Manuela Sommerfeld

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.

Angiotensin Type 2 Receptor Stimulation Ameliorates Left Ventricular Fibrosis and Dysfunction via Regulation of Tissue Inhibitor of Matrix Metalloproteinase 1/Matrix Metalloproteinase 9 Axis and Transforming Growth Factor β1 in the Rat Heart

Left ventricular (LV) remodeling is the main reason for the development of progressive cardiac dysfunction after myocardial infarction (MI). This study investigated whether stimulation of the angiotensin type 2 receptor is able to ameliorate post-MI cardiac remodeling and what the underlying mechanisms may be. MI was induced in Wistar rats by permanent ligation of the left coronary artery. Treatment with the angiotensin type 2 receptor agonist compound 21 ( 0.03 mg/kg) was started 6 hours post-MI and continued for 6 weeks. Hemodynamic parameters were measured by echocardiography and intracardiac catheter. Effects on proteolysis were studied in heart tissue and primary cardiac fibroblasts. Compound 21 significantly improved systolic and diastolic functions, resulting in improved ejection fraction (71.2±4.7% versus 53.4±7.0%; P<0.001), fractional shortening (P<0.05), LV internal dimension in systole (P<0.05), LV end-diastolic pressure (16.9±1.2 versus 22.1±1.4 mm Hg; P<0.05), ratio of early (E) to late (A) ventricular filling velocities, and maximum and minimum rate of LV pressure rise (P<0.05). Compound 21 improved arterial stiffness parameters and reduced collagen content in peri-infarct myocardium. Tissue inhibitor of matrix metalloproteinase 1 was strongly upregulated, whereas matrix metalloproteinases 2 and 9 and transforming growth factor &bgr;1 were diminished in LV of treated animals. In cardiac fibroblasts, compound 21 initially induced tissue inhibitor of matrix metalloproteinase 1 expression followed by attenuated matrix metalloproteinase 9 and transforming growth factor &bgr;1 secretion. In conclusion, angiotensin type 2 receptor stimulation improves cardiac function and prevents cardiac remodeling in the late stage after MI, suggesting that angiotensin type 2 receptor agonists may be considered a future pharmacological approach for the improvement of post-MI cardiac dysfunction.

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.

Transition from atherosclerosis to aortic aneurysm in humans coincides with an increased expression of RAS components

While the renin-angiotensin system (RAS) is widely recognized to be involved in atherosclerosis, its potential role in the progression from atherosclerotic lesions to abdominal aortic aneurysm (AAA) is poorly understood. The present study aimed to investigate which components of the RAS may render the atherosclerotic aorta aneurysmatic. The expression of renin, prorenin/renin receptor, angiotensinogen, AT1- and AT2 receptors, cathepsin D, cathepsin G and chymase was examined by immunoblotting and immunohistochemistry in human atherosclerotic, aneurysmatic and healthy aortic tissues obtained from patients undergoing elective repair or at autopsy. AT1- and AT2 receptor mRNA expression was determined using quantitative real-time RT-PCR. All investigated local RAS components were up-regulated in atherosclerotic as compared to healthy tissues. AAA compared to atherosclerosis was characterized by a further increase in the expression of all RAS components except for the AT2 receptor. Cathepsin D was exclusively up-regulated in AAA. Most RAS components co-localized with infiltrating leukocytes or mast cells pointing to their contribution to inflammatory processes. Due to their proteolytic features, some RAS components (cathepsin D and cathepsin G and chymase) may contribute to AAA formation by accessory mechanisms. Taken together, our data suggest that in humans, RAS activation is not just a key-player in the pathogenesis of atherosclerosis, but that a further increasing activation may be involved in the transition from atherosclerosis to AAA.

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.

