Lecithin

Lecithin is the most abundant membrane phospho-lipid in our cells. A study involving cells with a temperature-sensitive genetic defect in lecithin biosynthesis illustrates how essential it is for cell survival. When grown above a certain temperature, these cells were unable to Figure 1. The structure of lecithin represented schematically (A), as a formula (B), as a model (C), and symbolically (D). Such phospholipid bilayers are thought to constitute the basic structure of cell membranes. Illustration by Hans & Cassidy. Courtesy of Gale Group. make lecithin. Under these conditions the cells began to burst open and eventually died.

Several studies suggest that lecithin is involved in cell signaling, the process by which one cell initiates changes in another. For example, a hormone, neuro-transmitter, or growth factor secreted by one cell communicates with another by altering its cell membrane in some way, usually by activating an enzyme which breaks down phospholipid in the membrane. The breakdown products interact with an enzyme which sets into motion a domino effect of changes in cell growth, metabolism, function, and so on. Disruptions in this process may give rise to certain diseases. Some recent evidence suggests that lecithin deficiency may interfere with cell signaling and so may be a factor in the development of liver and colon cancer.

Lecithin plays an important role in the transport of fats and cholesterol from the liver to sites where they can be either used or stored. Since fats do not dissolve in water solutions like blood plasma, they are transported in spherical particles called lipoproteins. These particles can mix with water solutions because the water-friendly proteins, cholesterol and phospholipids are on the outside surface. The nonpolar fats associated with them make up the core, which is unexposed to water. Because lecithin is required for lipoprotein synthesis, a lecithin deficiency results in fats accumulating in the liver and leads to liver damage. Lecithin deficiency also leads to increased amounts of cholesterol in the blood and atherosclerosis, a disease in which narrowing of the arteries is caused primarily by the deposit of fats from the bloodstream.

Lecithin is the primary source of choline, the precursor of the neurotransmitter acetylcholine. Recent findings suggest a relationship between the lack of availability of lecithin to nerve cells which produce acetylcholine, and the progress of Alzheimer disease.