Analysis of glucosinolates from broccoli and other cruciferous vegetables by hydrophilic interaction liquid chromatography

Profiling glucosinolate metabolites in human urine and plasma after broccoli consumption using non-targeted and targeted metabolomic analyses

Broccoli is a popular brassica vegetable and its consumption may decrease the occurrence of cancer in certain populations. To gain insight into the metabolites that may induce physiological responses to broccoli intake, a non-targeted metabolomic approach and a targeted approach for analysis of glucosinolate metabolites were developed using high resolution accurate mass spectrometry. A human study was conducted in which 6 subjects consumed a single meal of 200 g of uncooked broccoli florets. The metabolomic analysis revealed changes in endogenous metabolites and a decrease in hippuric acid after broccoli consumption. Targeted analysis using high-resolution, accurate mass-mass spectrometry (HRAM-MS) enabled detection of low concentrations (nM) of glucosinolate metabolites in human urine and plasma. Glucosinolate metabolites were found in human urine (13) and plasma (8), respectively. Metabolites from methoxyl-indole glucosinolates, arising from broccoli consumption, are reported for the first time. Most glucosinolate metabolites reached their peak concentration in urine 2-4 h after consumption while, in plasma, peak maxima were achieved 2 h after intake. The results suggest that glucoraphanin metabolites (sulforaphane, sulforaphane cysteine, sulforaphane N-acetyl cysteine) and indole metabolites (ascorbigen and methoxyl ascorbigen from indole glucosinolates) may serve as marker compounds for the intake of broccoli.

The Diversity of Chemoprotective Glucosinolates in Moringaceae (Moringa spp.)

Glucosinolates (GS) are metabolized to isothiocyanates that may enhance human healthspan by protecting against a variety of chronic diseases. Moringa oleifera, the drumstick tree, produces unique GS but little is known about GS variation within M. oleifera, and even less in the 12 other Moringa species, some of which are very rare. We assess leaf, seed, stem, and leaf gland exudate GS content of 12 of the 13 known Moringa species. We describe 2 previously unidentified GS as major components of 6 species, reporting on the presence of simple alkyl GS in 4 species, which are dominant in M. longituba. We document potent chemoprotective potential in 11 of 12 species, and measure the cytoprotective activity of 6 purified GS in several cell lines. Some of the unique GS rank with the most powerful known inducers of the phase 2 cytoprotective response. Although extracts of most species induced a robust phase 2 cytoprotective response in cultured cells, one was very low (M. longituba), and by far the highest was M. arborea, a very rare and poorly known species. Our results underscore the importance of Moringa as a chemoprotective resource and the need to survey and conserve its interspecific diversity.

Chromatographic column evaluation for the untargeted profiling of glucosinolates in cauliflower by means of ultra-high performance liquid chromatography coupled to high resolution mass spectrometry

The untargeted profiling is a promising approach for the characterization of secondary metabolites in biological matrices. Thanks to the recent rapid development of high-resolution mass spectrometry (HRMS) instrumentations, the number of applications by untargeted approaches for biological samples profiling has widely increased in the recent years. Despite the high potentialities of HRMS, however, a major issue in natural products analysis often arises in the upstream process of compounds separation. A separation technique is necessary to avoid phenomena such as signal suppression, and it is especially needed in the presence of isomeric metabolites, which are otherwise indistinguishable. Glucosinolates (GLSs), a group of secondary metabolites widely distributed among plants, resulted to be associated to the prevention of some serious diseases, such as cancer. This led to the development of several methods for the analysis of GLSs in vegetables tissues. The issue of GLSs chromatographic separation has been widely studied in the past because of the difficulty in the analysis of this highly polar and variable class of compounds. Several alternatives to reversed phase (RP) chromatography, sometimes not compatible with the coupling of liquid chromatography with mass spectrometry, have been tested for the analysis of intact GLSs. However, the availability of new stationary phases, in the last years, could allow the re-evaluation of RP chromatography for the analysis of intact GLSs. In this work, a thorough evaluation of four RP chromatographic columns for the analysis of GLSs in cauliflower (Brassica oleracea L. var. botrytis) extracts by an ultra-high performance liquid chromatographic system coupled via electrospray source to a hybrid quadrupole-Orbitrap mass spectrometer is presented. The columns tested were the following: one column Luna Omega polar C₁₈, one column Kinetex Biphenyl, one column Kinetex core-shell XB-C₁₈, two columns Kinetex core-shell XB-C₁₈. After a previous optimization of the extraction method, cauliflower extracts were analyzed testing four different mobile phases onto the four columns for a total of sixteen different chromatographic conditions. The chromatographic systems were evaluated based on the number of detected and tentatively identified GLSs. Luna Polar stationary phase resulted to be the most suitable for the analysis of GLSs compared to Kinetex XB and Kinetex Biphenyl columns stationary phase. However, two in series Kinetex XB columns increased the number of tentatively identified GLSs compared to one Kinetex XB, showing the importance of column length in the analysis of complex mixtures. The data obtained with the best chromatographic system were deeply analyzed by MS/MS investigation for the final identification. Fiflty-one GLSs were tentatively identified, 24 of which have never been identified in cauliflower. Finally the linearity of the analytes response over the analyzed range of concentration was checked, suggesting that the developed method is suitable for both qualitative and quantitative analysis of GLSs in phytochemical mixtures.

