A hemoglobin vesicle (Hb-V) is an artificial oxygen carrier encapsulating a highly concentrated hemoglobin solution (40 g/dL) in a liposome. The in vivo safety and efficacy of Hb-V suspension as a transfusion alternative and structural stability during storage have been studied extensively. Because the intra liposomal Hb aqueous solution can possess colloid osmotic pressure (COP, 200− 300 Torr) that is much higher than that of blood plasma (20− 25 Torr), a question arises as to whether the lipid membrane senses the transmembrane diff erence in COP. We examined the membrane microviscosity using a fluorescence polarization technique. To avoid the interference of red Hb on the fluorescence measurement, we used human serum albumin (HSA) as a substitute for Hb. Both HSA and Hb solutions show high COP depending on the concentration. Encapsulation of HSA solution (40 g/dL) in the liposome decreased the membrane microviscosity at a lower temperature (949 ± 8 cP → 607 ± 10 cP at 25 °C). The result indicates that the transmembrane osmotic stress induced by HSA encapsulation expands the liposome maximally with increasing spherical surface area, and the membrane fl uidity is increased extremely. Even for such a condition, the lowest membrane microviscosity, 377 ± 10 cP at 60 °C, is much higher than that of DPPC liposome (40 ± 2 cP at 60 °C). Accordingly, Hb-V as well as HSA-V maintains a spherical structure and mechanical stability under transmembrane stress caused by high COP, as described in the literature.

Transmembrane difference in colloid osmotic pressure affects the lipid membrane fluidity of liposomes encapsulating a concentrated protein solution

254th National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.