title: Uptake, hydrolysis, and metabolism of pyridoxine-5'-beta-D-glucoside in Caco-2 cells.
abstract: An important dietary source of vitamin B-6, pyridoxine-5'-beta-D-glucoside (PNG), exhibits only partial bioavailability, which is limited by the extent of enzymatic cleavage of the beta-glucosidic bond to release metabolically available pyridoxine (PN). This laboratory showed that the intestinal hydrolysis of PNG is catalyzed by cytosolic PNG hydrolase (PNGH) and brush border lactase-phlorizin hydrolase (LPH). LPH-catalyzed PNG hydrolysis in vitro is competitively inhibited by lactose. In the present study, the uptake and hydrolysis of PNG were examined in Caco-2 human colon carcinoma cells, which express a functional LPH but exhibit no PNGH activity. PNG uptake at 37 degrees C was linear over 5-500 micromol/L PNG. Uptake was not significantly reduced when Na(+) was substituted with K(+), Li(+), or Tris in the medium. Increasing PNG concentration in the medium did not change intracellular concentrations of PN, pyridoxamine (PM), pyridoxamine 5'-phosphate (PMP), or pyridoxal 5'-phosphate (PLP); however, intracellular pyridoxal (PL) concentration increased. Intracellular PNG concentration was not significantly reduced in the presence of lactose, but the concentration of PL declined in proportion to extracellular lactose (P = 0.01). These results indicate that PNG can be absorbed intact in a Na(+)-independent process and is taken up by passive diffusion. The presence of lactose in this in vitro model of intestinal uptake reduced the enzymatic hydrolysis of PNG by lactase.
authors.affiliation: Food Science and Human Nutrition Department, University of Florida, Gainesville, FL, USA.
authors.forename: Amy D
authors.initials: AD
authors.lastname: Mackey
authors.forename: Robert J
authors.initials: RJ
authors.lastname: McMahon
authors.forename: Justin H
authors.initials: JH
authors.lastname: Townsend
authors.forename: Jesse F
authors.initials: JF
authors.lastname: Gregory
mesh_terms: D018938:Caco-2 Cells; D005960:Glucosides / Q000008:administration & dosage / Q000378:metabolism / Q000493:pharmacokinetics*; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D043322:Lactase / Q000378:metabolism; D007785:Lactose / Q000494:pharmacology; D011730:Pyridoxal / Q000032:analysis; D011736:Pyridoxine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000032:analysis / Q000378:metabolism / Q000493:pharmacokinetics*; D012964:Sodium / Q000494:pharmacology
chemical_list: D005960:Glucosides; C022945:5'-O-(glucopyranosyl)pyridoxine; D011730:Pyridoxal; D012964:Sodium; D043322:Lactase; D007785:Lactose; D011736:Pyridoxine