Chromatographic techniques for the determination of putative dietary anticancer compounds in biological fluids

Ascorbic Acid-Caused Quenching Effect of Protein Clusteroluminescence Probe: The Fast Fluorescent Detection of Ascorbic Acid in Vegetables

It is interesting and meaningful to explore fluorescent probes for novel rapid detection methods. In this study, we discovered a natural fluorescence probe, bovine serum albumin (BSA), for the assay of ascorbic acid (AA). Due to clusterization-triggered emission (CTE), BSA has the character of clusteroluminescence. AA shows an obvious fluorescence quenching effect on BSA, and the quenching effect increases with increasing concentrations of AA. After optimization, a method for the rapid detection of AA is established by the AA-caused fluorescence quenching effect. The fluorescence quenching effect reaches saturation after 5 min of incubation time and the fluorescence is stable within more than one hour, suggesting a rapid and stable fluorescence response. Moreover, the proposed assay method shows good selectivity and a wide linear range. To further study the mechanisms of AA-caused fluorescence quenching effect, some thermodynamic parameters are calculated. The main intermolecular force between BSA and AA is electrostatic, presumably leading to the inhibiting CTE process of BSA. This method also shows acceptable reliability for the real vegetable sample assay. In summary, this work will not only provide an assay strategy for AA, but also open an avenue for the application expansion of CTE effect of natural biomacromolecules.

Electrochemical Detection of Ascorbic Acid in Oranges at MWCNT-AONP Nanocomposite Fabricated Electrode

Ascorbic acid (AA) is an essential vitamin in the body, influencing collagen formation, as well as norepinephrine, folic acids, tryptophan, tyrosine, lysine, and neuronal hormone metabolism. This work reports on electrochemical detection of ascorbic acid (AA) in oranges using screen-print carbon electrodes (SPCEs) fabricated with multi-walled carbon nanotube- antimony oxide nanoparticle (MWCNT-AONP) nanocomposite. The nanocomposite-modified electrode displayed enhanced electron transfer and a better electrocatalytic reaction towards AA compared to other fabricated electrodes. The current response at the nanocomposite-modified electrode was four times bigger than the bare electrode. The sensitivity and limit of detection (LOD) at the nanocomposite modified electrode was 0.3663 [AA]/µM and 140 nM, respectively, with linearity from 0.16–0.640 μM and regression value R² = 0.985, using square wave voltammetry (SWV) for AA detection. Two well-separated oxidation peaks were observed in a mixed system containing AA and serotonin (5-HT); and the sensitivity and LOD were 0.0224 [AA]/µA, and 5.85 µΜ, respectively, with a concentration range from 23 to 100 µM (R² = 0.9969) for AA detection. The proposed sensor outperformed other AA sensors reported in the literature. The fabricated electrode showed great applicability with excellent recoveries ranging from 99 to 107 %, with a mean relative standard deviation (RSD) value of 3.52 % (n = 3) towards detecting AA in fresh oranges.

Ascorbic Acid determination in commercial fruit juice samples by cyclic voltammetry

A method was developed for assessing ascorbic acid concentration in commercial fruit juice by cyclic voltammetry. The anodic oxidation peak for ascorbic acid occurs at about 490 mV on a Pt disc working electrode (versus SCE). The influence of the potential sweep speed on the peak height was studied. The obtained calibration graph shows a linear dependence between peak height and ascorbic acid concentration in the domain (0.1-10 mmol.L(-1)). The equation of the calibration graph was y = 6.391x + 0.1903 (where y represents the value of intensity measured for the anodic peak height, expressed as muA and x the analyte concentration, as mmol.L(-1), r(2) = 0.9995, r.s.d. = 1.14%, n = 10, C(ascorbic acid) = 2 mmol.L(-1)). The developed method was applied to ascorbic acid assessment in fruit juice. The ascorbic acid content determined ranged from 0.83 to 1.67 mmol.L(-1) for orange juice, from 0.58 to 1.93 mmol.L(-1) for lemon juice, and from 0.46 to 1.84 mmol.L(-1) for grapefruit juice. Different ascorbic acid concentrations (from standard solutions) were added to the analysed samples, the degree of recovery being comprised between 94.35% and 104%. Ascorbic acid determination results obtained by cyclic voltammetry were compared with those obtained by the volumetric method with dichlorophenol indophenol. The results obtained by the two methods were in good agreement.

Effects of isoflavones on the coagulation and fibrinolytic system of postmenopausal women

OBJECTIVE

We evaluated the effects of soy isoflavone supplementation on hemostasis in healthy postmenopausal women.

