OBJECTIVE: Oxidative stress and oxidized high-density lipoprotein (HDL) 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), the levels of 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: Plasma MPO levels and CEC activity were examined in controls and lupus 
patients, and 3-chlorotyrosine (MPO specific) and 3-nitrotyrosine (derived from 
reactive nitrogen species) were quantified in human HDL. Multivariable linear 
models were used to estimate and test 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 (CQ). Murine HDL oxidation was 
quantified after NET inhibition in vivo.
RESULTS: SLE patients displayed higher MPO levels and diminished CEC compared to 
controls. SLE HDL had higher 3-nitrotyrosine and 3-chlorotyrosine content than 
control HDL, with site-specific oxidation signatures on apolipoprotein A-I. 
Experiments with human and murine NETs confirmed that chlorination was mediated 
by MPO and NOX, and nitration by NOS and NOX. Mice with lupus treated with the 
NET inhibitor Cl-amidine displayed significantly decreased HDL oxidation. CQ 
inhibited NET formation in vitro.
CONCLUSION: Active NOS, NOX, and MPO within NETs significantly modify HDL, 
rendering the lipoprotein proatherogenic. Since 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.