摘要:

A consolidated classification system is described for prokaryotic and eukaryotic N-acetyltransferases in accordance with the international rules for gene nomenclature. The root symbol (NAT) specifically identifies the genes that code for the N-acetyltransferases, and NAT* loci encoding proteins with similar function are distinguished by Arabic numerals. Allele characters, denoted by Arabic numbers or by a combination of Arabic numbers and uppercase Latin letters, are separated from gene loci by an asterisk, and the entire gene-allele symbols are italicized. Alleles at the different NAT* loci have been numbered chronologically irrespective of the species of origin. For designation of genotypes at a single NAT* locus, a slash serves to separate the alleles; in phenotype designations, which are not italicized, alleles are separated by a comma.

ISSN:0960-314X    

出版商:OVID    

年代:1995

数据来源: OVID

ISSN:0960-314X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Our previous studies (Sidhu JS et al. Arch Biochem Biophys 1993: 301, 103-113; Sidhu JS et al. In Vitro Toxicol 1994: 7, 225-242) demonstrated the importance of culturing primary rat hepatocytes with an overlay of extracellular matrix (ECM), together with optimal media formulations (WilliamsE or Chees), to efficiently maintain in vivo-like responsiveness of phenobarbital (PB)-inducible cytochrome P450 genes in vitro. In the present report, we have characterized culture conditions further by examining individual and interactive effects of dexamethasone (Dex) and PB on CYP2B1, CYP2B2, and CYP3A1 expression. Dex alone was not effective in enhancing CYP2B1 or CYP2B2 expression levels. However, together with PB, addition of low concentrations ( 10-9–10-8M) of Dex resulted in a marked potentiation of PB-inducible P450 gene expression. In contrast, at levels >10-7M, Dex profoundly inhibited PB induction of the CYP2B1 and CYP2B2 genes. The overall stimulatory response to Dex was more dramatic in cells cultured in Williams E than in Chees medium. Similarly, concentrations of PB < 0.5mM resulted in substantially reduced levels of CYP2B1 and CYP2B2 induction than those attainable at lower PB concentrations. These results suggest that Dex and PB function cooperatively to regulate the CYP2B1 and CYP2B2 genes, and that composite interactions may either negatively or positively regulate expression, in a concentration-dependent manner. CYP3A1 was not regulated in a similar biphasic fashion, as this gene was fully responsive even at high dose levels of PB or Dex. With respect to other marker genes evaluated, high Dex concentrations (> 10-7M) were only marginally inhibitory to β-naphthoflavone-mediated induction of CYP1A1 and CYP1A2 mRNAs, and did not perturb expression of the liver-selective serum albumin gene. Addition of Dex was critical, however, to maintain glutathione S-transferase Pi expression, a marker of hepatocyte dedifferentiation, in the repressed state. Defining optimal culture conditions for maintaining hepatocyte differentiationin vitroare requisite for establishing primary culture models enabling investigation of the molecular mechanisms of PB-mediated gene regulation.

ISSN:0960-314X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Cytochrome P450(CYP) 2C9 catalyses the metabolism of a wide range of drugs. Previous studies have shown the differences in the amino acid composition among CYP2C9 variants at Cys144/Arg, Tyr358/Cys, Leu359/Ile, and Gly417/Asp. PCR-endonuclease digestion methods have been developed to detect these four possible polymorphisms. The T416 —>C mutation in exon 3 of CYP2C9 (Cys144Arg) creates an Ava II site. In the 135 subjects we tested, all leukocyte DNA samples showed a complete Ava II digestion indicating homozygous C(Arg144). A Tyr358Cys mutation will create a Nsi I site at codon 1057-1063 in exon 7. In 40 subjects tested, all samples showed negative results. DNA sequencing on a few samples showed Tyr358Ile359.A mismatched PCR primer pair was then designed to detect codon C1061A (Leu359 —> Ile) mutation. In 115 subjects tested, 111 samples showed a complete Nsi I digestion (Ile359) and four samples showed heterozygous results. Another mismatched PCR primer pair was used to confirm the C1061codon in heterozygous subjects. The four heterozygous subjects showed partial digestion with endonuclease Kpn I, which confirmed the heterozygous Ile/Leu at amino acid 359. The G1236—>A mutation in exon of CYP2C9 (Gly417—> Asp) creates a Hph I site. In all 46 subjects,homozygous Gi236 (Gly417) was found. Most Chinese subjects actually haveArg144Tyr358Ile359Gly417in CYP2C9 as previously reported human-2. Furthermore, we found an A T—>(+12 position in intron 2) mutation in our CYP2C9 sequencing process. The mutation creates a Nla III site. In the 44 subjects we tested, all showed complete digestion. In conclusion, we found small inter-individual variation in CYP2C9 sequence among Chinese subjects, and that Cys144/Arg and Leu359/Ile are the two possible sites showing inter-racial polymorphism.

ISSN:0960-314X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

1,4-Benzodiazepine anxiolytics such as diazepam and halazepam are converted in vivo to oxazepam, an active metabolite with a hydroxyl group at the asymmetric C3 position. D-glucuronic acid couples with the C3 hydroxyl group of oxazepam to form pharmacologically inactive diastereomeric glucuronide conjugates. Conjugation with glucuronic acid is catalysed by the microsomal UDP-glucuronosyltransferase (UGT) enzyme system, which includes an undetermined number of isozymes. Although 1,4-benzodiazepines are ultimately cleared as oxazepam glucuronide, little is known about the particular UGT isozyme(s) responsible for the conjugation at the C3 position of these molecules.Microsomal preparations from three human livers were used to study the glucuronidation of (R,S)oxazepam invitro.The predominant formation of the S- over the R-glucuronide was reflected by the kinetic parameters: For (S)oxazepam glucuronide, the constants were Km = 0.18 ± 0.02 mM and Vmax= 202.6 ± 25.0 nmol min-1per mg protein; for (R)oxazepam glucuronide, they were Km = 0.22 ± 0.02 mM, Vmax= 55.4 ± 9.5 nmol min-1per mg protein. Inhibition studies suggest that the two diastereomeric glucuronidations are catalysed by different UGT isozymes. That is, there was competitive inhibition of (S)oxazepam glucuronidation by non-steroidal anti-inflammatory drugs (NSAIDs), including ketoprofen while (R)oxazepam glucuronidation was not equally inhibited by these compounds. The order of potency of inhibitors of (S)oxazepam glucuronidation in this study was the same as the rank order of substrates conjugated by UGT2B7; hyodeoxycholic acid, estriol, (S)naproxen, ketoprofen, ibuprofen, fenoprofen, clofibric acid, and morphine (in descending order). The inhibition profile of (S)oxazepam glucuronidation suggests that UGT2B7 is the catalysing enzyme.

ISSN:0960-314X    

出版商:OVID    

年代:1995

数据来源: OVID

ISSN:0960-314X    

出版商:OVID    

年代:1995

数据来源: OVID

ISSN:0960-314X    

出版商:OVID    

年代:1995

数据来源: OVID