertension and diabetes mellitus, affect the pathogenesis of dementia. Cerebrovascular damage due to vascular risk factors directly triggers vascular dementia, and it is becoming more apparent that vascular risk factors also increase the risk of neurodegenerative Alzheimer's disease, which is associated with the accumulation of neurotoxic proteins in the brain. Although disease-modifying therapy for dementia has not yet been established, several studies have shown that the management of vascular risk factors could possibly contribute to reducing the risk of developing dementia, thus making them important targets for dementia prevention. In this article, we review recent findings regarding the relationship between vascular risk factors and dementia, especially focusing on Alzheimer's disease, the underlying molecular mechanisms, and the potential strategies targeting these modifiable risk factors to prevent cognitive decline.

The Potential Therapeutic Capacity of Inhibiting the Brain Renin-Angiotensin System in the Treatment of Co-Morbid Conditions in Epilepsy

Epilepsy is one of the most prevalent neurological diseases and although numerous novel anticonvulsants have been approved, the proportion of patients who are refractory to medical treatment of seizures and have progressive co-morbidities such as cognitive impairment and depression remains at about 20-30%. In the last decade, extensive research has identified a therapeutic capacity of the components of the brain renin-angiotensin system (RAS) in seizure- and epilepsy-related phenomena. Alleviating the activity of RAS in the central nervous system is considered to be a potential adjuvant strategy for the treatment of numerous detrimental consequences of epileptogenesis. One of the main advantages of RAS is associated with its modulatory influence on different neurotransmitter systems, thereby exerting a fine-tuning control mechanism for brain excitability. The most recent scientific findings regarding the involvement of the components of brain RAS show that angiotensin II (Ang II), angiotensin-converting enzyme (ACE), Ang II type 1 (AT₁) and type 2 (AT₂) receptors are involved in the control of epilepsy and its accompanying complications, and therefore they are currently of therapeutic interest in the treatment of this disease. However, data on the role of different components of brain RAS on co-morbid conditions in epilepsy, including hypertension, are insufficient. Experimental and clinical findings related to the involvement of Ang II, ACE, AT₁, and AT₂ receptors in the control of epilepsy and accompanying complications may point to new therapeutic opportunities and adjuvants for the treatment of common co-morbid conditions of epilepsy.

Mechanisms and treatment of late-life depression

Depression predisposes to medical illnesses and advances biological aging indicated by shorter telomere length, accelerated brain aging and advanced epigenetic aging. Medical illnesses also increase the risk of late-life depression. The reciprocal relationships of depression with aging-related and disease-related processes have generated pathogenetic hypotheses and provided treatment targets. Targeting risk factors of vascular disease in mid-life is a logical approach in prevention of vascular depression. The depression-executive dysfunction and the vascular depression syndromes have clinical presentations and neuroimaging findings consistent with frontostriatal abnormalities. Dopamine D_2/3 agonists are effective in depression of Parkinson's disease and their efficacy needs to be assessed in these two syndromes. Computerized cognitive remediation targeting functions of the cognitive control network may improve both executive functions and depressive symptoms of late-life major depression. Significant progress has been made in neurostimulation treatments in depressed younger adults. TMS targeting deep structures responsible for mood regulation is well tolerated by older adults and its efficacy in syndromes of late-life depression needs to be studied. Efficacious psychotherapies for late-life depression exist, but are underutilized in part because of their complexity. Streamlined, stepped psychotherapies targeting behaviors assumed to result from dysfunction of brain networks implicated in late-life depression can be easy to learn and have potential for dissemination. However, their effectiveness needs further investigation. Depression increases the risk of dementing disorders. Antidepressants are rather ineffective in treating depression of demented patients, but long-term use of antidepressants may reduce the risk of dementia. However, confirmation studies are needed.

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.

