Neutrophils and NETosis in polycystic ovary syndrome: unraveling the immuno-metabolic thromboinflammatory axis.

Introduction: a new inflammatory paradigm in PCOS
Polycystic ovary syndrome (PCOS) has long been characterized by its classical triad—hyperandrogenism, oligo-anovulation, and polycystic ovarian morphology [1, 2]. Beyond these defining features, a growing body of clinical and biochemical evidence indicates that PCOS is frequently accompanied by chronic low-grade inflammation, metabolic stress, and increased cardiometabolic risk [3, 4]. Elevated circulating inflammatory markers, including C-reactive protein and leukocyte counts, have been consistently reported in PCOS populations, even after adjustment for adiposity [5, 6], suggesting that inflammatory processes may contribute to disease expression rather than merely reflect obesity-related confounding.
Within this context, neutrophils—the most abundant innate immune cells—have attracted increasing attention as potential mediators linking endocrine disturbance, metabolic dysregulation, and vascular dysfunction [7]. Unlike adaptive immune cells, neutrophils respond rapidly to metabolic and hormonal cues, including hyperinsulinemia, androgen excess, and adipose-derived cytokines [8]. This responsiveness positions neutrophils as plausible sensors and amplifiers of the inflammatory milieu observed in PCOS.
However, it is important to emphasize that direct mechanistic evidence defining neutrophil extracellular trap (NET) formation—a process in which neutrophils expel their DNA and associated proteins into the extracellular space—as a causal driver of PCOS pathology remains limited. While several studies report altered neutrophil counts, activation markers, and oxidative stress parameters in PCOS, most available data are cross-sectional, underpowered, and heterogeneous with respect to PCOS phenotypes. Moreover, many detailed insights into NET-mediated endothelial injury, platelet–neutrophil interactions, and thrombo-inflammatory signaling derive from studies in sepsis, diabetes, cardiovascular disease, and cancer.
Accordingly, this review explicitly distinguishes findings demonstrated in PCOS cohorts from mechanistic frameworks inferred from related inflammatory conditions. We present neutrophil- and NET-centered pathways as biologically plausible contributors to PCOS-associated metabolic, reproductive, and vascular dysfunction, rather than as established pathogenic drivers. By integrating PCOS-specific evidence with cautiously extrapolated mechanistic insights, this review aims to provide a structured conceptual framework to guide future hypothesis-driven research into the immuno-metabolic dimensions of PCOS.

Neutrophils as frontline effectors in metabolic and reproductive inflammation

Neutrophil activation signatures in PCOS
In women with PCOS, routine hematological indices reveal an activated neutrophil phenotype, characterized by elevated absolute neutrophil counts and increased neutrophil-to-lymphocyte ratios (NLR) compared with healthy controls—even after adjusting for age and BM [9, 10]. Beyond serving as a nonspecific inflammatory marker, this hematologic signature mirrors systemic neutrophil priming driven by hormonal and metabolic perturbations [11]. A study involving 266 women with PCOS demonstrated a positive correlation between NLR and free testosterone and an inverse association with HDL cholesterol, linking neutrophil activation not merely to inflammation, but to androgen excess, dyslipidemia, and cardiometabolic risk [12]. Collectively, these findings support the concept that persistent neutrophil activation and delayed apoptosis establish a chronic inflammatory setpoint that predisposes to both ovarian and systemic dysfunction.
Mechanistically, the metabolic milieu of PCOS constitutes an ideal pro-inflammatory incubator for neutrophil activation [5]. Hyperinsulinemia, a hallmark of PCOS, enhances neutrophil oxidative burst and prolongs survival through PI3K/Akt and MAPK signaling, while androgen excess further augments degranulation and reactive oxygen species (ROS) generation [13]. These stimuli converge to lower the activation threshold of circulating neutrophils, pushing them toward a pre-activated state even in the absence of overt infection. Functionally, such primed neutrophils exhibit enhanced expression of adhesion molecules (CD11b, CD62L), increased myeloperoxidase (MPO) release [14, 15], and exaggerated NETosis responses upon secondary stimulation [5].
Importantly, neutrophil dysregulation in PCOS does not occur in isolation, but is compounded by obesity and insulin resistance, which independently drive neutrophil activation [8, 16]. In obese and insulin-resistant states, neutrophils are among the first leukocytes to infiltrate expanding visceral adipose tissue, where they secrete IL-8, TNF-α, and elastase, establishing an early inflammatory niche that recruits monocytes and macrophages [5, 17]. This cellular infiltration precedes and sustains adipose macrophage polarization toward the pro-inflammatory M1 phenotype, perpetuating a self-reinforcing cycle of adipose tissue inflammation, lipotoxicity, and insulin resistance [18, 19]. Consequently, in PCOS—where obesity, insulin resistance, and hyperandrogenism frequently coexist—neutrophil activation becomes both a driver and a biomarker of metabolic derangement.
Beyond peripheral blood, recent studies suggest that this systemic neutrophil priming may extend to tissue compartments, including the ovary, endometrium, and vascular endothelium, where activated neutrophils release proteases, ROS, and NETs that alter local microenvironments [20, 21]. Such cross-compartmental activation links systemic metabolic stress to reproductive and vascular pathology, supporting a unifying hypothesis in which neutrophils serve as frontline effectors that translate metabolic imbalance into chronic inflammation.
In this context, elevated NLR in PCOS is not merely a clinical epiphenomenon but a quantifiable reflection of neutrophil-driven immuno-metabolic stress, heralding the transition from hormonal dysregulation to immune-mediated organ dysfunction.

Priming signals and cytokine milieu
Neutrophil activation in PCOS unfolds within a pro-inflammatory cytokine microenvironment characterized by elevated concentrations of interleukin-8 (IL-8), tumor necrosis factor-alpha (TNF-α), and interleukin-1β (IL-1β)—cytokines that collectively orchestrate neutrophil recruitment, priming, and effector activation [8]. In PCOS, the convergence of hyperandrogenism-driven adipokine dysregulation, insulin resistance, and macrophage infiltration sets up a permissive environment for neutrophil activation [22, 23]. These mediators, consistently reported in both serum and follicular fluid of women with PCOS, not only mark the systemic inflammatory tone but also provide critical directional cues that link metabolic stress to innate immune reprogramming [24].

