Thermal stability of DNA in DNA-induced DOTAP liposome aggregates

The influence on the melting of calf thymus DNA induced by cationic liposomes, commonly used in gene therapy, was studied by means of ultraviolet spectrophotometry and differential scanning calorimetry. Both the two methods reveal that DNA in DNA-induced liposome complexes undergoes a denaturation process at a much higher temperature than free DNA does. The extent of protection strongly depends on the charge ratio R(+/-) of liposome-DNA complexes. In the case of dioleoyl trimethyl ammonium propane (DOTAP) liposomes, the maximum of the stabilization occurs at R(+/-)=0.7, where the DNA is still native up to temperatures higher than 100 degrees C. This protection against denaturation up to higher temperatures might be of importance for bio-technological applications, such as biomolecular separation, antigene sequencing and for drug design purpose.