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Decrease, Tetrahydrobiopterin leads to Uncoupling, eNOS
Key Event Relationship Overview
AOPs Referencing Relationship
Life Stage Applicability
|All life stages||High|
Key Event Relationship Description
Oxidative stress leads to the excessive oxidation and depletion of BH4, resulting in eNOS uncoupling where eNOS produces superoxide rather than nitric oxide (Förstermann and Münzel, 2006).
Evidence Supporting this KER
BH4 is an essential cofactor for eNOS and is required for its enzymatic activity to produce NO. The depletion of BH4 leading to eNOS uncoupling is well-studied, thus there is strong biological plausibility for this link.
Two mouse studies showed limited BH4 availability induced eNOS uncoupling by reducing eNOS activity, leading to decreased nitric oxide and increased superoxide. In the mouse endothelial cell line sEnd.1, BH4 deficiency induced eNOS uncoupling as determined by superoxide production and impaired vasodilation (Crabtree et al., 2009). In primary aortic endothelial cells of GTPCH1-knockout mice, BH4 depletion significantly reduced eNOS activity, increased basal superoxide production and decreased NO bioactivity (Chuaiphichai et al., 2014). In rat hearts, BH4 content and eNOS activity were decreased in a time-dependent manner following myocardial ischemia with a marked decline after thirty minutes, while superoxide generation increased (Dumitrescu et al., 2007).
BAECs undergoing hypoxia and reoxygenation had decreased BH4 and decreased NO production, which was partially restored by treatment with the xanthine oxidase inhibitor oxypurinol, N-acetyl-l-cysteine (NAC) and NAC+BH4 (De Pascali et al., 2014). Inhibition of BH4 due to treatment with 4-HNE decreased eNOS activity and NO production in BAECs (Whitsett et al., 2007).
Many studies demonstrated that BH4 treatment reduced eNOS-mediated superoxide generation and increased NO formation in bovine, mouse, and rat endothelium (Chen et al., 2011; De Pascali et al., 2014; Landmesser et al., 2003; Ozaki et al., 2002; Shinozaki et al., 2000). Clinical studies reported improvement endothelial function in cardiovascular disease after treatment with BH4 (Wang et al., 2014). Oral treatment with BH4 in hypertensive patients significantly decreased blood pressure.
Uncertainties and Inconsistencies
The uncoupling of eNOS may also occur through other mechanisms such as S-glutathionylation of eNOS and depletion of L-arginine (Zweier et al., 2011).
Known modulating factors
Known Feedforward/Feedback loops influencing this KER
Domain of Applicability
The relationship between BH4 depletion and eNOS uncoupling was observed in humans (Jayaram et al., 2015), cows (Wang et al., 2008; Whitsett et al., 2007), mice (Chuaiphichai et al., 2014; Crabtree et al., 2009) and rats (Cervantes-Pérez et al., 2012; Dumitrescu et al., 2007).
Cervantes-Pérez, L.G., Ibarra-Lara, M. de la L., Escalante, B., Del Valle-Mondragón, L., Vargas-Robles, H., Pérez-Severiano, F., Pastelín, G., and Sánchez-Mendoza, M.A. (2012). Endothelial nitric oxide synthase impairment is restored by clofibrate treatment in an animal model of hypertension. Eur. J. Pharmacol. 685, 108–115.
Chen, C.-A., Lin, C.-H., Druhan, L.J., Wang, T.-Y., Chen, Y.-R., and Zweier, J.L. (2011). Superoxide induces endothelial nitric-oxide synthase protein thiyl radical formation, a novel mechanism regulating eNOS function and coupling. J. Biol. Chem. 286, 29098–29107.
Chuaiphichai, S., McNeill, E., Douglas, G., Crabtree, M.J., Bendall, J.K., Hale, A.B., Alp, N.J., and Channon, K.M. (2014). Cell-autonomous role of endothelial GTP cyclohydrolase 1 and tetrahydrobiopterin in blood pressure regulation. Hypertension 64, 530–540.
Crabtree, M.J., Tatham, A.L., Al-Wakeel, Y., Warrick, N., Hale, A.B., Cai, S., Channon, K.M., and Alp, N.J. (2009). Quantitative regulation of intracellular endothelial nitric-oxide synthase (eNOS) coupling by both tetrahydrobiopterin-eNOS stoichiometry and biopterin redox status: insights from cells with tet-regulated GTP cyclohydrolase I expression. J. Biol. Chem. 284, 1136–1144.
De Pascali, F., Hemann, C., Samons, K., Chen, C.-A., and Zweier, J.L. (2014). Hypoxia and reoxygenation induce endothelial nitric oxide synthase uncoupling in endothelial cells through tetrahydrobiopterin depletion and S-glutathionylation. Biochemistry (Mosc.) 53, 3679–3688.
Dumitrescu, C., Biondi, R., Xia, Y., Cardounel, A.J., Druhan, L.J., Ambrosio, G., and Zweier, J.L. (2007). Myocardial ischemia results in tetrahydrobiopterin (BH4) oxidation with impaired endothelial function ameliorated by BH4. Proc. Natl. Acad. Sci. U. S. A. 104, 15081–15086.
Förstermann, U., and Münzel, T. (2006). Endothelial nitric oxide synthase in vascular disease: from marvel to menace. Circulation 113, 1708–1714.
Jayaram, R., Goodfellow, N., Zhang, M.H., Reilly, S., Crabtree, M., De Silva, R., Sayeed, R., and Casadei, B. (2015). Molecular mechanisms of myocardial nitroso-redox imbalance during on-pump cardiac surgery. Lancet Lond. Engl. 385 Suppl 1, S49.
Landmesser, U., Dikalov, S., Price, S.R., McCann, L., Fukai, T., Holland, S.M., Mitch, W.E., and Harrison, D.G. (2003). Oxidation of tetrahydrobiopterin leads to uncoupling of endothelial cell nitric oxide synthase in hypertension. J. Clin. Invest. 111, 1201–1209.
Ozaki, M., Kawashima, S., Yamashita, T., Hirase, T., Namiki, M., Inoue, N., Hirata, K., Yasui, H., Sakurai, H., Yoshida, Y., et al. (2002). Overexpression of endothelial nitric oxide synthase accelerates atherosclerotic lesion formation in apoE-deficient mice. J. Clin. Invest. 110, 331–340.
Shinozaki, K., Nishio, Y., Okamura, T., Yoshida, Y., Maegawa, H., Kojima, H., Masada, M., Toda, N., Kikkawa, R., and Kashiwagi, A. (2000). Oral administration of tetrahydrobiopterin prevents endothelial dysfunction and vascular oxidative stress in the aortas of insulin-resistant rats. Circ. Res. 87, 566–573.
Wang, Q., Yang, M., Xu, H., and Yu, J. (2014). Tetrahydrobiopterin improves endothelial function in cardiovascular disease: a systematic review. Evid.-Based Complement. Altern. Med. ECAM 2014, 850312.
Wang, S., Xu, J., Song, P., Wu, Y., Zhang, J., Chul Choi, H., and Zou, M.-H. (2008). Acute inhibition of guanosine triphosphate cyclohydrolase 1 uncouples endothelial nitric oxide synthase and elevates blood pressure. Hypertension 52, 484–490.
Whitsett, J., Picklo, M.J., and Vasquez-Vivar, J. (2007). 4-Hydroxy-2-nonenal increases superoxide anion radical in endothelial cells via stimulated GTP cyclohydrolase proteasomal degradation. Arterioscler. Thromb. Vasc. Biol. 27, 2340–2347.