Monoclonal antibody-based enzyme-linked immunosorbent assay for glycyrrhizin and its aglycon, glycyrrhetic acid

Monoclonal Antibodies and Immunoassay for Medical Plant-Derived Natural Products: A Review

Owing to the widespread application value, monoclonal antibodies (MAbs) have become a tool of increasing importance in modern bioscience research since their emergence. Recently, some researchers have focused on the production of MAbs against medical plant-derived natural products (MPNP), the secondary metabolites of medical plants. At the same time, various immunoassay methods were established on the basis of these MPNP MAbs, and then rapidly developed into a novel technique for medical plant and phytomedicine research in the area of quality control, pharmacological analysis, drug discovery, and so on. Dependent on the research works carried out in recent years, this paper aims to provide a comprehensive review of MAbs against MPNP and the application of various immunoassay methods established on the basis of these MAbs, and conclude with a short section on future prospects and research trends in this area.

Chemical analysis of the Chinese herbal medicine Gan-Cao (licorice)

Gan-Cao, or licorice, is a popular Chinese herbal medicine derived from the dried roots and rhizomes of Glycyrrhiza uralensis, G. glabra, and G. inflata. The main bioactive constituents of licorice are triterpene saponins and various types of flavonoids. The contents of these compounds may vary in different licorice batches and thus affect the therapeutic effects. In order to ensure its efficacy and safety, sensitive and accurate methods for the qualitative and quantitative analyses of saponins and flavonoids are of significance for the comprehensive quality control of licorice. This review describes the progress in chemical analysis of licorice and its preparations since 2000. Newly established methods are summarized, including spectroscopy, thin-layer chromatography, gas chromatography, high-performance liquid chromatography (HPLC), liquid chromatography/mass spectrometry (LC/MS), capillary electrophoresis, high-speed counter-current chromatography (HSCCC), electrochemistry, and immunoassay. The sensitivity, selectivity and powerful separation capability of HPLC and CE allows the simultaneous detection of multiple compounds in licorice. LC/MS provides characteristic fragmentations for the rapid structural identification of licorice saponins and flavonoids. The combination of HPLC and LC/MS is currently the most powerful technique for the quality control of licorice.

Comparison between conventional indirect competitive enzyme-linked immunosorbent assay (icELISA) and simplified icELISA for small molecules

A simplified indirect competitive enzyme-linked immunosorbent assay (icELISA) for small molecules was established by modifying the procedure of conventional icELISA. The key change was that the analyte, antibody, and enzyme-labeled second antibody in the simplified icELISA were added in one step, whereas in conventional icELISA these reagents were added in two separate steps. Three small chemicals, namely zeatin riboside, glycyrrhetinic acid, and chlorimuron-ethyl, were used to verify the new assay format and compare the results obtained from conventional icELISA and simplified icELISA. The results indicated that, under optimized conditions, the new assay offered several advantages over the conventional icELISA, which are simpler, less time consuming and higher sensitive although it requires more amount of reagents. The assay sensitivity (IC50) was improved for 1.2-1.4-fold. Four licorice roots samples were analyzed by conventional icELISA and simplified icELISA, as well as liquid chromatography (LC). There was no significant difference among the content obtained from the three methods for each sample. The correlation between data obtained from conventional icELISA and simplified icELISA analyses was 0.9888. The results suggest that the simplified icELISA be useful for high throughput screening of small molecules.

Preparation of Neocarzinostatin Apoprotein Mutants and the Randomized Library on the Chromophore-Binding Cavity

W39F, F52Y, S98G, S98A, and S98C mutants of the neocarzinostatin apoprotein (apo-NCS) were newly prepared and investigated their physicochemical properties. The circular dichroism (CD) spectra of F78W, F52Y, S98A, S98G, S98C were superimposable with that of wild type 1R49 protein although the minor spectral change seemed to be in the ellipticity of W39F. The results suggest that position 52, 78, and 98 involving natural chromophore binding do not play a major role in the inducing overall structural changes of the protein. Conversely, the position 39 would be affected slightly. Ethidium bromide (EtdBr) binding to mutants was also evaluated by the monitoring of total fluorescence intensity and fluorescence polarization (FP). The observed dissociation constant in the FP study was 4.4 microM for wild type, 2.2 microM for S98A, 1.3 microM for S98G, 9.7 microM for S98C, respectively. When S98G and F52Y, the calculated maximum change of the total fluorescence intensity was increased, suggesting that the EtdBr binding to S98G or F52Y were slightly improved compared with the wild type. Then, a total of 14 amino acids randomly substituted phage displayed library of apo-NCS was successfully prepared, because substitution of the amino acid structured the chromophore-binding cavity were not change the overall structural features. The phages which bound glycyrrhetic acid conjugated bovine serum albumin were enriched from this library using phage display technique as the pilot experiments. Although more precision investigation still needs, it should be possible to select variants that have new functions not found in nature.

