摘要:

The sequence and organization of theCYP1Acluster on human chromosome 15 was determined. A human genomic clone from a BAC library, containing bothCYP1A1andCYP1A2genes, was isolated and sequenced. The results of Southern blot analysis using human genomic DNA were compatible with the structure of the BAC clone. TheCYP1A1andCYP1A2genes are separated by a 23 kb segment that contains no other open reading frames. TheCYP1A1andCYP1A2genes are in opposite orientation, revealing that the 5′ flanking region is in common between the two genes. Analysis of the sequence obtained revealed the presence of xenobiotic response elements (XREs) previously reported forCYP1A1andCYP1A2and several additional consensus sequences for putative XREs. The presence of all the XREs upstream of both genes suggest that some of the regulatory elements known to controlCYP1A1gene expression, could also controlCYP1A2gene expression.

ISSN:0960-314X    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Arylamines such as 2-naphthylamine and 4-aminobiphenyl are suspected human bladder procarcinogens that require bioactivation to DNA-reactive species to exert their carcinogenic potential. The goals of the present study were (i) to assay for the presence of the arylamine acetyltransferases NAT1 and NAT2, and of the cytochrome P450 isoform CYP1A2, in human bladder epithelium; and (ii) to determine whether the activities of these arylamine biotransforming enzymes differ between bladder cancer patients and control subjects. We measured in-vitro enzyme activities in biopsies of normal, undiseased bladder epithelium obtained from 103 bladder cancer patients. NAT1 activity was detectable in all samples, with mean levels higher than those found in human liver. Kinetic evidence also suggested low levels of NAT2 expression in this tissue, but there was no detectable CYP1A2 by either enzymatic or immunochemical measurements. We also compared several probe drug indices of in-vivo NAT1, NAT2 and CYP1A2 activity between 53 bladder cancer patients and 96 cancer-free control subjects who were carefully matched for age, gender and smoking status.NAT1andNAT2genotypes were also determined. No significant differences were found between bladder cancer patients and control subjects for a number of individual phenotypic or genotypic predictors of enzyme function. Our results suggest that although expression of particular arylamine biotransforming enzymes within the bladder tissue could play a significant role in locally bioactivating arylamine procarcinogens in theory, interindividual variations in CYP1A2, NAT1 and NAT2 activities do not significantly differ between bladder cancer patients and control subjects when potential arylamine exposures are controlled for in the experimental study design.

ISSN:0960-314X    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Serotonin receptor genes have always been considered excellent candidate genes in the aetiology of neurogenetic diseases. In this study, we assessed sequence variations of theHTR3Agene. For this purpose, we established exon-specific primers and analysed DNA samples from 165 unrelated individuals including 70 schizophrenic patients, 48 patients with bipolar affective disorder and 47 healthy control persons using polymerase chain reaction/single-strand conformational polymorphism analysis. We discovered six sequence variants, five of which represent polymorphisms. These polymorphisms could not be associated with schizophrenia and bipolar affective disorder (P= 0.055–1). We also detected a missense mutation in exon 9 in a schizophrenic patient at a conserved position (Pro391Arg). To determine the incidence of this substitution an extended set of 358 schizophrenic patients and 155 control individuals was investigated. The Pro391Arg mutation was not detected in these schizophrenic patients and controls screened. However, a second missense mutation (Arg344His) was detected in one schizophrenic patient, but not in any of the controls. These results suggest that the observed mutations inHTR3Aare rare and therefore do not play a major role in the aetiology of the disorder. Further studies are needed to support the hypothesis thatHTR3Amay contribute to the schizophrenia in these patients.

ISSN:0960-314X    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

In the present study, the occurrence of a modulatory effect of 14 neurotransmitters, precursors and metabolites on the cytochrome P450 2C9 (CYP2C9) enzyme activity, as determined by diclofenac 4-hydroxylation, was studied in human liver microsomes. Two indoleamines, 5-hydroxytryptamine (5-HT) and adrenaline, showed a non-competitive-type inhibitory effect of approximately 90% of the diclofenac 4-hydroxylase activity, with Kivalues of 63.5 (0.7 and 156 (89.3 μm, respectively. The rest of substances analysed were weak inhibitors or had no inhibitory effect. CYP2C subfamily is present in human brain, although CYP2C9 isozyme has not yet been identified in this tissue, and CYP2C9 is involved in the metabolism of psychoactive drugs. Therefore, the fact that endogenous compounds could modulate the CYP2C9 activity, suggests that an hypothetical local activity of brain CYP2C9 might be susceptible to regulatory mechanisms. The possible clinical implications of this modulation are discussed.

