Cardioprotection induced by AT1R blockade after reperfused myocardial infarction: association with regional increase in AT2R, IP3R and PKCepsilon proteins and cGMP

Antihypertensive Effect of a Novel Angiotensin II Receptor Blocker Fluorophenyl Benzimidazole: Contribution of cGMP, Voltage-dependent Calcium Channels, and BKCa Channels to Vasorelaxant Mechanisms

Background: The current study presents the novel angiotensin II receptor blocker fluorophenyl benzimidazole (FPD) as an antihypertensive agent in the SHR model of hypertension. We investigated the role of cGMP, voltage-dependent L-type calcium channels, and BK_Ca channels in the vasorelaxant mechanisms of FPD in the rat superior mesenteric artery.

Methods: The antihypertensive effect of FPD was examined using an invasive technique measuring blood pressure in SHR animals. Using a myograph, tension measurement was completed in the superior mesenteric artery to elucidate the mechanisms of vasorelaxation involving AT1 receptors, the NO/cGMP pathway, L-type calcium channels, and BK_Ca channels. Ion flux (Ca²⁺, K⁺) studies were conducted in aortic smooth muscle cells. Putative targets proteins were determined by in silico docking studies. A safety evaluation of FPD was carried out using Swiss albino mice.

Results: FPD significantly decreased blood pressure in SHR. It relaxed superior mesenteric arteries in a concentration-dependent manner and significantly inhibited angiotensin II-induced contraction. The relaxation response was also mediated by an increase in tissue cGMP levels, inhibition of L-type calcium channels, and the opening of BK_Ca channels. FPD further enhanced efflux of K⁺ and inhibited Bay K8644-stimulated Ca²⁺ influx in aortic smooth muscle cells and docked well in an in silico study with the targets. It was well tolerated in the toxicity study.

Conclusion: The present study reports the antihypertensive activity of novel AT-1 receptor blocker FPD at 50 and 100 mg kg⁻¹ with cGMP, L-type calcium channels, and BK_Ca channels as putative targets of vasorelaxation, and was found safe in oral toxicity.

Candesartan prevents resiniferatoxin-induced sensory small-fiber neuropathy in mice by promoting angiotensin II-mediated AT2 receptor stimulation

Sensory defects associated with small-fiber neuropathy (SFN) can lead to profound disabilities. The relationship between the sensory nervous system and modulation of the renin-angiotensin system (RAS) has been described and focused on pain and neurodegeneration in several animal models. We have recently developed an experimental model of functional sensory neuropathy showing thermal hypoalgesia and neuropeptide depletion without nerve fiber degeneration. Here, we aimed to determine whether the modulation of angiotensin II (Ang II) activity could prevent sensory neuropathy induced by RTX. Control and RTX mice received ramipril, an Ang II converting enzyme (ACE) inhibitor, (0.5 mg/kg/day) or candesartan, an Ang II type 1 receptor (AT1R) blocker (0.5 mg/kg/day), one day before vehicle or RTX administration, and each day for the next seven days. Ramipril did not have a beneficial effect in RTX mice, whereas candesartan prevented thermal hypoalgesia and reduced neuropeptide depletion in intraepidermal nerve fibers and dorsal root ganglion neurons. The preventive effect of candesartan was not observed in mice deficient for the Ang II type 2 receptor (AT2R) and was counteracted in wild type mice by EMA200, an AT2R antagonist (3 mg/kg/day). Thus, candesartan may promote AT2R activation by blocking AT1R and increasing Ang II production and enhance its mechanisms of neuroprotection in our RTX model. Our finding that candesartan prevents nociception deficits and neuropeptide depletion encourages the evaluation of its therapeutic potential in patients presenting SFN, particularly those who experience chemotherapy-induced SFN.

