Liposome complexation efficiency monitored by FRET

Authors: Catarina Madeira Luís M S Loura Manuel Prieto Aleksander Fedorov M Raquel AiresBarros

Publish Date: 2007/01/30

Volume: 36, Issue: 6, Pages: 609-620

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Abstract

Cationic lipid/DNA complexes lipoplexes are promising vehicles for DNA vaccines or gene therapy In these systems transfection efficiency is highly related to lipoplex charge ratio since lipoplexes with charge ratios ± lower than electroneutrality have most DNA uncovered by the liposomes and thus are unprotected from enzyme degradation However a large excess of cationic lipids is undesirable because of eventual cytotoxicity The aim of this work was to determine the minimum charge ratio from which all DNA molecules are complexed by the liposomes varying the lipid formulation and plasmid size using a new FRET fluorescence resonance energy transfer methodology The similarity of FRET results fluorescence intensity data and fluorescence decays of several charge ratios above ± ≥ 4 or 5 confirmed that once all DNA is covered by the liposomes additional lipid molecules do not affect the lipoplex multilamellar repeat distance It was also verified by FRET that the presence of helper lipid reduces the amount of cationic lipid required for DNA protection but does not affect the lipoplex multilamellar repeat distance This distance varies with the plasmid size when supercoiled plasmid is used being apparently larger when longer plasmids are used Our study indicates that despite the complexity of these systems not being totally described by our model FRET is an informative technique in lipoplex characterization

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