APOE ϵ 2 allele is an independent risk factor for vulnerable carotid plaque in ischemic stroke patients

Extracranial carotid artery atherosclerotic plaque and APOE polymorphisms: a systematic review and meta-analysis

Introduction

Carotid atherosclerotic plaque is an important independent risk factor for stroke. Apolipoprotein E (APOE) influences cholesterol levels and certain isoforms are associated with increased carotid atherosclerosis, though the exact association between APOE and carotid plaque is uncertain. The study aimed to evaluate the association between APOE and carotid plaque.

Methods

A systematic review was performed to retrieve all studies which examined the association between carotid plaque and APOE. This study was conducted in accordance with the PRISMA guidelines. Independent readers extracted the relevant data from each study including the type of imaging assessment, plaque definition, frequency of APOE E4 carrier status and type of genotyping. Meta-analyses with an assessment of study heterogeneity and publication bias were performed. Results were presented in a forest plot and summarized using a random-effects model.

Results

After screening 838 studies, 17 studies were included for systematic review. A meta-analysis of 5 published studies showed a significant association between ε4 homozygosity and carotid plaque [odds ratio (OR), 1.53; 95% CI, 1.16, 2.02; p = .003]. Additionally, there was a significant association between patients possessing at least one ε4 allele, heterozygotes or homozygotes, and carotid plaque (OR, 1.25; 95% CI, 1.03, 1.52; p = .03). Lastly, there was no association between ε4 heterozygosity and carotid plaque (OR, 1.08; 95% CI, 0.93, 1.26; p = .30).

Conclusion

APOE ε4 allele is significantly associated with extracranial carotid atherosclerotic plaque, especially for homozygous individuals.

Apolipoprotein E in Cardiometabolic and Neurological Health and Diseases

A preponderance of evidence obtained from genetically modified mice and human population studies reveals the association of apolipoprotein E (apoE) deficiency and polymorphisms with pathogenesis of numerous chronic diseases, including atherosclerosis, obesity/diabetes, and Alzheimer’s disease. The human APOE gene is polymorphic with three major alleles, ε2, ε3 and ε4, encoding apoE2, apoE3, and apoE4, respectively. The APOE gene is expressed in many cell types, including hepatocytes, adipocytes, immune cells of the myeloid lineage, vascular smooth muscle cells, and in the brain. ApoE is present in subclasses of plasma lipoproteins, and it mediates the clearance of atherogenic lipoproteins from plasma circulation via its interaction with LDL receptor family proteins and heparan sulfate proteoglycans. Extracellular apoE also interacts with cell surface receptors and confers signaling events for cell regulation, while apoE expressed endogenously in various cell types regulates cell functions via autocrine and paracrine mechanisms. This review article focuses on lipoprotein transport-dependent and -independent mechanisms by which apoE deficiency or polymorphisms contribute to cardiovascular disease, metabolic disease, and neurological disorders.

Effects of Apolipoprotein E polymorphism on carotid intima-media thickness, incident myocardial infarction and incident stroke

The Apolipoprotein E (APOE) gene polymorphism (rs429358 and rs7412) shows a well-established association with lipid profiles, but its effect on cardiovascular disease is still conflicting. Therefore, we examined the association of different APOE alleles with common carotid artery intima-media thickness (CCA-IMT), carotid plaques, incident myocardial infarction (MI) and stroke. We analyzed data from 3327 participants aged 20-79 years of the population-based Study of Health in Pomerania (SHIP) from Northeast Germany with a median follow-up time of 14.5 years. Linear, logistic, and Cox-regression models were used to assess the associations of the APOE polymorphism with CCA-IMT, carotid plaques, incident MI and stroke, respectively. In our study, the APOE E2 allele was associated with lower CCA-IMT at baseline compared to E3 homozygotes (β: - 0.02 [95% CI - 0.04, - 0.004]). Over the follow-up, 244 MI events and 218 stroke events were observed. APOE E2 and E4 allele were not associated with incident MI (E2 HR: 1.06 [95% CI 0.68, 1.66]; E4 HR: 1.03 [95% CI 0.73, 1.45]) and incident stroke (E2 HR: 0.79 [95% CI 0.48, 1.30]; E4 HR: 0.96 [95% CI 0.66, 1.38]) in any of the models adjusting for potential confounders. However, the positive association between CCA-IMT and incident MI was more pronounced in E2 carriers than E3 homozygotes. Thus, our study suggests that while APOE E2 allele may predispose individuals to lower CCA-IMT, E2 carriers may be more prone to MI than E3 homozygotes as the CCA-IMT increases. APOE E4 allele had no effect on CCA-IMT, plaques, MI or stroke.

