Single dose of empagliflozin increases in vivo cardiac energy status in diabetic db/db mice

In the EMPA-REG OUTCOME trial, empagliflozin, a potent and specific inhibitor of the sodium glucose co-transporter 2, showed impressive benefits on cardiovascular outcome in patients with Type 2 diabetes.1 Empagliflozin reduced three-point primary composite outcome (cardiovascular death, non-fatal myocardial infarction, or non-fatal stroke) by 14%, which was mainly attributed to a 38% relative risk reduction in cardiovascular death.1 A 35% relative risk reduction in hospitalization for heart failure and a 32% relative risk reduction in all-cause mortality was also reported.1 However, the underlying mechanisms explaining these beneficial outcomes are yet to be elucidated. Deprivation of cardiac energy, characterized by a decreased cardiac phosphocreatine-to-ATP ratio (PCr/ATP), has been proposed to play a major role in the development of heart failure.2 Empagliflozin increases plasma ketone body levels and it has therefore been hypothesized that a shift in energy substrate metabolism towards ketones or an increased availability of ketones as add-on fuel could explain the positive cardiovascular outcomes in the EMPA-REG study.3

To test the ‘fuel hypothesis’, we investigated whether an increase in plasma ketones by empagliflozin was accompanied by an increase in cardiac PCr/ATP. We administered a single dose of empagliflozin in fasting db/db mice, to simulate a situation in which plasma ketone levels are immediately increased. This acute experimental design allows investigating the effect of alterations in fuel availability on changes in cardiac PCr/ATP ratio without interference from other factors, such as cardiac remodelling after long-term treatment. Using 31P magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI), we measured in vivo cardiac PCr/ATP and function, respectively.