Gunnel Tybring

Platelet MAO activity and monoamine metabolites in cerebrospinal fluid in depressed and suicidal patients and in healthy controls

Platelet monoamine oxidase (MAO) activity and cerebrospinal fluid (CSF) concentrations of 5-hydroxyindoleacetic acid (5HIAA), homovanillic acid (HVA), and 4-hydroxy-3-methoxyphenylglycol (HMPG) were simultaneously measured in 20 currently depressed patients, 11 recovered depressed patients, 15 nondepressed suicide attempters, and 42 healthy control subjects. Both 5HIAA and HVA were positively and significantly correlated to platelet MAO activity in the healthy subjects, but not in any of the patient groups. Suicide attempters had significantly lower CSF 5HIAA than nonsuicidal patients.

Importance of genetic factors in the regulation of diazepam metabolism: Relationship to S‐mephenytoin, but not debrisoquin, hydroxylation phenotype

Single oral 10 mg doses of diazepam and demethyldiazepam were given on different occasions to 16 healthy subjects. The subjects included four poor hydroxylators of debrisoquin and three poor hydroxylators of mephenytoin. There was a correlation between the total plasma clearance of diazepam and demethyldiazepam (rs = 0.83; p < 0.01). There was no relationship between benzodiazepine disposition and debrisoquin hydroxylation. Poor hydroxylators of mephenytoin had less than half the plasma clearance of both diazepam (p = 0.0008) and demethyldiazepam (p = 0.0001) compared with extensive hydroxylators of mephenytoin. The plasma half‐lives were longer in poor hydroxylators than they were in extensive hydroxylators of mephenytoin for both diazepam (88.3 ± SD 17.2 and 40.8 ± 14.0 hours; p = 0.0002) and demethyldiazepam (127.8 ± 23.0 and 59.0 ± 16.8 hours; p = 0.0001). There was no significant difference in volume of distribution of the benzodiazepines between the phenotypes. This study shows that the metabolism of both diazepam (mainly demethylation) and demethyldiazepam (mainly hydroxylation) is related to the mephenytoin, but not to the debrisoquin, hydroxylation phenotype.

Use of omeprazole as a probe drug for Cyp2c19 phenotype in Swedish Caucasians: comparison with S-mephenytoin hydroxylation phenotype and Cyp2c19 genotype

A single oral dose of omeprazole (20 mg) was given orally to 160 healthy Caucasian Swedish subjects and tested as a probe for CYP2C19. The study was nonrandomized and included seven subjects previously classified as poor metabolizers (PM) of S-mephenytoin. The ratio between the plasma concentrations of omeprazole and hydroxyomeprazole (metabolic ratio; MR) was determined by HPLC in a blood sample drawn 3 h after drug intake. In 17 subjects the test was repeated and the MRs of omeprazole on the two occasions were correlated (rs = 0.85; p < 0.0001). There was a significant correlation between the MR of omeprazole and the S/R mephenytoin ratio among 141 subjects, in whom both ratios were determined (rs = 0.63, p < 0.001). All seven PMs of S-mephenytoin had higher MRs of omeprazole (7.1-23.8) than extensive metabolizers (EM) (0.1-4.9). All 160 subjects and another 15 Caucasian Swedish PMs previously phenotyped with mephenytoin were analysed with respect to the presence of the CYP2C19m1 allele by PCR amplification of the intron 4/exon 5 junction followed by Sma I digestion. EMs heterozygous for the CYP2C19m1 gene had MRs of omeprazole and S/R ratios of mephenytoin that were higher than those of subjects who were homozygous for the wild-type allele (p = 0.0001). Nineteen of the 22 PMs were homozygous for the CYP2C19m1 gene. Three were heterozygous for this allele. Thus, 41 of the 44 alleles (93%) of PMs were defective CYP2C19m1. One of the remaining three PM alleles was subsequently found to contain the CYP2C19m2 mutation, which has earlier been shown to be associated with the PM phenotype in Oriental populations. In conclusion, the phenotype determined by omeprazole correlated with that of mephenytoin, and was in good agreement with the genotype.

Carbamazepine metabolism in man. Induction and pharmacogenetic aspects.

