Anti-inflammatory effects of angiotensin receptor blockers in the brain and the periphery

Melatonin: a ferroptosis inhibitor with potential therapeutic efficacy for the post-COVID-19 trajectory of accelerated brain aging and neurodegeneration

The unprecedented pandemic of COVID-19 swept millions of lives in a short period, yet its menace continues among its survivors in the form of post-COVID syndrome. An exponentially growing number of COVID-19 survivors suffer from cognitive impairment, with compelling evidence of a trajectory of accelerated aging and neurodegeneration. The novel and enigmatic nature of this yet-to-unfold pathology demands extensive research seeking answers for both the molecular underpinnings and potential therapeutic targets. Ferroptosis, an iron-dependent cell death, is a strongly proposed underlying mechanism in post-COVID-19 aging and neurodegeneration discourse. COVID-19 incites neuroinflammation, iron dysregulation, reactive oxygen species (ROS) accumulation, antioxidant system repression, renin-angiotensin system (RAS) disruption, and clock gene alteration. These events pave the way for ferroptosis, which shows its signature in COVID-19, premature aging, and neurodegenerative disorders. In the search for a treatment, melatonin shines as a promising ferroptosis inhibitor with its repeatedly reported safety and tolerability. According to various studies, melatonin has proven efficacy in attenuating the severity of certain COVID-19 manifestations, validating its reputation as an anti-viral compound. Melatonin has well-documented anti-aging properties and combating neurodegenerative-related pathologies. Melatonin can block the leading events of ferroptosis since it is an efficient anti-inflammatory, iron chelator, antioxidant, angiotensin II antagonist, and clock gene regulator. Therefore, we propose ferroptosis as the culprit behind the post-COVID-19 trajectory of aging and neurodegeneration and melatonin, a well-fitting ferroptosis inhibitor, as a potential treatment.

Potential molecular pathways of angiotensin receptor blockers in the brain toward cognitive improvement in dementia

The alarming rise of cognitive impairment and memory decline and limited effective solutions present a worldwide concern for dementia patients. The multivariant role of the renin-angiotensin system (RAS) in the brain offers strong evidence of a role for angiotensin receptor blockers (ARBs) in the management of memory impairment by modifying glutamate excitotoxicity, downregulating inflammatory cytokines such as interleukin (IL)-1β, IL-6 and tumor necrosis factor (TNF)α, inhibiting kynurenine aminotransferase (KAT)-II, nucleotide-binding domain, leucine-rich-containing family and pyrin-domain-containing-3 (NLRP3) inflammasomes, boosting cholinergic activity, activating peroxisome proliferator-activated receptor (PPAR)-γ, countering cyclooxygenase (COX) and mitigating the hypoxic condition. The present work focuses on the intricate molecular mechanisms involved in brain-RAS, highlighting the role of ARBs, connecting links between evidence-based unexplored pathways and investigating probable biomarkers involved in dementia through supported preclinical and clinical literature.

The Pivotal Role of Angiotensin-Converting Enzyme Inhibitors and Angiotensin II Receptor Blockers in Hypertension Management and Cardiovascular and Renal Protection: A Critical Appraisal and Comparison of International Guidelines

Arterial hypertension is the main preventable cause of premature mortality worldwide. Across Latin America, hypertension has an estimated prevalence of 25.5-52.5%, although many hypertensive patients remain untreated. Appropriate treatment, started early and continued for the remaining lifespan, significantly reduces the risk of complications and mortality. All international and most regional guidelines emphasize a central role for renin-angiotensin-aldosterone system inhibitors (RAASis) in antihypertensive treatment. The two main RAASi options are angiotensin-converting enzyme inhibitors (ACEis) and angiotensin II receptor blockers (ARBs). Although equivalent in terms of blood pressure reduction, ACEis are preferably recommended by some guidelines to manage other cardiovascular comorbidities, with ARBs considered as an alternative when ACEis are not tolerated. This review summarizes the differences between ACEis and ARBs and their place in the international guidelines. It provides a critical appraisal of the guidelines based on available evidence from randomized controlled trials (RCTs) and meta-analyses, especially considering that hypertensive patients in daily practice often have other comorbidities. The observed differences in cardiovascular and renal outcomes in RCTs may be attributed to the different mechanisms of action of ACEis and ARBs, including increased bradykinin levels, potentiated bradykinin response, and stimulated nitric oxide production with ACEis. It may therefore be appropriate to consider ACEis and ARBs as different antihypertensive drugs classes within the same RAASi group. Although guideline recommendations only differentiate between ACEis and ARBs in patients with cardiovascular comorbidities, clinical evidence suggests that ACEis provide benefits in many hypertensive patients, as well as those with other cardiovascular conditions.

Effect of AT1 receptor blockade on cardiovascular outcome after cardiac arrest: an experimental study in rats

Angiotensin II receptor 1(AT1) antagonists are beneficial in focal ischemia/reperfusion (I/R). However, in cases of global I/R, such as cardiac arrest (CA), AT1 blocker's potential benefits are still unknown. Wistar male rats were allocated into four groups: Control group (CG)-animals submitted to CA by ventricular fibrillation induced by direct electrical stimulation for 3 min, and anoxia for 5 min; Group AT1 (GAT1)-animals subjected to CA and treated with 0.2 mg/kg of candesartan diluted in dimethylsulfoxide (DMSO) (0.1%); Vehicle Group (VG): animals subjected to CA and treated with 0.2 ml/kg of DMSO and Sham group (SG)-animals submitted to surgical interventions, without CA. Cardiopulmonary resuscitation consisted of group medications, chest compressions, ventilation, epinephrine (20 mcg/kg) and defibrillation. The animals were observed up to 4 h after spontaneous circulation (ROSC) return, and survival rates, hemodynamic variables, histopathology, and markers of tissue injury were analyzed. GAT1 group had a higher rate of ROSC (62.5% vs. 42.1%, p < 0.0001), survival (100% vs. 62.5%, p = 0.027), lower incidence of arrhythmia after 10 min of ROSC (10% vs. 62.5%, p = 0.000), and lower neuronal and cardiac injury scores on histology evaluation (p = 0.025 and p = 0.0052, respectively) than GC group. The groups did not differ regarding CA duration, number of adrenaline doses, or number of defibrillations. AT1 receptor blockade with candesartan yielded higher rates of ROSC and survival, in addition to neuronal and myocardial protection.

