Rosmarinic acid ameliorates skin inflammation and pruritus in allergic contact dermatitis by inhibiting mast cell-mediated MRGPRX2/PLC?1 signaling pathway

Background: Allergic contact dermatitis (ACD) is one of the most common dermatoses, which has high disease burden and quality of life impairment. Anti-histamine is not effective in a part of the ACD patients. Thus, the discovery of novel antipruritic therapy is of highly demand. Objective: In this study, we investigated the anti-pruritic effects of rosmarinic acid (RA) and explored the un-derlying mechanism. Method: SPF Balb/c mice were randomly divided into control group, ACD model group, RA group (1.0 mg/kg) and loratadine (LORA) group (1.5 mg/kg). Back epidermal thickness was recorded. H&E staining was used for pathological observation. Mast cell degranulation was assessed by toluidine blue staining. ELISA assay was employed to detect cytokines levels. Cortistatin-14 (CST-14) and Mas-related G protein-coupled receptor X2 (MRGPRX2) expression was detetcted by RT-PCR and western blot. Molecular docking assay was used to predict the affinity of RA and MRGPRX2. Surface plasmon resonance (SPR) assay was used to verify structure affinity of RA and MRGPRX2. Results: RA treatment significantly decreased epidermal keratinization and inflammatory cell infiltration in ACD mouse model. Administration of RA significantly reduced secretion of histamine, IL-13, and mRNA expression of CST-14. Furthermore, RA treatment increased mRNA expression of MRGPRX2. In addition, Molecular docking results predict that RA has a good affinity with MRGPRX2. RA displayed a structure affinity (KD = 8.89 x 10-4) with MRGPRX2 by SPR. RA inhibited CST-14 and Compound 48/80 (C48/80)-induced mast cell activation via MRGPRX2-PLC gamma 1-PKC-NF-kappa B signaling pathway. Conclusion: RA exhibits anti-pruritic and anti-inflammatory effects in ACD mice by inhibiting MRGPRX2-PLC gamma 1-PKC-NF-kappa B signaling pathway. RA might emerge as a potential drug for the treatment of pruritus and skin inflammation in the setting of ACD.