A general enzyme immunoassay for the licorice root component contained in traditional Chinese medicines

The development and application of a new enzyme immunoassay for general assay of the Glycyrrhizae radix (GR) component in Chinese traditional medicines is described. Three commercial GR-based medicines, Tohoku kanzo (GRTK), Seihoku Kanzo (GRSEK) and Sinkyo kanzo (GRSK) were used as GR specimens. Anti-GRSK serum was elicited from rabbits immunized with GRSK fragments. The presence of common proteins as specific antigens of GR was first established by Western blot analysis of extracts of GRSK, GRSEK or GRTK using anti-GRSK. The specific antigens were applied to develop an ELISA for the assay of GR extract. Anti-GRSK was put in competition with a sample or standard GR extract and immobilized GRSK components in microtiter plate wells. The proportion of antibody binding to the solid-phase GRSK component was detected using an enzyme-labeled second antibody. The ELISA method was specific to GRSK extract and showed low sensitivity for the assay of GRTK extract. The technique of selected antibody enzyme immunoassay (SAEIA) was applied to develop a sensitive general assay method. Solid-phase GRTK extract, rather than immobilized GRSK extract, was used in the SAEIA. The SAEIA possessed the same quantitative working range of between 1 and 100 micrograms/ml for the assay of each extract of GRTK, GRSK and GRSEK. The SAEIA was successful in the detection and quantitative measurement of GR component contents in Chinese traditional medicines.