摘要:

CYP2G1is an abundant, olfactory mucosa-specific cytochrome P450 enzyme active in the metabolism of sex steroids and xenobiotic substrates in mammalian animals. Two different humanCYP2Ggenes,CYP2GP1andCYP2GP2, were characterized in the present study. Polymorphisms in these genes were also studied.CYP2GP1contained a single nucleotide deletion in exon 2 (ΔC) and a 2.4-kb deletion between exons 3 and 7 (ΔE4–6), whereasCYP2GP2contained a nonsense mutation in exon 1 and another in exon 3. The coding region sequences in exons 1–3 and 7–9 of the two genes were 96.7% identical. Both genes were localized to human chromosome 19, and Southern blot analysis of human genomic DNA did not detect any additional copies of theCYP2Ggene. The occurrence of these loss-of-function mutations was analysed by polymerase chain reaction-based genotyping in more than 200 individuals. The ΔE4–6 deletion inCYP2GP1was detected in 94% of subjects (either homozygous or heterozygous), and an allele which does not contain this deletion was detected in 11.6% of individuals. The nonsense mutation inCYP2GP2exon 3 was detected in 86% of individuals (either homozygous or heterozygous); however, a potentially functionalCYP2GP2allele based on the absence of the nonsense mutation in exon 3 was also detected in 31% of individuals. These results indicate that a functionalCYP2Gallele is rare in humans. Analysis of the allelic distribution in different ethnic groups suggested that a functionalCYP2Gallele, if present, is more likely to be found in Black and Hispanic subjects.

ISSN:0960-314X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

UGT2B7 catalyses the glucuronidation of a diverse range of drugs, environmental chemicals and endogenous compounds. Hence, coding region polymorphisms ofUGT2B7are potentially of pharmacological, toxicological and physiological significance. Two variant UGT2B7 cDNAs encoding enzymes with either His or Tyr at residue 268 have been isolated. The variants, referred to asUGT2B7*1andUGT2B7*2, respectively, arise from a C to T transversion at nucleotide 802 of theUGT2B7coding region. Analysis of genomic DNA from 91 unrelated Caucasians and 84 unrelated Japanese demonstrated the presence of the variant alleles encodingUGT2B7*1andUGT2B7*2in both populations. However, while there was an approximately equal distribution of subjects homozygous for each allele in the Caucasian population, subjects homozygous for theUGT2B7*1allele were over 10-fold more prevalent thanUGT2B7*2homozygotes in Japanese. The frequencies of theUGT2B7*1andUGT2B7*2alleles were 0.511 and 0.489, respectively, in Caucasians, and 0.732 and 0.268, respectively, in Japanese. The 95% confidence intervals for the two alleles did not overlap between Caucasians and Japanese. Rates of microsomal androsterone, menthol and morphine (3-position) glucuronidation were determined for genotyped livers from Caucasian donors. Statistically significant inter-genotypic differences were not apparent for any of the three substrates. Although theUGT2B7polymorphism characterized here is probably not associated with altered enzyme activity, the results highlight the need to consider ethnic variability in assessing the consequences ofUGTpolymorphisms.

ISSN:0960-314X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

During the course of investigating the frequency of a CYP2A6 whole deletion-type polymorphism (CYP2A6*4C) in Japanese, an unexpectedly large population of heterozygotes forCYP2A6*4Cand the wild-type (CYP2A6*1A) was found. Cloning of a cDNA encoding CYP2A6 from the liver of individuals judged as heterozygotes forCYP2A6*4Cand theCYP2A6*1Awas carried out to identify the causal allele(s) responsible for a possible overestimation. A clone isolated from the liver cDNA library possessed 58 bp sequences in the 3′-untranslated region, which was replaced with the corresponding region of theCYP2A7gene. The same gene conversion existed in the genomic DNA, indicating that the replacement was not a cloning artifact. Based on the gene structure of the allele (CYP2A6*1B), this variant was thought to be one of the causal alleles responsible for overestimation of heterozygotes forCYP2A6*4CandCYP2A6*1A. To investigate this further, we developed a genotyping method which could distinguish theCYP2A6*1A, CYP2A6*1BandCYP2A6*4Calleles from each other. The results clearly showed thatCYP2A6*1Bwas the sole allele responsible for the overestimation. We conclude that the new genotyping method allows determination of six genotypes of theCYP2A6gene, simultaneously and precisely, in both Oriental and Caucasian populations.

