title: Effect of alachlor on hepatic cytochrome P450 enzymes in rats.
abstract: Alachlor ((2-chloro-N-methoxymethyl)-N-(2,6-diethylphenyl)acetamide) is a widely used preemergence herbicide which has been classified by the USEPA as a probable human carcinogen. The herbicide has been suggested to be metabolized by hepatic cytochrome P450 system. We examined the effects of alachlor on cytochrome P450 enzymes in rat liver microsomes. Rats were treated intraperitoneally with alachlor daily for 5 days, at doses of 25, 50 and 100 mg/kg. Among the cytochrome P450-dependent monooxygenase activities, 7-pentoxyresorufin O-depentylase, which is associated with CYP2B1, was dose-dependently increased by alachlor. The induction relative to control activity was 1.7-4.2-fold. The activities of CYP1A-dependent monooxygenases such as 7-ethoxy-resorufin O-deethylase and acetanilide 4-hydroxylase were also significantly increased by alachlor at doses of 50 and 100 mg/kg (1.7-2.1-fold). Furthermore, immunoblotting showed that alachlor significantly increased CYP2B1/2 and CYP1A1/2 protein levels by 4.2-6.3- and 1.8-fold, respectively. Although 7-ethoxycoumarin O-deethylase, bufuralol 1'-hydroxylase and 4-nitrophenol 2-hydroxylase activities were significantly increased by alachlor at higher doses (> or = 50 mg/kg), the induction ratios were less than 1.6-fold. The activities of other cytochrome P450-dependent monooxygenases, namely testosterone 7 alpha-hydroxylase, testosterone 2 alpha-hydroxylase, testosterone 6 beta-hydroxylase and lauric acid omega-hydroxylase, were not affected by alachlor at any dose. In addition, there was no significant change in the protein levels of CYP2C11/6, CYP2D1, CYP2E1, CYP3A2/1 and CYP4A1/2/3. These results suggest that alachlor selectively induces cytochrome P450 isoforms of the CYP1A and CYP2B subfamilies in rat liver microsomes, and that the expression of these isoforms is closely related to the toxicity of alachlor.
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: Nobumitsu
authors.initials: N
authors.lastname: Hanioka
authors.forename: Kayoko
authors.initials: K
authors.lastname: Watanabe
authors.forename: Reiko
authors.initials: R
authors.lastname: Yoda
authors.forename: Masanori
authors.initials: M
authors.lastname: Ando
mesh_terms: D015660:7-Alkoxycoumarin O-Dealkylase / Q000187:drug effects / Q000378:metabolism; D000081:Acetamides / Q000008:administration & dosage* / Q000378:metabolism / Q000633:toxicity; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D001835:Body Weight / Q000187:drug effects; D019363:Cytochrome P-450 CYP1A1 / Q000187:drug effects / Q000378:metabolism; D019388:Cytochrome P-450 CYP1A2 / Q000187:drug effects / Q000378:metabolism; D019362:Cytochrome P-450 CYP2B1 / Q000187:drug effects / Q000378:metabolism; D019392:Cytochrome P-450 CYP2E1 / Q000187:drug effects / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004579:Electron Transport / Q000187:drug effects; D006540:Herbicides / Q000008:administration & dosage* / Q000378:metabolism / Q000633:toxicity; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism; D006899:Mixed Function Oxygenases / Q000187:drug effects / Q000378:metabolism; D009929:Organ Size / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D013250:Steroid Hydroxylases / Q000187:drug effects
chemical_list: D000081:Acetamides; D006540:Herbicides; C000188:alachlor; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D013250:Steroid Hydroxylases; D015660:7-Alkoxycoumarin O-Dealkylase; D019392:Cytochrome P-450 CYP2E1; D001189:Aryl Hydrocarbon Hydroxylases; D019363:Cytochrome P-450 CYP1A1; D019388:Cytochrome P-450 CYP1A2; D019362:Cytochrome P-450 CYP2B1; C025619:steroid 16-beta-hydroxylase; C043872:bufuralol 1'-hydroxylase