Increasing Angiotensin-(1–7) Levels in the Brain Attenuates Metabolic Syndrome–Related Risks in Fructose-Fed Rats

Counter-regulatory renin-angiotensin system in hypertension: Review and update in the era of COVID-19 pandemic

Cardiovascular disease is the major cause of mortality and disability, with hypertension being the most prevalent risk factor. Excessive activation of the renin-angiotensin system (RAS) under pathological conditions, leading to vascular remodeling and inflammation, is closely related to cardiovascular dysfunction. The counter-regulatory axis of the RAS consists of angiotensin-converting enzyme 2 (ACE2), angiotensin (1-7), angiotensin (1-9), alamandine, proto-oncogene Mas receptor, angiotensin II type-2 receptor and Mas-related G protein-coupled receptor member D. Each of these components has been shown to counteract the effects of the overactivated RAS. In this review, we summarize the latest insights into the complexity and interplay of the counter-regulatory RAS axis in hypertension, highlight the pathophysiological functions of ACE2, a multifunctional molecule linking hypertension and COVID-19, and discuss the function and therapeutic potential of targeting this counter-regulatory RAS axis to prevent and treat hypertension in the context of the current COVID-19 pandemic.

The Impact of Angiotensin-Converting Enzyme-2/Angiotensin 1-7 Axis in Establishing Severe COVID-19 Consequences

The COVID-19 pandemic has put a tremendous stress on the medical community over the last two years. Managing the infection proved a lot more difficult after several research communities started to recognize the long-term effects of this disease. The cellular receptor for the virus was identified as angiotensin-converting enzyme-2 (ACE2), a molecule responsible for a wide array of processes, broadly variable amongst different organs. Angiotensin (Ang) 1-7 is the product of Ang II, a decaying reaction catalysed by ACE2. The effects observed after altering the level of ACE2 are essentially related to the variation of Ang 1-7. The renin-angiotensin-aldosterone system (RAAS) is comprised of two main branches, with ACE2 representing a crucial component of the protective part of the complex. The ACE2/Ang (1-7) axis is well represented in the testis, heart, brain, kidney, and intestine. Infection with the novel SARS-CoV-2 virus determines downregulation of ACE2 and interrupts the equilibrium between ACE and ACE2 in these organs. In this review, we highlight the link between the local effects of RAAS and the consequences of COVID-19 infection as they arise from observational studies.

The renin-angiotensin system and cardiovascular autonomic control in aging

Aging is the greatest independent risk factor for developing hypertension and cardiovascular-related diseases including systolic hypertension, vascular disease, ischemic events, arrhythmias, and heart failure. Age-related cardiovascular risk is associated with dysfunction of peripheral organ systems, such as the heart and vasculature, as well as an imbalance in the autonomic nervous system characterized by increased sympathetic and decreased parasympathetic neurotransmission. Given the increasing prevalence of aged individuals worldwide, it is critical to better understand mechanisms contributing to impaired cardiovascular autonomic control in this population. In this regard, the renin-angiotensin system has emerged as an important hormonal modulator of cardiovascular function in aging, in part through modulation of autonomic pathways controlling sympathetic and parasympathetic outflow to cardiovascular end organs. This review will summarize the role of the RAS in cardiovascular autonomic control during aging, with a focus on current knowledge of angiotensin II versus angiotensin-(1-7) pathways in both rodent models and humans, pharmacological treatment strategies targeting the renin-angiotensin system, and unanswered questions for future research.

Angiotensin (1- 7) peptide replacement therapy with plasma transfusion in COVID-19

Aim

To determine whether convalescent angiotensin (1−7) peptide replacement therapy with plasma (peptide plasma) transfusion can be beneficial in the treatment of critically ill patients with severe coronavirus 2 (SARS-CoV-2) infection.

Study design

Case series of 9 critically ill patients with laboratory-confirmed COVID-19 who met the following criteria: severe pneumonia with rapid progression and continuously high viral load despite antiviral treatment.

Peptide plasma: Plasma with angiotensin (1−7) content 8–10 times higher than healthy plasma donors was obtained from suitable donors. Peptide plasma transfusion was applied to 9 patients whose clinical status and/or laboratory profile deteriorated and who needed intensive care for 2 days.

Results

In our COVID-19 cases, favipiravir, low molecular weight heparin treatment, which is included in the treatment protocol of the ministry of health, was started. Nine patients with oxygen saturation of 93% and below despite nasal oxygen support, whose clinical and/or laboratory deteriorated, were identified. The youngest of the cases was 36 years old, and the oldest patient was 85 years old. 6 of the 9 cases had male gender. 3 cases had been smoking for more than 10 years. 4 cases had at least one chronic disease.

In all of our cases, SARS CoV2 lung involvement was bilateral and peptide plasma therapy was administered in cases when oxygen saturation was 93% and below despite nasal oxygen support of 5 liters/minute and above, and intensive care was required. Although it was not reflected in the laboratory parameters in the early period, 8 patients whose saturations improved with treatment were discharged without the need for intensive care. However, a similar response was not obtained in one case. Oxygen requirement increased gradually and, he died in intensive care process. An increase of the platelet count was observed in all cases following the peptide plasma treatment.

Conclusion

In this preliminary case series of 9 critically ill patients with COVID-19, administration of plasma containing angiotensin (1−7) was followed by improvement in their clinical status. The limited sample size and study design preclude a definitive statement about the potential effectiveness of this treatment, and these observations require evaluation in clinical trials.

