The Angiotensin AT2 Receptor: From a Binding Site to a Novel Therapeutic Target.

Discovered more than 30 years ago, the angiotensin AT2 receptor (AT2R) has evolved from a binding site with unknown function to a firmly established major effector within the protective arm of the renin-angiotensin system (RAS) and a target for new drugs in development. The AT2R represents an endogenous protective mechanism that can be manipulated in the majority of preclinical models to alleviate lung, renal, cardiovascular, metabolic, cutaneous, and neural diseases as well as cancer. This article is a comprehensive review summarizing our current knowledge of the AT2R, from its discovery to its position within the RAS and its overall functions. This is followed by an in-depth look at the characteristics of the AT2R, including its structure, intracellular signaling, homo- and heterodimerization, and expression. AT2R-selective ligands, from endogenous peptides to synthetic peptides and nonpeptide molecules that are used as research tools, are discussed. Finally, we summarize the known physiological roles of the AT2R and its abundant protective effects in multiple experimental disease models and expound on AT2R ligands that are undergoing development for clinical use. The present review highlights the controversial aspects and gaps in our knowledge of this receptor and illuminates future perspectives for AT2R research. SIGNIFICANCE STATEMENT: The angiotensin AT2 receptor (AT2R) is now regarded as a fully functional and important component of the renin-angiotensin system, with the potential of exerting protective actions in a variety of diseases. This review provides an in-depth view of the AT2R, which has progressed from being an enigma to becoming a therapeutic target.

Risk factors for elective and urgent open conversion after EVAR-a retrospective observational study.

BACKGROUND: Endovascular aortic aneurysm repair (EVAR) has become the standard procedure for treating infrarenal abdominal aortic aneurysms (AAA). Various associated complications can lead to open conversion (OC). Thorough follow-up after the procedure is mandatory for the early detection of complications. Persisting perfusion of the aneurysm, a so-called endoleak (EL), paired with structural instability because of aortic wall atrophy and impaired cell functionality induced by EVAR, results in a high risk for aortic rupture. PURPOSE: The goal of this study was to detect the risk factors for elective and urgent OC as a result of EVAR-induced pathophysiological changes inside the aortic wall. RESEARCH DESIGN: Retrospective data analysis was performed on all open aortic repairs from January 2016 to December 2020. DATA COLLECTION AND ANALYSIS: Fifty patients were identified as treated by OC for failure of an infrarenal EVAR. The patients were divided into two subgroups, here depending on the urgency of surgery. Statistical analysis of patient characteristics and outcomes was performed. RESULTS: The most common indications for OC were various types of EL (74%), resulting in an aortic rupture in 15 patients. Patients with insufficient or absent follow-up were treated more frequently in an emergency setting (16% vs. 63%). The mortality rate was higher in cases of emergency OC (3% vs. 26%). CONCLUSIONS: Particularly in cases of insufficient or absent follow-up, complications such as EL pose an enormous risk for fatal aortic rupture.

SGLT2 Inhibitor Empagliflozin Modulates Ion Channels in Adult Zebrafish Heart.

Empagliflozin, an inhibitor of sodium-glucose co-transporter 2 (iSGLT2), improves cardiovascular outcomes in patients with and without diabetes and possesses an antiarrhythmic activity. However, the mechanisms of these protective effects have not been fully elucidated. This study aimed to explore the impact of empagliflozin on ion channel activity and electrophysiological characteristics in the ventricular myocardium. The main cardiac ionic currents (INa, ICaL, ICaT, IKr, IKs) and action potentials (APs) were studied in zebrafish. Whole-cell currents were measured using the patch clamp method in the isolated ventricular cardiomyocytes. The conventional sharp glass microelectrode technique was applied for the recording of APs from the ventricular myocardium of the excised heart. Empagliflozin pretreatment compared to the control group enhanced potassium IKr step current density in the range of testing potentials from 0 to +30 mV, IKr tail current density in the range of testing potentials from +10 to +70 mV, and IKs current density in the range of testing potentials from -10 to +20 mV. Moreover, in the ventricular myocardium, empagliflozin pretreatment shortened AP duration APD as shown by reduced APD50 and APD90. Empagliflozin had no influence on sodium (INa) and L- and T-type calcium currents (ICaL and ICaT) in zebrafish ventricular cardiomyocytes. Thus, we conclude that empagliflozin increases the rapid and slow components of delayed rectifier K+ current (IKr and IKs). This mechanism could be favorable for cardiac protection.

