Consumption of certain fruits and vegetables is now widely associated with chemoprevention of degenerative diseases like cancer and cardiovacsular disorders because of their antioxidant components. Polyphenols, a heterogeneous group of compounds, are one of these constituents. Hibiscus esculentus L. (Family Malvaceae), commonly referred to as okro, okra, or lady's finger, is an important component of diet in Nigeria and other countries in sub-Saharan Africa. In this article, we describe the polyphenol composition and antioxidant potential of H. esculentus of Nigerian origin. Quercetin glucoside (quercetrin) and an unidentified flavonoid were detected. In vitro antioxidant assay of methanol extract of the fruits showed potent antioxidant/radical scavenging activities with 50% inhibitory concentration values of 25 and 43 microL when analyzed by the xanthine oxidase and 2-deoxyguanosine methods, respectively. These data suggest that H. esculentus, popular especially during the rainy season in Nigeria and many tropical West, Central, and Eastern African countries, is a good contributor to the antioxidant status and disease chemoprevention of people in these countries. less...

Polyphenols are abundant micronutrients in our diet that have been credited with chemoprevention of diseases associated with oxidative stress. In this study, we investigated the whole ripened fruit of Dacryodes edulis (G.Don) H.J Lam, a multipurpose tree growing in West and Central Africa and other countries bordering the Gulf of Guinea, for polyphenol content as well as its antioxidant/radical scavenging capacity. Analysis of the methanol extract of the fruit by high-performance liquid chromatography coupled to an ultraviolet dual-array detector and mass-selective detector revealed the presence of catechol (9.27 mg/kg), gallate (10.40 mg/kg), methylgallate (0.88 mg/kg), ellagic acid (3.10 mg/kg), quercetin (0.21 mg/kg), and quercetin rhamnoside (0.76 mg/kg). The extract showed very high antioxidant potential (50% inhibitory concentration [IC(50)] = 14 microL), but a rather weak radical scavenging activity (IC(50) = 357 microL), when tested in vitro with the xanthine oxidase and 2-deoxyguanosine assay model systems, respectively. These results suggest that consumption of D. edulis could contribute to prevention of diseases that are related to oxidative stress. less...

Propolis was included in the Argentine Food Code as a functional food. The chemical parameters and antioxidant properties of propolis samples from the same colonies of Apis mellifera in San Juan (Cuyo region, Western Argentine) were compared every month for 1 year using two collection methods. Chemical parameters were analyzed by the spectrophotometric method and fingerprinting using high-performance liquid chromatography with ultraviolet detection. The antioxidant activities of propolis samples were measured using model systems including the analysis of the scavenging activities for 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals and the beta-carotene bleaching assay. The results showed that propolis had a higher free radical scavenging and lipid peroxidation inhibitory capacity than butylated hydroxytoluene and quercetin, antioxidants used in the pharmaceutical and food industries. The concentration required to scavenge 50% of free radicals (SC(50)) values differed depending on the sample collection month. Samples collected in November had the highest antioxidant capacity. In all cases, SC(50) values of propolis samples obtained by scraping were similar to those collected from a wire mesh (5 microg/mL for ABTS and 20-30 microg/mL for DPPH radicals). A significant positive correlation was found between the antioxidant capacity and flavonoid content of each analyzed extract. The chemical profiles were very similar. Galangin (3,5,7-trihydroxyflavone), an antioxidant compound, was detected in all samples as a major compound. The chromatographic profile suggests that of Baccharis sp., which would be one of the botanical sources of propolis from western Argentina, and the content of galangin can be used as a parameter for evaluating propolis quality. Our results suggest that Argentine propolis from Cuyo is a promising source of bioactive compounds as ingredients for developing functional foods with a beneficial impact on oxidative stress. less...

