The Grapefruit Flavonoid Naringenin Inhibits Multiple Cardiac Ion Channels

Abstract Drinking fresh grapefruit juice is associated with a significant prolongation of the QT segment on the electrocardiogram (ECG) in healthy volunteers. Among the prominent flavonoids contained in citrus fruits, the flavanone naringenin is known to be a blocker of the human ether-a-go-go related gene (hERG) potassium channel. We hypothesized that naringenin could interfere with other major ion channels shaping the cardiac ventricular action potential (AP). To this end, we examined the effects of naringenin on the seven currents comprising the Comprehensive in vitro Pro-Arrhythmia (CiPA) panel for early arrhythmogenic risk assessment in drug discovery and development. We used automated patch-clamp of human ion channels heterologously expressed in mammalian cell lines to evaluate half-maximal inhibitory concentrations (IC50). Naringenin blocked all CiPA currents tested with IC50 values in the 30 µM – 100 µM concentration-range. The rank-order of channel sensitivity was the following: hERG > Kir2.1 > NaV1.5 late > NaV1.5 peak > KV7.1 > KV4.3 > CaV1.2. This multichannel inhibitory profile of naringenin suggests exercising caution when large amounts of grapefruit juice or other citrus juices enriched in this flavanone are drunk in conjunction with QT prolonging drugs or by carriers of congenital long QT syndromes.