To observe the protective effect of baicalin on bleomycin-induced pulmonary fibrosis in mice and its mechanism.

Totally 18 mice were divided into a control group, a bleomycin group and a baicalin group, with 6 mice in the each group. Mice in the bleomycin group and baicalin group were intratracheally administered with bleomycin (5 mg/kg) to establish a model of pulmonary fibrosis, and those in the control group were given the same volume of isotonic NaCl solution. Three days after modeling, mice in the baicalin group were intraperitoneally injected with baicalin (25 g/kg), while those in the control group and bleomycin group were given the same volume of isotonic NaCl solution every other day for 25 days. Then mice were sacrificed after 28 days of modeling. The hatmatoxylin-eosin (HE) staining and Masson staining were used to observe the severity of inflammation and fibrosis in the lung tissue. The pulmonary fibrosis score and hydroxyproline content were compared among the three groups. The messenger RNA (mRNA) expression levels of fibrilagen (Collagen 1a1, Collagen 3a1) and Wnt3a/β-catenin signal pathway related proteins [Wnt3a, matrix metalloproteinases-3 (MMP-3), MMP-9, Cyclin D1] were detected by real-time quantitative PCR (qPCR), and the expression levels of epithelial-mesenchymal transition (EMT) related proteins [Vimentin, alpha-smooth muscle actin (α-SMA)] and β-catenin were examined by Western-blotting.

Under the light microscope, the lung tissue was structurally intact and no inflammatory cell infiltration was observed in the control group; the lung tissue was structurally destroyed and inflammatory cells infiltrated, presenting diffuse pulmonary fibrosis in the bleomycin group; the inflammatory cell infiltration and pulmonary fibrosis in the baicalin group significantly reduced as compared with those in the bleomycin group. The pulmonary fibrosis score, hydroxyproline content, Collagen 1a1 mRNA, Collagen 3a1 mRNA, Wnt3a mRNA, MMP-3 mRNA, MMP-9 mRNA, Cyclin D1 mRNA, Vimentin, α-SMA and β-catenin all showed significant differences among the three groups (F = 12.012, 8.414, 46.224, 30.179, 85.912, 125.435, 19.521, 40.247, 72.731, 58.169, 70.471; all P < 0.001). Further pairwise comparison revealed that the above indicators in the bleomycin group were significantly higher than those in the control group, and the above indicators in the baicalin group were significantly lower than those in the bleomycin group (both P < 0.05).

Baicalin has protective effect on bleomycin-induced pulmonary fibrosis in mice, which may be related to the inhibition of Wnt3a/β-catenin signaling pathway and activation of EMT proteins.