摘要:

Usingin vitrotechniques, the present study demonstrates that CYP2D6, 2C19 and 3A4 are involved in N-demethylation of citalopram (CIT) enantiomers. Human liver microsome incubations performed with specific inhibitors of these three CYP isozymes have shown up to 60% inhibition of demethylcitalopram production. cDNA expressed human cytochrome P-450 3A4, 2C19 and 2D6 isozymes, but not CYP1A2, were identified to be involved in N-demethylation of CIT enantiomers. Kinetics using cDNA expressed CYP2C19 and CYP3A4 show Kmvalues in the same range: 198 µM, 211 µM for CYP2C19 and 169 µM, 163 µM for CYP3A4 for S- and R-CIT demethylation, respectively. In contrast, kinetics using cDNA expressed CYP 2D6 show a Kmof 18 µM and 22 µM for S- and R-CIT demethylation, respectively. Nevertheless, kinetics using cDNA expressed CYP2C19 and 3A4 have a range of Vmaxvalues ten times higher than that of CYP2D6. For this reason, intrinsic clearance values (Vmax/Km) for Sand R-CIT were within a small range for these three isozymes: 0.25 to 0.39 µlh-1x pmol-1of CYP. CYP2D6 has an opposite stereoselectivity in the biotransformation of CIT enantiomers than CYP2C19 and 3A4; the S/R ratios of the intrinsic clearance were 0.71, 1.57 and 1.37, respectively. Taking into account that CYP isozymes are expressed at various levels, CYP2D6, which is expressed at lower levels than CYP2C19 and CYP3A4, plays a minor role in the biotransformation of CIT enantiomers. These results confirm that the use of cDNA expressed CYP isozymes is a potent tool for the measurement of kinetic constants and help to predict clearance modifications of CIT enantiomers, especially in poor metabolizers of mephenytoin (with a CYP2C19 deficiency) or patients comedicated with potent CYP2C19 or 3A4 inhibitor(s). For instance, fluvoxamine (100µM) inhibits CIT N-demethylation by 64% in microsomes.

ISSN:0960-314X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Cytochrome CYP1A2, a liver enzyme responsible for the metabolic activation of a number of putative human carcinogens, exhibits wide inter-individual differences in activity. In order to characterize sources of variability in CYP1A2 activity, we phenotyped (with the caffeine test) 90 subjects of various ethnic backgrounds in Hawaii. Forty-three subjects were patients within-situcolorectal cancer treated by polypectomy and 47 were healthy population controls. Subjects were also administered a detailed lifestyle questionnaire, including a quantitative food frequency questionnaire, and were assessed for plasma levels of carotenoids, tocopherols, retinol, ascorbic acid, cholesterol and triglycerides. In a stepwise multiple regression, 27% of the overall variation in CYP1A2 activity was explained by seven variables. Plasma lutein explained the largest portion of the variance (7%) and was negatively associated with CYP1A2 activity (p<0.01), as were use of menopausal replacement estrogens (p=0.04), plasma alpha-tocopherol (p=0.05) and alcohol consumption (p=<0.01). Acetaminophen use (p=0.05), coffee consumption (p=0.05) and plasma lycopene (p=0.06) were positively associated with CYP1A2 activity. After adjustment for these variables, no association was found between CYP1A2 activity and sex, race, age, education, smoking, physical activity, weight, vitamin E supplements, the other plasma micronutrients measured, and dietary intakes of red meat, processed meat and cruciferous vegetables. Results were similar for colorectal cancer cases and controls. Almost two-thirds (73%) of the variability in CYP1A2 activity remained unexplained. This study confirms an enhancing effect of acetaminophen and coffee on CYP1A2 activity and suggests an inhibitory effect of estrogens, alcohol and food sources of lutein and alpha-tocopherol on this enzyme.

ISSN:0960-314X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

The incidence rate of testicular cancer has been steadily increasing during the last 50 years, and only cryptorchidism, i.e. undescended testes, has been identified as an important risk factor. An interplay between changing environmental factors and genetic susceptibility e.g. in foreign compound metabolizing enzymes, may have important influences on the riskThe aim of this study was to investigate if glutathione S-transferase µ (GSTµ ) deficiency, which in previous studies has been associated with malignant melanoma and cancers of the lung and bladder, is a risk factor of testicular cancer. Three hundred and seventy-eight men participated (80 seminomas, 104 non-seminomas and 194 controls) in a populationbased case-control studyThe phenotype of GSTµ was determined in 366 men by ELISA, the genotype was determined in 324 men by polymerase chain reaction. The concordance between geno- and phenotype was 94.4%. The odds ratio of having the GSTµ negative phenotype and testicular cancer was 1.08, (0.72-1.64; 95% confidence interval (CI)), and the odds ratio of having the GSTMlnuIl genotype and testicular cancer was 1.10; CI95%(0.71-1.70)This study provides no evidence of an association between phenotypically determined GSTµ deficiency orGSTM1null genotype and testicular cancer. The narrow confidence intervals rule out GSTµ, as a major single risk factor for testicular cancer.

