Bioreactivity of stent material: Activation of platelets, coagulation, leukocytes and endothelial cell dysfunction in vitro

Pharmacologic targeting of coagulation factors XII and XI by monoclonal antibodies reduces thrombosis in nitinol stents under flow

BACKGROUND

Cardiovascular implantable devices, such as vascular stents, are critical for the treatment of cardiovascular diseases. However, their success is dependent on robust and often long-term antithrombotic therapies. Yet, the current standard-of-care therapies often pose significant bleeding risks to patients. Coagulation factor (F)XI and FXII have emerged as potentially safe and efficacious targets to safely reduce pathologic thrombin generation in medical devices.

OBJECTIVES

To study the efficacy of monoclonal antibody-targeting FXII and FXI of the contact pathway in preventing vascular device-related thrombosis.

METHODS

The effects of inhibition of FXII and FXI using function-blocking monoclonal antibodies were examined in a nonhuman primate model of nitinol stent-related thrombosis under arterial and venous flow conditions.

RESULTS

We found that function-blocking antibodies of FXII and FXI reduced markers of stent-induced thrombosis in vitro and ex vivo. However, FXI inhibition resulted in more effective mitigation of thrombosis markers under varied flow conditions.

CONCLUSION

This work provides further support for the translation of contact pathway of coagulation inhibitors for their adjunctive clinical use with cardiovascular devices.

Enhanced Hemocompatibility and Cytocompatibility of Stainless Steel

The present study introduces an advanced surface modification approach combining electrochemical anodization and non-thermal plasma treatment, tailored for biomedical applications on stainless steel grade 316L (SS316L) surfaces. Nanopores with various diameters (100-300 nm) were synthesized with electrochemical anodization, and samples were further modified with non-thermal oxygen plasma. The surface properties of SS316L surfaces were examined by scanning electron microscopy, atomic force microscopy, X-ray photoemission spectroscopy, and Water contact angle measurements. It has been shown that a combination of electrochemical anodization and plasma treatment significantly alters the surface properties of SS316L and affects its interactions with blood platelets and human coronary cells. Optimal performance is attained on the anodized specimen featuring pores within the 150-300 nm diameter range, subjected to subsequent oxygen plasma treatment; the absence of platelet adhesion was observed. At the same time, the sample demonstrated good endothelialization and a reduction in smooth muscle cell adhesion compared to the untreated SS316L and the sample with smaller pores (100-150 nm). This novel surface modification strategy has significant implications for improving biocompatibility and performance of SS316L in biomedical applications.

In-hospital outcomes after acute myocardial infarction with obstructive coronary artery disease in critically ill patients hospitalized for non-cardiac disease

BACKGROUND

Acute myocardial infarction (AMI) is one of the major cardiac complications in patients hospitalized in the intensive care unit (ICU) for non-cardiac disease. A better knowledge of ischemic and bleeding risks in these patients is needed to identify those most likely to benefit from specific cardiac management. We therefore assessed the incidence and predictors of a composite outcome of severe ischemic event (AMI recurrence, ischemic stroke), major bleeding, or all-cause death in this setting.

METHODS

In this multicenter retrospective study, all consecutive adult patients admitted for non-cardiac disease to four French university hospital ICUs between January 2012 and December 2018 who had an AMI with obstructive coronary artery disease (OCAD) during the ICU stay were considered for inclusion. AMI with OCAD was defined as an elevated cardiac troponin value associated with at least one sign (clinical, electrocardiographic, or echocardiographic) suggestive of myocardial ischemia and presence of OCAD on coronary angiography. The primary endpoint was in-hospital occurrence of the composite outcome.

RESULTS

Ninety-six patients [median age 69 years, 22 women (23%), 59 with sepsis (61%), 35 with ST elevation (37%), median sequential organ failure assessment (SOFA) of 8 on the day of AMI] were included. The median peak cardiac troponin value was 131 (IQR 44-303) times the upper reference limit. Dual antiplatelet, therapeutic anticoagulation, and early mechanical reperfusion therapies were administered in 61 (64%), 68 (71%), and 47 (49%) patients, respectively. The composite outcome occurred in 48 (50%) patients. Severe ischemic events occurred in 17 (18%) patients and major bleeding in 26 (27%) patients; 26 patients (27%) died in the hospital. AMI management was not significantly different in patients with and without the composite outcome. A history of arterial hypertension (HR 2.05, 95% CI 1.01-4.16) and high SOFA score at the time of AMI (HR 1.07, 95% CI 1.00-1.15) were independent risk factors for the composite outcome.

