A preliminary comparison of the thrombogenic activity of vitronectin and other RGD-containing proteins when bound to surfaces

Variations in the ability of adsorbed fibrinogen to mediate platelet adhesion to polystyrene-based materials: a multivariate statistical analysis of antibody binding to the platelet binding sites of fibrinogen

Platelet adhesion to the surfaces of biomaterials preadsorbed with plasma previously has been shown to be mediated exclusively by surface-bound fibrinogen and does not seem to involve the other adhesion proteins in plasma (Tsai et al., J Biomed Mater Res 2002;60:348-359). In this study, the influence of surface-bound fibrinogen on platelet adhesion to five different types of polystyrene-based microtiter plates preadsorbed with plasma was analyzed relative to the amount of adsorbed fibrinogen and monoclonal antibody binding to the adsorbed fibrinogen. There was no significant correlation between platelet adhesion and the absolute amount of adsorbed fibrinogen. However, platelet adhesion was positively correlated to the ability of the adsorbed fibrinogen to bind three types of monoclonal antibodies. The antibodies used bound to the sites on fibrinogen thought to be involved in platelet binding (the two gamma chain C-terminal dodecapeptides and the RGDF and RGDS sequences in each of the Aalpha chains). A partial least-squares calibration model was used to analyze the relative importance of these binding sites in fibrinogen to platelet adhesion. The gamma chain C-terminal dodecapeptide was shown to be the most important site in adsorbed fibrinogen in mediating platelet adhesion.

Inhibition of platelet adhesion and aggregation by a defined region (Gly-486-Lys-502) of high molecular weight kininogen

Proteolytic cleavage of single chain high molecular weight kininogen (HK) by kallikrein releases the short-lived vasodilator bradykinin and leaves behind two-chain high molecular weight kininogen (HKa). HKa and particularly its His-Gly-Lys-rich domain 5 have been previously reported to exert anti-adhesive properties by binding to the extracellular matrix protein vitronectin (VN). In this study the ability of HKa and domain 5 to interfere with platelet adhesion and aggregation was investigated. In a purified system HKa and particularly domain 5 but not HK inhibited the binding of VN to the alpha(IIb)beta(3) integrin, whereas the binding of fibrinogen to this integrin was not affected. The region Gly-486-Lys-502 from the carboxyl terminus of the domain 5 was identified as responsible for inhibition of the VN-alpha(IIb)beta(3)-integrin interaction, as this portion was also found to mediate kininogen binding to VN. Through these interactions, HKa, the isolated domain 5, and the peptide Gly-486-Lys-502 abrogated the alpha(IIb)beta(3)-integrin-dependent adhesion of human platelets to VN but not to fibrinogen. The codistribution of VN and HKa at sites of ex vivo platelet aggregation was demonstrated by transmission immune electron microscopy, indicating that the described interaction is likely to take place in vivo. Moreover, domain 5 and the peptide Gly-486-Lys-502 dose-dependently blocked platelet aggregation, resembling the inhibitory effect of monoclonal antibody 13H1 against multimeric VN. Finally, treatment of mice with isolated domain 5 resulted in a significantly prolonged tail bleeding time. Taken together, our data emphasize the inhibitory role of HK domain 5 on platelet adhesion and aggregation; new anti-thrombotic compounds may become available on the basis of peptide Gly-486-Lys-502 of HK domain 5.

Platelet adhesion to polystyrene-based surfaces preadsorbed with plasmas selectively depleted in fibrinogen, fibronectin, vitronectin, or von Willebrand's factor

Four plasma proteins have been shown to be able to mediate platelet adhesion to synthetic materials when they are adsorbed as purified proteins: fibrinogen (Fg), fibronectin (Fn), vitronectin (Vn), and von Willebrand factor (vWF). Among them, Fg is thought to play a leading role in mediating platelet adhesion to plasma-preadsorbed biomaterials, but this has been established for only three types of materials so far in our laboratory. Furthermore, the role of Fn, Vn, and vWF in mediating platelet adhesion to plasma-preadsorbed surfaces is still unclear. The aim of the current study was to assess the importance of Fg, Fn, Vn, and vWF in mediating platelet adhesion to a series of polystyrene-based surfaces. The strategy applied in the present investigation was to compare platelet adhesion to surfaces preadsorbed with normal plasma, plasma selectively depleted in Fn or Vn or both Fn and Vn, plasma from donors who were genetically deficient in vWF, and serum. Few platelets adhered to the surfaces preadsorbed with serum, whereas depletion of Fn, Vn, or vWF from plasma did not decrease platelet adhesion significantly. Replenishment of exogenous Fg to serum before protein adsorption restored platelet adhesion to the surfaces, suggesting that Fg was the major plasma protein that mediated platelet adhesion. Also, we found that a surface density of adsorbed Fg far below the amount that usually adsorbs to synthetic surfaces was sufficient to support full-scale platelet adhesion.

