Inflammation and Diminished Omega-3 Fatty Acids Characterize Unstable Carotid Plaques

BACKGROUND:
The molecular process involved in transition from a stable to an unstable atherosclerotic plaque remains unclear. Inflammation is increasingly being invoked into the pathogenesis of plaque instability and increasing evidence suggests that consumption of long-chain omega-3 polyunsaturated fatty acids (PUFAs) protects against cardiovascular disease, especially fatal myocardial infarction and sudden cardiac death. We aimed to test the hypothesis that the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are related to carotid plaque instability and inflammation, and thus might be related to the prevention of stroke.
METHODS:
Patients with at least 50% internal carotid artery stenosis undergoing carotid endarterectomy were included in this study; plaque stability was determined on the basis of clinical criteria and confirmed histologically. Intra-plaque lipids were extracted and mass spectrometry was used for lipid analysis. Immunohistochemistry and enzyme linked immunosorbent assays (ELISA) were used for protein characterization. Statistical testing was performed using the two-tailed unpaired t-test and multivariable logistic regression.
RESULTS:
Carotid plaques were obtained from 41 patients (35 male; mean age 62, ages 44 - 84); 24 were considered stable and 17 unstable. Unstable carotid atherosclerotic plaques had significantly lower levels of the omega-3 fatty acids DHA (545.8 ± 98 ng/g vs. 270.7 ± 19.6 ng/g, p=.0096) and EPA (385.9 ± 68 ng/g vs. 216.4 ± 17.6 ng/g, p=.0189) compared to stable plaques. However, no differences were found in the levels of the omega-6 fatty acid arachidonic acid between stable and unstable carotid plaques (1644 ± 356 ng/g vs. 2611 ± 1207, p=.2003), respectively. Immunohistochemistry demonstrated an increased inflammatory infiltrate in unstable carotid plaques compared to stable ones, which was confirmed by ELISA (CD68⁺ cells [optical density], 0.461 ± 0.04 vs. 0.312 ± 0.03, p=.003). Other inflammatory molecules including matrix metalloprotease-9 (p=.0011) and soluble vascular cell adhesion molecule-1 (p=.0118) were significantly elevated in unstable carotid plaques compared to stable ones. Using multivariable logistic regression that included pro- and anti-inflammatory lipids and patient-associated comorbidities, only diminished levels of the omega-3 fatty acids DHA (OR 0.98, p=.024) and EPA (OR 0.97, p=.047) were associated with plaque instability.
CONCLUSIONS:
Unstable carotid plaques have decreased amounts of omega-3 fatty acids and an increased expression of various inflammatory molecules. These findings are consistent with epidemiological data demonstrating a diet rich in fish oil aids in atherosclerotic plaque stabilization, and suggest that carotid plaques have similar lipid physiology as coronary plaques. In addition, this data suggests that interventions that increase omega-3 fatty acid incorporation into carotid plaques may prevent stroke and improve the safety of carotid interventions.