Central administration of angiotensin-(1-7) stimulates nitric oxide release and upregulates the endothelial nitric oxide synthase expression following focal cerebral ischemia/reperfusion in rats

Transgenic rat with overproduction of ubiquitous angiotensin-(1-7) presents neuroprotection in a model of ischemia and reperfusion

Recent studies showed that angiotensin-(1-7) has cerebroprotective actions in stroke. In the present study, we aim to test whether tissue overexpression of Angiotensin-(1-7), mainly in the brain provides neuroprotection in a model of ischemia/reperfusion by bilateral common carotid arteries occlusion/reperfusion (BCCAo/R). Evaluation of neurological deficit scores and bilateral asymmetry test (BAT) were performed seven days after transient BCCAo/R in transgenic rats (TG-7371) overexpressing Angiotensin-(1-7) and Sprague-Dawley (SD) rats. To assess blood-brain barrier (BBB) permeability Evans blue dye (EB) was intravenously injected. Cytokine levels were quantified in the whole brain through Elisa assay and oxidative stress was measured 7 days after ischemia. The expression of AT₁ and Mas receptors and inducible nitric oxide synthase (iNOS) was evaluated by RT-PCR. Neurological deficits were observed in both SD-BCCAo/R and TG-BCCAo/R, contrasting to sham-operated groups. However, TG-BCCAo/R showed a significant lower neurological score and latency in BAT when compared with SD-BCCAo/R. BBB integrity in TG-BCCAo/R was improved, since these animals showed lower extravasation of EB than SD-BCCAo/R. Interestingly, TG-BCCAo/R presented lower levels of pro-inflammatory cytokines when compared to SD-BCCAo/R. Levels of IL-10 were higher in SD-BCCAo/R than in SD control and even higher in TG-BCCAo/R. TG-BCCAo/R animals presented decreased levels of TBARS and increase in SOD activity and GSH levels when compared to SD sham rats. RT-PCR results showed higher levels of AT₁ receptor and iNOS in SD-BCCAo/R compared to TG-BCCAo/R, but no difference was observed for Mas receptor. The present study shows that lifetime increase in cerebral expression of an Ang-(1-7)-producing fusion protein induces neuroprotection in experimental global cerebral ischemia and reperfusion, reassuring that, pharmacological strategies leading to increase in Ang-(1-7) can be an additional tool for stroke therapy.

Endothelial dysfunction: developmental mechanisms and therapeutic strategies

Introduction: Every year the importance of the normal functioning of the endothelial layer of the vascular wall in maintaining the health of the body becomes more and more obvious.

The physiological role of the endothelium: The endothelium is a metabolically active organ actively involved in the regulation of hemostasis, modulation of inflammation, maintenance of hemovascular homeostasis, regulation of angiogenesis, vascular tone, and permeability.

Risk factors for the development of endothelial dysfunction: Currently, insufficient bioavailability of nitric oxide is considered the most significant risk factor for endothelial dysfunction.

Mechanisms of development of endothelial dysfunction: The genesis of endothelial dysfunction is a multifactorial process. Among various complex mechanisms, this review examines oxidative stress, inflammation, hyperglycemia, vitamin D deficiency, dyslipidemia, excess visceral fat, hyperhomocysteinemia, hyperuricemia, as well as primary genetic defect of endotheliocytes, as the most common causes in the population underlying the development of endothelial dysfunction.

Markers of endothelial dysfunction in various diseases: This article discusses the main biomarkers of endothelial dysfunction currently used, as well as promising biomarkers in the future for laboratory diagnosis of this pathology.

Therapeutic strategies: Therapeutic approaches to the endothelium in order to prevent or reduce a degree of damage to the vascular wall are briefly described.

Conclusion: Endothelial dysfunction is a typical pathological process involved in the pathogenesis of many diseases. Thus, pharmacological agents with endothelioprotective properties can provide more therapeutic benefits than a drug without such an effect.

The Renin-Angiotensin-Aldosterone System, Nitric Oxide, and Hydrogen Sulfide at the Crossroads of Hypertension and COVID-19: Racial Disparities and Outcomes

Coronavirus disease 2019 is caused by SARS-CoV-2 and is more severe in the elderly, racial minorities, and those with comorbidities such as hypertension and diabetes. These pathologies are often controlled with medications involving the renin-angiotensin-aldosterone system (RAAS). RAAS is an endocrine system involved in maintaining blood pressure and blood volume through components of the system. SARS-CoV-2 enters the cells through ACE2, a membrane-bound protein related to RAAS. Therefore, the use of RAAS inhibitors could worsen the severity of COVID-19's symptoms, especially amongst those with pre-existing comorbidities. Although a vaccine is currently available to prevent and reduce the symptom severity of COVID-19, other options, such as nitric oxide and hydrogen sulfide, may also have utility to prevent and treat this virus.

Angiotensin-(1-7) Restores Microcirculation Profiles in Acute Pancreatitis: Secret of Telomerase Reverse Transcriptase

OBJECTIVES

The aim of this study was to investigate whether angiotensin (Ang)-(1-7)-mediated restoration of pancreatic microcirculation profiles and endothelial injury is associated with the expression of telomerase reverse transcriptase (TERT).

METHODS

Wild-type, TERT transgene, and TERT knockdown mice were used in this study, and acute pancreatitis model was induced by intraperitoneal injection of cerulein and lipopolysaccharide (LPS). Pancreatitis was confirmed by histopathology and serum amylase levels. Pancreatic microcirculation function was assessed by laser Doppler. Endothelial injury model was established by exposing endothelial cells to LPS. Proinflammatory cytokines were detected using enzyme-linked immunosorbent assay, endothelial permeability was detected using transwell assay, and mitochondrial dysfunction and mitochondrial reactive oxygen species (mtROS) were determined by performing confocal microscopy.

RESULTS

The effects of Ang-(1-7) in the treatment of pancreatic microcirculation dysfunction were associated with TERT expression. In addition, Ang-(1-7) protected against endothelial cell lesions via inhibiting the increase in endothelial cell permeability and release of proinflammatory cytokines in a TERT-dependent manner. Furthermore, TERT was involved in Ang-(1-7)-mediated attenuation of mitochondrial dysfunction and mtROS in LPS-induced endothelial cells.

CONCLUSIONS

Angiotensin-(1-7) restores pancreatic microcirculation profiles and reverses endothelial injury by inhibiting mtROS production and mitochondrial dysfunction in a TERT-dependent manner.

SARS-CoV-2 interacts with renin-angiotensin system: impact on the central nervous system in elderly patients

SARS-CoV-2 is a recently identified coronavirus that causes the current pandemic disease known as COVID-19. SARS-CoV-2 uses angiotensin-converting enzyme 2 (ACE2) as a receptor, suggesting that the initial steps of SARS-CoV-2 infection may have an impact on the renin-angiotensin system (RAS). Several processes are influenced by RAS in the brain. The neurological symptoms observed in COVID-19 patients, including reduced olfaction, meningitis, ischemic stroke, cerebral thrombosis, and delirium, could be associated with RAS imbalance. In this review, we focus on the potential role of disturbances in the RAS as a cause for central nervous system sequelae of SARS-CoV-2 infection in elderly patients.

Controlled Hemorrhage Sensitizes Angiotensin II-Elicited Hypertension through Activation of the Brain Renin-Angiotensin System Independently of Endoplasmic Reticulum Stress

Hemorrhagic shock is associated with activation of renin-angiotensin system (RAS) and endoplasmic reticulum stress (ERS). Previous studies demonstrated that central RAS activation produced by various challenges sensitizes angiotensin (Ang) II-elicited hypertension and that ERS contributes to the development of neurogenic hypertension. The present study investigated whether controlled hemorrhage could sensitize Ang II-elicited hypertension and whether the brain RAS and ERS mediate this sensitization. Results showed that hemorrhaged (HEM) rats had a significantly enhanced hypertensive response to a slow-pressor infusion of Ang II when compared to sham HEM rats. Treatment with either angiotensin-converting enzyme (ACE) 1 inhibitor, captopril, or ACE2 activator, diminazene, abolished the HEM-induced sensitization of hypertension. Treatment with the ERS agonist, tunicamycin, in sham HEM rats also sensitized Ang II-elicited hypertension. However, blockade of ERS with 4-phenylbutyric acid in HEM rats did not alter HEM-elicited sensitization of hypertension. Either HEM or ERS activation produced a greater reduction in BP after ganglionic blockade, upregulated mRNA and protein expression of ACE1 in the hypothalamic paraventricular nucleus (PVN), and elevated plasma levels of Ang II but reduced mRNA expression of the Ang-(1-7) receptor, Mas-R, and did not alter plasma levels of Ang-(1-7). Treatment with captopril or diminazene, but not phenylbutyric acid, reversed these changes. No treatments had effects on PVN protein expression of the ERS marker glucose-regulated protein 78. The results indicate that controlled hemorrhage sensitizes Ang II-elicited hypertension by augmenting RAS prohypertensive actions and reducing RAS antihypertensive effects in the brain, which is independent of ERS mechanism.