The Renin Angiotensin System as a Therapeutic Target in Traumatic Brain Injury

Traumatic brain injury (TBI) is a major public health problem, with limited pharmacological options available beyond symptomatic relief. The renin angiotensin system (RAS) is primarily known as a systemic endocrine regulatory system, with major roles controlling blood pressure and fluid homeostasis. Drugs that target the RAS are used to treat hypertension, heart failure and kidney disorders. They have now been used chronically by millions of people and have a favorable safety profile. In addition to the systemic RAS, it is now appreciated that many different organ systems, including the brain, have their own local RAS. The major ligand of the classic RAS, Angiotensin II (Ang II) acts predominantly through the Ang II Type 1 receptor (AT1R), leading to vasoconstriction, inflammation, and heightened oxidative stress. These processes can exacerbate brain injuries. Ang II receptor blockers (ARBs) are AT1R antagonists. They have been shown in several preclinical studies to enhance recovery from TBI in rodents through improvements in molecular, cellular and behavioral correlates of injury. ARBs are now under consideration for clinical trials in TBI. Several different RAS peptides that signal through receptors distinct from the AT1R, are also potential therapeutic targets for TBI. The counter regulatory RAS pathway has actions that oppose those stimulated by AT1R signaling. This alternative pathway has many beneficial effects on cells in the central nervous system, bringing about vasodilation, and having anti-inflammatory and anti-oxidative stress actions. Stimulation of this pathway also has potential therapeutic value for the treatment of TBI. This comprehensive review will provide an overview of the various components of the RAS, with a focus on their direct relevance to TBI pathology. It will explore different therapeutic agents that modulate this system and assess their potential efficacy in treating TBI patients.

Combination of Taurine and Black Pepper Extract as a Treatment for Cardiovascular and Coronary Artery Diseases

The shift in modern dietary regimens to "Western style" and sedentary lifestyles are believed to be partly responsible for the increase in the global burden of cardiovascular diseases. Natural products have been used throughout human history as treatments for a plethora of pathological conditions. Taurine and, more recently, black pepper have gained attention for their beneficial health effects while remaining non-toxic even when ingested in excess. Taurine, black pepper, and the major terpene constituents found in black pepper (i.e., β-caryophyllene; α-pinene; β-pinene; α-humulene; limonene; and sabinene) that are present in PhytoCann BP^® have been shown to have cardioprotective effects based on anti-inflammatory, antioxidative, anti-hypertensive and anti-atherosclerotic mechanisms. This comprehensive review of the literature focuses on determining whether the combination of taurine and black pepper extract is an effective natural treatment for reducing cardiovascular diseases risk factors (i.e., hypertension and hyperhomocysteinemia) and for driving anti-inflammatory, antioxidative and anti-atherosclerotic mechanisms to combat coronary artery disease, heart failure, myocardial infarction, and atherosclerotic disease.

Role of Angiotensin II in Cardiovascular Diseases: Introducing Bisartans as a Novel Therapy for Coronavirus 2019

Cardiovascular diseases (CVDs) are the main contributors to global morbidity and mortality. Major pathogenic phenotypes of CVDs include the development of endothelial dysfunction, oxidative stress, and hyper-inflammatory responses. These phenotypes have been found to overlap with the pathophysiological complications of coronavirus disease 2019 (COVID-19). CVDs have been identified as major risk factors for severe and fatal COVID-19 states. The renin-angiotensin system (RAS) is an important regulatory system in cardiovascular homeostasis. However, its dysregulation is observed in CVDs, where upregulation of angiotensin type 1 receptor (AT1R) signaling via angiotensin II (AngII) leads to the AngII-dependent pathogenic development of CVDs. Additionally, the interaction between the spike protein of severe acute respiratory syndrome coronavirus 2 with angiotensin-converting enzyme 2 leads to the downregulation of the latter, resulting in the dysregulation of the RAS. This dysregulation favors AngII/AT1R toxic signaling pathways, providing a mechanical link between cardiovascular pathology and COVID-19. Therefore, inhibiting AngII/AT1R signaling through angiotensin receptor blockers (ARBs) has been indicated as a promising therapeutic approach to the treatment of COVID-19. Herein, we review the role of AngII in CVDs and its upregulation in COVID-19. We also provide a future direction for the potential implication of a novel class of ARBs called bisartans, which are speculated to contain multifunctional targeting towards COVID-19.

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

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

Anti-Inflammatory Effects of Ang-(1-7) Bone-Targeting Conjugate in an Adjuvant-Induced Arthritis Rat Model

Rheumatoid arthritis (RA) is a chronic inflammatory condition of synovial joints that causes disability and systemic complications. Ang-(1-7), one of the main peptides in the renin-angiotensin (Ang) system (RAS), imposes its protective effects through Mas receptor (MasR) signaling. It has a short half-life, limiting its feasibility as a therapeutic agent. In this study, we evaluated the anti-inflammatory effects of Ang-(1-7)’s novel and stable conjugate (Ang. Conj.) by utilizing its affinity for bone through bisphosphonate (BP) moiety in an adjuvant-induced arthritis (AIA) rat model. The rats received subcutaneous injections of vehicle, plain Ang-(1-7), or an equivalent dose of Ang. Conj. The rats’ body weights, paws, and joints’ diameters were measured thrice weekly. After 14 days, the rats were euthanized, and the blood and tissue samples were harvested for further analysis of nitric oxide (NO) and RAS components’ gene and protein expression. The administration of Ang. Conj. reduced body weight loss, joint edema, and serum NO. Moreover, the Ang. Conj. treatment significantly reduced the classical arm components at peptide, enzyme, and receptor levels while augmenting them for the protective arm. The results of this study introduce a novel class of bone-targeting natural peptides for RA caused by an inflammation-induced imbalance in the activated RAS. Our results indicate that extending the half-life of Ang-(1-7) augments the RAS protective arm and exerts enhanced therapeutic effects in the AIA model in rats.

Captopril alleviates epilepsy and cognitive impairment by attenuation of C3-mediated inflammation and synaptic phagocytosis

Evidence from experimental and clinical studies implicates immuno-inflammatory responses as playing an important role in epilepsy-induced brain injury. Captopril, an angiotensin-converting enzyme inhibitor (ACEi), has previously been shown to suppress immuno-inflammatory responses in a variety of neurological diseases. However, the therapeutic potential of captopril on epilepsy remains unclear. In the present study, Sprague Dawley (SD) rats were intraperitoneally subjected to kainic acid (KA) to establish a status epilepticus. Captopril (50 mg/kg, i.p.) was administered daily following the KA administration from day 3 to 49. We found that captopril efficiently suppressed the KA-induced epilepsy, as measured by electroencephalography. Moreover, captopril ameliorated the epilepsy-induced cognitive deficits, with improved performance in the Morris water maze, Y-maze and novel objective test. RNA sequencing (RNA-seq) analysis indicated that captopril reversed a wide range of epilepsy-related biological processes, particularly the glial activation, complement system-mediated phagocytosis and the production of inflammatory factors. Interestingly, captopril suppressed the epilepsy-induced activation and abnormal contact between astrocytes and microglia. Immunohistochemical experiments demonstrated that captopril attenuated microglia-dependent synaptic remodeling presumably through C3–C3ar-mediated phagocytosis in the hippocampus. Finally, the above effects of captopril were partially blocked by an intranasal application of recombinant C3a (1.3 μg/kg/day). Our findings demonstrated that captopril reduced the occurrence of epilepsy and cognitive impairment by attenuation of inflammation and C3-mediated synaptic phagocytosis. This approach can easily be adapted to long-term efficacy and safety in clinical practice.

