Adsorbed glycoproteins in platelet adhesion onto polymer surfaces: significance of terminal galactose units

Sung Wan Kim - Early events in blood/material interactions

Sung Wan Kim's initial efforts as an independent investigator were focused on improving the understanding of the early events in blood/material interactions with the goal to develop blood compatible materials for application in medical devices and prostheses. These initial efforts were centered around blood protein adsorption on biomaterials and related mechanisms of thrombus formation (thrombosis). Ultimately, Sung Wan's efforts were expanded to studies of the non-thrombogenic nature of heparinized biomaterials, prostaglandin biomaterials, and block copolymer systems. These studies were supported by two NIH grants for 22 and 19 years, respectively, and a NIH Career Development Award. Moreover, these studies resulted in over 140 peer-reviewed publications and training of many students and postdoctoral scientists. The intent of this paper is to identify key concepts, papers, and contributions by Sung Wan and his colleagues that fall within the four aforementioned research categories. In this context, many of Sung Wan's early efforts contributed directly to Utah's biomaterials efforts and the Total Artificial Heart program at the time, while providing the foundation for the productive international Triangle Collaboration as well as his following work in polymer-controlled drug releasing systems.

Novel thromboresistant materials

The development of a clinically durable small-diameter vascular graft as well as permanently implantable biosensors and artificial organ systems that interface with blood, including the artificial heart, kidney, liver, and lung, remain limited by surface-induced thrombotic responses. Recent breakthroughs in materials science, along with a growing understanding of the molecular events that underlay thrombosis, has led to the design and clinical evaluation of a variety of biologically active coatings that inhibit components of the coagulation pathway and platelet responses by surface immobilization or controlled release of bioactive agents. This report reviews recent progress in generating synthetic thromboresistant surfaces that inhibit (1) protein and cell adsorption, (2) thrombin and fibrin formation, and (3) platelet activation and aggregation.

Alpha(1)-acid glycoprotein: an acute phase protein with inflammatory and immunomodulating properties

alpha(1)-Acid glycoprotein (AGP) is a protein with a molecular weight of 41-43 kDa and is heavily glycosylated (45%). Due to the presence of sialic acids, it is negatively charged (pI=2.7-3.2). AGP is an acute phase protein in all mammals investigated to date. The serum concentration of AGP rises several fold during an acute phase response, the systemic answer to a local inflammatory stimulus. Also, its glycosylation pattern can change depending on the type of inflammation. The biological function of this protein is not clear. A number of activities on different type of blood cells have been described. In vivo, AGP clearly has protective effects in several models of inflammation. Here we review the data supporting an anti-inflammatory and immunomodulating role of AGP.

Protein adsorption--effect of external lubricants at the interface

Upon exposure to blood, rapid adsorption of proteins is the initial event at the contacting surface, followed by the adhesion of platelets and other blood components. Surfaces absorbing albumin appear to possess antithrombotic character in discouraging adhesion of platelets. Therefore, for the development of a blood contacting device, the interfacial events are extremely important and need serious investigation. We have attempted to observe the variations in competitive adsorption of fibrinogen and albumin onto the polyetherurethane urea (PEUU) surface in the presence of external lubricant, such as calcium stearate and silicone fluid coating. It seems, in the presence of such mediators, that fibrinogen adsorption is increased relatively with reduction in albumin at the surface.

Effect of fabrication, sterilization and mediators--blood compatibility of polyurethanes

The possible changes in the surface and physical properties of polyether urethane urea (PEUU) implants, including their interaction with blood, due to the different preparation methods, sterilization techniques and long term storage in different environmental conditions have been investigated by conducting the studies of mechanical properties, contact angle, platelet adhesion and protein adsorption. Considerable variations in the mechanical properties have been observed for the PEUU grafts stored in different conditions. Changes in platelet adhesion and albumin adsorption have also been observed in the case of samples that underwent different sterilization methods. The effect of mediators like bromelain, an enzyme present in pineapple juice, on albumin adsorption and platelet adhesion on PEUU surfaces have been investigated. It seems the presence of pineapple juice increases the adsorption of albumin and reduces the adhesion of platelets on PEUU surfaces.

