Effect of early onset angiotensin converting enzyme inhibition on myocardial capillaries

Pharmacological Utility of PPAR Modulation for Angiogenesis in Cardiovascular Disease

Peroxisome proliferator activated receptors, including PPARα, PPARβ/δ, and PPARγ, are ligand-activated transcription factors belonging to the nuclear receptor superfamily. They play important roles in glucose and lipid metabolism and are also supposed to reduce inflammation and atherosclerosis. All PPARs are involved in angiogenesis, a process critically involved in cardiovascular pathology. Synthetic specific agonists exist for all PPARs. PPARα agonists (fibrates) are used to treat dyslipidemia by decreasing triglyceride and increasing high-density lipoprotein (HDL) levels. PPARγ agonists (thiazolidinediones) are used to treat Type 2 diabetes mellitus by improving insulin sensitivity. PPARα/γ (dual) agonists are supposed to treat both pathological conditions at once. In contrast, PPARβ/δ agonists are not in clinical use. Although activators of PPARs were initially considered to have favorable effects on the risk factors for cardiovascular disease, their cardiovascular safety is controversial. Here, we discuss the implications of PPARs in vascular biology regarding cardiac pathology and focus on the outcomes of clinical studies evaluating their benefits in cardiovascular diseases.

Inflammasome-Independent Role of NLRP3 Mediates Mitochondrial Regulation in Renal Injury

The NOD-like receptor family, pyrin domain containing-3 (NLRP3) inflammasome has been implicated in renal inflammation and fibrosis. However, the biological function of inflammasome-independent NLRP3 in non-immune cells is still unclear. We evaluated the role of inflammasome-independent NLRP3 in renal tubular cells and assessed the value of NLRP3 as a therapeutic target for acute kidney injury (AKI). Various renal tubular cell lines and primary cultured tubular cells from NLRP3 knockout (KO) mice were used for in vitro studies. We also tested the role of tubular NLRP3 in AKI with a unilateral ureter obstruction model (UUO). Hypoxia induced significant increase of NLRP3 independent of ASC, caspase-1, and IL-1β. NLRP3 in renal tubular cells relocalized from the cytosol to the mitochondria during hypoxia and bound to mitochondrial antiviral signal protein (MAVS). The deletion of NLRP3 or MAVS in renal tubular cells attenuated mitochondrial reactive oxygen species (ROS) production and depolarization of the mitochondrial membrane potentials under hypoxia. In response to UUO, NLRP3 KO mice showed less fibrosis, apoptosis, and ROS injury than wild type (WT) mice. Compared with WT kidney, mitophagy was up-regulated in NLRP3 KO kidney relative to the baseline and it was protective against AKI. Our results indicate that inflammasome-independent NLRP3 in renal tubular cells plays important role in mitochondrial ROS production and injury by binding to MAVS after hypoxic injury. This mitochondrial regulation in the absence of NLRP3 increases autophagy and attenuates apoptosis after UUO. We suggest that inflammasome-independent NLRP3 could be a therapeutic target of AKI to prevent the progression of chronic kidney disease.

Blood pressure normalization via pharmacotherapy improves cutaneous microvascular function through NO-dependent and NO-independent mechanisms

Hypertension is associated with endothelial dysfunction and vascular remodeling.

OBJECTIVE

To assess effects of antihypertensive pharmacotherapy on eNOS- and iNOS-dependent mechanisms and maximal vasodilator capacity in the cutaneous microvasculature.

METHODS

Intradermal microdialysis fibers were placed in 15 normotensive (SBP 111±2 mm Hg), 12 unmedicated hypertensive (SBP 142±2 mm Hg), and 12 medicated hypertensive (SBP 120±2 mm Hg) subjects. Treatments were control, iNOS-inhibited (1400w), and NOS-inhibited (l-NAME). Red cell flux, measured during local heating (42°C) and ACh dose-response protocols, was normalized to CVC (flux MAP^-1 ) and a percentage of maximal vasodilation (%CVC_max ).

RESULTS

Compared to normotensives, ACh-mediated vasodilation was attenuated in the hypertensive (P<.001), but not in medicated subjects (P=.83). NOS inhibition attenuated ACh-mediated vasodilation in normotensives compared to hypertensive (P<.001) and medicated (P<.001) subjects. With iNOS inhibition, there was no difference in ACh-mediated vasodilation between groups. Compared to the normotensives, local heat-induced vasodilation was attenuated in the hypertensives (P<.001), but iNOS inhibition augmented vasodilation in the hypertensives so this attenuation was abolished (P=.31). Compared to normotensives, maximal vasodilator capacity was reduced in the hypertensive (P=.014) and medicated subjects (P=.004).

CONCLUSIONS

In the cutaneous microvasculature, antihypertensive pharmacotherapy improved endothelial function through NO-dependent and NO-independent mechanisms, but did not improve maximal vasodilator capacity.

Vasopeptidase Inhibition Prevents Target Organ Damage and Improves Survival in Spontaneously Hypertensive Rats

Background. Vasopeptidase inhibition has been shown to be an effective antihypertensive principle but its long-term effects on hypertensive target organ damage are not known. We investigated the myocardial, vascular and renal effects of chronic vasopeptidase inhibition in arterial hypertension.

Methods and Results. One hundred and thirty-nine male spontaneously hypertensive rats aged 15 months were treated chronically with either the pure angiotensin-converting enzyme (ACE) inhibitor, ramipril (1 mg/kg/d in drinking water, n=46), or the vasopeptidase inhibitor AVE7688 (30 mg/kg/d in chow, n=46), or placebo (n=47) and followed up until they died. After six months, both ramipril and AVE7688 had markedly reduced plasma ACE activity, normalised blood pressure (BP), reduced left ventricular mass and improved systolic function to similar extents. Acetylcholine mediated relaxation of aortic rings was improved by both ramipril and AVE7688. There was substantial albuminuria in the placebo group (albumin-to-creatinine ratio 107±54 µg/mg), which was significantly reduced by ramipril to 57±34 µg/mg, and practically abolished in the AVE7688 group (22±12 µg/mg, p<0.05 vs. placebo and ramipril).Tubulointerstitial damage (semi-quantitative score) was significantly reduced by AVE7688 and ramipril. significantly reduced byAVE7688 and ramipril. Overall mortality was markedly reduced in the ramipril and AVE7688 groups (13% and 16% at six months, respectively), both p<0.05 vs. placebo (71%).

Conclusions. Vasopeptidase inhibition effectively controls BP and reduces myocardial, vascular and renal target organ damage, resulting in a markedly prolonged survival.At similar degrees of plasma ACE inhibition, AVE7688 compared to ramipril offers superior protection against hypertensive kidney damage.

Prehypertension: Underlying pathology and therapeutic options

Prehypertension (PHTN) is a global major health risk that subjects individuals to double the risk of cardiovascular disease (CVD) independent of progression to overt hypertension. Its prevalence rate varies considerably from country to country ranging between 21.9% and 52%. Many hypotheses are proposed to explain the underlying pathophysiology of PHTN. The most notable of these implicate the renin-angiotensin system (RAS) and vascular endothelium. However, other processes that involve reactive oxygen species, the inflammatory cytokines, prostglandins and C-reactive protein as well as the autonomic and central nervous systems are also suggested. Drugs affecting RAS have been shown to produce beneficial effects in prehypertensives though such was not unequivocal. On the other hand, drugs such as β-adrenoceptor blocking agents were not shown to be useful. Leading clinical guidelines suggest using dietary and lifestyle modifications as a first line interventional strategy to curb the progress of PHTN; however, other clinically respected views call for using drugs. This review provides an overview of the potential pathophysiological processes associated with PHTN, abridges current intervention strategies and suggests investigating the value of using the "Polypill" in prehypertensive subjects to ascertain its potential in delaying (or preventing) CVD associated with raised blood pressure in the presence of other risk factors.