The Role of the ACE2/MasR Axis in Ischemic Stroke: New Insights for Therapy

Ischemic stroke remains the leading cause of neurologically based morbidity and mortality. Current stroke treatment is limited to two classes of FDA-approved drugs: thrombolytic agents (tissue plasminogen activator (tPA)) and antithrombotic agents (aspirin and heparin), which have a narrow time-window (<4.5 h) for administration after onset of stroke symptoms. While thrombolytic agents restore perfusion, they carry serious risks for hemorrhage, and do not influence damage responses during reperfusion. Consequently, stroke therapies that can suppress deleterious effects of ischemic injury are desperately needed. Angiotensin converting enzyme-2 (ACE2) has been recently suggested to beneficially influence experimental stroke outcomes by converting the vasoconstrictor Ang II into the vasodilator Ang 1-7. In this review, we extensively discuss the protective functions of ACE2-Ang (1-7)-MasR axis of renin angiotensin system (RAS) in ischemic stroke.

Manifestation of renin angiotensin system modulation in traumatic brain injury

Traumatic brain injury (TBI) alters brain function and is a crucial public health concern worldwide. TBI triggers the release of inflammatory mediators (cytokines) that aggravate cerebral damage, thereby affecting clinical prognosis. The renin angiotensin system (RAS) plays a critical role in TBI pathophysiology. RAS is widely expressed in many organs including the brain. Modulation of the RAS in the brain via angiotensin type 1 (AT₁) and type 2 (AT₂) receptor signaling affects many pathophysiological processes, including TBI. AT₁R is highly expressed in neurons and astrocytes. The upregulation of AT₁R mediates the effects of angiotensin II (ANG II) including release of proinflammatory cytokines, cell death, oxidative stress, and vasoconstriction. The AT₂R, mainly expressed in the fetal brain during development, is also related to cognitive function. Activation of this receptor pathway decreases neuroinflammation and oxidative stress and improves overall cell survival. Numerous studies have illustrated the therapeutic potential of inhibiting AT₁R and activating AT₂R for treatment of TBI with variable outcomes. In this review, we summarize studies that describe the role of brain RAS signaling, through AT₁R and AT₂R in TBI, and its modulation with pharmacological approaches.

Circulating Angiotensin-(1-7) Is Reduced in Alzheimer's Disease Patients and Correlates With White Matter Abnormalities: Results From a Pilot Study

Introduction

Alzheimer’s disease (AD) is the leading cause of dementia worldwide. Despite the extensive research, its pathophysiology remains largely unelucidated. Currently, more attention is being given to the disease’s vascular and inflammatory aspects. In this context, the renin-angiotensin system (RAS) emerges as a credible player in AD pathogenesis. The RAS has multiple physiological functions, conducted by its two opposing axes: the classical, led by Angiotensin II (Ang II), and the alternative, driven by Angiotensin-(1–7) [Ang-(1–7)]. These peptides were shown to interact with AD pathology in animal studies, but evidence from humans is scarce. Only 20 studies dosed RAS molecules in AD patients’ bloodstream, none of which assessed both axes simultaneously. Therefore, we conducted a cross-sectional, case-control exploratory study to compare plasma levels of Ang II and Ang-(1–7) in AD patients vs. age-matched controls. Within each group, we searched for correlations between RAS biomarkers and measures from magnetic resonance imaging (MRI).

Methods

We evaluated patients with AD (n = 14) and aged-matched controls (n = 14). Plasma Ang II and Ang-(1–7) were dosed using ELISA. Brain MRI was performed in a 3 Tesla scan, and a three-dimensional T1-weighted volumetric sequence was obtained. Images were then processed by FreeSurfer to calculate: (1) white matter hypointensities (WMH) volume; (2) volumes of hippocampus, medial temporal cortex, and precuneus. Statistical analyses used non-parametrical tests (Mann-Whitney and Spearman).

Results

Ang-(1–7) levels in plasma were significantly lower in the AD patients than in controls [median (25th–75th percentiles)]: AD [101.5 (62.43–126.4)] vs. controls [209.3 (72–419.1)], p = 0.014. There was no significant difference in circulating Ang II. In the AD patients, but not in controls, there was a positive and significant correlation between Ang-(1–7) values and WMH volumes (Spearman’s rho = 0.56, p = 0.038). Ang-(1–7) did not correlate with cortical volumes in AD or in controls. Ang II did not correlate with any MRI variable in none of the groups.

Conclusion

If confirmed, our results strengthen the hypothesis that RAS alternative axis is downregulated in AD, and points to a possible interaction between Ang-(1–7) and cerebrovascular lesions in AD.

Renin-Angiotensin System and Alzheimer's Disease Pathophysiology: From the Potential Interactions to Therapeutic Perspectives

New roles of the Renin-Angiotensin System (RAS), apart from fluid homeostasis and Blood Pressure (BP) regulation, are being progressively unveiled, since the discoveries of RAS alternative axes and local RAS in different tissues, including the brain. Brain RAS is reported to interact with pathophysiological mechanisms of many neurological and psychiatric diseases, including Alzheimer's Disease (AD). Even though AD is the most common cause of dementia worldwide, its pathophysiology is far from elucidated. Currently, no treatment can halt the disease course. Successive failures of amyloid-targeting drugs have challenged the amyloid hypothesis and increased the interest in the inflammatory and vascular aspects of AD. RAS compounds, both centrally and peripherally, potentially interact with neuroinflammation and cerebrovascular regulation. This narrative review discusses the AD pathophysiology and its possible interaction with RAS, looking forward to potential therapeutic approaches. RAS molecules affect BP, cerebral blood flow, neuroinflammation, and oxidative stress. Angiotensin (Ang) II, via angiotensin type 1 receptors may promote brain tissue damage, while Ang-(1-7) seems to elicit neuroprotection. Several studies dosed RAS molecules in AD patients' biological material, with heterogeneous results. The link between AD and clinical conditions related to classical RAS axis overactivation (hypertension, heart failure, and chronic kidney disease) supports the hypothesized role of this system in AD. Additionally, RAStargeting drugs as Angiotensin Converting Enzyme inhibitors (ACEis) and Angiotensin Receptor Blockers (ARBs) seem to exert beneficial effects on AD. Results of randomized controlled trials testing ACEi or ARBs in AD are awaited to elucidate whether AD-RAS interaction has implications on AD therapeutics.

The counter regulatory axis of the renin angiotensin system in the brain and ischaemic stroke: Insight from preclinical stroke studies and therapeutic potential

Stroke is the 2nd leading cause of death worldwide and the leading cause of physical disability and cognitive issues. Although we have made progress in certain aspects of stroke treatment, the consequences remain substantial and new treatments are needed. Hypertension has long been recognised as a major risk factor for stroke, both haemorrhagic and ischaemic. The renin angiotensin system (RAS) plays a key role in blood pressure regulation and this, plus local expression and signalling of RAS in the brain, both support the potential for targeting this axis therapeutically in the setting of stroke. While historically, focus has been on suppressing classical RAS signalling through the angiotensin type 1 receptor (AT1R), the identification of a counter-regulatory axis of the RAS signalling via the angiotensin type 2 receptor (AT2R) and Mas receptor has renewed interest in targeting the RAS. This review describes RAS signalling in the brain and the potential of targeting the Mas receptor and AT2R in preclinical models of ischaemic stroke. The animal and experimental models, and the route and timing of intervention, are considered from a translational perspective.