Development of an efficient glucosinolate extraction method

BACKGROUND

Glucosinolates, anionic sulfur rich secondary metabolites, have been extensively studied because of their occurrence in the agriculturally important brassicaceae and their impact on human and animal health. There is also increasing interest in the biofumigant properties of toxic glucosinolate hydrolysis products as a method to control agricultural pests. Evaluating biofumigation potential requires rapid and accurate quantification of glucosinolates, but current commonly used methods of extraction prior to analysis involve a number of time consuming and hazardous steps; this study aimed to develop an improved method for glucosinolate extraction.

RESULTS

Three methods previously used to extract glucosinolates from brassicaceae tissues, namely extraction in cold methanol, extraction in boiling methanol, and extraction in boiling water were compared across tissue type (root, stem leaf) and four brassicaceae species (B. juncea, S. alba, R. sativus, and E. sativa). Cold methanol extraction was shown to perform as well or better than all other tested methods for extraction of glucosinolates with the exception of glucoraphasatin in R. sativus shoots. It was also demonstrated that lyophilisation methods, routinely used during extraction to allow tissue disruption, can reduce final glucosinolate concentrations and that extracting from frozen wet tissue samples in cold 80% methanol is more effective.

CONCLUSIONS

We present a simplified method for extracting glucosinolates from plant tissues which does not require the use of a freeze drier or boiling methanol, and is therefore less hazardous, and more time and cost effective. The presented method has been shown to have comparable or improved glucosinolate extraction efficiency relative to the commonly used ISO method for major glucosinolates in the Brassicaceae species studied: sinigrin and gluconasturtiin in B. juncea; sinalbin, glucotropaeolin, and gluconasturtiin in S. alba; glucoraphenin and glucoraphasatin in R. sativus; and glucosatavin, glucoerucin and glucoraphanin in E. sativa.

Development of an efficient glucosinolate extraction method

BACKGROUND

Glucosinolates, anionic sulfur rich secondary metabolites, have been extensively studied because of their occurrence in the agriculturally important brassicaceae and their impact on human and animal health. There is also increasing interest in the biofumigant properties of toxic glucosinolate hydrolysis products as a method to control agricultural pests. Evaluating biofumigation potential requires rapid and accurate quantification of glucosinolates, but current commonly used methods of extraction prior to analysis involve a number of time consuming and hazardous steps; this study aimed to develop an improved method for glucosinolate extraction.

RESULTS

Three methods previously used to extract glucosinolates from brassicaceae tissues, namely extraction in cold methanol, extraction in boiling methanol, and extraction in boiling water were compared across tissue type (root, stem leaf) and four brassicaceae species (B. juncea, S. alba, R. sativus, and E. sativa). Cold methanol extraction was shown to perform as well or better than all other tested methods for extraction of glucosinolates with the exception of glucoraphasatin in R. sativus shoots. It was also demonstrated that lyophilisation methods, routinely used during extraction to allow tissue disruption, can reduce final glucosinolate concentrations and that extracting from frozen wet tissue samples in cold 80% methanol is more effective.

CONCLUSIONS

We present a simplified method for extracting glucosinolates from plant tissues which does not require the use of a freeze drier or boiling methanol, and is therefore less hazardous, and more time and cost effective. The presented method has been shown to have comparable or improved glucosinolate extraction efficiency relative to the commonly used ISO method for major glucosinolates in the Brassicaceae species studied: sinigrin and gluconasturtiin in B. juncea; sinalbin, glucotropaeolin, and gluconasturtiin in S. alba; glucoraphenin and glucoraphasatin in R. sativus; and glucosatavin, glucoerucin and glucoraphanin in E. sativa.

Metabolomic assessment reveals an elevated level of glucosinolate content in CaCl₂ treated broccoli microgreens

Preharvest calcium application has been shown to increase broccoli microgreen yield and extend shelf life. In this study, we investigated the effect of calcium application on its metabolome using ultra-high-performance liquid chromatography with mass spectrometry. The data collected were analyzed using principal component analysis and orthogonal projection to latent structural discriminate analysis. Chemical composition comparison shows that glucosinolates, a very important group of phytochemicals, are the major compounds enhanced by preharvest treatment with 10 mM calcium chloride (CaCl2). Aliphatic glucosinolates (glucoerucin, glucoiberin, glucoiberverin, glucoraphanin, pentyl glucosinolate, and hexyl glucosinolate) and indolic glucosinolates (glucobrassicin, neoglucobrassicin, and 4-hydroxyglucobrassicin) were increased significantly in the CaCl2 treated microgreens using metabolomic approaches. Targeted glucosinolate analysis using the ISO 9167-1 method was further employed to confirm the findings. Results indicate that glucosinolates can be considered as a class of compounds that are responsible for the difference between two groups and a higher glucosinolate level was found in CaCl2 treated groups at each time point after harvest in comparison with the control group.

Rapid profiling of intact glucosinolates in Arabidopsis leaves by UHPLC-QTOFMS using a charged surface hybrid column

INTRODUCTION

The analysis of glucosinolates (GS) is traditionally performed by reverse-phase liquid chromatography coupled to ultraviolet detection after a time-consuming desulphation step, which is required for increased retention. Simpler and more efficient alternative methods that can shorten both sample preparation and analysis are much needed.

OBJECTIVE

To evaluate the feasibility of using ultrahigh-pressure liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (UHPLC-QTOFMS) for the rapid profiling of intact GS.

METHODOLOGY

A simple and short extraction of GS from Arabidopsis thaliana leaves was developed. Four sub-2 µm reverse-phase columns were tested for the rapid separation of these polar compounds using formic acid as the chromatographic additive. High-resolution QTOFMS was used to detect and identify GS.