CONCLUSIONS

Patients who have an AMI with OCAD during an ICU stay for non-cardiac disease are at risk of a composite outcome of severe ischemia, major bleeding, and death. A history of arterial hypertension and high SOFA scores were independent hazards for poor prognosis.

Dynamic investigation of zein-based degradable and hemocompatible coatings for drug-eluting stents: a microfluidic approach

Biodegradable stent coatings have shown great potential in terms of delivering drugs to a damaged vessel wall, and their release profiles are key elements governing the overall performance of drug-eluting stents (DESs). However, release and degradation kinetics are usually not tested under simulated physiological conditions or in dynamic environments, both essential aspects in the design of novel DESs. To bridge this gap, fused silica-based microfluidic systems, with either round or square channel cross-sections, were designed to mimic the microenvironment of a stented vessel. In particular, we fabricated and characterized microfluidic chips based on customizable channels, which were spray-coated with a naturally-derived, rutin-loaded zein solution, to perform a comprehensive study under flow conditions. Dynamic assays after 6 hours showed how the degradation of the zein matrix was affected by the cross-sectional conformation (∼69% vs. ∼61%, square and round channel, respectively) and the simulated blood fluid components (∼55%, round channel with a more viscous solution). The released amount of rutin was ∼81% vs. ∼77% and ∼78% vs. ∼74% from the square and round channels, using the less and more viscous blood-simulated fluids, respectively. Fitting the drug release data to Korsmeyer-Peppas and first-order mathematical models provided further insight into the mechanism of rutin release and coating behavior under flowing conditions. More importantly, whole blood tests with our newly developed microfluidic platforms confirmed the hemocompatibility of our zein-based coating. In detail, in-flow and static studies on the blood cell behavior showed a significant reduction of platelet adhesion (∼73%) and activation (∼93%) compared to the stainless-steel substrate, confirming the benefits of using such naturally-derived coatings to avoid clogging. Overall, our microfluidic designs can provide a key practical tool for assessing polymer degradation and drug release from degradable matrices under flowing conditions, thus aiding future studies on the development of hemocompatible, controlled-release coatings for DESs.

Redox-Activation of Neutrophils Induced by Pericardium Scaffolds

Implantation of scaffolds causes a local inflammatory response whereby the early recruitment of neutrophils is of great importance not only for fighting the infection, but also for facilitating effective regeneration. We used luminol-dependent chemiluminescence, flow cytometry, ELISA, and confocal microscopy to assess the responses of neutrophils after the exposure to the scaffold-decellularized bovine pericardium (collagen type I) crosslinked with genipin (DBPG). We demonstrated that DBPG activated neutrophils in whole blood causing respiratory burst, myeloperoxidase (MPO) secretion, and formation of neutrophil extracellular trap-like structures (NETs). In addition, we studied platelets, another important player of the immediate immune host response. We found that platelets triggered redox-activation of isolated neutrophils by the pericardium scaffold, and likely participate in the NETs formation. Free radicals generated by neutrophils and hypochlorous acid produced by MPO are potent oxidizing agents which can oxidatively degrade biological structures. Understanding the mechanisms and consequences of redox activation of neutrophils by pericardium scaffolds is important for the development of new approaches to increase the efficiency of tissue regeneration.

Hemocompatibility of all-trans retinoic acid-loaded citrate polymer coatings for vascular stents

Purpose

Current strategies implementing drug-eluting polymer stent coatings fail to fully address the lasting effects of endothelial suppression which ultimately result in delayed reendothelialization and thrombogenic complications. The present study investigates the in vitro hemocompatibility of all-trans retinoic acid loaded poly (1,8-octanediol-co-citrate) coatings (AtRA-POC coatings) for advanced intravascular stent technology. The ability of these materials in supporting endothelial restoration via migration and proliferation while inhibiting smooth muscle cell growth is also explored.

Methods

Using in vitro models, the hemocompatibility of AtRA-loaded POC-coated cobalt chromium (CoCr) vascular stents was evaluated in terms of platelet and inflammatory activity. Platelet activity was quantified by platelet adhesion and platelet activation, further supported by SEM visualization. Inflammatory activity was quantified by the production of proinflammatory cytokines by THP1 monocytes. Lastly, in vitro wound healing and an 5-Ethynyl-2'deoxyuridine (EdU) and pico green DNA assays were used in quantitating endothelial and smooth muscle cell migration and proliferation.