METHODS

In this double-blinded, placebo-controlled study, 47 postmenopausal women 47-66 y of age received 40 mg of soy isoflavone (n = 25) or 40 mg of casein placebo (n = 22) once a day for 6 mo. Levels of factors VII and X, fibrinogen, thrombin-antithrombin complex, prothrombin fragments 1 plus 2, antithrombin, protein C, total and free protein S, plasminogen, plasminogen activator inhibitor-1, and D-dimers were measured at baseline and 6 mo. Urinary isoflavone concentrations (genistein and daidzein) were measured as a marker of compliance and absorption using high-performance liquid chromatography. Baseline characteristics were compared by unpaired Student's t test. Within-group changes and comparison between the isoflavone and casein placebo groups were determined by a mixed effects model.

RESULTS

The levels of hemostatic variables did not change significantly throughout the study in the isoflavone group; however, the isoflavone group showed a statistically significant reduction in plasma concentration of prothrombin fragments 1 plus 2; both groups showed a statistically significant reduction in antithrombin, protein C, and free protein S levels. A significant increase in D-dimers was observed only in the isoflavone group. Plasminogen activator inhibitor-1 levels increased significantly in the placebo group. However, these changes were not statistically different between groups.

CONCLUSION

The results of the present study do not support a biologically significant estrogenic effect of soy isoflavone on coagulation and fibrinolysis in postmenopausal women. However, further research will be necessary to definitively assess the safety and efficacy of isoflavone.

Determination of major carotenoids in vegetables by capillary electrochromatography

A simple and rapid method for the isocratic separation and determination of carotenoids (carotenes and xanthophylls) in vegetables by CEC is described. The capillary column (100 microm ID, 25 cm effective length) was packed with 3 microm Hypersil ODS particles. The optimized mobile phase contained 60% ACN, 35% THF and 5% of a 5 mM Tris aqueous buffer of pH 8. beta-Carotene, lycopene and lutein were separated with efficiencies of 66 000-128 000 plates/m within a short time (less than 12 min for the last peak eluted, 13/13'-cis-beta-carotene). An excellent resolution of the three carotenoids, as well as partial resolution of their geometrical isomers, was achieved. Application to the determination of the analytes in carrot, tomato, spinach and corn was demonstrated.

Simultaneous quantification of CTN986 and its deglycosylation products in rat serum using liquid chromatography/tandem mass spectrometry

A quantitative method for the simultaneous determination of CTN986, a flavonol triglycoside, and its two deglycosylation products rutin and hirsutin in rat serum was developed and validated for the investigation of the pharmacokinetics of CTN986. Analytes were isolated from the serum samples (200 microL) prior to analysis by liquid chromatography/tandem mass spectrometry (LC/MS/MS) using C(18) solid-phase extraction, and were separated on a Zorbax C(8) reversed-phase column with an isocratic mobile phase consisting of methanol/isopropanol/water/formic acid (20:10:70:0.1, v/v/v/v). The protonated analytes generated in the positive ion mode were monitored through multiple reaction monitoring in an eletrospray ionization source. Calibration was performed by internal standardization with CTN987, a flavonoid structurally similar to CTN986, and regression curves were constructed ranging from 2 to 1000 ng/mL in 200 microL serum samples. The intra- and inter-day precision values were below 11% and accuracy was between -2.37 and 1.4% for all quality control samples. This quantitation method was successfully applied to pharmacokinetic studies of CTN986 in rats following oral and intravenous administration. Rutin and hirsutin were not detected in rat serum.

Validation of an HPLC method for the determination of scutellarin in rat plasma and its pharmacokinetics

A validated HPLC method was developed for the quantification of scutellarin in rat plasma using a liquid-liquid extraction and an ultraviolet detection. Chromatographic separation of scutellarin in plasma was performed on a C18 column, with a mobile phase of acetonitrile-water (23:77, v/v), adjusted to pH 2.5 with 1M phosphoric acid, and rutin was used as an internal standard. The calibration curve was linear over the range 0.1-100 microg/ml in rat plasma. The average extraction recoveries were 85.9+/-8.9, 71.0+/-4.6, 72.7+/-1.2% (n=3) at concentrations of 0.1, 2, 100 microg/ml, respectively, and the within-day and between-day precisions were less than 15%. After intravenous administration to rats over the doses range of 10-40 mg/kg, the plasma concentration-time curve of scutellarin was best conformed to three-compartment open model. The AUC of scutellarin was proportional to dose, and the systemic clearance (Cl), elimination half-life (t1/2beta) and apparent volume of distribution (Vc) were not significantly different among the three doses, suggestive of the linear pharmacokinetics characteristic of scutellarin after intravenous administration.

