Off-target effects of sodium-glucose co-transporter 2 blockers: Empagliflozin does not inhibit Na⁺/H⁺exchanger-1 or lower [Na⁺]_iin the heart

Aims: Emipagliflozin (EMPA) is a potent inhibitor of the renal sodium-glucose co-transporter 2 (SGLT2) and an effective treatment for type-2 diabetes. In patients with diabetes and heart failure, EMPA has cardioprotective effects independent of improved glycaemic control, despite SGLT2 not being expressed in the heart. A number of non-canonical mechanisms have been proposed to explain these cardiac effects, most notably an inhibitory action on cardiac Na⁺/H⁺ exchanger 1 (NHE1), causing a reduction in intracellular [Na⁺] ([Na⁺]_i). However, at resting intracellular pH (pH_i), NHE1 activity is very low and its pharmacological inhibition is not expected to meaningfully alter steady-state [Na⁺]_i. We re-evaluate this putative EMPA target by measuring cardiac NHE1 activity.

Methods and results: The effect of EMPA on NHE1 activity was tested in isolated rat ventricular cardiomyocytes from measurements of pH_i recovery following an ammonium pre-pulse manoeuvre, using cSNARF1 fluorescence imaging. Whereas 10 μM cariporide produced near-complete inhibition, there was no evidence for NHE1 inhibition with EMPA treatment (1, 3, 10, or 30 μM). Intracellular acidification by acetate-superfusion evoked NHE1 activity and raised [Na⁺]_i, reported by sodium binding benzofuran isophthalate (SBFI) fluorescence, but EMPA did not ablate this rise. EMPA (10 μM) also had no significant effect on the rate of cytoplasmic [Na⁺]_i rise upon superfusion of Na⁺-depleted cells with Na⁺-containing buffers. In Langendorff-perfused mouse, rat and guinea pig hearts, EMPA did not affect [Na⁺]_i at baseline nor pH_i recovery following acute acidosis, as measured by ²³Na triple quantum filtered NMR and ³¹P NMR, respectively.

Conclusions: Our findings indicate that cardiac NHE1 activity is not inhibited by EMPA (or other SGLT2i's) and EMPA has no effect on [Na⁺]_i over a wide range of concentrations, including the therapeutic dose. Thus, the beneficial effects of SGLT2i's in failing hearts should not be interpreted in terms of actions on myocardial NHE1 or intracellular [Na⁺].