Hydrolysis of diadenosine 5',5''-P',P''-triphosphate (Ap3A) by porcine aortic endothelial cells.

Goldman, S J; Gordon, Ellen L.; Slakey, Linda L.

doi:10.1161/01.res.59.3.362

Cited by 33 publications

(24 citation statements)

References 19 publications

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Section: Discussionmentioning

confidence: 82%

“…10,11,30,31 ADP released during platelet degranulation stimulates further platelet aggregation and release, and thus the process is autocatalytic. To prevent unregulated thrombus formation, ADP is rapidly degraded-1M ADP is degraded in whole blood within 3.2 minutes, and may be even faster in vivo because of ectoenzymes present on cell surfaces.…”

Section: Discussionmentioning

confidence: 99%

“…9 The researchers subsequently detected an enzyme with Ap3A and Ap4A hydrolytic activity on the surface of bovine vascular endothelium 11 contemporaneously with a second group who discovered an Ap3A hydrolase on porcine vascular endothelium. 10 Our search of the NCBI-GEO database also revealed NPP4 gene expression in a variety of human vascular endothelial cells.Diadenosine polyphosphates have been identified as potential substrates for the NPP family of enzymes. 14 A collaborative group of researchers partially purified membrane fractions of CHO cells stably transfected with NPP1, NPP2, or NPP3 to probe their activity with Ap3A, and all were observed to hydrolyze Ap3A with K m s in the low M range.…”

mentioning

confidence: 82%

“…10,11 We therefore stained by immunofluorescence a highly vascular human organ (brain, which accepts ϳ 30% of cardiac output blood flow) for NPP4 (Figure 1). Immunofluorescence of NPP4 in brain reveals that NPP4 is enriched on blood vessel surfaces and localizes to vascular walls, as highlighted in numerous branched vessels in the brain parenchyma (Figure 1).…”

Section: Npp4 Tissue Localization By Immunofluorescencementioning

confidence: 99%

“…9 The mechanism by which Ap3A promotes aggregation suggests that Ap3A is stored as a metabolically inactive or chemically masked molecule, which on release into the extracellular space is converted into a hemodynamically active form by an enzyme that liberates ADP from the dinucleotide. An enzyme capable of hydrolyzing Ap3A into AMP and ADP was partially characterized on the surface of intact porcine 10 and bovine 11 vascular endothelial cells more than 20 years ago. Before this, Luthje and Olgilvie linked weak Ap3A hydrolase activity in PRP to an extracellular glycoprotein, neither stored within nor released by platelets, with optimal enzymatic activity around pH 8.5 to 9.0, and a divalent cation dependence.…”

Section: Introductionmentioning

confidence: 99%

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NPP4 is a procoagulant enzyme on the surface of vascular endothelium

Albright

Chang

Robert

et al. 2012

Blood

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Ap3A is a platelet-dense granule component released into the extracellular space during the second wave of platelet aggregation on activation. Here, we identify an uncharacterized enzyme, nucleotide pyrophosphatase/phosphodiesterase-4 (NPP4), as a potent hydrolase of Ap3A capable of stimulating platelet aggregation and secretion. We demonstrate that NPP4 is present on the surface of vascular endothelium, where it hydrolyzes Ap3A into AMP and ADP, and Ap4A into AMP and ATP. Platelet aggregation assays with citrated platelet-rich plasma reveal that the primary and secondary waves of aggregation and dense granule release are strongly induced by nanomolar NPP4 in a concentration-dependent manner in the presence of Ap3A, while Ap3A alone initiates a primary wave of aggregation followed by rapid disaggregation. NPP2 and an active site NPP4 mutant, neither of which appreciably hydrolyzes Ap3A, have no effect on platelet aggregation and se- IntroductionThe formation of a platelet-rich thrombus stabilized by fibrin crosslinking is the final common pathway for arterial thrombosis, the most common disease process affecting adults in the United States. The first step in thrombus formation consists of platelet adhesion to the exposed subendothelial extracellular matrix at the site of vascular injury. Here, circulating blood platelets bind collagen via their GPVI receptors, and bind von Willebrand factor via GPIb, triggering inside-out activation of other surface integrins and the release of platelet granule contents into the extracellular space. 1 The release of preformed molecules stored in platelet-dense granules such as ADP, serotonin, and ionized calcium, then amplifies the clotting reaction beyond the platelet monolayer bound on the collagen surface to circulating platelets in the immediate vicinity of the damaged endothelium. This amplification is further augmented by the secretion of thromboxane A2. ADP binding to purinergic receptors on the platelet surface (P2Y1 and P2Y12) induces rapid calcium influx and mobilization resulting in platelet shape change, activation, and partial degranulation thus promoting platelet aggregation. On granule release, local ADP concentrations are estimated to exceed 500M, but ADP is quickly metabolized by ectoenzymes on the surface of endothelial cells (such as CD39 2,3 ) and soluble phosphohydrolyases in blood plasma which attenuate the prothrombotic response. [4][5][6][7] To sustain the clotting reaction, a slow and steady source of ADP at the site of the growing thrombus is required. Another preformed chemical released by platelet-dense granules at high concentrations, diadenosine triphosphate (Ap3A), has an ill-defined role in thrombus formation but has been suggested to provide a source of long-lasting ADP at the site of vascular injury.Ap3A is stored within platelet granules at high concentrations (ϳ20-30mM) and is released with ADP and ATP into the blood during thrombin-induced platelet aggregation at concentrations thought to range between 40 and 100M 8 (see supplemental Table ...

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Section: Discussionmentioning

confidence: 82%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 82%

Section: Npp4 Tissue Localization By Immunofluorescencementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

NPP4 is a procoagulant enzyme on the surface of vascular endothelium

Albright

Chang

Robert

et al. 2012

Blood

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Diadenosine polyphosphate (Ap_xA) as new neurotransmitters

Pintor

Miras‐Portugal

1993

Drug Development Research

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The presence of diadenosine polyphosphates (Ap,A), diadenosine tetraphosphate (Ap,A), diadenosine pentaphosphate (Ap,A), and diadenosine hexaphosphate (Ap6A), has been described in secretory granules of chromaffin cells, Torpedo synaptic vesicles, and rat brain synaptosomes. The release of these compounds by the action of secretagogues and depolarizing agents, in the presence of calcium, increases their importance as active neurotransmitters. TWO high affinity receptors have been described in the three neural models, with Kd values ranging from 0.08 t o 0.40 n M for the first binding site and from 5.6 t o 18 n M for the second, lower affinity binding site. Both binding sites exhibit a P,,-l i ke profile in chromaffin cells and Torpedo synaptic terminals, and a different pattern in rat brain synaptosomes, suggesting the presence of a novel P,-purinoceptor tentatively named PZd. Studies about the second messenger linked to this receptor, in chromaffin cells, demonstrate the mobilization of calcium from internal stores. Ap, A receptors at the extracellular milieu are responsible for the inhibition of catecholamine release stimulated by secretagogues. Finally, all diadenosine polyphosphates are destroyed by the action of an ecto-phosphodiesterase which, in chromaffin cells, shows Km values ranging from 1 to 4 FM. 0 1993 Wiley-Liss, Inc.

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