Induction of apoptosis by 7,8-dihydroneopterin: involvement of radical formation.
Interferon-gamma is a cytokine released in large amounts during cell-mediated immune response. It induces the expression of proinflammatory cytokines and enhances macrophage capacity to secrete reactive oxygen intermediates and the pteridines neopterin and 7,8-dihydroneopterin. To assay the role of these pteridines in the immune system several studies were performed. Thereby, 7,8-dihydroneopterin was found to induce apoptosis in T lymphocytes. In this study we report that caspases are involved in 7,8-dihydroneopterin-mediated apoptosis in Jurkat T cells. In connection with this result we found that 7,8-dihydroneopterin can increase Fas ligand expression detected in Western blot analysis and promoter reporter assays. Antioxidants potently reduced the effect of 7,8-dihydroneopterin on Fas ligand promoter activation suggesting an involvement of oxidative stress. In further investigations, ESR-measurements were performed to evaluate the role of 7,8-dihydroneopterin in the formation of radicals. We found that the pteridine in combination with the spin trap DMPO induces the production of DMPO-OH spin adducts. This reaction was sensitive to the presence of chelated metal ions and could completely be blocked by the addition of superoxide dismutase. These data suggest that 7,8-dihydroneopterin in aqueous solution leads to the formation of .OH radicals via generation of superoxide anion. We hypothesize that an overproduction of radicals caused by high levels of 7,8-dihydroneopterin is likely to be responsible for the pro-apoptotic effects observed in cell cultures and possibly contributes to the pathogenesis of diseases involving immune activation and elevated concentrations of neopterin-derivatives.
Wirleitner
B
B
Institute for Medical Chemistry and Biochemistry, University of Innsbruck, and Boltzmann Institute for AIDS Research, Innsbruck, Austria.
Czaputa
R
R
Oettl
K
K
Böck
G
G
Widner
B
B
Reibnegger
G
G
Baier
G
G
Fuchs
D
D
Baier-Bitterlich
G
G
D017209:Apoptosis / Q000187:drug effects*; D003497:Cyclic N-Oxides; D004578:Electron Spin Resonance Spectroscopy; D053222:Fas Ligand Protein; D006801:Humans; D017665:Hydroxyl Radical / Q000378:metabolism; D007371:Interferon-gamma / Q000378:metabolism; D019169:Jurkat Cells; D008562:Membrane Glycoproteins / Q000378:metabolism; D019798:Neopterin / Q000031:analogs & derivatives; D011621:Pteridines / Q000494:pharmacology*; D017382:Reactive Oxygen Species / Q000378:metabolism; D013113:Spin Labels; D013601:T-Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000276:immunology / Q000378:metabolism
D003497:Cyclic N-Oxides; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D008562:Membrane Glycoproteins; D011621:Pteridines; D017382:Reactive Oxygen Species; D013113:Spin Labels; C000976:7,8-dihydroneopterin; D017665:Hydroxyl Radical; C069977:2,2-dimethyl-5-hydroxy-1-pyrrolidinyloxy; D019798:Neopterin; D007371:Interferon-gamma