[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.目的： 研究中性粒细胞外陷阱（NETs）在程序性细胞死亡受体-1（PD-1）抑制剂相关心肌炎中的作用，探索靶向NETs的免疫检查点抑制剂相关心肌炎（ICIAM）治疗靶点。 方法： 选6周龄健康雄性BALB/c小鼠30只，分别编号并随机分为对照组（n=10）、模型组（n=10）和治疗组（n=10）。除对照组外，分别于第1和7天给小鼠皮下注射100 μl含有250 μg小鼠心肌肌钙蛋白I（TnI）肽段的弗氏完全佐剂（CFA）。第8天起每2天腹腔注射一次PD-1抑制剂（15 μg/只），共5次。PF-1355治疗组从造模开始前1天起连续16 d腹腔注射PF-1355（50 mg·kg-1·d-1）。观察各组小鼠一般状态，实时荧光定量聚合酶链式反应（RTFQ-PCR）评估中性粒细胞相关趋化因子、NETs和焦亡相关因子、促炎细胞因子的转录水平调控，免疫组化、免疫荧光检测和蛋白质印迹法反映焦亡相关分子的蛋白水平变化，超声心动图展示主要心功能指标改变，心肌病理对比炎性浸润程度。 结果： 模型组小鼠较对照组小鼠心肌NETs免疫荧光强度明显增加（2.49±0.08和0.99±0.26，P<0.001）。模型组心肌组织焦亡相关NOD样受体热蛋白结构域相关蛋白3（NLRP3）、剪切的含半胱氨酸的天冬氨酸蛋白水解酶（cleaved-Caspase 1）、含半胱氨酸的天冬氨酸蛋白水解酶1（Caspase 1）、剪切的Gasdermin-D（cleaved-GSDMD）、Gasdermin-D（GSDMD）、白细胞介素-1β（IL-1β）和白细胞介素-18（IL-18）的蛋白表达水平较对照组上调（均P<0.05）。PF-1355治疗后，相比于模型组，治疗组小鼠左心室射血分数（LVEF）（73.58%±5.31%和58.12%±3.19%，P<0.001）、左室缩短分数（LVFS）（39.78%±4.31%和33.89%±2.19%，P<0.001）升高；苏木精-伊红染色结果显示与模型组相比，治疗组炎性浸润面积百分比减少（30.12%±3.57%和14.92%±2.46%，P<0.001）；治疗组免疫荧光NETs生成较模型组减少（2.52±0.04和1.03±0.05，P<0.001）；治疗组NLRP3等焦亡相关分子水平较模型组下调（均P<0.05）。 结论： 在PD-1抑制剂相关的心肌炎中，NETs通过激活NLRP3炎症小体导致心肌细胞焦亡。特异性髓过氧化物酶抑制剂PF-1355通过调控NETs来下调NLRP3炎症小体激活，可能进一步挽救和逆转NETs介导的心肌焦亡损伤。.