Protective effect of placental mesenchymal stem cells on lung injury in rats with severe acute pancreatitis and its mechanism

Objective　To investigate the protective effect and mechanism of placental-derived mesenchymal stem cells (P-MSCs) on lung injury in rats with severe acute pancreatitis. Methods　A total of 36 healthy adult male SD rats were randomly divided into control group (n=12), SAP group (n=12) and P-MSCs group (n=12). SAP rat model was established by retrograde injection of 4% sodium taurocholate into biliopancreatic duct. P-MSCs (1×10⁶ cells/100 g) were delivered through the tail vein of the rats at 6 h after the induction of SAP. The rats were sacrificed 12 and 24 h after P-MSCs infusion. The ratio of wet to dry weight of lung tissue and the number of neutrophils, leukocytes and macrophages in bronchoalveolar lavage fluid (BALF) was calculated. The degree of pancreatic and lung injury was evaluated by HE staining. The concentration of amylase, lipase and inflammatory factors in serum was measured by ELISA. The MPO activity in pancreas and lung tissue was measured by MPO assay kit, and the mRNA expression levels of TNF-α, IL-1β in lung tissue were detected by RT-qPCR. The ratio of M1 and M2 in lung tissue was detected by immunofluorescence stain. Results　Compared with SAP group, the ratio of wet to dry weight of lung tissue in P-MSCs group significantly decreased, the number of neutrophils, leukocytes and macrophages in BALF were significantly reduced (P<0.001). HE staining results showed that, compared with SAP group, the pathological injury of pancreas and lung tissue in P-MSCs group was significantly reduced (P<0.001). The results of ELISA showed that compared with SAP group, the levels of amylase, lipase, IL-1β, IL-6 and TNF-α in serum were significantly decreased, the level of IL-10 was significantly increased (P<0.001). Compared with SAP group, the concentration of MPO in pancreas and lung tissue were significantly reduced (P<0.001). Immunofluorescence staining results showed that the number of M1 type macrophages in the lung tissue of the P-MSCs group was significantly reduced, and the number of M2 type macrophages was significantly increased (P<0.001). Conclusion　P-MSCs can reduce the inflammatory injury of lung in SAP rats, and its protective mechanism may be related to the induction of M2 polarization in pulmonary macrophages. DOI: 10.11855/j.issn.0577-7402.2020.12.02