Prevention of Cystic Fibrosis Diabetes

Acute systemic hyperglycemia causes oxidative stress and a pro-inflammatory response. The pro-inflammatory cytokines induced by hyperglycemia are toxic to islet insulin producing cells, and thus worsen glucose intolerance. Patients with cystic fibrosis (CF) have a high prevalence of CF related diabetes (CFRD) and up to 40% of CF adults develop CFRD. During the prediabetic phase in CF, there is progression from normal glucose homeostasis to high risk prediabetes characterized by episodes of acute hyperglycemia after meals and during respiratory exacerbations. The mild hyperglycemia seen in CF patients with high risk prediabetes following a meal would be expected to induce a degree of systemic inflammation and oxidative stress. These repetitive episodes, if left unchecked, could lead to progression of glucose impairment, worsening severity of oxidative stress and inflammation, and ultimately the development of CFRD, all via hyperglycemia-induced toxicity to beta cells. Furthermore, this process may be accelerated in CF because lung disease and resultant respiratory exacerbations are associated with oxidative stress and inflammation and this will further contribute to beta cell damage. Sitagliptin is a recently approved agent for type 2 diabetes and markedly enhances insulin secretion in the presence of hyperglycemia and has been shown to be effective in preventing postprandial hyperglycemia. The hypothesis to be tested in this project is that sitagliptin will prevent the development of CFRD in CF subjects with high risk prediabetes by blocking postprandial hyperglycemia. The investigators propose a randomized, double-blind, placebo-controlled, multicenter, 15-month longitudinal study in 118 CF subjects with high risk prediabetes to test this hypothesis. Specifically, the investigators aim to show that chronic treatment with sitagliptin: prevents the conversion to diabetes; results in preservation of beta cell function; reduces systemic measures of oxidative stress an