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A pro-convulsive carbamazepine metabolite: quinolinic acid in drug resistant epileptic human brain.

ABSTRACT: Drugs and their metabolites often produce undesirable effects. These may be due to a number of mechanisms, including biotransformation by P450 enzymes which are not exclusively expressed by hepatocytes but also by endothelial cells in brain from epileptics. The possibility thus exists that the potency of systemically administered central nervous system therapeutics can be modulated by a metabolic blood-brain barrier (BBB). Surgical brain specimens and blood samples (ex vivo) were obtained from drug-resistant epileptic subjects receiving the antiepileptic drug carbamazepine prior to temporal lobectomies. An in vitro blood-brain barrier model was then established using primary cell culture derived from the same brain specimens. The pattern of carbamazepine (CBZ) metabolism was evaluated in vitro and ex vivo using high performance liquid chromatography-mass spectroscopy. Accelerated mass spectroscopy was used to identify (14)C metabolites deriving from the parent (14)C-carbamazepine. Under our experimental conditions carbamazepine levels could not be detected in drug resistant epileptic brain ex situ; low levels of carbamazepine were detected in the brain side of the in vitro BBB established with endothelial cells derived from the same patients. Four carbamazepine-derived fractions were detected in brain samples in vitro and ex vivo. HPLC-accelerated mass spectroscopy confirmed that these signals derived from (14)C-carbamazepine administered as parental drug. Carbamazepine 10, 11 epoxide (CBZ-EPO) and 10, 11-dihydro-10, 11-dihydrooxy-carbamazepine (DiOH-CBZ) were also detected in the fractions analyzed. (14)C-enriched fractions were subsequently analyzed by mass spectrometry to reveal micromolar concentrations of quinolinic acid (QA). Remarkably, the disappearance of carbamazepine-epoxide (at a rate of 5% per hour) was comparable to the rate of quinolinic acid production (3% per hour). This suggested that quinolinic acid may be a result of carbamazepine metabolism. Quinolinic acid was not detected in the brain of patients who received antiepileptic drugs other than carbamazepine prior to surgery or in brain endothelial cultures obtained from a control patient. Our data suggest that a drug resistant BBB not only impedes drug access to the brain but may also allow the formation of neurotoxic metabolites.

SUBMITTER: Ghosh C

PROVIDER: S-EPMC4001854 | biostudies-other | 2012 Jun

REPOSITORIES: biostudies-other

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A pro-convulsive carbamazepine metabolite: quinolinic acid in drug resistant epileptic human brain.

Ghosh Chaitali C Marchi Nicola N Hossain Mohammed M Rasmussen Peter P Alexopoulos Andreas V AV Gonzalez-Martinez Jorge J Yang Hu H Janigro Damir D

Neurobiology of disease 20120309 3

Drugs and their metabolites often produce undesirable effects. These may be due to a number of mechanisms, including biotransformation by P450 enzymes which are not exclusively expressed by hepatocytes but also by endothelial cells in brain from epileptics. The possibility thus exists that the potency of systemically administered central nervous system therapeutics can be modulated by a metabolic blood-brain barrier (BBB). Surgical brain specimens and blood samples (ex vivo) were obtained from d ...[more]

PMID: 22426401

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Project description:BackgroundDrug-induced interstitial lung disease (DILD) is a lung injury caused by various types of drugs and is a serious problem in both clinical practice and drug development. Clinical management of the condition would be improved if there were DILD-specific biomarkers available; this study aimed to meet that need.MethodsBiomarker candidates were identified by non-targeted metabolomics focusing on hydrophilic molecules, and further validated by targeted approaches using the serum of acute DILD patients, DILD recovery patients, DILD-tolerant patients, patients with other related lung diseases, and healthy controls.ResultsSerum levels of kynurenine and quinolinic acid (and kynurenine/tryptophan ratio) were elevated significantly and specifically in acute DILD patients. The diagnostic potentials of these biomarkers were superior to those of conventional lung injury biomarkers, Krebs von den Lungen-6 and surfactant protein-D, in discriminating between acute DILD patients and patients with other lung diseases, including idiopathic interstitial pneumonia and lung diseases associated with connective tissue diseases. In addition to identifying and evaluating the biomarkers, our data showed that kynurenine/tryptophan ratios (an indicator of kynurenine pathway activation) were positively correlated with serum C-reactive protein concentrations in patients with DILD, suggesting the potential association between the generation of these biomarkers and inflammation. Our in vitro experiments demonstrated that macrophage differentiation and inflammatory stimulations typified by interferon gamma could activate the kynurenine pathway, resulting in enhanced kynurenine levels in the extracellular space in macrophage-like cell lines or lung endothelial cells. Extracellular quinolinic acid levels were elevated only in macrophage-like cells but not endothelial cells owing to the lower expression levels of metabolic enzymes converting kynurenine to quinolinic acid. These findings provide clues about the molecular mechanisms behind their specific elevation in the serum of acute DILD patients.ConclusionsThe serum concentrations of kynurenine and quinolinic acid as well as kynurenine/tryptophan ratios are promising and specific biomarkers for detecting and monitoring DILD and its recovery, which could facilitate accurate decisions for appropriate clinical management of patients with DILD.

