Broccoli sprouts: an exceptionally rich source of inducers of enzymes that protect against chemical carcinogens

The Effect of Cruciferous and Leguminous Sprouts on Genotoxicity, In vitro and In vivo

Vegetable consumption is associated with a reduced risk of colorectal cancer, which is the second most common cancer after lung/breast cancer within Europe. Some putative protective phytochemicals are found in higher amounts in young sprouts than in mature plants.

The effect of an extract of mixed cruciferous and legume sprouts on DNA damage induced by H2O2 was measured in HT29 cells using single cell microgelelectrophoresis (comet). Significant antigenotoxic effect (P ≤ 0.05) was observed when HT29 cells were pre-incubated with the extract (100 and 200 μL/mL) for 24 hours and then challenged with H2O2. A parallel design intervention study was carried out on 10 male and 10 female healthy adult volunteers (mean age = 25.5 years) fed 113 g of cruciferous and legume sprouts daily for 14 days. The effect of the supplementation was measured on a range of parameters, including DNA damage in lymphocytes (comet), the activity of various detoxifying enzymes (glutathione S-transferase, glutathione peroxidase, and superoxide dismutase), antioxidant status using the ferric reducing ability of plasma assay, plasma antioxidants (uric acid, ascorbic acid, and α-tocopherol), blood lipids, plasma levels of lutein, and lycopene. A significant antigenotoxic effect against H2O2-induced DNA damage was shown in peripheral blood lymphocytes of volunteers who consumed the supplemented diet when compared with the control diet (P = 0.04). No significant induction of detoxifying enzymes was observed during the study, neither were plasma antioxidant levels or activity altered. The results support the theory that consumption of cruciferous vegetables is linked to a reduced risk of cancer via decreased damage to DNA.

In vivo pharmacokinetics and regulation of gene expression profiles by isothiocyanate sulforaphane in the rat

Sulforaphane (SUL) is one member of the isothiocyanate class of cancer chemopreventive compounds that has been shown to be effective in blocking initiation and progression of carcinogenesis. Previously, many studies have shown that SUL can potently induce phase II detoxifying enzymes, which contributes to its chemopreventive functions. In this study, we used 4967 oligonucleotides microarray to assess the genes that are modulated by SUL in in vivo rat livers, as well as time course of expression of these genes. The pharmacokinetics of SUL was assessed after oral dose of 50 micromol of SUL. The plasma concentration occurred at 1 h and peaked around 20 microM at 4 h after dosing and declined with a half-life of about 2.2 h. Analysis of the gene expression data found various clusters of genes that are important in cellular defense mechanisms and cell cycle regulation. The most robust cluster of genes is the metallothionein-like genes (MT-1/2 and MT-1a), which are increased up to 10-fold by 2 to 4 h after SUL dosing. The second cluster of genes is the glutathione S-transferase-A3-like genes, which include aflatoxin B1 aldehyde reductase and aldehyde oxidase. These genes are increased slightly by 4 h and peaked at 12 h. Real-time polymerase chain reaction was performed to authenticate the mRNA expression of some of these genes. In summary, this in vivo study of SUL provides the first clue as to the plasma concentrations of SUL, in vivo mitogen-activated protein kinase activations in rat livers, as well as what other genes are modulated in addition to phase II detoxifying genes. The results from this study may yield better insights for its chemopreventive functions.

The effect of sulfur fertilizer on glucoraphanin levels in broccoli (B. oleracea L. var. italica) at different growth stages

Three sulfur (S) treatements were imposed by applying gypsum to three broccoli cultivars (Claudia, Marathon, and TB-234) known to differ in glucoraphanin content of mature seeds. The S treatments were control (very low added S), low S (23 kg S ha(-)(1)), and high S (92 kg S ha(-)(1)). The gypsum applications during the early vegetative phase of the three broccoli cultivars increased S uptake and the glucoraphanin content in each plant organ. There were significant genotypic differences for the content of both S and glucoraphanin in all plant organs at different growth stages with gypsum applications. A large increase in S and glucoraphanin content was found in the green heads of broccoli and mature seeds. S present in glucoraphanin accounted for only 4-10% of total S content in broccoli heads. However, S present in glucoraphanin in mature seeds accounted for 40-46% of the total S in the seeds of moderate and high glucoraphanin cultivars (Marathon and TB-234). The partitioning of S into glucoraphanin also increased with gypsum applications. Differences in S uptake, S distribution between organs, and partitioning of S into glucoraphanin largely explained the differences in glucoraphanin content in the green heads and mature seeds for the three broccoli cultivars and three S treatments.

