Showing papers by "Leif Bertilsson published in 1995"

Geographical/interracial differences in polymorphic drug oxidation. Current state of knowledge of cytochromes P450 (CYP) 2D6 and 2C19.

Abstract: The isoenzymes which catalyse the polymorphic hydroxylations of debrisoquine/sparteine and S-mephenytoin are cytochromes P450 2D6 and P450 2C19 (CYP2D6 and CYP2C19), respectively. CYP2D6 is involved in the stereospecific metabolism of several important groups of drugs, for example antiarrhythmics, antidepressants and neuroleptics. About 7% of Caucasians but only 1% of Orientals are poor metabolisers (PMs) of debrisoquine. The most common mutated allele CYP2D6B in Caucasian PMs is almost absent from their Oriental counterparts. On the other hand, the mean activity of CYP2D6 in Oriental extensive metabolisers (EMs) is lower than that in Caucasian EMs. This is due to the frequent distribution of a partially deficient CYP2D6 allele causing a Pro34-->Ser amino acid exchange in as many as 50% of Oriental alleles. This is the molecular genetic basis for slower metabolism of antidepressants and neuroleptics observed in Oriental compared with Caucasian people, and consequently for the lower dosages of these drugs used. While CYP2D6 catalyses the metabolism of lipophilic bases only, CYP2C19 is involved in the metabolism of acids (e.g. S-mephenytoin), bases (e.g. imipramine and omeprazole) and neutral drugs (e.g. diazepam). About 3% of Caucasians and 12 to 22% of Orientals are PMs of S-mephenytoin. Polymerase chain reaction-based genotyping techniques recently became available for the two CYP2C19 mutated alleles m1 and m2, which cause no enzyme to be expressed. M1 accounts for about 80% of the mutations responsible for the PM phenotypes in Caucasians, Oriental and Black people. Diazepam is partially demethylated by CYP2C19, and the high frequency of mutated alleles in Orientals is probably the reason why such populations have a slower metabolism and are treated with lower doses of diazepam than Caucasians. Omeprazole is to a major extent hydroxylated by CYP2C19, and there is an approximately 10-fold difference in oral clearance between EMs and PMs of S-mephenytoin. The separation of Caucasians from Orientals is fairly recent in the evolutionary process (40,000 to 60,000 years ago); the separation of Black from Caucasian/Oriental people occurred much earlier, about 150,000 years ago. As pronounced differences have been found between Caucasians and Orientals in the CYP2D6 and CYP2C19 enzymes, it might be expected that Black people will show even greater differences in this respect. Some studies have been performed with Black participants, but the picture is not clear. The mean CYP2D6 activity in Black EMs seems to be lower than that in Caucasian EMs and similar to that of Oriental EMs.(ABSTRACT TRUNCATED AT 400 WORDS)

Ultrarapid hydroxylation of debrisoquine in a Swedish population. Analysis of the molecular genetic basis.

Abstract: Hydroxylation of debrisoquine, catalyzed by the cytochrome P450 CYP2D6 exhibits genetic polymorphism, with large inter-individual differences in metabolic capacity. About 7% of Caucasians carry deficient CYP2D6 alleles and lack the CYP2D6 enzyme (poor metabolizers). We have shown in two Swedish families, individuals carrying duplicated or amplified functional CYP2D6L-genes (CYP2D6L2), causing the opposite phenomenon, ultrarapid metabolism of debrisoquine. In the present study, the occurrence of extra copies of CYP2D6L-alleles was studied in relation to debrisoquine metabolic ratio (MR) in 270 Swedish Caucasians including 64 selected subjects with very rapid metabolism (MR < or = 0.2). Thirteen of the 64 subjects carried a duplicated CYP2D6-gene as identified by EcoRI and XbaI restriction fragment length polymorphism and allele-specific polymerase chain reaction-amplification of genomic DNA. A new allele with three active CYP2D6L-genes was identified, characterized by an XbaI 54 kilobase fragment. This indicates a preference of the CYP2D6L-gene to be amplified compared to other CYP2D6 genes. Only one subject with an MR higher than 0.2 carried the duplicated CYP2D6L-allele, also being heterozygous for the defect CYP2D6B-allele. The overall frequency of the duplicated/amplified CYP2D6-allele was about 1%, and was present in 40% of subjects with MRs < or = 0.1. Thus, other variant CYP2D6-genes may exist that cause increased CYP2D6 activity. In conclusion, a haplotype with duplicated or amplified functional CYP2D6 genes predicts, with high accuracy, ultrarapid metabolism of debrisoquine. Genotyping for this CYP2D locus variant might be of value in patients not responding to generally recommended doses of CYP2D6 substrates, to distinguish between high metabolic capacity and noncompliance.

