PEGylated cationic liposome-DNA complexation in brine is pathway-dependent.
Cationic liposome-DNA (CL-DNA) complexes, are regarded as promising materials for safe and efficient delivery of genes for therapeutical applications. In order to be used in vivo, these complexes may be coated with a hydrophilic polymer (e.g. polyethylene-glycol, PEG) that provides steric stabilization towards adhesion of proteins and removal by the immune system. In this work we study the influence of the initial salt concentration (Cs) - which modulates the electrostatic interaction between oppositely charged vesicles and DNA - on the structure and stability of PEGylated CL-DNA particles. Previous small-angle X-ray scattering has shown that if non-PEGylated or PEGylated CL-DNA lamellar complexes are prepared in water, their structure is well defined with a high number of lipid membrane-DNA layers (larger than 20). Here we show that if these complexes are transferred to saline media (150mM NaCl or DMEM, both near physiological conditions), this structure remains nearly unchanged. Conversely, if PEGylated complexes are prepared in saline media, their lamellar structure is much looser, with fewer number of layers. This pathway dependent behavior of PEGylated complex formation in brine is modulated by the liposome membrane charge density and the mole fraction of PEG 2000 in the membranes, with the average number of layers decreasing with increasing Cs and in going from 5mol% to 10mol% PEG-lipid. Each of these structures (high and low number of layers) is stable with time, suggesting that despite complex formation being thermodynamically favored, the complexation process in PEGylated membranes, which determines the number of layers per particle, is kinetically controlled. In the extreme case (when polymer repulsions from 10mol% PEG-lipid are maximized and electrostatic attraction between PEGylated CLs and DNA are minimized at low membrane charge density) complex formation is suppressed at high Cs=150mM.
Department of Materials, University of California, Santa Barbara, CA 93106, USA; Department of Physics, University of California, Santa Barbara, CA 93106, USA; Molecular, Cellular & Developmental Biology Department, University of California, Santa Barbara, CA 93106, USA; Division of Physical Chemistry, Centre for Chemistry and Chemical Engineering, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden. Electronic address: brunobrasdasilva@gmail.com.
Bruno F B
BF
Silva
Ramsey N
RN
Majzoub
Chia-Ling
CL
Chan
Youli
Y
Li
Ulf
U
Olsson
Cyrus R
CR
Safinya
D000818:Animals; D002412:Cations; D002417:Cattle; D004247:DNA / Q000737:chemistry*; D005229:Fatty Acids, Monounsaturated / Q000737:chemistry*; D018014:Gene Transfer Techniques; D057927:Hydrophobic and Hydrophilic Interactions; D008081:Liposomes / Q000737:chemistry*; D010713:Phosphatidylcholines / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry*; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012492:Salts / Q000737:chemistry*; D053838:Scattering, Small Angle; D055672:Static Electricity; D013816:Thermodynamics; D014961:X-Ray Diffraction
D002412:Cations; D005229:Fatty Acids, Monounsaturated; D008081:Liposomes; D010713:Phosphatidylcholines; D000644:Quaternary Ammonium Compounds; D012492:Salts; C017082:brine; D011092:Polyethylene Glycols; D004247:DNA; C427203:calf thymus DNA; C017251:1,2-oleoylphosphatidylcholine; C070046:1,2-dioleoyloxy-3-(trimethylammonium)propane
CL–DNA; Gene therapy; Lipoplex; SAXS; Salt; Steric stabilization