This review establishes neutrophil extracellular traps (NETs) as central drivers of abdominal aortic aneurysm (AAA) progression, a life-threatening condition lacking effective drug therapies. It synthesizes groundbreaking evidence showing how NETs actively degrade the aortic wall by killing vascular muscle cells, amplifying inflammation, and promoting blood clots within the aneurysm. Crucially, we identify NET components (e.g., citrullinated histone H3) as novel diagnostic and prognostic biomarkers linked to aneurysm growth and rupture risk. Furthermore, the work highlights promising NET-targeting therapeutic strategies—including inhibitors of NET formation, degraders of existing NETs, and microbiome modulators—that significantly reduce AAA progression in preclinical models. By defining NETs as fundamental mediators and actionable targets, this review provides a transformative framework for developing the first pharmacological interventions to stabilize AAA, addressing a major unmet clinical need.

Abdominal aortic aneurysm (AAA), a potentially life-threatening dilation of the infrarenal aorta, characterized by progressive inflammatory infiltration, extracellular matrix degradation, and vascular smooth muscle cell (VSMC) depletion [1–3]. With no effective pharmacotherapies available, rupture carries a high mortality rate [4–6]. Inflammation is a recognized cornerstone of AAA pathogenesis, which operates within a complex interplay of genetic predisposition, biomechanical stress, metabolic disease, and environmental factors such as smoking, and involves innate and adaptive immune cells [7–9]. Traditionally viewed as first responders, neutrophils contribute to host defense beyond phagocytosis via a distinct process known as Neutrophil extracellular trap (NET) formation, or NETosis [10–12]. NETs, released by neutrophils, are web-like structures composed of decondensed chromatin decorated with cytotoxic granular proteins such as myeloperoxidase (MPO), neutrophil elastase (NE), and citrullinated histone H3 (CitH3), which function to ensnare pathogens [13–15]. Emerging translational and clinical evidence implicates neutrophil extracellular traps (NETs) as potential driver of AAA progression. It is important to note, however, that while these associations are compelling, the causal role of NETs in human AAA pathogenesis is still being delineated, with much of the mechanistic insight derived from preclinical models. Components of NETs, such as CitH3, cell-free DNA (cfDNA), and NE, are significantly elevated in both the plasma and tissues of AAA patients, and these elevations correlate with aneurysm size, growth rate, and severity [16–18]. Histologically, NETs localize within the aortic wall and intraluminal thrombus (ILT), where they mediate multifaceted damage [19, 20].

This review synthesizes evidence establishing NETs as fundamental drivers of AAA pathogenesis. It will specifically examine the molecular and cellular mechanisms by which NETs cause ECM degradation, induce VSMC death (apoptosis, ferroptosis) and phenotypic switching, amplify inflammation (cytokine cascades, pDC activation), and drive metabolic/epigenetic dysregulation. Systemic factors (gut dysbiosis, thromboinflammation) amplifying NETosis are explored. The translational potential of NET components as biomarkers and emerging NET-targeting therapeutic strategies are critically evaluated. Finally, challenges in translating these discoveries to meet the unmet clinical need in AAA management are addressed.

NETosis can be classified by stimulus (microbial vs. sterile), cellular outcome (lytic/suicidal vs. vital), and molecular pathway (NADPH oxidase-dependent vs. -independent). In the context of AAA, sterile inflammation-induced and thromboinflammatory NETosis are particularly relevant, driven by DAMPs, cytokines, and platelet-neutrophil interactions. A detailed summary of NETosis classifications is provided in Supplementary Table S1.

NETs actively promote the formation of ILT within AAA. Once established, the ILT functions as a dynamic repository, accumulating high concentrations of NET-derived components, such as DNA, CitH3, NE, MPO, and various proteases [10, 34]. This thrombotic niche fosters a potent pro-inflammatory microenvironment. Through the release of neutrophil-attracting chemokines, such as CXCL1 and CXCL8, the ILT recruits additional neutrophils to the site [19, 35]. This sustained neutrophil influx perpetuates NETosis and drives continuous degradation of the vascular wall. Notably, the ILT concentrates NET components to extraordinary levels. For instance, CitH3 accumulates within the thrombus at concentrations up to 30-fold higher than those found in the adjacent aortic wall [13, 18]. This concentrated reservoir serves as a potent platform for activating pDCs, stimulating robust type I IFN production, and thereby amplifying vascular inflammation [36].

