Bradykinin-mediated cardiovascular protective actions of ACE inhibitors. A new dimension in anti-ischaemic therapy?

Heart Failure With Preserved Ejection Fraction: An Evolving Understanding

Heart failure (HF) with preserved ejection fraction (HFpEF) is a clinical syndrome in which patients have signs and symptoms of HF due to high left ventricular (LV) filling pressure despite normal or near normal LV ejection fraction. It is more common than HF with reduced ejection fraction (HFrEF), and its diagnosis and treatment are more challenging than HFrEF. Although hypertension is the primary risk factor, coronary artery disease and other comorbidities, such as atrial fibrillation (AF), diabetes, chronic kidney disease (CKD), and obesity, also play an essential role in its formation. This review summarizes current knowledge about HFpEF, its pathophysiology, clinical presentation, diagnostic challenges, current treatments, and promising novel treatments. It is essential to continue to be updated on the latest treatments for HFpEF so that patients always receive the most therapeutic treatments. The use of GnRH agonists in the management of HFpEF, infusion of Apo a-I nanoparticle, low-level transcutaneous vagal stimulation (LLTS), and estrogen only in post-menopausal women are promising strategies to prevent diastolic dysfunction and HFpEF; however, there is still no proven curative treatment for HFpEF yet.

Angiotensin-converting enzyme inhibitors stimulate cerebral arteriogenesis

AIM

Arteriogenesis constitutes the most efficient endogenous rescue mechanism in cases of cerebral ischaemia. The aim of this work was to investigate whether angiotensin-converting enzyme inhibitors (ACEi) stimulates, and angiotensin II receptor type 1 blockers (ARB) inhibits cerebral collateral growth by applying a three-vessel occlusion (3-VO) model in rat.

METHODS

Cerebral collateral growth was measured post 3-VO (1) by assessing blood flow using the cerebrovascular reserve capacity (CVRC) technique, and (2) by assessing vessel diameters in the posterior cerebral artery (PCA) via the evaluation of latex angiographies. A stimulatory effect on arteriogenesis was investigated for ACEi administration ± bradykinin receptor 1 (B1R) and 2 (B2R) blockers, and an inhibitory effect was analysed for ARB administration. Results were validated by immunohistochemical analysis and mechanistic data were collected by human umbilical vein endothelial cell (HUVEC) viability or scratch assay and monocyte (THP-1) migration assay.

RESULTS

An inhibitory effect of ARB on arteriogenesis could not be demonstrated. However, collateral growth measurements demonstrated a significantly increased CVRC and PCA diameters in the ACEi group. ACEi stimulates cell viability and migration, which could be partially reduced by additional administration of bradykinin receptor 1 inhibitor (B1Ri). ACEi inhibits the degradation of pro-arteriogenic bradykinin derivatives, but combined ACEi + B1Ri + B1Ri (BRB) treatment did not reverse the stimulatory effect. Yet, co-administration of ACEi + BRB enhances arteriogenesis and cell migration.

CONCLUSION

We demonstrate a potent stimulatory effect of ACEi on cerebral arteriogenesis in rats, presumable via B1R. However, results imply a pleiotropic and compensatory effect of ACEi on bradykinin receptor-stimulated arteriogenesis.

The Endothelium as a Target for the Treatment of Heart Failure

The functional integrity of endothelial cells is a marker and a prerequisite for vascular health. It is well established that the endothelium not only modulates, but also mediates vascular disease processes. Certain diseases such as diabetes, dyslipidaemia, obesity, and arterial hypertension advance endothelial injury. The disease process induces cellular and functional changes in endothelial cells leading to a pathophysiological phenomenon referred to as endothelial cell dysfunction, which involves abnormal vasomotion, an imbalance in reactive oxygen species and nitric oxide, the activation of inflammation, and disruption of the coagulation process of the endothelial cells. With this knowledge, it is now known that vascular function plays a central role in the development and progression of heart failure (HF). HF is the primary cause of patient hospitalization. There is a strong desire to intervene and prevent the growing HF epidemic. Over the last decade, numerous therapies have been evaluated but few have led to positive results in the later stages of clinical trials. Efforts are currently being made to understand the pathophysiology of endothelial dysfunction and use this knowledge to identify novel agents or therapeutic targets that will improve the outcome of patients with HF and restore the normal function of the endothelium. The purpose of this review is to present a brief summary of the traditional approaches that have been taken to improve endothelial dysfunction and combat HF and, more importantly, to discuss some novel therapeutic approaches that are still under investigation, including the use of gene therapy and nanocarriers as means of delivering targets to the dysfunctional endothelium as treatment for HF.

