Nutrient requirements Choline

An alternative reaction for the remethylation of homocysteine to methionine can be accomplished by betaine homocysteine methyltrans-ferase, which uses betaine instead of 5-MTHF as the methyl donor. Unlike the MS reaction, which is believed to be ubiquitously present in all tissues, the betaine homocysteine methyl-transferase reaction occurs only in the liver and kidney. Betaine is not a required nutrient since the liver can synthesize betaine from choline. Betaine supplements, however, have been shown to lower plasma total homocysteine concentrations successfully in subjects with deficient homocysteine remethylation due to defects in MTHFR or MTRR and in those with deficient CBS activity. 

Choline, supplied as dietary PC or as free choline, is required in the diet by rats. Although it has not been established that choline is required by humans, it is probably an essential nutrient and may, in the future, be classified as an essential amine or vitamin, Its possible requirement is a concern to clinicians feeding patients by total parenteral nutrition (TpN), In this type of feeding, which may be used for a year or longer, the patient is sustained intravenously with an artificial, chemically defined diet. The choline in foods occurs mainly as PC rather than as free choline. PC is a more desirable dietary component because, when free choline is consumed in large amounts, it is degraded by the gut bacteria to produce trimethylamine, an odoriferous compound (Magil et ai, 1981). 

Choline is not made de novo in animal cells except by the methylation of PE to PC and subsequent hydrolysis of the choline moiety from PC. Therefore, choline is imported from extracellular sources. Choline is an important nutrient in the diet of animals and is required in the medium of animal cells in culture (H. Eagle, 1955). Choline is essential because of the cell s requirement for PC for growth and division. There are two distinct transport mechanisms for entry of choline into cells [5] a high affinity K or AT, < 5 pM), Na" -dependent transporter and a lower affinity K > 30 pM), Na -independent transporter. Several cDNAs encoding proteins that show high affinity transport of choline have been reported. 

Zeisel, S.H. Choline and choline esters as required nutrients during pregnancy and lactation. Choline, Phospholipids, Health, and Disease S.H. Zeisel, B.F. Szuhaj, Eds. AOCS Press Champaign, IL, I998 pp.l31-142. 

Phosphatidylcholine (lecithin) is not required in the diet because it can be synthesized in the body. The components of phosphatidylcholine (including choline) all can be produced, as shown in Figure 33.28. A pathway for de novo choline synthesis from glucose exists, but the rate of synthesis is inadequate to provide for the necessary amounts of choline. Thus, choline has been classified as an essential nutrient, with an Al (adequate intake) of 425 mg/day in females and 550 mg/day in males. 

Neural membrane glycerophospholipids are synthesized from three dietary components polyunsaturated fatty acids, uridine monophosphate (UMP), and choline (Farooqui and Horrocks, 2007). Administration of above nutrients increases the level of glycerophospholipids, specific pre- or postsynaptic proteins, and the number of dendritic spines - a requirement for new synapse formation (Wurtman et al., 2009 Kamphnis and Wurtman, 2009). These effects are markedly enhanced when animals receive all three compounds together. This multi-nutrient approach in animals has also been shown to decrease A plaque burden, improve learning and memory through increased cholinergic neurotransmission, and have a neuroprotective effect in several mouse models of AD (Wurtman et al., 2009 ... 

An Estimated Average Requirement (EAR) is the average daily nutrient intake level estimated to meet the requirements of half of the healthy individuals in a group. EARs have not been established for vitamin K, pantothenic acid, biotin, choline, chromium, fluoride, manganese, or other nutrients not yet evaluated via the DRI [cocess... 

Recommended dietary allowances for a male adult (daily intake, in foods and food supplements) of some nutrients, usually the amounts estimated as needed to prevent overt manifestation of deficiency disease in most persons. For the substances listed in smaller amounts the optimum intake, leading to the best of health, may be somewhat greater. Not shown, but probably or possibly required, are the essential fatty acids, />aminobenzoic acid, choline, vitamin D, vitamin K, chromium, manganese, cobalt, nickel, zinc, selenium, molybdenum, vanadium, tin, and silicon. 

The minimum manganese requirement of birds for the prevention of any of the above symptoms of deficiency depends upon three principal factors. These are (1) the breed, or even strain, of bird, (2) the quantity of calcium, phosphorus, and iron in the diet, and (3) the source, i.e., the form, of manganese supplied. The incidence of perosis may also be influenced by the level in the diet of several organic nutrients, of which choline and inositoU appear the most important. This aspect of perosis has been well reviewed by Jukes to 1941. 

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