Phosphatidylcholine

Phosphatidylcholines (PC) are a class of phospholipids that incorporate choline as a headgroup. They are a major component of biological membranes and can be easily obtained from a variety of readily available sources such as egg yolk or soy beans from which they are mechanically extracted or chemically extracted using hexane. They are also a member of the lecithin group of yellow-brownish fatty substances occurring in animal and plant tissues.

The name "lecithin" was originally defined from the Greek lekithos (λεκιθος, egg yolk) by Theodore Nicolas Gobley, a French chemist and pharmacist of the mid-19th century, who applied it to the egg yolk phosphatidylcholine that he identified in 1847 and finally completely described from a chemical structural point of view in 1874. Phosphatidylcholines are such a major component of lecithin that in some contexts the terms are sometimes used as synonyms. However, lecithin extract consists of a mixture of phosphatidylcholine and other compounds. It is also used along with sodium taurocholate for simulating fed- and fasted-state biorelevant media in dissolution studies of highly-lipophilic drugs.

Function
Phosphatidylcholine is a major constituent of cell membranes. Phosphatidylcholine is more commonly found in the exoplasmic or outer leaflet of a cell membrane. It is thought to be transported between membranes within the cell by phosphatidylcholine transfer protein (PCTP).

Phosphatidylcholine also plays a role in membrane-mediated cell signalling and PCTP activation of other enzymes.

Structure
The phospholipid is composed of a choline head group and glycerophosphoric acid with a variety of fatty acids, one being a saturated fatty acid (in the example, here palmitic or hexadecanoic acid, H3C-(CH2)14-COOH; margaric acid identified by Gobley in egg yolk, or heptadecanoic acid H3C-(CH2)15-COOH, also belong to that class); and one being an unsaturated fatty acid (here oleic acid, or 9Z-octadecenoic acid, as in Gobley's original egg yolk lecithin).

Phospholipase D catalyzes the hydrolysis of phosphatidylcholine to form phosphatidic acid (PA), releasing the soluble choline headgroup into the cytosol.

Senescence
Phosphatidylcholine is a vital substance that is in every cell in the human body. At birth and throughout infancy, phosphatidylcholine concentrations are high (as high as 90% of the cell membrane), but it is slowly depleted throughout the course of life, and may drop to as low as 10% of the cellular membrane in the elderly. Thus some researchers in the fields of health and nutrition have begun to recommend daily supplementation of phosphatidylcholine as a way of slowing down senescence and improving brain functioning and memory capacity.

Liver repair
Recent studies point to the many potential benefits of phosphatidylcholine for liver repair. One study shows phosphatidylcholine's healing effect with hepatitis A, hepatitis B, and hepatitis C. Phosphatidylcholine administration for chronic, active hepatitis resulted in significant reduction of disease activity.

Lipolysis
Some organizations promote the use of injected phosphatidylcholine, otherwise known as injection lipolysis, claiming the procedure can break down fat cells, and thus serve as an alternative to liposuction. It is important to note that while the procedure cites early experiments that showed lipolysis in cases of fat emboli, no peer-reviewed studies have shown any amount of lipolysis even remotely comparable to liposuction.

Ulcerative colitis
Phase IIa/b clinical trials performed at the Heidelberg University Hospital have shown that delayed release phosphatidylcholine is an anti-inflammatory, and secondly, is a surface hydrophobicity increasing compound with promising therapeutic potential in the treatment of inflammatory bowel disease.

Possible health risks
In addition to the increased caloric burden of a diet rich in fats like phosphatidylcholine, a recent report has linked the microbial catabolites of phosphatidylcholine with increased atherosclerosis through the production of choline, trimethylamine oxide, and betaine.