Dietary approach to attenuate oxidative stress, hypertension, and inflammation in the cardiovascular system

Imbalance between production and scavenging of superoxide anion results in hypertension by the inactivation of nitric oxide, and the increased oxidative stress from the resultant peroxynitrite that is produced promotes inflammatory processes such as atherosclerosis. Induction of phase 2 proteins promotes oxidant scavenging. We hypothesized that intake of dietary phase 2 protein inducers would ameliorate both hypertension and atherosclerotic changes in the spontaneously hypertensive stroke-prone rat. For 5 days/week for 14 weeks, we fed rats 200 mg/day of dried broccoli sprouts that contained glucoraphanin, which is metabolized into the phase 2 protein-inducer sulforaphane (Group A), sprouts in which most of the glucoraphanin was destroyed (Group B), or no sprouts (Group C). After 14 weeks of treatment, no significant differences were seen between rats in Groups B and C. Rats in Group A had significantly decreased oxidative stress in cardiovascular and kidney tissues, as shown by increased glutathione (GSH) content and decreased oxidized GSH, decreased protein nitrosylation, as well as increased GSH reductase and GSH peroxidase activities. Decreased oxidative stress correlated with better endothelial-dependent relaxation of the aorta and significantly lower (20 mm Hg) blood pressure. Tissues from Groups B and C had considerable numbers of infiltrating activated macrophages, indicative of inflammation, whereas animals in Group A had few detectable infiltrating macrophages. There is interest in dietary phase 2 protein inducers as means of reducing cancer incidence. We conclude that a diet containing phase 2 protein inducers also reduces the risk of developing cardiovascular problems of hypertension and atherosclerosis.

Cruciferous vegetables: cancer protective mechanisms of glucosinolate hydrolysis products and selenium

Dietetic professionals urge Americans to increase fruit and vegetable intakes. The American Institute of Cancer Research estimates that if the only dietary change made was to increase the daily intake of fruits and vegetables to 5 servings per day, cancer rates could decline by as much as 20%. Among the reasons cited for this health benefit are that fruits and vegetables are excellent sources of fiber, vitamins, and minerals. They also contain nonnutritive components that may provide substantial health benefits beyond basic nutrition. Examples of the latter are the glucosinolate hydrolysis products, sulforaphane, and indole-3-carbinol. Epidemiological studies provide evidence that the consumption of cruciferous vegetables protects against cancer more effectively than the total intake of fruits and vegetables. This review describes the anticarcinogenic bioactivities of glucosinolate hydrolysis products, the mineral selenium derived from crucifers, and the mechanisms by which they protect against cancer. These mechanisms include altered estrogen metabolism, protection against reactive oxygen species, altered detoxification by induction of phase II enzymes, decreased carcinogen activation by inhibition of phase I enzymes, and slowed tumor growth and induction of apoptosis.

Hydrolysis of glucosinolates to isothiocyanates after ingestion of raw or microwaved cabbage by human volunteers

