Insulin secretion chip (InS-chip) reveals two peaks within first-phase that temporally coincide with a transition in glucose metabolism.

First-phase glucose-stimulated insulin secretion is mechanistically linked to type 2 diabetes yet the underlying metabolism driving this early stage of secretion is difficult to discern due to significant islet-to-islet variability. Here, we miniaturize a fluorescence anisotropy immunoassay onto a microfluidic device to measure C-peptide secretion from individual islets as a surrogate for insulin (InS-chip). This method measures secretion from up to four islets at a time with [~]7 s resolution while providing an optical window for real-time live cell imaging. Using the InS-chip, we reveal for the first time two glucose-dependent peaks of insulin secretion (i.e., a double peak) within the first phase (<10 min). By combining real-time secretion and live cell imaging, we show that islets transition from glycolytic to OxPhos-driven metabolism at the nadir of the peaks. Overall, these data validate the InS-chip to measure glucose-stimulated insulin secretion while revealing the first-phase secretion contains two peaks defined by a shift in glucose metabolism. Significance StatementLoss of the first phase of glucose-stimulated insulin secretion is one of the earliest signs of type 2 diabetes (T2D). Yet current strategies to measure the early dynamics are inadequate due to the need to pool secretion from multiple islets. In this study, we designed an islet-on-a-chip microfluidic device (InS-chip) to measure insulin secretion from individual islets with <7 s temporal resolution. Our design leaves an optical window for coupled live cell imaging to tease apart the metabolism underlying secretion. Our data reveal that first-phase insulin secretion is composed of two peaks that coincide with a shift in glucose metabolism.