Specific activation of platelets by surface-adsorbed plasma proteins

The Influence of a Knitted Hydrophilic Prosthesis of Blood Vessels on the Activation of Coagulation System-In Vitro Study

The replacement of affected blood vessels of the polymer material can cause imbalances in the blood haemostatic system. Changes in blood after the implantation of vascular grafts depend not only on the chemical composition but also on the degree of surface wettability. The Dallon^® H unsealed hydrophilic knitted vascular prosthesis double velour was assessed at work and compare with hydrophobic vascular prosthesis Dallon^®. Spectrophotometric studies were performed in the infrared and differential scanning calorimetry, which confirmed the effectiveness of the process of modifying vascular prostheses. Determination of the parameters of coagulation time of blood after contact in vitro with Dallon^® H vascular prosthesis was also carried out. Prolongation of activated thromboplastin time, decreased activity of factor XII, IX and VIII, were observed. The prolonged thrombin and fibrinogen were reduced in the initial period of the experiment. The activity of plasminogen and antithrombin III and protein C were at the level of control value. The observed changes in the values of determined parameters blood coagulation do not exceed the range of referential values for those indexes. The observed changes are the result of considerable blood absorptiveness by the prosthesis of blood vessels and their sealing.

Zwitterionic polymer brushes via dopamine-initiated ATRP from PET sheets for improving hemocompatible and antifouling properties

A low-fouling zwitterionic surface strategy has been proven to be promising and effective for repelling nonspecific adsorption of proteins, cells and bacteria, which may eventually induce adverse pathogenic problems such as thrombosis and infection. Herein, a multi-step process was developed by a combination of mussel-inspired chemistry and surface-initiated atom transfer radical polymerization (SI-ATRP) technique for improving hemocompatible and anti-biofouling properties. Polyethylene terephthalate (PET) sheets were first treated with dopamine, and then the bromoalkyl initiators were immobilized on the poly(dopamine) functionalized surfaces, followed by surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) of 2-(dimethylamino) ethyl methacrylate (DMAEMA) monomer. Subsequently, the resulting PET sheets were ring-opening reacted with 1,3-propiolactone (PL) and 1,3-propanesultone (PS) to afford polycarboxybetaine and polysulfobetaine brushes, respectively. Characterizations of the PET sheets were undertaken by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), atomic force microscope (AFM), water contact angle (WCA) measurements, and X-ray photoelectron spectroscopy (XPS) analysis, respectively. The conversion rates of PDMAEMA to polyzwitterions were evaluated by XPS analysis. The remained PDMAEMA(weak cationic) and formed zwitterions(neutral) would form a synergetic antifouling and antibacterial surface. Hemocompatible and anti-biofouling properties were evaluated by total adsorption of protein as well as the adhesion of platelet, cell and bacterium. Zwitterionic polymer brushes grafted PET sheets showed outstanding hemocompatibility featured on reduced platelet adhesion and repelled protein adsorption. Meanwhile, the grafted PET sheets exerted excellent anti-biofouling property characterized by the resisted adhesion of Escherichia coli and 3T3 cells. In summary, zwitterionic polymer brushed modified PET sheets have a great potential for biomedical applications.

Improved antifouling properties and blood compatibility of 3-methacryloxypropyl trimethoxysilane – based zwitterionic copolymer modified composite membranes via in situ post-crosslinking copolymerization

In the present study, a new method to prepare stable antifouling and blood compatible membranes is developed, i.e., in situ post-crosslinking copolymerization.

