Showing papers by "Leif Bertilsson published in 1999"

Genetic polymorphism of xenobiotic metabolizing enzymes among Chinese lung cancer patients

Abstract: Polymorphisms in xenobiotic metabolizing enzymes have been implicated in inter-individual and inter-ethnic differences in cancer susceptibilty. Several studies have indicated an association between variant alleles of the human CYP1A1,CYP2E1 and GSTM1 genes and lung cancer. Activity of microsomal epoxide hydrolase (HYL1) has also been associated with lung cancer, and 2 variant alleles causing amino acid substitutions have been described. We have investigated genetic polymorphisms of the CYP1A1,CYP2E1,GSTM1 and HYL1 genes in 76 Chinese lung cancer patients and 122 healthy Chinese subjects. The allele frequency of the CYP1A1*2B allele was 0.21 among lung cancer patients and 0.20 in the reference group, whereas the corresponding values for the CYP1A1*2A allele were 0.34 and 0.36. The CYP2E1*5B and CYP2E1*6 alleles were less frequent among the cancer patients (0.20 and 0.22) compared with healthy subjects (0.25 and 0.26). The frequency distribution of the HYL1*2 allele was 0.49 among lung cancer patients and 0.42 in the reference group, and the corresponding frequencies for the HYL1*3 allele were 0.13 and 0.10. The homozygous GSTM1*0 genotype was found in 64% of lung cancer patients and in 66% of healthy subjects. Among heavy smokers, the frequency was 73%. The differences in the distribution of variant CYP1A1,CYP2E1 and GSTM1 alleles in lung cancer patients and healthy controls were not statistically significant. Our results indicate that the polymorphisms investigated are of minor importance as genetic susceptibility markers for lung cancer in this population. An increased risk for lung cancer in subjects carrying the HYL*3 allele was observed and suggests that polymorphism in this gene might possibly be a susceptibility factor in the Chinese population. Int. J. Cancer 81:325–329, 1999. © 1999 Wiley-Liss, Inc.

High and variable frequencies of CYP2C19 mutations : medical consequences of poor drug metabolism in Vanuatu and other Pacific islands

Abstract: Cytochrome P450 (CYP) 2C19 is polymorphic with poor metabolizers representing 3-6% of Europeans and Africans, and 13-23% of Asians. Greater than 99% of the poor metabolizer alleles in Asian populations are defined by two single base pair mutations (CYP2C19*2 and CYP2C19*3). We have recently reported an unprecedentedly high prevalence (71%) of CYP2C19-related poor metabolizer genotype individuals and poor metabolism of proguanil on two malarious islands of Vanuatu in eastern Melanesia. To elucidate this further, a total of 5538 individuals from 24 populations on 16 different islands of Vanuatu were genotyped. Of these, 61% had a poor metabolizer genotype (*2/*2, *2/*3 or *3/*3) with substantial variation among the populations (38-79%). The overall frequencies of CYP2C19*1 (wild-type), CYP2C19*2, and CYP2C19*3 were 0.223, 0.633, and 0.144, respectively. A significant linear correlation was observed between heterozygosity and South latitude (r = 0.552, P 0.05). Comparisons of genetic, linguistic and geographical patterns among populations suggest that short range gene flow is largely responsible for the current distribution of CYP2C19 alleles in Vanuatu. Taken together with previous studies of nuclear genetic loci of Pacific island populations, these data predict that the poor metabolizer genotype is common throughout Polynesia and Micronesia and may be even more prevalent in western Melanesia than in Vanuatu. This suggests that the majority of Pacific Islanders metabolize a wide variety of clinically important drugs to a significantly lower degree than the average European.

Ten percent of North Spanish individuals carry duplicated or triplicated CYP2D6 genes associated with ultrarapid metabolism of debrisoquine.

Abstract: Ten percent of North Spanish subjects carry duplicated or triplicated CYP2D6 genes associated with ultrarapid metabolism of debrisoquine

Decreased capacity for debrisoquine metabolism among black Tanzanians: analyses of the CYP2D6 genotype and phenotype.

