Diabetic cardiomyopathy has been reported to increase the risk of fatal ventricular arrhythmia. The beneficial effects of the selective sodium-glucose co-transporter 2 inhibitor have not been fully examined in the context of anti-arrhythmic therapy, especially its direct cardioprotective effects despite the negligible SGLT2 expression in cardiomyocytes. We aimed to examine the anti-arrhythmic effects of empagliflozin (EMPA) treatment on diabetic cardiomyocytes, with a special focus on Ca2+ handling. We conducted echocardiography and hemodynamic studies and studied electrophysiology, Ca2+ handling, and protein expression in C57BLKS/J-leprdb/db mice (db/db mice) and their non-diabetic lean heterozygous Leprdb/+ littermates (db/+ mice). Preserved systolic function with diastolic dysfunction was observed in 16-week-old db/db mice. During arrhythmia induction, db/db mice had significantly increased premature ventricular complexes (PVCs) than controls, which was attenuated by EMPA. In protein expression analyses, calmodulin-dependent protein kinase II (CaMKII) Thr287 autophosphorylation and CaMKII-dependent RyR2 phosphorylation (S2814) were significantly increased in diabetic hearts, which were inhibited by EMPA. Additionally, global O-GlcNAcylation significantly decreased with EMPA treatment. Furthermore, EMPA significantly inhibited ventricular cardiomyocyte glucose uptake. Diabetic cardiomyocytes exhibited increased spontaneous Ca2+ events and decreased sarcoplasmic reticulum (SR) Ca2+ content, along with impaired Ca2+ transient, all of which normalized with EMPA treatment. Notably, most EMPA-induced improvements in Ca2+ handling were abolished by the addition of an O-GlcNAcase (OGA) inhibitor. In conclusion, EMPA attenuated ventricular arrhythmia inducibility by normalizing the intracellular Ca2+ handling, and we speculated that this effect was, at least partly, due to the inhibition of O-GlcNAcylation via the suppression of glucose uptake into cardiomyocytes.
IntroductionRecent studies have demonstrated that sodium-glucose co-transporter-2 inhibitors (SGLT2-i) reduce the risk of atrial fibrillation (AF) in patients with diabetes mellitus (DM), in which oxidative stress due to increased reactive oxygen species (ROS) contributes to the pathogenesis of AF. We aimed to further investigate this, and examine whether the SGLT2-i empagliflozin suppresses mitochondrial-ROS generation and mitigates fibrosis.MethodsA high-fat diet and low-dose streptozotocin treatment were used to induce type-2 DM (T2DM) in Sprague-Dawley rats. The rats were randomly divided into three groups: control, DM, and DM treated with empagliflozin (30 mg/kg/day) for 8 weeks. The mitochondrial respiratory capacity and ROS generation in the atrial myocardium were measured using a high-resolution respirometer. Oxidative stress markers and protein expression related to mitochondrial biogenesis and dynamics as well as the mitochondrial morphology were examined in the atrial tissue. Additionally, mitochondrial function was examined in H9c2 cardiomyoblasts. Atrial tachyarrhythmia (ATA) inducibility, interatrial conduction time (IACT), and fibrosis were also measured.ResultsInducibility of ATA, fibrosis, and IACT were increased in rats with DM when compared to controls, all of which were restored by empagliflozin treatment. In addition, the rats with DM had increased mitochondrial-ROS with an impaired complex I-linked oxidative phosphorylation capacity. Importantly, empagliflozin seemed to ameliorate these impairments in mitochondrial function. Furthermore, empagliflozin reversed the decrease in phosphorylated AMPK expression and altered protein levels related to mitochondrial biogenesis and dynamics, and increased mitochondrial content. Empagliflozin also improved mitochondrial function in H9c2 cells cultured with high glucose medium.DiscussionThese data suggest that empagliflozin has a cardioprotective effect, at least in part, by reducing mitochondrial ROS generation through AMPK signaling pathways in the atrium of diabetic rats. This suggests that empagliflozin might suppress the development of AF in T2DM.