Long-term ingestion of Hibiscus sabdariffa calyx extract enhances myocardial capillarization in the spontaneously hypertensive rat

The effects of Hibiscus sabdariffa (HS) in lowering blood pressure in human and animal hypertension have been documented. This study investigated the effect of the water extract of the dried calyx of HS and Hibiscus anthocyanins (HAs) on left ventricular myocardial capillary length and surface area in spontaneously hypertensive rats (SHRs). Twelve-week-old male SHRs were divided into eight groups (six rats in each group). Three groups were given three doses; 10%, 15% and 20% of the water extract of HS in lieu of drinking water for 10 consecutive weeks (HS10, HS15 and HS20) with one group kept as control (C). Another three groups were given three doses of the HAs orally at doses of 50, 100 and 200 mg/kg for five consecutive days with one group kept as a control (C). Systolic (SBP) and diastolic (DBP) blood pressures, as well as heart rate (HR), were measured weekly. After the experimental protocols, the left ventricles (LV) of all rats were obtained. Capillary surface area density and length density were determined by unbiased sterological methods on 3 μm LV tissue samples from perfusion-fixed hearts. HS ingestion significantly reduced SBP, DBP and LV mass in a dose-dependent fashion but did not affect the HR. HS significantly increased surface area and length density of myocardial capillaries by 59%, 65% and 86%, and length density by 57%, 77% and 57%, respectively. Myocyte nuclear volume was significantly decreased in HS-treated rats. There was a decrease (although insignificant) in SBP and DBP with HA ingestion compared with controls. These changes suggest that the observed beneficial effect of HS on high BP in SHRs could be mediated through a reduction in the diffusion distance between capillaries and myocytes, as well as new vessel formation. It is proposed that these effects might be beneficial in restoring myocyte normal nutritional status compromised by the hypertrophic state of hypertension.

Do we need more than just powerful blood pressure reductions? New paradigms in end-organ protection

Antihypertensive therapy can lower the risk of cardiovascular morbidity and mortality. Yet, partly because of inadequate dosing, wrong pharmacological choices, and poor patient adherence, hypertension control remains suboptimal in the majority of hypertensive patients. Achieving greater blood pressure control requires a multifaceted approach that raises awareness of hypertension, uses effective therapies, and improves adherence. Particular classes of antihypertensive therapy have beneficial actions beyond blood pressure and studies have evaluated differences in cardiovascular protection among classes. The LIFE and HOPE studies showed between-class differences that may be due to effects other than blood pressure-lowering. In the ONTARGET study, telmisartan and ramipril provided similar cardiovascular protection but adherence was higher with telmisartan, which was better tolerated. This difference in compliance is likely to be important for long-term therapy. The selection of an agent for cardiovascular protection should depend on an appreciation of its composite properties, including any beneficial effects on tolerability and increased patient adherence, as these are likely to be advantageous for the long-term management of hypertension. This review examines the evidence that the effects beyond blood pressure provided by some antihypertensive agents can also lower the risk of cardiovascular, cerebrovascular, and renal events in patients with hypertension.

Circulatory therapeutics: use of antihypertensive agents and their effects on the vasculature

This review addresses the use of the different antihypertensive agents currently available and some in development, and their effects on the vasculature. The different classes of agents used in the treatment of hypertension, and the results of recent large clinical trials, dosing protocols and adverse effects are first briefly summarized. The consequences on blood vessels of the use of antihypertensive drugs and the differential effects on the biology of large and small arteries resulting in modulation of vascular remodelling and dysfunction in hypertensive patients are then described. Large elastic conduit arteries exhibit outward hypertrophic remodelling and increased stiffness, which contributes to raise systolic blood pressure and afterload on the heart. Small resistance arteries undergo eutrophic or hypertrophic inward remodelling, and impair tissue perfusion. By these mechanisms both large and small arteries may contribute to trigger cardiovascular events. Some antihypertensive agents correct these changes, which could contribute to improved outcome. The mechanisms that at the level of the vascular wall lead to remodelling and can be beneficially affected by antihypertensive agents will also be addressed. These include vasoconstriction, growth and inflammation. The molecular pathways contributing to growth and inflammation will be summarily described. Further identification of these signalling pathways should allow identification of novel targets leading to development of new and improved medications for the treatment of hypertension and cardiovascular disease.

Additional salutary effects of the combination of exercise training and an angiotensin-converting enzyme inhibitor on the left ventricular function of spontaneously hypertensive rats

OBJECTIVES

To investigate whether the combination of exercise training with the angiotensin-converting enzyme inhibitor lisinopril will have an additional beneficial effect on left ventricular function in spontaneously hypertensive rats.

DESIGN

Twelve-week-old male rats were assigned to treadmill running (Ht-Ex; 20 m/min at 5 degrees grade, 1 h/day, 5 days/week), or lisinopril treatment (Ht-Lis; 15 mg/kg per day by gavage), or treadmill running while treated with lisinopril (Ht-ExLis), and were compared with a sedentary group (Ht-Sed). Age-matched and sex-matched Wistar-Kyoto rats were controls.

METHODS

After 10 weeks of experimentation, left ventricular morphology and function were assessed from M-mode echocardiograms and transmitral Doppler spectra [early (E) and atrial peak velocities (A), their ratio (E/A), and E-wave deceleration time (Edec time) and slope (Edec slope)].

RESULTS

Ht-Sed exhibited prominent concentric left ventricular hypertrophy with systolic and diastolic dysfunctions evidenced by a significantly reduced fractional shortening (%FS) and 'pseudonormalization' of left ventricular filling, characterized by an apparently normal E/A ratio despite an underlying left ventricular relaxation abnormality. Exercise training did not significantly alter left ventricular morphology or function. Lisinopril alone attenuated left ventricular hypertrophy and enhanced diastolic function but had no significant effect on systolic function. Combining exercise training with lisinopril treatment increased %FS by 25%, decreased the E/A ratio and Edec slope by 35% and 37%, respectively, and increased Edec time by 82%.

CONCLUSION

Our results provide experimental evidence that lisinopril administration, when combined with moderate exercise training, is more promising in attenuating cardiac dysfunction than either agent alone in hypertension of a genetic origin.

Expression of vascular endothelial growth factor and receptor tyrosine kinases in cardiac ischemia/reperfusion injury

INTRODUCTION

Vascular endothelial growth factor (VEGF) expression is regulated by hypoxia and cytokines, including insulin-like growth factor (IGF)-1. We examined the influence of ischemia/reperfusion (I/R) on IGF-1, VEGF, fetal liver kinase (flk-1), fms-like tyrosine kinase-1 (flt-1), and laminin using an isolated hemoperfused working porcine heart model of acute ischemia (2 h) and reperfusion (4 h).

METHODS

Twenty-three porcine hearts were randomized into the following groups: five nonischemic control hearts (Group C), five I/R hearts with occlusion of the ramus circumflexus; three I/R hearts treated with quinaprilat, a potent angiotensin-converting enzyme (ACE) inhibitor (Group Q); five I/R hearts treated with angiotensin I (Group Ang I), and 5 I/R hearts treated with Ang I and quinaprilat (Group QA).

RESULTS

Compared to C, VEGF mRNA and protein contents were significantly increased in I/R and Ang I hearts. flk-1 and flt-1 were increased in I/R (2.2-/1.95-fold) and further elevated by Ang I (3.2-/3.4-fold) compared with C. Quinaprilat application attenuated the amount of VEGF significantly and of flk-1 slightly but not that of flt-1. In contrast, IGF-1 and IGF-1 receptor (IGF-1R) proteins were elevated in I/R hearts (3-/1.4-fold vs. C) and further increased in the presence of Q. These findings were accompanied by an elevation of laminin mRNA and protein levels. Moreover, we observed an increase in collagen Type IV and chondroitin sulfate content in I/R (2.9-/1.4-fold) and Ang I (3.5-/1.5-fold) hearts. Quinaprilat significantly reduced laminin and chondroitin sulfate proteins.

CONCLUSION

These data suggest that the VEGF/VEGF receptor and IGF-1-IGF-1R systems are activated by I/R. The benefits of ACE inhibition in attenuation of cardiac remodeling may be mediated by IGF-1.

