Angiotensin type 2 receptor in hypertensive cardiovascular disease

Impairment of microvascular endothelial Kir2.1 channels contributes to endothelial dysfunction in human hypertension

Hypertension is associated with decreased endothelial function through reduced contributions of nitric oxide (NO). We previously discovered that flow-induced NO production in resistance arteries of mice and humans critically depends on endothelial inwardly rectifying K+ (Kir2.1) channels. The goal of this study was to establish whether these channels contribute to the impairment of endothelial function, measured by flow-induced vasodilation (FIV) in peripheral resistance arteries of humans with hypertension. We measured FIV in vessels isolated from subcutaneous fat biopsies from 32 subjects: normotensive [n = 19; 30.6 ± 9.8 yr old; systolic blood pressure (SBP): 115.2 ± 7 mmHg; diastolic blood pressure (DBP): 75.3 ± 5.7 mmHg] and hypertensive (n = 13; 45.3 ± 15.3 yr old; SBP: 146.1 ± 15.2 mmHg; DBP: 94.4 ± 6.9 mmHg). Consistent with previous studies, we find that FIV is impaired in hypertensive adults as demonstrated by a significant reduction in FIV when compared with the normotensive adults. Furthermore, our data suggest that the impairment of FIV in hypertensive adults is partially attributed to a reduction in Kir2.1-dependent vasodilation. Specifically, we show that blocking Kir2.1 with ML133 or functionally downregulating Kir2.1 with endothelial-specific adenoviral vector containing dominant-negative Kir2.1 (dnKir2.1) result in a significant reduction in FIV in normotensive subjects but with a smaller effect in hypertensive adults. The Kir2.1-dependent vasodilation was negatively correlated to both SBP and DBP, indicating that the Kir2.1 contribution to FIV decreases as blood pressure increases. In addition, we show that exposing vessels from normotensive adults to acute high-pressure results in loss of Kir2.1 contribution, as high pressure impairs vasodilation. No effect is seen when these vessels were incubated with dnKir2.1. Overexpressing wtKir2.1 in the endothelium resulted in some improvement in vasodilation in arteries from all participants, with a greater recovery in hypertensive adults. Our data suggest that hypertension-induced suppression of Kir2.1 is an important mechanism underlying endothelial dysfunction in hypertension.NEW & NOTEWORTHY Impairment of endothelial function under high blood pressure is linked to the loss of inwardly rectifying K+ (Kir2.1) channels activity in human resistance arteries, leading to a reduction in flow-induced vasodilation and possibly leading to a vicious cycle between elevation of blood pressure, and further impairment of Kir2.1 function and flow-induced vasodilation.

Differential changes in end organ immune cells and inflammation in salt-sensitive hypertension: effects of increasing M2 macrophages

Salt-sensitive hypertension (SSHTN) is associated with M1 macrophage polarization and inflammatory responses, leading to inflammation-associated lymphangiogenesis and functional impairment across multiple organs, including kidneys and gonads. However, it remains unclear whether promoting M2 macrophage polarization can alleviate the hypertension, inflammation, and end organ damage in mice with salt sensitive hypertension (SSHTN). Male and female mice were made hypertensive by administering nitro-L-arginine methyl ester hydrochloride (L-NAME; 0.5 mg/ml) for 2 weeks in the drinking water, followed by a 2-week interval without any treatments, and a subsequent high salt diet for 3 weeks (SSHTN). AVE0991 (AVE) was intraperitoneally administered concurrently with the high salt diet. Control mice were provided standard diet and tap water. AVE treatment significantly attenuated BP and inflammation in mice with SSHTN. Notably, AVE promoted M2 macrophage polarization, decreased pro-inflammatory immune cell populations, and improved function in renal and gonadal tissues of mice with SSHTN. Additionally, AVE decreased lymphangiogenesis in the kidneys and testes of male SSHTN mice and the ovaries of female SSHTN mice. These findings highlight the effectiveness of AVE in mitigating SSHTN-induced elevated BP, inflammation, and end organ damage by promoting M2 macrophage polarization and suppressing pro-inflammatory immune responses. Targeting macrophage polarization emerges as a promising therapeutic approach for alleviating inflammation and organ damage in SSHTN. Further studies are warranted to elucidate the precise mechanisms underlying AVE-mediated effects and to assess its clinical potential in managing SSHTN.

Tolerability of Antihypertensive Medications: The Influence of Age

INTRODUCTION

Despite high prevalence of hypertension, few studies have analysed the adverse effects (AEs) of antihypertensive medications, especially in older patients.

AIM

To investigate the prevalence and associated factors of antihypertensive-related AEs, focusing on the influence of age on treatment tolerability.

METHODS

We retrospectively investigated antihypertensive-related AEs in patients evaluated at the Hypertension Clinic of Careggi Hospital, Florence, Italy, between January 2017 and July 2020. Multivariable regression models were generated to analyse variables associated with AEs in the overall sample and in participants ≥75 years.

