title: P-Glycoprotein attenuates brain uptake of substrates after nasal instillation.
abstract: OBJECTIVE
  Previous literature has suggested the absence of an effective barrier between the nasal mucosa and the brain for compounds administered via the nasal route. These experiments were conducted to elucidate the role of the blood-brain barrier efflux transporter P-glycoprotein (P-gp) in attenuating delivery of P-gp substrates to the brain after nasal administration in mice.
  
  
  METHODS
  Brain uptake of several radiolabeled P-gp substrates, was measured in P-gp-deficient and P-gp-competent mice following nasal instillation. Additional experiments were performed to assess the potential for enhancing brain uptake by inhibiting P-gp with intranasal rifampin.
  
  
  RESULTS
  All substrates examined were measurable in brain tissue within 2 min. Substrate accumulation in P-gp-deficient mice was higher than in P-gp-competent animals; the degree to which P-gp attenuated brain uptake after nasal administration was similar to that during in situ brain perfusion. Co-administration of rifampin enhanced brain uptake of relevant substrates, and resulted in complete elimination of P-gp-mediated transport for 3H- verapamil.
  
  
  CONCLUSIONS
  P-gp attenuates brain accumulation of intranasally-administered P-gp substrates. Thus, biochemical components of the blood-brain barrier, such as efflux transporters may influence brain penetration after nasal administration. Co-administration of a P-gp inhibitor enhances the brain uptake of relevant substrates, suggesting that the transporter barrier functions may be reversible.
authors.affiliation: Division of Drug Delivery and Disposition, School of Pharmacy, University of North Carolina, Chapel Hill, North Carolina 27599-7360, USA.
authors.forename: Candace L
authors.initials: CL
authors.lastname: Graff
authors.forename: Gary M
authors.initials: GM
authors.lastname: Pollack
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000502:physiology*; D000281:Administration, Intranasal; D000818:Animals; D001692:Biological Transport; D001812:Blood-Brain Barrier; D001921:Brain / Q000378:metabolism*; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D023421:Models, Animal; D004364:Pharmaceutical Preparations / Q000378:metabolism*; D010599:Pharmacokinetics; D013997:Time Factors
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D004364:Pharmaceutical Preparations