In the field of gene vaccine, liposomes composed of the ternary lipid composition

egg phosphatidylcholine (EPC), 1,2-dioleoyl-3-trimethylammonium propane (DOTAP) and l-α-dioleoyl phosphatidylethanolamine (DOPE) 2:1:1 molar have been successfully tested in vivo as DNA carriers against Hepatitis B [4] and [5]. see more More recently, the performance of EPC/DOPE/DOTAP carrying DNAhsp65 also against tuberculosis was evidenced by our group [6]. In this last case, the cationic liposomes were electrostatically complexed with DNA and vaccination in one intranasal single dose reduced the DNA dosage by 16 times when compared to the naked DNA. Moreover, the performance of these liposomes, in tuberculosis vaccination, has shown to be superior when compared to other DNA carriers such as (poly dl-lactide-co-glycolide-PLGA/trehalose dimicolate-TDM microspheres) as well as the respective encoding recombinant protein [7]. Despite the promising in vivo results, there is a lack of information about EPC, DOTAP and DOPE specific signaling pathway molecular interactions and surface miscibility, which should be correlated with the surface lipid packing as well as in vitro and in vivo liposome stability and DNA delivery [8] and [9]. The lipids of the ternary

EPC/DOTAP/DOPE mixture have different properties, such as: (i) EPC is a natural zwitterionic phospholipid with broad acyl chain (saturated and unsaturated) distribution; (ii) DOPE is also zwitterionic, though its polar amine headgroup is smaller and has a higher charge density than the choline group; (iii) DOPE and DOTAP are synthetic lipids with one double bond (18:1)

and with the same acyl chain length. (iv) DOTAP is a cationic phospholipid. The differences between these lipids probably result in distinct molecular interactions depending on the lipid composition. The majority of the experimental and theoretical studies on molecular interaction and miscibility are related to binary lipid IMP dehydrogenase mixtures, mostly composed of one cationic and one zwitterionic lipid [10], [11], [12] and [13]. Depending on the type of lipids, the molecular interactions and the monolayer properties are drastically modified. Considering the interaction between two zwitterionic lipids such as EPC and DOPE, there are some studies concerning the specific interactions of synthetic lipids. These systems were reported as non-ideal, for which the existence of intermolecular hydrogen bonds in PE plays an important role in determining the membrane properties [14] and [15]. The specific DOTAP/DOPE monolayer was considered, from a thermodynamic point of view, as an ideal mixture [16].