Lipid microsphere containing lipophilic heme: preparation and oxygen transportation under physiological conditions

Lipophilic heme (1-laurylimidazole-ligated 5,10,15,20-tetrakis(α,α,α,α-o-pivalamidophenyl)porphinatoiron(II) complex) is solubilized in lipid (triglyceride) at high concentrations and emulsified with a phospholipid in physiological salt solution, giving a deeply red-colored suspension of lipid microspheres (approx. 250 nm in diameter). The heme forms an oxygen adduct in a similar manner as oxyhemoglobin and the lipid microspheres take up and release oxygen reversibly at 37°C in the aqueous medium. The oxygen-transporting ability is comparable with that of the red blood cell. Intravenous injection of the heme/lipid microsphere solution to rabbits demonstrates that it transports oxygen even in vivo and that it is cleared from the blood stream with a half-life time of approx. 1 h.