Nucleosides
and nucleotides: natural bioactive substances in milk and colostrum.
Schlimme E, Martin
D, Meisel H.
Bundesanstalt fur Milchforschung, Institut fur Chemie und Physik,
Kiel, Germany.
schlimme@bafm.de
Nucleotides,
nucleosides and nucleobases belong to the non-protein-nitrogen (NPN)
fraction of milk. The largest amounts of ribonucleosides and ribonucleotides--ribose
forms only were considered in this review--were measured directly
after parturition in bovine milk and other ruminants as well as in
the milk of humans. Generally, concentrations of most of the nucleos(t)ides
tend to decrease gradually with advancing lactation period or nursing
time. The species-specific pattern of these minor constituents in
milk from different mammals is a remarkable property and confirms,
at least, the specific physiological impact of these minor compounds
in early life. The physiological capacity of these compounds in milk
is given by the total potentially available nucleosides. The main
dietary sources of nucleos(t)ides are nucleoproteins and nucleic acids
which are converted in the course of intestinal digestion into nucleosides
and nucleobases the preferred forms for absorption in the intestine.
Thus, nucleosides and nucleobases are suggested to be the acting components
of dietary and/or supplemented nucleic acid-related compounds in the
gut. They are used by the body as exogenous trophochemical sources
and can be important for optimal metabolic functions. Up to 15 % of
the total daily need for a breast-fed infant was calculated to come
from this dietary source. Concerning their biological role they not
only act as metabolites but are also involved as bioactive substances
in the regulation of body functions. Dietary nucleotides affect immune
modulation, e.g. they enhance antibody responses of infants as shown
by a study with more than 300 full-term healthy infants. Dietary nucleos(t)ides
are found to contribute to iron absorption in the gut and to influence
desaturation and elongation rates in fatty acid synthesis, in particular
long-chain polyunsaturated fatty acids in early stages of life. The
in vitro modulation of cell proliferation and apoptosis has been described
by ribonucleosides, in particular by modified components using human
cell culture models. Due to the bio- and trophochemical properties
of dietary nucleos(t)ides, the European Commission has allowed the
use of supplementation with specific ribonucleotides in the manufacture
of infant and follow-on formula. From the technochemical point of
view, the ribonucleoside pattern is influenced by thermal treatment
of milk. In addition ribonucleosides are useful indicators for quantifying
adulterations of milk and milk products.
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