Effect of Rosiglitazone and Ramipril on β-Cell Function in People With Impaired Glucose Tolerance or Impaired Fasting Glucose: The DREAM trial

OBJECTIVE: The objective of this study was to determine the degree to which ramipril and/or rosiglitazone changed β-cell function over time among individuals with impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT) who participated in the Diabetes Reduction Assessment With Ramipril and Rosiglitazone Medication (DREAM) Trial, which evaluated whether ramipril and/or rosiglitazone could prevent or delay type 2 diabetes in high-risk individuals. RESEARCH DESIGN AND METHODS: The present analysis included subjects (n = 982) from DREAM trial centers in Canada who had oral glucose tolerance tests at baseline, after 2 years, and at the end of the study. β-Cell function was assessed using the fasting proinsulin–to–C-peptide ratio (PI/C) and the insulinogenic index (defined as 30–0 min insulin/30–0 min glucose) divided by homeostasis model assessment of insulin resistance (insulinogenic index [IGI]/insulin resistance [IR]). RESULTS: Subjects receiving rosiglitazone had a significant increase in IGI/IR between baseline and end of study compared with the placebo group (25.59 vs. 1.94, P < 0.0001) and a significant decrease in PI/C (−0.010 vs. −0.006, P < 0.0001). In contrast, there were no significant changes in IGI/IR or PI/C in subjects receiving ramipril compared with placebo (11.71 vs. 18.15, P = 0.89, and −0.007 vs. −0.008, P = 0.64, respectively). The impact of rosiglitazone on IGI/IR and PI/C was similar within subgroups of isolated IGT and IFG + IGT (all P < 0.001). Effects were more modest in those with isolated IFG (IGI/IR: 8.95 vs. 2.13, P = 0.03; PI/C: −0.003 vs. −0.001, P = 0.07). CONCLUSIONS: Treatment with rosiglitazone, but not ramipril, resulted in significant improvements in measures of β-cell function over time in pre-diabetic subjects. Although the long-term sustainability of these improvements cannot be determined from the present study, these findings demonstrate that the diabetes preventive effect of rosiglitazone was in part a consequence of improved β-cell function.