ISSN:0960-314X    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Cytochrome P450 2A6 (CYP2A6) is involved in theC-oxidation of nicotine and in the metabolic activation of tobacco nitrosamines. Recent data have suggested thatCYP2A6genetic polymorphisms might play a role in tobacco dependence and consumption as well as in lung cancer risk. However, the previously published studies were based on a genotyping method that overestimated the frequencies of deficient alleles, leading to misclassification for theCYP2A6genotype. In this study, we genotyped DNA from 244 lung cancer patients and from 250 control subjects forCYP2A6(wild-type alleleCYP2A6*1, and two deficient alleles:CYP2A6*2, andCYP2A6*4, the latter corresponding to a deletion of the gene) using a more specific procedure. In this Caucasian population, we found neither a relation between genetically impaired nicotine metabolism and cigarette consumption, nor any modification of lung cancer risk related to the presence of defectiveCYP2A6alleles (odds ratio = 1.1, 95% confidence interval = 0.7–1.9).

ISSN:0960-314X    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Ultrarapid drug metabolism mediated by CYP2D6 is associated with inheritance of alleles with duplicated or amplified functionalCYP2D6genes. However, genotyping for duplicatedCYP2D6alleles only explains a fraction (10–30%) of the ultrarapid metabolizer phenotypes observed in Caucasian populations. Using a sample ofCYP2D6duplication-negative ultrarapid metabolizer subjects and selected control subjects with extensive metabolism, we examined parts of theCYP2D7pseudogene, and the promoter region and 5′-coding sequence ofCYP2D6for polymorphisms possibly associated with the ultrarapid metabolizer phenotype. In an initial screening of 17 subjects (13 ultrarapid metabolizers and four extensive metabolizers), we identified three DNA variants in the 5′-end of theCYP2D7pseudogene and 29 variants in the 5′-end of theCYP2D6gene. Five variants were then selected for examination in a larger sample of subjects having the ultrarapid metabolizer (n= 27) or extensive metabolizer phenotype (n= 77). Subsequent statistical analyses of allele, genotype and estimated haplotype distributions showed that the 31A allele of the 31G > A (Val11Met) polymorphism was significantly more frequent in ultrarapid metabolizer subjects than in extensive metabolizer subjects (P= 0.04). Also, estimation of haplotype frequencies suggested that one of the haplotypes with the 31A variant was significantly more frequent among the ultrarapid metabolizers compared with the extensive metabolizers (P= 0.03). The average metabolic ratio was significantly lower in subjects possessing the 31A allele compared with subjects homozygous for the 31G allele (P= 0.02). We also observed a non-significant over-representation of the G-allele of a −1584 C > G promoter polymorphism in the ultrarapid metabolizer group. Since our results are based on a relatively low number of subjects, further studies on larger samples and functional analyses of the polymorphisms detected are necessary to determine the role of the 31G > A and −1584C > G variants inCYP2D6duplication-negative ultrarapid metabolizer subjects.

ISSN:0960-314X    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Sulfotransferase (SULT) enzymes catalyze the sulfate conjugation of drugs, other xenobiotics, neurotransmitters and hormones. The genes for SULT1A1 and SULT1A2 contain common genetic polymorphisms that are associated with individual variations in levels of enzyme activity as well as variations in biochemical and physical properties. We set out to compare the frequencies of commonSULT1A1andSULT1A2alleles in Caucasian, Chinese and African-American subjects. Allele frequencies forSULT1A1*1,*2and*3in 242 Caucasian subjects were 0.656, 0.332 and 0.012, respectively. Frequencies of those same alleles were significantly different in 290 Chinese subjects: 0.914, 0.080 and 0.006, respectively, as were frequencies in 70 African-American subjects: 0.477, 0.294 and 0.229, respectively. Ethnic variation in allele frequencies was also observed forSULT1A2, with frequencies in Caucasian subjects forSULT1A2*1,*2and*3of 0.507, 0.389 and 0.104; frequencies in Chinese of 0.924 and 0.076 with no*3alleles observed; and, finally, in African-Americans frequencies of 0.637, 0.249 and 0.114, respectively. We also found thatSULT1A1*2andSULT1A2*2, the most common variant alleles for these two genes, were in positive linkage disequilibrium in all three populations studied, withD′ values of 0.776 in Caucasian (P< 0.001), 0.915 in Chinese (P< 0.001) and 0.864 in African-American subjects (P< 0.001). These observations represent a step towards determining the possible functional implications for individual variations in sulfate conjugation of common genetic polymorphisms forSULT1A1andSULT1A2.

