SGLT-2 inhibitors alter the cardiomyocytes’ function and reduce cytosolic calcium transients in a rat model of diabetic HFpEF

Diabetic cardiomyopathy is among major complications associated with diabetes and is accompanied by structural and functional abnormalities. However, its pathogenesis is not fully understood yet. Sodium-glucose cotransporter 2 inhibitors (SGLT2i) were initially introduced to treat type 2 diabetes mellitus. Nevertheless, recent research revealed markedly beneficial effects of SGLT2i on cardiovascular events in heart failure with preserved ejection fraction (HFpEF). Besides the more intensively studied Empagliflozin (EMPA), likewise Dapagliflozin (DAPA) was shown to reduce the risk of hospitalizations and mortality associated with HF. Addressing the altered electrophysiological behavior of cardiomyocytes (CMs) in diabetes, previous experimental models in rodents and in vitro studies have shown modulatory effects of SGLT2i on the cardiac calcium (Ca²⁺) handling. However, the modulatory effect thereof on the functionality and the Ca²⁺ transients in diabetic cardiomyopathy affected CMs are rather speculative.

We performed echocardiography of Otsuka Long-Evans Tokushima Fatty (OLETF) rats at baseline and at the stage of diabetic cardiomyopathy (44 weeks of age). Age-matched Long-Evans (LE) rats served as a healthy control group. The diabetic status was confirmed by blood glucose measurements at the final age. Furthermore, cell contraction as well as cytosolic and mitochondrial Ca²⁺ transients were analyzed in isolated CMs of OLETF and LE rats. Upon continuous contraction in a field stimulation chamber, the fluorescent signals of DAPA and EMPA (each 1 µM and 10 µM in concentration) pretreated CMs as well as untreated cells were recorded at 37°C.

Body and heart weight measurements showed markedly increased body weights in OLETF rats as well as a significantly reduced body to heart ratio. Echocardiography and blood glucose measurements confirmed diabetic cardiomyopathy in OLETF rats. Importantly, the intraventricular septum thickness (IVS) as well as a biatriale enlargement were observed in 44 weeks old rats, indicating diastolic dysfunction. Nevertheless, ejection fraction (EF) was still preserved in 44 weeks old OLETF rats (EF≥60%). Field stimulation confirmed preserved contraction abilities of OLETF CMs in comparison to healthy LE one’s. Nevertheless, DAPA and EMPA seem to significantly increase the cell shortening of both, healthy and diseased CMs accompanied by a rise in the time to peak (TPK) shortening. Concomitant Ca²⁺ measurments unveiled significantly reduced cytosolic Ca²⁺ transients and TPK Ca²⁺ levels in OLETF CMs in comparison to healthy control cells. In OLETF cells, the treatment with 1 µM or 10 µM DAPA led to a further reduction of the cytosolic Ca²⁺ amplitude, TPK Ca²⁺ levels, and time of cytosolic Ca²⁺ decay. Interestingly, the cytosolic Ca²⁺ transients of OLETF cells stayed unaffected by EMPA treatment. Likewise, the mitochondrial Ca²⁺ handling was not altered by the disease, as well as DAPA or EMPA treatment, respectively.

In our model of diabetic cardiomyopathy with HFpEF, DAPA treatment seems to reduce cytosolic but not mitochondrial Ca²⁺ transients. These results indicate major alterations of Ca²⁺ handling in diabetic CMs. Further, studies need to investigate the effect of SGLT2i on the CMs’ function as well as their electrophysiological properties.

This study was supported by Paracelsus Medical University (R-018/02/105/-JIR and FMS_023-23-KNMS) and by the Austrian Cardiology Society.