Phytosphingosine enhances moisture level in human skin barrier through stimulation of the filaggrin biosynthesis and degradation leading to NMF formation

Phytosphingosine (PHS) is a sphingoid that is a key component of phytoceramides NP, AP and EOP. PHS has been known to have anti-inflammation and antimicrobial activities and to stimulate epidermal differentiation. In addition, it is reported that PHS treatment notably increased phytoceramide content in keratinocytes. In this study, we tried to investigate whether PHS has any effect on the maturation of corneocytes such as formation of cornified envelope and natural moisturizing factor (NMF) that is also an essential event during the formation of skin barrier, stratum corneum. Special focus was made on the filaggrin (FLG) metabolism that is directly responsible for NMF production. PHS increased the expression of essential keratinocyte differentiation genes such as involucrin and transglutaminase 1 in cultured human keratinocytes. Interestingly, the expressions of FLG, caspase 14 and bleomycin hydrolase, all of which involved in NMF production in corneocytes, were significantly induced by PHS treatment in vitro. The effect of PHS on FLG metabolism was manifested as the increase of pyrrolidone carboxylic acid and skin hydration in vivo human skin. Results showed PHS had skin moisturizing effect by modulating FLG metabolic pathways and suggested to be an essential role in coordinated formation of the corneocyte envelope and NMF within.