CD39/vascular ATP diphosphohydrolase modulates xenograft survival

Tuning the Thromboinflammatory Response to Venous Flow Interruption by the Ectonucleotidase CD39

Objective- Leukocyte flux contributes to thrombus formation in deep veins under pathological conditions, but mechanisms that inhibit venous thrombosis are incompletely understood. Ectonucleotide di(tri)phosphohydrolase 1 ( ENTPD1 or Cd39), an ectoenzyme that catabolizes extracellular adenine nucleotides, is embedded on the surface of endothelial cells and leukocytes. We hypothesized that under venous stasis conditions, CD39 regulates inflammation at the vein:blood interface in a murine model of deep vein thrombosis. Approach and Results- CD39-null mice developed significantly larger venous thrombi under venous stasis, with more leukocyte recruitment compared with wild-type mice. Gene expression profiling of wild-type and Cd39-null mice revealed 76 differentially expressed inflammatory genes that were significantly upregulated in Cd39-deleted mice after venous thrombosis, and validation experiments confirmed high expression of several key inflammatory mediators. P-selectin, known to have proximal involvement in venous inflammatory and thrombotic events, was upregulated in Cd39-null mice. Inferior vena caval ligation resulted in thrombosis and a corresponding increase in both P-selectin and VWF (von Willebrand Factor) levels which were strikingly higher in mice lacking the Cd39 gene. These mice also manifest an increase in circulating platelet-leukocyte heteroaggregates suggesting heterotypic crosstalk between coagulation and inflammatory systems, which is amplified in the absence of CD39. Conclusions- These data suggest that CD39 mitigates the venous thromboinflammatory response to flow interruption.

Ectonucleotidases in Intestinal and Hepatic Inflammation

Purinergic signaling modulates systemic and local inflammatory responses. Extracellular nucleotides, including eATP, promote inflammation, at least in part via the inflammasome upon engagement of P2 purinergic receptors. In contrast, adenosine generated during eATP phosphohydrolysis by ectonucleotidases, triggers immunosuppressive/anti-inflammatory pathways. Mounting evidence supports the role of ectonucleotidases, especially ENTPD1/CD39 and CD73, in the control of several inflammatory conditions, ranging from infectious disease, organ fibrosis to oncogenesis. Our experimental data generated over the years have indicated both CD39 and CD73 serve as pivotal regulators of intestinal and hepatic inflammation. In this context, immune cell responses are regulated by the balance between eATP and adenosine, potentially impacting disease outcomes as in gastrointestinal infection, inflammatory bowel disease, ischemia reperfusion injury of the bowel and liver, autoimmune or viral hepatitis and other inflammatory conditions, such as cancer. In this review, we report the most recent discoveries on the role of ENTPD1/CD39, CD73, and other ectonucleotidases in the regulation of intestinal and hepatic inflammation. We discuss the present knowledge, highlight the most intriguing and promising experimental data and comment on important aspects that still need to be addressed to develop purinergic-based therapies for these important illnesses.

Increased degradation of ATP is driven by memory regulatory T cells in kidney transplantation tolerance

Regulatory T cells were recently proposed as the central actor in operational tolerance after renal transplantation. Tolerant patients harbor increased FoxP3hi memory Treg frequency and increased demethylation in the Foxp3 Treg-specific demethylated region when compared to stable kidney recipients and exhibit greater memory Treg suppressive capacities and higher expression of the ectonucleotidase CD39. However, in this particular and unique situation the mechanisms of action of Tregs were not identified. Thus, we analyzed the ability of memory Tregs to degrade extracellular ATP in tolerant patients, healthy volunteers, and patients with stable graft function under immunosuppression and determined the role of immunosuppressive drugs on this process. The conserved proportion of memory Tregs leads to the establishment of a pro-tolerogenic balance in operationally tolerant patients. Memory Tregs in tolerant patients display normal capacity to degrade extracellular ATP/ADP. In contrast, memory Tregs from patients with stable graft function do not have this ability. Finally, in vitro, immunosuppressive drugs may favor the lower proportion of memory Tregs in stable patients, but they have no effect on CD39-dependent ATP degradation and do not explain memory Treg lack of extracellular ATP/ADP degradation ability. Thus, intrinsic active regulatory mechanisms may act long after immunosuppressive drug arrest in operationally tolerant patients and may contribute to kidney allograft tolerance via the maintenance of CD39 Treg function.

