Abstract, FWF Project P16188 Immunosuppressive action of 4-amino tetrahydrobiopterin,
Ernst R. Werner, Division of Biological Chemistry, Biocenter,Medical University of Innsbruck
Tetrahydrobiopterin is a low molecular weight compound synthesized from guanosine 5' triphosphate, which is essential for specific hydroxylases, including the hydroxylation of aromatic amino acids and the biosynthesis of nitric oxide from L-arginine by nitric oxide synthases. In our preceeding project, we characterized the biochemistry of novel tetrahydrobiopterin derivatives, which had been developed in our laboratory. We found that these novel compounds were not only excellent tools to characterize the biochemical role of tetrahydrobiopterin in the nitric oxide synthase reaction, but also displayed exciting pharmacological properties. When applied to mice, the 4-amino analogue of tetrahydrobiopterin was at least as efficient as cyclosporin A in preventing allograft rejection. While cyclosporin A inhibited expression of interferon-gamma and of genes induced by this cytokine, the activation of the interferon-gamma axis in 4-amino tetrahydrobiopterin-treated animals remained as high as in control animals. Preliminary experiments suggest that the immunosuppressive potential of 4-amino tetrahydrobiopterin exceeds that of other nitric oxide synthase inhibitors.
The aim of the present project is to unravel the molecular mechanisms of the immuno-suppressive action of 4-amino tetrahydrobiopterin.To achieve this, we plan to study the effects of 4-amino tetrahydrobiopterin on gene expression in cultured cells and cell lines, in mixed lymphocyte reactions, which constitute an in vitro model for immune reactions, and in tissues of hearts transplanted to allogeneic mice. These effects of 4-amino tetrahydrobiopterin will be studied in relation to other nitric oxide synthase inhibitors, to the tetrahydrobiopterin parent compound and to cyclosporin A, an immunosuppressive drug widely used in clinical applications.We want to first use the powerful expression array screening technique techniques, and then verify the observations by quantifying the corresponding protein levels in cells and tissue sections. We will then compare these results with results obtained using cells and tissues from mice lacking inducible nitric oxide synthase to dissect action dependent and independent from this enzyme. Finally, we plan to pinpoint the detailed mechanism by unravelling the signal transduction pathways responsible for the observed alterations in the expression profiles.
With this project, we hope to characterize novel mechanisms of control of the immune response by pteridines. This knowledge could not only provide a step to the development of a new class of pterin-based immunosuppressive drugs, but also has the potential to identify novel targets for intervention in the immune system.
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