Different reactive species modulate the hypotensive effect triggered by angiotensins at CVLM of 2K1C hypertensive rats

Hypertension is associated with increased central activity of the renin-angiotensin system (RAS) and oxidative stress. Here, we evaluated whether reactive species and neurotransmitters could contribute to the hypotensive effect induced by angiotensin (Ang) II and Ang-(1-7) at the caudal ventrolateral medulla (CVLM) in renovascular hypertensive rats (2K1C). Therefore, we investigated the effect of Ang II, Ang-(1-7), and the Ang-(1-7) antagonist A-779 microinjected before and after CVLM microinjection of the nitric oxide (NO)-synthase inhibitor, (L-NAME), vitamin C (Vit C), bicuculline, or kynurenic acid in 2K1C and SHAM rats. Baseline values of the mean arterial pressure (MAP) in 2K1C rats were higher than in SHAM rats. CVLM microinjection of Ang II, Ang-(1-7), l-NAME, or bicuculline induced decreases in the MAP in SHAM and 2K1C rats. In addition, Vit C and A-779 produced decreases in the MAP only in 2K1C rats. Kynurenic acid increased the MAP in both SHAM and 2K1C rats. Only the Ang-(1-7) effect was increased by l-NAME and reduced by bicuculline in SHAM rats. L-NAME also reduced the A-779 effect in 2K1C rats. Only the Ang II effect was abolished by CVLM Vit C and enhanced by CVLM kynurenic acid in SHAM and 2K1C rats. Overall, the superoxide anion and glutamate participated in the hypotensive effect of Ang II, while NO and GABA participated in the hypotensive effect of Ang-(1-7) in CVLM. The higher hypotensive response of A-779 in the CVLM of 2K1C rats suggests that Ang-(1-7) contributes to renovascular hypertension.

Angiotensin-converting enzyme 2 activator, DIZE in the basolateral amygdala attenuates the tachycardic response to acute stress by modulating glutamatergic tone

The basolateral amygdala (BLA) is critical in the control of the sympathetic output during stress. Studies demonstrated the involvement of the renin-angiotensin system components in the BLA. Angiotensin-(1-7) [Ang-(1-7)], acting through Mas receptors, reduces stress effects. Considering that angiotensin-converting enzyme 2 (ACE2) is the principal enzyme for the production of Ang-(1-7), here we evaluate the cardiovascular reactivity to acute stress after administration of the ACE2 activator, diminazene aceturate (DIZE) into the BLA. We also tested whether systemic treatment with DIZE could modify synaptic activity in the BLA and its effect directly on the expression of the N-methyl-d-aspartate receptors (NMDARs) in NG108 neurons in-vitro. Administration of DIZE into the BLA (200 pmol/100 nL) attenuated the tachycardia to stress (ΔHR, bpm: vehicle = 103 ± 17 vs DIZE = 49 ± 7 p = 0.018); this effect was inhibited by Ang-(1-7) antagonist, A-779 (ΔHR, bpm: DIZE = 49 ± 7 vs A-779 + DIZE = 100 ± 15 p = 0.04). Systemic treatment with DIZE attenuated the excitatory synaptic activity in the BLA (Frequency (Hz): vehicle = 2.9 ± 0.4 vs. DIZE =1.8 ± 0.3 p < 0.04). NG108 cells treated with DIZE demonstrated decreased expression of l subunit NMDAR-NR1 (NR1 expression (a.u): control = 0.534 ± 0.0593 vs. DIZE = 0.254 ± 0.0260) of NMDAR and increases of Mas receptors expression. These data demonstrate that DIZE attenuates the tachycardia evoked by acute stress. This effect results from a central action in the BLA involving activation of Mas receptors. The ACE2 activation via DIZE treatment attenuated the frequency of excitatory synaptic activity in the basolateral amygdala and this effect can be related with the decreases of the NMDAR-NR1 receptor expression.

Improving Cerebrovascular Function to Increase Neuronal Recovery in Neurodegeneration Associated to Cardiovascular Disease

Mounting evidence indicates that the presence of cardiovascular disease (CVD) and risk factors elevates the incidence of cognitive impairment (CI) and dementia. CVD and associated decline in cardiovascular function can impair cerebral blood flow (CBF) regulation, leading to the disruption of oxygen and nutrient supply in the brain where limited intracellular energy storage capacity critically depends on CBF to sustain proper neuronal functioning. During hypertension and acute as well as chronic CVD, cerebral hypoperfusion and impaired cerebrovascular function are often associated with neurodegeneration and can lead to CI and dementia. Currently, all forms of neurodegeneration associated to CVD lack effective treatments, which highlights the need to better understand specific mechanisms linking cerebrovascular dysfunction and CBF deficits to neurodegeneration. In this review, we discuss vascular targets that have already shown attenuation of neurodegeneration or CI associated to hypertension, heart failure (HF) and stroke by improving cerebrovascular function or CBF deficits.

Central ANG-(1-7) infusion improves blood pressure regulation in antenatal betamethasone-exposed sheep and reveals sex-dependent effects on oxidative stress

Fetal exposure to betamethasone (BMX) as a consequence of glucocorticoid administration to women threatening premature delivery may lead to long-term deleterious effects on the cardiovascular system and dysregulation of blood pressure in exposed adults. Indeed, adult offspring of BMX sheep exhibit increased mean arterial pressure (MAP) and attenuated baroreflex sensitivity (BRS) that are associated with lower medullary and cerebrospinal fluid (CSF) angiotensin-(1-7) [(ANG-(1-7)] content. Thus we determined the effects of ANG-(1-7) supplementation in the CSF on MAP, BRS, blood pressure (BPV) and heart rate variability (HRV) in conscious animals. The peptide or artificial CSF (aCSF) was infused continuously into the lateral ventricle (intracerebroventricular) of 4-mo-old male and female BMX sheep for 2 wk. Analysis of data from males and females combined revealed that intracerebroventricular ANG-(1-7) significantly lowered MAP and heart rate and improved BRS as compared with baseline; intracerebroventricular aCSF did not change these indexes. Similar patterns were observed for altered hemodynamics and autonomic function produced by intracerebroventricular ANG-(1-7) in both sexes. Oxidative stress and MAP kinase (MAPK) activation were lower in tissues from the dorsomedial medulla (DMM) of ANG-(1-7)-treated males but were unchanged in the treated females, when assessed at the end of the treatment period. We conclude that in the face of ANG-(1-7) deficiency in CSF and medullary tissue in BMX sheep intracerebroventricular supplementation of ANG-(1-7) lowers MAP and restores the impaired autonomic function to a similar degree in both males and females; however, the attenuation of MAPK and oxidative stress within the DMM was evident only in males. NEW & NOTEWORTHY We demonstrate that intracerebroventricular angiotensin-(1-7) [(ANG-(1-7)] treatment for 2 wk in antenatal betamethasone-exposed sheep provides beneficial effects on blood pressure and autonomic function. The physiological improvements are accompanied by an attenuation of oxidative stress in males but not females. The finding that ANG-(1-7) supplementation lowers blood pressure and restores the impaired autonomic function in a model of fetal programming previously shown to exhibit a deficiency in cerebrospinal fluid and brain tissue illustrates the potential for new therapeutic strategies for reducing cardiovascular dysfunction arising from prenatal events.

Neuroprotection by post-stroke administration of an oral formulation of angiotensin-(1-7) in ischaemic stroke

NEW FINDINGS

What is the central question of this study? Angiotensin-(1-7) decreases cerebral infarct volume and improves neurological function when delivered centrally before and during ischaemic stroke. Here, we assessed the neuroprotective effects of angiotensin-(1-7) when delivered orally post-stroke. What is the main finding and its importance? We show that oral delivery of angiotensin-(1-7) attenuates cerebral damage induced by middle cerebral artery occlusion in rats, without affecting blood pressure or cerebral blood flow. Importantly, these treatments begin post-stroke at times coincident with the treatment window for tissue plasminogen activator, providing supporting evidence for clinical translation of this new therapeutic strategy.

