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The straight dope on cholesterol – Part II

The proteins that traffic collections of lipids are called apoproteins. Once bound to lipids they are called apolipoproteins, and the protein wrapped “vehicle” that transports the lipids are called lipoproteins. Many of you have probably heard this term before, but I’d like to ensure everyone really understands their important features. A crucial concept is that, for the most part, lipids go nowhere in the human body unless they are a passenger inside a protein wrapped vehicle called a lipoprotein. As their name suggests lipoproteins are part lipid and part protein. They are mostly spherical structures which are held together by a phospholipid membrane (which, of course, contains free cholesterol).

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Articles of Interest

A Review of Lipoproteins and Lipid Metabolism

Lipoproteins are important protein-lipid assemblies that are responsible for the transport of fats to different parts of the body via the bloodstream. The five major groups of lipoproteins are very low-density lipoprotein (VLDL), low-density lipoprotein (LDL), intermediate-density lipoprotein (IDL), high-density lipoprotein (HDL), and chylomicrons. LDL and HDL are of particular interest due to their impact on human health. For example, studies have shown that higher levels of LDL promote health problems and cardiovascular disease

Cholesterol and lipoproteins 101

Lipoproteins are multi-molecule complexes that transport and deliver cholesterol and other components to target tissues. Other components of lipoprotein include triglycerides, phospholipids and proteins.

Discovery of the Lipoproteins, Their Role in Fat Transport and Their Significance as Risk Factors

The idea of a fat transport system in the plasma of mammals evolved slowly over three centuries. At the turn of this century, it was discovered that plasma globulins contained lecithin and that the digestion of plasma proteins with pepsin liberated small amounts of fat and cholesterol. The high density lipoprotein (HDL) was first isolated from horse serum in 1929 and the low density lipoprotein (LDL) in 1950. It was then shown that flotation of plasma in the ultracentrifuge revealed an array of lipoproteins that included VLDL, LDL and HDL and permitted quantitation. Subsequently, it was discovered that the free fatty acids (FFA) in plasma were bound to albumin and varied with feeding and fasting.

Introduction to Lipids and Lipoproteins

Cholesterol and triglycerides are insoluble in water and therefore these lipids must be transported in association with proteins. Lipoproteins are complex particles with a central core containing cholesterol esters and triglycerides surrounded by free cholesterol, phospholipids, and apolipoproteins, which facilitate lipoprotein formation and function.

Lipids and Lipoproteins in 2020

Cholesterol and triglycerides are the major lipids in humans and are transported in plasma by lipoproteins. A lipoprotein is composed of cholesterol, triglycerides, and a single apolipoprotein B100 molecule (apoB) when secreted into plasma by the liver, and is referred to as a very low-density lipoprotein (VLDL).

Lipoproteins: Lipid Carriers

High-density lipoprotein (HDL): Removes cholesterol from tissues in the body and transports it to cells that need cholesterol and to the liver for removal. Low-density lipoprotein (LDL): Formed from VLDL after it delivers triglycerides to fat cells, Transports cholesterol to various cells. Very low density lipoprotein (VLDL): Transports triglycerides from the liver to fat cells.

Lipoproteins: When size really matters

Lipoproteins, the colloidal particles that transport insoluble lipids within blood, lymph and cerebral spinal fluid, are among the most studied structures in biology.

Plasma Lipoproteins

The lipoproteins in the circulation are complex aggregates of lipids and proteins that are not linked covalently to each other. They render the hydrophobic lipids compatible with the aqueous environment of body fluids and enable their transport throughout the body to tissues where they are required. Synthesis occurs mainly in the intestines and liver in all vertebrates and insects.

Protein May Be Heart Risk Factor

The substance, lipoprotein(a), or Lp(a), is a form of low-density lipoprotein, the so-called bad cholesterol, which can be deposited on artery walls and eventually cause heart disease. But the exact role of Lp(a) in the development of heart disease is still unclear, and it is not certain for which people it might be a risk factor.

The Function of Lipoproteins in the Body

Cholesterol and triglycerides are fatty molecules. Because of their fat-like properties, they are not able to easily circulate in the bloodstream. In order for cholesterol and triglycerides to travel in the blood, they are often carried by proteins that make the cholesterol and triglycerides more soluble in blood. This lipid and protein complex is referred to as a lipoprotein.