Cardioprotective effects of angiotensin II type 1 receptor blockade with candesartan after reperfused myocardial infarction: role of angiotensin II type 2 receptor

To determine whether angiotensin II (Ang II) type 2 (AT2)-receptor activation associated with cardioprotection induced by Ang II type 1 (AT1)-receptor blockade during ischaemia-reperfusion (IR) might be reflected in increased AT 2-receptor, IP3-(1,4,5- inositol trisphosphate type 2) receptor and PKC-ε (protein kinase C-ε) proteins and tissue cGMP (cyclic guanosine monophosphate), we measured in vivo left ventricular (LV) systolic and diastolic function and remodelling (echocardiogram/Doppler) and haemodynamics, and ex vivo infarct size, AT1-/AT 2receptor, IP3-receptor and PKC-ε proteins (immunoblots) and cGMP (enzyme immunoassay) in dogs with reperfused anterior acute myocardial infarction (MI) (90-minute ischaemia, 120-minute reperfusion). Compared with controls (C, n=6) in vivo, candesartan (1 mg/kg i.v. over 30-minute pre-ischaemia, n=6) effectively inhibited the Ang II pressor response (Δ%, -14±22% vs. -80±11, p<0.003) and decreased preload (122±35 vs. -2±16%, p<0.01), improved LV systolic ejection fraction (-29±4 vs. -11±5, p<0.03) and diastolic function (E/A ratio, -25±7 vs. 33±13, p<0.004), decreased the extent of LV asynergy (26±20 vs. -31±10% LV, p<0.05) and limited acute LV remodelling (expansion index 19±6 vs. -3±5, p<0.05; thinning ratio -22±2 vs. -4±2, p<0.0003). Ex vivo, candesartan decreased infarct size (55±2 vs. 27±2% risk, p<0.001) and increased infarct zone (IZ) AT2 -receptor protein by 8-fold (but not AT1-receptor protein), IP3-receptor protein by 12-fold, PKC-ε protein by 5-fold and cGMP by 40%. Cardioprotective effects of AT1-receptor blockade on acute IR injury, LV function, and remodelling may also involve AT 2-receptor activation and downstream signalling via IP3-receptor, PKC-ε and cGMP.

Upregulation of Angiotensin II Type 2 Receptor and Limitation of Myocardial Stunning by Angiotensin II Type 1 Receptor Blockers during Reperfused Myocardial Infarction in the Rat

Background: We have previously shown that angiotensin II type 1 receptor blockers induce cardioprotection and upregulate angiotensin II type 2 receptor during in vivo postischemicreperfusion in dogs. Whether angiotensin II type 1 receptor blockers upregulate angiotensin II type 2 receptors in rats is controversial, and whether surmountable and insurmountable angiotensin II type 1 receptor blockers exert similar protective effects during reperfused myocardial infarction is not known.

Methods: We assessed the effects of the surmountable angiotensin receptor blocker valsartan, and the insurmountable angiotensin receptor blocker irbesartan, on hemodynamics and left ventricular systolic and diastolic function (echocardiography/Doppler) in vivo and infarct size (triphenyl tetrazolium chloride method), and regional angiotensin II type 1 receptor and angiotensin II type 2 receptor expression (immunoblots) ex vivo, after anterior reperfused myocardial infarction in rats. The rats were randomized to four groups: intravenous valsartan (10 mg/kg, n = 8), irbesartan (10 mg/kg, n = 8), or saline vehicle (controls, n = 14) over 30 minutes before reperfused myocardial infarction, and sham (n = 8). Angiotensin II type 1 receptor blockade was assessed by the inhibition of angiotensin II pressor responses.

Results: Compared with the control group, both angiotensin receptor blockers significantly decreased infarct size, limited the increase in left atrial pressure, improved positive left ventricular dP/dtm,x and dP/dtm,,, improved left ventricular ejection fraction and diastolic function, and limited infarct expansion after reperfused myocardial infarction. Both angiotensin receptor blockers increased angiotensin II type 2 receptor protein in the postischemic-reperfused zone, with no change in angiotensin II type 1 receptor protein. There were no changes in the sham group.

Conclusion: The overall results indicate that the angiotensin receptor blockers valsartan and irbesartan both induce cardioprotection, limit myocardial stunning, and upregulate angiotensin II type 2 receptor protein expression after reperfused myocardial infarction in the rat. Patients who are already receiving angiotensin receptor blockers and develop acute coronary syndromes might benefit from these cardioprotective effects during reperfusion therapy.