Recombinant soluble apyrase APT102 inhibits thrombosis and intimal hyperplasia in vein grafts without adversely affecting hemostasis or re-endothelialization

Essentials New strategies are needed to inhibit thrombosis and intimal hyperplasia (IH) in vein grafts (VG). We studied effects of apyrase (APT102) on VGs and smooth muscle and endothelial cells (SMC/EC). APT102 inhibited thrombosis, SMC migration, and IH without impairing hemostasis or EC recovery. Apyrase APT102 is a single-drug approach to inhibit multiple processes that cause VG failure.

SUMMARY

Background Occlusion of vein grafts (VGs) after bypass surgery, owing to thrombosis and intimal hyperplasia (IH), is a major clinical problem. Apyrases are enzymes that scavenge extracellular ATP and ADP, and promote adenosine formation at sites of vascular injury, and hence have the potential to inhibit VG pathology. Objectives To examine the effects of recombinant soluble human apyrase, APT102, on platelets, smooth muscle cells (SMCs) and endothelial cells (ECs) in vitro, and on thrombosis and IH in murine VGs. Methods SMC and EC proliferation and migration were studied in vitro. Inferior vena cava segments from donor mice were grafted into carotid arteries of recipient mice. Results APT102 potently inhibited ADP-induced platelet aggregation and VG thrombosis, but it did not impair surgical hemostasis. APT102 did not directly inhibit SMC or EC proliferation, but significantly attenuated the effects of ATP on SMC and EC proliferation. APT102 significantly inhibited SMC migration, but did not inhibit EC migration, which may be mediated, at least in part, by inhibition of SMC, but not EC, migration by adenosine. At 4 weeks after surgery, there was significantly less IH in VGs of APT102-treated mice than in control VGs. APT102 significantly inhibited cell proliferation in VGs, but did not inhibit re-endothelialization. Conclusions Systemic administration of a recombinant human apyrase inhibits thrombosis and IH in VGs without increasing bleeding or compromising re-endothelialization. These results suggest that APT102 has the potential to become a novel, single-drug treatment strategy to prevent multiple pathologic processes that drive early adverse remodeling and occlusion of VGs.

Combination treatment of r-tPA and an optimized human apyrase reduces mortality rate and hemorrhagic transformation 6h after ischemic stroke in aged female rats

Recombinant tissue plasminogen activator (r-tPA) is the only FDA-approved drug treatment for ischemic stroke and must be used within 4.5h. Thrombolytic treatment with r-tPA has deleterious effects on the neurovascular unit that substantially increases the risk of intracerebral hemorrhage if administered too late. These therapeutic shortcomings necessitate additional investigation into agents that can extend the therapeutic window for safe use of thrombolytics. In this study, combination of r-tPA and APT102, a novel form of human apyrase/ADPase, was investigated in a clinically-relevant aged-female rat embolic ischemic stroke model. We propose that successfully extending the therapeutic window of r-tPA administration would represent a significant advance in the treatment of ischemic stroke due to a significant increase in the number of patients eligible for treatment. Results of our study showed significantly reduced mortality from 47% with r-tPA alone to 16% with co-administration of APT102 and r-tPA. Co-administration decreased cortical (47 ± 5% vs. 29 ± 5%), striatal (50 ± 2%, vs. 40 ± 3%) and total (48 ± 3%vs. 33 ± 4%) hemispheric infarct volume compared to r-tPA alone. APT102 improved neurological outcome (8.9±0.6, vs. 6.8 ± 0.8) and decreased hemoglobin extravasation in cortical tissue (1.9 ± 0.1mg/dl vs. 1.4 ± 0.1mg/dl) striatal tissue (2.1 ± 0.3mg/dl vs. 1.4 ± 0.1mg/dl) and whole brain tissue (2.0 ± 0.2mg/dl vs. 1.4 ± 0.1mg/dl). These data suggest that APT102 can safely extend the therapeutic window for r-tPA mediated reperfusion to 6h following experimental stroke without increased hemorrhagic transformation. APT102 offers to be a viable adjunct therapeutic option to increase the number of clinical patients eligible for thrombolytic treatment after ischemic stroke.