Low-Dose Empagliflozin Improves Systolic Heart Function after Myocardial Infarction in Rats: Regulation of MMP9, NHE1, and SERCA2a.

The effects of the selective sodium-glucose cotransporter 2 (SGLT2) inhibitor empagliflozin in low dose on cardiac function were investigated in normoglycemic rats. Cardiac parameters were measured by intracardiac catheterization 30 min after intravenous application of empagliflozin to healthy animals. Empagliflozin increased the ventricular systolic pressure, mean pressure, and the max dP/dt (p < 0.05). Similarly, treatment with empagliflozin (1 mg/kg, p.o.) for one week increased the cardiac output, stroke volume, and fractional shortening (p < 0.05). Myocardial infarction (MI) was induced by ligation of the left coronary artery. On day 7 post MI, empagliflozin (1 mg/kg, p.o.) improved the systolic heart function as shown by the global longitudinal strain (-21.0 ± 1.1% vs. -16.6 ± 0.7% in vehicle; p < 0.05). In peri-infarct tissues, empagliflozin decreased the protein expression of matrix metalloproteinase 9 (MMP9) and favorably regulated the cardiac transporters sarco/endoplasmic reticulum Ca2+-ATPase (SERCA2a) and sodium hydrogen exchanger 1 (NHE1). In H9c2 cardiac cells, empagliflozin decreased the MMP2,9 activity and prevented apoptosis. Empagliflozin did not alter the arterial stiffness, blood pressure, markers of fibrosis, and necroptosis. Altogether, short-term treatment with low-dose empagliflozin increased the cardiac contractility in normoglycemic rats and improved the systolic heart function in the early phase after MI. These effects are attributed to a down-regulation of MMP9 and NHE1, and an up-regulation of SERCA2a. This study is of clinical importance because it suggests that a low-dose treatment option with empagliflozin may improve cardiovascular outcomes post-MI. Down-regulation of MMPs could be relevant to many remodeling processes including cancer disease.

AT1-receptor blockade attenuates outward aortic remodeling associated with diet-induced obesity in mice.

The renin-angiotensin system (RAS) and obesity have been implicated in vascular outward remodeling, including aneurysms, but the precise mechanisms are not yet understood. We investigated the effect of the angiotensin receptor type 1 (AT1-receptor) antagonist telmisartan on aortic outward remodeling in a diet-induced obesity model in mice. C57/Black6J mice were fed either a low-fat diet (LFD) or a high-fat diet (HFD) for 14 weeks. One group of HFD mice was additionally exposed to telmisartan (3 mg/kg per day) for the last 4 weeks. HFD led to aortic outward remodeling, characterized by increased proteolysis, along with structural changes, such as fragmentation of elastic fibers and decreased elastin content. Vascular damage was associated with up-regulation of matrix metalloproteinase (MMP)-2 (MMP-2), MMP-3, MMP-12, cathepsin D, and cathepsin B. HFD aortae exhibited an enhanced inflammatory status, characterized by tumor necrosis factor α (TNF-α) and interleukin-1ß (IL-1ß) colocalized with adipocytes in the adventitia. HFD resulted in a significant increase in aortic dimensions, evident by ultrasound measurements. Telmisartan abolished aortic dilatation and preserved elastin content. HFD induced enhanced expression of aortic MMP-2, MMP-9, and TNF-α was abrogated by telmisartan. Adventitial proteolytic and inflammatory factors were also examined in samples from human abdominal aneurysms. The expression of TNF-α, IL-1ß, and MMP-9 was higher in the adventitial fat of diseased vessels compared with healthy tissues. Finally, adipocytes treated with TNF-α showed enhanced MMP-2, MMP-3, and cathepsin D, which was prevented by telmisartan. Taken together, HFD in mice induced aortic dilatation with up-regulation of matrix degrading and inflammatory pathways similar to those seen in human aortic aneurysmatic tissue. The HFD-induced vascular pathology was reduced by AT1-receptor antagonist telmisartan.

AT2 receptors in cardiovascular and renal diseases.

