Effect of grafted PEG on liposome size and on compressibility and packing of lipid bilayer

Olga Garbuzenko, Yechezkel Barenholz*, Aba Priev

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

264 Scopus citations

Abstract

The aim of this study was to elucidate the effect of various mole percentages (0-25 mol%) of 2000 Da polyethylene glycol- disteroylphosphoethanolamine (PEG-DSPE) in the presence or absence of 40 mol% cholesterol and the effect of degree of saturation of phosphatidylcholine (PC) on the size and the lipid bilayer packing of large unilamellar vesicles (LUV). Egg PC (EPC, unsaturated) LUV and fully hydrogenated soy PC (HSPC, saturated) LUV partial specific volume, specific compressibility, size, and packing parameter (PP) of lipids were characterized by measurements of density, ultrasonic velocity, specific turbidity, and dynamic light scattering. Liposome size and specific turbidity decreased with increase in temperature and PEG-DSPE mol%, except at 7 ± 2 mol%. At this PEG-DSPE mol%, an anomalous peak in liposome size of 15 ± 5 nm was observed. We attribute this effect mainly to the change in the spatial structure of the PEG-DSPE molecule, depending on whether the grafted PEG is in the mushroom or brush configuration. In the mushroom regime, i.e., when the grafted PEG is up to 4 mol% in LUV, the PEG moiety did not affect the additive PP of the lipids in the bilayer, and the PP value of PEG-DSPE is 1.044; while in the brush regime, i.e., when the grafted PEG is higher than 4 mol%, the PP of PEG-DSPE decreases exponentially, reaching the value of 0.487 at 30 mol% of grafted lipopolymer. The specific compressibility and additive PP values for the mixture of matrix lipid (EPC or HSPC), cholesterol, and PEG-DSPE for all liposome compositions investigated reached their maximum at 7 ± 2 mol% PEG-DSPE, the concentration of PEG-DSPE at which the highest biological stability of the LUV is achieved.

Original languageAmerican English
Pages (from-to)117-129
Number of pages13
JournalChemistry and Physics of Lipids
Volume135
Issue number2
DOIs
StatePublished - Jun 2005

Bibliographical note

Funding Information:
This study was supported by United States – Israel Binational Science Foundation Grant 1999324. NDT Instruments (Jerusalem, Israel) is acknowledged for supplying the small volume ultrasonic cell used. We thank Mr. Sigmund Geller for editorial assistance.

Keywords

  • Bulk compressibility
  • Liposome size
  • PEG-DSPE packing parameter

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