Tranilast Alleviates Rosacea-Like Inflammation via TLR4-Mediated MyD88/NF-κB and NLRP3 Signaling Pathway in Macrophages: An In Vitro and In Vivo Mechanistic Study

Objective: Rosacea is a common chronic inflammatory skin disease with unclear pathogenesis and limited treatment options. While the therapeutic efficacy of tranilast (TR) in rosacea has been established, the molecular mechanisms underlying this effect remain to be elucidated. Given that TR is known to suppress macrophage-mediated inflammation, this study aimed to investigate the underlying macrophage-related mechanisms in the anti-rosacea action of TR. Methods: J774A.1 cells were used for in vitro experiments, whereas a cathelicidin antimicrobial peptide LL-37 induced rosacea-like dermatitis model was established for in vivo studies; all animals were randomly allocated to groups. On the final intervention day, areas of erythema on mouse skin lesions were compared. Pathological changes were assessed via hematoxylin–eosin staining. Expression of key proteins in the Toll-like receptor 4 (TLR4)-mediated and NOD-like receptor family pyrin domain-containing 3 (NLRP3) mediated inflammtory pathways was evaluated by immunofluorescence staining and Western blotting. Immunohistochemical staining was conducted to assess F4/80 expression, and Western blotting was utilized to quantify protein expression levels of cathelicidin antimicrobial peptide and vascular endothelial growth factor. Data from multiple groups were compared using one-way analysis of variance. Results: TR alleviated symptoms of rosacea-like inflammation in mice, as demonstrated by the following findings: Erythema area decreased from 20.26 ± 1.44 mm 2 in the LL-37 group to 9.10 ± 1.21 mm 2 in the LL37+TR group ( P < 0.001), and a significant reduction in dermal inflammatory cell infiltration was found (LL-37 group vs. LL37+TR group, 342.20 ± 35.17 vs. 130.20 ± 19.92, P < 0.001). Western blotting showed pronounced downregulation of vascular markers cathelicidin antimicrobial peptide and vascular endothelial growth factor; immunofluorescence staining indicated that TR effectively reduced the expression levels of TLR4, TNF-α, and NLRP3. Western blotting further demonstrated reduced protein expression of TLR4, MyD88, p-p65, TNF-α, NLRP3, and IL-1β, whereas immunohistochemical staining showed a significant decrease in F4/80+ macrophage infiltration (13.20 ± 1.48 vs. 1.60 ± 0.55, P < 0.001). In both LL-37– and lipopolysaccharide-stimulated J774A.1 cells, TR consistently attenuated TLR4–MyD88–NF-κB signaling and NLRP3 inflammasome activation. The TLR4 inhibitor TLR4-C34 similarly suppressed NLRP3 expression, confirming TLR4 as an upstream regulator of NLRP3. Conclusion: Our findings demonstrate that TR ameliorates rosacea-like inflammation both in cell cutures and mice models, possibly through regulation of TLR4–MyD88–NF-κB signaling and NLRP3-mediated macrophage inflammatory responses, suggesting its therapeutic potential for rosacea, however, further clinical studies are warranted to validate its efficacy and safety.