Ketones, Muscle Metabolism, and SGLT2 Inhibitors - Protocol 1

Purpose/Objectives The EMPA-REG OUTCOME (NCT01131676) trial demonstrated that SGLT2 (sodium-glucose co-transporter) inhibition with empagliflozin markedly reduced cardiovascular (CV) mortality and hospitalization for heart failure. In diabetic patients treated with SGLT2 inhibitors, a rise in plasma ketone concentration consistently has been observed. This has led to the "ketone hypothesis" in which a shift from glucose/FFA (Free Fatty Acids) to ketone utilization by the heart results in enhanced left ventricular systolic/diastolic function and could, at least in part, explain the reduction in CV mortality and hospitalization for heart failure observed in the EMPA-REG OUTCOME trial. Methods Type 2 diabetic subjects with New York Heart Association (NYHA) Class II-III heart failure and ejection fraction less than 50% will be studied. Eligible subjects will undergo a baseline cardiac MRI to obtain quantitative measures of baseline cardiac functional parameters: chamber volumes and pressures, wall thickness, LV diastolic function (E/A ratio, peak LV filling rate, diastolic volume), LV systolic function (cardiac output, stroke volume, systolic volume, peak LV ejection rate). Baseline samples will be drawn for measurement of N-terminal pro-brain natriuretic peptide (NT-proBNP) , B-OH-butyrate, acetoacetate, glucose, FFA, lactate, pyruvate, glycerol, HCO3 (bicarbonate), insulin, glucagon, renin and aldosterone. Following completion of the baseline MRI and blood samples, subjects will be divided into three groups (12 subjects per group). Each group will receive a 6-hour (3-hour in group III) prime-continuous infusion of racemic B-OH-B (100 mg/mL solution; pH adjusted to 7.4) to increase the plasma B-OH-B concentration by \~0.5, \~2.0, and \~5.0 mmol/L. At the end of the infusion the MRI will be repeated. As a time control GROUP II subjects will receive a continuous infusion of sodium bicarbonate (0.12 M) for 6 hours (0.08 mg/kg/min) to mimic the rise in plasma bicarbonate concentration observed with B-OH-B infusion. Group II will return again to the RII (UT Health Research Imaging Institute) on a separate day for a cardiac positron emission tomography (PET) study to examine the effect of hyperketonemia on myocardial glucose uptake and blood flow. In \~14 days subjects will return for a repeat PET/18F-2-DOG (deoxyglucose) study with one exception: NaHCO3 (Sodium bicarbonate) will be infused instead of B-OH-B. The two studies will be performed in random order.