Cardiovascular therapeutics: A new potential for anxiety treatment?

Besides the well‐recognized risk factors, novel conditions increasing cardiovascular morbidity and mortality are emerging. Undesirable emotions and behavior such as anxiety and depression, appear to participate in worsening cardiovascular pathologies. On the other hand, deteriorating conditions of the heart and vasculature result in disturbed mental and emotional health. The pathophysiological background of this bidirectional interplay could reside in an inappropriate activation of vegetative neurohormonal and other humoral systems in both cardiovascular and psychological disturbances. This results in circulus vitiosus potentiating mental and circulatory disorders. Thus, it appears to be of utmost importance to examine the alteration of emotions, cognition, and behavior in cardiovascular patients. In terms of this consideration, recognizing the potential of principal cardiovascular drugs to interact with the mental state in patients with heart or vasculature disturbances is unavoidable, to optimize their therapeutic benefit. In general, beta‐blockers, central sympatholytics, ACE inhibitors, ARBs, aldosterone receptor blockers, sacubitril/valsartan, and fibrates are considered to exert anxiolytic effect in animal experiments and clinical settings. Statins and some beta‐blockers appear to have an equivocal impact on mood and anxiety and ivabradine expressed neutral psychological impact. It seems reasonable to suppose that the knowledge of a patient's mood, cognition, and behavior, along with applying careful consideration of the choice of the particular cardiovascular drug and respecting its potential psychological benefit or harm might improve the individualized approach to the treatment of cardiovascular disorders.

Pathophysiological Mechanisms of Hypertension Development Induced by Fructose Consumption

During the past several decades, there has been a dramatic increase in fructose consumption worldwide in parallel with epidemics of metabolic diseases. Accumulating evidence has suggested that excessive fructose consumption...

Retinal Protein O-GlcNAcylation and the Ocular Renin-angiotensin System: Signaling Cross-roads in Diabetic Retinopathy

It is well established that diabetes and its associated hyperglycemia negatively impact retinal function, yet we know little about the role played by augmented flux through the Hexosamine Biosynthetic Pathway (HBP). This offshoot of the glycolytic pathway produces UDP-Nacetyl- glucosamine, which serves as the substrate for post-translational O-linked modification of proteins in a process referred to as O-GlcNAcylation. HBP flux and subsequent protein O-GlcNAcylation serve as nutrient sensors, enabling cells to integrate metabolic information to appropriately modulate fundamental cellular processes including gene expression. Here we summarize the impact of diabetes on retinal physiology, highlighting recent studies that explore the role of O-GlcNAcylation- induced variation in mRNA translation in retinal dysfunction and the pathogenesis of Diabetic Retinopathy (DR). Augmented O-GlcNAcylation results in wide variation in the selection of mRNAs for translation, in part, due to O-GlcNAcylation of the translational repressor 4E-BP1. Recent studies demonstrate that 4E-BP1 plays a critical role in regulating O-GlcNAcylation-induced changes in the translation of the mRNAs encoding Vascular Endothelial Growth Factor (VEGF), a number of important mitochondrial proteins, and CD40, a key costimulatory molecule involved in diabetes-induced retinal inflammation. Remarkably, 4E-BP1/2 ablation delays the onset of diabetes- induced visual dysfunction in mice. Thus, pharmacological interventions to prevent the impact of O-GlcNAcylation on 4E-BP1 may represent promising therapeutics to address the development and progression of DR. In this regard, we discuss the potential interplay between retinal O-GlcNAcylation and the ocular renin-angiotensin system as a potential therapeutic target of future interventions.

Hemodynamic phenotyping of transgenic rats with ubiquitous expression of an angiotensin-(1-7)-producing fusion protein

Activation of the angiotensin (Ang)-converting enzyme (ACE) 2/Ang-(1-7)/MAS receptor pathway of the renin-angiotensin system (RAS) induces protective mechanisms in different diseases. Herein, we describe the cardiovascular phenotype of a new transgenic rat line (TG7371) that expresses an Ang-(1-7)-producing fusion protein. The transgene-specific mRNA and the corresponding protein were shown to be present in all evaluated tissues of TG7371 with the highest expression in aorta and brain. Plasma Ang-(1-7) levels, measured by radioimmunoassay (RIA) were similar to control Sprague-Dawley (SD) rats, however high Ang-(1-7) levels were found in the hypothalamus. TG7371 showed lower baseline mean arterial pressure (MAP), assessed in conscious or anesthetized rats by telemetry or short-term recordings, associated with increased plasma atrial natriuretic peptide (ANP) and higher urinary sodium concentration. Moreover, evaluation of regional blood flow and hemodynamic parameters with fluorescent microspheres showed a significant increase in blood flow in different tissues (kidneys, mesentery, muscle, spleen, brown fat, heart and skin), with a resulting decrease in total peripheral resistance (TPR). TG7371 rats, on the other hand, also presented increased cardiac and global sympathetic tone, increased plasma vasopressin (AVP) levels and decreased free water clearance. Altogether, our data show that expression of an Ang-(1-7)-producing fusion protein induced a hypotensive phenotype due to widespread vasodilation and consequent fall in peripheral resistance. This phenotype was associated with an increase in ANP together with an increase in AVP and sympathetic drive, which did not fully compensate the lower blood pressure (BP). Here we present the hemodynamic impact of long-term increase in tissue expression of an Ang-(1-7)-fusion protein and provide a new tool to investigate this peptide in different pathophysiological conditions.