Cabbage contains the glucosinolate sinigrin, which is hydrolyzed by myrosinase to allyl isothiocyanate. Isothiocyanates are thought to inhibit the development of cancer cells by a number of mechanisms. The effect of cooking cabbage on isothiocyanate production from glucosinolates during and after their ingestion was examined in human subjects. Each of 12 healthy human volunteers consumed three meals, at 48-h intervals, containing either raw cabbage, cooked cabbage, or mustard according to a cross-over design. At each meal, watercress juice, which is rich in phenethyl isothiocyanate, was also consumed to allow individual and temporal variation in postabsorptive isothiocyanate recovery to be measured. Volunteers recorded the time and volume of each urination for 24 h after each meal. Samples of each urination were analyzed for N-acetyl cysteine conjugates of isothiocyanates as a measure of entry of isothiocyanates into the peripheral circulation. Excretion of isothiocyanates was rapid and substantial after ingestion of mustard, a source of preformed allyl isothiocyanate. After raw cabbage consumption, allyl isothiocyanate was again rapidly excreted, although to a lesser extent than when mustard was consumed. On the cooked cabbage treatment, excretion of allyl isothiocyanate was considerably less than for raw cabbage, and the excretion was delayed. The results indicate that isothiocyanate production is more extensive after consumption of raw vegetables but that isothiocyanates still arise, albeit to a lesser degree, when cooked vegetables are consumed. The lag in excretion on the cooked cabbage treatment suggests that the colon microflora catalyze glucosinolate hydrolysis in this case.

Sulforaphane-induced G2/M phase cell cycle arrest involves checkpoint kinase 2-mediated phosphorylation of cell division cycle 25C

Previously, we showed that sulforaphane (SFN), a naturally occurring cancer chemopreventive agent, effectively inhibits proliferation of PC-3 human prostate cancer cells by causing caspase-9- and caspase-8-mediated apoptosis. Here, we demonstrate that SFN treatment causes an irreversible arrest in the G(2)/M phase of the cell cycle. Cell cycle arrest induced by SFN was associated with a significant decrease in protein levels of cyclin B1, cell division cycle (Cdc) 25B, and Cdc25C, leading to accumulation of Tyr-15-phosphorylated (inactive) cyclin-dependent kinase 1. The SFN-induced decline in Cdc25C protein level was blocked in the presence of proteasome inhibitor lactacystin, but lactacystin did not confer protection against cell cycle arrest. Interestingly, SFN treatment also resulted in a rapid and sustained phosphorylation of Cdc25C at Ser-216, leading to its translocation from the nucleus to the cytoplasm because of increased binding with 14-3-3beta. Increased Ser-216 phosphorylation of Cdc25C upon treatment with SFN was the result of activation of checkpoint kinase 2 (Chk2), which was associated with Ser-1981 phosphorylation of ataxia telangiectasia-mutated, generation of reactive oxygen species, and Ser-139 phosphorylation of histone H2A.X, a sensitive marker for the presence of DNA double-strand breaks. Transient transfection of PC-3 cells with Chk2-specific small interfering RNA duplexes significantly attenuated SFN-induced G(2)/M arrest. HCT116 human colon cancer-derived Chk2(-/-) cells were significantly more resistant to G(2)/M arrest by SFN compared with the wild type HCT116 cells. These findings indicate that Chk2-mediated phosphorylation of Cdc25C plays a major role in irreversible G(2)/M arrest by SFN. Activation of Chk2 in response to DNA damage is well documented, but the present study is the first published report to link Chk2 activation to cell cycle arrest by an isothiocyanate.

A novel natural inhibitor of extracellular signal-regulated kinases and human breast cancer cell growth

Water-soluble extracts of edible Vernonia amygdalina leaves were recently reported as potent inhibitors of cultured MCF-7 cells. The mechanism by which V. amygdalina inhibits MCF-7 cell growth has not been previously studied. The objective of this study was to evaluate the effects of V. amygdalina on the activities, DNA synthesis, and subsequent cell growth of extracellular signal-regulated protein kinases 1 and 2 (ERKs 1/2;). Treatment of cells with various concentrations (3-100 mg/ml) of water-soluble V. amygdalina extract potently inhibited ERK activities, DNA synthesis (P < 0.005), and cell growth (P < 0.01) in a concentration-dependent fashion, both in the absence and presence of serum. The growth rate of cells pretreated with 10 mg/ml V. amygdalina for 48 hrs before transfer to V. amygdalina-free medium was not significantly different (P > 0.05) from untreated cells. These results suggest that V. amygdalina, at least at concentrations up to 10 mg/ml, exhibits cytostatic action to retard the growth of human breast cancer cells. In addition, the ERK signaling pathways may be one or more of the intracellular targets for V. amygdalina antineoplastic actions.

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.

