Self-protection of PC12 cells by 6R-tetrahydrobiopterin from nitric oxide toxicity.
Nitric oxide (NO) has cytotoxic effects but NO producing neurons are resistant to NO toxicity. These results suggest the presence of self-protecting factors for NO toxicity. Recently, 6R-tetrahydrobiopterin (6R-BH4), a cofactor for NO synthase (NOS), has been reported to degrade NO raising the possibility that 6R-BH4 acts as a self-protecting factor for NO toxicity. In PC12 cells which have NOS, three-day culture with sodium nitroprusside (SNP) or NOC-12, NO generators, at 10-100 microM increased nitrite and nitrate concentrations in the culture medium and induced death of PC12 cells. Coadministration of 6R-BH4 (10 or 30 microM) with SNP or NOC-12 prevented cell death with reduction of nitrite and nitrate in the medium. Inhibition of 6R-BH4 synthesis by 2,4-diamino-6-hydroxypyrimidine (DAHP), an inhibitor for GTP cyclohydrolase I, decreased cellular 6R-BH4 content and viable cell number. The inhibiting effects of DAHP were restored by exogenous 6R-BH4. NOS activity, as estimated by nitrite concentrations in the medium, was unchanged by DAHP. Hypoxanthine and xanthine oxidase, which produce superoxide, mimicked the cell-protecting effect of 6R-BH4 which is reported to generate superoxide during its autoxidation. These results suggest that 6R-BH4 acts as a self-protecting factor for NO toxicity with generation of superoxide in NO-producing neurons.
Koshimura
K
K
Department of Medicine, Shimane Medical University, Izumo, Japan.
Murakami
Y
Y
Tanaka
J
J
Kato
Y
Y
D000818:Animals; D001708:Biopterins / Q000031:analogs & derivatives* / Q000494:pharmacology; D006136:GTP Cyclohydrolase / Q000037:antagonists & inhibitors; D019271:Hypoxanthine / Q000494:pharmacology; D009363:Neoplasm Proteins / Q000378:metabolism; D018696:Neuroprotective Agents / Q000494:pharmacology*; D009566:Nitrates / Q000378:metabolism; D009569:Nitric Oxide / Q000633:toxicity*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I; D009573:Nitrites / Q000378:metabolism; D009599:Nitroprusside / Q000494:pharmacology; D010084:Oxidation-Reduction; D016716:PC12 Cells / Q000187:drug effects*; D051381:Rats; D013400:Sugar Acids / Q000494:pharmacology; D013481:Superoxides / Q000378:metabolism; D014969:Xanthine Oxidase / Q000494:pharmacology
C017182:5-dehydro-3-deoxy-D-arabino-heptulosonic acid-7-phosphate; D009363:Neoplasm Proteins; D018696:Neuroprotective Agents; D009566:Nitrates; D020030:Nitric Oxide Donors; D009573:Nitrites; D013400:Sugar Acids; D013481:Superoxides; D009599:Nitroprusside; D001708:Biopterins; D019271:Hypoxanthine; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; C496322:Nos1 protein, rat; D014969:Xanthine Oxidase; D006136:GTP Cyclohydrolase; C003402:sapropterin