Angiotensin-(1-7) and Mas receptor in the brain

The renin-angiotensin system (RAS) is a key regulator of blood pressure and electrolyte homeostasis. Besides its importance as regulator of the cardiovascular function, the RAS has also been associated to the modulation of higher brain functions, including cognition, memory, depression and anxiety. For many years, angiotensin II (Ang II) has been considered the major bioactive component of the RAS. However, the existence of many other biologically active RAS components has currently been recognized, with similar, opposite, or distinct effects to those exerted by Ang II. Today, it is considered that the RAS is primarily constituted by two opposite arms. The pressor arm is composed by Ang II and the Ang II type 1 (AT1) receptor (AT1R), which mediates the vasoconstrictor, proliferative, hypertensive, oxidative and pro-inflammatory effects of the RAS. The depressor arm is mainly composed by Ang-(1-7), its Mas receptor (MasR) which mediates the depressor, vasodilatory, antiproliferative, antioxidant and anti-inflammatory effects of Ang-(1-7) and the AT2 receptor (AT2R), which opposes to the effects mediated by AT1R activation. Central Ang-(1-7) is implicated in the control of the cardiovascular function, thus participating in the regulation of blood pressure. Ang-(1-7) also exerts neuroprotective actions through MasR activation by opposing to the harmful effects of the Ang II/AT1R axis. This review is focused on the expression and regulation of the Ang-(1-7)/MasR axis in the brain, its main neuroprotective effects and the evidence regarding its involvement in the pathophysiology of several diseases at cardiovascular and neurological level.

Preserved glycemic control and baroreflex efficacy in young adult hypertensive female obese Zucker rats

Obese Zucker rats (OZRs) develop hypertension and hyperinsulinemia by 3 mo of age. Male OZRs also have diminished baroreflex-mediated activation of nucleus tractus solitarius (NTS) and bradycardia, which are improved by correcting their hyperglycemia. Conversely, 3-mo-old female OZRs and lean Zucker rats (LZRs) have equivalent baroreflex-mediated bradycardia that is impaired in 6-mo-old OZRs. We hypothesized that 3-mo-old female OZRs maintain NTS activation and baroreflexes coincident with glycemic control. We also hypothesized that 6-mo-old female OZRs develop impaired baroreflexes with hyperglycemia and diminished NTS activation. In 12- to 16-wk-old females, sympathetic nerve activity (SNA) and arterial pressure (AP) were higher in OZRs than LZRs. However, baroreflex-mediated inhibition of SNA and bradycardia were equivalent in female OZRs and LZRs. Unlike deficits in male OZRs, female OZRs and LZRs had no differences in phenylephrine-induced c-Fos expression in NTS or decreases in SNA and AP evoked by glutamate into NTS. Compared with hyperglycemia in male OZRs (217.9 ± 34.4 mg/dL), female OZRs had normal fed blood glucose levels (108.2 ± 1.6 mg/dL in LZRs and 113.6 ± 3.5 mg/dL in OZRs) with emerging glucose intolerance. Conscious 24- to 27-wk-old female OZRs had impaired baroreflex-mediated bradycardia, but fed blood glucose was modestly elevated (124.2 ± 5.2 mg/dL) and phenylephrine-induced c-Fos expression in NTS was comparable to LZRs. These data suggest that better glycemic control in 3-mo-old female OZRs prevents diminished NTS activation and baroreflexes, supporting the notion that hyperglycemia impairs these responses in male OZRs. However, 6-mo-old female OZRs had impaired baroreflex efficacy without diminished NTS activation or pronounced hyperglycemia, suggesting baroreflex deficits develop by different mechanisms in female and male OZRs.

Angiotensin-(1-7) Central Mechanisms After ICV Infusion in Hypertensive Transgenic (mRen2)27 Rats

Previous data showed hypertensive rats subjected to chronic intracerebroventricular (ICV) infusion of angiotensin-(1-7) presented attenuation of arterial hypertension, improvement of baroreflex sensitivity, restoration of cardiac autonomic balance and a shift of cardiac renin-angiotensin system (RAS) balance toward Ang-(1-7)/Mas receptor. In the present study, we investigated putative central mechanisms related to the antihypertensive effect induced by ICV Ang-(1-7), including inflammatory mediators and the expression/activity of the RAS components in hypertensive rats. Furthermore, we performed a proteomic analysis to evaluate differentially regulated proteins in the hypothalamus of these animals. For this, Sprague Dawley (SD) and transgenic (mRen2)27 hypertensive rats (TG) were subjected to 14 days of ICV infusion with Ang-(1-7) (200 ng/h) or 0.9% sterile saline (0.5 μl/h) through osmotic mini-pumps. We observed that Ang-(1-7) treatment modulated inflammatory cytokines by decreasing TNF-α levels while increasing the anti-inflammatory IL-10. Moreover, we showed a reduction in ACE activity and gene expression of AT1 receptor and iNOS. Finally, our proteomic evaluation suggested an anti-inflammatory mechanism of Ang-(1-7) toward the ROS modulators Uchl1 and Prdx1.