Key cytokine mediators
Mechanistically, IL-8 (CXCL8) acts as a central chemotactic and activating ligand, engaging CXCR1/2 receptors on neutrophils to drive directed migration, degranulation, and integrin-mediated adhesion to vascular endothelium. Elevated IL-8 levels in PCOS are thus not epiphenomenal but functionally potent, amplifying neutrophil infiltration into adipose and ovarian tissue and facilitating local oxidative and proteolytic damage [25]. TNF-α, another key cytokine elevated in PCOS, sustains this activation loop by upregulating endothelial adhesion molecules (ICAM-1, VCAM-1, and E-selectin), thereby enhancing neutrophil tethering and transmigration. Moreover, TNF-α signaling via NF-κB extends neutrophil lifespan by delaying apoptosis, ensuring persistence of an activated neutrophil pool that perpetuates tissue-level inflammation [26, 27]. IL-1β, produced by inflammasome-activated macrophages and granulosa cells, further potentiates this process by inducing secondary cytokine waves and promoting endothelial activation, creating a self-reinforcing inflammatory circuit within the ovarian microenvironment [24, 28].

Neutrophil–adipose crosstalk
Beyond the systemic circulation, neutrophil–adipose crosstalk emerges as a critical amplifier of inflammation [29]. Adipocytes exposed to metabolic or oxidative stress secrete neutrophil-recruiting chemokines such as CXCL1 and CXCL2, along with dysregulated adipokines (leptin, resistin, visfatin), which directly prime neutrophils for enhanced reactive oxygen species (ROS) production and NET formation [30]. This axis becomes particularly pronounced in PCOS, where hyperandrogenism-driven adipocyte hypertrophy and insulin resistance create a cytokine-saturated, lipotoxic microenvironment that continuously recruits and activates neutrophils [31]. Simultaneously, adipose-resident macrophages—polarized toward an M1-like phenotype—release TNF-α and IL-6, further fueling neutrophil priming and sustaining the feed-forward cycle of adipose inflammation.

Bridging metabolic dysfunction and NETosis
The interplay of cytokines, adipokines, and neutrophils creates a permissive environment in which metabolic disturbances directly drive neutrophil activation and NET formation in PCOS. Hyperandrogenism, insulin resistance, and adipose inflammation do more than correlate with neutrophil priming—they establish the biochemical and oxidative conditions necessary for sustained NETosis and thrombo-inflammatory signaling. In this framework, neutrophils act as both sensors of metabolic stress and effectors of ovarian, endometrial, and vascular dysfunction, placing them at the nexus of PCOS-associated immuno-metabolic dysregulation.

Hormonal modulation of neutrophil function
Hormonal imbalances that define PCOS exert direct and indirect regulatory effects on neutrophil phenotype, lifespan, and effector functions, thereby shaping innate-immune responses at both systemic and tissue levels. Androgen excess—a cardinal feature of many PCOS phenotypes—has been linked to altered neutrophil biology in several experimental and clinical contexts [32]. Androgens act through the androgen receptor (AR) expressed on myeloid precursors and mature neutrophils to modify granulopoiesis, bone-marrow egress, and peripheral survival; experimental models and clinical observations report androgen-driven increases in circulating neutrophil numbers and altered functional programs, including enhanced tissue recruitment and changes in bactericidal function [33, 34]. These androgenic effects can therefore expand the pool of readily activatable neutrophils and alter their inflammatory potential in metabolic tissues [35].
At the level of cell survival, androgen signaling has complex, context-dependent consequences. Several mechanistic studies demonstrate that androgens modulate neutrophil apoptosis and maturation programs: by influencing transcriptional regulators and survival signaling (e.g., PI3K/Akt and MAPK cascades), androgens may delay apoptosis or alter effector differentiation under inflammatory stress, thereby sustaining a pro-inflammatory neutrophil compartment that can contribute to chronic tissue injury [36–38]. However, the literature is not uniform—some reports show androgen-associated functional impairment rather than simple hyperactivation—underscoring that androgen effects depend on dose, timing, and the systemic inflammatory milieu [36].
Female sex steroids also exert strong modulatory control over neutrophil redox balance and effector behavior. Estrogens (17β-estradiol) signal via classical ERα/ERβ and membrane-associated estrogen receptors on neutrophils to influence ROS generation, degranulation, chemotaxis, and NET formation [39–41]. Several experimental studies report that estradiol modifies neutrophil metabolic pathways and can both augment NETosis and reduce or alter ROS-mediated cytotoxicity depending on the stimulus and receptor context—a duality that likely reflects receptor subtype expression, local estrogen concentration, and interacting co-signals in tissue microenvironments [40]. Thus, relative estrogen deficiency or dysregulated estrogen signaling in PCOS can shift neutrophils toward a higher oxidative-stress and NET-prone phenotype in some settings, while in others estrogens appear to suppress specific migration or activation responses [42].
Progesterone provides an additional immunoregulatory layer: in pregnancy and other high-progesterone states, progesterone has been shown to downregulate neutrophil ROS production and temper inflammatory responses, in part via modulation of intracellular signaling and transcriptional programs in myeloid cells [43, 44]. Reduced or dysregulated progesterone signaling—as may occur with anovulation and luteal phase defects in PCOS—could therefore remove an important brake on neutrophil activation, facilitating heightened oxidative responses and tissue-level inflammation [43].
Taken together, dysregulated progesterone signaling in PCOS may remove a critical checkpoint on neutrophil activation, promoting enhanced ROS production and inflammatory priming. This pro-oxidative state creates a cellular environment highly permissive to the formation of neutrophil extracellular traps. The following section explores the molecular pathways through which neutrophils execute NETosis, highlighting how these mechanisms intersect with the heightened oxidative and inflammatory milieu characteristic of PCOS Table 1.

