Plasma eicosanoid profiling in the course of proprotein convertase subtilisin-kexin type 9 inhibition: insights from a metabolomic analysis

Background

Treatment with monoclonal antibodies targeting circulating proprotein convertase subtilisin-kexin type 9 (PCSK9) was found to reduce all-cause mortality in addition to cardiovascular events, suggesting pleiotropic effects. Eicosanoids are bioactive metabolites involved in cardiovascular disease and have not yet been studied in the course of PCSK9 inhibition.

Methods

In this prospective translational single-center study, plasma samples were collected from 64 patients before and after initiation of PCSK9 inhibitor treatment. Metabolomic analyses were performed using liquid chromatography coupled to high-resolution mass spectrometry.

Results

A total of 62 bioactive eicosanoids were detected. Among the metabolites, four were significantly decreased by PCSK9 inhibition after one month and remained stable after 6 months (figure): arachidonic acid (p=0.003), 12,13-DiHOME (p<0.001), 9-HpODE_9.91 (p=0.007) and HpODE_7.71 (p=0.011). Phospholipase A2 levels were reduced by 40% after 1 month (p=0.003) and by additional 50% after 6 months of treatment (p=0.015), but did not correlate with eicosanoids (p=0.057). The change in arachidonic acid levels resulted in a significant increase in the ratio of omega-3 to omega-6 polyunsaturated fatty acids (p=0.002).

Conclusion

PCSK9 inhibition leads to significant changes in the eicosanoid profile already after one month, in particular to a downregulation of arachidonic acid. This discovery complements the presumed pleiotropic effects of PCSK9 inhibition and may provide additional benefit in the treatment of atherosclerotic disease.

Funding Acknowledgement

Type of funding sources: None.

Natural IgM attenuate formation of neutrophil extracellular traps induced by oxidation-specific epitopes in vitro and in vivo

Background

Neutrophil extracellular traps (NETs) emerged as important drivers of thrombus formation in acute myocardial infarction (AMI). Therefore, mechanistic understanding of inducers and modulators of NETosis at the site of occlusion is pivotal for new diagnostic and therapeutic approaches. Many triggers of NET formation have been described, among them oxidations-specific epitopes (OSE), products of lipid peroxidation. Extracellular vesicles (EV) carrying OSE are elevated in AMI. OSE-EV can be recognized by natural IgM antibodies exerting protective functions in cardiovascular disease by reducing the pro-inflammatory response to OSE.

Purpose

We hypothesized that EV-induced NET formation could be dampened by OSE-IgM in vitro and in vivo.

Methods

Patients were recruited after diagnosis of ST-segment elevation myocardial infarction (STEMI, n=51). Blood was aspirated from the culprit site during percutaneous coronary intervention and at several follow-up time points. Myocardial function was assessed by cardiac magnetic resonance (CMR) at 72 hours and 6 months. EV were isolated by ultracentrifugation and characterized by flow cytometry staining for CD45, CD41a, CD144, and OSE. Isolated EV were used for neutrophil stimulation in vitro and in vivo employing a murine injection model. NETs were visualized by immunofluorescence, staining for DNA, histones, citrullinated histone 3, and myeloperoxidase. NET markers and natural IgM recognizing OSE (OSE-IgM) in murine and patient plasma were measured by ELISA.

Results

EVs of endothelial, leukocyte, and platelet origin revealed a prominent absolute and relative increase of the OSE-carrying population as recognized by the malondialdehyde-specific antibody LR04. Plasma derived from the site of occlusion contained more and proportionally higher levels of OSE-EV derived from CD45+ cells than the intra-patient peripheral control. No difference was observed for EV of platelet origin, and the endothelial-derived subset of OSE-EV was decreased at the culprit site. OSE-EV and NET markers were positively associated in the circulation. Decreasing OSE-IgM levels during hospital stay indicated consumption of protective antibodies. EV isolated from AMI patient plasma were revealed to induce NET formation in neutrophils in vitro and after injection into mice in vivo, as measured by cell-free DNA and fluorescence microscopy of citrullinated histones in neutrophils. The LR04 IgM antibody, but not a control IgM, reduced the NETogenic effect of EV in both models. Consistently, higher circulating levels of EV and lower OSE-IgM were associated with a reduced ejection fraction in AMI patients at 72 hours and six months.

