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Query: UMLS:C0021051 (immunodeficiency)
 71,517 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Deoxyadenosine and deoxyguanosine are toxic to human lymphoid cells in culture and have been implicated in the pathogenesis of the immunodeficiency states associated with adenosine deaminase and purine nucleoside phosphorylase deficiency, respectively. We have studied the relative incorporation of several labeled nucleosides into DNA and into nucleotide pools to further elucidate the mechanism of deoxyribonucleoside toxicity. In the presence of an inhibitor of adenosine deaminase [erythro-9-(2-hydroxy-3-nonyl)adenine [EHNA], 5 muM], deoxyadenosine (1-50 muM) progressively decreased the incorporation of thymidine, uridine, and deoxyuridine into DNA, but did not affect uridine incorporation into RNA. This decrease in DNA synthesis was associated with increasing dATP and decreasing dCTP pools. Likewise, incubation of cells with deoxyguanosine caused an elevation of dGTP, depletion of dCTP, and inhibition of DNA synthesis. To test the hypothesis that dATP and dGTP accumulation inhibit DNA synthesis by inhibiting the enzyme ribonucleotide reductase, simultaneous rates of incorporation of [(3)H]uridine and [(14)C]thymidine into DNA were measured in the presence of deoxyadenosine plus EHNA or deoxyguanosine, and in the presence of hydroxyurea, a known inhibitor of ribonucleotide reductase. Hydroxyurea (100 muM) and deoxyguanosine (10 muM) decreased the incorporation of [(3)H]uridine but not of [(14)C]thymidine into DNA; both compounds also substantially increased [(3)H]cytidine incorporation into the ribonucleotide pool while reducing incorporation into the deoxyribonucleotide pool. In contrast, deoxyadenosine plus EHNA did not show this differential inhibition of [(3)H]uridine incorporation into DNA, and the alteration in [(3)H]cytidine incorporation into nucleotide pools was less impressive. These data show an association between accumulation of dATP or dGTP and a primary inhibition of DNA synthesis, and they provide support for ribonucleotide reductase inhibition as the mechanism responsible for deoxyguanosine toxicity. Deoxyadenosine toxicity, however, appears to result from another, or perhaps a combination of, molecular event(s).
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PMID:Purinogenic immunodeficiency diseases. Differential effects of deoxyadenosine and deoxyguanosine on DNA synthesis in human T lymphoblasts. 11 1

The inherited deficiency of adenosine deaminase (adenosine aminohydrolase; EC 3.5.4.4) activity in humans is associated with an immunodeficiency. Some of the immunodeficient and enzyme-deficient patients respond immunologically to periodic infusions of irradiated erythrocytes containing adenosine deaminase. It has been previously reported that erythrocytes and lymphocytes from immunodeficient ane enzyme-deficient children contained increased concentrations of ATP, and in the one child studied after erythrocyte infusion therapy, the intracellular level of ATP diminished. Using high-pressure liquid chromatography that resolves ATP and 2'-dATP, we have observed greater than 50-fold elevations of dATP in the erythrocytes of immunodeficient, adenosine deaminase-deficient patients but not in the erythrocytes of an immunocompetent adenosine deaminase-deficient patient. The erythrocyte dATP in two unrelated adenosine deaminase-deficient, immunodeficient patients disappeared after infusion of normal erythrocytes. We propose that deoxyadenosine, a substrate of adenosine deaminase, is the potentially toxic substrate in adenosine deaminase deficiency, and that the mediator of the toxic effect is dATP, a recognized potent inhibitor of ribonucleotide reductase.
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PMID:Deoxyadenosine triphosphate as a potentially toxic metabolite in adenosine deaminase deficiency. 27 65

