Characterization and Quantification of Luteolin-Metal Complexes in Aqueous Extract of Lonicerae Japonicae Flos and Huangshan Wild Chrysanthemum.

Luteolin is a flavonoid compound widely found in vegetables, fruits, and medicinal plants. In this study, the reaction conditions for luteolin and five metal ions (Ca2+, Mg2+, Zn2+, Fe3+, and Cu2+) to form complexes in hot water were optimized, which was at a molar ratio of 1 : 1 for luteolin and metal ions at 90°C in a volume of 20 mL for 2 h, and the ability of luteolin to form complexes with Cu2+ was the strongest. The DPPH scavenging test showed that luteolin exerted a dose-dependent effect on the clearance of free radicals; luteolin-Cu2+ complexes and luteolin-Fe3+ complexes accentuated the clearance of free radicals. Furthermore, we used high performance liquid chromatography (HPLC) to analyze luteolin in samples from two medicinal plants, obtained from the dissolution of aqueous extracts in two different solvents. The results showed that the peak areas for luteolin in the samples dissolved in 20% formic acid-methanol were significantly larger than those from the samples dissolved in methanol alone, with increases in the peak area being 135.6% (Lonicerae Japonicae Flos), and 161.16% (Huangshan wild chrysanthemum). The aforementioned results indicate that complexes formed from organic compounds and metal ions are present in the decoction of a plant.

Safety and anti-hyperglycemic efficacy of various tea types in mice.

Tea, a beverage consumed worldwide, has proven anti-hyperglycemic effects in animal models. Better efficacies of tea beverages are frequently associated with high-dose levels, whose safety attracts considerable attention. Based on the inherent nature of tea catechin oxidation, fresh tea leaves are manufactured into diverse tea types by modulating the oxidation degree of catechins. The present study aimed to assess various tea types for their safety properties and anti-hyperglycemic effects. Mice were allowed free access to tea infusion (1:30, w/v) for one week, and the rare smoked tea caused salient adverse reactions, including hepatic and gastrointestinal toxicities; meanwhile, the widely-consumed green and black teas, unlike the rare yellow tea, suppressed growth in fast-growing healthy mice. When mice were fed a high-fat diet and allowed free access to tea infusion (1:30, w/v) for 25 days, only yellow tea significantly reduced blood glucose. Therefore, various teas showed different safety profiles as well as anti-hyperglycemic efficacy strengths. To achieve an effective and safe anti-hyperglycemic outcome, yellow tea, which effectively suppressed high-fat diet-induced early elevation of hepatic thioredoxin-interacting protein, is an optimal choice.

Certain (-)-epigallocatechin-3-gallate (EGCG) auto-oxidation products (EAOPs) retain the cytotoxic activities of EGCG.

(-)-Epigallocatechin-3-gallate (EGCG) from green tea has anti-cancer effect. The cytotoxic actions of EGCG are associated with its auto-oxidation, leading to the production of hydrogen peroxide and formation of numerous EGCG auto-oxidation products (EAOPs), the structures and bioactivities of them remain largely unclear. In the present study, we compared several fundamental properties of EGCG and EAOPs, which were prepared using 5mg/mL EGCG dissolved in 200mM phosphate buffered saline (pH 8.0 at 37°C) and normal oxygen partial pressure for different periods of time. Despite the complete disappearance of EGCG after the 4-h auto-oxidation, 4-h EAOPs gained an enhanced capacity to deplete cysteine thiol groups, and retained the cytotoxic effects of EGCG as well as the capacity to produce hydrogen peroxide and inhibit thioredoxin reductase, a putative target for cancer prevention and treatment. The results indicate that certain EAOPs possess equivalent cytotoxic activities to EGCG, while exhibiting simultaneously enhanced capacity for cysteine depletion. These results imply that EGCG and EAOPs formed extracellularly function in concert to exhibit cytotoxic effects, which previously have been ascribed to EGCG alone.