Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.5.4.4 (adenosine deaminase)
5,136 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The leukemic cells of a patient with CD4+ prolymphocytic leukemia were treated in vitro with 5 microM deoxyadenosine and 60 microM 2'-deoxycoformycin (dCF), an inhibitor of adenosine deaminase (ADA). Following treatment, the leukemic cell dATP level increased to 378 pmol/10(6) cells on day 3, after which the level plateaued. Apoptosis was apparent following 4 h of incubation, and by day 8 34% of the chromatin was fragmented. Apoptosis also occurred in control cells, but to a lesser extent than in drug-treated cells. When the patient was treated with dCF, 4 mg/M2 i.v. the leukemic cell ADA activity was inhibited 24 h following treatment, and the lymphocyte dATP content increased to 303 pmol/10(6) cells by day 6. The lymphocyte count fell 60% in 1 week, but during this time there was no evidence of apoptosis in these cells. Thus, if dCF induces apoptosis in vivo, the effete cells may be rapidly cleared from the circulation and thus elude detection.
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PMID:Induction of apoptosis in CD4+ prolymphocytic leukemia by deoxyadenosine and 2'-deoxycoformycin. 152 66

Fludara I.V. (fludarabine phosphate) (9-beta-D-arabinosyl-2-fluoroadenine, F-ara-A) is an adenine nucleoside analogue resistant to adenosine deaminase that shows promising therapeutic activity in the clinical treatment of lymphocytic hematologic malignancies. F-ara-A is transported into cells, where it is converted to its 5'-triphosphate (F-ara-ATP), the principal active metabolite. Deoxycytidine kinase is the enzyme responsible for the initial step of this activation metabolism. The differential transport and phosphorylation of F-ara-A and accumulation of F-ara-ATP by normal and cancer cells may constitute the metabolic basis of its positive therapeutic index. The major action of F-ara-A is the inhibition of DNA synthesis. F-ara-ATP competes with deoxyadenosine triphosphate for incorporation into the A sites of the elongating DNA strand by DNA polymerases and terminates DNA synthesis at the incorporation sites. That action is potentiated by the decrease of cellular dATP that results from inhibition of ribonucleotide reductase by F-ara-ATP. In vitro experiments demonstrated that DNA polymerase delta is able to excise the incorporated F-ara-AMP residues from DNA with its 3' to 5' exonuclease activity. The terminal incorporation of F-ara-AMP into DNA results in deletion of genetic material. That mechanism may be responsible for the observed mutagenicity of Fludara I.V., and ultimately its cytotoxic action.
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PMID:Metabolism and action of fludarabine phosphate. 169 80

Conditions for labeling the dATP pool of V79 and 3T3 cells from [3H]deoxyadenosine (salvage) or [3H]adenine (via ribonucleotide reduction) were established. With deoxyadenosine the specific radioactivity of dATP reached a constant value after 60 min. In resting 3T3 cells this value was 30 times higher than in S-phase cells. Turnover of dATP and absolute rates of DNA synthesis and excretion of breakdown products of dATP were determined from the accumulation of isotope in various compartments and the specific activity of dATP. In S-phase cells the dATP pool had a half-life of 4 min, identical to that of dTTP determined earlier. Deoxyadenosine was the major breakdown product of dATP in the presence of an inhibitor of adenosine deaminase. The rate of deoxyadenosine excretion of V79 cells amounted to 4% of the rate of dATP incorporation into DNA. Inhibition of DNA replication increased deoxyadenosine excretion 5- to 10-fold, demonstrating a continued de novo synthesis of dATP, albeit at a slightly reduced rate. Our results fit a model involving a substrate cycle between dAMP and deoxyadenosine regulating the dATP pool, similar to the model of substrate cycles involved in the regulation of pyrimidine deoxyribonucleotide pools developed earlier.
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PMID:Dynamics of the dATP pool in cultured mammalian cells. 173 53

