Interactions of plasminogen and fibrinogen with model silica glass surfaces: adsorption from plasma and enzymatic activity studies

Multistage Anticoagulant Surfaces: A Synergistic Combination of Protein Resistance, Fibrinolysis, and Endothelialization

Anticoagulant surface modification of blood-contacting materials has been shown to be effective in preventing thrombosis and reducing the dose of anticoagulant drugs that patients take. However, commercially available anticoagulant coatings, that is, both bioinert and bioactive coatings, are typically based on a single anticoagulation strategy. This puts the anticoagulation function of the coating at risk of failure during long-term use. Considering the several pathways of the human coagulation system, the synergy of multiple anticoagulation theories may provide separate, targeted effects at different stages of thrombosis. Based on this presumption, in this work, negatively charged poly(sodium p-styrenesulfonate-co-oligo(ethylene glycol) methyl ether methacrylate) and positively charged poly(lysine-co-1-adamantan-1-ylmethyl methacrylate) were synthesized to construct matrix layers on the substrate by electrostatic layer-by-layer self-assembly (LBL). Amino-functionalized β-cyclodextrin (β-CD-PEI) was subsequently immobilized on the surface by host-guest interactions, and heparin was grafted. By adjusting the content of poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA), the interactions between modified surfaces and plasma proteins/cells were regulated. This multistage anticoagulant surface exhibits inertness at the initial stage of implantation, resisting nonspecific protein adsorption (POEGMA). When coagulation reactions occur, heparin exerts its active anticoagulant function in a timely manner, blocking the pathway of thrombosis. If thrombus formation is inevitable, lysine can play a fibrinolytic role in dissolving fibrin clots. Finally, during implantation, endothelial cells continue to adhere and proliferate on the surface, forming an endothelial layer, which meets the blood compatibility requirements. This method provides a new approach to construct a multistage anticoagulant surface for blood-contacting materials.

Control of Blood Coagulation by Hemocompatible Material Surfaces-A Review

Hemocompatibility of biomaterials in contact with the blood of patients is a prerequisite for the short- and long-term applications of medical devices such as cardiovascular stents, artificial heart valves, ventricular assist devices, catheters, blood linings and extracorporeal devices such as artificial kidneys (hemodialysis), extracorporeal membrane oxygenation (ECMO) and cardiopulmonary bypass. Although lower blood compatibility of materials and devices can be handled with systemic anticoagulation, its side effects, such as an increased bleeding risk, make materials that have a better hemocompatibility highly desirable, particularly in long-term applications. This review provides a short overview on the basic mechanisms of blood coagulation including plasmatic coagulation and blood platelets, as well as the activation of the complement system. Furthermore, a survey on concepts for tailoring the blood response of biomaterials to improve the hemocompatibility of medical devices is given which covers different approaches that either inhibit interaction of material surfaces with blood components completely or control the response of the coagulation system, blood platelets and leukocytes.

Blood compatible materials: state of the art

Devices that function in contact with blood are ubiquitous in clinical medicine and biotechnology. These devices include vascular grafts, coronary stents, heart valves, catheters, hemodialysers, heart-lung bypass systems and many others. Blood contact generally leads to thrombosis (among other adverse outcomes), and no material has yet been developed which remains thrombus-free indefinitely and in all situations: extracorporeally, in the venous circulation and in the arterial circulation. In this article knowledge on blood-material interactions and "thromboresistant" materials is reviewed. Current approaches to the development of thromboresistant materials are discussed including surface passivation; incorporation and/or release of anticoagulants, antiplatelet agents and thrombolytic agents; and mimicry of the vascular endothelium.

An Improved HPLC Fluorimetric Method for the Determination of Enfuvirtide Plasma Levels in HIV-Infected Patients

An improved HPLC fluorimetric method for the quantification of enfuvirtide in plasma of HIV-infected subjects was described and validated. The use of an internal standard improved the reproducibility and precision of the analysis. Our method showed lower limits of detection and quantification (LOD = 32 ng/mL, LOQ = 78 ng/mL), lower intraday (RSD% 1.25-2.95) and interday (RSD% 1.75-4.69) coefficients of variation, greater recovery (>100%), lower duration (16 minutes) and lower cost than previously described fluorimetric methods. Therefore, this method can be used as a reliable tool for pharmacokinetic studies of enfuvirtide.

Electrochemical processing of fibrinogen modified-graphite surfaces: Effect on plasmin generation from adsorbed plasminogen

With the aim to improve the fibrinolytic properties of carbons by different biological and electrochemical treatments, we modified graphite surfaces by fibrinogen adsorption and subsequent application of various constant potentials before submitting them to plasminogen adsorption. First, we verified that plasminogen (purified or present in human plasma) could adsorb onto these modified surfaces and that adsorbed plasminogen could be converted by t-PA (the principal physiological activator of plasminogen) to adsorbed plasmin. The catalytic properties of the generated enzyme were characterized in assay solutions containing t-PA, fibrinogen and the chromogenic substrate S-2403 (pyroGlu-Phe-Lys-p-nitroaniline, HCl). Experiments showed that the application of electrical potentials to the fibrinogen coating could indirectly affect the properties of the material. In the case of anodic potentials, the amidolytic activity of the generated plasmin was significantly enhanced. Especially, this activity was 10 times higher at a particular potential value.

