Effects of Nitric Oxide (NO) and Soluble Nucleoside Triphosphate Diphosphohydrolase (NTPDase) on Inhibition of Platelet Deposition In Vitro

In vitro investigation of enhanced hemocompatibility and endothelial cell proliferation associated with quinone-rich polydopamine coating

Recent investigations have demonstrated that polydopamine (PDA)-modified surfaces were beneficial to the proliferation of endothelial cells (ECs). In this work, PDA coated 316L stainless steels (316L SS) were thermally treated at 50, 100, and 150 °C respectively (hereafter designated as Th50, Th100, and Th150) and consequently produced diverse surface chemical components. In vitro hemocompatibility and vascular cell-material interactions with ECs and smooth muscle cells (SMCs) affected by surface characteristics have been investigated. The Th150, rich in quinone, showed the best hemocompatibility and could effectively inhibit platelet adhesion, activation, and fibrinogen conformation transition. The polydopamine-modified surfaces were found to induce dramatic cell-material interaction with enhanced ECs proliferation, viability and migration, release of nitric oxide (NO), and reduced SMCs proliferation. The inhibitory effect of SMCs proliferation might be associated with the surface catechol content. The coating on Th150 showed a good resistance to the deformation of compression and expansion of vascular stents. These results effectively suggested that the Th150 coating might be promising when served as a stent coating platform.

Thromboresistance characterization of extruded nitric oxide-releasing silicone catheters

Intravascular catheters used in clinical practice can activate platelets, leading to thrombus formation and stagnation of blood flow. Nitric oxide (NO)-releasing polymers have been shown previously to reduce clot formation on a number of blood contacting devices. In this work, trilaminar NO-releasing silicone catheters were fabricated and tested for their thrombogenicity. All catheters had specifications of L = 6 cm, inner diameter = 21 gauge (0.0723 cm), outer diameter = 12 gauge (0.2052 cm), and NO-releasing layer thickness = 200 ± 11 µm. Control and NO-releasing catheters were characterized in vitro for their NO flux and NO release duration by gas phase chemiluminescence measurements. The catheters were then implanted in the right and left internal jugular veins of (N = 6 and average weight = 3 kg) adult male rabbits for 4 hours thrombogenicity testing. Platelet counts and function, methemoglobin (metHb), hemoglobin (Hb), and white cell counts and functional time (defined as patency time of catheter) were monitored as measured outcomes. Nitric oxide-releasing catheters (N = 6) maintained an average flux above (2 ± 0.5) × 10(-10) mol/min/cm for more than 24 hours, whereas controls showed no NO release. Methemoglobin, Hb, white cell, and platelet counts and platelet function at 4 hours were not significantly different from baseline (α = 0.05). However, clots on controls were visibly larger and prevented blood draws at a significantly (p < 0.05) earlier time (2.3 ± 0.7 hours) into the experiment, whereas all NO-releasing catheters survived the entire 4 hours test period. Results indicate that catheter NO flux levels attenuated thrombus formation in a short-term animal model.

Effects of a highly palatable diet on lipid and glucose parameters, nitric oxide, and ectonucleotidases activity

Obesity has reached epidemic proportions worldwide and is stimulated by the ready availability of food rich in fat and sugar (highly palatable diet). This type of diet increases the risks of obesity-associated pathologies, such as insulin resistance and cardiovascular disease. Nitric oxide, a potent endogenous vasodilator, is decreased in these pathologies, mostly as a result of insulin resistance. Ectonucleotidases are ecto and soluble enzymes that regulate the availability of the nucleotides ATP, ADP, and AMP and the nucleoside adenosine in the vascular system, thereby affecting vasoconstriction, vasodilatation, and platelet aggregation homeostasis. The aim of this study was to evaluate the effects of a highly palatable diet on serum lipid and glucose parameters, nitric oxide, and ectonucleotidase activity. Forty male Wistar rats were fed 1 of 2 diets for either 45 days or 4 months: standard chow (SC, n = 10) or a highly palatable diet enriched with sucrose (HP, n = 10). Body mass, visceral fat mass, glucose tolerance, cholesterol (total, high-density lipoprotein (HDL) and non-HDL), serum triacylglycerol, liver triacylglycerol, and free glycerol were increased in the HP group after 45 days and after 4 months, whereas insulin levels were not different between the groups at either time. Furthermore, levels of nitric oxide metabolites and ATP, ADP, and AMP hydrolysis were significantly lower in the HP group (p < 0.05) after 4 months. In conclusion, the consumption of the HP diet for 4 months induced overall corporal and metabolic changes, and decreased nitric oxide metabolites and ectonucleotidase activity, thereby promoting an appropriate environment for the development of cardiovascular diseases, without apparent changes in insulin levels.