Convergent evidences from human and animal studies implicate angiotensin I-converting enzyme activity in cognitive performance in schizophrenia

In schizophrenia (SCZ), higher angiotensin I-converting enzyme (ACE) levels have been reported in patient's blood and cerebrospinal fluid (CSF). Hereby, we propose to explore whether the ACE activity levels are associated to cognitive performance in SCZ. Seventy-two patients with SCZ or schizoaffective disorder diagnosis, and 69 healthy controls (HCs) underwent a cognitive battery with parallel collection of peripheral blood samples to measure ACE activity. Significant higher ACE activity levels were confirmed in the plasma of SCZ patients compared with HCs (Student's t=-5.216; P<0.001). ACE activity significantly correlated to Hopkins delayed recall measures (r=-0.247; P=0.004) and Hopkins total (r=-0.214; P=0.012). Subjects grouped as high ACE activity (above average) had worse performance compared with low ACE activity level group for Hopkins delayed recall measure, even after correction for clinical condition, age, gender and years of education (P=0.029). The adjusted R squared for this final model was 0.343. This result was evident only comparing extreme groups for ACE activity, when splitting the sample in three groups with similar number of subjects. To clarify this finding, we performed an evaluation of the cognitive performance of transgenic mice with three copies of ACE gene in novel object recognition (NOR) test, which showed that such animals presented impairment in NOR (P<0.05) compared with two copies of wild-type animals. The results observed in SCZ patients and animal model suggest both the association of ACE to cognitive deficits in SCZ. This finding may support the evaluation of novel treatment protocols and/or of innovative drugs for specific intervention of cognitive deficits in SCZ envisioning concomitant ACE activity and behavior evaluations.

Long-term intracerebroventricular infusion of angiotensin II after kainate-induced status epilepticus: Effects on epileptogenesis, brain damage, and diurnal behavioral changes

Our previous studies revealed that Angiotensin (Ang) II has anticonvulsant effects in acute seizure models. However, data on its role in experimental models of epilepsy are missing. In the present study, we tested whether posttreatment with Ang II after kainate (KA)-induced status epilepticus (SE) can affect epileptogenesis, concomitant behavioral changes, and brain damage. The Wistar rats were intracerebroventricularly infused via osmotic mini-pumps with Ang II (1.52μg/μl/day for 28days) after SE. Spontaneous motor seizures (SMS) were video-recorded for up to three months. Locomotor activity, anxiety, and depression-like behavior were evaluated during the last week of drug infusion, while spatial memory was assessed during the 3rd month after SE. Angiotensin II decreased the latency for onset of the first SMS and increased the frequency of SMS two months after SE. The continuous peptide infusion exacerbated the KA-induced hyperactivity and caused depression-like behavior. The reduced anxiety of KA-treated rats was alleviated by Ang II exposure. The KA-induced deficit in the hippocampal-dependent spatial memory was not influenced by Ang II. However, Ang II partially prevented the neuronal damage in the hippocampus, specifically in the CA1 area. The role of AT1 and AT2 receptor activation in the effects of the octapeptide is discussed.

Administration of exogenous 1,25(OH)2D3 normalizes overactivation of the central renin-angiotensin system in 1α(OH)ase knockout mice

Previously, we reported that active vitamin D deficiency in mice causes secondary hypertension and cardiac dysfunction, but the underlying mechanism remains largely unknown. To clarify whether exogenous active vitamin D rescues hypertension by normalizing the altered central renin-angiotensin system (RAS) via an antioxidative stress mechanism, 1-alpha-hydroxylase [1α(OH)ase] knockout mice [1α(OH)ase(-/-)] and their wild-type littermates were fed a normal diet alone or with 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], or a high-calcium, high-phosphorus "rescue" diet with or without antioxidant N-acetyl-l-cysteine (NAC) supplementation for 4 weeks. Compared with their wild-type littermates, 1α(OH)ase(-/-)mice had high mean arterial pressure, increased levels of renin, angiotensin II (Ang II), and Ang II type 1 receptor, and increased malondialdehyde levels, but decreased anti-peroxiredoxin I and IV proteins and the antioxidative genes glutathione reductase (Gsr) and glutathione peroxidase 4 (Gpx4) in the brain samples. Except Ang II type 1 receptor, these pathophysiological changes were rescued by exogenous 1,25(OH)2D3 or NAC plus rescue diet, but not by rescue diet alone. We conclude that 1,25(OH)2D3 normalizes the altered central RAS in 1α(OH)ase(-/-)mice, at least partially, through a central antioxidative mechanism.