Hydrogel grafted surfaces: protein interaction and platelet adhesion

The blood compatibility of an artificial polymeric implant largely depends on the physicochemical nature of the polymer substrate. In the present study our aim is to develop an understanding of polymer surfaces having similar surface free energy, but different chemical characteristics. We attempted to graft hydrogels onto a silastic polyurethane (Angioflex) material and optimised the surface free energy to about 35.0 ergs/cm2. We compared the protein adsorption and platelet and lymphocyte adhesion on these surfaces. It is observed that there is a relative change in behavior because of the difference in chemical nature.

Adhesion and stability of blood cells onto polymer substrates: effect of glow discharge

The adhesion of platelets, red blood cells, and lymphocytes onto various polymer substrates, hydrophobic to hydrophilic in nature, has been studied. Cell adhesion is found to be higher on hydrophilic substrates. The stability of these adhered cells has also been studied under a flow rate of 20 ml/min. Further the effect of glow discharge treatment onto various substrates is investigated. It seems the stability is more on glow discharge treated substrates due to increased surface free energy.

Grafting of Synthetic Polyelectrolyte onto Polymer Surfaces—Comparison on Glow Discharge and 60Co-γ-Irradiation Method

Water soluble polyelectrolyte synthesised from natural rubber contains sulfamate and carboxylate groups similar to that of heparin. It is observed that synthetic heparinoid polyelectrolyte is capable of inhibiting blood coagulation. In the present study, we attempted to graft the same onto polystyrene and polymethylmethacrylate surfaces using glow discharge technique and 60Co-γ-irradiation method, and the surfaces were compared with respect to water contact angle and platelet adhesion parameters. Heparinised surfaces are also evaluated for relative comparison.

Modulation of human polymorphonuclear neutrophil functions by alpha 1-acid glycoprotein

alpha 1-Acid glycoprotein (alpha 1-AGP), a naturally occurring human plasma protein and acute-phase reactant, was extracted by a two-step procedure from sera collected from four healthy men. Its activity was tested in vitro on human polymorphonuclear (PMN) functions (migration, aggregation, O2- generation). alpha 1-AGP was not chemoattractant but inhibited the PMN response to the chemoattractant formylmethionyl-leucyl-phenylalanine without affecting spontaneous migration (Boyden and agarose methods of assessment). At concentrations between 0.15 and 0.45 mg/ml, alpha 1-AGP exerted an aggregating effect with a maximal effective concentration of 0.3 mg/ml. alpha 1-AGP inhibited superoxide generation by PMNs stimulated either by opsonized zymosan or phorbol myristate acetate. This inhibition varied according to the intensity of the stimulation. At low stimulus concentrations, a dose-dependent inhibition of membrane-associated PMN responsiveness to soluble or particulate stimuli was observed. These findings suggest that alpha 1-AGP may be able to prevent PMN activation in the course of inflammatory processes in vivo.

The influence of vaccines and hyper immune serums on protein/platelet interaction towards an artificial surface

Protein adsorption and platelet adhesion are two important biological processes arising at the blood prosthetic interface. The effect of certain commonly used vaccines and hyper immune serums namely tetanus toxoid, tetanus immunoglobulin, polyvalent anti-snake venum serum and anticholera vaccine to modulate the surface induced platelet adhesion to polycarbonate substrate was investigated using washed calf platelets in presence and absence of fibrinogen. This study also demonstrated the changes in protein-surface binding with few of these vaccines, using SDS - polyacrylamide gel electrophoresis. It seems, the addition of tetanus toxoid to the polymer-protein system increased the level of surface-bound albumin and reduced the fibrinogen-surface attachment. On the other hand, tetanus immunoglobulin reversed the effect. This itself may be one of the parameters for the observed reduction in platelet-surface attachment due to tetanus toxoid. The enhanced platelet adhesion with other vaccines, may be correlated with the availability of more fibrinogen receptors for the platelets to attach. A better understanding of the mechanism of these vaccines is needed in vivo conditions for interrelating these findings.

