Although chronic administration of
procymidone (a widely used dicarboximide fungicide) leads to an increased incidence of liver
tumors in mice, short-term genotoxicity studies proved negative. As
cytochrome P450 (CYP) induction has been linked to non-genotoxic
carcinogenesis, we investigated whether
procymidone administration causes induction of CYP-dependent
monooxygenases in liver, kidney and lung microsomes of male Swiss Albino CD1 mice after single or repeated (daily for three consecutive days) i.p. treatment with either 400 or 800 (1/10 or 1/20 of the DL(50)) mgkg(-1) b.w.
procymidone. CYP content and CYP3A1/2, 1A1, 1A2, 2B1/2, 2E1, 2A, 2D9 and 2C11 supported oxidations were studied using either the regio- and stereo-selective hydroxylation of
testosterone as multibiomarker or highly specific substrates as probes of various CYPs. While a single dose was uneffective, multiple
procymidone administration lead to marked inductions of various
monooxygenases: CYP3A1/2 in liver and lung (as measured by N-demethylation of
aminopyrine and
testosterone 6 beta-hydroxylase);
CYP2E1 in liver (
p-nitrophenol hydroxylation);
CYP1A1 in liver and kidney (deethylation of
ethoxyresorufin). Several hydroxylations were induced in the liver, including the CYP2A-linked 7 alpha (14-fold) as well
as 6 alpha (22-fold), 6 beta, 16 beta and 2 beta
hydroxylases. The pattern of inductions/suppressions recorded in the three different tissues suggests that
procymidone exerts complex effects on the CYP profile. Tissue-specific trends included a large number of inductions in the liver and suppressions in the lung. The main inductions were corroborated by immunoblotting analyses and Northern blotting showed that inductions of CYP3A1/2,
CYP2E1 and
CYP1A1/2 were paralleled by increased
mRNA levels. It was also found that CYP over-expression generates large amounts of
reactive oxygen species (ROS), especially in liver. These data may explain why in vitro short-term genotoxicity studies on
procymidone were negative, whereas in vivo long-term
carcinogenesis studies turned out positive: long-term CYP induction (e.g.
oxygen centered
free radicals over-production) can have a co-carcinogenic and/or promoting potential.