(433b) The Effects of Intermolecular Interactions On Transmission of Plasmid DNA Through Ultrafiltration Membranes

The
effects of intermolecular interactions on transmission of plasmid DNA through
ultrafiltration membranes.

There is considerable interest in
developing new methods for the purification of plasmid DNA for use as gene
therapy agents or DNA-based vaccines.  Several
previous studies have demonstrated that plasmid transmission through an
ultrafiltration membrane occurs by elongation of the plasmid in the converging
flow field into the membrane pore at large filtration flux.  However, these data were obtained with very
dilute DNA solutions, i.e., under conditions where there were no intermolecular
interactions between the DNA molecules. The objective of this work was to
examine the effect of DNA ? DNA interactions during ultrafiltration processes.

Experimental data were obtained
with plasmids from 3.0 and 16.9 kbp (kilo base pairs)
in size using Omega (modified polyethersulfone) ultrafiltration membranes.  In contrast to the behavior with dilute
solutions, the transmission of the plasmid DNA showed a distinct maximum at intermediate
values of the filtrate flux, with the sieving coefficient decreasing to near
zero at very high values of the flux. The critical filtrate flux for plasmid
transmission appears to remain independent of plasmid size, consistent with
results for dilute plasmid solutions. 
However, the maximum plasmid transmission was a strong function of the
plasmid size, with the extent of plasmid transmission decreasing with
increasing plasmid size.  The
experimental results were analyzed using available models for concentrated
polymer solutions to provide additional insights into the effects of intermolecular
interactions on plasmid elongation during ultrafiltration. These results provide
new insights into the factors governing the ultrafiltration of plasmid DNA
solutions.