The CYP1A2 (also known as phenacetin O-deethylase, caffeine demethylase, or antipyrine N-demethylase) catalyzes the oxidation (and, in
some cases, bioactivation) of arylamines, nitrosamines, and aromatic hydrocarbons and the bioactivation of promutagens and
procarcinogens, caffeine, and other substances. It is expressed in the liver to the extent of 13% (range of up to
40%), intestine, and stomach and is induced by smoking, PAHs, and isosafrole (a noncarcinogenic dietary compound). CYP1A2 is primarily
responsible for the activation of the carcinogen aflatoxin B1 under ordinary conditions of human exposure and the pneumotoxin ipomeanol.
The latter activation occurs in the liver and not in the lungs by CYP2F1 and CYP4B1 as previously thought. Evidence for polymorphism of
this isoform has been reported, and it is likely that low CYP1A2 activity will be associated with altered susceptibility to the bioactivation of
procarcinogens, promutagens, and other xenobiotics known to be substrates for this enzyme. The expression of the CYP1A2 gene in the
stomach becomes an important issue for gastric carcinogenesis induced by smoking and the metabolic activation of the procarcinogens,
arylamines, to mutagens. Clinical studies have suggested that the N-demethylation of imipramine is greater in smokers than in nonsmokers.
