Activated macrophages, characterized by increased inducible nitric oxide synthase
(iNOS) expression, participate in atherosclerosis and its complications. Cyclooxygenase
(COX) regulates iNOS activity. As both a substrate for and potential inhibitor of
COX, the omega-3 fatty acid, eicosapentaenoic acid (EPA), may reduce iNOS activity.
Icosapent ethyl is an ethyl ester of EPA, and was shown to reduce ischemic events
in high-risk patients (REDUCE-IT). We tested the effects of EPA on iNOS activity in
lipopolysaccharide (LPS)-activated macrophages.
METHODS AND RESULTS
Murine J774 macrophages were pretreated with vehicle, EPA (10, 20, 40 µM), (10 µM)
for 2 h, then challenged with LPS (1.0 µg/ml). After 24 h, iNOS activity was measured
by nitrite production using the Griess assay. As a positive control, the COX inhibitor
diclofenac was tested (1.0 µg/ml). Treatment with LPS increased nitrite production
by 465% (p < 0.001). EPA treatment reduced nitrite production in a significant, dose-dependent
manner by 40-77% at 10-40 µM, respectively, compared to LPS-alone. EPA at the lowest
concentration tested produced an effect similar to diclofenac, which reduced nitrite
levels by 40% (p < 0.01).
EPA reduced LPS-induced macrophage activation in a dose-dependent manner that was
reproduced to a lesser extent by diclofenac. These findings indicate a novel effect
of EPA on both COX and iNOS activity. The ability of EPA to reduce macrophage activity
may contribute to limiting atherothrombotic risk as evidenced in REDUCE-IT.