Polymerization liposome/lipid-heme as an oxygen transporter under physiological conditions

Copolymerized liposome of 1,2-bis(octadeca-2′,4′-dienoyl)-sn-glycero-3-phosphocholine and sodium 15-(1′-imidazolyl)pentadeca-trans-2,trans-4-dienoate is an effective carrier of [5α,10α,15α,20α-tetrakis [ο-[2′, 2′-dimethyl-20′-[2″-(trimethylammonio)ethyl] phosphonatoxyeicosanamido] phenyl] porphinato] iron(II) (lipid-heme): This polymerized liposome/lipid-heme transports molecular oxygen under physiological conditions (in pH 7, at 37°C). The lipid-heme is embedded and fixed in the bilayer of polymerized liposome based on hydrophilic-hydrophobic balance of the lipid-heme and/or coordination bond between the lipid-heme and the copolymerized imidazole residue. Solution properties of the polymerized liposome/lipid-heme are almost the same as those of human blood, and the solution is able to be stocked for months. Oxygen volume dissolved in the polymerized liposome/lipid-heme solution (100 mL) is determined to be ca. 22 mL by an ¹⁵O radiotracer method and by volumetry, which is comparable with that of human blood. Oxygen-binding affinity and rate constant of the polymerized liposome/lipid-heme are ca. 50 mmHg and 10⁴M^-1s^-1, respectively, which are also similar to those of hemoglobin in blood.