Pathophysiological Mechanisms and Correlates of Therapeutic Pharmacological Interventions in Essential Arterial Hypertension

Treating arterial hypertension (HT) remains a hard task. The hypertensive patient is often a subject with several comorbidities and metabolic abnormalities. Clinicians everyday have to choose the right drug for the single patient among the different classes of antihypertensives. Apart from lowering blood pressure, a main therapeutic target should be that of counteracting all the possible pathophysiological mechanisms involved in HT itself and in existing/potential comorbidities. All the ancillary positive and negative effects of the administered drugs should be considered: in particular, since hypertensive patients are often glucose intolerant/diabetic, carrier of serum lipids disorder, have already developed atherosclerotic diseases and endothelial dysfunction, they should not be treated with drugs negatively interfering with these conditions but with molecules that, if possible, improve them. The main pathophysiological mechanisms and correlates of therapeutic pharmacological interventions in essential HT are reviewed here.

Critical insights into the beneficial and protective actions of the kallikrein-kinin system

Hypertension is characterized by an imbalance between the renin-angiotensin system (RAS) and the kallikrein-kinin system (KKS). Angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin II AT-1 receptor antagonists (also known as sartans or ARBs) are potent modulators of these systems and are highly effective as first-line treatments for hypertension, diabetic nephropathies, and diseases of the brain and coronary arteries. However, these agents are mechanistically distinct and should not be considered interchangeable. In this mini-review, we provide novel insights into the often neglected roles of the KKS in the beneficial, protective, and reparative actions of ACEIs. Indeed, ACEIs are the only antihypertensive drugs that properly reduce the imbalance between the RAS and the KKS, thereby restoring optimal cardiovascular homeostasis and significantly reducing morbidity and the risk of all-cause mortality among individuals affected by hypertension and other cardiovascular diseases.

Extracellular and intracellular proteases in cardiac dysfunction due to ischemia-reperfusion injury

Various procedures such as angioplasty, thrombolytic therapy, coronary bypass surgery, and cardiac transplantation are invariably associated with ischemia-reperfusion (I/R) injury. Impaired recovery of cardiac function due to I/R injury is considered to be a consequence of the occurrence of both oxidative stress and intracellular Ca(2+)-overload in the myocardium. These changes in the ischemic myocardium appear to activate both extracellular and intracellular proteases which are responsible for the cleavage of extracellular matrix and subcellular structures involved in the maintenance of cardiac function. It is thus intended to discuss the actions of I/R injury on several proteases, with a focus on calpain, matrix metalloproteinases, and cathepsins as well as their role in inducing alterations both inside and outside the cardiomyocytes. In addition, modifications of subcellular organelles such as myofibrils, sarcoplasmic reticulum and sarcolemma as well as extracellular matrix, and the potential regulatory effects of endogenous inhibitors on protease activities are identified. Both extracellular and intracellular proteolytic activities appear to be imperative in determining the true extent of I/R injury and their inhibition seems to be of critical importance for improving the recovery of cardiac function. Thus, both extracellular and intracellular proteases may serve as potential targets for the development of cardioprotective interventions for reducing damage to the heart and retarding the development of contractile dysfunction caused by I/R injury.

Ramipril-like activity of Spondias mombin linn against no-flow ischemia and isoproterenol-induced cardiotoxicity in rat heart

The cardioprotective property of Spondias mombin (SM) was investigated and compared with that of the ACE inhibitor, ramipril. Alterations to markers of myocardial injury and indices of antioxidant capacity by isoproterenol (ISP) intoxication were significantly corrected in groups treated with SM. The inflammatory index was increased by 24% in ISP-intoxicated group compared with control (P < 0.001) but reduced in the groups administered ISP and treated with 100 or 250 mg/kg SM by 17% (P < 0.001) and 11% (P < 0.05) respectively. Serum lactate dehydrogenase activity and cholesterol level which were significantly increased in ISP-intoxicated group compared with control were reduced in groups administered ISP and treated with SM. Serum phosphate levels in groups administered ISP and treated with SM were significantly lower than values obtained for the ISP-intoxicated group (P < 0.001). Tissue catalase and superoxide dismutase activities as well as glutathione level were significantly increased in groups administered ISP and treated with SM compared to ISP-intoxicated group while MDA and nitrite levels were decreased. Disruption in the structure of cardiac myofibrils by ISP intoxication was reduced by treatment with SM. Comparable results were obtained for ramipril. These results are indicative of the potent cardioprotective property of SM.

Overview of the relationship between ischemia and congestive heart failure

Ischemic heart disease is the principal etiology of heart failure in the Western world. Myocardial ischemia is important in cardiac remodeling, a process that leads to a progressive change in the shape and size of the heart and significantly worsens the prognosis of patients with heart failure. Preventing ischemic events, therefore, is an important goal in the management of patients with coronary artery disease. Statins have been shown to reduce the number of ischemic events in these patients, whereas the benefit of beta-blocker and aldosterone antagonist therapy on ischemic causes of heart failure remains unclear. Several large trials involving patients with asymptomatic left ventricular dysfunction after myocardial infarction or heart failure have shown that angiotensin-converting enzyme (ACE) inhibitors reduce the incidence of progressive heart failure, death, and ischemic events, thus establishing ACE inhibitors as first-line therapy for these patients. Other lines of evidence have suggested that ACE inhibitor therapy may also benefit patients with preserved left ventricular function, a hypothesis that is being evaluated in three large, controlled, randomized trials. One of these trials, the Heart Outcomes Prevention Evaluation (HOPE) study, was terminated prematurely because it demonstrated the significant positive effects of the ACE inhibitor ramipril on cardiovascular outcomes in patients with coronary artery disease and preserved left ventricular function. A growing body of data confirms the relationship between ischemia and heart failure and the benefits of ACE inhibitor treatment in a broad range of high-risk patients.

