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Loss of ATP diphosphohydrolase activity with endothelial cell activation.

Robson SC, Kaczmarek E, Siegel JB, Candinas D, Koziak K, Millan M, Hancock WW, Bach FH - J. Exp. Med. (1997)

Bottom Line: This latter effect is mediated in a number of ways, including expression by EC of thrombomodulin and heparan sulfate, both of which are lost from the EC surface as part of the activation response to proinflammatory cytokines.Loss of these anticoagulant molecules potentiates the procoagulant properties of the injured vasculature.We describe here that the antithrombotic effects of the ATPDase, like heparan sulfate and thrombomodulin, are lost after EC activation, both in vitro and in vivo.

View Article: PubMed Central - PubMed

Affiliation: Sandoz Center for Immunobiology, Boston, Massachusetts, USA.

ABSTRACT
Quiescent endothelial cells (EC) regulate blood flow and prevent intravascular thrombosis. This latter effect is mediated in a number of ways, including expression by EC of thrombomodulin and heparan sulfate, both of which are lost from the EC surface as part of the activation response to proinflammatory cytokines. Loss of these anticoagulant molecules potentiates the procoagulant properties of the injured vasculature. An additional thromboregulatory factor, ATP diphosphohydrolase (ATPDase; designated as EC 3.6.1.5) is also expressed by quiescent EC, and has the capacity to degrade the extracellular inflammatory mediators ATP and ADP to AMP, thereby inhibiting platelet activation and modulating vascular thrombosis. We describe here that the antithrombotic effects of the ATPDase, like heparan sulfate and thrombomodulin, are lost after EC activation, both in vitro and in vivo. Because platelet activation and aggregation are important components of the hemostatic changes that accompany inflammatory diseases, we suggest that the loss of vascular ATPDase may be crucial for the progression of vascular injury.

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ATPDase enzymatic activity after EC activation by TNFα.  EC ATPDase activity was determined by measuring inorganic phosphate  release from ADP and ATP. An inhibitory effect was maximal by 4 h after  stimulation of pEC by TNFα as depicted here for ADP (data in graph are  expressed as means and SD; normality test passed). Statistical analysis confirmed significant differences to control quiescent EC values at both 2 and  4 h after EC activation; *P <0.005, Mann Whitney Rank Sum Test. Experiments studying ATPDase activity by [14C]ADP hydrolysis gave similar  results (data not shown).
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Figure 4: ATPDase enzymatic activity after EC activation by TNFα. EC ATPDase activity was determined by measuring inorganic phosphate release from ADP and ATP. An inhibitory effect was maximal by 4 h after stimulation of pEC by TNFα as depicted here for ADP (data in graph are expressed as means and SD; normality test passed). Statistical analysis confirmed significant differences to control quiescent EC values at both 2 and 4 h after EC activation; *P <0.005, Mann Whitney Rank Sum Test. Experiments studying ATPDase activity by [14C]ADP hydrolysis gave similar results (data not shown).

Mentions: Activation of 10–50 ng/ml pEC or hEC by human recombinant TNFα from 1 to 8 h, resulted in rapid loss of the EC antiaggregatory phenotype and the development of a permissive environment for platelet activation in response to the standard agonists in vitro (Fig. 3). ATPDase activity, as determined by both [14C]ADP hydrolysis and inorganic phosphate release from ATP and ADP, showed comparable patterns of inhibition at the time intervals examined. A trend towards inhibition was observed as early as 30 to 60 min after TNFα activation, and was maximal by 4 h; statistically significant differences between the ATPDase activities of the quiescent and TNFα stimulated EC at 2 and 4 h were confirmed (Fig. 4).


Loss of ATP diphosphohydrolase activity with endothelial cell activation.

Robson SC, Kaczmarek E, Siegel JB, Candinas D, Koziak K, Millan M, Hancock WW, Bach FH - J. Exp. Med. (1997)

ATPDase enzymatic activity after EC activation by TNFα.  EC ATPDase activity was determined by measuring inorganic phosphate  release from ADP and ATP. An inhibitory effect was maximal by 4 h after  stimulation of pEC by TNFα as depicted here for ADP (data in graph are  expressed as means and SD; normality test passed). Statistical analysis confirmed significant differences to control quiescent EC values at both 2 and  4 h after EC activation; *P <0.005, Mann Whitney Rank Sum Test. Experiments studying ATPDase activity by [14C]ADP hydrolysis gave similar  results (data not shown).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2196106&req=5

Figure 4: ATPDase enzymatic activity after EC activation by TNFα. EC ATPDase activity was determined by measuring inorganic phosphate release from ADP and ATP. An inhibitory effect was maximal by 4 h after stimulation of pEC by TNFα as depicted here for ADP (data in graph are expressed as means and SD; normality test passed). Statistical analysis confirmed significant differences to control quiescent EC values at both 2 and 4 h after EC activation; *P <0.005, Mann Whitney Rank Sum Test. Experiments studying ATPDase activity by [14C]ADP hydrolysis gave similar results (data not shown).
Mentions: Activation of 10–50 ng/ml pEC or hEC by human recombinant TNFα from 1 to 8 h, resulted in rapid loss of the EC antiaggregatory phenotype and the development of a permissive environment for platelet activation in response to the standard agonists in vitro (Fig. 3). ATPDase activity, as determined by both [14C]ADP hydrolysis and inorganic phosphate release from ATP and ADP, showed comparable patterns of inhibition at the time intervals examined. A trend towards inhibition was observed as early as 30 to 60 min after TNFα activation, and was maximal by 4 h; statistically significant differences between the ATPDase activities of the quiescent and TNFα stimulated EC at 2 and 4 h were confirmed (Fig. 4).

Bottom Line: This latter effect is mediated in a number of ways, including expression by EC of thrombomodulin and heparan sulfate, both of which are lost from the EC surface as part of the activation response to proinflammatory cytokines.Loss of these anticoagulant molecules potentiates the procoagulant properties of the injured vasculature.We describe here that the antithrombotic effects of the ATPDase, like heparan sulfate and thrombomodulin, are lost after EC activation, both in vitro and in vivo.

View Article: PubMed Central - PubMed

Affiliation: Sandoz Center for Immunobiology, Boston, Massachusetts, USA.

ABSTRACT
Quiescent endothelial cells (EC) regulate blood flow and prevent intravascular thrombosis. This latter effect is mediated in a number of ways, including expression by EC of thrombomodulin and heparan sulfate, both of which are lost from the EC surface as part of the activation response to proinflammatory cytokines. Loss of these anticoagulant molecules potentiates the procoagulant properties of the injured vasculature. An additional thromboregulatory factor, ATP diphosphohydrolase (ATPDase; designated as EC 3.6.1.5) is also expressed by quiescent EC, and has the capacity to degrade the extracellular inflammatory mediators ATP and ADP to AMP, thereby inhibiting platelet activation and modulating vascular thrombosis. We describe here that the antithrombotic effects of the ATPDase, like heparan sulfate and thrombomodulin, are lost after EC activation, both in vitro and in vivo. Because platelet activation and aggregation are important components of the hemostatic changes that accompany inflammatory diseases, we suggest that the loss of vascular ATPDase may be crucial for the progression of vascular injury.

Show MeSH
Related in: MedlinePlus