Results

Experimental examinations of platelet adhesion and activation demonstrate significant reductions in the platelet response to POC coated AtRA loaded stents when compared to bare CoCr stents. Such findings reveal AtRA-POC coatings to have significantly improved hemocompatibility compared to that of bare metal stents and at least as good as POC alone. Similarly, in reference to LPS-stimulated controls, Human monocyte-like THP1 cells in culture with AtRA-POC-CoCr stents for 24 hours showed reduced detection of proinflammatory cytokines, comparable to that of bare CoCr and untreated controls. This result supports AtRA-POC coatings as possessing limited immunological potential. Observations from in vitro endothelial and smooth muscle cell investigations demonstrate the ability of the drug AtRA to allow cell processes involved in restoration of the endothelium while inhibiting smooth muscle cell processes.

Conclusion

This study demonstrates AtRA loaded POC coatings are hemocompatible, noninflammatory, and provide a promising strategy in enhancing vascular stent techniques and clinical integration. Possessing hemocompatibility and immunological compatibility that is at least as good as bare metal stents as clinical standards support the use of AtRA-POC coatings for vascular applications. Additionally, selectively reducing smooth muscle cell proliferation while supporting endothelial cell proliferation and migration further demonstrates the potential of these materials in significantly improving the state of vascular stent technology in the area of stent thrombosis and neointimal hyperplasia.

Platelet phagocytosis by leukocytes in a patient with cerebral hemorrhage and thrombocytopenia caused by gram-negative bacterial infection

Bacteria-induced thrombocytopenia is a common clinical disease that is often ignored by clinical and scientific research. Thus, exploring the mechanism and principle of bacteria-induced thrombocytopenia could facilitate the development of new diagnostic, preventative, and treatment modalities for thrombocytopenia. This case report describes a case of platelet phagocytosis by neutrophils and monocytes in a patient with cerebral hemorrhage and thrombocytopenia caused by gram-negative bacterial infection. After the infection was eradicated, platelet phagocytosis was alleviated, and his platelet count normalized. Cellular immunity may be an important cause of bacteria-induced thrombocytopenia in patients with cerebral hemorrhage.

Neutrophil Extracellular Traps: Inflammation and Biomaterial Preconditioning for Tissue Engineering

Tissue injury initiates a tissue repair program, characterized by acute inflammation and recruitment of immune cells, dominated by neutrophils. Neutrophils prevent infection in the injured tissue through multiple effector functions, including the production of reactive oxygen species, the release of granules, the phagocytosis of invaders, and the extrusion of neutrophil extracellular traps (NETs). However, these canonical protective mechanisms can also have detrimental effects both in the context of infection and in response to sterile injuries. Of particular interest to biomaterials and tissue engineering is the release of NETs, which are extracellular structures composed of decondensed chromatin and various toxic nuclear and granular components. These structures and their dysregulated release can cause collateral tissue damage, uncontrolled inflammation, and fibrosis and prevent the neutrophil from exerting its prohealing functions. This review discusses our knowledge of NETs, including their composition and morphology, signaling pathways, inhibitors, and contribution to inflammatory pathologies, as well as their role in the resolution of inflammation. In addition, we summarize what is known about the release of NETs as a preconditioning event in the response to biomaterials and highlight future considerations to target the neutrophil response and enhance biomaterial-guided tissue repair and regeneration. Impact statement Neutrophil extracellular trap (NET) release is an active process programmed into the neutrophil's molecular machinery to prevent infection. However, the release of NETs on biomaterials appears to be a significant preconditioning event that influences the potential for tissue healing with largely detrimental consequences. Given their contribution to inflammatory pathologies, this review highlights the role of NETs in the response to biomaterials. Together, the studies discussed in this review suggest that biomaterials should be designed to regulate NET release to avoid maladaptive immune responses and improve the therapeutic potential of tissue-engineered biomaterials and their applications in the clinical setting.

Designing Better Cardiovascular Stent Materials - A Learning Curve

Cardiovascular stents are life-saving devices and one of the top 10 medical breakthroughs of the 21st century. Decades of research and clinical trials have taught us about the effects of material (metal or polymer), design (geometry, strut thickness, and the number of connectors), and drug-elution on vasculature mechanics, hemocompatibility, biocompatibility, and patient health. Recently developed novel bioresorbable stents are intended to overcome common issues of chronic inflammation, in-stent restenosis, and stent thrombosis associated with permanent stents, but there is still much to learn. Increased knowledge and advanced methods in material processing have led to new stent formulations aimed at improving the performance of their predecessors but often comes with potential tradeoffs. This review aims to discuss the advantages and disadvantages of stent material interactions with the host within five areas of contrasting characteristics, such as 1) metal or polymer, 2) bioresorbable or permanent, 3) drug elution or no drug elution, 4) bare or surface-modified, and 5) self-expanding or balloon-expanding perspectives, as they relate to pre-clinical and clinical outcomes and concludes with directions for future studies.