Comparative study of the effects of lacidipine and enalapril on the left ventricular cardiomyocyte remodeling in spontaneously hypertensive rats

Antihypertensive medications are the most efficient drugs in achieving regression of myocardial hypertrophy in both clinical studies and animal models of hypertension. Nevertheless, there is a lack of clear and concise comparative study of their effects on the modulation of cardiomyocyte morphology and function. Here, we assessed the tissue-protective actions of 2 of these drugs, the calcium channel blocker lacidipine (3 mg/kg/day) and the angiotensin-converting enzyme-inhibitor enalapril (10 mg/kg/day) in vivo, after 8 weeks of treatment of 12-week-old spontaneously hypertensive rats, as well as in vitro, after short-term (4 min) application to isolated cardiomyocytes. Left ventricular hypertrophy (LVH) was compared at organ, tissue, and single-cell level. Our data showed that both drugs prevented the LVH of 20-week-old spontaneously hypertensive rats, but only lacidipine significantly decreased the cardiomyocyte size. Similarly, the single-cell contractility was significantly lowered in lacidipine-treated rats only. The effect of lacidipine was initiated shortly after exposure to the drug in a dose-dependent manner at 0.5 Hz, as well as at 2 Hz, with EC(50) of 10(-7) mol/L. These results can help in understanding the effects of these drugs on the prevention of LVH.

Mechanisms of target organ damage caused by hypertension: therapeutic potential

Hypertension is a major risk factor for cardiovascular mortality and morbidity through its effects on target organs like the brain, heart, and kidney. Structural alterations in the microcirculation form a major link between hypertension and target organ damage. In this review, we describe damages related to hypertension in these target organs and the mechanisms involved in the pathogenesis of hypertension-induced cardiovascular diseases such as dementia, cardiac ischemia and remodeling, or nephropathy. We also focus on the therapeutical potential on the basis of such mechanisms. Several antihypertensive agents like diuretics, angiotensin converting enzyme (ACE) inhibitors, angiotensin II (Ang II) receptor antagonists, beta-blockers, or calcium channel blockers (CCBs) have been shown to reduce effectively hypertension associated cardiovascular events and to improve end organ damage. More recently, aldosterone antagonism has also shown beneficial effects. Part of the favorable effects of these agents is due to blood pressure lowering as such. Other mechanisms such as oxidative stress, inflammation, or endothelial dysfunction have appeared to play a key role in the pathogenesis of target organ damage and therefore represent another important pathway for therapy. In this review, we discuss the different therapeutic approaches aiming at reducing cardiovascular events and damages induced by hypertension.

Regulators of angiogenesis and strategies for their therapeutic manipulation

Angiogenesis provides a mechanism by which delivery of oxygen and nutrients is adapted to compliment changes in tissue mass or metabolic activity. However, maladaptive angiogenesis is integral to the process of several diseases common in Western countries, including tumor growth, vascular insufficiency, diabetic retinopathy and rheumatoid arthritis. Understanding the process of capillary growth, including the identification and functional analyses of key pro- and anti-angiogenic factors, provides knowledge that can be applied to improve/reverse these pathological states. Initially, angiogenesis research focused predominantly on vascular endothelial growth factor (VEGF) as a main player in the angiogenesis cascade. It is apparent now that participation of multiple angiogenic factors and signal pathways is critical to enable effective growth and maturation of nascent capillaries. The purpose of this review is to focus on recent progress in identifying angiogenesis signaling pathways that show promise as targets for successful induction or inhibition of capillary growth. The strategies applied to achieve these contradictory tasks are discussed within the framework of our existing fundamental knowledge of angiogenesis signaling cascades, with an emphasis on comparing the employment of distinctive tactics in modulation of these pathways. Innovative developments that are presented include: (1) inducing a pleiotropic response via activation or inhibition of angiogenic transcription factors; (2) modulation of nitric oxide tissue concentration; (3) manipulating the kallikrein-kinin system; (4) use of endothelial progenitor cells as a means to either directly contribute to capillary growth or to be used as a vehicle to deliver "suicide genes" to tumor tissue.

Long-term exercise training and angiotensin-converting enzyme inhibition differentially enhance myocardial capillarization in the spontaneously hypertensive rat

OBJECTIVES

To investigate whether combined treatment with lisinopril, an angiotensin-converting enzyme (ACE) inhibitor and exercise training would have an additive effect in enhancing the capillary supply of the left ventricular (LV) myocardium in spontaneously hypertensive rats (SHR).

DESIGN

Twelve-week-old male SHR were divided into four groups (10-12 each): sedentary, sedentary treated with lisinopril (15-20 mg/kg per day by gavage), exercise trained, and exercise trained while treated with lisinopril. Exercise training consisted of 1 h a day/5 days a week of running on a treadmill.

METHODS

After 10 weeks of experimental protocols, capillary surface density and length density were sterologically determined in 1 mum thick LV tissue samples from perfuse-fixed hearts.

RESULTS

Lisinopril significantly reduced systolic blood pressure (SBP) and LV mass in the sedentary with lisinopril and exercise trained with lisinopril groups but did not affect the heart rate (HR). Exercise training did not reduce SBP or LV mass, but significantly reduced HR in the exercise trained and exercise trained with lisinopril groups. Lisinopril treatment (sedentary with lisinopril), exercise training (exercise) and their combination (exercise trained with lisinopril) significantly increased myocardial capillary surface area density by 26, 38 and 65% and length density by 38, 48 and 67%, respectively.

CONCLUSION

Lisinopril administration and exercise training independently enhanced myocardial capillarization through a reduction of myocardial mass and stimulation of angiogenesis, respectively. A combination of the two treatments enhanced myocardial capillarization more than either intervention alone. This may aid in the restoration of the normal nutritional status of cardiac myocytes compromised by the hypertrophic state of hypertension.

Effects of ACE inhibition during fetal development on cardiac microvasculature in adult spontaneously hypertensive rats

BACKGROUND

Early angiotensin-converting enzyme (ACE) inhibition is able to re-program spontaneously hypertensive rats (SHR) to express an attenuated form of disease in adulthood.

METHODS

Three groups of animals (n=5 each) were studied: Wistar male rats, SHR males, and SHR males obtained from dams treated with enalapril maleate (15 mg/kg/day) during gestation. Animals were sacrificed 180 days after birth, and hearts were removed for stereological quantification. Volume [Vv] (myocytes, cardiac interstitium and intramyocardial vessels), length [Lv] (intramyocardial vessels), surface [Sv] densities (myocyte and intramyocardial vessels), and the mean cross-sectional area [a] (myocyte) were estimated.

RESULTS

Blood pressure (BP) was lower in Wistar group, higher in SHR group, and intermediate in SHR-enalapril group (respectively: 122+/-8.4, 194+/-11.4, and 158+/-7.6 mm Hg, p<0.0001). Increased Vv (p=0.016), Lv (p<0.01), and Sv (p<0.01) of intramyocardial vessels were observed in SHR-enalapril group when compared to untreated SHR. A small but significant reduction was observed in a of myocytes (p=0.045).

CONCLUSION

Prenatal ACE inhibition resulted in partial hypertension attenuation as well as left ventricular hypertrophy (LVH). The positive impact on the vascular compartment came along with little or no difference in myocytes and interstitium, suggesting the involvement of a direct mechanism.

