Prospecting for galanthamine and acetylcholinesterase inhibition activity in Indian Amaryllidaceae species
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Date
18-11-11
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University of Agricultural Sciences GKVK, Bangalore
Abstract
Galanthamine is an isoquinoline tertiary alkaloid originally derived from
bulbs of the Amaryllidaceae family of flowering plants that includes
daffodils and the common snowdrop (Galanthus woronowii).
Galanthamine reversibly and specifically binds to the active site of
acetylcholinesterase (AChE), thereby inhibiting the enzyme that
hydrolyzes the neurotransmitter acetylcholine into acetate and choline.
Galanthamine is used for the symptomatic treatment of Alzheimer’s
disease. Besides galanthamine, a few other acetylcholinesterase
inhibitors have been reported from Amaryllidaceae members as well as
from other families.
Unfortunately very little is known about the acetylcholine esterase
inhibition activity of Indian Amaryllidaceae members. In this study an
attempt has been made to evaluate the acetylcholine esterase inhibition
activity of a set of Amaryllidaceae members occurring in the country.
The specific objectives of the study were a) to evaluate selected Indian
Amaryllidaceae species for their in vitro acetylcholinesterase inhibition
activity and b) to undertake bioactivity guided fractionation and
characterization of compounds responsible for acetylcholinesterase
inhibition.
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We evaluated 134 bulbs, 55 leaves, 3 roots and 2 neck parts collected
from 139 plants belonging to 43 species of Indian Amaryllidaceae for
their galanthamine presence and content using TLC, HPLC, LC-MS.
Galanthamine was predominantly found in bulbs (85.82 %) followed by
leaves (20.00 %). Galanthamine content ranged from 0.037 to 1.5 % by
dry weight in the different members of Amaryllidaceae. Hippeastrum
solandriflorum, Hymenocallis caribeae and Zephyranthus rosea showed a
galanthamine content > 1%. Thus Indian Amaryllidaceae member could
be used as potential sources for the commercial extraction of
galanthamine.
Methanolic extract of leaves of Crinum asiaticum showed a significant
inhibition of AChE (IC50 = 10.52 μg/ml). However unlike the bulbs, the
leaves of the plant did not show any trace of galanthamine. Bioassay
guided fractionation of the crude extract of the leaves revealed the active
principle, lycorine (IC50 35.03 μg/ml). The structure of the molecule was
confirmed by its NMR and LC mass spectral data. Although lycorine has
been reported in literature (Ptak et al., 2009) to contain AChE inhibitory
activity, this is the first report of the molecule in the leaves of C.
asiaticum.