Hypothalamic Renin-Angiotensin System and Lipid Metabolism: Effects of Virgin Olive Oil versus Butter in the Diet

The brain renin-angiotensin system (RAS) has been recently involved in the homeostatic regulation of energy. Our goal was to analyse the influence of a diet rich in saturated fatty acids (butter) against one enriched in monounsaturated fatty acids (olive oil) on hypothalamic RAS, and their relationship with the metabolism of fatty acids. Increases in body weight and visceral fat, together with an increase in aminopeptidase A expression and reductions in AngII and AngIV were observed in the hypothalamus of animals fed with the butter diet. In this group, a marked reduction in the expression of genes related to lipid metabolism (LPL, CD36, and CPT-1) was observed in liver and muscle. No changes were found in terms of body weight, total visceral fat and the expression of hepatic genes related to fatty acid metabolism in the olive oil diet. The expressions of LPL and CD36 were reduced in the muscles, although the decrease was lower than in the butter diet. At the same time, the fasting levels of leptin were reduced, no changes were observed in the hypothalamic expression of aminopeptidase A and decreases were noted in the levels of AngII, AngIV and AngIII. These results support that the type of dietary fat is able to modify the hypothalamic profile of RAS and the body energy balance, related to changes in lipid metabolism.

2020 update on the renin-angiotensin-aldosterone system in pediatric kidney disease and its interactions with coronavirus

The last decade was crucial for our understanding of the renin-angiotensin-aldosterone system (RAAS) as a two-axis, counter-regulatory system, divided into the classical axis, formed by angiotensin-converting enzyme (ACE), angiotensin II (Ang II), and the angiotensin type 1 receptor (AT1R), and the alternative axis comprising angiotensin-converting enzyme 2 (ACE2), angiotensin-(1-7) (Ang-(1-7)), and the Mas receptor. Breakthrough discoveries also took place, with other RAAS endopeptides being described, including alamandine and angiotensin A. In this review, we characterize the two RAAS axes and the role of their components in pediatric kidney diseases, including childhood hypertension (HTN), pediatric glomerular diseases, congenital abnormalities of the kidney and urinary tract (CAKUT), and chronic kidney disease (CKD). We also present recent findings on potential interactions between the novel coronavirus, SARS-CoV-2, and components of the RAAS, as well as potential implications of coronavirus disease 2019 (COVID-19) for pediatric kidney diseases.

Research Progress of Alzheimer's Disease Therapeutic Drugs: Based on Renin-Angiotensin System Axis

It is widely recognized that Alzheimer's disease (AD) has a complicate link to renin-angiotensin system (RAS). It is known that cerebrovascular disease has some connections with AD, but most of the studies are still conducted in parallel or independently. Although previous research came up with large number of hypotheses about the pathogenesis of AD, it does not include the mechanism of RAS-related regulation of AD. It has been found that many components of RAS have been changed in AD. For example, the multifunctional and high-efficiency vasoconstrictor Ang II and Ang III with similar effects are changed under the action of other RAS signal peptides; these signal peptides are believed to help improve nerve injury and cognitive function. These changes may lead to neuropathological changes of AD, and progressive defects of cognitive function, which are association with some hypotheses of AD. The role of RAS in AD gradually attracts our attention, and RAS deserved to be considered carefully in the pathogenesis of AD. This review discusses the mechanisms of RAS participating in the three current hypotheses of AD: neuroinflammation, oxidative stress and amyloid-β protein (Aβ) hypothesis, as well as the drugs that regulate RAS systems already in clinical or in clinical trials. It further demonstrates the importance of RAS in the pathogenesis of AD, not only because of its multiple aspects of participation, which may be accidental, but also because of the availability of RAS drugs, which can be reused as therapies of AD.

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.

Brain Renin-Angiotensin System at the Intersect of Physical and Cognitive Frailty

The renin–angiotensin system (RAS) was initially considered to be part of the endocrine system regulating water and electrolyte balance, systemic vascular resistance, blood pressure, and cardiovascular homeostasis. It was later discovered that intracrine and local forms of RAS exist in the brain apart from the endocrine RAS. This brain-specific RAS plays essential roles in brain homeostasis by acting mainly through four angiotensin receptor subtypes; AT₁R, AT₂R, MasR, and AT₄R. These receptors have opposing effects; AT₁R promotes vasoconstriction, proliferation, inflammation, and oxidative stress while AT₂R and MasR counteract the effects of AT₁R. AT₄R is critical for dopamine and acetylcholine release and mediates learning and memory consolidation. Consequently, aging-associated dysregulation of the angiotensin receptor subtypes may lead to adverse clinical outcomes such as Alzheimer’s disease and frailty via excessive oxidative stress, neuroinflammation, endothelial dysfunction, microglial polarization, and alterations in neurotransmitter secretion. In this article, we review the brain RAS from this standpoint. After discussing the functions of individual brain RAS components and their intracellular and intracranial locations, we focus on the relationships among brain RAS, aging, frailty, and specific neurodegenerative diseases, such as Alzheimer’s disease, Parkinson’s disease, and vascular cognitive impairment, through oxidative stress, neuroinflammation, and vascular dysfunction. Finally, we discuss the effects of RAS-modulating drugs on the brain RAS and their use in novel treatment approaches.

