title: Liver tumor promoting effect of orphenadrine in rats and its possible mechanism of action including CAR activation and oxidative stress.
abstract: Orphenadrine (ORPH), an anticholinergic agent, is a cytochrome P450 (CYP) 2B inducer. CYP2B inducers are known to have liver tumor-promoting effects in rats. In this study, we performed a rat two-stage liver carcinogenesis bioassay to examine the tumor-promoting effect of ORPH and to clarify its possible mechanism of action. Male rats were given a single intraperitoneal injection of N-diethylnitrosamine (DEN) as an initiation treatment. Two weeks after DEN administration, rats were fed a diet containing ORPH (0, 750, or 1,500 ppm) for 6 weeks. One week after the ORPH-administration rats were subjected to two-thirds partial hepatectomy for the acceleration of hepatocellular proliferation. The number and area of glutathione S-transferase placental form-positive foci significantly increased in the DEN-ORPH groups. Real-time RT-PCR revealed increased mRNA expression levels of Cyp2b1/2, Mrp2 and Cyclin D1 in the DEN-ORPH groups and of Gpx2 and Gstm3 in the DEN-High ORPH group. Microsomal reactive oxygen species (ROS) production and oxidative stress markers such as thiobarbituric acid-reactive substances and 8-hydroxydeoxyguanosine were increased in the DEN-High ORPH group. Immunohistochemically, constitutively active/androstane receptor (CAR) were clearly localized in the nuclei of hepatocytes in the DEN-ORPH groups. These results suggest that ORPH causes nuclear translocation of CAR resulting in the induction of the liver tumor-promoting activity. Furthermore, oxidative stress resulting from ROS production is also involved in the liver tumor-promoting activity of ORPH.
authors.affiliation: Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, Japan. rmorita@cc.tuat.ac.jp
authors.forename: Reiko
authors.initials: R
authors.lastname: Morita
authors.forename: Atsunori
authors.initials: A
authors.lastname: Yafune
authors.forename: Ayako
authors.initials: A
authors.lastname: Shiraki
authors.forename: Megu
authors.initials: M
authors.lastname: Itahashi
authors.forename: Yuji
authors.initials: Y
authors.lastname: Ishii
authors.forename: Hirotoshi
authors.initials: H
authors.lastname: Akane
authors.forename: Fumiyuki
authors.initials: F
authors.lastname: Nakane
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Suzuki
authors.forename: Makoto
authors.initials: M
authors.lastname: Shibutani
authors.forename: Kunitoshi
authors.initials: K
authors.lastname: Mitsumori
mesh_terms: D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D018680:Cholinergic Antagonists / Q000008:administration & dosage / Q000633:toxicity*; D000090702:Constitutive Androstane Receptor; D004052:Diethylnitrosamine / Q000008:administration & dosage / Q000633:toxicity; D022781:Hepatocytes / Q000166:cytology / Q000378:metabolism; D008113:Liver Neoplasms / Q000139:chemically induced*; D008297:Male; D018727:Muscarinic Antagonists / Q000008:administration & dosage / Q000633:toxicity*; D009966:Orphenadrine / Q000008:administration & dosage / Q000633:toxicity*; D018384:Oxidative Stress / Q000187:drug effects*; D051381:Rats; D011916:Rats, Inbred F344; D017382:Reactive Oxygen Species / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*
chemical_list: D018680:Cholinergic Antagonists; D000090702:Constitutive Androstane Receptor; D018727:Muscarinic Antagonists; D017382:Reactive Oxygen Species; D018160:Receptors, Cytoplasmic and Nuclear; D004052:Diethylnitrosamine; D009966:Orphenadrine