ABSTRACT

As a target for stroke therapies, the angiotensin-converting enzyme 2-angiotensin-(1-7)-Mas [ACE2/Ang-(1-7)/Mas] axis of the renin-angiotensin system can be activated chronically to induce neuroprotective effects, in opposition to the deleterious effects of angiotensin II via its type 1 receptor. However, more clinically relevant treatment protocols with Ang-(1-7) that involve its systemic administration beginning after the onset of ischaemia have not been tested. In this study, we tested systemic post-stroke treatments using a molecule where Ang-(1-7) is included within hydroxypropyl-β-cyclodextrin [HPβCD-Ang-(1-7)] as an orally bioavailable treatment. In three separate protocols, HPβCD-Ang-(1-7) was administered orally to Sprague-Dawley rats after induction of ischaemic stroke by endothelin-1-induced middle cerebral artery occlusion: (i) to assess its effects on cerebral damage and behavioural deficits; (ii) to determine its effects on cardiovascular parameters; and (iii) to determine whether it altered cerebral blood flow. The results indicate that post-stroke oral administration of HPβCD-Ang-(1-7) resulted in 25% reductions in cerebral infarct volumes and improvement in neurological functions (P < 0.05), without inducing any alterations in blood pressure, heart rate or cerebral blood flow. In conclusion, Ang-(1-7) treatment using an oral formulation after the onset of ischaemia induces significant neuroprotection in stroke and might represent a viable approach for taking advantage of the protective ACE2/Ang-(1-7)/Mas axis in this disease.

Assessing the effects of Ang-(1-7) therapy following transient middle cerebral artery occlusion

The counter-regulatory axis, Angiotensin Converting Enzyme 2, Angiotensin-(1-7), Mas receptor (ACE2/Ang-1-7/MasR), of the renin angiotensin system (RAS) is a potential therapeutic target in stroke, with Ang-(1-7) reported to have neuroprotective effects in pre-clinical stroke models. Here, an extensive investigation of the functional and mechanistic effects of Ang-(1-7) was performed in a rodent model of stroke. Using longitudinal magnetic resonance imaging (MRI) it was observed that central administration of Ang-(1-7) following transient middle cerebral artery occlusion (MCAO) increased the amount of tissue salvage compared to reperfusion alone. This protective effect was not due to early changes in blood brain barrier (BBB) permeability, microglia activation or inflammatory gene expression. However, increases in NADPH oxidase 1 (Nox1) mRNA expression were observed in the treatment group compared to control. In order to determine whether Ang-(1-7) has direct cerebrovascular effects, laser speckle contrast imaging (LSCI) was performed to measure dynamic changes in cortical perfusion following reperfusion. Delivery of Ang-(1-7) did not have any effect on cortical perfusion following reperfusion however; it showed an indication to prevent the 'steal phenomenon' within the contralateral hemisphere. The comprehensive series of studies have demonstrated a moderate protective effect of Ang-(1-7) when given alongside reperfusion to increase tissue salvage.

Recent Advances in the Therapeutic and Diagnostic Use of Liposomes and Carbon Nanomaterials in Ischemic Stroke

The complexity of the central nervous system (CNS), its limited self-repairing capacity and the ineffective delivery of most CNS drugs to the brain contribute to the irreversible and progressive nature of many neurological diseases and also the severity of the outcome. Therefore, neurological disorders belong to the group of pathologies with the greatest need of new technologies for diagnostics and therapeutics. In this scenario, nanotechnology has emerged with innovative and promising biomaterials and tools. This review focuses on ischemic stroke, being one of the major causes of death and serious long-term disabilities worldwide, and the recent advances in the study of liposomes and carbon nanomaterials for therapeutic and diagnostic purposes. Ischemic stroke occurs when blood flow to the brain is insufficient to meet metabolic demand, leading to a cascade of physiopathological events in the CNS including local blood brain barrier (BBB) disruption. However, to date, the only treatment approved by the FDA for this pathology is based on the potentially toxic tissue plasminogen activator. The techniques currently available for diagnosis of stroke also lack sensitivity. Liposomes and carbon nanomaterials were selected for comparison in this review, because of their very distinct characteristics and ranges of applications. Liposomes represent a biomimetic system, with composition, structural organization and properties very similar to biological membranes. On the other hand, carbon nanomaterials, which are not naturally encountered in the human body, exhibit new modes of interaction with biological molecules and systems, resulting in unique pharmacological properties. In the last years, several neuroprotective agents have been evaluated under the encapsulated form in liposomes, in experimental models of stroke. Effective drug delivery to the brain and neuroprotection were achieved using stealth liposomes bearing targeting ligands onto their surface for brain endothelial cells and ischemic tissues receptors. Carbon nanomaterials including nanotubes, fullerenes and graphene, started to be investigated and potential applications for therapy, biosensing and imaging have been identified based on their antioxidant action, their intrinsic photoluminescence, their ability to cross the BBB, transitorily decrease the BBB paracellular tightness, carry oligonucleotides and cells and induce cell differentiation. The potential future developments in the field are finally discussed.

Angiotensin-(1-7) attenuates hypertension and cardiac hypertrophy via modulation of nitric oxide and neurotransmitter levels in the paraventricular nucleus in salt-sensitive hypertensive rats

Angiotensin-(1-7) [Ang-(1-7)] is a multifunctional bioactive angiotensin peptide which exerts a cardiovascular protective function mainly by opposing the effects of angiotensin II. We aimed to determine whether brain Ang-(1-7) regulates nitric oxide (NO) and neurotransmitter levels in the hypothalamic paraventricular nucleus (PVN), and influences sympathetic activity, blood pressure and cardiac hypertrophy in salt-sensitive hypertension. Dahl salt-sensitive rats receiving a high-salt (HS, 8% NaCl) or a normal-salt (NS, 0.3% NaCl) diet were treated with an intracerebroventricular (ICV) infusion of Ang-(1-7) for 6 weeks. Seven rats were measured in each group. In comparison with NS rats, HS rats exhibited significantly increased mean arterial pressure, plasma norepinephrine (NE) and cardiac hypertrophy. In addition, HS rats (compared to NS rats) had increased glutamate, NE and tyrosine hydroxylase (TH) expression, and reduced NO levels as well as reduced expression of γ-aminobutyric acid (GABA) and the 67 kDa isoform of glutamate decarboxylase (GAD67) in the PVN. Treatment with ICV infusion of Ang-(1-7) reversed these changes in the salt-sensitive hypertensive rats. The results suggest that the beneficial effects of brain Ang-(1-7) on salt-sensitive hypertension and cardiac hypertrophy are partly due to an elevation in the NO level and restoration of neurotransmitter balance in the PVN.

Angiotensin-(1-7) [Ang-(1-7)] is a multifunctional bioactive angiotensin peptide which exerts a cardiovascular protective function mainly by opposing the effects of angiotensin II.

The ACE2/Angiotensin-(1-7)/MAS Axis of the Renin-Angiotensin System: Focus on Angiotensin-(1-7)

The renin-angiotensin system (RAS) is a key player in the control of the cardiovascular system and hydroelectrolyte balance, with an influence on organs and functions throughout the body. The classical view of this system saw it as a sequence of many enzymatic steps that culminate in the production of a single biologically active metabolite, the octapeptide angiotensin (ANG) II, by the angiotensin converting enzyme (ACE). The past two decades have revealed new functions for some of the intermediate products, beyond their roles as substrates along the classical route. They may be processed in alternative ways by enzymes such as the ACE homolog ACE2. One effect is to establish a second axis through ACE2/ANG-(1-7)/MAS, whose end point is the metabolite ANG-(1-7). ACE2 and other enzymes can form ANG-(1-7) directly or indirectly from either the decapeptide ANG I or from ANG II. In many cases, this second axis appears to counteract or modulate the effects of the classical axis. ANG-(1-7) itself acts on the receptor MAS to influence a range of mechanisms in the heart, kidney, brain, and other tissues. This review highlights the current knowledge about the roles of ANG-(1-7) in physiology and disease, with particular emphasis on the brain.

The renin angiotensin system and the brain: New developments

The traditional renin-angiotensin system (RAS) is indispensable system in adjusting sodium homeostasis, body fluid volume, and controlling arterial blood pressure. The key elements are renin splitting inactive angiotensinogen to yield angiotensin (Ang-I). Ang-1 is then changed by angiotensin-1 converting enzyme (ACE) into angiotensin II (Ang-II). Using PubMed, Google Scholar, and other means, we searched the peer-reviewed literature from 1990 to 2013 for articles on newly discovered findings related to the RAS, especially focusing on how the system influences the central nervous system (CNS). The classical RAS is now considered to be only part of the picture; the discovery of additional RAS pathways in the brain and elsewhere has yielded a vastly improved understanding of how the RAS influences the CNS. Newly discovered effects of the RAS on brain tissue include neuroprotection, cognition, and cerebral vasodilation. A number of brain biochemical pathways are influenced by the brain RAS. Within various pathways, there are potential opportunities for classical pharmacologic interventions as well as the possibility of controlling gene expression.