Angiotensin-(1-7) Improves Integrated Cardiometabolic Function in Aged Mice

Angiotensin (Ang)-(1-7) is a beneficial renin–angiotensin system (RAS) hormone that elicits protective cardiometabolic effects in young animal models of hypertension, obesity, and metabolic syndrome. The impact of Ang-(1-7) on cardiovascular and metabolic outcomes during aging, however, remains unexplored. This study tested the hypothesis that Ang-(1-7) attenuates age-related elevations in blood pressure and insulin resistance in mice. Young adult (two-month-old) and aged (16-month-old) male C57BL/6J mice received Ang-(1-7) (400 ng/kg/min) or saline for six-weeks via a subcutaneous osmotic mini-pump. Arterial blood pressure and metabolic function indices (body composition, insulin sensitivity, and glucose tolerance) were measured at the end of treatment. Adipose and cardiac tissue masses and cardiac RAS, sympathetic and inflammatory marker gene expression were also measured. We found that chronic Ang-(1-7) treatment decreased systolic and mean blood pressure, with a similar trend for diastolic blood pressure. Ang-(1-7) also improved insulin sensitivity in aged mice to levels in young mice, without effects on glucose tolerance or body composition. The blood pressure–lowering effects of Ang-(1-7) in aged mice were associated with reduced sympathetic outflow to the heart. These findings suggest Ang-(1-7) may provide a novel pharmacological target to improve age-related cardiometabolic risk.

Comparison of Candesartan and Angiotensin-(1-7) Combination to Mito-TEMPO Treatment for Normalizing Blood Pressure and Sympathovagal Balance in (mREN2)27 Rats

Hypertensive transgenic (mRen2)27 rats exhibit impaired baroreflex sensitivity (BRS) for control of heart rate (HR). Intracerebroventricular infusion of Ang-(1-7) improves indices of vagal BRS independent of lowering mean arterial pressure (MAP), whereas AT1 receptor blockade normalizes MAP and indices of sympathetic tone without correcting the vagal BRS. Scavenging cellular reactive oxygen species (ROS) with tempol in brain fails to correct either hypertension or sympathovagal balance in these animals, despite reports that mitochondrial ROS contributes to Ang II-infusion hypertension. To examine effects of a putative preferential mitochondrial ROS scavenger in the brain of (mRen2)27 rats, ICV infusions of Mito-TEMPO (3.2 μg/2.5 μL/h) were compared with artificial cerebrospinal fluid (aCSF; 2.5 μL/h) and combination AT1 receptor antagonist candesartan (CAN: 4 μg/2.5 μL/h) plus Ang-(1-7) (0.1 μg/2.5 μL/h) treatment. MAP was lower after CAN + Ang-(1-7) treatment, and both vagal and sympathetic components of BRS and sympathovagal balance were improved. By contrast, Mito-TEMPO improved sympathetic components of BRS and tended to improve overall sympathovagal balance but failed to alter MAP in this model of hypertension. Although further studies are required to determine whether Mito-TEMPO or CAN + Ang-(1-7) treatment at the doses used altered mitochondrial ROS, optimal therapeutic benefits are achieved by shifting the balance from Ang II toward Ang-(1-7) in this model of chronic RAS-dependent hypertension.

Angiotensin-(1-7): Translational Avenues in Cardiovascular Control

Despite decades of research and numerous treatment approaches, hypertension and cardiovascular disease remain leading global public health problems. A major contributor to regulation of blood pressure, and the development of hypertension, is the renin-angiotensin system. Of particular concern, uncontrolled activation of angiotensin II contributes to hypertension and associated cardiovascular risk, with antihypertensive therapies currently available to block the formation and deleterious actions of this hormone. More recently, angiotensin-(1-7) has emerged as a biologically active intermediate of the vasodilatory arm of the renin-angiotensin system. This hormone antagonizes angiotensin II actions as well as offers antihypertensive, antihypertrophic, antiatherogenic, antiarrhythmogenic, antifibrotic and antithrombotic properties. Angiotensin-(1-7) elicits beneficial cardiovascular actions through mas G protein-coupled receptors, which are found in numerous tissues pivotal to control of blood pressure including the brain, heart, kidneys, and vasculature. Despite accumulating evidence for favorable effects of angiotensin-(1-7) in animal models, there is a paucity of clinical studies and pharmacokinetic limitations, thus limiting the development of therapeutic agents to better understand cardiovascular actions of this vasodilatory peptide hormone in humans. This review highlights current knowledge on the role of angiotensin-(1-7) in cardiovascular control, with an emphasis on significant animal, human, and therapeutic research efforts.

Sex differences in metabolic effects of angiotensin-(1-7) treatment in obese mice

Background

Angiotensin-(1-7) is a beneficial hormone of the renin-angiotensin system known to play a positive role in regulation of blood pressure and glucose homeostasis. Previous studies have shown that in high-fat diet (HFD)-induced obese male mice, circulating angiotensin-(1-7) levels are reduced and chronic restoration of this hormone reverses diet-induced insulin resistance; however, this has yet to be examined in female mice. We hypothesized angiotensin-(1-7) would improve insulin sensitivity and glucose tolerance in obese female mice, to a similar extent as previously observed in male mice.

Methods

Five-week-old male and female C57BL/6J mice (8–12/group) were placed on control diet or HFD (16% or 59% kcal from fat, respectively) for 11 weeks. After 8 weeks of diet, mice were implanted with an osmotic pump for 3-week subcutaneous delivery of angiotensin-(1-7) (400 ng/kg/min) or saline vehicle. During the last week of treatment, body mass and composition were measured and intraperitoneal insulin and glucose tolerance tests were performed to assess insulin sensitivity and glucose tolerance, respectively. Mice were euthanized at the end of the study for blood and tissue collection.