The central role of the ILT in driving NETosis-dependent pathology is underscored by the differential efficacy of NETosis inhibitors. Pharmacological agents targeting NET formation, such as PAD4 inhibitors, demonstrate significantly enhanced efficacy in attenuating AAA progression in experimental models possessing an ILT [27, 31]. These highlight the ILT not merely as a pathological feature, but as a crucial therapeutic target within the NETosis-amplifying cascade of AAA.

Circulating levels of key NET biomarkers—including CitH3, cfDNA, MPO, and NE—show strong correlations with established AAA risk factors and adverse clinical outcomes. Specifically, these biomarkers demonstrate significant associations with both AAA maximum diameter and annual expansion rate [16–18, 30, 37]. It is worth noting that Eilenberg et al. reported that elevated CitH3 levels are a predictive indicator for accelerated AAA growth [18].

NET components are consistently found at significantly higher concentrations within the AAA wall tissue and, in particular, are localized within the ILT [18–21, 26, 31, 37]. Furthermore, advances in molecular profiling, utilizing machine learning and multi-omics analyses, have identified distinct NET-related gene expression signatures (e.g., involving DUSP26, FCN1, MTHFD2, GPRC5C, SEMA4A, CCR7). These signatures hold considerable diagnostic potential as novel tools for predicting the likelihood and trajectory of AAA progression [33].

NET-derived biomarkers demonstrate significant promise as tools for monitoring responses to therapeutic interventions in AAA. Pharmacological strategies targeting NETosis—including PAD4 inhibitors (e.g., YW3-56), DNase1, resolvin D1, and PDK inhibitors (e.g., dichloroacetate, DCA)—consistently attenuate AAA progression in preclinical models. This therapeutic efficacy is paralleled by a measurable reduction in circulating NET biomarker levels, such as CitH3, cfDNA, and NE [5, 18, 19, 21, 23, 28, 31, 38]. Clinically, CitH3 levels decrease significantly following successful surgical AAA repair, underscoring their potential utility in tracking post-interventional outcomes [18]. Furthermore, emerging NET-targeting nanomedicine approaches (e.g., GlycoRNA nanoparticle-delivered siMT1 [GlycoRNA-NP-siMT1], lactoferrin-coated calcium dipicolinate nanoparticles [LaCD NP]) effectively reduce disease progression in preclinical AAA models [5, 38]. In these studies, the concomitant reduction in NET biomarkers serves as a critical quantitative readout for assessing treatment efficacy.

Despite these promising diagnostic and prognostic associations, the clinical translation of NET-derived biomarkers faces several challenges. Circulating levels of markers such as CitH3, cfDNA, MPO, and NE show marked heterogeneity across studies, influenced by variations in sample processing, detection methodologies, and patient cohort characteristics. The lack of standardized, validated assays and universally accepted clinical cut-off values currently prevents their routine application in clinical decision-making. Therefore, large-scale, multi-center prospective studies are crucial to harmonize detection protocols and definitively establish the utility of these biomarkers for risk stratification and monitoring therapeutic responses.

Metallothionein 1 (MT1) is significantly upregulated within human and murine AAA lesions, where it actively promotes NET formation [5]. To counteract this, glycoRNA-conjugated nanoparticles delivering MT1-targeting siRNA (GlycoRNA-NP-siMT1) achieve site-specific delivery to aneurysmal tissue. This nanotherapeutic platform effectively suppresses NET generation, pathological vascular remodeling, and aortic dilation through dual mechanisms: competitively inhibiting neutrophil infiltration while directly silencing pathogenic MT1 expression within inflammatory cells [5]. Parallel strategies target the proteolytic cascade centered on dipeptidyl peptidase I (DPPI/Cathepsin C), which activates NE and PR3 to drive NET release. Genetic deficiency in either DPPI or its downstream effectors confers protection against experimental AAA, confirming their non-redundant role in NET-driven pathogenesis [20]. Crucially, NE executes dual functions in this process—facilitating NET chromatin decondensation through histone degradation while independently contributing to extracellular matrix destruction within the aortic wall [5, 20].

