Poly(ethylene glycol)-conjugation and deoxygenation enable long-term preservation of hemoglobin-vesicles as oxygen carriers in a liquid state

The stability of hemoglobin vesicles (HbV) as an oxygen infusion was tested during the storage for 1 year at 4, 23, and 40 degrees C. The surface of t he HbV was modified with poly(ethylene glycol) (PEG), and the suspension wa s deoxygenated with nitrogen bubbling. The samples stored at 4 and 23 degre es C showed a stable dispersion state for 1 year, though the sample stored at 40 degrees C showed the precipitation and decomposition of vesicular com ponents, a decrease in pH, and 4% leakage of total Hb after 1 year. The PEG chains on the vesicular surface stabilize the dispersion state and prevent the aggregation and fusion due to their steric hindrance. The original met Hb content (ca. 3%) before the preservation gradually decreased to less tha n 1% in all the samples after 1 month due to the presence of homocysteine i nside the vesicles which consumed the residual oxygen and gradually reduced the trace amount of metHb. The rate of metHb formation was strongly depend ent on the partial pressure of oxygen, and no increase in metHb formation w as observed due to the intrinsic stability of the deoxygenated Hb. Preserva tion at 4 and 23 degrees C slightly reduced P-50 (increased the oxygen affi nity) from 38 Torr to 32 and 31 Torr, respectively. These results indicate the possibility that HbV suspension can be stared at room temperature for a t least I year.