NETosis: the cytotoxic frontier of neutrophil activation

Molecular pathways of NETosis
The process of NET formation, or NETosis, represents a specialized effector response in which neutrophils externalize a meshwork of chromatin fibers decorated with histones, granular enzymes, and cytotoxic peptides. Canonically, NETosis proceeds through a highly orchestrated series of intracellular events involving chromatin decondensation, histone citrullination mediated by peptidylarginine deiminase 4 (PAD4), and the translocation of neutrophil elastase (NE) and MPO from cytoplasmic granules into the nucleus, culminating in the extrusion of DNA–protein complexes into the extracellular space [45, 46]. Mechanistically, two major NETosis phenotypes have been delineated: (1) “Suicidal” NETosis, a slower and oxidant-dependent pathway that culminates in plasma membrane rupture and neutrophil death, and (2) “Vital” NETosis, a rapid, non-lytic process in which neutrophils remain functionally active, capable of migration, phagocytosis, and cytokine secretion following NET release [47]. In non-infectious contexts (metabolic disease, thrombosis), platelet–neutrophil interactions and oxidized phospholipids further trigger NET release [48].
The NADPH oxidase 2 (NOX2)–ROS–PAD4 axis is central to the canonical form of NETosis [49]. Upon activation by stimuli such as PMA, immune complexes, IL-8, or TNF-α, NOX2 assembles on the plasma membrane and endosomal compartments, generating superoxide (O₂•⁻) and downstream hydrogen peroxide (H₂O₂) [50]. These ROS act as critical second messengers that facilitate Ca2⁺ mobilization and PAD4 activation, leading to histone H3 citrullination and chromatin relaxation. In parallel, NE migrates to the nucleus, where it cleaves histones and disrupts chromatin–protein interactions, further promoting decondensation (56).
In non-infectious, sterile-inflammatory contexts such as metabolic disease, thrombosis, or PCOS, NETosis can be initiated through oxidized lipid species and platelet-derived cues rather than microbial PAMPs (54, 57). Activated platelets expressing P-selectin bind to neutrophil PSGL-1, initiating intracellular signaling via Src and Syk kinases that activate Raf–MEK–ERK cascades and drive NET release (58). Moreover, oxidized phospholipids, free fatty acids, and advanced glycation end-products (AGEs)—abundant in insulin resistance and hyperglycemia—can engage TLR4 and RAGE on neutrophils, augmenting NADPH oxidase activation and PAD4-dependent chromatin remodeling (59) [51]. Emerging evidence in inflammatory states demonstrates that platelet activation enhances platelet–T cell interactions, leading to dynamic changes in regulatory T cell subsets (T4regs and T8regs) and other T cell populations, which may exacerbate post-inflammatory immune responses [52, 53].
Recent insights further implicate mitochondrial ROS and metabolic rewiring in the initiation of “vital” NETosis. In this variant, mitochondrial depolarization and leakage of mitochondrial DNA act as DAMPs that fuel further NET release through oxidative phosphorylation–independent ROS signaling and HIF-1α-driven glycolytic adaptation (60). Such mechanisms are particularly relevant to PCOS, where systemic oxidative stress, hyperinsulinemia, and androgen excess establish a pre-activated metabolic state that lowers the threshold for both NOX2- and mitochondria-dependent NET formation (61). Table 2 summarizes the molecular pathways, cellular mediators, and functional consequences of NETosis relevant to PCOS and metabolic inflammation.

Collectively, these pathways define NETosis as a multi-signal integration process, wherein metabolic, hormonal, and inflammatory cues converge on a shared biochemical core—the ROS–PAD4–chromatin axis. This intersection positions NETosis not merely as an antimicrobial strategy but as a cytotoxic effector mechanism driving sterile inflammation, endothelial dysfunction, and thrombo-inflammatory propagation in PCOS and related metabolic disorders.

NETosis in the ovarian and endometrial microenvironment
Emerging evidence places NETosis at the center of ovarian microenvironmental dysregulation in PCOS. Clinical and experimental findings demonstrate elevated circulating and follicular fluid levels of NET biomarkers—including MPO–DNA complexes, citrullinated histone H3 (H3Cit), and cell-free double-stranded DNA (dsDNA)—in women with PCOS compared with healthy controls [54]. Quantitatively, NET-associated complexes are increased approximately 2- to threefold in both serum and follicular fluid, correlating positively with hyperandrogenemia and insulin resistance indices, while inversely correlating with oocyte quality and fertilization rate [5].

Follicular fluid NET biomarkers and functional implications
Although studies such as Lin et al. [5] report elevated NET markers in serum and follicular fluid of women with PCOS, these findings are constrained by small sample sizes (57 PCOS patients and 38 controls), limiting statistical power to detect robust correlations with metabolic or hormonal indices such as testosterone and HOMA-IR. Consequently, assertions that NET burden scales directly with hyperandrogenemia or insulin resistance in PCOS should be presented as plausible but not yet definitively proven.
Importantly, the pathophysiological consequences of elevated NET components in the follicular microenvironment are supported by parallel evidence: multiple studies link increased oxidative stress and inflammatory mediators in follicular fluid to reduced oocyte competence, lower fertilization rates, and poorer embryo quality in women with PCOS, providing a biologically plausible pathway by which NET-derived DNA, histones, and proteases could impair gamete quality and fertilization success [55].

Mechanistic insights: granulosa and cumulus cell impact
Mechanistically, the follicular fluid (FF) in PCOS constitutes a unique inflammatory–oxidative niche in which neutrophil-derived products can exert direct cytotoxic effects on granulosa and cumulus cells. Recent analyses report elevated markers of NETosis in both serum and follicular fluid from women with PCOS, indicating local NET deposition in the ovarian microenvironment [5]. Neutrophil extracellular traps release a cocktail of active mediators—MPO, NE, cathepsin G, and high-mobility group box 1 (HMGB1)—together with decondensed chromatin and histones; these components are well documented to produce oxidative damage, proteolytic cleavage of extracellular and cellular proteins, and direct cytotoxicity in other tissue contexts [56]. Thus, it is mechanistically plausible—and supported by related experimental data—that NETosis in the FF materially contributes to granulosa/cumulus cytotoxicity, mitochondrial dysfunction, and disruption of steroidogenic programs.

