Predictive value of comparative molecular field analysis modelling of naphthalene inhibition of human CYP2A6 and mouse CYP2A5 enzymes.
The objects of this study were first to compare how well the recently constructed structure-inhibition activity relationship models of mouse CYP2A5 and human CYP2A6 predict the interaction of naphthalene in liver microsomes and secondly to study if these CYP enzymes actually oxidize naphthalene. The CoMFA model of CYP2A5 predicted the IC(50) value of naphthalene to be 42 microM (18-115 microM 95% CL) whereas in the in vitro experiment the result was 74 microM (65-83 microM) with the corresponding values for CYP2A6 being 41 microM (18-112 microM) and 25 microM (21-30 microM), respectively. Naphthalene appeared to be a competitive inhibitor both for mouse and human liver microsomal coumarin 7-hydroxylase, which is the specific probe activity for CYP2A5 and CYP2A6. The K(i)-value for the mouse enzyme was between 12-26 microM and for the human enzyme 1.2-5.6 microM. A 1-h in vitro incubation of naphthalene with human and pyrazole treated mouse liver microsomes produced more 1-naphthol than 2-naphthol. Antibody against the purified CYP2A5 inhibited 50-60% of the formation of 1-naphthol and 30-40% of the formation of 2-naphthol. These results indicate that in silico CoMFA models predict relatively well the interaction of naphthalene with CYP2A5 and CYP2A6 and that these CYPs actually oxidize naphthalene in vitro. CoMFA CYP2A5 and CYP2A6 models are thus useful as a technique for elucidating the interaction and potency of untested chemicals with these CYPs.
Asikainen
Arja
A
Department of Environmental Sciences, University of Kuopio, Box 1627, 70211, Kuopio, Finland.
Tarhanen
Juhani
J
Poso
Antti
A
Pasanen
Markku
M
Alhava
Esko
E
Juvonen
Risto O
RO
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D065637:Cytochrome P-450 CYP2A6; D000072467:Cytochrome P450 Family 2; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D006801:Humans; D006900:Hydroxylation; D007700:Kinetics; D008297:Male; D051379:Mice; D008811:Mice, Inbred DBA; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D008954:Models, Biological; D009249:NADP / Q000378:metabolism; D009281:Naphthalenes / Q000494:pharmacology*; D010084:Oxidation-Reduction; D011237:Predictive Value of Tests
D004791:Enzyme Inhibitors; D009281:Naphthalenes; D009249:NADP; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C585710:CYP2A6 protein, human; C585520:Cyp2a5 protein, mouse; D065637:Cytochrome P-450 CYP2A6; D000072467:Cytochrome P450 Family 2