Atherosclerosis is a complex and common disease of the arteries which is a major cause of cardiovascular disease (CVD) and stroke worldwide. In 2006, in the United States alone, CVD (which includes high blood pressure, coronary heart disease, and stroke) accounted for 34.3% of total deaths. Considering this high percentage of deaths due to CVD, where atherosclerosis is the underlying cause, it is imperative that the current diagnostic and therapeutic techniques are improved to more effectively detect and cure these diseases. As a primary manufacturer of recombinant proteins, Creative Biomart provides recombinant proteins of several sources, grades and formulations for atherosclerosis research applications.
Atherosclerosis and its role in severe cardiovascular events
Continuing research within the last few decades has substantially improved our understanding of the processes underlying atherosclerosis. It has emerged that atherosclerosis is not just a bland deposition of lipids but involves complex physiological, biochemical and cellular processes. One aspect of these processes is the inflammatory response of the cells within the vessel wall and immune cells of the blood. This inflammatory response generally follows the lipid deposition and involves recruitment of immune cells to the site of lipid deposition by the endothelial cells lining the vessel wall. Lipid deposition usually starts on the luminal vascular sites that are prone to developing atherosclerosis which include curvatures and branches of the vessel. These sites experience a blood flow pattern that is substantially different from that experienced by the rest of the arterial network. Macrophages start accumulating at atherosclerosis prone sites, engorge cholesterol and become foam cells. These foam cells populate the sub-endothelial regions of the arteries which start to form the initial lesions called fatty streaks. Fatty streaks are not clinically significant structures as they do not cause any substantial clinical adverse events. But these fatty streaks are a first step in the complexities that follow over a longer period of a patient’s lifespan.
Fatty streaks serve as a precursor or seeding grounds for the formation of more advanced legions called plaques. Plaques present a more complex and challenging environment in the arterial lumen. In advanced stages of atherosclerosis, plaques can lead to a substantial loss of arterial elasticity and narrowing of the arterial lumen. The lumen of this artery starts losing its structural uniformity and becomes occluded with plaque. Such an occlusion, when clinically significant, can severely restrict blood flow affecting normal functioning of the organs and tissues downstream. Also, a more severe clinical event that can occur is the sudden loss of plaque integrity leading to plaque rupture. This process releases a significant amount of cellular debris, fibrous material and other plaque components into the blood stream causing clot formation which can get lodged into smaller arteries potentially causing myocardial infarction or stroke leading to death in many cases.
Inflammation in atherosclerosis plays a major role in causing the cardiovascular events discussed above. Endothelial cells lining the blood vessel lumen are actively involved in orchestrating the inflammatory processes at atherosclerosis prone vascular sites. It has been observed that the arterial endothelium expresses various adhesion molecules at the onset of atherosclerosis at higher levels compared to those expressed by normal endothelium. These adhesion molecules include P-selectin, E-selectin, intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1). The presence of adhesion molecules leads to a chain of events causing leukocyte arrest and transmigration across the endothelium via what is called the leukocyte adhesion cascade. This process leads to further complications of the disease as discussed above.
Accumulating evidence suggests that VCAM-1 is increased at the sites of atherosclerosis, and is known to contribute greatly in the tethering and firm adhesion events of leukocytes in atherosclerosis. VCAM-1, a member of the immunoglobulin gene superfamily, exhibits alternative splicing into two isoforms. Studies have indicated that monocyte adhesion and trans-endothelial migration occurs through interactions between these two isoforms of VCAM-1 (expressed by endothelial cells) and VLA-4 (the integrin expressed by monocytes). Monocyte adhesion and migration across the vascular endothelium is one of the major steps in atherosclerosis that leads to plaque formation and other complications discussed above.