Graphical Abstract

Association of antihypertensives during hospitalisation with acute respiratory failure in patients with viral pneumonia: A population-based case-control study

BACKGROUND

We aimed to identify associations between the risk of acute respiratory failure (ARF) and types of antihypertensive agents in patients with viral pneumonia.

METHODS

In this case-control study, data extracted from the Taiwan National Health Insurance Research Database were analysed. The base population comprised patients with viral pneumonia treated from 2000 to 2013. The case group comprised patients with ARF and the control group comprised participants without ARF. Adjusted odds ratios (ORs) were calculated using a multivariable logistic regression model.

RESULTS

In total, 4427 viral pneumonia patients with ARF and 4427 matched control participants without ARF were recruited. Patients with diabetes, alcohol-related disease, asthma, chronic kidney disease or end-stage renal disease, chronic obstructive pulmonary disease, cancer, congestive heart failure, stroke, acute pulmonary oedema and shock had increased odds of developing ARF, especially shock (adjusted OR = 49.3; 95% CI = 27.4, 88.7), cancer (12.6; 8.67, 18.2) and stroke (7.51; 5.32, 10.6). Increasing odds of developing ARF were noted in patients using potassium-sparing diuretics (2.95; 1.54, 5.64), loop diuretics (68.2; 48.1, 96.6), calcium channel blockers (1.64; 1.26, 2.13) and angiotensin-converting enzyme inhibitors (1.70; 1.15, 2.53). Patients with prescriptions of α-blockers (0.44; 0.26, 0.74), β-blockers (0.37; 0.26, 0.52), thiazides (0.38; 0.25, 0.59) and angiotensin receptor blockers (0.65; 0.51, 0.83) had lower odds of having ARF.

CONCLUSION

Patients with viral pneumonia who received α-blockers, β-blockers, thiazides or angiotensin receptor blockers during hospitalisation had a lower risk of developing ARF.

TLR4 and AT1R mediate blood-brain barrier disruption, neuroinflammation, and autonomic dysfunction in spontaneously hypertensive rats

Angiotensin II (AngII) is implicated in neuroinflammation, blood-brain barrier (BBB) disruption, and autonomic dysfunction in hypertension. We have previously shown that exogenous AngII stimulates Toll-like receptor 4 (TLR4) via AngII type 1 receptor (AT1R), inducing activation of hypothalamic microglia ex vivo, and that AngII-AT1R signaling is necessary for the loss of BBB integrity in spontaneously hypertensive rats (SHRs). Herein, we hypothesized that microglial TLR4 and AT1R signaling interactions represent a crucial mechanistic link between AngII-mediated neuroinflammation and BBB disruption, thereby contributing to sympathoexcitation in SHRs. Male SHRs were treated with TAK-242 (TLR4 inhibitor; 2 weeks), Losartan (AT1R inhibitor; 4 weeks), or vehicle, and age-matched to control Wistar Kyoto rats (WKYs). TLR4 and AT1R inhibitions normalized increased TLR4, interleukin-6, and tumor necrosis factor-α protein densities in SHR cardioregulatory nuclei (hypothalamic paraventricular nucleus [PVN], rostral ventrolateral medulla [RVLM], and nucleus tractus solitarius [NTS]), and abolished enhanced microglial activation. PVN, RVLM, and NTS BBB permeability analyses revealed complete restoration after TAK-242 treatment, whereas SHRs presented with elevated dye leakage. Mean arterial pressure was normalized in Losartan-treated SHRs, and attenuated with TLR4 inhibition. In conscious assessments, TLR4 blockade rescued SHR baroreflex sensitivity to vasoactive drugs, and reduced the SHR pressor response to ganglionic blockade to normal levels. These data suggest that TLR4 activation plays a substantial role in mediating a feed-forward pro-hypertensive cycle involving BBB disruption, neuroinflammation, and autonomic dysfunction, and that TLR4-specific therapeutic interventions may represent viable alternatives in the treatment of hypertension.

Inflammation: A Mediator Between Hypertension and Neurodegenerative Diseases

Hypertension is the most prevalent and modifiable risk factor for stroke, vascular cognitive impairment, and Alzheimer's disease. However, the mechanistic link between hypertension and neurodegenerative diseases remains to be understood. Recent evidence indicates that inflammation is a common pathophysiological trait for both hypertension and neurodegenerative diseases. Low-grade chronic inflammation at the systemic and central nervous system levels is now recognized to contribute to the physiopathology of hypertension. This review speculates that inflammation represents a mediator between hypertension and neurodegenerative diseases, either by a decrease in cerebral blood flow or a disruption of the blood-brain barrier which will, in turn, let inflammatory cells and neurotoxic molecules enter the brain parenchyma. This may impact brain functions including cognition and contribute to neurodegenerative diseases. This review will thus discuss the relationship between hypertension, systemic inflammation, cerebrovascular functions, neuroinflammation, and brain dysfunctions. The potential clinical future of immunotherapies against hypertension and associated cerebrovascular risks will also be presented.

Inflammation and Stroke Risk: A New Target for Prevention

New therapeutic approaches are required for secondary prevention of residual vascular risk after stroke. Diverse sources of evidence support a causal role for inflammation in the pathogenesis of stroke. Randomized controlled trials of anti-inflammatory agents have reported benefit for secondary prevention in patients with coronary disease. We review the data from observational studies supporting a role for inflammation in pathogenesis of stroke, overview randomized controlled trials of anti-inflammatory therapy in cardiac disease and discuss the potential implications for stroke prevention therapy.

Transcriptomic Analysis of Mouse Brain After Traumatic Brain Injury Reveals That the Angiotensin Receptor Blocker Candesartan Acts Through Novel Pathways

Traumatic brain injury (TBI) results in complex pathological reactions, where the initial lesion is followed by secondary inflammation and edema. Our laboratory and others have reported that angiotensin receptor blockers (ARBs) have efficacy in improving recovery from traumatic brain injury in mice. Treatment of mice with a subhypotensive dose of the ARB candesartan results in improved functional recovery, and reduced pathology (lesion volume, inflammation and gliosis). In order to gain a better understanding of the molecular mechanisms through which candesartan improves recovery after controlled cortical impact injury (CCI), we performed transcriptomic profiling on brain regions after injury and drug treatment. We examined RNA expression in the ipsilateral hippocampus, thalamus and hypothalamus at 3 or 29 days post injury (dpi) treated with either candesartan (0.1 mg/kg) or vehicle. RNA was isolated and analyzed by bulk mRNA-seq. Gene expression in injured and/or candesartan treated brain region was compared to that in sham vehicle treated mice in the same brain region to identify genes that were differentially expressed (DEGs) between groups. The most DEGs were expressed in the hippocampus at 3 dpi, and the number of DEGs reduced with distance and time from the lesion. Among pathways that were differentially expressed at 3 dpi after CCI, candesartan treatment altered genes involved in angiogenesis, interferon signaling, extracellular matrix regulation including integrins and chromosome maintenance and DNA replication. At 29 dpi, candesartan treatment reduced the expression of genes involved in the inflammatory response. Some changes in gene expression were confirmed in a separate cohort of animals by qPCR. Fewer DEGs were found in the thalamus, and only one in the hypothalamus at 3 dpi. Additionally, in the hippocampi of sham injured mice, 3 days of candesartan treatment led to the differential expression of 384 genes showing that candesartan in the absence of injury had a powerful impact on gene expression specifically in the hippocampus. Our results suggest that candesartan has broad actions in the brain after injury and affects different processes at acute and chronic times after injury. These data should assist in elucidating the beneficial effect of candesartan on recovery from TBI.