Abstract: The cytochrome P450 2D6 (CYP2D6) genotypes and phenotypes of 106 unrelated, healthy black Tanzanians of Bantu origin were investigated. The results revealed a population with a generally decreased capacity to metabolize the CYP2D6 substrate debrisoquine with 59% of the Tanzanian extensive metabolise

Disposition of debrisoquine in Caucasians with different CYP2D6-genotypes including those with multiple genes.

Abstract: Debrisoquine is a major prototypic in-vivo probe used to assess polymorphic CYP2D6 activity in humans, based on the 0-8 h urinary excretion of unchanged drug and its 4-hydroxy metabolite (the so-called metabolic ratio). The primary purpose of the study was to investigate further the relationship between genotype and phenotype by determining the overall disposition characteristics of the drug in selected groups of healthy Swedish Caucasian individuals. Debrisoquine (20 mg) was orally administered to five poor metabolizers with no functional CYP2D6 gene, five heterozygous extensive metabolizers, five homozygous extensive metabolizers, five ultrarapid metabolizers with duplicated/triplicated CYP2D6*2 genes and one individual with 13 copies of CYP2D6*2. Peak plasma levels of debrisoquine and 4-hydroxydebrisoquine were attained within 2-4 h and then declined in a multi-exponential fashion over 96 h. However, the post 8-h period of the elimination process was characterized by irregular fluctuations that prevented formal pharmacokinetic analysis. Nevertheless, marked differences were apparent in the compounds' plasma level-time profiles between the CYP2D6 genotypes. For example, in the case of debrisoquine, the mean ratio of the AUC(0-8) values was 22:22:7:6:1, corresponding to 0, 1, 2, 3/4 and 13 genes and, for 4-hydroxydebrisoquine, the respective values were 1:7:19:28:17. The 0-96 h urinary recovery of debrisoquine differed 100-fold between the genotypes, being essentially complete in poor metabolizers and zero in the individual with 13 CYP2D6*2 genes. 4-hydroxydebrisoquine excretion increased according to the number of functional CYP2D6 genes. A highly significant correlation (r(s) = 0.95, P < 0.001) was observed between the plasma AUC(0-8) ratio for debrisoquine to 4-hydroxydebrisoquine and the 0-8 h urinary metabolic ratio. This study demonstrates that the number of functional CYP2D6 alleles is critically important in the plasma concentration-time curves of debrisoquine and its CYP2D6-mediated 4-hydroxy metabolite. Concentration-related pharmacologic effects would be expected to be similarly affected by gene dosage and it is likely that the same situation also applies to other drugs whose elimination is importantly determined by this enzyme; for example, many antidepressants and neuroleptics, antiarrhythmic agents, beta-adrenoceptor antagonists and opiates.

The roles of cytochrome P450 3A4 and lA2 in the 3-hydroxylation of quinine in vivo

Abstract: Objective To investigate the roles of CYP3A4 and CYP1A2 in the 3-hydroxylation of quinine in vivo. Methods In a randomized, three-way crossover study, nine healthy Swedish volunteers received single oral doses of quinine hydrochloride (500 mg), quinine hydrochloride (500 mg) plus ketoconazole (100 mg twice daily for 3 days), and quinine hydrochloride (500 mg) plus fluvoxamine (25 mg twice daily for 2 days) on three different occasions. Blood and urine samples were collected before quinine intake and up to 96 hours thereafter. Plasma and urine samples were analyzed for both quinine and its main metabolite 3-hydroxyquinine with HPLC methods. Results Coadministration with ketoconazole (which inhibits CYP3A4) decreased the mean apparent oral clearance of quinine significantly (P .05) on the mean apparent oral clearance of quinine. Coadministration with ketoconazole also decreased the mean area under the plasma concentration versus time curve (AUC) of 3-hydroxyquinine (from 28.4 to 19.7 ¼mol · h · L−1; P < .001), whereas coadministration with fluvoxamine increased 3-hydroxyquinine AUC significantly (from 28.4 to 30.2 ¼mol · h · L−1; P < .05). Conclusion Cytochrome P450 3A4 is important for the 3-hydroxylation of quinine in vivo. On the other hand, CYP1A2 had no significant effect on this metabolic pathway. Clinical Pharmacology & Therapeutics (1999) 66, 454–460; doi:

Fluoxetine inhibits the metabolism of tolterodine-pharmacokinetic implications and proposed clinical relevance.

Abstract: Aims To investigate the change in disposition of tolterodine during coadministration of the potent cytochrome P450 2D6 (CYP2D6) inhibitor fluoxetine. Methods Thirteen patients received tolterodine l-tartrate 2 mg twice daily for 2.5 days, followed by fluoxetine 20 mg once daily for 3 weeks and then concomitant administration for an additional 2.5 days. They were characterized as extensive metabolizers (EM1 with one functional CYP2D6 gene, EM2 with two functional genes) or poor metabolizers (PM). Results Nine patients, three EM2 and four EM1 and two PM, completed the trial. Following tolterodine administration, the area under the serum concentration–time curve (AUC) of tolterodine was 4.4-times and 30-times higher among EM1 and PM, respectively, compared with EM2. The AUC of the 5-hydroxymethyl metabolite (5-HM) was not quantifiable in PM. Fluoxetine significantly decreased (P<0.002) the oral clearance of tolterodine by 93% in EM2 and by 80% in EM1. The AUC of 5-HM increased in EM2 and decreased in EM1. However, the exposure to the active moiety (unbound tolterodine +5-HM) was not significantly increased in the two phenotypes. The subdivision of the EM group showed a 2.1-fold increase in active moiety in EM2 but the exposure was still similar to EM1 compared with before the interaction. Conclusions The study suggests a difference in the pharmacokinetics of tolterodine and its 5-hydroxymethyl metabolite depending on the number of functional CYP2D6 genes. Fluoxetine significantly inhibited the hydroxylation of tolterodine. Despite the effect on the pharmacokinetics of tolterodine in extensive metabolizers, the clinical effect is expected to be within normal variation.

Effect of CYP2C19 polymorphism on serum levels of vitamin B12 in patients on long-term omeprazole treatment.

Abstract: Background: The S-mephenytoin hydroxylase is a polymorphic cytochrome P450 (CYP) enzyme, identified as CYP2C19, which catalyses the metabolism of omeprazole and some other drugs. Aim: To determine whether long-term treatment with omeprazole affects serum vitamin B12 levels, and if so to what extent it depends on CYP2C19 activity. Methods: Serum vitamin B12 levels (pmol/L) were assessed in 179 patients. Genotyping for wild-type (wt) and mutated (mut) CYP2C19 alleles was performed by allele-specific PCR amplification. Results: One-hundred and eleven of the patients received one dose of 20 mg omeprazole. No difference in B12 levels were found between heterozygous (wt/mut) (n = 23) and homozygous (wt/wt) (n = 85) patients (mean ± s.d., 350 ± 82 vs. 315 ± 87 pmol/L, respectively). Three patients were mut/mut, with serum vitamin B12 levels of 303 ± 50 pmol/L. In the 68 patients on long-term (>1 year) therapy with 20 mg omeprazole daily, serum vitamin B12 levels were lower in the heterozygous (wt/mut) (n = 19) compared to homozygous wt/wt (n = 49) (246 ± 71 vs. 305 ± 98 pmol/L, P = 0.01, respectively). In one patient (mut/mut) who was studied both after a single dose and after long-term (15 months) treatment with omeprazole, serum vitamin B12 decreased from 360 to 178 pmol/L. In the wt/mut, but not in the wt/wt group, serum vitamin B12 levels were significantly lower in patients on long-term therapy compared with those receiving one dose (246 ± 71 vs. 350 ± 82 pmol/L, P < 0.0001, respectively). Conclusions: CYP2C19 polymorphism significantly affected serum vitamin B12 levels in patients on long-term therapy with omeprazole. In the future, genotyping of CYP2C19 may be useful for patients in need of long-term treatment with omeprazole or other proton pump inhibitors.