Immobilization of selenocystamine on TiO2 surfaces for in situ catalytic generation of nitric oxide and potential application in intravascular stents

Immobilization of selenocystamine on TiO(2) film deposited on silicon wafer and 316 stainless steel stents for catalytic generation of nitric oxide was described. Polydopamine was used as the linker for immobilization of selenocystamine to the TiO(2) surface. In vitro stability of the immobilized selenocystamine was investigated and the result shows surface selenium loss occurs mostly in the first four weeks. The selenocystamine immobilized surface possesses glutathione peroxidase (GPx) activity, and the activity increases with the amount of grafted polydopamine. Such selenocystamine immobilized surfaces show the ability of catalytically decomposing endogenous S-nitrosothiols (RSNO), generating NO; thus the surface displays the ability to inhibit collagen-induced platelet acitivation and aggregation. Additionally, smooth muscle cells are inhibited from adhering to the selenocystamine immobilized sample when RSNO is added to the culture media. ELISA analysis reveals that cGMP in both platelets and smooth muscle cells significantly increases with NO release on selenocystamine immobilized samples. Two months in vivo results show that selenocystamine immobilized stents are endothelialized, and show significant anti-proliferation properties, indicating that this is a favorable method for potential application in vascular stents.

Hormetic acute response and chronic effect of ethanol on adenine nucleotide hydrolysis in rat platelets

The objective of this study was to verify the acute and chronic effects of ethanol on platelet NTPDase and 5'-nucleotidase activities. These enzymes modulate platelet function by regulating adenine nucleotide bioavailability and adenosine production. In the acute treatment, doses of 0.8, 2.0, 4.0, 6.0 and 8.0 g/kg ethanol were administered via orogastric tube, and induced a biphasic or hormetic effect on ATP, ADP and AMP platelet hydrolysis. Ethanol at a dose of 0.8 and 2.0 g/kg increased NTPDase activity (44 and 35%, P < 0.0001) with ATP as substrate, whereas when ADP was used there was only a tendency for NTPDase activity to increase. ATP and ADP hydrolysis decreased by 31-77% (P < 0.0001) in 4.0, 6.0 and 8.0 g/kg of ethanol compared to the control. AMP hydrolysis showed a tendency to increase at ethanol doses of 0.8 and 2.0 g/kg, but was inhibited by 45-100% (P < 0.0001) at the higher doses. Chronic treatment consisted of the oral administration of 20% ethanol solution during 31 weeks as the only source of liquid and inhibited NTPDase activity (15 and 20%, P < 0.05) with ATP and ADP as substrate, respectively. However, AMP hydrolysis by 5'-nucleotidase increased by 40% (P < 0.05). Thus, we speculate that the effects of ethanol on NTPDase and 5'-nucleotidase activities could be related with the platelets alterations commonly observed in alcohol users.

Intravascular ADP and soluble nucleotidases contribute to acute prothrombotic state during vigorous exercise in humans

