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Sepiapterin: From sapropterin to next-generation therapy
1Divisions of Metabolism, University Children's Hospital, Zürich, Switzerland.
Molecular Genetics and Metabolism
|May 12, 2026
Summary
Oral sepiapterin effectively increases tetrahydrobiopterin (BH4) levels in healthy individuals and shows promise in treating phenylketonuria (PKU). Sepiapterin demonstrates superior efficacy compared to sapropterin in reducing blood phenylalanine levels in PKU patients.
Area of Science:
- Biochemistry
- Pharmacology
- Genetics
Background:
- Tetrahydrobiopterin (BH4) is a crucial cofactor for enzymes like phenylalanine hydroxylase (PAH) and nitric oxide synthases.
- BH4 homeostasis involves de novo synthesis, recycling, and salvage pathways, with sepiapterin serving as a key precursor.
- 7,8-dihydrobiopterin (BH2) impacts BH4-dependent signaling and reflects pterin redox balance.
Purpose of the Study:
- To review the biochemical and clinical understanding of BH4 homeostasis.
- To evaluate sepiapterin as a precursor for BH4 and its therapeutic potential.
- To compare the efficacy of sepiapterin and sapropterin in managing phenylketonuria (PKU).
Main Methods:
- Integration of historical, chemical, biochemical, and clinical data on BH4.
- Assessment of sepiapterin uptake and intracellular conversion to BH4.
- Clinical trials (APHENITY and AMPLIPHY) evaluating sepiapterin's effect on blood phenylalanine levels in PKU patients.
Main Results:
- Oral sepiapterin administration leads to significant systemic BH4 exposure and increased cerebrospinal fluid BH4 levels in healthy volunteers.
- In PKU patients, sepiapterin significantly reduced blood phenylalanine levels.
- Sepiapterin demonstrated greater efficacy than sapropterin in lowering phenylalanine levels in PKU.
Conclusions:
- Sepiapterin is a promising therapeutic agent for BH4 deficiencies and PKU, potentially serving as a next-step therapy beyond sapropterin.
- Biomarker studies quantifying BH4, BH2, and their ratio are essential for understanding BH4 homeostasis and treatment response.
- Sepiapterin's mechanism involves cellular uptake and intracellular conversion, expanding BH4 pools effectively.
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