J. Cobaleda

Interethnic differences in drug metabolism: influence of genetic and environmental factors on debrisoquine hydroxylation phenotype

SummaryGenetic and environmental factors are determinants of the interindividual and interethnic variability in drug metabolism. The metabolism of several important drugs (e.g. haloperidol) cosegregates with that of debrisoquine. Thus, interethnic differences in debrisoquine hydroxylation polymorphism (CYP2D6) might be partly responsible for the variations in haloperidol disposition between races. The influence of tobacco, ethanol, caffeine, gender, and oral contraceptive use on the debrisoquine metabolic ratio (MR) has been analyzed in 633 Spanish healthy volunteers. MR was also determined in panels of healthy volunteers. 18 smokers were studied during a tobacco abstinence period, and 31 women three times during the same menstrual cycle. Among EMs, debrisoquine MR was significantly (P<0.05) lower during smoking cessation (mean antilog ± SD, 0.48 ± 0.29) compared to a smoking period (0.61 ± 0.23). During the lutheal phase of the menstrual cycle, debrisoquine MR was also significantly (P<0.01) lower (0.33 ± 0.41) compared to the ovulatory-phase (0.41 ± 0.34) and the phase before ovulation (0.44 ± 0.36). Among EMs, it is suggested that debrisoquine MR may be modified by tobacco smoking and sexual hormones. The clinical relevance of these findings remains unclear.

Debrisoquine oxidation phenotype during neuroleptic monotherapy.

Summary.The debrisoquine oxidation phenotype was determined in 91 schizophrenic patients on monotherapy with different neuroleptics and in 67 untreated healthy volunteers.The prevalence of poor metabolizers of debrisoquine was significantly higher in the patients (46.2%) than in the healthy subjects (7.5%). Treatment with phenothiazine antipsychotics (chlorpromazine, levomepromazine and thioridazine) was associated with a higher debrisoquine metabolic ratio than treatment with haloperidol. On the other hand, treatment with clothiapine appeared not to interfere with debrisoquine oxidation.Oral administration of 50 mg thioridazine daily to 8 healthy subjects resulted in a marked increase in the debrisoquine metabolic ratio and 4 of them were transformed into phenotypically poor metabolizers.The results confirm the fact that phenothiazines, and to a lesser extent haloperidol, inhibit the oxidative metabolism of debrisoquine. They show also that clothiapine administration does not disturb the debrisoquine metabolic ratio.

Debrisoquin oxidation polymorphism in a Spanish population

The capacity for debrisoquin metabolism was determined in 377 healthy Spanish volunteers by measuring the amount of debrisoquin and its main metabolite, 4‐hydroxydebrisoquin, in urine after an oral dose of debrisoquin. Debrisoquin oxidation was polymorphic, with 25 subjects (6.6%) phenotyped as poor metabolizers whereas 352 subjects (93.4%) were classified as extensive metabolizers. The metabolic ratio between debrisoquin and 4‐hydroxydebrisoquin (percent of dose) in 6‐hour urine samples ranged from 0.03 in extensive metabolizers to 93.5 in poor metabolizers. The proportion of poor metabolizers found is in the range observed in other white populations studied.

Oxidative polymorphism of debrisoquine in Parkinson's disease.

Oxidative phenotype and metabolic ratio (MR) of debrisoquine (DBQ) have been determined in 87 patients with Parkinsons disease and in 556 healthy control subjects. Three patients (3.45%) and 34 control subjects (6.12%), having an MR greater than 12.6, were classified as poor metabolisers (PM) of DBQ (ns). The distribution of MR values in the 84 Parkinsonian patients classified as extensive metabolisers (EM) showed a less efficient oxidative rate when compared with controls of the same phenotype (p less than 0.001). This difference may be due to enzymatic inhibition caused by drug treatment in 40 of these patients. As in patients not taking any drug known to inhibit the oxidation of DBQ, distribution of MR values was not different from that in controls. A negative correlation (r = -0.36, p less than 0.02) was found between MR of DBQ and age at onset of disease in patients free of drugs known to interact with DBQ metabolism. A higher rate of DBQ oxidation could be a genetic factor that delays the clinical onset of Parkinsons disease in predisposed people.

Increased risk for major depression associated with the short allele of the serotonin transporter promoter region (5-HTTLPR-S) and the CYP2C9*3 allele.

In the present study, we aimed to analyze the potential relevance of the polymorphism in the promoter region of the serotonin transporter (SERT or 5‐HTT) gene (5‐HTTLPR) and the risk of suffering major depression (MDD) in a population of patients previously genotyped for CYP2C9. Seventy white European psychiatric outpatients suffering from MDD and a group of 142 healthy volunteers (HVs) were studied. The frequency of subjects carrying the 5‐HTTLPR‐S allele was higher (P < 0.05) among MDD than in HV. The odds ratio associated with 5‐HTTLPR‐S allele was 2.03 for the MDD patients in comparison with the HV group. Previously, we found in this population that the CYP2C9*3 allele frequency was higher among this population of MDD patients than in HV. The frequency of subjects with the combination 5‐HTTLPR‐S and CYP2C9*3 alleles was higher (P < 0.01, odds ratio 3.47) in MDD than in HV. The present findings provide preliminary evidence about the greater risk of suffering MDD for individuals carrying both 5‐HTTLPR‐S and CYP2C9*3 alleles.

