Novel Glucagon Modulators and the Closed Loop System

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Abstract Targeting hyperglycemia in type 1 diabetes mellitus (T1DM) reduces diabetes-related complications. Physiologic insulin replacement using an insulin pump is the gold standard of treatment. This method relies on the patient being engaged in blood glucose monitoring and insulin delivery, especially for meal boluses. The fully integrated closed- loop system, comprised of continuous glucose monitoring and glucose-responsive insulin administration, and holds the promise of an "intelligent insulin pump." The ideal closed- loop system will obviate the need for user input. However, currently the closed-loop system is unable to respond to a meal in a timely fashion and insulin monotherapy fails to address postprandial hyperglycemia. Paradoxically, post-meal hyperglucagonemia is associated with postprandial hyperglycemia in T1DM. Glucagon suppressors such as the amylin analog, pramlintide, and the glucagon like peptide-1 (GLP-1) mimetic, exenatide, are new agents approved for use in diabetes. Amylin is the second beta cell hormone that is co-secreted with insulin. Amylin in the postprandial period reduces immediate postprandial hyperglycemia by suppressing glucagon and delaying gastric emptying. The hormone GLP-1 has similar actions to amylin and may also be beneficial in T1DM. The overall goal of this proposal is to merge the closed-loop system technology with these hormones, which are crucial to postprandial glucose homeostasis. In protocol 1, we will study 20 T1DM subjects with the fully closed-loop setting. Subjects will be randomized to either receive pramlintide or exenatide as a pre-meal bolus. We hypothesize that post- meal glucose concentrations will be better with adjunctive pramlintide/exenatide therapy than insulin alone. Protocol 2, will test the feasibility of continuous pramlintide and insulin in the closed loop setting versus insulin alone. Medtronic is the leader in the development of closed-loop system technology for glucose control and Dr. Heptulla has pioneered the use of pramlintide and exenatide in T1DM. These protocols will define the roles of these hormones in post-prandial glucose homeostasis in the closed loop setting. Moreover, this trial has the potential to lead to second-generation closed-loop system with multiple-hormone delivery. These protocols will have a direct impact on existing clinical guidelines and will improve glycemia even prior to the commercial availability of the closed-loop system.