Neutrophil extracellular trap-derived enzymes oxidize high-density lipoprotein: an additional proatherogenic mechanism in systemic lupus erythematosus.
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.


CONCLUSIONS
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.
Systemic Autoimmunity Branch, Intramural Research Program, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD 20892.
Carolyne K
CK
Smith
Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109.
Anuradha
A
Vivekanandan-Giri
Department of Medicine and Diabetes and Obesity Center of Excellence, University of Washington, Seattle, WA 98109.
Chongren
C
Tang
Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109.
Jason S
JS
Knight
Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109.
Anna
A
Mathew
Kidney Epidemiology and Cost Center and Biostatistics, University of Michigan, Ann Arbor, MI 48109.
Robin L
RL
Padilla
Kidney Epidemiology and Cost Center and Biostatistics, University of Michigan, Ann Arbor, MI 48109.
Brenda W
BW
Gillespie
Systemic Autoimmunity Branch, Intramural Research Program, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD 20892.
Carmelo
C
Carmona-Rivera
Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109.
Xiaodan
X
Liu
Department of Chemistry, Scripps-Florida, Jupiter, FL 33458.
Venkataraman
V
Subramanian
Systemic Autoimmunity Branch, Intramural Research Program, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD 20892.
Sarfaraz
S
Hasni
Department of Chemistry, Scripps-Florida, Jupiter, FL 33458.
Paul R
PR
Thompson
Department of Medicine and Diabetes and Obesity Center of Excellence, University of Washington, Seattle, WA 98109.
Jay W
JW
Heinecke
Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109.|Kidney Epidemiology and Cost Center and Biostatistics, University of Michigan, Ann Arbor, MI 48109.
Rajiv
R
Saran
Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109.
Subramaniam
S
Pennathur
Systemic Autoimmunity Branch, Intramural Research Program, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD 20892.
Mariana J
MJ
Kaplan
D000328:Adult; D000818:Animals; D002318:Cardiovascular Diseases / Q000201:enzymology; D005260:Female; D006801:Humans; D008075:Lipoproteins, HDL / Q000378:metabolism*; D008180:Lupus Erythematosus, Systemic / Q000097:blood / Q000201:enzymology*; D008297:Male; D051379:Mice; D008875:Middle Aged; D019255:NADPH Oxidases / Q000097:blood; D009504:Neutrophils / Q000201:enzymology*; D019001:Nitric Oxide Synthase / Q000097:blood; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000502:physiology*; D009195:Peroxidase / Q000097:blood
D008075:Lipoproteins, HDL; D009195:Peroxidase; D019001:Nitric Oxide Synthase; D019255:NADPH Oxidases