摘要:

Cytochrome P450 phenotyping provides valuable information about real-time activity of these important drug-metabolizing enzymes through the use of specific probe drugs. Despite more than 20 years of research, few conclusions regarding optimal phenotyping methods have been reached. Caffeine offers many advantages for CYP1A2 phenotyping, but the widely used caffeine urinary metabolic ratios may not be the optimal method of measuring CYP1A2 activity. Several probes of CYP2C9 activity have been suggested, but little information exists regarding their use, largely due to the narrow therapeutic index of most CYP2C9 probes. Mephenytoin has long been considered the standard CYP2C19 phenotyping probe, but problems such as sample stability and adverse effects have prompted the investigation of potential alternatives, such as omeprazole. Several well-validated CYP2D6 probes are available, including dextromethorphan, debrisoquin and sparteine, but, in most cases, dextromethorphan may be preferred due to its wide safety margin and availability. Chlorzoxazone remains the only CYP2E1 probe that has received much study. However, questions concerning phenotyping method and involvement of other enzymes have impaired its acceptance as a suitable CYP2E1 phenotyping probe. CYP3A phenotyping has been the subject of numerous investigations, reviews and commentaries. Nevertheless, much controversy regarding the selection of an ideal CYP3A probe remains. Of all the proposed methods, midazolam plasma clearance and the erythromycin breath test have been the most rigorously studied and appear to be the most reliable of the available methods. Despite the limitations of many currently available probes, with continued research, phenotyping will become an even more valuable research and clinical resource.

ISSN:0960-314X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Dihydropyrimidine dehydrogenase (DPD) degrades over 80% of administered 5-fluorouracil (5FU), thereby regulating the efficacy of this commonly used anticancer agent. DPD activity is highly variable (8-21-fold) and individuals with reduced activity have a high risk of 5FU toxicity.DPYDencodes DPD protein and 13 different mutations have been reported in DPD-deficient subjects. However, the contribution of these variant genotypes to polymorphic DPD activityin vivois not clear. The previously describedDPYDmutations are contained in 10 exons. These 10 exons were sequenced in a cohort of cancer patients with reduced (n= 23) or normal (n= 14) DPD activity to determine the contribution of each variant allele to low DPD activityin vivo.Eight of the 13 previously definedDPYDmutations (G62A, ΔTCAT295-298, C703T, G1003T, G1156T, ΔC1897, G2657A, and G2983T) were not detected. A previously defined exon 13 mutation (G1601A) was detected in three individuals with reduced DPD activity. An exon 14 splice donor site mutation (intron14 G1A) was detected in a normal DPD activity individual. It was demonstrated that T85C, A1627G and G2194A are common polymorphisms. A novel exonic mutation (T1679G) was detected in a patient with reduced DPD activity and 5FU toxicity. In addition, three novel common polymorphisms were detected in introns 10 and 13. Only three patients did not have any mutations and 30 had multipleDPYDmutations in the regions examined. However, only 17% (4/23) of the patients with a low DPD phenotype have a molecular basis for reduced activity. Although novelDPYDvariants have been identified in this study, the 17DPYDmutations now described do not entirely explain polymorphic DPD activity and toxic response to 5FU. These data emphasize the complex nature of the molecular mechanisms controlling polymorphic DPD activityin vivo.

ISSN:0960-314X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

NAT1, which biotransforms many carcinogens, is genetically polymorphic. This polymorphism has been postulated as a mechanism for susceptibility differences in cancer, possibly due to NAT1 activity differences. However, the relationship betweenNAT1genotype and phenotype is not clear. In our study of 110 Japanese, the frequency of theNAT1*10allele (0.53, 95% confidence interval 0.46-0.59) was higher than others have observed in Caucasians (0.16). From genotype frequency studies, 26.4% of the subjects belonged to theNAT1*10/*10genotype, 53.6% to theNAT1*4/*10genotype and 20% to theNAT1*4/*4genotype. NeitherNAT1*3norNAT1*11genotype was seen in these subjects. In female subjects, we found higher NAT1 activity inNAT1*4/*10subjects than inNAT1*4/*4subjects (n= 49; 2.63 versus 2.16 nmol/min/mg protein). NAT1 activity-difference betweenNAT1*4/*10andNAT1*10/*10was not statistically significant. Thus, not only the presence ofNAT1*10allele, but also other factors are suspected of increasing NAT1 activities. After full sequencing of 10 subjects, five individuals having the highest activities and five individuals having the lowest activities, we foundNAT1*18AandNAT1*18Bto be in the high activity group and the low activity group, respectively. The genotypes containing these variants were heterozygous, i.e.NAT1*4/*18AandNAT1*4/*18B.Due to rare frequencies of these variants, they cannot be considered as other effective, genetic factors on NAT1 activity. Age and tobacco smoking did not affect the relationship betweenNAT1genotype and phenotype.

