Abstract: BACKGROUND: Previous experiments have shown that Shixiang plaster can regulate the Nrf2-ARE signaling pathway and inhibit the glycosylation end product/nuclear factor κB pathway, effectively reducing oxidative stress and inflammation, and promoting wound repair, but the mechanism remains unclear.
OBJECTIVE: To study the therapeutic effect and mechanism of Shixiang plaster in a rat model of infectious wounds, with a particular focus on the changes in the content of growth factors and M2 macrophages in the wounds.
METHODS: Thirty-six male Sprague-Dawley rats, SPF grade, were selected. A rat model of infectious wounds was established using the skin lesion+bacteria implantation method. Model rats were randomized into model group (the wound was applied wetly with normal saline and then covered with a sterile dressing), the Befuji group (the wound was treated with Befuji, with recombinant bovine basic fibroblast growth factor as the main ingredient), and the Shixiang plaster group (the wound was treated with Shixiang plaster). Gross observations of the wound were performed and samples were taken at 3, 7, and 14 days after modeling. Hematoxylin-eosin staining and Masson staining were used to observe the histopathological changes, ELISA was used to detect the levels of platelet-derived growth factor, transforming growth factor β, and basic fibroblast growth factor in the wound tissues; flow cytometry and immunofluorescence were used to detect the content and localization of macrophages in wound tissues; and histological changes and the role of immune cells during the wound healing were analyzed.
RESULTS AND CONCLUSION: (1) On the 3rd, 7th, and 14th days after modeling, wound healing was fastest after intervention with Shixiang plaster, which was significantly better than the other two groups in both the early healing rate and the late healing rate. The healing effect in the Befuji group ranked second. (2) Treatment with Shixiang plaster in the early stage of inflammation (3 days) downregulated the levels of basic fibroblast growth factor and platelet-derived growth factor, inhibited the over-activation of M1-type macrophage, reduced the secretion of pro-inflammatory cytokines, and maintained the moderate inflammatory environment, which was compatible with the inflammatory response dominated by M1-type macrophage. At 7 days after the formation of wounds, Shixiang plaster upregulated the levels of basic fibroblast growth factor and platelet-derived growth factor, at which time M2-type macrophages gradually increased and transforming growth factor β levels were decreased. To conclude, Shixiang plaster alleviates inflammatory responses and promotes the formation of granulation tissue by regulating growth factors in a time-dependent manner. Combining with previous experimental studies, it is speculated that Shixiang plaster can activate the Nrf2-ARE signaling pathway to promote the polarization of M2 macrophages, achieving the effects of anti-inflammation and accelerating wound healing.

Key words: infectious wounds, M2-type macrophage polarization, growth factors, Shixiang plaster, Staphylococcus aureus, signaling pathways