Interactions among ACE, kinins and NO

Central administration of angiotensin-(1-7) stimulates nitric oxide release and upregulates the endothelial nitric oxide synthase expression following focal cerebral ischemia/reperfusion in rats

Angiotensin-(1-7) [Ang-(1-7)] is an endogenous peptide of the renin-angiotensin system with several beneficial effects that are often opposite to those attributed to angiotensin II (Ang II). Since there are no data available so far on the role of Ang-(1-7) after cerebral ischemia/reperfusion, in this paper, we investigated the central administration of Ang-(1-7) modulates in vivo the nitric oxide(NO) release and the endothelial NO synthase (eNOS) expression following focal cerebral ischemia/reperfusion in rats. Cerebral ischemia-reperfusion injury was induced by intraluminal thread occlusion of middle cerebral artery in the adult male rats. The levels of NO in ischemic tissues were measured by NO detection kits. Reverse transcription (RT)-PCR and western blot were used to determine messenger RNA (mRNA) and protein levels of the eNOS in ischemic tissues. The cerebral ischemic lesion resulted in a significant increase of NO release at 3 and 6h compared with sham operation group in our model after reperfusion, whereas both medium and high doses Ang-(1-7) markedly enhanced NO levels at 3-24h, and 3-72h after reperfusion, respectively. In addition, NO release increased was significantly induced by high-dose Ang-(1-7) compared with medium-dose Ang-(1-7) at 24-72 h after reperfusion. Medium and high-dose Ang-(1-7) significantly stimulated eNOS activation when compared with artificial cerebrospinal fluid (aCSF) treatment group at 3, 6, 12, 24, and 48h after reperfusion, however, no significant changes in eNOS expression were found between medium and high-dose Ang-(1-7) at different times after the ischemic insult. These findings indicate that medium and high-dose Ang-(1-7) stimulate NO release and upregulate eNOS expression in ischemic tissues following focal cerebral ischemia/reperfusion in rats.

The effects of nebivolol on apoptosis in a rat infarct model

BACKGROUND

In the present study, nitric oxide (NO) was investigated to see if it mediated effects of nebivolol on apoptosis in the rat myocardial infarction (MI) model.

METHODS AND RESULTS

Rats were divided into 3 groups: sham operated (sham-control), MI-induced (MI-control) and nebivolol treated (MI-nebivolol). The initial dose of nebivolol was administrated intravenously (iv) within 10 min of post-MI reperfusion and continued orally for 28 days. NO mediated effects of nebivolol were assessed either in the early (2(nd) day) or sub-acute (28(th) day) period of MI by histologic, hemodynamic and biologic studies. Left ventricular (LV) pressure changes were prevented with nebivolol (the increase in LV end-diastolic pressure and the decrease in maximum rise and fall rate of LV pressure (+dp/dt and -dp/dt) was significantly less in MI-nebivolol). Total and regional apoptotic indexes were significantly lower in the MI-nebivolol group (10.2 vs 7.1%, respectively on the 2(nd) day; p=0.004). Although plasma nitrite/nitrate, cyclic guanylate cyclase and peroxynitrite concentrations were high both in MI-control and MI-nebivolol groups on the 2(nd) day, these concentrations were decreased to the basal value on the 28(th) day in the MI-nebivolol group.

CONCLUSION

As a result, nebivolol treatment (initially by iv within 10 min of reperfusion and continued orally) reduced the myocardial apoptosis after MI. This beneficial effect of nebivolol is mediated by NO regulation.

Endothelial pathomechanisms in acute lung injury

Acute lung injury (ALI) and its most severe extreme the acute respiratory distress syndrome (ARDS) refer to increased-permeability pulmonary edema caused by a variety of pulmonary or systemic insults. ALI and in particular ARDS, are usually accompanied by refractory hypoxemia and the need for mechanical ventilation. In most cases, an exaggerated inflammatory and pro-thrombotic reaction to an initial stimulus, such as systemic infection, elicits disruption of the alveolo-capillary membrane and vascular fluid leak. The pulmonary endothelium is a major metabolic organ promoting adequate pulmonary and systemic vascular homeostasis, and a main target of circulating cells and humoral mediators under injury; pulmonary endothelium is therefore critically involved in the pathogenesis of ALI. In this review we will discuss mechanisms of pulmonary endothelial dysfunction and edema generation in the lung with special emphasis on the interplay between the endothelium, the immune and hemostatic systems, and highlight how these principles apply in the context of defined disorders and specific insults implicated in ALI pathogenesis.

Antiatherosclerotic effects of small-molecular-weight compounds enhancing endothelial nitric-oxide synthase (eNOS) expression and preventing eNOS uncoupling

Many cardiovascular diseases are associated with reduced levels of bioactive nitric oxide (NO) and an uncoupling of oxygen reduction from NO synthesis in endothelial NO synthase (eNOS uncoupling). In human endothelial EA.hy 926 cells, two small-molecular-weight compounds with related structures, 4-fluoro-N-indan-2-yl-benzamide (CAS no. 291756-32-6; empirical formula C16H14FNO; AVE9488) and 2,2-difluoro-benzo[1,3]dioxole-5-carboxylic acid indan-2-ylamide (CAS no. 450348-85-3; empirical formula C17H13F2NO3; AVE3085), enhanced eNOS promoter activity in a concentration-dependent manner; with the responsible cis-element localized within the proximal 263 base pairs of the promoter region. RNA interference-mediated knockdown of the transcription factor Sp1 significantly reduced the basal activity of eNOS promoter, but it did not prevent the transcription activation by the compounds. Enhanced transcription of eNOS by AVE9488 in primary human umbilical vein endothelial cells was associated with increased levels of eNOS mRNA and protein expression, as well as increased bradykinin-stimulated NO production. In both wild-type C57BL/6J mice and apolipoprotein E-knockout (apoE-KO) mice, treatment with AVE9488 resulted in enhanced vascular eNOS expression. In apoE-KO mice, but not in eNOS-knockout mice, treatment with AVE9488 reduced cuff-induced neointima formation. A 12-week treatment with AVE9488 or AVE3085 reduced atherosclerotic plaque formation in apoE-KO mice, but not in apoE/eNOS-double knockout mice. Aortas from apoE-KO mice showed a significant generation of reactive oxygen species. This was partly prevented by nitric-oxide inhibitor N(omega)-nitro-l-arginine methyl ester, indicating eNOS uncoupling. Treatment of mice with AVE9488 enhanced vascular content of the essential eNOS cofactor (6R)-5,6,7,8-tetrahydro-l-biopterin and reversed eNOS uncoupling. The combination of an up-regulated eNOS expression and a reversal of eNOS uncoupling is probably responsible for the observed vasoprotective properties of this new type of compounds.

On the mechanism of coronary vasodilation induced by angiotensin-(1-7) in the isolated guinea pig heart

Various mechanisms have been postulated to be involved in angiotensin-(1-7)-induced endothelium-dependent vasodilation. Here, we characterized the vasodilator action of angiotensin-(1-7) in the isolated guinea pig heart. Angiotensin-(1-7) (1-10 nmol, bolus) induced dose-dependent increase in the coronary flow. The coronary vasodilation induced by angiotensin-(1-7) was significantly reduced by the nitric oxide synthase inhibitor, L-N(G)-nitroarginine methyl ester (L-NAME) (100 microM) and abolished by a B(2) receptor antagonist, icatibant (100 nM). Coronary vasodilation induced by bradykinin (3 pmol, bolus) was inhibited by L-NAME and icatibant to similar extent as that induced by angiotensin-(1-7). Neither the selective AT(2) angiotensin receptor antagonist, PD123319 (1 microM), nor the antagonist of a putative angiotensin-(1-7) receptors, [D-alanine-7]-angiotensin-(1-7) (A-779, 1 microM), influenced the response to angiotensin-(1-7). In conclusion, in the isolated guinea pig heart angiotensin-(1-7) induces coronary vasodilation that is mediated by endogenous bradykinin and subsequent stimulation of nitric oxide release through endothelial B(2) receptors. In contrast to other vascular beds, AT(2) angiotensin receptors and specific angiotensin-(1-7) receptors do not appear involved in angiotensin-(1-7)-induced coronary vasodilation in the isolated guinea pig heart.

