Intracellular calcium ion concentration in epidermal cells elevated by yuzu extract

A research group led by Professor Takeshi Matsui of the School of Bioscience and Biotechnology at Tokyo University of Technology, in collaboration with POLA Innovation Center, announced on July 3 that they have revealed that extract from yuzu (citrus junos) residue promotes the elevation of intracellular calcium ion (Ca2⁺) concentration in epidermal cells. The results were presented at the "50th Annual Meeting of the Japanese Cosmetic Science Society" held at Yurakucho Asahi Hall in Chiyoda City, Tokyo Prefecture, from July 4 to 5.

In November last year, Matsui cooperated in the development of products that effectively utilize extract from the parts remaining after juicing yuzu fruit (sanoo) sold by the company. The company had revealed that this extract has an effect of making unnecessary stratum corneum cells easier to detach.

This time, the research group aimed to elucidate the mechanism of this action. In human keratinocytes (epidermal cells), the activity of protein TRPV4 is known to be important for controlling the barrier function of tight junctions (TJ) that connect cells to each other. It is also known that when TRPV4 is in an activated state, it promotes the formation of epidermal TJ which supports skin barrier function.

In this study, extract was prepared from yuzu residue from Kochi Prefecture using 50% ethanol aqueous solution. Human primary cultured keratinocytes (epidermal cells) were loaded with Ca2⁺ probe, and high-speed time-lapse imaging was performed after adding yuzu residue extract and TRPV4 inhibitors or TRPV4 activators, followed by Ca2⁺ imaging analysis. The results showed that when the extract was added, intracellular Ca2⁺ increased in most cells, promoting the activation of Ca2⁺ channels and other pathways.

When the extract was added to human keratinocytes treated with TRPV4 inhibitors, the intracellular Ca2⁺ elevation was suppressed. On the other hand, when TRPV4 activators were added to human keratinocytes, intracellular Ca2⁺ increased. This indicated the possibility that intracellular Ca2⁺ concentration increases when TRPV4 is activated, allowing Ca2⁺ to flow into cells through TRPV4.

The extract from yuzu residue was shown to enhance skin barrier function by activating TRPV4 and promoting TJ formation.

Matsui stated: "I believe this method will enable us to analyze intracellular Ca2⁺ responses in epidermal cells to various cosmetic ingredients. In the future, we plan to analyze in detail what kind of intracellular and morphological changes are promoted by the increase in epidermal intracellular Ca2⁺ concentration caused by yuzu sanoo extract."