Clorgyline (hydrochloride) is an irreversible, potent and selective monoamine oxidase (MAO) A inhibitor with Ki values of 0.054 and 58 μM and IC50 values of 0.0012 and 1.9 μM for MAO-A and MAO-B, respectively [1][2].

Monoamine oxidases (MAOs) are FAD depending enzymes and exists in two forms, namely MAO-A and MAO-B. MAOs are responsible for the regulation and metabolism of major monoamine neurotransmitters such as 5-hydroxytryptamine (5-HT), norepinephrine (NE), and dopamine (DA). MAO-A preferentially oxidizes serotonin. Human MAO-A inhibitors are antidepressants and antianxiety agents [1].

Clorgyline is an irreversible, potent and selective MAO-A inhibitor. In wild-type mice, clorgyline significantly inhibited MAO-A enzymatic activity by approximately 80%. Clorgyline also significantly elevated striatal levels of 5-HT and NE, and significantly decreased DOPAC levels, suggesting that inhibition of MAO-A activity decreased the metabolism of DA. In YAC128 HD mice, clorgyline (1.5 mg/kg for 21 days) inhibited MAO-A enzymatic activity in cortical tissue by approximately 90% and significantly elevated striatal 5-HT and NE levels. Clorgyline treatment also improved anxiety-like phenotypes and reduced depressive-like behavior [3].

References:
[1].  Abdelhafez OM, Amin KM, Ali HI, et al. Synthesis of new 7-oxycoumarin derivatives as potent and selective monoamine oxidase A inhibitors. J Med Chem. 2012 Dec 13;55(23):10424-36.
[2].  Mazouz F, Gueddari S, Burstein C, et al. 5-[4-(benzyloxy)phenyl]-1,3,4-oxadiazol-2(3H)-one derivatives and related analogues: new reversible, highly potent, and selective monamine oxidase type B inhibitors. J Med Chem. 1993 Apr 30;36(9):1157-67.
[3].  Garcia-Miralles M, Ooi J, Ferrari Bardile C, et al. Treatment with the MAO-A inhibitor clorgyline elevates monoamine neurotransmitter levels and improves affective phenotypes in a mouse model of Huntington disease. Exp Neurol. 2016 Apr;278:4-10.