Impact of AT2-receptor stimulation on vascular biology, kidney function, and blood pressure

Angiotensin II type 2 receptor agonist attenuates LPS-induced acute lung injury through modulating THP-1-derived macrophage reprogramming

Acute respiratory distress syndrome (ARDS) is a devastating respiratory disorder, characterized by overwhelming inflammation in the alveoli without effective pharmacological treatment. We aimed to investigate the effect and mechanism of angiotensin II type 2 receptor (AT2R) agonist, Compound 21 (C21), on the lipopolysaccharide (LPS)-induced acute lung injury (ALI) model. The protective effect of C21 was evaluated via enzyme-linked immunosorbent assay (ELISA), Western blot (WB), real-time PCR, and fluorescence microscopy in LPS-challenged THP1-derived macrophages. Besides, the in vivo efficacy of C21 was assessed using cell counting, ELISA, protein quantification, hematoxylin-eosin (H&E) staining, and WB in an LPS-induced ALI mouse model. The results showed that C21 significantly inhibited the secretion of pro-inflammatory cytokines (CCL-2, IL-6), overproduction of intracellular ROS, and activation of inflammatory pathways (NF-κB/NLRP3, p38/MAPK) in THP-1 cell-derived macrophages stimulated by LPS. In in vivo study, intraperitoneal injection of C21 could reduce airway leukocytes accumulation and chemokine/cytokine (keratinocyte chemoattractant (KC), IL-6) generation, as well as alleviate diffuse alveolar damage induced by LPS. Conclusively, the AT2R agonist C21 significantly inhibited LPS-stimulated excess inflammatory responses and oxidative stress in macrophages. Meanwhile, C21 could effectively alleviate acute inflammation and tissue damage in the lungs of ALI mice challenged by LPS. The results of this study bring new hope for the early treatment of ALI/ARDS.

End-Organ Damage in Hypertension: An Insight on a Differentiated Outpatient Consultation

OBJECTIVE

The objective of this study was to determine the prevalence of end-organ damage in hypertensive patients attending an outpatient consultation.

MATERIALS AND METHODS

Patients were selected from an outpatient consultation at a tertiary hospital care center. All patients who consulted between July 2022 and March 2023 were included. Data on demographic characteristics, blood pressure records, hypertension etiology, medication use, and the presence of target organ damage were collected.

RESULTS

A total of 73 patients were included in the study, with 34 patients being male (46.6%) and 39 patients being female (53.4%). The mean age of the patients was 49.8 years. Among the cases of hypertension, 14 (19.2%) were classified as secondary arterial hypertension (AH). The most common cause of secondary AH was obstructive sleep apnea (OSA) (42.9%). Approximately 23.2% of patients had documented end-organ damage potentially related to hypertension, with kidney disease being the most frequent (n = 10, 13.7%). The most commonly prescribed pharmacological classes were angiotensin-converting enzyme inhibitors and angiotensin II receptor antagonists (n = 46, 63%).

CONCLUSION

Despite numerous studies and trials on arterial hypertension, it remains a significant contributor to morbidity and mortality, necessitating the continued awareness of its long-term implications.

Differential expression of the angiotensin receptors (AT1, AT2, and AT4) in the placental bed of HIV-infected preeclamptic women of African ancestry

The Renin-Angiotensin-Aldosterone System (RAAS) is implicated in the pathophysiology of preeclampsia (PE). There is a paucity of data on uteroplacental angiotensin receptors AT1-2 and 4. We evaluated the immunoexpression of AT1R, AT2R, and AT4R within the placental bed of PE vs. normotensive (N) pregnancies stratified by HIV status. Placental bed (PB) biopsies (n = 180) were obtained from N and PE women. Both groups were stratified by HIV status and gestational age into early-and late onset-PE. Immuno-labeling of AT1R, AT2R, and AT4R was quantified using morphometric image analysis. Immunostaining of PB endothelial cells (EC) and smooth muscle cells of spiral arteries (VSMC) displayed an upregulation of AT1R expression compared to the N group (p < 0.0001). Downregulation of AT2R and AT4R expression was observed in PE vs. N group (p = 0.0042 and p < 0.0001), respectively. AT2R immunoexpression declined between HIV+ve and HIV-ve groups, while AT1R and AT4R displayed an increase. An increase in AT1R expression was noted in the EOPE-ve/+ve and LOPE-ve/+ve compared to N-ve/N+ve. In contrast, AT2R and AT4R expression decreased in EOPE-ve/+ve and LOPE-ve/+ve compared to N-ve/N+ve. We demonstrate a significant downregulation of AT2R and AT4R with a concomitant elevated AT1R immunoexpression within PB of HIV-infected PE women. In addition, a decline in AT2R and AT4R with an increase in AT1R immunoexpression in PE, EOPE, and LOPE vs. normotensive pregnancies, irrespective of HIV status. Thus highlighting differential immunoexpression of uteroplacental RAAS receptors based on pregnancy type, HIV status, and gestational age.

