[Experimental study on formation of neutrophil extracellular traps in human peripheral blood induced by paraquat in vitro]

To explore whether paraquat (PQ) can induce the formation of neutrophil extracellular traps (NETs) in human peripheral blood.

Neutrophils were isolated from healthy human peripheral blood, and the cells were identified by hematoxylin-eosin (HE) strain. The cells were treated with different concentrations of PQ [0 (as control), 200, 400, 600, 800, 1 000 and 1 200 μmol/L], and the cell viability was measured by cell proliferation and CCK-8 cytotoxicity detection kit, and the median lethal concentration of PQ was selected. The cells were treated with the median lethal concentration of PQ (PQ poisoning group), and the untreated cells were served as the control. Immunofluorescence staining was adopted to evaluate NETs formation. PicoGreen dye was used to determine the quantitative content of circulating free DNA. Western Blot was used to determine the expressions of citrullinated histone 3 (H3Cit) and myeloperoxidase (MPO) in the supernatant.

The purity of neutrophils was about 95% by HE staining. The cells were treated with different concentrations of PQ, and the result showed that the viability of cells was (58±2)% with 800 μmol/L PQ for treatment. The immunofluorescence showed that there were few expressions of H3Cit and MPO in neutrophils in the control group, and there was no NETs formation, which was composed of DNA, H3Cit and MPO. Compared with the control group, a large amount of NETs was generated from neutrophils stimulated by 800 μmol/L of PQ. Meanwhile, quantitative result showed that the content of cell free DNA in the supernatant was significantly increased in PQ poisoning group as compared with that of control group (μg/L: 2 235±462 vs. 561±87, P < 0.01). The protein expressions of H3Cit and MPO in the supernatant were also significantly increased as compared with those of control group [H3Cit protein expression (gray value): 0.23±0.03 vs. 0.11±0.01, MPO protein expression (gray value): 0.47±0.05 vs. 0.21±0.04, both P < 0.05].

800 μmol/L of PQ can induce the formation of NETs in human peripheral blood.