NETs as procoagulant scaffolds in the ovarian microvasculature
NETs also serve as procoagulant scaffolds within peri-follicular capillaries. The negatively charged DNA backbone and associated histones in NETs can bind von Willebrand factor and platelet receptors, concentrate tissue factor, and facilitate activation of the contact pathway (factor XII), thereby promoting local thrombin generation and fibrin formation. Multiple studies and reviews document NET-associated FXII activation and platelet entrapment as central mechanisms of microthrombus formation in diverse tissues, supporting the concept that NETs can precipitate microvascular occlusion in the ovarian microcirculation [57]. Platelet–NET aggregates further amplify coagulation and inflammatory signaling, creating a feed-forward loop that compromises capillary perfusion and tissue oxygen delivery [56].
These microvascular insults—NET-driven proteolysis plus NET-mediated microthrombosis—are expected to propagate oxidative stress and hypoxic signaling within the follicle. Endothelial and granulosa cells exposed to oxidative or perfusion stress activate NF-κB and stabilize HIF-1α, respectively, programs that drive inflammatory and survival gene expression (e.g., IL-6, VEGF, glycolytic reprogramming) and that have been associated with impaired follicular function in ovarian pathology [58, 59]. By linking NET deposition to both direct parenchymal injury and local ischemia, this model explains how NETosis can amplify HIF-1α and NF-κB activation in granulosa cells and thus perpetuate a self-sustaining inflammatory–hypoxic circuit in the PCOS follicular niche.
Although direct experiments specifically exposing human granulosa/cumulus cells to NET preparations remain limited, convergent evidence supports a mechanistic chain in which NET-derived proteases and ROS can (a) impair mitochondrial respiration and membrane potential; (b) induce DNA strand breaks and apoptotic signaling; and (c) degrade or dysregulate key steroidogenic enzymes required for estradiol/progesterone synthesis. The components of this chain are each supported in the literature: oxidative stress and protease exposure impair mitochondrial function and cause DNA fragmentation in ovarian somatic cells, and disturbed FF redox balance correlates with altered steroidogenic gene expression and poorer oocyte competence [60].

Integrative perspective: NETosis and immunometabolic dysregulation
PCOS can thus be conceptualized as an immuno-metabolic syndrome, where chronic low-grade inflammation primes neutrophils toward excessive NET formation. This establishes a mechanistic continuum linking systemic metabolic stress, oxidative imbalance, and local ovarian/endometrial injury. In this framework, neutrophils serve as both sensors and effectors, integrating metabolic, endocrine, and immune signals and situating NETosis at the core of reproductive, vascular, and inflammatory pathology in PCOS.

Systemic NETosis and thromboinflammatory propagation
NETs constitute a structural and biochemical bridge between innate immunity and the coagulation system: the DNA–histone backbone and associated neutrophil proteins act as both a physical scaffold and as a biochemical activator that concentrates platelets, fibrinogen, von Willebrand factor, and coagulation enzymes at sites of inflammation [61, 62]. Perfusion and in vitro clotting studies first demonstrated that NETs recruit platelets and red blood cells, promote fibrin deposition, and create a pro-thrombotic scaffold whose enzymatic and electrostatic properties facilitate thrombus formation; dismantling NETs with DNase or interrupting NET–platelet interactions reduces thrombus formation in these models [63].
At the molecular level, NET components directly engage coagulation pathways. Extracellular nucleosomes and NET-bound histones provide negatively charged surfaces that can activate the contact pathway via factor XII (FXII) autoactivation, while NET-associated tissue factor (TF) and TF-bearing microparticles amplify extrinsic pathway signaling in certain inflammatory contexts [64]. Neutrophil serine proteases (e.g., neutrophil elastase) and myeloperoxidase present within NETs further potentiate coagulation by degrading anticoagulant regulators (for example, thrombomodulin) and by enhancing thrombin generation. Together, these mechanisms convert local neutrophil activation into sustained intravascular coagulation and fibrin stabilization [65].
Beyond biochemical activation, cellular interactions magnify thromboinflammation: activated platelets bind to NETs and to neutrophils via P-selectin/PSGL-1 and integrin pathways, forming platelet–neutrophil aggregates that both promote further NET release and provide a nidus for coagulation complex assembly [66]. This reciprocal platelet–neutrophil crosstalk fosters thrombus growth and increases resistance of clots to fibrinolysis, thereby propagating microvascular occlusion in inflamed tissues. Clinical and experimental evidence implicates this axis across venous and arterial thrombosis and in immunothrombotic complications of systemic inflammatory diseases [67].
In the context of PCOS, these NET-driven thrombo-inflammatory mechanisms have important translational implications. Women with PCOS demonstrate early markers of vascular injury—including impaired endothelial function and increased carotid intima–media thickness (cIMT) as well as other indices of subclinical atherosclerosis—which consistently associate with insulin resistance, dyslipidemia, and low-grade systemic inflammation [68]. Mechanistically, NETosis provides a biologically plausible link: NETs and NET-derived components (histones, MPO, NE, extracellular DNA) induce endothelial activation and dysfunction and promote platelet capture, fibrin deposition, and contact-pathway/coagulation activation, thereby converting neutrophil priming into endothelial injury and microvascular thrombotic events [69]. Local NET–endothelium interactions can impair nitric oxide bioavailability, expose subendothelial matrix, and promote leukocyte and platelet adherence—events that collectively accelerate a pro-atherogenic, pro-thrombotic vascular phenotype in PCOS [70].
Finally, conceptualizing NETosis as an active mediator rather than a bystander reframes cardiovascular risk in PCOS: rather than asking whether women with PCOS simply have higher inflammatory markers, the critical question becomes whether sustained neutrophil priming and NET formation are mechanistic drivers of thrombo-inflammatory remodeling of the vasculature. If so, NET-directed diagnostics (e.g., circulating MPO–DNA or citrullinated histone H3) and targeted interventions (DNase, PAD4 inhibitors, anti-platelet strategies that disrupt platelet–neutrophil conjugation) could represent novel approaches to mitigate CV risk in PCOS—an avenue that urgently warrants prospective, mechanism-focused clinical investigation (see Fig. 1) [56].

Critical appraisal of NET studies in PCOS
While evidence implicates NETs in PCOS pathophysiology, several overarching methodological and interpretative limitations temper confidence in current conclusions. First, most clinical investigations rely on cross-sectional designs, which preclude causal inference and make it unclear whether elevated NETs drive PCOS-related metabolic and reproductive disturbances or merely reflect them. Second, PCOS is a heterogeneous syndrome, with variability in BMI, androgen levels, insulin resistance, and reproductive phenotypes; many studies do not stratify or adjust for these differences, limiting generalizability across patient subgroups. Third, NET quantification is inconsistent, with assays targeting dsDNA, MPO-DNA, or NE differing in sensitivity, specificity, and standardization, introducing inter-study variability that may obscure true biological trends. Fourth, the translation of mechanistic insights from animal or in vitro models remains tentative, as these systems may not recapitulate the complex interplay of metabolic, hormonal, and immune factors in human PCOS.
Taken together, although the neutrophil–NET axis is biologically plausible, the current human evidence remains preliminary. Importantly, NET formation does not occur in isolation; it interacts closely with platelets and the endothelium to propagate thrombo-inflammatory processes. Understanding these interactions is critical, as they may represent key mechanistic links between inflammation, coagulation, and the metabolic–reproductive disturbances observed in PCOS. This sets the stage for exploring the neutrophil–platelet–endothelium triad and its role in orchestrating thromboinflammation in women with PCOS.

