Identification of higenamine in Radix Aconiti Lateralis Preparata as a beta2-adrenergic receptor agonist

Aim： To screen beta2-adrenergic receptor Lateralis Preparata （RALP） as potential （β2-AR） agonists from Radix Aconiti drug leads for asthma using a sensitive cell-based agonist assay. Methods： The β2-AR gene was stably expressed by Chinese hamster ovary （CHO） cells also stably expressing a cyclic adenosine monophosphate （AMP） response element-linked enhanced green fluorescent protein reporter gene. The cells were used to screen agonists from high-performance liquid chromatographic fractions of an extract of RALE The fraction with the highest activity was selected for further compound isolation and the study of the structure-activity relationship. Its active compound was further identified by chromatography and mass spectrometry. Results： Bioactivity-directed fractionation of the crude extract of RALP led to the isolation and characterization of the effective compound, namely hignamine. It could dose-dependently relax the isolated guinea pig trachea strip precontraction, with acetylcholine with EC50 value of （2.60±0.36）× 10^5 mol/L. Further in vivo studies also displayed that hignamine could protect experimental asthma model induced by histamine in guinea pigs to prolong the latent periods of asthma. Conclusion： Hignamine, as a β2-AR agonist existing in the extract of RALP, is the key compound contributing to the successful relief of the bronchoconstriction.