Histidine-rich protein as a possible origin of free amino acids of stratum corneum

Non-invasive Microneedle Application Increases Ceramide and Natural Moisturizing Factors in a Reconstructed Human Skin Model

Recently, microneedling as a cosmetic product has attracted attention as one way to improve skin barrier function and moisturizing function to reduce wrinkle formation. However, some cases of erythema and edema have been reported as side effects. In order to develop safer microneedle cosmetics, we investigated whether microneedles can improve skin barrier function and moisturizing function even when applied in a non-invasive manner that does not penetrate the stratum corneum. We established the condition of non-penetrating microneedle application on reconstructed human full-thickness skin models and examined the effect on the skin models when microneedles were applied under this condition. Microneedle application increased the gene expression of serine palmitoyltransferase long chain base subunit (SPTLC) 3, filaggrin, and transglutaminase 1. The amount of ceramide produced by SPTLC was also increased by microneedle application. Gene expression of filaggrin-degrading enzymes and the amount of free amino acids, a product of filaggrin degradation, were also increased by microneedling. These results suggest that non-invasive microneedle application can improve skin barrier function and moisturizing function by increasing the amount of ceramide and natural moisturizing factors.

Hot spring bathing accelerates wound healing and enhances heat retention effect in guinea pigs

This study aimed to demonstrate the effects of hot springs on wound healing and heat retention by performing comparative experiments with tap water. The hot spring water used in this study was from an alkaline hot spring that was rich in sodium and chloride ions and exhibited high reducibility. Guinea pigs were divided into a hot spring bathing group and a tap water bathing group, and a bathing test was conducted for eight consecutive days. A comparison of the plasma amino acid composition between the two groups after the bathing test revealed differences in the concentrations of several amino acids associated with wound healing. Image analysis demonstrated that wounds made on the abdominal skin of guinea pigs were significantly contracted by hot spring bathing compared to that by tap water bathing, and histopathological findings showed that wound healing was accelerated. In the thermography test, changes in body surface temperature after bathing were investigated in both groups. The heat retention effect was not observed in the tap water bathing group after bathing, whereas it was enhanced in the hot spring bathing group until 30 min after bathing. In conclusion, this study demonstrated that hot spring bathing accelerates wound healing and has a more significant heat retention effect than tap water bathing.

The ion balance of Shotokuseki extract promotes filaggrin fragmentation and increases amino acid production and pyrrolidone carboxylic acid content in three-dimensional cultured human epidermis

Natural moisturizing factor (NMF) in the stratum corneum contributes to the retention of moisture there. The purpose of this study was to determine the penetration of ions in Shotokuseki extract (SE) into the three-dimensional cultured epidermis and the effect of NMF on the biosynthesis of amino acids and pyrrolidone carboxylic acid formation. Various ions, amino acids and pyrrolidone carboxylic acid were quantified by inductively coupled plasma mass spectrometry, fully automatic amino acid analyzer or high-performance liquid chromatography (HPLC) in three-dimensional cultured epidermis after application of SE. Gene expression levels of profilaggrin, calpain1, caspase14, and bleomycin hydrolase, which are involved in NMF production, were determined by reverse-transcription qPCR and bleomycin hydrolase activity was determined by aminopeptidase assay. The application of SE increased Na, K, Mg, Ca, Al, and Fe levels in three-dimensional cultured epidermis. The mRNA levels of the starting material of amino acid synthesis profilaggrin, and calpain1 and bleomycin hydrolase, which are involved in its fragmentation, increased. The activity of bleomycin hydrolase also increased. Furthermore, the levels of amino acids and pyrrolidone carboxylic acid increased in the three-dimensional cultured epidermis. This suggests that the ionic composition of SE may be involved in its moisturizing effect on the stratum corneum.

Filaggrin - revisited

Profilaggrin (proFLG) and its processing products are critical to the health and appearance of skin. The recent identification of loss-of-function filaggrin (FLG) mutations as a predisposing factor in ichthyosis vulgaris and atopic dermatitis has lead to a resurgent interest in this enigmatic protein. Here, we review the literature on the structure and many functions of proFLG, from its role as a filament-aggregating protein and a source of natural moisturizing factor (NMF), to the more recent discoveries of its role in epidermal barrier formation and its more speculative functions as an antimicrobial and sunscreen. Finally, we discuss the relationship of proFLG with dry skin, the influence of moisturizers on NMF generation and speculate on next generation of FLG research.

