Decreased coumarin 7-hydroxylase activities and CYP2A6 expression levels in humans caused by genetic polymorphism in CYP2A6 promoter region (CYP2A6*9).
One of seven poor metabolizers of coumarin found in Thai subjects was previously genotyped as heterozygote for the CYP2A6*4 (whole deletion) and CYP2A6*9. Thus, we aimed to investigate the relationship between the genetic polymorphism in the TATA box of the CYP2A6 gene (CYP2A6*9), expression levels of CYP2A6 mRNA and coumarin 7-hydroxylase activities in human livers. Levels of CYP2A6 mRNA were quantified by real-time quantitative reverse transcriptase-polymerase chain reaction. The mean expression levels of CYP2A6 mRNA in individuals with CYP2A6*1/*4, CYP2A6*1/*9 and CYP2A6*4/*9 were 58%, 71% and 21% of the individuals genotyped as CYP2A6*1/*1, respectively. The mean in-vitro coumarin 7-hydroxylase activities in subjects carrying CYP2A6*1/*4, CYP2A6*1/*9 and CYP2A6*4/*9 were 41%, 71% and 12%, respectively, compared to those of the subjects judged as wild-type. Vmax values for coumarin 7-hydroxylation in the liver microsomes from human subjects with genotypes of CYP2A6*1/*1, CYP2A6*1/*4, CYP2A6*1/*9 and CYP2A6*4/*9 were 0.58, 0.26, 0.44 and 0.13 nmol/min/nmol total P450, respectively. CYP2A6 protein levels in human liver microsomes with the CYP2A6*4 and the CYP2A6*9 alleles were markedly decreased. These results suggest that the genetic polymorphism in the promoter region of the CYP2A6 gene (CYP2A6*9) reduced the expression levels of CYP2A6 mRNA and protein in human livers, resulting in the decrease of coumarin 7-hydroxylase activities. Individuals judged as CYP2A6*4/*9 were expected to be poor metabolizers, having extremely low activity of CYP2A6.
Laboratory of Drug Metabolism, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.
Kazuma
K
Kiyotani
Hiroshi
H
Yamazaki
Masaki
M
Fujieda
Shunsuke
S
Iwano
Keiko
K
Matsumura
Soisungwan
S
Satarug
Pailin
P
Ujjin
Tsutomu
T
Shimada
F Peter
FP
Guengerich
Andrew
A
Parkinson
Goro
G
Honda
Kazuko
K
Nakagawa
Takashi
T
Ishizaki
Tetsuya
T
Kamataki
D000328:Adult; D000483:Alleles; D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism*; D044466:Asian People; D065637:Cytochrome P-450 CYP2A6; D005260:Female; D005787:Gene Frequency; D006579:Heterozygote; D006801:Humans; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism*; D008875:Middle Aged; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D011110:Polymorphism, Genetic; D020641:Polymorphism, Single Nucleotide; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
D012333:RNA, Messenger; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C585710:CYP2A6 protein, human; D065637:Cytochrome P-450 CYP2A6