Determination of urinary valproylcarnitine by gas chromatography-mass spectrometry with selected-ion monitoring

Evaluation of valproate effects on acylcarnitine in epileptic children by LC-MS/MS

BACKGROUND

Valproate (VPA) is a simple fatty acid and a substrate for the fatty acid β-oxidation pathway. Previous data suggested that the toxicity of VPA may be provoked by carnitine deficiency and the inhibition of mitochondrial β-oxidation.

OBJECTIVE

The aim of the present study was to elucidate the effect of VPA treatment on carnitine and isomer-differentiated acylcarnitine disposition, and determined the relationships between acylcarnitines and blood VPA levels in long-term treated patients with VPA and/or other antiepileptic drugs.

METHODS

Serum samples were obtained from children aged 1-15 years old treated for at least 6 months with VPA alone (n=28) or VPA combined with other anticonvulsants (n=23) and untreated controls (n=23). Serum acylcarnitines were separated from their isomers and quantified using high-performance liquid chromatography-tandem mass spectrometry.

RESULTS

We found higher 3-hydroxyisovalerylcarnitine levels and trace amounts of valproylcarnitine in both VPA monotherapy and polytherapy patients. Other acylcarnitines, hexanoylcarnitine, C12, C14:1-carnitines and the ratio of long-chain acylcarnitine to free carnitine were also higher in VPA polytherapy individuals than in controls. VPA monotherapy does not result in decreases in free carnitine or in the accumulation of long-chain acylcarnitines. Blood VPA concentrations correlated positively with hexanoylcarnitine, C12, C14:1, C16:1, C18:1-carnitines in all VPA-treated children (n=51).

CONCLUSION

Long-term VPA treatment in pediatric patients could affect some specific acylcarnitines, which is enhanced by the concomitant use of other anticonvulsants, and the formation of valproylcarnitine alone seems insufficient to develop severe carnitine deficiency at therapeutic doses of VPA.

Metabolic activation of carboxylic acids

BACKGROUND

Carboxylic acids constitute a large and heterogeneous class of both endogenous and xenobiotic compounds. A number of carboxylic acid drugs have been associated with adverse reactions, linked to the metabolic activation of the carboxylic acid moiety of the compounds, i.e., formation of acyl-glucuronides and acyl-CoA thioesters.

OBJECTIVE

The objective is to give an overview of the current knowledge on metabolic activation of carboxylic acids and how such metabolites may play a role in adverse reactions and toxicity.

METHODS

Literature concerning the formation and disposition of acyl glucuronides and acyl-CoA thioesters was searched. Also included were papers on the chemical reactivity of acyl glutathione-thioesters, and literature concerning possible links between metabolic activation of carboxylic acids and reported cellular and clinical effects.

RESULTS/CONCLUSION

This review demonstrates that metabolites of carboxylic acid drugs must be considered chemically reactive, and that the current knowledge about metabolic activation of this compound class can be a good starting-point for further studies on the consequences of chemically reactive metabolites.

Determination of valproic acid in human serum and pharmaceutical preparations by headspace liquid-phase microextraction gas chromatography-flame ionization detection without prior derivatization

An efficient and fast extraction technique for the enrichment of valproic acid from human blood serum samples using the headspace liquid phase microextraction (HS-LPME) combined with gas chromatography (GC) analysis has been developed. The extraction was conducted by suspending a 2 microL drop of organic solvent in a 1 mL serum sample; following 20 min of extraction, withdrawing organic solvent into a syringe and injection into a GC with a flame ionization detector (FID), without any further pre-treatment. Four organic solvents, 1-decanole, benzyl alcohol, 1-octanol and n-dodecane, were studied as extractants, and n-dodecane was found to be the most sensitive solvent for valproic acid. The results revealed that HS-LPME is suitable for the successful extraction of valproic acid from human blood serum samples. Parameters like extraction time, ionic strength, pH, organic solvent volume, and temperature of the sample were studied and optimized to obtain the best extraction results. An enrichment factor of 27-fold was achieved in 20 min. The procedure resulted in a relative standard deviation of <13.2% (n=7) and a linear calibration range from 2 to 20 microg mL(-1) (r>0.98), and the limit of detection was 0.8 microg mL(-1) in serum blank samples. Overall, LPME proved to be a fast, sensitive and simple tool for the preconcentration of valproic acid from real samples. The proposed method was also applied to the analysis of valproate in pharmaceutical preparations.

Effect of L-carnitine supplementation on acute valproate intoxication

We analyzed urinary valproate (VPA) metabolites and carnitine concentrations in a child who accidentally ingested 400 mg/kg VPA. The concentration of 4-en VPA, the presumed major factor in VPA-induced hepatotoxicity, was markedly increased, without liver dysfunction or hyperammonemia. The other major abnormality was decreased beta-oxidation and markedly increased omega-oxidation. After L-carnitine supplementation, VPA metabolism returned to normal. The level of valproylcarnitine was not increased and therefore was not affected by L-carnitine. L-Carnitine may be useful in treating patients with coma after VPA overdose.