SAR296968, a Novel Selective Na+/Ca2+ Exchanger Inhibitor, Improves Ca2+ Handling and Contractile Function in Human Atrial Cardiomyocytes

Abstract

Background: In reverse-mode, cardiac sodium-calcium exchanger (NCX) can increase the cytoplasmic Ca²⁺ concentration in response to high intracellular Na⁺ levels, which may contribute to diastolic contractile dysfunction. Furthermore, increased spontaneous Ca²⁺ release from intracellular stores can activate forward mode NCX. The resulting transient inward current causes delayed afterdepolarization (DAD)-dependent arrhythmias. Moreover, recently, NCX has been associated with impaired relaxation and reduced cardiac function in heart failure with preserved ejection fraction (HFpEF). Since NCX is upregulated in human chronic atrial fibrillation (AF) as well as heart failure (HF), specific inhibition may have therapeutic potential.

Objective: We tested the antiarrhythmic, lusitropic and inotropic effects of a novel selective NCX-inhibitor (SAR296968) in human atrial myocardium.

Methods and results: Right atrial appendage biopsies of 46 patients undergoing elective cardiac surgery in a predominant HFpEF cohort (n = 24/46) were investigated. In isolated human atrial cardiomyocytes, SAR296968 reduced the frequency of spontaneous SR Ca²⁺ release events and increased caffeine transient amplitude. In accordance, in isolated atrial trabeculae, SAR296968 enhanced the developed tension after a 30 s pause of electrical stimulation consistent with reduced diastolic sarcoplasmic reticulum (SR) Ca²⁺ leak. Moreover, compared to vehicle, SAR296968 decreased steady-state diastolic tension (at 1 Hz) without impairing developed systolic tension. Importantly, SAR296968 did not affect the safety parameters, such as resting membrane potential or action potential duration as measured by patch clamp.

Conclusion: The novel selective NCX-inhibitor SAR296968 inhibits atrial pro-arrhythmic activity and improves diastolic and contractile function in human atrial myocardium, which may have therapeutic implications, especially for treatment of HFpEF.

Keywords: HFpEF; NCX; Na+/Ca2+ exchanger; SAR296968.

Figure 1

Ca²⁺ sparks measurements in isolated human atrial myocytes. The numbers indicated are numbers of patients. The data points represent individual patients. Each data point was calculated as a mean from several cells within each patient. Ca²⁺ spark frequency is reduced by SAR296968, original line scans are shown in (A), and mean data in (B). Fluo-4 transient amplitude after rapid caffeine application is shown in (C), the transient amplitude is significantly increased at 3 µM, original caffeine transients in (D). The p-values are denoted above the corresponding groups, RM-mixed effects analysis with Bonferroni post-hoc test.

Figure 2

The numbers indicated are the numbers of patients. The data points represent individual patients. Each data point was calculated as the mean from several trabeculae within each patient. The mean data per patient shown for isolated human atrial trabeculae in steady-state (1 Hz) exposed to SAR296968. The diastolic tension is reduced by SAR296968 (A). The fractional difference in the developed tension compared to the vehicle was significantly increased (B), # indicates a significant difference from zero). Developed tension after 30 s rest (post-rest test) was significantly increased by SAR296968 at 3 µM (C). The original traces are shown in (D). The p-values are denoted above the corresponding groups, RM-mixed effects analysis with Bonferroni post-hoc test.

Figure 3

The numbers indicated are numbers of patients. The data points represent individual patients. Each data point was calculated as the mean from several cells within each patient. The mean data per patient for action potential characteristics were measured in isolated human atrial myocytes by the whole-cell patch clamp technique. (A) resting membrane potential, (B) AP amplitude, and (C) action potential duration (APD) at 90% of maximum repolarization were unaffected by SAR296968. The original traces are shown in (D). The p-values are denoted above the corresponding groups, RM-mixed effects analysis with Bonferroni post-hoc test.