scholarly journals Growth inhibition of transformed mouse fibroblasts by adenine nucleotides occurs via generation of extracellular adenosine.

1988 ◽  
Vol 263 (25) ◽  
pp. 12367-12372
Author(s):  
G A Weisman ◽  
K D Lustig ◽  
E Lane ◽  
N N Huang ◽  
I Belzer ◽  
...  
Keyword(s):  
Growth Inhibition ◽  
Adenine Nucleotides ◽  
Extracellular Adenosine ◽  
Mouse Fibroblasts

scholarly journals Homocysteine enhances the inhibitory effect of extracellular adenosine on the synthesis of proteins in isolated rat hepatocytes

1995 ◽  
Vol 310 (3) ◽  
pp. 893-896 ◽  
Author(s):  
S Tinton ◽  
P Buc-Calderon
Keyword(s):  
Protein Synthesis ◽  
Kinase Inhibitor ◽  
Adenine Nucleotides ◽  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Adenosine Kinase ◽  
Isolated Rat Hepatocytes ◽  
Extracellular Adenosine ◽  
Inhibition Of Protein Synthesis ◽  
Isolated Rat

Previous work has shown that extracellular adenosine inhibits the incorporation of radiolabelled leucine into proteins in isolated rat hepatocytes [Tinton, Lefebvre, Cousin and Buc Calderon (1993) Biochim. Biophys. Acta 1176, 1-6]. In this study, we investigated whether its metabolism into adenine nucleotides, inosine or S-adenosylhomocysteine (AdoHcy) is required to induce such an impairment. Incubation of isolated hepatocytes in the presence of adenosine at 0.5 or 1 mM reduces the synthesis of proteins by about 45% after 120 min of incubation. Such an inhibition occurred without cell lysis and was not modified by adding the adenosine kinase inhibitor 5-iodotubercidin (15 microM) or the adenosine deaminase inhibitor coformycin (0.1 microM). It is therefore unlikely that the anabolic and catabolic pathways of adenosine are involved in the inhibition of protein synthesis. Adenosine (1 mM) increased the level of AdoHcy and S-adenosylmethionine by 20- and 5-fold respectively after 60 min of incubation and reduced the methylation index. These events as well as the inhibition of protein synthesis were strongly enhanced in the presence of L-homocysteine (2 mM). It is therefore concluded that the metabolism of adenosine into AdoHcy, which is known to be a potent inhibitor of cellular methylation reactions, may play an important role in the control of translation.

scholarly journals Growth Inhibition of Polyoma-Transformed Cells by Contact with Static Normal Fibroblasts

1966 ◽  
Vol 1 (3) ◽  
pp. 297-310
Author(s):  
M. G. P. STOKER ◽  
MOIRA SHEARER ◽  
C. O'NEILL
Keyword(s):  
Cell Growth ◽  
Growth Inhibition ◽  
Normal Mouse ◽  
Inhibitory Effect ◽  
Mixed Cultures ◽  
Transformed Cells ◽  
Mouse Fibroblasts ◽  
General Change ◽  
Close Proximity

The growth of polyoma-transformed BHK21 cells was studied in mixed cultures with normal mouse fibroblasts. On coverslips in excess medium, normal fibroblasts undergo one or two divisions after the cells become contiguous. Py-cell growth was not inhibited by contact with confluent fibroblasts which were still dividing, but the Py cells were rapidly inhibited after contact with fibroblasts which had become static. Further experiments confirmed the earlier view that the inhibitory effect was not due to a general change in the medium but was only brought about when cells were in contact or close proximity.

Adenosine metabolism in human skin fibroblasts

1985 ◽  
Vol 248 (1) ◽  
pp. C21-C26 ◽  
Author(s):  
M. J. Holland ◽  
E. Murphy ◽  
J. K. Kelleher
Keyword(s):  
Initial Rate ◽  
Adenine Nucleotide ◽  
Adenine Nucleotides ◽  
Product Formation ◽  
Human Skin Fibroblasts ◽  
Metabolic Fate ◽  
Normal Cells ◽  
Extracellular Adenosine ◽  
Adenosine Concentration ◽  
The Media

When normal fibroblasts were incubated in media containing various initial concentrations of [8-14C]adenosine, ranging from 0.25 to 400 microM, under conditions where product formation was linear, greater than 90% of the intracellular label was found in adenine nucleotides, largely in the form of ATP, less than 1% of the intracellular label appeared in the nucleic acids, the remaining intracellular label was found in adenosine, inosine, and hypoxanthine, and the media contained two labeled products, inosine and hypoxanthine. Production of labeled inosine and hypoxanthine from adenosine was considerably lower in adenosine deaminase (ADA)-deficient cells than in normal cells and virtually eliminated in normal cells by the presence of 1 microM deoxycoformycin (a potent ADA inhibitor), suggesting that labeled inosine and hypoxanthine production requires ADA activity. Initial rates of deamination (inosine and hypoxanthine formation) and phosphorylation (adenine nucleotide formation) were estimated by examining the metabolic fate of [8-14C]adenosine in hypoxanthine phosphoribosyltransferase-deficient cells, which cannot recycle hypoxanthine. The estimate of the initial rate of phosphorylation exceeded that of deamination only at the lowest adenosine concentration examined (0.25 microM). The ratio of deamination to phosphorylation rose from approximately 1 at 0.41 microM to approximately 15 at 400 microM extracellular adenosine.

