Abstract 511: Mrp8 And Mrp14,Endogenous Activators of Toll-lLke Receptor4, are Associated with Rupture-Prone Human Atherosclerotic Plaques
Objectives: Atherosclerosis is a chronic, complex inflammatory process and is the underlying cause of stroke and myocardial infarction due to rupture of the atherosclerotic plaque leading to acute occlusion of the artery in the brain or heart. Macrophages, infiltrating atherosclerotic lesions, abundantly express Mrp8 and Mrp14. Recently Mrp8, Mrp14 and the complex Mrp8/14 have been identified as endogenous ligands of Tlr-4.The role of Tlr-4 in the development and progression of the atherosclerotic plaque is well recognized and it is associated with a rupture-prone plaque phenotype. Expression of Mrps in human plaques and its relation to plaque phenotype is unknown. For this, we investigated the levels of Mrp8, Mrp14 and Mrp8/14 complex in a large number of human atherosclerotic plaques.
Methods and results: Mrp8, Mrp14 and Mrp8/14 were quantified by ELISAs in human carotid endarterectomy specimens (186 patients) and plaque phenotype was determined by immunohistochemistry. Mrp levels were higher in the unstable (58 fibro-atheromatous, 64 atheromatous) compared to the stable (64 fibrous) plaques: Mrp8 p=0.001; Mrp14 p=0.001; Mrp8/14 p=0.01. Concomitantly, Mrp8, Mrp14 and Mrp8/14 were associated with characteristics of unstable plaques: more macrophages (p=0.024; p=0.002; p=0.076), less smooth muscle cells (p=0.041; p=0.001; p=0.074), larger lipid core (p=0.001; p=0.001; p=0.004), less collagen (p=0.440; p=0.011; p=0.372). Furthermore, Mrp plaque levels were positively correlated with the pro-inflammatory cytokines (IL-6 and IL-8) and matrix metalloproteinsases (MMP2, MMP8 and MMP9) plaque levels. EDA, marker of stable plaques, was negatively associated with Mrps plaque levels. Histological analysis revealed that Mrps are expressed by a subgroup of plaque macrophages localized in the plaque cap and shoulder, the most rupture-prone sites of an atherosclerotic plaque.
Conclusions: We show that Mrp8, Mrp14 and Mrp8/14 are strongly associated with the histological characteristics and inflammatory status of human rupture-prone plaques and identify Mrps as a potential marker for rupture-prone plaques.