The moisturizing effect of Capparis spinosa fruit extract targeting filaggrin synthesis and degradation

Abstract Background Small molecular natural products, such as betaine, have unique moisturizing advantages. Capparis spinosa L. fruit is rich in quaternary ammonium alkaloids such as betaine and stachydrine. However, few studies investigated its efficacy and mechanism on human skin. Objective Polysaccharides‐free C. spinosa fruit extract (CS) was obtained to study its moisturizing effect and mechanisms focusing on filaggrin (FLG) synthesis and degradation. Methods The clinical moisturizing test was carried out on human arms, calves, and faces after CS treatment for 0.5–6 h. The change in the level of FLG, caspase 14, loricrin, and transglutaminase 5 (TGM 5) was measured by immunofluorescence after CS treatment for 4 and 24 h in a reconstructed epidermis model. Also, the content of pyrrolidone carboxylic acid (PCA) in the stratum corneum was tested by high‐performance liquid chromatography (HPLC) both in the epidermis model and human calves. Results Compared with glycerin (positive control), 5% CS showed a strong skin hydration effect on arms and calves when applied for 0.5–6 h. Also, the face hydration increased at 0.5 and 4 h. In addition, 3% CS applied to the recombinant epidermis model under low humidity promoted the immunodetected levels of caspase 14 and PCA content but reduced the levels of FLG at 4 h, however, the levels of FLG, loricrin, and TGM 5 were promoted at 24 h. Meanwhile, CS treatment for 4 h in human calves increased the PCA content in the stratum corneum by 29.9%. Conclusions Topical application of CS on human skin showed an instant and long‐lasting increase in skin hydration by regulating the FLG network. It promoted FLG degradation to form PCA at 4 h both in vivo and in vitro, increasing FLG synthesis after 24 h, potentially reforming the FLG monomer reservoir to alleviate the skin's dry condition.