title: Thyroid hormone regulates the expression and function of P-glycoprotein in Caco-2 cells.
abstract: OBJECTIVE
  In patients with thyroid disorders, abnormalities in the pharmacokinetics of various drugs including digoxin, a substrate of P-glycoprotein (Pgp) which plays a crucial role in drug absorption and disposition, have been reported. In this study, we examined the effect of 3,5,3'-L-triiodothyronine (T(3)) on the function and expression of Pgp using the human intestinal epithelial cell line Caco-2.
  
  
  METHODS
  The effect of T(3) on the expression of Pgp and MDR1 mRNA was assessed by Western blotting and competitive polymerase chain reaction, respectively. Digoxin uptake and transport by Pgp was assessed using Caco-2 cell monolayers.
  
  
  RESULTS
  The expression of MDR1 mRNA was increased by T(3) treatment in a concentration-dependent manner. Pgp expression was also increased by 100 nM T(3), whereas it decreased on depletion of T(3). The amount of [(3)H]digoxin accumulated in Caco-2 cell monolayers treated with T(3) was diminished significantly compared with that in control cells. In addition, the basal-to-apical transcellular transport of [(3)H]digoxin was accelerated by T(3) treatment.
  
  
  CONCLUSIONS
  These results indicate that T(3) regulates the expression and function of Pgp. It is possible that changes in Pgp expression alter the pharmacokinetics of Pgp substrates in patients with thyroid disorders.
authors.affiliation: Department of Pharmacy, Kyoto University Hospital, Faculty of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Nishio
authors.forename: Toshiya
authors.initials: T
authors.lastname: Katsura
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Inui
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000096:biosynthesis* / Q000235:genetics*; D001693:Biological Transport, Active / Q000187:drug effects; D015153:Blotting, Western; D018938:Caco-2 Cells; D002316:Cardiotonic Agents / Q000378:metabolism; D016572:Cyclosporine / Q000494:pharmacology; D004077:Digoxin / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology; D007421:Intestine, Small / Q000187:drug effects / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013963:Thyroid Hormones / Q000502:physiology*; D014284:Triiodothyronine / Q000494:pharmacology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D002316:Cardiotonic Agents; D007166:Immunosuppressive Agents; D012333:RNA, Messenger; D013963:Thyroid Hormones; D014284:Triiodothyronine; D004077:Digoxin; D016572:Cyclosporine