title: Mechanisms of P-gp inhibition and effects on membrane fluidity of a new rifampicin derivative, 1,8-dibenzoyl-rifampicin.
abstract: OBJECTIVE
  To assess P-glycoprotein (P-gp)-modulation ability and the mechanisms of P-gp inhibition mediated by a new synthetic rifampicin derivative, 1,8-dibenzoyl-rifampicin (DiBenzRif), in an in vitro model of the blood-brain barrier (BBB), RBE4 cells, and in membrane mimetic models (liposomes).
  
  
  METHODS
  P-gp expression (western blot) and activity [rhodamine 123 accumulation studies] were assessed until 72h of exposure to DiBenzRif. The effects on intracellular ATP levels and on P-gp ATPase activity were studied using luciferin-luciferase bioluminescence assay. Membrane fluidity changes were tracked by steady-state anisotropy measurements. Non-P-gp-related rhodamine 123 accumulation was evaluated using liposomes prepared with the main lipids present in RBE4 cell membranes.
  
  
  RESULTS
  A significant increase in intracellular rhodamine 123 content was observed in DiBenzRif-treated cells at all tested time-points. This effect was associated with a significant reduction in ATP intracellular levels, the inhibition of P-gp ATPase activity and a significant increase in membrane fluidity. DiBenzRif also favoured rhodamine 123 accumulation in a liposomal model of RBE4 cells, suggesting that it may be useful in increasing intracellular levels of substances that passively diffuse into the cells.
  
  
  CONCLUSIONS
  DiBenzRif-induced inhibitory effect on P-gp increases xenobiotic accumulation in BBB cells, which may contribute to the development of therapeutic adjuvants to enhance brain penetration of drugs.
authors.affiliation: REQUIMTE, Laboratório de Toxicologia, Departamento de Ciências Biológicas, Faculdade de Farmácia, Universidade do Porto, Rua Jorge Viterbo Ferreira, 228, Porto 4050-313, Portugal. vvilasboas@ff.up.pt
authors.forename: Vânia
authors.initials: V
authors.lastname: Vilas-Boas
authors.forename: Renata
authors.initials: R
authors.lastname: Silva
authors.forename: Cláudia
authors.initials: C
authors.lastname: Nunes
authors.forename: Salette
authors.initials: S
authors.lastname: Reis
authors.forename: Luísa
authors.initials: L
authors.lastname: Ferreira
authors.forename: Cátia
authors.initials: C
authors.lastname: Vieira
authors.forename: Félix
authors.initials: F
authors.lastname: Carvalho
authors.forename: Maria de Lourdes
authors.initials: Mde L
authors.lastname: Bastos
authors.forename: Fernando
authors.initials: F
authors.lastname: Remião
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D001812:Blood-Brain Barrier / Q000187:drug effects*; D015153:Blotting, Western; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D008560:Membrane Fluidity / Q000187:drug effects*; D051381:Rats; D012293:Rifampin / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D012293:Rifampin