Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.5.4.17 (adenosine deaminase)
 5,206 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The role of platelets in the maintenance of endothelial barrier is examined in an in vitro model of the microvasculature. Human platelets (6,000/microliters) perfused through a cell column of endothelial-covered microcarriers decrease paracellular permeability of sodium fluorescein (mol wt 342) to 63% of baseline values. This effect is reversible and a second application and removal of platelets produces a similar response. This effect occurs within 5 min and reverses within 10 min after platelet removal. The reduction in permeability is not due to mechanical obstruction of endothelial junctions, since the number of recirculating platelets is not reduced and releasate from unstimulated 2-h platelet incubations also decreases permeability. Releasate from platelets stimulated with 0.1 U/ml of thrombin for 15 min have the same permeability reducing effect. In this system, the platelet factors serotonin (10(-3) M) and ADP (10(-4) M) have no effect on permeability. However, the platelet factors adenosine (10(-4) M), ATP (10(-5) M), and beta-agonists decrease permeability. None of these appear to account for platelet permeability activity, since activity is not blocked by agents directed against these mediators (adenosine deaminase, apyrase, 8-phenyltheophylline, or propranolol). The active factor(s) is stable at -20 degrees C, heat stable, sensitive to trypsin, and has an apparent molecular weight > 100. We conclude that unstimulated platelets release a factor(s) that enhances endothelial barrier in vitro and may be important in maintenance of the normal in vivo barrier.
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PMID:Platelets and a platelet-released factor enhance endothelial barrier. 147 5

The effect of platelets on polymorphonuclear leukocytes (PMN) O2- production was examined using autologous sheep and human cell systems. Coincubation of sheep platelets with sheep PMNs in the absence of thrombin resulted in a significant inhibition in basal PMN O2- production. The platelet-derived inhibitory activity was released into the medium and could be destroyed by adenosine deaminase suggesting that the inhibitor was adenosine. Addition of alpha-thrombin or platelet activating factor (PAF) enhanced PMN O2- production but only when platelets were present. The enhancement of O2- production in response to thrombin was dependent upon the thrombin concentration and the platelet-PMN ratio. With a platelet: PMN ratio of 30: 1, addition of 10 nM thrombin to sheep cells resulted in a 5-fold increase in O2- production, whereas addition of 10 nM PAF caused a 2-fold increase in O2-. Addition of thrombin or PAF to either PMNs or platelets by themselves did not initiate an increase in O2- generation. The response of human cells was similar except that both thrombin and PAF triggered a 2-fold increase in PMN O2- production in the presence of platelets. The platelet-derived enhancement activity was not released into the medium and was not blocked by WEB 2086, NDGA, ETYA, aspirin or adenosine deaminase. The enhancement effect appeared to be localized to the platelet membrane and we believe requires platelet-PMN contact.
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PMID:Platelet modulation of neutrophil superoxide anion production. 216 Jan 33

Supernates of thymic epithelial cell culture (STEC) strongly inhibit aggregation induced by addition of adenosine diphosphate (ADP: 1 microM) or thrombin (0.5 unit per ml) to washed platelet suspensions and accelerated the restoration from ADP-triggered aggregation. At the same time, STEC increased the level of platelet adenosine 3',5'-cyclic monophosphate (cyclic AMP) in a dose-dependent manner. Depending on the concentration used, thymosin fraction 5 increased the level of intracellular cyclic AMP ranging between 5 and 100 micrograms per ml, as well as inhibiting ADP-induced platelet aggregation. The activities of both STEC and thymosin fraction 5 were found to act exclusively on cyclic AMP phosphodiesterase activity in platelets. In contrast the supernates from Chang, HeLa, or HCC-M cells did not affect platelet aggregation induced by ADP, but slightly increased the cyclic AMP level (Chang, HeLa). Within 2 min after the treatment with STEC, more than 50% of the maximum inhibitory activity on platelet aggregation and increases in intracellular cyclic AMP were observed. These activities disappeared following STEC treatment with pronase E. STEC activity was found predominantly in the 1,000-50,000-dalton fractions. These activities were not altered when STEC was treated by adenosine deaminase. The level of prostaglandin E (PGE) derivatives in STEC was about two times that found in the control culture medium. These data suggest that the biological activity of STEC in the platelets might be attributed to thymosinlike polypeptides and PGE1.
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PMID:In vitro effect of a thymic epithelial culture supernate or thymosin fraction 5 on rabbit platelet aggregation and intracellular cyclic AMP levels. 282 98

Activity of adenosine deaminase (EC 3.5.4.4) was studied in thrombocytes of donors and patients with various hematological diseases. The enzymatic activity was decreased in acute leukemia, chronic myeloleukemia, chronic leukemia and blast transformation myeloma, microspherocytic and hypoplastic anemias. Variable level of the activity was observed in chronic lympholeukemia and non-Hodgkin disease. In all the diseases studied functions of thrombocytes were altered after treatment with various aggregating agents (ADP, thrombin, collagen, adrenaline, ristomycin).
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PMID:[Platelet adenosine desaminase in various hematological diseases]. 406 12

