The bioactive components of Coreopsis tinctoria (Asteraceae) capitula: Antioxidant activity in vitro and profile in rat plasma

The antioxidant components of Coreopsis tinctoria have not been clearly identified; thus, here eleven constituents were isolated and identified from the capitula of Coreopsis tinctoria, in which taxifolin (7), 3,5-di-O-caffeoylquinic acid (9) and 4,5-di-O-caffeoylquinic acid (10) were identified for the first time. All eleven compounds possessed antioxidant activities based on DPPH assay and cellular antioxidant activity assay. Especially, okanin (11) and isookanin (6) exhibited excellent DPPH scavenging activities with the EC50 of 6.2 and 10.6 µM, respectively, which were stronger than those of ascorbic acid and butylated hydroxytoluene (positive controls) with the EC50 of 30.4 and 45.8 µM, respectively. Okanin and isookanin showed comparable cellular antioxidant activities to quercetin with the IC50 of 11.0 and 14.4 µM, respectively. Additionally, the two most potent antioxidants, okanin and isookanin, were detectable and reached maximal concentration of 10.5 and 10.6 µM in plasma at 20 min after oral administration of 100 mg/kg ethanol extract of Coreopsis tinctoria capitula. In conclusion, our results indicate that Coreopsis tinctoria capitula might be developed as antioxidant sources.