Effect of cucurbit[7]uril on DPPC-containing liposomes: Interactions with the lipid bilayer

Liposomes, which are bilayer lipidic nanocarriers, have been utilized in many pharmaceutical applications to enhance the solubility and therapeutic index of drugs. Liposomes have also been used as carriers for smaller drug carriers, such as cucurbiturils, to achieve a more controlled release of the drug into the targeted site in the body. In this study, we investigated the effects of cucurbit[7]uril, a macrocyclic organic compound, on the integrity of liposome lipid membranes. The average liposome size, measured by dynamic light scattering, increased with increasing concentrations of cucurbit[7]uril. In addition, fluorescence spectroscopy was used to calculate an association constant (<i>K</i>_a) between cucurbit[7]uril and cholesterol of 3 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>×</mml:mo><mml:msup><mml:mn>10</mml:mn><mml:mn>6</mml:mn></mml:msup><mml:mo>/</mml:mo><mml:mrow><mml:mi>M</mml:mi></mml:mrow></mml:math>. This high <i>K</i>_a value demonstrated the ability of cucurbit[7]uril to reduce liposome stability by extracting cholesterol molecules from the lipid bilayer. Thermogravimetric analysis demonstrated the localization of cucurbit[7]uril molecules on the surface of the liposomes. As the concentration of cucurbit[7]uril increased, the thermal stability increased, i.e. the mass loss of the liposomal suspension decreased. The biocompatibility of cucurbit[7]uril was also investigated using a hemolysis test on human red blood cells. In conclusion, the current study is the first to explain the relationship between lipid membranes and cucurbit[7]uril. The results of this study can be used to develop a new drug delivery system comprising liposomes and cucurbit[7]uril.