Results

HFD increased body mass and adiposity in both sexes. Chronic angiotensin-(1-7) infusion significantly decreased body mass and adiposity and increased lean mass in obese mice of both sexes. While both sexes tended to develop mild hyperglycemia in response to HFD, female mice developed less marked hyperinsulinemia. There was no effect of angiotensin-(1-7) on fasting glucose or insulin levels among diet and sex groups. Male and female mice similarly developed insulin resistance and glucose intolerance in response to HFD feeding. Angiotensin-(1-7) improved insulin sensitivity in both sexes but corrected glucose intolerance only in obese female mice. There were no effects of sex or angiotensin-(1-7) treatment on any of the study outcomes in control diet-fed mice.

Conclusions

This study provides new evidence for sex differences in the impact of chronic angiotensin-(1-7) in obese mice, with females having greater changes in glucose tolerance with treatment. These findings improve understanding of sex differences in renin-angiotensin mechanisms in obesity and illustrate the potential for targeting angiotensin-(1-7) for treatment of this condition.

Sex differences in the metabolic effects of the renin-angiotensin system

Obesity is a global epidemic that greatly increases risk for developing cardiovascular disease and type II diabetes. Sex differences in the obese phenotype are well established in experimental animal models and clinical populations. While having higher adiposity and obesity prevalence, females are generally protected from obesity-related metabolic and cardiovascular complications. This protection is, at least in part, attributed to sex differences in metabolic effects of hormonal mediators such as the renin-angiotensin system (RAS). Previous literature has predominantly focused on the vasoconstrictor arm of the RAS and shown that, in contrast to male rodent models of obesity and diabetes, females are protected from metabolic and cardiovascular derangements produced by angiotensinogen, renin, and angiotensin II. A vasodilator arm of the RAS has more recently emerged which includes angiotensin-(1-7), angiotensin-converting enzyme 2 (ACE2), mas receptors, and alamandine. While accumulating evidence suggests that activation of components of this counter-regulatory axis produces positive effects on glucose homeostasis, lipid metabolism, and energy balance in male animal models, female comparison studies and clinical data related to metabolic outcomes are lacking. This review will summarize current knowledge of sex differences in metabolic effects of the RAS, focusing on interactions with gonadal hormones and potential clinical implications.

Anti-Hypertensive Action of Fenofibrate via UCP2 Upregulation Mediated by PPAR Activation in Baroreflex Afferent Pathway

Fenofibrate, an agonist for peroxisome proliferator-activated receptor alpha (PPAR-α), lowers blood pressure, but whether this action is mediated via baroreflex afferents has not been elucidated. In this study, the distribution of PPAR-α and PPAR-γ was assessed in the nodose ganglion (NG) and the nucleus of the solitary tract (NTS). Hypertension induced by drinking high fructose (HFD) was reduced, along with complete restoration of impaired baroreceptor sensitivity, by chronic treatment with fenofibrate. The molecular data also showed that both PPAR-α and PPAR-γ were dramatically up-regulated in the NG and NTS of the HFD group. Expression of the downstream signaling molecule of PPAR-α, the mitochondrial uncoupling protein 2 (UCP2), was up-regulated in the baroreflex afferent pathway under similar experimental conditions, along with amelioration of reduced superoxide dismutase activity and increased superoxide in HFD rats. These results suggest that chronic treatment with fenofibrate plays a crucial role in the neural control of blood pressure by improving baroreflex afferent function due at least partially to PPAR-mediated up-regulation of UCP2 expression and reduction of oxidative stress.

Angiotensin-(1-7) contributes to insulin-sensitizing effects of angiotensin-converting enzyme inhibition in obese mice

Angiotensin-converting enzyme (ACE) inhibitors reduce body weight, lower blood pressure (BP), and improve insulin sensitivity in animal models of cardiometabolic syndrome. These effects are generally attributed to reduced angiotensin (ANG) II formation; however, these therapies also increase levels of ANG-(1-7), a beneficial hormone opposing ANG II actions. We hypothesized that this ANG-(1-7) generation contributes to the insulin-sensitizing effects of ACE inhibition in obese mice. Adult male C57BL/6J mice were placed on a 60% high-fat diet for 11 wk. During the last 3 wk of diet, mice received normal water or water containing the ACE inhibitor captopril (50 mg/l) as well as the ANG-(1-7) mas receptor antagonist A779 (400 or 800 ng·kg^-1·min^-1) or saline vehicle via subcutaneous osmotic minipumps. At the end of treatment, arterial BP was measured, and hyperinsulinemic-euglycemic clamps were performed in conscious obese mice receiving vehicle, captopril, captopril plus A779, or A779 ( n = 6-13/group). Captopril reduced body weight (28 ± 2 vs. 41 ± 2 g saline; P = 0.001), lowered systolic BP (109 ± 6 vs. 144 ± 7 mmHg saline; P = 0.041), and improved whole-body insulin sensitivity (steady-state glucose infusion rate: 31 ± 4 vs. 16 ± 2 mg·kg^-1·min^-1 saline; P = 0.001) in obese mice. A779 attenuated captopril-mediated improvements in insulin sensitivity (23 ± 2 mg·kg^-1·min^-1; P = 0.042), with no effect on body weight (32 ± 2 g; P = 0.441) or BP (111 ± 7 mmHg; P = 0.788). There was no effect of A779 alone on cardiometabolic outcomes. These data suggest that insulin-sensitizing effects of ACE inhibition are in part due to activation of ANG-(1-7)/ mas receptor pathways and provide new insight into mechanisms underlying the positive metabolic effects of these therapies.

