Abstract: Objective: To investigate the protective effect of Lyophyllum ulmarium fibrinolytic enzyme (LUFE) on inflammatory injury induced by lipopolysaccharide (LPS) in vascular endothelial cells. Methods: An in vitro inflammation model was created by stimulating human umbilical vein endothelial cells (HUVEC) with LPS. The HUVEC were divided into five groups including control, model and low-, medium- and high-dose LUFE groups. The survival rate of HUVEC was determined by MTT assay. The levels of lactate dehydrogenase (LDH) activity, tumor necrosis factor α (TNF-α), interleukin 6 (IL-6), E-selectin and monocyte chemoattractant protein 1 (MCP-1) in the cell culture supernatant were investigated by enzyme-linked immunosorbent assay (ELISA). The Hoechst method was adopted to observe the adhesion between HUVEC and human acute monocytic leukemia cell line-1 (THP-1). The expression of intercellular cell adhesion molecule 1 (ICAM1) in HUVEC was detected by flow cytometry. Western blot assay was used to detect the expression and activation of toll-like receptor 4 (TLR4), mitogen-activated protein kinase (MAPK) and the major proteins involved in the nuclear factor κB (NF-κB) signaling pathway including myeloid differentiation factor 88 (MyD88), transforming growth factor β activated kinase 1 (TAK1) and phosphorylated TAK1 (p-TAK1). Results: LUFE inhibited the LPS-induced increase in the levels of LDH, TNF-α, IL-6, E-selectin and MCP-1 in the culture supernatant of HUVEC, decreased the expression level of ICAM-1, and reduced the adhesion of HUVEC to THP-1. Compared with the model group, the levels of TLR4 and MyD88, p-TAK1/TAK1 ratio, the ratio of phosphorylated c-Jun N-terminal kinase (p-JNK) to JNK, the ratio of phosphorylated protein-38 (p-p38) to p38, and the ratio of phosphorylated NF-κB (p-NF-κB) to NF-κB in all three LUFE treatment groups were significantly reduced (P < 0.05). Conclusion: LUFE has a protective effect on inflammatory injury in HUVEC, and its underlying mechanism may be though inhibiting the TLR4/MyD88/TAK1/NF-κB signaling pathway and the MAPK signaling pathway and thereby reducing the level of inflammatory factors.

Key words: Lyophyllum ulmarium fibrinolytic enzyme; lipopolysaccharide; endothelial cell; inflammation