Targeting calcineurin and associated pathways in cardiac hypertrophy and failure

Cardiac hypertrophy occurs in response to long-term increases in haemodynamic load related to a variety of physiological and pathological conditions. Cardiac hypertrophy developing in pathological conditions with increased load often progresses to a decompensated stage with cardiac contractile dysfunction, clinical signs of heart failure and premature death. Cardiac hypertrophy associated with adverse outcomes is said to be maladaptive. Conversely, there are settings where cardiac hypertrophy appears to be purely adaptive (e.g., hypertrophy in response to regular physical exercise). In these circumstances, hypertrophy is associated with preserved contractile performance and a favourable prognosis. Cardiac myocyte hypertrophy is controlled by growth factor receptors and mechanical stress sensors which activate a complex network of signalling pathways. These pathways promote a multitude of qualitative and quantitative changes in gene expression levels in cardiomyocytes. Reprogramming of gene expression, much more than cardiac (myocyte) hypertrophy per se, ultimately determines if cardiac hypertrophy will be adaptive or maladaptive. Pharmacological modification of gene expression in the hypertrophied heart may, therefore, be an attractive approach to prevent or even treat maladaptive hypertrophy and heart failure. Calcineurin is a serine-threonine phosphatase that is activated by sustained increases in [Ca2+]i in cardiomyocytes. Although it has been firmly established that calcineurin plays a critical role in the development of cardiac hypertrophy, the question of whether calcineurin activation serves an adaptive or maladaptive role is still unresolved. An answer to this question is crucial if calcineurin is to be developed as a drug target. The authors propose that calcineurin acts as a double-edged sword; excessive activation of calcineurin is maladaptive, its activation at endogenous levels and at specific subcellular microdomains, however, promotes adaptation. Calcineurin itself may, therefore, not be a convenient target for drug development. However, because maladaptive hypertrophy is ultimately a transcriptional disorder, definition of the transcriptional programme activated by distinct calcineurin activation levels may permit identification of novel, attractive drug targets.

Increased cardiac endothelial nitric oxide synthase expression in patients taking angiotensin-converting enzyme inhibitor therapy

BACKGROUND

The efficacy of angiotensin-converting enzyme (ACE) inhibitors has been demonstrated in large clinical trials, but knowledge of the underlying mechanisms remains incomplete. Therefore, this study investigated the impact of ACE inhibitor therapy on cardiac nitric oxide (NO) synthases in patients with coronary artery disease (CAD) or heart failure.

PATIENTS AND METHODS

The mRNA expression was quantified by standard calibrated competitive RT-PCR, protein expression by Western blotting and NOS activity by monitoring the conversion of [3H]arginine to [3H]citrulline during enzymatic formation of NO in tissue homogenates of myocardium of patients with, or without, ACE inhibitor treatment before elective coronary artery bypass grafting or heart transplantation.

RESULTS

The mRNA expression (amol microg(-1) RNA) of endothelial NO synthase (eNOS) was higher (22.5 +/- 4.8, n = 23) in the atrial myocardium of patients taking ACE inhibitor treatment, before elective coronary artery bypass grafting, compared with patients not taking this therapy (8.9 +/- 0.7, n = 33, P < 0.0001). The ACE inhibitor therapy increased eNOS protein expression from [(9 +/- 0.7) relative units (RUs) to (12 +/- 0.9) RUs, P < 0.05, respectively] and cardiac NOS activity from 17.6 +/- 1.3 to 23.7 +/- 1.1 pmol mg protein(-1) min(-1) (P < 0.001, respectively). Inducible and neuronal NO synthase expression was not changed by the ACE inhibition. A similar up-regulation of eNOS by ACE inhibition was found in the left ventricles of patients with heart failure. The augmented endothelial NOS expression and activity was not the result of differences in clinical characteristics and concomitant therapy between the patient groups.

CONCLUSION

Increased eNOS expression and activity might contribute to the beneficial effects of ACE inhibitor therapy in the treatment of CAD and heart failure.

17β-Oestradiol enhances the acute hypotensive effect of captopril in female ovariectomized spontaneously hypertensive rats

The objective of this study was to investigate whether the acute haemodynamic effects of angiotensin-converting enzyme inhibition with captopril could be enhanced by oestrogen administration, and then to evaluate the mechanisms involved in this enhancement. All experiments were performed in 18-week-old female spontaneously hypertensive rats arranged in three experimental groups: intact; ovariectomized (OVX); and ovariectomized plus treatment with 17beta-oestradiol (OVX + E2). These groups were used to evaluate the effects of captopril administration alone, or following bradykinin B2 receptor blockade or nitric oxide synthase inhibition, on a number of haemodynamic parameters (mean arterial pressure, cardiac index, vascular resistance and heart rate). The drop in mean arterial pressure and vascular resistance index in response to captopril was more pronounced in intact and ovariectomized rats treated with 17beta-oestradiol than in ovariectomized animals. Blockade of bradykinin B2 receptors or inhibition of nitric oxide synthesis attenuated the synergy between 17beta-oestradiol and captopril. It is concluded that ovariectomy blunted the blood pressure and vascular resistance index drop observed in intact rats in response to captopril. Treatment with 17beta-oestradiol prevented the blunted response to captopril in ovariectomized rats. Kinins and nitric oxide may be involved in the mechanisms of 17beta-oestradiol potentiation of the haemodynamic effects of captopril.

Endothelial dysfunction: Mechanisms of development and therapeutic options

Introduction. Vascular endothelial cells play a key role in cardiovascular regulation by producing a number of potent vasoactive agents, including the vasodilator molecule nitric oxide (NO) and the vasoconstrictor peptide endothelin (ET). Endothelial dysfunction. Endothelial dysfunction is recognized as the initial step in the atherosclerotic process. Impairment of NO synthesis, or increased inactivation of NO by superoxide radicals, may account for the increased peripheral vascular tone, as well as contribute to the clinical consequences of different pathophysiological conditions-which include vascular hypertrophy, increased platelet and monocyte adhesion to the endothelium, atherosclerosis, myocardial infarction and stroke. To date, most interventions attempting to improve endothelial dysfunction have targeted one or more of the numerous risk factors that can cause endothelial damage: hypertension (ACE inhibitors and calcium antagonists), hypercholesterolemia (lipid-lowering agents), cigarette smoking (cessation), sedentary lifestyle (increased physical activity), menopause (estrogen replacement therapy), and diabetes mellitus (control of metabolic abnormalities). Several pharmacologic agents have been suggested to achieve vascular protection through mechanisms that go beyond their primary therapeutic actions (ACE-and HMG-CoA reductase inhibitors). Beneficial changes to the endothelium might result from promotion of vasorelaxation, inhibition of vasoconstriction, reduction in the production of free radicals, or other mechanisms that protect the endothelium from injury. Conclusion. This study deals with the results of many experimental and clinical investigations. The possibility of using different classes of drugs was also established, including ACE inhibitors, Ca-antagonists, AT and endothelin receptor antagonists, direct activator of adenyl cyclase, statins, antioxidants, L-arginine, phosphodiesterase inhibitors, beta-blockers and organic nitrates. .

