PERMEABILITY CHARACTERISTICS OF HEMOGLOBIN DERIVATIVES ACROSS CULTURED ENDOTHELIAL-CELL MONOLAYERS

To better understand the vascular activity of hemoglobin-based (Hb-bas ed) oxygen carriers, the endothelial permeability characteristics of H b derivatives having various molecular masses were defined by using mo nolayers of bovine endothelial cells cultured on microporous membranes . The endothelial permeability of unmodified bovine Hb was almost twic e that of bovine serum albumin. Intramolecularly cross-linked human Hb showed slightly but significantly reduced permeability as compared wi th unmodified bovine Hb. Polyethyleneglycol modification or haptoglobi n binding to Hb further reduced the permeability, These properties wer e intensified in conditions in which the endothelial barrier function was reduced by pretreatment with either interleukin-6 (100 ng/mL, 21 h ours) or lipopolysaccharide (1 mu g/mL, 10 hours). In contrast, there was little permeability of liposome-encapsulated Hb, and it was almost unaffected by the pretreatments. These data provide the first informa tion that Hb derivatives with smaller molecular masses show larger tra nsendothelial flux. Because Hb is a potent scavenger of endothelium-de rived relaxing factor (EDRF), our observations support the idea that s maller Hb-based acellular oxygen carriers are potent vasoconstrictors as a result of abluminal EDRF scavenging.