Assembly and secretion of lipoproteins

Lipoproteins are secreted into the circulation from hepatocytes of the liver and enterocytes of the intestine. All plasma lipoproteins share a common structure consisting of a neutral lipid core of triacylglycerols (TGs) and cholesteryl esters surrounded by a surface monolayer of phospholipids, unesterified cholesterol and specific proteins called apolipoproteins (Fig. 1 and Chapter 18). The primary function of plasma lipoproteins is to transport hydrophobic, water-insoluble lipids in the circulation. The TG-rich lipoproreins deliver TGs made in the liver and intestine to other tissues in the body for either storage or utilization as an energy source. High-density lipoproteins are thought to remove cholesterol from peripheral tissues (i.e. tissues other than liver) and deliver it to the liver for excretion in bile in a process referred to as 'reverse cholesterol transport' (Chapters 16, 20). A high level of plasma lipids is a strong risk factor for development of cardiovascular disease (Chapter 22). The steady state level of lipoproteins in the cir-