Pleiotropic effects of cardiac drugs on healing post-MI. The good, bad, and ugly

Healing after myocardial infarction (MI) is a well-orchestrated time-dependent process that involves inflammation, tissue repair with extracellular collagen matrix (ECCM) deposition and scar formation, and remodeling of myocardial structure, matrix, vasculature, and function. Rapid early ECCM degradation followed by slow ECCM replacement and maturation during post-MI healing results in a prolonged window of enhanced vulnerability to adverse remodeling. Decreased ECCM results in adverse ventricular remodeling, dysfunction, and rupture. Inflammation, a critical factor in normal healing, if impaired results in adverse remodeling and rupture. Several therapeutic drugs prescribed after MI exert pleiotropic effects that suppress ECCM and inflammation during healing and may have good, bad, or ugly consequences. This article reviews the potential impact of pleiotropic effects of some prototypic cardiac drugs such as renin-angiotensin-aldosterone system (RAAS) inhibitors, statins, and thrombolytics during healing post-ST-segment-elevation MI (STEMI), with special focus on inflammation, ECCM and remodeling, and implications in the elderly.

Valsartan in the treatment of heart attack survivors

Survivors of myocardial infarction (MI) are at high risk of disability and death. This is due to infarct-related complications such as heart failure, cardiac remodeling with progressive ventricular dilation, dysfunction, and hypertrophy, and arrhythmias including ventricular and atrial fibrillation. Angiotensin (Ang) II, the major effector molecule of the renin–angiotensin–aldosterone system (RAAS) is a major contributor to these complications. RAAS inhibition, with angiotensin-converting enzyme (ACE) inhibitors were first shown to reduce mortality and morbidity after MI. Subsequently, angiotensin receptor blockers (ARBs), that produce more complete blockade of the effects of Ang II at the Ang II type 1 (AT₁) receptor, were introduced and the ARB valsartan was shown to be as effective as an ACE inhibitor in reducing mortality and morbidity in high-risk post-MI suvivors with left ventricular (LV) systolic dysfunction and and/or heart failure and in heart failure patients, respectively, in two major trials (VALIANT and Val-HeFT). Both these trials used an ACE inhibitor as comparator on top of background therapy. Evidence favoring the use of valsartan for secondary prevention in post-MI survivors is reviewed.

Chronic Angiotensin II Receptor Blockade Induces Cardioprotection During Ischemia by Increased PKC-ε Expression in the Mouse Heart

INTRODUCTION

This study was performed to investigate the role of chronic pretreatment with angiotensin II type 1 receptor antagonists (ARB) and angiotensin converting enzyme inhibitors (ACE-I) in myocardial infarction (MI) and ischemic preconditioning (iPC). Little is known about molecular mechanisms of MI and iPC, especially about protein kinase C (PKC) isozyme levels induced by chronic pharmacologic pretreatment with ARB and ACE-I. To address one of the most important signal molecules in iPC, the PKC system was investigated in an ischemia/reperfusion model using isolated mouse hearts.

METHODS

C57/BL6 mice were treated orally with candesartan cilexetil or ramipril for 2 weeks. Isolated perfused hearts were subjected to 60 minutes of left anterior descending occlusion and 30 minutes of reperfusion. IPC was performed by 3 cycles of 5 minutes of ischemia prior to the infarct ischemia. Infarct size was measured using the propidium iodide method, and PKC isoenzymes were detected by immunoblotting in the membrane and cytosolic fraction.

RESULTS

In the control group, iPC reduced infarct size from 59.8 +/- 4.2% to 24.5 +/- 1.7%. ARB pretreatment itself reduced the infarct size significantly (38.1 +/- 3.0%) in hearts without iPC. This protection could neither be enhanced by additional iPC (40.3 +/- 3.4%) nor blocked by the AT2-receptor antagonist PD123.319 (40.7 +/- 3.7%). The ARB-induced cardio protection, however, was abolished by chelerythrine (5 micromol/L) (71.7 +/- 6.6%, n = 11, P < 0.001). Furthermore, PKC-epsilon (PKC-epsilon) was significantly increased in the particulate fraction of ARB-pretreated mice. On the contrary, chronic treatment with ACE-I completely blocked iPC (57.7 +/- 3.9%, n = 12, P < 0.001) without any effect on infarct size itself (51.5 +/- 3.0%, n = 12). PKC-epsilon expression was significantly reduced.

