Anti-neuroinflammatory activities of extract and polymethoxyflavonoids from immature fruit peels of Citrus 'Hebesu'

Chronic neuroinflammation is reported to be associated in the progression of many neurodegenerative diseases and there is an increasing interest for the natural products as neuroprotective and anti-neuroinflammatory agents. In present research, we evaluated the potential inhibitory effects of extract, fractions, and isolated compounds from Citrus 'Hebesu' on lipopolysaccharide (LPS)-induced inflammatory responses using BV-2 murine microglial cells. The dried methanol extract (CH) was suspended in water and partitioned with hexane and ethyl acetate to give hexane soluble (CHH), ethyl acetate soluble (CHE), and water soluble (CHW) fractions. The extract (CH) and fractions CHH and CHE inhibited the expression of mRNA encoding pro-inflammatory cytokine interleukin (IL)-1 beta. CHE and CHH were further purified by various column chromatographic methods to obtain hesperidin (1), tangeretin (2), 5-hydroxy-6,7,8,3 ',4 '-pentamethoxyflavone (3), 3,5,6,7,8,3 ',4 '-heptamethoxyflavone (4), nobiletin (5), 3,4,5-trimethoxy-trans-cinnamic alcohol (6), and meranzin hydrate (7). Among them, three polymethoxyflavonoids, 3, 4, and 5 significantly inhibited the expression of IL-1 beta mRNA. Practical applications Citrus 'Hebesu' is a local cultivar in Hyuga City, Miyazaki prefecture, Japan and its immature fruits are consumed with different food recipes. Till now, there is no detailed study on the chemical constituents and anti-neuroinflammatory activity of this cultivar. In this study, seven compounds were isolated from the peels of immature fruits. Methanol extract, hexane, and ethyl acetate fractions and three polymethoxyflavonoids showed a significant inhibitory activity against expression of IL-1 beta mRNA. Consumption of peels of Citrus 'Hebesu' might play important role in the prevention and treatment of neurodegenerative diseases, however, detailed mechanism based in vivo studies are necessary in future for providing more scientific evidences.