Use of omeprazole as a probe drug for CYP2C19 phenotype in Swedish Caucasians: comparison with S-mephenytoin hydroxylation phenotype and CYP2C19 genotype

Abstract: 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.

Interphenotype differences in disposition and effect on gastrin levels of omeprazole—suitability of omeprazole as a probe for CYP2C19.

Abstract: 1. Fourteen healthy Swedish Caucasian subjects were given 20 mg of omeprazole orally each morning for 8 days. The subjects included five poor metabolisers (PM) of S-mephenytoin, four heterozygous extensive metabolisers (hetEM) and five subjects with a very rapid metabolism (rapidEM). 2. After the first dose, the relative mean areas under the plasma concentration vs time curve (AUC) of omeprazole in rapidEM, hetEM and PM were 1:3.7:20 (all different, P < 0.001). A similar relation was seen in the AUC(0,10 h) of the sulphone metabolite (1:3:12). Concentrations of hydroxyomeprazole were higher in EM than in PM confirming that the hydroxy, but not the sulphone metabolite, is formed by the S-mephenytoin hydroxylase (CYP2C19). After 8 days of treatment, the differences between groups were similar. 3. After both the first and the eighth doses, the omeprazole/hydroxyomeprazole plasma concentration ratio, determined 3 h after drug intake, correlated with the mephenytoin S/R ratio (rs = 0.94; P < 0.001; n = 14) suggesting that omeprazole might be used to phenotype for CYP2C19. 4. After the first dose of omeprazole, there was no difference in the AUC(0,10 h) of plasma gastrin between the three groups. From the first to the eighth dose, the AUC(0,10) of gastrin increased significantly in both hetEM and PM, while there was no change in the rapidEM. After the eighth dose, the AUC(0,10) of gastrin correlated significantly with the AUC of omeprazole in plasma (rs = 0.79; P < 0.01; n = 13).

Genetic analysis of the CYP2D locus in relation to debrisoquine hydroxylation capacity in Korean, Japanese and Chinese subjects.

Abstract: The CYP2D6 genotype and the debrisoquine and mephenytoin hydroxylation phenotypes were studied in 63 Oriental subjects including 21 Chinese, 21 Japanese and 21 Koreans. All subjects were extensive metabolizers of debrisoquine. The incidence of the S-mephenytoin poor metabolizer phenotype was 14% in

Phenotyping and genotyping of S-mephenytoin hydroxylase (cytochrome P450 2C19) in a Shona population of Zimbabwe

Abstract: The S-mephenytoin hydroxylase has recently been identified as cytochrome P450 2C19 (CYP2C19). This enzyme metabolizes mephenytoin, diazepam, omeprazole, and citalopram and has been shown to be polymorphically distributed. One clinical implication of CYP2C19-dependent drug metabolism for persons who reside in tropical regions is in the use of the antimalarial drug chloroguanide hydrochloride, which is apparently biotransformed to its active metabolite by this isozyme. In this investigation we studied mephenytoin metabolism in 103 black Zimbabwean Shona subjects. Four were identified as poor metabolizers (4%). This prevalence is comparable to that in white subjects (2% to 5%) but lower than the 15% to 20% incidence of poor metabolizers among Oriental subjects. Of the subjects phenotyped, 84 were genotyped for the G-->A mutation in exon 5 of CYP2C19, which creates a cryptic splice site, causing the production of a nonfunctional protein. Three of the four poor metabolizers were homozygous for this mutation, whereas the fourth one was heterozygous. The G-->A mutation has been shown to predict the incidence more than 60% of poor metabolizers among white subjects and Japanese subjects, and in the current investigation we also obtained a similar relationship in the black population.