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

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

Coronary Large Conductance Ca2+-Activated K+ Channel Dysfunction in Diabetes Mellitus

Diabetes mellitus (DM) is an independent risk of macrovascular and microvascular complications, while cardiovascular diseases remain a leading cause of death in both men and women with diabetes. Large conductance Ca2+-activated K+ (BK) channels are abundantly expressed in arteries and are the key ionic determinant of vascular tone and organ perfusion. It is well established that the downregulation of vascular BK channel function with reduced BK channel protein expression and altered intrinsic BK channel biophysical properties is associated with diabetic vasculopathy. Recent efforts also showed that diabetes-associated changes in signaling pathways and transcriptional factors contribute to the downregulation of BK channel expression. This manuscript will review our current understandings on the molecular, physiological, and biophysical mechanisms that underlie coronary BK channelopathy in diabetes mellitus.

Antiproteinuric and Hyperkalemic Mechanisms Activated by Dual Versus Single Blockade of the RAS in Renovascular Hypertensive Rats

This study aimed to investigate the antiproteinuric and hyperkalemic mechanisms activated by dual renin-angiotensin system (RAS) blockade in renovascular hypertensive rats (2-kidney 1-clip model [2K-1C]). Six weeks after clipping the left renal artery or sham operation (2K), rats were treated with losartan, enalapril, or both drugs for two weeks. We found that 2K-1C rats displayed higher tail-cuff blood pressure (BP), increased non-clipped kidney Ang II concentration, and more pronounced urinary albumin excretion than 2K. BP was decreased by the treatment with either enalapril or losartan, and the combination of both drugs promoted an additional antihypertensive effect in 2K-1C rats. Renal Ang II content and albuminuria were reduced by either enalapril or losartan in monotherapy and restored to control levels by dual RAS blockade. Albuminuria in 2K-1C rats was accompanied by downregulation of the glomerular slit protein podocin, reduction of the endocytic receptors megalin and cubilin, and a marked decrease in the expression of the ClC-5 chloride channel, compared to 2K animals. Treatment with losartan and enalapril in monotherapy or combination increased the expression of podocin, cubilin, and ClC-5. However, only the combined therapy normalized podocin, cubilin, and ClC-5 protein abundance in the non-clipped kidney of 2K-1C rats. Renovascular hypertensive 2K-1C rats had a lower concentration of plasma potassium compared to 2K rats. Single RAS blockade normalized potassium plasma concentration, whereas 2K-1C rats treated with dual RAS blockade exhibited hyperkalemia. Hypokalemia in 2K-1C rats was accompanied by an increase in the cleaved activated forms of α-ENaC and γ-ENaC and the expression of β-ENaC. Combined RAS blockade but not monotherapy significantly reduced the expression of these ENaC subunits in 2K-1C rats. Indeed, double RAS blockade reduced the abundance of cleaved-α-ENaC to levels lower than those of 2K rats. Collectively, these results demonstrate that the antiproteinuric effect of dual RAS blockade in 2K-1C rats is associated with the restored abundance of podocin and cubilin, and ClC-5. Moreover, double RAS blockade-induced hyperkalemia may be due, at least partially, to an exaggerated downregulation of cleaved α-ENaC in the non-clipped kidney of renovascular hypertensive rats.

125I-Angiotensin 1-7 binds to a different site than angiotensin 1-7 in tissue membrane preparations

PURPOSE

To study the receptor for Angiotensin (Ang) 1-7 using a radioligand (¹²⁵I-Ang 1-7)-binding assay. For more than a decade, Mas has been viewed as the receptor for Ang 1-7; however, Ang 1-7 binding has not been pharmacologically characterized in tissue membrane preparations.

METHODS

Radioligand-binding assays were carried out using tissue membrane preparations using radioiodinated Angiotensin 1-7 (¹²⁵I-Ang 1-7) to characterize its binding site. Non-radioactive ¹²⁷I-Ang 1-7 was used to test if the addition of an iodine to the tyrosine⁴ moiety of Ang 1-7 changes the ability of Ang 1-7 to competitively inhibit ¹²⁵I-Ang 1-7 binding.

RESULTS

¹²⁵I-Ang 1-7 binds saturably, with moderately high affinity (10-20 nM) to a binding site in rat liver membranes that is displaceable by ¹²⁷I-Ang 1-7 at nanomolar concentrations (IC₅₀ = 62 nM) while Ang 1-7 displaces at micromolar concentrations (IC₅₀ = 80 µM) at ~22 °C. This binding was also displaceable by inhibitors of metalloproteases at room temperature. This suggests that ¹²⁵I-Ang 1-7 binds to MMPs and/or ADAMs as well as other liver membrane elements at ~ 22 °C. However, when ¹²⁵I-Ang 1-7-binding assays were run at 0-4 °C, the same MMP inhibitors did not effectively compete for ¹²⁵I-Ang 1-7.

CONCLUSIONS

The addition of an iodine molecule to the tyrosine in position 4 of Ang 1-7 drastically changes the binding characteristics of this peptide making it unsuitable for characterization of Ang 1-7 receptors.