The anti-ischemic potential of angiotensin-converting enzyme inhibition: insights from the heart outcomes prevention evaluation trial

Therapy with an angiotensin-converting enzyme (ACE) inhibitor is established for reducing excessive blood pressure, reducing mortality in patients with congestive heart failure (CHF), preventing the development of CHF in patients with asymptomatic left ventricular (LV) dysfunction, and preventing death and CHF when initiated early after the onset of acute myocardial infarction (MI). Although these benefits have been attributed largely to hemodynamic mechanisms, recent preclinical and clinical evidence reveal ACE inhibition as potent in preventing ischemic events and in blocking an array of ischemic processes, including atherogenesis. A major contributor to this new evidence is the large, placebo-controlled Heart Outcomes Prevention Evaluation (HOPE) trial, which found that the ACE inhibitor ramipril ( 10 mg daily) prevented MI and other ischemic events in patients with a broad range of cardiovascular (CV) risks (including coronary artery disease, stroke, peripheral vascular disease, or diabetes plus one additional risk factor) but no LV dysfunction or history of heart failure at baseline. The data from the HOPE trial suggest a greatly expanded role for ramipril in the prevention and management of CV disease.

Effects of bradykinin on cardiovascular remodeling in renovascular hypertensive rats

Angiotensin converting enzyme (ACE) inhibitors inhibit both the formation of angiotensin II and the catabolism of bradykinin (BK). They prevent not only hypertension but also cardiac hypertrophy and fibrosis. An increase in BK level stimulates the expression of nitric oxide (NO) synthase (NOS) and induces prostaglandins, both of which are powerful vasodilator factors. The direct effect of BK against cardiac hypertrophy is still unclear. This study was performed to examine the cardioprotective effects of BK in hypertrophic models. Renovascular hypertensive (RHT) rats were treated with BK (1,000 ng/kg/day), BK+D-arginyl-[Hyp(3), Thi(5), D-Tic(7), Oic(8)]-bradykinin (HOE140) (a BK B(2) receptor antagonist), and BK+N(omega)-nitro-L-arginine methyl ester (L-NAME) (a NOS inhibitor) for 3 weeks. Blood pressure was measured and echocardiographic analysis performed during the treatment. Histological data were analyzed to confirm the hypotrophic effect of BK. Treatment with BK improved cardiac remodeling, reducing both the heart weight/body weight ratio and the left ventricular wall thickness. However, co-treatment with HOE140 or L-NAME reversed the anti-hypertrophic action of BK. In particular, cardiac fibrosis or perivascular fibrosis, along with collagen accumulation, were inhibited by treatment with BK, while HOE140 and L-NAME counteracted these changes. In addition, expressions of atrial natriuretic peptides (ANP) and brain natriuretic peptides (BNP), which are markers of cardiac abnormalities, were down-regulated by treatment with BK. These effects were reversed by co-treatment with HOE140 and L-NAME. Together, these results indicate that BK directly inhibits the progression of cardiac hypertrophy and cardiac fibrosis due to NO release via the BK B(2) receptor. The BK-NO pathway may play an important role in the progression of cardiac remodeling.

Antianginal efficacy of omapatrilat in patients with chronic angina pectoris

Angiotensin-converting enzyme inhibition is not an effective antianginal therapy. Experimental data suggest that broader vasopeptidase inhibition may decrease the magnitude of demand-induced myocardial ischemia. A randomized, double-blind, placebo controlled parallel study evaluated omapatrilat, an inhibitor of angiotensin-converting enzyme and neutral endopeptidase. The primary objective was to compare maximum duration of exercise at peak plasma concentrations. Exercise treadmill studies were performed in 348 patients who had chronic angina at baseline and after 4 weeks of therapy with 80 mg/day omapatrilat or placebo. Safety data were collected and reported for all patients. Treadmill exercise duration at peak was significantly prolonged in the omapatrilat group compared with the placebo group (76.6 +/- 84.2 vs 28.7 +/- 82.2 seconds difference from baseline, p <0.001). Similar statistically significant increases were seen in time to onset of level III/IV angina and time to onset of >/=0.1-mV ST-segment depression (p <0.001). The significant improvements in exercise duration and measurements of myocardial ischemia were not sustained 20 to 28 hours after dosing. Omapatrilat was generally well tolerated in this predominantly normotensive population. The incidence of serious adverse events was 5.2% in the 2 groups. Thus, omapatrilat, an investigational vasopeptidase inhibitor, is effective in prolonging exercise duration and parameters of demand-induced myocardial ischemia in patients who have chronic angina at peak concentrations. The data confirm the proof of principle that broader vasopeptidase inhibition beyond angiotensin-converting enzyme inhibition is required to alleviate symptoms of chronic angina.