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.

Preventing vascular effects on brain injury and cognition late in life: knowns and unknowns

For some researchers, the relationship between prevalent cardiovascular risk factors and late-life cognitive decline is not worthy of further study. It is already known that effective treatment of vascular risk factors lowers risk of such major outcomes as stroke and heart attack, the argument goes; thus, any new information about the relationship between vascular risk factors and another major outcome--late-life cognitive decline--is unlikely to have an impact on clinical practice. The purpose of this review is to probe the logic of this argument by focusing on what is known, and what is not known, about the relationship between vascular risk factors and late-life cognitive decline. The unknowns are substantial: in particular, there is relatively little evidence that current vascular risk factor treatment protocols are adequate to prevent late-life cognitive decline or the clinically silent brain injury that precedes it. In addition, there is relatively little understanding of which factors lead to differential vulnerability or resilience to the effects of vascular risk factors on silent brain injury. Differential effects of different classes of treatments are similarly unclear. Finally, there is limited understanding of the impact of clinically-silent neurodegenerative disease processes on cerebrovascular processes. Further study of the relationships among vascular risk factors, brain injury, and late-life cognitive decline could have a major impact on development of new vascular therapies and on clinical management of vascular risk factors, and there are promising avenues for future research in this direction.

Antihypertensive therapy and cerebral hemodynamics in executive mild cognitive impairment: results of a pilot randomized clinical trial

OBJECTIVES

To compare the effects of three antihypertensive medications on cerebral hemodynamic and cognitive function in hypertensive individuals with executive dysfunction.

DESIGN

Double-blind randomized clinical trial.

SETTING

Community.

PARTICIPANTS

Fifty-three individuals aged 60 and older with hypertension and executive dysfunction.

INTERVENTION

Lisinopril, candesartan, or hydrochlorothiazide for 1 year.

MEASUREMENTS

Cerebral blood flow velocity (BFV; transcranial Doppler ultrasonography during rest, sitting, standing, hypercapnia, and hypocapnia), cognition, and blood pressure were measured at baseline and after 6 and 12 months. Linear mixed models were used to compare the three groups.

RESULTS

Of the 53 participants, 47 had successful insonation (mean age 72; 70% white; 57% women). There was a tendency toward an increase in BFV in the candesartan group and a decrease in the lisinopril and hydrochlorothiazide groups (between-group P = .57) that was significant in those with low BFV at baseline (<median 27.6 cm/s, between-group P = .03). The candesartan group also had the greatest improvement in executive function (Trail Making Test Part B improved by 17.1 seconds, vs hydrochlorothiazide improved by 4.2 seconds and lisinopril worsened by 14.4 seconds, P = .008). Carbon dioxide vasoreactivity and vasomotor range declined significantly in the lisinopril (within-group P = .001 for vasoreactivity and .02 for vasomotor range) and hydrochlorothiazide groups (within-group P = .10 and .009, respectively) but not in the candesartan group (within-group P = .25 and .38, respectively; between-group P = .30 and .46, respectively).

CONCLUSION

Angiotensin receptor blockers may preferentially preserve cerebral hemodynamics and executive function in individuals with executive dysfunction. These findings warrant further investigation in a larger trial.

High salt intake abolishes AT(2)-mediated vasodilation of pial arterioles in rats

BACKGROUND

Angiotensin II (Ang II) induces constriction (AT(1)) and dilation (AT(2) receptors) of cerebral arterioles. High sodium intake induces changes in receptors expression and loss of AT(2)-mediated vasodilation in extracerebral vessels. We investigated whether high salt modifies the AT(2)-mediated response of cerebral arterioles.

