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Low cholesterol solubility in DODAB liposomes.

Carlos R Benatti1, Richard M Epand, M Teresa Lamy

  • 1Instituto de Física, Universidade de São Paulo, CP 66318, CEP 05315-970, São Paulo, SP, Brazil. benatti@if.usp.br

Chemistry and Physics of Lipids
|November 23, 2006
PubMed
Summary

The study reveals that adding ions stabilizes dioctadecyldimethylammonium bromide (DODAB) liposomes, increasing their transition temperature. Cholesterol

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Area of Science:

  • Lipid bilayer biophysics
  • Membrane biophysics
  • Physical chemistry of lipids

Background:

  • Dioctadecyldimethylammonium bromide (DODAB) is a cationic lipid forming liposomes.
  • Understanding DODAB liposome thermotropic properties is crucial for drug delivery and biomaterial applications.
  • Ionic strength and cholesterol content significantly influence lipid bilayer behavior.

Purpose of the Study:

  • To investigate the thermotropic properties of DODAB liposomes under varying ionic strengths and cholesterol concentrations.
  • To elucidate the phase behavior and structural organization of DODAB bilayers.
  • To determine the impact of ions and cholesterol on the gel/fluid transition temperature (Tm) of DODAB membranes.

Main Methods:

  • Electron Spin Resonance (ESR) spectroscopy using spin labels.
  • Analysis of ESR spectra to probe membrane fluidity and structure.
  • Systematic variation of ionic strength and cholesterol content in DODAB liposomes.

Main Results:

  • Increased ionic strength stabilizes the cationic lipid gel phase, raising the gel/fluid transition temperature (Tm).
  • DODAB membranes exhibit phase coexistence around Tm, even in high ionic strength conditions.
  • Cholesterol exhibits low solubility in DODAB bilayers, leading to domain coexistence at 15 mol% cholesterol. At 45 mol% cholesterol, domain coexistence is no longer detected.

Conclusions:

  • Ionic strength plays a critical role in stabilizing DODAB liposomes and modulating their phase transition temperature.
  • Cholesterol incorporation into DODAB bilayers results in phase separation at lower concentrations, with effects differing at higher concentrations.
  • ESR spin label analysis is effective in characterizing structural changes and phase behavior in complex lipid systems like DODAB.