Assessment for revascularization of transplanted pancreatic islets at subcutaneous site in mice with a highly sensitive imaging system

Background: The subcutaneous space is one of the ideal sites for pancreatic islet transplantation, owing to the minimal invasiveness and easy access. However, the results of pancreatic islet transplantation in subcutaneous sites remain unsatisfactory. One of the main obstacles to successful pancreatic islet transplantation in subcutaneous sites is poor revascularization. Therefore, the aim of this study was to evaluate the revascularization process at subcutaneous sites with a highly sensitive imaging system combining a dorsal skinfold chamber (DSC) technique and multiphoton laser scanning microscopy (MPLSM). Methods: A few pancreatic islets isolated from C57BL/6-Tg (CAG-EGFP) mice were syngeneically transplanted into nonmetallic DSCs mounted on the backs of C57BL/6J mice. Time-dependent changes in the newly formed vessels of pancreatic islets were imaged using MPLSM on days 1, 4, 7, 11, and 14 (n = 6). Texas Red was injected intravenously to visualize blood vessels. To evaluate islet graft revascularization, we measured vascular volume surrounding the islet using the Volocity system (Improvision). Results: The percentages of vascular volume at days 1 and 14 were assumed to be 0 and 100%, respectively. The vascular volume on each day was 9.4 ± 6.5% (day 4), 34.9 ± 11.2% (day 7), and 21.1 ± 4.6% (day 11). Conclusions: The present study showed that a highly sensitive imaging system combining the DSC technique and MPLSM was a useful tool to analyze the revascularization process of pancreatic islets in a subcutaneous site.