Metabolic reprogramming by N-acetyl-seryl-aspartyl-lysyl-proline protects against diabetic kidney disease

BACKGROUND AND PURPOSE

ACE inhibitors (ACEIs) and AT₁ receptor antagonists (ARBs) are first-line drugs that are believed to reduce the progression of end-stage renal disease in diabetic patients. Differences in the effects of ACEIs and ARBs are not well studied and the mechanisms responsible are not well understood.

EXPERIMENTAL APPROACH

Male diabetic CD-1 mice were treated with ACEI, ARB, N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP), ACEI + AcSDKP, ARB + AcSDKP, glycolysis inhibitors or non-treatment. Moreover, prolyl oligopeptidase inhibitor (POPi)-injected male diabetic C57Bl6 mice were treated with ACEI, AcSDKP and ARB or non-treatment. Western blot and immunofluorescent staining were used to examine key enzymes and regulators of central metabolism.

KEY RESULTS

The antifibrotic action of ACEI imidapril is due to an AcSDKP-mediated antifibrotic mechanism, which reprograms the central metabolism including restoring SIRT3 protein and mitochondrial fatty acid oxidation and suppression of abnormal glucose metabolism in the diabetic kidney. Moreover, the POPi S17092 significantly blocked the AcSDKP synthesis, accelerated kidney fibrosis and disrupted the central metabolism. ACEI partly restored the kidney fibrosis and elevated the AcSDKP level, whereas the ARB (TA-606) did not show such effects in the POPi-injected mice. ACE inhibition and AcSDKP suppressed defective metabolism-linked mesenchymal transformations and reduced collagen-I and fibronectin accumulation in the diabetic kidneys.

CONCLUSION AND IMPLICATIONS

The study envisages that AcSDKP is the endogenous antifibrotic mediator that controls the metabolic switch between glucose and fatty acid metabolism and that suppression of AcSDKP leads to disruption of kidney cell metabolism and activates mesenchymal transformations leading to severe fibrosis in the diabetic kidney.

The Other Angiotensin II Receptor: AT2R as a Therapeutic Target

The active hormone of the renin-angiotensin system (RAS), angiotensin II (Ang II), is involved in several human diseases, driving the development and clinical use of several therapeutic drugs, mostly angiotensin I converting enzyme (ACE) inhibitors and angiotensin receptor type I (AT₁R) antagonists. However, angiotensin peptides can also bind to receptors different from AT₁R, in particular, angiotensin receptor type II (AT₂R), resulting in biological and physiological effects different, and sometimes antagonistic, of their binding to AT₁R. In the present Perspective, the components of the RAS and the therapeutic tools developed to control it will be reviewed. In particular, the characteristics of AT₂R and tools to modulate its functions will be discussed. Agonists or antagonists to AT₂R are potential therapeutics in cardiovascular diseases, for agonists, and in the control of pain, for antagonists, respectively. However, controlling their binding properties and their targeting to the target tissues must be optimized.

Inhibition of Angiotensin-Converting Enzyme Ameliorates Renal Fibrosis by Mitigating DPP-4 Level and Restoring Antifibrotic MicroRNAs

Two class of drugs 1) angiotensin-converting enzyme inhibitors (ACEis) and 2) angiotensin II receptor blockers (ARBs) are well-known conventional drugs that can retard the progression of chronic nephropathies to end-stage renal disease. However, there is a lack of comparative studies on the effects of ACEi versus ARB on renal fibrosis. Here, we observed that ACEi ameliorated renal fibrosis by mitigating DPP-4 and TGFβ signaling, whereas, ARB did not show. Moreover, the combination of N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP), one of the substrates of ACE, with ACEi slightly enhanced the inhibitory effects of ACEi on DPP-4 and associated-TGFβ signaling. Further, the comprehensive miRome analysis in kidneys of ACEi+AcSDKP (combination) treatment revealed the emergence of miR-29s and miR-let-7s as key antifibrotic players. Treatment of cultured cells with ACEi alone or in combination with AcSDKP prevented the downregulated expression of miR-29s and miR-let-7s induced by TGFβ stimulation. Interestingly, ACEi also restored miR-29 and miR-let-7 family cross-talk in endothelial cells, an effect that is shared by AcSDKP suggesting that AcSDKP may be partially involved in the anti-mesenchymal action of ACEi. The results of the present study promise to advance our understanding of how ACEi regulates antifibrotic microRNAs crosstalk and DPP-4 associated-fibrogenic processes which is a critical event in the development of diabetic kidney disease.

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.

