Browsing by Subject "drug release"

Liposomes are nanosized drug delivery vesicles composed of phospholipid membranes. They present an attractive drug delivery system due to their bioavailability and flexibility. Liposomes can be prepared by different techniques. They can carry both hydrophobic and hydrophilic molecules and their surface can be modified with targeting molecules. Coating the liposome surface with the PEG derivative makes their pharmacokinetics easier to predict. There are several liposome-based medicinal products already on the market. Triggering of drug delivery systems by different external or internal stimuli allows precise control of drug release. Light-triggered drug release is an attractive alternative due to the easy control and regulation of the stimulus. The problem with light-triggered therapy has previously been the need to use high-energy ultraviolet light that penetrates badly to the tissues and is not safe. In TTA-UC process the low-energy red or green light is converted to high-energy blue light. In this process photosensitive molecules are excited by visible light and after that the energy is transferred from sensitizer to annihilator molecules. Collision of two annihilators leads to the excitation of the other molecule while the other returns back to its general energy state. The excitation breaks up with fluorescence. In this process the highly permeable and safe red light is converted to blue light which has enough energy to induce drug release. The aim of this work was to optimize liposomal preparation method and prepare a pegylated and stabile liposome formulation for TTA-UC process. Hydrophobic light sensitive molecules were loaded into the phospholipid membrane as much as possible. One of the problems in this work was to find proper methods to measure the concentrations of these molecules. The lipid composition for formulation was chosen after thermostability studies. As a quality control, the size, capability to load calcein and phase transition temperature of liposomes were measured. The quality control of light sensitive molecules was operated too. In this work, the formulation for TTA-UC was prepared. In further studies TTA-UC process happened with sufficient efficacy. The formulation was pegylated and stable in physiological conditions and the concentrations of the molecules were high enough. This was the very first time to get TTA-UC to happen in this kind of liposome formulation that may be useful as a drug carrier. Long-term stability studies and further optimization of TTA-UC method are needed in the future. Some drug release studies are important to arrange in the future, too.

Liposomes are nano-sized vesicles in which the aqueous phase is surrounded by lipid-derived bilayer. They are excellent drug vehicles for example in ocular drug delivery because they can, among other things, increase the bioavailability and stability of the drug molecules and reduce their toxicity. Liposomes are known to be safe to use, because they degrade within a certain period of time and they are biocompatible with the cells and tissues of the body. Owing to its structure, the surface of liposomes can also be easily modified and functionalized. Light-activated ICG liposomes allow drug release in a controlled manner at a given time and specific site. Their function is based on a small molecule called indocyanine green (ICG) which, after being exposed to laser light, absorbs light energy and thereby locally elevates the temperature of the lipid bilayer. As a result, the drug inside is released into the surroundings. The blood circulation time of liposomes has often been prolonged by coating the liposomes with polyethylene glycol (PEG). Although PEG is generally regarded as a safe and biocompatible polymer, it has been found to increase immunological reactions and PEG-specific antibodies upon repeated dosing. Conversely, hyaluronic acid (HA), is an endogenous polysaccharide, which is present in abundance for instance in vitreous. Thus, it could serve as a stealth coating material which extends the otherwise short half-life of liposomes. One of the main objectives of this thesis was to find out whether HA could be used to coat liposomes instead of PEG. In order to prepare HA-coated liposomes, one of the lipid bilayer phospholipids, DSPE, had to be first conjugated with HA. For the conjugation, potential synthesis protocols were sought from the literature. Ultimately two different reductive amination-based protocols were tested. Consequently, the protocol in which the conjugation was achieved via the aldehyde group of HA, proved to be working. Thereafter, HA-coated liposomes were prepared by thin film hydration from the newly synthesised conjugate as well as DPPC, DSPC and 18:0 Lyso PC. Calcein was encapsulated in the liposomes. HA-covered liposomes were then compared with uncoated and PEGylated liposomes by examining their phase transition temperatures, ICG absorbances, sizes, polydispersities, and both light and heat-induced drug releases. The aforementioned tests were also conducted when the effects of the HA and ICG doubling were examined and the possibility to manufacture HA liposomes with small size was assessed. HA-liposomes showed similar results as PEG-coated liposomes. In addition, successful extrusion of HA-liposomes through a 30 nm membrane was also demonstrated in the results. Doubling of HA did not significantly affect the results. In contrast, increasing the molar amount of ICG by double caused spontaneous calcein leakage even before any heat or light exposure. Based on these findings, HA could work as a coating material instead of PEG, yet further studies are required for ensuring this conclusion. The other key objective was to evaluate the stability of four different formulations, named as AL, AL18, AL16 and AL14, in storage and biological conditions. Based on the differences in the formulation phospholipid composition, the assumption was that AL would be the most stable of the group and that the stability would decrease so that AL18 and AL16 would be the next most stable and eventually AL14 would be the least stable formulation. As in the previous study, the liposomes were prepared by thin film hydration with calcein being encapsulated inside the liposomes. In the storage stability test, liposomes were stored in HEPES buffer at either 4 °C or at room temperature for one month. In the test conducted in physiological conditions, the liposomes were added either to porcine vitreous or fetal bovine serum (FBS) and the samples were incubated at 37 ºC for five days. Regardless of the experiment, phase transition temperatures as well as light and heat-induced drug releases were initially measured. As the test progressed, calcein release, ICG absorbance, size, and polydispersity were measured at each time point. The initial measurements confirmed the hypothesis about the stability differences of tested formulations. In the storage stability test, all formulations, except AL14, appeared to be stable throughout the study and no apparent differences between the formulations or temperatures were observed. On the other hand, the stability of liposomes stored in biological matrices varied so that the liposomes were more stable in vitreous than in FBS and the stability decreased in both media as expected.