8538 Pancreatic Islet Adaptations to Hyperglycemia Are Prevented by Glycolytic Inhibition and Amplified by Inhibiting Membrane Depolarization

Abstract Disclosure: N.B. Whitticar: None. B.P. List: None. N. Bruce: None. R. Bertram: None. C.S. Nunemaker: None. Long before type 2 diabetes ensues, pancreatic islets undergo functional changes to compensate for increasing insulin resistance. Primarily, the islets increase their ability to secrete insulin by augmenting the glucose-stimulated insulin secretion (GSIS) pathway. As metabolic syndrome worsens, islets become functionally exhausted, leading to cellular dysfunction and apoptosis. To avoid the negative consequences of this compensatory response, various steps of the GSIS pathway can be attenuated to restore normal functional levels before the islets fail. Determining which inhibitors can prevent the earliest adaptations to hyperglycemia may reveal the processes that play a causal role in islet failure. The chemicals mannoheptulose (MH), diazoxide (DZ), and nifedipine (NP) were chosen to inhibit the glucokinase enzyme, KATP-channel closure, and voltage-gated calcium channels, respectively. CD-1 mouse islets were placed in 20 mM glucose to simulate hyperglycemia along with a concentration of each inhibitory drug that reduced insulin secretion by 30-40%. After 48-hour treatment, glucose-stimulated calcium tests were performed to determine if the treatments could prevent the negative adaptation to hyperglycemia. Only islets treated with MH to reduce glycolytic activity maintained a normal calcium response. Islets in the MH group also retained a strong insulin response to glucose and were not depleted of insulin content. Unexpectedly, inhibition of calcium influx and insulin secretion with DZ or NF caused a substantial increase in basal insulin secretion compared to islets in standard culture (P<0.01, n=6; P=0.06, n=6, respectively). These results indicate that the signaling pathway that causes the adaptation to hyperglycemia lies upstream of KATP channels and downstream of glucokinase. Mathematical modeling using the Integrated Oscillator Model was able to replicate our results and suggests that high rates of glycolytic and mitochondrial metabolism are associated with the signal that adapts islets to hyperglycemia, and that reducing intracellular calcium in the face of high glucose further increases basal insulin secretion. Ongoing studies will determine if metabolic acceleration or altered membrane conductance are responsible for the earliest islet adaptations to hyperglycemia. Our results suggest that reducing metabolic activity, but not calcium influx, prevents adaptations to hyperglycemia in mouse islets. These findings can be applied to potentially prevent the progression of obesity and hyperinsulinemia into type 2 diabetes. Presentation: 6/2/2024