RESULTS

Among 622 subjects (mean age 64.8 years, 51.4% female), the most frequently reported AEs were calcium-channel blockers (CCB)-related ankle swelling (26.8%) and ACEi-induced cough (15.1%). Ankle swelling was more common in older patients (35.7% vs 22.3%, p = 0.001; odds ratio [OR] 1.94, 95%CI 1.289-2.912) and was independently associated with Body Mass Index (BMI, adjOR 1.073) and angiotensin-receptor antagonists (adjOR 1.864). The association with BMI was confirmed in older patients (adjOR 1.134). ACEi-induced cough showed similar prevalence in younger and older patients (13.9% vs 15.6%, p = 0.634), being independently associated with female sex (adjOR 2.118), gastroesophageal reflux disease (GERD, adjOR 2.488) and SNRI therapy (adjOR 8.114). The association with GERD was confirmed in older patients (adjOR 3.238).

CONCLUSIONS

CCB-related ankle swelling and ACEi-induced cough represent the most common antihypertensive-related AEs, also at old age. Older patients showed a two-fold increased risk of ankle swelling, that was also independently associated with BMI. ACEi-induced cough had similar prevalence at younger and old ages, being independently associated with GERD.

Unveiling Wide Spectrum Therapeutic Implications and Signaling Mechanisms of Valsartan in Diverse Disorders: A Comprehensive Review

Valsartan is an orally active non-peptide angiotensin receptor antagonist, an effective and well-tolerated anti-hypertensive drug. Besides its antihypertensive action, it has clinical implications in many other disorders, like heart failure (HF), arrhythmia, chronic kidney disease (CKD), diabetic complications (DM), atherosclerosis, etc. Besides angiotensin receptor blocking activity, valsartan reduces circulating levels of biochemical markers, such as hs-CRP, which is responsible for its anti-inflammatory and anti-oxidant activity. Moreover, valsartan also acts by inhibiting or inducing various signalling pathways, such as inducing autophagy via the AKT/mTOR/S6K pathway or inhibiting the TLR/NF-kB pathway. The current review exhaustively discusses the therapeutic implications of valsartan with specific emphasis on the mechanism of action in various disorders. The article provides a detailed spectrum of the therapeutic profile of valsartan and will likely be very useful to researchers working in the relevant research areas.

Angiotensin II Type 2 Receptor Antibodies in Glomerular Diseases

We evaluated the concentration of AT2R antibodies in 136 patients with primary and secondary glomerular diseases: membranous nephropathy (n = 18), focal and segmental glomerulosclerosis (n = 25), systemic lupus erythematosus (n = 17), immunoglobulin A (IgA) nephropathy (n = 14), mesangial (non-IgA) proliferative nephropathy (n = 6), c-ANCA vasculitis (n = 40), perinuclear anti-neutrophil cytoplasmic antibodies (p-ANCA) vasculitis (n = 16), and compared it with a healthy control group (22 patients). Serum creatinine levels, proteinuria, serum albumin, and total protein concentrations were prospectively recorded for 2 years. The mean levels of AT2R antibodies in the lupus nephropathy group were significantly higher compared to the control group, 64.12 ± 26.95 units/mL and 9.72 ± 11.88 units/mL, respectively. There was no association between this level and the clinical course of the disease. The AT2R levels in other kinds of glomerular disease were no different from the control group. We found significant correlations between AT1R and AT2R in patients with membranous nephropathy (r = 0.66), IgA nephropathy (r = 0.61), and c-ANCA vasculitis (r = 0.63). Levels of AT2R antibodies in systemic lupus erythematosus are higher compared to other types of glomerulonephritis, vasculitis, and a healthy control group. Levels of AT2R antibodies correlate with AT1R antibodies in the groups of patients with membranous nephropathy, IgA nephropathy, and c-ANCA vasculitis. These kinds of AT2R antibodies have a stimulative effect on AT2R, but we have not found the influence of these antibodies on the clinical course of glomerular diseases.

From cardiovascular system to brain, the potential protective role of Mas Receptors in COVID-19 infection

Coronavirus disease 2019 (COVID-19) has been declared a new pandemic in March 2020. Although most patients are asymptomatic, those with underlying cardiovascular comorbidities may develop a more severe systemic infection which is often associated with fatal pneumonia. Nonetheless, neurological and cardiovascular manifestations could be present even without respiratory symptoms. To date, no COVID-19-specific drugs are able for preventing or treating the infection and generally, the symptoms are relieved with general anti-inflammatory drugs. Angiotensin-converting-enzyme 2 (ACE2) may function as the receptor for virus entry within the cells favoring the progression of infection in the organism. On the other hand, ACE2 is a relevant enzyme in renin angiotensin system (RAS) cascade fostering Ang1-7/Mas receptor activation which promotes protective effects in neurological and cardiovascular systems. It is known that RAS is composed by two functional countervailing axes the ACE/AngII/AT1 receptor and the ACE/AngII/AT2 receptor which counteracts the actions mediated by AngII/AT1 receptor by inducing anti-inflammatory, antioxidant and anti-growth functions. Subsequently an "alternative" ACE2/Ang1-7/Mas receptor axis has been described with functions similar to the latter protective arm. Here, we discuss the neurological and cardiovascular effects of COVID-19 highlighting the role of the stimulation of the RAS "alternative" protective arm in attenuating pulmonary, cerebral and cardiovascular damages. In conclusion, only two clinical trials are running for Mas receptor agonists but few other molecules are in preclinical phase and if successful these drugs might represent a successful strategy for the treatment of the acute phase of COVID-19 infection.

