Reduced anxiety-like behavior in transgenic rats with chronically overproduction of angiotensin-(1–7): Role of the Mas receptor

Alamandine enhanced spatial memory in rats by reducing neuroinflammation and altering BDNF levels in the hippocampus and prefrontal cortex

Our study aims to determine the effects of alamandine, the newest component of the renin-angiotensin system, on cognitive functions, neuroinflammation, and oxidative stress in the pathophysiology of depression. 35 male Sprague dawley rats, three months old, weighing between 300 and 350 g, were used. The chronic, unpredictable mild stress model of depression was performed. Experimental animals were divided into five groups: control (C), depression (D), alamandine (50 µg/kg, ip) (D + ALA), A779 (300 µg/kg, ip) (D + A779), and both alamandine and A779 treatment groups (D + ALA + A779). After confirming the development of depression through behavioral tests, the animals' learning and memory performances were measured using the Morris water maze test. At the end of the experiment, the animals' prefrontal cortex, hippocampus, and blood samples were isolated for biochemical studies and gene expression analyses. The sucrose preference, open field, elevated plus maze, tail suspension, and forced swimming tests were performed to determine the animals' anxiety levels. There was a significant increase in anxiety-like behaviors in the D group and the A779-treated group, while alamandine exhibited an anxiolytic effect. Moreover, improvements in cognitive skills observed in the Morris water maze test were paralleled by molecular changes, including an increase in BDNF protein levels and NMDA receptor expression and a decrease in GABA levels. In addition, the levels of TNF-α, IL-1β, IL-6, and oxidative stress markers were increased in the depression groups while significantly decreased with alamandine treatment. It was concluded that alamandine has an anxiolytic effect and facilitates spatial memory by reducing neuroinflammation and oxidative stress.

Synthesis and analytical profile of new synthetic analogs of angiotensin 1-7, the main balancing peptide of the renin-angiotensin system

The heptapeptide angiotensin Asp-Arg-Val-Tyr-Ile-His-Pro (ANG 1-7) is a key member of the ACE2/ANG-(1-7)/MasR axis, which is considered a counter-regulator of the classical renin-angiotensin system (RAS) axis concerning its homeostatic and neuromodulatory functions. Four new analogs of ANG 1-7 with general structures of Asp-Arg-Val-Tyr-Ile-His-Xxx-NH2, where Xxx is 1-aminocyclopentanecarboxylic acid (Ac5c), 1-aminocyclohexane carboxylic acid (Ac6c), and (2S,4S)-4-amino-pyrrolidine-2-carboxylic acid, were synthesized and characterized by electrochemical, spectral, DFT calculational, and behavioral methods. The presence of a cis-oriented primary amino group at the molecule's C-terminus is coupled with the structural rigidity of the pyrrolidine Pro ring in the peptide molecule ANG-P1. While in ANG-P2, the cis-oriented primary amino group is connected to the peptide motif by means of the amino acid His leading to the formation of a proline/GABA cis-chimera. The partition coefficient values suggest better lipophilicity of the compounds ANG-P1 and ANG-P2 related to easier passage through the target membranes. The correlation coefficient between the theoretically predicted and experimentally determined logP values is 0.991. The ANG-P1 analog has features comparable to ANG 1-7, but the peptides ANG-P2, ANG-C5, and ANG-C6 exhibit distinct effects, particularly on anxiety-like behavior, according to a comparison of the novel analogs with the precursor peptide. Regardless of how they affect exploration in the open field test, they induce anxiogenic behavior in the elevated plus maze test. The ANG-C5 analog differs from the other analogs because it is unable to create antinociception, despite the fact that ANG 1-7 and its analogs generated notable antinociception.

Anxiolytic effect of alamandine in male transgenic rats with low brain angiotensinogen is dependent on activation of MrgD receptors

Alamandine is a peptide hormone belonging to the renin-angiotensin system (RAS). It acts through the Mas-related G-protein coupled receptor type D, MrgD, which is expressed in different tissues, including the brain. In the present study, we hypothesize that a lack of alamandine, through MrgD, could cause the anxiety-like behavior in transgenic rats with low brain angiotensinogen [TGR(ASrAOGEN)680]. Adult male transgenic rats exhibited a significant increase in the latency to feeding time in the novelty suppressed feeding test and a decrease in the percentage of time and entries in the open arms in the elevated plus maze. These effects were reversed by intracerebroventricular infusion of alamandine. Pretreatment with D-Pro7-Ang-(1-7), a Mas and MrgD receptor antagonist, prevented the anxiolytic effects induced by this peptide. However, its effects were not altered by the selective Mas receptor antagonist, A779. In conclusion, our data indicates that alamandine, through MrgD, attenuates anxiety-like behavior in male TGR(ASrAOGEN)680, which reinforces the importance of the counter-regulatory RAS axis as promising target for the treatment of neuropsychiatric disorders.

Role of brain renin-angiotensin system in depression: A new perspective

Depression is a mood disorder characterized by abnormal thoughts. The pathophysiology of depression is related to the deficiency of serotonin (5HT), which is derived from tryptophan (Trp). Mitochondrial dysfunction, oxidative stress, and neuroinflammation are involved in the pathogenesis of depression. Notably, the renin-angiotensin system (RAS) is involved in the pathogenesis of depression, and different findings revealed that angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) may be effective in depression. However, the underlying mechanism for the role of dysregulated brain RAS-induced depression remains speculative. Therefore, this review aimed to revise the conceivable role of ACEIs and ARBs and how these agents ameliorate the pathophysiology of depression. Dysregulation of brain RAS triggers the development and progression of depression through the reduction of brain 5HT and expression of brain-derived neurotrophic factor (BDNF) and the induction of mitochondrial dysfunction, oxidative stress, and neuroinflammation. Therefore, inhibition of central classical RAS by ARBS and ACEIs and activation of non-classical RAS prevent the development of depression by regulating 5HT, BDNF, mitochondrial dysfunction, oxidative stress, and neuroinflammation.

