The MDR1 gene product, P-glycoprotein, mediates the transport of the cardiac glycoside, digoxin

doi:10.1016/0006-291X(92)91593-F

Biochemical and Biophysical Research Communications

Volume 189, Issue 1, 30 November 1992, Pages 551-557

https://doi.org/10.1016/0006-291X(92)91593-F Get rights and content

Abstract

Digoxin, a widely used cardiac glycoside with a low therapeutic index, is known to interact with a large and diverse group of co-administered drugs, frequently leading to toxic accumulation of the glycoside. Establishing the mechanism(s) of these interactions, therefore, has potential clinical significance. The present studies implicate P-glycoprotein, the MDR1 gene product overexpressed in multidrug resistant cells, as the apical membrane protein responsible for the renal secretion of digoxin and provide an explanation for the occurrence of digoxin toxicity in the presence of certain co-administered medications. Since digoxin is considered a prototype for endogenous digitalis-like glycosides, the results also allow for speculation that endogenous digitalis-like glycosides may be the natural substrates for P-gp.

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P-glycoprotein activation by 1-(propan-2-ylamino)-4-propoxy-9H-thioxanthen-9-one (TX5) in rat distal ileum: ex vivo and in vivo studies
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In vitro studies showed that 1-(propan-2-ylamino)-4-propoxy-9H-thioxanthen-9-one (TX5) increases P-glycoprotein (P-gp) expression and activity in Caco-2 cells, preventing xenobiotic toxicity. The present study aimed at investigating TX5 effects on P-gp expression/activity using Wistar Han rats: a) in vivo, evaluating intestinal P-gp activity; b) ex vivo, evaluating P-gp expression in ileum brush border membranes (BBM) and P-gp activity in everted intestinal sacs; c) ex vivo, evaluating P-gp activity in everted intestinal sacs of the distal and proximal ileum. TX5 (30 mg/kg, b.w.), gavage, activated P-gp in vivo, given the significant decrease in the AUC of digoxin (0.25 mg/kg, b.w.). The efflux of rhodamine 123 (300 μM), a P-gp fluorescent substrate, significantly increased in TX5-treated everted sacs from the distal portion of the rat ileum, when P-gp activity was evaluated in the presence of TX5 (20 μM), an effect abolished by the P-gp inhibitor verapamil (100 μM). No increases on P-gp expression or activity were found in TX5-treated BBM of the distal ileum and everted distal sacs, respectively, 24 h after TX5 (10 mg/kg, b.w.) administration. In vivo, no differences were found on digoxin portal concentration between control (digoxin 0.025 mg/kg, b.w., intraduodenal) and TX5-treated (digoxin+TX5 20 μM, intraduodenal) rats. The observed discrepancies in digoxin results can be related to differences in TX5 dose administered and used methodologies. Thus, the results show that TX5 activates P-gp at the distal portion of the rat ileum, and, at the higher dose tested (30 mg/kg, b.w.), seems to modulate in vivo the AUC of P-gp substrates.
MRP2-mediated transport of etoposide in MDCKII MRP2 cells is unaffected by commonly used non-ionic surfactants
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The aim of the present study was to investigate the ability of non-ionic surfactants to inhibit MRP2-mediated transport in vitro in MDCKII MRP2 cells. Transport studies across MDCKII MRP2 cell monolayers were performed using ³H-etoposide and ³H-digoxin. 19 different non-ionic surfactants, including several polysorbates (PS), cremophor EL, vitamin E-TPGS, and n-nonyl β-D-glucopyranoside (NG), were investigated. Barrier function of the cells was investigated measuring TEER and transport of ¹⁴C-glycine. The amount of isotope was quantified using liquid scintillation counting. In MDCKII MRP2 cells a polarized transport of etoposide and digoxin in the secretory (basolateral to apical) direction with efflux ratios of 5.5 ± 0.7 and 18.5 ± 4.2, respectively, was measured. P-gp inhibitors such as valspodar and zosuquidar did not affect etoposide transport, and furthermore PS20 decreased secretory transport of digoxin, but not of etoposide. Transport of etoposide was therefore mainly MRP2-mediated and used as a probe to investigate pharmaceutical excipients. Non-ionic surfactants did not modulate etoposide transport across intact cell monolayers of MRP2 overexpressing MDCKII cells, although preliminary studies suggest that most were able to alter MRP2-mediated efflux of the fluorescent 5-chloromethylfluorescein (CMF). In conclusion, etoposide transport across MDCKII MRP2 cells was modulated by cyclosporin A, an inhibitor of MRP2 and P-gp, but not by specific P-gp inhibitors (valspodar and zosuquidar), which suggests that etoposide transport is primarily influenced by MRP2. In addition, commonly used non-ionic surfactants did not decrease MRP2-mediated etoposide transport in MDCKII MRP2 cells. These results suggest that etoposide transport in MDCKII MRP2 cells is a model system to investigate MRP2 interactions, and that surfactants may not have a large potential for increasing oral bioavailability of drugs through inhibition of MRP2 transport activity.
