The physiological activity of hydrolyzed keratin derived from feathers was previously unclear. We examined the physiological activity of hydrolyzed keratin and the underlying mechanisms involved. When hydrolyzed keratin was administered to cultured mammalian cells, it exhibited low toxicity and enhanced resistance to oxidative stress. It was determined that hydrolyzed keratin does not directly scavenge reactive oxygen species. Instead, it activates cells and upregulates the expression of antioxidant enzymes and glutathione. Furthermore, biochemical experiments using cultured cells revealed that the increase in antioxidant activity occurs via the ERK MAP kinase pathway. Additionally, experiments with the model organism Caenorhabditis elegans demonstrated that hydrolyzed keratin boosts antioxidant enzyme expression and extends both overall and healthspan. These results suggest that hydrolyzed keratin can enhance endogenous antioxidant activity. Hydrolyzed keratin is expected to be used in cosmetics such as hair care and skin care products, and it is also expected to improve the value of feathers.

Cosmetic products promoting eyelash growth have been marketed in European countries and the United States. These products contain prostaglandin F2-alpha (PGF_2α) analogues, which enhance eyelash growth. Previous studies have identified the presence of not only the PGF_2α analogues listed on the product labels but also other related compounds not mentioned. In this study, we developed an analytical method using high performance liquid chromatography (HPLC) to investigate the presence of PGF_2α analogues in commercially available eyelash serums in Japan. The target substances measured were bimatoprost, isopropyl cloprostenate, and ethyl tafluprostamide. Several HPLC methods were evaluated based on column separation and mobile phase conditions. The limit of quantification for the target substances ranged from 0.0001–0.0003% under the analytical conditions, corresponding to 1/100–1/300 of the concentration found in ophthalmic and cutaneous solutions containing bimatoprost. This level of sensitivity was sufficient for the measurements. Method validation through additive recovery tests yielded satisfactory results, with recovery/precision ranges of 101–103%, repeatability (RSD_r%) ranging from 0.21–1.8%, and intermediate precision (RSD_R%) ranging from 1.1–1.4%. The HPLC analysis showed that bimatoprost was not detectable in any of the eyelash serum samples. Ethyl tafluprostamide was detected in two samples labeled with this compound. Isopropyl cloprostenate was observed in two products, although it was below the limit of quantitation in one and detected above the lower limit of quantitation in the other. These concentrations were similar to or slightly lower than those previously reported. In contrast, isopropyl cloprostenate was only detected in one unlabeled sample. High performance liquid chromatography-tandem mass spectrometry (LC/MS/MS) analysis using the same and another lot of this product also detected isopropyl cloprostenate, indicating a labeling omission of this compound in these products.

Organoids are three-dimensional structures that self-organize from human pluripotent stem cells or primary tissue, potentially serving as a traceable and manipulatable platform to facilitate our understanding of organogenesis. Despite the ongoing advancement in generating organoids of diverse systems, biological applications of in vitro generated organoids remain as a major challenge in part due to a substantial lack of intricate complexity. The studies of development and regeneration enumerate the essential roles of highly diversified non-epithelial populations such as mesenchyme and endothelium in directing fate specification, morphogenesis, and maturation. Such human organoids allow for the study of direct and indirect inter-organ crosstalk recapitulating what is seen in health and disease. For example, we show in vitro modeling of the inter-coordinated specification and invagination of the human hepato-biliary-pancreatic (multi-organ) system in 3D stem cell culture, paving a way for the study of inter-organ connectivity failure such as biliary atresia. I herein summarize the evolving organoid technology at the cell-, tissue-, system-level complexity with a main emphasis on liver derivatives and discuss its state-of-art in disease modeling, drug discovery, tissue replacement therapy and personalized medicine.

The stratum corneum (SC) of the epidermis serves as a functional barrier against environmental factors such as pathogens, dehydration, and ultraviolet radiation. It is composed of multiple layers of dead corneocytes, which are terminally differentiated, enucleated keratinocytes. To elucidate the mechanism by which the uppermost stratum granulosum (SG1) cells undergo cell death to form the SC, we performed live imaging of intracellular Ca²⁺ and pH change in mice. Our findings revealed a prolonged increase in intracellular Ca²⁺ concentration (approximately 60 minutes) in SG1 cells, followed by intracellular acidification. To investigate the role of acidification, we developed a method to isolate SG1 cells from mice and conducted live imaging under various culture conditions. The results demonstrated that intracellular acidification is essential for the degradation of keratohyalin granules and nuclear DNA, hallmark features of cornification. Unlike apoptosis or necrosis, which often result in the removal of unnecessary cell debris, the SG1 cell death is unique in that the resulting dead cell bodies themselves form a functional biological barrier. Based on these findings, we propose the term “corneoptosis” to describe this distinct form of cell death in SG1 cells, where the dead cell remnants actively contribute to the formation of the stratum corneum. This study provides new insights into the molecular and cellular mechanisms underlying epidermal barrier formation and highlights the functional significance of corneoptosis in maintaining skin integrity.

Aging leads to tissue dysfunction through phenotypic changes in cells. The human dermal fibroblast is one of the targets of studies that have explored the relationship between cellular status and skin condition. Dermal fibroblasts are crucial in maintaining homeostasis of the dermal environment by producing extracellular matrix. Age-related changes in dermal fibroblasts cause various structural alterations in the dermis, such as loss of dermal papilla, fragmentation and disorganization of collagen fibrils, and replacement with abnormal elastic fibers. These changes are involved in impaired wound healing and a decrease in skin strength and elasticity. The skin is affected by a variety of exogenous and endogenous factors, such as UV exposure, smoking, pollutants, habitual facial expressions, race, and hormonal changes. These factors vary widely between individuals, making it challenging to capture cellular alterations that are purely due to aging. However, given the important findings that removing senescent cells from the body can extend lifespan and alleviate symptoms associated with aging, it will become more important to understand the mechanisms behind cellular senescence and accumulation of senescent cells in vivo. Technological progress has enabled the identification of spatially and functionally distinct fibroblast subpopulations in various skin samples. In particular, single-cell RNA sequencing is a powerful tool in aging research. For example, it has shown that human dermal fibroblasts from the sun-protected inguinal region consist of four major subpopulations, whose differences were found to be obscure in the elderly. We investigated transcriptional and phenotypic changes in a unique fibroblast cell line obtained from an adult male donor over 35 years at a single-cell level and identified a possible model of cellular aging and a novel gene related to suppression of cellular senescence. These findings may provide us with clues for developing new cosmetic approaches to prevent skin aging.