摘要:

A subgroup of 10–15% of Caucasians are termed phenotypical ‘intermediate metabolizers’ of drug substrates of CYP2D6 because they have severely impaired yet residual in-vivo function of this cytochrome P450. Genotyping based on the currently knownCYP2D6alleles does not predict this phenotype satisfactorily. A systematic sequencing strategy through 1.6 kb of theCYP2D65′-flanking sequence revealed six mutations of which three were exclusively associated with the functionalCYP2D6*2allele (−1496 C to G;−652 C to T; and−590 G to A), two were associated with the nonfunctional*4and with the functional*10-alleles (−1338 C to T and−912 G to A) and one (−1147 A to G) was seen in all*2,*4and*10-alleles investigated. The−1496 C to G mutation was found to be polymorphic withinCYP2D6*2alleles. In a family study, the wild-typeCYP2D6 *2[−1496 C]and the novel variant[−1496 G]allele co-segregated with lower and higher CYP2D6 in-vivo function, respectively, as shown by phenotyping using sparteine as probe drug. In a representative population sample selected for genotypes comprising oneCYP2D6*2and one non-functional allele, the median urinary metabolic ratio (MRs) for sparteine oxidation was 4.4-fold reduced in individuals with the variant allele (*2[−1496 G], MRs= 0.53,n= 27) compared with individuals lacking the mutation (*2[−1496 C], MRs= 2.33,n= 12;P<0.0001). The mutation−1496 C to G has an estimated frequency of approximately 20% in the general population and allows establishment of a genotype for the identification of over 60% of intermediate metabolizers in Caucasian populations.

ISSN:0960-314X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

A phase III study was performed to compare the efficacy and safety of lamotrigine (Lamictal1), desipramine (Norpramin1), and placebo in the treatment of unipolar depression. Desipramine is extensively metabolized by cytochrome P450 2D6 (CYP2D6), and kinetics of this compound are altered in poor metabolizers. Genotyping was utilized to exclude poor metabolizers in order to increase subject safety and to eliminate the need to continuously monitor plasma desipramine levels. As part of screening, subjects were genotyped for the *3(A), *4(B), and *5(D)alleles, which identify approximately 95% of poor metabolizers. Extensive metabolizers were eligible for randomization to the lamotrigine, desipramine, or placebo arm. Follow-up genotyping for the *6(T)and *7(E)alleles was performed after study enrollment and was used to identify poor metabolizers who may have been incorrectly identified as extensive metabolizers upon initial three-allele screening. Of 628 subjects screened for *3(A), *4(B), *5(D)alleles, 590 (93.9%) were classified as extensive metabolizers. The remaining 38 (6.1%) subjects were poor metabolizers and excluded. Subsequent *6(T)and *7(E)testing revealed that two poor metabolizers had been enrolled, and the follow-up genotyping provided an explanation for the high desipramine plasma concentrations in one subject. No differences in phenotypic or allelic frequencies were found between the study population and literature populations. However, the frequency of poor metabolizers varied among clinical sites (0–15%). For a compound that is extensively metabolized by CYP2D6, prescreening subjects for *3(A), *4(B), *5(D), *6(T)and *7(E)alleles can increase subject safety and eliminate the need to continuously monitor drug plasma concentrations.

ISSN:0960-314X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

The tricyclic antidepressant, doxepin, is formulated as an irrational mixture of E (trans) and Z (cis) stereoisomers (85% : 15%). We examined the stereoselective metabolism of doxepinin vitro, with the use of human liver microsomes, recombinant CYP2D6 and gas chromatography-mass spectrometry. In human liver microsomes over the concentration range 5–1500 μM, the rate ofZ-doxepinN-demethylation exceeded that ofE-doxepin above 100 μM in two of three livers. Eadie–Hofstee plots were curvilinear indicating the involvement of several enzymes inN-demethylation. Coincubation of doxepin with 7,8-naphthoflavone and ketoconazole reduced the rates ofN-demethylation ofE- andZ-doxepin by 30–50% and 40–60%, respectively, suggesting the involvement of CYP1A and CYP3A4, whilst quinidine had little effect onN-demethylation. In contrast, doxepin hydroxylation was exclusively stereospecific;E-doxepin andE-N-desmethyldoxepin were hydroxylated with high affinity in liver microsomes and by recombinant CYP2D6 (Kmin the range of 5–8 μM), but there was no evidence ofZ-doxepin hydroxylation. In ‘metabolic consumption’ experiments with liver microsomes (having measurable CYP2D6 activity) and initial substrate concentration of 1 μM, the consumption ofE-doxepin was greater (P<0.05,n= 5) than that ofZ-doxepin. Quinidine inhibited the consumption ofE-doxepin but did not affect the consumption ofZ-doxepin. WithN-desmethyldoxepin, quinidine inhibited the consumption ofE-N-desmethyldoxepin whereasZ-N-desmethyldoxepin appeared to be a terminal oxidative metabolite. In summary, CYP2D6 is a major oxidative enzyme in doxepin metabolism; predominantly catalysing hydroxylation with an exclusive preference for theE-isomers. The relatively more rapid metabolism ofE-isomeric forms, and the limited metabolic pathways for theZ-isomers may explain the apparent enrichment ofZ-N-desmethyldoxepin that is observedin vivo.

