Monoamine oxidase inhibition by some Nigerian medicinal plants

In Nigeria, a vast majority of the population use plants in the traditional health care system for various health conditions including those relating to the central nervous system (CNS). Scientific investigation of such medicinal plants is necessary for the justification of traditional uses and beliefs as well as their optimisation in the search for more effective and efficient therapeutic alternatives in healthcare. The current study was designed to identify some Nigerian medicinal plants with specific monoamine oxidase (MAO) inhibition. Therefore, twenty plant species used in traditional medicine were screened for MAO inhibitory activity using their methanol extracts at 0.1 and 1.0 mg/mL. A spectrophotometric assay was used to determine the inhibition of the oxidative deamination of 5-hydroxytryptamine and benzylamine by MAO-A and MAO-B, respectively, in the presence of the plant extracts. Clorgiline and rasagiline served as positive controls for MAO-A and MAO-B, respectively. P. nigrescens leaf exhibited the best selective MAO-A inhibitory activity (methanol leaf extract 1.0 mg/mL = 29.85 % inhibition) while X. aethiopica fruit was the most active against MAO-B selectively (methanol fruit extract 1.0 mg/mL = 44.51 % inhibition). Other plants which showed appreciable inhibition against the isoforms of MAO are Milicia excelsa stem bark, Musa paradisiaca leaf, Tetrapleura tetraptera fruit, and Tectona grandis young leaf. These findings support these plants traditional use and may lead to the discovery of novel MAO inhibitors.