Paulus Wohlfart

Interactions among ACE, kinins and NO

Time for primary review 22 days. nnAngiotensin converting enzyme (ACE) is a transmembrane zinc metallopeptidase that cleaves carboxy-terminal dipeptides from several peptides and is expressed in great amounts in vascular endothelial cells [1,2]. A soluble form of the enzyme is found in plasma which is presumably derived from the membrane-bound form by proteolytic cleavage [3]. ACE plays a major role in the regulation of the vascular tone by converting the biological inactive decapeptide angiotensin I (ANG I) into the vasoconstrictor and proliferative octapeptide angiotensin II (ANG II). In a similar manner, ACE inactivates the vasodilatory nonapeptide bradykinin (BK), which derives from a number of different sources [4].nnEndothelium-derived or exogenously added BK exerts its vasodilatory action through stimulation of endothelial B2 kinin receptors thereby causing the synthesis and release of vasodilator substances such as endothelium-derived hyperpolarizing factor (EDHF) [5], prostacyclin and nitric oxide (NO) [6]. Many of the effects of NO on platelets [7], smooth muscle cells [8], and cardiac myocytes [9,10] are mediated by activation of soluble guanylyl cyclase to synthesize cyclic GMP. The biological function of soluble guanylyl cyclase and NO/cyclic GMP in endothelial cells is not yet completely understood. One function of endothelial cyclic GMP may be a negative feed-back mechanism to turn off further NO synthesis [11,12]. Changes in the synthesis of ACE, BK and NO are associated with a number of cardiovascular conditions including hypertension, atherosclerosis or coronary heart disease. ACE inhibitors are able to treat these diseases by both, accumulation of endothelium-derived kinins and the inhibition of ANG II [13,14].nnThe separate effects of ACE, kinins as well as NO on the cardiovascular system have been thoroughly investigated and described. Since only a small amount of information is available concerning the physiological/pathophysiological significance of … nn* Corresponding author. Tel.: +49-69-305-6868, fax: +49-69-305-81252 wolfgang.linz{at}hmrag.com

Release of nitric oxide from endothelial cells stimulated by YC‐1, an activator of soluble guanylyl cyclase

In this study we examined the endothelium‐dependent effect of YC‐1–a benzyl indazole derivative which directly activates soluble guanylyl cyclase (sGC)–on vascular relaxation and nitric oxide (NO) and guanosine‐3′,5′‐cyclic monophosphate (cyclic GMP) in endothelial cells. In preconstricted rat aortic rings with intact endothelium, YC‐1 produced a concentration‐dependent relaxation. However, the concentration response curve was shifted rightward to higher concentrations of YC‐1, when (i) the aortas were pre‐treated with L‐NG‐nitroarginine methylester (L‐NAME) or (ii) the endothelium was removed. Incubation of bovine aortic endothelial cells (BAEC) with YC‐1 produced a concentration‐dependent NO synthesis and release as assessed using a porphyrinic microsensor. Pre‐incubating cells with L‐NAME or with 8‐bromo‐cyclic GMP decreased this effect indicating that the YC‐1 stimulation of NO synthesis is due to an activation of nitric oxide synthase, but not to an elevation of cyclic GMP. No direct effect of YC‐1 on recombinant endothelial constitutive NO synthase activity was observed. The YC‐1 stimulated NO release was reduced by 90%, when extracellular free calcium was diminished. In human umbilical vein endothelial cells (HUVEC), YC‐1 stimulated intracellular cyclic GMP production in a concentration‐ and time‐dependent manner. Stimulation of cyclic GMP was greater with a maximum concentration of YC‐1 compared to calcium ionophore A23187. Similar effects were observed in BAEC and rat microvascular coronary endothelial cells (RMCEC). When HUVEC and RMCEC were pre‐treated with L‐NG‐nitroarginine (L‐NOARG), the maximum YC‐1 stimulated cyclic GMP increase was reduced by 50%. These results indicate, that beside being a direct activator of sGC, YC‐1 stimulates a NO‐synthesis and release in endothelial cells which is independent of elevation of cyclic GMP but strictly dependent on extracellular calcium. The underlying mechanism needs to be determined further.