Purinergic signalling in the liver in health and disease

Purinergic signalling is involved in both the physiology and pathophysiology of the liver. Hepatocytes, Kupffer cells, vascular endothelial cells and smooth muscle cells, stellate cells and cholangiocytes all express purinoceptor subtypes activated by adenosine, adenosine 5'-triphosphate, adenosine diphosphate, uridine 5'-triphosphate or UDP. Purinoceptors mediate bile secretion, glycogen and lipid metabolism and indirectly release of insulin. Mechanical stress results in release of ATP from hepatocytes and Kupffer cells and ATP is also released as a cotransmitter with noradrenaline from sympathetic nerves supplying the liver. Ecto-nucleotidases play important roles in the signalling process. Changes in purinergic signalling occur in vascular injury, inflammation, insulin resistance, hepatic fibrosis, cirrhosis, diabetes, hepatitis, liver regeneration following injury or transplantation and cancer. Purinergic therapeutic strategies for the treatment of these pathologies are being explored.

Purinergic signaling in liver disease

Adenosine triphosphate (ATP) is essential for the myriad of metabolic processes upon which life is based and is known widely as the universal energy currency unit of intracellular biologic reactions. ATP, adenosine diphosphate, adenosine, as well as other purines and pyrimidines also serve as ubiquitous extracellular mediators which function through the activation of specific receptors (viz. P2 receptors for nucleotides and purinergic P1 receptors for adenosine). Extracellular nucleotides are rapidly converted to nucleosides, such as adenosine, by highly regulated plasma membrane ectonucleotidases that modulate many of the normal biological and metabolic processes in the liver - such as gluconeogenesis and insulin signaling. Under inflammatory conditions, as with ischemia reperfusion, sepsis or metabolic stress, ATP and other nucleotides can also act as 'damage-associated molecular patterns' causing inflammasome activation in innate immune cells and endothelium resulting in tissue damage. The phosphohydrolysis of ATP by ectonucleotidases, such as those of the CD39/ENTPD family, results in the generation of immune suppressive adenosine, which in turn markedly limits inflammatory processes. Experimental studies by others and our group have implicated purinergic signaling in experimental models of hepatic ischemia reperfusion and inflammation, transplant rejection, hepatic regeneration, steatohepatitis, fibrosis and cancer, amongst others. Expression of ectonucleotidases on sinusoidal endothelial, stellate or immune cells allows for homeostatic integration and linking of the control of vascular inflammatory and immune cell reactions in the liver. CD39 expression also identifies hepatic myeloid dendritic cells and efficiently distinguishes T-regulatory-type cells from other resting or activated T cells. Our evolving data strongly indicate that CD39 serves as a key 'molecular switch' and is an integral component of the suppressive machinery of myeloid, dendritic and T cells. Increased understanding of mechanisms of extracellular ATP scavenging and specifically conversion to nucleosides by ectonucleotidases of the CD39 family have also led to novel insights into the exquisite balance of nucleotide P2-receptor and adenosinergic P1-receptor signaling in inflammatory and hepatic diseases. Further, CD39 and other ectonucleotidases exhibit genetic polymorphisms in humans which alter levels of expression/function and are associated with predisposition to inflammatory and immune diseases, diabetes and vascular calcification, amongst other problems. Development of therapeutic strategies targeting purinergic signaling and ectonucleotidases offers promise for the management of disordered inflammation and aberrant immune reactivity.

Pulmonary natural killer T cells play an essential role in mediating hyperoxic acute lung injury

Critically ill patients are routinely exposed to high concentrations of supplemental oxygen for prolonged periods of time, which can be life-saving in the short term, but such exposure also causes severe lung injury and increases mortality. To address this therapeutic dilemma, we studied the mechanisms of the tissue-damaging effects of oxygen in mice. We show that pulmonary invariant natural killer T (iNKT) cells are unexpectedly crucial in the development of acute oxygen-induced lung injury. iNKT cells express high concentrations of the ectonucleotidase CD39, which regulates their state of activation. Both iNKT cell-deficient (Jα18(-/-)) and CD39-null mice tolerate hyperoxia, compared with wild-type control mice that exhibit severe lung injury. An adoptive transfer of wild-type iNKT cells into Jα18(-/-) mice results in hyperoxic lung injury, whereas the transfer of CD39-null iNKT cells does not. Pulmonary iNKT cell activation and proliferation are modulated by ATP-dependent purinergic signaling responses. Hyperoxic lung injury can be induced by selective P2X7-receptor blockade in CD39-null mice. Our data indicate that iNKT cells are involved in the pathogenesis of hyperoxic lung injury, and that tissue protection can be mediated through ATP-induced P2X7 receptor signaling, resulting in iNKT cell death. In conclusion, our data suggest that iNKT cells and purinergic signaling should be evaluated as potential novel therapeutic targets to prevent hyperoxic lung injury.