ISSN:0960-314X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

We have genotyped over 550 cases of acute leukaemia and 950 matched controls from a population-based case–control study, to investigate the impact cytochrome P450s 2D6, 2C19 and 1A1 have on susceptibility to adult acute leukaemia. Analysis included potential associations between polymorphic status and acute myeloid leukaemia (AML), acute lymphoblastic leukaemia (ALL), plus the FAB and cytogenetic subtypes therein. A significant increased risk was found for CYP2D6 poor metabolizer phenotype and acute leukaemia [odds ratio (OR) = 1.69, 95% confidence interval (CI) 1.17–2.43], a risk also found in AML and ALL. No interaction was found with smoking. However, a significant age-related association betweenCYP2D6polymorphism and acute myeloid leukaemia implied that the excess risk was confined to persons aged 40 years and over (OR 2.38, 95% CI 1.53–3.71). Amongst AML cases, increased odds ratios were observed in bothde-novo(OR 1.54, 95% CI 1.02–2.32) and secondary leukaemia (OR 2.83, 95% CI 0.91–8.77), and among patients with a chromosomal abnormality (OR 2.00, 95% CI 1.11–3.61). An increased risk was found for the CYP2C19 poor metabolizer phenotype (OR 1.68, 95% CI 0.97–2.92) which was also present in AML and ALL. For thisCYP450locus, an increased risk was suggested in secondary leukaemia (OR 2.67, 95% CI 0.44–16.3) and amongst AML cases with a chromosomal abnormality (OR 6.72, 95% CI 2.22–20.4). No difference inCYP1A1genotype distribution was found for acute leukaemia, AML, ALL or any other diagnostic classification group used. No significant interactions betweenCYP2D6,CYP2C19orCYP1A1were found.

ISSN:0960-314X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Smoking is the principal cause of lung cancer. However, not all smokers will develop this disease. Individual susceptibility to chemically induced cancer may be explained in part by genetic differences in the activation and detoxification of procarcinogens. The activation phase of polycyclic aromatic hydrocarbon (PAH) metabolism is governed by the enzyme CYP1A1, induced by PAH when it enters the body. The extent to which PAH induces CYP1A1 activity varies greatly from one subject to another. CYP1A1 inducibility has long been associated, although inconsistently, with an increased risk of lung cancer. In 1982, Kouri corroborated Kellerman's results with a new method for measuring inducibility, but few studies have reported using this method. The glutathioneS-transferases (GSTs) are involved in the detoxification phase of PAH, and the allelic deletion ofGSTM1has been also associated with an increased risk of lung cancer. We conducted a case–control study to examine the risk of lung cancer related, separately and together, to CYP1A1 inducibility,GSTM1polymorphism and cigarette smoking in a French population. The 611 subjects were 310 incident lung cancer cases and 301 hospital control subjects. We were able to constitute a DNA bank for 552 subjects (89.5%) and gather detailed information on smoking history for all of them. Inducibility could be measured for 195 cases and 183 control subjects. Results forGSTM1polymorphism concern 247 cases and 254 control subjects.GSTM1polymorphism and inducibility could both be assessed for 179 cases and 166 control subjects. The odds ratio related to inducibility was 1.7 [1.0–3.0] for medium and 3.1 (1.3–7.4) for hyper inducers. The association withGSTM1was 1.6 (1.0–2.6). With a reference category of subjects who were both low inducers and GSTM1(+), we found an odds ratio for lung cancer of 8.1 (2–31) for the subjects with both risk factors [i.e. GSTM1(–) and hyper inducers]. Our data did not reveal evidence of interaction between smoking and inducibility. On the other hand, we found an interaction of 3.6 (0.6–21) between inducibility andGSTM1.