Influence of steroid hormones on protein-platelet interaction at the blood-polymer interface

To develop artificial materials for prolonged use in the vascular system, the complicated process of surface-induced thrombosis needs to be better understood. Steroidal hormones have a profound role in thrombosis and haemostasis, although adequate studies are not available to demonstrate their part in the thromboembolic phenomena that occur at the blood-foreign material interface. We studied the interfacial phenomena of five steroid hormonal drugs, Sustanon, Menstrogen, Mixogen, Durabolin and Ovral and their interaction with proteins and platelets toward an artificial surface using contact angle, polyacrylamide gel electrophoresis, trace labelling methods, etc. This study demonstrates the effect of these hormones to modulate platelet-surface attachment in the presence of platelet inducers. The addition of steroid hormones to the polymer-protein system can inhibit the level of surface-bound albumin where the fibrinogen binding to an artificial surface has been enhanced or unaltered. Steroids also increase platelet-surface attachment to variable degrees. Prolonged use of steroids or the oestrogen-containing oral contraceptive agents may not be advisable for patients having an artificial implant in contact with blood.

In vitro and ex vivo platelet interactions with hydrophilic-hydrophobic poly(ethylene oxide)-polystyrene multiblock copolymers

Hydrophilic-hydrophobic multiblock copolymers synthesized from telechelic oligomers of poly(ethylene oxide) (PEO) and polystyrene (PS) have been used to study the influence of hydrophilic and hydrophobic balance on interfacial interactions of these surfaces with blood components. In vitro coagulation assays show no inherent ability of these amphiphilic surfaces to affect contact activation or coagulation factors. In vitro platelet adhesion and release reactions from rabbit platelet-rich plasma were shown to be greatest on Biomer and PS homopolymer surfaces and least on cross-linked PEO surfaces, with the PEO-PS block copolymers demonstrating intermediate responses. These same substrates were tested in a new low-flow, low-shear arterio-artery shunt system in rabbits. Whole blood occlusion times were not a direct function of hydrophilic content as both PEO and PS homopolymers and Biomer showed short occlusion times, while PEO-PS block copolymers prolonged occlusion times considerably, depending on composition. Overall, results suggest that PEO-PS block copolymers promote unique whole blood responses in contrast to homopolymer and Biomer controls which are more complex than direct correlations to bulk hydrophilic and hydrophobic contents.

The effect of antihypertensive drugs on protein adsorption, platelet adhesion, and blood coagulation toward an artificial surface

Protein adsorption and platelet adhesion are two important biological processes arising at the blood-prosthetic interface. The ability of certain antihypertensive and anticholesterol drugs, namely, clonidine, hydralazine, sembrina, frusemide, clofibrate, sorbitrate, thyroxine, etc., to modulate the surface-induced platelet adhesion to polycarbonate substrate was investigated using washed calf platelets in the presence and absence of fibrinogen. This study also demonstrated the changes in protein-surface binding with these drugs using electrophoretic techniques. It seems that the addition of these drugs to the polymer-protein system increased the level of surface-bound albumin variably. These drugs also reduced the fibrinogen surface concentration and inhibited the surface-induced platelet adhesion to variable degrees. Therefore, it may be possible that the enhanced albumin-surface concentration, or reduced fibrinogen-surface binding, in the presence of these drugs may be one of the parameters for a reduced platelet-surface attachment, which may also improve the blood compatibility of the substrate. A better understanding of the mechanism of these drugs under in vivo conditions is needed to correlate these findings.