AT&sub1; Receptor Blockade Prevents Microvascular Dysfunction Induced by Ischemia/Reperfusion Injury

Ischemia/reperfusion (I/R) in post-arterior post-capillary venules induces an acute inflammatory response, characterized by increased adherence and emigration of leukocytes and vascular permeability, all of which play important roles in cardiovascular disease. The aim of this study was to determine the roles of angiotensin II and AT1 receptor blockade in microvascular I/R injury in rats. Rats were anesthetized and intubated, then the peritoneum was opened and the mesentery was revealed. Small post-capillary venules were examined by in vivo fluorescence microscopy. The flow of erythrocytes and leukocytes was observed under the microscope and video recorded for later dynamic analyses. The superior mesenteric artery (SMA) was ligated with polyethylene tubing and released to induce I/R (20 min of ischemia/60 min of reperfusion). Subsequently, leukocyte adhesion, emigration and albumin leakage were compared with those of non-I/R controls. I/R injury was significantly suppressed by superfusing tissues with the AT1 receptor antagonist losartan (LO; 10 microM). The beneficial effects of LO were inhibited by topical application of either the bradykinin B2 receptor antagonist HOE140 (10 nM) or nitric oxide (NO) synthase inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME 10 microM). The effects of LO were lost in the presence of AT2 receptor blocker PD 123319 (PD). In conclusion, LO suppressed and protected against I/R injuries. The possible interaction between AT1 and AT2 receptors was also suggested.

Endothelial cell dysfunction: can't live with it, how to live without it

Endothelial cell dysfunction is emerging as an ultimate culprit for diverse cardiovascular diseases and cardiovascular complications of chronic renal diseases, yet the definition of this new syndrome, its pathophysiology, and therapy remain poorly defined. Here, I summarize some molecular mechanisms leading from hyperhomocystinemia, elevated asymmetric dimethylarginine, and advanced glycolation end product-modified protein level to the proatherogenic, prothrombogenic, and proinflammatory endothelial phenotype and offer a model of endothelial dysfunction based on the interconnectedness of diverse functions. Finally, several therapeutic strategies to prevent and correct endothelial dysfunction are discussed in the light of uncertainty of their action modulated by the endothelial dysfunction per se.

Effect of chronic exercise and Angiotensin-converting enzyme inhibition on rodent thoracic aorta

Vascular reactivity can be modulated by local physical factors as well as pharmacologic manipulations. The aim of this study was to evaluate the effects of chronic exercise (EX) with or without the ACEI captopril (CAP) on vascular reactivity. Sixty-four Sprague-Dawley male rats were randomized into 4 groups (n = 16): group 1, control; group 2, captopril; group 3, exercise; and group 4, exercise and captopril. After 10 weeks of treatment, rats were killed, and their thoracic aortas harvested. Vascular reactivity was studied in an organ chamber (n = 12). Aortic endothelium constitutive nitric oxyde synthase (NOS3) expression was determined by Western blot analysis (n = 4). Endothelial-dependent relaxation was increased in both CAP and EX rats relative to the control group. Maximal aortic relaxations were enhanced in the CAP group, and potencies of these mediators were enhanced in the EX group (P < 0.05 versus control). Combined treatment did not result in a synergistic effect. NOS3 relative expressions were: group 1, 100%; group 2, 241%; group 3, 64%; and group 4, 108%. Exercise enhanced both potencies and efficacies of the mediators studied, whereas CAP increased mainly their efficacies. NOS3 protein expression was up-regulated in CAP-treated rats but not in exercised rats. These findings suggest different mechanisms for the observed increased vascular reactivity.

Endothelial nitric oxide synthase-independent effects of an ACE inhibitor on coronary flow response to bradykinin in aged mice

ACE inhibitors are known to ameliorate cardiovascular complications in aging; however, their effects on the coronary circulation in relation to aging and eNOS dependence remain to be examined. Coronary flow responses to bradykinin with or without ACE inhibitors were examined in Langendorff-perfused hearts from young (16-20 weeks) and aged (16-20 months) control and eNOS mice. Western blot analysis was performed for cardiac eNOS, nNOS, and ACE. Baseline coronary flow was comparable between young and aged mice of both strains. Aging did not affect bradykinin-induced coronary flow in either strain. Interestingly, both acute and chronic treatment with an ACE inhibitor markedly augmented the flow response in aged control and eNOS mice. Aged eNOS mice were markedly hypertensive and had larger ventricular mass than control mice. The antihypertensive effect of temocapril was greater in aged eNOS mice, associated with reduction in the ventricular weight in both strains. Western blot analysis demonstrated an increased expression of eNOS in aged control mice, and ACE expression was increased in eNOS mice. These results indicate that coronary flow response to bradykinin is preserved in aged mice even in the absence of eNOS, and an ACE inhibitor augments this response by both eNOS-dependent and -independent mechanisms.

Angiotensin II, angiotensin II antagonists and spironolactone and their modulation of cardiac repolarization

Angiotensin II and aldosterone produce pro-arrhythmic effects by several mechanisms, including the modulation of voltage-dependent K(+) channels involved in human cardiac repolarization. Drugs that inhibit the renin-angiotensin-aldosterone system exert anti-arrhythmic actions that are related to the blockade of the pro-arrhythmic actions of angiotensin II and aldosterone. These anti-arrhythmic actions include inhibition of electrical and structural cardiac remodeling, inhibition of neurohumoral activation, reduction of blood pressure and stabilization of electrolyte disturbances. In this article, several angiotensin II AT(1) receptor antagonists (candesartan, E3174, eprosartan, irbesartan and losartan) and aldosterone receptor antagonists (canrenoic acid and spironolactone) that directly modulate the activity of the voltage-dependent K(+) channels are reviewed; the effects of these antagonists might be useful in the prevention and treatment of cardiac arrhythmias.

Enalapril attenuates angiotensin II-induced atherosclerosis and vascular inflammation

Angiotensin converting enzyme (ACE) inhibitors prevent a wide variety of key events underlying atherogenesis. Whether these actions depend solely on reduction of angiotensin II (Ang II) generation is still to be determined. This study was undertaken to determine whether enalapril, an ACE inhibitor, prevents atherosclerosis and vascular inflammation induced by Ang II in apolipoprotein E-deficient (apoE-KO) mice. Subcutaneous infusion of Ang II (1.44 mg/(kg day)) for 4 weeks increased blood pressure and accelerated atherosclerosis development in the carotid arteries. The expression of the endothelial adhesion molecules E-selectin, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1), as well as the chemokines monocyte chemotactic protein-1 (MCP-1) and macrophage-colony stimulating factor (M-CSF) was up-regulated in the aortas of Ang II-treated mice. Enalapril co-treatment (25 mg/(kg day), in drinking water) prevented the development of atherosclerosis without affecting blood pressure or circulating cholesterol. In addition to preventing the Ang II-induced over-expression of adhesion molecules and chemokines in the aorta, enalapril up-regulated the expression of peroxisome proliferator-activated receptors (PPARs)-alpha and -gamma, potential anti-inflammatory transcription factors. In the aortic arch, a lesion-prone site, the co-treatment with enalapril reduced the percentage of arterial wall occupied by macrophages and foam cells, medial sclerosis and elastin reduplication. Together, these data suggest an important role for Ang II-independent mechanisms in the antiatherogenic and anti-inflammatory effects of ACE inhibitors.