The renin-angiotensin system (RAS) plays an important role in the initiation and progression of cardiovascular and renal diseases. These actions mediated by AT1 receptor (AT1R) are well established and led to development of selective AT1R blockers (ARBs). In contrast, there is scientific evidence that AT2 receptor (AT2R) mediates effects different from and often opposing those of the AT1R. Meagrely expressed in healthy tissue the AT2R is upregulated in injuries providing an endogenous protection to inflammatory, oxidative and apoptotic processes. Interestingly the beneficial effects mediated by AT2R can be further enhanced by pharmacological intervention using the recently developed AT2R agonists. This review article summarizes our current knowledge about regulation, signalling and effects mediated by AT2R in health and disease, with emphasis on cardiac and renal systems. At the end a novel concept of natural protective systems will be introduced and discussed as an attractive target in drug development.

Long-Term Angiotensin II Receptor Blockade Limits Hypertension, Aortic Dysfunction, and Structural Remodeling in a Rat Model of Chronic Kidney Disease.

BACKGROUND/AIMS: Chronic kidney disease (CKD) is associated with large artery remodeling, endothelial dysfunction and calcification, with angiotensin II (Ang II) a known driver of these pathologies. We investigated long-term Ang II type 1 receptor inhibition with valsartan on aortic function and structure in the Lewis polycystic kidney (LPK) rat model of CKD. METHODS: Mixed sex LPK and Lewis control (total n = 28) treated (valsartan 60 mg/kg/day p.o. from 4 to 18 weeks) and vehicle groups were studied. Functional responses to noradrenaline (NA), potassium chloride and endothelium-dependent and independent relaxations were investigated in vitro using acetylcholine hydrochloride (ACh) and sodium nitroprusside (SNP), respectively. Effects of the nitric oxide synthase (NOS) substrate L-arginine, NOS inhibitor L-NAME and cyclooxygenase inhibitor indomethacin on ACh responses were examined. RESULTS: In the LPK, valsartan reduced systolic blood pressure and urinary protein, ameliorated exaggerated sensitivity to NA, and normalized endothelium-dependent (ACh-Rmax; 91 ± 7 vs. 59 ± 6%, p = 0.0001) and independent dysfunction (SNP-Rmax; 99 ± 1 vs. 82 ± 7%, p = 0.040), as well as improving NO-dependent relaxation (Rmax; -51 ± 6 vs. -26 ± 9%, p = 0.008). Valsartan also reduced aortic wall hypertrophy, elastin disruption/fragmentation, calcification, media cystic degeneration, and levels of matrix metalloproteinase 9. CONCLUSIONS: This study highlights the role of Ang II in driving vascular manifestations of CKD and indicates that early treatment can significantly limit pathological changes.

Prevention of liver cancer cachexia-induced cardiac wasting and heart failure.

AIMS: Symptoms of cancer cachexia (CC) include fatigue, shortness of breath, and impaired exercise capacity, which are also hallmark symptoms of heart failure (HF). Herein, we evaluate the effects of drugs commonly used to treat HF (bisoprolol, imidapril, spironolactone) on development of cardiac wasting, HF, and death in the rat hepatoma CC model (AH-130). METHODS AND RESULTS: Tumour-bearing rats showed a progressive loss of body weight and left-ventricular (LV) mass that was associated with a progressive deterioration in cardiac function. Strikingly, bisoprolol and spironolactone significantly reduced wasting of LV mass, attenuated cardiac dysfunction, and improved survival. In contrast, imidapril had no beneficial effect. Several key anabolic and catabolic pathways were dysregulated in the cachectic hearts and, in addition, we found enhanced fibrosis that was corrected by treatment with spironolactone. Finally, we found cardiac wasting and fibrotic remodelling in patients who died as a result of CC. In living cancer patients, with and without cachexia, serum levels of brain natriuretic peptide and aldosterone were elevated. CONCLUSION: Systemic effects of tumours lead not only to CC but also to cardiac wasting, associated with LV-dysfunction, fibrotic remodelling, and increased mortality. These adverse effects of the tumour on the heart and on survival can be mitigated by treatment with either the ß-blocker bisoprolol or the aldosterone antagonist spironolactone. We suggest that clinical trials employing these agents be considered to attempt to limit this devastating complication of cancer.

AT2 receptors targeting cardiac protection post-myocardial infarction.

