Baicalin alleviates bleomycin-induced pulmonary fibrosis and fibroblast proliferation in rats via the PI3K/AKT signaling pathway

Baicalin is an important flavonoid compound THAT is isolated from the Scutellaria baicalensis Georgi Chinese herb and plays a critical role in anti-oxidative, anti-inflammatory, anti-infection and anti-tumor functions. Although baicalin can suppress the proliferation of tumor cells, the underlying mechanisms of baicalin in bleomycin (BLM)-induced pulmonary fibrosis remain to be elucidated. Thus, the aim of the present study was to determine the role of baicalin in pulmonary fibrosis and fibroblast proliferation in rats. Hematoxylin and eosin (H&E) and Masson staining were used to measure the morphology of pulmonary fibrosis, ELIASA kits were used to test the ROS and inflammation, and western blotting and TUNEL were performed to study the apoptosis proteins. In vitro, MTT assay, flow cytometry, western blotting and immunofluorescence were performed to investigate the effects of baicalin on proliferation of fibroblasts. The most significantly fibrotic changes were identified in the lungs of model rats at day 28. Baicalin (50 mg/kg) attenuated the degree of pulmonary fibrosis, and the hydroxyproline content of the lung tissues was decreased in the baicalin group, compared with the BLM group. Further investigation revealed that baicalin significantly increased glutathione peroxidase (GSH-px), total-superoxide dismutase (T-SOD) and glutathione (GSH) levels, whilst decreasing that of serum malondialdehyde (MDA). TUNEL-positive cells were significantly decreased in rats treated with baicalin group, compared with the model group. Furthermore, it was found that BLM promoted fibroblasts viability in a dose-dependent manner in vivo, which was restricted following treatment with different concentrations of baicalin. Moreover, BLM promoted the expression levels of cyclin A, D and E, proliferating cell nuclear antigen, phosphorylated (p)-AKT and p-calcium/calmodulin-dependent protein kinase type. BLM also promoted the transition of cells from the G(0)/G(1) phase to the G(2)/M and S phases, and increased the intracellular Ca2+ concentration, which was subsequently suppressed by baicalin. Collectively, the results of the present study suggested that baicalin exerted a suppressive effect on BLM-induced pulmonary fibrosis and fibroblast proliferation.