Age-related differences in the cutaneous vascular response to exogenous angiotensin II

Angiotensin II (ANG II) is locally produced in human skin and contributes to the reflex vasoconstriction (VC) response in aged but not young skin. We hypothesized that the exogenous ANG II-mediated VC response would be greater in older adults and would be affected by inhibition of adrenoreceptor or ANG II type II receptor (AT₂R) pathways. Three microdialysis (MD) fibers were placed in the forearm skin of 11 young (26 ± 3 yr) and 11 older (68 ± 4 yr) individuals for perfusion of 1) Ringer solution (control), 2) adrenoreceptor blockade with yohimbine + propranolol, and 3) AT₂R inhibition with PD-123319. ANG II was then added to the perfusates at eight graded dose concentrations ranging from 10^-10 to 10^-3 M. Laser Doppler flux was measured at each MD site, and cutaneous vascular conductance (CVC) was calculated as CVC =  laser Doppler flux/mean arterial pressure and normalized to baseline CVC values collected before ANG II perfusion (%ΔCVC_baseline). At the control site, older adults (-34 ± 4%ΔCVC_baseline) exhibited a greater peak VC compared with young adults (-22 ± 2%ΔCVC_baseline, P < 0.05), which was attenuated with adrenoreceptor blockade. Young skin exhibited a vasodilation in response to lower ANG II doses that was inhibited with AT₂R inhibition. AT₂R inhibition also increased the VC response to higher ANG II doses such that young skin responded similarly to older skin. These results indicate that ANG II has a greater VC influence in older than young individuals. Furthermore, ANG II may be affecting multiple targets, including adrenergic and AT₂R pathways. NEW & NOTEWORTHY Intradermal perfusion of successive doses of angiotensin II (ANG II) revealed a role for ANG II type II receptors and dose-dependent, ANG II-mediated vasodilation in young but not older adults. In contrast, older adults exhibited greater vasoconstriction for a given dose of ANG II. The increased vasoconstriction in older adults was subsequently blunted with adrenoreceptor blockade, which indicates an interaction between ANG II and adrenergic signaling pathways in the cutaneous microcirculation.

Intracerebroventricular infusion of angiotensin AT2 receptor agonist novokinin aggravates some diabetes-mellitus-induced alterations in Wistar rats

Cumulative data suggest the significant role of the renin–angiotensin system in the development of the pathological consequences of diabetes mellitus (DM). Newly synthesized AT2 receptor agonists gained importance as a target for creating new antihypertensives. The aim of the present work was to study the effects of peptide AT2 agonist novokinin, infused intracerebroventricularly, on the consequences of the streptozotocin-induced type 1 DM (T1DM) in Wistar rats. Food and water consumption, body mass, urine excretion (metabolic cages), motor activity (open-field test), anxiety (elevated plus maze), nociception (paw pressure analgesimeter test), spatial memory (T-maze alternation test), and plasma levels of glucose and corticosterone (ELISA) were assessed 2 weeks after the T1DM induction. Novokinin increased water and food consumption, as well as urine output, and reduced mass gain in the control rats. Diabetic rats demonstrated hyperalgesia, increased level of plasma corticosterone, decreased motor and exploratory activity, and impaired spatial memory. Novokinin infusion increased water intake, diuresis, and mortality rate, decreased food intake, exacerbated diabetes-induced hyperalgesia, and provoked anxiety-like behavior but improved spatial memory in diabetic rats. These initial data suggest that angiotensin AT2 receptors participate in the pathogenesis of T1DM-induced complications in the function of the nervous system.

Centrally Mediated Cardiovascular Actions of the Angiotensin II Type 2 Receptor

Sustained increases in the activity of the sympathetic neural pathways that exit the brain and which increase blood pressure (BP) are a major underlying factor in resistant hypertension. Recently available information on the occurrence of angiotensin II type 2 receptors (AT2Rs) within or adjacent to brain cardiovascular control centers is consistent with findings that stimulation of these receptors lowers BP, particularly during hypertension of neurogenic origin. Until recently brain AT2R had not been considered by many to play a role in the central control of BP. Demonstration of these powerful antihypertensive effects of brain AT2R opens the door to reconsideration of their role in BP regulation, and their consideration as a novel therapeutic avenue for resistant hypertension.

Combined Angiotensin Receptor Modulation in the Management of Cardio-Metabolic Disorders

Cardiovascular and metabolic disorders, such as hypertension, insulin resistance, dyslipidemia or obesity are linked with chronic low-grade inflammation and dysregulation of the renin–angiotensin system (RAS). Consequently, RAS inhibition by ACE inhibitors or angiotensin AT1 receptor (AT1R) blockers is the evidence-based standard for cardiovascular risk reduction in high-risk patients, including diabetics with albuminuria. In addition, RAS inhibition reduces the new onset of diabetes mellitus. Yet, the high and increasing prevalence of metabolic disorders, and the high residual risk even in properly treated patients, calls for additional means of pharmacological intervention. In the past decade, the stimulation of the angiotensin AT2 receptor (AT2R) has been shown to reduce inflammation, improve cardiac and vascular remodeling, enhance insulin sensitivity and increase adiponectin production. Therefore, a concept of dual AT1R/AT2R modulation emerges as a putative means for risk reduction in cardio-metabolic diseases. The approach employing simultaneous RAS blockade (AT1R) and RAS stimulation (AT2R) is distinct from previous attempts of double intervention in the RAS by dual blockade. Dual blockade abolishes the AT1R-linked RAS almost completely with subsequent risk of hypotension and hypotension-related events, i.e. syncope or renal dysfunction. Such complications might be especially prominent in patients with renal impairment or patients with isolated systolic hypertension and normal-to-low diastolic blood pressure values. In contrast to dual RAS blockade, the add-on of AT2R stimulation does not exert significant blood pressure effects, but it may complement and enhance the anti-inflammatory and antifibrotic/de-stiffening effects of the AT1R blockade and improve the metabolic profile. Further studies will have to investigate these putative effects in particular for settings in which blood pressure reduction is not primarily desired.

