Schaefer - Figure 6 - Functions of HDL particles Text

As these various-sized HDL particles pass through the circulation, they interact via different mechanisms to transport cholesterol in different ways. The next 2 Figures discuss, first, the different mechanisms by which these HDL particles perform their functions, and second, the different cholesterol movements that these functions perform.

This Figure shows how each of these HDL particles interacts with different organs to enable the transfer of cholesterol. Work in collaboration with George Rothblat and colleagues[27] has demonstrated that:

• the very small, pre-beta1 particles serve as acceptors of free cholesterol and phospholipid, and when these particles are metabolized, it is by the kidney;
• as these small, pre-beta1 particles pick up free cholesterol, they become alpha4 particles;
• the alpha4 particles are acted upon by L-CAT, causing them to continue to pick up more cholesterol, via a receptor called the ABCG1 transporter located on macrophages in the plaques in the walls of atherosclerotic arteries, whence they become larger, alpha3 particles;
• as these HDL particles continue to circulate through the system, they continue to accumulate cholesterol via these same mechanisms, growing larger and larger until they become alpha1 particles;
• at this point the alpha1 HDL particles interact with a liver surface transporter called the scavenger receptor B1 (SRB1), which enables the alpha1 particles to transfer their cholesterol to the liver, from which it can be excreted in the bile;
• however, these alpha1 particles can also transfer their cholesterol ester back to the triglyceride-rich lipoproteins (VLDL, LDL particles) in exchange for triglycerides via the action of a transfer protein called cholesterol ester transfer protein (CETP).

Schaefer E. J Clin Lipidol. 2011; 5(6).