The Intestine Plays a Substantial Role in Human Vitamin B6 Metabolism: A Caco-2 Cell Model

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

doi:10.1371/journal.pone.0054113

Monique Albersen, Jessica De Ruijter + Show 7 more

Open Access

https://doi.org/10.1371/journal.pone.0054113

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Abstract

BackgroundVitamin 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.ObjectiveTo gain insight into the role of the intestine in human vitamin B6 metabolism.Materials and MethodsExpression 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.ResultsThe 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.ConclusionWe demonstrate, in a Caco-2 cell model, that the intestine plays a substantial role in human vitamin B6 metabolism.

Highlights

Vitamin B6 is present in a wide variety of foods, like meat, fish, milk products, potatoes, beans, nuts and several fruits and vegetables [1]
The enzymatic system involved in vitamin B6 metabolism (PK, pyridox(am)ine phosphate oxidase (PNPO) and pyridoxal phosphate (PLP)-phosphatase) is fully expressed in Caco-2 cells as well as in human intestine
We demonstrate, in a Caco-2 cell model, that the intestine plays a substantial role in human vitamin B6 metabolism

Summary

Introduction

Vitamin B6 is present in a wide variety of foods, like meat, fish, milk products, potatoes, beans, nuts and several fruits and vegetables [1]. In animal products, it is primarily found as pyridoxal phosphate (PLP) and pyridoxamine phosphate (PMP), whereas plant-derived products mostly contain pyridoxine (phosphate) (PN(P)). In 2003, a carrier-mediated mechanism for PN uptake in human intestinal epithelial Caco-2 (colorectal adenocarcinoma) cells was reported [6]. Uptake was inhibited by pyridoxamine (PM), but not by pyridoxal (PL) or PLP, suggesting that the transporter protein is selective for two of the three unphosphorylated B6 vitamers. The liver has been reported to be the major site for this conversion, whereas the exact role of the intestine remains to be elucidated

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