Vascularization of transplanted islets must be maintained to provide long-term
graft function. In vivo assessment of new vessel formation in islet
grafts has been poorly documented. The purpose of this study was to investigate whether neovascularization was detectable in vivo in a Feridex-labeled murine
syngeneic subcapsular islet mass using DCE
MRI over 180 days. Subcapsular transplants could be visualized at post-transplant days three, seven, 14, and 28 using T2-weighted
MRI and at post-transplant day 180 by
immunohistochemistry. Injection of the
contrast agent gadolinium (Gd)-
DTPA for DCE at three, seven, and 14 days showed increased signal in the transplant area consistent with new vessel formation. Areas under contrast enhancement curves suggested peak
angiogenesis at 14 days. At 180 days, there was no observable change in signal
intensity after contrast injection suggesting established vascularization or islet mass reduction.
Immunohistochemistry confirmed
MRI and DCE findings. These data suggest that islet
angiogenesis occurs early after transplantation and is likely established after one month of transplantation. This study provides an in vivo time-line of neovascularization in subcapsular islet
grafts. We anticipate that contrast extravasation captured by
MRI may provide useful monitoring of
graft angiogenesis if reproduced in a clinically relevant intraportal model.
