摘要:

Sulfate conjugation catalysed by phenol sulfotransferase (PST) is an important pathway in the metabolism of many drugs. Two isoforms of PST have been characterized biochemically in human tissues - a thermostable (TS), or phenol-metabolizing (P) and a thermolabile (TI.), or monoamine-metabolizing (M) form. Pharmacogenetic studies of TS and IT. PST activities in the human blood platelet showed that the activities of these two isoforms were regulated by separate genetic polymorphisms. Subsequently, a series of TS PST cDNAs were cloned, and, based on sequence homology, those cDNAs could be classified as members of two separate subgroups, designated here as 'TS PST1' and 'TS PST2' - indicating the existence of three rather than two PST isoforms; TS PST1, TS PST2 and TL PST. The genes encoding TS PST2,STP2, and TL PST,STM, have been cloned, structurally characterized and mapped to chromosome 16 - the same chromosome on which the TS PST1 gene,STP1, is localized. As a step toward molecular pharmacogenetic studies of sulfate conjugation in humans, we set out to clone and structurally characterizeSTP1, the remaining uncharacterized human PST gene. We found thatSTP1spanned approximately 4.4 kb and contained 9 exons. The first two exons, IA and IB, were identified by performing 5 -rapid amplification of cDNA ends (RACE) with human liver cDNA as template. Exons IA and IB were noncoding and represented two different cDNA 5' -untranslated region sequences. No canonical TATA box sequences were present within the 5 -flanking -flanking regions of the gene, i.e. regions flanking exons IA and IB. Finally, use of the long polymerase chain reaction made it possible to determine thatSTP1is located approximately 45 kb 5 -upstream fromSTP2on the short arm of human chromosome 16. Cloning and structural characterization ofSTP1, when combined with knowledge of the structures ofSTP2andSTM, will make it possible to study the molecular basis for the genetic regulation of PST activity in human tissue.

ISSN:0960-314X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The metabolism of benzo[a]pyrene (B]a[P) and its proximate mutagen B[a]P-7,8-dihydrodioI (7,8-diol) was investigated in the presence of human microsomal epoxide hydrolase and P450, 1A1, 1A2, 2C8, 2C9, 2C18, 2C 19, 2D6 and 3A4 expressed in the yeastSaccharomyces cerevisiae. P450, 1A1 had the highest turnover numbers for the formation of all B[a]P metabolites, including phenols and dihydrodiols. P450, 1A2, 2C8, 2C9, 2C18, 2C19 and 3A4, which are well represented in the liver, gave rise to the formation of appreciable amounts of 3-hydroxy-B[a]P and of some dihydrodiols from B[a|P. When 7,8-diol was used as substrate, P450 1A1 also exhibited the highest turnover numbers for the formation of tetrols, the hydrolysis products of the diolepoxides, whereas P450, 1 A2, 2C8, 2C19 and 3A4 showed moderate activities. In order to test the validity of the yeast system, the contribution of each P450 isoform to B[a]P and 7.8-dioI metabolism was evaluated as the product of the turnover numbers of recombinant P450s by specific contents of each P450 in human liver microsomes. Calculated formal ion rates for each B[a]P and 7.8-diol metabolite globally matched experimental values. There is evidence that P450 3A4 and 2C9 play a major role in the formation of 3-hydroxy-13[a]P from B[a]P. Accumulation of the proximate mutagen 7,8-diol was predicted to be mainly driven by P450, 1A2, 2C9 and 2C19, while formation of the genotoxic diolepoxides from 7,8-diol appeared to be dependent on P450, 1A2 and 3A4 in the liver.

