Monoamine oxidase B immobilized on magnetic nanoparticles for screening of the enzyme's inhibitors from herbal extracts

Monoamine oxidase B (MAO-B) was for the first time immobilized on magnetic nanoparticles to be used for screening of MAO-B inhibitors from herbal extracts. The immobilized enzyme was characterized with transmission electronic microscopy , Fourier transform infrared spectroscopy, thermal gravimetric analysis , and vibrating sample magnetometer. The immobilized enzyme retained 95% of the activity, while the thermostability was significantly increased. It was then used as solid phase extraction absorbent to extract MAO-B's ligands from two traditional Chinese medicinal plants, Cortex fraxini and Pericarpium granati . Calceolarioside B and ellagic acid were extracted from C. fraxini and P. granati, respectively, and both of them were found to be inhibitors of MAO-B with IC 50 of 40.95 ± 0.63 and 103.70 ± 2.34  μ M, respectively. This is the first report that calceolarioside B inhibits MAO-B activity. Furthermore, inhibitory mechanisms of both compounds were studied by molecular docking analysis, the results of which demonstrated that the affinity of calceolarioside B with monoamine oxidase B was stronger than that of ellagic acid. The method proposed in this work is highly efficient for screening of MAO-B inhibitors from complex mixtures, showing great potential in discovering anti-Parkinson's disease compounds present in medicinal plants.