Exercise and vascular function in sedentary lifestyles in humans

People with sedentary lifestyles engage in minimal or no physical activity. A sedentary lifestyle promotes dysregulation of cellular redox balance, diminishes mitochondrial function, and increases NADPH oxidase activity. These changes collectively increase cellular oxidative stress, which alters endothelial function by oxidizing LDL-C, reducing NO production, and causing eNOS uncoupling. Reduced levels of nitric oxide (NO) leads to vasoconstriction, vascular remodeling, and vascular inflammation. Exercise modulates reactive oxygen species (ROS) to modify NRF2-KEAP signaling, leading to the activation of NRF2 to alleviate oxidative stress. While regular moderate exercise activates NRF2 through ROS production, high-intensity intermittent exercise stimulates NRF2 activation to a greater degree by reducing KEAP levels, which can be more beneficial for sedentary individuals. We review the damaging effects of a sedentary lifestyle on the vascular system and the health benefits of regular and intermittent exercise.

Moderate-Intensity Exercise Improves Mesenteric Arterial Function in Male UC Davis Type-2 Diabetes Mellitus (UCD-T2DM) Rats: A Shift in the Relative Importance of Endothelium-Derived Relaxing Factors (EDRF)

The beneficial cardiovascular effects of exercise are well documented, however the mechanisms by which exercise improves vascular function in diabetes are not fully understood. This study investigates whether there are (1) improvements in blood pressure and endothelium-dependent vasorelaxation (EDV) and (2) alterations in the relative contribution of endothelium-derived relaxing factors (EDRF) in modulating mesenteric arterial reactivity in male UC Davis type-2 diabetes mellitus (UCD-T2DM) rats, following an 8-week moderate-intensity exercise (MIE) intervention. EDV to acetylcholine (ACh) was measured before and after exposure to pharmacological inhibitors. Contractile responses to phenylephrine and myogenic tone were determined. The arterial expressions of endothelial nitric oxide (NO) synthase (eNOS), cyclooxygenase (COX), and calcium-activated potassium channel (K_Ca) channels were also measured. T2DM significantly impaired EDV, increased contractile responses and myogenic tone. The impairment of EDV was accompanied by elevated NO and COX importance, whereas the contribution of prostanoid- and NO-independent (endothelium-derived hyperpolarization, EDH) relaxation was not apparent compared to controls. MIE 1) enhanced EDV, while it reduced contractile responses, myogenic tone and systolic blood pressure (SBP), and 2) caused a shift away from a reliance on COX toward a greater reliance on EDH in diabetic arteries. We provide the first evidence of the beneficial effects of MIE via the altered importance of EDRF in mesenteric arterial relaxation in male UCD-T2DM rats.

New Insight in Cardiorenal Syndrome: From Biomarkers to Therapy

Cardiorenal syndrome consists in the coexistence of acute or chronic dysfunction of heart and kidneys resulting in a cascade of feedback mechanisms and causing damage to both organs associated with high morbidity and mortality. In the last few years, different biomarkers have been investigated with the aim to achieve an early and accurate diagnosis of cardiorenal syndrome, to provide a prognostic role and to guide the development of targeted pharmacological and non-pharmacological therapies. In such a context, sodium-glucose cotransporter 2 (SGLT2) inhibitors, recommended as the first-line choice in the management of heart failure, might represent a promising strategy in the management of cardiorenal syndrome due to their efficacy in reducing both cardiac and renal outcomes. In this review, we will discuss the current knowledge on the pathophysiology of cardiorenal syndrome in adults, as well as the utility of biomarkers in cardiac and kidney dysfunction and potential insights into novel therapeutics.

