The synergistic anti-asthmatic effects of glycyrrhizin and salbutamol

Aim： To investigate the efficacy of glycyrrhizin （GL） combined with salbutamol （SA） as an anti-asthma therapy. Methods： Rat lung beta2-adrenergic receptor （β2-AR） mRNA level was measured by real-time RT PCR. Intracellular cAMP accumulation was evaluated with a reporter gene assay. An in vitro acetylcholine-induced guinea pig tracheal strip contraction model was used to test the relaxing effects of GL and SA. The anti-inflammatory effects of GL and SA were tested using tumor necrosis factor-α-induced NF-κB transcriptional activation reporter assay, I-κB Western blotting and interleukin-8 ELISA. An in vivo guinea pig asthma model was used to prove further the synergistic effect of GL and SA. Results： GL （0.3 μmol/L） increased mRNA levels of β2-AR in vivo and the accumulation of cAMP in vitro. The combination of GL and SA also resulted in significant complementary anti-inflammatory effects via inhibition of NF-κB activation, degradation of I-κB and production of interleukin-8. A significant synergistic effect of the combination was detected both in vitro and in vivo in a guinea pig mode. Conclusion： The results demonstrate that GL and SA have synergistic anti-asthmatic effects and offer the possibility of a therapeutic application of GL in combination with β2-AR agonists in the treatment of asthma.