Extracellular ATP and ADP trigger vasodilatatory and prothrombotic signalling events in the vasculature. Here, we tested the hypothesis that nucleotide turnover is activated in the bloodstream of exercising humans thus contributing to the enhanced platelet reactivity and haemostasis. Right atrial, arterial and venous blood samples were collected from endurance-trained athletes at rest, during submaximal and maximal cycle ergometer exercise, and after early recovery. ATP-specific bioluminescent assay, together with high-performance liquid chromatographic analysis, revealed that plasma ATP and ADP concentrations increased up to 2.5-fold during maximal exercise. Subsequent flow cytometric analysis showed that plasma from exercising subjects significantly up-regulated the surface expression of P-selectin in human platelets and these prothrombotic effects were diminished after scavenging plasma nucleotides with exogenous apyrase. Next, using thin layer chromatographic assays with [gamma-(32)P]ATP and (3)H/(14)C-labelled nucleotides, we showed that two soluble nucleotide-inactivating enzymes, nucleotide pyrophosphatase/phosphodiesterase and nucleoside triphosphate diphosphohydrolase, constitutively circulate in human bloodstream. Strikingly, serum nucleotide pyrophosphatase and hydrolase activities rose during maximal exercise by 20-25 and 80-100%, respectively, and then declined after 30 min recovery. Likewise, soluble nucleotidases were transiently up-regulated in the venous blood of sedentary subjects during exhaustive exercise. Human serum also contains 5'-nucleotidase, adenylate kinase and nucleoside diphosphate (NDP) kinase; however, these activities remain unchanged during exercise. In conclusion, intravascular ADP significantly augments platelet activity during strenuous exercise and these prothrombotic responses are counteracted by concurrent release of soluble nucleotide-inactivating enzymes. These findings provide a novel insight into the mechanisms underlying the enhanced risk of occlusive thrombus formation under exercising conditions.

Enzymes that hydrolyze adenine nucleotides in chronic renal failure: relationship between hemostatic defects and renal failure severity

The activities of the enzymes NTPDase (E.C.3.6.1.5, apyrase, ATP diphosphohydrolase, ecto-CD 39) and 5'-nucleotidase (E.C.3.1.3.5, CD 73) were analyzed in platelets from patients with chronic renal failure (CRF), both undergoing hemodialysis treatment (HD) and not undergoing hemodialysis (ND), as well as from a control group. The results showed an increase in platelet NTPDase activity in CRF patients on HD treatment (52.88%) with ATP as substrate (P<0.0001). ADP hydrolysis was decreased (33.68% and 39.75%) in HD and ND patients, respectively. In addition, 5'-nucleotidase activity was elevated in the HD (160%) and ND (81.49%) groups when compared to the control (P<0.0001). Significant correlation was found among ATP, ADP and AMP hydrolysis and plasma creatinine and urea levels (P<0.0001). Patients were compared statistically according the time of hemodialysis treatment. We found enhanced NTPDase and 5'-nucleotidase activities between 49 and 72 months on HD patients. Our result suggests the existence of alterations in nucleotide hydrolysis in platelets of CRF patients. Possibly, this altered nucleotide hydrolysis could contribute to hemostasis abnormalities found in CRF.

NTPDase and 5'-nucleotidase activities in rats with alloxan-induced diabetes

Diabetes is associated with a hypercoagulable state. In this study, we investigated the potential effects of alloxan-induced diabetes on the activities of the enzymes NTPDase (E.C. 3.6.1.5, apyrase, ATP diphosphohydrolase, ecto/CD39) and 5'-nucleotidase (E.C. 3.1.3.5, CD73) that can control the levels of ADP and adenosine, two substances that regulates platelet aggregation. In the alloxan-treated rats, NTPDase activity was significantly increased by 88 and 35% with ATP as substrate and by 156 and 58% with ADP as substrate in platelets and synaptosomes, respectively (P< 0.05). AMP hydrolysis was increased by 142% (platelets) and 70% (synaptosomes) in diabetic rats compared to control. These results demonstrate that alloxan-induced diabetes interferes with ATP, ADP, and AMP hydrolysis in platelets and synaptosomes. Taken together, these results may indicate that in diabetic rats both NTPDase and 5'-nuleotidase from the central nervous system (CNS) and platelets respond similarly with increased activity. Thus, we speculate that platelets could be used as a potential peripheral marker of central alterations in NTPDase and 5'-nucleotidase activities in diabetes.