Pharmacologic interactions
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Polysorbate 20 increases oral absorption of digoxin in wild-type Sprague Dawley rats, but not in mdr1a(-/-) Sprague Dawley rats
2016, International Journal of Pharmaceutics
Citation Excerpt :
The weight of the animals at the day of administration was 330–390 g for WT animal and 289–449 g for mdr1a KO animals. Digoxin was chosen as a marker substrate for P-gp mediated transport (de Lannoy and Silverman, 1992; Schinkel et al., 1997, 1995). Transport of 1 μCi/ml 3H-digoxin (25.13 nM) and 1 μCi·ml−114C-mannitol (18.18 μM) in HBSS supplemented with 10 mM HEPES (pH 7.4) was measured from the apical side (A–B transport) or to the basolateral side (B-A transport).
The aim was to investigate the ability of polysorbate 20 to alter oral digoxin absorption in vitro and drug exposure in vivo via modulation of transporter mediated efflux. Transport studies were performed in MDCKII-MDR1 and Caco-2 cells using ³H-digoxin. Pharmacokinetic studies were performed in wild type and mdr1a deficient Sprague Dawley rats. ³H-digoxin was quantified using liquid scintillation counting. The results showed an increased absorptive transport and a reduced secretory transport in MDCKII-MDR and Caco-2 cells as a function of polysorbate 20 concentrations. The secretory transport (B–A) of digoxin was reduced by 50% at lower polysorbate 20 concentrations than required to increase the absorptive transport (A-B). In vivo, the oral bioavailability of digoxin in wild type animal was increased by 10–25% (w/v) polysorbate 20. In mdr1a deficient Sprague Dawley rats 25% (w/v) polysorbate 20 did not alter the absorption of digoxin after oral administration, but digoxin exposure was significantly different between wild type and mdr1a deficient rats. In conclusion, polysorbate 20 increased absorptive transport across Caco-2 cell monolayers and in vivo in rats in a concentration dependent manner, most likely via inhibition of P-gp rather than through solubilization of digoxin.
Convallatoxin: A new P-glycoprotein substrate
2015, European Journal of Pharmacology
Digitalis-like compounds (DLCs), such as digoxin and digitoxin that are derived from digitalis species, are currently used to treat heart failure and atrial fibrillation, but have a narrow therapeutic index. Drug–drug interactions at the transporter level are frequent causes of DLCs toxicity. P-glycoprotein (P-gp, ABCB1) is the primary transporter of digoxin and its inhibitors influence pharmacokinetics and disposition of digoxin in the human body; however, the involvement of P-gp in the disposition of other DLCs is currently unknown.
In present study, the transport of fourteen DLCs by human P-gp was studied using membrane vesicles originating from human embryonic kidney (HEK293) cells overexpressing P-gp. DLCs were quantified by liquid chromatography–mass spectrometry (LC–MS).
The Lily of the Valley toxin, convallatoxin, was identified as a P-gp substrate (K_m: 1.1±0.2 mM) in the vesicular assay. Transport of convallatoxin by P-gp was confirmed in rat in vivo, in which co-administration with the P-gp inhibitor elacridar, resulted in increased concentrations in brain and kidney cortex. To address the interaction of convallatoxin with P-gp on a molecular level, the effect of nine alanine mutations was compared with the substrate N-methyl quinidine (NMQ). Phe343 appeared to be more important for transport of NMQ than convallatoxin, while Val982 was particularly relevant for convallatoxin transport.
We identified convallatoxin as a new P-gp substrate and recognized Val982 as an important amino acid involved in its transport. These results contribute to a better understanding of the interaction of DLCs with P-gp.

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The MDR1 gene product, P-glycoprotein, mediates the transport of the cardiac glycoside, digoxin

Abstract

Analyt. Biochem

Biochem. Biophys. Res. Commun

J. Biol. Chem

Biochim. Biophys. Acta

TiPS

J. Biol. Chem

Biochem. Biophys. Res. Commun

New. Engl. J. Med

J. Pharmacol. Exp. Ther

Clin. Physiol

Clin. Pharmacol. Ther

Can. J. Physiol. Pharmacol

J. Pharmacol. Exp. Ther