Serotonin, or 5-hydroxytryptamine (5-HT), is primarily metabolized by monoamine oxidase (MAO) enzymes, specifically MAO-A. MAO-A preferentially degrades serotonin, norepinephrine, and dopamine. This enzymatic action converts serotonin into 5-hydroxyindoleacetic acid (5-HIAA), a major metabolite excreted in urine.
MAO-A and MAO-B: Distinct Roles
While MAO-A plays a dominant role in serotonin metabolism, MAO-B also contributes, though to a lesser extent. MAO-B primarily metabolizes phenylethylamine and dopamine. Understanding the distinct substrate specificities of MAO-A and MAO-B is crucial for interpreting the effects of MAO inhibitors on serotonin levels and their associated therapeutic and adverse effects.
Selective MAO-A inhibitors (MAO-AIs) specifically target MAO-A, resulting in increased serotonin levels with potentially fewer side effects compared to non-selective MAO inhibitors. Conversely, non-selective MAO inhibitors (MAOIs) affect both MAO-A and MAO-B, impacting the metabolism of various monoamines and potentially causing more pronounced side effects. This difference is vital in clinical practice when considering treatment options.
