Acetylcholinesterase (AChE) inhibitory activity, antioxidant properties and phenolic composition of two Aframomum species

Abstract

Aframomum species are widely used as a food supplement and remedy in folklore medicine for the management of several diseases. This study was designed to investigate the acetylcholinesterase inhibitory activity and antioxidant properties of phenolic-rich extracts from two Aframomum species: Aframomum danielli (Hook F.) K. Schum (Zingiberaceae) and Aframomum melegueta (Roscoe) K. Schum (Zingiberaceae) seeds. Acetylcholinesterase inhibitory activity and antioxidant properties [inhibition of quinolinic acid (QA)-induced lipid peroxidation in rat brain, reducing properties, 2,2-azinobis (3-ethylbenzo-thiazoline-6-sulfonate) (ABTS) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging abilities] using in vitro models were evaluated. Phenolic composition of the seed extracts using reversed phase high performance chromatography (RP-HPLC) and gas chromatography coupled with flame ionization detector (GC-FID) were also assessed. Both extracts exhibited acetylcholinesterase inhibitory activity in a dose-dependent manner (125-1000 μg/mL); however, A. melegueta extract (IC50=373.33 μg/mL) had a significantly higher (p<0.05) acetylcholinesterase inhibitory activity than A. danielli extract (IC50=417.10 μg/mL). Furthermore, both extracts significantly decreased QA-elevated brain malondialdehyde (MDA) contents, reduced Fe3+ to Fe2+ and scavenged DPPH and ABTS radicals. Phenolic characterization of the seeds by RP-HPLC at 280 nm showed abundance of quercetin and kaempferol in A. melegueta and chlorogenic acid in A. danielli, whereas GC-FID revealed that p-hydroxybenzoic acid was abundant in both seeds. Inhibitory effect of these extracts on acetylcholinesterase activity and their antioxidant property could be attributed to the combined effect of phenolic and non-phenolic constituents of the seeds. These effects could be part of the possible biochemical mechanism by which these seeds elicit their protection against oxidative stress in brain; however, A. melegueta showed the more promising potential.