In vitro ion channel profile and ex vivo cardiac electrophysiology properties of the R(-) and S(+) enantiomers of hydroxychloroquine

Hydroxychloroquine (HCQ) is a derivative of the antimalaria drug chloroquine primarily prescribed for autoimmune diseases. Recent attempts to repurpose HCQ in the treatment of corona virus disease 2019 has raised concerns because of its propensity to prolong the QT-segment on the electrocardiogram, an effect associated with increased pro-arrhythmic risk. Since chirality can affect drug pharmacological properties, we have evaluated the functional effects of the R(-) and S(+) enantiomers of HCQ on six ion channels contributing to the cardiac action potential and on electrophysiological parameters of isolated Purkinje fibers. We found that R(-)HCQ and S(+)HCQ block human K_ir2.1 and hERG potassium channels in the 1 μM-100 μM range with a 2-4 fold enantiomeric separation. Na_V1.5 sodium currents and Ca_V1.2 calcium currents, as well as K_V4.3 and K_V7.1 potassium currents remained unaffected at up to 90 μM. In rabbit Purkinje fibers, R(-)HCQ prominently depolarized the membrane resting potential, inducing autogenic activity at 10 μM and 30 μM, while S(+)HCQ primarily increased the action potential duration, inducing occasional early afterdepolarization at these concentrations. These data suggest that both enantiomers of HCQ can alter cardiac tissue electrophysiology at concentrations above their plasmatic levels at therapeutic doses, and that chirality does not substantially influence their arrhythmogenic potential in vitro.

Cannabidiol inhibits multiple cardiac ion channels and shortens ventricular action potential duration in vitro

Cannabidiol (CBD) is a non-psychoactive component of Cannabis which has recently received regulatory consideration for the treatment of intractable forms of epilepsy such as the Dravet and the Lennox-Gastaut syndromes. The mechanisms of the antiepileptic effects of CBD are unclear, but several pre-clinical studies suggest the involvement of ion channels. Therefore, we have evaluated the effects of CBD on seven major cardiac currents shaping the human ventricular action potential and on Purkinje fibers isolated from rabbit hearts to assess the in vitro cardiac safety profile of CBD. We found that CBD inhibits with comparable micromolar potencies the peak and late components of the Na_V1.5 sodium current, the Ca_V1.2 mediated L-type calcium current, as well as all the repolarizing potassium currents examined except K_ir2.1. The most sensitive channels were K_V7.1 and the least sensitive were K_V11.1 (hERG), which underly the slow (I_Ks) and rapid (I_Kr) components, respectively, of the cardiac delayed-rectifier current. In the Purkinje fibers, CBD decreased the action potential (AP) duration more potently at half-maximal than at near complete repolarization, and slightly decreased the AP amplitude and its maximal upstroke velocity. CBD had no significant effects on the membrane resting potential except at the highest concentration tested under fast pacing rate. These data show that CBD impacts cardiac electrophysiology and suggest that caution should be exercised when prescribing CBD to carriers of cardiac channelopathies or in conjunction with other drugs known to affect heart rhythm or contractility.