Overexpression of CD39/nucleoside triphosphate diphosphohydrolase-1 decreases smooth muscle cell proliferation and prevents neointima formation after angioplasty

BACKGROUND

Growing evidence implicates the involvement of extracellular nucleotides in the regulation of platelet, leukocyte, endothelial cell (EC) and vascular smooth muscle cell (VSMC) phenotype and function. Within the quiescent vasculature, extracellular nucleotides are rapidly hydrolyzed by CD39, the dominant endothelial nucleoside triphosphate diphosphohydrolase (NTPDase-1). However, vascular CD39/NTPDase-1 activity is lost in EC activated by oxidative stress or proinflammatory mediators, and upon denudation of the endothelium following balloon injury. The consequent increase in extracellular nucleotide concentrations triggers signaling events leading to prothrombotic responses and increased VSMC proliferation.

OBJECTIVES

To investigate the effect of overexpressed CD39/NTPDase-1 in injured aorta.

METHODS

Using adenoviral-mediated gene transfer we expressed CD39/NTPDase-1 in mechanically denudated rat aortas. We measured intima formation by morphometry and VSMC proliferation by the [(3)H]-thymidine incorporation assay.

RESULTS

Targeted expression of CD39 in injured vessels increased NTPDase activity (from 2.91 +/- 0.31 to 22.07 +/- 6.7 nmols Pi mg(-1) protein, 4 days after exposure to the adenovirus) and prevented the formation of neointima. The thickness of the intimal layer in injured aortas exposed to Ad-CD39 was 26.2 +/- 3.9 microm vs. 51.8 +/- 6.1 microm and 64.4 +/- 22.2 microm (P < 0.001) in vessels treated with Ad-beta-gal and saline, respectively. Moreover, targeted expression of CD39/NTPDase-1 caused a 70% (P < 0.01) decrease in proliferation of VSMC isolated from transduced rat aortas as compared with VSMC derived from control vessels.

CONCLUSIONS

The presented data suggest that increasing CD39/NTPDase-1 activity in VSMC could represent a novel therapeutic approach for the prevention of stenosis associated with angioplasty and other occlusive vascular diseases.

The role of purinergic signaling in the liver and in transplantation: effects of extracellular nucleotides on hepatic graft vascular injury, rejection and metabolism

Extracellular nucleotides (e.g. ATP, UTP, ADP) are released by activated endothelium, leukocytes and platelets within the injured vasculature and bind specific cell-surface type-2 purinergic (P2) receptors. This process drives vascular inflammation and thrombosis within grafted organs. Importantly, there are also vascular ectonucleotidases i.e. ectoenzymes that hydrolyze extracellular nucleotides in the blood to generate nucleosides (viz. adenosine). Endothelial cell NTPDase1/CD39 has been shown to critically modulate levels of circulating nucleotides. This process tends to limit the activation of platelet and leukocyte expressed P2 receptors and also generates adenosine to reverse inflammatory events. This vascular protective CD39 activity is rapidly inhibited by oxidative reactions, such as is observed with liver ischemia reperfusion injury. In this review, we chiefly address the impact of these signaling cascades following liver transplantation. Interestingly, the hepatic vasculature, hepatocytes and all non-parenchymal cell types express several components co-ordinating the purinergic signaling response. With hepatic and vascular dysfunction, we note heightened P2- expression and alterations in ectonucleotidase expression and function that may predispose to progression of disease. In addition to documented impacts upon the vasculature during engraftment, extracellular nucleotides also have direct influences upon liver function and bile flow (both under physiological and pathological states). We have recently shown that alterations in purinergic signaling mediated by altered CD39 expression have major impacts upon hepatic metabolism, repair mechanisms, regeneration and associated immune responses. Future clinical applications in transplantation might involve new therapeutic modalities using soluble recombinant forms of CD39, altering expression of this ectonucleotidase by drugs and/or using small molecules to inhibit deleterious P2-mediated signaling while augmenting beneficial adenosine-mediated effects within the transplanted liver.

