PI3K-Inhibition im Pankreaskarzinommodell

Das Pankreaskarzinom ist eine Tumorerkrankung mit einer sehr schlechten Prognose. Die Diagnosestellung erfolgt häufig erst zu einem Zeitpunkt, bei dem die Erkrankung schon weit fortgeschritten ist. Die Entwicklung neuer Behandlungsstrategien, die dem Patienten ein längeres Überleben und eine Verbesserung der Lebensqualität ermöglicht, steht im Zentrum vieler aktueller Untersuchungen. Unsere Studie hatte das Ziel, die Auswirkung des PI3K Inhibitors BKM120 auf Pankreaskarzinomzelllinien mit unterschiedlichem kras und p53 Mutationsmuster zu überprüfen. Die Untersuchungen wurden in den Pankreaskarzinomzelllinien BxPC3(WT/mut), Capan2(mut/WT), HPAF-II(mut/mut), Panc02(WT/WT), L3.6pl(mut/WT) sowie MiaPaCa2(mut/mut) mit unterschiedlichem Mutationsmuster hinsichtlich kras und p53 durchgeführt. Zur PI3K Blockade verwendeten wir den Inhibitor BKM120. Der Einfluss der PI3K Inhibition auf das Zellwachstum, Migration, Expression angiogener und Resistenz-relevanter Faktoren, Transkriptionsfaktoren sowie auf die Aktivierung von Signalwegen untersuchten wir mittels verschiedener in vitro Verfahren. Unsere Ergebnisse zeigten, dass die PI3K Blockade in vitro zu einer Wachstumshemmung führt, diese war allerdings bei allen Zelllinien eher schwach ausgeprägt. Zudem ließ sich feststellen, dass durch BKM120 die Motilität der Tumorzellen in BxPC3(WT/mut), Capan2(mut/WT) und Panc02(WT/WT) signifikant inhibiert wurde. Außerdem konnte durch die PI3K Inhibition die Aktivität von Signalwegen moduliert werden, am stärksten wurde hierbei die AKTSer473, mTORSer2448 und RICTORThr1135 Phosphorylierung gehemmt. Hingegen wurde in unserer Untersuchung die Expression von HIF-1a, HIF-2a und c-Myc nicht durch BKM120 beeinflusst. Ein deutlicher Effekt konnte auf die Expression von VEGF-A, PDGF-B und MDR-1 festgestellt werden. BKM120 zeigt in vitro einen signifikanten Einfluss auf Teilbereiche der untersuchten Pankreaskarzinomzelllinien. Ein klarer Zusammenhang zwischen der Wirksamkeit von BKM120 und dem Mutationsstatus der Tumorzellen ließ sich jedoch nicht nachweisen

Echocardiographic Evaluation of LV Function in Patients with Tachyarrhythmia and Reduced Left Ventricular Function in Response to Rhythm Restoration

Aims: Tachyarrhythmia due to atrial fibrillation (AF) is often associated with reduced left ventricular (LV) function and has been proposed to cause arrhythmia-induced cardiomyopathy (AIC). However, the precise diagnostics of AIC and reversibility after rhythm restoration are poorly understood. Our aim was to investigate systolic LV function in tachycardic AF and to evaluate the direct effect of rhythm restoration. Methods: We prospectively studied 24 patients (71% male, age 65 ± 9 years) with tachycardic AF and newly diagnosed reduced left ventricular ejection fraction (LVEF). Just before and immediately after electrical cardioversion (ECV), transthoracic echocardiography was performed. Geometric as well as functional data were assessed. Results: Patients presented with a heart rate (HR) of 117.4 ± 21.6/min and a 2D-/3D-LVEF of 32 ± 9/31 ± 8%. ECV to sinus rhythm normalized HR to 77 ± 11/min with an increase of 2D-/3D-LVEF to 37 ± 9/37 ± 10% (p < 0.01 vs. baseline, each). Left ventricular geometry changed with an increase of end-diastolic volume (LVEDV) while end-systolic volume (LVESV) remained unchanged. Parameters concerning myocardial deformation (global longitudinal strain (GLS), strain rate (SR)) decreased whereas the RR interval-corrected GLS (GLSc) remained unchanged. In a simple linear regression model, GLS correlated with 2D- and 3D-LVEF not only before (pre) ECV, but also after (post) ECV. We demonstrate that the increase of LVEF and GLS (ratios pre/post) correlates with the change of HR (ΔHR; R2 = 0.20, 0.33 and 0.32, p < 0.05 each), whereas ratios of GLSc and SR do not significantly correlate with HR (R2 = 0.03 and 0.01, p = n.s. each). Conclusion: In patients with tachyarrhythmia and reduced ejection fraction, ECV leads to immediate improvement in EF and GLS while HR-corrected LV contractility remains unchanged. This suggests that the immediate effects of rhythm restoration are mostly related to changes in left ventricular volume, but not to an acute improvement of heart-rate independent contractility

