What are endogenous sources of cholesterol?
In the endogenous pathway, cholesterol is synthesized by the liver and extrahepatic tissues, and enters the circulation as a component of lipoproteins, or is secreted into bile.
Is cholesterol endogenous?
We define endogenous cholesterol as body cholesterol derived principally from biosynthesis and, to a lesser extent, from absorbed dietary cholesterol. The endogenous choles- terol was labeled by the intravenous administration of choles- terol-d7 tracer.
What transports endogenous cholesterol?
Chylomicrons – large particles that carry dietary lipid. Very low density lipoprotein – carry endogenous triglyceride and some cholesterol.
How is cholesterol synthesized?
Biosynthesis of cholesterol generally takes place in the endoplasmic reticulum of hepatic cells and begins with acetyl- CoA, which is mainly derived from an oxidation reaction in the mitochondria. However, acetyl-CoA can also be derived from the cytoplasmic oxidation of ethanol by acetyl-CoA synthetase.
Is LDL endogenous or exogenous?
Exogenous pathway, in which chylomicrons clear dietary lipids. Endogenous pathway, in which VLDL and LDL transport and distribute endogenously synthesized lipids (those synthesized in the body).
How is VLDL cleared?
VLDL. Very-low-density lipoproteins (VLDL) carry 90% of the serum TGs in the fasting state. Like chylomicron TG, VLDL TG is cleared from the circulation by the action of lipoprotein lipase (LPL), the lipolytic enzyme found on capillary endothelial cells.
What is the exogenous pathway?
The exogenous pathway is utilized by specialized antigen-presenting cells to present peptides derived from proteins that the cell has endocytosed. The peptides are presented on MHC class II molecules. This fuses with a late endosome containing the endocytosed, degraded proteins.
How does VLDL become LDL?
As the VLDL shrink, some of the apolipoproteins (C-series and E) transfer to HDL. Finally, the shrinking VLDL becomes an IDL and then an LDL. The LDL will attach to an apoprotein B100 or E receptor on hepatocytes or extrahepatic tissues and be taken into the cell where its component parts will be hydrolyzed.
When is cholesterol synthesized?
What is the precursor of cholesterol?
Cholesterol synthesis begins with acetyl-coenzyme A derived from mitochondria and transported to the cytosol. One molecule of acetyl-coenzyme A and one molecule of acetoacetyl-CoA are converted to HMG-CoA. HMG-CoA is then reduced to mevalonate by HMG-CoA reductase (HMGCR).
How is VLDL converted to LDL?
The triglycerides carried in VLDL are metabolized in muscle and adipose tissue by lipoprotein lipase releasing free fatty acids and IDL are formed. The IDL are further metabolized to LDL, which are taken up by the LDL receptor in numerous tissues including the liver, the predominant site of uptake.