Active hydroxymetabolites of antidepressants. Emphasis on E-10-hydroxy-nortriptyline

Abstract: Hydroxymetabolites of the antidepressants nortriptyline and desipramine, like the parent drugs, inhibit neuronal uptake of noradrenaline (norepinephrine). In both plasma and cerebrospinal fluid (CSF), the concentrations of the 10-hydroxymetabolites of nortriptyline (10-OH-NT) are usually higher than those of the parent drugs, but there is a pronounced interindividual variation in the plasma concentrations. This shows that during treatment with nortriptyline, hydroxymetabolites exert, at least in some patients, major effects on brain noradrenaline neurons. Hydroxymetabolites of antidepressants are formed by the polymorphic cytochrome P450 enzyme CYP2D6. Nortriptyline is hydroxylated by this enzyme in a highly stereospecific way to the (-)-enantiomer of E-10-OH-NT. Among Caucasians, 7% are poor metabolisers of the CYP2D6 probe drug debrisoquine. These patients will form very little hydroxymetabolite. The affinity of E-10-OH-NT for muscarinic acetylcholine receptors in vitro was only one-eighteenth of the affinity of nortriptyline for these receptors. In healthy individuals, nortriptyline decreased saliva flow to a significantly greater extent than either E-10-OH-NT or placebo. In an ultrarapid hydroxylator of nortriptyline treated with very high doses of nortriptyline, the plasma concentration of unconjugated 10-OH-NT was very high without any sign of anticholinergic adverse effects. These results show that hydroxymetabolites of nortriptyline have much less anticholinergic effect than the parent drug. When racemic E-10-OH-NT per se was given to healthy individuals, the plasma concentration of the (-)-enantiomer was 5-fold higher than that of (+)-E-10-OH-NT. The 2 enantiomers were eliminated in parallel with an elimination half-life of 8 to 10 hours. A combined in vitro and in vivo investigation showed that a mean of 64% of (+)-E-10-OH-NT was glucuronidated in the liver and subsequently eliminated in urine. Of the administered (-)-enantiomer, a mean of 36% was eliminated as glucuronide formed in the intestine and 35% was actively secreted as unchanged form in urine. Plasma protein binding, determined by ultrafiltration, of the (+)- and (-)-enantiomers of E-10-OH-NT was 54 and 69%, respectively, which is less than that of nortriptyline (92%). The concentration of E-10-OH-NT in CSF was 50% of the concentration of unbound in plasma. There seems to be a stereoselective active transport of E-10-OH-NT from the CSF to blood. We administered racemic E-10-OH-NT to 5 patients during a major depressive episode.(ABSTRACT TRUNCATED AT 400 WORDS)

Pharmacogenetics in clinical pharmacology and toxicology.

Abstract: An international symposium entitled Pharmacogenetics in clinical pharmacology and toxicology: a tribute to Werner Kalow was held in Toronto, Ontario, July 20, 1994. This subject was particularly important to discuss in the presence of Werner Kalow, 77 years young, who is considered as one of the grandfathers of this unique combination of medical research fields. It has become increasingly appreciated that dozens of human drug metabolism polymorphisms exist. The interindividual variabilities in drug metabolism discussed at this symposium do not represent small differences such as 50% or 3-fold but, rather, represent 10- to greater than 1000-fold differences. When attributed to a single gene, dramatic differences can be seen among family members, just as blue and brown eyes can occur in siblings. These differences can result in acute drug toxicity. In addition, there are chronic effects: over one's lifetime, striking differences in the metabolism of drugs, occupationally hazardous chemicals, and other envir...

Enantioselective determination of mianserin and its desmethyl metabolite in plasma during treatment of depressed Japanese patients.

Abstract: A method for the analysis of the enantiomers of mianserin and its main metabolite desmethylmianserin in plasma using a chiral AGP high performance liquid chromatography column is described. In the majority of 66 depressed Japanese patients, the concentration of the more active S(+)-mianserin was higher than that of the R(-)-enantiomer. The mean S/R ratio was 1.9 +/- 0.9 (SD) (range 0.5-4.8). The concentration of S(+)-varied between 19 and 223 nM, while that of the R(-)-mianserin varied between 14 and 72 nM. Among 42 of the 66 plasma samples in which the enantiomers of desmethylmianserin could be measured, the R-form predominated in all but one. S-Desmethylmianserin was in most of the samples present in concentrations of < 10 nM (limit of detection). Analysis of the enantiomers of mianserin and desmethylmianserin might allow the establishment of a closer relationship between plasma levels and clinical effects.