Systemic Candesartan Treatment Modulates Behavior, Synaptic Protein Levels, and Neuroinflammation in Female Mice That Express Human APOE4

Evidence suggests that angiotensin receptor blockers (ARBs) could be beneficial for Alzheimer’s disease (AD) patients independent of any effects on hypertension. However, studies in rodent models directly testing the activity of ARB treatment on behavior and AD-relevent pathology including neuroinflammation, Aβ levels, and cerebrovascular function, have produced mixed results. APOE4 is a major genetic risk factor for AD and has been linked to many of the same functions as those purported to be modulated by ARB treatment. Therefore, evaluating the effects of ARB treatment on behavior and AD-relevant pathology in mice that express human APOE4 could provide important information on whether to further develop ARBs for AD therapy. In this study, we treated female and male mice that express the human APOE4 gene in the absence (E4FAD−) or presence (E4FAD+) of high Aβ levels with the ARB prodrug candesartan cilexetil for a duration of 4 months. Compared to vehicle, candesartan treatment resulted in greater memory-relevant behavior and higher hippocampal presynaptic protein levels in female, but not male, E4FAD− and E4FAD+ mice. The beneficial effects of candesartan in female E4FAD− and E4FAD+ mice occurred in tandem with lower GFAP and Iba1 levels in the hippocampus, whereas there were no effects on markers of cerebrovascular function and Aβ levels. Collectively, these data imply that the effects of ARBs on AD-relevant pathology may be modulated in part by the interaction between APOE genotype and biological sex. Thus, the further development of ARBs could provide therapeutic options for targeting neuroinflammation in female APOE4 carriers.

Candesartan modulates microglia activation and polarization via NF-κB signaling pathway

Microglia are diverse cells that acquire different functional phenotypes in response to microenvironment in which they reside. Several transcriptional regulators have been identified that regulate different microglia phenotypes. They are mainly stimulated into two opposing phenotypes, classically (M1) and alternatively (M2) phenotype. Regulating microglia polarization from M1 to M2 state has been suggested as a potential therapeutic approach in treatment of CNS disorders. Candesartan, an angiotensin II type I receptors antagonist, exerts beneficial effects for antioxidant, anti-inflammation, neurotrophic, and anti-apoptotic function. However, the effect of candesartan on microglia polarization and underlying mechanisms remain unknown. In this study, the resting microglia were stimulated to M1 microglia with lipopolysaccharide (LPS) and interferon-γ (IFN-γ), and then treated with vehicle or candesartan for 24 h. RT-PCR was utilized to detect the mRNA expression of microglia phenotype markers and inflammatory cytokines. Microglia phenotype markers and toll-like receptor 4 (TLR4)/nuclear factor kappa B (NF-κB) pathway were determined by western blot. A neuron-microglia co-culture system was used to determine whether candesartan could ameliorate the neurotoxic effect of M1 microglia to oxygen-glucose deprivation (OGD) neuron. Candesartan treatment reduced the expression of M1 markers, and increased M2 markers. Meanwhile, candesartan reduced fluorescence intensity and protein level of M1 marker and enhanced M2 marker. Candesartan also regulated the neuroinflammatory response via reducing the release of pro-inflammatory cytokines and increasing anti-inflammatory cytokines in LPS + IFN-γ stimulated BV2 cells. Candesartan markedly inhibited the protein level of TLR4, the phosphorylation of IKBα and p65, and suppressed nuclear translocation of NF-κB p65. BAY 11-7085, a NF-κB inhibitor, remarkably enlarged the inhibitory effect of candesartan on NF-κB pathway. In addition, M1 phenotype microglia exacerbated post-OGD N2a cells death and LDH release, whereas candesartan reversed such neurotoxic effect. Candesartan treatment may ameliorate stroke-induced neuronal damage through shifting microglia to M2 phenotype in a TLR4/NF-κB-dependent manner.

Association between angiotensin receptor blockers and suicide: nationwide population-based propensity score matching study

BACKGROUND

Angiotensin receptor blockers (ARBs) have been reported to ameliorate anxiety and mood disorders in animal models. Cohort links between ARB use and suicide risk in humans require clarification.

METHODS

Data were obtained from the National Health Insurance Research Database. Patients diagnosed as having hypertension according to the criteria of the International Classification of Diseases, Ninth Revision, Clinical Modification (401-405) from January 1, 2000 to December 31, 2012 were enrolled as the target population. We defined enrollees who had received ARB prescriptions for at least 28 days as ARB users. Those who had never taken ARB prior or during the study period were defined as ARB nonusers and were propensity score-matched with ARB users. The end outcome was confirmation of a suicide attempt.

RESULTS

After propensity score matching was conducted, 40,976 ARB users and 40,976 nonusers were selected as the matched cohorts. The overall incidence rate of suicide attempt was significantly lower in ARB users than in nonusers (0.51 vs. 1.07 per 10,000 person-years; adjusted hazard ratio = 0.48, 95% confidence interval = 0.26-0.87). A Kaplan-Meier survival analysis with a log-rank test revealed a lower cumulative incidence of suicide attempt in ARB users than in nonusers (p < 0.001 for the unmatched cohort; p = 0.01 for the matched cohort).

CONCLUSIONS

ARB use was not associated with an increased risk for suicide compared with non-ARB use.

Increased levels of angiotensin II type 1 receptor autoantibodies in female infertility

In this study, the level of serum anti-angiotensin II type 1 receptor autoantibodies (AT1-AA) was determined. It was found that the positive rate of AT1-AA in serum of infertile women is higher than that of healthy non-pregnant women. Spearman correlation analysis showed that AT1-AA was negatively correlated with oocyte maturation rate (r = -0.29, P < 0.01) and AT1-AA was positively correlated with IL-6 (r = 0.68, P < 0.01). Logistic regression analysis showed that age, BMI, type of infertility, years of infertility, history of poor pregnancy outcome, condition of fallopian tube, and polycystic ovary syndrome were not factors influencing the level of AT1-AA in the serum of infertile patients. The results indicated that AT1-AA was involved in the pathological changes of infertile women. AT1-AA may be related to oocyte maturation disorder, ovulation disorder. Interestingly it appears to induce an inflammatory reaction, although the specific mechanism is not clear. However, the level of AT1-AA is not affected by individual differences in infertile patients.Abbreviations: E₂:estradiol; P:progesterone; RAS:Renin-angiotensin system; Ovras:renin-angiotensin system; ACE1:angiotensin-converting enzyme-1; AngII:angiotensin II; AT1R:Angiotensin II type 1 Receptor; BMI:Body Mass Index; AT1-A:anti-angiotensin II type 1 receptor autoantibodies.

