title: In vitro metabolism of chlorotriazines: characterization of simazine, atrazine, and propazine metabolism using liver microsomes from rats treated with various cytochrome P450 inducers.
abstract: The in vitro metabolism of chlorotriazines, simazine (SIZ), atrazine (ATZ), and propazine (PRZ) was studied using control, 3-methylcholanthrene-, phenobarbital-, pyridine-, dexamethasone-, and clofibrate-treated rat liver microsomes. The metabolites were determined by HPLC. The principal reactions by cytochrome P450 (P450) system were N-monodealkylation and isopropylhydroxylation in all rat liver microsomes. As a result, 2-chloro-4-ethylamino-6-amino-1,3,5-triazine (M1) (SIZ-M1 for SIZ and ATZ-M1 for ATZ) and 2-chloro-4-amino-6-isopropylamino-1,3, 5-triazine (M2) (ATZ-M2 for ATZ and PRZ-M2 for PRZ), 2-chloro-4-ethylamino-6-(1-hydroxyisopropylamino)-1,3,5-triazine (M3) (ATZ-M3 for ATZ), and 2-chloro-4-isopropylamino-6-(1-hydroxyisopropylamino)-1,3,5-triazi ne (M4) (PRZ-M4 for PRZ) were detected as the metabolites. N-bidealkylation and 2-hydroxylation were not found in this system. The formation rates of SIZ-M1, ATZ-M1, ATZ-M2, and PRZ-M2 were markedly induced by 3-methylcholanthrene, phenobarbital, and pyridine. On the other hand, the formation rates of ATZ-M3 and PRZ-M4 were significantly induced by phenobarbital, pyridine, and/or clofibrate, but not by 3-methylcholanthrene. The enzyme kinetics of chlorotriazine metabolism were examined by mean of Eadie-Hofstee analyses. Although there was no remarkable difference of Km for the products in chlorotriazine metabolism among the microsomes tested, the Vmax and Clint (Vmax/Km) for the products in chlorotriazine metabolism are affected by P450 inducers, except for dexamethasone. The formation rates of SIZ-M1, ATZ-M1, ATZ-M2, and PRZ-M2 were significantly correlated with 7-ethoxyresorufin O-deethylase, acetanilide 4-hydroxylase, 7-ethoxycoumarin O-deethylase, 4-nitrophenol 2-hydroxylase, and testosterone 7alpha-hydroxylase activities and CYP1A1/2 level, whereas the formation rates of ATZ-M3 and PRZ-M4 were significantly correlated with testosterone 16beta-hydroxylase, bufuralol 1'-hydroxylase, and 4-nitrophenol 2-hydroxylase activities and CYP2B1/2 level. These results suggest that the inducibility in metabolism of SIZ, ATZ, and PRZ is different between N-monodealkylation and isopropylhydroxylation and that the N-monodealkylation and isopropylhydroxylation are induced by CYP1A1/2, CYP2B1/2, and CYP2B1/2, respectively.
authors.affiliation: Division of Environmental Chemistry, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo, 158-8501, Japan. hanioka@nihs.go.jp
authors.forename: N
authors.initials: N
authors.lastname: Hanioka
authors.forename: H
authors.initials: H
authors.lastname: Jinno
authors.forename: T
authors.initials: T
authors.lastname: Tanaka-Kagawa
authors.forename: T
authors.initials: T
authors.lastname: Nishimura
authors.forename: M
authors.initials: M
authors.lastname: Ando
mesh_terms: D000818:Animals; D001280:Atrazine / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis*; D004790:Enzyme Induction; D006540:Herbicides / Q000378:metabolism*; D015151:Immunoblotting; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000096:biosynthesis; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012839:Simazine / Q000378:metabolism*; D014227:Triazines / Q000378:metabolism*
chemical_list: D006540:Herbicides; D007527:Isoenzymes; D014227:Triazines; D003577:Cytochrome P-450 Enzyme System; D001280:Atrazine; D012839:Simazine; C100043:propazine