Covalent deposition of zwitterionic polymer and citric acid by click chemistry-enabled layer-by-layer assembly for improving the blood compatibility of polysulfone membrane

Development of blood compatible membranes is critical for biomedical applications. Zwitterionic polymers have been proved to be resistant to nonspecific protein adsorption and platelet adhesion. In this work, two kinds of zwitterionic copolymers bearing alkynyl and azide groups are synthesized by atom transfer radical polymerization (ATRP) and subsequent reactions, namely alkynyl-poly(sulfobetaine methacrylate) (alkynyl-PSBMA) and azide-poly(sulfobetaine methacrylate) (azide-PSBMA). The copolymers are directly used to modify azido-functionalized polysulfone (PSf-N3) membrane via click chemistry-enabled layer-by-layer (LBL) assembly. Alkynyl-citric acid is then clicked onto the membrane when the outermost layer was azide-PSBMA. The chemical compositions, surface morphologies, and hydrophilicity of the zwitterionic polymer and citric acid multilayer modified membranes are characterized. The composite multilayer is resistant to protein adsorption and platelet adhesion and also prolongs clotting times, indicating that the blood compatibility is improved. Moreover, after clicking the small molecule anticoagulant alkynyl-citric acid onto the outermost of the zwitterionic multilayer, the membrane shows further improved anticoagulant property. The deposition of zwitterionic polymer and citric acid via click chemistry-enabled LBL assembly can improve the blood compatibility of the PSf membrane.

Ultrastructural characterization of surface-induced platelet activation on artificial materials by transmission electron microscopy

Platelet adhesion is one of the most pivotal events of blood clotting for artificial surfaces. However, the mechanisms of surface-induced platelet activation have not been fully been elucidated or visualized so far. In this study, we attempted to observe the internal structures and adhesion interfaces of human platelets attached to artificial surfaces by transmission electron microscopy (TEM) during the platelet activation process. We prepared observation samples by a conventional embedding method using EPON 812 resin. The sectioning was sliced perpendicular to the a-platelet/material interface. Observation by TEM indicates that internal granules coalesce in the center of the platelet accompanied by pseudopodial growth in the early stage of platelet activation. Pseudopodia from a platelet attach to the material interface not along a plane but at a point. In addition, along with the process of platelet activation, the gap between the platelet membrane and the material surface at the interface disappeared and a-platelet/material adhesion became much tighter. In the fully activated platelet stage, the platelet becomes thinner and tightly adheres to the substrate. As a result of comparative observation of an adherent platelet on polycarbonate (PC) and on amorphous carbon (a-C:H), it was found that internal granules release was inhibited more remarkably on a-C:H coating rather than on PC. Despite numerous technical difficulties in preparing sectional samples, such a study might prove the essential mechanism of biomaterial-related thrombosis, and it might become possible to modify the surfaces of materials to minimize material-related thrombosis.

Time sequence of blood activation by nanoporous alumina: Studies on platelets and complement system

In the present work, the time sequence of blood activation by alumina membranes with different porosities (20 and 200 nm in diameter) was studied. The membranes were incubated with whole blood from 2 min to 4 h. Platelet adhesion and activation in addition to complement activation was monitored at different time points. Evaluation of platelet adhesion and activation was done by determining the change in platelet number and the levels of thrombospondin-1 (TSP-1) in the fluid phase. Scanning electron microscopy studies were done to further evaluate platelet adhesion and morphology. Immunocytochemical staining was used to evaluate the presence of CD41 and CD62P antigens on the material surface. Complement activation was monitored by measuring C3a and sC5b-9 in plasma samples by means of enzyme immunoassays. Both alumina membranes displayed similar complement activation time profiles, with levels of C3a and sC5b-9 increasing with incubation time. A statistically significant difference between the membranes was found after 60 min of incubation. Platelet activation characteristics and time profile were different between the two membranes. Platelet adhesion increased over time for the 20 nm surface, while the clusters of microparticles on the 200 nm surface did not appreciably change during the course of the experiment. The release of TSP-1 increased with time for both membranes; however, much later for the 200 nm alumina (240 min) as compared to the 20 nm membrane (60 min). The surface topography of the alumina most probably influence protein transition rate, which in turn affects material platelet activation kinetics.

