Ultrahigh-performance liquid chromatography/tandem mass spectrometry method for evaluating enzyme activity and screening inhibitors of cyclooxygenase-2

Development of an Enzyme-Based Thin-Layer Chromatographic Assay for the Detection of Cyclooxygenase-2 Inhibitors

The search for new anti-inflammatory drugs with less side effects requires simple, fast and reliable screening methods. In this context, we have developed a sensitive thin-layer chromatographic (TLC) assay on silica gel plates to detect cyclooxygenase-2 (COX-2) inhibition. COX-2 catalyzes two sequential enzymatic reactions: a first oxygenation step that converts arachidonic acid into prostaglandin G2, and a subsequent reduction of prostaglandin G2 into prostaglandin H2. Our test is based on the co-oxidation during this peroxidation step of a co-substrate, N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD), leading to a blue-grey product. As a consequence, COX-2 inhibitors appear on the TLC plate after revelation as clear spots against the colored background. Parameters such as concentrations of enzyme, substrate, and chromogenic reagent have been optimized. The limit of detection was found to be below the microgram for standard COX-2 inhibitors such as celecoxib or ibuprofen. The developed TLC assay was also conclusive when applied to 60 various natural pure compounds and some complex natural extracts. Results demonstrated a COX-2 inhibitory activity mostly for triterpene and sterol derivatives. This COX-2 TLC assay appears as a suitable low-cost and reliable strategy for the screening of natural extracts to discover new anti-inflammatory compounds.

Characterization and screening of cyclooxygenase-2 inhibitors from Zi-shen pill by affinity ultrafiltration-ultra performance liquid chromatography mass spectrometry

ETHNOPHARMACOLOGICAL RELEVANCE

Zi-shen pill (ZSP) is a classical Chinese herbal formula used for treatment of benign prostatic hyperplasia (BPH).

AIM OF THE STUDY

To characterize and screen cyclooxygenase-2 (COX-2) inhibitors from ZSP extract.

MATERIALS AND METHODS

The ZSP extract was incubated with COX-2 and the potential ligands were screened out by affinity ultrafiltration. Celecoxib and glipizide were chosen as positive control and negative control drug, respectively. Affinity ultrafiltration-ultra performance liquid chromatography-mass spectrometry (UPLC-MS) method was used. In addition, in vitro COX-2 inhibitory assay and in silico molecular docking technique were used for further validation.

RESULTS

A total of 20 components were discovered and identified from ZSP ultrafiltrate by high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), among which 8 compounds were deduced as potential COX-2 inhibitors by their high specific binding values (>1.5). Inhibitory activities of demethyleneberberine, palmatine, berberine and timosaponin A-I were confirmed by an enzyme assay of COX-2, which validated the reliability of our approach. Molecular docking simulation investigated potential mechanism of action for these compounds.

CONCLUSION

The results revealed that affinity ultrafiltration UPLC-MS could successfully screen out the potential COX-2 inhibitors from complex Chinese herbal formula ZSP extract, indicating that its therapeutic effect on BPH was partly based on the enzyme active ingredients.

Establishment of a Charge Reversal Derivatization Strategy to Improve the Ionization Efficiency of Limaprost and Investigation of the Fragmentation Patterns of Limaprost Derivatives Via Exclusive Neutral Loss and Survival Yield Method

Sensitivity is generally an issue in bioassays of prostaglandins and their synthetic analogs due to their extremely low concentration in vivo. To improve the ionization efficiency of limaprost, an oral prostaglandin E1 (PGE1) synthetic analog, we investigated a charge reversal derivatization strategy in electrospray ionization mass spectrometry (ESI-MS). We established that the cholamine derivative exhibits much greater signal intensity in the positive-ion mode compared with limaprost in the negative ion mode. Collision-induced dissociation (CID) involved exclusive neutral mass loss and positive charge migration to form stable cationic product ions with the positive charge on the limaprost residue rather than on the modifying group. This has the effect of maintaining the efficiency and specificity of multiple reaction monitoring (MRM) and avoiding cross talk. CID fragmentation patterns of other limaprost derivatives allowed us to relate the dissociation tendency of different neutral leaving groups to an internal energy distribution scale based on the survival yield method. Knowledge of the energy involved in the production of stabilized positive ions will potentially assist the selection of suitable derivatization reagents for the analysis of a wide variety of lipid acids. Graphical Abstract ᅟ.

Immobilization of Cyclooxygenase-2 on Silica Gel Microspheres: Optimization and Characterization

In this study, immobilized COX-2 was successfully constructed through glutaraldehyde-mediated covalent coupling on functional silica gel microspheres. The optimum conditions, properties, and morphological characteristics of the immobilized COX-2 were investigated. The optimal immobilization process was as follows: about 0.02 g of aminated silica gel microspheres was activated by 0.25% GA solution for 6 h and mixed with 5 U of free recombinant COX-2 solution. Then, the mixture was shaken for 8 h at 20 °C. Results showed that the immobilized COX-2 produced by this method exhibited excellent biocatalytic activity, equivalent to that of free COX-2 under the test conditions employed. The best biocatalytic activity of immobilized COX-2 appeared at pH 8.0 and still maintained at about 84% (RSD < 7.39%, n = 3) at pH 10.0. For temperature tolerance, immobilized COX-2 exhibited its maximum biocatalytic activity at 40 °C and about 68% (RSD < 6.99%, n = 3) of the activity was maintained at 60 °C. The immobilized COX-2 retained over 85% (RSD < 7.26%, n = 3) of its initial biocatalytic activity after five cycles, and after 10 days storage, the catalytic activity of immobilized COX-2 still maintained at about 95% (RSD < 3.08%, n = 3). These characteristics ensured the convenient use of the immobilized COX-2 and reduced its production cost.