METHODS

Three-month-old male Wistar rats received drinking water supplemented or not with 1% NaCl. We measured at day 4 or 30 plasma aldosterone concentration, AT receptors expression (brain microvessels, western blot, RT-qPCR), internal diameter of pial arterioles (cranial window) following suffusion with Ang II (10(-6) mol/l, or 10(-8) mol/l + losartan 10(-5) mol/l), serotonin (5-HT, 10(-6) mol/l), sodium nitroprusside (10(-5) mol/l) and adenosine diphosphate (ADP, 10(-4) mol/l).

RESULTS

High salt did not modify arterial pressure, baseline arteriolar diameter, vasoconstriction to Ang II or 5-HT, nor vasodilation to SNP. High salt lowered plasma aldosterone concentration (d4 138 ± 71 not significant vs. control 338 ± 73; d30 150 ± 21 P < 0.05 vs. control 517 ± 79 μmol/l). AT receptors mRNA did not change while protein level of AT(2) receptors decreased at d4 (64 ± 9% of control, P < 0.05). AT(2)-mediated vasodilation (control d4; d30 8 ± 2; 5 ± 2%) was abolished at d4 (-2 ± 2%, P < 0.05) and reversed to vasoconstriction at d30 (-7 ± 2%, P < 0.05). ADP-induced vasodilation is abolished at d30 (2 ± 2, P < 0.05 vs. control 19 ± 4%).

CONCLUSION

High salt specifically abolishes AT(2)-mediated vasodilation, immediately, via decreased level of AT(2) receptor protein, and after 30 days, in association with abolition of endothelial vasodilation. Such loss of AT(2)-mediated vasodilation may be deleterious in case of stroke.

Olmesartan ameliorates peripheral nerve dysfunction in Zucker diabetic fatty rats

OBJECTIVE

Angiotensin (ANG) II type 1 receptor (AT1R) blockers have neuroprotective effects against neuronal lesions. The present study examines whether the AT1R blocker olmesartan improves peripheral nerve dysfunction in rats with type 2 diabetes.

METHODS

Fourteen-week-old male type 2 diabetic Zucker diabetic fatty (ZDF) rats were orally administered with olmesartan (6 mg/kg per day; n = 7) or not treated (n = 7) and then followed up for nine weeks. Age-matched and sex-matched nondiabetic lean rats served as controls (n = 7).

RESULTS

Olmesartan for 9 weeks did not influence blood glucose and A1c levels that were higher in untreated ZDF (U-ZDF) rats than in control rats. In U-ZDF rats, myelinated fiber density and myelin areas of myelinated fibers in peroneal nerves significantly increased and decreased, respectively, and the intraepidermal nerve fiber density (IENFD) of footpad skin tended to decrease. The U-ZDF rats developed mechanical hyperalgesia, thermal hypoalgesia and slower sensory and motor nerve conduction in the sciatic-tibial nerves. Olmesartan increased myelin areas and IENFD and ameliorated sensory nerve conduction deficits. These beneficial effects of olmesartan were associated with ANG II and insulin receptor upregulation in sensory neurons as well as deactivation of Erk1/2 in sciatic nerves.

CONCLUSION

Olmesartan appears to improve the structure and function of small and large nerves and upregulate ANG II and insulin receptors in sensory neurons of rats with type 2 diabetes.