ISSN:0960-314X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

CYP1A2 activity has been demonstrated to be bimodally or trimodally distributed in several populations, consistent with a codominant or recessive functional genetic polymorphism. However, studies aimed at identifying polymorphisms inCYP1A2have not yet adequately accounted for this distribution pattern. To search for functional polymorphisms, we performed genome-walking, polymerase chain reaction (PCR) sequencing, and cloning, and identified three novel polymorphisms in the 5′ flanking region ofCYP1A2: a T−3591G substitution, a G−3595T substitution, and a T−3605insertion. The frequency of the T−3591G substitution was determined by a PCR-restriction fragment length polymorphism assay, and found to be significantly higher (P< 0.0001) in Taiwanese (allele frequency 0.128,n= 125) compared to Caucasians (0.017,n= 87) or African Americans (0.024,n= 104). The functional consequence of the T−3591G and the G−3595T substitutions was determined by site-directed mutagenesis followed by transient transfection experiments. The T−3591G mutation was shown to be nonfunctional, while although the G−3595T mutation appeared to result in an increase in promoter activity, this was only to a small degree and therefore unlikely to be importantin vivo. In addition, we report 532 bases of 5′ flanking sequence further upstream than that reported to date, and four sequence discrepancies compared to the original published sequence (G−3649C, ΔT−3650, ΔA−4072, and C−4093ins).

ISSN:0960-314X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

The use of co-trimoxazole in HIV-positive patients has been associated with a high frequency (40–80%) of hypersensitivity reactions. This has been attributed to the bioactivation of the sulphonamide component, sulphamethoxazole (SMX), to its toxic hydroxylamine and nitroso metabolites. The aim of this study was to determine whether functionally significant polymorphisms in the genes coding for enzymes involved in SMX metabolism influence susceptibility to SMX hypersensitivity. HIV-positive patients with (n= 56) and without (n= 89) SMX hypersensitivity were genotyped for allelic variants inCYP2C9,GSTM1,GSTT1,GSTP1andNAT2using polymerase chain reaction (PCR) and/or PCR-restriction fragment length polymorphism analysis. TheCYP2C9*2/*3 genotype andCYP2C9*3allele frequencies were nine- and 2.5-fold higher in the hypersensitive group compared to non-sensitive patients, respectively, although they were not statistically significant when corrected for multiple testing. There were no differences in the frequencies of theGSTM1andGSTT1null genotypes, and the slow acetylator genotype, between hypersensitive and non-sensitive patients, whileGSTP1frequency was lower (although non-significant) in the hypersensitive group [21% versus 32%, odds ratio (OR) = 0.5,PC= 0.24]. Comparison of the genotype frequencies in HIV-positive and -negative patients showed that theNAT2slow acetylator genotype frequency in the HIV-positive patients (74%) was significantly (PC= 0.0003, OR = 2.3) higher than in control subjects (56%). Our results show that genetic polymorphisms in drug metabolizing enzymes are unlikely to be major predisposing factors in determining individual susceptibility to co-trimoxazole hypersensitivity in HIV-positive patients.

ISSN:0960-314X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

In children with acute lymphoblastic leukaemia (ALL) treated according to protocols of the Berlin-Frankfurt-Münster (BFM) study group, the initial response to prednisone is the strongest predictor of therapy outcome. Glutathione S-transferases (GSTs) have been implicated in glucocorticoid resistance. In order to assess a potential association of phenotypically relevant GST polymorphisms with prednisone response in childhood ALL, we conducted a case–control study of 45 prednisone poor-responders (cases) and 90 prednisone good-responders (controls) who were frequency matched according to initial white blood cell count. In addition, we analysed the association of GST genotypes with relapse of leukaemia. In univariate analysis, homozygous deletion ofGSTT1(null genotype) conferred a 6.7-fold reduction in risk of prednisone poor-response compared to individuals who were either heterozygous or homozygous forGSTT1[odds ratio (OR) = 0.15,P= 0.071; multivariate odds ratio = 0.18,P= 0.117].GSTM1andGSTP1genotypes did not show any association with prednisone response. In addition, risk of relapse was predicted strongest by theGSTT1genotype. In univariate analysis, theGSTT1null genotype conferred a 5.9-fold reduction in risk of relapse compared to the heterozygous or homozygous presence ofGSTT1(OR = 0.17,P= 0.095; multivariate OR = 0.23;P= 0.173). No associations of theGSTM1genotype with risk of relapse were observed.GSTP1codon 105 and codon 114 polymorphisms were predominantely associated with central nervous system relapse. Our results add further support to the hypothesis that genetic polymorphisms within specific GST genes might be of clinical importance in childhood ALL.