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.

The role of the brain renin-angiotensin system (RAS) in mild traumatic brain injury (TBI)

There is considerable interest in traumatic brain injury (TBI) induced by repeated concussions suffered by athletes in sports, military personnel from combat-and non-combat related activities, and civilian populations who suffer head injuries from accidents and domestic violence. Although the renin-angiotensin system (RAS) is primarily a systemic cardiovascular regulatory system that, when dysregulated, causes hypertension and cardiovascular pathology, the brain contains a local RAS that plays a critical role in the pathophysiology of several neurodegenerative diseases. This local RAS includes receptors for angiotensin (Ang) II within the brain parenchyma, as well as on circumventricular organs outside the blood-brain-barrier. The brain RAS acts primarily via the type 1 Ang II receptor (AT₁R), exacerbating insults and pathology. With TBI, the brain RAS may contribute to permanent brain damage, especially when a second TBI occurs before the brain recovers from an initial injury. Agents are needed that minimize the extent of injury from an acute TBI, reducing TBI-mediated permanent brain damage. This review discusses how activation of the brain RAS following TBI contributes to this damage, and how drugs that counteract activation of the AT₁R including AT₁R blockers (ARBs), renin inhibitors, angiotensin-converting enzyme (ACE) inhibitors, and agonists at type 2 Ang II receptors (AT₂) and at Ang (1-7) receptors (Mas) can potentially ameliorate TBI-induced brain damage.

Adiponectin: The Potential Regulator and Therapeutic Target of Obesity and Alzheimer's Disease

Animal and human mechanistic studies have consistently shown an association between obesity and Alzheimer’s disease (AD). AD, a degenerative brain disease, is the most common cause of dementia and is characterized by the presence of extracellular amyloid beta (Aβ) plaques and intracellular neurofibrillary tangles disposition. Some studies have recently demonstrated that Aβ and tau cannot fully explain the pathophysiological development of AD and that metabolic disease factors, such as insulin, adiponectin, and antioxidants, are important for the sporadic onset of nongenetic AD. Obesity prevention and treatment can be an efficacious and safe approach to AD prevention. Adiponectin is a benign adipokine that sensitizes the insulin receptor signaling pathway and suppresses inflammation. It has been shown to be inversely correlated with adipose tissue dysfunction and may enhance the risk of AD because a range of neuroprotection adiponectin mechanisms is related to AD pathology alleviation. In this study, we summarize the recent progress that addresses the beneficial effects and potential mechanisms of adiponectin in AD. Furthermore, we review recent studies on the diverse medications of adiponectin that could possibly be related to AD treatment, with a focus on their association with adiponectin. A better understanding of the neuroprotection roles of adiponectin will help clarify the precise underlying mechanism of AD development and progression.

Interactions of the Brain Renin-Angiotensin-System (RAS) and Inflammation in the Sensitization of Hypertension

Mounting evidence indicates that the renin-angiotensin (RAS) and immune systems interact with one another in the central nervous system (CNS) and that they are importantly involved in the pathogenesis of hypertension. Components comprising the classic RAS were first identified in the periphery, and subsequently, similar factors were found to be generated de novo in many different organs including the brain. There is humoral-neural coupling between the systemic and brain RASs, which is important for controlling sympathetic tone and the release of endocrine factors that collectively determine blood pressure (BP). Similar to the interactions between the systemic and brain RASs is the communication between the peripheral and brain immune systems. Systemic inflammation activates the brain’s immune response. Importantly, the RAS and inflammatory factors act synergistically in brain regions involved in the regulation of BP. This review presents evidence of how such interactions between the brain RAS and central immune mechanisms contribute to the pathogenesis of hypertension. Emphasis focuses on the role of these interactions to induce neuroplastic changes in a central neural network resulting in hypertensive response sensitization (HTRS). Neuroplasticity and HTRS can be induced by challenges (stressors) presented earlier in life such as a low-dose of angiotensin II or high fat diet (HFD) feeding in adults. Similarly, the offspring of mothers with gestational hypertension or of mothers ingesting a HFD during pregnancy are reprogrammed and manifest HTRS when exposed to new stressors as adults. Consideration of the actions and interactions of the brain RAS and inflammatory mediators in the context of the induction and expression of HTRS will provide insights into the etiology of high BP that may lead to new strategies for the prevention and treatment of hypertension.

Microglia mediated neuroinflammation - signaling regulation and therapeutic considerations with special reference to some natural compounds

Neuroinflammation plays a central role in multiple neurodegenerative diseases and neurological disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), cerebral ischemic injury etc. In this connection, microglia, the key players in the central nervous system, mediate the inflammatory response process. In brain injuries, activated microglia can clear the cellular debris and invading pathogens and release neurotrophic factors; however, prolonged microglia activation may cause neuronal death through excessive release of inflammatory mediators. Therefore, it is of paramount importance to understand the underlying molecular mechanisms of microglia activation to design an effective therapeutic strategy to alleviate neuronal injury. Recent studies have shown that some natural compounds and herbal extracts possess anti-inflammatory properties that may suppress microglial activation and ameliorate neuroinflammation and hence are neuroprotective. In this review, we will update some of the common signaling pathways that regulate microglia activation. Among the various signaling pathways, the Notch-1, mitogen-activated protein kinases (MAPKs), and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) have been reported to exacerbate microglia mediated neuroinflammation that is implicated in different neuropathological diseases. The search for natural compounds or agents, specifically those derived from natural herbal extracts such as Gastrodin, scutellarin, RG1 etc. has been the focus of many of our recent studies because they have been found to regulate microglia activation. The pharmacological effects of these agents and their potential mechanisms for regulating microglia activation are systematically reviewed here for a fuller understanding of their biochemical action and therapeutic potential for treatment of microglia mediated neuropathological diseases.

Renin-Angiotensin System in Lung Tumor and Microenvironment Interactions

The mechanistic involvement of the renin-angiotensin system (RAS) reaches beyond cardiovascular physiopathology. Recent knowledge pinpoints a pleiotropic role for this system, particularly in the lung, and mainly through locally regulated alternative molecules and secondary pathways. Angiotensin peptides play a role in cell proliferation, immunoinflammatory response, hypoxia and angiogenesis, which are critical biological processes in lung cancer. This manuscript reviews the literature supporting a role for the renin-angiotensin system in the lung tumor microenvironment and discusses whether blockade of this pathway in clinical settings may serve as an adjuvant therapy in lung cancer.