ISSN:0960-314X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

The prevalence of type 2 diabetes in the Oji-Cree of Northern Ontario is among the highest of any population in the world. We previously demonstrated that markersD8S264andD22S683were both linked and associated with type 2 diabetes in the Oji-Cree. Among the possible candidate genes for type 2 diabetes and related traits on chromosomes 8p and 22q wereNAT2andCYP2D6,respectively. We thus explored the possible association ofNAT2andCYP2D6alleles and diabetes-related traits in a sample of 112 Oji-Cree subjects with type 2 diabetes and 481 Oji-Cree subjects without type 2 diabetes. We found no difference in the allele and genotype frequencies of theNAT2G191A, C282T, C481T, G590A, A803G and G857A, and theCYP2D6G1934A polymorphisms between Oji-Cree subjects with and without type 2 diabetes. However, we found a significant association between theNAT2C282T polymorphism and plasma fasting glucose concentration. Specifically,NAT2282T/T homozygotes had significantly higher plasma fasting glucose than 282C/C homozygotes, and heterozygotes had intermediate levels of this trait. Thus, variation inNAT2orCYP2D6was not associated with the presence of type 2 diabetes, and would not be causative for this phenotype in Oji-Cree. However,NAT2might be a 'modifier gene' affecting the level of glycaemia in non-diabetic subjects.

ISSN:0960-314X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Polymorphisms in genes of xenobiotic-metabolizing enzymes are largely responsible for interindividual differences in ability to activate and detoxify genotoxic agents and therefore may influence individual susceptibility to environmental cancer. The tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), requires metabolic activation by cytochrome P450 (CYP) enzymes to generate DNA-reactive intermediates that induce mutations and cancer. In the current study, we investigated the role of the polymorphicCYP2E1andCYP2D6genes in the genotoxicity of NNK using the tandem-probe fluorescence in-situ hybridization (FISH) chromosome aberration assay as a marker. Our results, using whole blood cultures from 39 volunteers, indicated that NNK (0.12, 0.24 or 0.72 mM) induced a concentration-dependent increase in the frequency of chromosome aberration. The potential role ofCYP2E1andCYP2D6in NNK-induced genetic damage in cultured human lymphocytes was characterized using specific CYP inhibitors. Treatment of blood cultures with 25 μM diethyldithiocarbamate (DDC), a specificCYP2E1inhibitor, or 0.5 μM quinidine, a specificCYP2D6inhibitor, simultaneously with NNK, significantly decreased NNK-induced chromosome aberration. We also studied the role ofCYP2E1andCYP2D6allelic variants on NNK-induced chromosome aberration. Our results indicate that NNK induced a significantly higher level of chromosome aberration in cells with theCYP2E1 WT/*5Bgenotype compared to cells with theCYP2E1 WT/WT.In contrast, no difference in NNK-induced chromosome aberration was observed between cells with theCYP2D6extensive metabolizers compared to cells with theCYP2D6poor metabolizer genotypes. These results underscore the important role of polymorphic metabolizing genes in influencing the genotoxic responses to environmental mutagens and provide support to the reported findings linkingCYP2E1polymorphism to smoking-related lung cancer.

ISSN:0960-314X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

The UDP-glucuronosyltransferases (UGTs) comprise a large family of proteins capable of detoxifying a wide variety of both endogenous and exogenous substrates. The primary function of this gene superfamily is to catalyze the glycosylation of substrates such as biogenic amines, steroids, bile acids, phenolic compounds and various other pharmacologically relevant compounds, including numerous carcinogens, toxic environmental pollutants and prescription drugs. This conjugation increases the solubility of these compounds, allowing them to be excreted more readily through hepatic or renal mechanisms. This paper describes the genomic characterization and chromosomal localization of threeUGT2Bgenes which together comprise part of a large cluster of related sequences, including pseudogenes found on human chromosome 4q13. A genomic map spanning approximately 500-1000 kb of this region reveals the presence of three previously describedUGT2Bgenes, at least two previously uncharacterized pseudogenes and a significant number of remnant gene fragments and placesUGT2B4betweenUGT2B7andUGT2B15.Additionally, access to a large reference DNA bank allowed us to calculate allele frequencies for twoUGT2BSNPs: D85R inUGT2B15and Q458D inUGT2B4amongst 803 unrelated individuals representing five ethnic populations. The data presented here suggest a recent evolutionary history of gene duplication, mutation and rearrangement. Furthermore, they suggest that a re-evaluation of the current description of theUGT2Bgene family with respect to the number of specific genes, degree of allelic diversity and molecular evolution may be necessary.

ISSN:0960-314X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Histamine is involved in the pathophysiology of asthma, and histamineN-methyltransferase (HNMT) plays the dominant role in histamine metabolism in human bronchial epithelium. Levels of HNMT activity in human tissues are controlled, in part, by inheritance. A common C314T polymorphism within the HNMT gene results in a Thr105Ilc change in encoded amino acid, and the T314 allele is associated with decreased levels of both HNMT enzymatic activity and immunoreactive protein. Therefore, presence of the T314 allele would be expected to result in reduced histamine metabolism and increased bronchoconstriction. We characterized this common, functionally significant polymorphism in DNA samples from 237 randomly selected Caucasian control subjects and 192 samples from Caucasian asthmatic patients. Allele frequencies for the T314 HNMT allele were 0.08 in the control samples and 0.14 in samples from Caucasian asthmatic patients (odds ratio = 1.9,P< 0.01), indicating a significant increase in the frequency of subjects with low HNMT activity among asthmatics. The association between a common, functionally significant genetic polymorphism for HNMT and asthma suggests that individual variation in histamine metabolism might contribute to the pathophysiology and/or response to therapy of this disease.

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

ISSN:0960-314X    

出版商:OVID    

年代:2000

数据来源: OVID