RESULTS

A novel charged surface hybrid (CSH) column was found to provide excellent retention and separation of GS within a total running time of 11 min. Twenty-one GS could be identified based on their accurate mass as well as isotopic and fragmentation patterns. The method was applied to determine the changes in GS content that occur after herbivory in Arabidopsis. In addition, we evaluated its applicability to the profiling of other Brassicaceae species.

CONCLUSION

The method developed can profile the full range of GS, including the most polar ones, in a shorter time than previous methods, and is highly compatible with mass spectrometric detection.

Gastroprotective activity of hydroalcoholic extract obtained from the leaves of Brassica oleracea var. acephala DC in different animal models

ETHNOPHARMACOLOGICAL RELEVANCE

Brassica oleracea var. acephala DC has been extensively used in Brazilian traditional medicine to treat gastric ulcer.

AIM OF THE STUDY

This study was conducted to evaluate the antiulcerogenic property of hydroalcoholic extract obtained from the leaves of Brassica oleracea.

MATERIALS AND METHODS

Antiulcer assays were performed using the protocol of ulcer induced by ethanol/HCl, and non-steroidal anti-inflammatory drugs (NSAIDs). Parameters of gastric secretion (volume, pH and [H(+)]) were determined by the pylorus ligation model and mucus in gastric contents.

RESULTS

In the ethanol-induced ulcer model, we observed a significant reduction in all the parameters analyzed, obtaining curative ratios of 58.8 ± 11.5, 86.2 ± 12.2 and 42.8 ± 6.6% for the groups treated with 50 and 100mg/kg of extract and omeprazole (30 mg/kg), respectively. The dose of 25mg/kg of hydroalcoholic extract of Brassica oleracea showed no significant results. In the indomethacin-induced ulcer, the percentages of ulcer inhibition were 64.3 ± 9.9, 66.4 ± 12.3 and 81.2 ± 7.5% for the groups treated with 50 and 100mg/kg extract and positive control (cimetidine, 100mg/kg), respectively. The results showed a significant increase in pH and mucus production in the groups treated with Brassica oleracea when compared with the control group. No sign of toxicity was observed in the acute toxicity study.

CONCLUSIONS

The results of the present study show that hydroalcoholic extract of Brassica oleracea displays antiulcer activity, as demonstrated by the significant inhibition of ulcer formation induced using different models. The data suggest that the effectiveness of the extract is based on its ability to stimulate the synthesis of mucus, increase pH and decrease H(+) ions in the stomach. This work corroborates the ethnopharmacology use of Brassica oleracea preparations, contributing to its pharmacological validation by suggesting that preparations obtained from Brassica oleracea could be used for the development of new phytopharmaceuticals for the treatment of gastric ulcer.

Separation of purine and pyrimidine bases and nucleosides by hydrophilic interaction chromatography

The separation of 12 model compounds chosen among purine and pyrimidine bases and nucleosides was studied by using hydrophilic interaction chromatography (HILIC). The compounds investigated were small molecules with relevant properties for biomedical and pharmaceutical studies. The mixture of pyrimidines and purines was applied on a ZIC-HILIC 150 x 2.1 mm, 5 microm, and two TSKgel Amide-80 150 x 2.0 mm, 5 microm and 3 microm particle size columns. The retention of the analytes was studied by varying ACN%, ammonium formate concentration, pH, and column temperature. The results obtained confirmed the elution order of nucleobases, nucleosides, and nucleotides based on their hydrophobicity. The retention mechanism of the columns was studied considering the models used for describing partitioning and surface adsorption. The influence on retention of chromatographic conditions (ACN%, salt concentration, pH, and temperature) was described and discussed for both columns. The optimization of the conditions studied allowed to assess a gradient method for the separation of the 12 analytes. The developed method is a valuable alternative to existing methods for the separation of the compounds concerned.

Direct quantitation of glucoraphanin in dog and rat plasma by LC-MS/MS

A rapid method to quantify levels of the beta-thioglycoside N-hydroxyl sulfate, glucoraphanin, in dog and rat plasma to support pre-clinical toxicological and pharmacological studies has been developed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Glucoraphanin was extracted from plasma by protein precipitation with acetonitrile and separated via hydrophilic interaction liquid chromatography (HILIC) using a Luna 5microm Silica (2) 100A column (50mmx2.0mm) at a flow rate of 0.3mL/min. Solvent A consisted of 200mM ammonium acetate and formic acid (99:1, v/v) and Solvent B was acetonitrile. Initial conditions (90% Solvent B) were held for 0.01min after injection, decreased to 40% in 0.5min and held constant for 2.5min, returning to initial conditions for 3min (reequilibration time). Glucoraphanin was detected by MS/MS using a turbo ion spray interface as the ion source operating in negative ion mode. Acquisition was performed in multiple reaction monitoring mode at m/z 435.8-->96.7. The method was validated for the calibration range 10-2000ng/mL. Within- and between-run precision for the low, mid and high QC levels was 8% R.S.D. or less and accuracy ranged from 100 to 113%. The lower limit of quantification was 10ng/mL; calibration curves encompassed the range of plasma concentrations expected to be found in bioavailability and pharmacokinetics studies with glucoraphanin. The method has successfully been applied to the determination of glucoraphanin in dog and rat plasma and should be extendable to other species as well.

