Objective To establish a mouse model of acute lung injury ( ALI) and pulmonary fibrosis by low dose lipopolysaccharide ( LPS) intermittent intraperitoneal injection, and to explore the pathogenesis of ALI and pulmonary fibrosis induced by endotoxin. Methods Forty C57BL/6 mice were randomly divided into a control group, a 3-days LPS group, a 2-weeks LPS group, and a 4-weeks LPS group,with 10 mice in each group. LPS was injected intraperitoneally at dose of 5 mg/ kg for three consecutive daysin the three LPS groups. Equivalent normal saline was injected by the same way in the control group. The mice lung tissues were obtained respectively 3 days ( the control group and 3-days LPS group) , 2 weeks ( the 2-weeks LPS group) , and 4 weeks ( the 4-weeks LPS group) after LPS or saline stimulation. HE staining,Van-Gieson collagen staining, and Ashcroft fibrosis score assessment were applied to evaluate the development of inflammation and fibrosis in lung tissue at various stages of ALI after LPS-stimulation. The mRNA expression of type Ⅰ procollagen and alpha smooth muscle actin ( α-SMA) were detected by realtime PCR. The deposition of collagen and fibrosis in lung tissue were detected by hydroxyproline assay. The survival condition of each group was also recorded. Results Acute inflammation occurred in mice lung tissue 3 days after intraperitoneal injection of LPS. Collagen deposited in pulmonary interstitium2 weeks afterLPS-stimulation and formed typical pulmonary interstitial fibrosis 4 weeks later accompanying with increase of Ashcroft fibrosis score. Real-time PCR and hydroxyproline assay showed that the expression of collagen and α-SMA increased 3 days after LPS-stimulation and reached the peak 4 weeks later. The animals were all survived up to the endpoint of experiment. Conclusions Accompanying with inflammation, pulmonary fibrosis initiated at early stage of ALI induced by LPS. Intraperitoneal injection of LPS at dose of 5 mg/kg for three consecutive days was able to establish the mouse model of ALI and pulmonary fibrosis with high successrate and low animal mortality, which provide an ideal experimental platform for further investigation.
