Abstract Body (Do not enter title and authors here): Background: SGLT2 inhibitors have shown protective effects against heart failure with preserved ejection fraction (HFpEF), but the detailed cellular mechanisms are still unclear. SGLT2 inhibitors have shown effects on improving serum magnesium (Mg²⁺) levels. Our recent studies show that hypomagnesemia (HypoMg) and subsequent overexpression of a Mg²⁺ transporter with channel and kinase function, transient receptor potential cation channel subfamily M 7 (TRPM7), inflammation, and mitochondrial oxidative stress cause diabetic cardiac diastolic dysfunction (DD) and HFpEF.
Objective: We investigated the effects and mechanisms of a SGLT2 inhibitor dapagliflozin (Dapa) on DD induced by HypoMg.
Methods: C57BL/6J mice were fed with normal diet (2g/kg Mg²⁺) or a low-Mg diet (15-30 mg/kg Mg²⁺) for 6 weeks. Dapa treatment (oral 1.5 mg/kg/daily) started from the 4^th week of the low-Mg diet and lasted for 3 weeks. Echocardiography (Echo) was performed to study cardiac diastolic function. Mouse ventricles and isolated cardiomyocytes (CMs) were used for analysis. Human CM cell line RL-14 and mouse macrophage (Mj) cell line Raw264.7 were treated with normal (0.81 mM Mg²⁺) or low-Mg medium (0.04 mM Mg²⁺) with or without Dapa (5 mM) for 48 h. Cells, cell lysate and culture medium were used for mitochondrial ROS (mitoROS) test, protein assay and IL-1b secretion.
Results: Dapa treatment reversed HypoMg-induced DD with normalized E/e’ in Echo. When compared with HypoMg mice, Dapa treatment normalized serum Mg²⁺ levels, reduced urine Mg²⁺ loss, prevented TRPM7 overexpression in ventricles, suppressed mitochondrial oxidative stress, decreased the ratio of S-glutathionylated cardiac myosin binding protein C 3 (MyBPC3) to total MyBPC3, and alleviated inflammation. In the cell models, Dapa treatment inhibited HypoMg-induced TRPM7 overexpression and mitoROS overproduction in the human CM cell line. Nevertheless, Dapa treatment failed to suppress HypoMg-induced mitoROS overproduction and IL-1b secretion in the mouse Mj cell line, suggesting the primary effect of Dapa is on cardiomyocytes.
Conclusion: The SGLT2 inhibitor Dapa prevented cardiac diastolic dysfunction by elevating serum Mg²⁺ levels, preventing TRPM7 overexpression, suppressing cardiac inflammation, and reducing mitochondrial oxidative stress. Dapa effects are directly on cardiomyocytes.