The preparation of a urokinase-AT-III-PGE1-methyldopa complex, and its effects on platelet adhesion, coagulation times, protein adsorption, and fibrinolysis

Modifications of urokinase by substances possessing useful therapeutic activity permit combined action preparations to be obtained. Here an attempt was made to develop a complex having combined action for therapeutic activity. The possibility of repeatedly modified urokinase with antithrombin-III-methyldopa-prostaglandin E1 had been experimentally demonstrated. The complex was immobilized on albuminated substrate, which showed fibrinolytic, anticoagulant, and antiplatelet effects simultaneously, in addition to the normal antihypertensive action of methyldopa. The complex immobilized substrate also demonstrated an increase in albumin-surface attachment and a reduction in fibrinogen binding. This may be one of the parameters for a reduced platelet-surface attachment, which may also improve the blood compatibility of the substrate. The approaches suggested indicate the possible new ways of creating nonthrombogenic surfaces with wider applications. A better understanding of the mechanism of these complexes are needed in in vivo conditions to correlate these findings.

Permeability of PEUU membranes: their modification towards blood compatibility

An attempt was made to develop haemodialysis membranes using polyether urethane urea synthesised in our laboratory. It was observed that the processing parameters such as precipitation medium, precipitation temperature etc. can influence the porosity of the membrane and subsequently the permeability property. It was also noted that the permeability of the dried membrane was negligible even though it was kept in distilled water overnight before use. The effect of pH on permeability through the membrane was studied by dialysis experiment using mixtures of various components such as urea, creatinine, uric acid, inulin, albumin, NaCl and KCl at various pH. Standard cellulose acetate (CA) membrane was used for comparison. Membranes were also prepared using biomer solution by precipitating in distilled water at room temperature and the monomer, 2-hydroxy ethyl methacrylate (HEMA) was grafted onto it by glow discharge technique. It was found that the permeability was increased by HEMA grafting with some loss of tensile strength and strain. A comparative study of fibrinogen adsorption during dialysis and adsorption by direct exposure of samples to a mixture containing urea, uric acid, creatinine, dextran, fibrinogen and electrolytes like sodium and potassium ions was also done with 125I labelled fibrinogen. Platelet adhesion studies indicated that the number of adhered platelets was less on the HEMA grafted samples which may enhance blood compatibility. Finally, the membranes were subjected to different sterilization processes possible under wet conditions such as glutaraldehyde treatment and autoclaving. The contact angle, permeability, mechanical property and platelet adhesion studies indicated that the sterilization method can affect the performance of the membrane.

Changes in albumin/platelet interaction with an artificial surface--due to a antibiotics, pyridoxal phosphate, and lymphocytes

Protein adsorption and platelet adhesion are two important biological processes arising at the blood prosthetic interface. The effect of certain antibiotics, namely, neomycin, gentamicin, ampicillin, penicillin-G, and streptomycin to modulate the albumin polycarbonate surface interaction was investigated using 125I albumin from a protein mixture in the presence and absence of isolated calf lymphocytes. This study also demonstrated the changes in platelet-surface adhesion with these antibiotics. The effect of pyridoxal phosphate to modulate the red blood cell-mediated platelet-surface attachment was also attempted. It appears from pyridoxal phosphate studies that pyridoxal 5'-phosphate (PLP) could modify the surface-platelet attachment. It also inhibited the fibrinogen-induced platelet adhesion. It seems, the addition of antibiotics to the polymerprotein system increased the level of surface-bound albumin variably whereas lymphocytes incubated in the medium did not affect the surface-albumin concentration with time course. These antibiotics also inhibited the surface-induced platelet adhesion to variable degrees. Our earlier studies have indicated that certain antibiotics or antiplatelet drugs can inhibit the fibrinogen binding to an artificial surface. Therefore, it may be possible that the enhanced albumin-surface concentration or reduced fibrinogen-surface binding, in the presence of these antibiotics, may itself be one of the parameter for a reduced platelet-surface attachment, which may also improve the blood compatibility of the substrate. A better understanding of the mechanism of antibiotics is needed in in vivo conditions to correlate these findings.