Dietary glucoraphanin-rich broccoli sprout extracts protect against UV radiation-induced skin carcinogenesis in SKH-1 hairless mice

Feeding broccoli sprout extracts providing daily doses of 10 micromol of glucoraphanin to SKH-1 hairless mice with prior chronic exposure to UV radiation (30 mJ cm(-2) of UVB, twice a week, for 17 weeks) inhibited the development of skin tumors during the subsequent 13 weeks; compared to the controls, tumor incidence, multiplicity, and volume were reduced by 25, 47, and 70%, respectively, in the animals that received the protective agent.

Oral sulforaphane increases Phase II antioxidant enzymes in the human upper airway

BACKGROUND

Cellular oxidative stress is an important factor in asthma and is thought to be the principle mechanism by which oxidant pollutants such as ozone and particulates mediate their pro-inflammatory effects. Endogenous Phase II enzymes abrogate oxidative stress through the scavenging of reactive oxygen species and metabolism of reactive chemicals.

OBJECTIVE

We conducted a placebo-controlled dose escalation trial to investigate the in vivo effects of sulforaphane, a naturally occurring potent inducer of Phase II enzymes, on the expression of glutathione-s-transferase M1 (GSTM1), glutathione-s-transferase P1 (GSTP1), NADPH quinone oxidoreductase (NQO1), and hemoxygenase-1 (HO-1) in the upper airway of human subjects.

METHODS

Study subjects consumed oral sulforaphane doses contained in a standardized broccoli sprout homogenate (BSH). RNA expression for selected Phase II enzymes was measured in nasal lavage cells by RT-PCR before and after sulforaphane dosing.

RESULTS

All subjects tolerated oral sulforaphane dosing without significant adverse events. Increased Phase II enzyme expression in nasal lavage cells occurred in a dose-dependent manner with maximal enzyme induction observed at the highest dose of 200 g broccoli sprouts prepared as BSH. Significant increases were seen in all sentinel Phase II enzymes RNA expression compared to baseline. Phase II enzyme induction was not seen with ingestion of non-sulforaphane containing alfalfa sprouts.

CONCLUSION

Oral sulforaphane safely and effectively induces mucosal Phase II enzyme expression in the upper airway of human subjects. This study demonstrates the potential of antioxidant Phase II enzymes induction in the human airway as a strategy to reduce the inflammatory effects of oxidative stress.

CLINICAL IMPLICATIONS

This study demonstrates the potential of enhancement of Phase II enzyme expression as a novel therapeutic strategy for oxidant induced airway disease.

CAPSULE SUMMARY

A placebo-controlled dose escalation trial demonstrated that naturally occurring sulforaphane from broccoli sprouts can induce a potent increase in antioxidant Phase II enzymes in airway cells.

Oral sulforaphane increases Phase II antioxidant enzymes in the human upper airway

BACKGROUND

Cellular oxidative stress is an important factor in asthma and is thought to be the principle mechanism by which oxidant pollutants such as ozone and particulates mediate their pro-inflammatory effects. Endogenous Phase II enzymes abrogate oxidative stress through the scavenging of reactive oxygen species and metabolism of reactive chemicals.

OBJECTIVE

We conducted a placebo-controlled dose escalation trial to investigate the in vivo effects of sulforaphane, a naturally occurring potent inducer of Phase II enzymes, on the expression of glutathione-s-transferase M1 (GSTM1), glutathione-s-transferase P1 (GSTP1), NADPH quinone oxidoreductase (NQO1), and hemoxygenase-1 (HO-1) in the upper airway of human subjects.

METHODS

Study subjects consumed oral sulforaphane doses contained in a standardized broccoli sprout homogenate (BSH). RNA expression for selected Phase II enzymes was measured in nasal lavage cells by RT-PCR before and after sulforaphane dosing.

RESULTS

All subjects tolerated oral sulforaphane dosing without significant adverse events. Increased Phase II enzyme expression in nasal lavage cells occurred in a dose-dependent manner with maximal enzyme induction observed at the highest dose of 200 g broccoli sprouts prepared as BSH. Significant increases were seen in all sentinel Phase II enzymes RNA expression compared to baseline. Phase II enzyme induction was not seen with ingestion of non-sulforaphane containing alfalfa sprouts.

CONCLUSION

Oral sulforaphane safely and effectively induces mucosal Phase II enzyme expression in the upper airway of human subjects. This study demonstrates the potential of antioxidant Phase II enzymes induction in the human airway as a strategy to reduce the inflammatory effects of oxidative stress.

CLINICAL IMPLICATIONS

This study demonstrates the potential of enhancement of Phase II enzyme expression as a novel therapeutic strategy for oxidant induced airway disease.

CAPSULE SUMMARY

A placebo-controlled dose escalation trial demonstrated that naturally occurring sulforaphane from broccoli sprouts can induce a potent increase in antioxidant Phase II enzymes in airway cells.

Electrostatic repulsion hydrophilic interaction chromatography for isocratic separation of charged solutes and selective isolation of phosphopeptides

If an ion-exchange column is eluted with a predominantly organic mobile phase, then solutes can be retained through hydrophilic interaction even if they have the same charge as the stationary phase. This combination is termed electrostatic repulsion-hydrophilic interaction chromatography (ERLIC). With mixtures of solutes that differ greatly in charge, repulsion effects can be exploited to selectively antagonize the retention of the solutes that normally would be the best retained. This permits the isocratic resolution of mixtures that normally require gradients, including peptides, amino acids, and nucleotides. ERLIC affords convenient separations of highly charged peptides that cannot readily be resolved by other means. In addition, phosphopeptides can be isolated selectively from a tryptic digest.

