title: Absorption of folate by Caco-2 cells is not affected by high glucose concentration.
abstract: The aim of this work was to investigate the effect of high glucose exposure on the absorption of folate by Caco-2 cells. We verified that apical high glucose did not affect the apical uptake of [(3)H]folate. Both different concentrations of glucose (10-45 mM) and different exposure times (10 min-24 h) were tested. Furthermore, apical high glucose (30 mM) did not affect the intracellular steady-state levels of [(3)H]folate, and simultaneous apical and basolateral high glucose (30 mM) did not change the apical-to-basolateral apparent permeability (P(app)) to [(3)H]folate. Both the apical uptake and the steady-state intracellular levels of [(3)H]folate were strongly reduced by 5-methyltetrahydrofolate, methotrexate, SITS (4-acetamido-4'-isothiocyanato-2,2'-stilbenedisulfonic acid), DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid) and indomethacin, but were not affected or only hardly affected by p-aminohippuric acid and fumitremorgin C. Moreover, DIDS and indomethacin significantly reduced (by 50-60%) the apical-to-basolateral P(app) to [(3)H]folate, but [(3)H]folate present in the cells at the end of the experiment was higher in the case of indomethacin. Fumitremorgin C had no effect. The effect of the drugs tested was not changed or only hardly changed by high glucose. In conclusion, absorption of [(3)H]folate is not modulated by either apical or basolateral high glucose exposure in Caco-2 cells. Moreover, our results suggest that the apical uptake of [(3)H]folate by Caco-2 cells involves the Reduced Folate Transporter (but not the Organic Anion Transporter), and that Multidrug Resistance Protein and/or Organic Anion Transporter (but not Breast Cancer Resistance Protein) may mediate apical efflux of [(3)H]folate.
authors.affiliation: Department of Biochemistry (U38-FCT), Faculty of Medicine, University of Porto, 4200-319 Porto, Portugal. fmartel@med.up.pt
authors.forename: Fátima
authors.initials: F
authors.lastname: Martel
authors.forename: Pedro
authors.initials: P
authors.lastname: Gonçalves
authors.forename: Isabel
authors.initials: I
authors.lastname: Azevedo
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D018435:ATP Binding Cassette Transporter, Subfamily B / Q000187:drug effects / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D018938:Caco-2 Cells; D002463:Cell Membrane Permeability / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005492:Folic Acid / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D007213:Indomethacin / Q000494:pharmacology; D007408:Intestinal Absorption / Q000187:drug effects*; D007413:Intestinal Mucosa / Q000187:drug effects* / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000187:drug effects / Q000378:metabolism; D008727:Methotrexate / Q000494:pharmacology; D027361:Organic Anion Transporters / Q000187:drug effects / Q000378:metabolism; D058978:Reduced Folate Carrier Protein; D013763:Tetrahydrofolates / Q000494:pharmacology; D013997:Time Factors; D010130:p-Aminohippuric Acid / Q000494:pharmacology
chemical_list: D018435:ATP Binding Cassette Transporter, Subfamily B; D007211:Indoles; D026901:Membrane Transport Proteins; D027361:Organic Anion Transporters; D058978:Reduced Folate Carrier Protein; C548699:SLC19A1 protein, human; D013763:Tetrahydrofolates; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D005492:Folic Acid; C010522:tryptoquivaline; D005947:Glucose; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; C005984:5-methyltetrahydrofolate; D007213:Indomethacin; D010130:p-Aminohippuric Acid; D008727:Methotrexate