The cardioprotective effect of dual metallopeptidase inhibition: respective roles of endogenous kinins and natriuretic peptides

The objective of the present study was to assess the cardioprotective effect of dual NEP–ACE inhibition in relation to endogenous cardiac bradykinin (BK), its active metabolite des-Arg9-BK, endogenous brain natriuretic peptides (BNP), and cGMP. Rats were treated with the dual metallopeptidase inhibitor, omapatrilat, or the ACE inhibitor, ramipril, for 7 d (1 mg·kg–1·d–1). Hearts were then isolated and subjected to a zero-flow ischemia and reperfusion (except controls), in the absence or presence of either a B2-receptor antagonist (Hoe-140), a B1-receptor antagonist (Lys-Leu8-des-Arg9-BK), or the GC-A/GC-B-receptor antagonist (HS-142-1). Chronic omapatrilat and ramipril increased the amount of endogenous BK collected upon reperfusion, but only ramipril increased that of des-Arg9-BK. Only omapatrilat increased both peak BNP and peak cGMP upon reperfusion, those increases being blocked by Hoe-140. Chronic omapatrilat (but not ramipril) decreased the total noradrenaline and lactate dehydrogenase release during the reperfusion period. Importantly, only omapatrilat improved the functional recovery of the ischemic reperfused heart, with a reduced left ventricular end-diastolic pressure, and improved developed left ventricular pressure. All cardio protective effects of omapatrilat were blocked by Hoe-140 and by HS-142-1, but not by the B1-receptor antagonist. In conclusion, a chronic treatment with a dual metallopeptidase inhibitor demonstrated a cardioprotective action not observed with an ACE inhibitor in a context of severe ischemia in rat isolated hearts, which was mediated by both endogenous BK and BNP.Key words: ACE inhibitors, omapatrilat, bradykinin, natriuretic peptide, ischemia, reperfusion.

Genetic kininogen deficiency contributes to aortic aneurysm formation but not to atherosclerosis

Brown Norway (BN) and BN Katholiek (BN/Ka) rat strains are both susceptible to develop lesions in the internal elastic lamina (IEL) of the aorta. BN/Ka rats are characterized by a single point mutation in the kininogen gene leading to deficiency in high- and low-molecular-weight kininogen. Recently, a suggestive quantitative trait locus for lesions in the IEL of the abdominal aorta was identified in an F2 intercross between Dahl salt-sensitive (SS) and BN rats, implicating kininogen as a positional candidate gene. Therefore, BN and BN/Ka rat strains represent ideal model organisms with which to study the contribution of kininogen to the genetic predisposition to IEL lesion formation and to characterize the early events underlying vascular remodeling. Here we present data demonstrating that genetic kininogen deficiency promotes the formation of aneurysms in the abdominal aorta but not the development of atherosclerosis upon 12-wk treatment with an atherogenic diet. Aneurysm formation was associated with an enhanced elastolysis, increased expression of MMP-2 and MMP-3, downregulation of TIMP-4, and with FasL- and caspase-3-mediated apoptosis. Kininogen-deficient animals also featured changes in plasma cytokines compatible with apoptotic vascular damage, i.e., upregulation of IFN-gamma and downregulation of GM-CSF and IL-1beta. Finally, in response to atherogenic diet, kininogen-deficient animals developed an increase in HDL/total cholesterol index, pronounced fatty liver and heart degeneration, and lipid depositions in aortic media without atherosclerotic plaque formation. These findings suggest that genetic kininogen deficiency renders vascular tissue prone to aneurysmatic but not to atherosclerotic lesions.

Temporary losartan or captopril in young SHR induces malignant hypertension despite initial normotension

BACKGROUND

Exposure of normotensive rats to angiotensin-converting enzyme (ACE) inhibitors in early life causes hypertrophy of intrarenal arteries. Similar defects have been found in knockout mice lacking angiotensinogen, ACE, or angiotensin II type 1 (AT1) receptors. On the other hand, transient inhibition of the renin-angiotensin system from 2 weeks of age in spontaneously hypertensive rats (SHR), either with ACE inhibitors or with AT1 receptor antagonists partially prevents the increase in blood pressure. However, permanent treatment of SHR from conception onwards with ACE inhibitors completely prevents hypertension. Although these studies demonstrated protection from hypertension-induced changes in the heart and large arteries, renal arteries were not studied and follow-up did not extend beyond 6 months of age. We postulated that while brief exposure to ACE inhibitors or AT1 receptor antagonists in young SHR would temporarily decrease blood pressure, it would also be associated with development of intrarenal arterial malformation, and ultimately have deleterious effects.

METHODS

Direct effects on intrarenal arterial morphology of an ACE inhibitor (captopril, 100 mg/kg/day) and an AT1 receptor antagonist (losartan, 50 mg/kg/day), administered from the last week of gestation until 8 weeks of age were examined in SHR. After stopping treatment at 8 weeks, we continued to monitor blood pressure until spontaneous death.

RESULTS

Systolic blood pressure at 8 weeks was normalized by captopril and losartan (SHR control 187 +/- 8 mm Hg; captopril 118 +/- 5 mm Hg; and losartan 120 +/- 9 mm Hg). However, by 30 weeks, blood pressure had increased to control SHR levels. At 4 weeks, the media of renal arteries and arterioles was hypertrophied. Marked smooth muscle cell hyperplasia of cortical arteries resulted in significantly increased wall thickness by 8 weeks, despite similar external diameter. Arterial wall structure was disrupted, with fragmentation of elastic fibers and irregular distribution of collagen type I fibers. After stopping treatment, the rats gradually began to show poor health and all had died by 1 year of age, while all 1-year-old control SHR females were in good health. The cause of morbidity and mortality in the rats treated in early life was clearly malignant hypertension. Severe hypertrophy of renal arterioles was found, as well as cerebral hemorrhage.

CONCLUSION

Despite initial normalization of blood pressure interference with the renin-angiotensin system during a crucial stage of development in SHR can initiate marked smooth muscle cell hyperplasia and disruption of the wall structure of the intrarenal arteries. Subsequent progression of this intrarenal process after cessation of treatment suggests an independent process that eventually results in malignant hypertension and early death.

Differential regulation of in vivo angiogenesis by angiotensin II receptors

Angiotensin II (ANG II), a key regulator of blood pressure and body fluid homeostasis, exerts mitogenic effects on endothelial cells. We therefore hypothesized that ANG II could be a mediator between homeostatic changes within the vascular perfusion bed and growth factor-driven angiogenesis. In the present study, we applied the alginate implant angiogenesis model in mice with normal ANG II levels, elevated ANG II levels by transgenic overexpression of angiotensinogen (AOGEN), or in AT2 receptor-deficient mice. We demonstrate that a decrease in the amount of circulating ANG II by the angiotensin-converting enzyme (ACE) inhibitor enalapril or the AT1 receptor antagonist losartan induced a stimulation of in vivo angiogenesis implying an inhibitory function of ANG II through the AT1 receptor. However, the strong increase of angiogenesis in AOGEN-transgenic mice compared with mice with normal ANG II levels suggests additional stimulatory activity. We showed that the ANG II-induced stimulation of angiogenesis is linked to the AT2 receptor as an impaired induction of angiogenesis was obtained in AT2 receptor knockout mice. These findings provide the first evidence that the AT2 receptor mediates a stimulation of in vivo angiogenesis and indicate that ANG II is a humoral regulator of peripheral angiogenesis involving two receptor subtypes with opposing actions.

Kallikrein gene delivery attenuates cardiac remodeling and promotes neovascularization in spontaneously hypertensive rats

Hypertension that results in left ventricular (LV) hypertrophy and/or fibrosis can lead to cardiac dysfunction. Spontaneously hypertensive rats (SHR) develop high blood pressure and LV hypertrophy at an early age and are a popular model of human essential hypertension. To investigate the role of the tissue kallikrein-kinin system in cardiac remodeling, an adenovirus containing the human tissue kallikrein gene was injected intravenously into adult SHR and normotensive Wistar-Kyoto (WKY) rats. The blood pressure of WKY rats remained unchanged throughout the experiment. Alternatively, kallikrein gene transfer reduced blood pressure in SHR for the first 2 wk, but had no effect from 3 to 5 wk. Five weeks after kallikrein gene delivery, SHR showed significant reductions in LV-to-heart weight ratio, LV long axis, and cardiomyocyte size; however, these parameters were unaffected in WKY rats. Interestingly, cardiac collagen density was decreased in both SHR and WKY rats receiving the kallikrein gene. Kallikrein gene transfer also increased cardiac capillary density in SHR, but not in WKY rats. The morphological changes after kallikrein gene transfer were associated with decreases in JNK activation as well as transforming growth factor (TGF)-beta 1 and plasminogen activator inhibitor-1 levels in the heart. In addition, kallikrein gene delivery elevated LV nitric oxide and cGMP levels in both rat strains. These results indicate that kallikrein-kinin attenuates cardiac hypertrophy and fibrosis and enhances capillary growth in SHR through the suppression of JNK, TGF-beta 1, and plasminogen activator inhibitor-1 via the nitric oxide-cGMP pathway.

