Preparation and characterization of a surfactant-protein-(sp-) b-urokinase conjugate for targeting fibrinolytic activity to surfactant containing clots

摘要

Intraalveolar accumulation of fibrin rich material (_"hyaline membranes") is a hallmark of acute and chronic inflammatory lung diseases, includig ALI (acute lung injury) and ARDS (adult respiratory distress syndrome) (1)> Markedly increased procoagulant activities of the alveolar space, mainly attributable to the extrinsic pathway enzymes tissue factor and FVII, and depressed fibrinolytic capacities were found under inflammatory conditions 92). Fibrinogen leaking into the alveolar space due to an impaired capillary-endothelial and alveo-epithelial barrier function may thus be rapidly converted into fibrin. It was recently discovered, that polymerizing fibrin effects a severe loss of surfactant function by incorporating hydrophobic surfactant constituents (phospholipids, SP-B) (3). In vitro experiments revealed that fibrin clots embedding natural surfactant displayed markedly altered mechanical properties, and were less susceptable towards proteolysis by plasmin, trypsin or elastase. However complete lysis of such surfactant incorporating fibrin clots was noted to result in the liberation of intact surfactant material and marked improvement in surface tension properties (4,5). Dissolution of alveolar fibrin may thus represent an important feature for recovery from acute lung injury and prevention of fibrotic events. For targeting surfactant-containing closts, we constructed a hybridmolecule consisting of SP-B and the B-chain of urokinase (SPUC), and investigated in vitro the fibrinolytic and biophysical activities.