Different Neuroprotective Activities of Proanthocyanidin-Enriched Fractions of Lotus Species

Flavonoid-rich Lotus species are promising sustainable sources of bioactive phytochemicals due to their adaptability, high biomass production, and symbiosis with nitrogen-fixing Rhizobium spp. Among flavonoids, many beneficial effects for human health, ranging from antioxidant activities to the inhibition of carcinogenesis, are attributed to proanthocyanidins (PAs). This study compared the neuroprotective properties of leaf extracts from PA-rich Lotus corniculatus (Lc), PA-depleted Lotus tenuis (Lt), and Lc × Lt interspecific hybrid (Lh2) with intermediate PA levels. Acetone-soluble and -insoluble fractions from Lc and Lh2 contained flavan-3-ols and PA oligomers, while Lt lacked these compounds. Neuroprotective assays in SH-SY5Y cells and Caenorhabditis elegans revealed that Lc and, although to a lesser extent, Lh2 extracts enhanced cell viability and reduced motoneuron degeneration, whereas Lt extracts exhibited cytotoxicity and did not induce motoneuron viability rescue in C. elegans. Further analysis confirmed that pure flavan-3-ols, which represent the main components of the acetone-soluble fraction in Lc and Lh2, and cyanidin, which derives from the hydrolysis of their insoluble fractions, significantly promoted neuronal survival, while the flavonol quercetin showed no protective effects. These findings highlight the neuroprotective potential of PA-rich Lotus spp. and suggest their application as novel sources of health-promoting phytochemicals.