Lipoproteins are protein, phospholipid and cholesterol structures that are used to transport lipids in plasma. Lipoproteins are required for this transport role because lipids do not dissolve in the aqueous environment of the blood. A number of different lipoproteins classes are present in humans and these are named loosely on their varying densities; high density lipoprotein (HDL), intermediate density lipoprotein (IDL), low density lipoprotein (LDL) and very low density lipoprotein (VLDL). In addition, lipoprotein(a) and chylomicrons are also present. Gradient density centrifugation (figure 1) is a method that allows the separation of lipoproteins based on their densities. This method has been used in a research setting to characterise the various lipoproteins, and led to the discovery of heterogeneity within various lipoprotein classes. For example, LDL comprises of smaller denser particles as well as larger less dense particles. Cardiovascular risk is significantly associated with small dense LDL but not large less dense LDL.
Figure 1. Gradient density centrifugation schematic showing the typical lipoprotein sub-classes present.
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