Anti-Inflammatory and Barrier-Related Effects of Bidens bipinnata L. Fruit Ethanol Extract in an MC903-Induced AD-like Dermatitis Mouse Model and LPS-Stimulated RAW 264.7 Cells

Atopic dermatitis (AD) is a chronic inflammatory dermatosis driven by skin barrier impairment and immune dysregulation. This study aimed to investigate the anti-inflammatory and barrier-related effects of the ethanol extract of Bidens bipinnata L. fruits (EEBB) in a calcipotriol (MC903)-induced AD-like dermatitis mouse model and lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages. In vivo, repeated topical application of EEBB (60, 180, and 600 μg/day) significantly attenuated MC903-induced AD-like clinical symptoms, skin weight, and erythema index. Notably, EEBB significantly improved skin hydration-related parameters, including relative skin hydration readings and the post-application moisture retention profile, and partially restored filaggrin and loricrin expression in lesional skin, whereas dexamethasone showed limited effects on these hydration-related parameters under the present conditions. Histopathologically, EEBB ameliorated epidermal lesions and reduced inflammatory cell infiltration. Mechanistically, EEBB suppressed the levels of pro-inflammatory (TNF-α, IFN-γ) and Th2 (IL-4, IL-5) cytokines in lesional skin. In vitro, EEBB significantly inhibited the production of nitric oxide (NO) and prostaglandin E2 (PGE2), and downregulated inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) protein expression in RAW 264.7 cells. These effects were associated with inhibited phosphorylation of JNK and p38 MAPK, with no marked effect on ERK phosphorylation under the present conditions. In conclusion, EEBB effectively alleviated AD-like dermatitis, accompanied by improved skin hydration and restoration of barrier-related protein expression, attenuation of local inflammatory responses, and targeted inhibition of the MAPK signaling pathway.