Inflammation and endothelial dysfunction as therapeutic targets in patients with heart failure

Evidence suggests that vascular endothelium plays key role in the regulation of vascular tone, in the process of inflammation and in the thrombotic mechanisms. Recent studies indicate that it is an important component of the pathophysiological mechanisms of heart failure. Heart failure may induce endothelial dysfunction by different mechanisms, such as reduced synthesis and release of nitric oxide (NO), increased degradation of NO or by increased production of endothelin-1. In addition, endothelial dysfunction has been associated with the progression of heart failure. Alterations in neurotransmitters, hormones and also in physiological stimuli are present in heart failure and affect the vascular endothelium. Treatments with beneficial effects on endothelial dysfunction may also improve prognosis in patients with heart failure.

A Double Blind Randomized Trial to Compare the Effects of Eprosartan and Enalapril on Blood Pressure, Platelets, and Endothelium Function in Patients With Essential Hypertension

The renin-angiotensin system is the major contributor to development of hypertension, atherosclerosis, and many other cardiovascular diseases. Angiotensin II, one of the main effectors of this system, contributes to the pathogenesis of hypertension and plays an important role in monocyte, platelet, and endothelium interactions. The effects on platelet and endothelial function, either by angiotensin converting enzyme inhibitors or angiotensin receptor antagonists, are still not well understood. A double-blind, randomized, prospective trial of either enalapril (10-20 mg daily) or eprosartan (400-800 mg daily) over a 10-week period was conducted in 42 patients (27 males, 15 females). Platelet activation was evaluated by measuring platelet factor 4 (PF-4), beta-thromboglobulin (beta-TG), the ratio of platelet factor 4 to beta-thromboglobulin, and endothelial function by measuring total plasma nitrate levels, von Willebrand factor (vWF) levels, and blood flow using venous occlusive plethysmography. After a 10-week treatment with enalapril or eprosartan, the sitting blood pressure in both the enalapril group (from 152.2 +/- 18.7 mmHg to 141.9 +/- 23.5 mmHg, P < 0.05) and eprosartan group (from 151 +/- 10.0 mmHg to 142.3 +/- 12.9 mmHg, P < 0.05) was significantly reduced. Significant diastolic blood pressure (DPB) reduction (from 94 +/- 8.7 to 84.5 +/- 9.6 mmHg, P < 0.05) and a greater DBP reduction response were found in the eprosartan group (63% in eprosartan versus 25% in enalapril). Additionally, dose-dependent reductions in the indices of platelet activation and endothelial dysfunction were observed in patients administered high dose treatments of eprosartan and enalapril, and the beneficial effects of these agents were not correlated with the reduction of blood pressure using both agents. Eprosartan is effective and well-tolerated in the treatment of mid-to-moderate hypertension, and the DBP response reduction to eprosartin was better than that to enalapril. A high dose of either eprosartan or enalapril significantly decreased the indices of platelet activation and endothelial dysfunction in hypertensive patients. The benefits of both agents cannot be explained solely by their antihypertensive effects and possibly may be mediated through their unique effect on angiotensin blockade.

Vasopeptidase inhibition in a canine model of exercise-induced left ventricular dysfunction

1. The present study compared the acute efficacies of vasopeptidase inhibition with omapatrilat, nitroglycerin and angiotensin-converting enzyme (ACE) inhibition in exercise-induced myocardial dysfunction. Omapatrilat, a vasopeptidase inhibitor, inhibits both neutral endopeptidase and ACE. Whereas vasopeptidase inhibitors have demonstrated clinical efficacy in hypertension and heart failure, their effects in myocardial ischaemia remain unclear. 2. Omapatrilat (0.3 mg/kg) was compared with vehicle (saline), an ACE inhibitor (fosinoprilat; 0.44 mg/kg) and nitroglycerin (8.0 microg/kg per min), in an established canine model of exercise-induced myocardial dysfunction induced by progressive closure of an ameroid constrictor placed about the proximal circumflex coronary artery. Maximal treadmill exercise tests, terminated when heart rate failed to increase with increasing workload or failure to continue exercise, were performed in chronically instrumented dogs. 3. During exercise, omapatrilat and nitroglycerin similarly increased ischaemic wall thickening (P< or = 0.0001, ANOVA, 12 d.f.), whereas fosinoprilat and vehicle were without effect. Ischaemic zone ST changes were decreased with nitroglycerin (P = 0.0006, ANOVA, 12 d.f.) and tended to decrease with omapatrilat (P = 0.07, ANOVA, 12 d.f.). Peak exercise capacity was increased with nitroglycerin (9.7 +/- 1.1 vs 11.2 +/- 1.0 kcal, control vs 4 h, respectively; n = 6) and omapatrilat (9.7 +/- 0.8 vs 11.4 +/- 0.6 kcal, control vs 4 h, respectively; n = 6) and was unchanged with ACE inhibition (9.0 +/- 1.2 vs 9.5 +/- 1.1 kcal, control vs 4 h, respectively; n = 7). Omapatrilat differentially increased double product during exercise (P = 0.001, ANOVA, 12 d.f.) compared with other treatments. 4. During exercise-induced myocardial dysfunction, acute ACE inhibition did not attenuate ischaemic changes and failed to improve exercise capacity. Increased exercise capacity with omapatrilat was accompanied by a differential increase in double product, consistent with increased oxygen supply and demand. Improvements in ischaemic function were comparable between omapatrilat and nitroglycerin, suggesting that omapatrilat may represent a novel therapy in demand-induced ischaemia.

