apyrase and Vascular-Diseases

Well-established evidence links extracellular nucleotides to numerous vascular pathologies, including restenosis associated with angioplasty, atherosclerosis and transplant arteriosclerosis. Through activation of purinergic P2 receptors, extracellular nucleotides contribute to the pathogenesis of occlusive vascular diseases by mediating thrombosis, and vascular smooth muscle proliferation and migration. Therefore, there is a growing interest in the enzymes that hydrolyze nucleotides for their capability to modulate nucleotide-triggered pathologies. In this review, we present the current data addressing the therapeutic potential of nucleoside triphosphate diphosphohydrolases (NTPDases) to prevent intimal hyperplasia and treat vascular intimal disease. In addition, we discuss the mechanisms by which NTPDases exert protective effects in vascular function.

Topics: Animals; Antigens, CD; Apyrase; Constriction, Pathologic; Humans; Hydrolysis; Nucleotides; Receptors, Purinergic P2; Vascular Diseases

Platelets are responsible for maintaining vascular integrity. In thrombocytopenic states, vascular permeability and fragility increase, presumably due to the absence of this platelet function. Chemical or physical injury to a blood vessel induces platelet activation and platelet recruitment. This is beneficial for the arrest of bleeding (hemostasis), but when an atherosclerotic plaque is ulcerated or fissured, it becomes an agonist for vascular occlusion (thrombosis). Experiments in the late 1980s cumulatively indicated that endothelial cell CD39-an ecto-ADPase-reduced platelet reactivity to most agonists, even in the absence of prostacyclin or nitric oxide. As discussed herein, CD39 rapidly and preferentially metabolizes ATP and ADP released from activated platelets to AMP, thereby drastically reducing or even abolishing platelet aggregation and recruitment. Since ADP is the final common agonist for platelet recruitment and thrombus formation, this finding highlights the significance of CD39. A recombinant, soluble form of human CD39, solCD39, has enzymatic and biological properties identical to the full-length form of the molecule and strongly inhibits human platelet aggregation induced by ADP, collagen, arachidonate, or TRAP (thrombin receptor agonist peptide). In sympathetic nerve endings isolated from guinea pig hearts, where neuronal ATP enhances norepinephrine exocytosis, solCD39 markedly attenuated norepinephrine release. This suggests that NTPDase (nucleoside triphosphate diphosphohydrolase) could exert a cardioprotective action by reducing ATP-mediated norepinephrine release, thereby offering a novel therapeutic approach to myocardial ischemia and its consequences. In a murine model of stroke, driven by excessive platelet recruitment, solCD39 reduced the sequelae of stroke, without an increase in intracerebral hemorrhage. CD39 null mice, generated by deletion of apyrase-conserved regions 2 to 4, exhibited a decrease in postischemic perfusion and an increase in cerebral infarct volume when compared with controls. "Reconstitution" of CD39 null mice with solCD39 reversed these changes. We hypothesize that solCD39 has potential as a novel therapeutic agent for thrombotic diatheses.

Topics: Animals; Antigens, CD; Apyrase; Brain Ischemia; Cell Communication; Endothelium, Vascular; Hemostasis; Humans; Mutagenesis, Site-Directed; Nucleotides; Platelet Aggregation Inhibitors; Sympathetic Nervous System; Thrombosis; Vascular Diseases

Vascular smooth muscle cells (VSMCs) exhibit a high degree of plasticity when they undergo the progression from a normal to a disease condition, which makes them a potential target for evaluating early markers and for the development of new therapies. Purinergic signalling plays a key role in vascular tonus control, ATP being an inductor of vasoconstriction, whereas adenosine mediates a vasodilation effect antagonising the ATP actions. The control of extracellular ATP and adenosine levels is done by ectonucleotidases, which represent a potential target to be evaluated in the progression of cardiovascular diseases. In this study, we analysed the basal activity and expression of the ectonucleotidases in aortic rat VSMCs, and we further performed in silico analysis to determine the expression of those enzymes in conditions that mimicked vascular diseases. Cultured in vitro VSMCs showed a prominent expression of Entpd1 followed by Entpd2 and Nt5e (CD73) and very low levels of Entpd3. Slightly faster AMP hydrolysis was observed when compared to ATP and ADP nucleotides. In silico analysis showed that the ectonucleotidases were modulated after induction of conditions that can lead to vascular diseases such as, hypertensive and hypotensive mice models (Nt5e); exposition to high-fat (Entpd1 and Entpd2) or high-phosphate (Nt5e) diet; mechanical stretch (Entpd1, Entpd2 and Nt5e); and myocardial infarction (Entpd1). Our data show that VSMCs are able to efficiently metabolise the extracellular nucleotides generating adenosine. The modulation of Entpd1, Entdp2 and Nt5e in vascular diseases suggests these ectoenzymes as potential targets or markers to be investigated in future studies.

Topics: 5'-Nucleotidase; Adenosine; Adenosine Diphosphate; Adenosine Triphosphatases; Adenosine Triphosphate; Animals; Antigens, CD; Aorta; Apyrase; Computer Simulation; GPI-Linked Proteins; Mice; Muscle, Smooth, Vascular; Nucleotides; Rats; Rats, Wistar; Vascular Diseases

Topics: Animals; Antigens, CD; Apyrase; Blood Vessels; Fibrinolytic Agents; Humans; Tunica Intima; Vascular Diseases

Dr Simon C Robson (Harvard University) was interviewed by Emma Quigley (Commissioning Editor, Expert Opinion) on 14th August 2006. Born in the UK, Dr Simon Robson obtained his MB, ChB from the University of Cape Town, South Africa in 1978 and his PhD in Immunology in 1989. He worked in both South Africa and the UK before moving to the USA in 1994. Now an Associate Professor in Medicine at Harvard University, Dr Robson is conducting research dealing with the vascular biology of transplantation and specifically focussing on how endothelial and immune cell purinergic signalling is modulated by ecto-nucleotidases of the CD39 family (ecto-enzymes that hydrolyse extracellular nucleotides to generate nucleosides). In several studies funded by the NIH, ROTRF and other agencies, Dr Robson has been researching genomics, proteomics and the biology of CD39 in models of inflammation and immunity. Dr Robson has published > 200 papers and is on the Editorial Boards of many well-respected journals, including Expert Opinion on Therapeutic Targets.

Topics: Animals; Antigens, CD; Apyrase; Drug Delivery Systems; Enzyme Inhibitors; Humans; Vascular Diseases

A rapid radioassay was used to characterise the adenosine diphosphatase (ADPase) activities in human plasma. There was a major peak at pH 9.3, 80% of whose activity was attributable to non-specific alkaline phosphatase, with the remaining 20% probably due to a specific ADPase. There was also a small peak of ADPase activity at pH 4.0. Inhibitor and chromatographic studies showed that whilst much of this activity was attributable to non-specific acid phosphatase, there was a discrete acid ADPase. Assays of plasma ADPase activities in vascular disorders, including myocardial infarction, peripheral vascular disease and diabetes mellitus, reveal no alterations from control values. Activities of alkaline ADPase were elevated in both chronic and acute liver failure. Acid ADPase was also increased in chronic liver disease and it is suggested that alterations in ADPase activities in liver disorders may contribute to the haemostatic problems observed in these patients.

Topics: Acid Phosphatase; Acute Disease; Alkaline Phosphatase; Apyrase; Chromatography, Gel; Chronic Disease; Humans; Hydrogen-Ion Concentration; Kinetics; Liver Diseases; Myocardial Infarction; Phosphoric Monoester Hydrolases; Vascular Diseases