title: Effect of thiamine on 3H-MPP+ uptake by Caco-2 cells.
abstract: Recent studies on the intestinal uptake of the organic cation 1-methyl-4-phenylpyridinium (MPP+) showed that transport of this compound occurs through human extraneuronal monoamine transporter (hEMT). Moreover, it was recently described that alkaline phosphatase (ALP), an ecto-phosphatase anchored to the plasma membrane and able to dephosphorylate extracellular substrates or cell-surface proteins, is directly or indirectly involved in the modulation of MPP+ uptake by Caco-2 cells. The present study investigated a putative modulation of MPP+ intestinal apical uptake and ecto-ALP activity by thiamine (T+) and thiamine pyrophosphate (TPP, a T+ dietary precursor). For this purpose, we used Caco-2 cells, an enterocyte-like cell line derived from a human colonic adenocarcinoma, as an intestinal model. Ecto-ALP activity and N-[methyl-3H]-4-phenylpyridinium acetate (3H-MPP+) uptake were evaluated in intact Caco-2 cells. T+ and TPP were able to increase ecto-ALP activity, with an equal potency, and to decrease 3H-MPP+ apical uptake, with a similar potency. The effects of both compounds on ecto-ALP activity and 3H-MPP+ uptake were concentration-dependent. The results suggest that the effect of T+ and TPP on ecto-ALP activity may lead to inhibition of the intestinal absorption of other organic cations present in the diet. Another important conclusion is that the intestinal absorption of T+ may occur through hEMT, in Caco-2 cells.
authors.affiliation: Department of Biochemistry, University of Porto, 4200-319, Porto, Portugal. ccalhau@med.up.pt
authors.forename: Conceição
authors.initials: C
authors.lastname: Calhau
authors.forename: Fátima
authors.initials: F
authors.lastname: Martel
authors.forename: Cândido
authors.initials: C
authors.lastname: Hipólito-Reis
authors.forename: Isabel
authors.initials: I
authors.lastname: Azevedo
mesh_terms: D015655:1-Methyl-4-phenylpyridinium / Q000493:pharmacokinetics*; D000469:Alkaline Phosphatase / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D018938:Caco-2 Cells; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007700:Kinetics; D013831:Thiamine / Q000494:pharmacology*; D013835:Thiamine Pyrophosphate / Q000494:pharmacology; D014316:Tritium
chemical_list: D014316:Tritium; D000469:Alkaline Phosphatase; D013835:Thiamine Pyrophosphate; D015655:1-Methyl-4-phenylpyridinium; D013831:Thiamine