Inherited deficiency of the purine salvage enzyme adenosine deaminase (ADA) is responsible for approximately half the cases of autosomal recessive Severe Combined Immunodeficiency (SCID). Deficiency of ADA can also result in a much later-onset, milder immunodeficiency, while lesser degrees of enzyme deficiency can result in either late-onset immunodeficiency or grossly normal immunologic function. The full clinical spectrum of ADA deficiency is currently being more fully defined. Florid pathology is primarily restricted to the immune system and appears to result from accumulation of substrates (adenosine and deoxyadenosine) and metabolites (deoxy ATP). Studies indicate that these metabolites may preferentially accumulate in lymphoid cells and can interfere with lymphoid proliferation and function. There is evidence for several mechanisms, including induction of chromosome breaks, inhibition of ribonucleotide reductase needed for normal DNA synthesis, and inactivation of SAH hydrolase needed for normal methylation reactions. The enzyme is a 40 Kd monomer that is ubiquitous, and diagnosis can be made with many cell types including erythrocytes, lymphocytes and fibroblasts. Prenatal diagnosis has been made with chorionic villous samples, amniotic cells and fetal blood. The gene for ADA resides on the long arm of human chromosome 20, and both the expressed and structural gene have been isolated and characterized. Most patients with ADA SCID have single base pair mutations resulting in amino acid substitutions, although a splicing mutation and a deletion have been described. The treatment of choice is currently bone-marrow transplantation from a histocompatible related donor, if available. Haploidentical transplants have also been successful but appear to have higher failure rates in ADA deficients than in other types of SCID. Enzyme replacement, now using an enzyme modified to increase the half-life and decrease immunogenicity, has been reported as successful but longer-term efficacy remains to be evaluated. The disorder, despite its rarity, is for several reasons considered a prime candidate for gene therapy. Recently success has been obtained in introducing the gene into lymphoid stem cells and achieving long-term expression.
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PMID:Adenosine deaminase deficiency. 207 32

Deoxyadenosine (dAdo) has been recognized as the toxic metabolite in the immunodeficiency disease associated with adenosine deaminase (ADA) deficiency. Under ADA deficient conditions, dAdo accumulates intracellularly as deoxyadenosine triphosphate (dATP) which by interference with ribonucleotide reductase, prevents DNA synthesis. Recently, we and others have demonstrated that in cells rendered ADA deficient by treatment with deoxycoformycin, dAdo affects T-cell activation events which precede DNA synthesis, such as interleukin 2 receptor (IL-2R) expression and IL-2 production. Here we have analyzed interference of dAdo with the early events of T-cell activation. It is shown that dAdo affects the mitogen induced phosphatidyl inositol turnover. Furthermore dAdo interferes with increase of intracellular calcium. Deoxycytidine, although capable of preventing intracellular accumulation of dATP, cannot reverse the functional consequences of dAdo treatment. The ability of a cell to increase its cytoplasmic free Ca2+, as induced by ionomycin, is not affected by dAdo. The exact target for this novel effect of dAdo is at the present unknown.
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PMID:Interference of deoxyadenosine with transmembrane signaling events in human T lymphocytes. 230 14

High levels of deoxyadenosine and deoxyguanosine in patients with inherited deficiency of either adenosine deaminase or purine-nucleoside phosphorylase, respectively, are considered to be responsible for the associated immunological disorder. The mechanism involves phosphorylation to the corresponding deoxyribonucleoside triphosphates which subsequently inhibit the CDP-reducing activity of ribonucleotide reductase. Addition of deoxycytidine protects cells from the cytotoxic effects of deoxyadenosine and deoxyguanosine by competition for phosphorylation and by replenishing dCTP, the apparent limiting DNA precursor. Addition of cytidine, but not uridine, led to a reversal of deoxyguanosine and thymidine growth inhibition, comparable to that obtained with deoxycytidine. Analysis of the intracellular nucleotide pools showed that increased levels of cytidine ribonucleotides were sufficient to overcome the inhibitory effects of dGTP and dTTP on CDP reduction, thereby circumventing a depletion of the dCTP pool. A partial reversal of deoxyadenosine toxicity was also obtained with addition of cytidine. In this case little change in the dCTP level was observed, but a decreased dGTP pool appeared to be correlated with growth inhibition. High cytidine ribonucleotide levels partially prevented this effect. The present results may encourage the use of cytidine in combination with deoxycytidine as a pharmacological regime in treatment of immunodeficiency disease associated with increased deoxyribonucleotide levels.
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PMID:On the mechanism of deoxyribonucleoside toxicity in human T-lymphoblastoid cells. Reversal of growth inhibition by addition of cytidine. 387 78