The angiotensin AT2-receptor mediates tissue protective actions. Its regenerative potential has been tested in multiple disease models including models of myocardial infarction. These studies used different experimental approaches in order to detect AT2-receptor-related effects such as AT2-receptor deficiency or overexpression, treatment with an AT1-receptor blocker leading to indirect stimulation of the unopposed AT2-receptor, or studies using AT2-receptor agonists. It is a common finding in these studies that the AT2-receptor improves cardiac function in the early phase post-MI, and that this effect is preserved over periods of up to four months. Depending on the experimental protocol, the AT2R also attenuates post-MI left ventricular remodeling or protects the heart from early left ventricular thinning and rupture. In combination with AT1-receptor blockade or deficiency, post-MI cardiac hypertrophy is reduced. This article reviews studies on the role of the AT2-receptor in myocardial infarction with an emphasis on the most recent data obtained in studies using AT2-receptor agonists.

Angiotensin AT2 receptors reduce inflammation and fibrosis in cardiovascular remodeling.

The angiotensin AT2 receptor (AT2R), an important member of the "protective arm" of the renin-angiotensin system (RAS), has been recently defined as a therapeutic target in different pathological conditions. The AT2R activates complex signalling pathways linked to cellular proliferation, differentiation, anti-inflammation, antifibrosis, and induction or inhibition of apoptosis. The anti-inflammatory effect of AT2R activation is commonly associated with reduced fibrosis in different models. Current discoveries demonstrated a direct impact of AT2Rs on the regulation of cytokines, transforming growth factor beta1 (TGF-beta1), matrix metalloproteases (MMPs), and synthesis of the extracellular matrix components. This review article summarizes current knowledge on the AT2R in regard to immunity, inflammation and fibrosis in the heart and blood vessels. In particular, the differential influence of the AT2R on cardiovascular remodeling in preclinical models of myocardial infarction, heart failure and aneurysm formation are discussed. Overall, these studies demonstrate that AT2R stimulation represents a promising therapeutic approach to counteract myocardial and aortic damage in cardiovascular diseases.

Aortic Aneurysm: Finding the Right Target.

This Special Issue of Biomedicines highlights many important scientific findings in aneurysm research [...].

Identification of noncytotoxic and IL-10-producing CD8+AT2R+ T cell population in response to ischemic heart injury.

Emerging evidence suggests a cardioprotective role of the angiotensin AT2R, albeit the underlying cellular mechanisms are not well understood. We aimed in this article to elucidate a potential role of cardiac angiotensin AT2R in regulating cellular immune response to ischemic heart injury. Seven days after myocardial infarction in rats, double-immunofluorescence staining showed that AT2R was detected in a fraction of CD8(+) T cells infiltrating in the peri-infarct myocardium. We developed a method that allowed the isolation of myocardial infiltrating CD8(+)AT2R(+) T cells using modified MACS, and further characterization and purification with flow cytometry. Although the CD8(+)AT2R(-) T cells exhibited potent cytotoxicity to both adult and fetal cardiomyocytes (CMs), the CD8(+)AT2R(+) T cells were noncytotoxic to these CMs. The CD8(+)AT2R(+) T cells were characterized by upregulated IL-10 and downregulated IL-2 and INF-γ expression when compared with CD8(+)AT2R(-) T cells. We further showed that IL-10 gene expression was enhanced in CD8(+) T cells on in vitro AT2R stimulation. Importantly, in vivo AT2R activation engendered an increment of CD8(+)AT2R(+) T cells and IL-10 production in the ischemic myocardium. In addition, intramyocardial transplantation of CD8(+)AT2R(+) T cells (versus CD8(+)AT2R(-)) led to reduced ischemic heart injury. Moreover, the CD8(+)AT2R(+) T cell population was also demonstrated in human peripheral blood. Thus, we have defined the cardioprotective CD8(+)AT2R(+) T cell population, which increases during ischemic heart injury and contributes to maintaining CM viability and providing IL-10, hence revealing an AT2R-mediated cellular mechanism in modulating adaptive immune response in the heart.

Differential Regulation of MMPs, Apoptosis and Cell Proliferation by the Cannabinoid Receptors CB1 and CB2 in Vascular Smooth Muscle Cells and Cardiac Myocytes.

