Funktionelle Charakterisierung neu entwickelter SERCA2a-Modulatoren an humanem Myokard und isolierten Herzmuskelzellen der Ratte

Abstract

Decreased expression of cardiac sarcoplasmic calcium ATPase SERCA2a is known to play an important role in the pathogenesis of chronic heart failure. Thus stimulation of SERCA2a attracted increased attention as a promising therapeutic option. The present thesis analysed the effects of seventeen newly developed SERCA2a modulators on the contractility and calcium handling of isolated rat cardiomyocytes as well as on the contractility of muscle strip preparations of human end-stage failing myocardium. In single cell preparation experiments of rat cardiomyocytes epifluorescence microscopy was used for evaluation of SERCA2a activity by calcium transients, relaxation times, velocity of cytosolic calcium decrease and caffeine-induced calcium transients for indirectly measurement of sarcoplasmic reticulum (SR) calcium load. With regard to their inotropic effects, the seventeen agents could be divided into three groups: Five of them were shown to reduce the contractility of isolated rat cardiomyocytes or end-stage failing muscle strips in a dosage-dependent manner while their impact on calcium parameters was heterogeneous. Other ten of them revealed no major alterations on the contractility of cardiomyocytes. Finally, there could be identified two SERCA2a modulators, which increased the contractility of isolated rat cardiomyocytes in a dosage dependent manner. One of them called GPZ003362 also showed a positive inotropic effect on human end-stage failing myocardium muscle strips. An acceleration in calcium decrease as well as an increase in SR calcium load indicate an enhancement of SERCA2a activity. However, calcium transients and relaxation times were not altered. Due to the heterogeneous results regarding calcium cycling it remains unclear if GPZ003362 unrolls its inotropic effect by enhancement of SERCA2a activity or by a different mode of action. The other SERCA2a modulator called ENO114 also showed positive inotropic effects on isolated rat cardiomyocytes. In the muscle strip experiment a dosage dependent acceleration of relaxation could be detected, indicating an enhanced SERCA2a activity. However, the inotropic effect could not be seen on human muscle strips. Regarding the poor prognosis as well as the limited therapeutic options of chronic heart failure, the results of the SERCA2a modulators ENO114 and GPZ003362 are promising. Further studies are needed to clarify their mode of action and to determine their benefit for chronic heart failure.