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Tetrahydrobiopterin and cytokines
E R Werner1, G Werner-Felmayer, H Wachter
1Institute for Medical Chemistry and Biochemistry, University of Innsbruck, Austria.
Summary
Tetrahydrobiopterin biosynthesis is stimulated by cytokines, increasing its concentration. In humans, lower enzyme activity causes neopterin buildup, indicating immune challenges and impacting nitric oxide production.
Area of Science:
- Biochemistry
- Immunology
- Cell Biology
Background:
- Tetrahydrobiopterin (BH4) is a crucial cofactor synthesized from guanosine triphosphate.
- BH4 biosynthesis involves key enzymes like guanosine triphosphate cyclohydrolase I, 6-pyruvoyl tetrahydropterin synthase, and sepiapterin reductase.
- Cytokines, including gamma-interferon and tumor necrosis factor-alpha, modulate BH4 synthesis pathways.
Purpose of the Study:
- To elucidate the regulation of tetrahydrobiopterin biosynthesis by cytokines.
- To investigate the implications of enzyme activity variations in human cells on metabolite accumulation.
- To understand the role of BH4 as a cofactor in nitric oxide production.
Main Methods:
- Enzyme activity assays for guanosine triphosphate cyclohydrolase I and 6-pyruvoyl tetrahydropterin synthase.
- Measurement of intracellular tetrahydrobiopterin and neopterin derivative concentrations.
- Analysis of cytokine-induced changes in BH4 pathway enzyme activity in murine and human cell lines (monocytes, macrophages).
Main Results:
- Cytokines significantly enhance guanosine triphosphate cyclohydrolase I activity, increasing intracellular tetrahydrobiopterin levels.
- Human monocytes and macrophages exhibit low 6-pyruvoyl tetrahydropterin synthase activity, leading to neopterin derivative accumulation.
- Accumulated neopterin derivatives are released into extracellular fluids, correlating with impaired cell-mediated immunity.
- Stimulated tetrahydrobiopterin biosynthesis provides a necessary cofactor for nitric oxide synthesis from L-arginine.
Conclusions:
- Cytokine-mediated stimulation of tetrahydrobiopterin biosynthesis is a key regulatory mechanism.
- Deficient 6-pyruvoyl tetrahydropterin synthase activity in human immune cells contributes to disease-associated neopterin levels.
- Tetrahydrobiopterin plays a vital role in nitric oxide production, essential for immune function.