Angiotensin receptors and β-catenin regulate brain endothelial integrity in malaria

Cerebral malaria is characterized by cytoadhesion of Plasmodium falciparum-infected red blood cells (Pf-iRBCs) to endothelial cells in the brain, disruption of the blood-brain barrier, and cerebral microhemorrhages. No available antimalarial drugs specifically target the endothelial disruptions underlying this complication, which is responsible for the majority of malaria-associated deaths. Here, we have demonstrated that ruptured Pf-iRBCs induce activation of β-catenin, leading to disruption of inter-endothelial cell junctions in human brain microvascular endothelial cells (HBMECs). Inhibition of β-catenin-induced TCF/LEF transcription in the nucleus of HBMECs prevented the disruption of endothelial junctions, confirming that β-catenin is a key mediator of P. falciparum adverse effects on endothelial integrity. Blockade of the angiotensin II type 1 receptor (AT1) or stimulation of the type 2 receptor (AT2) abrogated Pf-iRBC-induced activation of β-catenin and prevented the disruption of HBMEC monolayers. In a mouse model of cerebral malaria, modulation of angiotensin II receptors produced similar effects, leading to protection against cerebral malaria, reduced cerebral hemorrhages, and increased survival. In contrast, AT2-deficient mice were more susceptible to cerebral malaria. The interrelation of the β-catenin and the angiotensin II signaling pathways opens immediate host-targeted therapeutic possibilities for cerebral malaria and other diseases in which brain endothelial integrity is compromised.

Identification of compound-protein interactions through the analysis of gene ontology, KEGG enrichment for proteins and molecular fragments of compounds

Compound-protein interactions play important roles in every cell via the recognition and regulation of specific functional proteins. The correct identification of compound-protein interactions can lead to a good comprehension of this complicated system and provide useful input for the investigation of various attributes of compounds and proteins. In this study, we attempted to understand this system by extracting properties from both proteins and compounds, in which proteins were represented by gene ontology and KEGG pathway enrichment scores and compounds were represented by molecular fragments. Advanced feature selection methods, including minimum redundancy maximum relevance, incremental feature selection, and the basic machine learning algorithm random forest, were used to analyze these properties and extract core factors for the determination of actual compound-protein interactions. Compound-protein interactions reported in The Binding Databases were used as positive samples. To improve the reliability of the results, the analytic procedure was executed five times using different negative samples. Simultaneously, five optimal prediction methods based on a random forest and yielding maximum MCCs of approximately 77.55 % were constructed and may be useful tools for the prediction of compound-protein interactions. This work provides new clues to understanding the system of compound-protein interactions by analyzing extracted core features. Our results indicate that compound-protein interactions are related to biological processes involving immune, developmental and hormone-associated pathways.

Angiotensin A/Alamandine/MrgD Axis: Another Clue to Understanding Cardiovascular Pathophysiology

The renin-angiotensin system (RAS) plays a crucial role in cardiovascular regulations and its modulation is a challenging target for the vast majority of cardioprotective strategies. However, many biological effects of these drugs cannot be explained by the known mode of action. Our comprehension of the RAS is thus far from complete. The RAS represents an ingenious system of "checks and balances". It incorporates vasoconstrictive, pro-proliferative, and pro-inflammatory compounds on one hand and molecules with opposing action on the other hand. The list of these molecules is still not definitive because new biological properties can be achieved by minor alteration of the molecular structure. The angiotensin A/alamandine-MrgD cascade associates the deleterious and protective branches of the RAS. Its identification provided a novel clue to the understanding of the RAS. Angiotensin A (Ang A) is positioned at the "crossroad" in this system since it either elicits direct vasoconstrictive and pro-proliferative actions or it is further metabolized to alamandine, triggering opposing effects. Alamandine, the central molecule of this cascade, can be generated both from the "deleterious" Ang A as well as from the "protective" angiotensin 1-7. This pathway modulates peripheral and central blood pressure regulation and cardiovascular remodeling. Further research will elucidate its interactions in cardiovascular pathophysiology and its possible therapeutic implications.

