Abstract
In this study, spectroscopic and chromatographic evidence is presented for the identification and characterization of the metabolites, valproyl glutamate (2-propylpentanoyl glutamate, VPA-GLU) and valproyl glutamine (2-propylpentanoyl glutamine, VPA-GLN) in the urine, serum, and cerebrospinal fluid (CSF) of patients on valproic acid (VPA) therapy. Moreover, the identification of valproyl glycine (2-propylpentanoyl glycine, VPA-GLY) in the serum and urine of patients on VPA, albeit in trace concentrations, is also reported here. The three amino acid conjugates excreted in urine accounted for about 1% of the VPA dose in four patients who were on VPA therapy chronically and had reached steady state. VPA-GLU was quantitatively the most prominent metabolite (0.66–13.1 μg/mg creatinine) compared with VPA-GLN (0.78–9.93 μg/mg creatinine) and VPA-GLY (trace-1.0 μg/mg creatinine) in overnight urine samples of all patients studied (n = 29). The relatively low serum concentrations of the three amino acid conjugates of VPA in six patients suggest that the metabolites are readily excreted once formed. In contrast, whereas VPA GLY was absent in the CSF of one patient on VPA, the concentrations of VPA-GLU and VPA-GLN in this CSF sample were 9 and 5 times, respectively, their corresponding serum concentrations.
Footnotes
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↵1 Current address: Department of Drug Metabolism, Johnson & Johnson Pharmaceutical Research and Development, Spring House, PA, 19477
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↵2 Current address: Department of Drug Metabolism, Merck & Co., Rahway, NJ 07065-0900.
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This work was supported by a program grant from the Medical Research Council of Canada and a program grant from the Medical Research Council of Canada, and was part of the doctoral dissertation of Gopaul (1998). A preliminary account of these studies was presented at the 6th European ISSX meeting, 1997 June 30–July 3, Gothenburg, Sweden.
- Abbreviations used are::
- VPA
- valproic acid
- VPA-GLY
- valproyl glycine (2-propylpentanoyl glycine)
- LC-MS/MS
- liquid-chromatography tandem mass-spectrometry
- GC-MS
- gas-chromatography mass-spectrometry
- CSF
- cerebrospinal fluid
- PFBBr
- 1-bromo-2,3,4,5,6-pentafluorotoluene
- DIPEA
- diisopropylethylamine
- TFA
- trifluoroacetic acid
- IS
- internal standard
- GC-MS NICI
- gas chromatography in negative ion chemical ionization
- MS
- mass spectrometer
- HPLC
- high performance liquid chromatography
- MRM
- multiple reaction monitoring
- CID
- collision-induced dissociation
- FVPA-GLN
- 2-fluoro valproyl glutamine
- VPA-GLN
- valproyl glutamine (2-propylpentanoyl glutamine)
- VPA-GLU
- valproyl glutamate (2-propylpentanoyl glutamate)
- VPA-ASP
- valproyl aspartate
- PFB
- pentafluorobenzyl
- Received September 3, 2002.
- Accepted October 7, 2002.
- The American Society for Pharmacology and Experimental Therapeutics
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