Abstract: Abstract: Objective To investigate the effect of neutrophil extracellular traps (NETs) on inflammation of rheumatoid arthritis (RA), especially angiogenesis. Methods The presence of NETs in synovial tissues of RA and osteoarthritis (OA) was observed by immunofluorescence assay. Neutrophils were isolated from peripheral blood of health volunteers. Neutrophils were cultured in vitro, the formation of NETs was observed. NETs were extracted as a stimulating agent. The effects of NETs on the proliferation of human umbilical vein endothelial cells (HUVECs) and synovial fibroblasts (RAFLS) were evaluated by MTT, and which were classified into two groups: HUVECs group and RAFLS group, with the following treatment: control and NETs (0.28 mg/L). Wound repair assay was employed to evaluate the effect on the cell migration stimulated with NETs. The experiment was divided into three groups: control, VEGF (40 μg/L VEGF) and NETs (0.28 mg/L NETs). Results (1) Compared with OA, NETs were found more in the synovial tissue of RA. (2) NETs formation was induced by stimulator in vitro. The concentration of extracted NETs- DNA was 27.8 mg/L. (3) MTT assay showed that compared with the control groups, low concentration of NETs (0.28 mg/L) promoted the proliferation of HUVECs (0.499 ± 0.011 vs. 0.393 ± 0.009, P＜0.05) and RAFLS (0.266 ± 0.007 vs. 0.192 ± 0.007, P＜0.05). (4) It was showed that a significant wound closure induced by low concentration of NETs (0.28 mg/L) was found compared with control. Conclusion Our present study suggests that NETs are found more in the synovial tissue of RA, and low concentration of NETs can promote angiogenesis in RA.

Key words: arthritis, rheumatoid, osteoarthritis, synovial membrane, fibroblasts, endothelial cells, neutrophil
extracellular traps, angiogenesis