Angiotensin generation in the brain: a re-evaluation

The existence of a so-called brain renin-angiotensin system (RAS) is controversial. Given the presence of the blood-brain barrier, angiotensin generation in the brain, if occurring, should depend on local synthesis of renin and angiotensinogen. Yet, although initially brain-selective expression of intracellular renin was reported, data in intracellular renin knockout animals argue against a role for this renin in angiotensin generation. Moreover, renin levels in brain tissue at most represented renin in trapped blood. Additionally, in neurogenic hypertension brain prorenin up-regulation has been claimed, which would generate angiotensin following its binding to the (pro)renin receptor. However, recent studies reported no evidence for prorenin expression in the brain, nor for its selective up-regulation in neurogenic hypertension, and the (pro)renin receptor rather displays RAS-unrelated functions. Finally, although angiotensinogen mRNA is detectable in the brain, brain angiotensinogen protein levels are low, and even these low levels might be an overestimation due to assay artefacts. Taken together, independent angiotensin generation in the brain is unlikely. Indeed, brain angiotensin levels are extremely low, with angiotensin (Ang) I levels corresponding to the small amounts of Ang I in trapped blood plasma, and Ang II levels at most representing Ang II bound to (vascular) brain Ang II type 1 receptors. This review concludes with a unifying concept proposing the blood origin of angiotensin in the brain, possibly resulting in increased levels following blood-brain barrier disruption (e.g. due to hypertension), and suggesting that interfering with either intracellular renin or the (pro)renin receptor has consequences in an RAS-independent manner.

Angiotensin-(1-7) and Alamandine on Experimental Models of Hypertension and Atherosclerosis

PURPOSE OF REVIEW

The purpose of this review was to summarize the current knowledge on the role of angiotensin-(1-7) [Ang-(1-7)] and alamandine in experimental hypertension and atherosclerosis.

RECENT FINDINGS

The renin-angiotensin system (RAS) is a very complex system, composed of a cascade of enzymes, peptides, and receptors, known to be involved in the pathogenesis of hypertension and atherosclerosis. Ang-(1-7), identified and characterized in 1987, and alamandine, discovered 16 years after, are the newest two main effector molecules from the RAS, protecting the vascular system against hypertension and atherosclerosis. While the beneficial effects of Ang-(1-7) have been widely studied in several experimental models of hypertension, much less studies were performed in experimental models of atherosclerosis. Alamandine has shown similar vascular effects to Ang-(1-7), namely, endothelial-dependent vasorelaxation mediated by nitric oxide and hypotensive effects in experimental hypertension. There are few studies on the effects of alamandine on atherosclerosis.

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.

Dietary fructose as a risk factor for non-alcoholic fatty liver disease (NAFLD)

Glucose is a major energy source for the entire body, while fructose metabolism occurs mainly in the liver. Fructose consumption has increased over the last decade globally and is suspected to contribute to the increased incidence of non-alcoholic fatty liver disease (NAFLD). NAFLD is a manifestation of metabolic syndrome affecting about one-third of the population worldwide and has progressive pathological potential for liver cirrhosis and cancer through non-alcoholic steatohepatitis (NASH). Here we have reviewed the possible contribution of fructose to the pathophysiology of NAFLD. We critically summarize the current findings about several regulators, and their potential mechanisms, that have been studied in humans and animal models in response to fructose exposure. A novel hypothesis on fructose-dependent perturbation of liver regeneration and metabolism is advanced. Fructose intake could affect inflammatory and metabolic processes, liver function, gut microbiota, and portal endotoxin influx. The role of the brain in controlling fructose ingestion and the subsequent development of NAFLD is highlighted. Although the importance for fructose (over)consumption for NAFLD in humans is still debated and comprehensive intervention studies are invited, understanding of how fructose intake can favor these pathological processes is crucial for the development of appropriate noninvasive diagnostic and therapeutic approaches to detect and treat these metabolic effects. Still, lifestyle modification, to lessen the consumption of fructose-containing products, and physical exercise are major measures against NAFLD. Finally, promising drugs against fructose-induced insulin resistance and hepatic dysfunction that are emerging from studies in rodents are reviewed, but need further validation in human patients.

FGF21 ameliorates the neurocontrol of blood pressure in the high fructose-drinking rats

Fibroblast growth factor-21 (FGF21) is closely related to various metabolic and cardiovascular disorders. However, the direct targets and mechanisms linking FGF21 to blood pressure control and hypertension are still elusive. Here we demonstrated a novel regulatory function of FGF21 in the baroreflex afferent pathway (the nucleus tractus solitarii, NTS; nodose ganglion, NG). As the critical co-receptor of FGF21, β-klotho (klb) significantly expressed on the NTS and NG. Furthermore, we evaluated the beneficial effects of chronic intraperitoneal infusion of recombinant human FGF21 (rhFGF21) on the dysregulated systolic blood pressure, cardiac parameters, baroreflex sensitivity (BRS) and hyperinsulinemia in the high fructose-drinking (HFD) rats. The BRS up-regulation is associated with Akt-eNOS-NO signaling activation in the NTS and NG induced by acute intravenous rhFGF21 administration in HFD and control rats. Moreover, the expressions of FGF21 receptors were aberrantly down-regulated in HFD rats. In addition, the up-regulated peroxisome proliferator-activated receptor-γ and -α (PPAR-γ/-α) in the NTS and NG in HFD rats were markedly reversed by chronic rhFGF21 infusion. Our study extends the work of the FGF21 actions on the neurocontrol of blood pressure regulations through baroreflex afferent pathway in HFD rats.

