Abstract
Context: Seaweeds contain bioactive compounds with different biological activities. They are used as functional ingredients for the development of therapeutic agents to combat degenerative diseases.Objective: This study investigated the phenolic composition, antioxidant activity, cholinesterase inhibitory and anti-amyloidogenic activities of aqueous extracts of Gracilaria beckeri (J.Agardh) Papenfuss (Gracilariaceae) (RED-AQ), Ecklonia maxima (Osbeck) Papenfuss (Lessoniaceae) (ECK-AQ), Ulva rigida (C.Agardh) Linnaeus (Ulvaceae) (URL-AQ) and Gelidium pristoides (Turner) Kützing (Gelidiaceae) (GEL-AQ).Materials and methods: Phenolic composition of the seaweed extracts was determined using liquid chromatography mass spectrometry. Radical scavenging and metal chelating activities were assessed in vitro. The effect of the extracts (21–84 µg/mL) on acetylcholinesterase and butyrylcholinesterase activities were also investigated using an in vitro colorimetric assay. Transmission electron microscope and thioflavin-T fluorescence assay were used to examine the anti-amyloidogenic activities of the extracts.Results: Phloroglucinol, catechin, epicatechin 3-glucoside were identified in the extracts. ECK-AQ (IC50=30.42 and 280.47 µg/mL) exhibited the highest OH• scavenging and metal chelating activities, while RED-AQ (41.23 and 334.45 µg/mL) exhibited the lowest. Similarly, ECK-AQ (IC50 = 49.41 and 52.11 µg/mL) exhibited higher inhibitory effects on acetylcholinesterase and butyrylcholinesterase activities, while RED-AQ (64.56 and 63.03 µg/mL) showed the least activities. Rapid formation of β-amyloid (Aβ1-42) fibrils and aggregates was observed in electron micrographs of the control after 72 and 96 h. The reduction of Aβ1-42 aggregates occurred after co-treatment with the seaweed extracts.Discussion and conclusion: ECK-AQ, GEL-AQ, URL-AQ and RED-AQ may possess neuroprotective potential and could be explored for the management of Alzheimer’s disease.
Highlights
Alzheimer’s disease is a neurological disorder which affects millions of aged individuals across the world (Li et al 2018)
Phloroglucinol was the only phlorotannin identified in ECK-AQ, RED-AQ and URL-AQ but was absent in GEL-AQ (Tables 1–4)
Our results revealed that ECK-AQ, RED-AQ, URL-AQ and GEL-AQ inhibited acetylcholinesterase activity which is consistent with the report of Shanmuganathan and Devi (2016)
Summary
Alzheimer’s disease is a neurological disorder which affects millions of aged individuals across the world (Li et al 2018) It is the most common kind of dementia that is characterized by redox imbalance in the neurons, cholinergic deficit, formation of neurotoxic amyloid senile plaques, neuroinflammation and neurodegeneration which leads to cognitive decline, learning problems and memory loss (Feng and Wang 2012; MendiolaPrecoma et al 2016). Some of the free radicals produced such as hydroxyl radicals are able to induce oxidative damage to the neurons which leads to cell death and progression of AD (Olasehinde et al 2017; Oboh, Ademosun, et al 2018a) Though cholinesterase inhibitors such as galathanmine, rivastigmine and prostigmine are preferred drugs used for the management of AD, these drugs are able to mitigate cholinergic deficit and cannot prevent or halt the progression of AD. There has been a great interest in the search for an alternative therapeutic approach for the treatment and/or management of AD
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