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PubMed2000

Nucleosides and nucleotides: natural bioactive substances in milk and colostrum.

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.

Animals↗
PubMed1993

Stimulation of astrocyte proliferation by purine and pyrimidine nucleotides and nucleosides.

Proliferation of brain astrocytes as a result of cell death has been well documented in vivo. Dying cells release purine and pyrimidine nucleosides and nucleotides and their deoxy derivatives both from soluble intracellular pools and from DNA and RNA. Previously, we have observed that purine nucleosides and nucleotides stimulate chick astrocyte proliferation in vitro. To further our analysis, we questioned whether pyrimidines or the deoxy derivatives of purine nucleosides and nucleotides might also be astrocyte mitogens. Pyrimidine nucleosides, nucleotides, and their deoxynucleotide derivatives were uniformly inactive. In contrast, deoxyguanosine, deoxyadenosine, and their mono-, di-, and triphosphates stimulated thymidine incorporation into astrocytes at concentrations similar to those at which their ribonucleoside and ribonucleotide analogues were active. Inosine, IMP, ITP, and hypoxanthine were active, whereas xanthine and xanthosine were not. However, XMP, XDP, and XTP stimulated thymidine incorporation. The effects of the nucleosides and deoxynucleosides were inhibited by antagonists of adenosine A2 receptors. These data indicate that most purine nucleosides, deoxynucleosides, and their 5' mono, di-, and triphosphate derivatives released from damaged cells are capable of stimulating astrocyte proliferation in vitro and may contribute to astrocyte proliferation in vivo following injury to the CNS.

Adenosine↗
PubMed2000

Effect of administration of nucleosides and nucleotides on protein turnover and the hypoxic myocardium.

Nucleotides and nucleosides have effects on improving energy metabolism and enhancing immune function. Under a surgical stress, requirement of nucleotides are increased as well as nitrogen. A well-balanced nucleoside solution (OG-VI) was developed for parenteral administration and its effect was examined in animals. The OG-VI solution contained 3.11% of nucleosides which was composed of inosine, guanosine monophosphate, cytidine, uridine and thymidine of 4:4:4:3:1 in molar ratio. The whole body protein turnover increased significantly in rats received total parenteral nutrition (TPN) with OG-VI after 70% hepatectomy and enhanced the fractional protein synthesis rates of the muscle and liver. Also myocardial contractility (%segment shortening, %SS) in dogs after occlusion of left anterior descending artery (LAD) was recovered to 70% after reperfusion in the OG-VI group. The creatine phosphate (PCr) / inorganic phosphate (Pi) was maintained the baseline level and did not decrease after hypoxia in the OG-VI group while PCr/ Pi was decreased after hypoxia in normal rat. These data suggested that the nucleoside-nucleotide (OG-VI) improved nitrogen metabolism and might stimulate synthesis of high-energy phosphate in recovery after severe surgical stress.

Animals↗
PubMed1995

Synthetic nucleosides and nucleotides. XXXV. Synthesis and biological evaluations of 5-fluoropyrimidine nucleosides and nucleotides of 3-deoxy-beta-D-ribofuranose and related compounds.

1-O-Acetyl-2,5-di-O-p-chlorobenzoyl-3-deoxy-D-ribofuranose (1), derived from the antibiotic cordycepin was coupled with trimethylsilylated derivatives (2a-c) of N4-propionylcytosine, N4-p-toluoyl-5-fluorocytosine and 5-fluorouracil in the presence of trimethylsilyl trifluoromethanesulfonate (TMS-triflate) to give fully acylated nucleosides (3a-b and 3d, respectively). Selective removal of the N4-propionyl group of 3a by treatment with hydrazine hydrate gave 2',5'-di-O-p-chlorobenzoyl-3'-deoxycytidine (4). Deamination of 4 with sodium nitrite in trifluoroacetic acid afforded 2',5'-di-O-p-chlorobenzoyluridine (3c) in good yield. Compounds 3a-d were saponified to give free 3'-deoxycytidine (5a), 5-fluoro-3'-deoxycytidine (5b), 3'-deoxyuridine (5c), and 5-fluoro-3'-deoxyuridine (5d), respectively. These 3'-deoxyribonucleosides (5a-d) were then converted to corresponding 5'-monophosphate and further phosphorylated to the 5'-triphosphates by the phosphoroimidazolidate method. The nucleosides (5a-d) were examined for growth-inhibitory effects on mouse leukemic L5178Y cells, and their IC50 values (microgram/ml) were 1.8, 33, 6.5, and 18, respectively. On the other hand, the antiviral activities of these compounds on a rhabdovirus, infectious hematopoietic necrosis virus (IHNV), were moderate (IC50 = 100-500 micrograms/ml in CHSE-214 cells). The 5'-triphosphates showed remarkable inhibitory effects on DNA polymerase beta and DNA polymerase alpha-primase purified from testes of the cherry salmon, Oncorhynchus masou, but not on common DNA polymerase alpha from same source.

Animals↗
PubMed1978

Antibodies to N6-(delta2-isopentenyl) adenosine and its nucleotide: interaction with purified tRNAs and with bases, nucleosides and nucleotides of the isopentenyladenosine family.