Improved hydrophilic interaction chromatography method for the identification and quantification of glucosinolates

An improved hydrophilic interaction liquid chromatography (HILIC) method has been developed to separate members of a closely related family of chemoprotective phytochemicals called glucosinolates. This method exploits the emergence of a second generation of HILIC chemistry, using a silica-based permanently zwitterionic stationary phase. These columns are more robust, durable, and glucosinolates separations are more reproducible than with the original polyhydroxyethyl aspartamide columns. Furthermore, the HILIC system that we report herein permits much greater alteration of the mobile phase composition for customized separation of glucosinolates from plant extracts, across a wide spectrum of polarity.

Safety, tolerance, and metabolism of broccoli sprout glucosinolates and isothiocyanates: a clinical phase I study

Broccoli sprouts are widely consumed in many parts of the world. There have been no reported concerns with respect to their tolerance and safety in humans. A formal phase I study of safety, tolerance, and pharmacokinetics appeared justified because these sprouts are being used as vehicles for the delivery of the glucosinolate glucoraphanin and its cognate isothiocyanate sulforaphane [1-isothiocyanato-(4R)-(methylsulfinyl)butane] in clinical trials. Such trials have been designed to evaluate protective efficacy against development of neoplastic and other diseases. A placebo-controlled, double-blind, randomized clinical study of sprout extracts containing either glucosinolates (principally glucoraphanin, the precursor of sulforaphane) or isothiocyanates (principally sulforaphane) was conducted on healthy volunteers who were in-patients on our clinical research unit. The subjects were studied in three cohorts, each comprising three treated individuals and one placebo recipient. Following a 5-day acclimatization period on a crucifer-free diet, the broccoli sprout extracts were administered orally at 8-h intervals for 7 days (21 doses), and the subjects were monitored during this period and for 3 days after the last treatment. Doses were 25 micromol of glucosinolate (cohort A), 100 micromol of glucosinolate (cohort B), or 25 micromol of isothiocyanate (cohort C). The mean cumulative excretion of dithiocarbamates as a fraction of dose was very similar in cohorts A and B (17.8 +/- 8.6% and 19.6 +/- 11.7% of dose, respectively) and very much higher and more consistent in cohort C (70.6 +/- 2.0% of dose). Thirty-two types of hematology or chemistry tests were done before, during, and after the treatment period. Indicators of liver (transaminases) and thyroid [thyroid-stimulating hormone, total triiodothyronine (T3), and free thyroxine (T4)] function were examined in detail. No significant or consistent subjective or objective abnormal events (toxicities) associated with any of the sprout extract ingestions were observed.

Protection against UV-light-induced skin carcinogenesis in SKH-1 high-risk mice by sulforaphane-containing broccoli sprout extracts

Aerobic life, UV solar radiation, genetic susceptibility, and immune status contribute collectively to the development of human skin cancers. In addition to direct DNA damage, UV radiation promotes the generation of reactive oxygen intermediates that can cause oxidative damage and inflammation, and ultimately lead to tumor formation. Treatment of murine and human keratinocytes with the isothiocyanate sulforaphane elevated phase 2 enzymes and glutathione and protected against oxidant toxicity. Topical application of sulforaphane-containing broccoli sprouts extracts induced the phase 2 response in mouse skin in vivo. Sulforaphane inhibited cytokine-dependent (gamma-interferon or lipopolysaccharide) induction of iNOS in RAW 264.7 macrophages. The UV-radiation-induced skin carcinogenesis in "initiated high-risk mice" was substantially inhibited by broccoli sprout extracts containing sulforaphane. After completion of the UV irradiation schedule (30 mJ/cm(2)/session twice a week for 20 weeks), groups of approximately 30 mice were treated topically on their backs (5 days a week for 11 weeks) with broccoli sprout extract containing either the equivalent to 0.3 micromol (low dose) or 1.0 micromol (high dose) sulforaphane, respectively. At this time point, the tumor incidence had reached 100% in the control mice. Tumor burden, incidence, and multiplicity were reduced by 50% in the animals that received the high dose of protector. Tumor incidence and multiplicity did not differ between the low dose-treated and the control groups, but the low dose treatment resulted in a substantial reduction of the overall tumor burden. Thus, topical application of sulforaphane-containing broccoli sprout extracts is a promising strategy for protecting against skin tumor formation after exposure to UV radiation.

Hydrophilic interaction chromatography

Separation of polar compounds on polar stationary phases with partly aqueous eluents is by no means a new separation mode in LC. The first HPLC applications were published more than 30 years ago, and were for a long time mostly confined to carbohydrate analysis. In the early 1990s new phases started to emerge, and the practice was given a name, hydrophilic interaction chromatography (HILIC). Although the use of this separation mode has been relatively limited, we have seen a sudden increase in popularity over the last few years, promoted by the need to analyze polar compounds in increasingly complex mixtures. Another reason for the increase in popularity is the widespread use of MS coupled to LC. The partly aqueous eluents high in ACN with a limited need of adding salt is almost ideal for ESI. The applications now encompass most categories of polar compounds, charged as well as uncharged, although HILIC is particularly well suited for solutes lacking charge where coulombic interactions cannot be used to mediate retention. The review attempts to summarize the ongoing discussion on the separation mechanism and gives an overview of the stationary phases used and the applications addressed with this separation mode in LC.