Transcatheter Aortic Valve Thrombogenesis: A Foreign Materials Perspective

PURPOSE

The initiation of thrombus formation in transcatheter aortic valves (TAVs) is not well understood. The foreign material components of a TAV may play a key role in TAV thrombogenesis. The goal of this study was to evaluate the thrombogenic potential of a TAV (entire valve) and its stent (with skirt).

METHODS

Blood was collected from eight human donors with citrate anticoagulation and later reconstituted with calcium chloride. A low-volume steady flow loop (flow rate = 0.8 L/min) was designed to facilitate three separate conditions (experimental duration = 1 h) per donor blood: (1) control (n = 8), (2) stent-with-skirt (leaflets removed from a 23 mm SAPIEN XT valve; n = 8) and (3) entire valve (an intact 23 mm SAPIEN XT valve; n = 8). Samples were collected at the start and end of each experiment. Serum D-Dimer and thrombin-antithrombin (TAT) concentrations were measured as markers of thrombogenicity.

RESULTS

There was no significant change in serum D-Dimer and TAT concentration with time for the control group. An increasing trend in D-Dimer and TAT concentration was observed with time for the stent-with-skirt group. Interestingly, there was a decreasing trend in serum D-Dimer and TAT concentration with time for the entire valve (leaflet dominating) group. Moreover, changes in D-Dimer and TAT concentration were significantly different between the stent-with-skirt and entire valve (leaflet dominating) groups.

CONCLUSION

Stent-with-skirt was found to impart the most prominent thrombogenic effect, indicating the significance of blood-stent and blood-skirt interactions in TAV thrombosis.

No association between blood count levels and whole-blood cobalt and chromium levels in 1,900 patients with metal-on-metal hip arthroplasty

Background and purpose - The accelerated wear of poorly functioning metal-on-metal (MoM) hip implants may cause elevated whole-blood cobalt (Co) and chromium (Cr) levels. Hematological and endocrinological changes have been described as the most sensitive adverse effects due to Co exposure. We studied whether there is an association between whole-blood Co/Cr levels and leukocyte, hemoglobin, or platelet levels. Patients and methods - We analyzed whole-blood Co and Cr values and complete blood counts (including leukocytes, hemoglobin, platelets) from 1,900 patients with MoM hips. The mean age at the time of whole-blood metal ion measurements was 67 years (SD 10). The mean time from primary surgery to whole-blood metal ion measurement was 8.2 years (SD 3.0). The mean interval between postoperative blood counts and metal ion measurements was 0.2 months (SD 2.7). Results - The median Co value was 1.9 µg/L (0.2-225), Cr 1.6 µg/L (0.2-125), mean leukocyte count 6.7 × 10⁹/L (SD 1.9), hemoglobin value 143 g/L (SD 13), and platelet count 277 × 10⁹/L (SD 70). We did not observe clinically significant correlations between whole-blood Co/Cr and leukocyte, hemoglobin, or platelet counts. Interpretation - Elevated whole-blood Co and Cr values are unlikely to explain abnormal blood counts in patients with MoM hips and the reason for possible abnormal blood counts should be sought elsewhere.

Platelet-to-lymphocyte and Neutrophil-to-lymphocyte Ratios Predict Target Vessel Restenosis after Infrainguinal Angioplasty with Stent Implantation

