PT  - JOURNAL ARTICLE
AU  - M Nakajima
AU  - T Yamamoto
AU  - K Nunoya
AU  - T Yokoi
AU  - K Nagashima
AU  - K Inoue
AU  - Y Funae
AU  - N Shimada
AU  - T Kamataki
AU  - Y Kuroiwa
TI  - Role of human cytochrome P4502A6 in C-oxidation of nicotine.
DP  - 1996 Nov 01
TA  - Drug Metabolism and Disposition
PG  - 1212--1217
VI  - 24
IP  - 11
4099  - http://dmd.aspetjournals.org/content/24/11/1212.short
4100  - http://dmd.aspetjournals.org/content/24/11/1212.full
SO  - Drug Metab Dispos1996 Nov 01; 24
AB  - Nicotine is primarily metabolized to cotinine in humans. In this study, human cytochrome P450 (CYP) isoform involved in cotinine formation was identified. The formation of cotinine in 16 human liver microsomes was determined with a 50 microM nicotine concentration and with a cytosol preparation as a source of aldehyde oxidase. Cotinine formation in human liver microsomes significantly correlated with immunochemically determined CYP2A6 levels (r = 0.663, p < 0.05), coumarin 7-hydroxylase activities (r = 0.831, p < 0.01), and cotinine 3'-hydroxylase activities (r = 0.735, p < 0.01) that are responsible for CYP2A6. In inhibition studies, cotinine formation in human liver microsomes was inhibited by coumarin and rabbit anti-rat CYP2A1 antibody specifically. When the capability of microsomes of B-lymphoblastoid cells expressing human CYPs to perform biotransformation of nicotine to cotinine was determined, cDNA-expressed CYP2A6 exhibited the highest cotinine formation. The KMapp values from microsome expressing CYP2A6 cDNA were similar to the value obtained from human liver microsomes. The large interindividual variabilities in cotinine formation and immunochemically determined CYP2A6 levels were observed in human liver microsomes, suggesting genetic polymorphism of CYP2A6. Nicotine is a new in vivo probe for phenotyping of CYP2A6 in humans.