Prostacyclin immobilized albuminated surfaces

The adhered platelets on artificial surfaces play a crucial role in inducing thrombosis. Therefore, it is very much desirable to have surfaces which can effectively retard platelet adhesion and aggregation. Prostaglandins like PGE2, PGE1 and PGD2 possess potent antiplatelet activity, but have very short half life. A chemically stable prostacyclin analog, 10,10-difluoro-13-dehydroprostacyclin (DF2-PGI2) seems to be promising. Polyelectrolyte (PE) synthesized from natural poly cis-1,4 isoprene has also been found to possess outstanding anticoagulant and antiplatelet activity. Modification of polyetherurethane urea (PEUU) by immobilizing DF2-PGI2 and poly-electrolyte in various combinations using glow discharge technique has been attempted. Surfaces thus modified showed negligible platelet adherence. The inhibition of platelet adherence in presence of inducing agents like fibrinogen, thrombin and ADP was also remarkable. The interactions of albumin and fibrinogen with the modified surfaces were studied using 125I labelled proteins.

Platelet adhesion and prevention at blood-polymer interface

It has been proposed that adsorbed glycoproteins such as fibrinogen and gamma-globulin induce platelet adhesion at blood-polymer interfaces. The importance of oligosaccharide groups in the glycoproteins proved to be responsible for platelet adhesion and aggregation via possible complex formation. Several studies have provided evidence that the proposed mechanism was involved in platelet adhesion on polymer surfaces. To minimize or prevent platelet adhesion on polymers, prostaglandins (PGs), potent inhibitors of platelet aggregation and PG-heparin (HEP) conjugate, were combined with polymers via physical dispersion or chemical immobilization on the surfaces. Albumin-HEP conjugate-adsorbed surfaces also showed significant reduction of platelet adhesion.

Inhibition of platelet adhesion to glow discharge modified surfaces

Plasma glow technique has created much interest in the field of surface modification of polymers due to its versatility of generating active polar groups on the surface without affecting the bulk properties. Here an attempt is made to inter-relate the surface properties and platelet adhesion on various polymeric substrates due to plasma treatments. Initially, a critical review of the process and development of thrombosis upon contact of an artificial surface with blood, has been provided, which has been extended with the need for surface modifications to improve their blood compatibility and the versatility of plasma treatments for such modifications have been emphasized. Phospholipids like phosphoryl choline, phosphatidyl choline and phosphoryl ethanolamine were attached to Angioflex surface by plasma glow. The role of such modified substrates to interact with platelets were investigated using Tyrode washed calf platelets. It seems, glow discharge modified phosphoryl choline bilayers dramatically inhibited the platelet-surface binding, which may be due to their biochemical resemblance with thromboresistant surfaces of human blood cells. Further, the behaviour of all phospholipids towards bloodpolymer interaction is not similar and may change depending on the nature of their functional groups, net charge of the phospholipid adsorbed surface and their interaction with platelets and its activation. It is possible to chemically immobilize lipid bilayers on standard polymers, using plasma glow, to improve their biological performance; by suitably selecting the phospholipid combinations.

Protein/platelet interaction with an artificial surface: effect of vitamins and platelet inhibitors

Protein adsorption and platelet adhesion are two important biological processes arising at the blood-prosthetic interface. The effect of Vitamins and antiplatelet drugs to modulate the surface induced platelet adhesion to polycarbonate was investigated using washed calf platelets in presence and absence of fibrinogen. This study also demonstrated the effects of Vitamins and antiplatelet drugs towards protein adsorption to an artificial surface. It seems Vitamin B6, Vitamin E, combinations of Aspirin-Persantine, Aspirin-Vitamin C, a synthetic Polyelectrolyte and Galactosamine reduced the fibrinogen (fg) surface concentration from a mixture of proteins. These antiplatelet agents also enhanced the albumin surface concentration. This itself may be one of the parameters to reduce the platelet adhesion towards an artificial surface. A combination of Aspirin-Vitamin C-Vitamin B6-Vitamin E inhibited the fibrinogen surface binding, which might be beneficial to improve the blood compatibility of an artificial surface.

