ISLET AND PANCREAS TRANSPLANTATION I

G. Parnaud¹, N. Niclauss², D. Bosco³, T. Berney^4
1Islet Isolation And Transplantation Center, Department Of Surgery, University of Geneva and Geneva University Hospital, Geneva/SWITZERLAND, ²Islet Isolation And Transplantation Center, Geneva University Hospital, Geneva/SWITZERLAND, ³Islet Isolation And Tranplantation Center, Geneva University Hospitals, Geneva/SWITZERLAND, ⁴Visceral And Transplantation Surgery, Geneva University Hospitals, Geneva/SWITZERLAND

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Introduction: Five years after islet transplantation, only 10 % of patients remains insulin independent. The exact cause for progressive islet dysfunction is undefined to date, but may be the result of adverse effects of immunosuppressive agents. In this study, we examined the effect of rapamycin, a key component of the immunosuppressive regimen in clinical islet transplantation, on islet cell replication in vivo. Methods: Streptozotocin (200 mg/kg i.p.) was used to induce diabetes in NOD/Scid mice at least 5 days before islet transplantation. Five hundred rat islets were transplanted under the left kidney capsule of normoglycemic or diabetic mice. Three days after transplantation, animals were randomly allocated into the experimental groups (control or rapamycin) and BrdU (5 mg/ml) was added to drinking water for 7 days. Mice were treated with rapamycin (0.3mg/kg/every day, i.p.) and control animals received appropriate vehicle treatment. An i.p. glucose tolerance test was performed on all animals at 10 days. Beta cell replication was determined by double immunofluorescence staining for insulin and BrdU. Data are expressed as % positive BrdU beta cells and as mean ± SEM for 3 or more independent experiments. Results: Although control and rapamycin-treated mice had similar blood glucose levels before and 2h after i.p. glucose injection, both the peak glucose levels and duration of the glucose excursion (AUC in mM of glucose over 120 min) were increased in rapamycin-treated mice when compared to control mice (830±95 vs. 284±42 rapamycin vs. control, P=0.0004). In non streptozotocin-treated mice, rapamycin decreased the % of BrdU positive beta cells within endogenous islets (0.66±0.16 vs. 1.71±0.41 rapamycin vs. control, P=0.029). Furthermore, rapamycin reduced the % of BrdU positive beta cell in transplanted islets (0.71±0.16 vs. 4.60±0.42 rapamycin vs. control, P<0.0001). Similar results were obtained with Ki67 staining as an alternative mean of identifying proliferating cells (0.14±0.05 vs. 0.92±0.21 rapamycin vs. control, P=0.008). When streptozotocin-treated mice were treated with rapamycin, the % of BrdU positive beta cell in the graft was also significantly decreased (1.39±0.28 vs. 3.96±0.71 rapamycin vs. control, P=0.004). Finally, the apoptotic rate in transplanted islets was very low and no significant difference was observed between control and rapamycin-treated mice. Conclusion: Our results indicate that rapamycin reduces the rate of pancreatic beta cell proliferation in transplanted rat islets but also in native pancreatic murine islets. It is therefore suggested that progressive graft islet dysfunction may result in part from an impairment of beta cell regeneration induced by rapamycin in transplanted patients.

Disclosure: All authors have declared no conflicts of interest.