In vivo bradykinin B2 receptor activation reduces renal fibrosis

Angiotensin-converting enzyme (ACE) inhibitors reduce the progression of various fibrotic renal diseases both in humans and in animal models. Unilateral ureteral obstruction (UUO) is an animal model of accelerated renal tubulointerstitial fibrosis that is attenuated by ACE inhibition. Although ACE inhibitors increase bradykinin concentrations in addition to their effect on angiotensin II formation, the role of bradykinin in renal fibrosis has not been studied. We show here that genetic ablation (B2(-/-) mice) or pharmacological blockade of the bradykinin B2 receptor increases UUO-induced interstitial fibrosis in mice, whereas transgenic rats expressing increased endogenous bradykinin show reduced UUO-induced interstitial fibrosis. The increased interstitial fibrosis in B2(-/-) mice was accompanied by a decreased activity of plasminogen activators (PAs) and metalloproteinase-2 (MMP-2), enzymes involved in ECM degradation, suggesting that the protective effects of bradykinin involve activation of a B2 receptor/PA/MMP-2 cascade. This ability of bradykinin to increase PA activity was confirmed in primary culture proximal tubular cells. Thus, in both mice and rats, bradykinin B2 receptor activation reduces renal tubulointerstitial fibrosis in vivo, most likely by increasing ECM degradation.

Impaired endothelium-mediated vasodilation in heart failure: clinical evidence and the potential for therapy

Numerous studies in the last decade have clearly shown an attenuated endothelium-dependent vasodilation in patients with chronic heart failure. This abnormality has been demonstrated in the peripheral, pulmonary, and coronary circulation in patients with both ischemic and nonischemic cardiomyopathy; its magnitude correlates with the severity of symptoms. Endothelial dysfunction in patients with cardiomyopathy and a relatively new onset of symptoms suggests that change in endothelial function occurs early in the course of the disease. In contrast to other circulatory beds, renal circulation has shown significant vasodilatory response to endothelial stimulation. The development of endothelial dysfunction may not be homogeneous, and its magnitude may differ among circulatory systems. Although the clinical implications of the attenuated endothelium-dependent vasodilation in heart failure are not clear, this condition may lead to decreased organ perfusion, impaired exercise tolerance, and progression of disease. Many therapeutic interventions have resulted in improvement of endothelial function in patients with heart failure. Some of these interventions have also proven effective in enhancing exercise capacity, symptoms, and survival in patients with heart failure. This association suggests a therapeutic role for improvement of endothelial function in patients with chronic heart failure.

A remarkable medical story: benefits of angiotensin-converting enzyme inhibitors in cardiac patients

The development of angiotensin-converting enzyme inhibitors (ACE inhibitors) has been one of the most remarkable stories in the treatment of cardiovascular diseases. Angiotensin converting enzyme inhibitors have several acute and sustained hemodynamic effects that are beneficial in the presence of left ventricular (LV) dysfunction. They increase cardiac output and stroke volume and reduce systemic vascular resistance as well as pulmonary capillary wedge pressure. The hemodynamic benefits are associated with improvement in the signs and symptoms of congestive heart failure (CHF) as well as decreased mortality, regardless of the severity of CHF. In patients with asymptomatic LV dysfunction, therapy with ACE inhibitors prevented the development of CHF and reduced hospitalization and cardiovascular death. They also increase survival when administered early after an acute myocardial infarction (MI). Most recently, ACE inhibition was associated with improved clinical outcomes in a broad spectrum of high-risk patients with preserved LV function. The mechanism of ACE inhibitors benefits is multifactorial and includes prevention of progressive LV remodeling, prevention of sudden death and arrhythmogenicity and structural stability of the atherosclerotic process. Evidence suggests that ACE inhibitors are underutilized in patients with cardiovascular diseases. Efforts should be directed to prescribe ACE inhibitors to appropriate patients in target doses. It is reasonable to believe that ACE inhibitors have a class effect in the management of LV dysfunction with or without CHF and acute MI. Whether the same is true for ACE inhibitors in the prevention of ischemic events is not known yet.

