title: Phorbol 12-myristate 13-acetate inhibits P-glycoprotein-mediated efflux of digoxin in MDCKII-MDR1 and Caco-2 cell monolayer models.
abstract: OBJECTIVE
  To investigate the effects of phorbol 12-myristate 13-acetate (PMA), a PKC activator, on P-glycoprotein-mediated efflux of digoxin in two cell transport models.
  
  
  METHODS
  Caco-2 cells, wild MDCKII cells (MDCKII-WT) and MDCKII cells transfected stably with human MDR1-gene encoding P-gp (MDCKII-MDR1) were examined. Cell viability was evaluated with MTT assay. Bidirectional transport of digoxin was evaluated in these cells. Intracellular ATP level was measured using ATP assay. P-gp ATPase activity was analyzed using a Pgp-Glo(TM) assay.
  
  
  RESULTS
  PMA (10 μmol/L) did not reduce the viability of the 3 types of cells. In Caco-2 and MDCKII-MDR1 cell monolayers, PMA (1, 10 and 100 nmol/L) dose-dependently inhibited the basolateral to apical transport of digoxin, but did not change the apical to basolateral transport. In addition, PMA did not affect both the basolateral to apical and apical to basolateral transport of digoxin in MDCKII-WT cell monolayer. In agreement with the above results, PMA dose-dependently reduced intracellular ATP level and stimulated P-gp ATPase activity in both Caco-2 and MDCKII-MDR1 cells. Verapamil (a positive control, 100 μmol/L) caused similar inhibition on digoxin efflux as PMA did, whereas 4α-PMA (a negative control, 100 nmol/L) had no effect.
  
  
  CONCLUSIONS
  PMA significantly inhibited P-gp-mediated efflux of digoxin in both Caco-2 and MDCKII-MDR1 cell monolayers via PKC activation.
authors.affiliation: Laboratory of Drug Metabolism and Pharmacokinetics, School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou 510006, China.
authors.forename: Yu-hua
authors.initials: YH
authors.lastname: Li
authors.affiliation: Laboratory of Drug Metabolism and Pharmacokinetics, School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou 510006, China.
authors.forename: Hui-chang
authors.initials: HC
authors.lastname: Bi
authors.affiliation: School of Pharmaceutical Sciences, Hainan Medical University, Haikou 571199, China.
authors.forename: Ling
authors.initials: L
authors.lastname: Huang
authors.affiliation: Laboratory of Drug Metabolism and Pharmacokinetics, School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou 510006, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Jin
authors.affiliation: Laboratory of Drug Metabolism and Pharmacokinetics, School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou 510006, China.
authors.forename: Guo-ping
authors.initials: GP
authors.lastname: Zhong
authors.affiliation: Laboratory of Drug Metabolism and Pharmacokinetics, School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou 510006, China.
authors.forename: Xu-nian
authors.initials: XN
authors.lastname: Zhou
authors.affiliation: Laboratory of Drug Metabolism and Pharmacokinetics, School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou 510006, China.
authors.forename: Min
authors.initials: M
authors.lastname: Huang
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors*; D001692:Biological Transport / Q000187:drug effects*; D018938:Caco-2 Cells; D045744:Cell Line, Tumor; D004077:Digoxin / Q000378:metabolism*; D006801:Humans; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D004077:Digoxin; D013755:Tetradecanoylphorbol Acetate