Losartan improved respiratory function and coenzyme Q content in brain mitochondria of young spontaneously hypertensive rats

Increased production of free radicals and impairment of mitochondrial function are important factors in the pathogenesis of hypertension. This study examined the impact of hypertension on mitochondrial respiratory chain function, coenzyme Q(9) (CoQ(9)), coenzyme Q(10) (CoQ(10)), and alpha-tocopherol content in brain mitochondria, and the effect of blockade of angiotensin II type 1 receptors (AT1R) in the prehypertensive period on these parameters. In addition, blood pressure, heart and brain weight to body weight ratios, and the geometry of the basilar artery supplying the brain were evaluated. In the 9th week blood pressure and heart weight/body weight ratio were significantly increased and brain weight/body weight ratio was significantly decreased in spontaneously hypertensive rats (SHR) when compared to Wistar rats (WR). The cross-sectional area of the basilar artery was increased in SHR. Glutamate-supported respiration, the rate of ATP production, and concentrations of CoQ(9), CoQ(10), and alpha-tocopherol were decreased in SHR. The succinate-supported function and cytochrome oxidase activity were not changed. The treatment of SHR with losartan (20 mg/kg/day) from 4th to 9th week of age exerted preventive effect against hypertension, heart and arterial wall hypertrophy, and brain weight/body weight decline. After the therapy, the rate of ATP production and the concentration of CoQ increased in comparison to untreated SHR. The impairment of energy production and decreased level of lipid-soluble antioxidants in brain mitochondria as well as structural alterations in the basilar artery may contribute to increased vulnerability of brain tissue in hypertension. Long-term treatment with AT1R blockers may prevent brain dysfunction in hypertension.

Use of angiotensin receptor blockers and risk of dementia in a predominantly male population: prospective cohort analysis

OBJECTIVE

To investigate whether angiotensin receptor blockers protect against Alzheimer's disease and dementia or reduce the progression of both diseases.

DESIGN

Prospective cohort analysis.

SETTING

Administrative database of the US Veteran Affairs, 2002-6. Population 819 491 predominantly male participants (98%) aged 65 or more with cardiovascular disease.

MAIN OUTCOME MEASURES

Time to incident Alzheimer's disease or dementia in three cohorts (angiotensin receptor blockers, lisinopril, and other cardiovascular drugs, the "cardiovascular comparator") over a four year period (fiscal years 2003-6) using Cox proportional hazard models with adjustments for age, diabetes, stroke, and cardiovascular disease. Disease progression was the time to admission to a nursing home or death among participants with pre-existing Alzheimer's disease or dementia.

RESULTS

Hazard rates for incident dementia in the angiotensin receptor blocker group were 0.76 (95% confidence interval 0.69 to 0.84) compared with the cardiovascular comparator and 0.81 (0.73 to 0.90) compared with the lisinopril group. Compared with the cardiovascular comparator, angiotensin receptor blockers in patients with pre-existing Alzheimer's disease were associated with a significantly lower risk of admission to a nursing home (0.51, 0.36 to 0.72) and death (0.83, 0.71 to 0.97). Angiotensin receptor blockers exhibited a dose-response as well as additive effects in combination with angiotensin converting enzyme inhibitors. This combination compared with angiotensin converting enzyme inhibitors alone was associated with a reduced risk of incident dementia (0.54, 0.51 to 0.57) and admission to a nursing home (0.33, 0.22 to 0.49). Minor differences were shown in mean systolic and diastolic blood pressures between the groups. Similar results were observed for Alzheimer's disease.

CONCLUSIONS

Angiotensin receptor blockers are associated with a significant reduction in the incidence and progression of Alzheimer's disease and dementia compared with angiotensin converting enzyme inhibitors or other cardiovascular drugs in a predominantly male population.

The rationale and design of the antihypertensives and vascular, endothelial, and cognitive function (AVEC) trial in elderly hypertensives with early cognitive impairment: role of the renin angiotensin system inhibition

BACKGROUND

Prior evidence suggests that the renin angiotensin system and antihypertensives that inhibit this system play a role in cognitive, central vascular, and endothelial function. Our objective is to conduct a double-blind randomized controlled clinical trial, the antihypertensives and vascular, endothelial, and cognitive function (AVEC), to compare 1 year treatment of 3 antihypertensives (lisinopril, candesartan, or hydrochlorothiazide) in their effect on memory and executive function, cerebral blood flow, and central endothelial function of seniors with hypertension and early objective evidence of executive or memory impairments.