Exploiting the current paradigm of blood-material interactions for the rational design of blood-compatible materials

The paradigm of tissue material interactions, which holds that protein adsorption is the first event following contact and determines the later interactions of cells, is invoked to propose a design strategy for biocompatibility. Control of protein interactions is the key element, and it is suggested that nonspecific protein adsorption must be prevented while the adsorption of specific proteins that are expected to result in appropriate bioactivity must be promoted. Modification with polyethylene oxide has been investigated extensively as a means of preventing nonspecific adsorption. Examples of proteins that could be targeted for specific adsorption are antithrombin III to prevent coagulation and albumin to minimize platelet adhesion. Two examples of surfaces designed for specific adsorption from the author's laboratory are discussed: the incorporation of thrombin binding peptides to give a thrombin scavenging surface, and the incorporation of lysine to give a plasminogen specific surface with the potential to dissolve clots.

Cell and protein adhesion studies in glaucoma drainage device development. The AGFID project team

AIM

To examine in vitro whether phosphorylcholine coating of poly(methylmethacrylate) can reduce the adhesion of fibrinogen, fibrin, human scleral fibroblast and macrophage compared with current biomaterials used in the construction of glaucoma drainage devices.

METHODS

Sample discs (n=6) of poly(methylmethacrylate), silicone, polypropylene, PTFE, and phosphorylcholine coated poly(methylmethacrylate) were seeded with fibrinogen, fibrin, fibroblast, and macrophages and incubated for variable lengths of time. The quantification was performed using radioactivity, spectrophotometry, ATP dependent luminometry, and immunohistochemistry respectively.

RESULTS

Fibrinogen and fibrin adhesion to phosphorylcholine coated poly(methylmethacrylate) were significantly lower than PMMA (p=0.004). Phosphorylcholine coating of poly(methylmethacrylate) also significantly reduced the adhesion of human scleral fibroblast (p=0.002) and macrophage (p=0.01) compared with PMMA. All the other biomaterials showed either similar or insignificantly different levels of adhesion to all the proteins and cells tested compared with PMMA.

CONCLUSION

Phosphorylcholine coating is a new material technology that offers considerable promise in the field of glaucoma drainage device development.

Diamond-like carbon coating and plasma or glow discharge treatment of mechanical heart valves

All mechanical heart valves (MHV) are thrombogenic. Application of surface modification technology to reduce the incidence of thrombus formation on MHV is a novel undertaking. This requires collaboration within the bioengineering and cardiothoracic surgery fields. From reviewing results of recent and past investigations, and our own preliminary study with diamond-like carbon coating (DLC) and plasma or glow discharge treatment (GDT) of MHV, we identify and discuss several potentially beneficial effects that may reduce the extent of valve-related thrombogenesis by surface modification. DLC and GDT may affect the surfaces of MHV in many ways, including cleaning of organic and inorganic debris, generating reactive and functional groups on the surface layers without affecting their bulk properties, and making the surfaces more adherent to endothelial cells and albumin and less adherent to platelets. These different effects of surface modification, separately or in combination, may transform the surfaces of MHV to be more thromboresistant in the vascular system.

The role of plasminogen activator inhibitor-1 as inhibitor of platelet and megakaryoblastic cell adhesion

In the present study the ability of plasminogen activator inhibitor type-1 (PAI-1) to interfere with platelet and megakaryoblastic cell adhesion was investigated. Both cell types exhibited integrin-dependent adhesion in a static system, mediated by alphaIIb beta3 on platelets and alpha v-integrins on different megakaryoblastic cell lines, even though they also expressed alphaIIb beta3. In a concentration-dependent manner, active, but not latent or complexed, PAI-1 abrogated cell adhesion onto vitronectin but not onto fibrinogen or other matrix substrata. Urokinase as well as thrombin neutralized the anti-adhesive effect of active PAI-1. The direct binding of vitronectin, but not of other matrix proteins, to integrin alphaIIb beta3 was blocked by active PAI-1 in a purified system. Since activated platelets release active and latent PAI-1 as well as structurally and functionally distinct forms of vitronectin, the described interactions appear to be physiologically significant. Co-distribution of vitronectin and PAI-1 at sites of fibrin polymers within platelet thrombi was demonstrated by transmission electron microscopy, suggesting an extracellular functional relationship of both release products with regard to cell adhesion. Our data emphasize the regulatory role of active PAI-1 in platelet adhesion to provisional matrix proteins as found during wound healing independent of its anti-proteolytic activity. Furthermore, megakaryocyte maturation may depend on the intact vitronectin-integrin adhesion system that is influenced by PAI-1, thereby proposing a regulatory role for the inhibitor in cellular differentiation.

