Browsing by Subject "p-glycoprotein"

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  • Sjöstedt, Noora (Helsingfors universitet, 2011)
    The blood-brain barrier (BBB) is a unique barrier that strictly regulates the entry of endogenous substrates and xenobiotics into the brain. This is due to its tight junctions and the array of transporters and metabolic enzymes that are expressed. The determination of brain concentrations in vivo is difficult, laborious and expensive which means that there is interest in developing predictive tools of brain distribution. Predicting brain concentrations is important even in early drug development to ensure efficacy of central nervous system (CNS) targeted drugs and safety of non-CNS drugs. The literature review covers the most common current in vitro, in vivo and in silico methods of studying transport into the brain, concentrating on transporter effects. The consequences of efflux mediated by p-glycoprotein, the most widely characterized transporter expressed at the BBB, is also discussed. The aim of the experimental study was to build a pharmacokinetic (PK) model to describe p-glycoprotein substrate drug concentrations in the brain using commonly measured in vivo parameters of brain distribution. The possibility of replacing in vivo parameter values with their in vitro counterparts was also studied. All data for the study was taken from the literature. A simple 2-compartment PK model was built using the Stella™ software. Brain concentrations of morphine, loperamide and quinidine were simulated and compared with published studies. Correlation of in vitro measured efflux ratio (ER) from different studies was evaluated in addition to studying correlation between in vitro and in vivo measured ER. A Stella™ model was also constructed to simulate an in vitro transcellular monolayer experiment, to study the sensitivity of measured ER to changes in passive permeability and Michaelis-Menten kinetic parameter values. Interspecies differences in rats and mice were investigated with regards to brain permeability and drug binding in brain tissue. Although the PK brain model was able to capture the concentration-time profiles for all 3 compounds in both brain and plasma and performed fairly well for morphine, for quinidine it underestimated and for loperamide it overestimated brain concentrations. Because the ratio of concentrations in brain and blood is dependent on the ER, it is suggested that the variable values cited for this parameter and its inaccuracy could be one explanation for the failure of predictions. Validation of the model with more compounds is needed to draw further conclusions. In vitro ER showed variable correlation between studies, indicating variability due to experimental factors such as test concentration, but overall differences were small. Good correlation between in vitro and in vivo ER at low concentrations supports the possibility of using of in vitro ER in the PK model. The in vitro simulation illustrated that in the simulation setting, efflux is significant only with low passive permeability, which highlights the fact that the cell model used to measure ER must have low enough paracellular permeability to correctly mimic the in vivo situation.
  • Tepponen, Tuomas (Helsingfors universitet, 2017)
    Multidrug resistance protein 1 (MDR1, p-glycoprotein) belongs to the ATP-binding cassette transporter family and it's encoded by ABCB1/MDR1 gene. It is a protein which transports many different kinds of compounds out of cells, for example from endocytes to the lumen with the use of energy from ATP. MDR1 is there for a restrictive factor for several orally administered drugs. It`s important to have knowledge about MDR1-inhibitors, in order to avoid harmful drug-drug and food-drug interactions that might affect medical treatment. The purpose of this master's thesis was to optimize an in vitro MDR1-vesicle uptake method and use it to screen inhibitors from compound libraries. To optimize the method, the effect of cholesterol loading on ATP-dependent transport of test substrate N-methylquinidine (NMQ) was evaluated, transport kinetics of the vesicles and kinetics of known inhibitors were also tested. With the optimized method, screening was done with a library of 25 food additives and a library of 42 synthetic compounds. The chemical structures of the synthetic compounds were analyzed manually in order to find factors that could explain their ability to inhibit MDR1. Only one inhibitor was found among food additives: curcumin. Other additives didn't increase or decrease the ATP-dependent transport of NMQ. Several inhibitors were found from the library of synthetic compounds, also a couple of compounds were found to increase the active transport of NMQ. Results indicate, that the additives used in this study have low risk to cause MDR1 mediated interactions, if curcumin is excluded. The inhibitory effect of curcumin should be investigated in in vivo-situation, because vesicle-based in vitro-results have tendency to overestimate results. Screening results of the synthetic compounds gives more confirmation to the usefulness of the screening method. The MDR1-inhibition screening method described in this Master`s thesis is valid, and it can be used to screen different compound libraries for MDR1-inhibitors. In the future it could be used to screen different kinds of compounds, which might end up inside humans and cause interactions with drugs.