Brain renin-angiotensin system in the pathophysiology of cardiovascular diseases

Cardiovascular diseases (CVD) are among the main causes of death globally and in this context hypertension represents one of the key risk factors for developing a CVD. It is well established that the peripheral renin-angiotensin system (RAS) plays an important role in regulating blood pressure (BP). All components of the classic RAS can also be found in the brain but, in contrast to the peripheral RAS, how the endogenous RAS is involved in modulating cardiovascular effects in the brain is not fully understood yet. It is a complex system that may work differently in diverse areas of the brain and is linked to the peripheral system by the circumventricular organs (CVO), which do not have a blood brain barrier (BBB). In this review, we focus on the brain angiotensin peptides, their interactions with each other, and the consequences in the central nervous system (CNS) concerning cardiovascular control. Additionally, we present potential drug targets in the brain RAS for the treatment of hypertension.

Macrophages in neuroinflammation: role of the renin-angiotensin-system

Macrophages are essential players of the innate immune system which are involved in the initiation and progression of various inflammatory and autoimmune diseases including neuroinflammation. In the past few years, it has become increasingly clear that the regulation of macrophage responses by the local tissue milieu is also influenced by mediators which were first discovered as regulators in the nervous or also cardiovascular system. Here, the renin-angiotensin system (RAS) is a major focus of current research. Besides its classical role in blood pressure control, body fluid, and electrolyte homeostasis, the RAS may influence (auto)immune responses, modulate T cells, and particularly act on macrophages via different signaling pathways. Activation of classical RAS pathways including angiotensin (Ang) II and AngII type 1 (AT₁R) receptors may drive pro-inflammatory macrophage responses in neuroinflammation via regulation of chemokines. More recently, alternative RAS pathways were described, such as binding of Ang-(1-7) to its receptor Mas. Signaling via Mas pathways may counteract some of the AngII/AT₁R-mediated effects. In macrophages, the Ang-(1-7)/Mas exerts beneficial effects on neuroinflammation via modulating macrophage polarization, migration, and T cell activation in vitro and in vivo. These data delineate a pivotal role of the RAS in inflammation of the nervous system and identify RAS modulation as a potential new target for immunotherapy with a special focus on macrophages.

Deficiency of angiotensin-converting enzyme 2 causes deterioration of cognitive function

The classical renin–angiotensin system (RAS), known as the angiotensin (Ang)-converting enzyme (ACE)/Ang II/Ang II type 1 (AT1) receptor axis, induces various organ damages including cognitive decline. On the other hand, the ACE2/Ang-(1–7)/Mas receptor axis has been highlighted as exerting antagonistic actions against the classical RAS axis in the cardiovascular system. However, the roles of the ACE2/Ang-(1–7)/Mas axis in cognitive function largely remain to be elucidated, and we therefore examined possible roles of ACE2 in cognitive function. Male, 10-week-old C57BL6 (wild type, WT) mice and ACE2 knockout (KO) mice were subjected to the Morris water maze task and Y maze test to evaluate cognitive function. ACE2KO mice exhibited significant impairment of cognitive function, compared with that in WT mice. Superoxide anion production increased in ACE2KO mice, with increased mRNA levels of NADPH oxidase subunit, p22^phox, p40^phox, p67^phox, and gp91^phox in the hippocampus of ACE2KO mice compared with WT mice. The protein level of SOD3 decreased in ACE2KO mice compared with WT mice. The AT1 receptor mRNA level in the hippocampus was higher in ACE2KO mice compared with WT mice. In contrast, the AT2 receptor mRNA level in the hippocampus did not differ between the two strains. Mas receptor mRNA was highly expressed in the hippocampus compared with the cortex. Brain-derived neurotrophic factor (BDNF) mRNA and protein levels were lower in the hippocampus in ACE2KO mice compared with WT mice. Taken together, ACE2 deficiency resulted in impaired cognitive function, probably at least in part because of enhanced oxidative stress and a decrease in BDNF.

Therapeutic potential of the renin angiotensin system in ischaemic stroke

The renin angiotensin system (RAS) consists of the systemic hormone system, critically involved in regulation and homeostasis of normal physiological functions [i.e. blood pressure (BP), blood volume regulation], and an independent brain RAS, which is involved in the regulation of many functions such as memory, central control of BP and metabolic functions. In general terms, the RAS consists of two opposing axes; the ‘classical axis’ mediated primarily by Angiotensin II (Ang II), and the ‘alternative axis’ mediated mainly by Angiotensin-(1–7) (Ang-(1–7)). An imbalance of these two opposing axes is thought to exist between genders and is thought to contribute to the pathology of cardiovascular conditions such as hypertension, a stroke co-morbidity. Ischaemic stroke pathophysiology has been shown to be influenced by components of the RAS with specific RAS receptor antagonists and agonists improving outcome in experimental models of stroke. Manipulation of the two opposing axes following acute ischaemic stroke may provide an opportunity for protection of the neurovascular unit, particularly in the presence of pre-existing co-morbidities where the balance may be shifted. In the present review we will give an overview of the experimental stroke studies that have investigated pharmacological interventions of the RAS.

Protective role of ACE2-Ang-(1-7)-Mas in myocardial fibrosis by downregulating KCa3.1 channel via ERK1/2 pathway

The intermediate-conductance Ca²⁺-activated K⁺ (K_Ca3.1) channel plays a vital role in myocardial fibrosis induced by angiotensin (Ang) II. However, as the antagonists of Ang II, the effect of angiotensin-converting enzyme 2 (ACE2)-angiotensin-(1-7)-Mas axis on K_Ca3.1 channel during myocardial fibrosis remains unknown. This study was designed to explore the function of K_Ca3.1 channel in the cardioprotective role of ACE2-Ang-(1-7)-Mas. Wild-type (WT) mice, hACE2 transgenic mice (Tg), and ACE2 deficiency mice (ACE2^-/-) were administrated with Ang II by osmotic mini-pumps. As the activator of ACE2, diminazene aceturate (DIZE) inhibited increase of blood pressure, collagen deposition, and K_Ca3.1 protein expression in myocardium of WT mice induced by Ang II. In Tg and ACE2^-/- mice, besides the elevation of blood pressure, Ang II induced transformation of cardiac fibroblast into myofibroblast and resulted in augmentation of hydroxyproline concentration and collagen deposition, as well as K_Ca3.1 protein expression, but the changes in ACE2^-/- mice were more obvious than those in Tg mice. Mas antagonist A779 reduced blood pressure, myocardium fibrosis, and myocardium K_Ca3.1 protein expression by Ang II in Tg mice, but activation of K_Ca3.1 with SKA-31 in Tg mice promoted the pro-fibrogenic effects of Ang II. Respectively, in ACE2^-/- mice, TRAM-34, the K_Ca3.1 blocker, and Ang-(1-7) inhibited increase of blood pressure, collagen deposition, and K_Ca3.1 protein expression by Ang II. Moreover, DIZE and Ang-(1-7) depressed p-ERK1/2/t-ERK increases by Ang II in WT mice, and after blockage of ERK1/2 pathway with PD98059, the K_Ca3.1 protein expression was reduced in WT mice. In conclusion, the present study demonstrates that ACE2-Ang-(1-7)-Mas protects the myocardium from hypertension-induced injury, which is related to its inhibiting effect on K_Ca3.1 channels through ERK1/2 pathway. Our results reveal that K_Ca3.1 channel is likely to be a critical target on the ACE2-Ang-(1-7)-Mas axis for its protective role in myocardial fibrosis and changes of K_Ca3.1 induced by homeostasis of ACE-Ang II-AT1 axis and ACE2-Ang-(1-7)-Mas axis may be a new therapeutic target in myocardial fibrosis.

Neuroprotective mechanisms of the ACE2-angiotensin-(1-7)-Mas axis in stroke

The discovery of beneficial neuroprotective effects of the angiotensin converting enzyme 2-angiotensin-(1-7)-Mas axis [ACE2-Ang-(1-7)-Mas] in ischemic and hemorrhagic stroke has spurred interest in a more complete characterization of its mechanisms of action. Here, we summarize findings that describe the protective role of the ACE2-Ang-(1-7)-Mas axis in stroke, along with a focused discussion on the potential mechanisms of neuroprotective effects of Ang-(1-7) in stroke. The latter incorporates evidence describing the actions of Ang-(1-7) to counter the deleterious effects of angiotensin II (AngII) via its type 1 receptor, including anti-inflammatory, anti-oxidant, vasodilatory, and angiogenic effects, and the role of altered kinase-phosphatase signaling. Interactions of Mas with other receptors, including bradykinin receptors and AngII type 2 receptors are also considered. A more complete understanding of the mechanisms of action of Ang-(1-7) to elicit neuroprotection will serve as an essential step toward research into potential targeted therapeutics in the clinical setting.