Late Treatment With Ramipril Increases Survival in Old Spontaneously Hypertensive Rats

Spontaneously hypertensive rats (SHR) begin to die from cardiovascular complications at approximately 15 months of age. We tested whether chronic ACE-inhibitor treatment would extend the lifespan of such old animals. We also studied cardiac hypertrophy and function, endothelial function and expression, and activity of NO synthase (eNOS). One hundred 15-month-old SHR were randomized into 3 groups, control (n=10), placebo-treated (n=45), and ramipril-treated with an antihypertensive dose of 1 mg. kg(-1). d(-1) in drinking water (n=45). Ex vivo experiments were performed after 15 months (control) and 21 months, when approximately 80% of the placebo group had died. Late treatment with ramipril significantly extended lifespan of the animals from 21 to 30 months. Fully established cardiac hypertrophy, observed in placebo-treated animals and in controls, was significantly reversed by ramipril treatment. In isolated working hearts, a significantly improved function associated with increased cardiac eNOS expression was seen versus placebo and control hearts. Endothelial dysfunction in isolated aortic rings from control and placebo-treated SHR was significantly improved by ACE inhibition and associated with enhanced NO release. Late treatment of SHR with the ACE inhibitor ramipril extended lifespan from 21 to 30 months, which is comparable to the lifespan of untreated normotensive Wistar-Kyoto rats. This lifespan extension, probably due to blood pressure reduction, correlated with increased eNOS expression and activity followed by a regression of left ventricular hypertrophy and cardiac and vascular dysfunction.

Cardioprotective effects of lixisenatide in rat myocardial ischemia-reperfusion injury studies

BackgroundLixisenatide is a glucagon-like peptide-1 analog which stimulates insulin secretion and inhibits glucagon secretion and gastric emptying. We investigated cardioprotective effects of lixisenatide in rodent models reflecting the clinical situation.MethodsThe acute cardiac effects of lixisenatide were investigated in isolated rat hearts subjected to brief ischemia and reperfusion. Effects of chronic treatment with lixisenatide on cardiac function were assessed in a modified rat heart failure model after only transient coronary occlusion followed by long-term reperfusion. Freshly isolated cardiomyocytes were used to investigate cell-type specific mechanisms of lixisenatide action.ResultsIn the acute setting of ischemia-reperfusion, lixisenatide reduced the infarct-size/area at risk by 36% ratio without changes on coronary flow, left-ventricular pressure and heart rate. Treatment with lixisenatide for 10 weeks, starting after cardiac ischemia and reperfusion, improved left ventricular end-diastolic pressure and relaxation time and prevented lung congestion in comparison to placebo. No anti-fibrotic effect was observed. Gene expression analysis revealed a change in remodeling genes comparable to the ACE inhibitor ramipril. In isolated cardiomyocytes lixisenatide reduced apoptosis and increased fractional shortening. Glucagon-like peptide-1 receptor (GLP1R) mRNA expression could not be detected in rat heart samples or isolated cardiomyocytes. Surprisingly, cardiomyocytes isolated from GLP-1 receptor knockout mice still responded to lixisenatide.ConclusionsIn rodent models, lixisenatide reduced in an acute setting infarct-size and improved cardiac function when administered long-term after ischemia-reperfusion injury. GLP-1 receptor independent mechanisms contribute to the described cardioprotective effect of lixisenatide. Based in part on these preclinical findings patients with cardiac dysfunction are currently being recruited for a randomized, double-blind, placebo-controlled, multicenter study with lixisenatide.Trial registration(ELIXA, ClinicalTrials.gov Identifier: NCT01147250)

The peroxisome proliferator-activated receptor-α (PPAR-α) agonist, AVE8134, attenuates the progression of heart failure and increases survival in rats

AbstractAim:To investigate the efficacy of the peroxisome proliferator-activated receptor-α (PPARα) agonist, AVE8134, in cellular and experimental models of cardiac dysfunction and heart failure.Methods:In Sprague Dawley rats with permanent ligation of the left coronary artery (post-MI), AVE8134 was compared to the PPARγ agonist rosiglitazone and in a second study to the ACE inhibitor ramipril. In DOCA-salt sensitive rats, efficacy of AVE8134 on cardiac hypertrophy and fibrosis was investigated. Finally, AVE8134 was administered to old spontaneously hypertensive rats (SHR) at a non-blood pressure lowering dose with survival as endpoint. In cellular models, we studied AVE8134 on hypertrophy in rat cardiomyocytes, nitric oxide signaling in human endothelial cells (HUVEC) and LDL-uptake in human MonoMac-6 cells.Results:In post-MI rats, AVE8134 dose-dependently improved cardiac output, myocardial contractility and relaxation and reduced lung and left ventricular weight and fibrosis. In contrast, rosiglitazone exacerbated cardiac dysfunction. Treatment at AVE8134 decreased plasma proBNP and arginine and increased plasma citrulline and urinary NOx/creatinine ratio. In DOCA rats, AVE8134 prevented development of high blood pressure, myocardial hypertrophy and cardiac fibrosis, and ameliorated endothelial dysfunction. Compound treatment increased cardiac protein expression and phosphorylation of eNOS. In old SHR, treatment with a low dose of AVE8134 improved cardiac and vascular function and increased life expectancy without lowering blood pressure. AVE8134 reduced phenylephrine-induced hypertrophy in adult rat cardiomyocytes. In HUVEC, Ser-1177-eNOS phosphorylation but not eNOS expression was increased. In monocytes, AVE8134 increased the expression of CD36 and the macrophage scavenger receptor 1, resulting in enhanced uptake of oxidized LDL.Conclusion:The PPARα agonist AVE8134 prevents post-MI myocardial hypertrophy, fibrosis and cardiac dysfunction. AVE8134 has beneficial effects against hypertension-induced organ damages, resulting in decreased mortality. The compound exerts its protective properties by a direct effect on cardiomyocyte hypertrophy, but also indirectly via monocyte signaling and increased endothelial NO production.

