Browsing by Subject "stabiilisuus"

Proteins are endogenous molecules that carry out most biological functions in vivo. They are called as the biological workhorses. Proteins are made up of polypeptide chains that usually fold in the three dimensional space to adopt a native stable conformation. Stability of proteins is dependent on the interplay of environmental factors (pH, temperature, ionic strength). For most proteins, the biological function closely relates to the structural attributes of the protein. Misfolding or unfolding of proteins often result in aggregation. Protein aggregation in vivo is known to cause debilitating and fatal diseases such as Alzheimer's, Huntington's, Parkinson's and age related macular degeneration (AMD). Instability (physical and chemical) of proteins in vitro is believed to result in aggregation. This is a huge concern for the biopharmaceutical industry as it not only limits the effectiveness of the manufacturing process but also poses a great risk of fatality in vivo due to the immunogenic nature of the aggregates. Mechanisms of protein aggregation are complex and not well understood. Regulatory requirements for patient safety in biopharmaceutical products require characterization and analysis of aggregates in protein drug formulations. This review provides an overview of protein aggregation in general and highlights the different analytical methods used to characterize protein aggregates in biopharmaceuticals. Neurotrophic factors influence survival, differentiation, proliferation and death of neuronal cells within the central nervous system. Human ciliary neurotrophic factor (hCNTF) has neuroprotective properties and is also known to influence energy balance. Consequently, hCNTF has potential therapeutic applications in neurodegenerative, obesity and diabetes related disorders. Clinical and biological applications of CNTF necessitate a recombinant expression system to produce large amounts of functional protein. Previous studies have reported that recombinant expression of CNTF in Escherichia coli (E. coli) was limited by low yields and the need to refold the protein from inclusion bodies. In this report, we describe a strategy to effectively screen fusion constructs and expression conditions for soluble hCNTF production in E. coli. Most conditions tested with the codon optimized hCNTF sequence in fusion with soluble tags resulted in soluble expression of the protein. The construct 6-His-CNTF showed soluble expression in all the conditions tested. Our results suggest that codon optimization of the hCNTF sequence is sufficient for soluble expression in E. coli. The recombinant hCNTF was found to bind to CNTFRα with an EC50 = 36 nM.

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.

The physical stability of plant-based beverages is often weak and is used to be improved by food additives. β-glucan and dextran are hydrocolloids that have been found to increase fluid viscosity and therefore may have the potential to replace E-coded hydrocolloids. The aim of this master's thesis was to investigate the effects of oat β-glucan and microbiologically produced dextran on the physical stability of a drinkable oat snack. In addition, the aim was to determine the importance of the molecular size and concentration of β-glucan for its stabilizing ability. The oat base without any added hydrocolloids served as a control. β-glucan and dextran were added to the oat base as extracts so that they replaced a certain volume of oat base water. To determine the concentration effect of β-glucan, an oat beverage containing a high molecular weight β-glucan extract extracted from oat bran was prepared in three different extract concentrations. To determine the effect of the molecular weight, an oat beverage containing an enzymatically hydrolyzed low molecular weight β-glucan extract was prepared. The effects of dextran were studied by preparing oat beverages containing exopolysaccharide extract (EPS) (dextran positive and negative sample). Samples were stored in a refrigerator for 14 days, during which time their stability was characterized by observing phase separation and measuring viscosity, particle size and turbidity. The stability of the beverage samples decreased because of sedimentation, leading to the visual phase separation at the top of the samples. The high molecular weight β-glucan extracted from the oat bran reduced sedimentation and phase separation, and stability and viscosity increased as the extract concentration increased from 5% to 7.5%, with almost invisible phase separation in the latter. Thereafter, increasing the extract concentration to 10% no longer reduced the phase separation, but resulted in a decrease in viscosity during storage. Low molecular weight β-glucan (extract content 10%) did not increase the stability of the oat base, and the viscosity of the sample decreased by about 60% during storage. The decrease in viscosity in these samples may be due to the aggregation of proteins and / or β-glucan due to the higher β-glucan content. The effects of dextran on the stability of the oat beverage remained unclear, as the dextran-positive and negative samples did not differ significantly in viscosity or phase separation, so further studies are needed. Based on this thesis, high molecular weight β-glucan appeared to be a potential substitute for food additives in oat-based beverage applications.