Formulating clinical strategies for angiotensin antagonism: a review of preclinical and clinical studies

Extensive animal studies and a growing number of human clinical trials have now definitively demonstrated the central role of the renin-angiotensin-aldosterone system in the expression and modulation of cardiovascular disease. In contrast to the original hypothesis, the benefits of angiotensin antagonism do not emanate from the antihypertensive effect alone. Subsequent extensive investigations of angiotensin blockade suggest that the benefits of this approach may also result from the pharmacologic alteration of endothelial cell function and the ensuing changes in the biology of the vasculature. The more recent availability of direct antagonists of the AT(1) angiotensin receptor has introduced an element of doubt into this realm of clinical decision making. The receptor antagonists and the more widely studied converting-enzyme inhibitors share many endpoint attributes. Nevertheless, the partially overlapping mechanisms of action for the two classes of angiotensin antagonists confer distinct pharmacologic properties, including side effect profiles, mechanisms of action, and theoretic salutary effects upon the expression of cardiovascular disease. The current review will attempt to contrast the biology of angiotensin converting-enzyme inhibition with angiotensin II receptor antagonism. A discussion of the differential effects of these drug classes on endothelial cell function and on the modulation of vascular disease will be utilized to provide a theoretic framework for clinical decision making and therapeutics.

Bradykinin protects the rabbit heart after cardioplegic ischemia via NO-dependent pathways

BACKGROUND

Depressed myocardial performance is an important clinical problem after open heart surgery. We hypothesized pretreating with bradykinin would pharmacologically precondition the heart and improve post-ischemic performance, and induce myocardial preconditioning by activating nitric oxide synthase.

METHODS

Thirty-three rabbit hearts underwent retrograde perfusion with Krebs-Henseleit buffer (KHB) followed by 50 minutes of 37 degrees C cardioplegic ischemia with St. Thomas' cardioplegia solution (StTCP). Ten control hearts received no pretreatment. Ten bradykinin-pretreated hearts received a 10-minute infusion of 0.1 microMol/L bradykinin-enriched KHB and cardioplegic arrest with 0.1 microMol/L bradykinin-enriched StTCP. Six other hearts received 0.1 microMol/L HOE 140, a selective B2 receptor antagonist, added to both the 0.1 microMol/L bradykinin-enriched KHB and 0.1 microMol/L bradykinin-enriched StTCP solutions. Finally, six other hearts received 100 microMol/L of N-omega-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase, added to both the 0.1 microMol/L bradykinin-enriched KHB and 0.1 microMol/L bradykinin-enriched StTCP solutions.

RESULTS

Bradykinin pretreatment significantly improved postischemic performance and coronary flow (CF) compared with control (LVDP: 53 +/- 5* vs 27 +/- 4 mm Hg; +dP/dtmax: 1,025 +/- 93* vs 507 +/- 85 mm Hg/s; CF: 31 +/- 3* vs 22 +/- 2 mL/min; *p < 0.05). Both HOE 140 and L-NAME abolished bradykinin-induced protection, resulting in recovery equivalent to untreated controls.

CONCLUSIONS

Bradykinin pretreatment improves recovery of ventricular and coronary vascular function via nitric oxide-dependent mechanisms. Pharmacologic preconditioning by bradykinin pretreatment may be an important new strategy for improving myocardial protection during heart surgery.

Comparison of vasopeptidase inhibitor, omapatrilat, and lisinopril on exercise tolerance and morbidity in patients with heart failure: IMPRESS randomised trial

BACKGROUND

We aimed to assess in patients with congestive heart failure whether dual inhibition of neutral endopeptidase and angiotensin-converting enzyme (ACE) with the vasopeptidase inhibitor omapatrilat is better than ACE inhibition alone with lisinopril on functional capacity and clinical outcome.

METHODS

We did a prospective, randomised, double-blind, parallel trial of 573 patients with New York Heart Association (NYHA) class II-IV congestive heart failure, left-ventricular ejection fraction of 40% or less, and receiving an ACE inhibitor. Patients were randomly assigned omapatrilat at a daily target dose of 40 mg (n=289) or lisinopril at a daily target dose of 20 mg (n=284) for 24 weeks. The primary endpoint was improvement in maximum exercise treadmill test (ETT) at week 12. Secondary endpoints included death and comorbid events indicative of worsening heart failure.

