Metabolism of HDL and LCAT Function

Metabolism of HDL

• High-density lipoproteins (HDL) are synthesized in the liver and intestine as nascent HDL.
• Nascent HDL contains free cholesterol, phospholipids (primarily lecithin), and apoproteins such as A, CII, and E.

Role of LCAT in HDL metabolism

• Lecithin-cholesterol acyl-transferase (LCAT) is a plasma enzyme that catalyzes the esterification of free cholesterol using fatty acids from lecithin.
• LCAT activity is promoted by apoprotein A.
• HDL can accept free cholesterol from other circulating lipoproteins and peripheral cell membranes.
• Any free cholesterol taken up by HDL undergoes esterification through the action of LCAT, resulting in spherical HDL particles.
• Spherical HDL particles, containing cholesteryl esters, enter hepatocytes via receptor-mediated endocytosis.
• Within the liver, cholesteryl esters are degraded to cholesterol.
• The cholesterol derived from cholesteryl esters is utilized for bile acid synthesis, lipoprotein formation, or excreted into bile.

Cardioprotective function of HDL

• HDL is referred to as "good cholesterol" due to its positive role in lipid metabolism and cardiovascular health.