Key Event Title
|Level of Biological Organization|
|endothelial cell of vascular tree|
Key Event Components
Key Event Overview
AOPs Including This Key Event
|AOP Name||Role of event in AOP|
|Homo sapiens||Homo sapiens||Moderate||NCBI|
|Bos taurus||Bos taurus||High||NCBI|
|Mus musculus||Mus musculus||High||NCBI|
|Rattus norvegicus||Rattus norvegicus||Low||NCBI|
|All life stages||Not Specified|
Key Event Description
Tetrahydrobiopterin (BH4) is an essential cofactor for a group of enzymes including aromatic acid hydroxylases, nitric oxide synthase (NOS) isoforms, and alkylglycerol monooxygenase (Wang et al., 2014). BH4 is synthesized from guanosine triphosphate through sequential reactions catalyzed by enzymes GTPCH-1, pyruvoyl tetrahydropterin synthase, and sepiapterin reductase (Tatham et al., 2009). During NOS catalysis, BH4 donates electrons to the ferrous-dioxygen complex in the oxygenase domain, leading to oxidation of L-arginine to N-hydroxy-Larginine and eventually conversion to citrulline and nitric oxide production (Chen et al., 2011; Crabtree et al., 2009). BH4 also stabilizes dimers of NOS isoforms, which is required for their enzymatic activity. When BH4 levels are decreased or limited, for example under oxidative stress conditions, BH4 can be oxidized to dihydrobiopterin (BH2) and then converted to biopterin. This reduction in BH4 availability results in NOS uncoupling where NOS is uncoupled from L-arginine oxidation and superoxide (or other reactive species) is produced rather than nitric oxide (Carnicer et al., 2012). Decreased BH4 have been demonstrated in a variety of vascular diseases such as hypertension, diabetes and atherosclerosis where endothelial dysfunction occurs.
How It Is Measured or Detected
Levels of BH4, BH2 and biopterin levels can be determined by reverse-phase high-performance liquid chromatography (HPLC) followed by electrochemical detection (for BH4) and fluorescence detection (for BH2 and biopterin) (Howells et al., 1986).
A LC-MS/MS method has been published by Zhao et al. (2009), which was validated for detection in human, monkey, dog, rabbit, rat and mouse plasma, and used to support a successful drug approval submission.
ELISA kits for BH4 are also commercially available.
In each case, care must be taken to protect the sample from oxidation, and BH4 is highly redox sensitive. Dithioerythritol is commonly used as a preservation agent.
Domain of Applicability
Decreased BH4 is observed in humans (Jayaram et al., 2015), cows (Abdelghany et al., 2017; Whitsett et al., 2007, Wang et al., 2008), mice (Adlam et al., 2012; Chuaiphichai et al., 2014; Crabtree et al., 2009; Tatham et al., 2009; Wang et al., 2008) and rats (Cervantes-Pérez et al., 2012).
Evidence for Perturbation by Stressor
AbdelGhany, T., Ismail, R., Elmahdy, M., Mansoor F, Zweier J, Lowe, F., and Zweier, JL. (2017). Cigarette Smoke Constituents Cause Endothelial Nitric Oxide Synthase Dysfunction and Uncoupling due to Depletion of Tetrahydrobiopterin with Degradation of GTP Cyclohydrolase. Nitric Oxide (Under review).
Adlam, D., Herring, N., Douglas, G., De Bono, J.P., Li, D., Danson, E.J., Tatham, A., Lu, C.-J., Jennings, K.A., Cragg, S.J., et al. (2012). Regulation of β-adrenergic control of heart rate by GTP-cyclohydrolase 1 (GCH1) and tetrahydrobiopterin. Cardiovasc. Res. 93, 694–701.
Carnicer, R., Hale, A.B., Suffredini, S., Liu, X., Reilly, S., Zhang, M.H., Surdo, N.C., Bendall, J.K., Crabtree, M.J., Lim, G.B.S., et al. (2012). Cardiomyocyte GTP cyclohydrolase 1 and tetrahydrobiopterin increase NOS1 activity and accelerate myocardial relaxation. Circ. Res. 111, 718–727.
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, W., Li, L., Brod, T., Saeed, O., Thabet, S., Jansen, T., Dikalov, S., Weyand, C., Goronzy, J., and Harrison, D.G. (2011). Role of increased guanosine triphosphate cyclohydrolase-1 expression and tetrahydrobiopterin levels upon T cell activation. J. Biol. Chem. 286, 13846–13851.
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.
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.
Howells, D.W., Smith, I., and Hyland, K. (1986). Estimation of tetrahydrobiopterin and other pterins in cerebrospinal fluid using reversed-phase high-performance liquid chromatography with electrochemical and fluorescence detection. J. Chromatogr. 381, 285–294.
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.
Tatham, A.L., Crabtree, M.J., Warrick, N., Cai, S., Alp, N.J., and Channon, K.M. (2009). GTP cyclohydrolase I expression, protein, and activity determine intracellular tetrahydrobiopterin levels, independent of GTP cyclohydrolase feedback regulatory protein expression. J. Biol. Chem. 284, 13660–13668.
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.
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.
Zhao Y, Cao J, Chen YS, Zhu Y, Patrick C, Chien B, Cheng A, Foehr ED. Detection of tetrahydrobiopterin by LC-MS/MS in plasma from multiple species. Bioanalysis. 2009;1(5):895-903.