Attenuation of heart failure due to coronary stenosis by ACE inhibitor and angiotensin receptor blocker

It is not known how the angiotensin-converting enzyme (ACE) inhibitor and angiotensin II receptor blocker (ARB) attenuate heart failure (HF) in viable ischemic hearts. To assess HF in a rat coronary stenosis (CS) model, we administered vehicle and quinapril or candesartan (or both) orally for 12 wk. Compared with the sham group, the vehicle group showed impaired myocardial perfusion, impaired coronary endothelial nitric oxide (NO) function in vitro, exhausted myocardial mitochondrial respiration, larger left ventricular (LV) dimensions and lower ejection fraction, lower LV rate of pressure development over time (dP/dt), lower slopes of LV end-systolic pressure-dimension relations (ESPDRs), and increased myocardial fibrosis. Treatment with quinapril or candesartan ameliorated these parameters without modifying the epicardial CS severity. Moreover, their combination maintained similar myocardial perfusion, despite a trend toward lower blood pressure, and showed distinctive neurohumoral modulation, normalized mitochondrial respiration, and increased ESPDR slopes. Thus improved myocardial blood flow and coronary flow reserve by quinapril or candesartan are the key to alleviate CS-induced HF, and their combination may have a therapeutic significance partly through ameliorated mitochondrial respiration and improved LV systolic function.

Angiotensin-converting enzyme inhibition in adult hypertensive rats: a stereological study of renal filtration surface area

1. Angiotensin-converting enzyme (ACE) inhibitor treatment leads to beneficial effects on kidney function. The aim of the present study was to determine whether ACE inhibition at high or low doses affects glomerular capillary surface area and length, glomerular number or total renal filtration surface area in rats with established hypertension and, if so, to determine whether these effects are mediated through bradykinin potentiation. 2. Spontaneously hypertensive rats (SHR) were treated with the ACE inhibitor perindopril at either 3 or 0.1 mg/kg per day (high and low doses, respectively) from 16 to 24 weeks of age. Some rats were concomitantly treated with the bradykinin B2 receptor antagonist S16118 (10 nmol/kg per day). Blood pressure was measured twice weekly during the treatment period. At 24 weeks of age, rats were perfusion fixed at 140 mmHg, the kidneys removed, embedded in resin and examined stereologically to estimate glomerular number and volume, length and surface area of glomerular capillaries and total renal filtration surface area. 3. High- and low-perindopril treatment significantly reduced systolic blood pressure compared with control SHR. However, the rats treated with low-dose perindopril were still considered hypertensive. Neither low-dose nor high-dose perindopril treatment had any observable effect on glomerular number (23 876 +/- 1201 vs 26 240 +/- 1465 glomeruli/kidney, respectively) or volume (2.25 +/- 0.21 and 1.96 +/- 0.06 x 10-3 mm3, respectively) compared with controls (glomerular number 25866 +/- 1210 glomeruli/kidney; glomerular volume 2.24 +/- 0.21 x 10-3 mm3). As a result, there was no significant difference in total renal filtration surface area between any of the experimental groups (8161.6 +/- 550.9, 8699.7 +/- 427.6, 9081.9 +/- 453.6, 8830.2 +/- 521.2 and 8559.4 +/- 341.4 mm2 for SHR, SHR low-dose perindopril, SHR low-dose perindopril + B2 antagonist, SHR high-dose perindopril and SHR high-dose perindopril + B2 antagonist, respectively). Coadministration of the bradykinin antagonist had no observable effect on any of the parameters studied. 4. In conclusion, because neither high-dose nor low-dose perindopril had any effect on total renal filtration surface area, the observed beneficial effects of ACE inhibition on kidney function are not the result of enhancement in glomerular capillary surface area.

Left and right coronary circulation in left ventricular hypertrophy: effects of angiotensin converting enzyme inhibition

The circulation in the left and right coronary beds in pressure overload-induced left ventricular (LV) hypertrophy was studied in Wistar male rats (n=6/group) that were subjected to abdominal aortic constriction or to sham-operation. From 3 to 6 weeks after surgery, the animals with aortic constriction received vehicle or 0.01, 0.1, or 1 mg/kg per day po of the angiotensin converting enzyme (ACE) inhibitor, ramipril. At 6 weeks, after measuring blood pressure in the carotid artery in vivo, the hearts were isolated and the left and right coronary beds subjected to independent perfusion. Minimum coronary vascular resistance per unit heart weight (MCVR/g) was determined in both beds during simultaneous infusion of 10 micromol/L adenosine. Aortic constriction resulted in a significant increase in blood pressure, LV weight/body weight ratio, and bilateral MCVR/g. Ramipril lowered arterial pressure in a dose-dependent manner and reversed the increased right MCVR/g at the anti-hypertensive dose, but it did not affect LV mass or left MCVR/g. These results suggest that both coronary hypertension and myocardial hypertrophy contribute to the global impairment of coronary circulation in LV hypertrophy. ACE inhibitors may improve coronary circulation in LV hypertrophy when administrated at an appropriate dose and for a sufficient period.

Inhibition of angiotensin-converting enzyme reduces susceptibility of hypertrophied rat myocardium to ventricular fibrillation

Left ventricular (LV) hypertrophy increases susceptibility to reperfusion arrhythmias and the angiotensin-converting enzyme inhibitor, ramipril, may reduce that susceptibility via regression of LV hypertrophy. Rats (n=12 per group) were subjected to abdominal aortic constriction (AC) or sham-operation (SH) and from 3 to 6 weeks after surgery, 3 AC groups received ramipril (0.01, 0.1, or 1 mg/kg per day p.o.) while the SH and 1 AC group received vehicle. Six weeks after surgery (ie after 3 weeks of treatment), the hearts were excised and subjected to independent Langendorf perfusion of left and right coronary beds. The left coronary bed was then subjected to ischemia (7 min) and reperfusion (5 min). Hypertrophied hearts from the vehicle AC group showed a significant increase in the incidence of reperfusion-induced ventricular fibrillation (VF) compared with control hearts from the SH group (92%* vs 33%: *p<0.05); this difference was abolished by ramipril (42%, 50%, and 42%, at 0.01, 0.1, or 1 mg/kg per day, respectively). The LV weight/body weight ratio was significantly increased in all AC groups (regardless of ramipril treatment) relative to the SH group. At the cellular level, myocyte length was significantly increased in the vehicle AC group, but was normalized by ramipril treatment (1 mg/kg per day). At the molecular level, atrial natriuretic factor (ANF) mRNA expression was also significantly increased in the vehicle AC group, but was again normalized by ramipril treatment (1 mg/kg per day). In conclusion, short-term treatment with ramipril reduced susceptibility to severe ventricular arrhythmias in hypertrophied rat hearts. This protection was achieved in the absence of a significant reduction in LV weight, but was accompanied by regression of myocyte hypertrophy, as reflected by reductions in cell size and ANF expression.

Beneficial effect of enalapril in spontaneously hypertensive rats cardiac remodeling with nitric oxide synthesis blockade

AIMS

To study the efficiency of an angiotensin converting enzyme inhibitor on the blood pressure (BP) and the myocardium remodeling when spontaneously hypertensive rats (SHRs) are submitted to nitric oxide synthesis (NOs) blockade (with L-NAME) and simultaneously treated.

METHODS

Young adult male SHRs were separated in four groups (n = 5) and treated for 20 days: Control, L-NAME, L-NAME+Enalapril, and Enalapril. The alterations of the BP, heart mass/body mass ratio and stereological parameters for myocytes, connective tissue and intramyocardial vessels were studied among the groups.

