(155g) Use of Liposome Encapsulated Hemoglobin (Leh) as an Oxygen Carrier to Cultured Cells

Oxygen supply to cultured cells is the most crucial issue in engineering large-scale and high-cell-density organ equivalents in vitro. The fact that usual culture medium holds only a small concentration of oxygen according to the Henry's low leads us to include hemoglobin-based oxygen carriers in culture medium. However, red blood cells show toxicity due to the free hemoglobin when they are broken up. Therefore, in this study, we investigated the feasibility of liposome-encapsulated hemoglobin (LEH), which was initially developed by Oxygenix Co. Ltd (Tokyo, Japan) for infusion to human patients, as an oxygen carrier to liver-derived cells. First, we investigated LEH's possible toxicity to cultured cells including both hepatoma Hep G2 cells and primary rat hepatocytes, when it comes into contact in a direct manner, that is, supplementation to the culture medium. We used a new type of LEH, in which the outer surfaces of the phospholipids bilayers of the capsules in a mean diameter of 269 nm are further modified with polyethyleneglycol to extend its in vivo residence time. Although cytotoxicities were observed in monolayer-cultured hepatoma Heg G2 cells which may have an abnormally increased lipid intake capability, there is no cytoxicities to monolayer-cultured rat hepatocytes. Second, using a flat-plate bioreactor to form an oxygen gradient in a small-scale culture, we investigated the effects of LEH on the morphologies and functions of rat hepatocytes. Direct supplementation of LEH to the culture medium completely recovered the deteriorated morphology and functions observed in the culture areas, near the outlet of the bioreactor, where oxygen is in shortage. These results first demonstrate the high feasibility of LEH uses in direct supplementation to culture medium and show a promise in engineering large-scale organ equivalents in vitro.