Myeloperoxidase activity predicts atherosclerotic plaque disruption and atherothrombosis

Abstract

AbstractBackgroundUnstable atherosclerotic plaque is characterized by increased myeloperoxidase (MPO) activity. As unstable plaque is vulnerable to disruption and ensuing thrombosis, we examined whether plaque MPO activity predicts atherothrombosis in a pre-clinical model and correlates with ruptured human atheroma.MethodsTo assess if plaque MPO activity predicts atherothrombosis, rabbits were subjected to aortic endothelial denudation, cholesterol feeding,in vivomagnetic resonance imaging (MRI) of MPO activity using MPO-Gd (gadolinium), followed by pharmacological triggering of atherothrombosis, histology, and MPO activity determined by liquid chromatography tandem mass spectrometry (LC-MSMS) by quantifying the MPO-specific product of hydroethidine, 2-chloroethidium. To correlate plaque MPO activity to ruptured human atheroma,ex vivodetermination of MPO activity by MPO-Gd retention in carotid endarterectomy (CEA) specimens was correlated within vivoMRI plaque phenotyping in patients, histology, and MPO activity determined by LC-MSMS.ResultsIn rabbits, pre-triggerin vivoMPO activity, validated by LC-MSMS and histology, was higher in thrombosis-prone than thrombosis-resistant plaques and lesion-free segments (R1 relaxation rate = 2.2 ± 0.4 versus 1.6 ± 0.2 and 1.5 ± 0.2 s-1, respectively, p<0.0001), and it predicted atherothrombosis. In CEA specimens, MPO-Gd retention was greater in histologic and MRI-graded American Heart Association (AHA) type VI than types III, IV and V plaques (ΔR1 relaxation rate from baseline = 48 ± 6 versus 16 ± 7, 17 ± 8 and 23 ± 8%, respectively, p<0.0001). This association was confirmed by comparing AHA grade to MPO activity determined by LC-MSMS (277 ± 338 versus 7 ± 6, 11 ± 12 and 42 ± 39 pmol 2-chloroethidium/mg protein for type VI versus type III-V plaques, respectively, p=0.0008).ConclusionsMPO activity is elevated in thrombosis-prone rabbit and ruptured human atheroma. Non-invasive molecular imaging of MPO activity predicts atherothrombosis, highlighting the potential of arterial MPO activity to detect vulnerable, destabilized atherosclerosis.