Thrombin adsorption

Parallel tests show that thrombin adsorption is minimal on well-prepared polyurethanes containing amorphous PEO, greater on PTMO, and very high on analogues of the hard segment (diisocyanate-diamine copolymers), thus paralleling the trends in platelet retention index p. This result is consistent with the postulate that protein adsorption must precede platelet adsorption. 

Preliminary thrombin adsorption isotherms were prepared by incubating 100 mg of heparin-PVA (control PVA) beads in centrifuge tubes (15 mL) with 0.6 mL of thrombin solution (3-1200 U/mL). Unlabelled purified human thrombin was spiked with I-labelled purified bovine thrombin. After adsorption for 15 minutes, the beads were washed twice with 5 mL of PBS and the supernatants counted. The amount of thrombin/gram of gel was determined. 

Preliminary thrombin adsorption isotherms (purified human thrombin spiked with purified bovine I-thrombin) have shown that... 

Parallel tests show that thrombin adsorption is minimal on SPU containing amorphous PEG, greater on the ones with PTMG and very high on hard segments analogs. 

E.W.Salzman, E.W.Merrill, Polyether-polyurethanes surfaces Thrombin adsorption, platelet adsorption, and ESCA scanning, J, Colloid Interface Sci. 76 594 (1980)... 

Thrombin adsorption was first measured with purified thrombin. In order to study its interaction with the polymers in plasma the thrombin molecule was blocked with a diisopropylphosphoryl group on the active serine site (DIP-thrombin). The adsorption of this... 

The thrombin adsorption was studied using a range of protease concentrations varying from 0 to 0,35 mg/ml. The curves show that... 

All the adsorption curves were analysed with respect to the most common adsorption isotherms used in chemisorption. The AT, thrombin and DlP-thrombin adsorptions seem to correspond respectively to a Tempkin isotherm (AT) or a Langmiur isotherm (thrombin). Then the equilibrium between the surface, the protein in solution and the adsorbed protein can be caracterised with an affinity constant. These values are reported in Table I. 

In contrast, thrombin does not compete with albumin but is quantitatively desorbed by polybrene. Moreover the quantities of thrombin adsorbed at saturation on both polymers are in the same ratio as the total negative charges borne by the polymers backbones. These results suggest that the protease interacts with the sulfonate and carboxyl functions which are nearly equivalent with respect to this interaction. This conclusion is consistent with the fact that thrombin adsorption obeys the Langmuir isotherm which means that the polymer surface is homogeneous and the heat of adsorption is independent of the surface coverage. 

The data on protein adsorption as affected by immobilized heparin is quite contradictory. In Refs.114> and115), serum albumin was shown to be predominantly adsorbed by the HCP, whereas in the majority of other works the observed dependence was the opposite. Table 14 compiles the results of the studies of the absorption of plasma proteins by HCP of two different types 64). Such thrombogenic proteins as fibrinogen and thrombin are seen to be the ones adsorbed most. 

Heparin can be attached to a variety of surfaces by means of complex formation with quaternary ammonium salts. Depending on the method used to attach heparin, the resulting surfaces may or may not release heparin when contacted with blood plasma. The removal of heparin from surfaces by plasma protein fractions was studied and it was found that alpha-globulins removed greater amounts than any other fraction. Heparinized surfaces adsorb proteins when exposed to blood or plasma. However, with the possible exception of thrombin, there is no consistent pattern of protein adsorption which can be related to their nonthrombogenicity. 

It has been shown that heparinized surfaces can be made which lose either no heparin or extremely small amounts of heparin upon exposure to plasma. These surfaces adsorb proteins and with the exception of thrombin, there is no consistent pattern of protein adsorption which can be related to their nonthrombogenicity. 

A study has been carried out on the interactions of blood with plasticised poly(vinyl chloride) biomaterials in a tubular form. The influence of different factors such as the biomaterial, antithrombotic agent, blood condition and the nature of the application is represented when considering the blood response in the clinical utilisation of the plasticised PVC. The PVC was plasticised with di-(2-ethylhexyl)phthalate (DEHP) and tri-(2-ethylhexyl)trimellitate (TEHTM)and in-vitro and ex-vivo procedures used to study the biomaterial with respect to the selection of the plasticiser. The blood response was measured in terms of the measurement of fibrinogen adsorption capacity, thrombin-antithrombin III complex and the complement component C3a. X-ray photoelectron spectroscopy was used for surface characterisation of the polymers and the data obtained indicated that in comparison with DEHP-PVC, there is a higher reactivity... 

Preprothromhin crm be determined immunologically, either using rmtipro-thrombin antibodies, cdter adsorption of the y -Cctrboxylated protein onto barium carbonate or using anti-preprothrombin tmtibodies that do not cross-react with prothrombin. Circulating concentrations of preprothromhin in vitamin K deficiency tue of the order of 150 to 1,500 nmol per L. If elevated preprothromhin is because of vitamin K deficiency, then it will fall on administration of the vitamin, whereas if it is the result of liver disease, then vitamin K supplements will have no effect. 

This chapter deals with a specific test of blood-surface interaction in vitro platelet retention in a column of beads (due to platelet adhesion and aggregation). Protein adsorption precedes platelet adsorption, and thus the in vitro platelet retention test involves competitive and sequential adsorption of proteins, the outcome of which produces surfaces having widely varying degrees of platelet retention. Except in the case of thrombin (3), plasma protein absorption on these surfaces has not been studied. 

Adsorption and Chromatography of Proteins on Porous Glass Activity Changes of Thrombin and Plasmin Adsorbed on Glass Surfaces... 

Adsorption the activities of free plasmin, trypsin, and phosphatase were greater than in the bound state, but free thrombin had less activity than bound thrombin. 

---