Shikonin alleviates allergic airway remodeling by inhibiting the ERK-NF-κB signaling pathway
Shikonin is a naphthoquinone extracted from the root of Lithospermum erythrorhizon, and has been reported to suppress allergic airway inflammation in mice. However, the underlying mechanisms are unclear and need to be further elucidated. In this study, shikonin (0.5, 2 or 4 mg/kg) was given intraperitoneally to ovalbumin (OVA)-challenged BALB/c mice. We found that the pathological airway remodeling of asthmatic mice was alleviated by shikonin, and the infiltrated inflammatory cells and collagen deposition in their lungs were reduced. Furthermore, the abnormal activation of extracellular signal-regulated kinase (ERK)/nuclear factor-κB (NF-κB) pathway and the elevation of matrix metalloproteinase 9 (MMP9) in the lung of asthmatic mice were suppressed by shikonin. The inactivation of NF-κB by shikonin was at least in part via inhibiting IκBα activation. In vitro, the treatment of shikonin inhibited the platelet-derived growth factor (PDGF)-induced proliferation of primary airway smooth muscle cells (ASMCs), and induced a G0/G1 arrest in these cells. In addition, ASMCs exposed to PDGF acquired an enhanced migratory ability, and the activities of MMP9 and matrix metalloproteinase 2 (MMP2) and expression of MMP9 of these cells were significantly up-regulated. These PDGF-induced alterations were also inhibited by shikonin. The inhibitory effects of shikonin on the proliferation and migration of ASMCs were comparable to pyrrolidinedithiocarbamate (PDTC), an inhibitor of NF-κB pathway. In conclusion, the present study sheds lights on how shikonin alleviates allergic airway remodeling.