Background: Patients suffering from heart failure with preserved ejection fraction (HFpEF) take a large share of all heart failure (HF) patients and account, based on the underlying definition, for 22–73% of all cases. The recently published EMPEROR-preserved trial clearly documented that Empagliflozin (Empa) is the first medical treatment significantly reducing the combined risk of cardiovascular death or HF hospitalization. However the molecular mechanisms for the beneficial effects of Empa still remain unclear.

Rational: The present study used a cardio-metabolic rat model to further elucidate the impact of Empa on 1) myocardial function and metabolism and 2) mitochondrial function.

Methods: At an age of 24 weeks, obese Zucker diabetic fatty/spontaneously hypertensive heart failure F1 hybrid (ZSF1) rats (n=30) were randomized into 2 groups: 1. HFpEF-con: receiving standard care (n=15) or 2. HFpEF-Empa: receiving standard chow and drinking water supplemented with Empa (30mg/kg) (n=15). ZSF1 lean animals (n=15) served as healthy controls. After 8 weeks echocardiography and invasive hemodynamic measurements were performed, myocardial mitochondrial function was assessed in saponin-skinned fibers using a Clark electrode (Strathkelvin Instruments) and organ tissue was snap frozen for molecular analyses. Metabolic key enzymes were assessed in left ventricular tissue homogenates by spectrophotometrical assays. Proteomic analysis was performed from LV samples of all three groups.

Results: At an age of 24 weeks HFpEF was confirmed by a reduced diastolic function as evident by an increase in E/é (lean: 17.5±0.7; HFpEF-con: 24.4±1.1; p<0.001), which was significantly attenuated after 8 weeks of Empa treatment (HFpEF-Empa: 19.4±0.8). Left ventricular ejection was preserved in all groups (lean: 68.1±1.2; HFpEF-con: 67.7±1.3; HFpEF-Empa: 67.9±1.0), whereas LV mass was significantly increased in the HFpEF-con group (lean: 702±16 mg; HFpEF-con: 991±31 mg; p<0.001) and significantly attenuated by Empa treatment (HFpEF-Empa: 885±26 mg). Measuring enzyme activities of key enzymes of different metabolic pathways (glycolysis, fatty acid oxidation, ketone body metabolism or TCA cycle) no significant differences were detected between the 3 groups. Assessment of mitochondrial function showed a significant reduced stimulation of oxygen consumption by fatty acids and a reduced V_max of mitochondrial complex-II and complex-IV in the HFpEF-con group. Both parameters were attenuated by Empa treatment. Proteomic analysis revealed major changes in proteins involved in mitochondrial oxidative phosphorylation like subunits of mitochondrial complex-I and complex-II. With respect to molecular markers for fibrosis and ventricular stiffness, a significant increased expression of collagen-1a1 and -3a1 and of detyrosinylated-tubulin was detected in the HFpEF-con group which was attenuated by Empa treatment.

Conclusion: The results of the present study clearly documented a beneficial effect of Empa on myocardial function in the present model of HFpEF. These effects were accompanied by positive effects on mitochondrial function and ventricular stiffness, possibly modulating diastolic function.