Immunocytochemical studies of protamine-induced blood-brain barrier opening to endogenous albumin

The cellular mechanisms of blood-brain barrier (BBB) opening to endogenous albumin in the mouse brain after intracarotid infusion of solutions of protamine free base (PB) or protamine sulfate (PS) were studied using quantitative immunocytochemistry. Ultrathin sections of brain samples embedded at low temperature in Lowicryl. K4M were exposed to anti-mouse albumin antiserum followed by protein A-gold. Using morphometry, the density of immunosignals (gold particles per m²) was recorded over four compartments: vascular lumen, endothelial profiles, subendothelial space (including the basement membrane), and brain parenchyma (neuropil). In addition, the adsorption of endogenous albumin evidenced by the number of gold particles per m of the endothelial luminal plasmalemma was quantitatively evaluated. In the applied experimental conditions, PB was found to be strongly cytotoxic as indicated by the appearance of rapid degenerative changes and the disruption of the endothelial lining with concomitant clumping of the blood plasma. The action of PS was milder, offering a better opportunity for detailed ultrastructural and morphometric examination of brain samples during consecutive steps of PS action (2, 5, 10 and 30 min). As early as 10 min after infusion of PS solution, the adsorption of blood plasma albumin to the endothelial luminal surface was increased 2.5 times. Simultaneously, the immunolabelling of the endothelial profiles and subendothelial space was significantly increased. These results suggest that BBB disruption occurs through enhanced adsorption of albumin or albumin-protamine complexes to the luminal plasmalemma, followed by transendothelial vesicular transport, rather than through modification of interendothelial junctional complexes. This process appears to be focally disseminated throughout the cerebral vascular network and declines at 30 min following infusion of PS solution.