Lipoproteins (more precisely, the plasma lipoprotein particles) are non-covalent aggregates ( proteids ) of lipids and proteins mizellenähnliche particles with a non-polar core of cholesterol esters and triglycerides, as well as a directed toward the aqueous phase case with polar, hydrophilic moieties form, comprising of protein, phospholipids and unesterified cholesterol from hydroxyl groups.
- 2.1 by function
- 2.2 Density
Plasma lipoprotein particles used in all classes of animals the transport of water-insoluble lipids (fats ) and cholesterol and cholesteryl ester in the blood. Basically include all particles both triglycerides and cholesterol and cholesteryl ester, but in very different amounts.
Plasma lipoprotein particles are produced in certain cells released into the blood and have a half -life of only a few days. Both their envelope and its contents are susceptible to oxidation by free radicals and there is some evidence that oxidative modification of low density lipoprotein is an important step in the pathogenesis of atherosclerosis.
For dispensing or receiving of each transported substance, they dock by means of their apoproteins to specific receptor proteins in the target cells.
Note: It can not be stressed strongly enough that both fatty acids, including saturated fat, and cholesterol are essential key building blocks of every cell membrane. Fat is also an energy supplier ( although can not cross the blood - brain barrier, ) of (but ) as the glucose can be metabolized in each mitochondrion. Plasma lipoprotein particles have the means of transport to transport these substances between the intestine, liver, and the rest of the body back and forth.
Neither fat nor cholesterol per se are bad. A certain percentage of the fatty acids in a lipid membrane must also be saturated. Nor are transport bad or evil. Only an excess (eg too much fat or too little fat in the diet, or a too high proportion of unsaturated fatty acids in the diet) is bad. In addition, a variety of causes (including dietary ) may interfere with the transport of fat between gut, liver and body cells, may sustainably (see insulin resistance).
According to hypotheses lead into the arterial wall penetrated ( such as their size or density) LDL-Partikel/sdLDL-Partikel if they or their content oxidize / is oxidized on further steps to atherosclerosis. But now you can see the "evil " LDL-/sdLDL-Partikel not fight because they are the ( only ) means of transport for cholesterol from the liver to the rest of the body cells. But one could work towards reducing their concentration in the event that this should also reduce this reduction in the number of LDL particles, the risk of atherosclerosis.
There are epidemiological studies, inferior to the relationships between the content of HDL particles, LDL particles and the incidence of certain diseases. There are also epidemiological studies showing correlations between the ratio of carbs to fats in the diet to the content of LDL particles in the blood, namely depending on the phenotype.
There are substances which demonstrably reduce LDL cholesterol, for example, Ethanol. Thus, either the number of LDL particles is meant, or the amount of cholesterol beinhaltetem. Thus, the cholesterol remaining in the liver, since the LDL particles are intended for transport.
If blood lipids or blood cholesterol levels are measured, rather the plasma lipoprotein particles are basically measured containing these substances. The measurement is carried out until 10 hours after the last meal and also waiving the measurement of chylomicrons, because this rather say something about the fat content of food in the intestine, as about problems with the Fett-/Cholesterin-Transport. Furthermore, there are also free fatty acids, which just so swimming in blood. Not every lab is different when measuring between IDL, LDL, sdLDL ( small dense ), lbLDL (large buoyant ). But it could be that exclusively classified as sdLDL particles can penetrate between the epithelial cells and into the vessel wall.
Because of these relationships, the HDL are commonly referred to as "good" and LDL as " bad," is to say, even if one takes too much cholesterol in the diet, the measured LDL particles should not be too numerous.
Lipoproteins mainly, as can be seen due to the English names, distinguished on the basis of the physical property of the density. Isolation of lipoproteins can be carried out via ultracentrifugation. About a density gradient, the particles could also be characterized via its density ( the density differences arise mainly due to a different ratio of protein to lipid content in the different lipoproteins ). Therefore, also a subdivision has been established in five classes:
There is a relatively large chylomicrons, VLDL, the IDL ( also described as Betalipoproteine ), LDL and HDL ( also referred to as Alphalipoprotein ).
A separation or characterization of lipoproteins is also possible by other methods such as electrophoresis.
Isolation of human low density lipoprotein ( which is the focus of atherosclerosis research ) from human blood plasma by ultracentrifugation ( centrifugation time: 2 hours; rotor speed: 60,000 revolutions / minute ) are possible, and is described in detail in the cited references.
- Chylomicrons are exclusively? formed in the cells of the intestinal wall. Their primary function is as triglycerides from the intestine (or the colon wall ) into our bloodstream and to the liver, muscle and adipose cells.
- Very low density lipoproteins (VLDL ) is formed exclusively in the liver cells and transported mainly ( there stored and newly synthesized ) triglycerides from the liver cells to the rest of the body cells.
- Intermediate density lipoproteins ( IDL) is a degradation product of VLDL and are in terms of size between VLDL and LDL. Normally, IDL are not detectable in the blood.
- Low Density Lipoproteins (LDL ) is formed in the liver cells and transported mainly cholesterol and cholesteryl ester from the liver to the rest of the cells of the body. One can continue in this class small dense LDL small dense LDL particles and
- Divide large buoyant LDL large buoyant LDL particles
- Lipoprotein a
On the density
The mammalian lipoproteins are listed with some of their sub-forms in the following table:
About the food fed cholesterol and triglycerides are absorbed by the intestinal tract and then delivered to the lymph via the thoracic duct into the venous blood in the form of chylomicrons. There they are by the action of endothelial lipases to the chylomicron remnants so-called (English remnant ) that will eventually be taken up by the liver. VLDL, IDL as its metabolites and especially LDL, transport cholesterol from the body itself synthesized and received by the chylomicron triglycerides from the liver to peripheral tissues. HDL ( HDL3 accurate ) take cholesterol mediated by the enzyme lecithin - cholesterol acyltransferase ( LCAT ) from the tissues, but also from other lipoproteins, and transport it to the liver ( reverse cholesterol transport ). The transported cholesterol in the lipoproteins is mainly esterified with fatty acids.
About 75% of the carbon and the hydrogen in energy-yielding substrates in metabolism are lipid components.
The transport proteins are called apolipoproteins ( APOLP ). Enter the lipid micelles stability and determine the metabolism of Lipidoproteine the turnover rate and direct them to specific target organs.
Lipid disorders can be detected via lipoproteins in the blood. The so-called lipoprotein a ( Lp (a ) spoken: Lipoprotein small "a") is considered a risk factor because it correlates with the occurrence of heart attacks.
For the qualitative and quantitative determination of the lipid fractions of the lipoproteins chromatographic methods such as are thin layer chromatography and gas chromatography, used in coupling with mass spectrometry.