Assessment of the Effects of a DPP-4 Inhibitor (Sitagliptin) Januvia on Immune Function in Healthy Individuals

Patients with diabetes have high blood sugar levels (hyperglycemia) because pancreatic b-cells no longer produce sufficient insulin. Insufficient b-cell function can be caused by an autoimmune killing of the b-cells in type 1 diabetes (T1D), or by poorly understood mechanisms in type 2 diabetes (T2D). Glucagon-like peptide -1 (GLP-1) improves function of the insulin-producing beta cells, but GLP-1 has a very short circulating half-life because it is cleaved by the enzyme dipeptidyl peptidase IV (DPP-4). One current treatment being used to improve glycemia control in patients with T2D is sitagliptin, an inhibitor of DPP-4. By inhibiting DPP-4, sitagliptin increases GLP-1 levels resulting in improved beta cell function. Sitagliptin is now being tested in individuals with new-onset T1D to determine whether it may help to preserve beta cell function. Because T1D is a disease in which the immune system destroys the insulin-producing beta cells in the pancreas, we wish to determine if and how sitagliptin alters immune function. Sitagliptin has been shown by Merck to be safe and effective with no overt immuno-toxicities. However, several lines of evidence suggest that DPP-4 inhibitors such as sitagliptin could be immunomodulatory. This randomized clinical trial will study immune function in healthy volunteers given short-term (4 week) treatment with either sitagliptin or placebo. During the study, we will take blood samples at various time intervals before, during and after treatment. We will compare the immune response with and without sitagliptin treatment using blood samples from healthy individuals. We will measure changes in the magnitude and type of immune responses. The study period is nine weeks. The study s primary outcome will be changes in blood plasma levels of a protein marker associated with decreased inflammation: Transforming Growth Factor-Beta1 (TGFb1). In addition, we plan to use these blood samples to measure sitagliptin s effect on expression levels of several cytokines (immune proteins). We will also measure the level of proliferation in stimulated PBMCs (blood immune cells) and gene expression in whole blood after sitagliptin treatment.