Transport of nitrated albumin across continuous vascular endothelium

Because modification of plasma albumin on tyrosine residues generates nitrated albumin (NOA) that may function as a mechanism of nitrogen monoxide clearance from microcirculation, we investigated biochemicaly and morphologically the cell surface binding and the transendothelial transport of NOA. An electron microscopic study was carried out with mouse lungs and hearts perfused in situ with NOA and NOA-Au complexes. The results indicate that NOA-Au can bind to the endothelial cell surface, and its binding can be blocked by albumin plus nitrotyrosine (NO-tyrosine) or abolished by excess NOA. We detected NOA-Au into perivascular spaces as early as 30 sec after the beginning of its perfusion. NOA, unlike native albumin, leaves the vascular lumina via both endothelial caveolae and open junctions. By cross-linking and ligand blotting analysis, we showed that NOA interacted with the same albumin binding proteins of 16-18, 30-32, 60, and 74 kDa as native albumin. ELISA performed on tissue homogenates obtained from the same specimens showed that NOA transport was 2- to 4-fold greater than native albumin. The augmented transendothelial transport of NOA reflects its transcytosis as well as its exit from the microcirculation via open junctions. The increased transport of NOA may serve as an important mechanism that protects a vascular bed against the damaging effects of nitrogen monoxide and peroxynitrite.