Enhancement of peptide coupling to hydroxyapatite and implant osseointegration through collagen mimetic peptide modified with a polyglutamate domain

Hydroxyapatite (HA) is a widely-used biomaterial for bone repair due to its high degree of osteoconductivity. However, strategies for improving HA performance by functionalizing surfaces with bioactive factors are limited. In this study, we explored the use of a HA-binding domain (heptaglutamate, "E7") to facilitate coupling of the collagen mimetic peptide, DGEA, to two types of HA-containing materials, solid HA disks and electrospun polycaprolactone matrices incorporating nanoparticulate HA. We found that the E7 domain directed significantly more peptide to the surface of HA and enhanced peptide retention on both materials in vitro. Moreover, E7-modified peptides were retained in vivo for at least two months, highlighting the potential of this mechanism as a sustained delivery system for bioactive peptides. Most importantly, E7-DGEA-coupled HA, as compared with DGEA-HA, enhanced the adhesion and osteoblastic differentiation of mesenchymal stem cells, and also increased new bone formation and direct bone-implant contact on HA disks implanted into rat tibiae. Collectively, these results support the use of E7-DGEA peptides to promote osteogenesis on HA substrates, and further suggest that the E7 domain can serve as a universal tool for anchoring a wide variety of bone regenerative molecules to any type of HA-containing material.

Procoagulant Behavior and Platelet Microparticle Generation on Nanoporous Alumina

In the present work, we have investigated platelet microparticle (PMP) generation in whole blood after contact with nanoporous alumina. Alumina membranes with pore sizes of 20 and 200 nm in diameter were incubated with whole blood and the number of PMP in the fluid phase was determined by flow cytometry. The role of the complement system in PMP generation was investigated using an analog of the potent complement inhibitor compstatin. Moreover, the procoagulant activity of the two pore size membranes were compared by measuring thrombin formation. Results indicated that PMP were not present in the fluid phase after whole blood contact with either of the alumina membranes. However, scanning electron microscope micrographs clearly showed the presence of PMP clusters on the 200 nm pore size alumina, while PMP were practically absent on the 20 nm membrane. We probed no influence of complement activation in PMP generation and adhesion and we hypothesize that other specific material-related protein—platelet interactions are taking place. A clear difference in procoagulant activity between the membranes could also be seen, 20 nm alumina showed 100% higher procoagulant activity than 200 nm membrane. By combining surface evaluation and flow cytometry analyses of the fluid phase, we are able to conclude that 200 nm pore size alumina promotes PMP generation and adhesion while the 20 nm membrane does not appreciably cause any release or adhesion of PMP, thus indicating a direct connection between PMP generation and nanoporosity.

Fibrinogen and von Willebrand factor mediated platelet adhesion to polystyrene under flow conditions

The roles of adsorbed fibrinogen (Fg) and von Willebrand factor (VWF) in mediating platelet adhesion to synthetic surfaces under flow were investigated using polystyrene (PS) as a model hydrophobic surface. We measured platelet adhesion to PS pre-adsorbed with Fg, VWF, normal plasma, afibrinogenemic plasma, VWF-deficient plasma and deficient plasmas with various concentrations of added Fg or VWF. Platelets in a red blood cell suspension were passed through a flow chamber at either low (50 or 100 s(-1)) or high (500 or 1000 s(-1)) shear. Adhesion to PS pre-adsorbed with afibrinogenemic plasma was very low under both low and high shear conditions, but was restored in a dose-dependent manner with addition of Fg. Less than 20 ng/cm(2)of adsorbed Fg was sufficient to support full-scale platelet adhesion under flow. At high shear rate, platelet adhesion on PS pre-adsorbed with VWF-deficient plasma was much less than on PS pre-adsorbed with normal plasma, but adhesion to PS pre-adsorbed with VWF-deficient plasma with added VWF was very similar to adhesion to PS pre-adsorbed with normal plasma. At low shear, adhesion to PS pre-adsorbed with VWF-deficient plasma was the same as on PS pre-adsorbed with normal plasma. As little as 1 ng/cm(2) of VWF adsorbed from plasma made platelet adhesion higher under high shear than under low shear. The effects of adsorbed Fg and VWF on the morphologies of platelets that adhered from suspensions flowing at high shear rates were also investigated. The lack of either Fg or VWF resulted in marked decreases in the extent of platelet spreading. Real-time observation of platelet adhesion under an epifluorescent microscope showed that platelets adhered to the surface in a linear pattern aligned in the direction of flow under high shear conditions.

