LC-MS/MS methods for direct measurement of sepiapterin and tetrahydrobiopterin in human plasma and clinical applications.

Aim: Tetrahydrobiopterin (BH 4 ), a natural cofactor of aromatic amino acid hydroxylases, and sepiapterin, a natural precursor of BH 4 , are endogenously present in human plasma. This is the first report on methods for direct quantification of sepiapterin and BH 4 in human plasma by LC-MS/MS for pharmacokinetic assessment . Materials & methods: The analytes in plasma were harvested from blood that were treated with 10% ascorbic acid (AA) to a final concentration of 1% AA. Results & conclusion: The quantification methods were validated for calibration ranges of 0.75-500 ng/ml and 0.5-500 ng/ml for sepiapterin and BH 4 , respectively. Quantification of analytes was challenging due to their susceptibility to redox reactions. The validated methods were utilized successfully to support clinical development of sepiapterin.