Conclusion

EV from AMI patients induced NETosis in vitro and in vivo. IgM recognizing malondialdehyde-epitopes diminished this effect indicating that the balance between OSE-EV and OSE-IgM during AMI may represent a potential prognostic and therapeutic target with impact on heart function.

Funding Acknowledgement

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): Vienna Science and Technology Fund (WWTF)

Proteomic profiling of acute stent thrombi reveals critical involvement of the complement system

Background

Stent thrombosis (ST) is a severe complication after primary percutaneous coronary intervention (pPCI) and associated with significant morbidity and mortality. Apart from procedure- and lesion-related parameters and patient-related factors. However, the underlying molecular and cellular mechanisms of ST are still not fully understood.

Purpose

We aimed to perform in-depth proteomic analysis of ST to understand its pathogenesis.

Methods

We recruited 77 patients suffering from ST after pPCI for myocardial infarction (MI). As controls, we included matched patients suffering from native vessel acute myocardial infarction (NT, n=154). Five cases of acute ST (within 24 h) and six cases of NT thrombi aspirated from the culprit site were subjected to shotgun proteomic analysis. Gene-set analysis was employed to screen for pathways differing between ST and NT. All-cause mortality was assessed using Kaplan-Meier analysis.

Results

9 patients presented with acute ST (<24 h, 11.7%), 18 patients with subacute ST (24 h to 30 days, 23.4%), 11 patients with late ST (30 days to 1 year, 14.3%) and 39 patients with very late ST (>1 year, 50.6%). ST was associated with increased all-cause mortality compared to NT (mean survival 129 vs. 109 months, log-rank p=0.032). We identified a total of 2438 proteins to be expressed in both ST and NT thrombi. Gene set analysis revealed the complement system to be highly active in acute ST compared to NT. Specifically, we found factors of both the classical (complement factor [C]1q, C1s) and alternative pathway (complement factor B) to be increased in ST, along with higher levels of C2, C3, C4a, C4b, C5, C8a and C9.

Conclusion

This hypothesis-generating study highlights a crucial role of the complement system in the pathogenesis of acute ST. Further studies are required to validate these findings in a larger cohort.

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): Austrian Science Fund

Neutrophil extracellular traps induce MCP-1 release from endothelial cells at the plaque rupture site in acute myocardial infarction

Introduction

Leukocyte-mediated inflammation is crucial in acute myocardial infarction (AMI). We recently observed that neutrophil extracellular traps (NETs) are increased at the culprit site, promoting activation and differentiation of fibrocytes, cells with mesenchymal and leukocytic properties. Fibrocyte migration is mediated by monocyte chemoattractant protein (MCP)-1 and C-C chemokine receptor type 2 (CCR2). We investigated the interplay between NETs, fibrocyte function, and MCP-1 in AMI.

Methods

Culprit site and femoral blood of AMI patients was drawn during percutaneous coronary intervention. We characterized CCR2 expression of fibrocytes by flow cytometry. MCP-1 and the NET marker citrullinated histone H3 (citH3) were measured by ELISA. Fibrocytes were treated in vitro with MCP-1. Human coronary arterial endothelial cells (hCAECs) were stimulated with isolated NETs, and MCP-1 was measured by ELISA and qPCR. The influence of MCP-1 on NET formation in vitro was assessed using isolated neutrophils.

Results

We have included 50 consecutive AMI patients into the study. NETs and concentrations of MCP-1 were increased at the CLS. NET stimulation of hCAECs induced MCP-1 on mRNA and protein level. Increasing MCP-1 gradient was associated with fibrocyte accumulation at the site of occlusion. In the presence of higher MCP-1 these fibrocytes expressed proportionally less CCR2 than peripheral fibrocytes. In vitro, MCP-1 dose-dependently decreased fibrocyte CCR2 and reduced ex vivo NET release of healthy donor neutrophils.

Conclusions

NETs induce endothelial MCP-1 release, presumably promoting a chemotactic gradient for leukocyte and fibrocyte migration. MCP-1 mediated inhibition of NET formation could point to a negative feedback loop. These data will shed light on vascular healing.

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): Austrian Science Fund