What methods exist to remove endotoxin contamination of plasmid DNA?
Endotoxin (lipopolysaccharide or LPS) is a cell wall component of all Gram negative bacteria such as E. coli. Endotoxin is a potent stimulator of the mammalian immune system in vivo, and it may decrease tissue culture cell viability and inhibit transfection efficiency in vitro. Significant amounts of endotoxin are released from E. coli during plasmid purification. Due to the large size of the micelles formed by endotoxin and the negative charges associated with it, endotoxin can carry over with plasmid DNA isolated by CsCl banding, anion-exchange and silica-gel purification methods (1-3). In some cases endotoxin contamination can be as high as 1,000-1,500EU/g of plasmid. For maximum consistency and when transfecting a broad variety of cell lines, it is best to use plasmid DNA containing as little endotoxin as possible.