Signaling pathways and genetics of brain Renin angiotensin system in psychiatric disorders: State of the art

Along the conventional pathways, Renin-angiotensin system (RAS) plays a key role in the physiology of the CNS and pathogenesis of psychiatric diseases. RAS is a complex regulatory pathway which is composed of several peptides and receptors and comprises two counter-regulatory axes. The classical (ACE1/AngII/AT1 receptor) axis and the contemporary (ACE2/Ang (1-7)/Mas receptor) axis. The genes coding for elements of both axes have been broadly studied. Numerous functional polymorphisms on components of RAS have been identified to serve as informative disease and treatment markers. This review summarizes the role of each peptide and receptor in the pathophysiology of psychiatric disorders (depression, bipolar disorders and schizophrenia), followed by a concise look at the role of genetic polymorphism of the RAS in the pathophysiology of these disorders.

Therapeutic potential and possible mechanisms of ginseng for depression associated with COVID-19

Recently, a global outbreak of COVID-19 has rapidly spread to various national regions. As the number of COVID-19 patients has increased, some of those infected with SARS-CoV-2 have developed a variety of psychiatric symptoms, including depression, cognitive impairment, and fatigue. A distinct storm of inflammatory factors that contribute to the initial disease but also a persistent post-acute phase syndrome has been reported in patients with COVID-19. Neuropsychological symptoms including depression, cognitive impairment, and fatigue are closely related to circulating and local (brain) inflammatory factors. Natural products are currently being examined for their ability to treat numerous complications caused by COVID-19. Among them, ginseng has anti-inflammatory, immune system stimulating, neuroendocrine modulating, and other effects, which may help improve psychiatric symptoms. This review summarizes the basic mechanisms of COVID-19 pneumonia, psychiatric symptoms following coronavirus infections, effects of ginseng on depression, restlessness, and other psychiatric symptoms associated with post-COVID syn-dromes, as well as possible mechanisms underlying these effects.

Multiomics profiling of the impact of an angiotensin (1-7)-expressing probiotic combined with exercise training in aged male rats

Angiotensin (1-7) [Ang (1-7)] is an active heptapeptide of the noncanonical arm of the renin-angiotensin system that modulates molecular signaling pathways associated with vascular and cellular inflammation, vasoconstriction, and fibrosis. Preclinical evidence suggests that Ang (1-7) is a promising therapeutic target that may ameliorate physical and cognitive function in late life. However, treatment pharmacodynamics limits its clinical applicability. Therefore, this study explored the underlying mechanisms altered by a genetically modified probiotic (GMP) that expresses Ang (1-7) combined with and without exercise training in an aging male rat model as a potential adjunct strategy to exercise training to counteract the decline of physical and cognitive function. We evaluated cross-tissue (prefrontal cortex, hippocampus, colon, liver, and skeletal muscle) multi-omics responses. After 12 wk of intervention, the 16S mRNA microbiome analysis revealed a main effect of probiotic treatment within- and between groups. The probiotic treatment enhanced α diversity (Inverse Simpson (F[2,56] = 4.44; P = 0.02); Shannon-Wiener (F[2,56] = 4.27; P = 0.02)) and β-diversity (F[2,56] = 2.66; P = 0.01) among rats receiving our GMP. The analysis of microbes' composition revealed three genera altered by our GMP (Enterorhabdus, Muribaculaceae unclassified, and Faecalitalea). The mRNA multi-tissue data analysis showed that our combined intervention upregulated neuroremodeling pathways on prefrontal cortex (i.e., 140 genes), inflammation gene expression in the liver (i.e., 63 genes), and circadian rhythm signaling on skeletal muscle. Finally, the integrative network analysis detected different communities of tightly (|r| > 0.8 and P < 0.05) correlated metabolites, genera, and genes in these tissues.NEW & NOTEWORTHY This manuscript uses a multiomics approach (i.e., microbiome, metabolomics, and transcriptomics) to explore the underlying mechanisms driven by a genetically modified probiotic (GMP) designed to express angiotensin (1-7) combined with moderate exercise training in an aged male rat model. After 12 wk of intervention, our findings suggest that our GMP enhanced gut microbial diversity while exercise training altered the transcriptional response in relevant neuroremodeling genes, inflammation, and circadian rhythm signaling pathways in an aging animal model.

The effects of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on ischemic stroke and the possible underlying mechanisms

Purpose: As of November 28, 2020, COVID-19 has been reported in 220 countries with 61,036,793 confirmed cases and 1,433,316 confirmed deaths; countries became vigilant around the world. In addition to SARS-CoV-2 causing pneumonia, many studies have reported ischemic stroke in patients with COVID-19. This article describes the effects and possible underlying mechanisms of SARS-CoV-2 on ischemic stroke.Materials and methods: A literature search was performed using PubMed, Web of Science, and other COVID-dedicated databases and the combination of the keywords 'SARS-CoV-2', 'COVID-19' and 'ischemic stroke' up to November 28, 2020.Results: SARS-CoV-2 invades the host through angiotensin converting enzyme 2 (ACE2). ACE2 is expressed not only in the lungs, but also in the brain and vascular endothelial cells. SARS-CoV-2 infection might cause direct vascular disease or enhance the immunogenic thrombosis environment through several mechanisms. SARS-CoV-2 infection can modulate the host immune response and can cause inflammation, coagulation disorders, renin angiotensin system disorders, hypoxia, and stress disorders, which may lead to the occurrence of ischemic stroke.Conclusions: Some patients with COVID-19 can develop ischemic stroke. Ischemic stroke has a high risk of causing disability and is associated with a high mortality rate. It is hoped that when medical staff treat patients with COVID-19, they would pay attention to the occurrence of ischemic stroke to improve the prognosis of patients with COVID-19.

Impact of genetic deletion of MrgD or Mas receptors in depressive-like behaviour in mice

OBJECTIVES

To evaluate the impact of genetic deletion of receptors of the counterregulatory arms of the renin-angiotensin system in depressive-like behaviours.