Abstract A comparison of alizarin red (AR) and fluorescein (FL) as target molecules in oxygen radical absorbance capacity (ORAC)-like methods is reported. Galangin, apigenin, ferulic acid, and coumaric acid decreased AR initial consumption rate, whereas quercetin, kaempferol, luteolin, caffeic acid, and sinapic acid inhibited its consumption through an induction time, associated with a repair mechanism. On the other hand, all compounds protected FL with a clear induction time. AR was more selective and provides ORAC-AR values considerably smaller for compounds of low reactivity. The ORAC-AR value for luteolin was nearly 200 times that of coumaric acid. However, the ratio of ORAC-FL values for luteolin and coumaric acid was only 1.2. This different selectivity implies that AR provides ORAC values more related to reactivity than FL. ORAC-AR values of infusions were considerably smaller than the corresponding ORAC-FL values. These differences are interpreted in terms of the capacity of FL to generate induction times, irrespective of the reactivity of the additive. It is proposed that comparison of ORAC-AR and ORAC-FL values could afford a rough estimation of the average reactivity of the antioxidants titrated by the ORAC-FL methodology. less...

Therapies to correct the DeltaF508 cystic fibrosis transmembrane conductance regulator (CFTR) folding defect require sensitive methods to detect channel activity in vivo. beta2 adrenergic receptor agonists, the CFTR stimuli commonly used in nasal potential difference assays, may not overcome the channel gating defects seen in DeltaF508 CFTR following plasma membrane localization. In this study we identify an agent, quercetin, that enhances detection of surface DeltaF508 CFTR, and is suitable for nasal perfusion. A screen of flavonoids in CFBE41o- cells stably transduced with DeltaF508 CFTR, corrected to the cell surface with low temperature growth, revealed that quercetin stimulated an increase in short-circuit current. This increase was dose-dependent in both fisher rat thyroid and CFBE41o- cells; high concentrations inhibited Cl(-) conductance. In CFBE41o- airway cells, quercetin (20 mug/ml) activated DeltaF508 CFTR, where beta2 adrenergic receptor agonist isoproterenol did not. Quercetin had small effects on cAMP levels, but did not produce detectable phosphorylation of isolated CFTR R-domain, suggesting activation independent of channel phorphorylation. When perfused in the nares of Cftr + mice, quercetin (20 microg/ml) produced hyperpolarization of potential difference that was absent in Cftr -/- mice. Finally, quercetin-induced dose-dependent hyperpolarization of nasal potential difference was also seen in normal human subjects. Quercetin activates CFTR mediated anion transport in respiratory epithelia in vitro and in vivo, and may be useful in studies intended to detect rescue of DeltaF508 CFTR by nasal potential difference. less...

Epidemiological and mechanistic evidence on the association of quercetin-rich food intake with lung cancer risk and carcinogenesis are inconclusive. We investigated the role of dietary quercetin and the interaction between quercetin and P450 and GST polymorphisms on lung cancer risk in 1822 incident lung cancer cases and 1991 frequency matched controls from the Environment And Genetics in Lung cancer Etiology (EAGLE) study. In non-tumor lung tissue from 38 adenocarcinoma patients, we assessed the correlation between quercetin intake and mRNA expression of the same P450 and GST metabolic genes. Multivariate odds-ratios (ORs) and 95% confidence intervals (CIs) for sex-specific quintiles of intake were calculated using unconditional logistic regression adjusting for putative risk factors. Frequent intake of quercetin-rich foods was inversely associated with lung cancer risk (OR=0.49;95% CI=0.37-0.67; p-trend<0.001), and did not differ by P450 or GST genotypes, gender, or histological subtypes. The association was stronger in subjects who smoked >20 cigarettes per day (OR=0.35;95% CI=0.19-0.66; p-trend=0.003). Based on a 2-sample t-test, we compared gene expression and high-versus-low consumption of quercetin-rich foods and observed an overall up-regulation of GSTM1, GSTM2, GSTT2, and GSTP1 as well as a down-regulation of specific P450 genes (p-values<0.05, adjusted for age and smoking status). In conclusion, we observed an inverse association of quercetin-rich food with lung cancer risk and identified a possible mechanism of quercetin-related changes in the expression of genes involved in the metabolism of tobacco-carcinogens in humans. Our findings suggest an interplay between quercetin intake, tobacco smoking, and lung cancer risk. Further research on this relationship is warranted. less...

