carcinogen. The activities of several P450 enzymes, including the
P4502A subfamily, are in humans associated with polymorphism
and are inducible by several xenobiotics (Su and Ding, 2004). Thus
the degree to which NAs are metabolically activated may vary
between individuals and result in variation in susceptibility to NA
exposure. It is assumed that the more polar the NAs are rapidly excreted
and therefore less likely to be metabolically activated. This
is part of the reason why the hydroxylated NAs are less potent carcinogens
than their un-substituted NAs (Lijinsky 1987, 301–356).