The effect of collagen I mimetic peptides on mesenchymal stem cell adhesion and differentiation, and on bone formation at hydroxyapatite surfaces

Integrin-binding peptides increase cell adhesion to naive hydroxyapatite (HA), however, in the body, HA becomes rapidly modified by protein adsorption. Previously we reported that, when combined with an adsorbed protein layer, RGD peptides interfered with cell adhesion to HA. In the current study we evaluated mesenchymal stem cell (MSC) interactions with HA disks coated with the collagen-mimetic peptides, DGEA, P15 and GFOGER. MSCs adhered equally well to disks coated with DGEA, P15, or collagen I, and all three substrates, but not GFOGER, supported greater cell adhesion than uncoated HA. When peptide-coated disks were overcoated with proteins from serum or the tibial microenvironment, collagen mimetics did not inhibit MSC adhesion, as was observed with RGD, however neither did they enhance adhesion. Given that activation of collagen-selective integrins stimulates osteoblastic differentiation, we monitored osteocalcin secretion and alkaline phosphatase activity from MSCs adherent to DGEA or P15-coated disks. Both of these osteoblastic markers were upregulated by DGEA and P15, in the presence and absence of differentiation-inducing media. Finally, bone formation on HA tibial implants was increased by the collagen mimetics. Collectively these results suggest that collagen-mimetic peptides improve osseointegration of HA, most probably by stimulating osteoblastic differentiation, rather than adhesion, of MSCs.

Oxygen radical production in neutrophils interacting with platelets and surface-immobilized plasma proteins: Role of tyrosine phosphorylation

The interaction between neutrophil granulocytes and platelets is considered to play an important role in the inflammatory process induced by an implanted foreign material. However, the cellular mechanisms involved remain incompletely understood. We used a luminol-dependent chemiluminescence (CL) technique to analyze the generation of reactive oxygen species (ROS) in human neutrophils interacting with different plasma protein-coated surfaces in the presence or absence of unstimulated or stimulated platelets. The role of tyrosine phosphorylation in the regulation of NADPH oxidase activity was evaluated with quantitative fluorescence microscopy and the specific tyrosine kinase inhibitor genistein. We found that the ROS-production is 2 to 3 times higher in neutrophils on immunoglobulin G (IgG)-coated surfaces than in cells interacting with albumin- or fibrinogen-coated surfaces. Incubation with superoxide dismutase and catalase revealed that about 45% of the ROS was released extracellularly on IgG surfaces whereas corresponding values were 90% and 85% in neutrophils interacting with albumin and fibrinogen, respectively. The presence of platelets markedly increased the extracellular generation of ROS, mainly in neutrophils interacting with IgG- or fibrinogen-coated surfaces whereas the intracellular production was only modestly affected. Quantitative fluorescence microscopy of neutrophils stained with FITC-conjugated anti-phosphotyrosine antibodies showed a correlation between tyrosine phosphorylation, cell spreading, and ROS production. Platelets markedly amplified the anti-phosphotyrosine staining on both fibrinogen- and IgG-coated surfaces whereas the low level of tyrosine phosphorylation in neutrophils on albumin-coated surfaces was not further elevated by platelets. Furthermore, the tyrosine kinase inhibitor genistein inhibited both extra- and intracellular ROS production in neutrophils regardless of the presence of platelets. We demonstrate that plasma protein coating and the presence of platelets are crucial for the inflammatory response of adhering neutrophils and that the oxidative response correlates with the extent of tyrosine phosphorylation of proteins in focal contacts.

