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The islets of Langerhans of the pancreas are the primary endocrine organ responsible for regulating whole body glucose homeostasis. The use of isolated primary islets for research development and training requires organ resection, careful digestion, and isolation of the islets from nonendocrine tissue. This process is time consuming, expensive, and requires substantial expertise. For these reasons, we sought to develop a more rapidly obtainable and consistent model system with characteristic islet morphology and function that could be employed to train personnel and better inform experiments prior to using isolated rodent and human islets. Immortalized β cell lines reflect several aspects of primary β cells, but cell propagation in monolayer cell culture limits their usefulness in several areas of research, which depend on islet morphology and/or functional assessment. In this manuscript, we describe the propagation and characterization of insulinoma pseudo-islets (IPIs) from a rat insulinoma cell line INS832/3. IPIs were generated with an average diameter of 200 μm, consistent with general islet morphology. The rates of oxygen consumption and mitochondrial oxidation-reduction changes in response to glucose and metabolic modulators were similar to isolated rat islets. In addition, the dynamic insulin secretory patterns of IPIs were similar to primary rat islets. Thus, INS832/3-derived IPIs provide a valuable and convenient model for accelerating islet and diabetes research.

Linking two pharmacophores that bind different cell surface receptors into a single molecule can enhance cell-targeting specificity to cells that express the complementary receptor pair. In this report, we developed and tested a synthetic multivalent ligand consisting of glucagon-like peptide-1 (GLP-1) linked to glibenclamide (Glb) (GLP-1/Glb) for signaling efficacy in β-cells. Expression of receptors for these ligands, as a combination, is relatively specific to the β-cell in the pancreas. The multivalent GLP-1/Glb increased both intracellular cAMP and Ca 2+ , although Ca 2+ responses were significantly depressed compared with the monomeric Glb. Moreover, GLP-1/Glb increased glucose-stimulated insulin secretion in a dose-dependent manner. However, unlike the combined monomers, GLP-1/Glb did not augment insulin secretion at nonstimulatory glucose concentrations in INS 832/13 β-cells or human islets of Langerhans. These data suggest that linking two binding elements, such as GLP-1 and Glb, into a single bivalent ligand can provide a unique functional agent targeted to β-cells.

We investigated the effects of glucose on the rates of oxygen consumption (OCR) and insulin secretion (ISR) by betaHC9 cells derived from mouse pancreatic islets with beta-cell hyperplasia. Our results demonstrate that the OCR by betaHC9 cells incubated in nutrient-rich DMEM is unaffected by glucose (0-25 mM), is dissociated from the ISR (which increases with the addition of glucose), and is always higher than that measured in PBS. Glucose (25 mM) increases both the OCR and ISR when added to nutrient-free PBS. On the basis of results presented here, we suggest that, contrary to the current consensus, the observed increases in the OCR by beta-cells upon addition of glucose to nutrient-free buffers may be unrelated to the process of glucose-stimulated insulin secretion (GSIS) and, instead, related to nutrient starvation. We believe that a reevaluation of the implication of changes in OCR upon glucose stimulation in the process of GSIS is warranted and that OCR and ISR measurements should be performed in more physiological media to avoid nutrient starvation artifacts.