Polymorphic oxidation of debrisoquine in lung cancer patients

Oxidative polymorphism of debrisoquine (DBQ) was assessed in 84 patients (81 male) with histologically proven bronchogenic carcinoma and in 143 healthy male smokers. 80 (95%) patients and 133 (93%) controls, with a metabolic ratio (MR) below 12.6, were classified as extensive metabolisers of DBQ (no significant difference between patients and controls). Only 1 of the 73 patients with epidermoid or microcytic carcinomas was classified as a poor metaboliser (PM) (P = 0.031 compared with controls). 63 patients (75%) and 110 controls (77%) showed a very fast oxidative rate, with MR values under 1 (not significant). The EM phenotype of DBQ might be a secondary genetic risk factor for developing bronchogenic carcinoma in male smokers.

Determination of debrisoquine and 4-hydroxydebrisoquine by high-performance liquid chromatography: application to the evaluation of CYP2D6 genotype and debrisoquine metabolic ratio relationship

Abstract The drug-metabolizing cytochrome P450 (CYP) enzyme CYP2D6 is involved in the metabolism of several clinically important drugs. So far more than 50 different CYP2D6 allelic variants have been described, and thus there is an increased need for routine high-performance liquid chromatography (HPLC) methods for the evaluation of the functional implication of CYP2D6 polymorphism. Debrisoquine is metabolized to 4-hydroxydebrisoquine by CYP2D6, and therefore it has been used widely to determine the hydroxylation capacity of the enzyme. The aim of the present study was to develop a simple, accurate HPLC method with ultraviolet detection for the measurement of debrisoquine and 4-hydroxydebrisoquine in urine for evaluation of the relationship between CYP2D6 enzyme activity and genotypes. For the HPLC determination, a C18 extraction column was used with a flow rate of 0.8mL/min and detection at 210nm. The compounds were eluted from the column in less than 10min. Coefficients of variation at all concentrations were less than 4% for both compounds. The debrisoquine/4-hydroxydebrisoquine ratio (debrisoquine metabolic ratio) was determined in a panel of 16 Caucasian healthy volunteers with zero (poor metabolizers), one, two or more than two (ultrarapid metabolizers) CYP2D6 active genes. Significant correlation (p<0.05) between the number of CYP2D6 active genes and the hydroxylation capacity of the enzyme was found. The present HPLC method was simple, fast and accurate, and thus will be useful for the evaluation of CYP2D6 hydroxylation capacity in pharmacogenetic studies.

Acetylator polymorphism in Parkinson's disease.

SummaryAcetylator phenotype has been determined using sulphamethazine in 100 patients with Parkinsons disease and in 93 age-matched normal control subjects. Sixty-nine patients and 54 control subjects were classified as slow acetylators (NS). No relation was found among acetylator polymorphism and age at onset or clinical stage of disease.Amongst slow acetylators, the percentage of acetylated sulphamethazine in plasma was significantly lower in patients than in controls. Despite this finding, the results do not support any relationship between acetylator polymorphism and the risk of developing Parkinsons disease.

Polymorphic Oxidation of Debrisoquine in Bladder Cancer

The oxidative polymorphism of debrisoquine has been determined in 125 patients with bladder cancer and in 556 healthy control subjects; 96.6% of patients and 93.9% of controls with a metabolic ratio of debrisoquine less than 12.6 were classified as extensive metabolizers of debrisoquine (P = NS). The distribution of frequencies of metabolic ratio values tended to have lower values in the patients (P less than 0.05), reflecting a higher oxidative rate of debrisoquine in urothelioma patients that cannot be explained solely in terms of enzymatic induction by drugs, tobacco or alcohol. Patients with a high occupational risk for urothelioma had lower metabolic ratio values (P = 0.03). Our results suggest that oxidative polymorphism of debrisoquine might be related to the pathogenesis of bladder cancer.

Debrisoquine Oxidation Phenotype in Psychiatric Patients

Between 5% and 10% of Caucasian populations exhibit poor metabolism of debrisoquine and sparteine (Clark 1985). Results obtained by our group indicate that among the Spanish population the percentage of poor metabolizers of debrisoquine is around 6% (Benitez et al. 1988). Generally the poor-metabolizer phenotype is at increased risk of toxicity when treated with drugs subjected to oxidative metabolism by the debrisoquine/sparteine type of path-way (Idle et al. 1983). A significant correlation between nortriptyline clearance and debrisoquine metabolic ratio has been demonstrated by Bertilsson et al. (1980). Steady-state concentrations of desipramine have also been shown to be highly correlated with the debrisoquine metabolic ratio (Bertilsson and Aberg-Wistedt 1983; Spina 1987).