Inhibition of monoamine oxidase A and B by demethoxycurcumin and bisdemethoxycurcumin

Two curcumin derivatives, demethoxycurcumin (DMC) and bisdemethoxycurcumin (BDMC), isolated from Curcuma longa were analyzed for their inhibitory activities against two isoforms of monoamine oxidase (MAO), which is involved in the catalysis of neurotransmitting monoamines. In the study, DMC and BDMC potently inhibited human MAO-B, with IC₅₀ values of 2.45 and 2.59 µM, respectively, and both compounds showed effective inhibitory activities against human MAO-A, with IC₅₀ values of 3.24 and 3.09 µM, respectively. The inhibitory activities of the two compounds were higher than those of curcumin. The removal of the methoxy or dimethoxy groups in curcumin might increase the inhibitory activities against human MAO-A and MAO-B. The inhibited activities were recovered to almost the values of the reversible references in the dialysis experiments with DMC and BDMC. DMC and BDMC showed competitive inhibition for MAO-A and MAO-B, respectively, with K_i values of 0.91 and 0.80 µM, respectively. These results suggest that the two curcumin derivatives may be useful or lead compounds in the treatment of related disorders as potent reversible MAO inhibitors.