AT2 receptor activities and pathophysiological implications

Although angiotensin II subtype-2 receptor (AT2R) was discovered over 2 decades ago, its contribution to physiology and pathophysiology is not fully elucidated. Current knowledge suggests that under normal physiologic conditions, AT2R counterbalances the effects of angiotensin II subtype-1 receptor (AT1R). A major obstacle for AT2R investigations was the lack of specific agonists. Most of the earlier AT2R studies were performed using the peptidic agonist, CG42112A, or the nonpeptidic antagonist PD123319. CGP42112A is nonspecific for AT2R and in higher concentrations can bind to AT1R. Recently, the development of specific nonpeptidic AT2R agonists boosted the efforts in identifying the therapeutic potentials for AT2R stimulation. Unlike AT1R, AT2R is involved in vasodilation by the release of bradykinin and nitric oxide, anti-inflammation, and healing from injury. Interestingly, the vasodilatory effects of AT2R stimulation were not associated with significant reduction in blood pressure. In the kidney, AT2R stimulation produced natriuresis, increased renal blood flow, and reduced tissue inflammation. In animal studies, enhanced AT2R function led to reduction of cardiac inflammation and fibrosis, and reduced the size of the infarcted area. Similarly, AT2R stimulation demonstrated protective effects in vasculature and brain.

Relationship between pre-stroke cardiovascular medication use and stroke severity

INTRODUCTION

Stroke is a major health problem with important morbidity and mortality. Various risk factors and cardiovascular medication groups are known to have an influence on stroke incidence, but less is known about the relation between medication use and stroke severity.

AIM

To determine if relationships exist between the pre-stroke cardiovascular medication use and stroke severity.

METHODS

A retrospective study was conducted on a database with anonymized data of 1974 patients with a suspected stroke, admitted to the Universitair Ziekenhuis (UZ) Brussel. Stroke severity was quantified using the National Institute of Health Stroke Scale (NIHSS). Cardiovascular medication groups were first included in a multivariable linear regression model. Second, to obtain clinically interpretable results, all variables that were retained in the final linear regression model were introduced in a cumulative odds ordinal logistic regression model with proportional odds.

RESULTS

Angiotensin II receptor blockers (ARBs), statins, and antiarrhythmics were significantly associated with stroke severity at the 10 % α level in a multivariable linear regression model, suggesting a possible effect of these medication groups on stroke severity. Only pre-stroke statin use showed a significant relationship with the NIHSS score in the ordinal logistic regression model with an adjusted odds ratio of 0.740 (95 % CI 0.580-0.944; p = 0.015).

CONCLUSION

Pre-stroke use of statins is significantly associated with lower stroke severity. No significant relationship was detected between pre-stroke use of other medication groups and stroke severity, defined by the NIHSS score.

Comparison of Efficacy of Long-term Oral Treatment with Telmisartan and Benazepril in Cats with Chronic Kidney Disease

Background

The efficacy and benefits of telmisartan in cats with chronic kidney disease (CKD) have not previously been reported.

Hypothesis

Long‐term treatment of cats with CKD using telmisartan decreases urine protein‐to‐creatinine ratio (UP/C) similar to benazepril.

Animals

Two‐hundred and twenty‐four client‐owned adult cats with CKD.

Methods

Prospective, multicenter, controlled, randomized, parallel group, blinded clinical trial with noninferiority design. Cats were allocated in a 1 : 1 ratio to either telmisartan (1 mg/kg; n = 112) or benazepril (0.5–1.0 mg/kg; n = 112) PO q24 h. The primary endpoint was prospectively defined as the change in proteinuria (benazepril:telmisartan) based on a log transformed weighted average of UP/C change from baseline (AUC 0→t/t) as a percentage compared using a confidence interval (CI) approach. Changes of UP/C from baseline were assessed on all study days and corrected for multiple comparisons.

Results

Telmisartan proved noninferior to benazepril in controlling proteinuria (CI, −0.035 to 0.268). At Day 180, UP/C compared to baseline in the telmisartan group was significantly lower (−0.05 ± 0.31; P = .016), whereas in the benazepril group the change (−0.02 ± 0.48) was not statistically significant (P = .136). Similar results were obtained at all assessment points with significant decrease in UP/C occurring with telmisartan but not benazepril.

Conclusion and Clinical Importance

Both telmisartan and benazepril were well tolerated and safe. Telmisartan proved to be noninferior to benazepril and significantly decreased proteinuria relative to baseline at all assessment points whereas benazepril did not.

Enhanced Natriuresis and Diuresis in Wistar Rats Caused by the Costimulation of Renal Dopamine D3 and Angiotensin II Type 2 Receptors

BACKGROUND

The kidney, via its regulation of sodium excretion, which is modulated by humoral factors, including the dopamine and renin-angiotensin systems, keeps the blood pressure in the normal range. We have reported a negative interaction between dopamine D3 and AT1 receptors (D3R and AT1R) in renal proximal tubule (RPT) cells. Here, we studied the interaction between D3R and AT2R in vitro and in vivo.