ISSN:0960-314X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

One of the most important mechanisms involved in host defense against xenobiotic chemicals and endogenous toxins is the glucuronidation catalysed by UDP-glucuronosyltransferase enzymes (UGT). The role of genetic factors in determining variable rates of glucuronidation is not well understood, but phenotypic evidence in support of such variation has been reported. In the present study, six single nucleotide polymorphisms were discovered in the first exon of theUGT1A7gene, which codes for the putative substrate-binding domain, revealing a high structural heterogeneity at theUGT1gene locus. The new UGT1A7 proteins differ in their primary structure at amino acid positions 129, 131 and 208, creating four distinct UGT1A7 allelic variants in the human population:UGT1A7*1(N129R131W208),*2(K129K131W208),*3(K129K131R208), and*4(N129R131R208). In functional studies, HEK cells stably transfected to express the four allelic UGT1A7 variants exhibited significant differences in catalytic activity towards 3-, 7-, and 9-hydroxy-benzo(a)pyrene.UGT1A7*3exhibited a 5.8-fold lower relativeVmaxcompared to wild-type*1, whereas*2and*4had a 2.6- and 2.8-fold lower relativeVmaxthan*1, respectively, suggesting that these mutations confer slow glucuronidation phenotype. Kinetic characterization suggested that these differences were primarily attributable to alteredVmax. Additionally, it suggested that each amino acid substitutions can independently affect the UGT1A7 catalytic activity, and that their effects are additive. The expression pattern of UGT1A7 studied herein and its catalytic activity profile suggest a possible role of UGT1A7 in the detoxification and elimination of carcinogenic products in lung. A population study demonstrated that a considerable proportion of the population (15.3%) was found homozygous for the low activity allele containing all three missense mutations,UGT1A7*3. These findings suggest that further studies are needed to investigate the impact of the low UGT1A7 conjugator genotype on individual susceptibility to chemical-induced diseases and responses to therapeutic drugs.

ISSN:0960-314X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

The aim of the present study was to investigate how the genetic polymorphism in glutathione transferase T1 (GSTT1) affects the metabolism and disposition of methyl chloride in humansin vivo. The 24 volunteers (13 males and 11 females) who participated in the study were recruited from a group of 208 individuals previously phenotyped for GSTT1 by measuring the glutathione transferase activity with methyl chloride in lysed erythrocytesex vivo. Eight individuals with high (+/+), eight with medium (+/0) and eight with no (0/0) GSTT1 activity were exposed to methyl chloride gas (10 p.p.m.) in an exposure chamber for 2 h. Uptake and disposition was studied by measuring the concentration of methyl chloride in inhaled air, exhaled air and blood. A two-compartment model with two elimination pathways corresponding to exhalation and metabolism was fitted to experimental data. The average net respiratory uptake of methyl chloride was 243, 158, and 44 μmol in individuals with high, intermediate and no GSTT1 activity, respectively. Metabolic clearance was high (4.6 l/min) in the +/+ group, intermediate (2.4 l/min) in the +/0 group, and close to zero in 0/0 individuals, while the exhalation clearance was similar in the three groups. No exposure related increase in urinaryS-methyl cysteine was detected. However, gender and the GSTT1 phenotype seemed to affect the background levels. In conclusion, GSTT1 appears to be the sole determinant of methyl chloride metabolism in humans. Thus, individuals with nonfunctional GSTT1 entirely lack the capacity to metabolize methyl chloride.

ISSN:0960-314X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

The aim of this study was to analyse whether substitution of phenylalanine in postion 124 of the human (h) 5-HT1Breceptor by cysteine, a naturally occurring variant of this receptor, modifies not only ligand binding, but also G-protein coupling and second messenger formation. Stably transfected rat C6 glioma cells, which express either the h5-HT1Bvariant receptor (VR) or the wild-type receptor (WTR) were used. In saturation experiments with [3H]5-carboxamidotryptamine ([3H]5-CT), the maximum binding (Bmax) of the VR amounted to only 60% of that to WTR. In competition experiments with 1 nm [3H]5-CT, the following 5-HT receptor ligands exhibited a higher affinity for the mutant receptor than for the WTR: L-694,247, 5-CT, 5-HT, sumatriptan (agonists listed at decreasing order of potency) and SB-224289 (a selective h5-HT1Breceptor inverse agonist with competitive antagonistic properties). In contrast, the mixed 5-HT1B/1Dreceptor antagonist GR-127935 exhibited equal affinity for both isoforms. The efficacy of L-694,247, 5-CT, 5-HT and sumatriptan in stimulating [35S]GTPγS binding (a measure of G protein coupling) to membranes of cells expressing the VR was approximately 50–65% lower compared to membranes of cells expressing the WTR, but their potency was 2.8–3.6-fold higher. SB-224289, which decreased [35S]GTPγS binding when given alone, but not GR-127935, was more potent in antagonizing the stimulatory effect of 5-CT on [35S]GTPγS binding to membranes expressing the VR compared to membranes expressing the WTR. In whole cells expressing the VR, 5-CT and sumatriptan inhibited the forskolin-stimulated cAMP accumulation 3.2-fold more potently than in cells expressing the WTR. In conclusion, our data suggest that the Phe-124-Cys mutation modifies the pharmacological properties of the h5-HT1Breceptor and may account for pharmacogenetic differences in the action of h5-HT1Breceptor ligands. Thus, the sumatriptan-induced vasospasm which occurs at low incidence as a side-effect in migraine therapy may be related to the expression of the (124-Cys)h5-HT1Breceptor in patients with additional pathogenetic factors such as coronary heart disease.

ISSN:0960-314X    

出版商:OVID    

年代:2000

数据来源: OVID