New allelic arrangement CYP2D6*36 x 2 found in a Japanese poor metabolizer of debrisoquine.
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Alleles↗
Biomedical subjects
Tetsuya Kamataki
Publications and source records attributed to Tetsuya Kamataki.
Hepatocyte nuclear factor-1alpha is a causal factor responsible for interindividual differences in the expression of UDP-glucuronosyltransferase 2B7 mRNA in human livers.
UDP-glucuronosyltransferase (UGT) 2B7 is one of the most important UGT isozymes expressed in human livers. This enzyme is reported to show more than 10-fold interindividual differences in its enzyme activities. Thus, the amounts of UGT2B7 mRNA in 12 human livers were quantified by quantitative reverse transcription-polymerase chain reaction. The amounts of UGT2B7 mRNA in the subjects ranged from 0.22 to 2.63 copies/10(3) copies of beta-actin. A novel point mutation (-253G to A) found in this study did not affect the level of UGT2B7 mRNA in the subjects. To clarify a causal factor(s) determining the expression level of UGT2B7 mRNA, we examined the correlation between the amounts of mRNAs for UGT2B7 and hepatocyte nuclear factor (HNF)-1alpha, which regulates the expression of UGT2B7 gene. HNF-1alpha mRNA was expressed at a level ranging from 2.99 to 24.76 copies/10(6) copies of beta-actin in the subjects. The amounts of mRNAs for UGT2B7 expressed in these individual liver samples were highly associated with the amount of mRNA for HNF-1alpha (r = 0.786, p = 0.002), suggesting that HNF-1alpha is a factor limiting the expression of UGT2B7 mRNA and a causal factor responsible for an interindividual difference in human livers.
DNA-Binding Proteins↗
Involvement of CYP2J2 and CYP4F12 in the metabolism of ebastine in human intestinal microsomes.
The purpose of the study was to elucidate human intestinal cytochrome P450 isoform(s) involved in the metabolism of an antihistamine, ebastine, having two major pathways of hydroxylation and N-dealkylation. The ebastine dealkylase in human intestinal microsomes was CYP3A4, based on the inhibition studies with antibodies against CYP1A, CYP2A, CYP2C, CYP2D, CYP2E, and CYP3A isoforms and their selective inhibitors. However, ebastine hydroxylase could not be identified. We then examined the inhibitory effects of anti-CYP4F antibody and 17-octadecynoic acid, an inhibitor of the CYP4 family, on ebastine hydroxylation in intestinal microsomes, since CYP4F was recently found to be the predominant ebastine hydroxylase in monkey intestine; and a novel CYP4F isoform (CYP4F12), also capable of hydroxylating ebastine, was found to exist in human intestine. However, the inhibitory effects were only partial (about 20%) and thus it was thought that, although human CYP4F was involved in ebastine hydroxylation, another predominant enzyme exists. Further screening showed that the hydroxylation was inhibited by arachidonic acid. CYP2J2 was selected as a candidate expressed in the intestine and closely related to arachidonic acid metabolism. The catalytic activity of recombinant CYP2J2 was much higher than that of CYP4F12. Anti-CYP2J antibody inhibited the hydroxylation to about 70% in human intestinal microsomes. These results demonstrate that CYP2J2 is the predominant ebastine hydroxylase in human intestinal microsomes. Thus, the present paper for the first time indicates that, in human intestinal microsomes, both CYP2J and CYP4F subfamilies not only metabolize endogenous substrates but also are involved in the drug metabolism.
Antibodies, Blocking↗
[P450 and carcinogenesis].
Multiple forms of cytochrome P450 play important roles in metabolic activation of a variety of environmental procarcinogens. Large species differences in substrate specificities between experimental animals and humans are critical factors in evaluation of chemical safety. To study the role of human P450s in genotoxic activation of environmental chemicals, transgenic bacteria expressing both human P450s and P450 reductase have been developed for the mutagenicity test. Mice lacking CYP1A2, and CYP1B1, and CYP2E1 were prepared to investigate the mechanism of procarcinogen activation in vivo. The first human transgenic animals were mice carrying human fetus-specific CYP3A7. Using these transgenic mice, mutagenic activation of a natural mycotoxin, aflatoxin B1, catalyzed by CYP3A7 in vivo was demonstrated. This observation was clear in extrahepatic tissues that did not express mouse CYP3A enzymes. In conclusion, P450s are key factors involved in metabolic activation of environmental procarcinogens for their biological actions.
