HONG KONG, CHINA. The contraction (depolarization) and resting (repolarization) periods of the heart cells are determined by the balance of the inward flow of calcium ions and the outward flow of potassium (K) ions. The major outward K currents are IKur (ultrarapid delayed rectified K+ current) and Ito (transient outward K+ current). The Class III antiarrhythmics (amiodarone, sotalol and dobutilide) work by blocking the outward K+ currents so as to increase the resting period (ERP) during which afib cannot be initiated. Ideally, only the K+ currents in the atria would be blocked since blocking them in the ventricles can lead to arrhythmias (proarrhythmic effects) and lengthening of the corrected QT interval (long-QT syndrome). IKur is only present in the atria, so a drug that would block only IKur would be a highly desirable antiarrhythmic.
Researchers at the University of Hong Kong now report that they may have found such a "drug" in the natural flavone, acacetin, derived from the traditional Chinese medicine Xuelianhua. Their experiments, so far, have only involved human heart cells and various animals, but are intriguing nevertheless. The researchers found that acacetin is non-toxic even when administered in relatively large doses. They also observed that it does not prolong the corrected QT interval in isolated rabbit hearts. Most importantly, they found that acacetin was highly effective in blocking both IKur and Ito, prolonged the atrial effective resting period (AERP), and prevented the induction of atrial fibrillation in dogs. As an added bonus, acacetin was also found to block the IKach (acetylcholine-activated K+ current), which may be instrumental in the initiation of vagally-induced afib.
Other research has shown that acacetin has anti-inflammatory effects, is an effective antioxidant, and exhibits anti-cancer effects in human prostate and lung cancer – truly a "super drug". The Chinese researchers conclude that oral acacetin is a promising agent for the prevention and treatment of atrial fibrillation.
Li, GR, et al. Acacetin, a natural flavone, selectively inhibits human atrial repolarization potassium currents and prevents atrial fibrillation in dogs. Circulation, Vol. 117, May 13, 2008, pp. 2449-57
Editor's comment: I usually do not report on cell culture and animal experiments since there is a distinct possibility that their results may not apply to humans. Nevertheless, I found the results of this study so fascinating that I decided to make an exception. As far as I know, acacetin is not available outside the laboratory, but Xuelianhua might be. Of course, there is no way of knowing whether this whole botanical medicine may have similar effects to the highly concentrated extract acacetin.