Abstract TP269: Reduction of Human Brain Adenosine Levels Following Remote Ischemic Preconditioning

Stroke ◽  
2013 ◽  
Vol 44 (suppl_1) ◽  
Author(s):  
Joshua R Dusick ◽  
Arzu Bilgin-Freiert ◽  
Kym F Faull ◽  
Nestor Gonzalez
Keyword(s):  
Blood Pressure ◽  
Ischemic Preconditioning ◽  
Aneurysmal Subarachnoid Hemorrhage ◽  
Adenine Nucleotides ◽  
High Energy ◽  
Protective Mechanisms ◽  
Extracellular Adenosine ◽  
Pressure Cuff ◽  
Cell Energy ◽  
Csf Levels

Introduction: Prior studies demonstrate that ischemic preconditioning (IP) alters adenosine metabolism. The significance of this effect is not fully understood, but evidence suggests that reduction in extracellular adenosine may represent use as an alternative fuel. Transformation into AMP/ADP may also replenish intracellular total adenine nucleotides (TAN), improving the potential high-energy phosphate bonds available in cells facing ischemia. In both cases, adenosine supports cell energy requirements and may be a key component of IP’s protective mechanisms. There are no previous studies of brain adenosine in human patients undergoing remote IP. Methods: In adults with aneurysmal subarachnoid hemorrhage (SAH), 3-4 remote IP sessions were conducted on non-consecutive days, 4-12 days after hemorrhage. Each session consisted of 4 5-min cycles of lower extremity blood pressure cuff inflation to 30mmHg above systolic blood pressure, followed by 5-min reperfusion. Patients had microdialysis (MD) probes to compare brain adenosine, inosine, xanthine and hypoxanthine before, immediately after, and 24h after RIPC. MD samples from 4 SAH ICU patients without IP were used as controls. Results: Five RIPC sessions in 3 patients resulted in complete MD data for comparison over time. In all, brain adenosine levels dropped from their baseline (pre-RIPC) level. Average pre-RIPC adenosine went from 19.2 (SD 14.4) fmol/mg to 7.9 (SD 8.6) immediately following the session (p=0.095) and to 3.2 (SD 4.5) by 24h (p=0.048). Adenosine metabolites inosine, xanthine, and hypoxanthine decreased or did not change over the same period, suggesting adenosine consumption rather than non-energy related catabolism. These changes in adenosine were not reflected in CSF levels, which did not change (p=0.5). Brain adenosine in control subjects did not decrease (baseline 0.26±0.17, 24h 6.6±9.3, p=0.27). Conclusion: Remote IP leads to decreased brain adenosine in SAH patients by 24 hours. Failure to demonstrate a concomitant rise in levels of metabolites suggests that adenosine is consumed by cells in the brain, as previously shown in animal models. This shift toward the energetic metabolism of adenosine may play a key role in the mechanisms of protection induced by IP.

scholarly journals A model for adenosine transport and metabolism

1992 ◽  
Vol 287 (2) ◽  
pp. 461-472 ◽  
Author(s):  
J J Centelles ◽  
M Cascante ◽  
E I Canela ◽  
R Franco
Keyword(s):  
Steady State ◽  
Adenine Nucleotides ◽  
Slight Modification ◽  
Nucleoside Transporters ◽  
Rate Equations ◽  
Nucleoside Transporter ◽  
State Equations ◽  
Extracellular Adenosine ◽  
Adenosine Transport ◽  
Control Patterns

1. A model is presented for adenosine transport and metabolism in different steady states. The model considers steady-state equations for metabolic enzymes based on information from the literature on their kinetic behaviour. 2. Assuming that extracellular adenosine and inosine are translocated by three transporters, we have devised rate equations for these nucleoside transporters which are valid when both nucleosides are present. Since the Na(+)-independent transporter can either incorporate nucleosides into the cell or release them, various conditions have been simulated in which inosine was either incorporated or released. 3. Control analyses are reported which show that the fluxes towards intracellular adenine nucleosides are controlled by ecto-5′-nucleotidase in some circumstances and by the nucleoside transporters in others. The nucleoside transporter is responsible for five fluxes (two Na+ dependent adenosine transport mechanisms, a Na(+)-dependent inosine transport, a Na(+)-independent adenosine transport and a Na(+)-independent inosine influx or efflux) but the control is not always positive for all these fluxes. The control patterns of these five fluxes indicate that, in the presence of extracellular adenosine and inosine, the intracellular metabolism of adenine derivatives would be highly dependent on the extracellular and intracellular concentrations of both nucleosides, on the ectoenzymes (5′-nucleotidase and adenosine deaminase) and on the transporter. 4. Predictions of the model were examined. The results indicate that a change in one independent variable (extracellular AMP concentration) makes the system evolve towards a new steady state which is far from the initial one and has a different control pattern. In contrast, simulation of inhibition of the carriers produces only slight modification of the fluxes since the concentrations of the metabolites change to counteract the effect. Thus, for instance, a 50% inhibition of the three carriers does not affect the flux towards intracellular adenine nucleotides. Finally, our model has confirmed that the evolution of the concentration of extracellular adenosine, when an increase in extracellular AMP is produced, agrees with the behaviour expected for a neurohormone.

