Section Metabolic Diagnostics, Department of Genetics, University Medical Center Utrecht, KC02.069.1, Lundlaan 6, 3584 EA, Utrecht, The Netherlands.
Department of Molecular Cancer Research and Center for Molecular Medicine, University Medical Center Utrecht, Utrecht, 3584 EA, The Netherlands.
J Inherit Metab Dis. 2017 Nov;40(6):883-891. doi: 10.1007/s10545-017-0061-3. Epub 2017 Aug 11.
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.
吡哆醛 5'-磷酸（PLP），维生素 B6 的代谢活性形式，作为许多酶反应的辅助因子，在大脑代谢中起着至关重要的作用。脑内 PLP 缺乏无论是遗传的还是获得性的，都会导致严重的抗药性癫痫发作，而补充维生素 B6 可以缓解。维生素 B6 缺乏的发病机制在很大程度上尚不清楚。为了更深入地了解脑内维生素 B6 缺乏的代谢后果，我们对维生素 B6 剥夺的 Neuro-2a 细胞进行了非靶向代谢组学研究。观察到一系列代谢物发生了显著变化。最令人惊讶的观察结果是丝氨酸和甘氨酸的减少，这两种氨基酸已知在维生素 B6 缺乏症患者的血浆中升高。为了研究丝氨酸和甘氨酸浓度降低的原因，我们对丝氨酸生物合成进行了代谢通量分析。代谢通量结果表明，维生素 B6 剥夺细胞中丝氨酸的从头合成显著减少。此外，甘氨酸和 5-甲基四氢叶酸的形成减少。因此，维生素 B6 对神经元细胞中丝氨酸的从头合成是必不可少的，而丝氨酸的从头合成对于维持细胞内丝氨酸和甘氨酸至关重要。这些发现表明，维生素 B6 反应性癫痫患者的脑内丝氨酸和甘氨酸浓度可能不足。体外观察到的细胞内 5-甲基四氢叶酸浓度低可能解释了一些依赖吡哆醇的癫痫患者对亚叶酸补充剂的有利但迄今未得到解释的反应。
