Target: BH4 acts as an essential cofactor for tyrosine hydroxylase (TH) and tryptophan hydroxylase (TPH). [1]

Hypothesis that treatment of hyperphenylalaninemic Pah(enu2/enu2) mice, a model of human PKU, with sapropterin dihydrochloride, a synthetic form of BH4, would stimulate TH and TPH activities leading to improved dopamine and serotonin synthesis despite persistently elevated brain phenylalanine. Sapropterin (20, 40, or 100mg/kg body weight in 1% ascorbic acid) was administered daily for 4 days by oral gavage to Pah(enu2/enu2) mice followed by measurement of brain biopterin, phenylalanine, tyrosine, tryptophan and monoamine neurotransmitter content. A significant increase in brain biopterin content was detected only in mice that had received the highest sapropterin dose, 100mg/kg. Blood and brain phenylalanine concentrations were unchanged by sapropterin therapy. Sapropterin therapy also did not alter the absolute amounts of dopamine and serotonin in brain but was associated with increased homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA), dopamine and serotonin metabolites respectively, in both wild type and Pah(enu2/enu2) mice. Oral sapropterin therapy likely does not directly affect central nervous system monoamine synthesis in either wild type or hyperphenylalaninemic mice but may stimulate synaptic neurotransmitter release and subsequent metabolism.[1]
In Sapropterin dihydrochloride‑treated Pah^enu2/enu2 (Pah −/−) mice and wild‑type (Pah +/+) mice: Significant increase in brain total biopterin content only at the highest dose (100 mg/kg), with peak at 2 h post‑gavage (22.8 ± 10.9 pmol/mg protein vs. untreated 9.9 ± 2.8 pmol/mg protein). [1]
Serum and brain phenylalanine concentrations remained unchanged by sapropterin treatment in both genotypes; the Pah −/− mice remained hyperphenylalaninemic (mean serum Phe 2591 ± 367 μM). [1]
Brain dopamine and serotonin absolute contents were not affected by sapropterin treatment. In untreated Pah −/− mice, dopamine was 145.4 ± 16.1 pmol/mg protein (∼54% of wild‑type), serotonin was 36.2 ± 4.5 pmol/mg protein (∼36% of wild‑type). [1]
Sapropterin treatment significantly increased brain homovanillic acid (HVA) and 5‑hydroxyindoleacetic acid (5‑HIAA), the metabolites of dopamine and serotonin respectively, in both genotypes (two‑way ANOVA, p < 0.01 for treatment effect). This suggests increased monoamine turnover without altered synthesis. [1]

sapropterin dihydrochloride was administered by gavage to hyperphenylalaninemic C57BL6-Pahenu2/enu2 mice (Pah−/−) or to wild type C57BL6 mice (Pah+/+) to evaluate the uptake of BH4 into brain and the effect of enteral BH4 administration upon brain monoamine neurotransmitter content. Sapropterin, 100 mg tablets, were dissolved in 1% ascorbic acid immediately prior to administration. The final sapropterin concentration was varied to yield different doses in identical volumes of solution to be administered to the mice. Mice received sapropterin (20, 40, or 100 mg/kg body weight) once daily for four days by gavage. A control group of mice received only 1% ascorbic acid vehicle without added sapropterin. During this period, the animals received standard mouse chow (21% protein by weight) and water ad libitum. On the fifth day, mice were euthanized at various time points following sapropterin administration for tissue harvest. During the time period between sapropterin gavage and euthanasia, mouse chow was withheld in order to minimize variability in blood amino acid concentrations caused by feeding. Animals were sedated using inhaled isoflurane anesthesia. Whole blood was collected by cardiac puncture, allowed to clot in an Eppendorf tube, and serum was separated by centrifugation. The mice were then euthanized by exsanguination and perfused with 20 ml normal saline via the left cardiac ventricle to clear blood from the cerebral circulation. Following decapitation, whole brain was rapidly excised from the cranium, split sagitally, and immediately submerged in liquid nitrogen. Half brains and serum samples were stored at −80°C until processing for amino acid or neurotransmitter analysis.[1]

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Animal model: C57BL6‑Pah^enu2/enu2 (Pah −/−) and wild‑type C57BL6 (Pah +/+) mice. [1]
Drug formulation: Sapropterin dihydrochloride tablets were dissolved in 1% ascorbic acid immediately before administration; concentration adjusted to deliver different doses in equal volume. [1]
Dosing regimen: Once daily by oral gavage at 20, 40, or 100 mg/kg body weight for 4 consecutive days. Control groups received 1% ascorbic acid vehicle only. [1]
Euthanasia and tissue collection: On day 5, after final gavage, mice were euthanized at various time points (up to 6 h). Food was withheld before euthanasia. Animals were anesthetized with isoflurane, blood collected by cardiac puncture, then perfused with 20 mL normal saline via left cardiac ventricle. Whole brain was rapidly excised, split sagittally, and frozen in liquid nitrogen. Half‑brains and serum stored at −80 °C. [1]

