Effect of Saxagliptin Treatment on Myocardial Fat Content, and Monocyte Inflammation

Obese, insulin resistant individuals have an excess of fat in the liver which is not attributable to alcohol or other known causes of liver disease, a condition defined as nonalcoholic fatty liver disease (NAFLD). The fatty liver is insulin resistant. Individuals with a fatty liver are more likely to have excess intra-abdominal fat as well as a reduction in circulating plasma adiponectin levels. A new class of antidiabetes medications known as dipeptidyl peptidase 4 (DPP-4) inhibitors (sitagliptin, saxagliptin) which enhance the circulating half life of Glucagon-like peptide-1 (GLP-1), an incretin hormone that enhances insulin secretion/ lowers glucose levels, have been approved to treat type 2 diabetes. More recently, it has been shown that these dipeptidyl peptidase 4 inhibitors can also decrease liver fat and inflammation in animal models of obesity by increasing circulating levels of GLP-1. It has been shown that GLP-1 enhances liver fat oxidation, reduces liver fat synthesis, and increases adiponectin levels in animal models in vivo. Recent reports suggest that NAFLD is associated with an increased risk of cardiovascular disease independent of associated cardiovascular risk factors. Furthermore type 2 diabetics and subjects with impaired glucose tolerance are characterized by an increase in both hepatic and myocardial fat and left ventricular (LV) dysfunction, particularly diastolic dysfunction. Myocardial steatosis is an independent predictor of diastolic dysfunction in type 2 diabetes mellitus as well as impaired glucose tolerance. However, the effect of saxagliptin therapy on liver and myocardial fat content, as well as LV systolic and diastolic function in patients with impaired glucose tolerance (IGT) or type 2 diabetes has not been previously studied. Recently, it has been demonstrated that myocardial triglyceride content is increased in type 2 diabetic patients and is associated with impaired left ventricular diastolic function, independently of age, body mass index (BMI), heart rate, visceral fat, and diastolic blood pressure. More recently, it has been shown that that obese normal glucose tolerant subjects, obese subjects with IGT, and type 2 diabetic subjects have increased myocardial fat compared to lean subjects. Thus, both IGT and type 2 diabetic subjects have increased myocardial steatosis and defects in LV function. GLP-1 has been shown to improve myocardial function and cardiac output in conscious chronically instrumented canine models of cardiac injury or heart failure. GLP-1 increased cardiac output and reduced left ventricular end diastolic pressure in association with reduced systemic vascular resistance, and it improved myocardial insulin sensitivity and myocardial glucose uptake in dogs with rapid pacing-induced dilated cardiomyopathy. However, no previous study has examined the effect of saxagliptin on myocardial fat or LV function in IGT or type 2 diabetic patients. Finally, the effect of saxagliptin on vascular inflammation and monocyte Nuclear Factor-KappaB (NFkappaB) remains to be studied. Patients with Impaired Glucose Tolerance (IGT)/ Impaired Fasting Glucose (IFG) have insulin resistance as a well established defect. Furthermore, as stated previously, both myocardial and hepatic steatosis as well as defects in LV function are well characterized in obese, insulin resistant patients with IGT. However, the effect of DPP IV inhibitors on hepatic and myocardial steatosis and monocyte inflammation in insulin resistant patients with IGT have not been previously studied.