The present study discovered that the pyroptosis and pyroptosis-associated proteins NLRP3, ASC, and caspase-1 were increased in lung tissue after MIRI. Pre-treatment with ticagrelor significantly attenuated these alterations.
A number of studies have shown that MIRI was able to induce ALI in rat models, which is consistent with our results[4, 5, 22, 23]. The lung appeared to be the frailest organ influenced by MIRI. Triggered by the clinical phenomenon of high pulmonary infection incidence in patients with AMI, we further investigated the MIRI-induced pyroptosis in the lungs. Organs’ ischemia-reperfusion injury is known to increase the local expression of pyroptosis[24, 25]. However, studies that evaluate one organ ischemia-reperfusion-induced pyroptosis in another organ are rare. Zhao et al. revealed that renal ischemia-reperfusion induced ALI and pyroptosis in lungs, while similar results were found in limb ischemia-reperfusion . Hailin and colleagues also showed that renal graft ischemia–reperfusion injury could lead to pyroptosis in the remote liver. In the present study, we found that pyroptosis occurred in lungs after MIRI, and the following two features might explain this observation. First, MIRI produced circulating cellular debris, which was recognized as a damage-associated molecular pattern, which activated NLRP3 and its downstream signaling pathway. Second, MIRI generated pro-inflammatory cytokines, including TNF, that might also induce NLRP3-associated pyroptosis. Thus, targeting these features may reduce the lung damage after MIRI. Further evaluation of the molecular mechanism is required.
Similar to our findings, previous studies found that ticagrelor attenuated NLRP3 in other animal models. Yochai and colleagues showed that after treating diabetic ZDF rats with ticagrelor (150 mg/kg daily) for 3 days following MIRI, the level of NLRP3 mRNA was significantly reduced in the ticagrelor group than the control, and ticagrelor reduced the caspase-1 expression in cardiomyocyte as detected by immunoblots. Later, Huan conducted ticagrelor management of daily 100 mg/kg administrations for 12 weeks in mice with type 2 diabetes mellitus, and found that ticagrelor reduced the myocardial NLRP3, caspase-1, and GSDMD-N levels, and attenuated the progress of diabetic cardiomyopathy. Notably, compared with SD rats, diabetes mellitus rats have more interaction with pyroptosis. For this reason, the effect of ticagrelor in diabetes mellitus rats might be attenuated in SD rats, and caution should be exercised when extrapolating to SD rats. Regarding nondiabetic research, Claudia and colleagues conducted a MIRI model and showed that ticagrelor administration for 3 days (150 mg/kg daily) reduced the myocardial expression of NLRP3 and protected the heart. The effects disappeared when isolated myocardial cells were treated. Thus, they concluded that ticagrelor may impart protective effects on the heart through platelets instead of targeting the myocardium directly. This result partly contrasts with the research from another study that showed 50 mg/kg of ticagrelor inhibited the activation of NLRP3 inflammasome by attenuating the oligomerization of ASC in macrophages, and reduced inflammation, including IL-1β, in alum-induced peritonitis and lipopolysaccharide-induced sepsis mice models independent of the P2Y12 signaling pathway. The differences might be due to the methodology, which mainly involved the myocardium in the former study versus macrophages, peritoneal cavity lavage fluid, and serum sample in the latter study. This notion indicates ticagrelor has diverse pathways regulating NLRP3 inflammasome in tissues and cells, and thus indicates the need for assessing ticagrelor in various models. Our study reported ticagrelor-reduced NLRP3 depended on pyroptosis in lung tissue. The dosage of 30 mg/kg and 100 mg/kg ticagrelor was hypothetically generated on the basis of this concentration attenuating ALI, and the doses were relatively low when compared to the aforementioned studies.
This study also has some limitations. First, we built the 120-minute ischemia and following 30-minute reperfusion protocol, which was a common protocol to establish MIRI, and a previous study observed apoptosis in lungs using this protocol. However, other timepoints for building a MIRI-induced lung pyroptosis model were not assessed. Second, the interaction between apoptosis and pyroptosis was not investigated in this study. Third, we only preliminarily revealed the association between MIRI and pyroptosis; the molecular mechanism needs to be further explored.