Monoamine Oxidase Inhibitory Components from the Roots of Sophora flavescens

In our search for monoamine oxidase (MAO) inhibitors from natural resources, we found that the methanol extract of the roots of Sophora flavescens showed an inhibitory effect on mouse brain monoamine oxidase (MAO). Bioactivity-guided isolation of the extract yielded two known flavonoids, formononetin (1) and kushenol F (2), as active compounds along with three inactive compounds, oxymatrine (3), trifolirhizin (4), and ${\beta}$-sitosterol (5). Formononetin (1) and kushenol F (2) showed significant inhibitory effects on MAO in a dose-dependent manner with $IC_{50}$ values of 13.2 and $69.9\;{\mu}M$, respectively. Formononetin (1) showed a slightly more potent inhibitory effect against MAO-B ($IC_{50}:\;11.0\;{\mu}M$) than MAO-A ($IC_{50}:\;21.2\;{\mu}M$). Kushenol F (2) also preferentially inhibited the MAO-B activity than MAO-A activity with the $IC_{50}$ values of 63.1 and $103.7\;{\mu}M$, respectively.