Increased Levels of Lectin-Like Oxidized Low-Density Lipoprotein Receptor-1 in Ischemic Stroke and Transient Ischemic Attack

Abstract

Background: Soluble lectin-like oxidized low-density lipoprotein receptor-1 (sLOX-1) has been shown to be increased in patients with acute ischemic stroke. Here, we evaluated plasma sLOX-1 levels and vascular carotid plaque LOX-1 (ie, OLR1) gene expression in patients with ischemic stroke and transient ischemic attack (TIA) with particular focus on their relation to time since symptom onset.

Methods and results: Plasma sLOX-1 (n=232) and carotid plaque OLR1 gene expression (n=146) were evaluated in patients who were referred to evaluation for carotid endarterectomy, as well as in healthy control plasma (n=81). Patients were categorized according to presence of acute ischemic stroke or transient ischemic attack (n=35) ≤7 days, >7 days ≤3 months (n=90), >3 months (n=40), or no reported symptoms before study inclusion (n=67). Our major findings were the following: (1) Patients with carotid atherosclerosis had increased plasma sLOX-1 levels as compared with controls. (2) Plaque OLR1 mRNA levels were increased in carotid plaques (n=146) compared with nonatherosclerotic vessels (ie, common iliac arteries of organ donors, n=10). (3) There were no differences in sLOX plasma levels or OLR1 gene expression when analyzed according to the time since relevant cerebral ischemic symptoms. (4) Also patients with severe carotid atherosclerosis without any previous ischemic events had raised sLOX-1 levels. (5) Immunostaining showed colocalization between LOX-1 and macrophages within the carotid plaques. (6) Also patients with acute stroke (within 7 days) caused by atrial fibrillation (n=22) had comparable raised sLOX-1 levels.

Conclusions: sLOX-1 levels are elevated in patients with ischemic stroke and transient ischemic attack independent of cause and time since the ischemic event.

Keywords: cerebrovascular disease/stroke; inflammation; ischemic stroke.

Figure 1

Plasma sLOX‐1 and plaque OLR1 mRNA expression in patients with carotid atherosclerosis. A, Soluble (s)LOX‐1 is increased in plasma of patients with carotid atherosclerosis (n=232) as compared with healthy controls (n=81) (P<0.001) with no differences between subgroups of patients with carotid atherosclerosis (ie, ischemic stroke or TIA <7 days [n=35], >7 days and ≤3 months [n=90], >3 months [n=40] before study inclusion or no reported symptoms [n=67]). B, OLR1 gene expression is increased in carotid plaques (n=146) as compared with control arteries (n=10). There are no differences in OLR1 gene expression between subgroups of patients with carotid atherosclerosis (ie, ischemic stroke or TIA <7 days [n=21], >7 days and ≤3 months [n=76], >3 months [n=21] before study inclusion, or no reported symptoms [None; n=28]). C, No correlation between plasma sLOX‐1 and plaque OLR1 gene expression in patients with carotid atherosclerosis (Spearman's r=0.15, P=0.18, n=81). Data are presented as mean and SEM. Analyses were performed using Kruskal–Wallis test, Mann–Whitney U test, and Spearman's rank correlation. *P<0.05, and ****P<0.0001 vs controls (Mann–Whitney). ctrs indicates controls; sLOX‐1, soluble lectin‐like oxidized low‐density lipoprotein receptor 1; TIA, transient ischemic attack.

Figure 2

Correlations of plaque OLR1 gene expression with mRNA levels of cell markers in carotid plaques (n=146). There is a positive correlation of OLR1 gene expression and the macrophage markers (A) CD68, (B) CD14, and (C) CD163. There is also a positive correlation with the endothelial marker CD31 (D) but a negative correlation with the SMC marker ACTA2 (E). The mRNA levels are normalized to the mean of 2 reference genes (GAPDH and β‐ACTIN). SMC indicates smooth muscle cells.

Figure 3

Histological staining of representative carotid plaque. Immunohistochemical staining of carotid plaque for lipid accumulation (A) Oil‐red‐O staining and (B) CD68⁺ cell (ie, macrophages), and (C) LOX‐1 show lipid accumulation, macrophage infiltration, and LOX‐1 distribution throughout the carotid plaque. LOX‐1 indicates lectin‐like oxidized low‐density lipoprotein receptor 1.

Figure 4

Fluorescence immunohistochemical staining of carotid plaques. Fluorescence immunohistochemical staining demonstrates colocalization between LOX‐1 (green) and (A) CD68 (macrophages, red), (B) CD31 (endothelial cells, red), and (C) aSMA (red). LOX‐1 indicates lectin‐like oxidized low‐density lipoprotein receptor 1; aSMA, alpha smooth muscle cells.