AVE3085, an enhancer of endothelial nitric oxide synthase, restores endothelial function and reduces blood pressure in spontaneously hypertensive rats

BACKGROUND AND PURPOSE Nitric oxide (NO) plays an important role in endothelial function, and impaired NO production is involved in hypertension. Therefore, compounds that regulate endothelial NO synthase (eNOS) may be of therapeutic benefit. A novel, low molecular weight compound AVE3085 is a recently developed compound with the ability to enhance eNOS transcription. The present study investigated the effects of AVE3085 in endothelial dysfunction associated with hypertension.

Female resistance to pneumonia identifies lung macrophage nitric oxide Synthase-3 as a therapeutic target

To identify new approaches to enhance innate immunity to bacterial pneumonia, we investigated the natural experiment of gender differences in resistance to infections. Female and estrogen-treated male mice show greater resistance to pneumococcal pneumonia, seen as greater bacterial clearance, diminished lung inflammation, and better survival. In vitro, lung macrophages from female mice and humans show better killing of ingested bacteria. Inhibitors and genetically altered mice identify a critical role for estrogen-mediated activation of lung macrophage nitric oxide synthase-3 (NOS3). Epidemiologic data show decreased hospitalization for pneumonia in women receiving estrogen or statins (known to activate NOS3). Pharmacologic targeting of NOS3 with statins or another small-molecule compound (AVE3085) enhanced macrophage bacterial killing, improved bacterial clearance, and increased host survival in both primary and secondary (post-influenza) pneumonia. The data identify a novel mechanism for host defense via NOS3 and suggest a potential therapeutic strategy to reduce secondary bacterial pneumonia after influenza. DOI: http://dx.doi.org/10.7554/eLife.03711.001

Cathepsin A mediates susceptibility to atrial tachyarrhythmia and impairment of atrial emptying function in Zucker diabetic fatty rats

AIMSnType 2 diabetes (T2D) is an independent risk factor for atrial fibrillation (AF) and stroke. The serine protease cathepsin A (CatA) is up-regulated in diabetes and plays an important role in the degradation of extracellular peptides. This study sought to delineate the role of CatA for the development of atrial remodelling under diabetic conditions.nnnMETHODS AND RESULTSnZucker Diabetic Fatty rats (ZDF) were treated with vehicle (n = 20) or CatA-inhibitor (SAR; 50 mg/kg; n = 20), and compared with age-matched non-diabetic littermates (Ctr, n = 20). Left-atrial (LA) emptying function [magnetic resonance imaging (MRI)] and atrial electrophysiological parameters were measured before sacrifice for histological and biochemical analysis. The impact of enhanced cardiac CatA expression on atrial remodelling was determined using CatA-transgenic mice. At the age of 9.5 months, atrial tissues of ZDF rats showed increased CatA gene expression and CatA-activity, along with increased AF-susceptibility and impaired LA-emptying function. CatA-inhibition reduced CatA-activity in ZDF comparable to Ctr values and decreased LA-fibrosis formation and connexin 43 lateralization. This was associated with shorter median duration of LA-tachyarrhythmia (12.0 ± 1.7 vs. 1.2 ± 0.47 s, P < 0.01) induced by burst pacing and diminished regions of slow conduction. Cardiac MRI revealed better LA-emptying function parameters (active per cent emptying: 29 ± 1 vs. 23 ± 2%, P < 0.01) after CatA-inhibition. CatA-inhibition reduced LA bradykinin-degrading activity in ZDF. Transgenic mice overexpressing CatA demonstrated enhanced atrial fibrosis formation and increased AF-susceptibility.nnnCONCLUSIONnT2D leads to arrhythmogenic atrial remodelling in ZDF rats. CatA-inhibition reduces LA bradykinin-degrading activity in ZDF and suppresses the development of atrial structural changes and AF-promotion, implicating CatA as an important mediator for AF-substrate in T2D.