Brain angiotensin-(1-7)/Mas axis: A new target to reduce the cardiovascular risk to emotional stress

Emotional stress is now considered a risk factor for several diseases including cardiac arrhythmias and hypertension. It is well known that the activation of neuroendocrine and autonomic mechanisms features the response to emotional stress. However, its link to cardiovascular diseases and the regulatory mechanisms involved remain to be further comprehended. The renin-angiotensin system (RAS) plays an important role in homeostasis on all body systems. Specifically in the brain, the RAS regulates a number of physiological aspects. Recent data indicate that the activation of angiotensin-converting enzyme/angiotensin II/AT1 receptor axis facilitates the emotional stress responses. On the other hand, growing evidence indicates that its counterregulatory axis, the angiotensin-converting enzyme 2 (ACE2)/(Ang)iotensin-(1-7)/Mas axis, reduces anxiety and attenuates the physiological responses to emotional stress. The present review focuses on angiotensin-(1-7)/Mas axis as a promising target to attenuate the physiological response to emotional stress reducing the risk of cardiovascular diseases.

Chronic Angiotensin-(1-7) Improves Insulin Sensitivity in High-Fat Fed Mice Independent of Blood Pressure

Angiotensin-(1-7) improves glycemic control in animal models of cardiometabolic syndrome. The tissue-specific sites of action and blood pressure dependence of these metabolic effects, however, remain unclear. We hypothesized that Ang-(1-7) improves insulin sensitivity by enhancing peripheral glucose delivery. Adult male C57BL/6J mice were placed on standard chow or 60% high-fat diet for 11 weeks. Ang-(1-7) (400 ng/kg per minute) or saline was infused subcutaneously during the last 3 weeks of diet, and hyperinsulinemic-euglycemic clamps were performed at the end of treatment. High-fat fed mice exhibited modest hypertension (systolic blood pressure: 137 ± 3 high fat versus 123 ± 5 mm Hg chow;P=0.001), which was not altered by Ang-(1-7) (141 ± 4 mm Hg;P=0.574). Ang-(1-7) did not alter body weight or fasting glucose and insulin in chow or high-fat fed mice. Ang-(1-7) increased the steady-state glucose infusion rate needed to maintain euglycemia in high-fat fed mice (31 ± 5 Ang-(1-7) versus 16 ± 1 mg/kg per minute vehicle;P=0.017) reflecting increased whole-body insulin sensitivity, with no effect in chow-fed mice. The improved insulin sensitivity in high-fat fed mice was because of an enhanced rate of glucose disappearance (34 ± 5 Ang-(1-7) versus 20 ± 2 mg/kg per minute vehicle;P=0.049). Ang-(1-7) enhanced glucose uptake specifically into skeletal muscle by increasing translocation of glucose transporter 4 to the sarcolemma. Our data suggest that Ang-(1-7) has direct insulin-sensitizing effects on skeletal muscle, independent of changes in blood pressure. These findings provide new insight into mechanisms by which Ang-(1-7) improves insulin action, and provide further support for targeting this peptide in cardiometabolic disease.

Neuron-Glia Crosstalk in the Autonomic Nervous System and Its Possible Role in the Progression of Metabolic Syndrome: A New Hypothesis

Metabolic syndrome (MS) is characterized by the following physiological alterations: increase in abdominal fat, insulin resistance, high concentration of triglycerides, low levels of HDL, high blood pressure, and a generalized inflammatory state. One of the pathophysiological hallmarks of this syndrome is the presence of neurohumoral activation, which involve autonomic imbalance associated to hyperactivation of the sympathetic nervous system. Indeed, enhanced sympathetic drive has been linked to the development of endothelial dysfunction, hypertension, stroke, myocardial infarct, and obstructive sleep apnea. Glial cells, the most abundant cells in the central nervous system, control synaptic transmission, and regulate neuronal function by releasing bioactive molecules called gliotransmitters. Recently, a new family of plasma membrane channels called hemichannels has been described to allow the release of gliotransmitters and modulate neuronal firing rate. Moreover, a growing amount of evidence indicates that uncontrolled hemichannel opening could impair glial cell functions, affecting synaptic transmission and neuronal survival. Given that glial cell functions are disturbed in various metabolic diseases, we hypothesize that progression of MS may relies on hemichannel-dependent impairment of glial-to-neuron communication by a mechanism related to dysfunction of inflammatory response and mitochondrial metabolism of glial cells. In this manuscript, we discuss how glial cells may contribute to the enhanced sympathetic drive observed in MS, and shed light about the possible role of hemichannels in this process.

Angiotensin-(1-7): beyond its central effects on blood pressure

Angiotensin (Ang) (1-7) is the main component of the depressor and protective arm of the renin-angiotensin system. Ang-(1-7) induces vasodilation, natriuresis and diuresis, cardioprotection, inhibits angiogenesis and cell growth and opposes the pressor, proliferative, profibrotic, and prothrombotic actions mediated by Ang II. Centrally, Ang-(1-7) induces changes in mean arterial pressure and this effect may be linked with its inhibitory neuromodulatory action on norepinephrine neurotransmission. The present review is focused on the role of Ang-(1-7) as a protective agent in the brain.