Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.7.49 (reverse transcriptase)
 31,746 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Tenofovir disoproxil fumarate (TDF), a nucleotide reverse transcriptase inhibitor, after conversion to tenofovir (TFV), is mainly eliminated by glomerular filtration and active tubular secretion. The major adverse effect of tenofovir is nephrotoxicity; however, the exact mechanism remains poorly understood. In this study, the ATP-binding cassette subfamily C member 11 (ABCC11; multidrug resistance protein 8 [MRP8]) transporter, which is abundant in proximal tubular cells, was demonstrated to act as an efflux transporter of tenofovir. Real-time PCR (RT-PCR) and indirect immunofluorescence assays were used to determine MRP8 overexpression in a continuous cell line. Tenofovir accumulations were assessed by cytotoxicity, cellular transport, and vesicular uptake assays. Substrate specificity was confirmed using MK-571, an MRP-specific inhibitor, and methotrexate, which served as a known substrate. Intracellular and intravesicular concentrations of tenofovir were determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The 50% cytotoxic concentration (CC50) of TDF in MRP8-overexpressing cells was 4.78 times higher than that of parental cells. Transport assays also showed that the intracellular accumulation of tenofovir in MRP8-overexpressing cells was 55 times lower than that in parental cells and was partly reversed by MK-571. Similarly, an "inside-out" vesicular uptake assay, using Sf9 inverted membrane vesicles to allow measuring of accumulation of the substrates into the vesicles, demonstrated a higher intravesicular concentration of tenofovir in MRP8-overexpressing vesicles than in Sf9 insect control vesicles. These effects were effectively reversed by increasing concentrations of the specific inhibitor MK-571. In conclusion, tenofovir is a new substrate of the MRP8 transporter. An alteration in the activity of this efflux pump may increase the intracellular accumulation of tenofovir in proximal renal tubular cells.
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PMID:Tenofovir Disoproxil Fumarate Is a New Substrate of ATP-Binding Cassette Subfamily C Member 11. 3102 21

The profound influence of ATP-binding cassette (ABC) transporters on the disposition of numerous drugs has led to increased interest in characterizing their expression profiles in various epithelial and endothelial barriers. The present work examined the presence and functional activity of five ABC efflux proteins, i.e., MRP 1-5, in freshly isolated human nasal epithelial cells and two in vitro models based on the human RPMI 2650 cell line. To evaluate the expression patterns of MRP1, MRP2, MRP3, MRP4, and MRP5 at the mRNA and protein levels in the ex vivo model and the differently cultured RPMI 2650 cells, reverse transcriptase polymerase chain reaction (RT-PCR), Western blot analysis, and indirect immunofluorescence staining were used. The functionality of the MRP transporters in the three models was assessed using efflux experiments and accumulation assays with the respective substrates and inhibitors. The mRNA and protein expression of all selected ABC transporters was detected in excised human nasal mucosa as well as in the corresponding cell culture models. Moreover, the functional expression of the MRP transport proteins was demonstrated in the three models for the first time. Therefore, the potential impact of multidrug resistance-associated proteins 1-5 on drug disposition after intranasal administration may be taken into consideration for future developments. The specimens of human nasal turbinate exhibited slightly lower efflux capacities of MRP1, MRP3, and MRP5 in relation to the submerged and ALI-cultured RPMI 2650 cells, but showed a promising comparability to both in vitro models concerning the activity of MRP2 and MRP4. In this regard, the different RPMI 2650 cell culture models will be able to provide useful experimental data in the preclinical phase to estimate the interaction of particular efflux transporters with drug candidates for nasal application.
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PMID:Activity of Multidrug Resistance-Associated Proteins 1-5 (MRP1-5) in the RPMI 2650 Cell Line and Explants of Human Nasal Turbinate. 2829 71


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