Rat cardiac myocyte adenosine transport and metabolism

1987 ◽  
Vol 252 (1) ◽  
pp. H54-H63 ◽  
Author(s):  
D. A. Ford ◽  
M. J. Rovetto
Keyword(s):  
Metabolic Flux ◽  
Cardiac Myocyte ◽  
Ventricular Myocytes ◽  
Adenine Nucleotide ◽  
Adenine Nucleotides ◽  
Nucleotide Metabolism ◽  
Adenosine Kinase ◽  
Maximal Velocity ◽  
Extracellular Adenosine ◽  
Minimum Estimate

Based on the importance of myocardial adenosine and adenine nucleotide metabolism, the adenosine salvage pathway in ventricular myocytes was studied. Accurate estimates of transport rates, separate from metabolic flux, were determined. Adenosine influx was constant between 3 and 60 s. Adenosine metabolism maintained intracellular adenosine concentrations less than 10% of the extracellular adenosine concentrations and thus unidirectional influx could be measured. Myocytes transported adenosine via saturable [Michaelis constant = 6.2 +/- 2.1 microM and maximal velocity (Vmax) = 9.58 +/- 0.98 X 10(-1) pmol X mg protein-1 X s-1] and nonsaturable (rate constant = 1.8 X 10(-3)/s) processes. A minimum estimate of the Vmax of myocytic adenosine kinase (2 pmol X mg protein-1 X s-1) indicated the saturable component of adenosine influx was independent of adenosine kinase activity. Saturable transport was inhibited by nitrobenzylthioinosine and verapamil (inhibitor constant = 17 +/- 5 microM). Extracellular adenosine taken up by myocytes was rapidly phosphorylated to adenine nucleotides. Not all extracellular adenosine, though, was phosphorylated on entering myocytes, since free, as opposed to protein-bound, intracellular adenosine was detected after digitonin extraction of cells in the presence of 1 mM ethylene-diaminetetraacetic acid.

scholarly journals Effect of inhibition of polyamine synthesis on the content of decarboxylated S-adenosylmethionine

1982 ◽  
Vol 202 (2) ◽  
pp. 519-526 ◽  
Author(s):  
Anthony E. Pegg ◽  
Hannu Pösö ◽  
Kay Shuttleworth ◽  
Richard A. Bennett
Keyword(s):  
Partial Hepatectomy ◽  
Ornithine Decarboxylase ◽  
Rat Liver ◽  
Adenine Nucleotides ◽  
3T3 Cells ◽  
Direct Inhibition ◽  
Polyamine Synthesis ◽  
Mouse Fibroblasts ◽  
Regenerating Rat Liver ◽  
Specific Inhibitors

1. The content of decarboxylated S-adenosylmethionine (AdoMet) in transformed mouse fibroblasts (SV-3T3 cells) was increased 500-fold to about 0.4fmol/cell when ornithine decarboxylase was inhibited by α-difluoromethylornithine. This increase was due to the absence of putrescine and spermidine, which serve as substrates for aminopropyltransferases with decarboxylated AdoMet as an aminopropyl donor, and to the enhanced activity of AdoMet decarboxylase brought about by depletion of spermidine. The increase in decarboxylated AdoMet content was abolished by addition of putrescine, but not by 1,3-diaminopropane. 2. 5′-Methylthiotubercidin also increased decarboxylated AdoMet content, presumably by direct inhibition of aminopropyl-transferase activities, but the increase in its content and the decline in spermidine content were much less than those produced by α-difluoromethylornithine. 3. Decarboxylated AdoMet content of regenerating rat liver was measured in rats treated with inhibitors of ornithine decarboxylase. The content was increased by 60% 32h after partial hepatectomy in control rats, by 90% when α-difluoromethylornithine was given to the partially hepatectomized rats, and by 330% when 1,3-diaminopropane was used to inhibit putrescine and spermidine synthesis. After 48h of exposure to 1,3-diaminopropane, which completely prevented the increase in spermidine after partial hepatectomy, there was a 5-fold rise in hepatic decarboxylated AdoMet concentration. These increases were prevented by treatment with putrescine or with methylglyoxal bis(guanylhydrazone), an inhibitor of AdoMet decarboxylase. 4. These results show that changes in AdoMet metabolism result from the administration of specific inhibitors of polyamine synthesis. The possible consequences of the accumulation of decarboxylated AdoMet, which could, for example, interfere with normal cellular methylation or lead to depletion of cellular adenine nucleotides, should be considered in the interpretation of results obtained with such inhibitors.

Sign in / Sign up

Export Citation Format

Share Document