ISSN:0960-314X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

An unstable variant of human butyrylcholinesterase (BChE) is described in four apparently unrelated individuals sensitive to succinylcholine. Sequencing of genomic DNA revealed a single nucleotide substitution which results in the replacement of amino acid residue Glyl 15 by Asp. This variant can be recognized by its increased instability under extremes of temperature such as heating and also freezing and thawing, both in homozygous and heterozygous states. When in heterozygous combination with the Atypical variant, it produces dibucaine and fluoride numbers which are intermediary between those of Atypical homozygotes and heterozygotes. After repeated freezing and thawing, however, these values approach those of homozygous Atypical plasma. Measurement of activity and immunoreactive BChE protein in plasma of individuals representing different combinations of this allele indicated that the presence of the Usual or Atypical enzymes seems to partially protect this variant from denaturation in vivo. Phenotyping fresh serum or plasma samples, before they are frozen, is critical for the identification of this, and possibly some other, unstable variants.

ISSN:0960-314X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Sorivudine, l-β-D-arabinofuranosyl-5-(E)-(2-bromovinyl)uracil, is a potent antiviral agent against varicella-zoster virus and herpes simplex virus type 1. However, sorivudine should not be used in combination with anticancer drugs such as 5-fluorouracil (5-FU) because (E)-5-(2-bromovinyI)uracil (BVU), a metabolite of sorivudine, inhibits the degradation of 5-FU, resulting in its accumulation in the blood and marked enhancement of the toxicity of 5-FU. Since phosphorolytic enzymes generate BVU from sorivudine, we investigated the distribution of the enzyme activity in rats. High activity was found in the cecal and large intestinal contents, while very low or no detectable activity in the liver, kidney, stomach, cecum, large intestine, and the stomach and small intestinal contents. These results suggest that intestinal microflora play an important role in BVU production. Therefore, we measured the phosphorylase activity in cell-free extracts from 23 aerobes, 16 anaerobes and a fungus.BacteroidesspeciesB. vulgatus,B. thetaiotaomicron,B. fragilis,B. uniformisandB. eggerthii, dominant members of intestinal microflora, had high activity to convert sorivudine to BVU. To elucidate the contribution of intestinal microflora to BVU productionin vivo, we administered sorivudine to rats treated with several antibiotics and measured the BVU concentration in the serum of rats. When sorivudine was given to rats treated with ampicillin or a mixture of bacitracin, neomycin and streptomycin, which decreased the numbers of viable aerobes and anaerobes, only a small amount of BVU was found in the serum. BVU concentration in the serum of rats treated with metronidazole to decrease the number of intestinal anaerobes was also very low. In contrast, BVU concentration in the serum of rats treated with kanamycin, which was used to decrease the number of aerobes selectively, was higher than that of non-treated rats. These results also suggest that BVU is produced by intestinal anaerobic bacteria especiallyBacteroidesspeciesin vivo.

ISSN:0960-314X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Whilst the majority of individuals within a British white population are able to convert greater than 90% of their dietary-derived trimethylamine to its N-oxide, outliers exist who show varying degrees of impairment. Such individuals excrete unoxidized trimethylamine in their urine and, if sufficiently compromised, may experience malodour problems (Fish- Odour Syndrome). Little information concerning this polymorphicN-oxidation process is available in other ethnic groups and the present study explores Jordanian, Ecuadorian and New Guinean populations. Subjects with a relative deficiency inN-oxidation were found in all three groups, with 1.7% (2/116) Jordanian, 3.8% (3/80) Ecuadorian and 11.0% (11/100) New Guinean excreting 80% or less of their total trimethylamine as theN-oxide. Two subjects from the Ecuadorian population (4% and 33% total trimethylamine as theN-oxide) exhibited frank trimethylaminuria. These observations suggest that a compromised ability to N-oxidize trimethylamine is detectable in several ethnic groups and that this polymorphic phenomenon may have a widespread existence.

ISSN:0960-314X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Single nucleotide substitutions are known to result in a different amino acid at one of four sites in cytochrome P4502C9 (CYP2C9) namely: residue 144: Arg/Cys; residue 358: Tyr/Cys; residue 359: Ile/Leu and residue 417: Gly/Asp. Polymerase chain reaction (PCR) - based amplification of the nucleotide fragments encompassing the four residues (144, 358-359 and 417) in 18 samples of human genomic DNA from a liver bank and one sample of DNA extracted from the blood of a known poor metabolizer of tolbutamide has been carried out. The products of PCR amplification were analysed by either allele-specific restriction endonucleases or probed with radioactively labelled allele-specific oligonucleotides in dot blot hybridizations. Fourteen individuals were homozygous for Arg144 and four were heterozygous Arg/Cys144. All individuals analysed were homozygous for Tyr358 (n=17) and for Gly417 (n=18). With the exception of one heterozygote the other 17 subjects were homozygous for IIe359. The genotype of the known poor metabolizer of tolbutamide was homozygous for Arg144, Leu359 and Gly417. The relative levels of expression of the Cys and Arg144 alleles was studied in the heterozygotes. A relative 5- to 10-fold greater expression of the Cys- over the Arg144 allele was noted in two heterozygotes. There was no apparent correlation of genotype to the hydroxylation of the known CYP2C9 substrates phenytoin, tolbutamide, torasemide and diclofenac. Apparent Kmvalues for the cDNA-expressed Arg144/Ile359, Cys144/ Ile359 and Arg144/Leu359 variants towards tolbutamide were 91µM, 62µM and 229µM, respectively. It is likely that functional changes occurring as a result of the Ile359Leu transition are responsible for the tolbutamide poor metabolizer phenotype.