RESULTS

The SHRs with NOs blockade showed a great modification of the myocardium with extensive areas of reparative and interstitial fibrosis and accentuated hypertrophy of the cardiac myocytes (cross sectional area 60% higher in animals taking L-NAME than in Control SHRs). Comparing the SHRs with NO deficiency (L-NAME group), the Control SHRs and the Enalapril treated SHRs significant differences were found in the BP and in all stereological parameters. The NO deficiency caused an important BP increment in SHRs that was partially attenuated by Enalapril. This Enalapril effect was more pronounced in Control SHRs. A significant increment of the intramyocardial vessels was observed in NO deficient SHRs and Control SHRs treated with Enalapril demonstrated by the stereology (greater microvascular densities in treated SHRs).

CONCLUSION

Enalapril administration showed a beneficial effect on vascular remodeling and myocardial hypertrophy in SHRs. In SHRs with NO blockade, however, the beneficial effect of Enalapril occurred only in vascular remodeling.

Myocardial changes after spironolactone in spontaneous hypertensive rats. A laser scanning confocal microscopy study

The present study aims to objectivate by laser scanning confocal microscopy, the cardiac structure of the spontaneously hypertensive rats (SHR) treated with different doses of spironolactone, either alone or in combination with an angiotensin converting enzyme inhibitor or with a calcium channel blocker. Thirty SHRs were divided into six groups and treated during 13 weeks as follows: control, spironolactone (5, 10 and 30 mg/kg/day), spironolactone + enalapril and spironolactone + verapamil. Spironolactone action on the SHR blood pressure (BP) was dose-dependent. The cardiac hypertrophy was affected by the treatment with spironolactone (high dose) or a combination of spironolactone and Enalapril. The myocardial structure was less affected by the spironolactone monotherapy (at all doses) showing hypertrophied cardiac myocytes, focal areas of the reactive fibrosis, inflammatory infiltrate. The treatment with spironolactone in combination with enalapril or verapamil prevented these alterations. In conclusion, the monotherapy with spironolactone had only a limited effect in the preservation of the myocardial structure and in the attenuation of the interstitial fibrosis in SHRs, even after high dose. This action on the myocardium is more efficient when the spironolactone (even in medium dose) was associated with enalapril or verapamil.

Inflammation, not hyperhomocysteinemia, is related to oxidative stress and hemostatic and endothelial dysfunction in uremia

BACKGROUND

Several cardiovascular risk factors are present in patients with chronic renal failure (CRF), among which are systemic inflammation and hyperhomocysteinemia. Increased oxidative stress, endothelial activation/dysfunction, and coagulation activation are considered integral components of the inflammatory response, but have also been proposed as mediators of plasma homocysteine (tHcy)-induced cell damage. Using correlation analysis, we assessed the relative contributions of inflammation and hyperhomocysteinemia in the abnormal oxidative stress, endothelial activation/dysfunction, and hemostasis activation in patients with CRF.

METHODS

The relationships of inflammatory proteins and tHcy with plasma markers of these processes were studied in 64 patients with CRF (serum creatinine 526 +/- 319 micromol/L) on conservative treatment, comparing the results with healthy controls (N = 15 to 40, depending on the measured variable) of similar sex and age.

RESULTS

Patients had significant increases in inflammatory cytokines (TNF-alpha and IL-8) and acute-phase proteins (C-reactive protein, fibrinogen and alpha1-antitrypsin). tHcy was increased in 87.5% of patients (mean = 27.1 micromol/L, range 6.5 to 118). Patients had significant increases in (1) indices of oxidative stress: TBARS (thiobarbituric acid-reactive species), a marker of lipid peroxidation and AOPP (advanced oxidation protein products), a marker of protein oxidation; (2) endothelial cell markers such as von Willebrand factor (vWF:Ag), soluble ICAM-1 and soluble thrombomodulin (sTM); (3) markers of intravascular thrombin generation: thrombin-antithrombin complexes (TAT) and prothrombin fragment F(1+2) (PF(1+2)); and (4) indices of activation of fibrinolysis: plasmin-antiplasmin complexes (PAP), fibrin degradation products (FnDP) and fibrinogen degradation products (FgDP). tHcy was significantly correlated with plasma creatinine (r = 0.29, P < 0.018) and with serum folate (r = -0.38, P < 0.002). However, no significant correlations were observed between tHcy and TBARS, AOPP, vWF:Ag, sICAM-1, sTM, TAT, F(1+2), sTF, PAP, FnDP, and FgDP. Conversely, acute-phase proteins showed significant, positive correlations with most markers of oxidative stress, endothelial dysfunction and hemostatic activation.

CONCLUSIONS

Systemic inflammation, which is closely associated with augmented oxidative stress, endothelial cell dysfunction and hemostatic activation, emerges as a major cardiovascular risk factor in CRF. tHcy is unrelated to these events. Thus, alternative mechanisms through which hyperhomocysteinemia could predispose to vascular lesion and thrombotic events in CRF needs to be investigated.

Rescue of impaired angiogenesis in spontaneously hypertensive rats by intramuscular human tissue kallikrein gene transfer

Angiogenesis represents a compensatory response targeted to preserve the integrity of tissues subjected to ischemia. The aim of the present study was to examine whether reparative angiogenesis is impaired in spontaneously hypertensive rats (SHR), as a function of progression of hypertension. In addition, the potential of gene therapy with human tissue kallikrein (HK) in revascularization was challenged in SHR and normotensive Wistar-Kyoto rats (WKY) that underwent excision of the left femoral artery. Expression of vascular endothelial growth factor and HK was upregulated in ischemic hindlimb of WKY but not of SHR. Capillary density was increased in ischemic adductor muscle of WKY (from 266+/-20 to 633+/-73 capillaries/mm(2) at 28 days, P<0.001), whereas it remained unchanged in SHR (from 276+/-20 to 354+/-48 capillaries/mm(2), P=NS), thus compromising perfusion recovery as indicated by reduced plantar blood flow ratio (0.61+/-0.08 versus 0.92+/-0.07 in WKY at 28 days, P<0.05). In separate experiments, saline or 5x10(9) pfu adenovirus containing the HK gene (Ad.CMV-cHK) or the beta-galactosidase gene (Ad.CMV-LacZ) was injected intramuscularly at 7 days after the induction of ischemia. Ad.CMV-cHK augmented capillary density and accelerated hemodynamic recovery in both strains, but these effects were more pronounced in SHR (P<0.01). Our results indicate that native angiogenic response to ischemia is impaired in SHR, possibly as a result of defective modulation of endothelial cell mitogens. Supplementation with kallikrein, one of the growth factors found to be deficient in SHR, restores physiological angiogenic response utilitarian for tissue healing. Our discoveries may have important implications in vascular medicine for therapeutic benefit.

Effect of angiotensin-converting enzyme inhibition on myocardial vascularization in the adolescent and adult spontaneously hypertensive rat

OBJECTIVE

To determine whether angiotensin-converting enzyme (ACE) inhibition treatment enhances myocardial vascularization in adolescent and adult spontaneously hypertensive rats (SHRs).

METHODS

Male SHRs were treated from 7 to 14 or from 16 to 24 weeks of age with the ACE inhibitor, perindopril, in either a low dose (0.1 mg/kg per day) or a high dose (1 mg/kg per day). Some rats were concomitantly treated with a bradykinin antagonist. At termination of treatment, the left ventricular wall was extensively sampled and the surface area density and length density of myocardial blood vessels stereologically determined.

RESULTS

High-dose perindopril treatment prevented the development of hypertension and left ventricular hypertrophy in adolescent SHRs and markedly reduced blood pressure and left ventricular size in adult SHRs. SHRs treated with the low dose of perindopril remained hypertensive, although there were significant reductions in blood pressure and left ventricular growth. High-dose perindopril treatment in adolescent SHRs led to a significant increase in the surface area density of blood vessels in the left ventricle after 4 weeks of treatment and an increase in both the surface area density and length density of blood vessels after 7 weeks of treatment Co-administration with the bradykinin antagonist did not reverse these effects. In contrast, ACE inhibitor treatment had no effect on myocardial vascularization in adult rats with established hypertension.