METHODS AND RESULTS

Stimulation of either the D3R or AT2R, by the intrarenal arterial infusion of PD128907, a D3R agonist, or CGP42112A, an AT2R agonist, induced natriuresis and diuresis that were enhanced by the simultaneous infusion of PD128907 and CGP42112A in Wistar rats. The D3/AT2 receptor interaction was confirmed in in vitro, i.e., stimulation of either the D3R or AT2R inhibited Na(+)-K(+)-ATPase activity that was enhanced by the costimulation of these receptors. D3R and AT2R colocalized and coimmunoprecipitated in kidney and RPT cells (RPTCs). Stimulation of one receptor increased the localization of the other receptor at the plasma cell membrane. ERK1/2-MAPK is involved in the signaling pathway of D3R and AT2R interaction because costimulation of D3R and AT2R significantly increased ERK1/2-MAPK expression in RPTCs; inhibition of ERK1/2-MAPK abolished the inhibition of Na(+)-K(+)-ATPase activity that was enhanced by D3R and AT2R costimulation.

CONCLUSIONS

Our current study indicates that D3R, in combination with AT2R, enhances natriuresis and diuresis, via ERK1/2-MAPK pathway, that may be involved in the regulation of blood pressure.

Hypotensive and sympathoinhibitory responses to selective central AT2 receptor stimulation in spontaneously hypertensive rats

The type 2 angiotensin receptor (AT2R) has been suggested to counterbalance the type 1 angiotensin receptor (AT1R) in the central regulation of blood pressure and sympathetic tone. In the present study we investigated the blood pressure responses to stimulation of central AT2Rs by the selective agonist Compound 21 in conscious spontaneously hypertensive rats (SHRs) and normotensive Wistar Kyoto rats (WKY rats). We also assessed the impact on noradrenaline [norepinephrine (NE)] plasma levels, autonomic function, spontaneous baroreflex sensitivity, and the possible involvement of the nitric oxide (NO) pathway and the AT1Rs. Chronic intracerebroventricular Compound 21 infusion lowered blood pressure and NE plasma levels in both rat strains. The night-time hypotensive effect was greater in SHRs compared with WKY rats. Compound 21 improved spontaneous baroreflex sensitivity more in SHRs than in WKY rats. These effects were abolished by co-administration of the AT2R antagonist PD123319 or the NO synthase inhibitor Nω-nitro-L-arginine methyl ester hydrochloride (L-NAME). Central AT1R blockade did not enhance the hypotensive response to Compound 21. Chronic selective stimulation of central AT2Rs lowers blood pressure through sympathoinhibition, and improves spontaneous baroreflex sensitivity more in SHRs than in WKY rats. These responses appear to require a functioning central NO pathway, but are not modified by central AT1R blockade. Collectively, the data demonstrate specific beneficial effects of stimulation of central AT2Rs in hypertension associated with increased sympathetic tone, and suggest that central AT2Rs may represent a potential new therapeutic target for the treatment of neurogenic hypertension.

2D-1H proton magnetic resonance spectroscopic imaging study on brain metabolite alterations in patients with diabetic hypertension

The aim of the present study was to investigate the possible metabolic alterations in the frontal cortex and parietal white matter in patients with diabetic hypertension (DHT) using proton magnetic resonance (MR) spectroscopic imaging. A total of 33 DHT patients and 30 healthy control subjects aged between 45 and 75 were included in the present study. All subjects were right‑handed. The spectroscopy data were collected using a GE Healthcare 1.5T MR scanner. The multi‑voxels were located in the semioval center (repetition time/echo time=1,500 ms/35 ms). The area of interest was 8x10x2 cm in volume and contained the two sides of the frontal cortex and the parietal white matter. The spectra data were processed using SAGE software. The ratios of brain metabolite concentrations, particularly for N‑acetylaspartate (NAA)/creatine (Cr) and Choline (Cho)/Cr were calculated and analyzed. Statistical analyses were performed using SPSS 17.0. The NAA/Cr ratio of the bilateral prefrontal cortex of the DHT group was significantly lower than that of the control group (left t=‑7.854, P=0.000 and right t=‑5.787, P=0.000), The Cho/Cr ratio was also much lower than the control group (left t=2.422, P=0.024 and right t=2.920, P=0.007). NAA/Cr ratio of the left parietal white matter of the DHT group was extremely lower than that of the control group (t=‑4.199, P=0.000). Therefore, DHT may result in metabolic disorders in the frontal cortex and parietal white matter but the metabolic alterations are different in various regions of the brain. The alteration in cerebral metabolism is associated with diabetes and hypertension. The ratios of NAA/Cr and Cho/Cr are potential metabolic markers for the brain damage induced by DHT.

Selective activation of angiotensin AT2 receptors attenuates progression of pulmonary hypertension and inhibits cardiopulmonary fibrosis

BACKGROUND AND PURPOSE

Pulmonary hypertension (PH) is a devastating disease characterized by increased pulmonary arterial pressure, which progressively leads to right-heart failure and death. A dys-regulated renin angiotensin system (RAS) has been implicated in the development and progression of PH. However, the role of the angiotensin AT2 receptor in PH has not been fully elucidated. We have taken advantage of a recently identified non-peptide AT2 receptor agonist, Compound 21 (C21), to investigate its effects on the well-established monocrotaline (MCT) rat model of PH.

