Effect of Chronic Incretin-based Therapy in Cystic Fibrosis

In recent years, diabetes has emerged as one of the most significant co-diseases that many Cystic Fibrosis (CF) patients develop. Type 1 and Type 2 diabetes results when either the body does not make enough insulin or the body does not respond correctly to this insulin. Insulin is a hormone which is made by cells in the pancreas and helps carry glucose (sugar) from the food we eat to the cells of the body for energy. While cystic fibrosis related diabetes (CFRD) has many features similar to both Type 1 and Type 2 diabetes, it is very different; therefore, treatment and care of CFRD is not the same.

The purpose of this research study is to examine and understand the various mechanisms that contribute to CFRD and gain a better understanding of potential means to treat CFRD. The primary objective is to determine effectiveness of chronic incretin-based therapy vs. placebo on insulin secretion in CF patients with indeterminate glucose tolerance, impaired glucose tolerance, or CFRD.

Insufficient incretin action has been associated with T2D. To study the possible link between insufficient incretin action and impaired insulin secretion in CFRD as in T2D, the present study will determine whether early intervention with incretin-based therapy using the DPP-4 inhibitor sitagliptin (Januvia®) to raise endogenous levels of the incretin hormones--i.e.--glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotrophic polypeptide (GIP) for a 6-month period will improve insulin secretion in CF patients with indeterminate glucose tolerance, impaired glucose tolerance or early CFRD.

Eligibility Criteria:
Inclusion Criteria:

* Confirmed diagnosis of CF, defined by positive sweat test or CFTR mutation analysis according to CFF diagnostic criteria
* Age ≥ 18y on date of consent
* Pancreatic insufficiency
* Recent OGTT consistent with Indeterminate-GT, IGT, CFRD w/o fasting hyperglycemia, or an established diagnosis of CFRD without fasting hyperglycemia
* For female subjects, negative urine pregnancy test at enrollment.

Exclusion Criteria:

* Established diagnosis of non-CF diabetes (i.e. T1D) or CFRD with fasting hyperglycemia, (fasting glucose \> 126 mg/dL)
* History of clinically symptomatic pancreatitis within last year,
* Prior lung or liver transplant,
* Severe CF liver disease, as defined by portal hypertension,
* Fundoplication-related dumping syndrome,
* Medical co-morbidities that are not CF-related or are unstable per investigator opinion (i.e. history of bleeding disorders, immunodeficiency),
* Acute illness or changes in therapy (including antibiotics) within 6 weeks prior to enrollment,
* Treatment with oral or intravenous corticosteroids within 6 weeks of enrollment,
* Hemoglobin \<10g/dL, within 90 days of Visit 1 or at Screening,
* Abnormal renal function, within 90 days of Visit 1 or at Screening; defined as Creatinine clearance \< 50 mL/min (based on the Cockcroft-Gault formula) or potassium \> 5.5mEq/L on non-hemolyzed specimen,
* A history of anaphylaxis, angioedema or Stevens-Johnson syndrome,
* Inability to perform study specific procedures (MMTT, GPA),
* Subjects, who in study team opinion, may be non-compliant with study procedures.