Isolation and investigation of potassium channel activity of Aconitum diterpene alkaloids

Background: Diterpene alkaloids isolated from Aconitum species exert activity on Na⁺ and K⁺ channels thus these compounds have strong cardiac effects. Depending on skeletal types and substitution patterns the binding affinity may be diverse. The majority of Aconitum alkaloids may cause arrhythmia and heart arrest by the activation of voltage-dependent Na⁺ channels. Others act as competitive antagonist of the arrhythmogenics by blocking the Na⁺ channel and the delayed rectifier K⁺ current. Those Na⁺ channel-blocking diterpene alkaloids which show activity on GIRK (G protein-activated inwardly rectifying potassium channel) and have no activity on hERG (human ether-à-go-go-related gene encoded potassium channel) may be useful in the treatment of chronic atrial fibrillation.

Methods: Diterpene alkaloids were isolated from the tuber of Aconitum firmum Rchb. by means of solvent-solvent extraction followed by multistep chromatographic methods (open column chromatography, centrifugal planar chromatography, preparative layer chromatography, gel filtration chromatography). The structures of the compounds were elucidated by ESI-MS-MS, ¹H-NMR, ¹³C-NMR, JMOD, ¹H,¹H-COSY, NOESY, HSQC and HMBC experiments. Electrophysiological effects of alkaloids were investigated on stable transfected HEK-hERG (Kv11.1) and HEK-GIRK1/4 (Kir3.1 and Kir3.4) cell lines using automated patch clamp equipment (Patchliner, Nanion).

Results: Karakoline, napelline, neoline, senbusine A, senbusine C, isotalatizidine, taurenine and aconitine were identified in A. firmum. The isolated alkaloids of A. firmum, together with eight other diterpene alkaloids previously isolated from Aconitum toxicum [1, 2] and Consolida orientalis [3] were studied. At 10µM and 30µM the tested compounds exerted low (3 – 19%) inhibitory activity on hERG channels. On GIRK channels neoline and songorine exerted the highest (51%) inhibitory activity, the other compounds showed moderate effect.

Acknowledgments: The research was funded by the Project “TÁMOP-4.2.1/B-09/1/KONV-2010 – 0005 – Creating the Center of Excellence at the University of Szeged”, supported by the EU and co-financed by European Fund.

Literatur:

[1] Csupor D et al. Helv Chim Acta 2006; 89: 2981 – 2986

[2] Csupor D et al. J Nat Prod 2008; 71: 1779 – 1782

[3] Hajdú Z et al. Biochem Syst Ecol 2005; 33: 1081 – 1085