PERTURBATION OF THE INTEGRITY OF THE BLOOD-BRAIN-BARRIER BY FIBRINOLYTIC ENZYMES

The action of fibrinolytic enzymes (plasmin, miniplasmin, neutrophil l eukocyte elastase) on the blood-brain barrier is investigated. The bin ding and the effects of the fibrinolytic enzymes are studied in the fi rst subcultivation of human brain capillary endothelial cells. I-125-l abeled plasmin, miniplasmin and neutrophil leukocyte elastase bind to confluent monolayers of cultured endothelial cells with dissociation c onstants of 1 x 10(-8) mol/l, 4.8 x 10(-7) mol/l and 1.8 x 10(-8) mol/ l, respectively, and the number of binding sites varies between 2.3 x 10(5) and 7.5 x 10(6) per cell. Following treatment of the cultured ce lls with purified and active-site titrated proteases, the changes in m orphology of individual cells are analyzed with computerized morphomet ry. At low concentrations (in nanomolar range) all studied fibrinolyti c proteases induce reduction of the cell area; the minimal size is ach ieved in 20-80 min after the application of an enzyme and the effect i s completely reversed in 15 min after its removal. A possible in-vivo consequence of these in-vitro findings is studied in an organ-perfusio n model: rat hemisphere is perfused with a protease solution followed by a circulating phase-borne tracer (horse-radish peroxidase). In perf used rat hemisphere, the fibrinolytic enzymes open the blood-brain bar rier to the circulation-borne tracer. These results support the concep t that fibrinolytic enzymes interact with the brain microvascular endo thelium and thus affect the integrity of the blood-brain barrier throu gh active cell contraction. Blood Coag Fibrinol 9:471-478 (C) 1998 Lip pincott Williams & Wilkins.