A number of inborn errors of purine metabolism have been associated with immunodeficiency diseases. From studies to the possible mechanism(s) leading to the defects in the immune system, it appeared that the accumulation of deoxyATP and deoxyGTP and the subsequent inhibition of ribonucleotide reductase played an important role. The inhibition of methylation pathways through the accumulation of s-adenosylmethionine seems to be a second valid concept. The amount to which certain subtypes of lymphoid cells were affected by the enzyme deficiencies was strongly related to the enzymatic make-up of the cells. Lymphoid cells from different maturation stages could be affected in a specific way, depending on the different enzyme activities of these cells. Studies on human lymphoblastic leukemias showed that, related to the immunological subtype, the different leukemias could be characterized by a different enzymatic make-up. In this paper we discuss the possibilities for a specific enzyme directed chemotherapy, directed against specific subtypes of human lymphoblastic leukemias. Experimental evidence indicates that for example the adenosine deaminase inhibitor 2'deoxycoformycin can be used as a specific drug against acute lymphoblastic leukemia with the T cell phenotype.
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PMID:Purine metabolism in relation to leukemia and lymphoid cell differentiation. 619 80

Deoxyadenosine (AdR) appears to be central to the molecular events mediating immunodeficiency in children born with adenosine deaminase (ADA) deficiency but it is still uncertain whether lymphotoxicity is due to AdR directly inhibiting transmethylation reactions in which S-adenosylmethionine is the methyl group donor, or is due to phosphorylation of AdR to deoxyadenosine triphosphate (dATP) which then inhibits ribonucleotide reductase or is due to other mechanisms. Using AdR and the ADA inhibitor deoxycoformycin (dCF) and assessing cell viability, nucleoside incorporation into RNA and DNA, as well as measuring deoxyribonucleoside triphosphate (dNTP) concentrations and S-adenosylhomocysteine (SAH) hydrolase activity, we have studied various types of human lymphoid cells and demonstrated in them the relative importance of the above two mechanisms of AdR toxicity. Treatment of normal resting peripheral blood lymphocytes in culture with AdR and dCF resulted in impaired viability. Although elevated dATP levels as well as decreased SAH hydrolase activities were both observed, the failure of a known inhibitor of ribonucleotide reductase (hydroxyurea) to produce toxicity, and the inability of deoxycytidine (CdR) to achieve a rescue effect, point to another mechanism, possibly inhibition of trans-methylation or ATP depletion being the more likely causes of toxicity in resting lymphocytes. The same mechanism may well account for the rapid and severe lymphopenia in patients treated with dCF. On the other hand, in cultured lymphoblasts in the exponential phase of growth. AdR and dCF produced marked inhibition of growth and cell death both in a Thy-ALL line and in a c-ALL line, in the absence of significant inhibition of SAH hydrolase, but with a substantial elevation in dATP concentrations and depressed levels of the other dNTP. Minor toxicity occurred in a proliferating B lymphoblast line despite almost complete inactivation of SAH hydrolase. These observations indicate inhibition of ribonucleotide reductase as the more likely mechanism of toxicity in rapidly proliferating lymphocytes. Other T-cells actively synthesizing DNA, such as PHA-stimulated or MLC activated lymphocytes and T-lymphoid colony forming cells, are also likely to be affected by the same mechanism. Indeed in PHA-stimulated lymphocytes, deoxycytidine caused significant although incomplete rescue from toxicity due to dCF and AdR. In patients with ADA deficiency or treated with ADA inhibitors, both mechanisms could be operative. These observations are also relevant to the possible use of dCF and AdR as immunosuppressive agents and for the removal of T-cells or residual Thy-ALL blasts from bone marr
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PMID:Mechanisms of deoxyadenosine toxicity in human lymphoid cells in vitro: relevance to the therapeutic use of inhibitors of adenosine deaminase. 623 Oct 47

