A Review of the Impact of Neutrophils and Neutrophil Extracellular Traps (NETs) on the Development of Aortic Aneurysms in Animal and Human Studies

The pathogenesis of the aortic aneurysm (AA) includes several mechanisms, such as chronic sterile inflammation and homeostasis imbalance, with arteriosclerosis, hemodynamic forces, and genetic factors. In addition to the roles of these processes in the development of AA, neutrophilic activity may play a pivotal role (mostly in inflammation and thrombus formation). Neutrophils, which play a crucial role in innate immunity, can release neutrophil extracellular traps (NETs), one of the mechanisms against fighting pathogens, beside phagocytosis and degranulation. NETs are structures composed of nuclear elements (eg, chromatin and modified histones) and granular and cytoplasmic components, which can lead to inflammation and coagulation changes. In addition, the exacerbation of NETosis (the process of NET formation) can be noticed in vascular diseases, including in the development of AA and myocardial infarction and in diabetes, hypertension, and COPD, which are the risk factors of the presence of AA. The discharge of NETs, which are extracellular materials formed by citrullinated histones (Cit-H), cell-free DNA fibers (cf-DNA), and granular and cytoplasmic molecules, is a newly identified method of neutrophil activation that can be activated by endogenous inflammatory stimuli, which contribute to AA development. Cit-H and cf-DNA can be used as biomarkers of AA growth. By understanding the neutrophilic influence of NET release, a new pathway of screening AA growth (by measurement of biomarkers of NETosis) and pharmacological assessment (by repression of NET formation) can be developed. This review summarizes the current knowledge about the influence of NETs on AA growth in human and animal studies.