SummaryThe metabolism of carbamazepine (CBZ) was studied in 3 groups of subjects: (1) 6 healthy volunteers given a single dose of 200mg carbamazepine; (2) 4 epileptic patients on carbamazepine monotherapy; and (3) 5 patients receiving carbamazepine in combination with other anticonvulsants. Carbamazepine kinetics in the patients were investigated by use of 15N-CBZ. The mean plasma clearances of carbamazepine were 19.8, 54.6 and 113.3 ml/h/kg in groups 1, 2 and 3, respectively. The increased clearance in the patients was mainly due to an induction of the epoxide-diol pathway, as reflected by an increased urinary excretion of the trans-CBZ-diol metabolite. The urinary excretion (as a percentage of the administered dose) of 9-hydroxymethyl-10-carbamoyl-acridan (9-OH-CBZ) was also increased, whereas the excretion of 2-OH-CBZ and 3-OH-CBZ in groups 2 and 3 were decreased in comparison with group 1.As it has been suggested that 9-OH-CBZ is formed from carbamazepine- 10,11-epoxide (CBZ-E) or trans-CBZ-diol, the formation of 9-OH-CBZ was investigated in 3 patients with trigeminal neuralgia treated with carbamazepine or CBZ-E as monotherapy on separate occasions. The urinary excretion of 9-OH-CBZ was 1.9, 3.3 and 4.0% of the trans-CBZ-diol excretion during CBZ-E therapy and 23, 32 and 24%, respectively, during carbamazepine administration. Thus only a minor part of the 9-OH-CBZ excreted in urine during carbamazepine therapy is formed via the epoxide-diol pathway.Data on plasma concentrations of carbamazepine and CBZ-E, and on urinary excretion of trans-CBZ-diol from 4 patients on carbamazepine therapy were used to calculate the plasma clearance of CBZ-E. The hydration of CBZ-E during carbamazepine therapy was found to be induced, but to a lesser extent than the epoxidation of carbamazepine.The interrelationship between carbamazepine-epoxidation and oxidative metabolic reactions of some other drugs was also studied in 8 healthy volunteers. Carbamazepine-epoxidation was not correlated to 4-hydroxylation of debrisoquine, oxidation of sparteine, 3- and 4-hydroxylation and demethylation of antipyrine, demethylation of amitriptyline, or total metabolism of theophylline.

Pharmacokinetics of losartan and its metabolite E-3174 in relation to the CYP2C9 genotype.

Losartan is metabolized by polymorphic CYP2C9 to E‐3174. Our aim was to evaluate the pharmacokinetics of losartan and E‐3174 in relation to the CYP2C9 genotype.

Plasma levels of chlorimipramine and its demethyl metabolite during treatment of depression

The biochemical and antidepressant effects of chlorimipramine (Cl) were studied in depressed patients after 3 wk of treatment. In vitro studies performed with rat brain slices incubated in human plasma showed that chlorimipramine and its demethyl metabolite (DMCI) are fairly specific blockers of serotonin and norepinephrine uptake. The uptake inhibition of serotonin and norepinephrine in plasma drawn from patients during treatment correlated with the plasma levels of parent drug and metabolite. Treatment with Cl caused a decrease of the main serotonin (5‐HIAA) and norepinephrine metabolites (HMPG) but had no significant mean effect on the major dopamine metabolite (HVA) or on tryptophan in cerebrospinal fluid (CSF). The 5‐HIAA decrease in CSF correlated with the plasma concentration of Cl within the range 80 to 360 nmole/l. The HMPG decrease in CSF correlated with plasma DMCI concentration. The patients were subdivided into two groups, those with “low” and those with “high” CSF 5‐HIAA. In patients with a “high” pretreatment CSF 5‐HIAA, there was a positive correlation between amelioration of depression and plasma level of DMCI. In this patient group there also was a correlation between HMPG alteration and amelioration of depression. This finding supports the hypothesis that patients with “high” CSF 5‐HIAA levels benefit from treatment with norepinephrine uptake blockers. In the patient group with “low” CSF 5‐HIAA, correlations between plasma levels of Cl and DMCI and amelioration were consistently negative, albeit not significant, supporting the idea that these patients are a biochemical subgroup within the depressive illness with a different reaction to antidepressant drugs than those with “high” CSF 5‐HIAA levels.

Autoinduction of carbamazepine metabolism in children examined by a stable isotope technique

Autoinduction of carbamazepine (CBZ) metabolism was investigated in 3 children (10 to 13 yr old) using tetradeuterium‐labeled CBZ (CBZ‐D4). Prior to treatment, CBZ and CBZ‐D4 given as a mixture had almost identical kinetics in each patient. During maintenance therapy with CBZ, part of the CBZ was exchanged for CBZ‐D4 on 3 occasions. The clearance of CBZ‐D4 given on the second day of therapy was 0.036 ± 0.003 1 · kg−1 · hr−1, whereas it had been 0.028 ± 0.003 before treatment. After 17 to 32 days of treatment, clearance doubled (0.056 ± 0.010) but during the next 4 mo there was no further increase, indicating that the autoinduction was complete within 1 mo. As a corollary there was a decrease in steady‐state plasma levels.

CYP2C19 genotype and phenotype determined by omeprazole in a Korean population.

