title: Transepithelial transport of diphenhydramine across monolayers of the human intestinal epithelial cell line Caco-2.
abstract: OBJECTIVE
  The transepithelial transport characteristics of the antihistamine, diphenhydramine, were studied in human intestinal Caco-2 cell monolayers to elucidate the mechanisms of its intestinal absorption.
  
  
  METHODS
  The transepithelial transport and the cellular accumulation of diphenhydramine were measured using Caco-2 cell monolayers grown in Transwell chambers.
  
  
  RESULTS
  The transepithelial transport of diphenhydramine from the apical to basolateral side was saturable, and the flux and cellular accumulation of diphenhydramine were dependent on the apical extracellular pH (pH 7.4 > 6.5 > 5.5). Transport and accumulation of diphenhydramine from the apical side were inhibited by another antihistamine, chlorpheniramine, while typical substrates for the renal organic cation transport system such as tetraethylammonium, cimetidine and guanidine had no effect. The transepithelial transport and cellular accumulation of diphenhydramine from the basolateral side were also pH-dependent and inhibited by chlorpheniramine. In addition, intracellular diphenhydramine preloaded was preferentially effluxed to the apical side, suggesting the involvement of the secretory pathway in diphenhydramine transport. Furthermore, diphenhydramine uptake from both the apical and basolateral sides was stimulated by preloading monolayers with chlorpheniramine (trans-stimulation effect).
  
  
  CONCLUSIONS
  Transepithelial transport of diphenhydramine across Caco-2 cells is mediated by pH-dependent, specific transport systems that exist in both the apical and basolateral membranes.
authors.affiliation: Department of Pharmacy, Kyoto University Hospital, Faculty of Medicine, Kyoto University, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Mizuuchi
authors.forename: T
authors.initials: T
authors.lastname: Katsura
authors.forename: Y
authors.initials: Y
authors.lastname: Hashimoto
authors.forename: K
authors.initials: K
authors.lastname: Inui
mesh_terms: D000465:Algorithms; D018938:Caco-2 Cells; D002744:Chlorpheniramine / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D004155:Diphenhydramine / Q000378:metabolism*; D004347:Drug Interactions; D004847:Epithelial Cells / Q000378:metabolism*; D006634:Histamine H1 Antagonists / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007413:Intestinal Mucosa / Q000166:cytology / Q000378:metabolism
chemical_list: D006634:Histamine H1 Antagonists; D002744:Chlorpheniramine; D004155:Diphenhydramine