Phosphodiesterase 5 inhibitory activity of the canthin-6-one alkaloids and roots from Eurycoma longifolia and Eurycoma harmandiana

Eurycoma longifolia (EL) and Eurycoma harmandiana (EH), both natural medicinal plants belonging to the Simaroubaceae family, are well-known for their ability to enhance male performance. The present study investigated the intact root of EL and EH for phosphodiesterase-5 (PDE-5) inhibitory activity. Apart from canthin-6-one alkaloids, β -carboline alkaloids, and quassinoids, were screened for their inhibitory activity against PDE-5. Additionally, this study examines the in vitro root and callus cultures of EL and EH to determine their activity in PDE-5 inhibition. Our results indicate that the canthin-6-one alkaloids group, which includes canthin-6-one-9- O - β -glucopyranoside, 9-methoxy-canthin-6-one, canthin-6-one, and 9-hydroxy-canthin-6-one, exhibit potency against PDE-5 enzymatic inhibition, with IC 50 values of 2.86 ± 0.23, 3.30 ± 1.03, 4.31 ± 0.52, and 4.66 ± 1.13 µM, respectively. The ethanolic extract of the intact root of EL and EH, and the in vitro root culture of EH exhibited a high accumulation of canthin-6-one alkaloids as 1.50 ± 0.04, 2.12 ± 0.03, and 3.48 ± 0.08 mg/g dry weight, respectively, which showed a high potency on PDE-5 inhibitory activity. Our findings indicated that in vitro root culture of EH could be used to replace the intact plants and the canthin-6-one-9- O - β -glucopyranoside should be further investigated for development as a health-supplementary agent.