Polyethyleneimine-DNA Interactions

Abstract

Polyethyleneimine (PEI) is a cationic polymer with primary, secondary and tertiary amino groups separated by an ethylene bridge. PEI is available in both linear and branched forms, and many molecular weight forms are available commercially. PEI is amongst the first and very versatile transfection agents to deliver DNA to cells for gene targeted studies and therapeutic applications. By virtue of their cationic nature under physiologically compatible ionic and pH conditions, PEI can bind with DNA. Using total intensity and dynamic laser light scattering studies, we determined the efficacy of linear (22 kDa and 25 kDa) and branched (0.6 kDa, 1.2 kDa 10 kDa and 25 kDa) PEI to condense a 5256 base pair plasmid DNA (pGL3). Linear PEIs were more efficacious than branched PEIs in condensing plasmid DNA to nanoparticles. EC50 values (concentration of PEI at 50% condensation) were 0.054 and 0.075 microgram per milliliter, respectively, for linear and branched PEIs when the condensing buffer contained 10 mM Na+. Hydrodynamic radii of DNA nanoparticles were comparable (158 nm for linear and 150 nm for branched) when PEIs were used as condensing agents. Straight lines were obtained when log[EC50] was plotted against log[Na+], where Na+ is the sodium ion concentration in the buffer used for plasmid DNA condensation. The slope of this plot, dlog[EC50]/dlog[Na+] is a quantitative measure of the relationship between multivalent and monovalent ions in condensing plasmid DNA. Our results showed a slightly negative (−0.016) slope for 22 kDa and 25kDa linear PEIs and slightly positive (0.033) slope for 25 kDa branched PEI. Taken together, our data show that PEIs are excellent promoters of DNA condensation to nanoparticles. Plasmid DNA condensation might be a possible mechanism by which PEIs drive DNA transportation in cells.