The congenital absence of adenosine deaminase in humans results in severe combined immunodeficiency. To clarify the process whereby thymocytes are destroyed in the absence of adenosine deaminase activity, we induced a parallel condition in mice through the injection of an inhibitor of adenosine deaminase, deoxycoformycin. We have observed that deoxycoformycin, in addition to maintaining high levels of dATP in thymocytes, blocks the progression of thymocyte differentiation at two points. As a result of the first block, the cortex is depleted of immature cortical thymocytes while CD4+CD8+ thymocytes with functionally rearranged T-cell receptors survive. As a result of the second block, the CD4+CD8+ thymocytes are prevented from further differentiation to mature CD4+CD8- or CD4-CD8+ T lymphocytes and accumulate at the corticomedullar junction and in the medulla. These observations suggest that the maintenance of dNTP pools by adenosine deaminase is critical to at least two stages of thymocyte differentiation.
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PMID:Adenosine deaminase and thymocyte maturation. 182 94

Deoxyadenosine triphosphate (dATP) is present in adenosine deaminase (ADA)-deficient or ADA-inhibited human red cells and in the red cells of the opossum Didelphis virginiana. In order to investigate the functions of dATP in the red cell, red cells were treated with 2'-deoxycoformycin (dCf), a powerful inhibitor of ADA, and incubated with phosphate, deoxyadenosine and glucose. These red cells in which ATP was almost completely replaced by dATP, had the same shape, lactate production, nucleotide consumption, stability of reduced glutathione, osmotic fragility and cell deformability as red cells containing ATP. Cells merely depleted of ATP showed reduced viability. This indicates that dATP compensates well for the absence of ATP and acts as an energy-transferring molecule to maintain cell viability. These results indicate that the accumulation of dATP or the reduction of ATP is not the cause of the hemolysis observed after dCf administration.
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PMID:Deoxyadenosine triphosphate acting as an energy-transferring molecule in adenosine deaminase inhibited human erythrocytes. 191 76

Hydroxyurea, an inhibitor of ribonucleotide reductase, blocks replication of vaccinia virus. However, when medium containing hydroxyurea and dialyzed serum was supplemented with deoxyadenosine, the block to viral reproduction was circumvented, provided that an inhibitor of adenosine deaminase was also present. Deoxyguanosine, deoxycytidine, and deoxythymidine were ineffective alone and did not augment the deoxyadenosine effect. In fact, increasing concentrations of deoxyguanosine and deoxythymidine, but not deoxycytidine, eliminated the deoxyadenosine rescue, an effect that was reversed by the addition of low concentrations of deoxycytidine. These results suggested that the inhibition of viral replication by hydroxyurea was primarily due to a deficiency of dATP. Deoxyribonucleoside triphosphate pools in vaccinia virus-infected cells were measured at the height of viral DNA synthesis after a synchronous infection. With 0.5 mM hydroxyurea, the dATP pool was greater than 90% depleted, the dCTP and dGTP pools were 40 to 50% reduced, and the dTTP pool was increased. Assay of ribonucleotide reductase activity in intact virus-infected cells suggested that hydroxyurea may differentially affect reduction of the various substrates of the enzyme.
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PMID:Deoxyadenosine reverses hydroxyurea inhibition of vaccinia virus growth. 201 60

An experimental model of adenosine deaminase deficiency was established on the human T cell line Jurkat by using 2'-deoxycoformycin, a strong specific inhibitor of the enzyme. When deoxyadenosine was added to the inhibited cells, the nucleotide profile was modified reproducing that found in lymphocytes from adenosine deaminase-deficient children. The metabolism of phosphoinositides, analyzed by either the release of [3H]inositol phosphates or the breakdown of 32P-prelabeled phosphatidyl inositides, was compared in normal and modified cells where dATP was accumulated. No modification in 32P labeling of phosphoinositides was detectable within the 32P-loading period. However, when the cells were stimulated by phytohemagglutinin or anti-CD3 monoclonal antibody, the phosphoinositide hydrolysis was strongly reduced in the dATP-containing lymphoblasts. This decrease was correlated with the intracellular dATP concentration.
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PMID:Influence of adenosine deaminase inhibition on the phosphoinositide turnover in the initial stages of human T cell activation. 215 10