Study of the adsorption of fibrinogen on gold-coated silicon wafer by an impedance method

In 0.1 mol/l KH(2)PO(4)-Na(2)HPO(4) (pH 7.80) buffer solution, the potential of zero charge (PZC) and the open circuit potential of gold-coated silicon were determined to be about -0.6 and +0.10 V (vs SCE), respectively. The open circuit potential was higher than the PZC, which indicated that the surface of the gold-coated electrode had a positive charge. The ellipsometry experiment showed that the adsorption of fibrinogen onto the gold-coated silicon wafer surface arrived at a saturated state when the adsorption time exceeded 50 min. The percentage of surface without adsorbed protein, theta, was about 63%. This means that the proportion of surface actually occupied by fibrinogen was only about 37% after the adsorption arrived at saturation. The solution/protein capacitance value was determined in an impulse state around -0.59 V (vs SCE) and was stable (4.2x10(-5) F) at other potentials.

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.

Thermally Induced Transient Activity Changes of Plasmin Adsorbed onto Bare and Fibrinogen-Modified Graphite and Glassy Carbon Surfaces

The occurrence of a thermally induced first-order transition affecting the amidolytic activity of plasmin adsorbed onto bare and protein-modified graphite and glassy carbon was demonstrated in the 10-45 degrees C temperature range in the presence of a chromogenic substrate. Modification of the surfaces was achieved upon spontaneous adsorption of plasmin to surfaces bearing a coating of fibrinogen, whether electrochemically oxidized or not. The amount of fibrinogen adsorbed at graphite was determined by ELISA. The kinetics of the transition was characterized by its starting temperature (T(c)), which was between 14 and 19 degrees C, the first-order rate constant, and the activation energy E(a) deduced from Arrhenius plots. Results showed the absence of a correlation between T(c), E(a), and contact angle variations. It is therefore likely that these variables address separate steps in a complex pathway of reactions undergone by plasmin under mild thermal constraints. Copyright 2001 Academic Press.

Adsorption of plasminogen from human plasma to lysine-containing surfaces

The objective of this work is to develop blood-contacting surfaces that will dissolve nascent clots that may begin to form on them. Surfaces were prepared consisting of a polyurethane to which a coating reagent was attached covalently by photochemical methods. The coating reagent was a polyacrylamide with lysine and benzophenone (for photochemical attachment) moieties pendant to the chains. It was hypothesized that via the lysine moieties such surfaces would show specific binding affinity for plasminogen, the principal component of the fibrinolytic system in blood. Surfaces of varying lysine content in which the lysine was bound through the alpha-amino groups, leaving the epsilon-amino groups free, were investigated. A control surface in which the lysine was bound through the epsilon-amino groups was also examined. Advancing water contact angles showed the surfaces to be hydrophilic. Hydrophilicity was found to decrease as the lysine content increased. Adsorption of plasminogen from plasma was studied using radioiodinated plasminogen as a tracer. For the epsilon-lysine surfaces, adsorption increased with increasing lysine content and reached a value of 1.2 microg/cm(2) for the surface with the highest lysine content, that is, in the range expected for a compact monolayer of plasminogen. The control surfaces, which contained either no lysine or lysine in which the epsilon-amino groups were unavailable, adsorbed very small amounts of plasminogen. Immunoblots were obtained for the proteins eluted from the surfaces after incubation with plasma. For the control surfaces, most of the proteins tested for (some 20 in all) were present. However, for the surface containing the highest concentration of epsilon-lysine, only plasminogen was detected in a significant amount. It is concluded that the epsilon-lysine surface adsorbs plasminogen to the exclusion of the other plasma proteins. Studies to examine the fibrinolytic properties of these surfaces will constitute the next phase of this work.

Randomness and biospecificity: random copolymers are capable of biospecific molecular recognition in living systems

Biospecific molecular recognition in living systems is known to be based on the lock and key principle as proposed by Emil Fischer. Based on this concept, biospecific polymers have been produced synthetically by attaching biospecific 'keys' to the polymer chain. We postulate that biospecificity can be achieved by alternative means, namely random substitution of a preformed polymer with suitable chemical groups or random copolymerization of suitable functional monomers. Such polymers, we suggest, will contain arrangements of the chemical functions which mimic natural biospecific sites and the probability of occurrence of such arrangements will depend on the average composition of the polymer. In support of this principle, we have developed several functional random copolymer systems which possess a variety of biological properties depending on the type of chemical function. Examples are: polymers possessing anticoagulant properties similar to those of heparin; polymers which interact specifically with components of the immune system; and polymers which, in contact with cells, affect their growth and metabolism. In the case of statistical copolymers possessing 'DNA-like' properties obtained by phosphorylation of hydroxylated polystyrene derivatives, Monte Carlo simulations were used to determine the distribution of phosphodiester (PDE) groups along the chains and to compute the probabilities of occurrence of particular arrangements of PDE found in the 'DNA-like' sites. The results showed that these sites are made up of PDE groups separated by distances that closely match those between the same groups along a generatrix of the DNA double-helix cylinder. These findings offer the prospect of manufacturing polymeric biomaterials endowed with biomimetic character. Moreover, they provide the basis for a hypothesis regarding the appearance of biospecificity at the origin of life, suggesting that biospecific structures may have evolved by natural selection from purely random copolymers. It is likely therefore that biospecificity is a continuous function of randomness, arising from purely statistical distributions of reactivity and evolving into precisely defined structures such as those involved in ligand-receptor interactions.