The neutrophil–platelet–endothelium triad: orchestrating thromboinflammation

Platelet activation and P-selectin signaling in PCOS
Platelets act as rapid sentinels of vascular and tissue injury and, when activated, display P-selectin on their surface membranes—a key adhesion molecule that binds PSGL-1 on neutrophils and initiates neutrophil rolling, firm adhesion, and intracellular signaling cascades that culminate in NET release [71]. Mechanistically, P-selectin–PSGL-1 engagement transduces signals through Syk and calcium flux that activate PAD4 and other downstream effectors, promoting chromatin decondensation and extracellular trap formation; thus, P-selectin is not merely adhesive but pro-NETotic [72].
Platelet-derived microparticles (PMPs) and small extracellular vesicles extend the reach of platelets beyond direct cell–cell contact [73]. PMPs carry a cargo of bioactive lipids, oxidized phospholipids, and surface receptors that can prime neutrophils for an enhanced oxidative burst and NET formation; oxidized phospholipids, in particular, have been shown to promote NETosis in arterial models, providing a biochemical basis for PMP-mediated neutrophil activation [48]. In addition, PMPs expose phosphatidylserine and tissue factor, which accelerate local thrombin generation and create a procoagulant microenvironment that synergizes with NET scaffolds to stabilize thrombi [74].
Clinical and translational data indicate that platelet activation and PMP biology are altered in PCOS, although the literature is still evolving. Several studies report increased circulating platelet microparticles and elevated platelet activation markers (for example, SCUBE1 and platelet arginase activity) in women with PCOS, findings that implicate heightened platelet responsiveness and a greater reservoir of vesicular mediators capable of modulating neutrophil behavior [75]. These observations create a plausible mechanistic pathway in PCOS: metabolic and hormonal perturbations (hyperandrogenism, insulin resistance) promote platelet hyperreactivity and PMP release, which in turn primes neutrophils to NETose within adipose, ovarian, and vascular beds.
The downstream consequences of platelet-driven NETosis are highly thrombogenic and self-amplifying. NETs present a sticky extracellular scaffold composed of DNA, histones, and neutrophil proteases that bind von Willebrand factor (vWF), trap platelets, and promote fibrin deposition, thereby accelerating thrombus growth and conferring resistance to fibrinolysis [65]. Furthermore, NET components (notably histones) directly activate platelets via Toll-like receptors (TLR2/4) and integrin signaling, increasing platelet aggregation and thrombin generation—closing a feed-forward loop in which platelets drive NET formation and NETs further activate platelets and coagulation [76].
Taken together, these mechanistic and clinical threads support a model in PCOS whereby platelet activation and PMP release prime neutrophils for NETosis, and NETs provide a prothrombotic scaffold that recruits and activates additional platelets and coagulation factors, producing an escalating thrombo-inflammatory loop with potential consequences for ovarian microvasculature, endometrial receptivity, and long-term cardiovascular risk [77].

Endothelial dysfunction and prothrombotic reprogramming
Endothelial cells (ECs) exposed to NET components undergo profound functional reprogramming, shifting from physiological vascular homeostasis toward inflammation‑driven endothelial injury and a pro‑coagulant phenotype [78]. Histones embedded in NETs, particularly H3 and H4, exert direct cytotoxicity on ECs, triggering membrane damage, oxidative stress, and attenuation of NO bioavailability—a key mediator of endothelial vasodilatory and anti‑thrombotic capacity [79]. For instance, purified NETs increased endothelial permeability and raised surface expression of E‑selectin, ICAM‑1, VCAM‑1, as well as TF activity in human umbilical vein endothelial cells (HUVECs) [80].
Mechanistically, NET‑derived histones bind to endothelial cell TLR2/TLR4 and trigger NF‑κB and MAPK‑mediated upregulation of adhesion molecules (ICAM‑1, VCAM‑1, E‑selectin), thereby promoting neutrophil and platelet tethering [81]. Simultaneously, NETs provide a scaffold for vWF, fibrin, platelets, and red blood cells, facilitating a localized pro‑thrombotic microenvironment [82]. Endothelium exposed to NETs also demonstrates increased generation of ROS and reduced eNOS activity, leading to diminished NO and endothelial vasodilatory reserve—a recognized feature of early atherothrombotic transition [83].
In the context of PCOS, endothelial dysfunction is well‑documented: studies consistently show reduced flow‑mediated dilation (FMD), elevated soluble ICAM‑1 and VCAM‑1, and increased endothelin‑1 levels compared with matched controls [84]. When viewed through the neutrophil–NET lens, these observations can be reinterpreted: endothelial injury in PCOS is not merely a downstream consequence of insulin resistance and hormonal imbalance, but may reflect active participation of a neutrophil–platelet–endothelium axis that orchestrates inflammation, coagulation, and vascular remodeling. NET‑mediated endothelial activation thus bridges reproductive, metabolic, and vascular pathology in PCOS.
Indeed, in PCOS, the interplay of hyperinsulinemia, androgen excess, adipose dysfunction, and neutrophil priming creates a milieu in which NET release and endothelial adhesion‑molecule upregulation converge. Activated endothelium displays increased TF expression, triggering extrinsic and intrinsic coagulation cascades and contributing to a pro‑thrombotic endovascular surface [80]. Platelet–neutrophil aggregates formed on this activated surface further amplify thrombin generation and fibrin deposition, establishing a feed‑forward loop of vascular inflammation and thrombosis [50].
Moreover, the reduction in NO bioavailability in PCOS—which has been attributed to insulin resistance, oxidative stress, and dyslipidemia—may also reflect genetic predisposition influencing endothelial resilience [85]. NET components degrade the endothelial glycocalyx, impair shear‑stress-mediated eNOS activation, and increase endothelial permeability, thereby exposing the sub‑endothelial matrix and activating platelets [86]. This vascular thrombo-inflammatory state not only drives local endothelial dysfunction, but also intersects with systemic metabolic regulation, creating a feedback loop that links neutrophil activation to tissue-level metabolic stress.
Building on this concept, the crosstalk between neutrophils and metabolic tissues emerges as a central mechanism in PCOS pathophysiology. In the following section, we explore how neutrophils interact with adipose tissue, liver, and pancreatic islets, translating metabolic dysregulation into innate immune activation and amplifying both NET formation and systemic inflammation. By examining these interactions in detail, we can better understand how neutrophils serve as pivotal mediators linking vascular, metabolic, and reproductive disturbances in PCOS, setting the stage for a focused discussion on their crosstalk with metabolic tissues.