Role of peroxynitrite in the process of vascular tone regulation by nitric oxide and prostanoids--a nanotechnological approach

The production of peroxynitrite (ONOO(-)) in the endothelium decreases NO bioavailability, decreases vasorelaxation and changes vascular tone. ONOO(-) can also influence the production of prostacyclin-another vasorelaxant. We used a nanotechnological approach (nanosensors) to elucidate the release of NO, O(2)(-), and ONOO(-) in endothelium and their effect on production of prostanoids. The basal ONOO(-) concentration near the endothelium (3-5 microm) varied from 1 to 50 nmol/L and maximal calcium ionophore stimulated ONOO(-), did not exceed 900 nmol/L. The highest ONOO(-) concentrations were produced in ischemia/reperfusion atherosclerosis, diabetes, aging and vary among different racial groups (higher in Blacks than in Whites). ONOO(-) decreased PGI(2) activity with IC(50) approximately 150 nmol/L for 8 min reaction time, but has no effect of short reaction time. Prostaglandin E(1) decreased NO, O(2)(-), and ONOO(-) by limiting Ca(2+) flux into endothelium, decreased edema and vasoconstriction during ischemia/reperfusion. In endothelium (HUVEC's) of Black's the ONOO(-) concentrations were high 750+/-50 nmol/L while the lowest concentrations of vasorelaxants were 275+/-25 nmol/L of NO, 150+/-15 pb/100 microg protein of 6-keto-PGF(1)(alpha) as compared to White's (420+/-30 and 470+/- nmol/L for ONOO(-) and NO respectively and 280+/-20 pg/100 mg protein for 6-keto-PGF(1)(alpha)).

Nitric oxide, angiotensin II, and hypertension

Although initially adaptive, the changes that accompany hypertension, namely, cell growth, endothelial dysfunction, and extracellular matrix deposition, eventually can become maladaptive and lead to end-organ disease such as heart failure, coronary artery disease, and renal failure. A functional imbalance between angiotensin II (Ang II) and nitric oxide (NO) plays an important pathogenetic role in hypertensive end-organ injury. NO, an endogenous vasodilator, inhibitor of vascular smooth muscle and mesangial cell growth, and natriuretic agent, is synthesized in the endothelium by a constitutive NO synthase. NO antagonizes the effects of Ang II on vascular tone, cell growth, and renal sodium excretion, and also down-regulates the synthesis of angiotensin-converting enzyme (ACE) and Ang II type 1 receptors. On the other hand, Ang II decreases NO bioavailability by promoting oxidative stress. A better understanding of the pathophysiologic mechanisms involved in hypertensive end-organ damage may aid in identifying markers of cardiovascular susceptibility to injury and in developing therapeutic interventions. We propose that those antihypertensive agents that lower blood pressure and concomitantly restore the homeostatic balance of vasoactive agents such as Ang II and NO within the vessel wall would be more effective in preventing or arresting end-organ disease.

Celiprolol, A Vasodilatory β-Blocker, Inhibits Pressure Overload–Induced Cardiac Hypertrophy and Prevents the Transition to Heart Failure via Nitric Oxide–Dependent Mechanisms in Mice

Background— The blockade of β-adrenergic receptors reduces both mortality and morbidity in patients with chronic heart failure, but the cellular mechanism remains unclear. Celiprolol, a selective β 1 -blocker, was reported to stimulate the expression of endothelial NO synthase (eNOS) in the heart, and NO levels have been demonstrated to be related to myocardial hypertrophy and heart failure. Thus, we aimed to clarify whether celiprolol attenuates both myocardial hypertrophy and heart failure via the NO-signal pathway.

Methods and Results— In rat neonatal cardiac myocytes, celiprolol inhibited protein synthesis stimulated by either isoproterenol or phenylephrine, which was partially suppressed by N G -nitro- l -arginine methyl ester (L-NAME). Four weeks after transverse aortic constriction (TAC) in C57BL/6 male mice, the ratio of heart weight to body weight (mg/g) (8.70±0.42 in TAC, 6.61±0.44 with celiprolol 100 mg · kg −1 · d −1 PO, P <0.01) and the ratio of lung weight to body weight (mg/g) (10.27±1.08 in TAC, 7.11±0.70 with celiprolol 100 mg · kg −1 · d −1 PO, P <0.05) were lower and LV fractional shortening was higher in the celiprolol-treated groups than in the TAC group. All of these improvements were blunted by L-NAME. Celiprolol treatment significantly increased myocardial eNOS and activated phosphorylation of eNOS. Myocardial mRNA levels of natriuretic peptide precursor type B and protein inhibitor of NO synthase, which were increased in the TAC mice, were decreased in the celiprolol-treated mice.

Conclusions— These findings indicated that celiprolol attenuates cardiac myocyte hypertrophy both in vitro and in vivo and halts the process leading from hypertrophy to heart failure. These effects are mediated by a selective β 1 -adrenergic receptor blockade and NO-dependent pathway.

Pulmonary endothelium in acute lung injury: from basic science to the critically ill

BACKGROUND

Pulmonary endothelium is an active organ possessing numerous physiological, immunological, and metabolic functions. These functions may be altered early in acute lung injury (ALI) and further contribute to the development of acute respiratory distress syndrome (ARDS). Pulmonary endothelium is strategically located to filter the entire blood before it enters the systemic circulation; consequently its integrity is essential for the maintenance of adequate homeostasis in both the pulmonary and systemic circulations. Noxious agents that affect pulmonary endothelium induce alterations in hemodynamics and hemofluidity, promote interactions with circulating blood cells, and lead to increased vascular permeability and pulmonary edema formation.

OBJECTIVE

We highlight pathogenic mechanisms of pulmonary endothelial injury and their clinical implications in ALI/ARDS patients.

A nitric oxide‐releasing derivative of enalapril, NCX 899, prevents progressive cardiac dysfunction and remodeling in hamsters with heart failure

Nitric oxide (NO) production is known to be impaired in heart failure. A new compound (NCX 899), a NO-releasing derivative of enalapril was characterized, and its actions were evaluated in Bio 14.6 cardiomyopathic (CM) hamsters with heart failure. The hamsters were randomized to oral treatment for 4 weeks with vehicle (n=11), NCX 899 (NCX, 25 mg/kg, n=10), or enalapril (25 mg/kg, n=10). In the vehicle group, fractional shortening by echocardiography decreased (-23.6+/-2.0%) and LV end-diastolic dimension) increased (+10.9+/-1.0%), whereas fractional shortening increased (+17.5+/-4.4%) in NCX and was unchanged in the enalapril group (both P<0.01 vs. vehicle). End-diastolic dimension decreased only in NCX. LV contractility (LVdP/dt max and Emax) was significantly greater in NCX than in enalapril or vehicle, while relaxation (Tau) was shortened in both NCX and enalapril vs. vehicle. ACE activity was inhibited equally by NCX and enalapril in the CM hamster, and plasma nitrate levels were increased only in NCX (P<0.05 vs. enalapril and vehicle). In aortic strips endothelium-independent relaxation occurred only with NCX. The superior effects of NO-releasing enalapril (NCX) vs. enalapril alone to enhance vascular effects, increase LV contractility and prevent unfavorable remodeling and are consistent with vascular delivery of exogenous NO. NCX 899 may hold promise for the future treatment of heart failure.

