Empagliflozin attenuates arrhythmogenesis in diabetic cardiomyopathy by normalizing intracellular Ca²⁺ handling in ventricular cardiomyocytes

Abstract

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.

Roles of O-GlcNAcylation in Mitochondrial Homeostasis and Cardiovascular Diseases

“…The cardiovascular system is complex, and the posttranslational modification of serine and threonine residues in nuclear, cytoplasmic and mitochondrial proteins by O-GlcNAcylation is considered an important regulatory mechanism in the cardiovascular system. Changes in O-GlcNAcylation may lead to many metabolic imbalances and affect cardiovascular function; and this process has an prominent role in heart remodeling [55,120,121], heart failure [22,26,122], diabetic cardiomyopathy [123][124][125], ischemic heart disease [24,42,126], hypertension [127] and arrhythmia [128,129]. Protein O-GlcNAcylation reprograms the cardiac substrate metabolism under chronic stress to advantageously alter adaptation [130].…”

Foetal recapitulation of nutrient surplus signalling by O‐GlcNAcylation and the failing heart

“…It is therefore noteworthy that sodium–glucose cotransporter 2 (SGLT2) inhibitors – which are effective in the prevention and treatment of chronic heart failure – can promote nutrient deprivation signalling through AMPK and SIRT1 ( Figure ) 171 . Although SGLT2 is not expressed in cardiomyocytes, SGLT2 inhibition prevents CaMKII activation, spontaneous calcium sparks and impaired calcium transients in the hearts of mice with experimental type 2 diabetes 172 . These effects might be mediated by an indirect action of SGLT2 inhibitors to inhibit the late sodium current, potentially mediated by either interference with CaMKII or by an action to attenuate O‐GlcNAcylation of Na v 1.5, 119,173 since these effects of SGLT2 inhibition were prevented by inhibition of OGA 172 .…”

“…171 Although SGLT2 is not expressed in cardiomyocytes, SGLT2 inhibition prevents CaMKII activation, spontaneous calcium sparks and impaired calcium transients in the hearts of mice with experimental type 2 diabetes. 172 These effects might be mediated by an indirect action of SGLT2 inhibitors to inhibit the late sodium current, potentially mediated by either interference with CaMKII or by an action to attenuate O-GlcNAcylation of Na v 1.5, 119,173 since these effects of SGLT2 inhibition were prevented by inhibition of OGA. 172 The investigators proposed that the reduction in O-GlcNAcylation was related to an observed reduction of glucose uptake by cardiomyocytes following SGLT2 inhibition, an action that is unrelated to the presence or absence SGLT2 protein 172,174,175 but possibly related to a direct or indirect effect of SGLT2 inhibitors to inhibit GLUT1.…”

“…172 These effects might be mediated by an indirect action of SGLT2 inhibitors to inhibit the late sodium current, potentially mediated by either interference with CaMKII or by an action to attenuate O-GlcNAcylation of Na v 1.5, 119,173 since these effects of SGLT2 inhibition were prevented by inhibition of OGA. 172 The investigators proposed that the reduction in O-GlcNAcylation was related to an observed reduction of glucose uptake by cardiomyocytes following SGLT2 inhibition, an action that is unrelated to the presence or absence SGLT2 protein 172,174,175 but possibly related to a direct or indirect effect of SGLT2 inhibitors to inhibit GLUT1. 8,171 The observation that the cardiac benefits of SGLT2 inhibitors were abrogated by OGA inhibition suggests that amelioration of O-GlcNAcylation may represent one of the mechanisms by which enhanced AMPK and SIRT1 signalling following SGLT2 inhibition leads to cardiovascular benefits.…”

Significance of Endothelial Dysfunction Amelioration for Sodium–Glucose Cotransporter 2 Inhibitor-Induced Improvements in Heart Failure and Chronic Kidney Disease in Diabetic Patients

“…The beneficial effects of SGLT2is on DCM are shown in Table 1 . SGLT2is have multiple beneficial factors that improve DCM [ 99 , 100 , 101 , 102 , 103 , 104 , 105 , 106 , 107 , 108 , 109 , 110 ]. SGLT2is decreased fibrosis, reduced inflammation and improved systolic function.…”