Mammalian mismatches in nucleotide metabolism: implications for xenotransplantation

Acute humoral rejection (AHR) limits the clinical application of animal organs for xenotransplantation. Mammalian disparities in nucleotide metabolism may contribute significantly to the microvascular component in AHR; these, however remain ill-defined. We evaluated the extent of species-specific differences in nucleotide metabolism. HPLC analysis was performed on venous blood samples (nucleotide metabolites) and heart biopsies (purine enzymes) from wild type mice, rats, pigs, baboons, and human donors.Ecto-5'-nucleotidase (E5'N) activities were 4-fold lower in pigs and baboon hearts compared to human and mice hearts while rat activity was highest. Similar differences between pigs and humans were also observed with kidneys and endothelial cells. More than 10-fold differences were observed with other purine enzymes. AMP deaminase (AMPD) activity was exceptionally high in mice but very low in pig and baboon hearts. Adenosine deaminase (ADA) activity was highest in baboons. Adenosine kinase (AK) activity was more consistent across different species. Pig blood had the highest levels of hypoxanthine, inosine and adenine. Human blood uric acid concentration was almost 100 times higher than in other species studied. We conclude that species-specific differences in nucleotide metabolism may affect compatibility of pig organs within a human metabolic environment. Furthermore, nucleotide metabolic mismatches may affect clinical relevance of animal organ transplant models. Supplementation of deficient precursors or application of inhibitors of nucleotide metabolism (e.g., allopurinol) or transgenic upregulation of E5'N may overcome some of these differences.

The calcium activated nucleotidases: A diverse family of soluble and membrane associated nucleotide hydrolyzing enzymes

It has long been known that the salivary glands of hematophagous (blood-feeding) arthropods secrete soluble apyrases, which are potent nucleotide hydrolyzing enzymes capable of hydrolyzing extracellular ATP and ADP, the latter being a major agonist contributing to platelet aggregation. Only recently, however, has the identification of proteins homologous to these apyrases been reported in non-blood-feeding organisms such as rodents and humans. In this review, we present an overview of the diverse family of apyrases first described in the blood-feeding arthropods, including the identification and characterization of the soluble and membrane-bound vertebrate enzymes homologous to these arthropod apyrases. We also describe the enzymatic properties and nucleotide specificities of the expressed enzymes, and insights gained into the structure and function of this calcium activated nucleotidase (CAN) family from biophysical, mutagenesis and crystallography studies. The potential therapeutic value of these proteins is also discussed.

Ecto-nucleotidases of the CD39/NTPDase family modulate platelet activation and thrombus formation: Potential as therapeutic targets

Extracellular nucleotide P2-receptor-mediated effects on platelets, leukocytes and endothelium are modulated by ecto-nucleotidases. These ecto-enzymes hydrolyze extracellular nucleotides to the respective nucleosides. The dominant ecto-nucleotidase expressed by the endothelium, by monocytes and vascular smooth muscle cells is CD39/NTPDase1. Ecto-nucleotidase biochemical activity of CD39 is lost at sites of acute vascular injury, such as in ischemia reperfusion and immune graft rejection. CD39L(Like)1/NTPDase2, a related protein, is associated with the basolateral surface of endothelium, the adventitia of vessels and microvascular pericytes. CD39/NTPDase1 hydrolyzes both tri- and diphosphonucleosides and blocks platelet aggregation responses to ADP. In contrast, CD39L1/NTPDase2, a preferential nucleoside triphosphatase, activates platelets by preferentially converting ATP to ADP, the major agonist of platelet P2 receptors. Spatial and temporal expression of NTPDases in the vasculature appears to control platelet activation, thrombus size and stability by regulating phosphohydrolytic activity and consequent P2 receptor signaling. Constitutively circulating microparticles appear to be associated with functional NTPDases, and accumulation of these at sites of vascular injury might influence local thrombus formation and evolution. The phenotype of the cd39-null mouse is in keeping with disordered thromboregulation with heightened susceptibility to inflammatory vasculary reactions, increased permeability and high levels of tissue fibrin. Paradoxically, these mutant mice also exhibit a bleeding phenotype with differential platelet P2Y1 desensitization. Over-expression of CD39 at sites of vascular injury and inflammation by adenoviral vectors, by transgenesis or by the use of pharmacological modalities with soluble derivatives has been shown to have major potential in several animal models tested to date. Future clinical applications will involve the development of new therapeutic strategies to various inflammatory vascular diseases and in transplantation.