FINDINGS

Week 12 ETT increased similarly in the omapatrilat and lisinopril groups (24 vs 31 s, p=0.45). The two drugs were fairly well tolerated, but there were fewer cardiovascular-system serious adverse events in the omapatrilat group than in the lisinopril group (20 [7%] vs 34 [12%], p=0.04). There was a suggestive trend in favour of omapatrilat on the combined endpoint of death or admission for worsening heart failure (p=0.052; hazard ratio 0.53 [95% CI 0.27-1.02]) and a significant benefit of omapatrilat in the composite of death, admission, or discontinuation of study treatment for worsening heart failure (p=0.035; 0.52 [0.28-0.96]). Omapatrilat improved NYHA class more than lisinopril in patients who had NYHA class III and IV (p=0.035), but not if patients with NYHA class II were included.

INTERPRETATION

Our findings suggest that omapatrilat could have some advantages over lisinopril in the treatment of patients with congestive heart failure. Thus use of vasopeptidase inhibitors could constitute a potentially important treatment for further improving the prognosis and well being of patients with this disorder.

Endothelial function as a therapeutic target in coronary artery disease

In healthy individuals, endothelial cells regulate a host of functions including vasomotor tone, thrombosis/ fibrinolysis, and cell-cell interactions. The development of endothelial dysfunction may be a common pathway by which cardiovascular risk factors impact plaque formation, growth, and rupture. Many pharmacologic and nonpharmacologic interventions known to decrease cardiovascular risk also improve endothelial function. For these reasons, some have suggested that improvement in endothelial function may be an important therapeutic target in the treatment of coronary artery disease.

The role of endothelin, protein kinase C and free radicals in the mechanism of the post-ischemic endothelial dysfunction in guinea-pig hearts

Transient ischemia has been shown to impair endothelium-dependent, but not endothelium-independent, coronary vasodilation, indicating selective endothelial dysfunction. Here a hypothesis was tested that agonist mediated activation of protein kinase C (PKC) and the related overproduction of the oxidative species contribute to the mechanism of the endothelial dysfunction. Perfused guinea-pig hearts were subjected either to 30 min global ischemia/30 min reperfusion or to 30 min aerobic perfusion with a PKC activator, phorbol ester (1 n M, PMA). Coronary flow responses to a bolus of acetylcholine (ACh) and sodium nitroprusside (SNP) were used as measures of endothelium-dependent and endothelium-independent vascular function, respectively. Salicylate hydroxylation was used as the assay for the myocardial hydroxyl radical (.OH) formation. Both ischemia/reperfusion and PMA impaired the ACh response and augmented the myocardial.OH production. The effect of ischemia/reperfusion on the ACh response: (i) was fully prevented by a PKC inhibitor, chelerythrine (2microM) and a mixed endothelin blocker, bosentan (20microM); (ii) was partially prevented by an endothelin converting-enzyme inhibitor, phosphoramidon (40microM), and superoxide dismutase (150-500 U/ml, SOD) and (iii) was affected neither by catalase (600 U/ml) nor by losartan (20microM) and captopril (250microM), nor by prazosin (10microM). SOD, but not bosentan, partially prevented the effect of PMA on the ACh response. None of the interventions studied affected the SNP response. The reperfusion-induced.OH release was attenuated by chelerythrine and bosentan, was not affected by prazosin and was increased by SOD. These results implicate the following sequence of events in the mechanism of the post-ischemic endothelial dysfunction: ischemia/reperfusion, endothelin-induced PKC activation, increased production of superoxide and/or some of its toxic metabolite, damage to the endothelium and endothelial dysfunction. The results argue against the contribution of angiotensin II, adrenergicalpha(1)-receptors and kinins in the mechanism of the post-ischemic endothelial dysfunction in guinea-pig hearts.

Amlodipine enhances NO production induced by an ACE inhibitor through a kinin-mediated mechanism in canine coronary microvessels

Our previous study found that angiotensin-converting enzyme (ACE) inhibitors and amlodipine induce NO release from coronary microvessels through a kinin-dependent mechanism. The goal of this study was to determine whether amlodipine could potentiate NO formation during ACE inhibition. Coronary microvessels were isolated from 16 mongrel dogs. Nitrite, the hydration product of NO, from coronary microvessels was quantified by using the Griess reaction. Bradykinin and kallikrein all significantly increased nitrite release from coronary microvessels in a concentration-dependent manner. The ACE inhibitor, ramiprilat, potentiated these effects. Amlodipine also markedly potentiated nitrite production by ramiprilat. For instance, amlodipine (10(-10) M) enhanced nitrite release induced by ramiprilat (10(-7) M) from 122 +/- 9 to 168 +/- 14 pmol/mg (p < 0.05 vs. ramiprilat). Nitrite release potentiated by ramiprilat and amlodipine was entirely blocked by N(omega)-nitro-L-arginine methyl ester (L-NAME, an inhibitor of NO synthase), HOE 140 (Icatibant, a specific B2-kinin receptor antagonist), and dichloroisocoumarin (DCIC, a serine protease inhibitor that blocks local kinin formation). These results clearly show that there is a synergistic effect on NO formation when amlodipine is combined with ACE inhibition. Our data suggest that kinin-mediated coronary NO production may contribute importantly to the beneficial therapeutic action of ACE inhibitors, especially in combination with amlodipine in the treatment of heart disease.

