Cationic
reagents are commonly used to facilitate DNA delivery, and transfection
experiments are typically initiated in cell culture where the optimal
charge ratio is determined. While transfection rates are often enhanced
at higher +/– charge ratios, the cellular toxicity associated
with the greater amounts of cationic components at elevated charge
ratios is often not considered. In addition, the prolonged effects
of cationic lipid uptake on cell viability are not evident in a typical
24–48 h transfection experiment. In this study, we compare
the transfection efficiency of cationic lipoplexes to effects on viability
of cultured cells in both the short and long term (7 days). Our results
indicate that, while minimal toxicity is evident 24 h after exposure
to DOTAP-based lipoplexes, cell viability continues to decline and
ultimately compromises reporter gene expression at longer times. Substitution
of a naturally occurring cationic amphiphile, sphingosine, for DOTAP
greatly reduces toxicity and allows high expression to be maintained
over prolonged periods.