Very-low-density lipoprotein (VLDL), density relative to extracellular water, is a type of

lipoprotein A lipoprotein is a biochemical assembly whose primary function is to transport hydrophobic lipid (also known as fat) molecules in water, as in blood plasma or other extracellular fluids. They consist of a triglyceride and cholesterol center, sur ...

made by the

liver The liver is a major metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...

. VLDL is one of the five major groups of lipoproteins (

chylomicrons Chylomicrons (from the Greek χυλός, chylos, meaning ''juice'' (of plants or animals), and micron, meaning ''small''), also known as ultra low-density lipoproteins (ULDL), are lipoprotein particles that consist of triglycerides (85–92%), ...

, VLDL,

intermediate-density lipoprotein Intermediate-density lipoproteins (IDLs) belong to the lipoprotein particle family and are formed from the degradation of very low-density lipoproteins as well as high-density lipoproteins. IDL is one of the five major groups of lipoproteins (chylo ...

low-density lipoprotein Low-density lipoprotein (LDL) is one of the five major groups of lipoprotein that transport all fat molecules around the body in extracellular water. These groups, from least dense to most dense, are chylomicrons (aka ULDL by the overall density ...

high-density lipoprotein High-density lipoprotein (HDL) is one of the five major groups of lipoproteins. Lipoproteins are complex particles composed of multiple proteins which transport all fat molecules (lipids) around the body within the water outside cells. They are t ...

) that enable fats and

cholesterol Cholesterol is the principal sterol of all higher animals, distributed in body Tissue (biology), tissues, especially the brain and spinal cord, and in Animal fat, animal fats and oils. Cholesterol is biosynthesis, biosynthesized by all anima ...

to move within the water-based solution of the bloodstream. VLDL is assembled in the

from

triglycerides A triglyceride (from ''wikt:tri-#Prefix, tri-'' and ''glyceride''; also TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids. Triglycerides are the main constituents of body fat in humans and oth ...

, and

apolipoprotein Apolipoproteins are proteins that bind lipids (oil-soluble substances such as fats, cholesterol and fat soluble vitamins) to form lipoproteins. They transport lipids in blood, cerebrospinal fluid and lymph. The lipid components of lipoprotei ...

s. VLDL is converted in the bloodstream to

(LDL) and

(IDL). VLDL particles have a diameter of 30–80

nanometers 330px, Different lengths as in respect to the molecular scale. The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm), or nanometer (American and British English spelling differences#-r ...

(nm). VLDL transports

endogenous Endogeny, in biology, refers to the property of originating or developing from within an organism, tissue, or cell. For example, ''endogenous substances'', and ''endogenous processes'' are those that originate within a living system (e.g. an ...

products, whereas

transport

exogenous In a variety of contexts, exogeny or exogeneity () is the fact of an action or object originating externally. It is the opposite of endogeneity or endogeny, the fact of being influenced from within a system. Economics In an economic model, an ...

(dietary) products. In the early 2010s both the lipid composition and protein composition of this lipoprotein were characterised in great detail.

Physical properties

Very-low-density lipoprotein size is variable, with diameters ranging from approximately 35 to 70 nm. Some researchers further classify VLDL particles into VLDL1 and VLDL2 based on size (as measured by

Svedberg In chemistry, a Svedberg unit or svedberg (symbol S, sometimes Sv) is a non- SI metric unit for sedimentation coefficients. The Svedberg unit offers a measure of a particle's size indirectly based on its sedimentation rate under acceleration ...

flotation units), where VLDL1 particles are larger and contain more triglycerides, while other researchers create a tripartite system by subdividing VLDL1 into larger VLDL1 and smaller VLDL2 and relabeling VLDL2 as VLDL3.

Function

Very-low-density lipoproteins transport endogenous

phospholipids Phospholipids are a class of lipids whose molecule has a hydrophilic "head" containing a phosphate group and two hydrophobic "tails" derived from fatty acids, joined by an alcohol residue (usually a glycerol molecule). Marine phospholipids typi ...