Site specific targeting in atherosclerosis
The concept of site specific targeting using molecules expressed on the surface of inflamed cells mimics leukocyte adhesion to sites of inflammation. It has opened new avenues in developing innovative diagnostics and therapeutics. Extensive biomedical research in the last few decades, especially in the area of cell adhesion, has enabled the development of molecular targets that are specific to the disease and also to the site where the disease is more active. Various inflammatory diseases are characterized by unique molecular signatures. These molecular signatures can be defined by one or more molecules that play a major role in the initiation, development or progression of the disease under consideration. Thus, a site specific targeting system can be tailor made for each inflammatory disease that presents a unique molecular signature. Atherosclerosis is also an inflammatory disease characterized by elevated ex
Blood based diagnostics for atherosclerosis
Blood based diagnostic techniques are conceptually simple and primitive assays exist for detecting the presence of atherosclerosis using markers of inflammation. A number of inflammatory markers have been identified for this purpose. Examples include C-reactive protein (CRP), cytokines such as interleukin-1 (IL-1), tumor necrosis factor-α (TNF-α) and transforming growth factor-β (TGF-β), and soluble adhesion molecules such as sICAM-1, sVCAM-1, sP-selectin and sE-selectin. Since many of these markers are implicated in a range of inflammatory diseases, it is difficult to correlate their levels with atherosclerosis development unless a combination method is used where levels of these markers are coupled with other indications of atherosclerosis. This motivates the development of a diagnostic technique that utilizes more than one aspect of atherosclerosis, e.g. the number of endothelial cells and their activation state, may improve our ability to detect atherosclerosis early in its development so that adverse clinical events may be avoided.
Recent studies in atherosclerosis have indicated that the endothelium in the vascular segments affected by atherosclerosis is subject to wear and tear due to hydrodynamic and biochemical processes. This led to the hypothesis that such wear and tear would cause substantial vascular damage and an increase in circulating endothelial cells (CECs). The defects in the endothelial cell adhesive mechanisms (e.g. the reduced affinity of the integrins) are caused by the action from cytokines, mechanical forces or nitric oxide (NO). These mechanisms are responsible for endothelial cell detachment.
Endothelial cells at the sites of atherosclerosis experience biochemical insults in addition to mechanical forces. Hence the detached endothelial cells may carry a unique molecular signature. The most obvious molecular candidate would be VCAM-1 since it is over-expressed at sites of atherosclerosis as discussed in previous paragraphs. Thus, development of a blood based assay that can determine the nature and number of CECs in blood samples from atherosclerotic patients using a marker such as VCAM-1 could serve as an excellent diagnostic tool.
1. Berry J D, Liu K, Folsom A R, et al. Prevalence and Progression of Subclinical Atherosclerosis in Younger Adults With Low Short-Term but High Lifetime Estimated Risk For Cardiovascular Disease The Coronary Artery Risk Development in Young Adults Study and Multi-Ethnic Study of Atherosclerosis[J]. Circulation, 2009, 119(3): 382-389.
2. Ross R. Atherosclerosis—an inflammatory disease[J]. New England journal of medicine, 1999, 340(2): 115-126.
3. VanderLaan P A, Reardon C A, Getz G S. Site specificity of atherosclerosis site-selective responses to atherosclerotic modulators[J]. Arteriosclerosis, thrombosis, and vascular biology, 2004, 24(1): 12-22.
4. Grey E, Bratteli C, Glasser S P, et al. Reduced small artery but not large artery elasticity is an independent risk marker for cardiovascular events[J]. American journal of hypertension, 2003, 16(4): 265-269.
5. Guezguez B, Vigneron P, Lamerant N, et al. Dual role of melanoma cell adhesion molecule (MCAM)/CD146 in lymphocyte endothelium interaction: MCAM/CD146 promotes rolling via microvilli induction in lymphocyte and is an endothelial adhesion receptor[J]. The Journal of Immunology, 2007, 179(10): 6673-6685.
6. Magyar M T, Szikszai Z, Balla J, et al. Early-onset carotid atherosclerosis is associated with increased intima-media thickness and elevated serum levels of inflammatory markers[J]. Stroke, 2003, 34(1): 58-63.