High Levels of Soluble Lectinlike Oxidized Low-Density Lipoprotein Receptor-1 Are Associated With Carotid Plaque Inflammation and Increased Risk of Ischemic Stroke

Abstract

Background When the lectinlike oxidized low-density lipoprotein (ox LDL) receptor-1 ( LOX -1), a scavenger receptor for ox LDL , binds ox LDL , processes leading to endothelial dysfunction and inflammation are promoted. We aimed to study release mechanisms of LOX -1 and how circulating levels of soluble LOX -1 ( sLOX -1) relate to plaque inflammation and future risk for ischemic stroke. Methods and Results Endothelial cells and leukocytes were used to study release of sLOX -1. Plasma levels of sLOX -1 were determined in 4703 participants in the Malmö Diet and Cancer cohort. Incidence of ischemic stroke was monitored. For 202 patients undergoing carotid endarterectomy, levels of sLOX -1 were analyzed in plasma and plaque homogenates and related to plaque inflammation factors. Endothelial cells released sLOX -1 when exposed to ox LDL . A total of 257 subjects experienced stroke during a mean follow-up of 16.5 years. Subjects in the highest tertile of sLOX -1 had a stroke hazard ratio of 1.75 (95% CI, 1.28-2.39) compared with those in the lowest tertile after adjusting for age and sex. The patients undergoing carotid endarterectomy had a significant association between plasma sLOX -1 and the plaque content of sLOX -1 ( r=0.209, P=0.004). Plaques with high levels of sLOX -1 had more ox LDL , proinflammatory cytokines, and matrix metalloproteinases. Conclusions Our findings demonstrate that ox LDL induces the release of sLOX -1 from endothelial cells and that circulating levels of sLOX -1 correlate with carotid plaque inflammation and risk for ischemic stroke. These observations provide clinical support to experimental studies implicating LOX -1 in atherosclerosis and its possible role as target for cardiovascular intervention.

Keywords: atherosclerosis; ischemic stroke; lectinlike oxidized low‐density lipoprotein receptor‐1; soluble lectinlike oxidized low‐density lipoprotein receptor‐1.

Figure 1

Kaplan‐Meier survival curve per tertile of soluble lectinlike oxidized low‐density lipoprotein receptor‐1 (sLOX‐1) in the Malmö Diet and Cancer cohort. The numbers below the figure denote the number of patients at risk per tertile of sLOX‐1 and the number of events between parentheses. Log‐rank test for trend across tertiles: P<0.001.

Figure 2

In vitro cultured human umbilical vein endothelial cells (HUVECs) stimulated with 25 μg/mL of oxidized low‐density lipoprotein (oxLDL) induce a release of soluble lectinlike oxLDL receptor‐1 (sLOX‐1) into the medium (lines representing mean and SEM; results are pooled from 3 individual experiments) (A) and peripheral blood mononuclear cells (PBMCs) stimulated with tumor necrosis factor‐α induce the release of sLOX‐1 in a dose‐dependent pattern (lines representing mean and SEM) (B). Each data point represents a single well replicate. Level of significance is marked: *P=0.01, **P<0.01, ****P<0.001.

Figure 3

Immunohistochemistry showing the colocalization of lectinlike oxidized low‐density lipoprotein receptor‐1 (LOX‐1), CD68, and neutral lipids (Oil Red O) in plaque tissue from the Carotid Plaque Imaging Project. A, LOX‐1. B, Isotype control. C, Oil Red O (neutral lipids). D, CD68 (macrophages). E, α‐Actin (smooth muscle cells). Bar=50 μm.

Figure 4

Scatter plot showing the positive correlation between plasma soluble lectinlike oxidized low‐density lipoprotein receptor‐1 (sLOX‐1; arbitrary units/mL) and plaque sLOX‐1 (arbitrary units/g wet weight plaque) content in the Carotid Plaque Imaging Project cohort (Spearman's correlation: r=0.209, P=0.004).