[OP.7C.05] ANGIOTENSIN AT2 RECEPTOR AGONIST, COMPOUND 21, PREVENTS ABDOMINAL AORTIC ANEURYSM PROGRESSION AND THE DECREASE OF AORTIC WALL DISTENSIBILITY IN THE RAT

Objective: We studied the effects of selective AT2 receptor agonist, compound 21, (C21) treatment on experimental abdominal aortic aneurysm (AAA) formation in rats. Design and method: AAA was induced by perfusion of isolated aortic segments with elastase in normotensive Wistar rats. Treatment with C21 (0.03 mg/kg daily) was started after operation and continued for 14 days. Sham operated animals and vehicle-treated animals after aneurysm induction (AI) served as controls. Aortic diameter and blood velocities were measured infrarenally before and on days 7 and 14 post operation via ultrasound biomicroscopy. Analysis of pulse propagation velocity (PPV) and distensibility was performed using the Vevo Vasc® software. Hemodynamic parameters were measured via tail cuff and intraventricular Samba catheter. Aortic tissue expressions of MMP9, IL6, IL1beta, NFkappaB and MLKL as well as serum cytokines were analysed. Results: On day 14 post AI, infrarenal aortic diameter of AAA group was increased 1,55-fold compared to sham operated animals (2.65 mm ± 0.05, n = 8 vs. 1.7 mm ± 0.068, n = 6; p < 0.0001). C21 significantly decreased aortic diameter by 20% on day 7 post AI and by 28% on day 14 compared to vehicle-treated animals (1.9 mm ± 0.06, vs. 2.65 mm ± 0.06; p < 0.0001). Left ventricle parameters and blood pressure were not influenced by AI nor by additional treatment with C21. AI significantly reduced infrarenal blood velocity, distensibility and increased PPV. All these pathological effects were significantly ameliorated in C21 treated rats (p < 0, 0001; p < 0, 0001; p = 0, 0205; 2-wayANOVA). Treatment with C21 also reduced the expression of inflammatory markers IL1 beta, NF kappa B, protease MMP9 and MLKL, the marker of necroptotic cell death in the aortic media. Moreover, C21 reduced the increase of TGF-beta1 in serum (p = 0, 0055). Conclusions: The angiotensin AT2 receptor agonist, C21, prevents abdominal aortic aneurysm progression in the rat without affecting blood pressure or left ventricle parameters. C21 also prevents the decline of infrarenal aortic blood velocity, reduces the decrease of aortic wall distensibility at aneurysm site and the AAA-induced increase of inflammatory and necroptotic markers.

RIMONABANT IMPROVES HEART FUNCTION AFTER MYOCARDIAL INFARCTION IN THE RAT: PP.13.481

Objectives: The effects of the selective cannabinoid-1 receptor (CB1) antagonist, rimonabant, on postinfarct cardiac function in rats were investigated. Design and Methods: Myocardial infarction (MI) was induced in Wistar rats by permanent ligation of the left coronary artery. Treatment with rimonabant (10 mg/kg i.p daily) was started 7d before MI and continued for 6 weeks. Hemodynamic parameters were measured via transthoracic Doppler echocardiography and intracardiac Samba catheter. Arterial stiffness was studied using pulse wave analysis. The expression of cytokines and apoptotic markers was determined in heart tissue. Results: Rimonabant significantly improved systolic heart function: fractional shortening (35.8 ± 6.0% vs. 20.3 ± 4.0%, p < 0.05) and ejection fraction (63.2 ± 8.4% vs. 39.3 ± 6.8%, p < 0.05) were increased in comparison to vehicle, whereas E/A ratio was lower in treatment group (3.3 ± 0.7 vs. 4.7 ± 0.7, p < 0.05). Rimonabant treatment lowered left ventricle end-diastolic pressure (11.2 ± 2.3mmHg vs. 14.9 ± 1.31mmHg, p < 0.05) and increased dP/dtmax (11228 ± 250mmHg/s vs. 7953 ± 274mmHg/s, p < 0.01) compared to vehicle. Arterial stiffness parameters- pulse pressure, augmentation pressure- and index - were significantly decreased (p < 0.05) in the rimonabant group compared to vehicle. Heart/body weight ratio was also lower after rimonabant treatment (p < 0.05), whereas systolic blood pressure and heart rate were not changed. Analysis of locomotor behavior demonstrated an increased activity of rimonabant - treated rats (p < 0.01). The increase of protein expression of IL-1 beta in the heart tissues from vehicle group was completely abolished by rimonabant treatment. Apoptosis markers were not changed. Conclusion: The cannabinoid-1 receptor antagonist, rimonabant, improves systolic and diastolic heart function and decreases arterial stiffness in rats 6 weeks after myocardial infarction. Reduced inflammation in the heart may contribute to cardiac protection by rimonabant.

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.