Walnut supplementation after fructose-rich diet is associated with a beneficial fatty acid ratio and increased ACE2 expression in the rat heart

Increased fructose consumption has been linked with chronic inflammation and metabolic syndrome (MetS). Activation of the renin-angiotensin system (RAS) and NF-κB have been detected in MetS. Walnuts are a rich source of polyunsaturated omega-3 fatty acids (n-3 PUFA) that were suggested to exert anti-inflammatory effects related to cardio-metabolic health. We hypothesized that walnut supplementation has the capacity to revert unfavorable fructose-rich diet (FRD)-induced activation of cardiac RAS and NF-κB in male rats. Due to the lack of similar studies, we investigated the effects of walnut supplementation (6 weeks) on the expression of four RAS molecules (ACE, ACE2, AT1R, and AT2R) and NF-κB in rat heart after FRD (10% w/v, 9 weeks). In addition, we followed the changes in the n-6/n-3 PUFA ratio in the total pool of heart lipids after both treatments to elucidate the walnut effects on fatty acids in the heart. 36 animals (9 per group) participated in the experiment. FRD significantly increased the ACE protein level in the heart (p < 0.001). Walnut supplementation significantly increased the ACE2 protein level in the heart of FRD (p < 0.001). In addition, walnut supplementation showed a significant main effect on the arachidonic acid/eicosapentaenoic acid ratio (p = 0.004). Walnut supplementation significantly reduced this ratio, in comparison with both, the control group (C vs. FW, p < 0.05) and the FRD group (F vs. FW, p < 0.05). However, walnut treatment failed to revert the significant effect of fructose (p < 0.001) on the elevation of NF-κB protein level. Our results suggest a beneficial effect of walnut supplementation on ACE2 protein level and n-6/n-3 PUFA level in the heart of the animal model of MetS. Such results highlight the approach of omega-3-rich walnut supplementation in the stimulation of endogenous production of favorable molecules in the heart which could be an affordable nutritional treatment formaintenance of cardio-metabolic health.

Hypertension and COVID-19: Current Evidence and Perspectives

Coronavirus disease 2019 (COVID-19) outbreak, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), represents a real challenge for health-care systems worldwide. Male sex, older age and the coexistence of chronic comorbidities have been described as the most relevant conditions associated with a worse prognosis. Early reports suggested that hypertension might represent a risk factor for susceptibility to SARS-CoV-2 infection, a more severe course of COVID-19 and increased COVID-19-related deaths. Nevertheless, the independent role of hypertension remains under debate, since hypertension is often associated with the older age and other cardiovascular (CV) risk factors in the general population, which may also contribute to the SARS-Cov-2 infection and COVID-19. Moreover, the role of antihypertensive drugs, primarily angiotensin-converting inhibitors (ACEIs) and ARBs (angiotensin receptor blockers) in COVID-19 development and outcome appears controversial. Indeed, preclinical studies using these classes of drugs have suggested a potential upregulation of angiotensin-converting-enzyme 2 (ACE2) which is the key binding receptor promoting cell entry of SARS-CoV-2 in the organism. Renin–angiotensin system (RAS) blockers may potentially upregulate ACE2, hence, it has been initially hypothesized that these agents might contribute to a higher risk of SARS-CoV-2 infection and progressive course of COVID-19. However, several clinical reports do not support a detrimental role of RAS blockers in COVID-19, and an intense debate about the withdrawal or maintenance of chronic therapy with ACEi/ARB has been developed. In this review we will discuss the available evidence on the role of hypertension and antihypertensive drugs on SARS-CoV-2 infection and COVID-19 development.

Endothelial Dysfunction in Hypertension: Current Concepts and Clinical Implications

Endothelium plays a fundamental role in the cardiovascular system, forming an interface between blood and adjacent tissues by regulating the vascular tone through the synthesis of nitric oxide, prostaglandins and other relaxing factors. Endothelial dysfunction is characterized by vasoconstriction, cell proliferation and shifting toward a proinflammatory and prothrombic state. In hypertension endothelial dysfunction may be involved in the initiation and development of vascular inflammation, vascular remodeling, and atherosclerosis and is independently associated with increased cardiovascular risk. Different conditions such as impaired vascular shear stress, inflammation and oxidative stress, activation of the renin angiotensin system have been described as important pathophysiological mechanisms involved in the development of endothelial dysfunction. The release of extracellular vesicles by neighboring cells in the vascular wall has emerged as an important regulator of endothelial function and with potential antihypertensive properties and beneficial effects by counteracting the hypertension mediated organ damage. Furthermore, macrovesicles are emerging as an innovative therapeutic approach for vascular protection, allowing the delivery of bioactive molecules, such as miRNA and drugs interacting with the renin angiotensin system. In this review we summarize the available evidence about the pathophysiological implications of endothelial dysfunction in cardiovascular diseases, focusing on hypertension and its sequelae, and the potential innovative therapeutic strategies targeting the endothelium with the aim to improve vascular function and remodeling.