Biocompatibility of sulphonated polyurethane surfaces

Surfaces of medical devices made of polymeric materials may promote thrombosis and inflammation. Therefore, in an attempt to produce surfaces which might diminish biomaterial-mediated thrombosis and inflammation, surface derivatization with 2-acrylamido-2-methylpropanesulphonic acid (AMPS) was carried out. The derivatization procedure generates free radicals which initiate the copolymerization of AMPS monomers directly to a polyurethane surface. In an in vitro blood loop study using non-anticoagulated human blood, the resulting AMPS-derivatized material completely abrogates the generation of fibrinopeptide A, decreases the production of beta-thromboglobulin and C3a, and decreases the adherence of platelets. The derivatized material also attracts fewer adherent neutrophils when implanted in mice. However, AMPS derivatization unexpectedly increases the recruitment of macrophages to implanted material and promotes the formation of adherent sleeve thrombi on central venous catheters indwelling in non-anticoagulated canine femoral veins. Thus, AMPS derivatization has highly variable effects on inflammatory and thrombotic systems. Further investigation is clearly required to determine the mechanisms underlying both desired and adverse effects.

Use of adhesion-defective mutants of Staphylococcus aureus to define the role of specific plasma proteins in promoting bacterial adhesion to canine arteriovenous shunts

We used an ex vivo canine arteriovenous shunt model, previously developed to study plasma protein adsorption and thrombogenesis on polymeric biomaterials, to define the role of host proteins in promoting adhesion of Staphylococcus aureus. Either polyethylene or polyvinyl chloride tubings were exposed to canine blood for 5, 15, or 60 min at a flow rate of 300 ml/min and then were flushed in phosphate-buffered saline (PBS), cut into 1.5-cm segments, and stored at -70 degrees C. After thawing, each segment was preincubated in 0.5% albumin in PBS to prevent nonspecific staphylococcal attachment to surfaces that were not exposed to blood. Each segment was then incubated with 4 x 10(6) CFU of [3H]thymidine-labelled S. aureus per ml for 60 min at 37 degrees C in an in vitro adhesion assay. Two site-specific mutants of S. aureus were tested: one specifically defective in adhesion to surface-bound fibronectin (FnAd-def) and the other defective in adhesion to fibrinogen (FgAD-def) [corrected]. Compared with their respective parental strains, the FgAd-def, but not the FnAd-def, mutant of S. aureus showed a strong (> 80%) decrease in attachment to ex vivo tubings. The adhesion of each strain of S. aureus onto polyethylene was consistently more than twofold higher than the adhesion onto polyvinyl chloride segments exposed to flowing blood for 5 or 15 min, but adhesion became similar to that on polyvinyl chloride after 60 min of exposure. In conclusion, the specific adhesion-defective mutants of S. aureus suggested that fibrinogen was the most active adhesion-promoting protein in a short-term blood-material interaction. The experimental approach described in this study should prove useful for screening materials thought to be resistant to protein-mediated staphylococcal adhesion and colonization.

Adhesion of human peripheral lymphocytes on biomaterials preadsorbed with fibronectin and vitronectin

The adhesion of human peripheral lymphocytes (HPL) was studied after preadsorption of fibronectin (FN) and vitronectin (VN) on hydrophilic glass and hydrophobic octadecyl glass. The adhesion of HPL was shown to be dependent not only on the wettability but also on the protein preadsorbed. Vitronectin expressed not only a higher extent of adhesion under static conditions but also a stronger interaction with HPL, indicated by the low detachment under shear stress. The flow experiments also demonstrated that FN adsorbed on octadecyl glass may undergo conformational changes because HPL could be easily removed. Scanning electron microscopy revealed that HPL on both FN- and VN-coated glass spread well whereas particularly on FN-coated octadecyl glass less cell spreading was observed; moreover, some round cells were detected. The typing of adherent HPL by immunofluorescence microscopy showed that on FN- and VN-coated glass about 70% of all HPL were T-cells (CD 3+). However, on octadecyl glass, particularly on VN, a smaller percentage of CD 3+ cell was observed. The testing for the beta 1 integrin--the receptor for FN and the alpha v integrin--the receptor for VN demonstrated that about 70% of all cells on FN-coated glass were positive for the beta 1 integrin. On VN-coated glass, however, only 5% of HPL were positive for the beta 1 integrin. Although on VN a high adhesion and strong binding of HPL was observed, no presence of the alpha v integrin was detected.

