Twenty years ago, we never imagined that one molecule could sense temperature and sensory irritations by cosmetics on the skin. In 1997, it was discovered that an ion channel called TRPV1 responded to not only high temperature but also capsaicin, which dramatically changed our understanding of sensory perception on the skin. We have clarified that TRPA1, which was found in 2003, is related to sensory irritation by various ingredients. In addition, I mention examples of applications to cosmetics.

Proteins are continuously damaged by various intrinsic and extrinsic factors, such as changes in pH and temperature, UV exposure, and oxidative stress loading, which affect intracellular pathways. Most of the damaged proteins are eliminated by protein degradation systems, but some of them are restored by protein repair systems. The formation of L-isoaspartyl (L-isoAsp), D-aspartyl (D-Asp), and D-isoaspartyl residues within proteins, arising from both deamidation of L-asparagine residues and isomerization and/or racemization of L-aspartyl residues, is a frequent chemical modification that alters their conformation and leads to abnormal aggregation. Protein L-isoaspartyl/D-aspartyl O-methyltransferase (PIMT, EC 2.1.1.77) is known as a repair enzyme for L-isoAsp or D-Asp residues in proteins. PIMT is expressed in various tissues such as the brain, liver, heart, and kidney, but its function within the skin is unclear. In this study we demonstrated that the PIMT protein was expressed in human dermal fibroblasts and that the PIMT protein level in fibroblasts was decreased both with aging and by UVB irradiation. Our data indicated that the decrease in PIMT expression level caused an accumulation of L-isoAsp-containing proteins in fibroblasts. Further, UVB irradiation induced isomerization of aspartic acids on its own. These findings suggested that it was important to maintain an adequate PIMT level in the skin. We found that a Birch bark extract and a Wine extract were effective in protecting fibroblasts against the UVB-induced decreases in PIMT protein levels and that the Wine extract was effective even for regeneration. Therefore, “restoring denatured proteins” by PIMT might be a novel and effective approach to anti-aging skin care.

In the past, skincare products have only focused on the function of caring for the skin. In practical use, however, base makeup products such as foundations are applied on dried cosmetic films of skincare products. Generally speaking, in order to obtain a natural finish, the foundations should be applied evenly. Hence, we aimed to develop new formulations of skincare products which have excellent compatibility with makeup foundations. Silicone surfactants provide a lower surface tension than hydrocarbon surfactants. Due to this low surface tension, excellent spreading capacity and skin compatibility are thought to be obtainable. We reported a novel silicone surfactant, 3-(10-carboxydecyl)-1,1,1,3,5,5,5-heptamethyl trisiloxane (CDTS) and found an α-form hydrated crystalline phase (often referred to as “α-gel,” especially in the cosmetics field), composed of CDTS, polyoxyethylen (e 5 mol) glyceryl monostearate (GMS-5), fatty alcohol, and water. In this study, we first investigated the fundamental physical properties of CDTS. The water solubility of CDTS is quite low (ca. 17 μmol/L) and its approximate pK_a is 5.7 at 20 ºC. Titration curves also indicated that CDTS is a weak acid. We observed a microemulsion (ME) phase containing CDTS, GMS-5, fatty alcohol, dimethicone, and hydrogenated polydecene. A novel fine nanoemulsion, whose diameter was less than 100 nm, was obtained by the dilution of the microemulsion phase with the water phase. The obtained fine emulsion was applied for tribology tests. Tribological characteristics indicated that the fine emulsion containing the CDTS α-form hydrated crystal is superior to conventional fine emulsions composed of polyoxyethylene 60 mol hydrogenated castor oil, from the viewpoint of low friction at application. Moreover, powder foundation could be applied evenly on the dried cosmetic film of fine emulsions containing CDTS.

In order to prevent photoaging and to provide a younger impression of appearance, the composite powder was examined for its year-round UV-A protection effect and for improvement of skin color by its make-up effect. However, in recent years, many limitations have been imposed on the use of powders, including fine titanium dioxide and zinc oxide, in consideration of issues such as nanoparticles, dissolution into water and scattering into air. In addition, organic UV protection agents also have restrictions on their use due to their irritation and environmental risks. From the above background, iron oxides and titanium dioxide were fixed on the sericite surface by combining the original pulverizing and dispersion processes with bead mill and the spray-drying process. As a coated particle, titanium dioxide could be used as a UV-B protective material, and the pulverized iron oxides could be used as UV-A protective materials. The obtained composite powder was capable of protecting against ultraviolet rays in a wide range from UV-A to UV-B. In addition, it was confirmed that this composite powder had a reddish high chroma tone, and the powder foundation containing this composite powder gave a healthy impression of appearance. Therefore, the prepared composite powder that possesses these functions is thought to be a useful material with defensive and improvement effects on senior skin.

