Canadian Medical Guide > Chemicals and Drugs > Lipids > Lipoproteins Terms and Definitions

Lipoproteins

Medical Definition:	Any of the lipid-protein complexes in which lipids are transported in the blood. Lipoprotein particles consist of a spherical hydrophobic core of triglycerides or cholesteryl esters surrounded by an amphipathic monolayer of phospholipids, cholesterol, and apolipoproteins. (From Dorland, 27th ed)
Guide Notes:	GEN or unspecified; prefer specifics; /blood: consider also HYPERLIPOPROTEINEMIA; /defic: consider also HYPOLIPOPROTEINEMIA & specifics

Lipoproteins Categories.

	Chylomicrons - A class of lipoproteins that carry dietary cholesterol and triglycerides from the small intestines to the tissues.
	Lipoprotein(a) - A family of lipoprotein particles varying in density and size depending on the protein-lipid ratio and the protein composition. These particles consist of apolipoprotein B-100 covalently linked to apolipoprotein-a by one or two disulfide bonds. There is a correlation between high plasma levels of this lipoprotein and increased risk for atherosclerotic cardiovascular disease.
	Lipoprotein-X - An abnormal lipoprotein which is present in large amounts in individuals suffering from obstructive liver diseases. It exists as a bilayer vesicle of equimolar phospholipids and unesterified cholesterol containing small amounts of plasma proteins (mainly albumin) in its internal aqueous compartment together with some apolipoproteins adsorbed on its surface. Separates with LDL by ultracentrifugation.
	Lipoproteins, HDL - A class of lipoproteins frequently divided into HDL2 and HDL3 and the minor variant HDL1. HDL promote transport of cholesterol from extrahepatic tissue to the liver for excretion in the bile. Synthesized by the liver as discoid "nascent HDL" particles lacking a lipid core, they accumulate a core of cholesterol esters during reverse cholesterol transport and transfer them to the liver directly or indirectly via other lipoproteins. HDL also shuttle apolipoproteins C-II and E to and from triglyceride-rich lipoproteins during catabolism of the lipoproteins. Serum HDL cholesterol has been negatively correlated with premature coronary heart disease. (Dorland, 28th ed)
	Lipoproteins, LDL - A class of lipoproteins responsible for transport of cholesterol to extrahepatic tissues. They are formed in the circulation when very-low-density lipoproteins are degraded first to intermediate-density lipoproteins and then to LDL by the gain and loss of specific apolipoproteins and the loss of most of their triglycerides. LDL are taken up and catabolized by both the liver and extrahepatic tissues by specific receptor-mediated endocytosis. (Dorland, 28th ed)
	Lipoproteins, VLDL - A class of lipoproteins that transport triglycerides from the intestine and liver to adipose and muscle tissues. Synthesized by the liver, they contain primarily triglycerides in their lipid cores, with some cholesterol esters. As their triglycerides are cleaved by endothelial lipoprotein lipase and transferred to hepatic tissues, the VLDL (very-low-density lipoprotein) particles lose most of their apolipoprotein C and become intermediate-density lipoproteins. (Dorland, 28th ed)
	Platelet Factor 3 - A lipoprotein with pronounced electronegative surface charge found in association with platelet membrane and platelet granules. In the sequence of blood coagulation reactions, it is required for activation of factor VIII and for the conversion of prothrombin to thrombin.
	Vitellogenin - A serum and yolk protein which has been characterized as a calcium-binding glycolipophosphoprotein. It is induced by estrogen or juvenile hormone and is essential for yolk formation in various insect species.

Lipoproteins Medical Definitions and Terms

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