Insulin Secretion and Insulin Sensitivity Change in Different Stages of Adult-Onset Type 1 Diabetes: A...

Background/Objectives: Previous studies reported impairments in insulin secretion during different stages of type 1 diabetes (T1D), while data regarding insulin sensitivity and immunological changes are still controversial. We analyzed the following: (a) insulin secretion, (b) insulin sensitivity, and (c) pro-inflammatory interleukin-17 (IL-17) levels in peripheral blood in 17 healthy first-degree relatives in stage 1 (FDRs1) (GAD⁺, IA2⁺), 34 FDRs in stage 0 (FDRs0) (GAD^-, IA2A^-), 24 recent-onset T1D (R-T1D) patients in the insulin-requiring state (IRS), 10 in clinical remission (CR), and 18 healthy unrelated controls (HC). Methods: Insulin secretion was evaluated by an IVGTT and a glucagon stimulation test, expressed as a first-phase insulin response (FPIR) and a basal/stimulated C-peptide. Insulin sensitivity was tested by the euglycemic hyperinsulinemic clamp, expressed as an M value. Results: FDRs1 had a lower FPIR than FDRs0 (p < 0.05) and HC (p < 0.001) but higher than RT1D-IRS (p < 0.001) and RT1D-CR (p < 0.01). Moreover, FDRs1 had lower basal/stimulated C-peptide than FDRs0 (p < 0.01/p < 0.05) and HC (p < 0.001/p = 0.001) but higher levels than RT1D-IRS (p < 0.001/p < 0.001). However, the M value was similar among FDRs1, FDRs0, and HC (p = 1.0) but higher than RT1D-IRS (p < 0.001) and RT1D-CR (p < 0.01), while RT1D-IRS and RT1D-CR had lower M than HC (p < 0.001; p < 0.001; respectively). FDRs1 had higher IL-17 than FDRs0 (p < 0.001) and HC (p < 0.05). RT1D-IRS had higher IL-17 than FDRs0 (p < 0.001) and HC (p < 0.001), which was similar to RT1D-CR vs. FDRs0 (p < 0.001) and HC (p < 0.05). Conclusions: Early changes in pre-T1D might involve an initial decline of insulin secretion associated with a pro-inflammatory attack, which does not influence insulin sensitivity, whereas later, insulin sensitivity deterioration seems to be associated with the prominent reduction in insulin secretion.