Retention of thrombin by polytetrafluoroethylene: influence on the adsorption of fibrinogen/fibrin

Beads of polytetrafluoroethylene were used to investigate adsorption of thrombin and the influence of the adsorbed protease on a subsequent deposition of fibrinogen. Adsorption of active thrombin was not detected by a specific fluorogenic substrate unless > 0.1 units/ml had been applied. Adsorption was considerably improved by albumin, which protected soluble thrombin from inactivation by hydrophobic surfaces. Retention of active thrombin was optimal at ca. 0.1% albumin and decreased at higher concentrations. After incubation with plasma, negligible thrombin activity was detected at the polytetrafluoroethylene beads by the fluorogenic substrate. However, repeated incubation with fresh plasma samples resulted in adsorbed activity rising with each step. This result suggested that thrombin activity should also accumulate at a polytetrafluoroethylene surface in vivo if fresh blood is permanently flowing past. Adsorbed thrombin improved the subsequent retention of fibrinogen, monitored by an antibody technique. Concomitantly, fibrinopeptides A, AP and AY were slowly released whilst fibrinopeptide B was not detectable before 24 h.

Interactions of thermally denatured fibrinogen on polyethylene with plasma proteins and platelets

During the investigation of fibrin deposition onto hydrophobic polymers in contact with human blood, a model was developed in which fibrinogen was denatured and irreversibly coated onto a polyethylene surface by heating to 70 degrees C for 10 min. The denatured fibrinogen-polyethylene surface is resistant to fluid wall shear rates of up to 550 s-1 and the fibrinogen does not desorb in the presence of plasma proteins. Compared to uncoated polyethylene, little albumin or fibrinogen adsorbs to heat-denatured fibrinogen. Thrombin binds to the denatured fibrinogen-coated polyethylene with low affinity and also acts on the surface-bound denatured fibrinogen and cleaves fibrinopeptide A (FPA) quantitatively. Washed, 51Cr-labeled platelets do not adhere to the thermally denatured fibrinogen at either low or high shear rates compared to surfaces coated with undenatured fibrinogen (p < 0.01). These observations support the role of the D domain of fibrinogen in platelet adhesion because this is the region that is denatured by heating. In contrast, the E domain of fibrinogen is not altered by heating to 70 degrees C and hence remains susceptible to thrombin and/or plasmin cleavage. The characteristics of this surface are such that it can be used to develop fibrin-coated surfaces for use in studies of thrombus formation on artificial surfaces.

A comparison of the adsorption of three adhesive proteins to biomaterial surfaces

The adsorption of three cell adhesive proteins with known thrombogenic activity [fibrinogen (FGN), fibronectin (FN), and vitronectin (VN)] was quantified from mono-component protein solutions, from a quaternary-component protein solution, and from plasma and diluted plasma in order to compare their potential for adsorption to polymeric substrates from solutions of varying complexity. The surfaces studied included polyethylene (PE), silicone rubber (SR), Teflon-FEP (FEP), and two polyetherurethanes: one with a poly(tetramethylene oxide) soft segment (PTMO-PU) and one with a poly(ethylene oxide) soft segment (PEO-PU). The adsorption of these proteins from single-component solutions followed the Freundlich isotherm and the adhesive proteins showed similar trends in Freundlich parameters for surfaces of similar surface wettability. Adsorption from a quaternary-component solution composed of physiological molar ratios of the three proteins and human serum albumin (HSA) revealed a significant enrichment of adsorbed vitronectin as determined from ratios of the adsorbed surface fraction of each protein to its respective bulk fraction. The other proteins' adsorption was enriched to a lesser extent in the decreasing order of FGN greater than FN greater than HSA for all surfaces. The relative enrichment of VN from plasma was also high as compared with its bulk concentration, whereas the enrichment of FGN, FN, and HSA was much lower and of approximately the same magnitude. Compared with the three other proteins, VN showed a resistance to displacement from the polymer substrates as either the plasma concentration was increased or the length of contact with plasma and diluted plasma was increased.

