Phenolic composition, antioxidant activity, anticholinesterase potential and modulatory effects of aqueous extracts of some seaweeds on β-amyloid aggregation and disaggregation.

Seaweeds contain bioactive compounds with different biological activities. They are used as functional ingredients for the development of therapeutic agents to combat degenerative diseases. This study investigated the phenolic composition, antioxidant activity, cholinesterase inhibitory and anti-amyloidogenic activities of aqueous extracts of (J.Agardh) Papenfuss (Gracilariaceae) (RED-AQ), (Osbeck) Papenfuss (Lessoniaceae) (ECK-AQ), (C.Agardh) Linnaeus (Ulvaceae) (URL-AQ) and (Turner) Kützing (Gelidiaceae) (GEL-AQ). Phenolic composition of the seaweed extracts was determined using liquid chromatography mass spectrometry. Radical scavenging and metal chelating activities were assessed . The effect of the extracts (21-84 µg/mL) on acetylcholinesterase and butyrylcholinesterase activities were also investigated using an colorimetric assay. Transmission electron microscope and thioflavin-T fluorescence assay were used to examine the anti-amyloidogenic activities of the extracts. Phloroglucinol, catechin, epicatechin 3-glucoside were identified in the extracts. ECK-AQ (IC=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 (IC = 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 (Aβ) fibrils and aggregates was observed in electron micrographs of the control after 72 and 96 h. The reduction of Aβ aggregates occurred after co-treatment with the seaweed extracts. ECK-AQ, GEL-AQ, URL-AQ and RED-AQ may possess neuroprotective potential and could be explored for the management of Alzheimer's disease.