Abstract: BACKGROUND: Moist exposed burn ointment (MEBO) can inhibit inflammation, reduce oxidative stress, and accelerate wound healing. It has been widely used in the treatment of burn wounds, skin radiation damage, and diabetic foot disease, and has achieved significant results. However, the research on its mechanism is still in a blank stage.
OBJECTIVE: To investigate the effects of MEBO on wound healing and expression of α-smooth muscle actin in a rat burn model through the transforming growth factor β1 (TGF-β1)/Smad family member 3 (Smad3) signaling pathway.
METHODS: Eighty specific-pathogen free male Sprague-Dawley rats were randomly divided into a sham scald group, a model group, a MEBO group, and a TGF-β1 group. Except for the sham scald group, rats in the other groups were treated with a circular scald apparatus (2.5 cm in diameter) to construct rat models. Rats in the MEBO group were treated with MEBO. Rats in the TGF-β1 group were treated with TGF-β1. Rats in the sham scald and model groups were treated with physiological saline. On the 21st day, the rats were killed under anesthesia, and wound healing was observed in each group. Hematoxylin-eosin staining was used to observe the pathological manifestations of the rat wound. Immunohistochemical staining was used to detect the expression of epidermal growth factor receptor and α-smooth muscle actin. Enzyme-linked immunosorbent assay was used to detect the expression of inflammatory factors, tumor necrosis factor-α, interleukin-1β, and interleukin-6, in rat serum. Xanthine oxidase method and thiobarbituric acid coloration method were used to detect the levels of oxidative stress indicators, superoxide dismutase and malondialdehyde, in wound tissue. Western blot was used to detect the protein expression of TGF-β1, and phospho-Smad3 in rat wound tissue. 
RESULTS AND CONCLUSION: Compared with the sham scald group, the wound healing rate and the levels of epidermal growth factor receptor, α-smooth muscle actin, superoxide dismutase, TGF-β1, and phospho-Smad3 were significantly reduced (P < 0.05); and the levels of tumor necrosis factor-α, interleukin-1β, interleukin-6, and malondialdehyde were increased significantly in the model group (P < 0.05). Compared with the model group, the wound healing rate and the levels of epidermal growth factor receptor, α-smooth muscle actin, superoxide dismutase, TGF-β1, and phosoho-Smad3 were significantly increased in the MEBO group and TGF-β1 group (P < 0.05). Epithelial tissue basically formed covering the wound surface, and the collagen tissue was clearly visible in the MEBO group and TGF-β1 group. Compared with the model group, the levels of tumor necrosis factor-α, interleukin-1β, interleukin-6, and malondialdehyde were significantly decreased in the MEBO group and TGF-β1 group (P < 0.05). However, these above-mentioned indicators showed no significant difference between the MEBO group and the TGF-β1 group (P > 0.05). To conclude, MEBO can reduce oxidative stress and inflammation in burn rats by activating the TGF-β1/Smad3 signaling pathway, and increase the expression level of α-smooth muscle actin, thereby promoting wound healing. 

Key words: burn, transforming growth factor β1, Smad family member 3, moist exposed burn ointment, wound healing, α-smooth muscle actin