Vessel wall proteins adhesive for platelets

Platelet adhesion to the vessel wall is the first step in the development of a haemostatic plug or thrombus. In vitro studies of platelet adhesion in flowing blood have become possible due to the development of suitable perfusion chambers. With the use of such chambers, adhesion to subendothelium and to isolated connective tissue components from the vessel wall has been realized. Such studies have begun to shed light on the molecular basis of the adhesion process. Von Willebrand factor (vWF), fibronectin, and collagen types I and III have been shown to be the most important adhesive proteins. The functional domains involved in vWF and fibronectin are being identified and the platelet receptors for these ligands have been established. A complicated picture of multiple mutually supportive ligand-receptor interactions has emerged. These insights are critical for the development of thrombo-resistant biomaterials.

Vitronectin and proliferative intraocular disorders. II. Expression of cell surface receptors for fibronectin and vitronectin in periretinal membranes

Several cell types participate in the formation of vitreoretinal traction membranes in proliferative intraocular disorders. The communication between these cells involves hormones, growth factors, and the interaction with extracellular matrix molecules. We have previously demonstrated a partial colocalisation of two potent mediators of cell attachment, fibronectin and vitronectin, in periretinal membranes from patients with proliferative vitreoretinopathy (PVR). We found a similar pattern of vitronectin and fibronectin deposition in proliferative diabetic retinopathy (PDR) (n = 6). Now we show the expression of the corresponding cell surface receptors, integrins, for fibronectin and vitronectin by proliferating cells in 22 periretinal membranes, including traumatic (n = 8) and idiopathic (n = 8) PVR as well as PDR membranes (n = 6). Integrins are membrane receptors for extracellular matrix macromolecules which are involved in such basic biological phenomena as embryogenesis and metastasis. Future studies on the pathogenesis of vitreoretinal proliferation will have to focus on the initiation, maintenance, and regulation of this intercellular communication network involving attachment proteins and integrins.

The role of vitronectin as multifunctional regulator in the hemostatic and immune systems

Vitronectin (= complement S-protein) belongs to the group of structurally and functionally homologous adhesive proteins (fibrinogen, fibronectin, von Willebrand factor) which are essential in the procoagulant phase of the hemostatic system, interacting with platelets and the vessel wall. In addition to a structural motif in vitronectin responsible for this interaction (cell attachment domain) other functional domains in the protein molecule exist that contribute to its multifunctional role as regulator in the immune system (complement) as well as in fibrinolysis. These various activities and the ubiquitous distribution of vitronectin in the organism are discussed with regard to structure-function relationships of the protein molecule. Vitronectin may thus provide a conceptual molecular link between cell adhesion, humoral immune response and the hemostatic system, particularly at the blood-vessel wall interphase.

Fibrinogen-independent platelet adhesion and thrombus formation on subendothelium mediated by glycoprotein IIb-IIIa complex at high shear rate

Platelet adhesion and thrombus formation on subendothelium, studied at a shear rate of 2,600 s-1, were inhibited by two synthetic peptides known to interact with GPIIb-IIIa. One peptide (HHLGGAKQAGDV) corresponds to the carboxyl terminal segment of the fibrinogen gamma-chain (gamma 400-411) and the other (RGDS) contains the amino acid sequence Arg-Gly-Asp (RGD) common to fibronectin, von Willebrand factor, vitronectin and the alpha-chain of fibrinogen. Neither platelet adhesion nor thrombus formation were decreased in a patient with severe congenital fibrinogen deficiency and this was equally true when his blood was further depleted of the small amounts of fibrinogen present utilizing an anti-fibrinogen antibody. In normal subjects, adhesion and thrombus formation were inhibited by the Fab' fragments of a monoclonal anti-GPIIb-IIIa antibody (LJ-CP8), which interferes with the interaction of platelets with all four adhesive proteins in both the fluid and solid phase. However, another anti-GPIIb-IIIa antibody (LJ-P5) that had minimal effects on the interaction of platelets with fibrinogen, but inhibited to varying degrees platelet interaction with other adhesive proteins, was equally effective. The findings demonstrate that, at a shear rate of 2,600 s-1, adhesive proteins other than fibrinogen are involved in GPIIb-IIIa-mediated platelet adhesion and thrombus formation on subendothelium. In addition, since LJ-P5 inhibited the binding of soluble von Willebrand factor and vitronectin, these adhesive proteins may be involved in platelet thrombus formation. In contrast to the results obtained at a shear rate of 2,600 s-1, fibrinogen could play a role in mediating platelet-platelet interactions with weak agonists or lower shear rates.