METHODS/DESIGN

The overall experimental design of the AVEC trial is a 3-arm double blind randomized controlled clinical trial. A total of 100 community eligible individuals (60 years or older) with hypertension and early cognitive impairment are being recruited from the greater Boston area and randomized to lisinopril, candesartan, or hydrochlorothiazide ("active control") for 12 months. The goal of the intervention is to achieve blood pressure control defined as SBP < 140 mm Hg and DBP < 90 mm Hg. Additional antihypertensives are added to achieve this goal if needed. Eligible participants are those with hypertension, defined as a blood pressure 140/90 mm Hg or greater, early cognitive impairment without dementia defined (10 or less out of 15 on the executive clock draw test or 1 standard deviation below the mean on the immediate memory subtest of the repeatable battery for the assessment of neuropsychological status and Mini-Mental-Status-exam >20 and without clinical diagnosis of dementia or Alzheimer's disease). Individuals who are currently receiving antihypertensives are eligible to participate if the participants and the primary care providers are willing to taper their antihypertensives. Participants undergo cognitive assessment, measurements of cerebral blood flow using Transcranial Doppler, and central endothelial function by measuring changes in cerebral blood flow in response to changes in end tidal carbon dioxide at baseline (off antihypertensives), 6, and 12 months. Our outcomes are change in cognitive function score (executive and memory), cerebral blood flow, and carbon dioxide cerebral vasoreactivity.

DISCUSSION

The AVEC trial is the first study to explore impact of antihypertensives in those who are showing early evidence of cognitive difficulties that did not reach the threshold of dementia. Success of this trial will offer new therapeutic application of antihypertensives that inhibit the renin angiotensin system and new insights in the role of this system in aging.

TRIAL REGISTRATION

Clinicaltrials.gov NCT00605072.

The renin-angiotensin system is upregulated in the cortex and hippocampus of patients with temporal lobe epilepsy related to mesial temporal sclerosis

PURPOSE

As reported by several authors, angiotensin II (AngII) is a proinflammatory molecule that stimulates the release of inflammatory cytokines and activates nuclear factor kappaB (NFkappaB), being also associated with the increase of cellular oxidative stress. Its production depends on the activity of the angiotensin converting enzyme (ACE) that hydrolyzes the inactive precursor angiotensin I (AngI) into AngII. It has been suggested that AngII underlies the physiopathological mechanisms of several brain disorders such as stroke, bipolar disorder, schizophrenia, and disease. The aim of the present work was to localize and quantify AngII AT1 and AT2 receptors in the cortex and hippocampus of patients with temporal lobe epilepsy related to mesial temporal sclerosis (MTS) submitted to corticoamygdalohippocampectomy for seizure control.

METHOD

Immunohistochemistry, Western blot, and real-time PCR techniques were employed to analyze the expression of these receptors.

RESULTS

The results showed an upregulation of AngII AT1 receptor as well as its messenger ribonucleic acid (mRNA) expression in the cortex and hippocampus of patients with MTS. In addition, an increased immunoexpression of AngII AT2 receptors was found only in the hippocampus of these patients with no changes in its mRNA levels.

DISCUSSION

These data show, for the first time, changes in components of renin-angiotensin system (RAS) that could be implicated in the physiopathology of MTS.

The effect of angiotensin II and IV on ERK1/2 and CREB signalling in cultured rat astroglial cells

