[Investigate the role of neutrophil extracellular traps in immune checkpoint inhibitor-associated myocarditis with programmed death protein-1 inhibitors involvement].

Objective: To investigate the role of neutrophil extracellular traps (NETs) in immune checkpoint inhibitor-associated myocarditis (ICIAM) with programmed death protein-1 (PD-1) inhibitors involvement, and to explore the therapeutic potential of targeting NETs in the treatment of ICIAM. Methods: Thirty 6-week-old male BALB/c mice were randomly divided into control group ( n =10), myocarditis group ( n =10), and treatment group ( n =10). Apart from the control group, each mouse was subcutaneously injected with 100 μl of complete Freund's adjuvant containing 250 μg of mouse cardiac troponin I peptide on the 1st and 7th day. Starting on the 8th day, PD-1 inhibitor (15 μg/per mouse) was intraperitoneally injected every other day for a total of 5 times. Since 1 day before the beginning of PD-1+TnI injection, the treatment group was injected with PF-1355 (50 mg·kg-1 ·d-1 ) for 16 consecutive days. The mice's general state was observed during the whole process. Real-time fluorescence quantitative PCR (RTFQ-PCR) was carried out to evaluate the transcriptional regulation of neutrophil related chemokines, NETs, pyronecrosis related factors and proinflammatory cytokines. Immunohistochemistry, immunofluorescence and western blot were applied to determine the changes of pyrosis related molecules. Echocardiography showed the differences of main cardiac indexes while cardiac pathology compared the degree of inflammatory infiltration in 3 gruops. Results: The immunofluorescence intensity of myocardial NETs in the myocarditis group was significantly increased compared to the control group mice (2.49±0.08 and 0.99±0.26, P <0.001). The protein expression levels of pyroptosis-related NLRP3, cleaved-Caspase 1, Caspase 1, cleaved-GSDMD, GSDMD, IL-1β and IL-18 in myocardial tissue of the model group were higher than those of the control group (all P <0.05). After treatment with PF-1355, compared to the myocarditis group, the left ventricular ejection fraction (LVEF) (73.58%±5.31% and 58.12%±3.19%, P <0.001) and left ventricular fraction shortening (LVFS) (39.78%±4.31% and 33.89%±2.19%, P <0.001) increased. H-E staining showed a reduction in inflammatory infiltration area in the treatment group compared to the myocarditis group (30.12%±3.57% and 14.92%±2.46%, P <0.001). The immunofluorescence intensity of NETs decreased in the treatment group compared to the myocarditis group (2.52±0.04 and 1.03±0.05, P <0.001). The levels of NLRP3 and other pyroptosis-related molecules were downregulated in the treatment group compared to the myocarditis group (all P< 0.05). Conclusions: NETs lead to myocardial cell pyroptosis by activating the NLRP3 inflammasome in PD-1 inhibitor-associated myocarditis. The specific MPO inhibitor PF-1355 shows a therapeutic potential by regulating the formation of NETs, decreasing NLRP3 level and relieving myocardial pyroptosis, thus reducing myocardial damage.