Background: Microalgae are aquatic chlorophyll-containing organisms comprising unicellular microscopic forms, and their biomasses are potential sources of bioactive compounds, biofuels and food-based products. However, the neuroprotective effects of microalgal biomass have not been fully explored. In this study, biomass from two Chlorella species was characterized, and their antioxidant, anticholinesterase and anti-amyloidogenic activities were investigated.

Results: GC-MS analysis of the extracts revealed the presence of some phenols, sterols, steroids, fatty acids and terpenes. Ethanol extract of Chlorella sorokiniana (14.21 mg GAE/g) and dichloromethane extract of Chlorella minutissima (20.65 mg QE/g) had the highest total phenol and flavonoid contents, respectively. All the extracts scavenged 2,2-diphenyl-1-picrylhydrazyl, 2,2-azinobis (3-ethylbenzothiazoline-6-sulfonate) and hydroxyl radicals. The highest metal chelating activity of the extracts was observed in the ethanol extracts of C. minutissima (102.60 μg/mL) and C. sorokiniana (107.84 μg/mL). Furthermore, the cholinesterase inhibitory activities of the extracts showed that ethanol extract of C. sorokiniana (13.34 μg/mL) exhibited the highest acetylcholinesterase inhibitory activity, while dichloromethane extract of C. minutissima (11.78 μg/mL) showed the highest butyrylcholinesterase inhibitory activity. Incubation of the β-amyloid protein increased the aggregation of amyloid fibrils after 96 h. However, ethanol extract of C. sorokiniana and C. minutissima inhibited further aggregation of Aβ1-42 and caused disaggregation of matured protein fibrils compared to the control. This study reveals the modulatory effects of C. sorokiniana and C. minutissima extracts on some mediators of Alzheimer's disease and provides insights into their potential benefits as functional food, nutraceutics or therapeutic agent for the management of this neurodegenerative disease.