Effects of valproic acid on organic acid metabolism in children: a metabolic profiling study.

Young children are at increased risk for valproic acid (VPA) hepatotoxicity. Urinary organic acid profiles, as a surrogate of mitochondrial function, were obtained in children 1.9 to 17.3 years of age (n = 52) who were undergoing treatment with VPA for seizure disorders. Age-matched patients receiving treatment with carbamazepine (CBZ; n = 50) and healthy children not undergoing treatment (n = 22) served as controls. Age-related changes in organic acid profiles were observed in all three groups. Although the untreated and CBZ control groups were indistinguishable from each other with respect to the principal-component analysis (PCA) score plots of the subjects, a distinct boundary was apparent between the VPA and each of the control groups. Interindividual variability was observed in the VPA-induced alterations in endogenous pathways corresponding to branched-chain amino acid metabolism and oxidative stress. The data suggest that more detailed metabolomic analysis may provide novel insights into biological mechanisms and predictive biomarkers for children at highest risk for serious toxicity.

CYP1B1 expression in rat testis and Leydig cells is not inducible by aryl hydrocarbon receptor agonists.

1. Cytochrome P450 1B1 (CYP1B1) is highly expressed in testis, but there is conflicting information regarding the inducibility of testicular CYP1B1 by aryl hydrocarbon receptor (AhR) agonists. 2. To assess AhR-mediated regulation, testicular CYP1B1 expression was measured following treatment of adult rats with 3-methylcholanthrene and various dosages of benzo[a]pyrene and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The effect of TCDD on CYP1B1 expression in R2C rat Leydig and MA-10 mouse Leydig cells in culture was also determined. 3. Immunoblot analysis showed that treatment with benzo[a]pyrene at dosages up to 200 mg/kg/day and 3-methylcholanthrene at 25 mg/kg/day did not induce testicular CYP1B1 expression. Treatment with TCDD at dosages of 1, 5 or 100 microg/kg had no effect, but testicular CYP1B1 protein levels were increased by approximately 50% at dosages of 10 and 50 microg/kg. 4. CYP1B1 mRNA levels in MA-10 and CYP1B1 protein levels in R2C cells were not induced by exposure to TCDD (10-1000 nM). 5. Overall, the results indicate that rodent testicular CYP1B1 is not inducible by AhR agonists.

Role of individual human cytochrome P450 enzymes in the in vitro metabolism of hydromorphone.

1. The aim was to identify the individual human cytochrome P450 (CYP) enzymes responsible for the in vitro N-demethylation of hydromorphone and to determine the potential effect of the inhibition of this metabolic pathway on the formation of other hydromorphone metabolites. 2. Hydromorphone was metabolized to norhydromorphone (apparent Km = 206 - 822 microM, Vmax = 104 - 834 pmol min(-1) mg(-1) protein) and dihydroisomorphine (apparent Km = 62 - 557 microM, Vmax = 17 - 122 pmol min(-1) mg(-1) protein) by human liver microsomes. 5. In pooled human liver microsomes, troleandomycin, ketoconazole and sulfaphenazole reduced norhydromorphone formation by an average of 45, 50 and 25%, respectively, whereas furafylline, quinidine and omeprazole had no effect. In an individual liver microsome sample with a high CYP3A protein content, troleandomycin and ketoconazole inhibited norhydromorphone formation by 80%. 5. The reduction in norhydromorphone formation by troleandomycin and ketoconazole was accompanied by a stimulation in dihydroisomorphine production. Recombinant CYP3A4, CYP3A5, CYP2C9 and CYP2D6, but not CYP1A2, catalysed norhydromorphone formation, whereas none of these enzymes was active in dihydroisomorphine formation. 6. In summary, CYP3A and, to a lesser extent, CYP2C9 catalysed hydromorphone N-demethylation in human liver microsomes. The inhibition of norhydromorphone formation by troleandomycin and ketoconazole resulted in a stimulation of microsomal dihydroisomorphine formation.

Influence of CYP2C9 genotypes on the formation of a hepatotoxic metabolite of valproic acid in human liver microsomes.

The present study investigated the effect of cytochrome P450 2C9 (CYP2C9) genetic polymorphism on the biotransformation of valproic acid (VPA) to its hepatotoxic metabolite, 4-ene-VPA, and compared that to the formation of the inactive 4-OH-VPA and 5-OH-VPA. cDNA-expressed CYP2C9(*)2 and CYP2C9(*)3 variants were less efficient than the CYP2C9(*)1 wild type in catalyzing the formation of these metabolites, as assessed by the ratio of Vmax and apparent Km (in vitro intrinsic clearance). The reduced efficiency by CYP2C9(*)2 was due to a reduced Vmax, whereas, in the case of CYP2C9(*)3, it was the result of increased apparent Km. The formation rates of 4-ene-VPA, 4-OH-VPA, and 5-OH-VPA in human liver microsomes were reduced by 29, 28, and 31%, respectively, in samples with one mutated CYP2C9 allele, and by 61, 73, and 58%, respectively, in samples with two mutated CYP2C9 alleles. Overall, the homozygote and heterozygote CYP2C9(*)2 and CYP2C9(*)3 genotypes may compromise hepatic VPA biotransformation.