Abstract
Cholinesterases, involved in acetylcholine catabolism in the central and peripheral nervous system, have been strongly linked with neurodegenerative diseases. Current therapeutic approaches using synthetic drugs present several side effects. Hence, there is an increasing research interest in naturally-occurring dietary polyphenols, which are also considered efficacious. Food processing by-products such as brewer’s spent grain (BSG) would be a potential bio-source of polyphenols. In this study, polyphenol-rich BSG extracts using 60% acetone and 0.75% NaOH solutions were generated, which were further subjected to liquid–liquid partitioning using various organic solvents. The water-partitioned fractions of the saponified extracts had the highest total polyphenol content (6.2 ± 2.8 mgGAE/g dw) as determined by Folin–Ciocalteu reagent, while the LC-MS/MS showed ethyl acetate fraction with the highest phenolics (2.9 ± 0.3 mg/g BSG dw). The best inhibitions of acetyl- (37.9 ± 2.9%) and butyryl- (53.6 ± 7.7%) cholinesterases were shown by the diethyl ether fraction of the saponified extract. This fraction contained the highest sum of quantified phenolics (99 ± 21.2 µg/mg of extract), and with significant (p < 0.01) inhibitory contribution of decarboxylated-diferulic acid. Amongst the standards, caffeic acid presented the highest inhibition for both cholinesterases, 25.5 ± 0.2% for acetyl- and 52.3 ± 0.8% for butyryl-cholinesterase, respectively, whilst the blends insignificantly inhibited both cholinesterases. The results showed that polyphenol-rich BSG fractions have potentials as natural anti-cholinesterase agents.
Highlights
Evidence in the current literature suggests a strong link to the protective effects of dietary polyphenols towards the prevention of so called “diseases of civilization”, i.e., chronic non-communicable diseases, and protective effects justified via the “biochemical scavenger theory” [1,2]
Polyphenol standards, p-coumaric acid (p-CA), ferulic acid (FA), caffeic acid (CafA), protocatechuic acid (ProA), 4-hydroxybenzoic acid (4-HBA) and +(-)catechin (Cat), chemicals, reagents (Folin Ciocalteu, Ellman’s or 5,5 -Dithiobis(2-nitrobenzoic acid)( DTNB), inhibitor standard, proteins, substrates and enzymes necessary to determine in vitro the total phenolic content and cholinesterase inhibitory activities were purchased from Merck
brewer’s spent grain (BSG) represent a clear opportunity to be exploited as a potential source of bioactive compounds if processed in the right way, and further its corresponding polyphenolic extracts be accepted and utilized in health and food processing
Summary
Evidence in the current literature suggests a strong link to the protective effects of dietary polyphenols towards the prevention of so called “diseases of civilization”, i.e., chronic non-communicable diseases, and protective effects justified via the “biochemical scavenger theory” [1,2]. Choline is an important quaternary amine responsible for the structural integrity and signaling functions of cell membranes, which directly affects the cholinergic neurotransmission [6]. Acetylcholine and butyrylcholine are important metabolites of choline; acetylcholine is the main neurotransmitter at autonomic preganglionic nerve terminals and mostly prevalent in cholinergic synapses of the central and peripheral nervous system [7,8]. A decrease of acetylcholine levels in the cholinergic synapses in the brain regions seems to be a critical element in the development of AD. Cholinesterases, i.e., acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), are enzymes that hydrolyze acetylcholine and butyrylcholine, respectively, and their inhibition is a current therapeutic target [4]. Some plant-derived alkaloids such as galantamine, tacrine and physostigmine are used and have shown symptomatic improvement in AD [5]
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