Cannabinoids (CB) are implicated in cardiovascular diseases via the two main receptor subtypes CB1R and CB2R. This study investigated whether cannabinoids regulate the activity of matrix metalloproteases (MMP-2, MMP-9) in vascular smooth muscle cells (VSMCs) and in cells of cardiac origin (H9c2 cell line). The influence of CB1- and CB2 receptor stimulation or inhibition on cell proliferation, apoptosis and glucose uptake was also evaluated. We used four compounds that activate or block CB receptors: arachidonyl-2-chloroethylamide (ACEA)-CB1R agonist, rimonabant-CB1R antagonist, John W. Huffman (JWH133)-CB2R agonist and CB2R antagonist-6-Iodopravadoline (AM630). Treatment of cells with the CB2R agonist JWH133 decreased cytokine activated secretion of proMMP-2, MMP-2 and MMP-9, reduced Fas ligand and caspase-3-mediated apoptosis, normalized the expression of TGF-beta1 and prevented cytokine-induced increase in glucose uptake into the cell. CB1R inhibition with rimonabant showed similar protective properties as the CB2R agonist JWH133, but to a lesser extent. In conclusion, CB1R and CB2R exert opposite effects on cell glucose uptake, proteolysis and apoptosis in both VSMCs and H9c2 cells. The CB2R agonist JWH133 demonstrated the highest protective properties. These findings may pave the way to a new treatment of cardiovascular diseases, especially those associated with extracellular matrix degradation.

Small animal Look-Locker inversion recovery (SALLI) for simultaneous generation of cardiac T1 maps and cine and inversion recovery-prepared images at high heart rates: initial experience.

PURPOSE: To develop a single magnetic resonance (MR) imaging approach for comprehensive assessment of cardiac function and tissue properties in small animals with high heart rates. MATERIALS AND METHODS: All animal studies were approved by the local animal care committee. Small animal Look-Locker inversion recovery (SALLI) was implemented on a clinical 3.0-T MR unit equipped with a 70-mm solenoid coil. SALLI combines a segmented, electrocardiographically gated, inversion recovery-prepared Look-Locker-type pulse sequence with a multimodal reconstruction framework. Temporal undersampling and radial nonbalanced steady-state free precession enabled acceleration of data acquisition and reduction of motion artifacts, respectively. Nine agarose gel phantoms were used to investigate different sequence settings. For in vivo studies, 10 Sprague-Dawley rats were evaluated to establish normal T1 values before and after injection of gadopentetate dimeglumine. Seven rats with surgically induced acute myocardial infarction were examined to test the feasibility of detecting myocardial injury. In vitro T1 behavior was studied with linear regression analysis, and in vivo T1 differences between infarcted and remote areas were tested by using the Wilcoxon signed rank test. RESULTS: Phantom studies demonstrated systematic behavior of the T1 measurements, and T1 error could be reduced to 1.3% ± 7.4 by using a simple linear correction algorithm. The pre- and postcontrast T1 of myocardium and blood showed narrow normal ranges. In the area of infarction, SALLI demonstrated hypokinesia (on cine images), myocardial edema (on precontrast T1 maps), and myocardial necrosis (on postcontrast T1 maps and late gadolinium enhancement images). CONCLUSION: An MR imaging method enabling simultaneous generation of cardiac T1 maps and cine and inversion recovery-prepared images at high heart rates is presented. SALLI allows for simultaneous and time-efficient assessment of cardiac T1 behavior, function, and late gadolinium enhancement at high heart rates.

Use of MALDI Mass Spectrometry Imaging to Identify Proteomic Signatures in Aortic Aneurysms after Endovascular Repair.

Endovascular repair (EVAR) has become the standard procedure in treating thoracic (TAA) or abdominal aortic aneurysms (AAA). Not entirely free of complications, a persisting perfusion of the aneurysm after EVAR, called Endoleak (EL), leads to reintervention and risk of secondary rupture. How the aortic wall responds to the implantation of a stentgraft and EL is mostly uncertain. We present a pilot study to identify peptide signatures and gain new insights in pathophysiological alterations of the aortic wall after EVAR using matrix-assisted laser desorption or ionization mass spectrometry imaging (MALDI-MSI). In course of or accompanying an open aortic repair, tissue sections from 15 patients (TAA = 5, AAA = 5, EVAR = 5) were collected. Regions of interest (tunica media and tunica adventitia) were defined and univariate (receiver operating characteristic analysis) statistical analysis for subgroup comparison was used. This proof-of-concept study demonstrates that MALDI-MSI is feasible to identify discriminatory peptide signatures separating TAA, AAA and EVAR. Decreased intensity distributions for actin, tropomyosin, and troponin after EVAR suggest impaired contractility in vascular smooth muscle cells. Furthermore, inability to provide energy caused by impaired respiratory chain function and continuous degradation of extracellular matrix components (collagen) might support aortic wall destabilization. In case of EL after EVAR, this mechanism may result in a weakened aortic wall with lacking ability to react on reinstating pulsatile blood flow.

