Inhibition of rat brain monoamine oxidase activities by psoralen and isopsoralen: Implications for the treatment of affective disorders

Psoralen and isopsoralen. furocoumarins isolated from the plant Psoralea co rylifolia L., were demonstrated to exhibit in vitro inhibitory actions on m onoamine oxidase (MAO) activities in rat brain mitochondria, preferentially inhibiting MAO-A activity over MAO-B activity. This inhibition of enzyme a ctivities was found to be dose-dependent and reversible. For MAO-A, the IC5 0 values are 15.2+/-1.3 muM psoralen and 9.0+/-0.6 muM isopsoralen. For MAO -B, the IC50 values are 61.8+/-4.3 muM psoralen and 12.8+/-0.5 muM isopsora len. Lineweaver-Burk transformation of the inhibition data indicates that i nhibition by both psoralen and isopsoralen is non-competitive for MAO-A. Th e K-i values were calculated to be 14.0 muM for psoralen and 6.5 muM for is opsoralen. On the other hand, inhibition by both psoralen and isopsoralen i s competitive for MAO-B. The K-i values were calculated to be 58.1 muM for psoralen and 10.8 muM for isopsoralen. These inhibitory actions of psoralen and isopsoralen on rat brain mitochondrial MAO activities are discussed in relation to their toxicities and their potential applications to treat aff ective disorders.