Quantitative determination of glycyrrhizinic acid by square-wave voltammetry and high-pressure liquid chromatography

Novel adsorptive stripping square-wave voltammetric method as well as a new high-pressure liquid chromatographic method for direct determination of glycyrrhizinic acid in dosage pharmaceutical preparation, used against virus infections, have been developed. Glycyrrhizinic acid is an electrochemically active compound, which undergoes irreversible reduction on a mercury electrode surface in an aqueous medium. Its redox properties were studied thoroughly by means of square-wave voltammetry, as one of the most advanced electroanalytical technique. The voltammetric response depends mainly on the pH of the medium, composition of the supporting electrolyte, as well as the parameters of the excitement signal. It was also observed that the voltammetric properties strongly depend on the accumulation time and potential, revealing significant adsorption of glycyrrhizinic acid onto the mercury electrode surface. Upon this feature, an adsorptive stripping voltammetric method for quantitative determination of glycyrrhizinic acid was developed. A simple, sensitive and precise reversed phase HPLC method with photodiode array UV detection has also been developed, mainly for comparison and conformation of the results obtained with the voltammetric method.

Enzyme-linked immunosorbent assay for glycyrrhizin using anti-glycyrrhizin monoclonal antibody and an eastern blotting technique for glucuronides of glycyrrhetic acid

Hybridomas secreting a monoclonal antibody against glycyrrhizin were produced by fusing splenocytes from a mouse immunized against a glycyrrhizin-bovine serum albumin conjugate with the hypoxanthine-aminopterin-thymidine-sensitive mouse myeloma cell line, P3-X63-Ag8-653. A very weak cross-reaction with glycyrrhetinic acid monoglucuronide and glycyrrhetic acid occurred. An enzyme-linked immunosorbent assay (ELISA) that had an effective measuring range of 20 -200 ng/mL of glycyrrhizin was established using this monoclonal antibody. In addition, a method named eastern blotting for the detection of glycyrrhizin was investigated. In this method, we developed a new way to separate the glycyrrhizin molecule into two functional parts using a simple and well-known chemical reaction. The sugar parts were oxidized by sodium periodate to give dialdehydes, which reacted with amino groups on the protein and covalently bound to the adsorbent membrane. The monoclonal antibody bound to the aglycone part of the glycyrrhizin molecule for immunostaining. This method was validated by immunocytolocalization of glycyrrhizin in fresh Glycyrrhiza root.

Direct determination of serum glycyrrhetic acid by a monoclonal antibody-based inhibition ELISA using ibuprofen for releasing serum albumin-bound glycyrrhetic acid

We found that ibuprofen (IBU) had a potential for releasing serum albumin-bound glycyrrhetic acid (GA). Based on this observation, IBU was used to pretreat samples for the determination of serum GA levels by an inhibition ELISA. This method, termed IBU method was evaluated by the recovery of GA from human serum albumin (HSA) or normal human serum (NHS) that contained the exogeneously added GA (37-1000 ng/ml). The mean recovery of GA from HSA and NHS samples treated with IBU were 104.7 and 105.2%, respectively, whereas those without IBU pretreatment were 2.8 and 10.7%, respectively. Comparison of IBU method and chloroform extraction method revealed that the GA content of serum samples pretreated by each method were almost the same. These results suggest that IBU method is useful as a serum processing procedure for the determination of serum GA levels by an inhibition ELISA.

Enzyme-linked immunosorbent assay of neocarzinostatin chromophore (NCS-chr) by use of a monoclonal antibody against NCS-chr analog

A monoclonal antibody against NCS-chr was prepared and characterized. Because of the instability of NCS-chr, chemically synthesized stable analog compound, termed PS, was used as a hapten of immunogen. The obtained antibody, termed APS, reacted with NCS-chr, but neither with NCS, NCS-polystyrene-maleic acid conjugate (SMANCS), nor UV-irradiated NCS-chr. Epitope analysis using the compounds that have a structure similar to PS showed that APS recognized the total structure, particularly cyclopenten moiety, of PS. These results suggest that APS recognizes the enediyne structure of NCS-chr. Next, the inhibition enzyme-linked immunosorbent assay (ELISA) for determination of NCS-chr was established. The standard curve showed that the microgram order of NCS-chr were accurately measurable by the established ELISA. Furthermore, it was revealed that the established ELISA was more sensitive than the antibiotic activity determination, termed Bio-assay. The established ELISA will be useful as a quantitative method of NCS-chr.