Aflatoxin B1↗
Genetically engineered bacterial cells co-expressing human cytochrome P450 with NADPH-cytochrome P450 reductase: prediction of metabolism and toxicity of drugs in humans.
Genetically engineered bacterial cells expressing human cytochrome P450 (CYP) have been developed as new tools to predict the metabolism and toxicity of drugs in humans. There are various host cells for the heterologous expression of a form of CYP. Among them, bacterial cells such as Escherichia coli (E. coli) have advantages with regard to ease of use and high yield of protein. CYP protein could be first expressed by the modification of the N-terminal amino acid sequence in E. coli cells in 1991. Since then, many forms of human CYP have been successfully expressed in E. coli cells. Since the E. coli cells do not possess endogeneous electron transport systems to support the full catalytic activity of CYP, E. coli strains co-expressing both human CYP and NADPH-cytochrome P450 reductase (OR) have been established. Each form of CYP expressed in the E. coli cells efficiently catalyzed the oxidation of a representative substrate at an efficient rate, indicating that the OR was sufficiently expressed to support the catalytic activity of CYP. According to the studies performed so far, the modification of the N-terminal amino acid sequence of CYP did not seem to affect the catalytic properties of CYP. The human CYP expressed in the E. coli cells were applicable for studies to determine a metabolic pathway(s) of drugs and to estimate kinetic parameters of drug metabolism by human CYP. Drug-drug interactions caused by inhibition of the metabolism of drugs by human CYP could also be examined by in vitro inhibition studies with CYP expressed in the E. coli cells. Recently, human CYP was co-expressed with the OR in Salmonella typhimurium (S. typhimurium) cells used for mutation assay (Ames test) by applying the technology for the expression of human CYP and the OR in E. coli cells, to evaluate whether chemicals including drugs are metabolically activated by human CYP and show mutagenicity. These strains of bacteria are considered as useful tools to study the metabolism and the toxicity of drugs in humans.
Journal Article↗
Novel mutations of the CYP2A6 gene in a Thai population with lowered capacity of coumarin 7-hydroxylation.
We explored genetic polymorphisms in a Thai population which exhibited a low capacity to metabolize coumarin. The following two silent single nucleotide polymorphisms (SNPs) were found: 1) SNP, 020228Kiyotani001; GENE NAME, CYP2A6; ACCESSION NUMBER, NT_011139; LENGTH, 25 base; 5'-AAACTACCTGCAG/TCTGAACACAGAG-3'. 2) SNP, 020228Kiyotani002; GENE NAME, CYP2A6; ACCESSION NUMBER, NT_011139; LENGTH, 25 base; 5'-AATCCCCAGCAC/TTTCCTGAATGAG-3'. These two mutations (G144A and C1245T), which were located in exon 1 and exon 8 of the CYP2A6 gene, were found in two subjects among nine poor metabolizers for coumarin.
Journal Article↗
A major genotype in UDP-glucuronosyltransferase 2B15.
A novel single nucleotide polymorphism (SNP) was found in exon 6 of the UDP-glucuronosyltransferase (UGT) 2B15 gene from healthy Japanese populations. The SNP was as follows: SNP, 020228Toide001; GENE NAME, UGT2B15; ACCESSION NUMBER, U08854, AF180322, and NM_001078; LENGTH, 25 base; 5'-AGCTTGCCAAAAC/AAGGAAAGAAGAA-3'. This SNP was expected to cause a change of an amino acid residue at the position 523 (Thr to Lys) located in a putative co-factor binding region. The allele frequency of this SNP was 79% in Japanese, suggesting this polymorphism to be a major genotype in Japanese people.
Journal Article↗
A mutation in the flavin-containing monooxygenase 3 gene and its effects on catalytic activity for N-oxidation of trimethylamine in vitro.
To clarify the mutation of the flavin-containing monooxygenase (FMO) 3 gene causing fish-odor syndrome, we analyzed the FMO3 gene of a Thai subject who possibly suffered from fish-odor syndrome. A novel mutation, a single-base substitution from G to A at the position of 265 (G265A), was identified in exon 3. The mutation caused an amino acid substitution from valine to isoleucine at residue 58 (V58I). The mutated FMO3 protein with V58I exhibited the reduced trimethylamine N-oxidase activity when it was expressed in E. coli. The V(max)/K(m) value for the activity of the mutant-type FMO3 was about 5 times lower than that for the wild-type FMO3.