Candesartan Neuroprotection in Rat Primary Neurons Negatively Correlates with Aging and Senescence: a Transcriptomic Analysis

Preclinical experiments and clinical trials demonstrated that angiotensin II AT₁ receptor overactivity associates with aging and cellular senescence and that AT₁ receptor blockers (ARBs) protect from age-related brain disorders. In a primary neuronal culture submitted to glutamate excitotoxicity, gene set enrichment analysis (GSEA) revealed expression of several hundred genes altered by glutamate and normalized by candesartan correlated with changes in expression in Alzheimer's patient's hippocampus. To further establish whether our data correlated with gene expression alterations associated with aging and senescence, we compared our global transcriptional data with additional published datasets, including alterations in gene expression in the neocortex and cerebellum of old mice, human frontal cortex after age of 40, gene alterations in the Werner syndrome, rodent caloric restriction, Ras and oncogene-induced senescence in fibroblasts, and to tissues besides the brain such as the muscle and kidney. The most significant and enriched pathways associated with aging and senescence were positively correlated with alterations in gene expression in glutamate-injured neurons and, conversely, negatively correlated when the injured neurons were treated with candesartan. Our results involve multiple genes and pathways, including CAV1, CCND1, CDKN1A, CHEK1, ICAM1, IL-1B, IL-6, MAPK14, PTGS2, SERPINE1, and TP53, encoding proteins associated with aging and senescence hallmarks, such as inflammation, oxidative stress, cell cycle and mitochondrial function alterations, insulin resistance, genomic instability including telomere shortening and DNA damage, and the senescent-associated secretory phenotype. Our results demonstrate that AT₁ receptor blockade ameliorates central mechanisms of aging and senescence. Using ARBs for prevention and treatment of age-related disorders has important translational value.

The effects of captopril on lipopolysaccharide-induced sickness behaviors in rats

Neuro-immune mediators play an important role in the development of sickness behaviors. In the present study, the effect of captopril on sickness behaviors caused by lipopolysaccharide (LPS) was studied in the rats. The animals were randomized into the following groups: control, sham, 10 mg kg^-1 captopril - LPS (Capto 10-LPS), 50 mg kg^-1 captopril - LPS (Capto 50-LPS), and 100 mg kg^-1 captopril - LPS (Capto 100-LPS). Behavioral tests including open-field (OF), elevated plus maze (EPM) and forced swimming (FS) test were performed, and the serum level of interleukin-6 (IL-6) was assessed. In OF, the number of crossings in the central zone in Capto 10-LPS, Capto 50-LPS, and Capto 100-LPS groups was higher than that of the sham group. In EPM, the open arm entry numbers in the sham group were lower compared to the control group. Furthermore, pretreatment by captopril increased the entries to the open arms. In FS test, the immobility time of the sham group was longer than that of the control group. In Capto 10-LPS, Capto 50-LPS, and Capto 100-LPS groups, immobility was shorter compared to the sham group. In addition, the IL-6 level was higher in the sham group compared to the control group, and treatment with 50 and 100 mg kg^-1 of captopril restored the IL-6 level in comparison with the sham group. Results confirmed that pretreatment with captopril ameliorated LPS-caused sickness behaviors and attenuated IL-6 as an inflammatory marker in the rats.

Neuroinflammation in hypertension: the renin-angiotensin system versus pro-resolution pathways

Overstimulation of the pro-inflammatory pathways within brain areas responsible for sympathetic outflow is well evidenced as a primary contributing factor to the establishment and maintenance of neurogenic hypertension. However, the precise mechanisms and stimuli responsible for promoting a pro-inflammatory state are not fully elucidated. Recent work has unveiled novel compounds derived from omega-3 polyunsaturated fatty acids (ω-3 PUFAs), termed specialized pro-resolving mediators (SPMs), which actively regulate the resolution of inflammation. Failure or dysregulation of the resolution process has been linked to a variety of chronic inflammatory and neurodegenerative diseases. Given the pathologic role of neuroinflammation in the hypertensive state, SPMs and their associated pathways may provide a link between hypertension and the long-standing association of dietary ω-3 PUFAs with cardioprotection. Herein, we review recent progress in understanding the RAS-driven pathophysiology of neurogenic hypertension, particularly in regards to the chronic low-grade neuroinflammatory response. In addition, we examine the potential for an impaired resolution of inflammation process in the context of hypertension.

Microglia and brain angiotensin type 1 receptors are involved in desensitising baroreflex by intracerebroventricular hypertonic saline in male Sprague-Dawley rats

High salt diet alters cardiovascular control by increasing concentration of sodium ions (Na⁺) in cerebrospinal fluid (CSF) and is a risk factor for hypertension. Hypernatremic conditions activate microglia and upregulate renin-angiotensin system in the brain. Thus, we checked if chronic elevation of CSF Na⁺ affects neural control of circulatory system via microglia and brain angiotensin type 1 receptors (AT1Rs). Normotensive adult male Sprague-Dawley rats received two-week intracerebroventricular (ICV) infusion of either isoosmotic saline (0.9% NaCl); hyperosmotic saline (5% NaCl); 5% NaCl with minocycline - inhibitor of microglia; 5% NaCl with losartan - AT1R blocker. Fluid intake, urine output, and urinary Na⁺ excretion were measured before and during ICV infusions. At the end of ICV infusions, blood pressure and heart rate were recorded in awake rats at rest, in response to acute air jet stressor, during pharmacological evaluation of baroreflex, and after autonomic ganglia blockade. CSF and blood were collected for evaluation of Na⁺ concentration. Baroreflex was blunted in rats ICV infused with 5% NaCl. ICV treatment with losartan or minocycline prevented decrease in baroreflex sensitivity. Hemodynamic parameters at rest, in response to acute stressor and autonomic ganglia blockade were similar in all groups. Neither treatment affected water intake, urine output and urinary Na⁺ excretion. ICV infusion of 5% NaCl resulted in higher concentration of Na⁺ in CSF than in control group (0.9% NaCl) and in plasma. Our results indicate that chronic ICV infusion of hyperosmotic saline blunts baroreflex in normotensive rats and this desensitization is mediated by microglia and AT1Rs.

Targeting toll-like receptor 4 signalling pathways: can therapeutics pay the toll for hypertension?