Bradykinin pretreatment improves ischemia tolerance of the rabbit heart by tyrosine kinase mediated pathways

BACKGROUND

Depressed myocardial performance is an important clinical problem after open-heart surgery. We hypothesized that: (1) pretreating the heart with bradykinin improves postischemic performance, and (2) bradykinin activates protein tyrosine kinase (TK).

METHODS

Twenty-seven adult rabbit hearts underwent retrograde perfusion with Krebs-Henseleit buffer (KHB) followed by 50 min of 37 degrees C cardioplegic ischemia with St. Thomas' cardioplegia solution (StTCP). Ten control hearts received no pretreatment. Ten bradykinin-pretreated hearts received a 10-minute infusion of 0.1 microM bradykinin-enriched KHB and cardioplegic arrest with 0.1 microM bradykinin-enriched StTCP. Seven others received 40 microM Genistein (Research Biochemicals, Natick, MA), a selective inhibitor of TK, added to both the 0.1-microM bradykinin-enriched KHB and 0.1-microM bradykinin-enriched StTCP solutions.

RESULTS

Bradykinin pretreatment significantly improved postischemic myocardial performance and coronary flow (CF) compared with control (left ventricular developed pressure: 53 +/- 5 vs 27 +/- 4 mm Hg; +dP/dt(max): 1,025 +/- 93 vs 507 +/- 85 mm Hg/s; CF: 31 +/- 3 vs 22 +/- 2 mL/min; p < 0.05). Inhibition of TK with Genistein prevented this improvement in myocardial function, resulting in recovery equivalent to untreated controls.

CONCLUSIONS

Bradykinin pretreatment may be an important new strategy for improving myocardial protection during heart surgery. The molecular mechanism of action may be similar to those activated by ischemic preconditioning.

Captopril administration reduces thrombus formation and surface expression of platelet glycoprotein IIb/IIa in early postmyocardial infarction stage

Long-term administration of the angiotensin-converting enzyme inhibitor captopril in survivors of myocardial infarction (MI) reduces the risk of cardiovascular death, recurrence of MI, and unstable angina, suggesting that captopril may possess antithrombotic properties that have not been clearly elucidated. We assessed the short-term antithrombotic effects of captopril on platelet aggregation, platelet-subendothelium interaction, and the expression of major glycoproteins on platelet surface. A double-blind study was carried out in 25 patients with MI. Blood samples were taken before (baseline) and 12 days after treatment in both the control and captopril groups. Platelet aggregation was tested by conventional aggregometry using common activating agents. Platelet interaction with deeply damaged subendothelial surface was evaluated in a perfusion model, with blood maintained under flow conditions. Deposition of platelets was quantified by using computer-assisted morphometric techniques on histological sections, and it was expressed as a percentage of total vessel surface covered by platelets (CS) and as a ratio between large aggregates (T) and surface covered by platelets (100XT/CS). Glycoprotein expression was measured using flow cytometric techniques. Aggregometric responses showed no significant variations; however, in the captopril group, 100XT/CS decreased after 12 days of treatment (100XT/CS: 36+/-12.1% captopril versus 64+/-8.0% baseline; P=0.005). This parameter was also significantly decreased from that found in control group patients (100XT/CS:67=/-4.5%, P=0.008). Flow cytometry showed a 30% reduction in glycoprotein IIb/IIIa expression (P=0.02). Captopril reduced the formation of large aggregates in a perfusion system, which might be related to a down-regulation of glycoprotein IIb/IIIa complex on the platelet surface. These results suggest that captopril exerts an antiplatelet effect that may contribute to its beneficial action in MI.

Practical considerations of the pharmacology of angiotensin receptor blockers

A review of the drug class of angiotensin receptor blockers (ARBs) as well as the ARBs currently available by prescription in the United States is presented. The importance of angiotensin II production by non-angiotensin-converting enzyme (non-ACE) pathways, particularly human chymase, is discussed. Emphasis is placed on the mechanism of action of ARBs and the different binding kinetics of these agents. Although all ARBs, as a group, block the AT1 receptor, they may differ in the pharmacological characteristics of their binding and be classified as either surmountable or insurmountable antagonists. Mechanisms of surmountable and insurmountable antagonism as well as possible benefits of these blocking characteristics are discussed in relation to the various ARBs. The cardiovascular effects of activation of the two main subtypes of angiotensin receptors (AT1 and AT2) are presented. In addition to their treatment of hypertension, ACE inhibitors are recognized as being effective in the management of heart failure, left ventricular hypertrophy, recurrent myocardial infarctions, and renal disease. ARBs are currently indicated only for the treatment of hypertension; however, in vitro and in vivo pharmacological studies as well as preliminary clinical data suggest that ARBs, like ACE inhibitors, may also provide effective protection against end-organ damage in these conditions.