The association of a genetic deficiency of adenosine deaminase (ADA) with immunodeficiency disease has emphasized the importance of deoxyadenosine and adenosine metabolism for human lymphocyte function. However, information concerning the endogenous production and metabolism of deoxyadenosine and adenosine in normally growing human T and B lymphoblasts is lacking. In the present experiments, we used a diverse series of cell lines deficient in individual enzymes of purine metabolism to quantitate the de novo formation of deoxyadenosine and adenosine in human T lymphoblasts (CEM), B lymphoblasts (WI-L2), and histiocytic lymphoma cells (DHL-9). The B lymphoblasts and histiocytic lymphoma cells generated deoxyadenosine at a rate of 60 to 80 pmol/hr/10(7) cells. This value was several fold greater than the rate of production of deoxyadenosine by T cells (6 to 7 pmol/hr/10(7) cells). Deoxyadenosine synthesis required ribonucleotide reductase activity, and was maximal during the S-phase of the cell cycle. The T and B lymphoblasts formed relatively similar amounts of adenosine (870 to 1620 pmol/hr/10(7) cells) throughout the cell cycle. In ADA-deficient cells, a major fraction of the deoxyadenosine synthesized de novo was excreted into the extracellular space. These results establish that the endogenous synthesis and metabolism of deoxyadenosine (but not adenosine) is distinctly different in T and B lymphoblasts.
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PMID:Differential production of deoxyadenosine by human T and B lymphoblasts. 635 3

The occurrence of severe immunodeficiency disease in children with inherited adenosine deaminase deficiency, and reports of remission induction in T-cell acute lymphoblastic leukaemia with the adenosine deaminase inhibitor deoxycoformycin, prompted a study of the effects of deoxyadenosine on resting peripheral blood lymphocytes (PBL) and chronic lymphocytic leukaemic (CLL) lymphocytes in short-term culture. In the presence of an inhibitor of adenosine deaminase, micromolar concentrations of dAdo caused elevation of deoxyadenosine-5'-triphosphate (dATP) pools and in vitro lysis of non-dividing PBL and CLL lymphocytes. This death of non-replicating cells indicates a mechanism of deoxyadenosine toxicity independent of DNA replication and ribonucleotide reductase inhibition. Similar changes occurred in vivo in a patient with advanced CLL who responded to treatment with deoxycoformycin, 0.1 mg/kg, days 1-5, with a fall in the WCC from 102.0 x 10(9)/1 to 6.8 x 10(9)/l over 21 d. Therapeutic blockade of deoxyadenosine catabolism deserves further investigation both in the treatment of lymphoproliferative disease and as a method lympholytic immunosuppression.
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PMID:Deoxycoformycin-induced response in chronic lymphocytic leukaemia: deoxyadenosine toxicity in non-replicating lymphocytes. 697 47

Adenosine deaminase (adenosine aminohydrolase, EC 3.5.4.4)-deficient patients recently were found to have abnormally high levels of dATP, a negative allosteric effector of ribonucleotide reductase (ribonucleoside-diphosphate reductase, 2'-deoxyribonucleoside-diphosphate:oxidized thioredoxin 2'-oxidoreductase, EC 1.17.4.1). Therefore it was proposed that the immunodeficiency associated with adenosine deaminase deficiency is mediated through inhibition of ribonucleotide reductase and hence DNA replication. HeLa cells, treated with an adenosine deaminase inhibitor, erythro-9(2-hydroxy-3-nonyl)adenine, and deoxyadenosine to mimic the adenosine deaminase-deficient state, were monitored to determine directly the effects on ribonucleotide reductase activity and levels. A low concentration of erythro-9-(2-hydroxy-3-nonyl)adenine, which did not inhibit cell growth, nevertheless retarded the cells in G2 + M phase of the cell cycle and increased reductase activity. Reductase activity was also elevated in cells treated with a low level of deoxyadenosine which did not affect the cell cycle or cell growth. However, ribonucleotide reductase activity was reduced to one-half of the control value in cells treated with either enough deoxyadenosine to inhibit cell growth or with a combination of erythro-9(2-hydroxy-3-nonyl)adenine and deoxyadenosine, each at concentrations which individually do not inhibit cell growth. Removal of deoxynucleotides, particularly dATP, from these extracts increased ribonucleotide reductase activity to several-fold higher than control values. The reduced activity of ribonucleotide reductase in the simulated adenosine deaminase-deficient HeLa cells provides direct evidence for the thesis that adenosine deaminase deficiency disease is mediated through elevated levels of dATP which inhibit ribonucleotide reductase. In addition, the cell cycle patterns and ribonucleotide reductase levels suggest that the regulatory substance(s) that controls the level of ribonucleotide reductase is not operative until the late S or G2 phase of the cell cycle.
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PMID:Adenosine deaminase impairment and ribonucleotide reductase activity and levels in HeLa cells. 699 99


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