Changes in protein adsorption on polycarbonate due to L-ascorbic acid

When a synthetic material is introduced into blood, plasma proteins are rapidly adsorbed on to its surface, followed by the attachment of formed elements of blood, leading to thrombus formation. Previous research reported that vitamin C (L-ascorbic acid) prolongs the clotting time due to the formation of vitamin C-calcium complexes, which reduce the availability of Ca2+ ions for the clotting mechanism in in vitro conditions. Contact angle and platelet adhesion studies have indicated that vitamin C modifies the surface-protein interaction and surface-platelet binding at the interface. In this paper an increased thickness of protein layer deposited on the polycarbonate substrate has been observed in the presence of vitamin C (approximately 50 A) using ellipsometric measurements. Further polyacrylamide gel electrophoresis (PAG) and infrared attenuated total reflection spectroscopy (IR-ATR) techniques have provided a better understanding of the interfacial phenomena. It seems, that the adsorption of albumin is increased, relatively, in the presence of vitamin C, when compared with that of fibrinogen and gamma-globulin from an equal amount of protein mixture.

The antithrombotic effect of prostaglandin E1 immobilized on albuminated polymer matrix

For intravascular implantation, a biofunctional surface seems to retard surface thrombosis upon synthetic materials. Prostaglandins, like PGI2, PGE1, and PGD2, etc., are believed to stimulate membrane-bound adenyl cyclase and thereby raise intracellular levels of c-AMP within platelets, which inhibit platelet adhesion and aggregation. A new procedure is suggested for the immobilization of prostaglandin E1 on an albuminated polymer matrix, through glutaraldehyde coupling. Materials thus prepared show dramatic antiplatelet effects, with regard to platelet adhesion, when compared with albumin-immobilized surfaces. The affinity of various modified surfaces toward platelet adhesion is studied, using washed platelets suspended in Tyrode's solution. Octane contact angle studies are used to develop an understanding of the varied nature of bound substrates at equilibrium on polymer surfaces. These are studied at the solid/liquid interface, which is closest to in vivo conditions. The plasma recalcification time demonstrates the anticoagulant properties of various surfaces. A possible role of PGE1 in reducing platelet activity in the presence and absence of vitamin C is discussed. This technique may be used in the development of non-thrombogenic surfaces on existing biomedical polymers. Simultaneous pharmaceutical modification of the blood with vitamin C may enhance the blood compatibility of the surface.

Structural relevance of adsorbed aminosugars on polycarbonate - antithrombogenicity

The effects of glucosamine, galactosamine, and mannosamine on platelet adhesion and coagulation induced by an artificial surface were investigated. Glucosamine and galactosamine showed both antiplatelet and anticoagulant effects, but in case of mannosamine none of the above effects was found significant. The three analogs studied were having the same molecular weight and common molecular structure, however from our preliminary observations it could be suggested, that the spatial arrangement of functional groups in the glucopyranose ring at C2, C4 positions were important for it's activity.

Surface modification of polycarbonate with synthetic polyelectrolyte-anticoagulant activity

Natural rubber with C = C bonds had been modified by reaction with chlorosulfonyl isocyanate (CSI) and 70% of the products were obtained, which yielded polyelectrolyte on treatment with NaOH, having sulfamate and carboxylate groups. The polyelectrolyte showed anticoagulant activity. This might be due to the presence of both sulfamate and carboxylate groups arranged in a steric manner in the molecule as that of Heparin. Surface energy parameters, platelet adhesion and plasma recalcification time were investigated. Possible comparison with heparin had been demonstrated.