Biological Chemistry - Berezov T. T., Korovkin B. F. 1998

Vitamins
Vitamin-like Substances
Choline

Choline was first isolated from Bile by A. Strecker in 1892, at which time it was also named. The Biological Role of choline became clear much later, when it was shown to be a structural component of a more complex organic phosphorus-containing compound—phosphatidylcholine, or lecithin (see Chapter 11), discovered in egg yolk and Brain tissue. It has been proven that the special role of lecithin as a dietary factor is due to choline rather than its phosphorus-containing component. Subsequent experiments demonstrated that omitting choline from the diet of animals leads to fatty Liver. Conversely, adding it to the diet helps clear this fat. Further research established that choline is synthesized in sufficient quantities within the Human and Animal body and cannot be considered a true dietary factor; however, under certain conditions, such as dietary Protein deficiency, secondary choline deficiency develops. Due to these reasons, choline has been classified among Vitamin-like substances, or “partial Vitamins”.

In Structure, choline is an aminoethyl alcohol containing three methyl groups attached to the nitrogen atom:

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It is readily soluble in Water and alcohol. In the animal body, it is not free choline that is synthesized, but rather choline as part of Phospholipids. The Donors of methyl groups are Methionine (as part of S-adenosylmethionine) or Serine and Glycine (during the synthesis of methyl groups). Consequently, under conditions of protein deficiency—which in turn may be due to dietary protein shortage or of endogenous origin—symptoms of choline deficiency develop: fatty infiltration of the liver, hemorrhagic renal dystrophy, impaired Blood clotting (impaired synthesis of clotting factor V—accelerin), and others.

Information regarding the MECHANISM OF ACTION of choline indicates that it serves primarily as a constituent of biologically active acetylcholine, a neurotransmitter of nerve impulses. In addition, choline participates in Transmethylation reactions during The Biosynthesis of methionine, purine and pyrimidine NUCLEOTIDES, phospholipids, and so forth.

The main dietary sources of choline for humans are liver, Kidneys, meat, fish products, and cabbage. There are no precise data on human requirements for choline. To a large extent, these requirements are determined by the body's supply of dietary protein, vitamin B₁₂, and Folic acid.