GABA transaminase (GABA-T)

Class

small molecule; irreversible enzyme inhibitor

Pathway

irreversibly inhibits GABA-T, the enzyme responsible for GABA catabolism, increasing CNS GABA levels.

GABA transaminase (GABA-T) is a mitochondrial enzyme that breaks down gamma-aminobutyric acid (GABA), the principal inhibitory neurotransmitter in the central nervous system. GABA acts by damping neuronal excitability; when its degradation is slowed, GABA accumulates in and around synapses, reinforcing inhibitory signaling throughout the brain. This is the biological rationale for inhibiting GABA-T: by preventing GABA breakdown rather than by directly stimulating GABA receptors, the approach raises the brain's overall inhibitory tone in a more physiological, sustained manner. Because irreversible inhibition permanently inactivates existing enzyme molecules, effects persist until new enzyme is synthesized, giving a long duration of action from intermittent dosing. This mechanism is of central importance in epilepsy, a disorder characterized by excessive, poorly controlled neuronal excitation, where boosting inhibitory GABA signaling can raise the seizure threshold and reduce seizure frequency, particularly in forms of epilepsy that respond poorly to other antiseizure mechanisms. Because GABA-T is also expressed outside the brain, including in the retina, modulating it has effects beyond the intended therapeutic target, which is a general consideration whenever an enzyme with broad tissue distribution is chosen for inhibition. Understanding GABA-T illustrates a broader principle in neuropharmacology: therapeutic benefit can be achieved either by activating a receptor directly or by prolonging the life of an endogenous ligand already produced by the body.