A lack of adequate or accepted research methodology has been a major obstacle to study herbal medicines. In this study, instead of the prevalent hyphenated chromatographies, common high performance liquid chromatography equipped with ultraviolet detector (HPLC-UV) and multivariate statistical analysis were utilized to assess the qualities of total flavones of sea buckthorn (TFS), an 85% ethanol extract of the sea buckthorn berries. Two complementary HPLC-UV methods were developed, validated and combined to comprehensively determine the ingredients in TFS. Principal component analysis (PCA) and partial least square-discriminant analysis (PLS-DA) of the combined analytical data showed that the six batches of TFS could be well differentiated. Hierarchical cluster analysis (HCA) using Ward's minimum variance method of the PLS-DA loading matrix demonstrated the known ingredients (quercetin, kaempferol, isorhamnetin, oleanolic acid and ursolic acid) and three unknown ingredients in TFS significantly contributed to the quality differences. A PLS regression model indicated that the results of the present method correlated well with the content of total flavones, which is now the quality control approach of TFS. Results from this study indicated that the proposed method is reliable for the quality reassessment of some widely used herbal extracts. less...

We found that the acetone extract of the peel of Japanese persimmon (Diospyros kaki 'Fuyu') inhibits melanin biosynthesis in mouse B16 melanoma cells. The activity-guided purification of the extract resulted in isolation of two active compounds, which have been identified as flavonoid glycosides, isoquercitrin (quercetin-3-O-glucoside) and hyperin (quercetin-3-O-galactoside) by spectral analysis. Isoquercitrin and hyperin strongly inhibited the production of melanin (IC(50): 21.7 and 18.2 microM, respectively). The inhibitory effects were found to be mediated by suppression of tyrosinase expression. less...

High-speed countercurrent chromatography (HSCCC) was successfully used to isolate three bioactive compounds, i.e., amygdalin from bitter almond and taxifolin-3-glucoside and quercetin-3-galactoside (hyperoside) from water extract of Agrimonia pilosa Ledeb, respectively. From 1 g of the crude extract 65 mg of amygdalin was isolated at 97% purity using a two-phase solvent system composed of ethyl acetate-n-butanol-water (5:2:5, v/v) by preparative HSCCC. From a 400 mg amount of crude extract of Agrimonia pilosa Ledeb, 11 mg of taxifolin-3-glucoside and 8 mg of hyperoside were isolated at 96% purity using a two-phase solvent system composed of ethyl acetate-methanol-water (25:1:25, v/v) similarly by preparative HSCCC. The final structural identification was performed by MS, (1)H-NMR and (13)C-NMR Spectra. less...

Background and purpose: Quercetin is a major flavonoid that contributes to the reduced risk of cardiovascular disease associated with dietary ingestion of fruits and vegetables. We have pharmacologically characterized the effect of quercetin, and its sulphate and glucuronide metabolites, on vasoconstrictor and vasodilator responses in the porcine isolated coronary artery. Experimental approach: Segments of the porcine coronary artery were prepared for either isometric tension recording or determination of cyclic GMP content. The effect of quercetin and metabolites on submaximal responses to U46619 was examined in the presence and absence of substance P, bradykinin, forskolin, sodium nitroprusside (SNP) and glyceryl trinitrate (GTN). Key results: Quercetin and quercetin 3'-sulphate inhibited endothelin and U46619-induced contractions with greater potency (three- to fivefold) against the former, while quercetin 3-glucoronide was inactive. Quercetin enhanced both the cyclic GMP content of the artery (threefold) and cyclic GMP-dependent relaxations to GTN and SNP (two to threefold), but forskolin-induced relaxations were unaffected. Although the effect of quercetin was qualitatively similar to that noted for UK-114,542, a selective inhibitor of phosphodiesterase 5, it was still evident against SNP-induced relaxations in the presence of 10 nM UK-114,542. Quercetin and quercetin 3'-sulphate significantly reduced the development of GTN-associated 'tolerance'. Conclusions and implications: Quercetin and quercetin 3'-sulphate inhibited receptor-mediated contractions of the porcine isolated coronary artery by an endothelium-independent action. Quercetin selectively enhanced cyclic-GMP-dependent relaxations by a mechanism not involving phosphodiesterase 5 inhibition. In addition, quercetin and quercetin 3'-sulphate opposed GTN-induced tolerance in vitro, which may be beneficial for patients treated for angina pectoris. less...