Neutral and Anionic Liposome-Encapsulated Hemoglobin: Effect of Postinserted Poly(ethylene glycol)-distearoylphosphatidylethanolamine on Distribution and Circulation Kinetics

V. D. Awasthi, D. Garcia, R. Klipper, B. A. Goins, W. T. Phillips

Research output: Contribution to journalArticlepeer-review

77 Scopus citations

Abstract

To prepare long-circulating liposomes, poly(ethylene glycol) (PEG)-lipid is usually mixed with other lipid components before vesicle formation. PEG-lipids can also be postinserted in the outer layer of liposomes after the preparation. In this study, PEG-distearoylphosphatidylethanolamine was incorporated by postinsertion technique into liposome-encapsulated hemoglobin (LEH) carrying neutral or negative charge. Postinsertion technique improved the encapsulation efficiency of hemoglobin from about 0.0017 to 0.017 (hemoglobin/phospholipid, molar ratio) for a similar lipid composition. Thus, neutral, anionic, PEG-neutral, and PEG-anionic LEHs were made and labeled with technetium-99m to follow their biodistribution. A small dose of LEH (∼15 mg of phospholipid) was injected intravenously in rabbits, and its distribution was monitored by blood sampling, gamma camera imaging, and tissue radioactivity counting on necropsy. The 24-h blood levels of neutral, PEG-neutral, anionic, and PEG-anionic LEHs were 14, 40.3, 13.1, and 35.7% of injected dose, respectively; calculated T1/2 values of circulation were 8.9, 19.3, 9.6, and 16.5 h, respectively. PEGylatlon also influenced accumulation of LEH in the reticuloendothelial system. Liver uptake of neutral LEH dropped from 52. 1 to 19.1%, whereas that of anionic LEH came down from 35.3 to 11.5% on PEGylation. In contrast, PEGylation increased the spleen uptake by 8.5- and 2.5-fold for neutral and anionic LEH, respectively. The results demonstrate that PEGylation by postinsertion not only improves the circulation t 1/2 of LEH but also enhances hemoglobin content inside the vesicles for better oxygen-carrying capacity.

Original languageEnglish (US)
Pages (from-to)241-248
Number of pages8
JournalJournal of Pharmacology and Experimental Therapeutics
Volume309
Issue number1
DOIs
StatePublished - Apr 1 2004

ASJC Scopus subject areas

  • Molecular Medicine
  • Pharmacology

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