Skin penetration of topically applied white mustard extract and its effects on epidermal Langerhans cells and cytokines.

White mustard (Sinapis alba L.), a traditional Chinese medicine, is widely used in China for clinical prevention and treatment of the common winter diseases of asthma and bronchitis by percutaneous administration in the summer. The present study is to investigate the skin penetration behavior of white mustard extract to elucidate the possible mechanism underlying its immune regulation activity. The principle active compound of the extract, sinapine thiocyanate (ST), was used as a marker. The skin penetration of ST in white mustard extract was examined in vitro and in vivo. In vitro study on excised guinea pig hairless skin using Franz diffusion cell revealed ST can permeate through the skin and also accumulate in the skin. In vivo study was carried out on the guinea pig hairless skin for 24 h, and then skin was excised for frozen section, ST from the sections were extracted to quantify the amount of drug in different skin layers. The detailed distribution of ST showed that it accumulated in the epidermis, especially in the stratum corneum. After treatment with white mustard extract for 24h, the skin was stained with ATPase, and the morphometric parameters of epidermal LCs were compared to the untreated control through image-analysis system. A statistically significant reduction in LC density and increase in shape factor were observed. Cytokines related to LCs migration including interleukin 1β (IL-1β) and tumor necrosis factor α (TNF-α) were also measured after white mustard extract treated at different time points. Compared to the untreated group, white mustard extract significantly enhanced the release of IL-1β and TNFα. The morphometric changes of LCs and the local cytokine release after topical white mustard treatment may explain the activity of the white mustard extract against asthma and bronchitis.