ABSTRACT
The inflorescences of Pseudognaphalium liebmannii are used as folk medicine to treat various respiratory diseases. In this work, we report the isolation of seven known flavones: 5-hydroxy-3,7-dimethoxyflavone 1, 5,8-dihydroxy-3,7-dimethoxyflavone 2, 5,7-dihydroxy-3,8-dimethoxyflavone 3 (gnaphaliin A), 3,5-dihydroxy-7,8-dimethoxyflavone 4 (gnaphaliin B), 3,5-dihydroxy-6,7,8-trimethoxyflavone 5, 3,5,7-trimethoxyflavone 6 and 3-O-methylquercetin 7. All these flavones except 1 and 6 showed a relaxant effect on guinea pig tracheal preparation with EC50 between 69.91 ± 15.32 and 118.72 ± 7.06 µM. Aminophylline (EC50 = 122.03 ± 7.05 µM) was used as a relaxant reference drug. The active flavones shifted the concentration-response curves of forskolin and nitroprusside leftward, and significantly reduced the EC50 values of these drugs. Furthermore, these flavones dose-dependently inhibited phosphodiesterase (PDE) in an in vitro assay. This reveals that the inflorescences of P. liebmannii contain several flavones with relaxant effect on airway smooth muscle and with PDEs inhibition that contribute to supporting the anti-asthmatic traditional use.
ABSTRACT
OBJECTIVE: This work was aimed to investigate the pharmacodynamic interactions between gnaphaliins A and B with ipratropium bromide (IBR) and salbutamol (SAL) using the guinea pig trachea model through application of the combination index (CI)-isobologram equation. METHODS: The guinea pig trachea rings in isolated chamber with Krebs-Henseleit solution (37°C) were contracted with carbachol (3 µm), and then, concentration-relaxant effect curves were constructed for individual drugs and in combination at fixed constant ratios (1 : 1, 3 : 1 and 1 : 3). Median effect and combination index (CI)-isobologram equations were used for determining interactions. KEY FINDINGS: Gnaphaliin A and gnaphaliin B showed clear synergistic interaction with salbutamol, reducing the dose of salbutamol more than sevenfolds to produce the same relaxant effect. However, the combination of either flavonoids with ipratropium bromide showed no interaction. CONCLUSIONS: Applying the combination index-isobologram method, we determined that gnaphaliin A and gnaphaliin B have synergistic effect with salbutamol due probably to their inhibitory effect on phosphodiesterases to maintain high levels of cAMP in the tracheal smooth muscle. However, these compounds did not show any effect with ipratropium.