Particulate matter (PM), such as air pollutants and pollens, are known to cause skin aging through skin inflammation. It is important to develop formulations which protect the skin from PM. We previously developed a conventional water-in-oil emulsion with a synthetic surfactant, distearyldimonium chloride, modified bentonite (C-W/O), which protects skin from allergens. In the present study, we developed a novel water-in-oil emulsion with a natural surfactant, lecithin, modified bentonite (N-W/O).
The microarray analysis was performed using total RNA extracted from a reconstructed human epidermis (RHE) stimulated with urban aerosols or cedar pollen for 6 hours in order to develop an epidermal inflammation model by PM for the evaluation of topical formulations. We then compared the efficacy of N-W/O and C-W/O to prevent epidermal degradation. Tissues and culture media were collected 24 hours after the urban aerosol or cedar pollen stimulation for a histological assay, and the quantification of MMP1 and CXCL8 secretion.
The expression levels of pro-inflammatory cytokines and chemokines, such as IL1A and CXCL8, and matrix metalloproteinases, including MMP1, MMP3, and MMP9, were significantly up-regulated by the PM stimulation. As a result of ranking based on the pathway enrichment analysis, oxidative stress-related pathways, such as MAPK-mediated signaling, HIF-1 signaling, IL-1 signaling, and ROS-induced cellular signaling, were ranked high in the urban dust- and cedar pollen-treated groups. A thickened stratum corneum, thinned vital layer, and cleaved E-cadherin were observed by hematoxylin and eosin staining and immunohistochemical staining of E-cadherin. The secretion of MMP1 and CXCL8 was also into the media significantly increased. N-W/O prevented the degradation of epidermal integrity and secretion of inflammatory proteins more effectively than C-W/O.
The present results showed that N-W/O made using natural surfactant is useful at protecting skin from PM, such as urban aerosols and cedar pollen.

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