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Biochimica et Biophysica Acta 1379 1998 391–398
2-Methoxy-4-nitroaniline and its isomers induce cytochrome P4501A
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CYP1A enzymes with different selectivities in the rat liver
Masakuni Degawa
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, Masafumi Nakayama, Yoshihiro Konno, Kazuhiro Masubuchi,
Yasushi Yamazoe
Faculty of Pharmaceutical Sciences, Tohoku UniÕersity, Aramaki-Aza Aoba, Aoba-ku, Sendai 980-77, Japan
Received 22 August 1997; accepted 5 September 1997
Abstract
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We reported previously that 2-methoxy-4-nitroaniline 2-MeO-4-NA is a selective inducer of cytochrome P4501A2
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CYP1A2 in the rat liver, and its molecular size is the smallest among known CYP1A2-selective inducers. In the present
study, a structure-activity relationship on the CYP1A2-selective induction has been investigated using isomeric nitroani-
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sidines and their related chemicals. Western blot analyses revealed that the chemicals removed a substituent amino,
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methoxyl or nitro group from a 2-MeO-4-NA molecule had no capacity for inducing CYP1A enzymes in rat livers. On the
other hand, isomeric nitroanisidines such as 2-MeO-4-NA, 2-MeO-5-NA and 4-MeO-2-NA induced both CYP1A2 and
CYP1A1 enzymes with different selectivities. As judged from the induced levels of CYP1A proteins, 2-MeO-4-NA
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CYP1A2rCYP1A1 ratio; 9.5 and 4-MeO-2-NA 0.3 were the most selective inducers of CYP1A2 and CYP1A1,
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respectively, among the isomeric nitroanisidines 0.44 mmolrkg used. The induced level of CYP1A2 protein was in the
order 2-MeO-4-NA ) 2-MeO-5-NA ) 4-MeO-2-NA, although no significant difference was observed on their CYP1A2
mRNA level. On the contrary, increases in the levels of CYP1A1 mRNA and protein were in the order 4-MeO-2-NA )
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2-MeO-5-NA ) 2-MeO-4-NA. The present findings indicate that all three substituents amino, methoxyl and nitro groups
are necessary components of nitroanisidines for induction of CYP1A enzymes, and also show that regio-isomeric positions
of these substituents determine the selectivity in the induction of CYP1A enzymes. q 1998 Elsevier Science B.V.
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Keywords: 2-Methoxy-4-nitroaniline; Cytochrome P4501A; Enzyme induction; Rat liver
1. Introduction
Carcinogenic aromatic amines, such as 4-
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aminoazobenzene derivatives 1,2 and food-derived
Abbreviations: CYP1A2, cytochrome P4501A2; 2-MeO-4-NA,
2-methoxy-4-nitroaniline; 2-OH-4-NA, 2-hydroxy-4-nitroaniline;
4-NA, 4-nitroaniline; 2-MeO-A, 2-methoxy-aniline; 3-NAS, 3-
nitroanisole; 2-MeO-5-NA, 2-methoxy-5-nitroaniline; 4-MeO-2-
NA, 4-methoxy-2-nitroaniline
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Corresponding author. Fax: q81 22-217 6826.
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heterocyclic amines 3,4 , increase selectively cy-
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tochrome P4501A2 CYP1A2 , which mediates
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metabolic activation N-hydroxylation of carcino-
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genic aromatic amines 5–7 . The activity andror
inducibility of CYP1A2 in the liver are suggested to
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be a host factor s determining the susceptibility to
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hepatocarcinogenic aromatic amines 8–10 .
Although the induction of CYP1A enzymes by
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aryl hydrocarbons Ah and polyhalogenated aro-
matic hydrocarbons, is considered to occur through a
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cytosolic Ah receptor AhR -mediated pathway 11–
0304-4165r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved.
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PII S0304-4165 97 00118-9