MRI tracks transplanted pancreatic cells labeled with iron-oxide contrast

CONTEXT: The emerging therapy of islet transplantation has shown great promise for diabetes patients. When grafted in the liver, pancreatic islet cells, which restore normoglycemia, have helped individuals with type 1 diabetes become insulin-independent. Doctors at the Martinos Center for Biological Imaging at Massachusetts General Hospital are investigating a method for tracking the fate of these islets in vivo with MRI. In initial animal studies, Dr. Anna Moore and colleagues used in-house synthesized magnetic iron oxide nanoparticles that detect transplanted pancreatic islets in vivo but do not hinder the cells' ability to produce insulin. To introduce this imaging method in a clinical setting, Moore's team tested the technique using Feridex, a widely available FDA-approved iron oxide-based contrast agent.

RESULTS: Human pancreatic islet cells tagged with iron oxide nanoparticles and transplanted under the kidney capsule in mice retained their ability to secrete insulin and restore normoglycemia in diabetic animals. They were readily detectable by in vivo MRI up to 188 days after transplantation (Evgenov N et al. In vivo imaging of islet transplantation. Nat Med 2006;12:144-148). In a more relevant clinical scenario, pancreatic islet cells were labeled with Feridex and transplanted through the portal vein into the liver. They appeared as dark voids on T2-weighted gradient-echo pulse sequences, whereas nonlabeled islets were not detectable by MRI.

IMAGE: In vivo imaging of human pancreatic islet cells labeled with Feridex in clinically relevant model of intrahepatic transplantation in mice (A). Nonlabeled islets are not detectable by MRI (B). (Provided by A. Moore)

IMPLICATIONS: Results indicate MRI can follow the fate of islet cells labeled with Feridex in a mouse model. The protocol will be applied to baboons at the Martinos Center before clinical trials involving humans. The next step is to find a means of detecting islet function noninvasively to measure the insulin that is secreted by these cells, Moore said.