Deoxyadenosine blockade of G0 to G1 transition in lymphocytes: possible involvement of protein kinases

Adenosine deaminase inhibition

Adenosine deaminase is a critical enzyme in purine metabolism that regulates intra and extracellular adenosine concentrations by converting it to inosine. Adenosine is an important purine that regulates numerous physiological functions by interacting with its receptors. Adenosine and consequently adenosine deaminase can have pro or anti-inflammatory effects on tissues depending on how much time has passed from the start of the injury. In addition, an increase in adenosine deaminase activity has been reported for various diseases and the significant effect of deaminase inhibition on the clinical course of different diseases has been reported. However, the use of inhibitors is limited to only a few medical indications. Data on the increase of adenosine deaminase activity in different diseases and the impact of its inhibition in various cases have been collected and are discussed in this review. Overall, the evidence shows that many studies have been done to introduce inhibitors, however, in vivo studies have been much less than in vitro, and often have not been expanded for clinical use.

A carbon ion beam irradiated MWCNT/AuNPs composite sensor for a sensitive assay of purine-nucleosides of DNA

Sensor for purine nucleosides has been developed using irradiation with high energy carbon ion beam.

High adenosine and deoxyadenosine concentrations in mononuclear cells of hemodialyzed patients

Infections are one of the most important complications of hemodialysis (HD). The high concentrations of adenosine (Ado) and of its metabolites during HD may contribute to the dialysis-induced immune deficiency through their known ability to alter lymphocyte function. The influence of HD on Ado metabolism was assessed in mononuclear cells through the measurement of (1) the concentrations of nucleosides in mononuclear cells and (2) the activities of mononuclear cell Ado deaminase (MCADA) and Ado kinase, two enzymes involved in Ado concentration regulation. Nine end-stage renal failure hemodialyzed patients (five men and four women; mean age, 69 +/- 10 yr) and eight healthy volunteers (four men and four women; mean age, 53 +/- 19 yr) were included in the study. Before HD, Ado, deoxyadenosine, and inosine concentrations were respectively 2.9-, 2.5-, and 2.5-fold higher in mononuclear cells of patients than in healthy volunteers. During HD, Ado concentration decreased by 34%, whereas inosine concentration increased by 27%. Before HD, MCADA activity level was 2.1-fold lower in patients than in control subjects. After HD, MCADA activity increased by nearly 50% but remained lower than in control subjects. Ado kinase activity level of patients did not differ from that of control subjects and was unchanged by HD. The influence of Ado on in vitro mononuclear cell proliferation and interferon-gamma production also was evaluated. Ado inhibited cell proliferation and interferon-gamma production in a dose-dependent manner, and these inhibitions were stronger for patients than for healthy volunteers. The high concentrations of Ado and deoxyadenosine in mononuclear cells and the low MCADA activity level likely are involved in the immune defect of patients who are undergoing HD.

The CP-I subunit of adenosine deaminase complexing protein from calf kidney is identical to human, mouse, and rat dipeptidyl peptidase IV

The CP-I subunit of calf kidney adenosine deaminase complexing protein (ADCP), isolated by affinity chromatography based on Sepharose-4B immobilized adenosine deaminase, is identical with dipeptidyl peptidase IV. This finding is based on the following results: (a) Its M(r) = 110 kD, as determined by sodium dodecyl sulphate polyacrylamide gel electrophoresis; (b) its catalytic activity toward Gly-Pro-p-nitroanilide; (c) its inhibition by serine protease inhibitor; and (d) by two peptide sequences resulting from its trypsin proteolysis. Accordingly, the CP-I subunit of ADCP isolated from bovine kidney is DPPIV (CD26). Thus, as anticipated, the high affinity between ADA subunits prevails even when they originate in different species.

Adenosine inhibits DNA synthesis stimulated with TSH, insulin, and phorbol 12-myristate 13-acetate in rat thyroid FRTL-5 cells

Adenosine has been shown to modulate cell proliferation in FRTL-5 thyroid cells, although the mechanisms by which this interaction occurs is still unclear. In the present study we investigated the effects of adenosine on the 3H-thymidine incorporation, cell cycle kinetics, and expression of the transcription factor c-Fos in cells stimulated via three different mitogenic pathways, i.e., by thyroid stimulating hormone (TSH) [adenosine 3',5'-cyclic monophosphate(cAMP)], insulin (tyrosine kinase), or phorbol 12-myristate 13-acetate (protein kinase C). Addition of adenosine to cells grown in medium containing hormones and serum did not inhibit the incorporation of 3H-thymidine. If adenosine was added to hormone-deprived cells together with any of the tested mitogens, the stimulation of the 3H-thymidine incorporation was inhibited in a dose-dependent manner. The inhibition was significantly lower when the cells were preincubated with TSH or insulin for 48 h. Flow cytometric studies showed that adenosine evoked an inhibition of the cells in the G0/G1 phase. Submaximal doses of adenosine (10 nM-10 microM) were able to induce c-Fos expression in FRTL-5 cells. However, the mitogen-induced expression of c-Fos was not reduced by maximal dose of adenosine (100 microM). The effect of adenosine on DNA synthesis was not dependent on pertussis toxin-sensitive G-proteins. In addition, adenosine A1- or A2- receptor antagonists did not block the effect of adenosine. The effect of adenosine was abolished by treatment of the cells with adenosine deaminase, suggesting that the observed effect was not mediated by a metabolite of adenosine. The results suggest that adenosine is an effective blocker of mitogen-evoked DNA synthesis of FRTL-5 cells, provided that adenosine is administered simultaneously with the mitogen.