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Evidence of melatonin synthesis by human lymphocytes and its physiological significance: possible role as intracrine, autocrine, and/or paracrine substance
Author(s) -
CarrilloVico Antonio,
Calvo Juan R.,
Abreu Pedro,
Lardone Patricia J.,
GarcíaMauriño Sofía,
Reiter Russel J.,
Guerrero Juan M.
Publication year - 2004
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fj.03-0694fje
Subject(s) - melatonin , intracrine , autocrine signalling , paracrine signalling , pineal gland , biology , medicine , endocrinology , microbiology and biotechnology , biochemistry , receptor
It has been historically assumed that the pineal gland is the major source of melatonin (N‐acetyl‐ 5‐methoxytryptamine) in vertebrates. Melatonin plays a central role in fine‐tuning circadian rhythms in vertebrate physiology. In addition, melatonin shows a remarkable functional versatility exhibiting antioxidant, oncostatic, antiaging, and immunomodulatory properties. Melatonin has been identified in a wide range of organisms from bacteria to human beings. Its biosynthesis from tryptophan involves four well‐defined intracellular steps catalyzed by tryptophan hydroxylase, aromatic amino acid decarboxylase, serotonin‐N‐acetyltransferase, and hydroxyndole‐O‐methyltransferase. Here, for the first time, we document that both resting and phytohemagglutinin‐stimulated human lymphocytes synthesize and release large amounts of melatonin, with the melatonin concentration in the medium increasing up to five times the nocturnal physiological levels in human serum. Moreover, we show that the necessary machinery to synthesize melatonin is present in human lymphocytes. Furthermore, melatonin released to the culture medium is synthesized in the cells, because blocking the enzymes required for its biosynthesis or inhibiting protein synthesis in general produced a significant reduction in melatonin release. Moreover, this inhibition caused a decrease in IL‐2 production, which was restored by adding exogenous melatonin. These findings indicate that in addition to pineal gland, human lymphoid cells are an important physiological source of melatonin and that this melatonin could be involved in the regulation of the human immune system, possibly by acting as an intracrine, autocrine, and/or paracrine substance