Exposure of fibrinogen-adherent platelets to plasma proteins: a new method for studying protein interactions with platelets

To understand the effects of mediators in coagulating blood at biomaterial surfaces, it is important to use methods that resemble the normal sequence of events in wound healing around implants. The initial adhesion of platelets from whole blood onto material surfaces is mediated by the fibrinogen receptor glycoprotein IIb/IIIa, as shown in a previous study (Broberg et al., J Lab Clin Med 2002; 139:163-172). In this study, isolated platelets were adhered to fibrinogen and exposed to IgG, von Willebrand factor, or thrombin. The response was detected as the number of adherent platelets, the spreading of platelets, the exposure of CD62P (P-selectin), and the release of platelet factor 4 (PF4), ADP, and ATP. These results were compared to the response of platelets adhering to surfaces coated with the same proteins. Fibrinogen-adherent platelets exposed to thrombin generated the significantly highest exposure of CD62P and release of PF4, ADP, and ATP. When platelets were adhered to different protein coatings, von Willebrand factor generated the most CD62P exposure, IgG generated the most PF4 release, and thrombin generated the highest concentration of ADP. These results indicate that protein interactions with platelets may generate different results, depending on the mode of protein exposure.

Fibrinogen adsorption and platelet interactions on polymer membranes

The hemocompatibility of four different wettable polymer membranes, namely Cuprophan (CE), polyether-polycarbonate (PC-PE), polysulfone (PSU), and polyetherimide (PEI), was investigated with respect to fibrinogen (Fng) adsorption and platelet adhesion/activation. In order to estimate the polar and dispersion components of the surface free energy, contact angles using water/vapor and water/n-hexadecane systems were measured. Adsorption of fibrinogen was studied using fluorescence-labeled protein. The adsorption isotherms showed that the amount and the affinity of adsorbed Fng increased with decreasing surface wettability of the membranes, which correlates with the dispersion and polar components of the surface free energy. The conformational changes of adsorbed Fng were detected by measuring the difference between monoclonal antibody binding to the conformation-sensitive epitope in the D-domain and the binding of polyclonal anti-Fng antibody. The anticipated conformational/orientational changes were greater for PEI and PSU membranes (the least wettable membranes) and negligible for the more wettable PC-PE and CE membranes. In addition, a possible relationship with the degree of platelet activation was found, showing negligible platelet adhesion on PC-PE and CE, but high platelet adhesion on PEI and PSU. Furthermore, platelets were spread to a large extent on PEI, while the formation of aggregates was observed on PSU. This may correspond to the anticipated differences in the conformational state of Fng on both membranes.

GpIIb/IIIa is the main receptor for initial platelet adhesion to glass and titanium surfaces in contact with whole blood

Platelets are the first cells to adhere to a surface in contact with blood and are capable of mediating several different responses after contact with different protein-coated surfaces. They are the main source of growth factors such as platelet-derived growth factor and are therefore important in the healing process. In this study, initial platelet adhesion to and spread on hydrophilic and hydrophobic (methylized) glass and titanium with similar wettability were investigated. Whole coagulating blood was used to simulate the in vivo situation shortly after implantation, in which bleeding precedes inflammation and wound healing. Several different antibodies directed against platelet integrins and receptors (CD9, FcgammaRII, GPIIb/IIIa, vitronectin receptor, GPIb/V/IX) were used in an attempt to block platelet adhesion to the surfaces. Immunofluorescence results show that initial platelet adhesion to all the surfaces we investigated can be almost completely inhibited (approximately 95%) by clone M148, an antibody against the GPIIb/IIIa complex (integrin alpha(IIb)beta(3); CD41/CD61), but not with other antibodies to the separate parts of the integrin. Antibodies known to inhibit fibrinogen binding to GPIIb/IIIa after adenosine diphosphate- and collagen- induced aggregation had very little effect on initial platelet adhesion. None of the other integrins were found to have such an effect on initial platelet adhesion. Antibody clone M148 was furthermore found to inhibit platelet spreading. This study shows that regardless of wettability and the biomaterial used, initial adhesion of platelets appears to be mediated by GPIIb/IIIa binding to surface adsorbed fibrinogen.

