Identification of anti-asthmatic compounds in Pericarpium citri reticulatae and evaluation of their synergistic effects

Aim: To investigate the anti-asthmatic mechanisms of the traditional Chinese medicine Pericarpium citri reticulatae (PCR). Methods: The alkaloid section (AS) of PCR was extracted using an ion exchange resin, separated, and purified into different fractions by semi-preparative HPLC. These fractions were screened for beta2-adrenergic receptor (beta(2)AR) agonistic activity using rat beta(2)AR-transfected CHO-CRE-EGFP cells. AS and its isolated components were characterized by ultra-performance liquid chromatography/quadrupole time-of-flight MS (UPLC/Q-Tof MS) and were evaluated for their spasmolytic and antitussive activities both in vitro and in vivo in a guinea pig model. Results: We demonstrated that the AS component responsible for activating beta(2)AR signaling was synephrine. Both AS and synephrine showed significant spasmolytic effects on acetylcholine chloride (ACh)-induced contractions in isolated guinea pig trachea, and they protected against histamine-induced experimental asthma by prolonging the latent period. We further identified stachydrine as the antitussive component that could significantly reduce citric acid-induced coughing. The combination of these two bioactive compounds had a more potent spasmolytic activity in comparison with the single use of synephrine or stachydrine. Conclusion: We conclude that synephrine and stachydrine are the key components of AS that mediate asthma relief due to their synergism when used in combination.