Browsing by Subject "intestinal absorption"

Sort by: Order: Results:

Now showing items 1-2 of 2
  • Koskenkorva, Tiina (Helsingfors universitet, 2012)
    Elucidation of transporter- and/or metabolic enzyme-mediated drug interactions is important part of early drug development. However the knowledge about clinical consequences of transporter-mediated drug-drug interactions is still limited and more investigation is needed to improve our understanding. MDR1 transporter, widely distributed on the pharmacokinetic barriers in the body (e.g. intestine) and has been shown no limit the bioavailability of drugs. Substrates of MDR1 are exposed to limited intestinal drug absorption and intestinal drug-drug interactions due to inhibition of the transporter. In predicting the clinical significance of an interaction, the principal obstacle has been the limited ability to appropriately scale the preclinical data into in vivo situation. In vitro-in vivo correlations on the extent of MDR1's influence on absorption and standardized predicting methods for drug-drug interactions using the inhibitory constants (IC50 and Ki) would greatly increase the value of in vitro studies. Current in vitro and in silico methods for prediction of the influence of MDR1 on intestinal absorption and related drug-drug interactions are discussed in the literature review. In addition, the latest regulatory draft guidances (FDA, EMA) are reviewed. Aliskiren has been shown to be a sensitive MDR1 substrate in vivo and high affinity substrate for the transporter in vitro. The objective of the experimental work was to study the MDR1-mediated transport of aliskiren and the related drug-drug interactions in vitro and in silico. Vesicular transport assay was used to obtain kinetic parameters for aliskiren (Km and Vmax) and inhibitor potencies (IC50) for ketoconazole, verapamil, itraconazole and its metabolite hydroxyitraconazole. Ki was further calculated for itraconazole and hydroxyitraconazole. Aliskiren showed high affinity to MDR1 transporter with a Km value 5 µM, consistent to what was reported previously in different assay systems. The interactions between aliskiren and the inhibitors in vitro correlated to the observed interactions in vivo in humans. In addition, hydroxyitraconazole was shown to be a potent inhibitor of MDR1-mediated transport of aliskiren in vitro. This suggests that hydroxyitraconazole may contribute to the pronounced interaction observed between aliskiren and itraconazole in a clinical interaction study. A compartmental absorption and transit (CAT) model with added enterocyte compartments and MDR1 efflux was used to describe the influence of MDR1 on intestinal absorption of aliskiren in humans. The integration of kinetic parameters (Km) from in vitro studies requires further optimization on how to describe the intracellular drug concentrations in the model. Aliskiren is however suitable MDR1 probe substrate to be used in in vitro and in vivo trials in humans and therefore gives a good basis for developing vitro-in vivo predictive models.
  • Hallila, Susanna (Helsingfors universitet, 2013)
    There is a strong need for new in vitro methods in early drug development that predict in vivo conditions more reliably. One of the prerequisites for successful drug therapy is sufficient permeability. A drug needs to be transported through a cell membrane before it can have a pharmacological effect. Therefore, the drug-cell interactions are studied in the early stage of the drug development process. The literature review of this work covers the traditional in vitro and in silico methods of predicting the permeability of drugs across the intestinal membrane. The widely applied methods are reviewed briefly and the predictability of the methods is evaluated. Moreover, the surface plasmon resonance (SPR) technique is introduced. The principle of SPR and its applications for predicting intestinal permeability using lipid membranes resembling the intestinal membrane and for studying drug-cell interactions are discussed. The advantage of the SPR technique is that it is an optical method which allows real-time monitoring under a constant flow without labeling agents. The aim of the experimental part of this work was to evaluate the suitability of the SPR technique for cell-based studies to monitor drug-cell interactions in native cellular environments. Previously, the SPR technique has been almost merely used in routine biomolecular interaction analysis. Recently, the SPR technique has also been applied to cellbased assays but in those studies the reason for the SPR signal responses is generally poorly discussed. The objective of the experimental study was to evaluate and optimize different cell culturing approaches for living cell sensing for SPR, i.e. cells immobilized on the roof of the PDMS molded flow channel in the SPR instrument and cells immobilized directly on the SPR sensor surface. ARPE-19 cells were immobilized on the PDMS substrates but the challenge of imaging cell monolayers on PDMS molded SPR flow channels suggested that immobilizing the cells directly on the SPR sensor surface would be a more straightforward procedure. Hence, ARPE-19 and MDCKII cell culturing protocols were optimized for successful immobilization of confluent cell monolayers directly on the SPR sensor surface. However, ARPE-19 cells showed poor resistance against shear stress in the flow channel; whereas MDCKII cells showed much better resistance against shear stress in the flow channel. Therefore, only MDCKII cells immobilized on the SPR sensor surfaces were used for drug-cell interaction studies. After three days of culture MDCKII cells were exposed to test compounds in separate SPR measurements. The used test compounds were propranolol, D-mannitol, D-glucose and HSPC:Chol liposomes. During the SPR measurements, the changes in the SPR peak minimum angular position and SPR peak minimum intensity were recorded in real-time, and these were further used for analysis after the measurements. The results showed that clear differences in both SPR signals between propranolol and D-mannitol were observed when the cells were exposed to the test compounds. Propranolol diffuses effectively by the transcellular pathway into cells whereas D-mannitol uses the paracellular pathway. This indicates that the introduced SPR approach may be a potential in vitro method in order to provide real-time information on the permeability of drugs and possibly on cell uptake mechanisms of nanoparticles for a better mechanistic understanding of drug-cell interactions on a cellular level.