The immune system plays a prominent role in the initiation and maintenance of hypertension. The innate immune system, via toll-like receptors (TLRs), identifies distinct signatures of invading microbes and damage-associated molecular patterns and triggers a chain of downstream signalling cascades, leading to secretion of pro-inflammatory cytokines and shaping the adaptive immune response. Over the past decade, a dysfunctional TLR-mediated response, particularly via TLR4, has been suggested to support a chronic inflammatory state in hypertension, inducing deleterious local and systemic effects in host cells and tissues and contributing to disease progression. While the underlying mechanisms triggering TLR4 need further research, evidence suggests that sustained elevations in BP disrupt homeostasis, releasing endogenous TLR4 ligands in hypertension. In this review, we discuss the emerging role of TLR4 in the pathogenesis of hypertension and whether targeting this receptor and its signalling pathways could offer a therapeutic strategy for management of this multifaceted disease. LINKED ARTICLES: This article is part of a themed section on Immune Targets in Hypertension. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.12/issuetoc.

Gastrodin attenuates microglia activation through renin-angiotensin system and Sirtuin3 pathway

Microglia activation and its mediated production of proinflammatory mediators play important roles in different neurodegenerative diseases; hence, modulation of microglia activation has been considered a potential therapeutic strategy to ameliorate neurodegeneration. This study was aimed to determine whether Gastrodin, a common herbal agent known to possess neuroprotective property, can attenuate production of proinflammatory mediators in activated microglia through the renin-angiotensin system (RAS) and Sirtuin3 (SIRT3). Expression of various members of the RAS including ACE, AT₁, AT_2, and SIRT3 in activated microglia was assessed by immunofluorescence and Western blot in hypoxic-ischemia brain damage (HIBD) in postnatal rats, and in BV-2 microglia in vitro challenged with lipopolysaccharide (LPS) with or without Gastrodin treatment. Expression of NOX-2, a subunit of NADPH oxidase, and proinflammatory mediators including iNOS and TNF-α, was also evaluated. The present results showed that expression of ACE, AT₁, NOX-2, iNOS and TNF-α was markedly increased in activated microglia in the corpus callosum of HIBD rats, and in LPS stimulated BV-2 microglia. Remarkably, the expression was markedly attenuated following Gastrodin treatment. Conversely, Gastrodin enhanced AT₂ and SIRT3 protein expression. In BV-2 microglia treated with Azilsartan, a specific inhibitor of AT₁ (AT₁I group), NOX-2 expression was decreased whereas that of SIRT3 in LPS + AT₁I and LPS + Gastrodin group was increased when compared with the controls. In LPS + AT₁I + Gastrodin group, SIRT3 expression was further augmented. More importantly, Gastrodin effectively reduced caspase 3 protein expression level in the HIBD rats coupled with a significant decrease in caspase 3 positive cells. We conclude that Gastrodin can exert its protective effects against the hypoxic-ischemia brain damage in the present experimental HIBD model. It is suggested that this is mainly through suppression of expression of RAS (except for AT₂ and SIRT3) and proinflammatory mediators e.g. TNF-α in activated microglia.

Azilsartan as "Add-On" Treatment with Methotrexate Improves the Disease Activity of Rheumatoid Arthritis

Objective

The present study aimed to evaluate the efficacy and safety of azilsartan (Azil) as “add-on” treatment with methotrexate (MTX) in patients with active rheumatoid arthritis (RA).

Methods

This single center, randomized, placebo-controlled, double-blind, pilot study included 64 patients with active RA. Patients received either placebo or Azil in addition to their currently used MTX doses for 90 days. The primary outcomes were DAS-28, SDAI, HAQ-DI, CDAI, EGA, and swollen and tender joints count. The secondary outcomes were the changes in the pain visual analogue scale (VAS-100), serum levels of TNF-α, IL-1β, IL-6, and anti-CCP, the lipid profile, and the markers of kidney and liver functions in the two groups at baseline and after 90 days.

Results

After 90 days, most clinical scores were significantly better in the Azil-treated group than in the placebo group. All inflammatory biomarkers were significantly improved after treatment with MTX + Azil compared to baseline and placebo group. No safety concerns were reported during the study period.

Conclusions

Azilsartan improved the effects of methotrexate on the clinical scores and certain inflammatory biomarkers of patients with active RA.

Trial Registration

The protocol was registered under the number 507/SA/1024 at the local clinical studies database, College of Medicine, Sulaimani University.

Molecular Basis of the Brain Renin Angiotensin System in Cardiovascular and Neurologic Disorders: Uncovering a Key Role for the Astroglial Angiotensin Type 1 Receptor AT1R

The central renin angiotensin system (RAS) is one of the most widely investigated cardiovascular systems in the brain. It is implicated in a myriad of cardiovascular diseases. However, studies from the last decade have identified its involvement in several neurologic abnormalities. Understanding the molecular functionality of the various RAS components can thus provide considerable insight into the phenotypic differences and mechanistic drivers of not just cardiovascular but also neurologic disorders. Since activation of one of its primary receptors, the angiotensin type 1 receptor (AT1R), results in an augmentation of oxidative stress and inflammatory cytokines, it becomes essential to investigate not just neuronal RAS but glial RAS as well. Glial cells are key homeostatic regulators in the brain and are critical players in the resolution of overt oxidative stress and neuroinflammation. Designing better and effective therapeutic strategies that target the brain RAS could well hinge on understanding the molecular basis of both neuronal and glial RAS. This review provides a comprehensive overview of the major studies that have investigated the mechanisms and regulation of the brain RAS, and it also provides insight into the potential role of glial AT1Rs in the pathophysiology of cardiovascular and neurologic disorders.

Targeting Renin-Angiotensin System Against Alzheimer's Disease

Renin Angiotensin System (RAS) is a hormonal system that regulates blood pressure and fluid balance through a coordinated action of renal, cardiovascular, and central nervous systems. In addition to its hemodynamic regulatory role, RAS involves in many brain activities, including memory acquisition and consolidation. This review has summarized the involvement of RAS in the pathology of Alzheimer’s disease (AD), and the outcomes of treatment with RAS inhibitors. We have discussed the effect of brain RAS in the amyloid plaque (Aβ) deposition, oxidative stress, neuroinflammation, and vascular pathology which are directly and indirectly associated with AD. Angiotensin II (AngII) via AT1 receptor is reported to increase brain Aβ level via different mechanisms including increasing amyloid precursor protein (APP) mRNA, β-secretase activity, and presenilin expression. Similarly, it was associated with tau phosphorylation, and reactive oxygen species generation. However, these effects are counterbalanced by Ang II mediated AT2 signaling. The protective effect observed with angiotensin receptor blockers (ARBs) and angiotensin converting enzyme inhibitors (ACEIs) could be as the result of inhibition of Ang II signaling. ARBs also offer additional benefit by shifting the effect of Ang II toward AT2 receptor. To conclude, targeting RAS in the brain may benefit patients with AD though it still requires further in depth understanding.

Candesartan ameliorates brain inflammation associated with Alzheimer's disease

AIMS

Alzheimer's disease (AD) pathology is associated with brain inflammation involving microglia and astrocytes. The renin-angiotensin system contributes to brain inflammation associated with AD pathology. This study aimed to investigate the role of candesartan, an angiotensin II type 1 receptor blocker, in modulation of glial functions associated with AD.