CONCLUSION

Chronic AT1-receptor antagonism is capable of protecting the heart against myocardial infarction in a PKC-epsilon-dependent way. Furthermore, chronic treatment with ACE-I is suggested to have suppressing effects on iPC, possibly caused by reduced PKC-epsilon expression.

AT2 receptor and apoptosis during AT1 receptor blockade in reperfused myocardial infarction in the rat

We assessed whether upregulation of the angiotensin II (AngII) type 2 receptor (AT2R) during AngII type 1 receptor (AT1R) blockade might induce apoptosis in the in vivo rat model of reperfused myocardial infarction (RMI) and whether addition of an AT2R blocker abolishes that effect. We measured in vivo hemodynamics and left ventricular (LV) systolic and diastolic function (echocardiograms/Doppler), and ex vivo infarct size (triphenyl tetrazolium chloride), regional AT1R and AT2R proteins (immunoblots), and apoptosis (TUNEL assay and DNA ladder) after regional anterior RMI (60 min ischemia, 90 min reperfusion) in Sprague-Dawley rats randomized to intravenous AT1R blockade with candesartan (1 mg/kg, n = 9) or saline (controls, n = 14) over 30 min before RMI, and sham (n = 8). We also assessed the effect of AT2R blockade (PD123319, 10 mg/kg i.v.) plus candesartan on infarct size and apoptosis. Compared to controls, candesartan significantly (p < 0.001) limited increases in left atrial pressure, improved positive LV dP/dtmax and negative dP/dtmin, normalized LV ejection fraction, improved LV diastolic function, limited infarct expansion, decreased infarct size and apoptosis, and increased AT2R protein (not AT1R) in the reperfused ischemic zone. There were no changes in sham hearts. PD123319 abolished the candesartan-induced decrease in infarct size and LV dysfunction but not the decrease in apoptosis. Thus, during AT1R blockade in the in vivo rat model of RMI, regional AT2R upregulation contributes to the beneficial effect on infarct size and LV dysfunction but not on apoptosis, suggesting that the apoptosis is AT1R not AT2R-mediated.

Valsartan-induced cardioprotection involves angiotensin II type 2 receptor upregulation in dog and rat models of in vivo reperfused myocardial infarction

BACKGROUND

Cardioprotection with angiotensin II (AngII) type 1 receptor (AT(1)R) blockade was associated with AngII type 2 receptor (AT(2)R) upregulation and activation during in vivo reperfused myocardial infarction (RMI) in dogs, but it is unclear whether this occurs in rats. Methods and results In vivo hemodynamics, left ventricular (LV) function, infarct size, and AT(1)R/AT(2)R protein (immunoblots) after anterior RMI were measured in rats (60 minutes ischemia, 90 minutes reperfusion, n=30) and dogs (90 minutes ischemia, 120 minutes reperfusion, n=22) randomized to pretreatment with valsartan (10 mg/kg, intravenously) or vehicle control, and vehicle sham groups. AT(1)R blockade was confirmed by inhibition of AngII pressor responses at the dose used. Compared with dog and rat controls, valsartan decreased infarct size (52 versus 31% and 47 versus 33%, respectively), improved left ventricular ejection fraction (-32 versus -14% and -46 versus -21%, respectively), limited infarct expansion and infarct thinning, and improved diastolic function after RMI. In both species, AT(2)R protein in the infarct zone decreased in controls and increased with valsartan. Sham animals showed no changes.

CONCLUSIONS

AT(1)R blockade with valsartan induces short-term cardioprotection associated with enhanced AT(2)R expression in both dog and rat models of in vivo RMI.

Nitric oxide, an iceberg in cardiovascular physiology:

The endothelium is now recognized not only as a physical barrier between blood and vascular wall, but also as an important and strategically located organ with multiple endocrine and paracrine functions. By releasing vasoactive substances, the endothelium acts as an inhibitory regulator of vascular contraction, leukocyte adhesion, vascular smooth muscle cell growth, and platelet aggregation. This review intends to demonstrate how much the picture of the biological functions of nitric oxide has changed in cardiovascular physiology, extending beyond its vessel-relaxing activity, as well as to highlight new insights into the factors affecting its bioavailability and regulation in relation with many cardiovascular diseases.

