Rational design of MAO-B-activated fluorescent probe for activity evaluation and its biomedical applications

Monoamine oxidase mainly includes two isoforms, monoamine oxidase A (MAO-A) and monoamine oxidase B (MAO-B), of which MAO-B is a crucial metabolic enzyme, acts on dopamine and β-phenylethylamine and can be selectively inhibited by pargyline. MAO-B has emerged as a significant drug target for a variety of nervous system diseases. In the present work, a highly selective and sensitive fluorescent probe named 3-aminopropyl (3-oxo-3H-phenoxazin-7-yl) carbamate (AHPC) was designed and developed. AHPC showed good stability and cell membrane permeability in biological systems, and could detect endogenous MAO-B activity in real time, and accurately evaluate the changes of MAO-B under H₂O₂-induced oxidative stress. In addition, AHPC was able to detect the distribution of MAO-B in different organs. As MAO-B is an important drug target, we developed a high-throughput, visual screening system for MAO-B inhibitors based on AHPC. Glycyrrhizae radix et rhizome was screened from 272 kinds of Chinese medicine and displayed strong inhibitory effect toward MAO-B. After further separation of Glycyrrhizae radix et rhizome, it was found that Licoisoflavone B was the main active ingredient to inhibit MAO-B activity in different enzyme sources, and was expected to be a lead compound for the treatment of MAO-B-related diseases. In conclusion, with the advantages of fluorescent probe technology, we not only developed a handy molecular tool for real-time detection of MAO-B distribution and function in complex biosystems, but also established a high-throughput visualization method for screening MAO-B inhibitors from traditional Chinese medicine, which are promising for the treatment of many MAO-B-related diseases.