Contribution of angiotensin-converting enzyme and angiotensin II to ischemic stroke: their role in the formation of stable and unstable carotid atherosclerotic plaques

Molecular Pathways of Vulnerable Carotid Plaques at Risk of Ischemic Stroke: A Narrative Review

The concept of vulnerable carotid plaques is pivotal in understanding the pathophysiology of ischemic stroke secondary to large-artery atherosclerosis. In macroscopic evaluation, vulnerable plaques are characterized by one or more of the following features: microcalcification; neovascularization; lipid-rich necrotic cores (LRNCs); intraplaque hemorrhage (IPH); thin fibrous caps; plaque surface ulceration; huge dimensions, suggesting stenosis; and plaque rupture. Recognizing these macroscopic characteristics is crucial for estimating the risk of cerebrovascular events, also in the case of non-significant (less than 50%) stenosis. Inflammatory biomarkers, such as cytokines and adhesion molecules, lipid-related markers like oxidized low-density lipoprotein (LDL), and proteolytic enzymes capable of degrading extracellular matrix components are among the key molecules that are scrutinized for their associative roles in plaque instability. Through their quantification and evaluation, these biomarkers reveal intricate molecular cross-talk governing plaque inflammation, rupture potential, and thrombogenicity. The current evidence demonstrates that plaque vulnerability phenotypes are multiple and heterogeneous and are associated with many highly complex molecular pathways that determine the activation of an immune-mediated cascade that culminates in thromboinflammation. This narrative review provides a comprehensive analysis of the current knowledge on molecular biomarkers expressed by symptomatic carotid plaques. It explores the association of these biomarkers with the structural and compositional attributes that characterize vulnerable plaques.

Association of renin-angiotensin system genes polymorphisms and risk of premature ST elevation myocardial infarction in young Mexican population

: The renin-angiotensin system plays an important role in the regulation of blood pressure and the development of coronary artery disease. The aim was to examine the association of the insertion deletion in the angiotensin-converting enzyme gene, M235T and T174M polymorphisms in the angiotensinogen gene with ST elevation acute myocardial infarction (STEAMI) in young Mexican population. We analyzed 242 unrelated patients with STEAMI 45 or less years of age, admitted to a cardiovascular intense care unit, and 242 individuals without STEAMI matched by age and sex, recruited from January 2006 and June 2013. The polymorphisms insertion deletion, M235T and T174M were determined in all participants by a polymerase chain-reaction-restriction fragment length polymorphism assay. There was a significant difference in the insertion deletion genotype distribution between two groups (P = 0.03) and a higher percentage of the T allele M235T polymorphism in the group of STEAMI patients (P = 0.02). The T174M polymorphism was not associated (P = 0.08). The insertion deletion and M235T polymorphisms, smoking, hypertension, familial history of cardiovascular disease and dyslipidemia were independent risk factors for STEAMI. Our results identified that the D allele from the insertion deletion and M235T but not T174M polymorphisms represent an independent risk factor for STEAMI in young Mexican population.

Increased expression of inhibitor of apoptosis proteins in atherosclerotic plaques of symptomatic patients with carotid stenosis

Vascular remodeling and atheromatous lesion formation are determined in part by the balance between apoptosis and survival of vascular smooth muscle cells (VSMCs). In the chronic stages, apoptosis of VSMCs in the atherosclerotic plaques contributes to the weakening and potential rupture of the plaque causing pathologies such as acute coronary syndrome. The higher incidence of apoptosis in the plaques of symptomatic than in asymptomatic patients has been demonstrated, but the expression of survival proteins, including the inhibitor of apoptosis proteins (IAPs), has not been thoroughly examined. The aim of this study was to investigate the immunohistochemical expression of cellular inhibitor of apoptosis protein-2 (cIAP2), x-linked inhibitor of apoptosis protein (XIAP), and survivin in normal carotid arteries, and carotid endarterectomy specimens of symptomatic and asymptomatic patients with carotid stenosis. The results demonstrated stronger immunopositivity to smooth muscle myosin heavy chain antigen (SM-MHC) (sm2), proliferating cell nuclear antigen (PCNA), and p50 subunit of NF-kappabeta in the asymptomatic plaques than in symptomatic plaques. Furthermore, there was higher expression of cIAP2, XIAP, and survivin in the symptomatic than in the asymptomatic plaques and this paralleled caspase-3 expression. The increased expression of IAPs in symptomatic plaques could be due to endogenous defense mechanism to protect against the pro-apoptotic effect of the inflammatory stimuli that are released in the plaques. This could be involved in the stabilization of symptomatic atheromatous plaques and may prove a potential therapeutic target.

Angiotensin II induces histomorphologic features of unstable plaque in a murine model of accelerated atherosclerosis

BACKGROUND

We explored the role of angiotensin II in determining the histomorphometric features of plaque stability in apolipoprotein E-deficient mice submitted to ligation of the carotid artery.

METHODS

Six-month-old apolipoprotein E-deficient mice underwent ligation of the common left carotid artery and were immediately assigned to receive either angiotensin II (1.4 mg . kg(-1) . d(-1) subcutaneously) or vehicle (phosphate-buffered saline; control) via a subcutaneous osmotic minipump for 4 weeks.

RESULTS

Ligated arteries from control animals developed intimal lesions composed of macrophage foam cell plaques, which accumulated adjacent to the internal elastic lamina and were surrounded by a fibromuscular layer. Angiotensin II-treated mice had a greater intimal area (threefold), which was accompanied by a fivefold increase in the foam cell area. Lesions from angiotensin II-treated mice also displayed complex morphology characterized by intralesional neovasculature and hemorrhage. The content of active matrix metalloproteinase 2, mainly colocalized with macrophage foam cells, and the production of the inflammatory mediators monocyte chemoattractant protein 1 and vascular cell adhesion molecule 1 were also increased by angiotensin II treatment. Although angiotensin II induced vessel expansion and lumen loss to a similar extent, only vessel enlargement correlated with intimal area.

CONCLUSIONS

Taken together, this study's results support a role of angiotensin II in plaque vulnerability by promoting intraplaque neovascularization/hemorrhage, inflammation, and expansive remodeling.