Vascular endothelial dysfunction and pharmacological treatment

The endothelium exerts multiple actions involving regulation of vascular permeability and tone, coagulation and fibrinolysis, inflammatory and immunological reactions and cell growth. Alterations of one or more such actions may cause vascular endothelial dysfunction. Different risk factors such as hypercholesterolemia, homocystinemia, hyperglycemia, hypertension, smoking, inflammation, and aging contribute to the development of endothelial dysfunction. Mechanisms underlying endothelial dysfunction are multiple, including impaired endothelium-derived vasodilators, enhanced endothelium-derived vasoconstrictors, over production of reactive oxygen species and reactive nitrogen species, activation of inflammatory and immune reactions, and imbalance of coagulation and fibrinolysis. Endothelial dysfunction occurs in many cardiovascular diseases, which involves different mechanisms, depending on specific risk factors affecting the disease. Among these mechanisms, a reduction in nitric oxide (NO) bioavailability plays a central role in the development of endothelial dysfunction because NO exerts diverse physiological actions, including vasodilation, anti-inflammation, antiplatelet, antiproliferation and antimigration. Experimental and clinical studies have demonstrated that a variety of currently used or investigational drugs, such as angiotensin-converting enzyme inhibitors, angiotensin AT1 receptors blockers, angiotensin-(1-7), antioxidants, beta-blockers, calcium channel blockers, endothelial NO synthase enhancers, phosphodiesterase 5 inhibitors, sphingosine-1-phosphate and statins, exert endothelial protective effects. Due to the difference in mechanisms of action, these drugs need to be used according to specific mechanisms underlying endothelial dysfunction of the disease.

Effect of a Selective Mas Receptor Agonist in Cerebral Ischemia In Vitro and In Vivo

Functional modulation of the non-AT₁R arm of the renin-angiotensin system, such as via AT₂R activation, is known to improve stroke outcome. However, the relevance of the Mas receptor, which along with the AT₂R forms the protective arm of the renin-angiotensin system, as a target in stroke is unclear. Here we tested the efficacy of a selective MasR agonist, AVE0991, in in vitro and in vivo models of ischemic stroke. Primary cortical neurons were cultured from E15-17 mouse embryos for 7–9 d, subjected to glucose deprivation for 24 h alone or with test drugs, and percentage cell death was determined using trypan blue exclusion assay. Additionally, adult male mice were subjected to 1 h middle cerebral artery occlusion and were administered either vehicle or AVE0991 (20 mg/kg i.p.) at the commencement of 23 h reperfusion. Some animals were also treated with the MasR antagonist, A779 (80 mg/kg i.p.) 1 h prior to surgery. Twenty-four h after MCAo, neurological deficits, locomotor activity and motor coordination were assessed in vivo, and infarct and edema volumes estimated from brain sections. Following glucose deprivation, application of AVE0991 (10⁻⁸ M to 10⁻⁶ M) reduced neuronal cell death by ~60% (P<0.05), an effect prevented by the MasR antagonist. By contrast, AVE0991 administration in vivo had no effect on functional or histological outcomes at 24 h following stroke. These findings indicate that the classical MasR agonist, AVE0991, can directly protect neurons from injury following glucose-deprivation. However, this effect does not translate into an improved outcome in vivo when administered systemically following stroke.

An update of the role of renin angiotensin in cardiovascular homeostasis

The renin angiotensin system (RAS) is thought to be the body's main vasoconstrictor system, with physiological effects mediated via the interaction of angiotensin II with angiotensin I receptors (the "classic" RAS model). However, since the discovery of the heptapeptide angiotensin 1-7 and the development of the concept of the "alternate" RAS system, with its ability to reduce arterial blood pressure, our understanding of this physiologic system has changed dramatically. In this review, we focus on the newly discovered functions of the RAS, particularly the potential clinical significance of these developments, especially in the realm of new pharmacologic interventions for treating cardiovascular disease.

Angiotensin-(1-7) induces cerebral ischaemic tolerance by promoting brain angiogenesis in a Mas/eNOS-dependent pathway

BACKGROUND AND PURPOSE

As a newer component of the renin-angiotensin system, angiotensin-(1-7) [Ang-(1-7) ] has been shown to facilitate angiogenesis and protect against ischaemic damage in peripheral tissues. However, the role of Ang-(1-7) in brain angiogenesis remains unclear. The aim of this study was to investigate whether Ang-(1-7) could promote angiogenesis in brain, thus inducing tolerance against focal cerebral ischaemia.

EXPERIMENTAL APPROACH

Male Sprague-Dawley rats were i.c.v. infused with Ang-(1-7), A-779 (a Mas receptor antagonist), L-NIO, a specific endothelial NOS (eNOS) inhibitor, endostatin (an anti-angiogenic compound) or vehicle, alone or simultaneously, for 1-4 weeks. Capillary density, endothelial cell proliferation and key components of eNOS pathway in the brain were evaluated. Afterwards, rats were subjected to permanent middle cerebral artery occlusion (pMCAO), and regional cerebral blood flow (rCBF), infarct volume and neurological deficits were measured 24 h later.

KEY RESULTS

Infusion of Ang-(1-7) for 4 weeks significantly increased brain capillary density via promoting endothelial cell proliferation, which was accompanied by eNOS activation and up-regulation of NO and VEGF in brain. These effects were abolished by A-779 or L-NIO. More importantly, Ang-(1-7) improved rCBF and decreased infarct volume and neurological deficits after pMCAO, which could be reversed by A-779, L-NIO or endostatin.

CONCLUSIONS AND IMPLICATIONS

This is the first evidence that Ang-(1-7) promotes brain angiogenesis via a Mas/eNOS-dependent pathway, which enhances tolerance against subsequent cerebral ischaemia. These findings highlight brain Ang-(1-7)/Mas signalling as a potential target in stroke prevention.

Protective axis of the renin-angiotensin system in the brain

The RAS (renin-angiotensin system) is composed of two arms: the pressor arm containing AngII (angiotensin II)/ACE (angiotensin-converting enzyme)/AT1Rs (AngII type 1 receptors), and the depressor arm represented by Ang-(1-7) [angiotensin-(1-7)]/ACE2/Mas receptors. All of the components of the RAS are present in the brain. Within the brain, Ang-(1-7) contributes to the regulation of BP (blood pressure) by acting at regions that control cardiovascular function such that, when Ang-(1-7) is injected into the nucleus of the solitary tract, caudal ventrolateral medulla, paraventricular nucleus or anterior hypothalamic area, a reduction in BP occurs; however, when injected into the rostral ventrolateral medulla, Ang-(1-7) stimulates an increase in BP. In contrast with AngII, Ang-(1-7) improves baroreflex sensitivity and has an inhibitory neuromodulatory role in hypothalamic noradrenergic neurotransmission. Ang-(1-7) not only exerts effects related to BP regulation, but also acts as a cerebroprotective component of the RAS by reducing cerebral infarct size and neuronal apoptosis. In the present review, we provide an overview of effects elicited by Ang-(1-7) in the brain, which suggest a potential role for Ang-(1-7) in controlling the central development of hypertension.

