Studies on antithrombogenicity of immobilized urokinase

Abstract

Urokinase (UK), a plasminogen activator was immobilized on nylon and silicone surface by application of a newly devised technique.The antithrombogenicity of these materials was studied in vitro and UK-immobilized nylon tubes were applied clinically, which proved to be available as antithrombogenic material.Methods: In our newly devised technique of immobilization of UK, nitrophthalic anhydride (NP) was used as an anti-urokinase inhibitor, polyethylene imine (PEI) and Gantrez (G), a copolymer of maleic anhydride and methyl vinyl ether were used to increase the quantity of UK immobilized on carrier. The nylon tubes immobilized UK in this technique were shown as “nyl-G·NP-UK” and the silicone tubes, as “sil-G·NP-UK”. Details of the immobilization procedures are shown Fig. 1.The antithrombogenicity of these materials was investigated in vitro, in two different ways: one was lysis areas by standard fibrin plate method and the other was thrombus formation time (TFT) according to the method of Chandler. In the latter studies, a comparison was made with non-treated nylon and silicone tubes, NP-immobilized nylon tubes, G-immobilized nylon tubes and casein-immobilized nylon tubes.UK-immobilized nylon tubes, 2mm in outer diameter, 1.7mm in internal diameter were applied to surgical drains in 28 patients who had undergone thyroid, breast and thoracic surgery. Three of these were served as IVH tubes. All these tubes had been disinfected using ethylene oxide gas (EOG) before the clinical use.Silicone tubes, 3mm in outer diameter, 2mm in internal diameter were used as control materials. Fibrinolytic activity was also tested before and after the clinical application of the materials by the standard fibrin plate method.Results: Thrombus formation time of nyl-G·NP-UK was over 45 minutes.That of sil-G·NP-UK was various, however, longer than that of other materials. These results are illustrated in Fig. 2.When the UK-immobilized tubes were clinically applied as drains, blood coagula did not form in the lumina of the tubes for the duration of the clinical application, while in the case of silicone tubes, blood coagula obstructed the lumina within 12-48 hours. The patency of these tubes are summarized in Table 1.Even after termination of clinical application, the UK-immobilized tubes maintained the plasminogen activating activities.Discussion: The UK-immobilized nylon tubes showed excellent thromboresistance, both in vitro and in vivo, and such is attributed to the specificity of the surface of the material covered with UK and NP. Silicone is one of the most widely applied clinical materials, however, the degree of antithrombogenicity revealed to be unsatisfactory (Fig. 2).Antithrombogenicity regarding the UK-immobilized silicone tubes are to be investigated.In our clinical studies, the drainage with our newly devised tubes was excellent and the patency of the tubes was also satisfactory.The UK-immobilized nylon tubes show a great promise for application as antithrombogenic materials.