Cellular Antioxidant Activity and Pharmacokinetic Study of Polymethoxylated Flavonoids in Extract of Citrus reticulata 'Chachi' Peel

A rat pheochromocytoma (PC12) cell line was used to study the effects of several polymethoxylated flavonoids (PMEs) and extract of Citrus reticulata 'chachi' peel (ECRP) on hydrogen peroxide (H2O2)-induced apoptosis. In PC12 cells, H2O2-induced apoptosis was accompanied by rising malondialdehyde (MDA) level, as well as reducing activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px). However, treating PC12 cells with PMFs and ECRP blocked H2O2-induced apoptosis by decreasing the MDA level and augmenting the activities of SOD and GSH-Px. Moreover, liquid chromatography coupled with UV detection was developed to simultaneously determine nobiletin and tangeretin in rat plasma after oral administration of ECRP, using quercetin as the internal standard. Plasma samples extracted by liquid-liquid extraction were separated on a Phenomenex Luna C-18 column and detected by a UV detector. The calibration curves were linear over the range of 5.5 - 2757 ng mL(-1) for nobiletin (r(2) > 0.999) and 6.3 - 2847 ng miri for tangeretin (r(2) > 0.999), respectively. The lower limits of quantification were 0.2 ng mL(-1) for nobiletin and tangeretin. The intra- and inter-day precisions were less than 15% and the accuracies ranged from 3.4% to 12.2%. The recoveries of nobiletin and tangeretin were 91.1% - 95.4% and 93.7 - 96.2% respectively. Nobiletin and tangeretin remained stable at low temperatures (-20 degrees C and 4 degrees C) and after freeze thaw cycles. The validated method was successfully applied to investigate the pharmacokinetics of the main PMFs of ECRP extract after oral administration to rat.