Type 1 diabetes (T1D) begins when autoreactive T-cells infiltrate the islet of Langerhans and begin to deplete the insulin-secreting ?-cells. This infiltration and concurrent inflammation are known as insulitis and represent the asymptomatic phase of T1D. The asymptomatic or `pre-symptomatic' phase may take place years to prior to clinical presentation. A method to diagnose insulitis and ?-cell mass decline prior to overt diabetes does not exist. Some therapeutic treatments have been shown to delay T1D onset such as the immunotherapy ?CD3, but a method to track drug efficacy is lacking completely. A non-invasive method to diagnose insulitis and ?-cell decline would provide a window for therapeutic treatment where endogenous ?-cell mass could be retained, as well as providing a method to determine treatment efficacy via identifying drug `responders' vs `non- responders'. During T1D progression, the islet microvasculature increases permeability due to insulitis. Magnetic nanoparticle MRI contrast accumulation has previously been suggested as a measure of ongoing insulitis and increased islet permeability. Contrast enhanced ultrasound (CEUS) using gas-filled microbubbles (MBs) measures acoustic backscatter at sub-harmonic frequencies and is clinically approved. A novel, sub-micron `nanobubble' (NB) ultrasound contrast agent has been developed and shown to extravasate and accumulation in tumors. In this project we will utilize echogenic NBs that we have demonstrated can accumulate in diseased pancreata during the pre-symptomatic phase of T1D. Preliminary data shows that NBs increase CEUS signal by accumulating in the pancreas prior to overt disease. Our overall goal is to determine what aspects of immune cell infiltration into the islet determine NB accumulation prior to T1D onset and determine if therapeutic reversal reduces NB accumulation and CEUS signal. Towards this goal we will examine 2 specific aims: 1) Determine the mechanism(s) by which autoreactive T-cell infiltration increases CEUS signal in the pancreas; 2) Characterize if NB CEUS signal changes reflect T1D therapeutic reversal. Developing a diagnostic to detect pre-symptomatic T1D and monitor treatment efficacy, will be essential for prevention of T1D. If such a modality could be established, it would have a major impact by lessening the burden of diabetes management and reducing complications like hypoglycemia, retinopathy, neuropathy, and nephropathy.
The insulin secreting ?-cells reside in the pancreatic islets and are depleted following autoreactive T-cell infiltration. My research will use contrast enhanced ultrasound with a novel contrast agent that leaks from the islet vasculature into the surrounding tissue during this infiltration prior to overt diabetes. Detecting this increased vascular leakage that proceeds type 1 diabetes can indicate disease progression, allowing for early therapeutic intervention and monitoring the efficacy of treatments aimed at saving ?-cell mass.
