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Clozapine is an atypical neuroleptic used to manage treatment-resistant schizophrenia which is known to inhibit cardiac hERG/K V 11.1 potassium channels, a pharmacological property associated with increased risk of potentially fatal Torsades de Pointes (TdP) and sudden cardiac death (SCD). Yet, the long-standing clinical practice of clozapine does not show a consistent association with increased incidence of TdP, although SCD is considerably higher among schizophrenic patients than in the general population. Here, we have established the inhibitory profile of clozapine at the seven cardiac ion currents proposed by the ongoing comprehensive in vitro pro-arrhythmia (CiPA) initiative to better predict new drug cardio-safety risk. We found that clozapine inhibited all CiPA currents tested with the following rank order of potency: K V 11.1 > Na V 1.5 (late current) ≈ Ca V 1.2 ≈ Na V 1.5 (peak current) ≈ K V 7.1 > K V 4.3 > K ir 2.1 (outward current) . Half-maximal inhibitory concentrations (IC 50 ) at the repolarizing K V 11.1 and K V 7.1 channels, and at the depolarizing Ca V 1.2 and Na V 1.5 channels fell within a narrow half-log 3-10 µM concentration range, suggesting that mutual compensation could explain the satisfactory arrhythmogenic cardio-safety profile of clozapine. Although the IC 50 values determined herein using an automated patch-clamp (APC) technique are at the higher end of clozapine plasmatic concentrations at target therapeutic doses, this effective antipsychotic appears prone to distribute preferentially into the cardiac tissue, which supports the clinical relevance of our in vitro pharmacological findings., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Drinking fresh grapefruit juice is associated with a significant prolongation of the QT segment on the electrocardiogram (ECG) in healthy volunteers. Among the prominent polyphenols contained in citrus fruits and primarily in grapefruit, the flavonoid naringenin is known to be a blocker of the human ether-a-go-go related gene (hERG) potassium channel. Here we hypothesized that naringenin could interfere with other major ion channels shaping the cardiac ventricular action potential (AP). To test this hypothesis, we examined the effects of naringenin on the seven channels comprising the Comprehensive in vitro Pro-Arrhythmia (CiPA) ion channel panel for early arrhythmogenic risk assessment in drug discovery and development. We used automated population patch-clamp of human ion channels heterologously expressed in mammalian cells to evaluate half-maximal inhibitory concentrations (IC 50 ). Naringenin blocked all CiPA ion channels tested with IC 50 values in the 30-100 µM concentration-range. The rank-order of channel sensitivity was the following: hERG > K ir 2.1 > Na V 1.5 (late current) > Na V 1.5 (peak current) > K V 7.1 > K V 4.3 > Ca V 1.2. This multichannel inhibitory profile of naringenin suggests exercising caution when large amounts of grapefruit juice or other citrus juices enriched in this flavonoid polyphenol are drunk in conjunction with QT prolonging drugs or by carriers of congenital long-QT syndromes., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)