The isolation and purification of glucoraphanin from broccoli seeds by solid phase extraction and preparative high performance liquid chromatography

Plant foods contain not only essential nutrients, e.g. protein, amino acids, vitamins and minerals, but also phytochemicals that have added health benefits. One such class of phytochemicals are the glucosinolates. Glucosinolates, particularly glucoraphanin, are predominant in plants of the Brassica genus, most notably in vegetables such as broccoli. There is a growing interest in the role glucoraphanin plays in chemoprotection and as a result there is a requirement to accurately determine the levels of glucoraphanin in vegetable products. Reverse phase ion pair high performance liquid chromatography (HPLC) is the method of choice; however, this work has been hindered by the lack of available standard reference materials. Broccoli seeds, which are particularly rich in glucoraphanin (20-50 mg/g), have proved to be ideal for the isolation of glucoraphanin on the preparative scale. A novel preparative scale HPLC method with simple compound recovery has been developed to meet the need for a glucoraphanin standard.

Potent activation of mitochondria-mediated apoptosis and arrest in S and M phases of cancer cells by a broccoli sprout extract

We have previously shown that broccoli sprouts are a rich source of chemopreventive isothiocyanates, which potently induce carcinogen-detoxifying enzymes and inhibit the development of mammary and skin tumors in rodents. However, the principal isothiocyanate present in broccoli sprout extracts, sulforaphane, not only induces carcinogen-detoxifying enzymes but also activates apoptosis and blocks cell cycle progression. In this article, we show that an aqueous extract of broccoli sprouts potently inhibits the growth of human bladder carcinoma cells in culture and that this inhibition is almost exclusively due to the isothiocyanates. Isothiocyanates are present in broccoli sprouts as their glucosinolate precursors and blocking their conversion to isothiocyanates abolishes the antiproliferative activity of the extract. Moreover, the potency of isothiocyanates in the extract in inhibiting cancer cell growth was almost identical to that of synthetic sulforaphane, as judged by their IC50 values (6.6 versus 6.8 micromol/L), suggesting that other isothiocyanates in the extract may be biologically similar to sulforaphane and that nonisothiocyanate substances in the extract may not interfere with the antiproliferative activity of the isothiocyanates. Further study showed that the isothiocyanate extract of broccoli sprouts activated the mitochondria-mediated apoptosis pathway and halted cells in S and M phases. Cell cycle arrest was associated with down-regulation of Cdc25C and disruption of mitotic spindles. These data show that broccoli sprout isothiocyanate extract is a highly promising substance for cancer prevention/treatment and that its antiproliferative activity is exclusively derived from isothiocyanates.

Geographic patterns of herbivory and resource allocation to defense, growth, and reproduction in an invasive biennial, Alliaria petiolata

We investigated geographic patterns of herbivory and resource allocation to defense, growth, and reproduction in an invasive biennial, Alliaria petiolata, to test the hypothesis that escape from herbivory in invasive species permits enhanced growth and lower production of defensive chemicals. We quantified herbivore damage, concentrations of sinigrin, and growth and reproduction inside and outside herbivore exclusion treatments, in field populations in the native and invasive ranges. As predicted, unmanipulated plants in the native range (Hungary, Europe) experienced greater herbivore damage than plants in the introduced range (Massachusetts and Connecticut, USA), providing evidence for enemy release, particularly in the first year of growth. Nevertheless, European populations had consistently larger individuals than US populations (rosettes were, for example, eightfold larger) and also had greater reproductive output, but US plants produced larger seeds at a given plant height. Moreover, flowering plants showed significant differences in concentrations of sinigrin in the invasive versus native range, although the direction of the difference was variable, suggesting the influence of environmental effects. Overall, we observed less herbivory, but not increased growth or decreased defense in the invasive range. Geographical differences in performance and leaf chemistry appear to be due to variation in the environment, which could have masked evolved differences in allocation.

Effects of glucosinolate-rich broccoli sprouts on urinary levels of aflatoxin-DNA adducts and phenanthrene tetraols in a randomized clinical trial in He Zuo township, Qidong, People's Republic of China

Residents of Qidong, People's Republic of China, are at high risk for development of hepatocellular carcinoma, in part due to consumption of aflatoxin-contaminated foods, and are exposed to high levels of phenanthrene, a sentinel of hydrocarbon air toxics. Cruciferous vegetables, such as broccoli, contain anticarcinogens. Glucoraphanin, the principal glucosinolate in broccoli sprouts, can be hydrolyzed by gut microflora to sulforaphane, a potent inducer of carcinogen detoxication enzymes. In a randomized, placebo-controlled chemoprevention trial, we tested whether drinking hot water infusions of 3-day-old broccoli sprouts, containing defined concentrations of glucosinolates, could alter the disposition of aflatoxin and phenanthrene. Two hundred healthy adults drank infusions containing either 400 or < 3 micromol glucoraphanin nightly for 2 weeks. Adherence to the study protocol was outstanding; no problems with safety or tolerance were noted. Urinary levels of aflatoxin-N(7)-guanine were not different between the two intervention arms (P = 0.68). However, measurement of urinary levels of dithiocarbamates (sulforaphane metabolites) indicated striking interindividual differences in bioavailability. An inverse association was observed for excretion of dithiocarbamates and aflatoxin-DNA adducts (P = 0.002; R = 0.31) in individuals receiving broccoli sprout glucosinolates. Moreover, trans, anti-phenanthrene tetraol, a metabolite of the combustion product phenanthrene, was detected in urine of all participants and showed a robust inverse association with dithiocarbamate levels (P = 0.0001; R = 0.39), although again no overall difference between intervention arms was observed (P = 0.29). Understanding factors influencing glucosinolate hydrolysis and bioavailability will be required for optimal use of broccoli sprouts in human interventions.