Brain penetration: Oral Sapropterin dihydrochloride at 100 mg/kg significantly increased brain total biopterin content, with a >2‑fold increase at 2 h post‑dose (22.8 ± 10.9 vs. 9.9 ± 2.8 pmol/mg protein). Lower doses (20 and 40 mg/kg) did not produce a statistically significant increase. Brain biopterin remained elevated above baseline for at least 6 h. [1]
No effect on serum or brain phenylalanine, tyrosine (except an unexplained effect at highest dose), or tryptophan (except a modest effect on serum tryptophan). [1]

High‑dose Sapropterin dihydrochloride (100 mg/kg/day for 4 days) was well tolerated in both wild‑type and Pah^enu2/enu2 mice; no overt signs of toxicity reported. [1]
No measurement of LD50, organ toxicity, or plasma protein binding provided. [1]

Mol Genet Metab. 2016 Jan;117(1):5-11.

Sapropterin hydrochloride is the dihydrochloride of sapropterin. It is used for the diagnosis and treatment of a variant of phenylketonuria (HPA) associated with tetrahydrobiopterin deficiency. It is a natural cofactor for phenylalanine hydroxylase, tyrosine hydroxylase, tryptophan hydroxylase, and nitric oxide synthase. It can be used both as a diagnostic reagent and as a coenzyme. It contains sapropterin.
See also: Sapropterin (with active fraction).

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Pharmacological Indications
Sapropterin dihydrochloride is indicated for the treatment of hyperphenylalaninemia (HPA) in adults and children of all ages with phenylketonuria (PKU), in whom this treatment has been shown to be effective. Sapropterin (Dipharma) is also indicated for the treatment of hyperphenylalaninemia (HPA) in patients of all ages with tetrahydrobiopterin (BH4) deficiency, in whom this treatment has been shown to be effective. Kuvan is indicated for the treatment of hyperphenylalaninemia (HPA) in patients with phenylketonuria (PKU) of all ages, and has been shown to be effective in this treatment. Kuvan is also indicated for the treatment of hyperphenylalaninemia (HPA) in patients with tetrahydrobiopterin (BH4) deficiency of all ages, and has been shown to be effective in this treatment. Treatment of Hyperphenylalaninemia

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Sapropterin dihydrochloride is the synthetic form of BH4, an essential cofactor for TH and TPH, the rate‑limiting enzymes in dopamine and serotonin synthesis. In PKU, elevated brain phenylalanine competitively inhibits TH and TPH, leading to monoamine deficiencies. This study tested whether high‑dose oral BH4 could overcome this inhibition. Although brain biopterin increased, absolute dopamine and serotonin levels did not change, but their metabolites HVA and 5‑HIAA increased, suggesting BH4 may stimulate synaptic release and metabolism of monoamines, possibly via a presynaptic BH4 receptor. The Pah^enu2/enu2 mouse model is not BH4‑responsive for blood phenylalanine lowering. This study used doses up to 5‑fold higher than typical human clinical doses. [1]

C9H17CL2N5O3

314.17

C, 34.41; H, 5.45; Cl, 22.57; N, 22.29; O, 15.28

69056-38-8

Tetrahydrobiopterin;17528-72-2;Sapropterin;62989-33-7

135409471

White to off-white solid powder

1.9±0.1 g/cm3

506.6±60.0 °C at 760 mmHg

260.2±32.9 °C

0.0±3.0 mmHg at 25°C

1.822

-4.22

8

6

2

19

405

3

Cl[H].Cl[H].O([H])[C@@]([H])([C@]([H])(C([H])([H])[H])O[H])[C@@]1([H])C([H])([H])N([H])C2=C(C(N([H])C(N([H])[H])=N2)=O)N1[H]

(6R)-2-Amino-6-((1R,2S)-1,2-dihydroxypropyl)-5,6,7,8-tetrahydro-4(1H)-pteridinone dihydrochloride

6R-BH4 dihydrochloride; 6R-Tetrahydro-L-biopterin dihydrochloride; Sapropterin HCl; BioMarin T 1401; Biopten; SN0588; SUN-0588; Tetrahydro-6-biopterin; Dapropterin; Phenoptin; THB; BPH4; 6R-BH4; Tetrahydrobiopterin, sapropterin; trade name Kuvan; Tetrahydrobiopterin Dihydrochloride, R-THBP Dihydrochloride

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: Please store this product in a sealed and protected environment (e.g. under nitrogen), avoid exposure to moisture.

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Solubility in Formulation 1: 100 mg/mL (318.30 mM) in PBS (add these co-solvents sequentially from left to right, and one by one), clear solution; with sonication.

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 (Please use freshly prepared in vivo formulations for optimal results.)