Contribution of extracellular adenine nucleotide degradation to adenosine formation and internal salvage of adenosine via adenosine kinase were quantified in macrovascular porcine endothelial cells. Microcarrier beads covered with endothelial cells were kept in a perfusion column at a flow rate of 2 ml/min. Total adenine nucleotide (AN) release was quantified with a sensitive firefly luciferin-luciferase assay after enzymatic rephosphorylation of AMP and ADP to ATP. Adenosine (ADO) was measured by radioimmunoassay or high-pressure liquid chromatography (HPLC) techniques. Basal AN and ADO release under steady-state conditions were 2.2 and 13.8 pmol.min-1 x ml column volume (CV)-1, respectively. Inhibition of adenosine deaminase with erythro-9-(2-hydroxy-3-nonyl)adenine (5 x 10(-6) M) enhanced ADO release by 3.3 pmol.min-1 x ml CV-1, and AN release remained unchanged (2.8 pmol.min-1 x ml CV-1). Inhibition of adenosine kinase by 5-iodotubercidine (10(-5) M) greatly enhanced ADO release by 97.7 pmol.min-1 x ml CV-1, while AN release was unaffected. Inhibition of ecto-5'-nucleotidase by alpha,beta-methylene-ADP (5 x 10(-5) M) enhanced AN release from 2.6 to 8.2 pmol.min-1 x ml CV-1 and reduced ADO release by an equivalent extent. Stimulation of endothelial cells with Ca ionophore A23187 dose dependently augmented AN and ADO release to 2,013.2 and 92.5 pmol.min-1 x ml CV-1, respectively. Thrombin (1 U/ml) enhanced AN release from 5.0 to 8.7 pmol.min-1 x ml CV-1, whereas several other endothelium-dependent and -independent vasodilators including acetylcholine, bradykinin, isoproterenol, and norepinephrine were proven to have no significant effect.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Formation and salvage of adenosine by macrovascular endothelial cells. 845 72

ATP and ADP are simultaneously released from activated platelets in equimolar concentrations. Micromolar concentrations of ATP inhibit platelet aggregation by both competitive and non-competitive mechanisms. The current studies addressed the question of how platelets respond to agonists in the presence of nanomolar and micromolar concentrations of ATP and ADP alone or in combination. This is a significant issue since the concentration of ATP +/- ADP may vary widely within a microenvironment depending upon the source and cause for the release of the nucleotides. ATP (1-10 nM) was found to significantly enhance the thromboxane A2 analog, U44619-, collagen- and thrombin-induced platelet aggregations. Conversely, ATP at 1-100 microM inhibited these same reactions. ADP, in general, behaved exactly opposite to ATP. When equal amounts of ATP and ADP were added together the ADP response appeared to predominate. The observed ATP-induced response was not due to a hydrolytic product as evidenced by an unaltered response to ATP in the presence of adenosine deaminase or the ATP generating system, creatine phosphate plus creatine phosphokinase. Adenosine (1-10 nM), like ADP, inhibited agonist-induced platelet aggregation. The stimulation of agonist-induced platelet aggregation by 1-10 nM extracellular ATP appears to depend upon the phosphorylation of platelet membrane ecto proteins. The ATP analog, beta gamma-methylene ATP, that is incapable of serving as a phosphate donor for protein kinases, inhibited rather than stimulated agonist-induced platelet aggregation. The dual response of platelets to low and high concentrations of extracellular ATP +/- ADP may play a physiological role in hemostasis and thrombosis under normal and pathological conditions.
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PMID:A possible dual physiological role of extracellular ATP in the modulation of platelet aggregation. 904 33

von Willebrand factor (vWF) is stored and released from endothelial secretory granules called Weibel-Palade (WP) bodies. Acute release can be induced by thrombin, histamine, and other mediators of thrombosis or inflammation. Their effect is thought to be mediated by an increase in intracellular free calcium ([Ca2+]i). Purine nucleotides such as adenosine triphosphate (ATP) and adenosine diphosphate (ADP) are released from platelet dense granules and from ischemic tissues and are important regulators of platelet function and vascular tone. In the present study, we investigated whether they could also induce exocytosis from cultured endothelial cells. ATP (1 to 100 micromol/L) induced a dose-related increase in vWF release, with a 2.3-fold maximal increase after 30 minutes. Similar responses were observed with ADP. ATP induced calcium mobilization from intracellular stores, an effect mimicked by 2-methylthio-ATP, a selective agonist for P2y receptors. However, 2-methylthio-ATP-induced vWF release was only 43% of the ATP response. ATP-induced vWF release was also associated with a twofold increase in cellular cyclic adenosine monophosphate (cAMP) content, and was potentiated by 3-isobutyl-1-methylxanthine ([IBMX] added to increase cAMP levels by blocking cellular phosphodiesterases) and 8-bromo-cAMP and inhibited by more than 50% by Rp-8-CPT-cAMPS, a competitive protein kinase A inhibitor. Adenosine but not 2-methylthio-ATP mimicked the ATP-induced increase in cAMP. ATP-induced vWF release was partly inhibited by adenosine deaminase, which degrades adenosine generated from ATP in the incubation medium. Adenosine (1 to 100 micromol/L) failed to induce vWF release, but potentiated the secretory response to 2-methylthio-ATP and thrombin without modifying the calcium response to these agents. Our results suggest that ATP/ADP can induce vWF release from endothelial cells via dual activation of P2y and adenosine A2 receptors. ATP/ADP-induced exocytosis could be involved in the regulation of thrombus formation and ischemia-reperfusion injuries. Further, we provide evidence that a receptor-mediated increase in cellular cAMP can potentiate the secretory response to calcium-mobilizing agents.
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PMID:Purine nucleotides induce regulated secretion of von Willebrand factor: involvement of cytosolic Ca2+ and cyclic adenosine monophosphate-dependent signaling in endothelial exocytosis. 941 75

