Guanosine triphosphate cyclohydrolase I regulates nitric oxide synthesis in renal proximal tubules.
The synthesis of nitric oxide by proximal tubule-inducible nitric oxide synthase requires tetrahydrobiopterin as a cofactor. To determine whether tetrahydrobiopterin synthesis is required for nitric oxide production, nitrite release by mouse proximal tubule cells treated with 2,4-diamino-6-hydroxypyrimidine, an inhibitor of the rate-limiting enzyme in the de novo synthesis of tetrahydrobiopterin from guanosine triphosphate, guanosine triphosphate cyclohydrolase I, was measured. Treatment with lipopolysaccharide (0.1 micrograms/mL) and interferon-gamma (100 U/mL) for 12 h increased nitrite production from 2.7 +/- 0.2 to 25.4 +/- 1.3 nmol/mg of protein (P < 0.001; N = 9). 2,4-Diamino-6-hydroxypyrimidine (6 mM) reduced lipopolysaccharide/interferon-gamma-induced nitrite production by 53.1 +/- 3.4%. Sepiapterin, a substrate for tetrahydrobiopterin synthesis via the dihydrofolate reductase-dependent pterin salvage pathway, prevented the inhibition by 2,4-diamino-6-hydroxypyrimidine, an effect that was blocked by methotrexate. In conclusion, guanosine triphosphate cyclohydrolase I activity is required for cytokine-induced nitric oxide production by proximal tubular epithelium. The inhibition of guanosine triphosphate cyclohydrolase I could prove useful in the treatment of nitric oxide-mediated renal disorders.
Amoah-Apraku
B
B
Department of Pharmacology, University of Florida College of Medicine, Gainesville, USA.
Tang
S S
SS
Ingelfinger
J R
JR
Guzman
N J
NJ
D000818:Animals; D002470:Cell Survival; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D006136:GTP Cyclohydrolase / Q000037:antagonists & inhibitors / Q000502:physiology*; D007042:Hypoxanthines / Q000494:pharmacology; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism*; D008727:Methotrexate / Q000494:pharmacology; D051379:Mice; D009569:Nitric Oxide / Q000096:biosynthesis*; D009994:Osmolar Concentration; D011621:Pteridines / Q000494:pharmacology; D011622:Pterins
D007042:Hypoxanthines; D011621:Pteridines; D011622:Pterins; D009569:Nitric Oxide; C016727:sepiapterin; D006136:GTP Cyclohydrolase; C017202:2,4-diaminohypoxanthine; D008727:Methotrexate