The clinical translation of NET-targeting therapies faces significant hurdles. Current preclinical models—particularly acute angiotensin II infusion in mice which induces AAA over weeks—fail to adequately recapitulate the slow, smoldering inflammation that characterizes human AAA progression over years or decades [41–43]. Further complicating translation, the therapeutic efficacy of many NET inhibitors is thrombus-dependent, necessitating validation in models that faithfully mimic human disease progression timelines.

Therapeutic specificity and safety remain paramount. Furthermore, the therapeutic suppression of NETosis raises legitimate concerns regarding the impairment of innate antimicrobial defense. Systemic inhibition of neutrophil function, for instance via PAD4 blockade or DNase administration, could potentially increase susceptibility to infections. Therefore, achieving cell- and context-specificity—for example, through localized delivery systems such as nanoparticles or the development of inhibitors targeting disease-specific NET components—is paramount to maximizing safety. Patient stratification based on infection risk and immunocompetence will also be a crucial consideration for future clinical application. While PAD4 inhibitors show promise due to functional redundancy in host immunity, targeting downstream effectors (e.g., SMC ferroptosis pathways) may offer superior safety profiles.

NET heterogeneity—driven by stimulus-specific activation, disease stage, and anatomically distinct microenvironments—demands precision interventions tailored to individual pathological contexts [44–46]. Validation of NET biomarkers (e.g., CitH3, cfDNA) through large-scale longitudinal clinical studies is imperative for robust diagnostic and prognostic applications. Spatially resolved multi-omics approaches combined with advanced molecular imaging (e.g., Ly6G-NP-MPI) will enable comprehensive mapping of NET spatiotemporal dynamics within AAA microenvironments.

Future success will require: (1) Combinatorial strategies concurrently targeting NETs and complementary pathogenic pathways (e.g., MMPs, cytokine networks, renin-angiotensin signaling), (2) Prioritization of interventions for established aneurysms rather than prevention-only paradigms, and (3) Identification of NET-driven patient endotypes (e.g., high-CitH3 phenotypes, rapid progressors) to enable personalized therapeutic stratification.

The promising preclinical data now necessitate a decisive transition to clinical validation. Future success is contingent upon initiating early-phase human trials to evaluate the safety, tolerability, and bioactivity of NET-inhibiting agents. These studies should prioritize patient populations with a high unmet need, such as those with rapidly expanding aneurysms, and utilize the emerging NET-related biomarkers (e.g., plasma CitH3) for patient enrichment and pharmacodynamic assessment.

NETs are emerging as key regulators within the multifactorial network of AAA pathogenesis, integrating neutrophil activation with SMC death, ECM degradation, inflammation, thrombosis, and metabolic reprogramming. Their consistent detection in human AAA tissues and circulation, coupled with strong correlations to disease severity and expansion, underscores their clinical relevance. Preclinical strategies targeting NET formation, degradation, and their downstream effects demonstrate robust efficacy in attenuating AAA progression, with nanotechnology offering promising avenues for enhanced site-specific delivery.

Despite this promise, translating these findings necessitates focused future efforts. First, the clinical utility of NET-derived biomarkers requires validation in large-scale, longitudinal cohorts to establish standardized thresholds for risk stratification. Second, the refinement of targeted delivery systems is crucial to maximize therapeutic efficacy while minimizing systemic impact on host defense. Third, combination therapies concurrently targeting NETs and complementary pathways (e.g., MMPs, renin-angiotensin system) should be explored to achieve synergistic effects in established aneurysms. Finally, identifying NET-driven patient endotypes will be essential for personalizing therapeutic interventions. By addressing these priorities, NETosis inhibition can evolve from a compelling preclinical concept into a viable clinical strategy for stabilizing AAA.