A study of the mediators involved in the protection induced by exogenous kinins in the isolated rat heart

The aim of this study was to determine whether endothelium-derived mediators and the endocannabinoid system were involved in the cardioprotective effects induced by exogenous kinins, namely bradykinin and its active metabolites, des-Arg(9)-bradykinin. Isolated rat hearts were submitted to a 20-min stabilisation period, followed by 90 min of low-flow ischemia (flow rate, 0.6 ml min(-1)) before a 60-min reperfusion period. Perfusion of bradykinin (BK, 30 nM) or des-Arg(9)-bradykinin (DBK, 30 nM) was initiated 1 min before the ischemia and maintained during the entire ischemic period. Perfusion with BK reduced infarct size, when measured at the end of the 60-min reperfusion. This effect was blocked by the B2-receptor antagonist, HOE140 (30 nM). Likewise, DBK reduced infarct size, effect that was blocked by the B1-receptor antagonist (30 nM Lys(0)-Leu(8)-DBK). The cardioprotective effect of both BK and DBK was abolished by the cannabinoid CB1-receptor antagonist (1 microM SR141716A), but not by the CB2-receptor antagonist (1 microM SR144528). Neither the NO synthase inhibitor, N-nitro-L-arginine (NNLA, 30 microM), the COX inhibitor, indomethacin (2.8 microM), nor the CYP450 inhibitor, clotrimazole (1 microM), prevented the cardioprotective effect of the kinins. However, a combined treatment with those three inhibitors abolished completely the ability of BK and DBK to reduce infarct size. In conclusion, exogenously administered BK and DBK exert a protective effect against ischemia in an isolated heart model. Endothelium-derived mediators such as nitric oxide, prostanoids, and endothelium-derived hyperpolarizing factor, as well as an SR141716A-sensitive mediator, appear to be involved in this beneficial effect.

Important role of nitric oxide in the effect of angiotensin-converting enzyme inhibitor imidapril on vascular injury

To examine the possible role of the bradykinin-NO system in the action of ACE inhibitors, we studied the effects of imidapril, an ACE inhibitor, on inflammatory vascular injury by using AT1a-receptor-deficient (AT1aKO) mice. A polyethylene cuff was placed around the femoral artery of AT1aKO mice and wild-type (WT; C57BL/6J) mice. Neointimal area in cross sections of the artery was measured 14 days after cuff placement. A low dose of imidapril (1 mg/kg per day), which did not affect blood pressure, was administered by gavage. Expression of monocyte chemoattractant protein (MCP)-1 and tumor necrosis factor (TNF)-alpha was detected by immunohistochemical staining and reverse transcriptase-polymerase chain reaction (RT-PCR) 7 days after the operation. Neointimal formation, vascular smooth muscle cell proliferation, and expression of MCP-1 and TNF-alpha were attenuated in the injured artery in AT1aKO mice compared with those in WT mice. Imidapril inhibited neointimal formation, DNA synthesis of vascular smooth muscle cells, and expression of MCP-1 and TNF-alpha in AT1aKO mice as well as in WT mice. In addition, imidapril increased tissue cGMP content after cuff placement. These inhibitory effects of imidapril were significantly reduced or abolished by a bradykinin receptor antagonist, Hoechst 140, or an NO synthase inhibitor, L-NAME, both in WT and AT1aKO mice. Treatment with imidapril did not change AT2 receptor and ACE expression detected by RT-PCR in the injured artery. These results indicate that not only blockade of angiotensin II production but also activation of the bradykinin-NO system plays an important role in the beneficial effects of imidapril on vascular remodeling.

Nitric oxide-releasing drugs

Pharmacological compounds that release nitric oxide (NO) have been useful tools for evaluating the broad role of NO in physiology and therapeutics. NO deficiency has been implicated in the genesis and evolution of several disease states. Both medical needs and commercial opportunities have fostered attempts to modulate NO in the human body for therapeutic gain. Strategies for NO modulation encompass antiinflammatory, sexual dysfunction, and cardiovascular indications. Apart from newly developed drugs, several commonly used cardiovascular drugs exert their beneficial action, at least in part, by modulating the NO pathway. This review discusses the fundamental pharmacological properties and mechanisms of action of NO-releasing drugs. Some of these compounds may enter in the clinical arena providing important therapeutic benefits in human diseases.

Nitric oxide, human diseases and the herbal products that affect the nitric oxide signalling pathway

1. Nitric oxide (NO) is formed enzymatically from l-arginine in the presence of nitric oxide synthase (NOS). Nitric oxide is generated constitutively in endothelial cells via sheer stress and blood-borne substances. Nitric oxide is also generated constitutively in neuronal cells and serves as a neurotransmitter and neuromodulator in non-adrenergic, non-cholinergic nerve endings. Furthermore, NO can also be formed via enzyme induction in many tissues in the presence of cytokines. 2. The ubiquitous presence of NO in the living body suggests that NO plays an important role in the maintenance of health. Being a free radical with vasodilatory properties, NO exerts dual effects on tissues and cells in various biological systems. At low concentrations, NO can dilate the blood vessels and improve the circulation, but at high concentrations it can cause circulatory shock and induce cell death. Thus, diseases can arise in the presence of the extreme ends of the physiological concentrations of NO. 3. The NO signalling pathway has, in recent years, become a target for new drug development. The high level of flavonoids, catechins, tannins and other polyphenolic compounds present in vegetables, fruits, soy, tea and even red wine (from grapes) is believed to contribute to their beneficial health effects. Some of these compounds induce NO formation from the endothelial cells to improve circulation and some suppress the induction of inducible NOS in inflammation and infection. 4. Many botanical medicinal herbs and drugs derived from these herbs have been shown to have effects on the NO signalling pathway. For example, the saponins from ginseng, ginsenosides, have been shown to relax blood vessels (probably contributing to the antifatigue and blood pressure-lowering effects of ginseng) and corpus cavernosum (thus, for the treatment of men suffering from erectile dysfunction; however, the legendary aphrodisiac effect of ginseng may be an overstatement). Many plant extracts or purified drugs derived from Chinese medicinal herbs with proposed actions on NO pathways are also reviewed.

Autoradiographic analysis of rat brain kinin B1 and B2 receptors: normal distribution and alterations induced by epilepsy

Kindling-induced seizures constitute an experimental model of human temporal lobe epilepsy that is associated with changes in the expression of several inflammatory proteins and/or their receptors in distinct brain regions. In the present study, alterations of kinin receptors in the brain of amygdaloid-kindled rats were assessed by means of in vitro autoradiography, using (125)I-labeled 3-4 hydroxyphenyl-propionyl-desArg(9)-D-Arg degrees -[Hyp(3), Thi(5), D-Tic(7), Oic(8)]-bradykinin (B(1) receptors) and (125)I-labeled 3-4 hydroxyphenyl-propionyl-D-Arg degrees -[Hyp(3), Thi(5), D-Tic(7), Oic(8)]-bradykinin (B(2) receptors) as ligands. Results demonstrate that B(2) receptors are widely distributed throughout the brain of control rats. The highest densities were observed in lateral septal nucleus, median preoptic nucleus, dentate gyrus, amygdala, spinal trigeminal nucleus, mediovestibular nucleus, inferior cerebellar peduncles, and in most of cortical regions (0.81-1.4 fmol/mg tissue). In contrast, very low densities of B(1) receptors were detected in all analyzed areas from control rats (0.18-0.26 fmol/mg tissue). When assessed in kindled rats, specific binding sites for B(2) receptors were significantly decreased (41 to 76%) in various brain areas. Conversely, B(1) receptor binding sites were markedly increased in kindled rats, especially in hippocampus (CA2 congruent with CA1 congruent with CA3), Amy and entorhinal, peririnal/piriform, and occipital cortices (152-258%). Data show for the first time that kindling-induced epilepsy results in a significant decline of B(2) receptor binding sites, accompanied by a striking increase of B(1) receptor labeling in the rat brain. An altered balance between B(1) and B(2) receptor populations may play a pivotal role in the onset and/or maintenance of epilepsy.