METHODS

8-12 weeks-old male mice wild type (WT, C57BL/6J) and mice with genetic deletion of MrgD (MrgD KO) or Mas receptors (Mas KO) were subjected to the Forced Swim Test (FST) and the Tail Suspension Test (TST). Brain-derived neurotrophic factor (BDNF) levels were measured by enzyme-linked immunosorbent assay (ELISA). Blockade of Mas was performed by acute intracerebroventricular (icv) injection of its selective antagonist, A779.

RESULTS

No statistical difference in immobility time was observed between MrgD KO and WT male animals subjected to FST and TST. However, acute icv injection of A779 significantly increased the immobility time of MrgD KO male mice subjected to FST and TST, suggesting the involvement of Mas in preventing depressive-like behaviour. Indeed, Mas KO male animals showed increased immobility time in FST and TST, evidencing a depressive-like behaviour in these animals, in addition to a reduction in BDNF levels in the prefrontal cortex and hippocampus. No changes in BDNF levels were observed in MrgD KO male animals.

CONCLUSION

Our data showed that Mas plays an important role in the neurobiology of depression probably by modulating BDNF expression. On the contrary, lack of MrgD did not alter depressive-like behaviour, which was supported by the lack of alterations in BDNF levels.

Renin-angiotensin system: The underlying mechanisms and promising therapeutical target for depression and anxiety

Emotional disorders, including depression and anxiety, contribute considerably to morbidity across the world. Depression is a serious condition and is projected to be the top contributor to the global burden of disease by 2030. The role of the renin-angiotensin system (RAS) in hypertension and emotional disorders is well established. Evidence points to an association between elevated RAS activity and depression and anxiety, partly through the induction of neuroinflammation, stress, and oxidative stress. Therefore, blocking the RAS provides a theoretical basis for future treatment of anxiety and depression. The evidence for the positive effects of RAS blockers on depression and anxiety is reviewed, aiming to provide a promising target for novel anxiolytic and antidepressant medications and/or for improving the efficacy of currently available medications used for the treatment of anxiety and depression, which independent of blood pressure management.

COVID-19 causes neuronal degeneration and reduces neurogenesis in human hippocampus

Recent investigations of COVID-19 have largely focused on the effects of this novel virus on the vital organs in order to efficiently assist individuals who have recovered from the disease. In the present study we used hippocampal tissue samples extracted from people who died after COVID-19. Utilizing histological techniques to analyze glial and neuronal cells we illuminated a massive degeneration of neuronal cells and changes in glial cells morphology in hippocampal samples. The results showed that in hippocampus of the studied brains there were morphological changes in pyramidal cells, an increase in apoptosis, a drop in neurogenesis, and change in spatial distribution of neurons in the pyramidal and granular layer. It was also demonstrated that COVID-19 alter the morphological characteristics and distribution of astrocyte and microglia cells. While the exact mechanism(s) by which the virus causes neuronal loss and morphology in the central nervous system (CNS) remains to be determined, it is necessary to monitor the effect of SARS-CoV-2 infection on CNS compartments like the hippocampus in future investigations. As a result of what happened in the hippocampus secondary to COVID-19, memory impairment may be a long-term neurological complication which can be a predisposing factor for neurodegenerative disorders through neuroinflammation and oxidative stress mechanisms.

Renin-Angiotensin System in Huntington's Disease: Evidence from Animal Models and Human Patients

The Renin-Angiotensin System (RAS) is expressed in the central nervous system and has important functions that go beyond blood pressure regulation. Clinical and experimental studies have suggested that alterations in the brain RAS contribute to the development and progression of neurodegenerative diseases. However, there is limited information regarding the involvement of RAS components in Huntington's disease (HD). Herein, we used the HD murine model, (BACHD), as well as samples from patients with HD to investigate the role of both the classical and alternative axes of RAS in HD pathophysiology. BACHD mice displayed worse motor performance in different behavioral tests alongside a decrease in the levels and activity of the components of the RAS alternative axis ACE2, Ang-(1-7), and Mas receptors in the striatum, prefrontal cortex, and hippocampus. BACHD mice also displayed a significant increase in mRNA expression of the AT1 receptor, a component of the RAS classical arm, in these key brain regions. Moreover, patients with manifest HD presented higher plasma levels of Ang-(1-7). No significant changes were found in the levels of ACE, ACE2, and Ang II. Our findings provided the first evidence that an imbalance in the RAS classical and counter-regulatory arms may play a role in HD pathophysiology.

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.

Impact of ACE2 genetic variant on antidepressant efficacy of SSRIs

Identification of a new axis of angiotensin-converting enzyme 2 (ACE2)/angiotensin (1-7)/Mas receptor, in the renin-angiotensin system (RAS), has opened a new insight regarding the role of RAS and angiotensin in higher brain functions. ACE2 catabolizes angiotensin II and produces angiotensin (1-7), an agonist of Mas receptor. Mice lacking the Mas receptor (angiotensin 1-7 receptor) exhibit anxiety-like behaviours. The present study was conducted to test the hypothesis of the involvement of ACE2 genetic variant (G8790A) on response to selective serotonin reuptake inhibitors (SSRIs). In a randomised control trial, 200 newly diagnosed Iranian patients with major depressive disorder completed 6 weeks of fluoxetine or sertraline treatment. Patients with a reduction of 50% or more in the Hamilton Rating Scale for Depression score were considered responsive to treatment. G8790A polymorphism was determined in extracted DNAs using restriction fragment length polymerase chain reaction method. Our results show that the A allele and AA and GA genotypes were significantly associated with better response to SSRIs (p = 0.008; OR = 3.4; 95% CI = 1.4-8.5 and p = 0.027; OR = 3.3, 95% CI = 1.2-9.2, respectively). Moreover, patients with GA and AA genotypes responded significantly better to sertraline (p = 0.0002; OR = 9.1; 95% CI = 2.4-33.7). The A allele was significantly associated with better response to sertraline (p = 0.0001; OR = 7.6; 95% CI = 2.5-23.3). In conclusion, our results confirm the role of G8790A in response to some SSRIs.

