Study of interaction between liposomes abd plasmid DNA: Hydrophobicity and Circular Dichroism

NADIA S. CHIARAMONI; LETICIA C. BACCARINI; MARÍA C. TAIRA; SILVIA DEL V. ALONSO

Montevideo, Uruguay

Congreso; 6th International Conference of biological Physics, 5th Southern Cone Biophysical Congress, 34th Annual Meeting of the Argentinean Biophysical Society, ICBP2007; 2007

Study of the interaction between liposomes and plasmid DNA: Hydrophobicity and Circular Dichroism. Chiaramoni, N.S., Bacarinni, L.C., Taira, M.C., and Alonso, S. Previous studies indicate that liposomes can associate DNA (Gregoriadis et al. 1996). But little is known about this association. We analyzed three liposomes formulations: cationic (EPC:DOPE:DOTAP 16:8:1 molar|ratio); non-charged (EPC:DMPE:Chol 2:2:1 molar ratio) and polymeric (DC8,9PC:DMPE:Chol 2:2:1 molar ratio, irradiated with uv light). We studied the conformation that adopts DNA with liposomes by circular dichroism. Spectra between 190 and 320 nm were analyzed during a titration with 0.2 to 1 mM of liposomes. The 275 nm band was analyzed: absence indicates change in the baise pair number per turn of the double helix; increase indicates B to A passage. We obtained a decrease in the baise pair number in the case of cationic and a less significant change in the case of non-charged: obtained spectra could correspond to an intermediate state between B and A. These results are in agreement with Zuidam and co-workers (1999): DNA conformation doesn’t change significantly with non-charged liposomes but its suffers a condensation in presence of DOTAP. We won’t be able to perform CD of polymeric liposomes because of the high scattering but they has low association efficiency so DNA conformation should not change significantly. Changes in membrane hydrophobicity were analyzed to see if there is any correlation with DNA conformation. Results indicated that cationic liposomes had the highest HF, followed by non-charged liposomes. These results are in agreement with Bennett and co-workers (1997): lipids containing oleoyl groups had more associated water than lipids containing myristoyl gropus. Polymeric liposomes had a very low HF, indicating a high rigidity (Alonso-Romanowsky et al. 2003). Obtained results indicate that could be a correlation between membrane rigidity and DNA conformation: with high HF DNA suffers a condensation and this could produce a better association to liposomes. References: Alonso-Romanowski, S., Chiaramoni, N.S., Lioy, V.S., Gargini, R.A., Viera, L.I., and Taira, M.C. (2003). Chem. Phys. of Lipids. 122:191-203. Bennett, M.J., Aberle, A.M., Balasubramaniam, R.P., Malone, J.G., Malone, R.W., Nantz, M.H. (1997). J. Med. Chem. 40: 4069-4078. Gregoriadis G, Saffie R, Hart SL (1996). J Drug Target 3: 469-475 Zuidam, N.J., Barenholz, Y., and Minsky, A. (1999). FEBS Letters. 457: 419-422.