Royal jelly (RJ) is a natural product which the honeybee secretes as a special diet for a queen bee. It is one of the natural products in which various functionalities, such as antibacterial effects, immunomodulating properties, and estrogen-like action, were reported. We investigated the effect of the RJ extract on the moisturizing effect by topical application in humans. The stratum corneum moisture was increased significantly after four weeks by using the RJ extract lotion compared to placebo lotion. RJ extract contained a characteristic ingredient, 10-hydroxy-2-decenoic acid (10H2DA) and 10-hydroxydecanoic acid (10HDAA), etc. However, the mechanism of stratum corneum moisture and its contributing ingredient have not yet been elucidated. We have investigated the effects of 10H2DA and 10HDAA on the free amino acids content in the stratum corneum using a cultured human three-dimensional epidermis model. Additionally, the effect of 10H2DA and 10HDAA on the amounts of filaggrin (FLG) and aquaporin 3 (AQP3) were investigated at the mRNA level and by immunohistochemistry using a cultured human epidermis model. It was determined that 10H2DA increases the free amino acids in the stratum corneum of the cultured human epidermis model, and that it increased FLG on both the mRNA and protein levels. On the other hand, these actions are not observed by treatment of 10HDAA. The mRNA and protein level of AQP3 did not increase with 10H2DA or 10HDAA use. It was thought that the increase in the amount of FLG and the increase in the free amino acids of the epidermis and the stratum corneum, respectively, by 10H2DA were participating in the moisturizing function of the stratum corneum by the continuous use of RJ extract lotion.
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