Inhibition of brain mitochondrial monoamine oxidases by the endogenous compound 5-hydroxyoxindole

Abstract

5-Hydroxyoxindole is a recently identified endogenous compound. Its physiological role remains unclear but certain evidence exists, that it may share some regulatory properties with isatin, a known endogenous inhibitor of monoamine oxidase (MAO) type B (MAO-B). In this study several oxidized indoles were tested for their in vitro inhibition of MAO type A (MAO-A) and B of rat brain non-synaptic mitochondria. 5-Hydroxyoxindole was less potent MAO-A inhibitor ( ic 50 56.8 μM) than isatin (31.8 μM) and especially 5-hydroxyisatin (6.5 μM), but it was the only highly selective MAO-A inhibitor among the all compounds studied ( ic 50 MAO-A: ic 50 MAO-B=0.044). Thus, the in vitro data suggest that MAO-A may represent potential target for 5-hydroxyoxindole.