Role of 3-hydroxy-3-methylglutaryl coenzyme a reductase inhibitors, angiotensin-converting enzyme inhibitors, cyclooxygenase-2 inhibitors, and aspirin in anti-inflammatory and immunomodulatory treatment of cardiovascular diseases

The immunologic response in atherosclerosis involves not only intrinsic cells of the artery wall, but also circulating leukocytes, lymphocytes, and macrophages. Interaction of various arms of the immune response modulates plaque development and stability, and it is conceivable that immunologic effects of some cardiovascular therapies may contribute to their mechanism of benefit. The preponderance of data has accrued with the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins). Statin effects, such as inhibition of T cell activation, tissue factor expression, or reduction of platelet hyperreactivity, may elicit beneficial effects in vitro and in vivo in patients with coronary artery disease. Moreover, aspirin may limit oxidation of lipoproteins and fibrinogen, and it may inhibit cytokine-induced nitric oxide synthase II expression. The hypothesis that selective inhibition of cyclooxygenase-2 (COX-2) may increase risk of myocardial infarction is controversial and may also be of questionable clinical significance. Finally, angiotensin-converting enzyme (ACE) inhibitors not only reduce proinflammatory mediators, such as interleukin-6, but also enhance the concentration of anti-inflammatory cytokines, such as interleukin-10. Because ACE is expressed at the shoulder region of atherosclerotic plaques, and ACE activity is enhanced in unstable plaques, ACE inhibition may also contribute to plaque stability. This article reviews the potential immunomodulatory potencies of aspirin, COX-2 inhibitors, statins, and ACE inhibitors as established pharmacotherapy in patients with coronary artery disease.

Chronic effects of angiotensin-converting enzyme inhibition on kinin receptor binding sites in the rat spinal cord

With the use of in vitro receptor autoradiography, this study aims at determining whether the higher level of kinin B(2) receptor density in the spinal cord of the spontaneously hypertensive rat (SHR) is secondary to arterial hypertension and whether chronic treatment with angiotensin I-converting enzyme inhibitors (ACEI) can regulate neuronal B(1) and B(2) receptors. SHR received, from the age of 4 wk, one of the two ACEI (lisinopril or zofenopril, 10 mg x kg(-1) x day(-1)) or for comparison, the selective AT(1) antagonist (losartan, 20 mg x kg(-1) x day(-1)) in their drinking water for a period of 4, 12, and 20 wk. Age-matched untreated SHR and Wistar-Kyoto rats (WKY) were used as controls. B(2) receptor binding sites in most laminae were higher in SHR than in WKY from the age of 8 to 24 wk. Whereas B(1) receptor binding sites were significantly present in young SHR and WKY, they were barely detectable in adult rats. ACEI (16 and 24 wk) and AT(1) antagonist (24 wk) enhanced the number of B(2) without changing B(1) receptor binding sites. However, at 8 wk the three treatments significantly increased B(1) and decreased B(2) receptors in lamina I. It is concluded that 1) the higher density of B(2) receptors in the spinal cord of SHR is not due to hypertension, 2) kinin receptors are regulated differently by ACEI in neuronal and vascular tissues, and 3) aging may have a profound impact on levels of B(1) and B(2) receptors in the rat spinal cord.

The therapeutic potential of bradykinin B2 receptor agonists in the treatment of cardiovascular disease

The nonapeptide bradykinin (BK) is a Janus-faced hormone, which exerts pathophysiological as well as pronounced beneficial physiological effects, mainly by stimulation of BK B(2) receptors. In various animal models and in humans it has been shown that the stimulation of BK B(2) receptors is not only implicated in the pathogenesis of inflammation, pain and tissue injury but also in powerful cardioprotective mechanisms. Either exogenous administration of BK or locally increased BK concentrations as a consequence of the inhibition of its metabolic breakdown by angiotensin-converting enzyme inhibitors, reveal the significant contribution of BK in powerful cardioprotective mechanisms. These are mainly triggered by the synthesis and release of the vasorelaxant, anti-hypertrophic and anti-atherosclerotic endothelial mediators nitric oxide, prostaglandins and tissue-type plasminogen activator, by ischaemic preconditioning and by an increase in insulin sensitivity. Consequently, BK B(2) receptor agonists may have important clinical value in the treatment and prevention of various cardiovascular disorders such as hypertension, ischaemic heart disease, left ventricular hypertrophy, ventricular remodelling and congestive heart failure as well as diabetic disorders by mimicking the reported beneficial effects of BK. However, none of the currently known potent and selective peptide and non-peptide agonists of BK B(2) receptors--RMP-7 (lobradamil, Cereport; Alkermes), JMV-1116 (Fournier), FR-190997 (Fujisawa) and FR-191413 (Fujisawa)--have been selected for a clinical assessment in cardiovascular indications. One major challenge of this approach is the still unanswered question of whether there is a sufficient safe therapeutic window between potential cardioprotective and pro-inflammatory effects following BK B(2) receptor agonism.

Down-regulation of bradykinin B2-receptor mRNA in the heart in pressure-overload cardiac hypertrophy in the rat

To determine the potential role of the cardiac kallikrein-kinin system in the development of cardiac hypertrophy, we studied the expression patterns of kallikrein, kininogen, and bradykinin receptor mRNA in the heart by polymerase chain reaction during the development of pressure-overload-induced left ventricular hypertrophy (LVH) in rats. The abdominal aortic constriction produced LVH after 7, 14, and 28 days. Neither mRNA levels for high-molecular-weight (H-) or low-molecular-weight (L-) kininogens and T-kininogen, nor those for tissue kallikreins, changed during LVH. B(2)-receptor mRNA levels in the left ventricles decreased 4 and 7 days after aortic constriction, subsequently returning to the levels in sham-operated animals. B(2)-receptor densities in cardiac membrane preparations obtained 4 days after aortic constriction significantly decreased compared to preparations from sham-operated rats, whereas the receptor affinity was unchanged. Down-regulation of B(2)-receptor mRNA levels was abolished by oral administration of an angiotensin II type 1 (AT1) receptor antagonist, candesartan, for 4 days after aortic constriction. Both cardiomyocytes and nonmyocytes obtained from neonatal rat hearts expressed B(2)-receptor mRNA in vitro, and the levels were not changed in either cell type by culture with 1 microM angiotensin II (Ang II). However, when a mixture of cardiomyocytes and nonmyocytes was cultured with 1 microM Ang II, B(2)-receptor mRNA levels decreased within 12 hr; this in vitro effect of Ang II was inhibited by the AT1-receptor antagonist losartan. These results indicate that the mechanical load in the myocardium caused by pressure-overload rapidly produces a down-regulation of B(2)-receptor expression during the initial stage of LVH, probably mediated by activating the AT1-receptor.

Effect of combination therapy with dipyridamole and quinapril in diabetic nephropathy

BACKGROUND/AIMS

Dipyridamole stimulates nitric oxide action via inhibition of phosphodiesterase and also has an antioxidant effect. ACE inhibitor reduces glomerular pressure and enhances NO action via increased bradykinin. Thus, we evaluated the effect of the combination of dipyridamole and ACE inhibitor in diabetic nephropathy.

METHODS

Streptozotocin-induced diabetic rats at 2 weeks were treated with dipyridamole, quinapril or both. The expression of NOS and NAD(P)H oxidase p47phox was investigated using immunohistochemistry and western blot, and urinary albumin, cGMP and lipid peroxidation products (LPO) were measured at 4 weeks.

