A rapid thin-layer chromatography bioautographic method for detecting the monoamine oxidase inhibitors in plants

It is well known that the isolation of monoamine oxidase (MAO) inhibitors from natural sources is an important strategy for drug development in the treatment of depression, Parkinson's disease and Alzheimer's disease. The present work describes developing a thin-layer chromatography (TLC) bioautographic method for detecting MAO inhibitors from plant extracts. The basic principle of the method is that the enzyme oxidises tryptamine into an aldehyde which in turn reacts with 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide to form a blue formazan which makes a blue-coloured background on the TLC plates. Inhibitors of MAO produced white spots on the background. The new TLC bioautographic method has several advantages such as lower consumption of the enzyme, shorter experimental time, more easily observed background of TLC plate and better reproducibility. The detection limits were 10 ng for several known MAO inhibitors.