CONCLUSION

ACE inhibitor treatment enhances vascularization in the adolescent heart through reductions in myocardial mass, but not capillary growth. ACE inhibition in the adult heart with established hypertension reduces left ventricular hypertrophy, but does not enhance myocardial capillarization.

The effect of treatment with low dose ACE inhibitor and/or diuretic on coronary microvasculature in stroke-prone spontaneously hypertensive rats

Angiotensin II is considered to have angiogenic properties. Nevertheless, several authors reported an increase in coronary capillary density after treatment with ACE inhibitors. The aim of the present study was to evaluate the effect of treatment with low doses of ACE inhibitor perindopril, low doses of the diuretic indapamide, or a combination of the two on microvascular structure in hearts from stroke-prone spontaneously hypertensive rats (SHR-sp). Young adult male SHR treated with indapamide (0.24 mg/kg/day), perindopril (0.76 mg/kg/day), or both were compared with untreated animals after 8 or 14 weeks of treatment. Survival of SHR-sp was significantly increased after treatment. Only perindopril alone or in combination with indapamide significantly decreased blood pressure and cardiac mass. Treatment also significantly increased capillary and myocyte densities but arteriolar density tended to decrease. External and internal diameters significantly increased in treated animals while arteriolar thickness remained the same. Thus, thickness in vessels of the same size was the greatest in untreated animals, followed by indapamide- and perindopril-treated rats with the thinnest walls in rats with combined treatment, and the treatment resulted in a significant increase in the lumen to wall ratio. Capillary and arteriolar growth responses in treated animals seem to indicate that the two are independently regulated processes. Treatment with indapamide alone at this dosage did not significantly influence most responses but in combination with perindopril it strengthened the effect of perindopril.

Angiotensin II and retinal pericytes migration

Angiotensin II (Ang II) appears to participate in the regulation of neovascularization processes in the retina. Migration of perimural cells such as pericytes plays a key role in regulation of angiogenesis. We hypothesize that Ang II stimulates migration of retina pericytes. For this we studied the effects of Ang II on migration of bovine retinal pericytes using modified Boyden chambers and collagen IV-covered polyester membranes. Ang II stimulated migration of pericytes by 54.8 +/- 9.7% (n = 10, p < 0.001). This effect was blocked by an AT(1) receptor antagonist (Losartan) but not by an AT(2) receptor antagonist (PD123319). We determined using checkerboard assays (n = 3) that Ang II induces migration of pericytes by chemotaxis (gradient-dependent), in opposition to chemokinesis (nondirected). Thus, Ang II via its AT(1) receptor acts as a chemotactic factor and stimulates migration of retina microvascular pericytes. This effect may contribute to Ang II-induced regulation of neovascularization processes in the retina.

Angiotensin-converting enzyme inhibition modifies angiotensin but not kinin peptide levels in human atrial tissue

Angiotensin-converting enzyme (ACE) converts angiotensin I (Ang I) to angiotensin II (Ang II) and metabolizes bradykinin and kallidin peptides. Decreased Ang II levels and increased kinin peptide levels are implicated in the mediation of the therapeutic effects of ACE inhibition. However, alternative non-ACE pathways of Ang II formation have been proposed to predominate in human heart. We investigated the effects of ACE inhibition on cardiac tissue levels of angiotensin and kinin peptides. High-performance liquid chromatography-based radioimmunoassays were used to measure angiotensin peptides and hydroxylated and nonhydroxylated bradykinin and kallidin peptides in right atrial appendages of subjects who had been prepared for cardiopulmonary bypass. Peptide levels in subjects who received ACE inhibitor therapy were compared with those who did not receive ACE inhibitor therapy. ACE inhibition reduced Ang II levels, which was associated with an 80% reduction in the Ang II/Ang I ratio. ACE inhibition did not modify either bradykinin or kallidin peptide levels or the bradykinin-(1-7)/bradykinin-(1-9) ratio. The 80% reduction in the Ang II/Ang I ratio by ACE inhibition indicated a primary role for ACE in the conversion of Ang I to Ang II in atrial tissue. These data support a role for reduced Ang II levels but do not support a role for increased kinin peptide levels in mediating the direct cardiac effects of ACE inhibition.

Pharmacology and cardiovascular implications of the kinin-kallikrein system

Kinins are peptide hormones that can exert a significant influence on the regulation of blood pressure and vascular tone due to their vasodilatatory, natriuretic and growth modulating activity. Their cardiovascular involvement in physiological and pathophysiological situations has been studied intensively since inhibitors for angiotensin I-converting enzyme and selective receptor antagonists have become available for pharmacologically potentiating or inhibiting kinin-mediated reactions. Molecular biological analysis and the establishment of genetically modified animal models have also allowed newer information to be acquired on this subject. In this review, the components and cardiovascularly relevant mechanisms of the kinin-kallikrein system shall be described. Organ-specific effects concerning the kidneys, the vascular system, the heart and nervous tissue shall also be illustrated. On this issue, the physiological functions and pathophysiological implications of the kinin-kallikrein system should be clearly distinguished from the many, mostly endothelium-mediated protective effects which occur during ACE inhibition due to the potentiation of kinin effects. Finally, a view shall also be cast upon newly discovered targets of action, which could be exploited for therapeutically altering the kinin-kallikrein system.

Early captopril prevents myocardial infarction-induced hypertrophy but not angiogenesis

Delayed captopril, started after the healing phase of myocardial infarction, improves perfusion by reducing tissue weight without affecting the vascular capacity of the heart. Early captopril, during the healing phase, prevents reactive hypertrophy, but the effects on angiogenesis are unknown. Therefore, the effects of early captopril (2 g/l drinking water, from 1 day until 3 weeks after myocardial infarction) on regional coronary flow related to tissue mass, were studied in isolated perfused hearts from rats, subjected to coronary artery ligation. Regional maximal vascular capacity was measured during nitroprusside-induced vasodilation, using radioactive microspheres. Maximal vascular capacity was not changed by captopril. Reactive hypertrophy in infarcted hearts only reached statistical significance in the left ventricular free wall. Since captopril prevented hypertrophy but did not affect regional capacity, peak tissue perfusion was improved. Indicating effects on metabolism, captopril restored the increased lactate/purine ratio in infarcted hearts. Thus, early captopril treatment prevented post-myocardial infarction hypertrophy but did not suppress angiogenesis, thus beneficially influencing the vascularization/tissue mass ratio, probably reflected by preservation of aerobic metabolism.

Angiotensin-converting enzyme gene expression in skeletal muscle in patients with chronic heart failure

BACKGROUND

Skeletal muscle factors may influence functional limitation in patients with heart failure. The renin-angiotensin system is activated in chronic heart failure. Treatment with angiotensin-converting enzyme (ACE) inhibitors improve symptoms and prognosis. The goal of this study was to quantify and localize skeletal muscle ACE-mRNA in patients with chronic heart failure and in control subjects, and to elucidate skeletal muscle fiber area and capillary density.

METHODS AND RESULTS

Biopsies from the lateral vastus muscle were taken from 9 patients before and after treatment with enalapril and in 10 control subjects. ACE-mRNA was quantified with reverse transcription polymerase chain reaction. Immunohistochemistry was used to localize ACE within skeletal muscle. No difference in ACE-mRNA transcripts between patients and control subjects was detected, nor did ACE gene expression change after treatment with enalapril. The number of ACE-mRNA transcripts was related to muscle fiber area, whereas an inverse relationship between the number of ACE transcripts and capillary density was found. ACE was detected in the endothelial cells of capillaries in skeletal muscle.

CONCLUSION

ACE is expressed in skeletal muscle and is confined to endothelial cells. The close relationship between capillary density and number of ACE transcripts indicate that activation of the renin-angiotensin system has an impact on capillary growth.

