Lycii fructus extract ameliorates hydrogen peroxide-induced cytotoxicity through indirect antioxidant action.

Lycii Fructus is the dried ripe fruits of Lycium chinense and L. barbarum, which has long been used as a traditional food material in East Asia. The purpose of this study was to investigate the role of the indirect antioxidative action in the Lycii fructus extract (LFE)-induced cytoprotective effect in vitro. LFE significantly enhanced the expression of the drug-metabolizing enzyme genes and intracellular glutathione level in mouse hepatoma Hepa1c1c7 cells. LFE stimulated the nuclear translocation of aryl hydrocarbon receptor as well as nuclear factor (erythroid-derived 2)-like 2. The pretreatment of LFE for 24 h, but not for 30 min, completely inhibited the cytotoxic effect of hydrogen peroxide. Furthermore, chlorogenic acid, one of the main constituents of LFE, showed cytoprotection against hydrogen peroxide with the enhanced phase 2 enzyme gene expression. These results suggested that LFE exhibits a cytoprotective effect, possibly through the enhancement of the antioxidant gene expression. ABBREVIATIONS: LFE: Lycii Fructus extract; GSH: glutathione; NQO1: NAD(P)H:quinone oxidoreductase 1; HO-1: heme oxygenase-1; GCLC: glutamate-cysteine ligase, catalytic subunit; xCT: a component of cysteine/glutamate antiporter (cystine/glutamate exchanger); CYP1A1: cytochrome P450 1A1; GSH: glutathione; AhR: aryl hydrocarbon receptor; Nrf2: nuclear factor (erythroid-derived 2)-like 2; CGA: chlorogenic acid; RT-PCR: reverse transcription-polymerase chain reaction; DTT: dithiothreitol; PMSF: phenylmethylsulfonyl fluoride; ARE: antioxidant response element; XRE: xenobiotic responsive element.

A novel tag-free probe for targeting molecules interacting with a flavonoid catabolite.

3,4-Dihydroxyphenylacetic acid (DOPAC) is one of the colonic microflora-produced catabolites of quercetin 4'-glucoside (Q4'G). Although the interaction of DOPAC with cellular proteins might be involved in its biological activity, the actual proteins have not yet been identified. In this study, we developed a novel tag-free DOPAC probe to label the targeted proteins by the copper(I)-catalyzed azide alkyne cycloaddition (CuAAC) and verified its efficacy. Various labeled proteins were detected by the DOPAC probe with the azide labeled biotin and a horseradish peroxidase (HRP)-streptavidin complex. Furthermore, a pulldown assay identified Keap1 and aryl hydrocarbon receptor (AhR) as the target proteins for the phase 2 enzyme up-regulation.

3,4-Dihydroxyphenylacetic acid is a predominant biologically-active catabolite of quercetin glycosides.

Since dietary flavonoid glycosides, including quercetin 4'-glucoside from onion, are poorly absorbed from the gastrointestinal tract, they are converted into smaller phenolic acids, which can be absorbed into the circulation. The purpose of this study was to compare the effects of the major phenolic acid catabolites of quercetin 4'-glucoside, including 3,4-dihydroxyphenylacetic acid (DOPAC), 3-hydroxyphenylacetic acid, 3,4-dihydroxybenzoic acid (protocatechuic acid) and hippuric acid, on the antioxidant activity and phase II cytoprotective enzyme induction in vitro. Both DOPAC and protocatechuic acid, having a catechol moiety, exhibited both DPPH radical scavenging and superoxide dismutase-like activities, whereas 3-hydroxyphenyl acetic acid and hippuric acid did not. DOPAC also more potently enhanced the gene expression of several phase II drug-metabolizing enzymes than the other phenolic acid catabolites. DOPAC significantly inhibited the hydrogen peroxide-induced cytotoxicity in hepatocytes with the enhancement of the total glutathione S-transferase activity. In conclusion, DOPAC may play a key role in the antioxidative potential of the colonic lumen after the ingestion of the quercetin glycoside-rich onion.

Ascorbic acid synergistically potentiates phloxine b-induced photocytotoxicity in human acute promyelocytic leukemia cells.

Ascorbic acid (AsA) is known as an antioxidant but concomitantly possesses a pro-oxidant property. Because the impact of AsA on photodynamic therapy response is unclear, we investigated the effect of AsA on photocytotoxicity induced by phloxine B in human acute promyelocytic leukemia HL-60 cells. AsA synergistically enhanced phloxine B-induced photocytotoxic effects, including inhibition of cell proliferation, DNA ladder formation, and caspase-3 activation, whereas AsA itself showed no photocytotoxicity. AsA also enhanced the consumption of the reduced glutathione level compared with the cells treated with phloxine B alone under the light condition. Combination of AsA with phloxine B under the light condition enhanced the phosphorylation of c-Jun N-terminal kinase and p38 mitogen-activated protein kinase (MAPK). These effects were completely cancelled by catalase. These results suggest that AsA synergistically enhances phloxine B-induced photocytotoxicity, possibly through the extracellular oxidative stress-dependent MAPK pathway activation.