title: Effects of continuous exposure to digoxin on MDR1 function and expression in Caco-2 cells.
abstract: The Caco-2 cell line has been used widely for studying intestinal permeability and several transport functions, and express the multidrug resistance transporter MDR1/P-glycoprotein. Previously, the transient exposure to digoxin for 24 h was found to induce MDR1 mRNA in Caco-2 cells. Here, a digoxin-tolerant Caco-2 subline (Caco/DX) was newly established by the continuous exposure of Caco-2 cells to digoxin, and the effects of continuous exposure to digoxin on MDR1 were examined. The 50% growth inhibitory concentration (IC(50)) values for digoxin in Caco-2 and Caco/DX cells were 17.2 and 81.4 nM, respectively. The IC(50) values for paclitaxel, an MDR1 substrate, were 1.0 and 547 nM, respectively, whereas the cytotoxicity of 5-fluorouracil was comparable in both cells. The uptake and efflux of Rhodamine123, an MDR1 substrate, in Caco/DX cells were significantly less and greater, respectively, than those in Caco-2 cells, and these transports were affected by the addition of ciclosporin. The expression of MDR1 mRNA in Caco/DX cells was approximately 2- and 1.7-fold compared with Caco-2 cells and Caco-2 cells treated with 100 nM digoxin for 24 h, respectively. On the other hand, MRP1 mRNA in Caco/DX cells was unchanged. These observations confirmed that the continuous exposure to digoxin, as well as the transient exposure, induced MDR1 in Caco-2 cells.
authors.affiliation: Department of Hospital Pharmacy, Faculty of Pharmaceutical Sciences, Kyoto Pharmaceutical University, 5 Nakauchi-cho, Misasagi, Yamashina-ku, Kyoto 607-8414, Japan. takara@mb.kyoto-phu.ac.jp
authors.forename: Kohji
authors.initials: K
authors.lastname: Takara
authors.forename: Masayuki
authors.initials: M
authors.lastname: Tsujimoto
authors.forename: Noriaki
authors.initials: N
authors.lastname: Ohnishi
authors.forename: Teruyoshi
authors.initials: T
authors.lastname: Yokoyama
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000096:biosynthesis* / Q000235:genetics; D018938:Caco-2 Cells / Q000187:drug effects* / Q000378:metabolism; D004077:Digoxin / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation / Q000187:drug effects* / Q000502:physiology; D006131:Growth Inhibitors / Q000008:administration & dosage; D006801:Humans; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D006131:Growth Inhibitors; D012333:RNA, Messenger; D004077:Digoxin