Coupling of a High-resolution Monoamine Oxidase-A Inhibitor Assay and HPLC-SPE-NMR for Advanced Bioactivity Profiling of Plant Extracts

Introduction - Depression is a mental disease causing large personal and socio-economic problems, and new improved drugs are therefore needed. Selective monoamine oxidase A (MAO-A) inhibitors are potential anti-depressants, but discovering new MAO-A inhibitors from natural sources by bioassay-guided approaches are a lengthy and time-consuming process. New analytical technologies that allow simultaneously chemical and biological screening of extracts are therefore urgently needed. Method - In the present study we describe coupling of a photometric microplate-based high-resolution MAO-A inhibitor assay with a hyphenated system consisting of high-performance liquid chromatography, solid-phase extraction and tube transfer nuclear magnetic resonance (HPLC-SPE-ttNMR). The standard compound clorgyline, and an extract of black pepper (Piper nigrum L.), representing a complex plant matrix, were used for proof-of-concept. Results - The work with clorgyline showed that the microplate-based high-resolution assay produced MAO-A inhibition profiles that easily allowed detection of submicrogram amounts of this selective MAO-A inhibitor. Furthermore, the HPLC-SPE-ttNMR/high-resolution MAO-A inhibition assay platform allowed identification of piperine and two piperine analogues as the main MAO-A inhibitors in the black pepper petroleum ether extract. Conclusion - The HPLC-SPE-ttNMR/high-resolution MAO-A inhibition assay platform is a powerful tool for fast and efficient identification of new MAO-A inhibitors from complex extracts, and promise future advancement in the search for new antidepressants from natural sources. Copyright (C) 2012 John Wiley & Sons, Ltd.