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Monitoring of SPIO labeled islet grafts in liver of diabetic rats by MRI imaging

Objective To investigate the possibility of monitoring superparamagnetic iron oxide (SPIO) labeled islet grafts in vivo by magnetic resonance imaging (MRI). Methods Islet grafts were labeled with SPIO in vitro and transplanted into the liver of streptomycin-induced diabetic rats. There were 4 groups, including 2 syngeneic groups (Wistar to Wistar transplantation, one group receiving SPIO labeled islets,and the other group unlabeled islets as control) and 2 allogeneic groups (Lewis to Wistar transplantation, one group receiving SPIO labeled islets, and the other group unlabeled islets as control). Poly-L-Lysine (PLL) was used to increase the labeling efficiency of SPIO. After transplantation, MRI was performed regularly, fed glucose level was monitored, and animals were sampled for pathological examination. Results Only SPIO labeled islets could be detected by MRI. The relative number of islets detected by MRI in syngeneic group receiving labeled islets at week 1,2 and 3 following transplantation was (89.6±2.2)%, (87.5±14.4)% and (74.5±19.5)% respectively, and the relative number in allogeneic groups receiving labeled islets at these time points were (43.2±17.2)%, (36.5±13.0)% and (26.5±17.4)% respectively. Statistical significance was observed as the result of a paired student's t test (P 16.8 mmol/L at first week following transplantation,and no intact islets could be found in liver sections since that time. Conclusion Results of MRI correlate to fed glucose level monitoring and pathological examination. Application of this elegant imaging technique provides a direct, noninvasive and continuous way to monitor the distribution and survival of islet grafts in vivo. 
 
Key words: 
Islets of Langerhans;  Transplants;  Magnetic resonance imaging;  Rat