RESULTS

NAD(P)H oxidase and urinary LPO were significantly enhanced in diabetes, and suppressed by each treatment to the same extent. The nNOS expression in macula densa and eNOS increased significantly with combination therapy compared to quinapril treatment alone contributing to an enhanced urinary excretion of cGMP and to maintain the creatinine clearance. Increased albuminuria in diabetes was reduced more effectively with combination therapy to the control level than with single treatments.

CONCLUSION

Combination therapy with dipyridamole and quinapril suppressed urinary LPO via reduction of NAD(P)H oxidase increase in diabetes. The combination therapy reduced microalbuminuria to the control level and maintained creatinine clearance with enhanced nNOS and eNOS expression compared to quinapril alone.

Activation of bradykinin B1 receptor by ACE inhibitors

ACE or kininase II inhibitors are very important, widely used therapeutic agents for the treatment of a variety of diseases. Although they inhibit ACE, thus, angiotensin II release and bradykinin (BK) inactivation, this inhibition alone does not suffice to explain their successful application in medical practice. Enalaprilat and other ACE inhibitors at nanomolar concentrations activate the BK B1 receptor directly in the absence of ACE and the peptide ligands, des-Arg-kinins. The inhibitors activate at the Zn-binding pentameric consensus sequence HEXXH (195 -199) of B1, a motif also present in the active centers of ACE but absent from the BK B2 receptor. ACE inhibitors, when activating the B1 receptor, elevate intracellular calcium [Ca2+]i and release NO from cultured cells. Activation by ACE inhibitor was abolished by Ca-EDTA, a B1 receptor antagonist, by a synthetic undecapeptide representing the 192-202 sequence in the B1 receptor, and by site-directed mutagenesis of H195 to A. With the exception of the B1 receptor blocker, these agents and the mutation did not affect the actions of the peptide ligand des-Arg10-Lys1-BK. Ischemia and inflammatory cytokines induce B1 receptors and elevate its expression. Direct activation of the B1 receptor by ACE inhibitors can contribute to their therapeutic efficacy, for example, by releasing NO in vascular beds, or to some of their side effects.

Regulation of endothelial-type NO synthase expression in pathophysiology and in response to drugs

In many types of cardiovascular pathophysiology such as hypercholesterolemia and atherosclerosis, diabetes, cigarette smoking, or hypertension (with its sequelae stroke and heart failure) the expression of endothelial NO synthase (eNOS) is altered. Both up- and downregulation of eNOS have been observed, depending on the underlying disease. When eNOS is upregulated, the upregulation is often futile and goes along with a reduction in bioactive NO. This is due to an increased production of superoxide generated by NAD(P)H oxidase and by an uncoupled eNOS. A number of drugs with favorable effects on cardiovascular disease upregulate eNOS expression. The resulting increase in vascular NO production may contribute to their beneficial effects. These compounds include statins, angiotensin-converting enzyme inhibitors, AT1 receptor antagonists, calcium channel blockers, and some antioxidants. Other drugs such as glucocorticoids, whose administration is associated with cardiovascular side effects, downregulate eNOS expression. Stills others such as the immunosuppressants cyclosporine A and FK506/tacrolimus or erythropoietin have inconsistent effects on eNOS. Thus regulation of eNOS expression and activity contributes to the overall action of several classes of drugs, and the development of compounds that specifically upregulate this protective enzyme appears as a desirable target for drug development.

Regulation of cardiac remodeling by nitric oxide: focus on cardiac myocyte hypertrophy and apoptosis

Cardiac hypertrophy occurs in pathological conditions associated with chronic increases in hemodynamic load. Although hypertrophy can initially be viewed as a salutary response, ultimately, it often enters a phase of pathological remodeling that may lead to heart failure and premature death. A prevailing concept predicts that changes in gene expression in hypertrophied cardiac myocytes and cardiac myocyte loss by apoptosis contribute to the transition from hypertrophy to failure. In recent years, nitric oxide (NO) has emerged as an important regulator of cardiac remodeling. Specifically, NO has been recognized as a potent antihypertrophic and proapoptotic mediator in cultured cardiac myocytes. Studies in genetically engineered mice have extended these findings to the in vivo situation. It appears that low levels and transient release of NO by endothelial NO synthase exert beneficial effects on the remodeling process by reducing cardiac myocyte hypertrophy, cavity dilation and mortality. By contrast, high levels and sustained production of NO by inducible NO synthase seem to be maladaptive by reducing ventricular contractile function, and increasing cardiac myocyte apoptosis, and mortality. In the future, these novel insights into the role of NO in cardiac remodeling should allow the development of novel therapeutic strategies to treat cardiac remodeling and failure.

Cross talk between adipose tissue cells: impact on pathophysiology

The metabolic functionality of adipose tissue is intimately dependent on local communication between various cell types. It influences not only the equilibrium between lipogenesis and lipolysis but also between hypertrophic and hyperplastic growth, thereby determining the role adipose tissue plays in the insulin resistance syndrome.

Obesity, atherosclerosis and the vascular endothelium: mechanisms of reduced nitric oxide bioavailability in obese humans

It is now well established that obesity is an independent risk factor for the development of coronary artery atherosclerosis. The maintenance of vascular homeostasis is critically dependent on the continued integrity of vascular endothelial cell function. A key early event in the development of atherosclerosis is thought to be endothelial cell dysfunction. A primary feature of endothelial cell dysfunction is the reduced bioavailability of the signalling molecule nitric oxide (NO), which has important anti atherogenic properties. Recent studies have produced persuasive evidence showing the presence of endothelial dysfunction in obese humans NO bioavailability is dependent on the balance between its production by a family of enzymes, the nitric oxide synthases, and its reaction with reactive oxygen species. The endothelial isoform (eNOS) is responsible for a significant amount of the NO produced in the vascular wall. NO production can be modulated in both physiological and pathophysiological settings, by regulation of the activity of eNOS at a transcriptional and post-transcriptional level, by substrate and co-factor provision and through calcium dependent and independent signalling pathways. The present review discusses general mechanisms of reduced NO bioavailability including factors determining production of both NO and reactive oxygen species. We then focus on the potential factors responsible for endothelial dysfunction in obesity and possible therapeutic interventions targetted at these abnormalities.

ACE inhibition and atherogenesis

Recent clinical studies such as HOPE, SECURE, and APRES show that angiotensin-converting enzyme (ACE) inhibitors like ramipril improve the prognosis of patients with a high risk of atherothrombotic cardiovascular events. Atherosclerosis, as a chronic inflammatory condition of the vascular system, can turn into an acute clinical event through the rupture of a vulnerable atherosclerotic plaque followed by thrombosis. ACE inhibition has a beneficial effect on the atherogenic setting and on fibrinolysis. Endothelial dysfunction is the end of a common process in which cardiovascular risk factors contribute to inflammation and atherogenesis. By inhibiting the formation of angiotensin II, ACE inhibitors prevent any damaging effects on endothelial function, vascular smooth muscle cells, and inflammatory vascular processes. An increase in the release of NO under ACE inhibition has a protective effect. Local renin-angiotensin systems in the tissue are involved in the inflammatory processes in the atherosclerotic plaque. Circulating ACE-containing monocytes, which adhere to endothelial cell lesions, differentiate within the vascular wall to ACE-containing macrophages or foam cells with increased local synthesis of ACE and angiotensin II. Within the vascular wall, angiotensin II decisively contributes to the instability of the plaque by stimulating growth factors, adhesion molecules, chemotactic proteins, cytokines, oxidized LDL, and matrix metalloproteinases. Suppression of the increased ACE activity within the plaque can lead to the stabilization and deactivation of the plaque by reducing inflammation in the vascular wall, thus lessening the risk of rupture and thrombosis and the resultant acute clinical cardiovascular events. The remarkable improvement in the long-term prognosis of atherosclerotic patients with increased cardiovascular risk might be the clinical result of the contribution made by ACE inhibition in the vascular wall.