ISSN:0960-314X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

The 4'-hydroxyIation of S-mephenytoin is polymorphic in man. The poor metabolizer (PM) phenotype exhibits a lower frequency in Caucasians (2–5%) compared to Oriental populations (13–23%). Previous studies from our laboratory have described two mutations (CYP2C19mland CYP2C19m2) which account for ~100% of Oriental and ~85% of Caucasian PM alleles. The present study examined whether the genotype predicted the phenotype in Japanese, Filipino and Saudi Arabian populations, and compared the frequencies of the defective CYP2C19 alleles in these populations with those found in European-Americans, Chinese-Taiwanese, and African-Americans from North Carolina. Among 53 Japanese, 15% were PMs and among 52 Filipinos 23% were PMs. Among 97 Saudi Arabians, only two were PMs. There was a complete concordance between genotype and phenotype in all three populations. The incidence of CYP2C19mlwas 0.23 (95% confidence limits 0.15–0.31) in Japanese, 0.39 (95% confidence limits 0.29–0.48) in Filipinos, 0.32 (95% confidence limits 0.26–0.38) in Chinese- Taiwanese, 0.15 (95% confidence limits 0.10–0.20) in Saudi Arabians, 0.13 (95% confidence limits 0.08–0.17) in European-Americans, and 0.25 in African-Americans from North Carolina (95% confidence limits 0.14–0.31). The incidence of CYP2CJ9mlin Saudi Arabians was similar to that found in European-Americans, and significantly lower than that found in Oriental populations or African-Americans (p<0.05). CYP2C19m2was not found in European-Americans, Saudi Arabians or African-Americans (95% confidence limits 0–0.014). The incidence of CYP2C19m2in the three Oriental populations ranged from 0.10 (95% confidence limits 0.05–0.17) in Japanese and 0.08 (95% confidence limits 0.03–0.13) in Filipinos to 0.06 (95% confidence limits 0.03–0.08) in Chinese-Taiwanese.

ISSN:0960-314X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

The catechoI-O-methyltransferase (COMT) gene occurs as two polymorphic alleles, which code for a high activity thermostable and low activity thermolabile form of the enzyme. We devised a fast solid-phase minisequencing assay for genotyping theCOMTgene at nucleotide position 544 encoding amino acid residue 158. The method was applied to correlate the genotype of theCOMTgene with the biological activity of theCOMTenzyme. In red blood cells from individuals homozygous for G at nucleotide position 544 coding for Val-158, the activity ofCOMTranged from 0.55–1.03 pmol min-1mg-1protein, and in individuals homozygous for A at position 544 coding for Met-158, the activity ranged from 0.21–0.43 pmol min-1mg-1Heterozygotes showed intermediate activities of 0.20–0.88pmol min-1mg-1. The thermostability (heated/unheated) at 48º C of the high activity form was shown to be about twofold compared to that of the low activity form of the enzyme. By analysing 76 individual samples and three pooled samples representing altogether 3140 individuals using the solidphase minisequencing method, the twoCOMTalleles were shown to be equally distributed in the Finnish population. No statistically significant difference in the frequencies of theCOMTalleles was found when comparing the normal population with a sample of 158 Finnish patients with Parkinson's disease.

ISSN:0960-314X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

PolymorphicN-acetyltransferase (NAT2) genotypes were determined in 106 unrelated Emiratis by PCR-RFLP analysis to obtain estimates of allele frequencies. Thirteen different genotypes were found, four associated with the rapid acetylator phenotype and nine with the slow acetylator phenotype. Among 67 phenotypically slow acetylators, there was 100% concordance between phenotype and genotype. Among 39 phenotypically rapid acetylators, 37 possessed at least one wild type allele; a 95% concordance with genotype. Seven different NAT2 alleles associated with slow acetylation were found. The commonest was aNAT2*5 type (C481T) allele which occurred with a frequency of 0.53, a significantly higher frequency than has been reported for other ethnic groups. A second slow allele, aNAT2*6 type (G590A), occurred with a frequency of 0.21. The most common genotypes found wereNAT2*5/*5 homozygotes,NAT2*5/*6 heterozygotes andNAT2*4/*5 heterozygotes with frequencies of 0.25, 0.25 and 0.22 respectively. The high overall prevalence of alleles associated with slow acetylation (173/212; 81.6%) among Emiratis is consistent with previously reported high frequency of the slow acetylator phenotype in Arabs. Two apparently new slow alleles were identified but have not yet been fully characterized. One appears to be aNAT2*5 variant allele. The other uncharacterized allele appears likely to contain an entirely new mutation associated with slow acetylation.

ISSN:0960-314X    

出版商:OVID    

年代:1997

数据来源: OVID