Tetrahydrobiopterin

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Tetrahydrobiopterin
Tetrahydrobiopterin structure.png
Systematic (IUPAC) name
(6R)-2-Amino-6-[(1R,2S)-1,2-dihydroxypropyl]-5,6,7,8-tetrahydropteridin-4(1H)-one
Clinical data
Licence data US FDA:link
Pregnancy
category
  • US: C (Risk not ruled out)
Legal status
Routes of
administration
Oral
Pharmacokinetic data
Biological half-life 4 hours (healthy adults)
6–7 hours (PKU patients)
Identifiers
CAS Number 17528-72-2 YesY
ATC code A16AX07 (WHO)
PubChem CID: 44257
IUPHAR/BPS 5276
DrugBank DB00360 YesY
ChemSpider 40270 YesY
ChEBI CHEBI:59560 YesY
ChEMBL CHEMBL1201774 N
Chemical data
Formula C9H15N5O3
Molecular mass 241.25 g/mol
  • O=C2\N=C(/NC=1NC[C@@H](NC=12)[C@@H](O)[C@@H](O)C)N
  • InChI=1S/C9H15N5O3/c1-3(15)6(16)4-2-11-7-5(12-4)8(17)14-9(10)13-7/h3-4,6,12,15-16H,2H2,1H3,(H4,10,11,13,14,17)/t3-,4+,6-/m0/s1 YesY
  • Key:FNKQXYHWGSIFBK-RPDRRWSUSA-N YesY
 NYesY (what is this?)  (verify)

Tetrahydrobiopterin (BH4, THB, trade name Kuvan) or sapropterin (INN) is a naturally occurring essential cofactor of the three aromatic amino acid hydroxylase enzymes, used in the degradation of amino acid phenylalanine and in the biosynthesis of the neurotransmitters serotonin (5-hydroxytryptamine, 5-HT), melatonin, dopamine, norepinephrine (noradrenaline), epinephrine (adrenaline), and is a cofactor for the production of nitric oxide (NO) by the nitric oxide synthases.[1] Chemically, its structure is that of a reduced pteridine derivative.

History

Tetrahydrobiopterin was discovered to play a role as an enzymatic cofactor. The first enzyme found to use tetrahydrobiopterin is phenylalanine hydroxylase (PAH).[2]

Biosynthesis

Tetrahydrobiopterin is biosynthesized from guanosine triphosphate (GTP) by three chemical reactions mediated by the enzymes GTP cyclohydrolase I (GTPCH), 6-pyruvoyltetrahydropterin synthase (PTPS), and sepiapterin reductase (SR).[3]

Functions

Tetrahydrobiopterin has the following responsibilities as a cofactor:

Tetrahydrobiopterin has multiple roles in human biochemistry. One is to convert amino acids such as phenylalanine, tyrosine, and tryptophan to precursors of dopamine and serotonin, major monoamine neurotransmitters. Due to its role in the conversion of L-tyrosine into L-dopa, which is the precursor for dopamine, a deficiency in tetrahydrobiopterin can cause severe neurological issues unrelated to a toxic buildup of L-phenylalanine; dopamine is a vital neurotransmitter, and is the precursor of norepinephrine and epinephrine. Thus, a deficiency of BH4 can lead to systemic deficiencies of dopamine, norepinephrine, and epinephrine. In fact, one of the primary conditions that can result from GTPCH-related BH4 deficiency is dopamine-responsive dystonia;[4] currently, this condition is typically treated with carbidopa/levodopa, which directly restores dopamine levels within the brain.