Reduction of QT and QTc dispersion during long-term treatment of systemic hypertension with enalapril

We report, in conjunction with other findings, the evolution of the dispersion of QT and QTc in patients who for the last 7 years have been treated with enalapril for systemic hypertension with left ventricular (LV) hypertrophy. Twenty-four essential hypertensive patients who had received no previous treatment took enalapril (20 mg twice daily) for 7 years. In a pretreatment placebo phase and 8 weeks and 1, 3, 5, 6, and 7 years after the start of therapy, cardiovascular parameters were determined by two-dimensional guided M-mode echocardiography, and the QT interval and corrected QT interval (QTc) and their dispersions were obtained from amplified standard 12-lead electrocardiograms. Therapy rapidly reduced blood pressure (BP) from 156/105 mm Hg to normal values; at 7-year follow-up, BP was 130/84 mm Hg (p <0.001 with respect to the placebo phase). LV mass index decreased progressively until at 5-year follow-up the reduction had reached 39% (p <0.001), after which neither LV mass index nor any structural parameter underwent any further significant change. LV pump function was also significantly better after 7 years of treatment. During this time, QT and QTc decreased significantly, as did the dispersion of both QT (from 61+/-21 to 37+/-14 ms) and QTc (from 67+/-27 to 41+/-16 ms). We conclude that long-term enalapril treatment of hypertensive patients with LV hypertrophy not only induces marked regression of LV mass and improved LV systolic function, but also reduces the dispersions of QT and QTc, which probably reduces the likelihood of ventricular arrhythmias and improves prognosis.

Contribution of bradykinin to the cardioprotective action of angiotensin converting enzyme inhibition in hypertension and after myocardial infarction

Angiotensin converting enzyme (ACE) is identical with kininase II. Besides reducing the production of angiotensin II, inhibition of ACE potentiates the biological actions of endogenous kinins. In hypertension-induced left ventricular hypertrophy, potentiation of endogenous kinins contributes to the improvement of cardiac function and energy metabolism and to capillary proliferation effected by ACE inhibitors. In myocardial infarction (MI), the potentiation of kinins has been shown to be involved in the reduction of infarct size and improvement of cardiac function by ACE inhibition. The cardioprotective actions of ACE inhibition in MI seem to be, in part, mediated by the augmentation of myocardial blood flow, especially in the ischemic region of the heart.

Structural adaptation to ischemia in skeletal muscle: effects of blockers of the renin-angiotensin system

OBJECTIVE

To investigate the effects of long-term treatment with blockers of the renin-angiotensin system on capillarization and growth of fibers in ischemic hind-limb muscles and in muscles under normal growth conditions.

METHODS

Ischemia was induced by partial ligation of the left common iliac artery.

RESULTS

Ischemia resulted in a significant increase in capillary and fiber density in the soleus muscle, a significant decrease in mean fiber size and a decrease in muscle cross-sectional area after 4 weeks compared with the contralateral nonischemic muscle. Ischemia also significantly decreased the muscle: body weight ratio of the left soleus muscle. We observed no significant effect on total number of capillaries and capillary: fiber ratio, suggesting that ischemia did not result in an increase in capillarization in this muscle. Treatments with subhypotensive and with hypotensive doses of the angiotensin converting enzyme (ACE) inhibitor benazeprilat, the angiotensin (Ang) II AT1 antagonist valsartan, or the Ang II AT2 antagonist PD 123 319 for 4 weeks did not influence any of the above-described changes in the normal and ischemic muscles and treatment effects were also independent of the degree of reduction of blood pressure.

CONCLUSION

Treatments with an ACE inhibitor and with Ang II receptor antagonists in dose ranges that moderately lower blood pressure do not influence vessel density and any of the other structural adaptations after hind-limb ischemia. Administrations of ACE inhibitors and Ang II AT1 antagonists may therefore be adequate and beneficial therapies under ischemic conditions, such as in the treatment of hypertension complicated by intermittent claudication, for which treatment must not increase ischemia.

Molecular mechanism of angiotensin II type I and type II receptors in cardiac hypertrophy of spontaneously hypertensive rats

We administered angiotensin (Ang) II receptor type 1 (AT1) blockade (losartan; 10 or 40 mg/kg per day), type II receptor (AT2) blockades (PD123319; 100 mg/kg per day), or angiotensin-converting enzyme (ACE) inhibitor (enalapril; 30 mg/kg per day) to spontaneously hypertensive rats (SHR) from 10 to 20 weeks of age. At the end of the treatment, high doses of losartan and enalapril significantly reduced the arterial systolic blood pressure compared with the untreated SHR to the level of WKY rats. But low doses of losartan and PD123319 were without effect. High doses of losartan and enalapril also significantly reduced both the left ventricular (LV) weight and the ratio of LV to body weight compared with the untreated SHR, which were still larger than that of WKY rats. However, the collagen concentration of SHR treated with high doses of losartan or enalapril was completely reduced to the level of WKY rats. Using reverse transcription polymerase chain reaction, we examined the mRNA expression for ACE, AT1, and AT2 in experimental animals. The enhanced AT1 mRNA expression was significantly decreased in the SHR treated with a high dose of losartan or PD123319 compared with the untreated SHR. The level of ACE mRNA was also decreased in the SHR treated with a high dose of losartan or enalapril. The level of AT2 mRNA was not significantly different between the Wistar-Kyoto rats and the SHR; however, this expression was decreased significantly after the treatment with a high dose of losartan or PD123319. These results indicate that AT1 receptor and ACE, but not AT2 receptor, play a crucial role in the remodeling of matrix tissue but a smaller role in the development of the hypertrophy of LV myocyte in SHR and that the LV/body weight changes do not fully account for the complete suppression of hypertension.

Effects of angiotensin-converting enzyme inhibition and angiotensin II AT1 receptor antagonism on cardiac parameters in left ventricular hypertrophy

Left ventricular hypertrophy (LVH) is considered to be an independent risk factor giving rise to ischemia, arrhythmia, and left ventricular dysfunction. In this article, we summarize recent studies performed in our laboratory to investigate (1) the contribution of the renin-angiotensin system to the cardiac remodeling process, which is triggered by myocardial infarction (MI) or hypertension-induced cardiac hypertrophy; (2) the effects of angiotensin-converting enzyme (ACE) inhibition and angiotensin AT1 receptor antagonism on cardiac parameters, such as myocardial infarct size, cardiac hypertrophy, heart function, and myocardial metabolism; (3) the mechanism of an ACE inhibitor-induced increase in cardiac capillary density in spontaneously hypertensive rats (SHR) and stroke prone SHR (SHR-SP). We observed that AT1 receptor gene expression in rat vascular smooth muscle cells (but not in rat coronary endothelial cells) was markedly enhanced after an ischemic insult in vitro. In a rat model in which MI was induced by coronary artery ligation, the AT1 receptor mRNA levels were transiently increased after MI and reached a peak level 24 hours post-MI. The AT2 receptor gene expression increased in a pattern similar to that of the AT1 receptor. ACE expression at the protein level in the repairing scar, which was demonstrated by monoclonal antibody staining, started to increase 2 weeks after MI and reached a peak level 3 weeks post-MI. Furthermore, long-term treatment with an ACE inhibitor limited infarct size, prevented cardiac hypertrophy, and improved heart function in the rat MI model. In SHR-SP, long-term treatment with either an ACE inhibitor or an AT1 receptor antagonist improved cardiac function and metabolism. Cardiac metabolism was even improved after low-dose ACE inhibitor treatment, which did not prevent hypertension and cardiac hypertrophy. In both SHR and SHR-SP, we found that the ACE inhibitor ramipril significantly increased capillary length density independently of its antihypertensive and antihypertrophic actions. Most of the cardiac effects of the ACE inhibitor could be abolished by a bradykinin B2 receptor antagonist. Thus, these cardiac effects of ACE inhibitors can be ascribed, at least under our experimental conditions, to ACE inhibitor-induced bradykinin potentiation.