Project description:BACKGROUND: The aim of this study was to investigate the effect of two genetic polymorphisms in the coding regions (exon 3 and exon 4) of the EPHX1 gene, ie, 337T>C and 416A>G, respectively, on the metabolism of carbamazepine (CBZ) 10,11-epoxide (the active metabolite of CBZ) by evaluating the variation in serum CBZ 10,11-epoxide levels 4 hours after administration of the drug. Moreover, we reported the genotype frequencies of the CYP3A4*22 (rs 35599367, C>T) variant and its influence on the metabolism of CBZ. METHODS: The analysis was performed in 50 patients receiving CBZ as monotherapy. DNA was extracted from leukocytes using a commercially available kit. Serum CBZ 10,11-epoxide levels were measured by high-performance liquid chromatography. Allelic discrimination was performed using polymerase chain reaction-restriction fragment length polymorphism. Statistical analysis of the difference in mean values for CBZ 10,11-epoxide levels according to genotype was performed using the Student's t-test with Statistical Package for the Social Sciences version 13 software. RESULTS: Fourteen percent of the study group were CC, 42% were CT, and 44% were TT for the EPHX1 337T>C variant. No GG homozygote was identified for the EPHX1 416A>G variant; 64% were AA and 36% were AG. When we compared serum CBZ 10,11-epoxide levels 4 hours after drug administration, we found no statistically significant difference between the 337 CC, CT, and TT genotypes. Similarly, no difference in serum CBZ 10,11-epoxide levels was found between 416A>G AA and AG. Genotype frequencies for the CYP3A4*22 (rs 35599367 C>T) allelic variant were 94% for CC and 6% for CT, with no statistically significant difference in serum CBZ 10,11-epoxide levels between these genotypes 4 hours after administration of the drug (2.6±1.3 ?g/?L and 2.5±1.2 ?g/?L, respectively). CONCLUSION: Although there is some evidence of involvement of these polymorphisms in enzyme activity in vitro, we found no interference with CBZ metabolism in vivo.

Project description:Some of the tryptophan catabolites produced through the kynurenine pathway (KP), and more particularly the excitotoxin quinolinic acid (QA), are likely to play a role in the pathogenesis of Alzheimer's disease (AD). We have previously shown that the KP is over activated in AD brain and that QA accumulates in amyloid plaques and within dystrophic neurons. We hypothesized that QA in pathophysiological concentrations affects tau phosphorylation. Using immunohistochemistry, we found that QA is co-localized with hyperphosphorylated tau (HPT) within cortical neurons in AD brain. We then investigated in vitro the effects of QA at various pathophysiological concentrations on tau phosphorylation in primary cultures of human neurons. Using western blot, we found that QA treatment increased the phosphorylation of tau at serine 199/202, threonine 231 and serine 396/404 in a dose dependent manner. Increased accumulation of phosphorylated tau was also confirmed by immunocytochemistry. This increase in tau phosphorylation was paralleled by a substantial decrease in the total protein phosphatase activity. A substantial decrease in PP2A expression and modest decrease in PP1 expression were observed in neuronal cultures treated with QA. These data clearly demonstrate that QA can induce tau phosphorylation at residues present in the PHF in the AD brain. To induce tau phosphorylation, QA appears to act through NMDA receptor activation similar to other agonists, glutamate and NMDA. The QA effect was abrogated by the NMDA receptor antagonist memantine. Using PCR arrays, we found that QA significantly induces 10 genes in human neurons all known to be associated with AD pathology. Of these 10 genes, 6 belong to pathways involved in tau phosphorylation and 4 of them in neuroprotection. Altogether these results indicate a likely role of QA in the AD pathology through promotion of tau phosphorylation. Understanding the mechanism of the neurotoxic effects of QA is essential in developing novel therapeutic strategies for AD.

Dataset Information

A pro-convulsive carbamazepine metabolite: quinolinic acid in drug resistant epileptic human brain.

Publications

A pro-convulsive carbamazepine metabolite: quinolinic acid in drug resistant epileptic human brain.

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