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. 2013;8(1):e54113.
doi: 10.1371/journal.pone.0054113. Epub 2013 Jan 14.

The intestine plays a substantial role in human vitamin B6 metabolism: a Caco-2 cell model

Monique Albersen  1 , Marjolein Bosma, Nine V V A M Knoers, Berna H B de Ruiter, Eugène F Diekman, Jessica de Ruijter, Wouter F Visser, Tom J de Koning, Nanda M Verhoeven-Duif
Affiliations

The intestine plays a substantial role in human vitamin B6 metabolism: a Caco-2 cell model

Monique Albersen et al. PLoS One. 2013.

Abstract

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.

Materials and 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.

Conclusion: We demonstrate, in a Caco-2 cell model, that the intestine plays a substantial role in human vitamin B6 metabolism.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. The different vitamin B6 vitamers and their intracellular conversions.
PK = pyridoxal kinase. PNPO = pyridox(am)ine phosphate oxidase. PLP-Ph = PLP-phosphatase.
Figure 2
Figure 2. Expression of the enzymes involved in vitamin B6 metabolism in human cell lines and tissue lysates.
Actin was used as a loading control (cell lysates only). Depicted are representations of at least duplicates. PK = pyridoxal kinase. PNPO = pyridox(am)ine phosphate oxidase. PLP-Ph = PLP-phosphatase. Small Int = small intestine. HepG2 = HepG2 cells. Caco-2 = Caco-2 cells.
Figure 3
Figure 3. Intracellular amounts of PLP during incubation with no B6 vitamers, PN, PM and PL.
Depicted are means ± SE of triplicates.
Figure 4
Figure 4. Changes in apical and basolateral amounts of PL during incubation with PN (A) or PM (B).
Depicted are means ± SE of triplicates.
Figure 5
Figure 5. Hypothesis of human intestinal vitamin B6 metabolism.
See this image and copyright information in PMC

References

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