Amperometric biosensor for ascorbic acid

A L-ascorbic acid biosensor based on ascorbate oxidase has been developed. The enzyme was extracted from the mesocarp of cucumber (Cucumis sativus) by using 0.05 mol L-1 phosphate buffer, pH 5.8 containing 0.5 mol L-1 NaCl. After the dialysis versus phosphate buffer 0.05 mol L-1 pH 5.8, the enzyme was immobilized onto nylon net through glutaraldehyde covalent bond. The membrane was coupled to an O2 electrode and the yielding reaction monitored by oxygen depletion at -600 mV using flow injection analysis optimized to 0.1 mol L-1 phosphate buffer pH 5.8, as the carrier solution and flow-rate of 0.5 mL min-1. The ascorbic acid calibration curve was linear from 1.2x10-4 to 1.0x10-3 mol L-1. The evaluation of biosensor lifetime leads to 500 injections. Commercial pharmaceutical samples were analyzed with the proposed method and the results were compared with those obtained by high-performance liquid chromatography (HPLC).

Analysis of vitamin E derivatives in serum using coordinated ion spray mass spectrometry

A method for the extraction and analysis of tocopherols from serum using coordinated ion spray (CIS) mass spectrometry was developed and tested. The tocopherols were extracted from serum and analyzed by direct infusion into the mass spectrometer, bypassing the need for a liquid chromatography step. CIS is a method for improving the ionization efficiency of non-polar compounds by adding metal ions to the electrospray solvent. The non-polar analytes appear as metal adducts in the resulting mass spectrum. Silver was used as the metal ion for the CIS, causing analyte masses to be increased by 107 and 109 Da from the two main silver isotopes. Vitamin E succinate was added to the samples before extraction and was used as an internal standard to compensate for any variations in the extraction efficiency or mass spectrometric response. alpha-Tocopherol and an ether-linked analogue known as alpha-TEA were analyzed in concentrations from 1.25-40 microg/mL (1.9-60 pg consumed). The response curve was constructed by comparing the response of the analytes to the internal standard and gave linear results with r2 values greater than 0.98. This new method was shown to be sensitive, reproducible, fast and required very small amounts of analyte.

Determination of scutellarin in rat plasma by high-performance liquid chromatography with ultraviolet detection

A validated high-performance liquid chromatography method is described for the determination of scutellarin in rat plasma using a liquid-liquid extraction and ultraviolet (UV) absorbance detection. The separation used a Diamonsil ODS column (250 mm x 4.6mm i.d., 5 microm particle size) with an isocratic mobile phase consisting of methanol-acetonitrile-50mM dihydrogen ammonium phosphate buffer (22:15:63 (v/v/v), adjusted to pH 2.5 with 1M phosphoric acid). The ultraviolet detector operated at 335 nm. Plasma samples were extracted with ethyl acetate after acidification. The extraction recovery of scutellarin ranged from 68.1 to 80.5%. High selectivity and a low quantitation limit (0.050 microg/ml) were achieved. The linear range was 0.050-12.5 microg/ml, correlation coefficient r=0.9981. The method has a good reproducibility, R.S.D. values were below 7.9% for within-day and between-day precision. The method is simple, rapid, and applicable to preliminary pharmacokinetic studies of scutellarin in rats.

The interaction of anthocyanins with bilitranslocase

Bilitranslocase (TC 2.A.65.1.1) is an organic anion membrane carrier expressed at the sinusoidal domain of the liver plasma membrane and in epithelial cells of the gastric mucosa. Its substrates are sulfobromophthalein, bilirubin, and nicotinic acid. This work reports on the identification of a new class of bilitranslocase substrates, i.e., anthocyanins. Seventeen out thes 20 compounds tested behaved as competitive inhibitors of bilitranslocase transport activity (K(I)=1.4-22 microM). Their structure-activity relationship reveals that mono- and di-glucosyl anthocyanins, the anthocyanin species occurring in food, are better ligands than the corresponding aglycones. Moreover, the first interaction of anthocyanins with the carrier occurs through hydrophilic moieties, such as the 3-glucosyl moiety and the B ring for the monoglucosides, through the 5-glucosyl moiety and the A ring for the diglucosides, and through either the B or the A ring for the aglycones. These findings suggest that bilitranslocase could play a role in the bioavailability of anthocyanins.