Co-adsorbed fibrinogen and von Willebrand factor augment platelet procoagulant activity and spreading

Previously we observed that platelets adherent to surfaces preadsorbed with blood plasma exhibited 1.3 to 2.4 times greater procoagulant activity than platelets on surfaces adsorbed with fibrinogen (Fg) only. These observations suggested that the adhesion proteins adsorbed from plasma may activate platelets in a cooperative, or synergistic manner. In the present study, polystyrene surfaces adsorbed with both Fg and vWF induced up to three times greater procoagulant activity than surfaces adsorbed with Fg or vWF only. The amounts of Fg and vWF adsorbed from binary mixtures that resulted in increased procoagulant activity were found to be similar to the amounts that adsorbed to PS from 100% plasma. The effect of adsorbed adhesion proteins on platelet spreading was also investigated. The proportion of fully spread platelets increased, depending on the adhesion protein preadsorbed to the surface, in the following order: vWF < Fg < Fn < (vWF + Fg) < Vn < plasma.

The respiratory burst response of surface-adhering leukocytes. A key to tissue engineering

Biomaterials implanted into tissue will participate in the complex signalling between cells during wound healing. Recent studies have revealed that crucial cellular signalling pathways are regulated by the extra- and intracellular redox states and that reactive oxygen species function as intercellular signal molecules. Biomaterials have been shown to affect the respiratory burst response of surface-adhering leukocytes, thus interfering with major regulatory functions of cells also in surrounding tissues. The respiratory burst of surface-adhering leukocytes may thus be a key event in the understanding of biomaterial interaction with tissues, and the aim of this review is to highlight this field of research.

Von Willebrand factor, a key protein in the exposure of CD62P on platelets

When a biomaterial is introduced into the body water, electrolytes, and proteins adsorb to the surface. Platelets are then the first cells to interact with the surface adsorbed protein layer. We have studied the role of von Willebrand factor (vWF) for platelet-protein interaction by measuring different platelet responses to protein- and plasma-coated hydrophobic glass surfaces. A high exposure of CD62P on the platelet surface was seen after 10 min of incubation on platelets interacting with vWF and normal plasma-coated surfaces (79 and 67%, respectively). On the surfaces coated with albumin and factor VIII deficient plasma, the exposure was low (11 and 27%, respectively). A higher formation of filipodial extensions on the platelets was seen on the surfaces coated with vWF and normal plasma than on the surfaces coated with albumin or factor VIII deficient plasma. No significant differences were seen between the surfaces regarding the platelet release of PF4, ATP, or phospholipids. As shown by these results, vWF is a specific regulator of the exposure of CD62P by platelets and hence important for the interaction between platelets and later arriving neutrophils at biomaterial surfaces.

The effect of adsorbed fibrinogen, fibronectin, von Willebrand factor and vitronectin on the procoagulant state of adherent platelets

Procoagulant (activated) platelets provide a site for assembly of the prothrombinase complex which can rapidly convert prothrombin into thrombin (a potent inducer of clot formation). Previously, we reported that adhesion of platelets to surfaces preadsorbed with blood plasma caused them to become procoagulant. In the present study we investigated the effect of adsorbed adhesion proteins (fibrinogen (Fg), fibronectin (Fn), von Willebrand factor (vWF) and vitronectin (Vn)) on the procoagulant activity of adherent platelets. Adsorbed Fn, vWF and Fg promoted platelet adhesion in the following order: Fn < vWF = Fg. However, these proteins promoted platelet activation (thrombin generation per adherent platelet) in the following order: Fg < Fn < vWF. Adsorption with a series of dilutions of normal plasma, serum, and plasmas deficient in or depleted of von Willebrand factor (de-vWF), fibronectin (de-Fn), vitronectin (de-Vn), or both vitronectin and fibronectin (de-VnFn) resulted in varied platelet adhesion, but little difference in platelet activation. However, preadsorption with dilute de-vWF plasma induced lower procoagulant activity than normal plasma. Preadsorption with normal plasma resulted in higher levels of platelet activation than preadsorption with Fg, suggesting that adsorption of plasma proteins other than Fg caused the high levels of activation observed for plasma preadsorbed surfaces.

