The interaction of DPPC and DPPA liposomes with some ligands; The calorimetric investigation and the structural analysis of formed complexes

Author: Levan Cheishvili
Keywords: DPPC, DPPA, liposomes, cholesterol, calcium, calorimetry
Annotation:

Liposomes represent biocompatible drug carrier nanosystems which are capable to deliver drugs, incorporated in them, unaltered to damaged tissues. One of the goals of the following research was to determine how the thermodynamic nature and the structural organization of liposomes were altered through their interaction with various ligands. Cholesterol and calcium were employed as ligands. In the research we used DPPC (Dipalmitoylphosphatidylcholine) and DPPA (Dipalmitoylphosphatidic acid) liposomes. Moreover, in the research there were used the following appliances: highly-sensitive differential scanning microcalorimeter (DASM-4A, Pushchino, Russia) and conventional rotary evaporator (Buchi, Flawil, Switzerland). Initially, we wanted to find out whether cholesterol would be incorporated into the structure of ready-prepared liposomes or not. We needed it in order to determine the possibility of the incorporation of drugs, which are more or less similar to the structure and the chemical composition of cholesterol, for instance, doxorubicin, into the structure of ready-prepared liposomes in a similar manner. Based on the calorimetric curves, while heating, cholesterol molecules are incorporated into the structure of ready-prepared liposomes. The obtained result allows us to consider the possibility of doxorubicin incorporation into ready-prepared DPPC liposomes in a similar manner. We also wanted to find out whether cholesterol-containing liposomes would be formed without using an evaporator or not. According to results, by mixing DPPC lipids with water(in the presence of cholesterol), DPPC liposomes are still formed without using an evaporator, and later on, a gradual incorporation of cholesterol into newly formed liposomes also takes place during a heating process. That is, the suspension needs to be heated several times in order to occur the incorporation of cholesterol molecules into newly formed DPPC liposomes about in the same amount as in case of ready-prepared DPPC liposomes, prepared without using an evaporator, during the first heating cycle of the suspension. As to the other ligand – calcium – it plays an important role in cell homeostasis. A direct delivery of calcium-containing salts or ionic calcium to damaged tissues by liposomes is a very effective route. Eventually, by the research it’s concluded that the incorporation of ionic calcium into liposomes in this way is highly unrecommended. It’s much wiser to incorporate calcium ions or calcium-containing drugs into liposomes by passive loading technique. It will be much more effective and in terms of the safety of health, risk caused by its presumable side effects, in fact, will be brought to zero.