Contrast Enhanced Ultrasound with Submicron-Sized Contrast Agents Detects Diabetes Progression in Mouse Models of Type 1 Diabetes

In type 1 diabetes (T1D) the decline in beta-cell mass occurs many years prior to clinical presentation. A non-invasive method to diagnose insulitis and beta-cell mass decline prior to diabetes does not exist. During T1D progression, the islet microvasculature increases permeability due to insulitis. Iron oxide nanoparticle MRI contrast accumulation has previously been suggested as a measure of ongoing insulitis. Contrast enhanced ultrasound (CEUS) using gas-filled microbubbles (MBs) measures acoustic backscatter at sub-harmonic frequencies and is clinically approved. Sub-micron sized ‘nanobubbles’ (NBs) have previously been developed and show extravasation in tumors. Here we tested whether these sub-micron sized NBs show disease-mediated extravasation in mouse models of T1D. We performed CEUS measurements following NB infusion in NOD mice and control (NOD;Rag1ko and C57Bl6) mice. We also examined fluorescent coverage (FC) following rhodamine-labeled bubble delivery in these animals, through isolating pancreata for histology and quantifying FC and insulitis scores. We observed progressive increased CEUS signal accumulation in pancreas of 4w and 10w NOD mice, which was absent in NOD kidneys (p < 0.001). Rag1ko controls showed minimal CEUS signal in pancreas and kidney. The FC was limited to the pancreata of NOD mice and was substantially higher in endocrine compared to exocrine tissue (p = 0.002). NOD mouse islets also had substantially more FC compared to Rag1ko (p < 0.0001), and showed a correlation between NOD insulitis score and FC (p=0.043). Thus, CEUS with NB contrast agents can detect disease progression prior to T1D onset, which will be important for early T1D diagnosis and monitoring of disease prevention or reversal.