Pyridoxine (VB6) restores the down‐regulation of serine palmitoyltransferase mRNA expression in keratinocytes cultured in highly oxidative conditions through enhancement of the intracellular antioxidant system

Abstract

Background

Pyridoxine (VB₆), which acts as a coenzyme in the biosynthesis of niacin, is formulated in pharmaceuticals to treat skin roughness. However, the mechanism of action of VB₆ is not known precisely.

Objective

This study was conducted to clarify the influence of highly oxidative conditions on the expression of skin moisture‐related mRNAs and to evaluate the preventive effects of VB₆ focusing on antioxidant behaviour.

Methods

Intracellular levels of reactive oxygen species (ROS) in normal human epidermal keratinocytes (NHEKs) were determined using the 2′,7′‐dichlorofluorescein diacetate assay. Real‐time PCR was employed to investigate the influence of higher oxidative conditions on the expression of mRNAs encoding serine palmitoyl transferase (SPT) and filaggrin, and to characterize the mechanism of the antioxidant effect of VB₆. Intracellular glutathione was quantified using an assay based on the glutathione recycling system with 5,5′‐dithiobis (2‐nitrobenzoic acid) reagent and glutathione reductase. Carbonylated proteins (CPs) were semi‐quantified by detecting aldehyde residues.

Results

Treatment of NHEKs with BSO increased the level of intracellular CPs by interfering with intracellular glutathione synthesis. Further, treatment with BSO down‐regulated the expression level of SPT mRNA, but VB₆ restored SPT mRNA expression in BSO‐treated NHEKs. VB₆ decreased the level of intracellular CPs with or without BSO treatment in a dose‐dependent manner. In addition, VB₆ increased levels of intracellular NADH/NADPH and glutathione through the activation of nuclear factor E2‐related factor 2 (Nrf2) signalling.

Conclusion

These results suggest that highly oxidative conditions cause an impaired skin barrier function due to the down‐regulation of SPT that results in skin roughness. VB₆ improved the down‐regulation of SPT mRNA expression initiated by highly oxidative conditions by enhancing the intracellular antioxidant system.

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