Anti-atopic effect of Viola yedoensis ethanol extract against 2,4-dinitrochlorobenzene-induced atopic dermatitis-like skin dysfunction

Viola yedoensis Makiho (VY, Violaceae) is a well-known medicinal herb in Chinese medicine, which is traditionally used to treat inflammation-related disorders, including allergic skin reactions. Although studies have uncovered its anti-inflammatory effects and corresponding bioactive constituents, the exact mechanism of action is still unclear in treating allergic skin reactions. Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by severe pruritus, dry, edema and inflamed skin. It affects people's quality of life seriously and causes huge economic losses to society. This study proposes VY as a possible remedy for atopic dermatitis since its traditional usage and superior anti-inflammatory effects. Atopic dermatitis-like skin lesion was induced by topical application of 2,4-dinitrochlorobenzene (DNCB) in ICR mice. After treatment with Viola yedoensis Makiho ethanol extract (VYE) or dexamethasone (positive control) for 3 weeks, skin pathological observation and the molecular biological index were performed for therapeutic evaluation, including visual inspection in the change of the stimulated skin, scar formation, pathological morphology by hematoxylin and eosin (HE) staining, the measurement of interleukin IL-1β, IL-6 and tumor necrosis factor-alpha (TNF-α) levels in serum as well as spleen index. The expression of inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2) were analyzed by western blot. The ratio of CD4+/CD8+ T lymphocyte in the spleen was detected by flow cytometry. Meanwhile, immunohistochemistry staining for CD68 identified the number of activated macrophages in skin lesions. Additionally, a reliable ultrahigh-performance liquid chromatography coupled with a Q exactive hybrid quadrupole-orbitrap mass spectrometry (UHPLC-Q-Orbitrap-MS) method was established for the systematic identification and characterization of main components in VYE. VYE alleviated DNCB-stimulated AD-like lesions symptoms as evidenced by a significant decrease in hypertrophy, hyperkeratosis, and infiltration of inflammatory cells in dorsal skin. The levels of IL-1β, IL-6, and TNF-α in serum were suppressed in mice treated with VYE as compared to the DNCB-induced model group. Also, the administration of VYE reduced the ratio of CD4+/CD8+ T lymphocyte in the spleen and the number of activated macrophages stimulated by DNCB. Besides, the expression of iNOS and COX-2 were down-regulated in the dorsal skin. VYE showed therapeutic effects on atopic