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.

Angiotensin (1-7) Expressing Probiotic as a Potential Treatment for Dementia

Increasing life expectancies are unfortunately accompanied by increased prevalence of Alzheimer's disease (AD). Regrettably, there are no current therapeutic options capable of preventing or treating AD. We review here data indicating that AD is accompanied by gut dysbiosis and impaired renin angiotensin system (RAS) function. Therefore, we propose the potential utility of an intervention targeting both the gut microbiome and RAS as both are heavily involved in proper CNS function. One potential approach which our group is currently exploring is the use of genetically-modified probiotics (GMPs) to deliver therapeutic compounds. In this review, we specifically highlight the potential utility of utilizing a GMP to deliver Angiotensin (1-7), a beneficial component of the renin-angiotensin system with relevant functions in circulation as well as locally in the gut and brain.

Alamandine through MrgD receptor induces antidepressant-like effect in transgenic rats with low brain angiotensinogen

Alamandine (Ala¹-Arg²-Val³-Tyr⁴-Ile⁵-His⁶-Pro⁷), a heptapeptide hormone of the renin-angiotensin system (RAS), exerts its effects through the Mas-related G-protein coupled receptor of the type D, MrgD, which is expressed in different tissues, including the brain. In the present study, we tested the hypothesis that alamandine could attenuate the depression-like behavior observed in transgenic rats with low brain angiotensinogen, TGR (ASrAOGEN)680. Transgenic rats exhibited a significant increase in the immobility time in forced swim test, a phenotype reversed by intracerebroventricular infusion of alamandine. Pretreatment with D-Pro⁷-Ang-(1-7), a Mas/MrgD receptor antagonist, prevented the antidepressant-like effect induced by this peptide demonstrating, for the first time, that alamandine through MrgD receptor, can modulate depression-like behavior in TGR (ASrAOGEN)680. This result shows an action of alamandine which strengthens the importance of the counter-regulatory arms of the RAS in fight and treatment of neuropsychiatric diseases.

The Renin-Angiotensin System in Huntington's Disease: Villain or Hero?

Huntington’s Disease (HD) is an autosomal dominant, progressive neurodegenerative disorder characterized by severe symptoms, including motor impairment, cognitive decline, and psychiatric alterations. Several systems, molecules, and mediators have been associated with the pathophysiology of HD. Among these, there is the Renin-Angiotensin System (RAS), a peptide hormone system that has been associated with the pathology of neuropsychiatric and neurodegenerative disorders. Important alterations in this system have been demonstrated in HD. However, the role of RAS components in HD is still unclear and needs further investigation. Nonetheless, modulation of the RAS components may represent a potential therapeutic strategy for the treatment of HD.

Neuropsychiatric Properties of the ACE2/Ang-(1-7)/Mas Pathway: A Brief Review

The current pharmacological strategies for the management of anxiety disorders and depression, serious conditions which are gaining greater prevalence worldwide, depend on only two therapeutic classes of mood-stabilizing drugs: Serotonin Reuptake Inhibitors (SSRIs) and Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs). Although first line agents with proven efficacy, their clinical success in the management of anxiety disorders and depression is still considered highly complex due to the multifaceted nature of such conditions. Several studies have shown a possible therapeutic target could be found in the form of the Angiotensin-Converting Enzyme [ACE] type 2 (ACE2), Angiotensin [Ang]-(1-7) and Mas receptor pathway of the Renin- Angiotensin System (RAS), which as will be discussed, has been described to exhibit promising therapeutic properties for the management of anxiety disorders and depression. In this article, the literature to describe recent findings related to the role of the RAS in anxiety and depression disorders was briefly revised. The literature used covers a time range from 1988 to 2019 and were acquired from the National Center for Biotechnology Information's (NCBI) PubMed search engine. The results demonstrated in this review are promising and encourage the development of new research for the treatment of anxiety and depression disorders focusing on the RAS. In conclusion, the ACE2/Ang-(1-7)/Mas pathway may exhibit anxiolytic and anti-depressive effects through many possible biochemical mechanisms both centrally and peripherally, and result in highly promising mental health benefits which justifies further investigation into this system as a possible new therapeutic target in the management of neuropsychiatric disorders, including any as of yet undescribed risk-benefit analysis compared to currently-implemented pharmacological strategies.

How Does SARS-CoV-2 Affect the Central Nervous System? A Working Hypothesis

Interstitial pneumonia was the first manifestation to be recognized as caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2); however, in just a few weeks, it became clear that the coronavirus disease-2019 (COVID-19) overrun tissues and more body organs than just the lungs, so much so that it could be considered a systemic pathology. Several studies reported the involvement of the conjunctiva, the gut, the heart and its pace, and vascular injuries such as thromboembolic complications and Kawasaki disease in children and toddlers were also described. More recently, it was reported that in a sample of 214 SARS-CoV-2 positive patients, 36.4% complained of neurological symptoms ranging from non-specific manifestations (dizziness, headache, and seizures), to more specific symptoms such hyposmia or hypogeusia, and stroke. Older individuals, especially males with comorbidities, appear to be at the highest risk of developing such severe complications related to the Central Nervous System (CNS) involvement. Neuropsychiatric manifestations in COVID-19 appear to develop in patients with and without pre-existing neurological disorders. Growing evidence suggests that SARS-CoV-2 binds to the human Angiotensin-Converting Enzyme 2 (ACE2) for the attachment and entrance inside host cells. By describing ACE2 and the whole Renin Angiotensin Aldosterone System (RAAS) we may better understand whether specific cell types may be affected by SARS-CoV-2 and whether their functioning can be disrupted in case of an infection. Since clear evidences of neurological interest have already been shown, by clarifying the topographical distribution and density of ACE2, we will be able to speculate how SARS-CoV-2 may affect the CNS and what is the pathogenetic mechanism by which it contributes to the specific clinical manifestations of the disease. Based on such evidences, we finally hypothesize the process of SARS-CoV-2 invasion of the CNS and provide a possible explanation for the onset or the exacerbation of some common neuropsychiatric disorders in the elderly including cognitive impairment and Alzheimer disease.