ISSN:0960-314X    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

The polymorphisms of the important xenobiotic metabolizing enzymes CYP2D6, CYP2C19 and CYP2E1 have been studied extensively in a large number of populations and show significant heterogeneity in the frequency of different alleles/genotypes and in the prevalence of the extensive and poor metabolizer phenotypes. Understanding of inter-ethnic differences in genotypes is important in prediction of either beneficial or adverse effects from therapeutic agents and other xenobiotics. Since no data were available for Australian Aborigines, we investigated the frequencies of alleles and genotypes forCYP2D6, CYP2C19andCYP2E1in a population living in the far north of Western Australia. Because of its geographical isolation, this population can serve as a model to study the impact of evolutionary forces on the distribution of different alleles for xenobiotic metabolizing enzymes. TwelveCYP2D6alleles were analysed. The wild-type allele *1was the most frequent (85.8%) and the non-functional alleles (*4, *5, *16) had an overall frequency of less than 10%. Only one subject (0.4%) was a poor metabolizer for CYP2D6 because of the genotype *5/*5. ForCYP2C19, the frequencies of the *1(wild-type) and the non-functional (*2and *3) alleles were 50.2%, 35.5% and 14.3%, respectively. The combinedCYP2C19genotypes (*2/*2, *2/*3or *3/*3) correspond to a predicted frequency of 25.6% for theCYP2C19poor metabolizer phenotype. ForCYP2E1, only one subject had the rarec2allele giving an overall allele frequency of 0.2%. ForCYP2D6andCYP2C19, allele frequencies and predicted phenotypes differed significantly from those for Caucasians but were similar to those for Orientals indicating a close relationship to East Asian populations. Differences between Aborigines and Orientals in allele frequencies forCYP2D6*10andCYP2E1 c2may have arisen through natural selection, or genetic drift, respectively.

ISSN:0960-314X    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Paraoxonase (PON1) is a protein component of high-density lipoprotein (HDL) particles that protects against oxidative damage to both low-density lipoprotein and HDL and detoxifies organophosphorus pesticides and nerve agents. A wide range of expression levels of PON1 among individuals has been observed. We examined the promoter region of PON1 for genetic factors that might affect PON1 activity levels. We conducted a deletion analysis of thePON1promoter region in transient transfection assays and found that cell-type specific promoter elements for liver and kidney are present in the first 200 bp upstream of the coding sequence. Sequence analysis of DNA from a BAC clone and a YAC clone identified five polymorphisms in the first 1000 bases upstream of the coding region at positions −108, −126, −162, −832 and −909. Additionally, the promoter sequences of two individuals expressing high levels of PON1 and two individuals expressing low levels of PON1 were analysed. The two polymorphisms at −126 and −832 had no apparent effect on expression level in the reporter gene assay. The polymorphisms at position −909, −162 (a potential NF-I transcription factor binding site) and −108 (a potential SP1 binding site) each have approximately a two-fold effect on expression level. The expression level effects of the three polymorphisms appear not to be strictly additive and may depend on context effects.

ISSN:0960-314X    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

The aryl hydrocarbon receptor (AHR) is a ligand-dependent transcriptional regulator of several genes including the cytochrome P4501 (CYP1) family as well as genes encoding factors involved in cell growth and differentiation. In mice, several polymorphic forms of the AHR are known, some of which have altered affinity for toxic and carcinogenic ligands. Remarkably little genetic variation has been detected in the humanAHRgene. In studies on humanAHR, Kawajiriet al.(Pharmacogenetics1995; 5:151–158) reported a variation at codon 554 that results in an amino acid change from arginine to lysine; the frequency of the variant allele in a Japanese population (n= 277) was 0.43. We investigated the Lys554allele in 386 individuals of various ethnic origins and found the frequency to be: 0.58 in Ivory Coast Africans (n= 58); 0.53 in a mixed African group (n= 20); 0.39 in Caribbean-Africans (n= 55); 0.32 in Canadian Chinese (n= 41); 0.14 in North American Indians (n= 47); 0.12 in French Canadian Caucasians (n= 20); 0.11 in a mixed ethnicity North American group (n= 45); 0.09 in Canadian Inuits (n= 22); and 0.07 in German Caucasians (n= 78). We expressed the human Lys554allele in an in-vitro transcription-translation system and found that the receptor bearing the R554L substitution had an equivalent ability to that of the wild-type receptor to bind to a dioxin-responsive element following treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The Lys554allele also was equivalent to the wild-type receptor at stimulatingCYP1A1mRNA expression when transfected into TCDD-treated receptor-deficient mouse Hepa-1 cells. It is not yet known if any of the wide variations in allele frequency at codon 554 are related to ethnic differences in susceptibility to adverse effects of environmental chemicals.

ISSN:0960-314X    

出版商:OVID    

年代:2001

数据来源: OVID