Biochemistry of HDL/LDL

Lipids are transported in blood by lipoproteins. Lipoproteins are non-covalent aggregates of lipid and protein. These form micelle-like particles with a non-polar center of cholesterol esters and triglycerides. The envelope is oriented to the aqueous phase and consists of protein, phospholipids and the hydroxyl groups of non-estered cholesterol.

The most different lipoproteins can be separated by electrophoreses or ultracentrifugation. Lipoproteins are classified in 5 classes according to their thickness: VLDL, IDL, LDL, HDL und VHDL. These classes can be partly subdivided. In the organism LDL can easily become oxidized e.g. by oxygen radicals or metal cat-ions.

In the sub-endothelial matrix the invading macrophages greedily grasp this oxidized LDL, grow unlimited and finally form foam cells. If these foam cells are overloaded by oxidized LDL, they burst and release various chemotactic factors. These attract further macrophages that likewise can invade the sub-endothelial matrix. According to what is presently known this is how the atherosclerotic plaque is formed. If this plaque becomes a fissure or rupture proagulant factors are released. This again may lead to formation of a thrombus and thus to vessel occlusion.

Clinical significance of HDL/LDL

Increased cholesterol levels or LDL in blood are connected to development of atherosclerosis or coronary heart diseases in many studies. Apart from this an increased cholesterol level also has a role in the development of Alzheimer’s disease.

Clinical or research use of HDL/LDL

Evaluation of the lipid metabolism for assessment of a risk situation

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