Salt ions and related parameters affect PEI-DNA particle size and transfection efficiency in Chinese hamster ovary cells.

Transfection efficiency is directly associated with the expression level and quantity of recombinant protein after the transient transfection of animal cells. The transfection process can be influenced by many still-unknown factors, so it is valuable to study the precise mechanism and explore these factors in gene delivery. Polyethylenimine (PEI) is considered to have high transfection efficiency and endosome-disrupting capacity. Here we aimed to investigate optimal conditions for transfection efficiency by setting different parameters, including salt ion concentration, DNA/PEI ratio, and incubation time. We examined the PEI-DNA particle size using a Malvern particle size analyzer and assessed the transfection efficiency using flow cytometry in Chinese hamster ovary-S cells. Salt ions, higher amounts of PEI tended to improve the aggregation of PEI-DNA particles and the particle size of PEI-DNA complexes and the transfection efficiency were increased. Besides, the particle size was also found to benefit from longer incubation time. However, the transfection efficiency increased to maximum of 68.92 % at an incubation time of 10 min, but decreased significantly thereafter to 23.71 %, when incubating for 120 min (P < 0.05). Besides, PEI-DNA complexes formed in salt-free condition were unstable. Our results suggest DNA and PEI incubated in 300 mM NaCl at a ratio of 1:4 for 10 min could achieve the optimal transfection efficiency. Our results might provide guidance for the optimization of transfection efficiency and the industrial production of recombinant proteins.