The interaction of antibodies directed toward N6-(delta2-isopentenyl)adenosine, i6Ado, or its nucleotide with related bases, nucleosides, nucleotides and purified tRNAs is described. The selectivity of the antibody preparation was tested in inhibition experiments utilizing a sensitive radioimmunoassay to quantitate the binding of [3H]i6Ado to the antibody. Purified tRNAs containing various modified nucleosides adjacent to the 3'-end of the anticodon were tested to provide information about the selectivity of the antibody preparation toward nucleotides in this position of the tRNA chain. Antibodies directed against the nucleotide hapten were used to purify tRNAs which contain i6Ado and to quantitate the amount of that nucleotide. The same order of selectivity was expressed whether the nucleotides were free or in a tRNA molecule. Interaction of the antibody with compounds from the i6Ado family demonstrated dominance of the hydrophobic isopentenyl group and the importance of positional differences of modifications.

Adenosine↗
PubMed1975

Nucleotide and nucleoside stimulation of glucagon secretion.

The effects of various nucleosides and nucleotides upon glucagon secretion from the isolated perfused rat pancreas were studied. Increasing glucagon secretion was found with increasing concentrations of exogenous cyclic AMP (2 X 10(-4) M, 2 X 10(-3) M and 1 X 10(-2) M). Stimulation of alpha cell secretion was also found with 2 X 10(-3) M 2'AMP, 3'AMP, 5'AMP, ADP, Adenosine, NADP, and NADPH. One X 10(-3) M cyclic GMP elicited significant glucagon secretion. The pattern of glucagon release was similar in all cases with peak secretion occurring during the 30- to 90-s time period following initiation of the stimulus. No significant increase of glucagon secretion was found in response to ATP, guanosine, 2'GMP, 3'GMP, 5'GMP, GTP, xanthosine, inosine, adenine, xanthine, thymidine, cytidine, ribose, nicotinamide, and uric acid. On the basis of the above results, the structural requirement for stimulation of glucagon secretion appears to be adenine linked to ribose, with phosphate groups being unnecessary. The conclusion of this study is that a new class of compounds capable of stimulating glucagon secretion has been identified, and important questions are thus raised about the mechanism of the action of exogenous cyclic AMP.

Animals↗
PubMed1982

Modulation of the vasoconstrictor response to adrenergic stimulation by nucleosides and nucleotides.

The ability of nucleosides and nucleotides to modulate adrenergic neuromuscular transmission was examined in the isolated, perfused rat mesentery. The nucleosides adenosine and cytidine and the stable nucleotide of ATP, beta, gamma-methylene ATP (APPCP), and GTP depressed in a concentration-dependent manner the vasoconstrictor response to nerve stimulation (NS). APPCP and cytidine required concentrations less than those of adenosine or GTP to cause inhibition of the constriction to NS. Guanosine had no apparent effect on the constriction to NS, whereas cytidine 5'-triphosphate enhanced this response. In contrast to the inhibitory effect of several nucleotides and nucleosides on the response to NS, only adenosine depressed the vasoconstriction to exogenous norepinephrine (NE). APPCP, GTP, cytidine 5'-triphosphate and guanosine were essentially equipotent in potentiating the vasoconstriction to NE; cytidine had no apparent effect. The ability of these agents to enhance vasoconstriction is not specific for alpha adrenergic receptor-mediated effects inasmuch as APPCP also potentiated the vasopressor response to KCl. Theophylline abolished the depressant effects of adenosine, cytidine, APPCP and GTP on the vasoconstriction to NS and the ability of adenosine to inhibit the constrictor response to NE. Theophylline did not inhibit the ability of APPCP to potentiate the vasoconstriction to NE. These results indicate that the nucleosides adenosine, guanosine and cytidine and the nucleotides APPCP and GTP act prejunctionally, possibly at a common receptor, to inhibit the neuronal release of NE. In addition, the data suggest the existence of two postjunctional sites, one that is inhibitory and selective for adenosine and another that enhances vasoconstrictor responses and is activated by nucleotides and guanosine.

Adenosine↗
PubMedDate not supplied

Effects of total parenteral nutrition with nucleoside and nucleotide mixture on D-galactosamine-induced liver injury in rats.

The effect of a nucleoside-nucleotide mixture on liver injury of rats induced by D-galactosamine was studied by examining changes in function and histopathology of the liver. Animals with liver damage received total parenteral nutrition with glucose and amino acids supplemented with a nucleoside-nucleotide mixture containing inosine, cytidine, GMP, uridine and thymidine, or with uridine which inhibits galactosamine injury, or with liver cell extract containing flavin adenine dinucleotide and nucleic acid derivatives. As control, animals with liver damage received total parenteral nutrition with glucose and amino acids only. The serum GOT and GPT concentrations were significantly lower in the group supplemented with nucleoside-nucleotide mixture than those in other groups. A large dose (1.2 g/kg) of uridine inhibited liver injury, but a lower dose (0.14 g/kg) did not have any effect, whereas nucleoside-nucleotide mixture containing the same amount of uridine inhibited the injury. Liver cell extract also did not improve liver function. Thus infusion of a physiological and balanced mixture of nucleosides or nucleotides may improve liver function in rats with liver injury.

Animals↗
PubMed1985

Purine nucleoside and nucleotide regulation of high affinity [3H]glutamate and [3H]aspartate uptake into rat brain synaptosomes.

Purine nucleotides may interact with neurotransmitter transport sites either via specific receptor sites or as donors of high energy phosphate groups. This study shows that purine nucleotides and nucleosides have no effect on the high affinity transport of aspartate. However, the inhibition of high affinity glutamate transport by ATP and GTP may be mediated through a mechanism involving membrane protein phosphorylation.

Animals↗