Irshaid Ym

Variability of coumarin 7- and 3-hydroxylation in a Jordanian population is suggestive of a functional polymorphism in cytochrome P450 CYP2A6

AbstractObjective: To determine the variability of coumarin 7- and 3-hydroxylation in a human population and to evaluate the evidence for the existence of genetic polymorphism in these pathways. 7-Hydroxylation of coumarin is considered to be a detoxication pathway, whilst 3-hydroxylation, which predominates in rats, leads to hepatotoxicity in the rat. Coumarin metabolic phenotypes could aid in refining the risk evaluation for humans of dietary and environmental exposure to coumarin and for the chronic use of coumarin in high doses as a drug to treat lymphoedema and certain cancers.nn Methods: Healthy male and female Jordanian volunteers (n= 103) were administered 2 mg coumarin by mouth and collected their 0–8-h urines. These, together with pre-dose blank urines, were analysed by selected-ion monitoring gas chromatography mass spectrometry for their content of the coumarin metabolites 7-hydroxycoumarin (7OHC) and 2-hydroxyphenylacetic acid (2OHPAA), the latter arising from the 3-hydroxylation pathway.nn Results: After coumarin administration, excretion of both 7OHC and 2OHPAA was highly variable. A coumarin metabolic ratio (2OHPAA/7OHC) was suggestive of polymorphism. At least one subject had a metabolic response similar to an individual known to be both phenotypically and genotypically (CYP2A6 gene) 7-hydroxylation-deficient.nn Conclusion: In the light of the finding of high variability and possible polymorphism in both the 7- and 3-hydroxylation of coumarin in a human population, we recommend a reappraisal of the risk evaluation of human exposure to coumarin, particularly in pharmaceutical doses.

Metoprolol α-hydroxylation is a poor probe for debrizoquine oxidation (CYP2D6) polymorphism in Jordanians

The frequency distribution of the 8-h urinary ratio of log metoprolol/α-hydroxymetoprolol was assessed in 65 healthy, unrelated Jordanian volunteers.There was no apparent bimodality in the frequency distribution of this ratio among the subjects studied. The frequency of the poor metabolizer phenotype of metoprolol α-hydroxylation was 1.5% (one subject). There was a significant correlation (r=0.61, P<0.05, n=39) between the log metoprolol/α-hydroxymetoprolol and the log debrisoquine/4-hydroxydebrisoquine ratios. However, the frequency of poor metabolizer status of debrisoquine among the 39 subjects was 7.7% (three subjects). Only one of the poor metabolizers of debrisoquine was also a poor metabolizer of metoprolol α-hydroxylation.These findings indicate that metoprolol α-hydroxylation by CYP2D6 represents a poor probe for studying debrisoquine polymorphism in Jordanians.

Dextromethorphan O-demethylation polymorphism in Jordanians

SummaryThe O-demethylation of dextromethorphan (DMT) to dextrorphan (DRP) was studied in 241 unrelated, healthy Jordanian volunteers (171 males, 70 females). Urine was collected for 8 h following a single oral dose of DMT bromhydrate 30 mg. A thin-layer chromatographic (TLC) technique was used to identify the metaboliser phenotype.The frequency of the poor metaboliser phenotype was found to be 2.9% (approximate 95% confidence interval 0.8–5.0%).Applying the Hardy-Weinberg Law, the frequency of the recessive autosomal gene controlling poor metabolism was 0.17 (95% confidence interval 0.108–0.232).

SIMULTANEOUS HIGH PERFORMANCE LIQUID CHROMATOGRAPHIC DETERMINATION OF DAPSONE AND MONOACETYLDAPSONE IN HUMAN PLASMA AND URINE

A rapid, specific and a one‐stage protein precipitation method for simultaneous estimation of dapsone (DDS) and monoacetyldapsone (MAD) concentration in plasma and urine using high performance liquid chromatography (HPLC) is described. The applicability of the method for monitoring DDS and MAD blood levels in two different acetylator phenotype volunteers following the administration of 100‐mg oral dose of DDS was shown. Cumulative urinary excretion of DDS and MAD were studied in the same volunteers.

Acetylator phenotypes of Jordanian diabetics

SummaryThe acetylator phenotype was determined in 31 insulin-dependent (IDDM) and 110 noninsulin-dependent (NIDDM) Jordanian diabetics, and was compared to that of 160 healthy volunteers of the same ethnic group. Dapsone was used as the test drug.The rapid acetylator phenotype was slightly less frequent in IDDM and slightly more frequent in NIDDM. Neither of the differences was significant. When acetylator status in the two types of diabetes mellitus was compared, there was a significant difference among the two groups.Patients with IDDM had a higher percentage of the slow acetylator phenotype when compared to NIDDM patients. The association between acetylator status and IDDM in Jordanians, which agrees with that reported for the Saudi Arabian population, is the reverse of what is found in European populations.The results demonstrate ethnic differences in acetylator status among IDDM patients.

Lack of association between glucose-6-phosphate dehydrogenase deficiency and dextromethorphan O-demethylation polymorphism

Oxidation of drugs by the mixed-function oxidase system (cytochrome P-450) is one of the most important pathways of drug metabolism. This reaction requires nicotinamide adenine dinucleotide phosphate ( N A D P H ) and molecular oxygen. Genetic variations in oxidative drug metabolism are well recognized [1]. Regarding the oxidation of certain drugs subjects in a given population may be divided into either poor or extensive oxidizers [1]. The poor oxidizer status is inherited in an autosomal recessive fashion [2]. Oxidation polymorphism of the debrisoquine/sparteine type which also affects dextromethorphan (DMT) O-demethylat ion represents the most widely studied form of genetic variation in drug oxidation [3]. Glucose-6-phosphate dehydrogenase (G6PD) is the first enzyme in the hexose monophospha te shunt, its deficiency is inherited in a sex-linked incomplete co-dominant fashion [4] and it catalyzes a reaction which generates N A D P H [5]. Since this reaction is a major source of N A D P H in the body, the question arises about the influence of G6PD deficiency and the consequent reduction of N A D P H production on oxidation phenotyping. We observed during a previous study to identify the frequency of D M T O-demethylat ion poor metabolizer state that one of our poor metabolizers was also G6PD deficient. Based on this observation and on the theoretical role of G6PD deficiency in influencing oxidation of drugs, the D M T O-demethylat ion phenotyping in a group of G6PD deficient individuals was studied to answer the question: Is G6PD deficiency associated with D M T O-demethylat ion poor metabolizer status? Members of two families with G6PD deficiency were recruited for the study. All participants had normal serum creatinine and alanine aminotransferase. Subjects with G6PD deficiency were asymptomatic. The study protocol was approved by the local university Ethics Commit tee and an informed written consent was obtained f rom all individuals. Red blood cell G6PD activity was measured according to the Boehringer Mannheim G6PD diagnostic Kit using the method originally described by Kornberg et al. [6]. Just before going to bed each participant was asked to empty his/her urinary bladder and to ingest a single 30 mg capsule of dext romethorphan HBr. Urine was then collected for an 8 hour overnight period. Urine volume was recorded and a 20 ml aliquot was kept frozen at -20 °C pending analysis. Dext romethorphan O-demethylat ion phenotyping was accomplished by the method of Guttendoff et al. [7]. The metabolizer phenotype and G6PD activity of members of two families are shown in Table 1. There was only another poor metabolizer of D M T among studied