Targeting the renin angiotensin system for the treatment of anxiety and depression

Emotional disorders like anxiety and depression are responsible for considerable morbidity and mortality all over the world. Several antidepressant and anxiolytic medications are available for the treatment of anxiety and depression. However, a significant number of patients either do not respond to these medications or respond inadequately. Hence, there is a need to identify novel targets for the treatment of anxiety and depression. In this review we focus on the renin angiotensin system (RAS) as a potential target for the treatment of these disorders. We review work that has evaluated the effects of various compounds targeting the RAS on anxiety- and depression-like behaviors. Further, we suggest future work that must be carried out to fully exploit the RAS for the treatment of anxiety and depression. The RAS provides an attractive target for both the identification of novel anxiolytic and antidepressant medications and/or for enhancing the efficacy of currently available medications used for the treatment of anxiety and depression.

Overexpression of angiotensin converting enzyme 2 reduces anxiety-like behavior in female mice

Accumulating evidence has revealed an intricate role for the renin-angiotensin system (RAS) in the progression or alleviation of stress-related disorders. Along these lines, the 'pro-stress' actions of angiotensin-II (Ang-II) are largely thought to be mediated by the angiotensin type-1a receptor (AT1aR). On the other hand, a counter regulatory limb of the RAS that depends on the conversion of Ang-II to angiotensin-(1-7) by angiotensin-converting enzyme 2 (ACE2) has been postulated to exert stress-dampening actions. We have previously found that augmenting ACE2 activity is potently anxiolytic and blunts stress-induced activation of the hypothalamic-pituitary-adrenal (HPA) axis in male mice. Whether increasing ACE2 activity also relieves stress and anxiety in females has not yet been determined. Consequently, this series of experiments tests the hypothesis that augmenting ACE2 expression is anxiolytic and dampens the activity of the HPA axis in female mice. Using the Cre-LoxP system, we generated female mice that were homo-, heterozygous or wild-type for a mutated allele resulting in ubiquitous overexpression of ACE2. Next, we used qPCR to determine that levels of ACE2 mRNA isolated from central and peripheral tissues was dependent on genotype. That is, mice homo- and heterozygous for the ACE2 overexpression had significantly greater levels of ACE2 mRNA relative to littermate matched wild-type controls. Interestingly, anxiety-like behavior as determined by the elevated plus maze, light-dark box and novelty-induced hypophagia tests was also affected by genotype. Specifically, ACE2 overexpression significantly decreased anxiety-like behavior in paradigms dependent on approach-avoidance conflict and novelty; however, locomotor activity was similar amongst the genotypes. Final experiments measured plasma corticosterone to evaluate whether increasing ACE2 alters basal and/or stress-induced HPA axis activity. In contrast to what was previously found in males, increasing ACE2 expression had no effect on plasma corticosterone under basal conditions or subsequent to an acute restraint challenge. Collectively, these results suggest that increasing ACE2 expression potently elicits anxiolysis in female mice without altering HPA axis activity.

Angiotensinergic receptors in the medial amygdaloid nucleus differently modulate behavioral responses in the elevated plus-maze and forced swimming test in rats

The brain renin-angiotensin system (RAS) has been implicated in anxiety and depression disorders, but the specific brain sites involved are poorly understood. The medial amygdaloid nucleus (MeA) is involved in expression of behavioral responses. However, despite evidence of the presence of all angiotensinergic receptors in this amygdaloid nucleus, regulation of anxiety- and depressive-like behaviors by angiotensinergic neurotransmissions within the MeA has never been reported. Thus, the present study aimed to investigate the role angiotensin II (AT₁ and AT₂ receptors) and angiotensin-(1-7) (Mas receptor) receptors present within the MeA in behavioral responses in the elevated plus-maze (EPM) and forced swimming test (FST). For this, male Wistar rats had cannula-guide bilaterally implanted into the MeA, and independent sets of animals received bilateral microinjections of either the selective AT₁ receptor antagonist losartan, the selective AT₂ receptor antagonist PD123319, the selective Mas receptor antagonist A-779 or vehicle into the MeA before the EPM and FST. Treatment of the MeA with either PD123319 or A-779 decreased the EPM open arms exploration, while losartan did not affect behavioral responses in this apparatus. However, intra-MeA microinjection of losartan decreased immobility in the FST. Administration of either PD123319 or A-779 into the MeA did not affect the immobility during the FST, but changed the pattern of the active behaviors swimming and climbing. Altogether, these results indicate the presence of different angiotensinergic mechanisms within the MeA controlling behavioral responses in the FST and EPM.

Effects of renal ischemia injury on brain in diabetic and non-diabetic rats: Role of angiotensin II type 2 receptor and angiotensin-converting enzyme 2

Clinically, patients with diabetes mellitus (DM) are more susceptible to ischemic renal injury (IRI) than non-diabetic (ND) patients. Besides, IRI predisposes distant organ dysfunctions including, neurological dysfunction, in which the major contributor remains renin-angiotensin system (RAS). Interestingly, the role of depressor arm of RAS on IRI-associated neurological sequalae remains unclear. Hence, this study aimed to delineate the role of angiotensin II type 2 receptor (AT2R) and angiotensin-converting enzyme 2 (ACE2) under the same. ND and Streptozotocin-induced DM rats with bilateral IRI were treated with AT2R agonist-Compound 21 (C21) (0.3 mg/kg/day, i.p.) or ACE2 activator-Diminazene Aceturate (Dize), (5 mg/kg/day, p.o.) either alone or as combination therapy. Effect of IRI on neurological functions were assessed by behavioural, biochemical, and histopathological analysis. Immunohistochemistry, ELISA and qRT-PCR experiments were conducted for evaluation of the molecular mechanisms. We found that in ND and DM rats, IRI causes increased hippocampal MDA and nitrite levels, augmented inflammatory cytokines (granulocyte-colony stimulating factor, glial fibrillary acidic protein), altered protein levels of Ang II, Ang-(1-7) and mRNA expressions of At1r, At2r and Masr. Treatment with C21 and Dize effectively normalised above-mentioned pathological alterations. Moreover, the protective effect of C21 and Dize combination therapy was better than respective monotherapies, and more likely, exerted via augmentation of protein and mRNA levels of depressor arm components. Thus, AT2R agonist and ACE2 activator therapy prevents the development of IRI-associated neurological dysfunction by attenuating oxidative stress and inflammation, upregulating depressor arm of RAS in brain under ND and DM conditions.

