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Effect of helper lipids on the interaction of DNA with cationic lipid monolayers studied by specular neutron
A P Dabkowska1, D J Barlow, R A Campbell
1Institute of Pharmaceutical Science, School of Biomedical Sciences, King's College London, London, UK.
Insights
DNA interaction with lipid monolayers was quantified. Despite varying DNA amounts and lipid compositions, the DNA layer thickness remained constant, crucial for gene delivery system models.
Area of Science:
- Biophysical Chemistry
- Materials Science
- Nanotechnology
Background:
- Understanding DNA-lipid interactions is key for developing effective gene delivery systems.
- Cationic lipids are commonly used in gene delivery, but their interaction with DNA in multicomponent systems requires further elucidation.
Purpose of the Study:
- To quantify the binding of DNA to cationic lipid monolayers with and without neutral helper lipids.
- To investigate the influence of helper lipids (dioleoylphosphatidylethanolamine, cholesterol) and surface pressure on DNA binding.
- To determine the structural characteristics, specifically the thickness, of the DNA-lipid layer.
Main Methods:
- Specular neutron reflection for quantifying bound DNA.
- Surface pressure-area isotherms to study monolayer behavior.
- Brewster angle microscopy for visualizing monolayer structure.
Main Results:
- DNA binding varied significantly with lipid composition and surface pressure, with dimethyldioctadecylammonium bromide monolayers binding the most DNA.
- DNA content ranged from 8-39 vol% relative to the monolayer.
- The thickness of the DNA-containing layer remained remarkably constant at approximately 18-25 Å, irrespective of DNA binding levels or lipid composition.
Conclusions:
- This study provides the first direct quantification of DNA binding to multicomponent lipid monolayers containing helper lipids.
- The constant layer thickness suggests a robust structural organization of DNA within the lipid monolayer.
- Findings offer critical insights into interaction parameters for advanced gene delivery vector design.
Abstract:
The interaction of DNA with monolayers of the cationic lipid dimethyldioctadecylammonium bromide, with/without 50 mol % of a neutral "helper" lipid, either dioleoylphosphatidylethanolamine or cholesterol, has been studied using specular neutron reflection, surface pressure-area isotherms, and Brewster angle microscopy. The amount of DNA bound to the lipid head groups has been comprehensively quantified in the range of 8-39 vol% of DNA with respect to the monolayer composition (monolayers composed of dimethyldioctadecylammonium bromide binding the most DNA and monolayers containing dioleoylphosphatidylethanolamine binding the least) and surface pressure (DNA binding being greatest at highest surface pressures). Surprisingly, regardless of these variables, the thickness of the DNA-containing layer remained approximately constant between 18 and 25 Å. This systematic study is the first direct quantification of the binding of DNA with two different helper-lipid-containing multicomponent monolayers, an important step toward understanding interaction parameters in more realistic models of gene delivery systems.
