Study of the Effect of Sitagliptin on Glucose (Sugar) Metabolism in Patients With Heart Failure

Screening: Patients will be screened based on existing clinic information regarding NYHA class (New York Heart Association functional class) and heart failure characteristics. Patients will be approached in clinic after completing clinical care for that visit regarding participation in this trial. If the patient agrees to participate, informed consent will be obtained at this time. At enrollment: Patients will be queried as to whether they have undergone previous nuclear medicine scans in the previous year in order to ensure that they do not exceed current standards for total annual radiation exposure. Undergo a baseline combined 18-FDG (18F-2-fluoro-2-deoxy-D-glucose fluorodeoxyglucose) PET/13N-NH3 PET/CT to assess the heart's ability to utilize blood sugar and coronary blood flow. This will take approximately 3-4 hours. This is a nuclear medicine procedure which is commonly used to assess myocardial viability as well as global heart function. It involves injection of a radioisotope-labeled tracers (18-FDG and 13N-NH3) intravenously followed by the measurement of myocardial uptake using a tomographic scanner. Venous blood samples performed during a 75g oral glucose load during the 18-FDG portion will assist with quantitation of myocardial glucose uptake and of measurements of insulin sensitivity. Perfusion (13N-NH3) images will be repeated during infusion of adenosine 0.14 mg/kg/min in order to assess coronary flow reserve. A computed tomography scan will be performed at the same time as the baseline PET scan for attenuation correction. Blood draws to measure changes in fasting insulin, blood sugar, lipid profile, and ADMA levels. Approximately 45 cc or 3 tablespoons of blood will be drawn and saved for possible future analysis. 18-FDG/13N-NH3 PET scans are routinely performed on patients with ischemic heart disease. While this study will use standard protocol for these examinations, they are not currently part of standard of care for nonischemic heart failure. However, they are important in testing the hypothesis of this study. 3\) Begin sitagliptin 100 mg daily for four weeks. If calculated creatinine clearance is 30-49 cc/min by the Cockcroft-Gault formula, sitagliptin dose will be reduced to 50 mg daily for four weeks as per manufacturer guidelines. There will be no placebo arm. This will be an open-label study. Patients will be advised regarding potential side effects to prompt notification of study personnel. They will be instructed to contact the investigators for any concerns or evidence of adverse effects. 4\) At four weeks: Repeat FDG/NH3 PET as above to compare to pretreatment scan. This will take approximately 3-4 hours. Blood draws to measure changes in fasting insulin, blood sugar, lipid profile, and ADMA (asymmetrical dimethylarginine) levels. Approximately 45 cc or 3 tablespoons of blood will be drawn and saved for possible future analysis.