Low-density lipoprotein

Low-density lipoprotein (LDL) represents one of the principal lipoproteins involved in the transport of lipids within the body's extracellular fluid. LDL serves the primary function of conveying lipid molecules to cells, and its role is essential in various physiological processes. However, LDL has been closely associated with the process of atherosclerosis, a significant contributor to cardiovascular disease.

Classification of Lipoproteins

Lipoproteins are complex particles composed of core lipids, surrounded by phospholipids and apolipoproteins. These particles facilitate the transport of hydrophobic lipid molecules in the blood, which is primarily composed of water. They are classified based on their density into five major groups from least dense to most dense: chylomicrons, very low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), LDL, and high-density lipoprotein (HDL).

Structure and Function of LDL

LDL particles are made up of a single molecule of apolipoprotein B-100 and about 80% of their weight is composed of lipids, including cholesterol and triglycerides. LDL particles are characterized by a core of esterified cholesterol and triglycerides surrounded by a single layer of free cholesterol and phospholipids.

The primary role of LDL is to transport cholesterol and other fats to peripheral tissues, where they are either used for cell membrane synthesis or stored in adipose tissue. The LDL particles bind to LDL receptors on the cell surface, are internalized and then the cholesterol is released for use by the cell.

LDL and Atherosclerosis

Despite its essential role, LDL is often referred to as "bad cholesterol" due to its role in atherosclerosis, a condition characterized by the build-up of plaque within the artery walls. This occurs when LDL particles become oxidized and initiate an inflammatory response, leading to the recruitment of monocytes and the formation of foam cells. Over time, this process leads to the development of atherosclerotic plaques, which can obstruct blood flow and contribute to the risk of heart attack or stroke.

References

• Feingold KR, Grunfeld C. Introduction to Lipids and Lipoproteins. [Updated 2021 Jul 26]. In: Feingold KR, Anawalt B, Boyce A, et al., editors. Endotext [Internet]. South Dartmouth (MA): MDText.com, Inc.; 2000-.
• Tabas I, Williams KJ, Borén J. Subendothelial lipoprotein retention as the initiating process in atherosclerosis: update and therapeutic implications. Circulation. 2007 Oct 16;116(16):1832-44. doi: 10.1161/CIRCULATIONAHA.106.676890. PMID: 17938300.
• Libby P, Buring JE, Badimon L, Hansson GK, Deanfield J, Bittencourt MS, Tokgözoğlu L, Lewis EF. Atherosclerosis. Nat Rev Dis Primers. 2019 Jun 20;5(1):56. doi: 10.1038/s41572-019-0106-z. PMID: 31222035.
• Williams KJ, Tabas I. The response-to-retention hypothesis of early atherogenesis. Arterioscler Thromb Vasc Biol. 1995 May;15(5):551-61. doi: 10.1161/01.atv.15.5.551. PMID: 7749869.

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