Aleksandra Grzesiak

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 (AT2) receptor stimulation on postinfarct cardiac function with the use of the novel nonpeptide AT2 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-1&bgr;, and interleukin-2 expression, suggesting an antiinflammatory effect. Conclusions— Direct AT2 receptor stimulation may be a novel therapeutic approach to improve post-MI systolic and diastolic function by antiapoptotic and antiinflammatory mechanisms.

The past, present and future of angiotensin II type 2 receptor stimulation

Studying the angiotensin type 2 receptor (AT2) has been problematic in the past because a pharmacological tool for direct, specific in vitro and in vivo stimulation of the receptor has been lacking. Consequently, current knowledge about AT2 receptor signalling and function had to be obtained by indirect approaches, like studying animals or cells with genetically altered AT2 receptor expression levels, inhibitory experiments using specific AT2 receptor antagonists, stimulation with angiotensin II under concomitant angiotensin II type 1 receptor blockade or stimulation with the peptide agonist CGP42112A, which has additional AT2 receptor antagonistic properties. The recently developed non-peptide AT2 receptor agonist Compound 21 now, for the first time, allows direct, selective and specific AT2 receptor stimulation in vitro and in vivo . This new tool will certainly revolutionise AT2 receptor research, enable many new insights into AT2 receptor function and may also have the potential to become a future medical drug. This article reviews milestone findings about AT2 receptor functional properties obtained by ‘conventional’ experimental approaches within the last 20 years. Moreover, it provides an overview of the first results obtained by direct AT2 receptor stimulation with Compound 21, comprising effects on alkaline secretion, neurite outgrowth, blood pressure and post-infarct cardiac function.

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 β-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.

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 ∼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. STEM CELLS 2009;27:2488–2497

Telmisartan prevents aneurysm progression in the rat by inhibiting proteolysis, apoptosis and inflammation

Objectives We investigated the effects of treatment with the angiotensin II type 1 receptor antagonist, telmisartan, on abdominal aortic aneurysm formation in normotensive rats. Methods Abdominal aortic aneurysm was induced by perfusion of an isolated aortic segment with elastase. Treatment with telmisattan (0.5 mg/kg per day) or hydralazine (15 mg/kg per day) was started after surgery and continued for 14 days. Sham-operated animals and vehicle-treated animals after aneurysm induction served as controls. Aortic diameter was measured using ultrasound before aneurysm induction and on days 7 and 14 after aneurysm induction. Results On day 14, aortic diameter was increased two-fold in the vehicle-treated group compared to sham-operated animals (2.02 ± 0.12 vs. 0.87 ± 0.02 mm, P < 0.005, n = 8). Telmisartan treatment significantly reduced aneurysmal size (1.65 ± 0.06 vs. 2.02 ± 0.12 mm in vehicle, P < 0.05, n = 8), whereas treatment with hydralazine had no effect. Matrix metallopeptidase 3, cathepsin D, nuclear factor kappa B, tumour necrosis factor alpha, transforming growth factor-1 beta, as well as caspase 3, p53 and Fas ligand proteins, were significantly downregulated in aortic tissue under telmisartan compared to vehicle treatment. Serum monocyte chemoattractant protein 1 levels were also significantly decreased. Telmisartan and hydralazine reduced blood pressure to a similar extent within the observation period. Conclusion The angiotensin II type 1 receptor antagonist, telmisartan, prevents abdominal aortic aneurysm progression independently of blood pressure reduction by inhibiting proteolysis, apoptosis and inflammation in aortic tissue.

Estrogen receptor α 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 StimulationCLINICAL PERSPECTIVE: 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 (AT2) receptor stimulation on postinfarct cardiac function with the use of the novel nonpeptide AT2 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-1&bgr;, and interleukin-2 expression, suggesting an antiinflammatory effect. Conclusions— Direct AT2 receptor stimulation may be a novel therapeutic approach to improve post-MI systolic and diastolic function by antiapoptotic and antiinflammatory mechanisms.

Angiotensin II Type 2 Receptor StimulationCLINICAL PERSPECTIVE

Background— This study is the first to examine the effect of direct angiotensin II type 2 (AT2) receptor stimulation on postinfarct cardiac function with the use of the novel nonpeptide AT2 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-1&bgr;, and interleukin-2 expression, suggesting an antiinflammatory effect. Conclusions— Direct AT2 receptor stimulation may be a novel therapeutic approach to improve post-MI systolic and diastolic function by antiapoptotic and antiinflammatory mechanisms.