Cardiac c-kit+AT2+ cell population is increased in response to ischemic injury and supports cardiomyocyte performance.

The expression pattern of angiotensin AT2 receptors with predominance during fetal life and upregulation under pathological conditions during tissue injury/repair process suggests that AT2 receptors may exert an important action in injury/repair adaptive mechanisms. Less is known about AT2 receptors in acute ischemia-induced cardiac injury. We aimed here to elucidate the role of AT2 receptors after acute myocardial infarction. Double immunofluorescence staining showed that cardiac AT2 receptors were mainly detected in clusters of small c-kit+ cells accumulating in peri-infarct zone and c-kit+AT2+ cells increased in response to acute cardiac injury. Further, we isolated cardiac c-kit+AT2+ cell population by modified magnetic activated cell sorting and fluorescence activated cell sorting. These cardiac c-kit+AT2+ cells, represented approximately 0.19% of total cardiac cells in infarcted heart, were characterized by upregulated transcription factors implicated in cardiogenic differentiation (Gata-4, Notch-2, Nkx-2.5) and genes required for self-renewal (Tbx-3, c-Myc, Akt). When adult cardiomyocytes and cardiac c-kit+AT2+ cells isolated from infarcted rat hearts were cocultured, AT2 receptor stimulation in vitro inhibited apoptosis of these cocultured cardiomyocytes. Moreover, in vivo AT2 receptor stimulation led to an increased c-kit+AT2+ cell population in the infarcted myocardium and reduced apoptosis of cardiomyocytes in rats with acute myocardial infarction. These data suggest that cardiac c-kit+AT2+ cell population exists and increases after acute ischemic injury. AT2 receptor activation supports performance of cardiomyocytes, thus contributing to cardioprotection via cardiac c-kit+AT2+ cell population.

Comparative efficacy of empagliflozin and drugs of baseline therapy in post-infarct heart failure in normoglycemic rats.

The study aimed to investigate the effects of the sodium-glucose co-transporter 2 (SGLT2) inhibitor empagliflozin on chronic heart failure (HF) in normoglycemic rats. The effects of empagliflozin were compared with the standard medications for HF, e.g., angiotensin-converting enzyme (ACE) inhibitor fosinopril, beta-blocker bisoprolol, and aldosterone antagonist spironolactone. Myocardial infarction (MI) was induced in male Wistar rats via permanent ligation of the left descending coronary artery. One-month post MI, 50 animals were randomized into 5 groups (n = 10): vehicle-treated, empagliflozin (1.0 mg/kg), fosinopril (10 mg/kg), bisoprolol (10 mg/kg), and spironolactone (20 mg/kg). All medications except empagliflozin were titrated within a month and administered per os daily for 3 months. Echocardiography, 24-hour urine volume test, and treadmill exercise tests were performed at the beginning and at the end of the study. Treatment with empagliflozin slowed the progression of left ventricular dysfunction: LV sizes and ejection fraction were not changed and the minute volume was significantly increased (from 52.0 ± 15.5 to 61.2 ± 21.2 ml/min) as compared with baseline. No deaths occurred in empagliflozin group. The 24-hour urine volume tends to be higher in empagliflozin and spironolactone groups than in vehicle and fosinopril group. Moreover, empagliflozin exhibited maximal physical exercise tolerance in comparison with all investigated groups (289 ± 27 s versus 183 ± 61 s in fosinopril group, 197 ± 95 s in bisoprolol group, and 47 ± 46 s in spironolactone group, p = 0.0035 for multiple comparisons). Sodium-glucose co-transporter 2 inhibitor empagliflozin reduced progression of left ventricular dysfunction and improved tolerance of physical exercise in normoglycemic rats with HF. Empagliflozin treatment was superior with respect to physical tolerance compared with fosinopril, bisoprolol, and spironolactone.

The kallikrein-kinin pathway as a mechanism for auto-control of brown adipose tissue activity.

