Quinidine

Trial of dextromethorphan/quinidine to treat levodopa-induced dyskinesia in Parkinson's disease.[Pubmed:28370447]

Mov Disord. 2017 Jun;32(6):893-903.

BACKGROUND: Nondopaminergic pathways represent potential targets to treat levodopa-induced dyskinesia in Parkinson's disease (PD). This pilot-study (NCT01767129) examined the safety/efficacy of the sigma-1 receptor-agonist and glutamatergic/monoaminergic modulator, dextromethorphan plus Quinidine (to inhibit rapid dextromethorphan metabolism), for treating levodopa-induced dyskinesia. METHODS: PD patients were randomized to dextromethorphan/Quinidine (45 mg/10 mg twice daily)/placebo in two 2-week double-blind, crossover treatment periods, with intervening 2-week washout. After 14 days, a 2-hour intravenous levodopa-infusion was administered. Patient examinations were videotaped before infusion ("off" state) and every 30 minutes during and afterwards until patients returned to "off." The primary endpoint was dyskinesia-severity during infusion measured by Unified Dyskinesia Rating Scale part 3 area-under-curve scores (blinded expert rated). Additional endpoints included other dyskinesia/motor assessments, global measures of clinical-change, and adverse-events. RESULTS: A total of 13 patients were randomized and completed the study (efficacy-evaluable population). Dyskinesia-severity was nonsignificantly lower with dextromethorphan/Quinidine than placebo during infusion (area-under-curve 966.5 vs 1048.8; P = .191 [efficacy-evaluable patients]), and significantly lower in a post-hoc sensitivity analysis of the per-protocol-population (efficacy-evaluable patients with >/= 80% study-drug-compliance, n = 12) when measured from infusion start to 4-hours post-infusion completion (area-under-curve 1585.0 vs 1911.3; P = .024). Mean peak dyskinesia decreased significantly from infusion-start to return to "off" (13.3 vs 14.9; P = .018 [efficacy-evaluable patients]). A total of 9 patients rated dyskinesia "much/very much improved" on dextromethorphan/Quinidine versus 1-patient on placebo. Dextromethorphan/Quinidine did not worsen PD-motor scores, was generally well tolerated, and was associated with more frequent adverse events. CONCLUSION: This study provides preliminary evidence of clinical benefit with dextromethorphan/Quinidine for treating levodopa-induced dyskinesia in PD. Larger studies with a longer treatment duration need to corroborate these early findings. (c) 2017 International Parkinson and Movement Disorder Society.

Intramolecular Hydrogen Bonds in Conformers of Quinine and Quinidine: An HF, MP2 and DFT Study.[Pubmed:28178218]

Molecules. 2017 Feb 7;22(2). pii: molecules22020245.

Quinine is an alkaloid with powerful antimalarial activity, isolated from the bark of Peru's cinchona trees. Quinidine is an erythro diastereoisomer of quinine also exhibiting antimalarial activity. Conformational studies performed so far had never identified conformers with intramolecular hydrogen bonds (IHB). The current study shows the possibility of conformers with an IHB between the quinuclidine and quinoline moieties of these molecules. The study was performed at different levels of theory: Hartree Fock (HF) with the 6-31G(d,p) basis set, Density Functional Theory (DFT) with the B3LYP functional and the 6-31+G(d,p) basis set and Moller-Plesset Perturbation Theory (MP2) with the 6-31+G(d,p) basis set, to confirm the results. The results suggest that the stabilising effect of this IHB is weaker or comparable with respect to the stabilising effect of the preferred mutual orientation of the two moieties. Although the IHB-containing conformers may not be the lowest energy ones, their relative energy is sufficiently low for them to be included among the possible ones responsible for the compounds' antimalarial activity.

Dual Mechanism for Inhibition of Inwardly Rectifying Kir2.x Channels by Quinidine Involving Direct Pore Block and PIP2-interference.[Pubmed:28188270]

J Pharmacol Exp Ther. 2017 May;361(2):209-218.

Class IA antiarrhythmic drug Quinidine was one of the first clinically used compounds to terminate atrial fibrillation and acts as multichannel inhibitor with well-documented inhibitory effects on several cardiac potassium channels. In the mammalian heart, heteromeric assembly of Kir2.1-2.3 channels underlies IK1 current. Although a low-affinity block of Quinidine on Kir2.1 has already been described, a comparative analysis of effects on other Kir2.x channels has not been performed to date. Therefore, we analyzed the effects of Quinidine on wild-type and mutant Kir2.x channels in the Xenopus oocyte expression system. Quinidine exerted differential inhibitory effects on Kir2.x channels with the highest affinity toward Kir2.3 subunits. Onset of block was slow and solely reversible in Kir2.2 subunits. Quinidine inhibited Kir2.x currents in a voltage-independent manner. By means of comparative Ala-scanning mutagenesis, we further found that residues E224, F254, D259, and E299 are essential for Quinidine block in Kir2.1 subunits. Analogously, Quinidine mediated Kir2.3 inhibition by binding corresponding residues E216, D247, D251, and E291. In contrast, Kir2.2 current block merely involved corresponding residue D260. Using channel mutants with altered (phosphatidylinositol 4,5-bisphosphate PIP2) affinities, we were able to demonstrate that high PIP2 affinities (i.e., Kir2.3 I214L) correlate with low Quinidine sensitivity. Inversely, mutant channels interacting only weakly with PIP2 (i.e., Kir2.1 K182Q, and L221I) are prone to a higher inhibitory effect. Thus, we conclude that inhibition of Kir2.x channels by Quinidine is mediated by joint modes of action involving direct cytoplasmic pore block and an impaired channel stabilization via interference with PIP2.