ISSN:0960-314X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

The variability in a liver bank and tissue distribution of three probe UDP-glucuronosyltransferase (UGT) activities were determined as a means to predict interindividual differences in expression and the contribution of extrahepatic metabolism to presystemic and systemic clearance. Formation rates of acetaminophen-O-glucuronide (APAPG), morphine-3-glucuronide (M3G), and oestradiol-3-glucuronide (E3G) as probes for UGT1A6, 2B7, and 1A1, respectively, were determined in human kidney, liver, and lung microsomes, and in microsomes from intestinal mucosa corresponding to duodenum, jejunum and ileum. While formation of E3G and APAPG were detectable in human kidney microsomes, M3G formation rates from kidney microsomes approached the levels seen in liver, indicating significant expression of UGT2B7. Interestingly, rates of E3G formation in human intestine exceeded the hepatic rates by several fold, while APAPG and M3G formation rates were low. The intestinal apparentKmvalue for E3G formation was essentially identical to that seen in liver, consistent with intestinal UGT1A1 expression. No UGT activities were observed in lung. Variability in APAPG and M3G activity across a bank of 20 human livers was modest (⩽7-fold), compared to E3G formation, which varied approximately 30-fold. The E3G formation rates were found to segregate by UGT1A1 promoter genotype, with wild-type (TA)6rates significantly greater than homozygous mutant (TA)7individuals. Kinetic analyses were performed to demonstrate that the promoter mutation altered apparentVmaxwithout significantly affecting apparentKm. These results suggest that glucuronidation, and specifically UGT1A1 activity, can profoundly contribute to intestinal first pass metabolism and interindividual variability due to the expression of common allelic variants.

ISSN:0960-314X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Cigarette smoking can induce CYP1A1 in the lung. Induction requires the aryl hydrocarbon receptor (AHR) and aryl hydrocarbon receptor nuclear translocator (ARNT) proteins. Lung samples from seven of 75 Finnish patients who smoked until the time of surgery exhibited absent or low levels of CYP1A1 protein, mRNA and enzymatic activity, suggesting that these individuals might be genetically non or poorly inducible for CYP1A1. All seven lung samples expressed normal levels of AHR mRNA and ARNT mRNA, indicating that they did not carry inactivating polymorphisms in the 5′ upstream regulatory regions of these genes. Sequencing of cDNAs encompassing the complete coding regions ofAHRandARNTidentified a previously known codon 554 polymorphism inAHR, which was present in the homozygous state in one individual. This polymorphism, which leads to an amino acid substitution, has previously been reported either to have no effect or to enhance CYP1A1 induction. Previously unreported silent single nucleotide polymorphisms were identified in codon 44 ofAHRand codon 189 of ARNT. 1500 bp of genomic sequence from the 5′ upstream regulatory sequence of theCYP1A1gene was also sequenced in the non-inducible individuals. A nucleotide substitution polymorphism at position –459 was detected in the heterozygous state in two individuals. This polymorphic site does not reside in any known regulatory sequence. The completeCYP1A1coding sequence and intron/exon boundaries were then sequenced. None of the non or poorly inducible individuals exhibited any polymorphisms, either homozygous or heterozygous compared to representative inducible individuals or the previously publishedCYP1A1sequence. Thus, no polymorphisms in theAHR, ARNTorCYP1A1genes were identified that could be responsible for the non/low inducibility phenotype observed.

ISSN:0960-314X    

出版商:OVID    

年代:2000

数据来源: OVID

ISSN:0960-314X    

出版商:OVID    

年代:2000

数据来源: OVID

ISSN:0960-314X    

出版商:OVID    

年代:2000

数据来源: OVID