Glucoregulatory Hormone Interactions in Diabetes

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Project Summary/Abstract Hypoglycemia and its adverse effects on brain function remain the major factor limiting the use of intensified insulin therapy that has been shown to prevent or delay the long-term complications in type 1 diabetes (T1DM). Higher cognitive functions (e.g. working memory) that involve the prefrontal cortex are particularly sensitive to neuroglycopenia. This proposal seeks continued support of a long-term RO-1 grant with the long-term goal of documenting the health benefits of insulin delivery strategies that minimize the risk of frequent bouts of hypoglycemia in T1DM patients. The specific aims of the current project outlined below use functional magnetic resonance imaging (fMRI) and magnetic resonance spectroscopy (MRS) techniques to assess the changes in brain function and fuel metabolism caused by acute hypoglycemia and acute hyperglycemia in T1DM patients with hypoglycemia unawareness (versus hypoglycemia-aware T1DM patients and healthy controls) as well as the potential beneficial impact of employing closed-loop insulin delivery systems to improve brain function in hypoglycemia unaware T1DM individuals. The protocols rely heavily on human investigation involving non-diabetic as well as hypoglycemia aware and unaware T1DM subjects exposed to experimental mild and moderate hypoglycemia and acute hyperglycemia using the glucose clamp technique while undergoing brain imaging. However, we also take advantage of the power of rodent diabetic models to test specific mechanistic hypotheses. The primary hypothesis of this proposal is that hypoglycemia unaware T1DM patients not only have impaired hormonal and symptomatic responses, but also lack another key hypoglycemia defense mechanism, namely the capacity of the brain to activate motivation/reward circuits due to adaptive increases in brain glucose transport and metabolism as well as stimulation of the polyol pathway. The specific aims are to determine: 1) If T1DM patients with hypoglycemia unawareness (vs. T1DM and non-diabetic controls) lose the capacity to elicit brain responses to visual food cues as well as functional connectivity in striatal and a variety of other brain regions in response to food cues during mild and moderate hypoglycemia using the glucose clamp technique; 2) If patients with T1DM and hypoglycemia unawareness display adaptive changes causing excessive increases in brain glucose transport and metabolism in response to acute hyperglycemia that induce adverse neurocognitive effects within the pre-frontal cortex, a key brain region for cognitive function not previously examined in humans using magnetic resonance spectroscopy (MRS). In addition, mechanistic studies will be conducted in diabetic rats exposed to recurrent hypoglycemia to define the molecular mechanisms driving the changes in brain fuel metabolism induced by intensive insulin treatment; and 3) if reducing glycemic variability with a closed loop insulin delivery system in patients with hypoglycemia unawareness can reverse alterations in brain glucose transport/metabolism as well as functional connectivity, thereby reverse brain dysfunction induced by current intensive T1DM insulin treatment.