Unravelling the complex drug–drug interactions of the cardiovascular drugs, verapamil and digoxin, with P-glycoprotein

Abstract

SynopsisDrug-drug interactions (DDIs) and associated toxicity from cardiovascular drugs represents a major problem for effective co-administration of cardiovascular therapeutics. A significant amount of drug toxicity from DDIs occurs because of drug interactions and multiple cardiovascular drug binding to the efflux transporter P-glycoprotein (Pgp), which is particularly problematic for cardiovascular drugs because of their relatively low therapeutic indexes. The calcium channel antagonist, verapamil and the cardiac glycoside, digoxin, exhibit DDIs with Pgp through non-competitive inhibition of digoxin transport, which leads to elevated digoxin plasma concentrations and digoxin toxicity. In the present study, verapamil-induced ATPase activation kinetics were biphasic implying at least two verapamil-binding sites on Pgp, whereas monophasic digoxin activation of Pgp-coupled ATPase kinetics suggested a single digoxin-binding site. Using intrinsic protein fluorescence and the saturation transfer double difference (STDD) NMR techniques to probe drug-Pgp interactions, verapamil was found to have little effect on digoxin-Pgp interactions at low concentrations of verapamil, which is consistent with simultaneous binding of the drugs and non-competitive inhibition. Higher concentrations of verapamil caused significant disruption of digoxin-Pgp interactions that suggested overlapping and competing drug-binding sites. These interactions correlated to drug-induced conformational changes deduced from acrylamide quenching of Pgp tryptophan fluorescence. Also, Pgp-coupled ATPase activity kinetics measured with a range of verapamil and digoxin concentrations fit well to a DDI model encompassing non-competitive and competitive inhibition of digoxin by verapamil. The results and previous transport studies were combined into a comprehensive model of verapamil-digoxin DDIs encompassing drug binding, ATP hydrolysis, transport and conformational changes.

Cooperativity between verapamil and ATP bound to the efflux transporter P-glycoprotein

“…[31, 42, 43]. With this technique, the protein is selectively excited with a radio frequency (RF) outside of the frequency of ligand proton NMR peaks, which disperses the RF throughout the protein by spin diffusion.…”

“…The STDD NMR procedure for membrane proteins was performed as described previously [31, 43]. All the STDD NMR samples contained 1 µM Pgp reconstituted into liposomes in 80% deuterated 100 mM KPi buffer, pD 7.4.…”

“…The 1 H STD NMR spectrum with liposomes and ligands was subtracted from the 1 H STD NMR spectrum of Pgp reconstituted in liposomes with ligands (Δ I ) to isolate specific interactions between the ligand and Pgp. The STDD amplification factor was calculated using the following equation [31, 44]: $$\text{italicSTDD Amplificaiton Factor}=\frac{false[Lfalse]\mathrm{normal\Delta }I}{false[Pfalse]I_0}$$ where [P] is the protein concentration and I 0 is the amplitude of the 1 H NMR peaks in the absence of excitation pulses.…”

Intracellular Unbound Atorvastatin Concentrations in the Presence of Metabolism and Transport

“…It is possible that the apical efflux transport of ATV is inhibited by the endogenous substrate. Since P-gp has been reported to have multiple binding sites (Ruth et al, 2001;Mayer et al, 2002;Ledwitch et al, 2016), cooperative binding of endogenous substrates or metabolites could be involved.…”

Role of heart rate in mechanisms of compensation and decompensation in patients with CHF and sinus rhythm or atrial fibrillation and methods for safe and effective control of the heart rhythm. Part 1. Sinus rhythm

“…Кстати, и сочетание дигоксина с верапа-милом позволяло лучше контролировать ЧСС при сниже-нии риска ночной брадикардии и появления пауз на ЭКГ [91]. Однако последняя комбинация в настоящее время используется с осторожностью, так как при ее примене-нии возрастает риск побочных эффектов из-за увеличения концентрации обоих препаратов в крови [92]. Интересно, что еще в 70-е годы в отделе ОЗМиСН НИИ кардиологии им.…”