Angiotensin-Ⅱ and angiotensin-(1-7) imbalance affects comorbidity of depression and coronary heart disease

A large body of evidence suggests a relationship between depression and coronary heart disease (CHD). Angiotensin-Ⅱ (Ang-Ⅱ) and angiotensin-(1-7) [Ang-(1-7)] are considered to exert biological effects in both conditions. Here, we aimed to determine the role of Ang-Ⅱ and Ang-(1-7) in the occurrence of comorbid depression in patients with CHD. Our study included 214 CHD patients and 100 matched healthy controls. Serum Ang-Ⅱ and Ang-(1-7) levels were assessed by ELISA, and the depression symptoms were evaluated by the nine-item Patient Health Questionnaire (PHQ-9). Linear regression and correlation analyses were used to estimate the associations between PHQ-9 scores and Ang-Ⅱ and Ang-(1-7) serum levels. Six single-nucleotide polymorphisms (SNPs) spanning the angiotensin converting enzyme 2 (ACE2) and MAS1 genes were genotyped. The associations between SNPs and depression risk in CHD patients were examined using logistic regression analysis with adjustment for age and gender. Decreased Ang-(1-7) (P < 0.05) and an elevated Ang-Ⅱ/Ang-(1-7) ratio (P < 0.01) were observed in CHD patients with depression compared to CHD patients without depression. PHQ-9 scores were negatively correlated with Ang-(1-7) level (r=-0.44, P < 0.01) and positively correlated with the Ang-Ⅱ/Ang-(1-7) ratio (r = 0.33, P < 0.05). Furthermore, carriers of risk allele T for CHD with depression had significantly higher PHQ-9 scores (P < 0.05), lower Ang-(1-7) level (P < 0.01), and higher Ang-Ⅱ/Ang-(1-7) ratio (P < 0.05) than those CC carriers. Collectively, our results firstly showed that Ang-(1-7) serum level in CHD patients may protect against comorbid depression. Moreover, the imbalance between Ang-Ⅱ and Ang-(1-7) may contribute to depression in CHD patients.

Angiotensin (1-7) through modulation of the NMDAR-nNOS-NO pathway and serotonergic metabolism exerts an anxiolytic-like effect in rats

Although recent studies have shown that angiotensin (1-7) (Ang [1-7]) exerts anti-stress and anxiolytic-like effects, the underlying mechanisms remain elusive. The ventral hippocampus (VH) is proposed to be a critical brain region for mood and stress management through the N-methyl-d-aspartate receptor (NMDAR) signaling pathway. However, the role of VH NMDAR signaling in the effects of Ang (1-7) remains unclear. In the present study, Ang (1-7) was injected into the bilateral VH of stressed rats, or in combination with a Fyn kinase inhibitor, NMDAR antagonist, neuronal nitric oxide synthase (nNOS) inhibitor, or nitric oxide (NO) scavenger. Anxiety-like behaviors were assessed using the open field test and elevated plus maze test, while alterations in NMDAR-nNOS-NO signaling and serotonergic metabolism were examined in the VH. After 21 days of chronic restraint stress, anxiety-like behaviors were evident. Levels of phosphorylated NR2B (a key NMDAR subunit), its upstream kinase Fyn, as well as activity of nNOS and monoamine oxidase (MAO) were markedly reduced. In contrast, levels of serotonin were increased. Bilateral VH infusion of Ang (1-7) recovered NMDAR-nNOS-NO signaling and MAO-mediated serotonin metabolism, as well as reducing anxiety-like behaviors in stressed rats. These effects were diminished by blockade of MasR (Ang [1-7]-specific receptor), Fyn kinase, NMDAR, nNOS, or NO production. Altogether, these findings indicate that Ang (1-7) exerts anxiolytic effects through modulation of the NMDAR-nNOS-NO pathway and serotonergic metabolism. Future translational research should focus on the relationship between Ang (1-7), glutamatergic neurotransmission, and serotonergic neurotransmission in the VH.

Angiotensin (1-7) delivered orally via probiotic, but not subcutaneously, benefits the gut-brain axis in older rats

To (1) investigate the efficacy of multiple doses of an orally delivered probiotic bacteria Lactobacillus paracasei (LP) modified to express angiotensin (1-7) (LP-A) in altering physiologic parameters relevant to the gut-brain axis in older rats and to (2) compare this strategy with subcutaneous delivery of synthetic Ang(1-7) peptide on circulating Ang(1-7) concentrations and these gut-brain axis parameters. Male 24-month-old F344BN rats received oral gavage of LP-A, or subcutaneous injection of Ang(1-7) for 0×, 1×, 3×, or 7×/week over 4 weeks. Circulating RAS analytes, inflammatory cytokines, and tryptophan and its downstream metabolites were measured by ELISA, electrochemiluminescence, and LC-MS respectively. Microbiome taxonomic analysis of fecal samples was performed via 16S-based PCR. Inflammatory and tryptophan-related mRNA expression was measured in colon and pre-frontal cortex. All dosing regimens of LP-A induced beneficial changes in fecal microbiome including overall microbiota community structure and α-diversity, while the 3×/week also significantly increased expression of the anti-inflammatory species Akkermansia muciniphila. The 3×/week also increased serum serotonin and the neuroprotective analyte 2-picolinic acid. In the colon, LP-A increased quinolinate phosphoribosyltransferase expression (1×/week) and increased kynurenine aminotransferase II (1× and 3×/week) mRNA expression. LP-A also significantly reduced neuro-inflammatory gene expression in the pre-frontal cortex (3×/week: COX2, IL-1β, and TNFα; 7×/week: COX2 and IL-1β). Subcutaneous delivery of Ang(1-7) increased circulating Ang(1-7) and reduced angiotensin II, but most gut-brain parameters were unchanged in response. Oral-but not subcutaneous-Ang(1-7) altered physiologic parameters related to gut-brain axis, with the most effects observed in 3×/week oral dosing regimen in older rats.

