Elsevier

Atherosclerosis

Volume 234, Issue 2, June 2014, Pages 295-302
Atherosclerosis

Review
Endothelial microparticles as conveyors of information in atherosclerotic disease

https://doi.org/10.1016/j.atherosclerosis.2014.03.019Get rights and content

Highlights

  • Review of the role of microparticles in pathogenesis of atherosclerotic disease.

  • Potential of endothelial microparticles as novel biomarkers of atherosclerosis.

  • Use of a novel diagnostic approach to stratify patients most at risk of stroke.

  • Microparticles as signalling molecules in cardiovascular disease.

  • Endothelial microparticles in atherosclerosis.

Abstract

Endothelial microparticles (EMPs) are complex submicron membrane-shed vesicles released into the circulation following endothelium cell activation or apoptosis. They are classified as either physiological or pathological, with anticoagulant or pro-inflammatory effects respectively. Endothelial dysfunction caused by inflammation is a key initiating event in atherosclerotic plaque formation. Athero-emboli, resulting from ruptured carotid plaques are a major cause of stroke. Current clinical techniques for arterial assessment, angiography and carotid ultrasound, give accurate information about stenosis but limited evidence on plaque composition, inflammation or vulnerability; as a result, patients with asymptomatic, or fragile carotid lesions, may not be identified and treated effectively. There is a need to discover novel biomarkers and develop more efficient diagnostic approaches in order to stratify patients at most risk of stroke, who would benefit from interventional surgery. Increasing evidence suggests that EMPs play an important role in the pathogenesis of cardiovascular disease, acting as a marker of damage, either exacerbating disease progression or triggering a repair response. In this regard, it has been suggested that EMPs have the potential to act as biomarkers of disease status. In this review, we will present the evidence to support this hypothesis and propose a novel concept for the development of a diagnostic device that could be implemented in the clinic.

Section snippets

Microparticles

Microparticles (MPs) are anucleoid submicron fragments (50 nm–1 μm diameter) of plasma membranes made up of oxidised phospholipids and specific proteins that represent the cells from which they originate. To date, MPs have been identified as particles released from vascular and blood-related cells such as endothelial cells, platelets, erythrocytes, leukocytes and smooth muscle cells, as demonstrated by their cell-specific surface proteins [1]. MPs were once referred to as ‘cell debris’ [2],

Microparticle release

A number of inflammatory or physical stimuli are able to induce cell activation or apoptosis via different signalling pathways resulting in disruption of lipid membrane asymmetry and cytoskeleton proteins [5]. In turn, this causes budding of the plasma membrane and release of MPs [6] (Fig. 1). Plasma membrane remodelling results from an imbalance between the cytoplasmic and outer plasma membrane aminophospholipids. Cytoplasmic aminophospholipids include phosphatidylserine (PS) and

Endothelial microparticle (EMP) composition and structure

MPs are complex vesicular structures, that consist of an inner and outer phospholipid bilayer containing membrane proteins and receptors [14], [15] (Fig. 1). The protein constituents of MPs are dependent on the cell type they were derived from, and the nature of the stimuli which cells are subjected to, as shown by proteomic analysis of MPs released in vitro from cultured cells [15].

EMPs have also been shown to contain mRNA and micro RNAs (miRs) [16], [17], [18]. MiRs are short non-coding RNAs

Detection of endothelial microparticles

MPs are detected using flow cytometry, a technique which separates cells or particles by their size, granularity and cell-surface antigens, using antibody-conjugated fluorophores [22]. MPs can be more accurately quantified by the addition of a known volume of size and density-specific fluorescently-labelled microbeads to the sample [23].

No single marker for EMPs exists, as many antigens are also present on a number of different cell sub-sets, therefore, for accurate identification a panel of

Atherosclerotic plaque formation

Atherosclerosis is a known chronic inflammatory disease characterised by atheromatous plaque deposition in the vascular bed. Plaque formation is a complex process largely driven by high blood cholesterol, endothelial activation and inflammation-induced vascular cell remodelling with deposition of extracellular matrix (ECM), lipid and calcification. Plaque instability and possible rupture may lead to athero-emboli triggering a major cardiovascular event, such as stroke or myocardial infarction.

Current biomarkers of cardiovascular disease

The risk of developing cardiovascular disease can be assessed by calculating a Framingham risk score, which takes into account, hypertension and high blood LDL, low HDL, and smoking. Typically, atherosclerosis remains undetected until a rupture or a reduction in blood flow results in a cardiovascular event, such as transient ischaemic attack, stroke or myocardial infarction.

There are many studies identifying new biomarkers associated with standard risk factors of cardiovascular disease [40]. A

Evidence of EMPs as a biomarker of atherosclerosis/cardiovascular disease

The vascular endothelium is of paramount importance in arterial wall integrity and blood flow regulation [43] and its activation can lead to cell membrane disruption by apoptosis and EMP release [25]. Our group has previously demonstrated that the pro-inflammatory cytokine, tumour necrosis factor-alpha (TNF-α), stimulated significant release of EMPs from human aortic endothelial cells in vitro, an effect which was abrogated by the TNF-α-binding drug, certolizumab [24]. In patients with Systemic

Detrimental effect of EMPs in atherosclerotic disease

A number of studies have provided evidence on how MPs may be interacting with plaque initiation, formation and stability, although the exact mechanism remains largely unknown. Shear stress and turbulent flow, potential plaque-initiating factors, have been shown to stimulate endothelial cell apoptosis in endarterectomy plaques, which may favour EMP release. EMPs may also attenuate the bioavailability of endothelial nitric oxide, a well-known vasodilator, by stimulating the formation of free

A protective role for EMPs in atherosclerosis

Reports show that EMPs could play a protective role in disease by carrying proteins that possess anti-coagulant and anti-inflammatory properties. For example, Perez-Casal et al. demonstrated that EMPs were released when human endothelial cells were exposed to activated protein C (APC) [82]. Protein C has been shown to have an anti-coagulant and anti-inflammatory role since it can reduce the production of i) thrombin by inactivating factors Va & VIII, ii) tissue factor and iii) cytokines IL-1,

Summary

Despite the current understanding of atherosclerotic plaque development and rupture and the ominous outcome of thrombosis in asymptomatic patients, the question of what causes the transition from a stable to an unstable plaque has yet to be elucidated. Identifying a way of predicting patients' susceptibility to plaque rupture could have enormous cost-saving benefits in the clinic. Although research to explore the use of EMPs as biomarkers of disease has progressed substantially over the last

Funding

Manchester Royal Infirmary, Central Manchester University Hospitals NHS Foundation Trust (AA09299).

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    These authors contributed equally to this work.

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