[Show abstract][Hide abstract] ABSTRACT: Natural moisturizing factors (NMFs) play an important role in maintaining the physical properties of the stratum corneum (SC). The relationship between SC water content and NMFs has long been investigated. Recently, we demonstrated that potassium lactate as an NMF increased SC water content more than sodium lactate did. The details of the moisturizing mechanism of NMFs, however, were not revealed. We, therefore, investigated the cause of the SC moisturizing effect of potassium lactate in comparison with sodium lactate. Using differential scanning calorimetry, we found that potassium lactate increased the bound water content of plantar SC more than what sodium lactate did. We also found, however, that the bound water content of the potassium lactate solution was less than that of the sodium lactate solution, suggesting that potassium lactate increased the water molecules interacting with SC components. Moreover, potassium lactate increased the ratio of hydrogen/deuterium exchange at 1340/cm, which represents the OH bending mode, of plantar SC spectra obtained by the attenuated total reflectance infrared spectroscopy. We assign this band to the OH group of the serine residue. These results suggest that potassium lactate increases the water-holding capacity of the SC by increasing interaction between water molecules and the OH group of serine in SC keratin.
[Show abstract][Hide abstract] ABSTRACT: Hara et al. found that the topical application of .BETA.-galactosylceramide significantly increases the amounts of ceramides in the stratum corneum (SC), a major family of intercellular lipids of the SC, and corrects atopic dry skin conditions in human. Recently we synthesized O-.BETA.-D-galactosyl-N-stearoyl-L-serine-hexylamide (Gal-Ser-diamide), an L-serine derivative that mimics .BETA.-galactosylceramide. In this study, we examined its direct effects on the intercellular lipid organization which plays a crucial role in maintaining the barrier properties of the skin, using an in vitro model of the SC lamellae. We observed a dose-dependent decrease in the trans-membrane water loss when Gal-Ser-diamide was added to the lipid components of the model SC lamellae. Unlike the control sample, the membranes treated with lipids containing Gal-Ser-diamide were completely covered with a continuous lipid film, including a lamellar structure confirmed by SEM and TEM analyses. X-ray diffraction studies also revealed an ordering and close packing of the model SC lamellae in response to the concentration of Gal-Ser-diamide. These findings suggest that Gal-Ser-diamide improves the epidermal barrier function not only by enhancing the ceramide synthesis, but also by reinforcing the SC lamellar structure.