Blockade of endothelial enzymes: new therapeutic targets

Nitric oxide (NO) is the principal vasoactive substance produced by the vascular endothelium with antitrombotic, antiatherogenic and vasodilator actions. The loss of these functions is now known as endothelial dysfunction (ED) and it has been proposed that it is the final common pathway in cardiovascular disease. At the moment there is an important body of evidence that supports the proposal that ED is a consequence of an imbalance between the free radicals, NO, superoxide (O(-)(2)) and peroxynitrate (ONOO(-)). This imbalance is the result of the actions of well known risk factors associated with an inappropriate diet and infection-inflammation. Angiotensin-converting enzyme (ACE) inhibitors are highly effective against a variety of cardiovascular disorders. Experimental and clinical studies have demonstrated a beneficial effect of ACE inhibition on endothelial function. This action is mainly due to an increase in the concentration of bradykinin, which stimulates NO production. ACE inhibitors also block the formation of angiotensin II that results in a lower production of O(-)(2). These effects lead to improve the imbalance between NO and O(-)(2) observed in cardiovascular disease. This proposal is supported by different clinical trials that have shown that the ACE inhibitors with higher affinity by the tissular ACE, such as quinapril, are the most effective in reversing ED principally by accumulating bradykinin. Recently, the HOPE study conducted in patients at a high risk of cardiovascular events, showed how ramipril, an ACE inhibitor with high affinity by tissular ACE, decreased the mortality rate due to cardiovascular disease independently of changes in blood pressure.

Effects of an HMG-CoA reductase inhibitor in combination with an ACE inhibitor or angiotensin II type 1 receptor antagonist on myocardial metabolism in ischemic rabbit hearts

We investigated the effects of a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, pravastatin, an angiotensin converting enzyme (ACE) inhibitor, temocaprilat, and an angiotensin II type 1 (AT1) receptor antagonist, CV-11974, on myocardial metabolism during ischemia in isolated rabbit hearts using phosphorus 31-nuclear magnetic resonance (31P-NMR) imaging. Forty-five minutes of continuous normothermic global ischemia was carried out. Pravastatin, temocaprilat, CV-11974 or a nitric oxide synthase inhibitor, L-NAME was administered from 60 min prior to the global ischemia. Japanese white rabbits were divided into the following experimental groups, a control group (n=7), a group treated with pravastatin (P group; n=7), a group treated with pravastatin and temocaprilat (P+T group; n=7), a group treated with pravastatin and CV-11974 (P+CV group; n=7), and a group treated with pravastatin and L-NAME (P+L-NAME group; n=7). During ischemia, P group, as well as either P+T group or P+CV group, showed a significant inhibition of the decreases in adenosine triphosphate (ATP) and intracellular pH (pHi) (p<0.01, respectively, at the end of ischemia compared to the control group as well as P+L-NAME group), and a significant inhibition of the increase in inorganic phosphate (Pi) (p<0.01, respectively, compared with the control group as well as P+L-NAME group). These results suggest that pravastatin significantly improved myocardial energy metabolism during myocardial ischemia. This beneficial effect was dependent on NO synthase. However, this beneficial effect was not enhanced by either temocaprilat or CV-11974.

Nitric oxide donors and cardiovascular agents modulating the bioactivity of nitric oxide: an overview

Nitric oxide (NO) mediates multiple physiological and pathophysiological processes in the cardiovascular system. Pharmacological compounds that release NO have been useful tools for evaluating the pivotal role of NO in cardiovascular physiology and therapeutics. These agents constitute two broad classes of compounds, those that release NO or one of its redox congeners spontaneously and those that require enzymatic metabolism to generate NO. In addition, several commonly used cardiovascular drugs exert their beneficial action, in part, by modulating the NO pathway. Here, we review these classes of agents, summarizing their fundamental chemistry and pharmacology, and provide an overview of their cardiovascular mechanisms of action.

Bradykinin enhances sympathetic neurotransmission in rat blood vessels

Bradykinin evokes endothelium-dependent relaxation in some vascular beds; on the other hand, the possibility has been demonstrated that in certain organs, such as the adrenal medulla or atria, bradykinin may enhance transmitter release from the sympathetic nerves. We hypothesized that bradykinin may also enhance postganglionic sympathetic neurotransmission in blood vessels. To test this hypothesis, we recorded excitatory junction potentials (EJPs), a measure of sympathetic purinergic neurotransmission, in rat mesenteric resistance arteries with a conventional microelectrode technique. EJPs were elicited by repetitive perivascular nerve stimulation (1 Hz, 20 to 50 V, 30 to 60 micros, 11 pulses). In this preparation, bradykinin (10(-7) or 10(-6) mol/L) significantly enhanced the amplitude of EJPs without altering the resting membrane potential. This effect of bradykinin was blocked by Hoe 140, a bradykinin B2 receptor antagonist, but not by des-Arg(9),[Leu(8)]-bradykinin, a bradykinin B1 receptor antagonist. The cyclooxygenase inhibitor indomethacin or NO synthase inhibitor N(G)-nitro-L-arginine did not alter the effect of bradykinin. Captopril, an ACE inhibitor, but not candesartan, an angiotensin II type 1 receptor antagonist, enhanced the action of a low concentration (10(-8) mol/L) of bradykinin on EJPs. These findings suggest that in rat mesenteric resistance arteries, bradykinin enhances sympathetic purinergic neurotransmission, presumably through presynaptic bradykinin B2 receptors. The clinical relevance of the present findings remains unclear; however, the fact that the ACE inhibitor, but not the angiotensin II type 1 receptor antagonist, enhanced the action of bradykinin on sympathetic neurotransmission may warrant further investigation.

Nutritional factors in the pathobiology of human essential hypertension

Endothelial cells produce vasodilator and vasoconstrictor substances. Dietary factors such as sodium, potassium, calcium, magnesium, zinc, selenium, vitamins A, C, and E, and essential fatty acids and their products such as eicosanoids can influence blood pressure, cardio- and cerebrovascular diseases, and concentrations of blood lipids and atherosclerosis. There might be a close interaction between these dietary factors, sympathetic and parasympathetic nervous systems, the metabolism of essential fatty acids, nitric oxide, prostacyclin, and endothelium in human essential hypertension. A deficiency in any one factor, dietary or endogenous, or alterations in their interactions with each other, can lead to endothelial dysfunction and development of hypertension. Therefore, alterations in the metabolism of essential fatty acids might be a predisposing factor to the development of essential hypertension and insulin resistance.

Interactions among challenges of hydromineral balance, angiotensin-converting enzyme, and cystine aminopeptidase

Enzymatic cleavage of some peptides could be included among the mechanisms of water-electrolyte homeostasis. To test this hypothesis, the angiotensin-converting activity (ACE) of plasma and the L-cystine-di-beta-naphthylamidase activity (CAP) of plasma and of soluble and particulate fractions from different areas of the central nervous system (CNS) were investigated in rats submitted to treatments eliciting hydromineral imbalance. CAP in the CNS was unchanged by hydromineral challenges. The correlations observed between plasma osmolality and CAP, and plasma CAP and ACE suggested a contribution of these activities to the restoration of basal water-electrolyte and blood pressure conditions through the hydrolysis of vasopressin, oxytocin, angiotensin I and bradykinin.