Effects of Atrial Fibrillation on the Human Ventricle

Rationale: Atrial fibrillation (AF) and heart failure often coexist, but their interaction is poorly understood. Clinical data indicate that the arrhythmic component of AF may contribute to left ventricular (LV) dysfunction. Objective: This study investigates the effects and molecular mechanisms of AF on the human LV. Methods and Results: Ventricular myocardium from patients with aortic stenosis and preserved LV function with sinus rhythm or rate-controlled AF was studied. LV myocardium from patients with sinus rhythm and patients with AF showed no differences in fibrosis. In functional studies, systolic Ca2+ transient amplitude of LV cardiomyocytes was reduced in patients with AF, while diastolic Ca2+ levels and Ca2+ transient kinetics were not statistically different. These results were confirmed in LV cardiomyocytes from nonfailing donors with sinus rhythm or AF. Moreover, normofrequent AF was simulated in vitro using arrhythmic or rhythmic pacing (both at 60 bpm). After 24 hours of AF-simulation, human LV cardiomyocytes from nonfailing donors showed an impaired Ca2+ transient amplitude. For a standardized investigation of AF-simulation, human iPSC-cardiomyocytes were tested. Seven days of AF-simulation caused reduced systolic Ca2+ transient amplitude and sarcoplasmic reticulum Ca2+ load likely because of an increased diastolic sarcoplasmic reticulum Ca2+ leak. Moreover, cytosolic Na+ concentration was elevated and action potential duration was prolonged after AF-simulation. We detected an increased late Na+ current as a potential trigger for the detrimentally altered Ca2+/Na+-interplay. Mechanistically, reactive oxygen species were higher in the LV of patients with AF. CaMKII (Ca2+/calmodulin-dependent protein kinase IIδc) was found to be more oxidized at Met281/282 in the LV of patients with AF leading to an increased CaMKII activity and consequent increased RyR2 phosphorylation. CaMKII inhibition and ROS scavenging ameliorated impaired systolic Ca2+ handling after AF-simulation. Conclusions: AF causes distinct functional and molecular remodeling of the human LV. This translational study provides the first mechanistic characterization and the potential negative impact of AF in the absence of tachycardia on the human ventricle

Atrial Fibrillation Burden Specifically Determines Human Ventricular Cellular Remodeling

BACKGROUND Atrial fibrillation (AF) can either be a consequence or an underlying mechanism of left ventricular systolic dysfunction. Patients included in the CASTLE-AF (Catheter Ablation vs. Standard Conventional Treatment in Patients With LV Dysfunction and AF) trial who suffered from AF and left ventricular systolic dysfunction benefited from an AF burden 50%.OBJECTIVES This analysis tried to explain the clinical findings of the CASTLE-AF trial regarding AF burden in a "back-to-bench" approach. METHODS To study the ventricular effects of different AF burdens, experiments were performed using human ventricular induced pluripotent stem cell-derived cardiomyocytes undergoing in vitro AF simulation. Epifluorescence microscopy, action potential measurements, and measurements of sarcomere regularity were conducted.RESULTS Induced pluripotent stem cell-derived cardiomyocytes stimulated with AF burden of 60% or higher displayed typical hallmarks of heart failure. Ca2 thorn transient amplitude was significantly reduced indicating negative inotropic effects. Action potential duration was significantly prolonged, which represents a potential trigger for arrhythmias. A significant decrease of sarcomere regularity could explain impaired cardiac contractility in patients with high AF burden. These effects were more pronounced after 7 days of AF simulation compared with 48 hours.CONCLUSIONS Significant functional and structural alterations occurred at the cellular level at a threshold of w50% AF burden as it was observed to be harmful in the CASTLE-AF trial. Therefore, these translational results may help to understand the findings of the CASTLE-AF trial. (J Am Coll Cardiol EP 2022;8:1357-1366) (c) 2022 by the American College of Cardiology Foundation