Tunable pDNA/DODAB:MO lipoplexes: The effect of incubation temperature on pDNA/DODAB:MO lipoplexes structure and transfection efficiency

• pDNA:DODAB:MO's lipoplexes structure is sensitive to the lipoplex incubation temperature.
• Increase in the incubation temperature has a similar effect on aggregate morphology as the observed with an increase in MO content.
• A phase lipid separation occurs at 50 °C with the migration of DODAB molecules to the lipoplex surface.
• This positive charge re-localization influences the lipoplexes structure, DNA release and cell transfection efficiency.

Dioctadecyldimethylammonium bromide (DODAB):1-monooleoyl-rac-glycerol (MO) cationic liposomes were reported as a promising alternative to common transfection agents, showing superior effectiveness on the transfection of the 293T mammalian cell line with pSV-β-gal plasmid DNA. The study of DODAB:MO aggregates in the absence of DNA has indicated that their morphology depends on the balance between DODAB's tendency to form bilayer structures and MO's propensity to form inverted non-lamellar structures. Other parameters, such as the temperature have proved to be crucial in the definition of the morphology of the developed nanocarrier. Therefore, in this work, a step forward to the current gene carrier system will be given by studying the effect of the tunable parameters (incubation temperature and MO content) on the structure of pDNA:DODAB:MO lipoplexes. More importantly, the implications that these tunable parameters could have in terms of lipoplex transfection efficiency will be investigated. Dynamic light scattering (DLS), zeta (ζ) potential, cryo-transmission electron microscopy (cryo-TEM) and ethidium bromide (EtBr) exclusion were used to assess the formation, structure and destabilization of pDNA:DODAB:MO lipoplexes at DODAB molar fractions of (1:1) and above equimolarity (2:1, 4:1) prepared at incubation temperatures from 25 to 50 °C. Experimental results indicate that pDNA:DODAB:MO's structure is sensitive to the lipoplex incubation temperature, resulting in particles of distinct size, superficial charge and structure. These variations are also visible on the complexation dynamics of pDNA, and subsequent release upon incubation with the model proteoglycan heparin (HEP), at 25 and 50 °C. Increase in temperature leads to re-organization of DODAB and MO molecules within the liposomal formulation, causing a positive charge re-localization in the lipoplex surface, which not only alters its structure but also its transfection efficiency. Altogether, these results confirm that in the DODAB:MO carriers, an increase in the incubation temperature has a similar effect on aggregate morphology as the observed with an increase in MO content. This conclusion is extended to the pDNA:DODAB:MO lipoplexes morphology and subsequent transfection efficiency defining new strategies in lipoplexes preparation that could be used to modulate the properties of other lipid formulations for nonviral gene delivery applications.

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