Intravenous apyrase administration reduces arterial thrombosis in a rabbit model of endothelial denudation in vivo

The role of adenine nucleotides on vascular and platelet functions has long been established. Apyrase (CD39) takes part of a family of ecto-enzymes that hydrolyze adenosine diphosphate and adenosine triphosphate. The participation of apyrase in the thromboregulatory system is under study. An in vivo experimental model of acute arterial thrombosis was used to test the hypothesis that administering a soluble form of potato apyrase could prevent thrombus formation. Twenty-five white New Zealand male rabbits suffered balloon aortic endothelium denudation and, after 15 days, they were submitted to a thrombosis-triggering protocol with a procoagulant (Russel's viper venom) and epinephrine. After the thrombosis-triggering protocol, 12 animals received two soluble apyrase administrations intravenously (with 90 min intervals), while 13 control animals received no apyrase. Three hours after the triggering protocol, the animals were killed and the rate and area of arterial thrombosis were analyzed. The rate of thrombosis in the apyrase group was significantly lower than that of the control group (16.7 versus 69%, respectively; P = 0.015), as was the area of thrombosis (1.7 +/- 4.3 versus 21.7 +/- 37.4 mm2, respectively; P = 0.008). Our results confirm that apyrase participates in homeostasis through a potent anti-thrombotic effect.

Soluble NTPDase: An additional system of nucleotide hydrolysis in rat blood serum

The participation of a nucleoside triphosphate diphosphohydrolase in the nucleotide hydrolysis by rat blood serum was evaluated. Nucleoside triphosphate diphosphohydrolase and phosphodiesterase are enzymes possibly involved in ATP and ADP hydrolysis. The specific activity of the phosphodiesterase activity (using thymidine 5'-monophosphate p-nitrophenyl ester as substrate) was 4.92 +/- 0.73 (mean +/- SD, n = 10) nmol p-nitrophenol.min(-1).mg(-1) protein and the specific activities for ATP and ADP were 1.31 +/- 0.37 (mean +/- SD, n = 7) and 1.36 +/- 0.25 (mean +/- SD, n = 5) nmol Pi.min(-1).mg(-1) protein, respectively. A competition plot demonstrated that ATP and ADP hydrolysis occurs at the same active site. The effect of suramin and phenylalanine on ATP, ADP and thymidine 5'-monophosphate p-nitrophenyl ester hydrolysis was investigated. The results were opposite considering the hydrolysis of ATP and ADP and that of the substrate marker for the enzyme phosphodiesterase. These results are indicative of the presence of, at least, two enzymes participating in the serum nucleotide hydrolysis. The presence of cAMP did not affect the hydrolysis velocity of ATP and ADP, while thymidine 5'-monophosphate p-nitrophenyl ester hydrolysis was inhibited by cAMP by approximately 47%, suggesting that the hydrolysis of the ATP and ADP, under our assay conditions, occurs at a different site from the phosphodiesterase site. Both enzyme activities, in the rat blood serum, may be involved in the modulation of the nucleotide/nucleoside ratio in the circulation, serving an in vivo homeostatic and antithrombotic function. In addition, the phosphodiesterase may act on DNA or RNA liberated upon tissue injury and/or cell death.

Reversal of thrombin-induced deactivation of CD39/ATPDase in endothelial cells by HMG-CoA reductase inhibition: effects on Rho-GTPase and adenosine nucleotide metabolism

Adenosine triphosphate and diphosphate that activate platelet, leukocyte, and endothelium functions are hydrolyzed by endothelial CD39/ATPDase. Because CD39/ATPDase is downregulated in endothelial cells by inflammation and this may be affected by HMG-CoA reductase inhibitors, we examined the role of cerivastatin and simvastatin in regulation of endothelial CD39/ATPDase expression, metabolism of ATP/ADP, and function in platelets. Thrombin-stimulated endothelial cells in vitro were treated with the statins, and hydrolysis of exogenous ADP and ATP was assessed by high-performance liquid chromatography and malachite green assay. Platelet aggregation studies were performed with endothelial cell supernatants as triggers. CD39/ATPDase surface expression by endothelial cells was determined immunologically by fluorescence-activated cell sorter, mRNA expression by RT-PCR, and thrombin-induced dissociation of Rho-GTPases by Western blotting. Treatment by simvastatin or cerivastatin restored impaired metabolism of exogenous ATP and ADP in thrombin-activated endothelial cells by preventing thrombin-induced downregulation of CD39/ATPDase. In platelet aggregation studies, ATP and ADP supernatants of thrombin-activated endothelial cells were less stimulatory in the presence of statins than in their absence. Data show that statins preserve CD39/ATPDase activity in thrombin-treated endothelial cells involving alterations by statins of Rho-GTPase function and CD39/ATPDase expression. Preservation of adenine nucleotide metabolism may directly contribute to the observed anti-thrombotic and anti-inflammatory actions of statins.