Background Diabetic cardiomyopathy is an important complication of diabetes mellitus (DM) and reported to increase the risk of fatal ventricular arrhythmias. Recent clinical trials showed that empagliflozin (EMPA), a selective sodium-glucose co-transporter 2 (SGLT2) inhibitor, improved cardiovascular outcomes regardless of the presence of diabetes and the traditional cardiovascular risk factors. Despite the promising benefit of EMPA on heart failure treatment, its beneficial effect in the context of anti-arrhythmic therapy has not been fully examined. We therefore aimed to examine anti-arrhythmic effect of acute EMPA treatment especially onto calcium (Ca2+) handling in diabetic cardiomyocytes. Methods We assessed echocardiography, hemodynamic study, electrophysiology, Ca2+ handling and protein expression in C57BLKS/J-leprdb/db mice (db/db mice), a leptin receptor-deficient model of obesity and Type 2 diabetes, and their non-diabetic lean heterozygous Leprdb/+ littermates (db/+ mice). Results The 16-week-old db/db mice had preserved systolic function but exhibited diastolic dysfunction. In arrhythmia induction using ex-vivo Langendorff-perfused hearts, db/db mice showed a significantly increased premature ventricular complex (PVC) by 2x Ca2+ and 1μM isoproterenol load than control, which was attenuated by EMPA perfusion (1 μM). Diabetic cardiomyocytes showed an increased frequency of spontaneous Ca2+ sparks and waves, and decreased Ca2+ transient amplitude and sarcoplasmic reticulum (SR) Ca2+ content. Ca2+ transient decay tau and time to 50% decay were significantly prolonged in diabetic cardiomyocytes. These data indicating the impaired Ca2+ handling in diabetic cardiomyocytes were normalized by acute administration of EMPA (1 μM), while the administration of NHE inhibitor (Cariporide 10 μM) did not show significant differences. In the protein expression analysis, CaMKII Thr287 autophosphorylation and CaMKII-dependent RyR2 S2814 phosphorylation were significantly increased in diabetic hearts, which were inhibited by short-term (30 min) perfusion of EMPA (1 μM). The expressions of SERCA2a and phospholamban were not significantly different among three groups. Lastly, whole hearts O-GlcNAcylation, one of the important post translational modifications, was significantly reduced by EMPA treatment. Conclusion EMPA improved intracellular Ca2+ handling and attenuated arrhythmogenesis in mice with diabetic cardiomyopathy at the diastolic dysfunction phase, suggesting that EMPA may exhibit this anti-arrhythmic effect by normalization of intracellular calcium handling via inhibiting O-GlcNAcylation. Funding Acknowledgement Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): Boehringer Ingelheim
Purpose: Phrenic nerve injury (PNI) is one of the important complications during cryoballoon (CB) ablation. Recording diaphragmatic compound motor action potentials (CMAPs) during CB ablation can predict PNI. CMAP monitoring may be inaccurate when CMAP amplitudes are low. We examined the effect of positioning an electrocardiography (ECG) electrode at the dorsal side. Methods: We retrospectively analyzed the cases of 197 consecutive patients who underwent CB ablation for pulmonary vein isolation (PVI) (April 2016 to December 2018) at our institution. CMAP amplitudes were monitored using two recording methods just before cryoapplication. (a) Conventional method: right-arm ECG electrode positioned 5 cm above the xiphoid on the ventral side; left-arm ECG electrode positioned along the costal margin. (b) Our original method: right-arm electrode positioned 5 cm above the xiphoid on the dorsal side; left-arm electrode positioned along the costal margin. Results:The CMAP amplitude during right phrenic nerve pacing was significantly higher at the dorsal side than the ventral side (0.80 ± 0.31 mV vs 0.66 ± 0.29 mV, P < .01). Similarly, the CMAP amplitude during left phrenic nerve pacing was significantly higher at the dorsal side than the ventral side (0.92 ± 0.39 mV, 0.73 ± 0.37 mV, P < .01). PNI occurred in six patients (3.0%); three patients experienced transient PNI, another three patients experienced persistent PNI, and none developed permanent PNI.Conclusions: CMAP amplitudes were significantly high at the dorsal side compared to the ventral side. Monitoring phrenic nerve function using an ECG electrode at the dorsal side is a simple and easy procedure. K E Y W O R D S atrial fibrillation, compound motor action potential, cryoballoon, phrenic nerve injury, pulmonary vein isolation | 329 MIZUKAMI et Al.
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