Identification of bioactive compounds in Shaoyao-Gancao decoction using β2-adrenoceptor affinity chromatography

Shaoyao-Gancao decoction, a Chinese herbal formula, is composed of Paeoniae Radix alba and Glycyrrhiza Radix et rhizoma. It has been widely used to treat muscle spasms and asthma. However, little is known about the bioactive components of Shaoyao-Gancao decoction. In the present study, the bioactive compounds in water-extract of Shaoyao-Gancao decoction were separated by the immobilized β₂ -adrenoceptor affinity column and identified using quadrupole time-of-flight mass spectrometry. The affinity constants of the separated compounds that bind to β₂ -adrenoceptor were determined by frontal analysis. Compound bioactivity was tested in a rat tracheal smooth muscle relaxation assay. We identified the bioactive compounds in the water extract of Shaoyao-Gancao decoction that bound to the β₂ -adrenoceptor as paeoniflorin and liquiritin. Paeoniflorin and liquiritin had only one binding site on the immobilized β₂ -adrenoceptor, and the affinity constants were (2.16 ± 0.10) × 10⁴  M^-1 and (2.95 ± 0.15) × 10⁴  M^-1 , respectively. Both compounds induced a concentration-dependent relaxation of tracheal smooth muscle following K⁺ -stimulated contraction, and the relaxation effects were abrogated by the β₂ -adrenoceptor antagonist, ICI 118551. Therefore, paeoniflorin and liquiritin are bioactive compounds in Shaoyao-Gancao decoction and the β₂ -adrenoceptor affinity chromatography is a useful tool for identifying potential β₂ -adrenoceptor ligands in natural products used in traditional Chinese medicine.