Angiotensin peptides produced by the brain renin-angiotensin system have established roles in cognition, but there is no mechanistic basis of angiotensin effects on memory. Astroglial cells present throughout the whole brain, synthesize all the components of the renin-angiotensin system and express angiotensin receptors; therefore our aim was to assess changes in intracellular signalling pathways related to memory formation, particularly the activation of CREB and ERK1/2 in astroglial cells grown in the presence of angiotensin peptides. Cultured rat astroglial cells were treated for 24 h with 10 microM angiotensin II and/or 10 microM angiotensin IV in the presence or absence of 100 microM losartan (AT1-receptor antagonist) or 100 microM PD123319 (AT2-receptor antagonist). Both angiotensin peptides alone were without effect on culture protein levels and cell viability and did not induce oxidative stress, but both peptides together slightly elevated cell growth rates and increased damaged, apoptotic cell numbers. This effect was most probably mediated by the AT1 receptor. Angiotensin II but not angiotensin IV increased intracellular calcium via activation of AT1 receptor. Angiotensin IV but not angiotensin II increased extracellular-regulated protein kinases 1 and 2 (ERK1/2) by 65% and T202, T204 phosphorylated ERK1/2 levels by 36%; this effect was blocked in part by both losartan and PD123319. Angiotensin II but not angiotensin IV increased cyclic AMP-responsive element binding protein (CREB) expression by almost 100% and elevated Ser 133-phosphorylated CREB levels by 56%. These effects were also inhibited in part by both losartan and PD123319. Our results indicate that CREB activation in cultured rat glial cells is mediated mostly by angiotensin II. Angiotensin IV appears to affect the ERK1/2 pathway.

Inhibition of the renin-angiotensin system and the prevention of stroke

BP is the most important determinant of the risk of stroke. A small reduction in BP results in a substantial reduction of both ischemic and hemorrhagic stroke. Any of the commonly used antihypertensive drugs lower the incidence of stroke, with larger reductions in BP resulting in larger reductions in risk. Experimental evidence has linked the renin-angiotensin system (RAS) to the development and progression of cerebrovascular disease. Inhibition of the RAS has beneficial cerebrovascular effects and may reduce the risk of stroke in a manner possibly independent from the alterations of BP. Some clinical trials even suggest that ACE inhibitors and angiotensin II type 1 receptor antagonists (angiotensin receptor blockers [ARBs]) exert cerebroprotective effects beyond BP lowering, but the evidence is controversial. Studies on specific protective actions of antihypertensive drugs are generally hampered by the fact that any treatment-related difference in BP may play a dominant role in the prevention of stroke. There are also indications that the protective potency of ARBs might be superior to that of ACE inhibitors, due to their differential activation of angiotensin II type 2 receptors, but the clinical relevance of this mechanism is unclear. Some studies in primary prevention of stroke, acute stroke, and secondary prevention show advantages for ARBs beyond controlling BP alone. In primary prevention, the LIFE randomized trial showed a significant difference in stroke rate in favor of losartan compared with atenolol despite similar reductions in BP. In acute stroke, the role of hypertension and its treatment remains controversial. ACCESS, however, suggested that an ARB is safe in hypertensive acute stroke patients and may offer advantages independent from BP control. In secondary stroke prevention, there are very few antihypertensive trials. These trials show that BP lowering is at least as successful as in primary prevention, but the absolute stroke risk is much higher. An ACE inhibitor was effective compared with placebo in the PROGRESS trial. The MOSES study showed that eprosartan prevented vascular events more effectively than nitrendipine, despite similar BP-lowering effects. Hypertension is not only the most important risk factor for stroke, but is also closely correlated with cognitive decline and dementia. Therefore, prevention of cognitive decline or even improvement of slightly diminished brain function should be an important goal for antihypertensive treatment in the future. Some clinical data suggest advantages for ACE inhibitors, ARBs, and calcium channel antagonists. Currently, however, the existing data are not sufficient for clinical recommendations. Therefore, ongoing trials will further define the exact role of inhibitors of the RAS and are urgently needed in secondary prevention, in acute stroke, and in the prevention of cognitive decline.

