Neutrophil Extracellular Trap–Derived Enzymes Oxidize High‐Density Lipoprotein: An Additional Proatherogenic Mechanism in Systemic Lupus Erythematosus

Abstract

Objective Oxidative stress and oxidized high-density lipoprotein (oxHDL) are implicated as risk factors for cardiovascular disease (CVD) in systemic lupus erythematosus (SLE). Yet, how HDL is oxidized and rendered dysfunctional in SLE remains unclear. Neutrophil extracellular traps (NETs), which are elevated in lupus, possess oxidant-generating enzymes including myeloperoxidase (MPO), NADPH oxidase (NOX) and nitric oxide synthase (NOS). We hypothesized that NETs mediate HDL oxidation, impairing cholesterol efflux capacity (CEC). Methods Control and lupus plasma MPO levels and CEC activity were examined; 3-chlorotyrosine (MPO-specific) and 3-nitrotyrosine (derived from reactive nitrogen species) were quantified in human HDL. Multivariable linear models estimated and tested differences between groups. HDL was exposed to NETs from control and lupus neutrophils in the presence or absence of MPO, NOX, NOS inhibitors and chloroquine. Murine HDL oxidation was quantified after NET inhibition in vivo. Results SLE subjects displayed higher MPO levels and diminished CEC. SLE HDL had higher 3-nitrotyrosine and 3-chlorotyrosine content, with site-specific oxidation signatures on apoA1. Experiments with human and murine NETs confirmed that chlorination is mediated by MPO and NOX, and nitration by NOS and NOX. Lupus mice treated with the NET-inhibitor Cl-amidine displayed significantly decreased oxHDL. Chloroquine inhibited NET formation in vitro. Conclusion Active NOS, NOX and MPO within NETs significantly modify HDL, rendering the lipoprotein proatherogenic. As NET formation is enhanced in SLE, these findings support a novel role for NET-derived lipoprotein oxidation in SLE-associated CVD and identify additional proatherogenic roles of neutrophils and putative protective roles of antimalarials in autoimmunity.

Mechanism of interferon-gamma production by monocytes stimulated with myeloperoxidase and neutrophil extracellular traps

“…Indeed, it has been shown that myeloperoxidase, lactoperoxidase, and eosinophil peroxidase have a central role in oxidative damage associated with inflammatory disorders by utilizing hydrogen peroxide and halides/pseudo halides to generate the corresponding hypohalous acid [31]. NETs have been reported to contain oxidative enzymes, including myeloperoxidase, NADPH oxidase, and nitric oxide synthase [32]. Therefore, the inhibitory effect of PDTC on IFN-gamma production by monocytes may be related to both its role as a low molecular weight thiol antioxidant and its potent inhibition of NF-kB.…”

Oxidative Modifications of Protein Tyrosyl Residues Are Increased in Plasma of Human Subjects with Interstitial Lung Disease

“…Human neutrophils and monocytes were isolated by buoyant density centrifugation as described previously (21)(22)(23)(24)(25). The human monocytes were purified by adhesion, cultured in 35-mm plastic dishes (2 3 10 6 cells/dish; BD Biosciences, San Jose, CA), and incubated in 2 mM L-glutamine supplemented RPMI-1640 without phenol red (Life Technology, Carlsbad, CA).…”

Lupus high-density lipoprotein induces proinflammatory responses in macrophages by binding lectin-like oxidised low-density lipoprotein receptor 1 and failing to promote activating transcription factor 3 activity

“…When HDL becomes oxidised, it loses its cardioprotective effects and displays impaired cholesterol efflux capacity and decreased ability to block low-density lipoprotein (LDL) oxidation 4–10. We recently demonstrated that neutrophil extracellular traps in lupus promote proatherogenic modifications (3-nitrotyrosine and 3-chlorotyrosine oxidation) in HDL and that oxidised lupus HDL displays impaired cholesterol efflux capacity 7. What remains unclear is whether this modified SLE HDL promotes aberrant myeloid cell responses, leading to atherogenesis and systemic inflammation.…”