Inhibition of acetylcholinesterase by Hedychium gardnerianum from S. Miguel (Azores)

Some species of Zingiberaceae have been the subject of a range of chemical and pharmacological investigations due to their significance in traditional medicine. The properties attributed to these plants are due to their richness in active compounds, such as terpenes and terpenoids. Cholinesterase inhibitors were introduced in the therapy of Alzheimer Disease in the 1990s. The hopes and interest raised by these drugs are well demonstrated by the 41,370 references listed by PubMed under ‘Acetylcholinesterase inhibitors’. In particular, the scientific community is searching for novel acetylcholinesterase inhibitors displaying less secondary effects. Extracts from Hedychium gardnerianum young leaves (Yl), mature leaves (Ml), stems (St), rhizomes (Rh), seeds (Se) and fruits (Fr) were prepared by sequentially extracting with dichloromethane (DCM) and metanol (MeOH) at room temperature. Essential oil from leaves was extracted by hydrodistillation using a modified Clavenger. Acetylcholinesterase (AChE) inhibition was assayed using a modification of the Ellman method [1]. All the fractions assayed inhibited AChE activity, although to different extents. Dichloromethane extracts were always more active than methanol extracts. The strongest inhibition was displayed by mature leaves, fruits and seeds (Ml>Fr>Se), with IC50 values between 0.74 and 2.54mg/mL, and by the essential oil, with IC50 of 1.14mg/mL, which are comparable to the value for alpha-pinene, a known AChE inhibitor (IC50=1.43mg/mL). Our results indicate that Hedychium gardnerianum, an abundant and fast-growing plant in the Azores, is a promising source of AChE inhibitors. More work is being carried out to fully characterize the active compounds and their mechanisms of action.

References: 1. Ellman, G.L. Courtney, K.D. Andres, V. Feather-Stone, R.M. (1961) Biochem. Pharmacol. 7 88–95.