MAS-mediated antioxidant effects restore the functionality of angiotensin converting enzyme 2-angiotensin-(1-7)-MAS axis in diabetic rat carotid

We hypothesized that endothelial AT₁-activated NAD(P)H oxidase-driven generation of reactive oxygen species during type I-diabetes impairs carotid ACE2-angiotensin-(1–7)-Mas axis functionality, which accounts for the impaired carotid flow in diabetic rats. We also hypothesized that angiotensin-(1–7) chronic treatment of diabetic rats restores carotid ACE2-angiotensin-(1–7)-Mas axis functionality and carotid flow. Relaxant curves for angiotensin II or angiotensin-(1–7) were obtained in carotid from streptozotocin-induced diabetic rats. Superoxide or hydrogen peroxide levels were measured by flow cytometry in carotid endothelial cells. Carotid flow was also determined. We found that endothelial AT₁-activated NAD(P)H oxidase-driven generation of superoxide and hydrogen peroxide in diabetic rat carotid impairs ACE2-angiotensin-(1–7)-Mas axis functionality, which reduces carotid flow. In this mechanism, hydrogen peroxide derived from superoxide dismutation inhibits ACE2 activity in generating angiotensin-(1–7) seemingly by activating I_Cl,SWELL, while superoxide inhibits the nitrergic Mas-mediated vasorelaxation evoked by angiotensin-(1–7). Angiotensin-(1–7) treatment of diabetic rats restored carotid ACE2-angiotensin-(1–7)-Mas axis functionality by triggering a positive feedback played by endothelial Mas receptors, that blunts endothelial AT₁-activated NAD(P)H oxidase-driven generation of reactive oxygen species. Mas-mediated antioxidant effects also restored diabetic rat carotid flow, pointing to the contribution of ACE2-angiotensin-(1–7)-Mas axis in maintaining carotid flow.

Angiotensin converting enzyme 2/Ang-(1-7)/mas axis protects brain from ischemic injury with a tendency of age-dependence

BACKGROUND

The angiotensin (Ang) converting enzyme 2 (ACE2)/Ang-(1-7)/Mas receptor pathway is an important component of the renin-angiotensin system and has been suggested to exert beneficial effects in ischemic stroke.

AIMS

This study explored whether the ACE2/Ang-(1-7)/Mas pathway has a protective effect on cerebral ischemic injury and whether this effect is affected by age.

METHODS

We used three-month and eight-month transgenic mice with neural over-expression of ACE2 (SA) and their age-matched nontransgenic (NT) controls. Neurological deficits and ischemic stroke volume were determined following middle cerebral artery occlusion (MCAO). In oxygen and glucose deprivation (OGD) experiments on brain slices, the effects of the Mas receptor agonist (Ang1-7) or antagonist (A779) on tissue swelling, Nox2/Nox4 expression reactive oxygen species (ROS) production and cell death were measured.

RESULTS

(1) Middle cerebral artery occlusion -induced ischemic injury and neurological deficit were reduced in SA mice, especially in eight-month animals; (2) OGD-induced tissue swelling and cell death were decreased in SA mice with a greater reduction seen in eight-month mice; (3) Ang-(1-7) and A779 had opposite effects on OGD-induced responses, which correlated with changes in Nox2/Nox4 expression and ROS production.

CONCLUSIONS

Angiotensin converting enzyme 2/Ang-(1-7)/Mas axis protects brain from ischemic injury via the Nox/ROS signaling pathway, with a greater effect in older animals.

Cerebroprotective action of angiotensin peptides in stroke

The goal of the present review is to examine the evidence for beneficial actions of manipulation of the RAS (renin-angiotensin system) in stroke, with particular focus on Ang-(1-7) [angiotensin-(1-7)] and its receptor Mas. The RAS appears to be highly involved in the multifactorial pathophysiology of stroke. Blocking the effects of AngII (angiotensin II) at AT1R (AngII type 1 receptor), through the use of commonly prescribed ACE (angiotensin-converting enzyme) inhibitors or AT1R blockers, has been shown to have therapeutic effects in both ischaemic and haemorrhagic stroke. In contrast with the deleterious actions of over activation of AT1R by AngII, stimulation of AT2Rs (AngII type 2 receptors) in the brain has been demonstrated to elicit beneficial effects in stroke. Likewise, the ACE2/Ang-(1-7)/Mas axis of the RAS has been shown to have therapeutic effects in stroke when activated, countering the effects of the ACE/AngII/AT1R axis. Studies have demonstrated that activating this axis in the brain elicits beneficial cerebral effects in rat models of ischaemic stroke, and we have also demonstrated the cerebroprotective potential of this axis in haemorrhagic stroke using stroke-prone spontaneously hypertensive rats and collagenase-induced striatal haemorrhage. The mechanism of cerebroprotection elicited by ACE2/Ang-(1-7)/Mas activation includes anti-inflammatory effects within the brain parenchyma. The major hurdle to overcome in translating these results to humans is devising strategies to activate the ACE2/Ang-(1-7)/Mas cerebroprotective axis using post-stroke treatments that can be administered non-invasively.

Neuronal over-expression of ACE2 protects brain from ischemia-induced damage

Angiotensin (Ang) II exaggerates cerebral injury in ischemic damage. Angiotensin-converting enzyme type 2 (ACE2) converts Ang II into Ang (1-7) and thus, may protect against the effects of Ang II. We hypothesized that neuronal ACE2 over-expression decreases ischemic stroke in mice with Ang II overproduction. Human renin and angiotensinogen double transgenic (RA) mice and RA mice with neuronal over-expression of ACE2 (SARA) were used for the study. The mean arterial pressure (MAP) was calculated from telemetry-recorded blood pressure (BP). SARA mice were infused peripherally with Norepinephrine to "clamp" the BP, or intracerebroventricularly-infused with a Mas receptor antagonist (A-779). Middle cerebral artery occlusion (MCAO) surgery was performed to induce permanent focal ischemic stroke. Cerebral blood flow (CBF) and neurological function were determined. Two days after surgery, brain samples were collected for various analyses. Results showed: 1) When compared to chronically hypertensive RA mice, SARA mice had lower basal MAP, less MCAO-induced infarct volume, and increased CBF, neurological function and cerebral microvascular density in the peri-infarct area; 2) These changes in SARA mice were not altered after MAP "clamping", but partially reversed by brain infusion of A-779; 3) Ang (1-7)/Ang II ratio, angiogenic factors, endothelial nitric oxide synthase (eNOS) expression and nitric oxide production were increased, whereas, NADPH oxidase subunits and reactive oxygen species were decreased in the brain of SARA mice. ACE2 protects brain from ischemic injury via the regulation of NADPH oxidase/eNOS pathways by changing Ang (1-7)/Ang II ratio, independently of MAP changes.

Ang(1-7) treatment attenuates β-cell dysfunction by improving pancreatic microcirculation in a rat model of Type 2 diabetes

AIMS

Pancreatic microcirculation plays a pivotal role in the physiological function and survival of β-cells. Ang(1- 7) is a novel component of the renin angiotensin system (RAS) that has beneficial effects on microcirculation. In the present study, we investigated the effects of systemic Ang(1-7) administration (with or without its receptor Mas antagonist A- 779) on pancreatic microcirculation and β-cell function.

METHODS

These effects were studied in vivo using a rat model of Type 2 diabetes (T2DM). Pancreatic microcirculation and islet microvessel density were measured; and β-cell function, insulin content, and the apoptosis of islet cells were assessed, respectively. Additionally, we evaluated endothelial nitric oxide synthase (eNOS) expression and nitric oxide (NO) concentration in islets.

RESULTS

After Ang(1-7) intervention, pancreatic microcirculation and intra-islet microvessel density were significantly improved (p<0.05), and more importantly, first-phase insulin secretion of β-cells as well as relative insulin content in islets were increased, and the amount of apoptotic islet cells was decreased (p<0.05). And eNOS expression and NO release were up-regulated in pancreatic islets by Ang(1-7) administration (p<0.05). These positive effects of Ang(1-7) were prevented by the addition of A-779 (p<0.05).

CONCLUSIONS

Our findings suggest that systemic Ang(1-7) treatment could attenuate β-cell dysfunction and ameliorate islet cell apoptosis in T2DM rats by improving pancreatic microcirculation, perhaps through the mechanism of endothelial vasodilation.

Functional deterioration of endothelial nitric oxide synthase after focal cerebral ischemia

Endothelial nitric oxide synthase (eNOS) dysfunction is related to secondary injury and lesion expansion after cerebral ischemia. To date, there are few reports about postischemic alterations in the eNOS regulatory system. The purpose of the present study was to clarify eNOS expression, Ser1177 phosphorylation, and monomer formation after cerebral ischemia. Male Wistar rats were subjected to transient focal cerebral ischemia. Endothelial nitric oxide synthase messenger RNA (mRNA) and protein expression increased ≈ 8-fold in the ischemic lesion. In the middle cerebral artery core, eNOS-Ser1177 phosphorylation increased 6 hours after ischemia; however, there was an approximately 90% decrease in eNOS-Ser1177 phosphorylation observed 24 hours after ischemia that continued until at least 7 days after ischemia. Endothelial nitric oxide synthase monomer formation also increased 24 and 48 hours after ischemia (P<0.05), and protein nitration progressed in parallel with monomerization. To assess the effect of a neuroprotective agent on eNOS dysfunction, we evaluated the effect of fasudil, a Rho-kinase inhibitor, on eNOS phosphorylation and dimerization. Postischemic treatment with fasudil suppressed lesion expansion and dephosphorylation and monomer formation of eNOS. In conclusion, functional deterioration of eNOS progressed after cerebral ischemia. Rho-kinase inhibitors can reduce ischemic lesion expansion as well as eNOS dysfunction in the ischemic brain.