Distinct pro-inflammatory properties of myeloid cell-derived apolipoprotein E2 and E4 in atherosclerosis promotion

Polymorphisms in the apolipoprotein E (apoE) gene are risk factors for chronic inflammatory diseases including atherosclerosis. The gene product apoE is synthesized in many cell types and has both lipid transport–dependent and lipid transport–independent functions. Previous studies have shown that apoE expression in myeloid cells protects against atherogenesis in hypercholesterolemic ApoE^−/− mice. However, the mechanism of this protection is still unclear. Using human APOE gene replacement mice as models, this study showed that apoE2 and apoE4 expressed endogenously in myeloid cells enhanced the inflammatory response via mechanisms independent of plasma lipoprotein transport. The data revealed that apoE2-expressing myeloid cells contained higher intracellular cholesterol levels because of impaired efflux, causing increasing inflammasome activation and myelopoiesis. In contrast, intracellular cholesterol levels were not elevated in apoE4-expressing myeloid cells, and its proinflammatory property was found to be independent of inflammasome signaling and related to enhanced oxidative stress. When ApoE^−/− mice were reconstituted with bone marrow from various human APOE gene replacement mice, effective reduction of atherosclerosis was observed with marrow cells obtained from APOE3 but not APOE2 and APOE4 gene replacement mice. Taken together, these results documented that apoE2 and apoE4 expression in myeloid cells promotes inflammation via distinct mechanisms and promotes atherosclerosis in a plasma lipoprotein transport–independent manner.

Carotid intima media thickness and blood biomarkers of atherosclerosis in patients after stroke or myocardial infarction

AIM

To test if circulating levels of markers of inflammation, endothelial function, and chronic infections, as well as association between these markers and carotid intima media thickness (CIMT), depend on the stage of atherosclerosis expressed as a history of a major vascular event.

METHODS

The associations were analyzed separately in 75 healthy controls, 79 patients 3-6 months after the first-ever non-cardioembolic ischemic stroke (IS), and 37 patients 3-6 months after the first-ever myocardial infarction (MI). Data were collected prospectively in 2005. We measured high sensitivity C-reactive protein (hs-CRP), procalcitonin, E-selectin, intercellular adhesion molecule-1 (ICAM-1), serum level of immune complexes (IC), and identified antibodies against Herpes simplex virus type 1 (HSV), Cytomegalovirus, Chlamydia pneumonia, and Helicobacter pylori. Correlations with CIMT were determined using Pearson R and verified after adjustment for age, sex, hypertension, diabetes, and statin therapy.

RESULTS

Median ICAM-1 concentration was significantly lower in controls than in post-IS patients (188 μg/L vs 215 μg/L), and significantly lower in post-IS patients than in post-MI patients (215 μg/L vs 260 μg/L). Control patients also had significantly lower IC level (0.03 U/L) and HSV antibody index (6.0) compared to both post-IS (0.6 U/L, 9.6) and post-MI (0.4 U/L, 9.2) patients. CIMT was correlated with age (Pearson R=0.38, P=0.001) in the control group, immune complexes (R=0.26, P=0.023) in the post-IS group, and with hs-CRP (R=0.40, P=0.017) in the post-MI group. These correlations were confirmed using multiple regression analysis.

CONCLUSIONS

Our study supports linear correlations between CIMT and IC and hs-CRP levels. However, these associations seem to depend on the type of vascular burden.

Comparison of carotid atherosclerotic plaque characteristics between patients with first-time and recurrent acute ischaemic stroke using B-mode ultrasound

OBJECTIVES

The differences between initial and recurrent stroke plaques are not defined. Hence, a nested case-control study was conducted to evaluate the association of stroke recurrence with the echogenic characteristics of carotid plaques in patients with ischaemic stroke.

METHODS

One hundred and four patients with 1-year recurrent acute ischaemic stroke were enrolled and compared with 104 control patients (first-time ischaemic stroke) matched for age, gender, stroke severity and treatment allocation. Based on the Mannheim Carotid Intima-Media Thickness Consensus (2004-2006), the number of carotid plaques and echogenicity between the two groups of patients were compared.

RESULTS

As compared to patients with first-time stroke, those with recurrent stroke showed significantly higher prevalence of heart disease (13.46 vs 28.85%, P = 0.0066) and presence of intracranial stenosis (55.77 vs 89.90%, P < 0.0001). During the 1-year follow-up, patients with recurrent stroke had a significantly higher rate of unstable plaques (80.41%) than patients with first-time stroke (64.21%, P = 0.036). Also, patients with recurrent stroke had a significantly larger number of plaques than patients with first-time stroke (P = 0.0152). Multivariate conditional logistic regression analysis (after adjustment for heart disease and intracranial stenosis) identified an association between 1-year stroke recurrence and the presence of unstable plaques (hazard ratio 3.077; 95% CI: 1.133-8.355).

CONCLUSION

Stroke recurrence is related to advanced atherosclerosis defined by carotid plaque and its characteristics.