Establishing the Inhibition of the Serine Protease Plasmin as a Skin Anti-Aging Pathway

Plasmin is a serine protease induced by UV-irradiation in skin that contributes to inflammation. We showed that plasmin is upregulated in photo-exposed facial skin and that this correlates with increased transepidermal water loss (TEWL). Plasmin activity upregulates downstream pathways such as pro-inflammatory cytokines and matrix-metalloproteinases (MMPs). In addition, the plasminogen system modulates cutaneous melanogenesis. In this study, we investigated potential skin-aging effects of plasmin with a dual inhibitor of plasmin and its activator urokinase (uPA). We established a range of in vitro and ex vivo assays to investigate inflammation, MMP-9 activation, and collagen modulation, and the melanogenesis modulation activity of plasmin. A specific plasmin inhibitor, Amidinobenzyl Benzylsulfonyl D-Seryl Homophenylalaninamide Acetate (ABSHA), was used in these assays to downregulate these effects. We found that ABSHA was able to down-regulate UV-irradiation-induced MMP-9 expression, and subsequent collagen IV degradation, ex vivo. In addition, the increased melanin synthesis in epidermal melanocytes was reduced significantly by ABSHA. Furthermore, dermal fibroblasts treated with the plasmin inhibitor showed increased collagen I synthesis. We further investigated these effects in a two-month, monocentric, placebo-controlled human study on female Chinese volunteers. We found a significant increase in collagen density by ultrasound measurement and an increase in elasticity by cutometer assessment in the group using a formulation consisting of a 10 ppm ABSHA solution. This resulted in decreased wrinkle volumes on both the forehead and crow's feet as shown by Primos CR. Looking at age spots, there was a decrease in overall ITA degrees and melanin density as well as in the total age spot area. Our results establish plasmin as a skin-aging enzyme. Using specific inhibitors against plasmin shows promise against age-induced skin conditions.