Deoxyadenosine has been implicated as the toxic metabolite causing profound lymphopenia in immunodeficient children with a genetic deficiency of adenosine deaminase (ADA), and in adults treated with the potent ADA inhibitor deoxycoformycin. However, the biochemical basis for deoxyadenosine toxicity toward lymphocytes remains controversial. The present experiments have examined in detail the sequential metabolic changes induced in nondividing human peripheral blood lymphocytes by incubation with deoxyadenosine plus deoxycoformycin, or with 2-chlorodeoxyadenosine (CdA), an ADA resistant deoxyadenosine congener with anti-leukemic and immunosuppressive properties. The lymphotoxic effect of deoxyadenosine and CdA required their phosphorylation, and was inhibited by deoxycytidine. As early as 4 h after exposure to the deoxynucleosides, strand breaks in lymphocyte DNA began to accumulate, and RNA synthesis decreased. These changes were followed by a significant fall in intracellular NAD levels at 8 h, a drop in ATP pools at 24 h, and cell death by 48 h. Incubation of the lymphocytes with 5 mM nicotinamide, a NAD precursor and an inhibitor of poly(ADP-ribose) synthetase, prevented NAD depletion. The nicotinamide treatment also rendered the lymphocytes highly resistant to deoxyadenosine and CdA toxicity, without altering dATP formation or the accumulation of DNA strand breaks. The poly(ADP-ribose) synthetase inhibitor 3-aminobenzamide exerted a similar although less potent effect. These results suggest that NAD depletion, probably triggered by poly(ADP-ribose) formation, is the principle cause of death in normal resting human lymphocytes exposed to deoxyadenosine plus deoxycoformycin, or to CdA.
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PMID:Mechanism of deoxyadenosine and 2-chlorodeoxyadenosine toxicity to nondividing human lymphocytes. 257 98

Adenosine inhibition of hormone-sensitive adenylate cyclase activity was investigated using isolated myocardial membranes prepared from rat hearts. When cyclase activity was determined in membranes, using [alpha-32P]ATP as substrate, 10(-5) M adenosine inhibited isoproterenol-stimulated adenylate cyclase activity by 25% but did not inhibit basal activity or fluoride (5 mM) activation of the enzyme. The adenosine reduction of isoproterenol-sensitive cyclase activity was dependent on GTP but was not prevented by 10(-3) M theophylline. Adenosine neither appeared to compete with ATP for the substrate converting site of the enzyme nor reduced 5'-guanylyl imidodiphosphate activation of the enzyme. Inasmuch as lower concentrations of adenosine had no influence on enzyme activity, endogenous adenosine may be present in the adenylate cyclase assay. To obviate the effects of endogenous adenosine, the adenylate cyclase assay was then modified to a 2'-deoxy system with [alpha-32P]dATP used as the substrate in the presence of adenosine deaminase. With this assay system, the 15% inhibition of isoproterenol-stimulated adenylate cyclase activity produced by the adenosine receptor agonists, 10(-8) M 2-chloroadenosine or phenylisopropyladenosine, was prevented by 10(-4) M 8-phenyltheophylline or isobutylmethylxanthine (IBMX), respectively. While under these assay conditions, 10(-7) M 2',5'-dideoxyadenosine, a P-site analogue, did not influence the hormone-sensitive cyclase activity. The 35% reduction of the hormone-sensitive enzyme produced by this analogue at 10(-5) M was not prevented by IBMX. These results suggest that nanomolar concentrations of adenosine analogues interact with a methylxanthine-sensitive adenosine receptor that mediates the attention of membrane hormone-sensitive adenylate cyclase activity.
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PMID:Adenosine inhibition of catecholamine-stimulated cardiac membrane adenylate cyclase. 258 60

2'-Deoxycoformycin (dCF), a potent adenosine deaminase inhibitor, has been reported to display greater toxicity for T than for B lymphoblasts. Since this compound can block DNA replication and since this effect is mediated by the intracellular ATP/dATP balance, its possible effect on DNA ligase was investigated. dCF at relatively low concentrations (1 microM), in association with dATP (100 microM), is a strong inhibitor of DNA ligase in T blasts, whereas it has no significant effect in B blasts at this concentration. The AMP-ligase complex is the target of the observed inhibition because the combined presence of the inhibitor and dATP results in a more stable dAMP-ligase complex. Because of this observation and of the greater adenosine deaminase activity observed in T cells, the dATP mediated dCF inhibition of ligase might be the crucial replication target of T cell toxicity. These observations are discussed in terms of T immunodeficiencies including Graft Versus Host Disease and related syndromes.
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PMID:dATP-mediated inhibition of DNA ligase by 2'-deoxycoformycin in T and B cell leukemia. 278 73


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