Browsing by Subject "inhibition"
Now showing items 1-2 of 2
-
(2015)MRP2 is an efflux-transporter from the group of ABC-transporters located in the apical side of cell membranes mainly in the liver, intestine, kidneys and lungs. This transporter is associated with multidrug resistance, a phenomenon where the absorption of a drug to the cell is prevented by the transporter as it transports the compound out of the cell. To overcome this phenomenon, inhibitors and substrates for MRP2 are constantly studied. Several flavonoids have been presented of being inhibitors and the research of these compounds continues. Pharmaceutical excipients are also another major group of compounds that possess inhibitory effects towards MRP2. Excipients, as well as flavonoids, are an increasingly studied section of drug interactions and today it may be evaluated that excipients are not thought as inert compounds as has been presented for several years. For now the research of MRP2 interactions focuses mainly on in vitro studies. In the experimental part of this thesis the effects of natural compounds and pharmaceutical excipients are studied towards MRP2 with the vesicular transport assay (VT-assay) with MRP2- Spodoptera frugiperda 9 (Sf9)-membrane vesicles using 5(6)-carboxy-2,'7'-dichlorofluorescein (CDCF) as probe. A total of 157 compounds are screened using this in vitro method and hits are further experimented studying IC50 and Ki values. Potential compounds are also tested with two types of particle size measurements (Dynamic light scattering and nephelometer) to evaluate inhibition caused by microaggregates. Some compounds are also studied with liquid chromatograph-mass spectrometry (LC-MS) to determine possible substrates for MRP2. 19 (12%) hits were found from the library of 157 compounds. These hits included 6 stimulators (CDCF transport increased ≥ 150%) and 13 inhibitors (CDCF transport decreased ≤ 50%). IC50 determination was conducted for 12 inhibitors with best-fit values of: Ellagic acid 10.4 µM, gossypin 17.4 µM, morin dihydrate 19.4 µM, myricetin 27.1 µM, nordihydroguaiaretic acid (NDGA) 36.2 µM, octyl gallate 20.3 µM, silybin 52.3 µM, pluronic ®F98 6.9 µM, lutrol F127 ~ 8.2 µM and tannic acid 1.99 µM. Ki determination was conducted for 3 compounds where best-fit values were myricetin 42.9 ± 47.4 µM, gossypin 19.4 ± 12.5 µM and tannic acid 0.0538 ± 0.0398 µM. Ki determination allowed determination of inhibition type: competitive inhibition for tannic acid and gossypin, noncompetitive inhibition for myricetin. Particle sizes studied with dynamic light scattering (DLS) and a nephelometer did not show any significant aggregate formation and inhibition by that mechanism can be ruled out granted that the measurement method should be optimised. Stimulators baicalein, baicalin, digitoxigenin and inhibitors myricetin, gossypin and tannic acid were studied finally with the VT-assay with LC-MS as detector in search of substrates for MRP2. With significant changes in ‚àíATP and +ATP at 50 µM was gossypin. To conclude, gossypin possesses competitive inhibition towards MRP2 and exhibits sings of being a substrate for the transporter as well. Further studies need to be performed to confirm these findings.
-
(2022)OATP2B1 is a transmembrane transport protein expressed widely in the human body and transports both endogenous compounds and several drugs from outside the cell into the cytoplasm. The abundant expression of OATP2B1 in pharmacokinetically important tissues such as in the intestine, liver, and kidney suggests an important role in the drug absorption and elimination process, although research data on the clinical significance of OATP2B1 is still limited. Several drugs inhibit the function of OATP2B1, creating a risk for drug-drug interactions. OATP inhibition by some inhibitors is time-dependent, which may lead to more potent in vivo effects than expected. In this study, the time dependence of OATP2B1 inhibition by five different drugs was evaluated using OATP2B1-overexpressing HEK293 cells. IC50 values of inhibitors for OATP2B1-mediated uptake of DBF and E1S were determined with and without preincubation for 20 minutes. In addition, the in vivo interaction potential of the inhibitors in the intestine, liver, and other tissues was evaluated by utilizing the FDA and EMA guidelines. All five drugs showed effective and concentration-dependent OATP2B1 inhibition with IC50 values of 0.12– 8.82 µM. Furthermore, the inhibition of OATP2B1-mediated DBF uptake by ticagrelor and atorvastatin was time-dependent, while the effect of pre-incubation remains below the limit for the other inhibitors. The inhibitory effect of ticagrelor continued even after the inhibitor was removed from the inhibition buffer. All five inhibitors showed the potential to cause in vivo OATP2B1 inhibition in the intestine, which could result in decreased absorption of the co-administered substrate drug. About erlotinib, the risk of interaction also appeared in the liver, which could reduce the transfer of the substrate drug to the liver and thus lower its elimination rate. In this study, pre-incubation did not affect the in vivo interaction potential of the inhibitor drugs. The results indicate that drug-induced inhibition of OATP2B1 may be time-dependent and therefore can lead to interactions at lower concentrations than expected. For this reason, evaluating the time dependence would be appropriate when assessing transport protein-mediated interaction risk. The results of this study can be utilized in designing clinical interaction studies and in understanding the results.
Now showing items 1-2 of 2