VLDL IDL LDL

Question 0

Metabolism of VLDL

Answer 0

Half life of VLDL in serum is only 1 to 3 hour
When they reach the peripheral tissue apo C II activates LPL which liberated fatty acids that are taken up by adipose tissue and muscle
The remnant is designated as IDL

Question 1

Synthesis of VLDL

Answer 1

They are synthesis in liver from glycerol and fatty acids and incorporated to VLDL along with hepatic cholestrol and apo B 100 ,C II and E
Apo B 100 is the major apoprotein present in VLDL when it is secreted
Apo E and C are obtained from HDL in plasma

Question 2

Function of VLDL

Answer 2

The VLDL carries triglycerols from liver to peripheral tissue for energy needs

Question 3

IDL

Answer 3

VLDL is converted to IDL
It contain TAG and more of cholesterol
IDL converted to LDL

Question 4

Function of LDL

Answer 4

About 75% of plasma cholesterol is incorporated into LDL particles
LDL transport cholesterol from liver to the peripheral tissue

Question 5

Cholesterol thus liberated in the cell has three major fates :

Answer 5

It is used for synthesis of other steroids like steroid hormones
Cholesterol may be incorporated into membranes
Cholesterol may be esterified to MUFA by acyl cholesterol acyl transferase ACAT for storage

Question 6

LDL clinical application

Answer 6

The LDL concentration in blood has positive correlation with incidence of cardiovascular diseases
A fraction of cholesterol is taken up by macrophages this is not regulated pathway
Increase level of LDL or modification of LDL by glycation or oxidation increase the fraction of cholesterol taken up by macrophages

Question 7

LDL and atherosclerosis

Answer 7

LDL infiltrate tthrough arterial walls and are taken up by macrophages or scavenger cells
This is the starting event of atherosclerosis leading to myocardial infraction
When this cells become engorged with cholesterol, foam cells are formed, that get deposited in the sub endothelial space triggering formation of atheromatous plaque
Procoagulant changes are induced in the endothelium resulting in increased changes of thrombosis and coronary artery disease

Question 8

Lp X

Answer 8

An abnormal form of LDL, identified as lipoprotein X , predominates in the circulation of patients suffering from lecithin cholesterol acyl transferase deficiency or cholestatic liver disease in both cases there is an elevation in the level of circulating free cholesterol and phospholipids.

Question 9

Scavenger receptor

Answer 9

Macrophages ingest a variety of negatively charged macromolecules that includes modified LDLs.Macrophages scavenger receptors are type I type II class A receptors, class B receptors , mucin like receptors and endotheliai receptors 
After binding ligand the scavenger receptors can either be internalized , similar tp the process of internalization of LDL receptors or they can remain on the cell surface and transfer lipid into the cell through caveolae

Question 10

Lipoprotein A

Answer 10

Lipoprotein a or Lp (a) should not be confused with apo A . Lp a is very strongly associated with myocardial infarction and is sometimes called the little rascal
Lp a when present , is attached to apo B 100 by a disulfide bond
In 40% population , there is no detectable level of Lp a in serum in 20% of population the Lp a concentration in blood is more than 30 mg/dl and these persons are susceptible for heart attack at a younger age
Lp a has significant homology with plasminogen so it interferes with plasminogen activation and impairs fibrinolysis