Mast Cell Stabilization: New Mechanism Underlying the Therapeutic Effect of Intense Pulsed Light on Rosacea

Background: Rosacea, a chronic inflammatory disorder of the facial skin, is effectively treated by intense pulsed light (IPL). Objective: To explore the potential molecular mechanism underlying the photobiomodulation effect of IPL for rosacea treatment. Methods: Skin samples from patients with rosacea were subjected to histological and immunohistological staining. Ten patients were followed up after IPL treatment using the VISIA ® skin analysis system, and the severity was assessed. In vivo , skin changes in mice with rosacea-like inflammation induced by intradermal injection of 320 μM LL-37 with or without IPL treatment were evaluated using L*a*b colorimetry as well as histological and immunological staining. In vitro , LL-37-stimulated mast cells (MCs) with or without IPL treatment were evaluated for protein expression of matrix metalloproteinase (MMP)-9, kallikrein-related peptidase 5 (KLK5), and cathelicidin using western blotting and qRT-PCR. Results: : Profound infiltration of inflammatory cells and evident MC degranulation were found in rosacea skin lesions. The expression of rosacea-related biomarkers and inflammatory cytokines was higher in lesion areas than in non-lesional areas, as demonstrated via immunochemical staining. In all patients, rosacea severity reduced after IPL therapy. In vivo, IPL alleviated inflammation in mice with rosacea-like inflammation, as demonstrated by the significantly decreased MMP-9, KLK5, and cathelicidin expression and reduced percentage of degranulating MCs. In vitro , IPL decreased MMP-9, KLK5, and cathelicidin expression in P815 cells, reducing the release of inflammatory cytokines and inhibiting rosacea-like inflammatory reactions. Conclusion: The photobiomodulation effect of IPL for rosacea treatment may inhibit MC degranulation and alleviate inflammatory reactions.