Low cellular pyridoxal 5ʹ-phosphate levels decrease neurotransmitter and glutathione concentrations and increase susceptibility to hydrogen peroxide toxicity in SH-SY5Y cells

Objectives Pyridoxal 5ʹ-phosphate (PLP) is an active and major form of vitamin B 6 (VB 6 ) in the body. PLP is essential as a cofactor for many enzymes involved in amino acid metabolism, and VB 6 deficiency is associated with neurological disorders, such as epileptic-like symptoms, depression and confusion. However, the link between neuronal dysfunction and VB 6 deficiency is unclear. In this study, we investigated how neuronal cells are affected by low cellular PLP levels using the neuroblastoma SH-SY5Y cell line. Methods SH-SY5Y cells were cultured in pyridoxine-free medium supplemented with 10% fetal bovine serum and cell viability, intracellular PLP concentration, and metabolites were evaluated. Pyridoxine-free medium supplemented with 10% FBS contained 3 nM of PLP derived from FBS. Media containing various concentration of PLP were prepared using pyridoxine-free medium. Additionally, reactive oxygen species level and cell viability were assessed when cells were treated with 100 μM of hydrogen peroxide in media containing different concentrations of PLP. Results SH-SY5Y cells had a decreased intracellular PLP level of 38 pmol/mg protein but proliferated when cells were cultured in the PLP-non-added medium. Metabolome analysis revealed the levels of neurotransmitters such as dopamine, norepinephrine, and 4-aminobutyric acid were decreased in cells cultured in the PLP-non-added medium compared with the PLP-added medium. The concentration of glutathione, an antioxidant, was also reduced. Furthermore, when cells were cultured in the PLP-non-added medium, hydrogen peroxide treatment reduced cell viability and increased intracellular reactive oxygen species levels in a concentration-dependent manner. These findings show that a growth environment low in VB 6 decreases cellular glutathione and reduces resistance to oxidative stress. Conclusions Overall, these findings show that low VB 6 not only reduces neurotransmitter production, but also reduces glutathione levels, rendering cells more susceptible to oxidative stress and increasing the risk of neurodegenerative changes.