Journal Article↗
Twenty one novel single nucleotide polymorphisms (SNPs) of the CYP2A6 gene in Japanese and Caucasians.
We sequenced all nine exons and exon-intron junctions of the CYP2A6 gene from 33 Japanese and 28 Caucasians. We found twenty one single nucleotide polymorphisms (SNPs) including four SNPs causing amino acid substitutions, one silent SNP in exon 5, one SNP in a 5'-flanking region, four SNPs in a 3'-untranslated region, and eleven SNPs in introns. The four mutations (13G>A and 86G>A in exon 1, and 2134A>G and 2161C>T in exon 4) causing amino acid substitutions (Gly(5)Arg, Ser(29)Asn, Lys(194)Glu, and Arg(203)Ser), respectively, were as follows: SNP, 020719Kiyotani004; GENE NAME, CYP2A6; ACCESSION NUMBER, NG_000008.4; LENGTH, 25 base; 5'-ATGCTGGCCTCAG/AGGATGCTTCTGG-3'. SNP, 020719Kiyotani005; GENE NAME, CYP2A6; ACCESSION NUMBER, NG_000008.4; LENGTH, 25 base; 5'-AGCAGAGGAAGAG/ACAAGGGGAAGCT-3'. SNP, 020719Kiyotani011; GENE NAME, CYP2A6; ACCESSION NUMBER, NG_000008.4; LENGTH, 25 base; 5'-CGCTTTGACTATA/GAGGACAAAGAGT-3'. SNP, 020719Kiyotani012; GENE NAME, CYP2A6; ACCESSION NUMBER, NG_000008.4; LENGTH, 25 base; 5'-CTGTCACTGTTGC/TGCATGATGCTAG-3'. New alleles having these SNPs were designated as CYP2A6( *)13-CYP2A6( *)16.
Journal Article↗
[Genetic polymorphisms of drug metabolizing enzymes].
Multiple forms of CYP exist in humans. P450s comprise a superfamily of enzymes. These P450s play important roles in the oxidation of structurally diverse endobiotics and xenobiotic chemicals including anticancer drugs and carcinogens. The genes encoding most of the CYP1, CYP2, and CYP3 families show genetic polymorphism. In this article, we describe recent findings that these polymorphic enzymes can abolish or quantitatively or qualitatively alter drug metabolism in humans.
Aryl Hydrocarbon Hydroxylases↗
[Association between genetic polymorphism and lung cancer risk].
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Aryl Hydrocarbon Hydroxylases↗
Genetic polymorphism of CYP2A6 gene and tobacco-induced lung cancer risk in male smokers.
Cytochrome P450 2A6 (CYP2A6) is the principal enzyme involved in the metabolic activation of tobacco-specific nitrosamines to their ultimate carcinogenic forms and metabolism of nicotine. We investigated the effects of the CYP2A6*4, an entire CYP2A6 gene deletion-type polymorphism, on lung cancer risk and daily cigarette consumption in Japanese male smokers via a hospital-based case control study. The frequency of the CYP2A6*4 variant was compared in 370 lung cancer patients and 380 control smokers. A markedly reduced adjusted odds ratio for lung cancer risk, 0.23 [95% confidence interval, 0.08-0.67], was seen in the group with homozygous deletion (*4/*4) when the odds ratio for a group with homozygous wild (*1A/*1A) was defined to be 1.00 by logistic regression. The subjects with lung cancer were additionally divided into three groups according to the histological classification of the cancer and examined for an association with the CYP2A6 polymorphism. The *4/*4 genotype was not found in patients with squamous cell carcinoma (0 of 105) or small cell carcinoma (0 of 44), indicating that subjects with the *4/*4 genotype have low risk for lung cancers, particularly those caused by tobacco smoke. Furthermore, a significant reduction of daily cigarette consumption was observed in smokers with the *4/*4 genotype, suggesting a possibility that complete lack of CYP2A6 appeared to affect the smoking behavior. These data suggest that male smokers possessing the *1A/*1A genotype have higher risk for tobacco-induced lung cancers.
Adult↗