Heinrich Mächler

cAMP- and Ca2+/calmodulin-dependent protein kinases mediate inotropic, lusitropic and arrhythmogenic effects of urocortin 2 in mouse ventricular myocytes

BACKGROUND AND PURPOSE Urocortin 2 is beneficial in heart failure, but the underlying cellular mechanisms are not completely understood. Here we have characterized the functional effects of urocortin 2 on mouse cardiomyocytes and elucidated the underlying signalling pathways and mechanisms.

If blocking potency of ivabradine is preserved under elevated endotoxin levels in human atrial myocytes

Lower heart rate is associated with better survival in patients with multiple organ dysfunction syndrome (MODS), a disease mostly caused by sepsis. The benefits of heart rate reduction by ivabradine during MODS are currently being investigated in the MODIfY clinical trial. Ivabradine is a selective inhibitor of the pacemaker current If and since If is impaired by lipopolysaccharide (LPS, endotoxin), a trigger of sepsis, we aimed to explore If blocking potency of ivabradine under elevated endotoxin levels in human atrial cardiomyocytes. Treatment of myocytes with S-LPS (containing the lipid A moiety, a core oligosaccharide and an O-polysaccharide chain) but not R595 (an O-chain lacking LPS-form) caused If inhibition under acute and chronic septic conditions. The specific interaction of S-LPS but not R595 to pacemaker channels HCN2 and HCN4 proves the necessity of O-chain for S-LPS–HCN interaction. The efficacy of ivabradine to block If was reduced under septic conditions, an observation that correlated with lower intracellular ivabradine concentrations in S-LPS- but not R595-treated cardiomyocytes. Computational analysis using a sinoatrial pacemaker cell model revealed that despite a reduction of If under septic conditions, ivabradine further decelerated pacemaking activity. This novel finding, i.e. If inhibition by ivabradine under elevated endotoxin levels in vitro, may provide a molecular understanding for the efficacy of this drug on heart rate reduction under septic conditions in vivo, e.g. the MODIfY clinical trial.

Inhibition of Orai1-mediated Ca2+ entry is a key mechanism of the antiproliferative action of sirolimus in human arterial smooth muscle

Sirolimus (rapamycin) is used in drug-eluting stent strategies and proved clearly superior in this application compared with other immunomodulators such as pimecrolimus. The molecular basis of this action of sirolimus in the vascular system is still incompletely understood. Measurements of cell proliferation in human coronary artery smooth muscle cells (hCASM) demonstrated a higher antiproliferative activity of sirolimus compared with pimecrolimus. Although sirolimus lacks inhibitory effects on calcineurin, nuclear factor of activated T-cell activation in hCASM was suppressed to a similar extent by both drugs at 10 μM. Sirolimus, but not pimecrolimus, inhibited agonist-induced and store-operated Ca(2+) entry as well as cAMP response element binding protein (CREB) phosphorylation in human arterial smooth muscle, suggesting the existence of an as-yet unrecognized inhibitory effect of sirolimus on Ca(2+) signaling and Ca(2+)-dependent gene transcription. Electrophysiological experiments revealed that only sirolimus but not pimecrolimus significantly blocked the classical stromal interaction molecule/Orai-mediated, store-operated Ca(2+) current reconstituted in human embryonic kidney cells (HEK293). A link between Orai function and proliferation was confirmed by dominant-negative knockout of Orai in hCASM. Analysis of the effects of sirolimus on cell proliferation and CREB activation in an in vitro model of arterial intervention using human aorta corroborated the ability of sirolimus to suppress stent implantation-induced CREB activation in human arteries. We suggest inhibition of store-operated Ca(2+) entry based on Orai channels and the resulting suppression of Ca(2+) transcription coupling as a key mechanism underlying the antiproliferative activity of sirolimus in human arteries. This mechanism of action is specific for sirolimus and not a general feature of drugs interacting with FK506-binding proteins.