A hydrophilic interaction chromatography coupled to a mass spectrometry for the determination of glutathione in plant somatic embryos

An electrospray ionization mass spectrometric (ESI-MS) determination of glutathione (GSH), a sulfur-containing tripeptide (gamma-Glu-Cys-Gly) with regulation and detoxication functions in metabolisms of most living organisms, from nanomolar to micromolar levels is described. A hydrophilic interaction chromatography (HILIC) with an isocratic elution using a mobile phase containing acetonitrile and an aqueous 0.00005% solution of trifluoroacetic acid (60/40%, v/v) was applied for the separation of GSH. The peptide detection was achieved in the presence of L-ascorbic acid which significantly enhanced the signal intensity of the molecular ion GSH [M+H]+ (m/z 308). The calibration curve was linear (R2=0.9995) in the concentration range from 2 nM to 10 microM with a detection limit (LOD, S/N=3) of 0.5 nM. The excellent detection limit, and the excellent selectivity and high reproducibility of this method enabled determination of GSH in a single plant somatic embryo of a Norway spruce (Picea abies). The average amount of GSH in the single somatic embryos (n=18) was 9 pmol per embryo. Owing to our results, it can be supposed that the proposed HILIC/ESI-MS analysis might be used for GSH determination in microscopic cell structures and in single cell analyses.

Analysis of glucosinolates, isothiocyanates, and amine degradation products in vegetable extracts and blood plasma by LC–MS/MS

Dietary glucosinolates are under intensive investigation as precursors of cancer-preventive isothiocyanates. Quantitation of the dose and bioavailability of glucosinolates and isothiocyanates requires a comprehensive analysis of the major dietary glucosinolates, isothiocyanates, and related metabolites. We report a liquid chromatography with tandem mass spectrometric detection (LC-MS/MS) analytical method for the comprehensive analysis of the seven major dietary glucosinolates, related isothiocyanates, and putative amine degradation products. The parent glucosinolates were sinigrin, gluconapin, progoitrin, glucoiberin, glucoraphanin, glucoalyssin, and gluconasturtiin. The LC-MS/MS analysis method for these compounds was developed and validated; a standard addition analysis protocol was used generally to avoid the requirement for stable isotopic standards. Where stable isotopic standards were available, internal standardization with these gave estimates in agreement with those obtained by the standard addition analysis protocol. For glucosinolates, negative ion electrospray LC-MS/MS analysis was performed. Isothiocyanates and amines were prederivatized to the corresponding thiourea and N-acetamides, respectively, and were quantified by positive ion electrospray LC-MS/MS. The limits of detection were 0.5-2 pmol; the recoveries for glucosinolates, isothiocyanates, and amines were 85-90%, 50-85%, and 60-70%, respectively; and the intra- and interbatch coefficients of variation were 1-4% and 3-10%, respectively. These methods provide facile access to comprehensive analytical data on the major dietary glucosinolates and related metabolites to quantify inputs and metabolic formation of these compounds in cancer prevention and related studies.

Orthogonal method development using hydrophilic interaction chromatography and reversed-phase high-performance liquid chromatography for the determination of pharmaceuticals and impurities

A hydrophilic interaction chromatography (HILIC) method has been developed and validated as a secondary or orthogonal method complementary to a reversed-phase HPLC (RP-HPLC) method for quantitation of a polar active pharmaceutical ingredient and its three degradation products. The HILIC method uses a diol column and a mobile phase consisting of acetonitrile/water and ammonium chloride. The compounds of interest show significant differences in retention behaviors with the two very different chromatographic systems, which are desired in developing orthogonal methods. The HILIC method is validated and has met all validation acceptance criteria for the support of drug development activities.

Glucoraphanin and 4-hydroxyglucobrassicin contents in seeds of 59 cultivars of broccoli, raab, kohlrabi, radish, cauliflower, brussels sprouts, kale, and cabbage

The importance of dietary sulforaphane in helping maintain good health continues to gain support within the health-care community and awareness among U.S. consumers. In addition to the traditional avenue for obtaining sulforaphane, namely, the consumption of appropriate cruciferous vegetables, other consumer products containing added glucoraphanin, the natural precursor to sulforaphane, are now appearing in the United States. Crucifer seeds are a likely source for obtaining glucoraphanin, owing to a higher concentration of glucoraphanin and the relative ease of processing seeds as compared to vegetative parts. Seeds of several commonly consumed crucifers were analyzed not only for glucoraphanin but also for components that might have negative health implications, such as certain indole-containing glucosinolates and erucic acid-containing lipids. Glucoraphanin, 4-hydroxyglucobrassicin, other glucosinolates, and lipid erucic acid were quantified in seeds of 33 commercially available cultivars of broccoli, 4 cultivars each of kohlrabi, radish, cauliflower, Brussels sprouts, kale, and cabbage, and 2 cultivars of raab.