Enzymes that hydrolyze adenine nucleotides in diabetes and associated pathologies

The activities of the enzymes NTPDase (E.C. 3.6.1.5, apyrase, ATP diphosphohydrolase, ecto-CD39) and 5'-nucleotidase (E.C. 3.1.3.5, CD73) were analyzed in platelets of type 2 diabetic, hypertensive and type 2 diabetic/hypertensive patients. The results showed an increase in platelet NTPDase activity in type 2 diabetic (34% and 72%), hypertensive (32% and 70%) and type 2 diabetic/hypertensive patients (30% and 55%) when compared to control (P<.01) with ATP and ADP as substrate, respectively. 5'-Nucleotidase activity was elevated in the hypertensive (60%) and type 2 diabetic/hypertensive (53%) groups when compared to the control and type 2 diabetic group (P<.01). No differences in sensitivity to inhibitors was detected between the platelets of controls and type 2 diabetic/hypertensive patients. No effects on the enzyme activities were observed when pharmacological doses of propranolol, captopril, furosemide, chlorpropamide, acetylsalicylic acid and glibenclamide were administered. Furthermore, changes in platelet adhesiveness and reactivity were found in all groups tested. In conclusion, we may postulate that NTPDase and 5'-nucleotidase from platelets are altered in patients with type 2 diabetes and hypertension. Probably, such alterations are involved in compensatory physiological responses in these diseases and are related to other important mechanisms of thromboregulation.

Synthesis and characterization of polymethacrylate-based nitric oxide donors

A synthetic path for the preparation of methacrylic homo- and copolymers containing secondary amine groups that can be converted into nitric oxide (NO) releasing N-diazeniumdiolates is described. The polymers are obtained by a multistep procedure involving synthesis of methacrylate monomers containing boc-protected secondary amine sites, free radical benzoyl peroxide initiated polymerization, deprotection of the amine sites, and subsequent reaction of the polymers with NO in the presence of sodium methoxide. Monomers with both linear and cyclic pendant secondary amines are examined as polymer building blocks. In most cases, polymers are obtained for both types with compositions that agree well with initial monomer ratios and with number average molecular weights (M(n)) ranging from 1.69 to 2.58 x 10(6) Da. The final N-diazeniumdiolated methacrylic amine polymers are shown to release NO for extended periods of time with "apparent" t(1/2) values ranging from 30 to 60 min when suspended in phosphate buffer, pH 7.4. Total NO loading and release for these materials can reach 1.99 micromol per mg of polymer and is proportional to the amine content of the polymer. It is further shown that by using a dimethacrylate cross-linking agent in conjunction with the various methacrylate amines, suspension polymerization methods can be employed to create small (100-200 microm) polymeric methacrylate microbeads. Such microbeads that can be sequentially deprotected and converted to NO release particles via in-situ diazeniumdiolate formation as carried out for the non-crosslinked polymers.

Distribution of ectonucleoside triphosphate diphosphohydrolases 1 and 2 in rat cochlea

Extracellular ATP and other extracellular nucleotides acting via P2 receptors in the inner ear initiate a wide variety of signalling pathways important for regulation of hearing and balance. Ectonucleotidases are extracellular nucleotide-metabolising enzymes that modulate purinergic signalling in most tissues. Major ectonucleotidases in the cochlea are likely members of the ectonucleoside triphosphate diphosphohydrolase (E-NTPDase) family. In this study, we provide a detailed description of NTPDase1 and NTPDase2 distribution in cochlear tissues using immunocytochemistry. E-NTPDase immunoreactivity was not equally distributed in the tissues bordering scala media. It was observed in the organ of Corti, including sensory and supporting cells, but was notably absent from Reissner's membrane and most of the marginal cells of the stria vascularis. NTPDase1 expression was most prominent in the cochlear vasculature and cell bodies of the spiral ganglion neurones, whereas considerable NTPDase2 immunoreactivity was detected in the stria vascularis. Both E-NTPDases were expressed in the cuticular plates of the sensory hair cells and nerve fibres projecting from the synaptic area underneath the inner and outer hair cells. E-NTPDase localisation corresponds to the reported distribution of some P2X receptor subunits (P2X(2) in particular) in sensory, supporting and neural cells and also P2Y receptor distribution in the vasculature and secretory tissues of the lateral wall. The role for E-NTPDases in purinergic signalling is most likely to regulate extracellular nucleoside triphosphate and diphosphate levels and thus provide termination for extracellular ATP signalling that has been linked to control of cochlear blood flow, electrochemical regulation of sound transduction and to neurotransmission in the cochlea.