Increasing dihydrobiopterin causes dysfunction of endothelial nitric oxide synthase in rats in vivo

• Published in: American journal of physiology. Heart and circulatory physiology Vol. 301; no. 3; pp. H721 - H729
• Main Authors: Noguchi, Katsuhiko, Hamadate, Naobumi, Matsuzaki, Toshihiro, Sakanashi, Mayuko, Nakasone, Junko, Uchida, Taro, Arakaki, Kumiko, Kubota, Haruaki, Ishiuchi, Shogo, Masuzaki, Hiroaki, Sugahara, Kazuhiro, Ohya, Yusuke, Sakanashi, Matao, Tsutsui, Masato
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 01.09.2011
• Subjects: Acetylcholine - pharmacology; Analysis of Variance; Animals; Biopterins - analogs & derivatives; Biopterins - metabolism; Blood Pressure - drug effects; Cardiovascular system; Cells; Dose-Response Relationship, Drug; Endothelium, Vascular - drug effects; Endothelium, Vascular - enzymology; Endothelium, Vascular - physiopathology; Folic Acid Antagonists - pharmacology; Hypertension; Male; Methotrexate - administration & dosage; Nitric oxide; Nitric Oxide - metabolism; Nitric Oxide Donors - pharmacology; Nitric Oxide Synthase Type III - metabolism; Nitroprusside - pharmacology; Oxidation-Reduction; Phosphorylation; Physiology; Protein Multimerization; Pterins - administration & dosage; Pterins - metabolism; Rats; Rats, Wistar; Rodents; Superoxide Dismutase - metabolism; Superoxides - metabolism; Tetrahydrofolate Dehydrogenase - metabolism; Up-Regulation; Vasodilation - drug effects; Vasodilator Agents - pharmacology
• DOI: 10.1152/ajpheart.01089.2010
• ISSN: 0363-6135

An elevation of oxidized forms of tetrahydrobiopterin (BH(4)), especially dihydrobiopterin (BH(2)), has been reported in the setting of oxidative stress, such as arteriosclerotic/atherosclerotic disorders, where endothelial nitric oxide synthase (eNOS) is dysfunctional, but the role of BH(2) in the regulation of eNOS activity in vivo remains to be evaluated. This study was designed to clarify whether increasing BH(2) concentration causes endothelial dysfunction in rats. To increase vascular BH(2) levels, the BH(2) precursor sepiapterin (SEP) was intravenously given after the administration of the specific dihydrofolate reductase inhibitor methotrexate (MTX) to block intracellular conversion of BH(2) to BH(4). MTX/SEP treatment did not significantly affect aortic BH(4) levels compared with control treatment. However, MTX/SEP treatment markedly augmented aortic BH(2) levels (291.1 ± 29.2 vs. 33.4 ± 6.4 pmol/g, P < 0.01) in association with moderate hypertension. Treatment with MTX alone did not significantly alter blood pressure or BH(4) levels but decreased the BH(4)-to-BH(2) ratio. Treatment with MTX/SEP, but not with MTX alone, impaired ACh-induced vasodilator and depressor responses compared with the control treatment (both P < 0.05) and also aggravated ACh-induced endothelium-dependent relaxations (P < 0.05) of isolated aortas without affecting sodium nitroprusside-induced endothelium-independent relaxations. Importantly, MTX/SEP treatment significantly enhanced aortic superoxide production, which was diminished by NOS inhibitor treatment, and the impaired ACh-induced relaxations were reversed with SOD (P < 0.05), suggesting the involvement of eNOS uncoupling. These results indicate, for the first time, that increasing BH(2) causes eNOS dysfunction in vivo even in the absence of BH(4) deficiency, demonstrating a novel insight into the regulation of endothelial function.