Monoamine oxidase

Copper-containing flavine enzyme which causes the degradation of various monoamines (see below biogenic amines) via oxidative deamination. Natural substrates of monoamine oxidase are, among others, catecholamines (adrenalin, noradrenalin), serotonin, tyramine or histamine.

Inhibition of monoamine oxidase (MAO inhibitor) leads to synaptic concentration of epinephrine, norepinephrine and serotonin. This effect is used in the therapy of depression.

Two subtypes are distinguished:

• MAO-A: mainly presynaptic occurrence
• MAO-B: Together with MAO-A, MAO-B occurs predominantly postsynaptically.

Monoaminooxidase inhibitors (MAO inhibitors) or also -MAO inhibitors (MAOI) belong to the antidepressants. They exert their effect by (reversibly or irreversibly) blocking monoaminooxidases, which increases the concentration of monoamines in neurons.

MAO-inhibitors are divided into two categories:

• selectivity for a type of enzyme (selective or non-selective)
• and
• Reversibility (reversible or irreversible).

Reversibility means that the drug only binds weakly to one or both enzymes. It releases the enzyme unchanged again at the latest when the phamacone is broken down. Irreversible MAO inhibitors, on the other hand, bind the monoaminoxodase enzymes permanently. In order to cancel their effect, the MAO must first be newly formed. The organism needs several weeks for this.

Selective inhibitors of MAO-A (e.g. moclobemide, reversible) only inhibit type A monoamine oxidase. They show an antidepressive effect and are generally well tolerated. Selectively MAO-B inhibiting agents (e.g. selegiline, rasagiline, both irreversible) are primarily used in the treatment of Parkinson's disease.

Non-selective MAO-inhibitors(e.g. tranylcypromine) inhibit MAO-A and MAO-B equally. They are highly effective in the treatment of depression and anxiety disorders.