Changes in environmental humidity affect the water-holding property of the stratum corneum and its free amino acid content, and the expression of filaggrin in the epidermis of hairless mice

BACKGROUND

Seasonal changes affect the condition of skin and may trigger various cutaneous disorders.

OBJECTIVE

To clarify the effects of the environmental humidity on the skin pathology, we studied the effects of the humidity on a water-holding function of the stratum corneum.

METHODS

We evaluated the skin surface conductance, amino acid in the stratum corneum, and immunoreactivity of filaggrin of the epidermis of hairless mice kept in different environmental humidity.

RESULTS

Skin surface conductance in the stratum corneum of hairless mice 3-7 days after transfer from a humid environment (>80% relative humidity) to a dry (<10% relative humidity) environment, was significantly lower than that of the mice transferred from a normal environment (relative humidity=40-70%) to a dry environment. The free amino acid content in the stratum corneum significantly decreased 24 h after we transferred the mice from a normal to a dry condition, then it recovered to the original level within 3 days, while the mice transferred from a humid to a dry condition showed a significantly lower amino acid content even 7 days after the transfer. No obvious change was observed in the relative composition of the major components of the free amino acids during the experiments. Immunoreactivity of filaggrin, which is the main precursor of free amino acids in the stratum corneum, also became faint in the epidermis of the mice transferred from a humid or normal to a dry environment.

CONCLUSION

These results suggested that a drastic decrease in the environmental humidity reduced the total free amino acid generation and consequently induced skin surface dryness in the stratum corneum.

Enhanced permeation and stratum corneum structural alterations in the presence of dithiothreitol

Stratum corneum protein biochemical and biophysical structural contributions to the barrier properties of human epidermis were determined in the presence of the reducing agent dithiothreitol (DTT). Mannitol and sucrose permeation through human epidermis in the presence of 0 to 50 mM DTT in PBS (pH 7.4) was measured in symmetric, side-by-side diffusion cells (32 degrees C). DTT enhancement ratios, KP(DTT)/KP(PBS), ranging from 1.6 to 32, were dependent on skin donor and DTT concentrations. DTT did not alter stratum corneum uptake of mannitol or sucrose nor mannitol solubility in DTT/PBS solutions. Stratum corneum biophysical structure was ascertained by FTIR in solvent replacement experiments. DTT-induced protein conformational alterations were apparent in the emergence of an Amide I band near 1615 cm-1, which is generally associated with beta-sheet-like conformers. Therefore, DTT alters stratum corneum biophysical structure through interactions with proteins. After exposure of stratum corneum protein sheets to DTT/PBS solutions, the free thiol concentration increased from < 1 nmol SH/mg protein sheet to approx. 130 nmol/mg. The enhanced permeation which increased with increasing concentrations of DTT, was associated with diffusion mechanisms involving the cornified cells of the stratum corneum. These results indicate that corneocyte protein integrity does contribute to barrier function of the skin and influences the transport of polar solutes.

Effects of aging and xerosis on the amino acid composition of human skin

Amino acid compositions of skin samples from young and old subjects and from age-matched donors with dry skin syndrome (xerosis) were examined. The amino acid contents of the free amino acid (FAA) fraction, soluble hydrolysate (SH) fraction, and whole cell hydrolysate (WCH) were determined. The greatest differences were observed between the FAA compositions of the young and old normal subjects. Xerosis did not appear to affect the amino acid compositions of samples from young subjects as much as old subjects. Overall, the effect of aging on the amino acid contents was more pronounced than the effect of xerosis. The amino acid composition of the FAA showed a high degree of similarity to filaggrin, whereas the WCH showed a similarity to keratin.

Stratum corneum hydration and amino acid content in xerotic skin

The relationship between clinical severity, the hydration state of the skin surface as assessed by a conductance with a 3.5 MHz high frequency impedance meter, and the amino acid content of the stratum corneum (SC) of six patients with ichthyosis vulgaris and 30 elderly persons with varying degrees of xerosis was investigated. With an increase in the severity of xerosis the SC showed a decrease in hydration and in its extractable amino acid content. There was a significant correlation between the hydration state and amino acid content of the SC. Although there was a significant correlation between the amino acid content of the lower leg SC and that of the forearm SC in the same subject, the former was generally lower, corresponding to the greater incidence of xerosis on the lower leg. These results suggest that a decreased amount of amino acids may be the result of low profilaggrin biosynthesis in the epidermis and that this is involved in the pathogenesis of these xerotic skin conditions. Clinical improvement of the xerosis following treatment with a urea-containing cream was not accompanied by any significant change in the amino acid content of the SC.