EXPERIMENTAL APPROACH

A single s.c. injection of MCT (50 mg·kg(-1) ) was used to induce PH in 8-week-old male Sprague Dawley rats. After 2 weeks of MCT administration, a subset of animals began receiving either 0.03 mg·kg(-1) C21, 3 mg·kg(-1) PD-123319 or 0.5 mg·kg(-1) A779 for an additional 2 weeks, after which right ventricular haemodynamic parameters were measured and tissues were collected for gene expression and histological analyses.

KEY RESULTS

Initiation of C21 treatment significantly attenuated much of the pathophysiology associated with MCT-induced PH. Most notably, C21 reversed pulmonary fibrosis and prevented right ventricular fibrosis. These beneficial effects were associated with improvement in right heart function, decreased pulmonary vessel wall thickness, reduced pro-inflammatory cytokines and favourable modulation of the lung RAS. Conversely, co-administration of the AT2 receptor antagonist, PD-123319, or the Mas antagonist, A779, abolished the protective actions of C21.

CONCLUSIONS AND IMPLICATIONS

Taken together, our results suggest that the AT2 receptor agonist, C21, may hold promise for patients with PH.

Angiotensin type 2 receptors: blood pressure regulation and end organ damage

In most situations, the angiotensin AT2-receptor (AT2R) mediates physiological actions opposing those mediated by the AT1-receptor (AT1R), including a vasorelaxant effect. Nevertheless, experimental evidence vastly supports that systemic application of AT2R-agonists is blood pressure neutral. However, stimulation of AT2R locally within the brain or the kidney apparently elicits a systemic blood pressure lowering effect. A systemic effect of AT2R stimulation on blood pressure can also be achieved, when the prevailing effect of continuous background AT1R-stimulation is attenuated by low-dose AT1R blockade. Despite a lack of effect on blood pressure, AT2R stimulation still protects from hypertensive end-organ damage. Current data and evidence therefore suggest that AT2R agonists will not be suitable as future anti-hypertensive drugs, but that they may well be useful for end-organ protection in combination with established anti-hypertensives.

Molecular targets of antihypertensive peptides: understanding the mechanisms of action based on the pathophysiology of hypertension

There is growing interest in using functional foods or nutraceuticals for the prevention and treatment of hypertension or high blood pressure. Although numerous preventive and therapeutic pharmacological interventions are available on the market, unfortunately, many patients still suffer from poorly controlled hypertension. Furthermore, most pharmacological drugs, such as inhibitors of angiotensin-I converting enzyme (ACE), are often associated with significant adverse effects. Many bioactive food compounds have been characterized over the past decades that may contribute to the management of hypertension; for example, bioactive peptides derived from various food proteins with antihypertensive properties have gained a great deal of attention. Some of these peptides have exhibited potent in vivo antihypertensive activity in both animal models and human clinical trials. This review provides an overview about the complex pathophysiology of hypertension and demonstrates the potential roles of food derived bioactive peptides as viable interventions targeting specific pathways involved in this disease process. This review offers a comprehensive guide for understanding and utilizing the molecular mechanisms of antihypertensive actions of food protein derived peptides.

Reporter mouse strain provides a novel look at angiotensin type-2 receptor distribution in the central nervous system

Angiotensin-II acts at its type-1 receptor (AT1R) in the brain to regulate body fluid homeostasis, sympathetic outflow and blood pressure. However, the role of the angiotensin type-2 receptor (AT2R) in the neural control of these processes has received far less attention, largely because of limited ability to effectively localize these receptors at a cellular level in the brain. The present studies combine the use of a bacterial artificial chromosome transgenic AT2R-enhanced green fluorescent protein (eGFP) reporter mouse with recent advances in in situ hybridization (ISH) to circumvent this obstacle. Dual immunohistochemistry (IHC)/ISH studies conducted in AT2R-eGFP reporter mice found that eGFP and AT2R mRNA were highly co-localized within the brain. Qualitative analysis of eGFP immunoreactivity in the brain then revealed localization to neurons within nuclei that regulate blood pressure, metabolism, and fluid balance (e.g., NTS and median preoptic nucleus [MnPO]), as well as limbic and cortical areas known to impact stress responding and mood. Subsequently, dual IHC/ISH studies uncovered the phenotype of specific populations of AT2R-eGFP cells. For example, within the NTS, AT2R-eGFP neurons primarily express glutamic acid decarboxylase-1 (80.3 ± 2.8 %), while a smaller subset express vesicular glutamate transporter-2 (18.2 ± 2.9 %) or AT1R (8.7 ± 1.0 %). No co-localization was observed with tyrosine hydroxylase in the NTS. Although AT2R-eGFP neurons were not observed within the paraventricular nucleus (PVN) of the hypothalamus, eGFP immunoreactivity is localized to efferents terminating in the PVN and within GABAergic neurons surrounding this nucleus. These studies demonstrate that central AT2R are positioned to regulate blood pressure, metabolism, and stress responses.