The intercellular transport of lipids through the aqueous circulatory system as well as within tissues and other body fluids requires the packaging of these hydrophobic molecules into water soluble carriers (lipoproteins) and their regulated targeting to appropriate tissues by receptor-mediated endocytic pathways as well as scavenger receptor-mediated pathways.1 Lipoproteins have been classified into several major groups on the basis of the density at which they float by ultracentrifugation. In the plasma, chylomicrons and very low density lipoproteins (VLDL) are large particles that have a high lipid to protein ratio and are the major carriers of triglycerides. Intermediate density lipoproteins (IDL) and low density lipoproteins (LDL) are intermediate sized particles that are high in cholesterol and cholesteryl esters; in humans, LDL are the principal cholesterol transporting lipoproteins in the plasma. High density lipoproteins (HDL) are the smallest particles and contain the highest protein to lipid ratio. Certain kinds of HDL particles are involved in the process of "reverse cholesterol transport," a pathway whereby these particles acquire cholesterol from peripheral tissues and transport it to the liver for excretion.2 In addition to the plasma, lipoproteins are also present in other body fluids such as the cerebrospinal fluid (CSF). In contrast to plasma, the majority of CSF lipoproteins are HDL-like in both density and size (see below).3,4
Was this article helpful?
Discover secrets, myths, truths, lies and strategies for dealing effectively with cholesterol, now and forever! Uncover techniques, remedies and alternative for lowering your cholesterol quickly and significantly in just ONE MONTH! Find insights into the screenings, meanings and numbers involved in lowering cholesterol and the implications, consideration it has for your lifestyle and future!