The CYP2D6 allele frequencies in our Japanese subjects differed from those determined in previous studies of white subjects or mainland Chinese subjects. Individuals homozygous for *10 who have relatively low in vivo CYP2D6 activity represent almost 20% of the Japanese population. In addition, we did not identify any subjects with amplified *2 among our 98 Japanese men.
Interindividual variability of the activity of CYP1A2 may be expected to affect cancer susceptibility, since the enzyme is capable of activating several carcinogens. In the present study, we found three new polymorphisms in the 5′ ′ ′ ′-flanking region (CYP1A2/B) and intron 1 (CYP1A2/C and CYP1A2/D) of CYP1A2 in Japanese by using polymerase chain reaction-single strand conformation polymorphism. We developed methods to detect these polymorphisms by polymerase chain reaction-restriction fragment length polymorphism and performed a population study (159 subjects) to estimate the frequencies of the alleles. Cytochrome P450 (CYP) enzymes play an important role in the metabolism of endogenous and exogenous substrates. Human CYP1A2 has been shown to be responsible for the 3-demethylation of caffeine, the initial major step in the biotransformation of caffeine in humans. 1) CYP1A2 is also known to be involved in the metabolic activation of numerous carcinogens such as 2-aminofluorene, 3-amino-1-methyl-5H-pyrido[4,3-b]-indole (Trp-P-2) and 2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine (PhIP).2-4) Several studies on the CYP1A2-dependent metabolism of caffeine or phenacetin have demonstrated that this enzyme is expressed in human livers at a variety of levels among individuals.5, 6) Considerable interindividual variability in the activities of CYP1A2-dependent N-oxidation of 2-naphthylamine, 7) 2-acetylaminofluorene 8) and 4-aminobiphenyl has also been noted.9) The sequence analysis of Japanese DNA samples in our previous study suggested that the considerable variation in the level of CYP1A2 expression was not due to mutation of the exonic, intronic, or 5′-flanking regions.10) However, our recent study clarified that genetic polymorphism existed in the 5′-flanking region of the human CYP1A2 gene in Japanese subjects.
11)This mutation affects the CYP1A2 inducibility. Further, we discovered three additional polymorphisms of the CYP1A2 gene by using the polymerase chain reaction single-strand conformation polymorphism (PCR-SSCP) method in the 5′-flanking region and intron 1 of the CYP1A2 gene (data not shown). The four CYP1A2 mutations are summarized in Fig. 1. CYP1A2/A was already reported by our group. 11) CYP1A2/B, CYP1A2/C and CYP1A2/D are new polymorphic alleles.In this report, we describe methods to detect the three mutated alleles by PCR-restriction fragment length polymorphism (PCR-RFLP) and we present an estimate of the allele frequencies in a Japanese population.The use of human blood for this study had been approved by the Hokkaido University Ethics Committee. The 159 subjects were all healthy Japanese. Genomic DNA was extracted from peripheral leukocytes with phenol-chloroform, followed by ethanol precipitation.12) DNA was dissolved in 10 mM Tris-HCl (pH 8.0) containing 1 mM EDTA, and stored at 4°C until PCR reactions. Four CYP1A2 genotypes were detected by PCR-RFLPs. The sequences of the primers for PCR are shown in Table I. 13,14) PCR was performed to detect the CYP1A2/A genotype using primers P1 and P2, 1...
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