Among all fruits tested in vitro for their anti-platelet property, tomato had the highest activity followed by grapefruit, melon, and strawberry, whereas pear and apple had little or no activity. Tomato extract (20-50 microl of 100% juice) inhibited both ADP- and collagen-induced aggregation by up to 70% but could not inhibit arachidonic acid-induced platelet aggregation and concomitant thromboxane synthesis under similar experimental conditions. The anti-platelet components (MW <1000 Da) in tomatoes are water soluble, heat stable and are concentrated in the yellow fluid around the seeds. The active fractions were separated using gel filtration and HPLC. The aqueous fraction (110 000 xg supernatant) of tomatoes containing anti-platelet activity was subjected to gel filtration column chromatography (Biogel P2 column). The activity was fractionated into two peaks, peak-3 and peak-4 (major peak). Subsequently, peak-4 was further purified by HPLC using a reversed-phase column. NMR and mass spectroscopy studies indicated that peak F2 (obtained from peak 4) contained adenosine and cytidine. Deamination of peak F2 with adenosine deaminase almost completely abolished its anti-platelet activity, confirming the presence of adenosine in this fraction. In comparison, deamination of peak-4 resulted in only partial loss of inhibitory activity while the activity of peak-3 remained unaffected. These results indicate that tomatoes contain anti-platelet compounds in addition to adenosine. Unlike aspirin, the tomato-derived compounds inhibit thrombin-induced platelet aggregation. All these data indicate that tomato contains very potent anti-platelet components, and consuming tomatoes might be beneficial both as a preventive and therapeutic regime for cardiovascular disease.
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PMID:Effects of tomato extract on human platelet aggregation in vitro. 1145 56

In spite of the high abundance and species diversity of diatoms, only a few bioactive compounds from them have been described. The present study reveals a high number of mammalian cell death inducing substances in biofilm-associated diatoms sampled from the intertidal zone. Extracts from the genera Melosira, Amphora, Phaeodactylum and Nitzschia were all found to induce leukemia cell death, with either classical apoptotic or autophagic features. Several extracts also contained inhibitors of thrombin-induced blood platelet activation. Some of this activity was caused by a high content of adenosine in the diatoms, ranging from 0.07 to 0.31 microg/mg dry weight. However, most of the bioactivity was adenosine deaminase-resistant. An adenosine deaminase-resistant active fraction from one of the extracts was partially purified and shown to induce apoptosis with a distinct phenotype. The results show that benthic diatoms typically found in the intertidal zone may represent a richer source of interesting bioactive compounds than hitherto recognized.
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PMID:Marine benthic diatoms contain compounds able to induce leukemia cell death and modulate blood platelet activity. 2009 2

In this study we have investigated the role of extracellular ATP on thrombin induced-platelet aggregation (TIPA) in washed human platelets. ATP inhibited TIPA in a dose-dependent manner and this inhibition was abolished by apyrase but not by adenosine deaminase (ADA) and it was reversed by extracellular magnesium. Antagonists of P2Y1 and P2Y12 receptors had no effect on this inhibition suggesting that a P2X receptor controlled ATP-mediated TIPA inhibition. ATP also blocked inositol phosphates (IP1, IP2, IP3) generation and [Ca(2+)]i mobilization induced by thrombin. Thrombin reduced cAMP levels which were restored in the presence of ATP. SQ-22536, an adenylate cyclase (AC) inhibitor, partially reduced the inhibition exerted by ATP on TIPA. 12-lipoxygenase (12-LO) inhibitors, nordihidroguaretic acid (NDGA) and 15(S)-hydroxy-5,8,11,13-eicosatetraenoic acid (15(S)-HETE), strongly prevented ATP-mediated TIPA inhibition. Additionally, ATP inhibited the increase of 12(S)-hydroxy-5,8,10,14-eicosatetraenoic acid (12(S)-HETE) induced by thrombin. Pretreatment with both SQ-22536 and NDGA almost completely abolished ATP-mediated TIPA inhibition. Our results describe for the first time that ATP implicates both AC and 12-LO pathways in the inhibition of human platelets aggregation in response to agonists.
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PMID:ATP antagonizes thrombin-induced signal transduction through 12(S)-HETE and cAMP. 2382 7


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