BH4 also serves as a catalyst for the production of nitric oxide. Among other things, nitric oxide is involved in vasodilation, which improves systematic blood flow. The role of BH4 in this enzymatic process is so critical that some research points to a deficiency of BH4 – and thus, of nitric oxide – as being a core cause of the neurovascular dysfunction that is the hallmark of circulation-related diseases such as diabetes.[5]

Clinical usage

Phenylketonuria

A deficit in tetrahydrobiopterin biosynthesis and/or regeneration can result in phenylketonuria (PKU) from excess L-phenylalanine concentrations or hyperphenylalaninemia (HPA), as well as monoamine and nitric oxide neurotransmitter deficiency or chemical imbalance. The chronic presence of PKU can result in severe brain damage, including symptoms of mental retardation, microcephaly, speech impediments such as stuttering, slurring, and lisps, seizures or convulsions, and behavioral abnormalities, among other effects.

Tetrahydrobiopterin, developed by BioMarin under the brand name Kuvan and approved by the United States (U.S.) Food and Drug Administration (FDA) on December 13, 2007 and European Medicines Agency (EMA) in 2008, is a synthetic preparation of the dihydrochloride salt of the substance containing ascorbic acid, used in the treatment of PKU and tetrahydrobiopterin deficiencies.[6] Sapropterin is the first non-dietary treatment for patients with PKU that has been shown in randomized, double-blind trials to be effective in lowering blood phenylalanine levels.[7]

Cardiovascular disease

Since NO production is important in regulation of blood pressure and blood flow, thereby playing a significant role in cardiovascular diseases, tetrahydrobiopterin is a potential therapeutic target. In the endothelial cell lining of blood vessels, endothelial NOS is dependent on tetrahydrobiopterin availability.[8] Increasing tetrahydrobiopterin in endothelial cells by augmenting the levels of the biosynthetic enzyme GTPCH can maintain endothelial NOS function in experimental models of disease states such as diabetes,[9] atherosclerosis, and hypoxic pulmonary hypertension.[10] However, treatment of patients with existing coronary artery disease with oral tetrahydrobiopterin is limited by oxidation of tetrahydrobiopterin to the inactive form, dihydrobiopterin, with little benefit on vascular function .[11]

Tetrahydrobiopterin may be of benefit in the management and treatment of intractable diastolic heart failure, based on research in mice. There are fewer ways to manage systolic heart failure than for diastolic heart failure.[12]

Research

Other than PKU studies, tetrahydrobiopterin has participated in clinical trials studying other approaches to solving conditions resultant from a deficiency of tetrahydrobiopterin. These include autism, ADHD, hypertension, endothelial dysfunction, and chronic kidney disease.[13][14] As of September 2010, no results are available. Experimental studies suggest that tetrahydrobiopterin regulates deficient production of nitric oxide in cardiovascular disease states, and contributes to the response to inflammation and injury, for example in pain due to nerve injury.

Autism

In 1997, a small pilot study was published on the efficacy of tetrahydrobiopterin (BH4) on relieving the symptoms of autism, which concluded that it "might be useful for a subgroup of children with autism" and that double-blind trials are needed, as are trials which measure outcomes over a longer period of time.[15] In 2010, Frye et al. published a paper which concluded that it was safe, and also noted that "several clinical trials have suggested that treatment with BH4 improves ASD symptomatology in some individuals."[16]

Adverse effects

The most common adverse effects, observed in more than 10% of patients, include headache and a running or obstructed nose. Diarrhea and vomiting are also relatively common, seen in at least 1% of patients.[17]

Interactions

No interaction studies have been conducted. Because of its mechanism, tetrahydrobiopterin might interact with dihydrofolate reductase inhibitors like methotrexate and trimethoprim, and NO-enhancing drugs like nitroglycerin, molsidomine, minoxidil, and PDE5 inhibitors. Combination of tetrahydrobiopterin with levodopa can lead to increased excitability.[17]

See also

References

  1. The role of nitric oxide in the hypothalamic control of LHRH and oxytocin release, sexual behavior and aging of the LHRH and oxytocin neurons; FOLIA HISTOCHEMICA ET CYTOBIOLOGICA; Author: Jarosław Całka; Department of Functional Morphology, Division of Animal Anatomy, University of Warmia and Mazury, Olsztyn, Poland; 2005; page 4
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  13. ClinicalTrials.gov: Search results for Kuvan
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External links