Increased inducible nitric oxide synthase and arginase II expression in heart failure: no net nitrite/nitrate production and protein S-nitrosylation.

Our objective was to address the balance of inducible nitric oxide (NO) synthase (iNOS) and arginase and their contribution to contractile dysfunction in heart failure (HF). Excessive NO formation is thought to contribute to contractile dysfunction; in macrophages, increased iNOS expression is associated with increased arginase expression, which competes with iNOS for arginine. With substrate limitation, iNOS may become uncoupled and produce reactive oxygen species (ROS).

Systematic analysis of functional and structural changes after coronary microembolization: a cardiac magnetic resonance imaging study.

Objectives: Our study aimed to detect the morphological und functional effects of coronary microembolization (ME) in vivo by cardiac magnetic resonance (CMR) imaging in an established experimental animal model.

Background: Post-mortem morphological alterations of coronary ME include perifocal inflammatory edema and focal microinfarcts. Clinically, the detection of ME after successful coronary interventions identifies a population with a worse long-term prognosis.

How much myocardial damage is necessary to enable detection of focal late gadolinium enhancement at cardiac MR imaging?

Purpose: To assess the visibility of small myocardial lesions at magnetic resonance (MR) imaging and to estimate how much myocardial damage is necessary to enable detection of late gadolinium enhancement (LGE) in vivo.

Materials And Methods: The study was approved by the local bioethics committee. Coronary microembolization was performed by injecting 300,000 microspheres into the distal portion of the left anterior descending artery in 18 anesthetized minipigs to create multifocal areas of myocardial damage.

No impact of protein phosphatases on connexin 43 phosphorylation in ischemic preconditioning.

Cardiac connexin 43 (Cx43) is involved in infarct propagation, and the uncoupling of Cx43-formed channels reduces infarct size. Cx43-formed channels open upon Cx43 dephosphorylation, and ischemic preconditioning (IP) prevents the ischemia-induced Cx43 dephosphorylation. In addition to the sarcolemma, Cx43 is also present in the cardiomyocyte mitochondria.

Inducible nitric oxide synthase expression and cardiomyocyte dysfunction during sustained moderate ischemia in pigs.

In acute myocardial ischemia, regional blood flow and function are proportionally reduced. With prolongation of ischemia, function further declines at unchanged blood flow. We studied the involvement of an inflammatory signal cascade in such progressive dysfunction and whether dysfunction is intrinsic to cardiomyocytes.

Mitochondrial respiration and membrane potential after low-flow ischemia are not affected by ischemic preconditioning.

Mitochondrial function following prolonged ischemia and subsequent reperfusion is better preserved by ischemic preconditioning (IP). In the present study, we analyzed whether or not IP has an impact on mitochondrial function at the end of a sustained ischemic period. Göttinger minipigs were subjected to 90-min low-flow ischemia without (n=5) and with (n=5) a preconditioning cycle of 10-min ischemia and 15-min reperfusion.

Microdialysis-based analysis of interstitial NO in situ: NO synthase-independent NO formation during myocardial ischemia.

Objectives: Nitric oxide (NO) synthesis by NO synthases (NOS) requires oxygen. However, although counterintuitive, NO synthesis is increased in ischemic myocardium. Accordingly, mechanisms independent of the NOS pathway have been suggested to contribute to NO synthesis during ischemia.

Loss of ischemic preconditioning's cardioprotection in aged mouse hearts is associated with reduced gap junctional and mitochondrial levels of connexin 43.

Connexin 43 (Cx43) is localized at left ventricular (LV) gap junctions and in cardiomyocyte mitochondria. A genetically induced reduction of Cx43 as well as blockade of mitochondrial Cx43 import abolishes the infarct size (IS) reduction by ischemic preconditioning (IP). With progressing age, Cx43 content in ventricular and atrial tissue homogenates is reduced.

Translocation of connexin 43 to the inner mitochondrial membrane of cardiomyocytes through the heat shock protein 90-dependent TOM pathway and its importance for cardioprotection.

We have previously shown that connexin 43 (Cx43) is present in mitochondria, that its genetic depletion abolishes the protection of ischemia- and diazoxide-induced preconditioning, and that it is involved in reactive oxygen species (ROS) formation in response to diazoxide. Here we investigated the intramitochondrial localization of Cx43, the mechanism of Cx43 translocation to mitochondria and the effect of inhibiting translocation on the protection of preconditioning. Confocal microscopy of mitochondria devoid of the outer membrane and Western blotting on fractionated mitochondria showed that Cx43 is located at the inner mitochondrial membrane, and coimmunoprecipitation of Cx43 with Tom20 (Translocase of the outer membrane 20) and with heat shock protein 90 (Hsp90) indicated that it interacts with the regular mitochondrial protein import machinery.

Inhibition of Na+/H+-exchanger with sabiporide attenuates the downregulation and uncoupling of the myocardial beta-adrenoceptor system in failing rabbit hearts.

Chronic heart failure (HF) is characterized by left ventricular (LV) structural remodeling, impaired function, increased circulating noradrenaline (NA) levels and impaired responsiveness of the myocardial beta-adrenoceptor (betaAR)-adenylyl cyclase (AC) system. In failing hearts, inhibition of the sodium/proton-exchanger (NHE)-1 attenuates LV remodeling and improves LV function. The mechanism(s) involved in these cardioprotective effects remain(s) unclear, but might involve effects on the impaired betaAR-AC system.

Connexin 43 in cardiomyocyte mitochondria and its increase by ischemic preconditioning.

Objective: Connexin 43 (Cx43) is involved in infarct size reduction by ischemic preconditioning (IP); the underlying mechanism of protection, however, is unknown. Since mitochondria have been proposed to be involved in IP's protection, the present study analyzed whether Cx43 is localized at mitochondria of cardiomyocytes and whether such localization is affected by IP.