Stereospecific analysis of omeprazole supports artemisinin as a potent inducer of CYP2C19

Abstract: The purpose of the study was to determine the enantiomer pharmacokinetics of omeprazole and 5-hydroxy-omeprazole before and after administration of the antimalarial artemisinin to confirm artemisinin's ability to induce CYP2C19. Nine healthy male Vietnamese subjects were given a single 20 mg dose of omeprazole orally 1 week before (day - 7) artemisinin administration. Artemisinin was then given orally (500 mg) for 7 days (days 1-7). On days 1 and 7, a single 20 mg dose of omeprazole was coadministered with artemisinin. After a washout period of 6 days, a single 20 mg dose of omeprazole was again administered together with a single 500 mg of artemisinin (day 14). Stereoselective pharmacokinetics of omeprazole and 5-hydroxyomeprazole was determined on days of omeprazole administration. Seven days of artemisinin administration significantly decreased the AUC of both omeprazole enantiomers (day 7), compared with day 1 (P < 0.001). All values were normalized after the washout period. Artemisinin increased the AUC ratio of R-5-hydroxyomeprazole/R-omeprazole significantly (P < 0.01) on day 7. The AUC ratio of omeprazole sulphone/S-omeprazole did not differ between study days. Artemisinin decreased the AUC of S-omeprazole to the same extent as that of R-omeprazole in extensive CYP2C19 metabolizers. suggesting that artemisinin induces a different enzyme in addition to CYP2C19. These results support and strengthen earlier findings that artemisinin induces CYP2C19 as well as at least one enzyme other than CYP3A4.

Pronounced Differences in the Disposition of Clomipramine Between Japanese and Swedish Patients

Abstract: The aim of this study was to compare the disposition of the tricyclic antidepressant clomipramine (C) in Japanese and Swedish patients receiving continuous treatment. Therapeutic drug monitoring data for C and the active metabolite N-desmethylclomipramine (DC) in Japanese patients receiving monotherapy (N = 12) and in those receiving C plus benzodiazepines (BZDs) (N = 96) as well as in Swedes receiving C monotherapy (N = 131) and in those receiving C plus BZDs (N = 43) were used. A population kinetic approach with Bayesian feedback was used to estimate the individual clearance values for C. The relationships between kinetic variables and covariates were evaluated by linear multiple regression. The median (25% and 75% quartiles, respectively) oral clearance of C was 12.7 L/hr (11.6, 30.6) in Japanese patients receiving C monotherapy, 18.1 L/hr (5.6, 31.8) in Japanese patients receiving C plus BZDs, 62.7 L/hr (40.0, 90.6) in Swedish patients receiving C monotherapy, and 56.5 L/hr (34.3, 74.1) in Swedish patients receiving C plus BZDs. When combining all populations in a linear multiple regression, clearance was correlated with ethnic group (p < 0.00001) and age (p < 0.0005), but it was uncorrelated with gender, body weight, and administration of BZDs. The C/DC plasma concentration ratios were 1.08 in Japanese patients receiving C monotherapy, 0.90 in Japanese patients receiving C plus BZDs, 0.51 in Swedish patients receiving C monotherapy, and 0.49 in Swedish patients receiving C plus BZDs. Thus, the lower oral clearance of C in Japanese patients compared with that in Swedish patients is not accounted for by the lower body weight in Japanese patients or by concomitant treatment with BZDs and is therefore likely to be a true ethnic difference. The higher C/DC ratio implicates a more pronounced serotonergic than noradrenergic effect in Japanese patients than in Swedish patients.