Complete intra-atrial implantation of a mitral-valve prosthesis in a severely calcified mitral annulus

[1] Kurazumi H, Mikamo A, Suzuki R, Hamano K. Mitral-valve replacement for a severely calcified mitral annulus: a simple and novel technique. Eur J Cardiothorac Surg 2011;39:407—9. [2] Nataf P, Pavie A, Jault F, Bors V, Cabrol C, Gandjbakhch I. Intraatrial insertion of a mitral prosthesis in a destroyed or calcified mitral annulus. Ann Thorac Surg 2009;36:776—8. Letters to the Editor / European Journal of Cardio-thoracic Surgery 40 (2011) 1546—1553 1547

The Anti-Cancer Multikinase Inhibitor Sorafenib Impairs Cardiac Contractility by Reducing Phospholamban Phosphorylation and Sarcoplasmic Calcium Transients

Tyrosine-kinase inhibitors (TKIs) have revolutionized cancer therapy in recent years. Although more targeted than conventional chemotherapy, TKIs exhibit substantial cardiotoxicity, often manifesting as hypertension or heart failure. Here, we assessed myocyte intrinsic cardiotoxic effects of the TKI sorafenib and investigated underlying alterations of myocyte calcium homeostasis. We found that sorafenib reversibly decreased developed force in auxotonically contracting human myocardia (3u2009µM: −25u2009±u20094%, 10u2009µM: −29u2009±u20097%, 30u2009µM: −43u2009±u200912%, pu2009<u20090.01), reduced peak cytosolic calcium concentrations in isolated cardiomyocytes (10u2009µM: 52u2009±u20098.1% of baseline, pu2009<u20090.001), and slowed cytosolic calcium removal kinetics (RT50, RT10, Tau, pu2009<u20090.05). Beta-adrenergic stimulation induced augmentation of calcium transient (CaT) amplitude was attenuated in sorafenib-treated cells (2.7u2009±u20090.3-fold vs. 3.6u2009±u20090.2-fold in controls, pu2009<u20090.001). Sarcoplasmic reticulum (SR) calcium content was reduced to 67u2009±u20094% (pu2009<u20090.01), and SR calcium re-uptake slowed (pu2009<u20090.05). Sorafenib significantly reduced serine 16 phosphorylation of phospholamban (PLN, pu2009<u20090.05), while PLN threonine 17 and CaMKII (T286) phosphorylation were not altered. Our data demonstrate that sorafenib acutely impairs cardiac contractility by reducing S16 PLN phosphorylation, leading to reduced SR calcium content, CaT amplitude, and slowed cytosolic calcium removal. These results indicate myocyte intrinsic cardiotoxicity irrespective of effects on the vasculature and chronic cardiac remodeling.

Atrial fibrillation in transcatheter aortic valve implantation patients: Incidence, outcome and predictors of new onset

BACKGROUNDnThere is controversial evidence if atrial fibrillation (AF) alters outcome after transcatheter aortic valve implantation (TAVI). TAVI itself may promote new-onset AF (NOAF).nnnMETHODSnWe performed a single-center study including 398 consecutive patients undergoing TAVI. Before TAVI, patients were divided into a sinus rhythm (SR) group (n=226, 57%) and baseline AF group (n=172, 43%) according to clinical records and electrocardiograms. Furthermore, incidence and predictors of NOAF were recorded.nnnRESULTSnBaseline AF patients had a significantly higher 1-year mortality than the baseline SR group (19.8% vs. 11.5%, p=0.02). NOAF occurred in 7.1% of patients with prior SR. Previous valve surgery was the only significant predictor of NOAF (HR 5.86 [1.04-32.94], p<0.05). NOAF was associated with higher rehospitalization rate (62.5 vs. 34.8%, p=0.04), whereas mortality was unaffected.nnnCONCLUSIONSnThis study shows that NOAF is associated with higher rates of rehospitalization but not mortality after TAVI. Overall, patients with pre-existing AF have higher mortality.

Re-sternotomy as an unwelcome side-effect of unknown effervescent tablet intake?

Four hours after surgery for aortic valve stenosis and tricuspid valve regurgitation, an unknown foreign body was present on the routine chest X-ray. We performed re-sternotomy in order to retrieve this foreign body. The foreign body was easy to move on fluoroscopy but we could not extract it. We concluded that the foreign body was in a subdiaphragmatic location. As a consequence, we performed gastroscopy. A white, frothy mass (similar to an undissolved effervescent tablet) within an ulcerated lesion was seen and partially extracted.

A TRPC3 blocker, Pyr3, prevents stent-induced arterial remodeling

Background TRPC-mediated Ca entry has been implicated in the control of smooth muscle proliferation and might represent a pivotal mechanism underlying in-stent restenosis. As we have observed significant expression of TRPC3 in human smooth muscle from coronary arteries as well as from aorta, we tested the efficiency of a recently discovered TRPC3-selective Ca entry blocker, Pyr3 (10 μM) to prevent vascular smooth muscle proliferation and stent implantation-induced hyperplasia of human aorta.