Application of Euglena gracilis-Derived Peptides as a Cosmetic Ingredient to Prevent Allergic Skin Inflammation

Bioactive peptides have a wide range of therapeutic activities. They have emerged as interesting candidates for cosmetic ingredients. Euglena gracilis contains high amounts of proteins consisting of all 20 proteinogenic amino acids. As a result, it is thus proposed that enzymatic peptides from E gracilis proteins would have multiple biological activities. To verify their potential application in cosmetics, the therapeutic effects of E gracilis-derived peptides (BPE) on allergic inflammation were evaluated in this study. In 2D skin models, HaCaT cells were used to assess cell viability, a fluorescence of 2',7'-dichlorofluorescein diacetate was used to evaluate reactive oxygen species (ROS) contents, and an enzyme linked immunosorbent assay (ELISA) analysis of tumor necrosis factor alpha (TNF-alpha) reflected inflammatory response. Meanwhile, transcriptome analysis was performed to reveal the changes in gene expression. In 3D skin models, hematoxylin-eosin staining revealed the barrier-repairing ability of BPE. Filaggrin (FLG) and loricrin (LOR) levels were measured by their immunofluorescence. ELISA analysis of thymic stromal lymphopoietin (TSLP) also reflected the inflammatory response. A double-blind clinical trial was conducted to evaluate the erythema and itch, which reflects the degree of inflammation. Sodium lauryl sulfate, lipopolysaccharide, and histamine were used to induce allergic responses in vitro and in vivo. In 2D skin models, BPE increased cell viability from 41 to 55%. It also decreased intracellular ROS content from 100% to 61%. Combined with the decrease in TNF-alpha expression, it showed that BPE exerted multiple biological activities, including antioxidant and anti-inflammatory activities. According to the transcriptome analysis, BPE significantly changed the amounts of inflammation- and immune-response-related genes and enhanced the anti-inflammatory ability of cells. In 3D skin models, hematoxylin-eosin staining showed that BPE repaired the damages induced by Poly I:C and lipopolysaccharides. After BPE treatment, filaggrin and LOR expressions reached 124 and 127% of the negative control, respectively, and the TSLP content significantly increased. It suggested that BPE treatment significantly alleviated inflammatory response and repaired the inflammation-induced damages. Furthermore, clinical trials in vivo also showed that BPE significantly suppressed allergic inflammation. The simulative experiments in 2D and 3D skin models as well as clinical trials verified that BPE had therapeutic effects on allergic inflammation. Our results propose BPE as a novel cosmetic ingredient to prevent allergic responses.