An in vitro and in silico approach to cholinesterase inhibitory and antioxidant effects of the methanol extract, furanocoumarin fraction, and major coumarins of Angelica officinalis L. fruits

Abstract

Cholinesterase inhibitory and antioxidant activities of the methanol extract, furanocoumarin fraction, and major coumarins (imperatorin, xanthotoxin, and bergapten) of the fruits of Angelica officinalis L. growing in Poland were determined in the current study. Cholinesterase inhibition was tested against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) at 12.5, 25, 50, and 100 μg mL⁻¹ using ELISA microplate reader. Antioxidant activity of the samples was tested by in vitro models including radical scavenging activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH), N,N-dimethyl-p-phenylendiamine (DMPD) as well as ferrous ion-chelation capacity, ferric-(FRAP) and phosphomolibdenum-reducing antioxidant power (PRAP) assays at 500, 1000, and 2000 μg mL⁻¹. The extract was found to have strong inhibition against BChE (85.65 ± 1.49%) and low inhibition against AChE (27.49 ± 2.01%) at 100 μg mL⁻¹. Four major coumarins; imperatorin, isoimperatorin, xanthotoxin, and bergapten were identified in the extract by HPLC. Imperatorin (83.98 ± 0.99%), xanthotoxin (88.04 ± 0.83%), and bergapten (86.69 ± 2.56%) displayed strong inhibition towards BChE. Molecular docking studies confirmed potent interactions between BChE and the tested furanocoumarins. The samples did not possess radical scavenging activity against DPPH and DMPD, whereas they possessed a moderate level of FRAP and PRAP at the tested concentrations. To the best of our knowledge, the current work constitutes the first study on cholinesterase inhibitory and antioxidant activities of A. officinalis.

Introduction

The genus Angelica L. belongs to the family Apiaceae (syn. Umbelliferae) and comprises more than 60 species of medicinally important biennial or perennial herbs, which are distributed widely in Asia, Europe, and North America. Among its species; Angelica sinensis (Oliv.) Diels is a reputed Chinese plant, whose roots have been traditionally used for memory deficits (Wang et al., 2010). Several species of the genus Angelica such as Angelica dahurica (Kim et al., 2002), Angelica sinensis (Kang et al., 2001, Kang et al., 2003, Kim et al., 2007), and Angelica archangelica (Sigurdsson and Gudbjarnason, 2007) have been studied for their neurobiological effects on memory enhancement through cholinesterase inhibition. Cholinesterase inhibitors have become one of the most prescribed drug classes for the treatment of Alzheimer's disease (AD), which is characterized by abnormal shortage of neurotransmitter called “acetylcholine” (ACh) and butyrylcholine (BCh) in the brain (Orhan et al., 2006). Since ACh and BCh are hydrolyzed by acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), inhibition of the cholinesterases is important to increase ACh and BCh levels. On the other hand, oxidative injury caused by free radical formation and iron accumulation has been revealed to be some other factors in AD pathogenesis (Altamura and Muckenthaler, 2009).

In some previous studies, strong cholinesterase inhibitory effect of the Angelica species has been attributed to their rich coumarin content. Taking these findings into account, in the current study, we attempted to establish cholinesterase inhibitory and antioxidant activity of the methanol extract, furanocoumarin fraction, and major coumarins (imperatorin, xanthotoxin, and bergapten) of the fruits of Angelica officinalis L. For this purpose, AChE and BChE inhibitory activity was tested by spectrophotometric method of Ellman et al. (1961) at 12.5, 25, 50, and 100 μg mL⁻¹ concentrations. Molecular docking studies were also performed to establish interaction between the major coumarins and active gorge of BChE. Antioxidant activity of the samples was determined using anti-radical test methods against 2,2-diphenyl-1-picrylhydrazyl (DPPH) and N,N-dimethyl-p-phenylendiamine (DMPD) radicals as well as ferrous ion-chelation capacity, ferric-(FRAP) and phosphomolibdenum-reducing antioxidant power (PRAP) methods at 500, 1000, and 2000 μg mL⁻¹.