Platelet-to-lymphocyte (PLR), neutrophil-to-lymphocyte (NLR) and lymphocyte-to-monocyte (LMR) ratios are associated with the occurrence of critical limb ischemia in peripheral artery disease (PAD). We therefore investigated whether PLR, NLR or LMR are linked to target vessel restenosis (TVR) following infrainguinal angioplasty and stenting. Moreover, we studied on-treatment platelet reactivity and neutrophil-platelet aggregate (NPA) formation as potential underlying mechanisms. Platelet, neutrophil, lymphocyte and monocyte counts were determined one day after angioplasty and stenting in 95 stable PAD patients. Platelet reactivity and NPA formation in response to protease-activated receptor-1 stimulation were measured by light transmission aggregometry (LTA) and flow cytometry, respectively. PLR and NLR were significantly higher in patients who subsequently developed TVR (both p < 0.05). In contrast, LMR did not differ significantly between patients without and with TVR (p = 0.28). A PLR ≥ 91 and NLR ≥2.75 were identified as the best thresholds to predict TVR, providing sensitivities of 87.5% and 81.3%, and specificities of 34.9% and 50.8%, respectively, and were therefore defined as high PLR and high NLR. TVR occurred significantly more often in patients with high PLR and high NLR than in those with lower ratios (both p < 0.05). Patients with high PLR and high NLR exhibited significantly increased on-treatment platelet aggregation compared to those with lower ratios, and patients with high PLR had higher levels of NPA formation (all p < 0.01). In conclusion, PLR and NLR predict TVR after infrainguinal angioplasty with stent implantation. Platelet activation and neutrophil-platelet interaction may be involved in the underlying pathomechanisms.

Ticagrelor Exerts Immune-Modulatory Effect by Attenuating Neutrophil Extracellular Traps

Neutrophils through the release of neutrophil extracellular traps (NETs) containing active tissue factor (TF) are key components of thrombo-inflammation. Platelets-neutrophils interplay in ST elevation myocardial infarction (STEMI) promotes NET formation via inorganic polyphosphates (polyP) released by thrombin-activated platelets. NETs, however, are also induced by biomaterials in a platelet-independent manner. Considering the possible pleiotropic effects of Ticagrelor beyond platelet inhibition and the clinical need for novel antithrombotic strategies targeting inflammation, we investigated the effects of Ticagrelor on polyP and stent-induced NETs in STEMI. Neutrophils from healthy individuals and patients receiving Ticagrelor were stimulated with polyP or drug-eluting stents (DES) to produce NETs. To induce TF expression, neutrophils were further incubated with plasma obtained from the infarct-related artery (IRA) of STEMI patients. The effects of Ticagrelor on NETs and TF loading were assessed using fluorescence microscopy, flow cytometry, myeloperoxidase(MPO)/DNA complex ELISA, and a Western blot. Ticagrelor interrupts platelet–neutrophil interaction by attenuating NETs induced by polyP. However, Ticagrelor does not affect polyP secretion from thrombin-activated platelets. Similarly, the intracellular production of TF in neutrophils triggered by IRA plasma is not hindered by Ticagrelor. Furthermore, DES induce NETs and synchronous stimulation with IRA plasma leads to the formation of thrombogenic TF-bearing NETs. Ticagrelor inhibits stent-induced NET release. These findings suggest a novel immune-modulatory effect of Ticagrelor when it attenuates the formation of thrombogenic NETs.

The blood compatibility challenge. Part 3: Material associated activation of blood cascades and cells

Following protein adsorption/activation which is the first step after the contact of material surfaces and whole blood (part 2), fibrinogen is converted to fibrin and platelets become activated and assembled in the form of a thrombus. This thrombus formation is the key feature that needs to be minimized in the creation of materials with low thrombogenicity. Further aspects of blood compatibility that are important on their own are complement and leukocyte activation which are also important drivers of thrombus formation. Hence this review summarizes the state of knowledge on all of these cascades and cells and their interactions. For each cascade or cell type, the chapter distinguishes statements which are in widespread agreement from statements where there is less of a consensus. STATEMENT OF SIGNIFICANCE: This paper is part 3 of a series of 4 reviews discussing the problem of biomaterial associated thrombogenicity. The objective was to highlight features of broad agreement and provide commentary on those aspects of the problem that were subject to dispute. We hope that future investigators will update these reviews as new scholarship resolves the uncertainties of today.

Mitigation of monocyte driven thrombosis on cobalt chrome surfaces in contact with whole blood by thin film polar/hydrophobic/ionic polyurethane coatings

