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Vol. 110, No. 3, 2008
Issue release date: June 2008
Cardiology 2008;110:145–152

The Additive Effects of the Active Component of Grapefruit Juice (Naringenin) and Antiarrhythmic Drugs on HERG Inhibition

Lin C. · Ke X. · Ranade V. · Somberg J.
Department of Pharmacology, Division of Clinical Pharmacology, Rush University Medical Center, Chicago, Ill., USA

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Background: Grapefruit juice causes significant QT prolongation in healthy volunteers and naringenin has been identified as the most potent human ether-a-go-go-related gene (HERG) channel blocker among several dietary flavonoids. The interaction between naringenin and IKr-blocking antiarrhythmic drugs has not been studied. We evaluated the effect of combining naringenin with IKr-inhibiting antiarrhythmic drugs on cardiac IKr. Methods and Results:IKr current was studied by using HERG expressed in Xenopus oocytes, and the two-electrode voltage clamp technique was employed. Antiarrhythmic drugs (azimilide, amiodarone, dofetilide and quinidine) were tested. Experiments were performed at room temperature. Naringenin blocked HERG current dose dependently with an IC50 of 173.3 ± 3.1 µM. Naringenin 100 µM alone inhibited HERG current by 31 ± 6%, and this inhibitory effect was increased with coadministration of 1 or 10 µM antiarrhythmic drugs. When 100 µM naringenin was added to antiarrhythmic drugs, greater HERG inhibition was demonstrated, compared to the current inhibition caused by antiarrhythmic drugs alone. Addition of naringenin significantly increased current inhibition (p < 0.05). Conclusions: There is an additive inhibitory effect on HERG current when naringenin is combined with IKr-blocking antiarrhythmic drugs. This additive HERG inhibition could pose an increased risk of arrhythmias by increasing repolarization delay and possible repolarization heterogeneity.

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