Preparation of hemoglobin-containing liposomes using octyl glucoside and octyltetraoxyethylene.
Hemoglobin (Hb) was encapsulated in phosphatidylcholine vesicles by removal of the detergent n-octyl beta-D-glucoside (OG) or n-octyltetraoxyethylene (C8E4) out of mixed detergent-lipid micelles in Hb solution. Three types of apparatus were used for dialysis. Dialysis buffer flow rates, the surface area of the dialysis membranes, and detergent-lipid interactions determined the rate of dialysis, which influenced liposome size and lamellarity. Slow dialysis led to the formation of multilamellar liposomes, at increased dialysis rates Hb liposomes became smaller and unilamellar. Hb was enclosed at highest concentrations in larger liposomes, which included the negatively charged lipid phosphatidylserine or phosphatidic acid as a membrane component. Co-encapsulation of the allosteric factor inositol hexaphosphate led to oxygen dissociation curve values almost identical to those of whole blood. The oxygen-release capacity of Hb liposome suspensions in the physiological partial pressure range was comparable to whole blood. Storage of Hb liposomes for 2 months leaves oxygen-carrying characteristics virtually unchanged, with met-Hb levels increasing to only 11% of total Hb. Preparation of Hb liposomes by dialysis of octyl glucoside or C8E4 is a mild and efficient method for encapsulation of Hb. Since these Hb liposomes can be produced in scale-up batch sizes, they are a candidate for use as an oxygen-carrying blood surrogate.