, and

cholesteryl esters 300px, Cholesteryl oleate, a member of the cholesteryl ester family Cholesteryl esters are a type of dietary lipid and are ester derivatives of cholesterol. The ester bond is formed between the carboxylate group of a fatty acid and the hydroxyl g ...

. They function as the body's internal transport mechanism for lipids. In addition they can assist in long-range transport of hydrophobic intercellular messengers, like the morphogen

Indian hedgehog (protein) Indian hedgehog homolog (Drosophila), also known as IHH, is a protein which in humans is encoded by the ''IHH'' gene. This cell signaling protein is in the hedgehog signaling pathway. The several mammalian variants of the '' Drosophila'' hedgeho ...

Changes during circulation

Nascent VLDL released from the liver contains

apolipoprotein B100 Apolipoprotein B (ApoB) is a protein that in humans is encoded by the gene. Its measurement is commonly used to detect the risk of atherosclerotic cardiovascular disease. Isoforms The protein occurs in the plasma in two main isoforms, Apo ...

apolipoprotein C1 Apolipoprotein C-I is a protein component of lipoproteins that in humans is encoded by the ''APOC1'' gene. Function The protein encoded by this gene is a member of the apolipoprotein C family. This gene is expressed primarily in the liver, ...

(apoC1),

apolipoprotein E Apolipoprotein E (Apo-E) is a protein involved in the metabolism of fats in the body of mammals. A subtype is implicated in Alzheimer's disease and cardiovascular diseases. It is encoded in humans by the gene ''APOE''. Apo-E belongs to a family ...

(apoE),

cholesteryl ester 300px, Cholesteryl oleate, a member of the cholesteryl ester family Cholesteryl esters are a type of dietary lipid and are ester derivatives of cholesterol. The ester bond is formed between the carboxylate group of a fatty acid and the hydroxyl g ...

s, and

. As it circulates in blood, it picks up

apolipoprotein C-II Apolipoprotein C-II (Apo-CII, or Apoc-II), or apolipoprotein C2 is a protein that in humans is encoded by the gene. The protein encoded by this gene is secreted in plasma, where it is a component of very low density lipoproteins and chylomic ...

(apoC-II) and additional apoE donated from

(HDL). At this point, nascent VLDL becomes a mature VLDL. Once in circulation, VLDL will come in contact with

lipoprotein lipase Lipoprotein lipase (LPL) (EC 3.1.1.34, systematic name triacylglycerol acylhydrolase (lipoprotein-dependent)) is a member of the lipase gene family, which includes pancreatic lipase, hepatic lipase, and endothelial lipase. It is a water-solubl ...

(LPL) in the capillary beds in the body (adipose, cardiac, and skeletal muscle). LPL will remove triglycerides from VLDL for storage or energy production. VLDL now meets back up with HDL where apoC-II is transferred back to HDL (but keeps apoE). HDL also transfers cholesteryl esters to the VLDL in exchange for phospholipids and triglycerides via

cholesterylester transfer protein Cholesteryl ester transfer protein (CETP), also called plasma lipid transfer protein, is a plasma protein that facilitates the transport of cholesteryl esters and triglycerides between the lipoproteins. It collects triglycerides from very-low ...

(CETP). As more and more triglycerides are removed from the VLDL because of the action of LPL and CETP enzymes, the composition of the molecule changes, and it becomes intermediate-density lipoprotein (IDL). Fifty percent of IDLs are recognized by receptors in the liver cells because of the apolipoprotein B-100 (apoB-100) and apoE they contain and are endocytosed. The other 50% of IDL lose apoE; when their cholesterol content becomes greater than the content of triglyceride, they become LDL, with apoB-100 as the primary apolipoprotein. The LDL is taken into a cell via the LDL receptor via endocytosis, where the contents are either stored, used for cell membrane structure, or converted into other products such as steroid hormones or bile acids.

Notes and references

{{DEFAULTSORT:Very Low-Density Lipoprotein Lipoproteins

Physical properties

Function

Changes during circulation

See also

Notes and references