MAOB

Monoamine oxidase B (MAO-B) is a mitochondrial enzyme that catalyzes the oxidative deamination of monoamines. It helps regulate levels of neurotransmitters such as dopamine, as well as trace amines like phenylethylamine and benzylamine. In humans, MAO-B is widely expressed in the brain, with high activity in astrocytes and dopaminergic neurons, and is also present in the liver and platelets. During the deamination reaction, MAO-B generates hydrogen peroxide, which can contribute to oxidative stress; activity can increase with age in some brain regions.

MAO-A and MAO-B differ in substrate preference. MAO-A preferentially metabolizes serotonin, norepinephrine, and dopamine, whereas MAO-B preferentially metabolizes phenylethylamine and benzylamine, though both enzymes can metabolize dopamine. The enzyme’s distribution and activity influence the regulation of monoamine signaling and can affect responses to psychoactive and antidepressant medications.

Pharmacology and clinical use center on MAO-B inhibitors, particularly in Parkinson’s disease. Drugs such as selegiline, rasagiline, and safinamide reduce the breakdown of dopamine, allowing lower doses of levodopa and improved motor function. Selegiline and rasagiline are generally irreversible MAO-B inhibitors at clinical doses; safinamide is reversible and also possesses additional non-MAO-B activities that modulate glutamate release. Dietary restrictions to avoid hypertensive crises are less stringent with selective MAO-B inhibitors but still advisable in some contexts; combining MAO-B inhibitors with other serotonergic drugs can raise the risk of serotonin syndrome.

Research uses include imaging MAO-B activity with PET ligands and studying MAO-B’s role in aging and neurodegenerative diseases. The MAOB gene is located on the X chromosome (Xq28).