Cardiomyocyte stiffness in diastolic heart failure

Background - Heart failure with preserved left ventricular (LV) ejection fraction (EF) is increasingly recognized and usually referred to as diastolic heart failure (DHF). Its pathogenetic mechanism remains unclear, partly because of a lack of myocardial biopsy material. Endomyocardial biopsy samples obtained from DHF patients were therefore analyzed for collagen volume fraction (CVF) and sarcomeric protein composition and compared with control samples. Single cardiomyocytes were isolated from these biopsy samples to assess cellular contractile performance. Methods and Results - DHF patients (n=12) had an LVEF of 71 ± 11%, an LV end-diastolic pressure (LVEDP) of 28±4 mm Hg, and no significant coronary artery stenoses. DHF patients had higher CVFs (7.5±4.0%, P<0.05) than did controls (n=8, 3.8±2.0%), and no conspicuous changes in sarcomeric protein composition were detected, Cardiomyocytes, mechanically isolated and treated with Triton X-100 to remove all membranes, were stretched to a sarcomere length of 2.2 μm and activated with solutions containing varying [Ca2+]. Compared with cardiomyocytes of controls, cardiomyocytes of DHF patients developed a similar total isometric force at maximal [Ca2+], but their resting tension (Fpassive) in the absence of Ca2+ was almost twice as high (6.6±3.0 versus 3.5±1.7 kN/m2, P<0.001). F passive and CVF combined yielded stronger correlations with LVEDP than did either alone. Administration of protein kinase A (PKA) to DHF cardiomyocytes lowered Fpassive to control values. Conclusions - DHF patients had stiffer cardiomyocytes, as evident from a higher F passive, at the same sarcomere length. Together with CVF, F passive determined in vivo diastolic LV dysfunction. Correction of this high Fpassive by PKA suggests that reduced phosphorylation of sarcomeric proteins is involved in DHF

Right-ventricular failure is associated with increased mitochondrial complex II activity and production of reactive oxygen species.

Objective: Reactive oxygen species (ROS) have been implicated in the progression of ventricular hypertrophy to congestive heart failure. However, the source of increased oxidative stress in cardiomyocytes remains unclear. Methods: Here we examined NADPH oxidase and mitochondria as sources of ventricular ROS production in a rat model of right-ventricular (RV) failure (CHF) induced by pulmonary arterial hypertension (PAH). Results: Western analysis showed increased expression of the catalytic subunit gp9

Peroxynitrite-induced alpha-actinin nitration and contractile alterations in isolated human myocardial cells

Objective: Peroxynitrite-mediated myocardial protein nitration has been associated with a depressed cardiac pump function. In the present study, an attempt was made to elucidate the molecular background of peroxynitrite-evoked alterations in the human myocardium. Methods: Isometric force generation was measured in permeabilized human ventricular myocytes and biochemical methods were employed to identify the proteins affected by peroxynitrite-induced nitrotyrosine formation. Results: The maximal Ca2+-activated isometric force (pCa = 4.75) decreased to zero with increasing concentrations of peroxynitrite in a concentration-dependent manner (IC50: 55 ± 4 μM; based on a total of 75 myocytes). However, there were no differences before and after the application of 50 μM peroxynitrite in the Ca 2+-sensitivity of force production (pCa50: 5.89 ± 0.02 and 5.86 ± 0.04), in the steepness of the Ca2+-force relationship (nHill: 2.22 ± 0.11 and 2.42 ± 0.25), and in the actin-myosin turnover kinetics (ktr at saturating [Ca2+]: 1.14 ± 0.03 1/s and 1.05 ± 0.07 1/s) (P > 0.05). Nevertheless, 50 μM peroxynitrite greatly deteriorated the cross-striation pattern and induced a slight, but significant, increase in the passive force component (from 2.1 ± 0.1 to 2.5 ± 0.2 kN/m2; n = 57 cells), reflecting ultrastructural alterations. Western immunoblots revealed that 50 μM peroxynitrite selectively induced the nitration of a protein with an apparent molecular mass of about 100 kDa. Subsequent immunoprecipitation assays identified this nitrated protein as α-actinin, a major Z-line protein. Conclusions: These results suggest α-actinin as a novel target for peroxynitrite in the human myocardium; its nitration induces a contractile dysfunction, presumably by decreasing the longitudinal transmission of force between adjacent sarcomeres