Nitric oxide and cardiovascular protection

Nitric oxide (NO) plays a critical role in ischemic heart disease and ischemia-reperfusion. There is an increasing body of evidence to support the role of NO in myocardial and vascular protection in disease. The finding that NO might act as a trigger of late ischemic preconditioning (IPC) might lead to the development of novel anti-ischemic therapy. The role of NO signaling in the cardioprotective effects of ACE inhibitors and angiotensin II type 1 receptor(AT(1)) receptor antagonists is an active area of study.

Nitric oxide and cardioprotection during ischemia-reperfusion

Coronary artery reperfusion is widely used to restore blood flow in acute myocardial infarction and limit its progression. However, reperfusion of ischemic myocardium results in reperfusion injury and persistent ventricular dysfunction even when achieved after brief periods of ischemia. Normally, small amounts of nitric oxide (NO) generated by endothelial NO synthase (eNOS) regulates vascular tone. Ischemia-reperfusion triggers the release of oxygen free radicals (OFRs) and a cascade involving endothelial dysfunction, decreased eNOS and NO, neutrophil activation, increased cytokines and more OFRs, increased inducible NO synthase (iNOS) and marked increase in NO, excess peroxynitrite formation, and myocardial injury. Low doses of NO appear to be beneficial and high doses harmful in ischemia-reperfusion. eNOS knock-out mice confirm that eNOS-derived NO is cardioprotective in ischemia-reperfusion. iNOS overexpression increases peroxynitrite but did not cause severe dysfunction. Increased angiotensin II (AngII) after ischemia-reperfusion inactivates NO, forms peroxynitrite and produces cardiotoxic effects. Beneficial effects of angiotensin-converting-enzyme inhibition and AngII type 1 (AT(1)) receptor blockade after ischemia-reperfusion are partly mediated through AngII type 2 (AT(2)) receptor stimulation, increased bradykinin and NO. Interventions that enhance NO availability by increasing eNOS might be beneficial after ischemia-reperfusion.

Influence of angiotensin II type 1-receptor antagonist CV11974 on infarct size and adjacent regional function after ischemia-reperfusion in dogs

The presence of nonischemic regional dysfunction at the adjacent region of the ischemic myocardium was demonstrated in clinical studies. Recent studies demonstrated an angiotensin II type 1 (AT1)-receptor antagonist reduced myocardial ischemia-reperfusion injury. We investigated the role of the adjacent region after reperfusion by studying the effects of AT1-receptor antagonist on myocardial function and infarct size. We investigated 12 open-chest anesthetized dogs undergoing 90 min of left anterior descending coronary artery occlusion followed by 4 h of reperfusion. Six dogs injected with an AT1-receptor antagonist (CV11974) immediately after reperfusion were compared with 6 control dogs. Percent systolic shortening (%SS) was measured by two sets of the pair sonomicrometer crystals implanted to adjacent and remote nonischemic myocardium. After 4 h of reperfusion, infarct size was measured. There were no significant differences of the %SS at baseline between two regions. In both groups, %SS at adjacent region after reperfusion was significantly decreased as compared with remote region. There were no significant differences between the two groups. Infarct size, as a percentage of the area at risk, was smaller in the AT, group than in control group (25.49+/-7.53% vs 68.58+/-26.88% P<0.01). AT1-receptor antagonist reduces infarct size. This effect is not related to the change of regional myocardial function at adjacent region after reperfusion.

Effects of combination of angiotensin-converting enzyme inhibitor and angiotensin receptor antagonist on inflammatory cellular infiltration and myocardial interstitial fibrosis after acute myocardial infarction

OBJECTIVES

The goal of this study was to compare the relative efficacy of an angiotensin-converting enzyme (ACE) inhibitor and an angiotensin receptor blocker (ARB) in suppressing the histopathologic changes that lead to ventricular remodeling after an acute myocardial infarction (AMI).

BACKGROUND

Myocardial interstitial fibrosis in the noninfarcted region is a major histologic landmark resulting in cardiac dysfunction after AMI. However, the relative potency of an ACE inhibitor and ARB on suppressing the histopathologic changes was unclear.

