A Glycemic Threshold Above Which the Improvement of β-Cell Function and Glycemia in Response to Insulin Therapy Is Amplified in Early Type 2 Diabetes: The Reversal of Glucotoxicity
Ravi Retnakaran, Jiajie Pu, Chang Ye, Alexandra Emery, Stewart B. Harris, Sonja M. Reichert, Hertzel C. Gerstein, Natalia McInnes, Caroline K. Kramer, Bernard Zinman
Abstract
OBJECTIVE: Alleviation of unrecognized glucotoxicity, with resultant recovery of β-cell function, could amplify the glucose-lowering effect of pharmacotherapy and contribute to the variable therapeutic response observed among patients with type 2 diabetes (T2D). However, clinical evidence supporting this concept is lacking. Short-term intensive insulin therapy (IIT) can ameliorate glucotoxicity and improve β-cell function in early T2D. Thus, for evidence of recovery of glucotoxicity-associated β-cell dysfunction, we sought to determine whether there exists a baseline fasting glucose threshold above which the post-IIT improvement in both β-cell function and glycemia is amplified. RESEARCH DESIGN AND METHODS: IIT (glargine, lispro) was administered for 3 weeks to 108 adults with T2D (mean duration 1.8 ± 1.4 years). Oral glucose tolerance tests before and after IIT enabled assessment of β-cell function by Insulin Secretion-Sensitivity Index-2 and insulinogenic index/HOMA-insulin resistance. For each level of baseline fasting glycemia from 6.0 to 10.5 mmol/L, we modeled the difference in IIT-induced percentage change in β-cell function between those at/above the indicated glucose level and those below it. RESULTS: The relationship between baseline fasting glucose and the differential change in β-cell function was nonlinear. Instead, this relationship was best fit by a cubic regression model with inflection (amplification) at fasting glucose at 9.3 mmol/L. Moreover, baseline fasting glucose at 9.3 mmol/L also identified the inflection point at which nonlinear reductions in fasting glucose and 2-h glucose, respectively, were both amplified. CONCLUSIONS: The respective improvements in β-cell function and glycemia in response to short-term IIT are amplified in those in whom baseline fasting glucose exceeds a defined threshold, consistent with reversal of glucotoxicity.