The Pathophysiologic Role of the Brain Renin-Angiotensin System in Stroke Protection: Clinical Implications

The brain possesses the same renin-angiotensin system (RAS) as the systemic circulation. Recent experimental studies have shown that the brain RAS plays an important role in stroke and neuronal protection through its effector peptide angiotensin (Ang) II. Ang II exerts its stroke-protective effects through stimulation of Ang II type 2 (AT2) receptors. Angiotensin receptor blockers (ARBs) exert a dual influence, which is important in their stroke protective effects. They selectively block the Ang II type 1 (AT1) receptors, decreasing local vasoconstriction, and allow free Ang II to stimulate the unoccupied AT2 receptor and increase local vasodilation, resulting in the alleviation of local brain ischemia and limiting the volume and extent of brain loss. In contrast, angiotensin-converting enzyme (ACE) inhibitors, by decreasing the amount of Ang II production, may diminish the stroke-protective effects of Ang II. This perhaps could be a reason for the inferior stroke-protective effect of ACE inhibitors compared with ARBs, which has been demonstrated in several clinical trials. The evidence for this effect of ARBs compared with ACE inhibitors, however, is only indirect. Ongoing clinical trials with head-to-head comparisons of ARBs and ACE inhibitors will hopefully provide the needed information.

Predictors of stroke in high-risk patients after acute myocardial infarction: insights from the VALIANT trial

AIMS

We sought to determine risk models for predicting early and late stroke in a large cohort of high-risk post-myocardial infarction (MI) patients.

METHODS AND RESULTS

We prospectively analysed data from 14 703 patients in the VALIANT trial with acute MI complicated by heart failure, left ventricular (LV) systolic dysfunction, or both. Patients were randomized 0.5-10 days after acute MI to valsartan, captopril, or their combination. We evaluated risk factors for early (<45 days) and late (>45 days) stroke by using multivariable Cox proportional hazards regression analyses with stepwise variable selection techniques applied to 92 pre-specified potential predictor variables. After randomization, 463 (3.2%) patients had fatal (n = 124) or non-fatal (n = 339) strokes, with 134 strokes occurring in the first 45 days. The strokes were classified as ischaemic (348), haemorrhagic (40), or of indeterminate cause (75). Estimated glomerular filtration rate and heart rate when in sinus rhythm were the most powerful predictors of early stroke (<45 days after MI), whereas diastolic blood pressure (DBP) >90 mmHg, prior stroke, and atrial fibrillation (AF) were the most powerful predictors of stroke overall. Ejection fraction and sex were not predictive of stroke in this cohort.

CONCLUSION

Among high-risk patients presenting with MI but without initial neurological symptoms, the risk of stroke 6 weeks thereafter is 0.94% (95% CI 0.78-1.09). Of the most powerful baseline predictors of stroke, DBP and AF are amenable to therapeutic interventions and thus merit special attention in these patients.

Angiotensin receptor blockers and cerebral protection in stroke

Stroke is a burden of modern civilization, causing death and disability. Nowadays it is universally accepted that inhibition of the renin-angiotensin system by angiotensin-converting enzyme inhibitors or angiotensin II type 1 (AT1) receptor blockers (ARBs) can effectively decrease the incidence of stroke in patients at risk. Here, we summarize current knowledge concerning the molecular mechanisms of the beneficial effects of inhibition of the renin-angiotensin system in stroke, with an emphasis on mechanisms beyond blood pressure reduction; in particular, neuroprotection. All major clinical studies comparing the effectiveness of ARBs with placebo or other blood pressure decreasing drugs in stroke are mentioned and commented on. These clinical data are complemented by data from a selection of animal experiments pivotal for the understanding of neuroprotective actions of ARBs. Clinical studies have shown that ARBs can be superior to other antihypertensive drugs in the prevention of stroke, even if there are no differences in blood pressures. Findings from animal experiments suggest that the underlying mechanisms include not just inhibition of the detrimental peripheral and central actions of angiotensin II mediated by AT1-receptors, but also stimulation of unopposed angiotensin II type 2 (AT2) receptors that are upregulated in the area of ischaemia. ARBs have been proven to be effective in the prevention of stroke via mechanisms that are both dependent on and independent of the antihypertensive abilities of the drugs.