Crosstalk between neutrophils and metabolic tissues
Adipose tissue, liver, and pancreas are not inert bystanders but active immuno-metabolic organs where neutrophils infiltrate in response to metabolic stress, establishing a feedback loop between innate immunity and metabolic dysfunction [87]. In obesity—a frequent comorbidity of PCOS—neutrophils are among the first immune cells to localize in expanding adipose depots, releasing NE, ROS, and pro‑inflammatory cytokines, thereby recruiting macrophages and worsening insulin resistance [88]. Indeed, neutrophil elastase secretion by infiltrating neutrophils has been shown to degrade insulin receptor substrate 1 (IRS1) in hepatocytes and adipocytes, promoting systemic insulin resistance [88].
Although direct neutrophil–tissue studies in PCOS remain sparse, the general immuno-metabolic literature provides strong mechanistic analogues. For example, a recent study of visceral adipose tissue in humans with obesity found neutrophil abundance to correlate with homeostatic model assessment of insulin resistance (HOMA‑IR) and with mRNA expression of IL1B and IL8 in the adipocyte fraction [89]. In PCOS, the convergence of hyperandrogenism‑driven adipokine dysregulation, insulin resistance, and macrophage infiltration arguably sets up a permissive environment for neutrophil activation: elevated adipokines such as leptin, resistin, and visfatin have been documented in PCOS and linked to chronic inflammatory signaling in adipose and reproductive tissues [90].
Adipokines modulate neutrophil behavior: leptin, for instance, primes neutrophils for enhanced ROS release, delayed apoptosis, and increased degranulation, thereby creating a granulocyte–adipokine feedback loop that drives tissue inflammation and metabolic dysfunction. Although specific PCOS‑neutrophil studies are lacking, analogous data in obesity and metabolic syndrome support this model [91].
In the liver and pancreas, neutrophil infiltration and NET (neutrophil extracellular trap) release may further impair local insulin signaling. NETs and neutrophil‑derived proteases are increasingly recognized as drivers of hepatic steatosis and pancreatic β‑cell stress, contributing to the metabolic derangements seen in PCOS (e.g., non‑alcoholic fatty liver disease and β‑cell dysfunction) [92]. As such, the neutrophil–metabolic tissue crosstalk emerges as a crucial liaison linking reproductive/metabolic dysfunction in PCOS: neutrophils become both effectors of local tissue injury (adipose, hepatic, pancreatic) and amplifiers of systemic inflammation, thereby bridging hormonal, metabolic, and immune dysregulation [5].
Collectively, this metabolic tissue network reinforces a model in which neutrophils are not simply by‑standers but central participants in the pathophysiology of PCOS. They sense metabolic distress (insulin resistance, lipotoxic adipokine signals, androgen excess), respond via activation and NETosis, and subsequently mediate tissue‑level damage and systemic propagation of inflammation and thrombosis. Recognizing neutrophils as central drivers of immuno-metabolic dysfunction highlights the therapeutic potential of targeting the neutrophil–NET axis. The next section explores current and emerging strategies aimed at modulating neutrophil activity, NET formation, and the downstream inflammatory consequences in PCOS.

Therapeutic frontiers: targeting the neutrophil–NET axis in PCOS

Current anti-inflammatory approaches
Although no clinical trials have yet directly used NET‑targeting agents in PCOS, several established therapies used for PCOS exert indirect effects on the neutrophil–NETosis axis and therefore merit conceptual exploration. For example, metformin, a first‑line agent in PCOS for insulin resistance, has been shown in patients with type 2 diabetes to blunt NET formation: in vitro, metformin prevented chromatin decondensation and DNA release and in vivo reduced circulating NET biomarkers (e.g., dsDNA, citrullinated histone H3) independent of glucose‑lowering effects [93]. Mechanistically, metformin inhibited PKC‑βII membrane translocation and NADPH oxidase activation in neutrophils, thereby lowering the activation threshold for NETosis [94]. In a PCOS context—characterized by insulin resistance, oxidative stress, and neutrophil priming—the ability of metformin to reduce NETs may translate into diminished neutrophil‑driven inflammation, improved ovarian microenvironment, and lower systemic thrombo‑inflammatory risk.
Likewise, thiazolidinediones (e.g., pioglitazone) used in some PCOS settings may reduce oxidative stress, adipocyte‐derived inflammatory signaling, and neutrophil activation thresholds (though direct NETosis data are limited). Additionally, antioxidant therapies—including N‑acetylcysteine, vitamin D supplementation, and melatonin—aim to reduce ROS, which are critical co‐factors for NETosis induction. While there is no direct PCOS‑specific NETosis trial, these therapies provide a mechanistic foundation for immuno-metabolic modulation of the neutrophil–NET axis.
Although direct NET-targeting trials in PCOS are not yet available, observational and preclinical evidence suggests that established therapies—including metformin, thiazolidinediones, and antioxidants—may indirectly mitigate NET-driven ovarian and systemic inflammation. In PCOS patients, these interventions improve insulin resistance, reduce oxidative stress, and may lower neutrophil priming, providing a translational rationale for their effect on NETosis-related outcomes.
Therefore, current anti‑inflammatory therapies in PCOS, though not explicitly designed for NET inhibition, may indirectly suppress neutrophil activation, NET formation, and subsequent tissue injury—forming a practical “back‐door” into the neutrophil–NET therapeutic space.