Electroacupuncture Improved Chronic Cerebral Hypoperfusion-Induced Anxiety-Like Behavior and Memory Impairments in Spontaneously Hypertensive Rats by Downregulating the ACE/Ang II/AT1R Axis and Upregulating the ACE2/Ang-(1-7)/MasR Axis

Electroacupuncture (EA) can effectively alleviate anxiety disorders and memory impairments caused by various neurodegenerative diseases; however, the molecular mechanisms underlying its neuroprotective effects are unclear. Previous studies have shown that the renin-angiotensin system (RAS) comprises of two axes with mutual antagonism: the classical angiotensin converting enzyme/angiotensin II/angiotensin II type 1 receptor (ACE/Ang II/AT1R) axis and the protective angiotensin converting enzyme 2/angiotensin-(1-7)/Mas receptor (ACE2/Ang-(1-7)/MasR) axis. In this study, we observed that chronic cerebral hypoperfusion (CCH) mediated anxiety-like behavior and memory impairments in spontaneously hypertensive rats (SHR) via upregulation of the hippocampal classical axis (ACE/Ang II/AT1R) and the partial hippocampal protective axis (ACE2/Ang-(1-7)). However, Ang II levels were much higher than those of Ang-(1–7), indicating that the ACE/Ang II/AT1R axis plays a dominant role in the comorbidity of CCH and hypertension. Moreover, candesartan cilexetil (Canc) and perindopril (Peril) were used as positive control drugs. We found that EA, Canc, and Peril attenuated CCH-induced anxiety-like behavior and memory impairments in SHR, potentially via downregulation of the hippocampal classical axis (ACE/Ang II/AT1R) and upregulation of the whole hippocampal protective axis (ACE2/Ang-(1-7)/MasR). These results suggest that EA therapy for CCH with hypertension may be mediated by two hippocampal RAS axes.

Genetic Models

Genetically altered rat and mouse models have been instrumental in the functional analysis of genes in a physiological context. In particular, studies on the renin-angiotensin system (RAS) have profited from this technology in the past. In this review, we summarize the existing animal models for the protective axis of the RAS consisting of angiotensin-converting enzyme 2 (ACE2), angiotensin-(1-7)(Ang-(1-7), and its receptor Mas. With the help of models with altered expression of the components of this axis in the brain and cardiovascular organs, its physiological and pathophysiological functions have been elucidated. Thus, novel opportunities for therapeutic interventions in cardiovascular diseases were revealed targeting ACE2 or Mas.

ACE2 in Brain Physiology and Pathophysiology: Evidence from Transgenic Animal Models

Angiotensin-converting enzyme 2 (ACE2) is a protein consisting of two domains, the N-terminus is a carboxypeptidase homologous to ACE and the C-terminus is homologous to collectrin and responsible for the trafficking of the neutral amino acid transporter B(0)AT1 to the plasma membrane of gut epithelial cells. The carboxypeptidase domain not only metabolizes angiotensin II to angiotensin-(1–7), but also other peptide substrates, such as apelin, kinins and morphins. In addition, the collectrin domain regulates the levels of some amino acids in the blood, in particular of tryptophan. Therefore it is of no surprise that animals with genetic alterations in the expression of ACE2 develop a diverse pattern of phenotypes ranging from hypertension, metabolic and behavioural dysfunctions, to impairments in serotonin synthesis and neurogenesis. This review summarizes the phenotypes of such animals with a particular focus on the central nervous system.

Coupling corticotropin-releasing-hormone and angiotensin converting enzyme 2 dampens stress responsiveness in male mice

This study used mice to evaluate whether coupling expression of corticotropin-releasing hormone (CRH) and angiotensin converting enzyme 2 (ACE2) creates central interactions that blunt endocrine and behavioral responses to psychogenic stress. Central administration of diminazene aceturate, an ACE2 activator, had no effect on restraint-induced activation of the hypothalamic-pituitary-adrenal (HPA) axis; however, mice that ubiquitously overexpress ACE2 had reduced plasma corticosterone (CORT) and pituitary expression of POMC mRNA. The Cre-LoxP system was used to restrict ACE2 overexpression to CRH synthesizing cells and probe whether HPA axis suppression was the result of central ACE2 and CRH interactions. Within the paraventricular nucleus of the hypothalamus (PVN), mice with ACE2 overexpression directed to CRH had a ≈2.5 fold increase in ACE2 mRNA, which co-localized with CRH mRNA. Relative to controls, mice overexpressing ACE2 in CRH cells had a decreased CORT response to restraint as well as decreased CRH mRNA in the PVN and CEA and POMC mRNA in the pituitary. Administration of ACTH similarly increased plasma CORT, indicating that the blunted HPA axis activation that accompanies ACE2 overexpression in CRH cells is centrally mediated. Anxiety-like behavior was assessed to determine whether the decreased HPA axis activation was predictive of anxiolysis. Mice with ACE2 overexpression directed to CRH cells displayed decreased anxiety-like behavior in the elevated plus maze and open field when compared to that of controls. Collectively, these results suggest that exogenous ACE2 suppresses CRH synthesis, which alters the central processing of psychogenic stress, thereby blunting HPA axis activation and attenuating anxiety-like behavior.

