CONTEXT: In type 1 diabetes, the body's immune system mistakenly launches an attack on insulin-producing beta cells, sending T cells to invade pancreatic islets. Until recently, physicians could track type 1 diabetes only by monitoring blood levels of antibodies directed against pancreatic islet proteins. The test, however, usually detected type 1 diabetes late in its progression, after most islet beta cells had been destroyed and autoimmune processes had been played out. Researchers at Massachusetts General Hospital and Boston's Joslin Diabetes Center are using magnetofluorescence contrast nanoparticles, monitored with high-field MR, to devise a better test. It measures the permeability of the small blood vessels surrounding and within the islets, an early marker of this inflammation.
RESULTS: The technique has been successfully tested on a mouse model. For imaging, long-circulating magnetofluorescent nanoparticles were used. They consist of a superparamagnetic iron oxide (SPIO) core, a crosslinked dextran coating, and amino groups to which Alexa-488 fluorochrome is attached. Transgenic mice were imaged with an 8.5T micro-MR scanner 24 hours after contrast injection. Contrast accumulation was monitored in vivo, and a positive correlation between probe accumulation and insulitis was documented.
IMAGE: Higher MR relativities were measured in the pancreas of normal mice compared with diabetic mice 24 hours after contrast injection. (Image reprinted with permission of Proceedings of the National Academy of Science)
IMPLICATIONS: This imaging strategy may prove invaluable in helping identify early insulitis and for monitoring therapeutic interventions aimed at stopping its progression. MGH has already safely used the method in human clinical trials to detect the spread of prostate cancers to the lymph nodes.