Melatonin

Melatonin (N-[2-(5-metho\y-l H-indol-3-yl)ethyl]acctamide, N-acetyl-5-methoxytrypt-aminc: molecular weight 232) contains 12"» nitrogen.

Abbreviations

5-HT 5-hydroxytryptamine (serotonin)

5-HTOL 5-bydroxytryptophol

EMS eosinophils myalgia syndrome

PAPS 3'-phosphoadenosine 5'-phosphosulfate

6-SMT 6-sulfatoxymelaromn

Nutritional summary

Function: Melatonin, a hormone produced by brain, retina, and pineal gland, participates iti the coordination of sleep patterns, thermoregulation, and possibly reproductive cycles to daylight.

Sources: The body's production is dependent on adequate availability of L-trypto-phan, niacin, vitamin 136, endogenous I y generated SAM (methionine, folate, and vitamin BI2), biopterin. pantotheratc. ascorbate, and iron. Requirements. Endogenous synthesis is usually adequate.

Deficiency: Inadequacies of nutrients needed for endogenous synthesis may sometimes limit production, possibly contributing to insomnia and sexual dysfunction. Excessive intake; Many commercial melatonin preparations have been found to contain potentially toxic contaminants similar to those thought to have caused

S.IOI Mrlarotiin eosinophil^- myalgia syndrome in some users of tryptophan supplements. Other consequences of supplemental intakes of melatonin have not been adequately evaluated.

Endogenous sources

Melatonin is synthesized in brain, retina, and pineal gland. This endogenous synthesis proceeds in steps catalyzed by four enzymes and requires L-tryptophan. biopterin. niacin, vitamin B6, methionine, folate, vitamin B12. puntoihcrate. ascorbate. and iron. 5-HT is an intermediate of melatonin synthesis, produced by the first two steps.

The synthetic sequence is initiated by tryptophan 5-monooxygcnase (EC1.14.16.4, requires iron and ascorbate) in pinealoeytes and raphe neurons as well as tissues outside the brain including beta-cells of the islets of Langcrhans, enteroehromaffin cells of pancreas and smalt intestine, mast cells and mononuclear leukocytes. The hydroxyla-tion of 1.-tryptophan requires Iclrahydropteridinc as a cofactor and is inhibited by high concentrations of 1.-phenylalanine. A calcium ion-triggered protein kinase phos-phorylatcs and thereby activates tryptophan 5-monooxygenase; melatonin, the ultimate end product, inhibits it.

In the next step, aromatic-L-a mi no-acid decarboxylase (EC4.1.1.28). generates 5-HT. This PL P-dependcnt enzyme is also present in basal ganglia, sympathetic nerves, and adrenal medulla, where it acts mainly on L-tryptophan and DOPA. When aromatic-L-amino-acid decarboxylase generates tryptamine by acting on L-tryptophan. 5-HT synthesis can be completed subsequently by tryptophan 5-monooxygenase.

Significant quantities of tryptamine may be ingested with certain types of cheese or with foods exposed to bacterial action,

5-HT can then be acetylated by aralkylaminc N-acetyl transferase (EC2.3.1.87) and finally converted into N-acetyl-5-methoxytryptanune (melatonin) by acetyl serotonin O-methyl trans I erase (EC2,1.1.4).

Dietary sources

Normally, very little melatonin is obtained from food. Commercial preparations are now w:idely available as dietary supplements. Foods containing significant amounts of 5-111 include bananas (0.02mg'g), pineapples and vvalnuts (Hclandcr and Some, 2000). A few foods contain signilicant amount of the melatonin precursor 5-hydroxy-tryptamine (5-HT. serotonin), including bananas (0.02 mg'g). pineapples and walnuts (Helander and Some. 2000>.

Note: Eosinophilia myalgia syndrome (EMS) w ith symptoms that include fatigue, pain, depression, sleep disturbance, and verbal memory impairment may be caused by contaminants in commercial preparations of 5-hydroxytryptophan (Klarskov et til.. 1999) and melatonin (Laforee et aL 1999).

Digestion and absorption

Melatonin absorption proceeds rapidly from the proximal small intestine via an incompletely understood process (Aldbous et «/., 1985). Fractional absorption has been l-Tryptophan

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