The expression of angiotensin-converting enzyme 2-angiotensin-(1-7)-Mas receptor axis are upregulated after acute cerebral ischemic stroke in rats

There is now unequivocal evidence that the angiotensin-converting enzyme 2(ACE2)-Ang-(1-7)-Mas axis is a key component of the renin-angiotensin system (RAS) cascade, which is closely correlated with ischemic insult occurrence. Our previous studies demonstrated that the Ang-(1-7), was an active member of the brain RAS. However, the ACE2-Ang-(1-7)-Mas axis expression after cerebral ischemic injury are currently unclear. In the present study, we investigated the time course of ACE2-Ang-(1-7) and Mas receptor expression in the acute stage of cerebral ischemic stroke. The content of Ang-(1-7) in ischemic tissues and blood serum was measured by specific EIA kits. Real-time PCR and western blot were used to determine messenger RNA (mRNA) and protein levels of the ACE2 and Mas. The cerebral ischemic lesion resulted in a significant increase of regional cerebral and circulating Ang-(1-7) at 6-48 h compared with sham operation group following focal ischemic stroke (12h: 7.276±0.320 ng/ml vs. 2.466±0.410 ng/ml, serum; 1.024±0.056 ng/mg vs. 0.499±0.032, brain) (P<0.05). Both ACE2 and Mas expression were markedly enhanced compared to the control in the ischemic tissues (P<0.05). Mas immunopositive neurons were also seen stronger expression in the ischemic cortex (19.167±2.858 vs. 7.833±2.483) (P<0.05). The evidence collected in our present study will indicate that, ACE2-Ang-(1-7)-Mas axis are upregulated after acute ischemic stroke and would play a pivotal role in the regulation of acute neuron injury in ischemic cerebrovascular diseases.

ACE2-Ang-(1-7)-Mas Axis in Brain: A Potential Target for Prevention and Treatment of Ischemic Stroke

The renin-angiotensin system (RAS) in brain is a crucial regulator for physiological homeostasis and diseases of cerebrovascular system, such as ischemic stroke. Overactivation of brain Angiotensin-converting enzyme (ACE) - Angiotensin II (Ang II) - Angiotensin II type 1 receptor (AT1R) axis was found to be involved in the progress of hypertension, atherosclerosis and thrombogenesis, which increased the susceptibility to ischemic stroke. Besides, brain Ang II levels have been revealed to be increased in ischemic tissues after stroke, and contribute to neural damage through elevating oxidative stress levels and inducing inflammatory response in the ischemic hemisphere via AT1R. In recent years, new components of RAS have been discovered, including ACE2, Angiotensin-(1-7) [Ang-(1-7)] and Mas, which constitute ACE2-Ang-(1-7)-Mas axis. ACE2 converts Ang II to Ang-(1-7), and Ang-(1-7) binds with its receptor Mas, exerting benefical effects in cerebrovascular disease. Through interacting with nitric oxide and bradykinin, Ang-(1-7) could attenuate the development of hypertension and the pathologic progress of atherosclerosis. Besides, its antithrombotic activity also prevents thrombogenic events, which may contribute to reduce the risk of ischemic stroke. In addition, after ischemia insult, ACE2-Ang-(1-7)-Mas has been shown to reduce the cerebral infarct size and improve neurological deficits through its antioxidative and anti-inflammatory effects. Taken together, activation of the ACE2-Ang-(1-7)-Mas axis may become a novel therapeutic target in prevention and treatment of ischemia stroke, which deserves further investigations.

Angiotensin (1-7) contributes to nitric oxide tonic inhibition of vasopressin release during hemorrhagic shock in acute ethanol intoxicated rodents

AIMS

Acute ethanol intoxication (AEI) attenuates the arginine vasopressin (AVP) response to hemorrhage leading to impaired hemodynamic counter-regulation and accentuated hemodynamic stability. Previously we identified that the ethanol-induced impairment of circulating AVP concentrations in response to hemorrhage was the result of augmented central nitric oxide (NO) inhibition. The aim of the current study was to examine the mechanisms underlying ethanol-induced up-regulation of paraventricular nucleus (PVN) NO concentration. Angiotensin (ANG) (1-7) is an important mediator of NO production through activation of the Mas receptor. We hypothesized that Mas receptor inhibition would decrease central NO concentration and thus restore the rise in circulating AVP levels during hemorrhagic shock in AEI rats.

MAIN METHODS

Conscious male Sprague-Dawley rats (300-325 g) received a 15 h intra-gastric infusion of ethanol (2.5 g/kg+300 mg/kg/h) or dextrose prior to a fixed-pressure (~40 mm Hg) 60 min hemorrhage. The Mas receptor antagonist A-779 was injected through an intracerebroventricular (ICV) cannula 15 min prior to hemorrhage.

KEY FINDINGS

PVN NOS activity and NO were significantly higher in AEI compared to DEX-treated controls at the completion of hemorrhage. ICV A-779 administration decreased NOS activity and NO concentration, partially restoring the rise in circulating AVP level at completion of hemorrhage in AEI rats.

SIGNIFICANCE

These results suggest that Mas receptor activation contributes to the NO-mediated inhibitory tone of AVP release in the ethanol-intoxicated hemorrhaged host.

Regulation of cardiovascular remodeling by the counter-regulatory axis of the renin-angiotensin system

The counter-regulatory axis of the renin-angiotensin system (RAS) is a novel therapeutic target in cardiovascular disease. Pathophysiological effects mediated via angiotensin II (Ang II) are well established in regulation of blood pressure, cardiac and vascular remodeling, and renal sodium handling, which lead to disorders such as hypertension and associated end-organ damage, atherosclerosis and heart failure. The counter-regulatory axis of the RAS is centered on the angiotensin-converting enzyme 2/angiotensin-1-7 (Ang-[1-7])/Mas receptor axis and has been shown to inhibit many detrimental phenotypes in cardiovascular disease. More recently, an alternative peptide, angiotensin-(1-9) (Ang-[1-9]), has been reported as a potential new member of this axis. This review will discuss the cardiovascular regulatory roles of Ang-(1-7) and Ang-(1-9) in the counter-regulatory axis of the RAS, and the potential for new therapeutic approaches in cardiovascular disease.

Anti-inflammatory effects of angiotensin-(1-7) in ischemic stroke

Previously we demonstrated that central administration of angiotensin-(1-7) [Ang-(1-7)] into rats elicits significant cerebroprotection against ischemic stroke elicited by endothelin-1 induced middle cerebral artery occlusion. Ang-(1-7), acting via its receptor Mas, reduced cerebral infarct size, and rats exhibited improved performance on neurological exams. These beneficial actions of Ang-(1-7) were not due to inhibition of the effects of endothelin-1 on cerebral vasoconstriction or effects on cerebral blood flow, and so we considered other potential mechanisms. Here we investigated the possibility that the Ang-(1-7)-induced cerebroprotection involves an anti-inflammatory effect, since stroke-induced cerebral damage includes an excessive intracerebral inflammatory response. Our quantitative RT-PCR analyses revealed that central Ang-(1-7) treatment attenuates the increased expression of mRNAs for inducible nitric oxide synthase (iNOS), several pro-inflammatory cytokines and cluster of differentiation molecule 11b (microglial marker) within the cerebral cortex following endothelin-1 induced stroke. Western blotting confirmed similar changes in iNOS protein expression in the cerebral cortex. In support of these observations, immunostaining revealed the presence of immunoreactive Mas on activated microglia within the cerebral cortical infarct zone, and in vitro experiments demonstrated that lipopolysaccharide-induced increases in nitric oxide production in glial cultures are attenuated by Ang-(1-7) acting via Mas. Collectively these findings demonstrate an anti-inflammatory action of Ang-(1-7) in the brain, and suggest that the cerebroprotective action of this peptide in ischemic stroke may involve effects on nitric oxide generation by microglia.