Differential mirroring between in vivo insulin secretion and ex vivo islet function in individuals with and without...

Insulin secretion measured in vivo reflects the integrated output of pancreatic islets within a multi-organ regulatory network, whereas ex vivo stimulation of isolated human islets captures intrinsic, islet-autonomous secretory competence. Whether these two levels of β cell function mirror each other in humans remains unclear. We studied 63 individuals undergoing partial pancreatectomy who underwent preoperative OGTT with model-based assessment of β cell function and provided pancreatic tissue for ex vivo islet isolation and glucose stimulation. Ex vivo function was quantified as the stimulation index at 16.7 mmol/l glucose (SI16.7) and related to in vivo indices of insulin secretion. SI16.7 was reduced in islets from people with T2D but showed marked inter-individual variability with overlapping distributions between individuals with and without T2D. In non-diabetic individuals, no significant associations were detected between SI16.7 and OGTT-derived indices. In contrast, in people with T2D, SI16.7 was positively associated with multiple measures of glucose-driven insulin secretion and inversely with potentiation. In multivariable analysis, a composite index of intrinsic glucose-dependent β cell competence remained independently related to SI16.7. These findings indicate that a direct correspondence between systemic β cell function and intrinsic islet secretory capacity emerges only in T2D. This state-dependent alignment suggests that loss of network-mediated regulation may unmask islet-intrinsic defects, allowing ex vivo islet performance to better reflect in vivo insulin secretion and supporting integrated in vivo-ex vivo phenotyping as a tool for functional stratification of T2D.