Methods And Results: Western blot analysis on mitochondrial preparations isolated from rat, mouse, pig, and human hearts showed the presence of Cx43.

Regional differences of myocardial infarct development and ischemic preconditioning.

Unlabelled: The spatial and temporal development of myocardial infarction depends on the area at risk (AAR), the severity and duration of blood flow reduction (energy supply) as well as on heart rate and regional wall function (energy demand). Both supply and demand can vary within the AAR of a given heart, potentially resulting in differences in infarct development. We therefore retrospectively analyzed infarct size (IS, %AAR, TTC) in 24 anesthetized pigs in vivo following 90 min hypoperfusion and 120 min reperfusion of the LAD coronary artery, which supplies parts of the LV septum (LVS) and anterior free wall (LVAFW).

Coronary microembolization does not induce acute preconditioning against infarction in pigs-the role of adenosine.

Objective: After coronary microembolization (ME) adenosine is released from ischemic areas of the microembolized myocardium. This adenosine dilates vessels in adjacent nonembolized myocardium and increases coronary blood flow. For ischemic preconditioning (IP) to protect the myocardium against infarction, an increase in the interstitial adenosine concentration (iADO) prior to the subsequent ischemia/reperfusion is necessary.

Inhibition of the Na+/H+ exchanger attenuates the deterioration of ventricular function during pacing-induced heart failure in rabbits.

Aims: Inhibition of the Na+/H+-exchanger (NHE) preserves myocardial morphology and function in rat and mouse models of hypertrophy and failure. The mechanism(s) involved in such cardioprotective effects remain(s) unclear, but might involve blockade of increased protein kinase activity as observed in untreated hearts.

Methods And Results: We investigated the functional, morphological and biochemical consequences of NHE-inhibition with BIIB722 in rabbits with pacing-induced heart failure (HF).

Glucocorticoid treatment prevents progressive myocardial dysfunction resulting from experimental coronary microembolization.

Background: The frequency and importance of microembolization in patients with acute coronary syndromes and during coronary interventions have recently been appreciated. Experimental microembolization induces immediate ischemic dysfunction, which recovers within minutes. Subsequently, progressive contractile dysfunction develops over several hours and is not associated with reduced regional myocardial blood flow (perfusion-contraction mismatch) but rather with a local inflammatory reaction.

Stress kinase phosphorylation is increased in pacing-induced heart failure in rabbits.

In hearts with chronic left ventricular (LV) systolic dysfunction secondary to hypertension or myocardial infarction, MAPK phosphorylation and/or activity are increased. Whether other settings of LV dysfunction not associated with ischemia-reperfusion are also characterized by increased MAPK phosphorylation or activity is unknown. After 3 wk of rapid LV pacing (400 beats/min), eight rabbits displayed clinical signs of heart failure (HF), and echocardiography revealed an increase in LV end-diastolic diameter from 15.

Ischemic preconditioning preserves connexin 43 phosphorylation during sustained ischemia in pig hearts in vivo.

During myocardial ischemia, connexin 43 (Cx43) is dephosphorylated in vitro, and the subsequent opening of gap junctions formed by two opposing Cx43 hexamers was suggested to propagate ischemia/reperfusion injury. Reduction of infarct size (IS) by ischemic preconditioning (IP) involves activation of protein kinase C (PKC) and p38 mitogen activated protein kinase (MAPK), both of which can phosphorylate Cx43. We now studied in anesthetized pigs whether IP impacts on Cx43 phosphorylation by measuring the density of non-phosphorylated and total Cx43 (confocal laser) during normoperfusion and 90-min ischemia in non-preconditioned and preconditioned hearts.

Serum but not myocardial TNF-alpha concentration is increased in pacing-induced heart failure in rabbits.

In animals and patients with severe heart failure (HF), the serum tumor necrosis factor-alpha (TNF-alpha) concentration is increased. It is, however, still controversial whether or not such increased serum TNF-alpha originates from the heart itself or is of peripheral origin secondary to gastrointestinal congestion and increased endotoxin concentration. We therefore now examined TNF-alpha in serum, myocardium, and liver of sham-operated and HF rabbits.

No ischemic preconditioning in heterozygous connexin43-deficient mice.

Protein kinase Cepsilon (PKCepsilon) plays a central role in ischemic preconditioning (IP) in mice and rabbits, and activated PKCepsilon colocalizes with and phosphorylates connexin43 (Cx43) in rats and humans. Whether or not Cx43 contributes to the mechanism(s) of IP in vivo is yet unknown. Therefore, wild-type (n = 8) and heterozygous Cx43-deficient mice (n = 8) were subjected to 30 min occlusion and 120 min reperfusion of the left anterior descending coronary artery.

Myocardial dysfunction with coronary microembolization: signal transduction through a sequence of nitric oxide, tumor necrosis factor-alpha, and sphingosine.

Coronary microembolization results in progressive myocardial dysfunction, with causal involvement of tumor necrosis factor-alpha (TNF-alpha). TNF-alpha uses a signal transduction involving nitric oxide (NO) and/or sphingosine. Therefore, we induced coronary microembolization in anesthetized dogs and studied the role and sequence of NO, TNF-alpha, and sphingosine for the evolving contractile dysfunction.

Coronary microembolization: the role of TNF-alpha in contractile dysfunction.

Coronary microembolization is a frequent complication of atherosclerotic plaque rupture in acute coronary syndromes and during coronary interventions. Experimental coronary microembolization results in progressive contractile dysfunction associated with a local inflammation. We studied the causal role of tumor necrosis factor-alpha (TNF-alpha) in the progressive contractile dysfunction resulting from coronary microembolization.