ISSN:0960-314X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The arylamine N-acetyltransferase (NAT2) is a polymorphic enzyme which is expressed in the liver in a genotype-determined manner. NAT2 is involved in activation and inactivation of carcinogens through N-acetylation. We studied the role of this polymorphism in the development of hepatocellular carcinoma (HCC). One hundred consecutive patients diagnosed for HCC and 258 healthy volunteers were studied for NAT2 genotype. The occurrence of seven enzymeinactivating and silent point mutations in the coding region of the NAT2 gene was studied by mutation-specific PCR amplification. An excess of subjects homozygous for NAT2 loss of function alleles was observed among patients with HCC (68% vs 53.9% controls). The relationship between the slow acetylator NAT2 genotype and HCC risk is more pronounced in patients lacking serum HBV and HCV markers. The additional determination of alleles of the cytochrome P450 2D6 (CYP2D6) gene in the same subjects confirmed our previous findings that subjects with two active CYP2D6 genes are at increased risk of developing HCC. The genetic polymorphism of NAT2 is a relevant factor in the risk for developing HCC (inverse odds ratio slow vs rapid - 1.8: 95% CI 1.1-3.0). The inverse odds ratio for subjects with two risk genotypes (two defect NAT2 genes and two or more active CYP2D6 genes) is 2.6 (95% CI 1.6-4.4) for all patients with HCC, and 5.6 (95% CI 1.4-33.3) for patients without serum viral markers.

ISSN:0960-314X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The relationship between genetic polymorphism and imipramine metabolism has never been studied in a family study. A sparteine/mephenytoin test was carried out in 31 parents and 20 siblings of 18 Danish poor metabolizers of sparteine (PMs). One week later, each subject took 25 mg imipramine followed by urine collection for 24 h. The urinary content of imipramine, desipramine, 2-hydroxy-imipramine and 2-hydroxy-desipramine was assayed by HPLC. There were 10PMs (20%; 9.8-33%, 95% confidence interval) and 41 extensive metabolizers of sparteine (EMS) among parents and siblings. In 26 of the 28 PMSamong probands and relatives, there were concordance between phenotype and genotype: D6-A/D6-D (n=2), D6-A/D6-B (n=5), D6-B/ (n=15) or D6-B/D6-D (n=4). Two PMSwere apparently heterozygous (EMS), D6-wt/ D6-B. Accordingly, based on the present sample of 28 PMSthe specificity of the genotype test was 100% and the sensitivity was 92.9%. Two EMSwere homozygous dominant D6-wt/ and 39 were heterozygous EMs: D6-wt/D6-D (n=5). D6-wt/D6-B (n=27), D6- wt/D6-A (n=6), D6-wt/D6-wt* (unknown mutation) (n=1). As previously reported in a population study the hydroxylation ratios (i.e. 2-hydroxymetaboIite over parent compound) of imipramine were much lower in PMSthan in EMS. This and the pedigrees confirmed the co-segregation of sparteine oxidation, imipramine 2-hydroxylation and the CYP2D6 genotype. None of the hydroxylation ratios could separate EMSand PMscompletely, mainly because the 2-hydroxylation of imipramine also depends on P450s other than CYP2D6.

ISSN:0960-314X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The polymorphic metabolism of S-mephenytoin and the distribution of two known deleterious mutantCYP2C19alleles was determined among 114 healthy unrelated black Ethiopians. Six subjects (5.2%) were poor metabolizers (PMs) of S-mephenytoin. The frequencies of the defectiveCYP2C19*2(CYP2C19m1) andCYP2C19*3(CYP2C19m2) alleles were 0.14 and 0.02, respectively. Three of the PMs were homozygous for theCYP2C19*2allele and the remaining three PMs were heterozygous for both theCYP2C19*2andCYP2C19*3mutant alleles. It is concluded that the frequency of PMs for S-mephenytoin is similar in Ethiopians, Zimbabweans and Caucasians and that theCYP2C19*3allele, for the lirst time identified in a black population, together with theCYP2C19*2allele account for all of the defectiveCYP2C19alleles among the Ethiopan PMs.

