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

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.

The value of plasma vitamin B6 profiles in early onset epileptic encephalopathies

“…Vitamin B 6 kinetic studies The results of our in vivo kinetic studies in three probands are in accordance with observations in rodents and in vitro cell models (Sakurai et al 1987;Albersen et al 2013) showing that PL and PA are the most abundant plasma vitamin B 6 vitamers following PN intake. PN was rapidly cleared from plasma while PLP showed a slow but steady increase.…”

Vitamin B-6 Metabolism and Interactions with TNAP

“…Although liver is a major site of vitamin B-6 metabolism, small doses of pyridoxine and pyridoxamine can be converted to pyridoxal in the intestine prior to release into the portal circulation in the mouse (Sakurai et al 1987(Sakurai et al , 1988. Similar results were reported with cultured Caco-2 cells (Albersen et al 2013). The main transport forms of vitamin B-6 in blood are pyridoxal and pyridoxal phosphate, which is released from the liver associated primarily with albumin .…”

Quality and stability of extemporaneous pyridoxal phosphate preparations used in the treatment of paediatric epilepsy

“…However, in vivo it is likely that PAP is hydrolysed and subsequently excreted as pyridoxic acid in urine . It is known that the B6 vitamers are mostly absorbed in their non‐phosphorylated form and do not cross the gastro‐intestinal wall in appreciable amounts before hydrolysis . In addition, upon measurement of the B6 vitamer blood levels of patients on PLP supplementation, PAP is not detected in significant amounts (Unpublished data Laboratory of Mills P, 2016).…”