METHODS

Rats with AMI were randomized to fosinopril, valsartan or a combination of the two drugs for two or four weeks. The total, type I and type III collagen and activated fibroblasts and macrophages were quantified by histomorphometry. The expression of transforming growth factor-beta 1 (TGF-beta 1) messenger ribonucleic acid (mRNA) was determined by reverse transcription polymerase chain reaction.

RESULTS

Acute myocardial infarction resulted in significant elevation of total (p < 0.001) and type I (p < 0.001) collagen and a twofold increase in TGF-beta 1 mRNA expression (p < 0.001) in the septum at two and four weeks. Macrophages and activated myofibroblasts infiltrated extensively in the infarct zone. Treatment with valsartan or combination therapy normalized the total and type I collagen (p < 0.001) as well as TGF-beta 1 mRNA level (p < 0.01) in the septum and was associated with the suppression of macrophages and myofibroblasts in the infarct zone (p < 0.01). Fosinopril was less effective than valsartan or combination therapy.

CONCLUSIONS

The use of valsartan, especially combined with fosinopril, was more effective than fosinopril in the suppression of histopathologic changes resulting in cardiac remodeling after AMI. This study has important therapeutic implications in pharmacotherapy of clinical practice.

Enhanced regional AT(2)-receptor and PKC(epsilon) expression during cardioprotection induced by AT(1)-receptor blockade after reperfused myocardial infarction

We assessed the effects of the angiotensin II (Ang II) type 1 receptor (AT1-receptor) blocker, candesartan, (CN, 1 mg/kg i.v. over 30 minutes pre-ischaemia) alone or after intracoronary administration of Ang II type 2 receptor (AT2-receptor) blocker (PD 123319), protein kinase C (PKC) inhibitor (chelerythrine), endothelial nitric oxide (NO) synthase inhibitor (N(G)-monomethyl-L-arginine or L-NMMA), and bradykinin (BK) -B2 receptor inhibitor (HOE140) on in vivo left ventricular (LV) function and remodelling (echocardiograms/Doppler) and haemodynamics in 30 dogs with reperfused anterior infarction (90 minutes ischaemia, 120 minutes reperfusion), and ex vivo infarct size, AT1-receptor/AT2-receptor proteins and PKC(epsilon) (immunoblots), and cyclic guanosine 3', 5' monophosphate (cGMP, immunoassay). Compared with controls, CN inhibited the Ang II pressor response, reduced LV preload, improved LV systolic and diastolic function, limited LV remodelling, decreased infarct size, and increased AT2-receptor and PKC(epsilon) proteins in the infarct zone (IZ), and these responses were abrogated by PD 123319, chelerythrine, L-NMMA and HOE140. In addition, the increase in LV cGMP with CN was attenuated by PD 123319, L-NMMA and HOE140. The overall results suggest that AT2-receptor activation and signalling via BK, PKC(epsilon) and cGMP contribute to cardioprotection associated with AT1-receptor blockade during ischaemia-reperfusion injury.

Effect of chronic AT(1) receptor antagonism on postischemic functional recovery and AT(1)/AT(2) receptor proteins in isolated working rat hearts

To determine whether chronic angiotensin II (Ang II) type I receptor (AT(1)R) antagonism improves recovery of left ventricular (LV) function after ischemia-reperfusion (IR) and increases AT(1)R and Ang II type 2 receptor (AT(2)R) protein expression in isolated working rat hearts, rats were randomized to pretreatment with either losartan (30 mg/kg/day) or UP269-6 (3 mg/kg/day), or no drug (control), for 1 week or 3 weeks before IR (50 min perfusion, 25 min ischemia, 40 min reperfusion). In vitro LV work and power and ex vivo AT(1)R and AT(2)R proteins (immunoblots) were measured. Compared to baseline perfusion, LV work and power showed variable recovery in control, losartan, and UP269-6 groups. Compared to control, losartan preserved recovery of LV work and power while UP269-6 showed less recovery after IR at both 1 week and 3 weeks. Both antagonists increased AT(2)R but not AT(1)R protein. The duration of pretreatment did not affect the expression of AT(1)R or AT(2)R proteins. The results indicate that chronic AT(1)R blockade over 1 or 3 weeks increases AT(2)R (not AT(1)R) protein expression and may preserve but not improve postischemic functional recovery compared to controls in isolated working rat hearts.