Hypertension, a Moving Target in COVID-19: Current Views and Perspectives

Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) associates with a considerable high rate of mortality and represents currently the most important concern in global health. The risk of more severe clinical manifestation of COVID-19 is higher in males and steeply raised with age but also increased by the presence of chronic comorbidities. Among the latter, early reports suggested that arterial hypertension associates with higher susceptibility to SARS-CoV-2 infection, more severe course and increased COVID-19-related deaths. Furthermore, experimental studies suggested that key pathophysiological hypertension mechanisms, such as activation of the renin-angiotensin system (RAS), may play a role in COVID-19. In fact, ACE2 (angiotensin-converting-enzyme 2) is the pivotal receptor for SARS-CoV-2 to enter host cells and provides thus a link between COVID-19 and RAS. It was thus anticipated that drugs modulating the RAS including an upregulation of ACE2 may increase the risk for infection with SARS-CoV-2 and poorer outcomes in COVID-19. Since the use of RAS-blockers, ACE inhibitors or angiotensin receptor blockers, represents the backbone of recommended antihypertensive therapy and intense debate about their use in the COVID-19 pandemic has developed. Currently, a direct role of hypertension, independent of age and other comorbidities, as a risk factor for the SARS-COV-2 infection and COVID-19 outcome, particularly death, has not been established. Similarly, both current experimental and clinical studies do not support an unfavorable effect of RAS-blockers or other classes of first line blood pressure lowering drugs in COVID-19. Here, we review available data on the role of hypertension and its management on COVID-19. Conversely, some aspects as to how the COVID-19 affects hypertension management and impacts on future developments are also briefly discussed. COVID-19 has and continues to proof the critical importance of hypertension research to address questions that are important for global health.

Activation of angiotensin type 2 receptor attenuates testosterone-induced hypertension and uterine vascular resistance in pregnant rats†

Preeclampsia is a pregnancy-related hypertensive disorder with unclear mechanisms. While hypersensitivity to angiotensin II via vasoconstrictive angiotensin type-1 receptor (AT1R) is observed in preeclampsia, the importance of vasodilatory angiotensin type-2 receptor (AT2R) in the control of vascular dysfunction is less clear. We assessed whether AT1R, AT2R, and endothelial nitric oxide synthase (eNOS) expression are altered in placental vessels of preeclamptic women and tested if ex vivo incubation with AT2R agonist Compound 21 (C21; 1 μM) could restore AT1R, AT2R, and eNOS balance. Further, using a rat model of gestational hypertension induced by elevated testosterone, we examined whether C21 (1 μg/kg/day, oral) could preserve AT1R and AT2R balance and improve blood pressure, uterine artery blood flow, and vascular function. Western blots revealed that AT1R protein level was higher while AT2R and eNOS protein were reduced in preeclamptic placental vessels, and AT2R agonist C21 decreased AT1R and increased AT2R and eNOS protein levels in preeclamptic vessels. In testosterone dams, blood pressure was higher, and uterine artery blood flow was reduced, and C21 treatment reversed these levels similar to those in controls dams. C21 attenuated the exaggerated Ang II contraction and improved endothelium-dependent vasorelaxation in uterine arteries of testosterone dams. These C21-mediated vascular effects were associated with decreased AT1R and increased AT2R and eNOS protein levels. C21 also increased serum nitrate/nitrite and bradykinin production in testosterone dams and attenuated the fetoplacental growth restriction. Thus, AT1R upregulation and AT2R downregulation are observed in preeclampsia and testosterone model, and increasing AT2R activity could help restore AT1R and AT2R balance and improve gestational vascular function.

Mas Receptor Activation Contributes to the Improvement of Nitric Oxide Bioavailability and Vascular Remodeling During Chronic AT1R (Angiotensin Type-1 Receptor) Blockade in Experimental Hypertension

Angiotensin (1-7) production increases during AT1R (angiotensin type-1 receptor) blockade. The contribution of Ang (1-7) (angiotensin [1-7]) and its receptor (MasR) to the favorable effect of angiotensin receptor blockers on remodeling and function of resistance arteries remains unclear. We sought to determine whether MasR contributes to the improvement of vascular structure and function during chronic AT1R blockade. Spontaneously hypertensive rats were treated with Ang (1-7) or olmesartan ± MasR antagonist A-779, or vehicle, for 14 days. Blood pressure was measured by tail cuff methodology. Mesenteric arteries were dissected and mounted on a pressurized micromyograph to evaluate media-to-lumen ratio (M/L) and endothelial function. Expression of MasR and eNOS (endothelial nitric oxide synthase) was evaluated by immunoblotting, plasma nitrate by colorimetric assay, and reactive oxygen species production by dihydroethidium staining. Independently of blood pressure, olmesartan significantly reduced M/L and improved NO bioavailability, A-779 prevented these effects. Likewise, Ang (1-7) significantly reduced M/L and NO bioavailability. MasR expression was significantly increased by Ang (1-7) as well as by olmesartan, and it was blunted in the presence of A-779. Both Ang (1-7) and olmesartan increased eNOS expression and plasma nitrite which were reduced by A-779. Superoxide generation was attenuated by olmesartan and Ang (1-7) and was blunted in the presence of A-779. These MasR-mediated actions were independent of AT2R activation since olmesartan and Ang (1-7) increased MasR expression and reduced M/L in Ang II (angiotensin II)-infused AT2R knockout mice, independently of blood pressure control. A-779 prevented these effects. Hence, MasR activation may contribute to the favorable effects of AT1R antagonism on NO bioavailability and microvascular remodeling, independently of AT2R activation and blood pressure control.