Hyperglycemia elicits anxiety-like behaviors in zebrafish: Protective role of dietary diphenyl diselenide

Diabetes mellitus (DM) is a chronic metabolic disease that may comorbid with various psychiatric disorders, such as anxiety and depression. The search for effective therapeutics to alleviate hyperglycemia and complications resulting from DM is continuous. Here we investigate the effects of diphenyl diselenide (DD), an organoselenium compound with several pharmacological properties, in a zebrafish model of hyperglycemia. Fish were fed for 74 days with a diet containing 3 mg/Kg DD, a concentration chosen after experiments based in a dose-response curve (DD 1, 2 and 3 mg/Kg) that did not cause overt toxicity (mortality, weight loss and neurobehavioral deficits). In the last 14 days of the experimental period, fish were concomitantly exposed to a glucose solution (111 mM). Afterwards, blood glucose levels, brain selenium (Se) content, and behavioral analysis aiming to assess anxiety-like behaviors and locomotor/exploratory activities were performed. In the novel tank diving test, glucose decreased vertical exploration and fish spent less time in the lit area when tested in the light-dark test, suggesting increased anxiety-like behavior. Moreover, DD decreased blood glucose levels in hyperglycemic fish as well as prevented the development of anxiety-related symptoms. DD diet alone did not change glycemia and behavioral parameters, but increased Se levels in the brain without affecting the cellular viability. Collectively, our findings highlight the growing utility of this zebrafish hyperglycemia model as a valuable strategy for further research in DM field and neuroprotective approaches.

The depressor axis of the renin–angiotensin system and brain disorders: a translational approach

All the components of the classic renin–angiotensin system (RAS) have been identified in the brain. Today, the RAS is considered to be composed mainly of two axes: the pressor axis, represented by angiotensin (Ang) II/angiotensin-converting enzyme/AT1 receptors, and the depressor and protective one, represented by Ang-(1–7)/ angiotensin-converting enzyme 2/Mas receptors. Although the RAS exerts a pivotal role on electrolyte homeostasis and blood pressure regulation, their components are also implicated in higher brain functions, including cognition, memory, anxiety and depression, and several neurological disorders. Overactivity of the pressor axis of the RAS has been implicated in stroke and several brain disorders, such as cognitive impairment, dementia, and Alzheimer or Parkinson’s disease. The present review is focused on the role of the protective axis of the RAS in brain disorders beyond its effects on blood pressure regulation. Furthermore, the use of drugs targeting centrally RAS and its beneficial effects on brain disorders are also discussed.

Within the Brain: The Renin Angiotensin System

For many years, modulators of the renin angiotensin system (RAS) have been trusted by clinicians for the control of essential hypertension. It was recently demonstrated that these modulators have other pleiotropic properties independent of their hypotensive effects, such as enhancement of cognition. Within the brain, different components of the RAS have been extensively studied in the context of neuroprotection and cognition. Interestingly, a crosstalk between the RAS and other systems such as cholinergic, dopaminergic and adrenergic systems have been demonstrated. In this review, the preclinical and clinical evidence for the impact of RAS modulators on cognitive impairment of multiple etiologies will be discussed. In addition, the expression and function of different receptor subtypes within the RAS such as: Angiotensin II type I receptor (AT1R), Angiotensin II type II receptor (AT2R), Angiotensin IV receptor (AT4R), Mas receptor (MasR), and Mas-related-G protein-coupled receptor (MrgD), on different cell types within the brain will be presented. We aim to direct the attention of the scientific community to the plethora of evidence on the importance of the RAS on cognition and to the different disease conditions in which these agents can be beneficial.

The hemoglobin derived peptide LVV-hemorphin-7 evokes behavioral effects mediated by oxytocin receptors

LVV-hemorphin-7 (LVV-h7) is bioactive peptide resulting from degradation of hemoglobin β-globin chain. LVV-h7 is a specific agonist of angiotensin IV receptor. This receptor belongs to the class of insulin-regulated aminopeptidases (IRAP), which displays oxytocinase activity. Herein, our aims were to assess whether: i) LVV-h7 modifies centrally organized behavior and cardiovascular responses to stress and ii) mechanisms underlying LVV-h7 effects involve activation of oxytocin (OT) receptors, probably as result of reduction of IRAP proteolytic activity upon OT. Adult male Wistar rats (270-370g) received (i.p.) injections of LVV-h7 (153nmol/kg), or vehicle (0.1ml). Different protocols were used: i) open field (OP) test for locomotor/exploratory activities; ii) Elevated Plus Maze (EPM) for anxiety-like behavior; iii) forced swimming test (FST) test for depression-like behavior and iv) air jet for cardiovascular reactivity to acute stress exposure. Diazepam (2mg/kg) and imipramine (15mg/kg) were used as positive control for EPM and FST, respectively. The antagonist of OT receptors (OTr), atosiban (1 and 0,1mg/kg), was used to determine the involvement of oxytocinergic paths. We found that LVV-h7: i) increased the number of entries and the time spent in open arms of the maze, an indicative of anxiolysis; ii) provoked antidepressant effect in the FS test; and iii) increased the exploration and locomotion; iv) did not change the cardiovascular reactivity and neuroendocrine responses to acute stress. Also, increases in locomotion and the antidepressant effects evoked by LVV-h7 were reverted by OTr antagonist. We conclude that LVV-h7 modulates behavior, displays antidepressant and anxiolytic effects that are mediated in part by oxytocin receptors.

The renin-angiotensin system: a possible new target for depression

Depression remains a debilitating condition with an uncertain aetiology. Recently, attention has been given to the renin-angiotensin system. In the central nervous system, angiotensin II may be important in multiple pathways related to neurodevelopment and regulation of the stress response. Studies of drugs targeting the renin-angiotensin system have yielded promising results. Here, we review the potential beneficial effects of angiotensin blockers in depression and their mechanisms of action. Drugs blocking the angiotensin system have efficacy in several animal models of depression. While no randomised clinical trials were found, case reports and observational studies showed that angiotensin-converting enzyme inhibitors or angiotensin receptor blockers had positive effects on depression, whereas other antihypertensive agents did not. Drugs targeting the renin-angiotensin system act on inflammatory pathways implicated in depression. Both preclinical and clinical data suggest that these drugs possess antidepressant properties. In light of these results, angiotensin system-blocking agents offer new horizons in mood disorder treatment.