Monocytes are active at the crossroads between inflammation and coagulation processes since they can secrete pro-inflammatory cytokines and express tissue factor (TF), a major initiator of coagulation. Cobalt-chrome (CoCr), a metal alloy, used as a biomaterial for vascular stents, has been shown to be potentially pro-thrombotic and pro-inflammatory. Research work with a polymer from a family of degradable-polar hydrophobic ionic polyurethanes (D-PHI), called HHHI, has been shown to exhibit anti-inflammatory responses from human monocytes. We have generated multifunctional polyurethane thin films (MPTF) based on the HHHI chemistry, as a thin coating for CoCr and have evaluated the reactivity of blood with MPTF-coated CoCr. The results showed that the coating of CoCr with MPTF derived from HHHI prevents thrombin generation, reduces coagulation activation, and suppresses fibrin formation in whole blood. Activation of monocytes was also suppressed at the surface of MPTF-coated CoCr and specifically the decrease in thrombin generation was accompanied by a significant decrease in TF and pro-inflammatory cytokine levels. Mass spectroscopy of the adsorbed proteins showed lower levels of fibrinogen, fibronectin and complement C3, C4, and C8 when compared to CoCr. We can conclude that MPTFs reduce the pro-thrombotic and pro-inflammatory phenotype of monocytes and macrophages on CoCr, and prevent clotting in whole blood.

Coating of cobalt chrome substrates with thin films of polar/hydrophobic/ionic polyurethanes: Characterization and interaction with human immunoglobulin G and fibronectin

Biomaterial implants often lead to specific tissue reactions that could compromise their bio-integration and/or optimal cellular interactions. Polyurethanes (PU) are of particular interest as coatings to mask CoCr's bioactivity, since they are generally more biocompatible than metal substrates, present a broad range of chemistry, and have highly tunable-mechanical properties. In the current work, complex polyvinyl-urethanes (referred to as D-PHI materials) are studied for their surface phase structures: specifically, an original D-PHI polymer (O-D-PHI) and a differential formulation with relatively higher hydrophobic and ionic content (HHHI) are of interest. The PUs are diluted in tetrahydrofuran (THF) to generate thin films which differentially influence the physical and chemical properties of the D-PHI coatings. AFM images over time show the gradual appearance of domains exhibiting crystalline organisation, and whose shape and size were dependent on D-PHI thickness (thin films vs non-solvent cast resin materials). After three weeks, a complete stabilization of the crystal state is observed. The thin coatings are stable in an aqueous and 37 °C environment. The adsorption of two human plasmatic proteins Immunoglobulin G (IgG) and Fibronectin (Fn), involved in inflammation and coagulation, was studied. The exposure of specific protein sequences (IgG-Fab, Fn-Cell Binding Domain and Fn-N-terminal domain) were dramatically reduced on both D-PHI materials when compared to bare metal CoCr. The implications of these findings would be relevant to defining coating strategies used to improve the blood clotting and immune cell reactivity to CoCr implant materials.

Biocompatible Carbon-Based Coating as Potential Endovascular Material for Stent Surface

Stainless steel 316L is a material commonly used in cardiovascular medicine. Despite the various methods applied in stent production, the rates of in-stent restenosis and thrombosis remain high. In this study graphene was used to coat the surface of 316L substrate for enhanced bio- and hemocompatibility of the substrate. The presence of graphene layers applied to the substrate was investigated using cutting-edge imaging technology: energy-filtered low-voltage FE-SEM approach, scanning electron microscopy (SEM), Raman spectroscopy, and atomic force microscopy (AFM). The potential of G-316L surface to influence endothelial cells phenotype and endothelial-to-mesenchymal transition (EndoMT) has been determined. Our results show that the bio- and hemocompatible properties of graphene coatings along with known radial force of 316L make G-316L a promising candidate for intracoronary implants.

In vitro induction of NETosis: Comprehensive live imaging comparison and systematic review

BACKGROUND

Multiple inducers of in vitro Neutrophil Extracellular Trap (NET) formation (NETosis) have been described. Since there is much variation in study design and results, our aim was to create a systematic review of NETosis inducers and perform a standardized in vitro study of NETosis inducers important in (cardiac) wound healing.

METHODS

In vitro NETosis was studied by incubating neutrophils with PMA, living and dead bacteria (S. aureus and E. coli), LPS, (activated) platelets (supernatant), glucose and calcium ionophore Ionomycin using 3-hour periods of time-lapse confocal imaging.

RESULTS

PMA is a consistent and potent inducer of NETosis. Ionomycin also consistently resulted in extrusion of DNA, albeit with a process that differs from the NETosis process induced by PMA. In our standardized experiments, living bacteria were also potent inducers of NETosis, but dead bacteria, LPS, (activated) platelets (supernatant) and glucose did not induce NETosis.

CONCLUSION

Our systematic review confirms that there is much variation in study design and results of NETosis induction. Our experimental results confirm that under standardized conditions, PMA, living bacteria and Ionomycin all strongly induce NETosis, but real-time confocal imaging reveal different courses of events.