Pregnancy upregulates angiotensin type 2 receptor expression and increases blood flow in uterine arteries of rats

Normal pregnancy is associated with decreased uterine vascular contraction and increased blood flow even though angiotensin II (AngII) levels are increased. AngII not only activates the angiotensin type 1 receptor (AT1R) to mediate vasoconstriction but also angiotensin type 2 receptor (AT2R) to cause vasodilation. We hypothesized that upregulation of AT2R expression and function accounts for increased uterine artery blood flow during pregnancy. Virgin, pregnant (at different days of gestation) and post-partum Sprague-Dawley rats were used to determine uterine artery hemodynamics using micro ultrasound and plasma angiotensin II levels by ELISA. Isolated uterine arteries were examined for AT1R and AT2R expression and isometric contraction/relaxation. Plasma AngII levels were steady up to mid-pregnancy, increased as pregnancy advanced, reaching a peak in late pregnancy, and then restored to pre-pregnant levels after delivery. The pattern of increase in AngII levels mirrored a parallel increase in uterine blood flow. AT1R expression did not change, but AT2R expression increased during pregnancy correlating with uterine blood flow increase. Treatment with the AT2R antagonist PD123319 reduced uterine arterial blood flow. Vasoconstriction to angiotensin II was blunted in pregnant rats. Treatment with PD123319 caused greater enhancement of AngII contraction in pregnant than virgin rats. Ex vivo exposure of estradiol to uterine arterial rings dose dependently upregulated AT2R expression, that was inhibited by estrogen receptor antagonist. These results demonstrate that elevated AngII levels during gestation induce an increase in uterine blood flow via heightened AT2R-mediated signaling. Estrogens appear to directly upregulate uterine vascular AT2R independent of any endogenous factors.

Downregulation of AT2R decreases the responsiveness of BKCa channels to angiotensin II in patients with hypertension

Angiotensin II (Ang II) modulates blood pressure via Ang II type 1 receptor (AT₁R) and type 2 receptor (AT₂R). The activation of AT₂R relaxes vascular tone through opening large-conductance Ca²⁺-activated potassium (BK_Ca) channels in vascular smooth muscle cells (SMCs). In the present study, we studied the role of the AT₂R-BK_Ca pathway in patients with hypertension. The mesenteric arterial SMCs (MSMCs) were obtained from normotensive patients (NP) and hypertensive patients (HP). BK_Ca currents were recorded with patch clamp and the expressions of mRNAs and proteins of AT₁R/AT₂R were analyzed by RT-PCR and Western blotting, respectively. Ang II significantly increased the macroscopic BK_Ca currents at the whole cell level, while increased the open probability and decreased the mean close time of BK_Ca channels at the single channel level with AT₁R blockade by valsartan in NP. However, Ang II had no effect on the BK_Ca currents at the same condition in HP. Furthermore, the expressions of mRNA and protein of AT₂R but not AT₁R were markedly decreased in the MSMCs of HP compared to that of NP. The data suggest that AT₂R is well functioned in the MSMCs in NP but not in HP and deficiency in the AT₂R-BK_Ca pathway may contribute to the development of hypertension.

Role of the ACE2‑Ang‑(1‑7)‑Mas axis in blood pressure regulation and its potential as an antihypertensive in functional foods (Review)

The renin‑angiotensin system (RAS) serves a critical role in blood pressure regulation and prevention of cardiovascular diseases. Efforts to develop functional foods that enhance the RAS have focused on inhibition of angiotensin‑converting enzyme (ACE) activity in the ACE‑angiotensin II (Ang II)‑Ang II type 1 receptor axis. ACE2 and the Mas receptor are important components of this axis. ACE2 catalyzes Ang II into Ang‑(1‑7), which then binds to the G‑protein‑coupled receptor Mas. In addition, it induces nitric oxide release from endothelial cells and exerts antiproliferative, vasodilatory and antihypertensive effects. The present review examined recent findings regarding the physiological and biological roles of the ACE2‑Ang‑(1‑7)‑Mas axis in the cardiovascular system, discussed potential food‑derived ACE2‑activating agents, and highlighted initiatives, based on this axis, that aim to develop functional foods for the treatment of hypertension.