Increased expression of P-selectin in patients with chronic atrial fibrillation

Previous studies have shown that platelets are activated during atrial fibrillation (AF). However, prophylactic therapy with aspirin is not associated with a reduction of thromboembolic complications in patients with AF. Stimulation of platelet thrombin and ADP receptors causes a release of P-selectin, which is not affected by aspirin. The purpose of this study was to assess the influence of AF on platelet P-selectin expression. Blood samples from 30 patients were studied ex vivo. Nineteen patients had chronic AF (> 3 months), 11 patients were in sinus rhythm (SR). P-selectin expression was determined by flow cytometry (antibody binding capacity [BC]) at baseline and after platelet stimulation with adenosine diphosphate (ADP) and thrombin receptor activating peptide (TRAP). To determine the effect of heart rate and atrial pressure (RAP), measurements were repeated after 10 minutes of ventricular pacing (120 beats/min) in patients with SR. P-selectin expression was increased in patients with AF at baseline (AF: 1329 +/- 81 BC vs SR: 968 +/- 108 BC; P < 0.05) and after stimulation with ADP (AF: 1445 +/- 101 BC vs SR: 1061 +/- 109 BC; P < 0.05) and TRAP (AF: 13,783 +/- 2442 BC vs SR: 5977 +/- 800 BC; P < 0.05). RAP (2.0 +/- 0.5 vs 6.0 +/- 0.8 mmHg; P < 0.01) and atrial rate (75 +/- 5 vs 114 +/- 5 beats/min; P < 0.001) increased during ventricular pacing. However, P-selectin levels remained stable. AF was accompanied by increased P-selectin expression. In contrast, increased ventricular rate and elevated atrial pressure alone had no effect on platelet activity. Further studies are needed to determine if platelet ADP receptor inhibitors offer a therapeutic benefit in patients with AF.

Platelet adhesion and procoagulant activity induced by contact with radiofrequency glow discharge polymers: roles of adsorbed fibrinogen and vWF

The potential hemocompatibility of radiofrequency glow discharge (RFGD) polymers made by copolymerization of mixtures of hexafluoropropene and ethylene (C(3)F(6)/C(2)H(4)) or acrylic acid and 1,7-octadiene was investigated using in vitro assays for platelet adhesion and platelet catalyzed thrombin generation. Thrombin generation rate normalized to platelet number was used as a measurement of platelet activation (procoagulant activity). RFGD polymers produced by copolymerization of acrylic acid and 1, 7-octadiene contained varying amounts of carboxylic acid species as determined by electron spectroscopy for chemical analysis (ESCA). These polymers induced little variation in platelet adhesion, thrombin generation, or platelet activation. RFGD polymerization of C(3)F(6) and C(2)H(4) resulted in polymers with varying proportions of fluorinated species, as determined by ESCA. Fibrinogen adsorption from plasma was maximal on a polymer made with 25% C(3)F(6) (75% C(2)H(4)) in the feed. However von Willebrand factor (vWF) adsorption was greater on polymers made with increased %C(3)F(6) in the feed. Platelet adhesion decreased with increasing %C(3)F(6) in the feed. Thrombin generation was lowest for platelets adherent to polymers made from both C(3)F(6) and C(2)H(4). Therefore, procoagulant activity of platelets increased for polymers made with increased %C(3)F(6) in the feed, similar to the trend in vWF adsorption. These findings suggest that increased incorporation of fluorinated species into RFGD polymers leads to decreased platelet adhesion and increased platelet activation (which is possibly due to increased vWF adsorption).