Omeprazole (20 mg orally) was given to 103 healthy Korean subjects and blood was taken 3 h after administration. The plasma concentration ratio of omeprazole and hydroxyomeprazole, used as an index of CYP2C19 activity, was bimodally distributed. Thirteen subjects (12.6%) were identified as poor metabolizers (PMs) with an omeprazole hydroxylation ratio of 6.95 or higher. Among the 206 CYP2C19 alleles, CYP2C19*2 and CYP2C19*3 were found in 43 alleles (21%) and 24 alleles (12%), respectively. Twelve subjects (12%) carried two defect alleles (*2/*2, *2/*3 or *3/*3), 43 subjects (42%) were heterozygous for a mutated (*2 or *3) and a wild type (*1) allele, and the remaining 48 subjects (47%) were homozygous for the wild type allele. The distributions of the metabolic ratio between these three genotype groups were significantly different (Kruskal-Wallis test: p < 0.0001). The genotypes of 19 additional Korean PMs has been identified in a previous mephenytoin study. From a total of 32 PMs, 31 were genotypically PMs by analysis of the CYP2C19*2 and *3 alleles and only one PM subject was found to be heterozygous for the *1 and *2 alleles. At present it cannot be judged whether this subject has a defective allele with a so-far unidentified mutation or a true wild type allele. We thus confirm a high incidence (12.6%) of PMs of omeprazole in Koreans and of the 32 Korean PMs 97% could be identified by the genotype analysis.

The role of CYP2C9 genotype in the metabolism of diclofenac in vivo and in vitro

Abstract. Introduction: The polymorphic cytochrome P450 enzyme 2C9 (CYP2C9) catalyses the metabolism of many drugs including S-warfarin, acenocoumarol, phenytoin, tolbutamide, losartan and most of the non-steroidal anti-inflammatory drugs. Diclofenac is metabolised to 4′-hydroxy (OH), the major diclofenac metabolite, 3′-OH and 3′-OH-4′-methoxy metabolites by CYP2C9. The aim of the present study was to clarify the impact of the CYP2C9 polymorphism on the metabolism of diclofenac both in vivo and in vitro. Subjects, materials and methods: Twenty healthy volunteers with different CYP2C9 genotypes [i.e. CYP2C9*1/*1 (n=6), *1/*2 (n=3), *1/*3 (n=5), *2/*3 (n=4), *2/*2 (n=1), *3/*3 (n=1)] received a single 50-mg oral dose of diclofenac. Plasma pharmacokinetics [peak plasma concentration (Cmax), half-life (t1/2) and area under the plasma concentration–time curve (AUCtotal)] and urinary recovery of diclofenac and its metabolites were compared between the genotypes. Diclofenac 4′-hydroxylation was also analysed in vitro in 16 different samples of genotyped [i.e. CYP2C9*1/*1 (n=7), *1/*2 (n=2), *1/*3 (n=2), *2/*3 (n=2), *2/*2 (n=2), *3/*3 (n=1)] human liver microsomes. Results: Within each genotype group, a high variability was observed in kinetic parameters for diclofenac and 4′-OH-diclofenac (6- and 20-fold, respectively). No significant differences were found between the different genotypes either in vivo or in human liver microsomes. No correlation was found between the plasma AUC ratio of diclofenac/4′-OH-diclofenac and that of losartan/E-3174, previously determined in the same subjects. Conclusion: No relationship was found between the CYP2C9 genotype and the 4′-hydroxylation of diclofenac either in vivo or in vitro. This, together with the lack of correlation between losartan oxidation and diclofenac hydroxylation in vivo raises the question about the usefulness of diclofenac as a CYP2C9 probe.

Enantioselective hydroxylation of omeprazole catalyzed by CYP2C19 in Swedish white subjects

Stereoselective disposition of omeprazole and its formed 5‐hydroxy metabolite were studied in five poor metabolizers and five extensive metabolizers of S‐mephenytoin. After a single oral dose of omeprazole (20 mg), the plasma concentrations of the separate enantiomers of the parent drug and the 5‐hydroxy metabolite were determined for 10 hours after drug intake. In poor metabolizers, the area under the plasma concentration versus time curve [AUC(0–8)] of (+)‐omeprazole was larger and that of the 5‐hydroxy metabolite of this enantiomer was smaller than the AUC(0–8) values in extensive metabolizers (p < 0.001). The mean AUC(0–8) of the (‐)‐enantiomer of omeprazole was also higher in poor metabolizers than in extensive metabolizers, but only 3.1‐fold compared with 7.5‐fold for (+)‐omeprazole. The rate of formation of the hydroxy metabolite from (‐)‐omeprazole was low and not significantly different in poor and extensive metabolizers. These results show that (+)‐omeprazole is to a major extent hydroxylated by CYP2C19. Also (‐)‐omeprazole may partly be metabolized by this enzyme but is mainly metabolized by another enzyme, presumably CYP3A4, to the achiral sulfone metabolite. The plasma concentration ratio of omeprazole to 5‐hydroxyomeprazole obtained 3 hours after the drug intake has been used to distinguish between extensive and poor metabolizer phenotypes. With use of the ratio between the (+)‐enantiomers of the parent drug and the metabolite, a better discrimination between phenotypes was obtained. The ratio between the (‐)‐enantiomers also separated the phenotypes but was less discriminatory. For the future, measurement of total concentrations will suffice for phenotyping.