Long-Term Regulation of the Local Renin-Angiotensin System in the Myocardium of Spontaneously Hypertensive Rats by Feeding Bioactive Peptides Derived from Spirulina platensis

This study investigated the long-term (8 weeks) anti-hypertensive effects of 10 mg/kg tripeptides isolated from Spirulina platensis, Ile-Gln-Pro (IQP) and Val-Glu-Pro (VEP), and S. platensis hydrolysates (SH) on spontaneously hypertensive rats. The treatment period was 6 weeks, and observation continued for another 2 weeks. After treatment, weighted systolic blood pressure, weighted diastolic blood pressure, left ventricular mass index, and right ventricular mass index of groups treated with IQP, VEP, and SH were significantly lower than those of the group treated with distilled water, even when the treatments had been withdrawn for 2 weeks. Quantitative real-time polymerase chain reaction, enzyme-linked immunosorbent assay, and Western blotting showed the mRNA expression levels and protein/peptide concentrations of the main components of the renin angiotensin system in myocardium were significantly affected by treatment: angiotensin converting enzyme, angiotensin II, and angiotensin type 1 receptor were down-regulated, whereas angiotensin type 2 receptor, angiotensin converting enzyme 2, angiotensin-(1-7), and Mas receptor were up-regulated.

AT2R autoantibodies block angiotensin II and AT1R autoantibody-induced vasoconstriction

Activating autoantibodies to the angiotensin type 1 receptor (AT1R) are associated with hypertensive disorders. The angiotensin type 2 receptor (AT2R) is known to counter-regulate the actions of AT1R. We investigated whether AT2R autoantibodies produced in immunized rabbits will activate AT2R and suppress the vasopressor responses to angiotensin II and AT1R-activating autoantibodies. Five rabbits immunized with a peptide corresponding to the second extracellular loop of AT2R developed high AT2R antibody titers. Rabbit anti-AT2R sera failed to directly dilate isolated rat cremaster arterioles; however, when co-perfused with angiotensin II or AT1R-activating autoantibodies, the anti-AT2R sera significantly inhibited their contractile effects. Rabbit anti-AT2R sera recognized a predominant sequence near the N-terminus of the AT2R second extracellular loop. A decoy peptide based on this sequence effectively reversed the opposing effect of the anti-AT2R sera on angiotensin II-induced contraction of rat cremaster arterioles. A similar blockade of the anti-AT2R sera effect was observed with the AT2R antagonist PD 123319 and the guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one. Rabbit anti-AT2R sera reacted specifically with AT2R. No cross-reactivity with AT1R was observed. Blood pressure did not change in immunized animals. However, the pressor responses to incremental angiotensin II infusions were blunted in immunized animals. Thirteen subjects with primary aldosteronism demonstrated increased AT2R autoantibody levels compared with normal controls. In conclusion, AT2R autoantibodies produced in immunized rabbits have the ability to activate AT2R and counteract the AT1R-mediated vasoconstriction. These autoantibodies provide useful and selective tools for the study of their roles in blood pressure regulation and possible therapeutic intervention.

Activation of upregulated angiotensin II type 2 receptors decreases carotid pulse pressure in rats with suprarenal abdominal aortic coarctation

Our aim was to determine whether angiotensin type 2 receptors (AT2R) are involved in the depression of carotid pulse pressure (PP) in rats with suprarenal aortic coarctation (SrC). We tested the effects of losartan, PD123319, and CGP42112 on PP in SrC and Sham-operated anesthetized rats. PP increased in SrC rats. Neither losartan nor PD123319 affected PP in SrC and Sham-operated rats. CGP42112 reduced PP, in SrC rats, combined with losartan. Moreover, PD123319 blocked this effect. AT2R protein increased in the thoracic aortas of SrC rats. Thus, upregulated AT2R stimulation by CGP42112 mediates depression of PP in rats under pressure overloading.

AT(2) receptor and tissue injury: therapeutic implications

The renin-angiotensin system (RAS) plays an important role in the initiation and progression of tissue injuries in the cardiovascular and nervous systems. The detrimental actions of the AT1 receptor (AT1R) in hypertension and vascular injury, myocardial infarction and brain ischemia are well established. In the past twenty years, protective actions of the RAS, not only in the cardiovascular, but also in the nervous system, have been demonstrated. The so-called protective arm of the RAS includes AT2-receptors and Mas receptors (AT2R and MasR) and is characterized by effects different from and often opposing those of the AT1R. These include anti-inflammation, anti-fibrosis, anti-apoptosis and neuroregeneration that can counterbalance pathological processes and enable recovery from disease. The recent development of novel, small-molecule AT2R agonists offers a therapeutic potential in humans with a variety of clinical indications.

Opportunities for targeting the angiotensin-converting enzyme 2/angiotensin-(1-7)/mas receptor pathway in hypertension

It is well known that the renin-angiotensin system (RAS) plays a pivotal role in the pathophysiology of cardiovascular diseases. This is well illustrated by the great success of ACE inhibitors and angiotensin (Ang) II AT(1) blockers in the treatment of hypertension and its complications. In the past decade, the classical concept of RAS orchestrated by a series of enzymatic reactions culminating in the linear generation and action of Ang II has expanded and become more complex. From the discoveries of new components such as the angiotensin converting enzyme 2 and the receptor Mas emerged a novel concept of dual opposite branches of the RAS: one vasoconstrictor and pro-hypertensive composed of ACE/Ang II/AT1; and other vasodilator and anti-hypertensive composed of ACE2/Ang-(1-7)/Mas. In this review we will discuss recent findings concerning the biological role of the ACE2/Ang-(1-7)/Mas arm in the cardiovascular system and highlight the initiatives to develop potential therapeutic strategies based on this axis for treating hypertension.

