title: Transport evaluation of salicylic acid and structurally related compounds across Caco-2 cell monolayers and artificial PAMPA membranes.
abstract: The purpose of this study was to evaluate passive vs. proton-dependent active transport mechanisms of salicylic acid (SA) and four structurally related anions. Transport was studied across Caco-2 cell monolayers and artificial lipid membranes (PAMPA) under pH-gradient and iso-pH conditions. Kinetic permeability parameters were provided by bidirectional Caco-2 experiments and concentration-dependency measurements. The transport route and putative transporters involved in SA transport were studied using EDTA and several inhibitors. SA and lipophilic 5-chlorosalicylic acid and 2-hydroxy-1-naphthoic acid reached saturation with increasing compound concentration indicating active transport. Permeation of 5-hydroxysalicylic acid and 5-hydroxyisophthalic acid was not saturated indicating passive transport. PAMPA with pure passive diffusion underestimated the transport of SA compared to Caco-2. Opening up the paracellular tight junctions by EDTA did not increase the transport of SA under the pH-gradient conditions confirming the hypothesis of pure transcellular transport of SA. Active transport of SA remained concentration-dependent even without the pH-gradient, and was reduced by the known MCT1 and OATP-B inhibitors and structurally related anions. Overall, several permeability test protocols are needed to obtain a more complete picture of transport properties of salicylic acid and structurally related compounds.
authors.affiliation: Division of Pharmaceutical Technology, University of Helsinki, Helsinki, Finland. maija.koljonen@helsinki.fi
authors.forename: Maija
authors.initials: M
authors.lastname: Koljonen
authors.forename: Katja
authors.initials: K
authors.lastname: Rousu
authors.forename: Jakub
authors.initials: J
authors.lastname: Cierny
authors.forename: Ann Marie
authors.initials: AM
authors.lastname: Kaukonen
authors.forename: Jouni
authors.initials: J
authors.lastname: Hirvonen
mesh_terms: D001692:Biological Transport; D018938:Caco-2 Cells; D004492:Edetic Acid / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008567:Membranes, Artificial; D010539:Permeability; D010743:Phospholipids / Q000378:metabolism; D020156:Salicylic Acid / Q000493:pharmacokinetics*
chemical_list: D008567:Membranes, Artificial; D010743:Phospholipids; D004492:Edetic Acid; D020156:Salicylic Acid