Right ventricular diastolic dysfunction and the acute effects of sildenafil in pulmonary hypertension patients

Aims: This study investigated whether right ventricular (RV) diastolic function is impaired in pulmonary hypertension (PH) patients, and whether it is related to RV mass and afterload. In addition, the effects of an acute reduction of RV afterload by the oral intake of sildenafil were studied. Finally, we assessed whether diastolic function is related to cardiac parameters of disease severity. Methods and results: Twenty-five PH patients and 11 control subjects were studied. Right-heart catheterization and N-terminal pro-brain natriuretic peptide (NT-proBNP) sampling were performed in patients. MRI measured RV ejection fraction, mass, and diastolic function. Isovolumic relaxation time (IVRT), normalized early peak filling rate (E), atrium-induced peak filling rate (A), and E/A ratio described diastolic function. Compared to control subjects, patients had prolonged mean (± SD) IVRT (133.5 ± 53.2 vs 29.3 ± 20.8 ms, respectively; p < 0.001), decreased E (3.0 ± 1.6 vs 6.4 ± 2.5

SIH--a novel lipophilic iron chelator--protects H9c2 cardiomyoblasts from oxidative stress-induced mitochondrial injury and cell death

Recent evidence suggests that oxidative stress is a common denominator in many aspects of cardiovascular pathogenesis. Free cellular iron plays a crucial catalytic role in the formation of highly toxic hydroxyl radicals, and thereby it may aggravate the contribution of oxidative stress to cardiovascular disease. Therefore, iron chelation may be an effective therapeutic approach, but the progress in this area is hindered by the lack of effective agents. In this study, using the rat heart myoblast-derived cell line H9c2, we aimed to investigate whether the novel lipophilic iron chelator salicylaldehyde isonicotinoyl hydrazone (SIH) protects the cells against hydrogen peroxide (H2O2)-induced cytotoxicity. Exposure of cells to 100 μmol/l H2O2 has within 4 h induced a complete dissipation of their mitochondrial membrane potential (ΔΨm) . Co-treatment with SIH dose-dependently reduced (EC50 = 0.8 μmol/l) or even completely abolished (3 μmol/l) this collapse. Furthermore, the latter SIH concentration was capable to fully prevent alterations in cell morphology, and inhibited both apoptosis (annexin-V staining, nuclear chromatin shrinkage, TUNEL positivity) and necrosis (propidium iodide staining), even 24 h after the H2O2 exposure. In comparison, deferoxamin (a commercially available hydrophilic iron chelator used in clinical practice and most previous studies) was cytoprotective only at three-order higher and clinically unachievable concentrations (EC50 = 1300 μmol/l). Thus, in this study, we present iron chelation as a very powerful tool by which oxidative stress-induced myocardial damage can be prevented

Does myocardial fibrosis hinder contractile function and perfusion in idopathic dilated cardiomyopathy ? PET and MR imaging study

Purpose: To prospectively evaluate, by using positron emission tomography (PET) and magnetic resonance (MR) imaging, the interrelationships between regional myocardial fibrosis, perfusion, and contractile function in patients with idiopathic dilated cardiomyopathy (DCM). Materials and Methods: The study protocol was approved by the hospital ethics committee, and all subjects gave written informed consent. Sixteen patients with idiopathic DCM (mean age, 54 years ± 11 [standard deviation]; nine men) and six healthy control subjects (mean age, 28 years ± 2; five men) were examined with PET and MR tissue tagging. Oxygen 15-labeled water and carbon monoxide were used as tracers at PET to assess myocardial blood flow (MBP) and the perfusable tissue index (PTI), which is inversely related to fibrosis. MBF was determined at rest and during pharmacologically induced hyperemia. Maximum circumferential shortening (