BIOLUMINESCENCE IMAGING OF ISLET TRANSPLANTATION IN VIVO

Abstract

O68 Aims: Islet transplantation is an emerging therapy for type I diabetes. Currently there is no effective method to accurately tract the fate of transplanted islet mass in vivo. Our aim was to develop a real-time non-invasive bioluminescence imaging (BLI) system in a mouse islet transplant model to quantify the proportion of islets that successfully engraft and to detect graft injury early. Methods: Murine islets expressing light-emitting luciferase driven by a rat insulin promoter (RIP) were isolated from a transgenic mouse line Tg(RIP-luc) of FVB background. The islets were transplanted to intraperitoneal (IP) cavity, beneath kidney capsule (KC), and to subcutaneous (SC) or intrahepatic (IH) sites of syngeneic wild type FVB or allogeneic Balb/C mice that were either normal or induced to diabetics with straptozotozin. Recipient mice were injected IP with substrate luciferin at doses of 100 ∼ 400 μg/gm body weight; luminescent light emitted were captured by a cooled CCD camera and analyzed using Living Image and IGOR IMAGE software. Recipient mouse serum glucose post-transplant was monitored using a Glucometer. Results: The kinetics of luminescence light emission was determined for each graft site. The magnitude of bioluminescence measured varied with time after the injection of luciferin. Optimal time for detecting light emission from islets transplanted at SC, KC, IP, and IH sites was determined as 20, 12, 10, and 12 minutes after IP injection of luciferin, respectively. Clearance of substrate under anaesthesia was rapid within the first hour and was completed by 3∼ 4 hours. Strong BLI signals were detected when as few as 10 of the Tg(RIP-luc) islets were transplanted at either one of the four sites tested. There is a liner relationship between the number of islets transplanted and islet luminescence intensity. Islet luminescence intensity was relatively stable for at least 3 months when transplanted at all four sites of syngeneic recipients. In allogeneic diabetic transplant models, 200 RIP-luc islets transplanted under kidney capsule or in liver generated strong BLI signals and corrected recipient mouse hyperglycemia soon after the transplant. Preliminary studies indicated that the BLI signal intensity declined a few days before the rise in mouse serum glucose levels during graft rejection. Conclusions: BLI is a sensitive and rapid assay for evaluating islet mass post-transplant in vivo. There is a rapid and dramatic change in the magnitude of luminescence post-luciferin injection; comparisons of quantitative data must take into consideration the time after injection for any given transplant. These models may be used as high throughput models for assessment and screening of novel therapeutic procedures aimed at increasing functional islet survival. In addition, an early bioluminescence decay of islet allograft may serve as an indicator that precedes an irreversible decay in islet mass and a complete loss of blood sugar control.