Antidepressant-like Effects of Orthosiphon stamineus: Integrated Evidence from In Silico, In Vitro, and a Reserpine-Induced Depression Model

Background: Traditional antidepressants are associated with undesirable side effects, limited efficacy, and delayed therapeutic responses. Natural products have emerged as a potential alternative to these drugs. This research aimed to investigate the antidepressant-like activity and possible mechanism of Orthosiphon stamineus (OS) leaf ethanolic extract. Methods: Molecular docking and in vitro studies were performed to assess the inhibitory activity of ethanolic extracts of OS leaves against the monoamine oxidase (MAO-A) enzyme. Behavioral tests were used to evaluate the antidepressant-like activity of the 95% ethanol extract in reserpine-treated rats, followed by histopathological examination and measurement of hippocampal serotonin (5-HT), norepinephrine (NE), and brain-derived neurotrophic factor (BDNF). Results: The main active compounds, particularly rosmarinic acid and eupatorin, exhibited favorable binding affinities to the MAO-A active site. The 95% and 50% ethanol extracts of OS showed dose-dependent MAO-A inhibitory activity with ICs50 of 88.67 and 103.2 µg/mL, respectively. The 95% ethanol extract of OS leaves showed a significant reduction in immobility time, restored locomotor activity, and preserved hippocampal morphology. Notably, the higher dose of OS extract (150 mg/kg) significantly enhanced hippocampal expression of 5-HT and NE, with a moderate upregulation of BDNF. Conclusions: These findings suggest that the 95% ethanol extract of OS leaves exhibits promising antidepressant-like effects, which may be mediated through monoamine modulation and BDNF expression and partially through MAO-A enzyme inhibition.