Role of late sodium current in modulating the proarrhythmic and antiarrhythmic effects of quinidine.[Pubmed:19084812]

Heart Rhythm. 2008 Dec;5(12):1726-34.

BACKGROUND: Quinidine is used to treat atrial fibrillation and ventricular arrhythmias. However, at low concentrations, it can induce torsade de pointes (TdP). OBJECTIVE: The purpose of this study was to examine the role of late sodium current (I(Na)) as a modulator of the arrhythmogenicity of Quinidine in female rabbit isolated hearts and cardiomyocytes. METHODS: Epicardial and endocardial monophasic action potentials (MAPs), ECG signals, and ion channel currents were measured. The sea anemone toxin ATX-II was used to increase late I(Na). RESULTS: Quinidine had concentration-dependent and often biphasic effects on measures of arrhythmogenicity. Quinidine increased the duration of epicardial MAP (MAPD(90)), QT interval, transmural dispersion of repolarization (TDR), and ventricular effective refractory period. Beat-to-beat variability of MAPD(90) (BVR), the interval from peak to end of the T wave (Tpeak-Tend) and index of Tpeak-Tend/QT interval were greater at 0.1 to 3 micromol/L than at 10-30 micromol/L Quinidine. In the presence of 1 nmol/L ATX-II, Quinidine caused significantly greater concentration-dependent and biphasic changes of Tpeak-Tend, TDR, BVR, and index of Tpeak-Tend/QT interval. Quinidine (1 micromol/L) induced TdP in 2 and 13 of 14 hearts in the absence and presence of ATX-II, respectively. Increases of BVR, index of Tpeak-Tend/QT interval, and Tpeak-Tend were associated with Quinidine-induced TdP. Quinidine inhibited I(Kr), peak I(Na), and late I(Na) with IC(50)s of 4.5 +/- 0.3 micromol/L, 11.0 +/- 0.7 micromol/L, and 12.0 +/- 0.7 micromol/L. CONCLUSION: Quinidine had biphasic proarrhythmic effects in the presence of ATX-II, suggesting that late I(Na) is a modulator of the arrhythmogenicity of Quinidine. Enhancement of late I(Na) increased proarrhythmia caused by low but not high concentrations of Quinidine.

Short QT syndrome. Genotype-phenotype correlations.[Pubmed:16226079]

J Electrocardiol. 2005 Oct;38(4 Suppl):75-80.

The short QT syndrome is a new congenital entity associated with familial atrial fibrillation and/or sudden death or syncope. Three different gain-of-function mutations in genes encoding for cardiac potassium channels (KCNH2, KCNQ1, and KCNJ2) have been identified up to now to cause short QT syndrome. The syndrome is characterized electrocardiographically by a shortened QTc interval less than 300 to 320 milliseconds and a lack of adaptation during increasing heart rates. During programmed electrical stimulation, atrial and ventricular effective refractory periods are shortened, and in a high percentage, ventricular tachyarrhythmias are inducible. Sudden cardiac death occurs in all age groups and even in newborns. Therapy for choice seems to be the implantable cardioverter-defibrillator because of the high incidence of sudden death. However, ICD therapy may be associated with an increased risk of inappropriate therapies for T wave oversensing, which, however, can be resolved by reprogramming ICD detection algorithms. The impact of sotalol, ibutilide, flecainide, and Quinidine on QT prolongation has been evaluated. But only Quinidine effectively suppressed gain-of-function in IKr, along with prolongation of the QT interval. Furthermore, in patients with a mutation in HERG (SQT1), Quinidine rendered ventricular tachyarrhythmias noninducible and restored the QT interval/heart rate relationship toward a reference range. It may serve as an adjunct to ICD therapy or as possible alternative treatment especially for children and newborns.

Effects of flecainide and quinidine on Kv4.2 currents: voltage dependence and role of S6 valines.[Pubmed:12721103]

Br J Pharmacol. 2003 Apr;138(8):1475-84.

1. The effects of flecainide and Quinidine were studied on wild-type Kv4.2 channels (Kv4.2WT), channels with deletion of the N-terminal domain (N-del) and channels with mutations in the valine residues located at positions 402 and 404 in the presence (V[402,404]I) or in the absence (N-del/V[402,404]I) of the N-terminus. 2. The experiments were performed at 37 degrees C on COS7 cells using the whole-cell configuration of the patch-clamp technique. 3. Flecainide and Quinidine inhibited Kv4.2WT currents in a concentration-dependent manner (IC(50)=23.6+/-1.1 and 12.0+/-1.4 microMat +50 mV, respectively), similar to their potency for the rest of the constructs at the same voltage. In Kv4.2WT channels, flecainide- and Quinidine-induced block increased as channel inactivation increased. In addition, the inhibition produced by Quinidine, but not by flecainide, increased significantly at positive test potentials. Similar effects were observed in N-del channels. However, in V[402,404]I and N-del/V[402,404]I channels, the voltage dependence of block by both Quinidine and flecainide was lost, without significant modifications in potency at +50 mV. 4. These results point to an important role for S6 valines at positions 402 and 404 in mediating voltage-dependent block by Quinidine and flecainide.