Emerging neutrophil-targeted therapies
A more radical therapeutic frontier is the direct targeting of the neutrophil–NET machinery. Several experimental agents and strategies are now being developed for thrombo‑inflammatory, autoimmune, and metabolic diseases—and are conceptually applicable to PCOS. PAD4 inhibitors: PAD4 is the enzyme responsible for histone citrullination, a pivotal early step in NET formation. Experimental inhibition of PAD4 (e.g., using Cl‑amidine derivatives) reduces NET burden, vascular injury, and atherogenesis in preclinical models [95]. Given the heightened neutrophil priming and vascular risk status in PCOS, PAD4 inhibition represents a logical translational target.
Dornase α/DNase I‑based NET degradation strategies: By enzymatically digesting extracellular chromatin webs, DNase approaches reduce NET‑mediated tissue damage and thrombosis in experimental settings [96]. Although not yet tested in PCOS, given the pro‑thrombotic milieu associated with PCOS, NET–DNase strategies warrant investigation. MPO/NE blockers: MPO and NE are granule enzymes released during NETosis and contribute to oxidative damage, endothelial injury, and tissue remodeling. Targeted inhibition of these enzymes is in development for cardiovascular and inflammatory disease and may be conceptually extended to PCOS. Chemokine receptor antagonists/IL‑8‑CXCR1/2 blockade: Since IL‑8 is a major upstream driver of neutrophil chemotaxis and NETosis, pharmacologic antagonism of IL‑8 or its receptor axis (CXCR1/CXCR2) is under exploration in oncology and inflammatory disease [56]. In PCOS, where IL‑8 axis activation is likely given metabolic and adipose stress, IL‑8 antagonists may reduce neutrophil migration into ovarian/adipose tissue and blunt NET‑driven local damage.
Collectively, these emerging therapies move beyond “treating symptoms” to directly modulating neutrophil function and NETosis—offering a precision immuno‑metabolic strategy in PCOS. The translational gap remains large (no PCOS‑specific trials yet), but the mechanistic rationale is compelling.

Nanomedicine and precision immunomodulation
In the era of precision medicine, nanotechnology offers the ability to target the neutrophil–NET–platelet axis at the cellular level. Nanocarriers can be engineered to deliver ROS-sensitive payloads, enzyme inhibitors, or receptor blockers selectively to neutrophils, platelets, or vascular endothelium in the PCOS micro-environment [97]. For example, nanodelivery systems have been proposed for DNase I, PAD4 inhibitors, or P-selectin/PSGL-1 blockers, thereby localizing therapy to sites of neutrophil activation and minimizing systemic side effects [98].
In PCOS, where adipose tissue, ovarian stroma, and microvasculature may harbor activated neutrophils and NET deposition, such precision immunomodulation could selectively suppress the neutrophil–NET axis without broadly impairing host defense. Future directions include nanoparticle systems bearing dual targeting (e.g., neutrophil receptor + adipose microenvironment ligand) and ROS‐responsive release of anti‐NET agents timed to metabolic stress windows (e.g., post‐ovulation, insulin surge). While at present preclinical only, these nanomedicine strategies embody the frontier of personalized immuno-metabolic therapy in PCOS.
Nanocarrier-based delivery of NET-modulating agents represents a precision immuno-metabolic strategy that could selectively target neutrophil-rich ovarian and adipose microenvironments. By minimizing systemic immune suppression, such approaches may offer clinically actionable therapies tailored to high-NET PCOS phenotypes.

Translational and implementation considerations
Translating neutrophil–NET‑targeted strategies into clinical practice for PCOS requires careful navigation of patient heterogeneity, safety, and integration with existing clinical management paradigms. First, robust biomarkers are essential for patient stratification, treatment selection, and monitoring response. In multiple clinical contexts, circulating markers such as cell‑free DNA (dsDNA), myeloperoxidase (MPO)–DNA complexes, and citrullinated histone H3 (CitH3) have been validated as indicators of NETosis and correlate with disease severity or activity in systemic inflammatory and thrombo‑inflammatory disorders (e.g., cardiovascular disease, autoimmune conditions) [50, 66]. In PCOS specifically, increased levels of dsDNA, neutrophil elastase (NE), and MPO‑DNA in both serum and follicular fluid compared with controls provide preliminary evidence that NET biomarkers can reflect systemic and local immune perturbations in PCOS populations [5]. Beyond NET‑specific markers, inflammatory biomarkers such as neutrophil–platelet aggregates, neutrophil–lymphocyte ratio (NLR), and classic cytokines like IL‑6/IL‑8 also show elevations in PCOS, underscoring the interplay between innate immune activation and metabolic dysfunction [99]. Embracing these biomarkers in clinical protocols could guide selection of women most likely to benefit from NET‑modulating therapies. For example, subtypes marked by pronounced metabolic or inflammatory signatures (e.g., hyperandrogenic with obesity and insulin resistance) are more likely to exhibit heightened NET‑associated inflammation, whereas subtypes with milder metabolic features may derive less direct benefit from NET‑focused intervention. This is consistent with evidence that phenotypes A and B of PCOS (hyperandrogenic and anovulatory phenotypes) are associated with worse insulin resistance, dyslipidemia, and metabolic syndrome relative to other phenotypes, reflecting a higher inflammatory and cardiometabolic risk burden that may intersect with neutrophil activation and NETosis pathways [100].
Second, safety considerations are paramount when modulating innate immune pathways. Neutrophils and NETs are central to host defense and tissue repair, so agents like PAD4 inhibitors or DNase risk impairing pathogen clearance or wound healing if deployed indiscriminately. Biomarker‑guided approaches and targeted delivery (e.g., nanocarrier systems) may minimize off‑target immunosuppression by concentrating therapy in ovarian, adipose, or vascular microenvironments rather than systemic compartments [101]. Antioxidant strategies—such as N‑acetylcysteine (NAC), glutathione enhancers, or combinations of vitamins E and C—have demonstrated the ability to suppress ROS‑driven NET formation in vitro, lowering NETosis markers while preserving basal neutrophil function [102]. These antioxidant pathways intersect with ROS‑dependent NET mechanisms and may offer safer ways to modulate NET formation in PCOS without directly impairing innate immunity.
Third, cytokine‑pathway modulation represents another translational route. Cytokines such as IL‑8 signal through CXCR1/2 to drive neutrophil chemotaxis and NETosis, and preclinical data show that IL‑8 blockade reduces NET formation in disease models [103]. Therapeutics that antagonize upstream cytokine drivers of neutrophil activation could therefore indirectly reduce NET burden, complement anti‑oxidative strategies, and be more readily integrated with existing treatments like metformin or insulin sensitizers.
Fourth, integration with current PCOS therapies is necessary for real‑world utility. Established treatments (e.g., metformin, thiazolidinediones, lifestyle interventions) already modulate metabolic and inflammatory axes and may have indirect effects on neutrophil priming and NETosis. Combining NET‑focused therapies with these agents could enhance efficacy while preserving hormone‑centric benefits. Moreover, intervention timing (e.g., around ovulation induction or fertility treatment cycles) should be evaluated for optimal immuno-metabolic impact.
Finally, implementation science will require thoughtful trial design and outcome selection. Biomarker-based inclusion criteria, early-phase safety trials of PAD4 inhibitors or DNase in well-characterized PCOS subgroups, and careful selection of composite endpoints capturing metabolic, reproductive, and vascular outcomes will be essential. Figure 2 visually integrates these translational strategies with PCOS phenotypes, NET biomarkers, and targeted interventions, providing a roadmap for bridging mechanistic insights into actionable clinical pathways.

