Introduction: Interleukin-1β is a major cytokine to exacerbate subsequent inflammatory reaction with activation of inflammatory cells, and it is activated within cytoplasm by NLRP3 inflammasome which is a large protein complex. Islet transplantation is a treatment option for insulin dependent diabetes mellitus, however, a large number of transplanted islets is lost early after islet transplantation due to instant blood-mediated inflammatory reaction which is mainly characterized as nonspecific innate immune responses including cytokine reaction. Among of cytokines after islet transplantation, IL-1β is known as a key factor of islet injury. In this study, we hypothesized that inhibiting NLRP3 inflammasome after transplantation with MCC950 that is inflammasome inhibitor can improve islet survival and blood glucose level. Materials and Methods: Isolated islets from C57BL/6J mice were cultured in cytokine-cocktail-containing medium to investigate gene expression of NLRP3 and IL-1β with / without MCC950. Syngeneic islet transplantation through portal vein using C57BL/6J mice was performed to investigate the role of MCC950, on the glycemic fluctuation after transplant. Streptozotocin-induced diabetic C57BL/6J mice treated or untreated with MCC950 underwent islet transplantation into the liver, and blood glucose level was measured for 1 month. Additionally, survival ratio and cell viability of islets were measured in vitro assay with / without MCC950 in the presence of cytokine cocktail in culture medium. Immunohistological staining of transplanted site was performed at 3h, 6h and 12h after islet transplantation to evaluate migration of macrophage and apoptosis of transplanted islets.
Results: Cytokine exposure of islets induced upregulation of Nlrp3 and Il1b, and MCC950 restored them. In the transplant model, MCC950 improved glycemic control and increased normoglycemia ratio compared to control group (p < 0.05). The role of MCC950 on the isolated islets were investigated by counting cultured-islets after 4 days and the remnant ratio of islets were calculated. The remnant ratio of MCC950 treatment group was 69% at 4 days after culturing which was significantly higher than that of cytokine treated group (p < 0.001). Additionally, cultured islets were stained with Hoeschest 33342 and PI to assess cell viability. Cytokine stimulation to the culturing islets resulted in significantly lower cell viability of islets compared to control group, and inhibition of NLRP3 inflammasome improved it (77.9% in MCC950 group, 66.4% in cytokine stimulation group, p < 0.05 ). Histopathological exam of liver as a transplant site revealed that MCC950 reduced IL-1β or F4/80 positive cells and apoptotic islet cells at early after transplantation.
Conclusion: Inhibition of NLRP3 inflammasome may improve glycemic control of islet transplantation through suppressing migration of macrophages and apoptosis of islets.