Inflammatory biomarkers for predicting cardiovascular disease

The pathology of cardiovascular disease (CVD) is complex; multiple biological pathways have been implicated, including, but not limited to, inflammation and oxidative stress. Biomarkers of inflammation and oxidative stress may serve to help identify patients at risk for CVD, to monitor the efficacy of treatments, and to develop new pharmacological tools. However, due to the complexities of CVD pathogenesis there is no single biomarker available to estimate absolute risk of future cardiovascular events. Furthermore, not all biomarkers are equal; the functions of many biomarkers overlap, some offer better prognostic information than others, and some are better suited to identify/predict the pathogenesis of particular cardiovascular events. The identification of the most appropriate set of biomarkers can provide a detailed picture of the specific nature of the cardiovascular event. The following review provides an overview of existing and emerging inflammatory biomarkers, pro-inflammatory cytokines, anti-inflammatory cytokines, chemokines, oxidative stress biomarkers, and antioxidant biomarkers. The functions of each biomarker are discussed, and prognostic data are provided where available.

Renin-angiotensin system, hypertension, and chronic kidney disease: pharmacogenetic implications

About 80% of CKD (chronic kidney disease) patients are hypertensive, and kidney function and blood pressure are clearly related to both physiologic and pathologic conditions in a "vicious cycle". In this pathologic scenario, there is a renin-angiotensin system (RAS) hyperactivity associated to progression of renal damage. Current guidelines indicate as the first choice of antihypertensive intervention, the pharmacologic blockade of the RAS. Nonetheless, both response to treatment and renal protection have considerable inter-individual variability. The main aims of this review are to describe the genetic characteristics of RAS components and to identify the possible pharmacogenetic implications for RAS-blocker drugs in the hypertension-CKD scenario. To date, RAS polymorphisms have not been consistently associated to antihypertensive response and studies focusing on CKD are scarce. Nonetheless, pharmacogenetic studies for the RAS-blocker drugs could still be further explored, especially with new generation tools and focusing not only on the antihypertensive response, but also on renal protection as well.

The angiotensin-converting enzyme 2/angiotensin-(1-7)/Mas receptor axis: a potential target for treating thrombotic diseases

Despite many therapeutic advances leading to increasingly effective drug treatments, thrombotic events (such as ischaemic stroke, pulmonary embolism, deep venous thrombosis and acute myocardial infarction) still represent a major worldwide cause of morbidity and mortality. Remarkable effort has been made to identify new drug targets. There is growing evidence indicating that the recently described counter-regulator axis of the renin-angiotensin system (RAS), composed of Angiotensin-Converting Enzyme 2 (ACE2), Angiotensin-(1-7) and the Mas receptor, has protective effects against thrombosis. In addition, it could be considered as a promising target for treating or preventing this disease. In this narrative review, we focused on the recent findings of the role of the ACE2/Angiotensin-(1-7)/Mas axis on the haemostatic process and its therapeutic potential.

LOX-1 and angiotensin receptors, and their interplay

The renin-angiotensin system (RAS) plays an important role in regulating blood pressure, water-salt balance and the pathogenesis of cardiovascular diseases. Angiotensin II (Ang II) is the physiologically active mediator and mediates the main pathophysiological actions in RAS. Ang II exerts the effects by activating its receptors, primarily type 1 (AT1R) and type 2 (AT2R). Most of the known pathophysiological effects of Ang II are mediated by AT1R activation. The precise physiological function of AT2R is still not clear. Generally, AT2R is considered to oppose the effects of AT1R. Lectin-like oxidized low-density lipoprotein scavenger receptor-1 (LOX-1) is one of the major receptors responsible for binding, internalizing and degrading ox-LDL. The activation of LOX-1 has been known to be related to many pathophysiological events, including endothelial dysfunction and injury, fibroblast growth, and vascular smooth muscle cell hypertrophy. Many of these alterations are present in atherosclerosis, hypertension, and myocardial ischemia and remodeling. A growing body of evidence suggests the existence of a cross-talk between LOX-1 and Ang II receptors. Their interplays are embodied in the reciprocal regulation of their expression and activity. Their interplays are involved in a series of signals. Recent studies suggests that reactive oxygen species (ROS), nitric oxide (NO), protein kinase C (PKC) and mitogen activated protein kinases (MAPKs) are important signals responsible for their cross-talk. This paper reviews these aspects of dyslipidemia and RAS activation.