Separation and purification of glucosinolates from crude plant homogenates by high-speed counter-current chromatography

Glucosinolates are anionic, hydrophilic plant secondary metabolites which are of particular interest due to their role in the prevention of cancer and other chronic and degenerative diseases. The separation and purification of glucosinolates from a variety of plant sources (e.g. seeds of broccoli, arugula and the horseradish tree), was achieved using high-speed counter-current chromatography (HSCCC). A high-salt, highly polar system containing 1-propanol-acetonitrile-saturated aqueous ammonium sulfate-water (1:0.5:1.2:1), was run on a semi-preparative scale and then transferred directly to preparative scale. Up to 7 g of a concentrated methanolic syrup containing about 10% glucosinolates was loaded on an 850-ml HSCCC column, and good separation and recovery were demonstrated for 4-methylsulfinylbutyl, 3-methylsulfinylpropyl, 4-methylthiobutyl, 2-propenyl and 4-(rhamnopyranosyloxy)benzyl glucosinolates. Multiple injections (5 to 6 times) were performed with well-preserved liquid stationary phase under centrifugal force. Pooled sequential runs with broccoli seed extract yielded about 20 g of its predominant glucosinolate, glucoraphanin, which was produced at > 95% purity and reduced to powdered form.

Development of a flow amperometric enzymatic method for the determination of total glucosinolates in real samples

The first amperometric flow analyzer, based on the biosensor concept, capable of determining total glucosinolates in real samples, is described. Myrosinase was immobilized on aminopropyl-modified controlled pore glass, which was then used for the construction of a packed-bed reactor. Myrosinase catalyzes the hydrolysis of glucosinolates (sinigrin) to glucose (among the other products), which is then oxidized by the action of glucose oxidase to produce hydrogen peroxide. The glucose enzyme electrode is based on a multimembrane architecture and was mounted on an amperometric flow cell (hydrogen peroxide detection at a platinum anode poised at +0.65 V vs Ag/AgCl/3M KCl). Different membrane types and different activation procedures were tested. The system was optimized to various working parameters, either as a glucose electrode or as a glucosinolate analyzer. The interference effect of various compounds was also investigated. Application of the method to real samples was carried out using glucose/glucose, hydrolyzed sinigrin and glucose/sinigrin solution as calibrators of the glucose electrode and the glucosinolate analyzer. Deviations due to the enantioselectivity of glucose oxidase to the beta-glucose anomer were observed, and a data elaboration protocol is proposed. The possibility of the simultaneous determination of glucose and glucosinolates is also demonstrated.

Influence of temperature and ontogeny on the levels of glucosinolates in broccoli (Brassica oleracea Var. italica) sprouts and their effect on the induction of mammalian phase 2 enzymes

Broccoli inflorescences have been recognized as components of healthy diets on the basis of their high content of fiber, vitamin C, carotenoids, and glucosinolates/isothiocyanates. Broccoli sprouts have been recently shown to have high levels of glucoraphanin (4-methylsulfinylbutyl glucosinolate), the precursor of the chemoprotective isothiocyanate, sulforaphane. This study evaluated the effects of temperature and developmental stage on the glucosinolate content of broccoli sprouts. Seedlings cultivated using a 30/15 degrees C (day/night) temperature regime had significantly higher glucosinolate levels (measured at six consecutive days postemergence) than did sprouts cultivated at lower temperatures (22/15 and 18/12 degrees C; p < 0.001). Both higher (33.1 degrees C) and lower (11.3 degrees C) constant temperatures induced higher glucosinolate levels in sprouts grown to a uniform size. Glucosinolate levels were highest in cotyledons and lowest in roots of sprouts dissected both early and late in the 11 day developmental span investigated. Nongerminated seeds have the highest glucosinolate levels and concordantly greater induction of mammalian phase 2 detoxication enzymes. Levels decline as sprouts germinate and develop, with consistently higher glucosinolate content in younger developmental stages, independent of the temperature regime. Temperature stress or its associated developmental anomalies induce higher glucosinolate levels, specific elevations in glucoraphanin content, and parallel induction of phase 2 chemoprotective enzymes.

Single column approach for the liquid chromatographic separation of polar and non-polar glucosinolates from broccoli sprouts and seeds

Ion-pair and hydrophilic interaction chromatographies are considered to be complementary methods of choice for analyzing intact glucosinolates from broccoli. Ion-pair chromatography resolves non-polar glucosinolates, such as those containing indole moieties, while hydrophilic interaction chromatography is superior for separating polar glucosinolates, such as glucoraphanin and glucoiberin. Reversed-phase separations using hydrophilic endcapped C18-bonded silica and a 50 mM ammonium acetate-methanol gradient mobile phase resolve both polar and non-polar glucosinolates negating the need for switching columns.

Direct analysis of single leaf disks for chemopreventive glucosinolates

Natural isothiocyanates, produced during plant tissue damage from methionine-derived glucosinolates, are potent inducers of mammalian phase 2 detoxification enzymes such as quinone reductase (QR). A greatly simplified bioassay for glucosinolates based on induction and colorimetric detection of QR activity in murine hepatoma cells is described. It is demonstrated that excised leaf disks of Arabidopsis thaliana (ecotype Columbia) can directly and reproducibly substitute for cell-free leaf extracts as inducers of murine QR, which reduces samples preparation to a minimum and maximizes throughput. A comparison of 1 and 3 mm diameter leaf disks indicated that QR inducer potency was proportional to disk circumference (extent of tissue damage) rather than to area. When compared to the QR inducer potency of the corresponding amount of extract, 1 mm leaf disks were equally effective, whereas 3 mm disks were 70% as potent. The QR inducer potency of leaf disks correlated positively with the content of methionine-derived glucosinolates, as shown by the analysis of wild-type plants and mutant lines with lower or higher glucosinolate content. Thus, the microtitre plate-based assay of single leaf disks provides a robust and inexpensive visual method for rapidly screening large numbers of plants in mapping populations or mutant collections and may be applicable to other glucosinolate-producing species.