The intestine plays a substantial role in human vitamin B6 metabolism: a Caco-2 cell model.
BACKGROUND
Vitamin B6 is present in various forms (vitamers) in the diet that need to be metabolized to pyridoxal phosphate (PLP), the active cofactor form of vitamin B6. In literature, the liver has been reported to be the major site for this conversion, whereas the exact role of the intestine remains to be elucidated.


OBJECTIVE
To gain insight into the role of the intestine in human vitamin B6 metabolism.


METHODS
Expression of the enzymes pyridoxal kinase (PK), pyridox(am)ine phosphate oxidase (PNPO) and PLP-phosphatase was determined in Caco-2 cells and in lysates of human intestine. Vitamin B6 uptake, conversion and excretion were studied in polarized Caco-2 cell monolayers. B6 vitamer concentrations (pyridoxine (PN), pyridoxal (PL), PLP, pyridoxamine (PM), pyridoxamine phosphate (PMP)) and pyridoxic acid (PA) were quantified by ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) using stable isotope-labeled internal standards.


RESULTS
The enzymatic system involved in vitamin B6 metabolism (PK, PNPO and PLP-phosphatase) is fully expressed in Caco-2 cells as well as in human intestine. We show uptake of PN, PM and PL by Caco-2 cells, conversion of PN and PM into PL and excretion of all three unphosphorylated B6 vitamers.


CONCLUSIONS
We demonstrate, in a Caco-2 cell model, that the intestine plays a substantial role in human vitamin B6 metabolism.
Department of Medical Genetics, University Medical Center, Utrecht, Utrecht, The Netherlands.
Monique
M
Albersen
Marjolein
M
Bosma
Nine V V A M
NV
Knoers
Berna H B
BH
de Ruiter
Eugène F
EF
Diekman
Jessica
J
de Ruijter
Wouter F
WF
Visser
Tom J
TJ
de Koning
Nanda M
NM
Verhoeven-Duif
D015153:Blotting, Western; D018938:Caco-2 Cells; D056945:Hep G2 Cells; D006801:Humans; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000378:metabolism*; D011730:Pyridoxal / Q000378:metabolism; D011731:Pyridoxal Kinase / Q000378:metabolism; D011733:Pyridoxamine / Q000031:analogs & derivatives / Q000378:metabolism; D011735:Pyridoxic Acid / Q000378:metabolism; D011736:Pyridoxine / Q000378:metabolism; D053719:Tandem Mass Spectrometry; D025101:Vitamin B 6 / Q000378:metabolism*
D011730:Pyridoxal; D011735:Pyridoxic Acid; D011733:Pyridoxamine; D025101:Vitamin B 6; D011731:Pyridoxal Kinase; D011736:Pyridoxine; C010627:pyridoxamine phosphate