ISSN:0960-314X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

CYP2C9 is involved in the metabolism of warfarin and a wide array of other therapeutic agents. It also appears to play a role, along with other cytochrome P450 enzymes, in the metabolism of benzo[α]pyrene, a carcinogen in tobacco smoke. A relatively common allelic variant (termed R144C, Cys144or more recentlyCYP2C9*2) has been described that results in the substitution of cysteine for arginine at residue 144 and appears to reduce enzyme activity. We therefore examined the possible association between the presence of theCYP2C9*2variant allele and risk of lung cancer using peripheral blood DNA from 329 incident cases of lung cancer (152 African-American and 177 Caucasian) and 700 (239 African-American and 461 Caucasian) population controls in Los Angeles County, California. Among the population controls the frequency of theCYP2C9*2variant allele was lower (p=0.00002) among African-Americans (0.036) than among Caucasians (0.100). The presence of theCYP2C9*2variant allele was not associated with a decreased risk of lung cancer; slight but nonstatistically significant elevations in risk were observed for both African-Americans [odds ratio (OR) 1.22, 95% confidence interval (CI) 0.48-3.11] and Caucasians (OR=1.55, 95% CI 0.96-2.48). The ORs were slightly and nonsignificantly elevated for all histologic types without substantive variation. The association also did not vary materially according to smoking history or whether subjects had the homozygous deletion of the GSTM1 gene. We found no support for the hypothesis that theCYP2C9*2variant allele decreases the risk of lung cancer. The role of P450s, including CYP2C9, in benzo[α]pyrene metabolism is not fully defined, and CYP2C9 catalyses detoxication as well as activation steps. Thus it is not inconceivable that diminished CYP2C9 activity could increase metabolic activation of benzo[α]pyrene to carcinogenic intermediates. Nonetheless, the small increased risk associated theCYP2C9*2variant allele in our data is consistent with chance and should not be overinterpreted.

ISSN:0960-314X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Occurrence or specific types of mutations found in oncogenes or tumor suppressor genes may partially be determined by activities of toxifying or detoxifying enzymes, such as glutathione S-transferases (GST) M1 and T1, arylamine N-acetyltransferase (NAT2), microsomal epoxide hydrolase, and the cytochrome P-450 enzymes 2D6, 1A1, 2A6, and 2E1. In an explorative observational study, 69 bladder cancer patients were analysed for acquired mutations in the p5 3 tumor suppressor gene. The same patients were studied for the polymorphic traits of xenobiotic metabolism given above which were characterized from blood cell DNA by molecular methods. In 20 patients, single point mutations in p5 3 were detected whereas five patients carried two mutations: thus in total 25 mutations were detected. Twelve of these were G:C-A:T transitions, six were A:T- G:C transitions and seven were transversions (three G:C - T:A, two A:T- T:A, one G:C- C:G, and one A:T-C:G. There was no correlation between the types of p53 mutations and lifetime smoking or occupational history. In correlation with xenobiotic metabolism, 86% of the seven transversion mutations were found in homozygously deficient individuals for GSTM1 compared to only 44% of GSTM1 deficiency in the carriers of the 18 transition mutations of p53 (p0.06). A similar trend was seen for NAT2: six of the seven carriers of transversion mutations had twoslowNAT2 alleles. No apparent associations were seen for the other polymorphic traits which were studied. In conclusion, low or deficient activities of two conjugating enzymes of foreign compound metabolism, GSTM1 and NAT2, may influence types of acquired mutations in p53 in bladder cancer.

ISSN:0960-314X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Omeprazole (20 mg orally) was given to 103 healthy Korean subjects and blood was taken 3 h alter administration. The plasma concentration ratio of omeprazole and hydroxyomeprazole, used as an index of CYP2C19 activity, was bimodally distributed. Thirteen subjects (12.6%) were identified as poor metabolizers (PMs) with an omeprazole hydroxylation ratio of 6.95 or higher. Among the 206CYP2C19alleles,CYP2C19*2andCYP2C19*3were found in 43 alleles (21%) and 24 alleles (12%), respectively. Twelve subjects (12%) carried two defect alleles (*2/*2, *2/*3 or *3/*3), 43 subjects (42%) were heterozygous for a mutated (*2 or *3) and a wild type (*1) allele, and the remaining 48 subjects (47%) were homozygous for the wild type allele. The distributions of the metabolic ratio between these three genotype groups were significantly different (Kruskal-VVallis test:p0.0001). The genotypes of 19 additional Korean PMs has been identified in a previous mephenytoin study. From a total of 32 PMs, 31 were genotypically PMs by analysis of theCYP2C19*2and *3 alleles and only one PM subject was found to be heterozygous for the *7 and *2 alleles. At present it cannot be judged whether this subject has a defective allele with a so-far unidentified mutation or a true wild type allele. We thus confirm a high incidence (12.6%) of PMs of omeprazole in Koreans and of the 32 Korean PMs 97% could be identified by the genotype analysis.

ISSN:0960-314X    

出版商:OVID    

年代:1996

数据来源: OVID