Effects of topical application of a tri-herb formula on inflammatory dry-skin condition in mice with oxazolone-induced atopic dermatitis

Atopic dermatitis (AD) is a chronic relapsing inflammatory and pruritic skin disease, affecting 10-20% of the population worldwide. Paeonia suffruticosa Andrews (Paeoniaceae) (Cortex Moutan) and Mentha haplocalyx Briq. (Labiatae) (Herba Menthae) have shown beneficial effects on AD. Calendula officinalis L. (Asteraceae) is commonly used for treating skin rashes and wounds. In the present study, a three-herbs formula including Cortex Moutan and Herba Menthae, together with C. officinalis at 1:1:1 weight ratio was used as a topical agent and its therapeutic effects on AD was investigated. In vitro effects of individual herbs and three-herbs formula (0.125–1 mg/ml) were examined using cytokine release assay on human mast HMC-1 cells, inflammation test on murine macrophage RAW cells and human keratinocyte (HaCaT) cells, and migration scratch assay on human umbilical vein endothelial cells (HUVEC). The contributing functional pathway of three-herbs formula in AD was explored using Western Blot assay in HMC-1 cells. Oxazolone-induced AD-like mice model was also used to investigate the in vivo therapeutic effect of the topical application of the three-herbs formula. Herba Menthae, Cortex Moutan, and three-herbs formula significantly reduced the production of IL-6 and tumor necrosis factor (TNF)-α in HMC-1 cells, inhibited the expression of IL-6, IL-8 and CCL2 in TNF-α/IFN-γ stimulated HaCaT cells, and suppressed the lipopolysaccharide (LPS)-induced nitric oxide (NO) production in RAW 264.7 cells. Moreover, Herba Menthae and three-herbs formula significantly suppressed CCL2 and TNF-α production in LPS-induced RAW 264.7 cells. C. officinalis and three-herbs formula promoted wound healing in HUVEC. For intracellular mechanisms, three-herbs formula inhibited the expressions of molecules in STAT1 and STAT3-dependent pathways. In vivo model showed that topical application of three-herbs formula on challenged ear reduced ear swelling and mice scratching frequencies. H&E and toluidine blue staining of the challenged ear tissue demonstrated that three-herbs formula reduced the epidermal thickness and mast cell infiltration, respectively. The three-herbs formula of Cortex Moutan, Herba Menthae and C. officinalis at 1:1:1 (w/w) exhibited anti-inflammatory effect and promotion of cell migration in vitro. It also alleviated ear redness, swelling, epidermal thickness and inflammation of the OXA-induced AD mice. These findings suggest a potential beneficial role of the topical application of the three-herbs formula for treatment of AD.