METHODS

Focusing on the role of candesartan in glial inflammation, we evaluated inflammatory mediators' levels, secreted by lipopolysaccharide-induced microglia following candesartan treatment. Also, short-term intranasal candesartan effects on amyloid burden and microglial activation were investigated in 5 familial AD mice.

RESULTS

Candesartan showed anti-inflammatory effects and shifted microglial activation toward a more neuroprotective phenotype. Candesartan decreased the lipopolysaccharide-induced nitric oxide synthase and cyclooxygenase-2 expression levels, which was accompanied by an induction of arginase-1 expression levels and enhanced Aβ_1-42 uptake by microglia. Moreover, intranasally administered candesartan to AD mice model significantly reduced the amyloid burden and microglia activation in the hippocampus.

CONCLUSIONS

These results thus shed light on the neuroprotective role of candesartan in the early stage of AD, which might relate to modulation of microglial activation states.

Brain Renin-Angiotensin System and Microglial Polarization: Implications for Aging and Neurodegeneration

Microglia can transform into proinflammatory/classically activated (M1) or anti-inflammatory/alternatively activated (M2) phenotypes following environmental signals related to physiological conditions or brain lesions. An adequate transition from the M1 (proinflammatory) to M2 (immunoregulatory) phenotype is necessary to counteract brain damage. Several factors involved in microglial polarization have already been identified. However, the effects of the brain renin-angiotensin system (RAS) on microglial polarization are less known. It is well known that there is a “classical” circulating RAS; however, a second RAS (local or tissue RAS) has been observed in many tissues, including brain. The locally formed angiotensin is involved in local pathological changes of these tissues and modulates immune cells, which are equipped with all the components of the RAS. There are also recent data showing that brain RAS plays a major role in microglial polarization. Level of microglial NADPH-oxidase (Nox) activation is a major regulator of the shift between M1/proinflammatory and M2/immunoregulatory microglial phenotypes so that Nox activation promotes the proinflammatory and inhibits the immunoregulatory phenotype. Angiotensin II (Ang II), via its type 1 receptor (AT1), is a major activator of the NADPH-oxidase complex, leading to pro-oxidative and pro-inflammatory effects. However, these effects are counteracted by a RAS opposite arm constituted by Angiotensin II/AT2 receptor signaling and Angiotensin 1–7/Mas receptor (MasR) signaling. In addition, activation of prorenin-renin receptors may contribute to activation of the proinflammatory phenotype. Aged brains showed upregulation of AT1 and downregulation of AT2 receptor expression, which may contribute to a pro-oxidative pro-inflammatory state and the increase in neuron vulnerability. Several recent studies have shown interactions between the brain RAS and different factors involved in microglial polarization, such as estrogens, Rho kinase (ROCK), insulin-like growth factor-1 (IGF-1), tumor necrosis factor α (TNF)-α, iron, peroxisome proliferator-activated receptor gamma, and toll-like receptors (TLRs). Metabolic reprogramming has recently been involved in the regulation of the neuroinflammatory response. Interestingly, we have recently observed a mitochondrial RAS, which is altered in aged brains. In conclusion, dysregulation of brain RAS plays a major role in aging-related changes and neurodegeneration by exacerbation of oxidative stress (OS) and neuroinflammation, which may be attenuated by pharmacological manipulation of RAS components.

The interplay between Angiotensin II, TLR4 and hypertension

Hypertension is a multifactorial disease. Although a number of different underlying mechanisms have been learned from the various experimental models of the disease, hypertension still poses challenges for treatment. Angiotensin II plays an unquestionable role in blood pressure regulation acting through central and peripheral mechanisms. During hypertension, dysregulation of the Renin-Angiotensin System is associated with increased expression of pro-inflammatory cytokines and reactive oxygen species causing kidney damage, endothelial dysfunction, and increase in sympathetic activity, among other damages, eventually leading to decline in organ function. Recent studies have shown that these effects involve both the innate and the adaptive immune response. The contribution of adaptive immune responses involving different lymphocyte populations in various models of hypertension has been extensively studied. However, the involvement of the innate immunity mediating inflammation in hypertension is still not well understood. The innate and adaptive immune systems intimately interact with one another and are essential to an effectively functioning of the immune response; hence, the importance of a better understanding of the underlying mechanisms mediating innate immune system during hypertension. In this review, we aim to discuss mechanisms linking Angiotensin II and the innate immune system, in the pathogenesis of hypertension. The newest research investigating Angiotensin II triggering toll like receptor 4 activation in the kidney, vasculature and central nervous system contributing to hypertension will be discussed. Understanding the role of the innate immune system in the development of hypertension may bring to light new insights necessary to improve hypertension management.

Compromised blood-brain barrier permeability: novel mechanism by which circulating angiotensin II signals to sympathoexcitatory centres during hypertension

Angiotensin II (AngII) is a pivotal peptide implicated in the regulation of blood pressure. In addition to its systemic vascular and renal effects, AngII acts centrally to modulate the activities of neuroendocrine and sympathetic neuronal networks, influencing in turn sympatho-humoral outflows to the circulation. Moreover, a large body of evidence supports AngII signalling dysregulation as a key mechanism contributing to exacerbated sympathoexcitation during hypertension. Due to its hydrophilic actions, circulating AngII does not cross the blood-brain barrier (BBB), signalling to the brain via the circumventricular organs which lack a tight BBB. In this review, we present and discuss recent studies from our laboratory showing that elevated circulating levels of AngII during hypertension result in disruption of the BBB integrity, allowing access of circulating AngII to critical sympathoexcitatory brain centres such as the paraventricular nucleus of the hypothalamus and the rostral ventrolateral medulla. We propose the novel hypothesis that AngII-driven BBB breakdown constitutes a complementary mechanism by which circulating AngII, working in tandem with the central renin-angiotensin system, further exacerbates sympatho-humoral activation during hypertension. These results are discussed within the context of a growing body of evidence in the literature supporting AngII as a pro-inflammatory signal, and brain microglia as key cell targets mediating central AngII actions during hypertension.

Primary hypertension is a disease of premature vascular aging associated with neuro-immuno-metabolic abnormalities

There is an increasing amount of data indicating that primary hypertension (PH) is not only a hemodynamic phenomenon but also a complex syndrome involving abnormal fat tissue distribution, over-activity of the sympathetic nervous system (SNS), metabolic abnormalities, and activation of the immune system. In children, PH usually presents with a typical phenotype of disturbed body composition, accelerated biological maturity, and subtle immunological and metabolic abnormalities. This stage of the disease is potentially reversible. However, long-lasting over-activity of the SNS and immuno-metabolic alterations usually lead to an irreversible stage of cardiovascular disease. We describe an intermediate phenotype of children with PH, showing that PH is associated with accelerated development, i.e., early premature aging of the immune, metabolic, and vascular systems. The associations and determinants of hypertensive organ damage, the principles of treatment, and the possibility of rejuvenation of the cardiovascular system are discussed.