Vitamin B6 is essential for serine de novo biosynthesis

Rúben J. Ramos,Nanda M. Verhoeven‐Duif,Mia L. Pras‐Raves,Johan Gerrits,Maria van der Ham,Hubertus Prinsen,Marcel Willemsen,Boudewijn Burgering,Judith J. Jans

doi:10.1007/s10545-017-0061-3

Rúben J. Ramos, Nanda M. Verhoeven‐Duif + Show 7 more

Open Access

https://doi.org/10.1007/s10545-017-0061-3

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Abstract

Pyridoxal 5′-phosphate (PLP), the metabolically active form of vitamin B6, plays an essential role in brain metabolism as a cofactor in numerous enzyme reactions. PLP deficiency in brain, either genetic or acquired, results in severe drug-resistant seizures that respond to vitamin B6 supplementation. The pathogenesis of vitamin B6 deficiency is largely unknown. To shed more light on the metabolic consequences of vitamin B6 deficiency in brain, we performed untargeted metabolomics in vitamin B6-deprived Neuro-2a cells. Significant alterations were observed in a range of metabolites. The most surprising observation was a decrease of serine and glycine, two amino acids that are known to be elevated in the plasma of vitamin B6 deficient patients. To investigate the cause of the low concentrations of serine and glycine, a metabolic flux analysis on serine biosynthesis was performed. The metabolic flux results showed that the de novo synthesis of serine was significantly reduced in vitamin B6-deprived cells. In addition, formation of glycine and 5-methyltetrahydrofolate was decreased. Thus, vitamin B6 is essential for serine de novo biosynthesis in neuronal cells, and serine de novo synthesis is critical to maintain intracellular serine and glycine. These findings suggest that serine and glycine concentrations in brain may be deficient in patients with vitamin B6 responsive epilepsy. The low intracellular 5-mTHF concentrations observed in vitro may explain the favourable but so far unexplained response of some patients with pyridoxine-dependent epilepsy to folinic acid supplementation.

Highlights

Pyridoxal 5′-phosphate (PLP), the metabolically active form of vitamin B6, plays a pivotal role in brain metabolism and development (Surtees et al 2006)
Our observations indicate that additional factors next to GABA play a role in the pathogenesis of vitamin B6 deficiency
To establish whether the absence of PL in the medium resulted in intracellular vitamin B6 deficiency, we quantified the intracellular concentrations of PL, pyridoxamine (PM), pyridoxine (PN), the 5′-phosphorylated forms (PLP, PMP and PNP, respectively) and the breakdown product pyridoxic acid (PA) (Fig. S1)

Summary

Introduction

Pyridoxal 5′-phosphate (PLP), the metabolically active form of vitamin B6, plays a pivotal role in brain metabolism and development (Surtees et al 2006). Five inborn errors of metabolism are known to affect vitamin B6 concentrations: pyridoxine-dependent epilepsy (αaminoadipic semialdehyde dehydrogenase (antiquitin) deficiency; OMIM #266100), hyperprolinemia type II (1pyrroline-5-carboxylate dehydrogenase deficiency; OMIM #239510), pyridox(am)ine 5′-phosphate oxidase deficiency (PNPO deficiency; OMIM #610090), hypophosphatasia (tissue non-specific alkaline phosphatase (TNSALP) deficiency; OMIM #241500) and proline synthetase co-transcribed bacterial homologue deficiency (PROSC deficiency; OMIM #604436). These diseases, except for most cases of

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