Brown adipose tissue (BAT) is known to secrete regulatory factors in response to thermogenic stimuli. Components of the BAT secretome may exert local effects that contribute to BAT recruitment and activation. Here, we found that a thermogenic stimulus leads to enhanced secretion of kininogen (Kng) by BAT, owing to induction of kininogen 2 (Kng2) gene expression. Noradrenergic, cAMP-mediated signals induce KNG2 expression and release in brown adipocytes. Conversely, the expression of kinin receptors, that are activated by the Kng products bradykinin and [Des-Arg9]-bradykinin, are repressed by thermogenic activation of BAT in vivo and of brown adipocytes in vitro. Loss-of-function models for Kng (the circulating-Kng-deficient BN/Ka rat) and bradykinin (pharmacological inhibition of kinin receptors, kinin receptor-null mice) signaling were coincident in showing abnormal overactivation of BAT. Studies in vitro indicated that Kng and bradykinin exert repressive effects on brown adipocyte thermogenic activity by interfering the PKA/p38 MAPK pathway of control of Ucp1 gene transcription, whereas impaired kinin receptor expression enhances it. Our findings identify the kallikrein-kinin system as a relevant component of BAT thermogenic regulation that provides auto-regulatory inhibitory signaling to BAT.

Estrogen receptor alpha supports cardiomyocytes indirectly through post-infarct cardiac c-kit+ cells.

Despite previous studies demonstrating a cardioprotective role of estradiol via its estrogen receptor (ER)alpha, the underlying mechanisms remain unclear. Here we aimed to define ERalpha-involved mechanisms against cardiac injury. Seven days after myocardial infarction in male rats, cardiac ERalpha was upregulated in post-infarct cardiac c-kit+ cells accumulating in periinfarct myocardium as shown by Western blotting and immunofluorescence staining. Further, we isolated post-infarct cardiac c-kit+ cell population by modified magnetic activated cell sorting (MACS) and fluorescence activated cell sorting (FACS), and confirmed predominant ERalpha expression in this post-infarct cardiac c-kit+ cell population by real-time PCR. These post-infarct cardiac c-kit+ cells, characterized by upregulated transcription factors implicated in cardiogenic differentiation (GATA-4, Notch-2) and genes required for self-renewal (Tbx3, Akt), maintained a stable phenotype in vitro for more than 3 months. ERalpha stimulation supported proliferation but prevented differentiation of undifferentiated myoblast cells. When adult myocytes isolated from infarcted rat hearts were co-cultured with post-infarct cardiac c-kit+ cells, ERalpha stimulation inhibited apoptosis and enhanced survival of these myocytes. These findings suggest that cardiac ERalpha supports survival of cardiomyocytes through post-infarct cardiac c-kit+ cells, which may contribute to cardioprotection against cardiac injury.

Angiotensin II type 2 receptor stimulation: a novel option of therapeutic interference with the renin-angiotensin system in myocardial infarction?

BACKGROUND: This study is the first to examine the effect of direct angiotensin II type 2 (AT(2)) receptor stimulation on postinfarct cardiac function with the use of the novel nonpeptide AT(2) receptor agonist compound 21 (C21). METHODS AND RESULTS: Myocardial infarction (MI) was induced in Wistar rats by permanent ligation of the left coronary artery. Treatment with C21 (0.01, 0.03, 0.3 mg/kg per day IP) was started 24 hours after MI and was continued until euthanasia (7 days after MI). Infarct size was assessed by magnetic resonance imaging, and hemodynamic measurements were performed via transthoracic Doppler echocardiography and intracardiac Millar catheter. Cardiac tissues were analyzed for inflammation and apoptosis markers with immunoblotting and real-time reverse transcription polymerase chain reaction. C21 significantly improved systolic and diastolic ventricular function. Scar size was smallest in the C21-treated rats. In regard to underlying mechanisms, C21 diminished MI-induced Fas-ligand and caspase-3 expression in the peri-infarct zone, indicating an antiapoptotic effect. Phosphorylation of the p44/42 and p38 mitogen-activated protein kinases, both involved in the regulation of cell survival, was strongly reduced after MI but almost completely rescued by C21 treatment. Furthermore, C21 decreased MI-induced serum monocyte chemoattractant protein-1 and myeloperoxidase as well as cardiac interleukin-6, interleukin-1beta, and interleukin-2 expression, suggesting an antiinflammatory effect. CONCLUSIONS: Direct AT(2) receptor stimulation may be a novel therapeutic approach to improve post-MI systolic and diastolic function by antiapoptotic and antiinflammatory mechanisms.