Overview of cholesterol and lipoprotein metabolism in the brain, liver and extrahepatic organs

Cholesterol is essential for the development and growth of the fetus and newborn animal. In addition, even in the adult animal there is continuous turnover of sterol in cell membranes as cell division and membrane remodeling take place. In most species, the majority of de novo sterol synthesis occurs in the extrahepatic tissues. This cholesterol is returned to the liver principally carried in high density lipoproteins. The liver secretes cholesterol into the plasma carried in very low density lipoproteins and the remnants of these lipoproteins, as well as low density lipoproteins, then move back into the liver through the LDL receptor mechanism. Cholesterol synthesis in the brain occurs at very high rates in the developing fetus and newborn animal, but there is little, if any, cholesterol taken up into this compartment from circulating low density lipoproteins. Once the animal matures, synthesis declines to very low levels and there is virtually no exchange of this sterol between the brain compartment and the i circulating cholesterol pool.