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What Are Microparticles?
Microparticles are groups of molecules that are joined together in an enclosed structure, similar to a vesicle. They are released from cells and travel through the blood. Cells release these membrane vesicles during cell activation or programmed cell death. The source of most microparticles include cells that line blood vessels, red blood cells, white blood cells and platelets.
During cell activation, a molecule interacts with a cell and causes a response. A byproduct of the process is the shedding of microparticles. During programmed cell death, the cell contracts, causing microparticles to rip away from the dying cell.
Microparticles consist primarily of lipids and proteins. The outer layer of the vesicle is a phospholipid bilayer composed of negatively charged molecules including phosphatidylserine and phosphatidylethanolamine. Microparticles are also dotted with antigens that indicate which cells released them.
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The Role of Microparticles in Cardiovascular Disease
Although not conclusive, it is possible that the stress imparted by microparticles on the cells of the circulatory system contribute to the development of cardiovascular disease. Microparticles may damage the cells that line the interior walls of blood vessels. This reduces the normal function of these cells, which could eventually lead to high blood pressure and the build up of plaque in blood vessels. It is also possible that the symptoms of cardiovascular disease, which are brought on by other factors, such as poor diet and sedentary lifestyle, initiate the production of microparticles. There is only partial evidence to support the idea that microparticles cause cardiovascular disease.
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Formation of Blood Clots
Microparticles in cardiovascular diseases may be responsible for the development of clots, which can lead to heart attacks or stroke. In order for a clot to form, a membrane must have contact with a negatively charged phospholipid, such as phosphatidylserine, which is present in microparticles. Microparticles facilitate the binding of clotting factors to a membrane, which eventually leads to clot formation.
Research studies have shown that some diseases which cause an increase in clotting have an abnormally high level of microparticles. In some diseases characterized by excessive bleeding, the microparticle level is low. This is not a direct link between clotting and microparticles, but there is a relationship between the two.
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Possible Cause of Inflammation
Inflammation is another factor associated with cardiovascular disease and microparticles may play a role in it. When certain molecules (monocytes, neutrophils) bind to the surface of blood vessels, the blood vessels become inflamed. Microparticles may cause these molecules to bind to blood vessels by causing the expression of adhesion receptors on the cell surface. It does this by delivering arachidonic acid to the cells. Usually, it is microparticles derived from platelets that cause inflammation. Inflammation of blood vessels is a factor in the development of atherosclerosis, which is the hardening of arteries due to the accumulation of plaque.
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1. "Microparticles in Cardiovascular Disease." Oxford Journals. http://cardiovascres.oxfordjournals.org/content/59/2/277.long
2. "Microparticles in Cardiovascular Diseases." Ion Channel Research. http://www.ionchannels.org/showabstract.php?pmid=12909311