Preserved glucagon-like peptide-1 responses to oral glucose, but reduced incretin effect, insulin secretion and sensitivity in young Asians with type 2 diabetes mellitus

Objective: Youth onset type 2 diabetes mellitus (YT2DM) is a globally rising phenomenon with substantial Asians representation. The understanding of its pathophysiology is derived largely from studies in the obese African-American and Caucasian populations, while studies on incretin effect are scarce. We examined the insulin resistance, ?-cell function (BC), glucagon-like peptide (GLP)-1 hormone and incretin effect in Asian YT2DM. Research design and methods: This case-control study recruited 25 Asian YT2DM and 15 healthy controls, matched for gender, ethnicity and body mass index. Serum glucose, insulin, C peptide and GLP-1 were sampled during 2-hour oral glucose tolerance tests (OGTTs) and 1-hour intravenous glucose tolerance tests (IVGTTs). Insulin sensitivity was derived from the Quantitative Insulin Sensitivity Check Index (QUICKI), Oral Glucose Insulin Sensitivity Index (OGIS) in OGTT and surrogate index of SI from the minimal model (calculated SI, CSI). Acute insulin response (AIR) was obtained from IVGTT. Total BC was computed as incremental area under the curve of insulin/incremental area under the curve of glucose, during OGTT (BCOG) and IVGTT (BCIV), respectively. Disposition index (DI) was calculated using the product of insulin sensitivity and insulin secretion. GLP-1 response to oral glucose was calculated as incremental area under the curve of GLP-1 (?AUCGLP-1). Per cent incretin effect was estimated as 100×(BCOG-BCIV)/BCOG). Results: The YT2DM had marked impairment in BC (>80% reduction in AIR and BCOG, p <0.001) and lower QUICKI ( p<0.001), OGIS (p<0.001) and CSI (p=0.015) compared with controls. There was no difference in GLP-1 at all time points and ?AUCGLP-1 but the per cent incretin effect was reduced in the YT2DM compared with controls (12.1±8.93 vs 70.0±4.03, p <0.001). Conclusions: Asian YT2DM showed similar GLP-1 response to oral glucose as controls but reduced incretin effect, BC and insulin sensitivity. The lack of compensatory mechanisms, as shown by the DI may be partly ascribed to the impaired incretin effect, similar to that of adult T2DM.