Clinical data examples
To complement mechanistic insights, selected clinical studies illustrate the potential of NET biomarkers as actionable translational tools in PCOS. Women with PCOS exhibit elevated serum and follicular fluid levels of citrullinated histone H3 (citH3) and neutrophil elastase compared with age- and BMI-matched controls, correlating with insulin resistance, hyperandrogenism, and systemic inflammation [5]. Preclinical data from a DHEA-induced PCOS rat model demonstrate that DNase I treatment reduces hepatic NET deposition and improves glucose metabolism [5]. These findings highlight a “high-NET” PCOS phenotype, identifying patients at heightened risk for metabolic, vascular, and reproductive complications. Incorporating NET biomarkers into clinical protocols could enable patient stratification and guide targeted NET-modulating therapies—such as PAD4 inhibitors, DNase, or antioxidants—in combination with standard-of-care interventions, ultimately improving metabolic and reproductive outcomes.

Conclusion
Neutrophils and NETosis emerge as central orchestrators linking the reproductive, metabolic, and vascular derangements of PCOS. Far from passive bystanders, neutrophils serve as frontline effectors of metabolic inflammation, generating reactive oxygen species, releasing proteolytic enzymes, and forming neutrophil extracellular traps that directly injure endothelium, prime platelets, and propagate thrombo-inflammatory cascades. This coordinated neutrophil–NET axis provides a mechanistic bridge connecting hyperandrogenism, insulin resistance, adipose dysfunction, and ovarian microvascular pathology.
Recognizing PCOS as a neutrophil-centered immuno-metabolic syndrome reframes the disease beyond classical endocrine and reproductive paradigms. It positions the neutrophil–NET axis not only as a biomarker of disease severity, but also as a therapeutic target capable of restoring immune–metabolic homeostasis, improving ovulatory function, and mitigating long-term cardiovascular and thrombotic risk.
Future interventions that selectively modulate neutrophil activation, ROS generation, or NET formation—such as PAD4 inhibitors, ROS scavengers, DNase-based therapies, or blockade of neutrophil–platelet interactions—hold promise to shift PCOS management from symptomatic hormone modulation toward precision immuno-metabolic therapy. In this light, neutrophils and NETosis are not merely participants but drivers of PCOS pathophysiology, offering a unifying conceptual framework and a roadmap for next-generation translational research.

Core conclusions summary

Neutrophil–NET Axis in PCOS Pathophysiology
Emerging evidence suggests that NET formation may link oxidative stress, inflammation, and metabolic dysregulation in PCOS, potentially contributing to ovarian dysfunction, endothelial activation, and systemic thrombo-inflammatory risk.

Indirect NET Modulation by Current Therapies
Agents such as metformin, thiazolidinediones, and antioxidants could influence neutrophil priming and NET formation, but their NET-specific effects in PCOS remain largely untested and inferred from related conditions.

Experimental NET-Targeted Interventions
PAD4 inhibitors, DNase I, MPO/NE blockers, and IL-8/CXCR1/2 antagonists represent potential strategies to modulate NETosis directly, yet their clinical relevance in PCOS is still speculative.

Precision Approaches and Nanomedicine
Nanocarrier-based delivery systems may allow targeted modulation of neutrophil–NET activity in ovarian, adipose, or vascular microenvironments, but these approaches are preclinical and require validation in PCOS-specific contexts.

Biomarker-Guided Stratification as a Future tool
NET-related biomarkers—including citrullinated histone H3, MPO–DNA complexes, and cell-free dsDNA—could help identify high-NET phenotypes and inform therapy selection, though standardization and prospective clinical studies are still needed.

Core framework overview
Polycystic ovary syndrome (PCOS) is increasingly recognized as a disorder in which hormonal and metabolic disturbances—hyperandrogenism, insulin resistance, adipose inflammation, and oxidative stress—interact to prime neutrophils and promote immune activation. This priming may enhance neutrophil extracellular trap (NET) formation, which in turn can amplify endothelial injury, thrombo-inflammatory signaling, and tissue-level perturbations in the ovary, endometrium, and vasculature. While direct causal evidence in PCOS remains limited, this framework integrates endocrine, metabolic, and immunological dimensions to provide a structured lens for understanding how neutrophil and NET-mediated pathways could contribute to systemic and organ-specific dysfunction in affected women.

Key terminology briefing

Neutrophil Extracellular Traps (NETs) Web-like structures composed of DNA, histones, and granule proteins released by neutrophils via a process known as NETosis. NETs can trap pathogens but also promote inflammation, endothelial injury, and thrombo-inflammatory signaling.

Neutrophil-to-Lymphocyte Ratio (NLR) A circulating biomarker reflecting systemic inflammation, calculated as the ratio of neutrophils to lymphocytes in peripheral blood.

PAD4 (Peptidyl Arginine Deiminase 4) An enzyme critical for histone citrullination, a key step in NET formation.

Cytokines and Adipokines Soluble signaling molecules released by immune and adipose cells, respectively, that modulate inflammation and metabolic responses.

Oxidative Stress/ROS (Reactive Oxygen Species) Imbalance between pro-oxidant molecules and antioxidant defenses, contributing to cellular and tissue injury.