Prevention of autoimmune diabetes in NOD mice by troglitazone is associated with modulation of ICAM-1 expression on pancreatic islet cells and IFN-γ expression in splenic T cells

Thiazolidinediones acting as PPAR-γ agonists are a new generation of oral antidiabetics addressing insulin resistance as a main feature of type-2 diabetes. In accordance to our results, pre-clinical studies have demonstrated that the thiazolinedione troglitazone prevents the development of insulin-dependent autoimmune type-1 diabetes. To investigate whether TGZ acts by affecting the ICAM-1/LFA-1 pathway and/or the Th1/Th2 cytokine balance in NOD mice, we analysed the IL-1β-induced ICAM-1 expression on islet-cells and the LFA-1, CD25, IL-2, IFN-γ, IL-4, and IL-10 expression on splenocytes. After 200 days of oral TGZ administration, islet cells from TGZ-treated NOD mice showed a reduced ICAM-1 expression in response to the pro-inflammatory cytokine IL-1β. The expression of the ligand LFA-1 on CD4 + and CD8 + T-cells was comparable to that of placebo- and untreated controls. Also, the expression of Th1/Th2 cytokines was comparable in groups receiving TGZ or Placebo. Nevertheless, the investigated NOD mice segregated into IFN-γ low- and IFN-γ high producers as revealed by cluster analysis. Interestingly, the majority of TGZ-treated mice belonged to the cluster of IFN-γ low producers. Thus, the prevention of autoimmune diabetes in NOD mice by TGZ seems to be associated with suppression of IL-1β-induced ICAM-1 expression leading to a reduced vulnerability of pancreatic β-cells during the effector stage of β-cell destruction. In addition, IFN-γ production was modulated, implicating that alteration of the Th1/Th2 cytokine balance might have contributed to diabetes prevention. The findings of this study suggest that TGZ exerts its effects by influencing both the β-cells as the target of autoimmune β-cell destruction and the T-cells as major effectors of the autoimmune process.