Dehydroevodiamine and hortiamine, alkaloids from the traditional Chinese herbal drug Evodia rutaecarpa, are IKr blockers with proarrhythmic effects in vitro and in vivo.

Evodiae fructus is a widely used herbal drug in traditional Chinese medicine. Evodia extract was found to inhibit hERG channels. The aim of the current study was to identify hERG inhibitors in Evodia extract and to investigate their potential proarrhythmic effects. Dehydroevodiamine (DHE) and hortiamine were identified as IKr (rapid delayed rectifier current) inhibitors in Evodia extract by HPLC-microfractionation and subsequent patch clamp studies on human embryonic kidney cells. DHE and hortiamine inhibited IKr with IC50s of 253.2±26.3nM and 144.8±35.1nM, respectively. In dog ventricular cardiomyocytes, DHE dose-dependently prolonged the action potential duration (APD). Early afterdepolarizations (EADs) were seen in 14, 67, 100, and 67% of cells after 0.01, 0.1, 1 and 10µM DHE, respectively. The proarrhythmic potential of DHE was evaluated in 8 anesthetized rabbits and in 8 chronic atrioventricular block (cAVB) dogs. In rabbits, DHE increased the QT interval significantly by 12±10% (0.05mg/kg/5min) and 60±26% (0.5mg/kg/5min), and induced Torsade de Pointes arrhythmias (TdP, 0.5mg/kg/5min) in 2 rabbits. In cAVB dogs, 0.33mg/kg/5min DHE increased QT duration by 48±10% (P<0.05*) and induced TdP in 2/4 dogs. A higher dose did not induce TdP. In human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), methanolic extracts of Evodia, DHE and hortiamine dose-dependently prolonged APD. At 3µM DHE and hortiamine induced EADs. hERG inhibition at submicromolar concentrations, APD prolongation and EADs in hiPSC-CMs and dose-dependent proarrhythmic effects of DHE at micromolar plasma concentrations in cAVB dogs should increase awareness regarding proarrhythmic effects of widely used Evodia extracts.

Natural products as potential human ether-a-go-go-related gene channel inhibitors - outcomes from a screening of widely used herbal medicines and edible plants.

Inhibition of the human ether-a-go-go-related gene channel is the single most important risk factor leading to acquired long QT syndrome. Drug-induced QT prolongation can cause severe cardiac complications, including arrhythmia, and is thus a liability in drug development. Considering the importance of the human ether-a-go-go-related gene channel as an antitarget and the daily intake of plant-derived foods and herbal products, surprisingly few natural products have been tested for channel blocking properties. In an assessment of possible human ether-a-go-go-related gene liabilities, a selection of widely used herbal medicines and edible plants (vegetables, fruits, and spices) was screened by means of a functional two-microelectrode voltage-clamp assay with Xenopus oocytes. The human ether-a-go-go-related gene channel blocking activity of selected extracts was investigated with the aid of a high-performance liquid chromatography-based profiling approach, and attributed to tannins and alkaloids. Major European medicinal plants and frequently consumed food plants were found to have a low risk for human ether-a-go-go-related gene toxicity.

Natural products as potential human ether-a-go-go-related gene channel inhibitors - screening of plant-derived alkaloids.

Inhibition of the cardiac human ether-a-go-go-related gene channel is a problematic off-target pharmacological activity and, hence, a major safety liability in clinical practice. Several non-cardiac drugs have been restricted in their use, or even removed from the market due to this potentially fatal adverse effect. Comparatively little is known about the human ether-a-go-go-related gene inhibitory potential of plant-derived compounds. In the course of an ongoing human ether-a-go-go-related gene in vitro study, a total of 32 structurally diverse alkaloids of plant origin as well as two semi-synthetically obtained protoberberine derivatives were screened by means of an automated Xenopus oocyte assay. Protopine, (+)-bulbocapnine, (+)-N-methyllaurotetanine, (+)-boldine, (+)-chelidonine, (+)-corynoline, reserpine, and yohimbine reduced the human ether-a-go-go-related gene current by ≥ 50% at 100 µM, and were submitted to concentration-response experiments. Our data show that some widely occurring plant-derived alkaloids carry a potential risk for human ether-a-go-go-related gene toxicity.

Gram-scale purification of dehydroevodiamine from Evodia rutaecarpa fruits, and a procedure for selective removal of quaternary indoloquinazoline alkaloids from Evodia extracts.

Dehydroevodiamine (DHE) is a major bioactive constituent in the traditional Chinese herbal drug Evodiae fructus (Wu zhu yu). The compound has been shown to possess pronounced cardiovascular and neuropharmacological activities in vitro and in vivo. For quality control purposes and follow-up studies assessing potential safety risks of DHE, we developed a simple and efficient two-step protocol for gram-scale purification of DHE. An alkaloidal fraction was obtained by cation-exchange solid phase extraction, and DHE and the minor alkaloid hortiamine were purified by isocratic preparative RP-HPLC. The DHE content in different commercial batches of Evodiae fructus, and in a series of commercially available Evodia-containing TCM products was assessed. A daily intake of up to mg amounts of DHE was calculated from recommended doses of these products. A method for the selective removal of quaternary indoloquinazoline alkaloids from Evodia extracts was developed.

Phytochemical profiling of Curcuma kwangsiensis rhizome extract, and identification of labdane diterpenoids as positive GABAA receptor modulators.

An ethyl acetate extract of Curcuma kwangsiensis S.G. Lee & C.F. Liang (Zingiberaceae) rhizomes (100 µg/ml) enhanced the GABA-induced chloride current (IGABA) through GABAA receptors of the α1ß2γ2S subtype by 79.0±7.0%. Potentiation of IGABA was measured using the two-microelectrode voltage-clamp technique and Xenopus laevis oocytes. HPLC-based activity profiling of the crude extract led to the identification of 11 structurally related labdane diterpenoids, including four new compounds. Structure elucidation was achieved by comprehensive analysis of on-line (LC-PDA-ESI-TOF-MS) and off-line (microprobe 1D and 2D NMR) spectroscopic data. The absolute configuration of the compounds was established by comparison of experimental and calculated ECD spectra. Labdane diterpenes represent a new class of plant secondary metabolites eliciting positive GABAA receptor modulation. The highest efficiency was observed for zerumin A (maximum potentiation of IGABA by 309.4±35.6%, and EC50 of 24.9±8.8 µM).

HERG channel inhibitors in extracts of Coptidis rhizoma.

Inhibition of the hERG channel delays repolarization and prolongs the QT interval and cardiac action potential which can lead to sudden death. Several drugs have been withdrawn from the market due to hERG channel inhibition. In the search of hERG channel inhibitors of natural origin, we established an HPLC-based profiling approach which combines HPLC-microfractionation and bioactivity testing on Xenopus laevis oocytes. The methanolic extract of the TCM herbal drug Coptidis rhizoma (Coptis chinensis Franch., Ranunculaceae) reduced the peak tail hERG current by 31.7 ± 2.0% at 100 µg/mL. HPLC-based activity profiling pointed towards berberine as the active constituent. However, hERG inhibition by 100 µM of a reference sample of berberine (16.3 ± 1.6%) was less pronounced than previously reported. Subsequent LC-PDA-MS analysis showed that berberine collected by microfractionation of the Coptis extract had been, in part, transformed to active dihydroberberine. Formic acid added to the HPLC mobile phase to reduce peak tailing of protoberberine alkaloids acted as a reducing reagent according to the mechanism of the Leuckart-Wallach reaction. Among other structurally related protoberberines tested, dihydroberberine (30.1 ± 10.1% at 100 µM) was the most potent hERG inhibitor.