Human skin is influenced by ultraviolet-B (UV-B) irradiation. UV-B induces DNA damage and mitochondrial damage in epidermal keratinocytes； then accumulation of excessive DNA damage and damaged mitochondria finally leads to apoptosis. Recently, we investigated effective means to repair or to eliminate fatal damage leading to excessive apoptosis in UV-B-exposed normal human epidermal keratinocytes (NHEKs) . Concerning repair of DNA damage, we previously established a method for measuring activity of cellular DNA polymerase (pol) which synthesizes DNA strands in the repair system in NHEKs, and found that Rhodomyrtus tomentosa fruit extract, which has properties to protect epidermal keratinocytes from UV-B-induced apoptosis, enhanced activity of pol in UV-B-irradiated NHEKs. With regard to repair and elimination of mitochondrial damage, we focused on mitophagy, which is the cellular function to remove dysfunctional mitochondria by autophagy. In the present study, we detected mitophagy and evaluated mitochondrial reductase activity providing an indication of cell viability in UV-B-irradiated NHEKs. As a result of evaluating the influence of UV-B irradiation on mitophagy in NHEKs, we observed that mitophagy became weak after irradiation with 40 mJ/cm² UV-B. In addition, mitochondrial reductase activity also decreased at 24 h after irradiation. Following these results, we also found that Rhodomyrtus tomentosa fruit extract suppressed the UV-B-induced decrease in mitophagy and in mitochondrial reductase activity. Furthermore, we investigated influence of UV-B irradiation and effect of the extract on mitochondrial membrane potential in NHEKs to elucidate the mechanisms of modulating mitophagy. The results showed that the extract retained normal function of mitophagy by decreasing mitochondrial membrane potential in advance. In conclusion, it was suggested that the enhancement of inherent cellular DNA repair properties and the efficient elimination of the mitochondrial damage are essential for protecting the epidermal keratinocytes from UV-B-induced excessive apoptosis.

We had found that skin dullness is caused by old corneocytes remaining on the skin surface due to the decrease of kallikrein (KLK)-5 activity of an exfoliating enzyme in skin. Furthermore, the increase of KLK-5 activity by our cosmetics formulation indicated a decrease of corneocyte area and skin dullness. In this study, we focused on KLK-7 which is similar to KLK-5 and decided to use plant extracts to determine whether skin dullness could be reduced via increased KLK-7 activity. In the primary screening, rosemary extract significantly increased KLK-7 gene expression and keratinocyte growth using RT-qPCR and WST-8 assay. Next, skin lotion containing rosemary extract was applied on half the face twice a day for 4 weeks as a clinical test. As a result, it was confirmed that the human stratum corneum KLK-7 activity increased in the group using skin lotion containing rosemary extract compared to the placebo. Furthermore, the stratum corneum area significantly decreased, and the skin dullness and stiff feeling by the subjects decreased, especially in female subjects using rosemary skin lotion. Water content and TEWL were not significantly different between the groups. The present study results suggest that rosemary extract may improve skin dullness and stiff feeling via a decrease of surface aggregation and corneocyte area in the stratum corneum by the increased KLK-7 activity. Because rosemary extract also indicated the growth of epidermal keratinocytes, it was considered that rosemary extract is useful for skin dullness and stiffness related to epidermal turnover that decrease with age.

Sugars are essential nutrients for daily activities, but the glycation is known to trigger the changes to the three-dimensional structure of proteins by the induction of a lysine-arginine crosslink and to affect the activities and physical properties of proteins. In the skin, influences of aging due to glycation appear in proteins with a long half-life period, such as collagen or elastin, and glycation induces the browning reaction of skin proteins and accumulates cross-linking advanced glycation end products (AGEs), which leads to signs of skin aging such as wrinkles, a dull aspect, and the decline of firmness and elasticity. However, few studies have reported on the influence of glycosylated basement membrane on the maintenance of epidermal functions. In this study, we focused on the effect of glycation on epidermal function, and found that the production of ATP and the expressions of filaggrin (FLG), serine palmitoyltransferase 2 (SPTLC2) and transglutaminase 1 (TGM1) were decreased in keratinocytes incubated on glyceraldehyde-induced glycosylated collagen or basement membrane extract. We also found that Thymus serpyllum extract suppressed the decrease of ATP production and expressions of FLG, TGM1 and SPT, suggesting that this extract might be a promising ingredient for skin hydration and barrier repair by protecting against glycation-induced epidermal dysfunction.