Lipoprotein
|
WikiDoc Resources for Lipoprotein |
|
Articles |
|---|
|
Most recent articles on Lipoprotein Most cited articles on Lipoprotein |
|
Media |
|
Powerpoint slides on Lipoprotein |
|
Evidence Based Medicine |
|
Clinical Trials |
|
Ongoing Trials on Lipoprotein at Clinical Trials.gov Clinical Trials on Lipoprotein at Google
|
|
Guidelines / Policies / Govt |
|
US National Guidelines Clearinghouse on Lipoprotein
|
|
Books |
|
News |
|
Commentary |
|
Definitions |
|
Patient Resources / Community |
|
Patient resources on Lipoprotein Discussion groups on Lipoprotein Patient Handouts on Lipoprotein Directions to Hospitals Treating Lipoprotein Risk calculators and risk factors for Lipoprotein
|
|
Healthcare Provider Resources |
|
Causes & Risk Factors for Lipoprotein |
|
Continuing Medical Education (CME) |
|
International |
|
|
|
Business |
|
Experimental / Informatics |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Lipoproteins are complex particles composed of a water-repelling core of mainly lipids as non-polar cholesterol esters (CEs) and triglycerides (TGs) surrounded by an amphipathic phospholipid monolayer that includes unesterified free cholesterol (FC) and proteins known as apolipoproteins or aproteins. Apolipoproteins provide a framework for lipoprotein assembly; determine the metabolic fate of the lipoprotein by activating or inhibiting key enzymes; and finally act as ligands for receptor molecules. Lipoproteins are classified into five classes, defined by their respective density on electrophoresis as Chylomicrons, Very Low Density Lipoproteins (VLDL), Intermediate Density Lipoproteins (IDL), Low Density Lipoprotein (LDL) and High Density Lipoproteins (HDL).
Definition
Classification
Lipoproteins can be classified according to their density, size and constituents. It is also possible to classify lipoproteins as "alpha" and "beta", akin to the classification of proteins in serum protein electrophoresis. The lipoproteins that have a low density are the triglyceride rich proteins which include chylomicrons, chylomicron remnants and VLDL. LDL, HDL and lipoprotein(a) have a less triglyceride content and a higher density.
Shown below is a table summarizing the structure of each lipoprotein.[1]
Class |
Origin |
Size (nm) |
Density (g/mL) |
Electrophoretic Mobility |
Triglyceride (%) |
Cholesteryl Ester (%) |
Free Cholesterol (%) |
Phospholipid (%) |
Protein (%) |
Apolipoprotein |
Chylomicron |
Intestine |
80–500 |
<0.93 |
α2 |
86 |
3 |
2 |
7 |
2 |
B-48, E, A-I, A-II, A-IV, C |
VLDL |
Liver |
30–80 |
0.95–1.006 |
Pre-β |
55 |
12 |
7 |
18 |
8 |
B-100, A-I, C-I, C-II, C-III, E |
IDL |
VLDL |
25–35 |
1.006–1.019 |
Slow pre-β |
23 |
29 |
9 |
19 |
19 |
B-100, E |
LDL |
IDL |
21.6 |
1.019–1.063 |
β |
6 |
42 |
8 |
22 |
22 |
B-100 |
HDL2 |
Liver, intestine |
10 |
1.063–1.125 |
α |
5 |
17 |
5 |
33 |
40 |
A-I, A-II, A-IV |
HDL3 |
Liver, intestine |
7.5 |
1.125–1.210 |
α |
3 |
13 |
4 |
25 |
55 |
A-I, A-II |
Lp(a) |
Liver |
30 |
1.055–1.085 |
Slow pre-β |
3 |
33 |
9 |
22 |
33 |
B-100, apo(a) |
Function
The lipids are often an essential part of the complex, even if they seem to have no catalytic activity themselves. To isolate transmembrane lipoproteins from their associated membranes, detergents are often needed.
All cells use and rely on fats and, for all animal cells, cholesterol as building blocks to create the multiple membranes which cells use to both control internal water content, internal water soluble elements and to organize their internal structure and protein enzymatic systems.
Lipoproteins in the blood, a water medium, carry fats around the body. The protein particles have charged groups aimed outward so as to attract water molecules; this makes them soluble in the salt water based blood pool. Triglyceride-fats and cholesterol are carried internally, shielded by the protein particle from the water.
The interaction of the proteins forming the surface of the particles with (a) enzymes in the blood, (b) with each other and (c) with specific proteins on the surfaces of cells determine whether triglycerides and cholesterol will be added to or removed from the lipoprotein transport particles.
Regarding atheroma development and progression vs. regression, the key issue has always been cholesterol transport patterns, not cholesterol concentration itself.
Shown below is a table summarizing the function of each lipoprotein.
| Lipoprotein | Function |
| Chylomicron | Carries triacylglycerol (fat) from the intestines to the liver and to adipose tissue |
| Chylomicron remnant | |
| Very low density lipoprotein (VLDL) | Carries newly synthesised triacylglycerol from the liver to adipose tissue |
| Intermediate density lipoprotein (IDL) | Intermediate between VLDL and LDL, not usually detectable in the blood |
| Low density lipoprotein (LDL) | Carries cholesterol from the liver to cells of the body, sometimes referred to as the "bad cholesterol" lipoprotein |
| High density lipoprotein (HDL) | Collects cholesterol from the body's tissues and brings it back to the liver, sometimes referred to as the "good cholesterol" lipoprotein |
| Lipoprotein(a) |
References
- ↑ Ballantyne, Christie M. (2009). Clinical lipidology : a companion to Braunwald's heart diseas. Philadelphia, PA: Saunders/Elsevier. ISBN 1-4160-5469-3.