Browsing by Subject "ihmsalkion kantasolu"

Pharmaceutical companies are currently facing increasing developmental costs, and at the same time, less new compounds are being brought to the market. In vitro -metabolism studies and toxicity assessment of new drug candidates are crucial, as early as possible, to prevent their withdrawal in later development phases. Used study systems are, however, limited and new improved technologies are being investigated. Notable, drug induced liver toxicity and alterations in the liver function are frequent reasons for the drug removals from the development. Human embryonic stem cell (hESC) is one of the most powerful cell types known. hESCs have not only the possibility to divide indefinitely but these cells have also the ability to differentiate to all mature cell types of the human body, such as hepatocytes. This makes them potentially very valuable for pharmaceutical development, in order to create a functional in vitro -model, mimicking the liver tissue. In the literature part, the three dimensional (3D) -hepatic differentiation of mouse and human ESCs in vitro, are discussed. Traditional 2D-culture systems do not adequately mimic the microenvironment of three dimensionally organized native tissue. In 2D-cultures cells grow as a monolayer, when the cell morphology is flattened leading to poor cell-cell and cell-matrix contacts and preventing from the tissue formation. In 3D-culture systems, cells are able to form tissue-like cell integrations, spheroids, and thus, remain their functionality and viability significantly longer. Hydrogels are commonly used biomaterials in 3D-cell cultivation and well known in various areas of tissue engineering for their nano scale porosity and ability to surround cells in 3D-polymer network. In addition, they are capable to absorb large volumes of water and functionalized, in various ways, to improve the required biological or mechanical properties. In the experimental part, the main purpose was to differentiate human hepatic progenitor cells to mature hepatocyte-like cells in three dimensional (3D) -biomaterials. Overall, four different hydrogels (cellulose nanofiber (CNF) hydrogel, HydroMatrixTM, ExtracelTM and PuraMatrixTM) were used as 3D-cell culture scaffolds. Several hepatic cell functions (albumin and urea production and cytochrome P450 (CYP) 3A4 activity) were measured in 2D- and 3D-cultures and compared with the human hepatic carcinoma cells, HepG2, which are often used in drug development. Differentiated hepatocyte-like cells did not show CYP3A4 activity and they produced less albumin and urea compared with HepG2 cells. However, working with hESCs is very demanding and the research in this area is only in the beginning. Therefore, the poor cell functionality results did not come up as a surprise.