Sulforaphane inhibits growth of a colon cancer cell line

OBJECTIVE

The consumption of cruciferous vegetables has a protective effect on the development of colorectal cancer. The phytochemical Sulforaphane is an isothiocyanate found almost exclusively in cruciferous vegetables. We have studied the effect of Sulforaphane on cell proliferation of an HT-29 colon cancer cell line.

MATERIALS AND METHODS

HT-29 colon cancer cells were cultured in 96-well microtitre plates. Sulforaphane (in concentrations ranging from 0.01 to 0.1 mmol) were added to the wells. Cell proliferation was measured using the colourimetric assay technique.

RESULTS

The proliferation of colon cancer cells was significantly reduced by Sulforaphane at concentrations of >/=0.02 mmol.

CONCLUSION

These findings may help explain the epidemiologically proven protective effect of vegetables against colon cancer.

Phase 1 study of multiple biomarkers for metabolism and oxidative stress after one-week intake of broccoli sprouts

Little is known about the direct effect of broccoli sprouts on human health. So we investigated the effect of broccoli sprouts on the induction of various biochemical oxidative stress markers. Twelve healthy subjects (6 males and 6 females) consumed fresh broccoli sprouts (100 g/day) for 1 week for a phase 1 study. Before and after the treatment, biochemical examination was conducted and natural killer cell activity, plasma amino acids, plasma PCOOH (phosphatidylcholine hydroperoxide), the serum coenzyme Q(10), urinary 8-isoprostane, and urinary 8-OHdG (8-hydroxydeoxyguanosine) were measured. With treatment, total cholesterol and LDL cholesterol decreased, and HDL cholesterol increased significantly. Plasma cystine decreased significantly. All subjects showed reduced PCOOH, 8-isoprostane and 8-OHdG, and increased CoQ(10)H(2)/CoQ(10) ratio. Only one week intake of broccoli sprouts improved cholesterol metabolism and decreased oxidative stress markers.

Ontogenic variations of ascorbic acid and phenethyl isothiocyanate concentrations in watercress (Nasturtium officinale R.Br.) leaves

Watercress (Nasturtium officinale R.Br.) is the richest source of glucosinolate nasturtiin, which on hydrolysis produces phenethyl isothiocyante (PEITC). Interest in growing watercress is stimulated since demonstration of the role of PEITC in protection against cancers associated with tobacco specific carcinogens. Twenty-one days old watercress seedlings were transplanted into growth chambers (16-h days/8-h nights of 25/22 degrees C and photosynthetic photon flux (PPF) of approximately 265 micromol m(-2) s(-)(1)). The study was replicated three times. Leaves were analyzed for PEITC and ascorbic acid concentrations at transplant, and harvested at 10-days intervals until 60 days after transplant. The PEITC and ascorbic acid concentrations were the highest in leaves harvested at 40 days and the lowest at transplant. Leaves harvested at 40 days produced about 150% higher PEITC concentrations compared to the leaves at transplant. Both PEITC and ascorbic acid concentrations of leaves increased linearly with age until 40 days after transplant after which there was no significant increase. Seedlings at transplant had the lowest dry mass and leaf area, while plants harvested at 60 days had the highest dry mass and leaf area.

Kale carotenoids remain stable while flavor compounds respond to changes in sulfur fertility

Dietary intake of certain carotenoids has been associated with a reduced risk of disease. Kale (Brassica oleracea L. Acephala Group) has the highest levels of carotenoids lutein and beta-carotene, and is an excellent source of minerals among the green leafy vegetable crops. However, Brassica vegetables contain glucosinolate (GS) and S-methylcysteine sulfoxide (MCSO). While these sulfur compounds have medicinal value, they are also responsible for the bitter, acrid flavors that are often regarded as objectionable by consumers. Therefore, the objectives of this study were to investigate the influence of increased S fertility levels on (1) elemental accumulation, (2) GS and MCSO production, and (3) the accumulation patterns of carotenoid pigments in the leaves of three kale cultivars. Winterbor, Redbor, and Toscano kale were greenhouse-grown using nutrient solution culture with S treatment concentrations of 4, 8, 16, 32, and 64 mg of S/L. Decreasing S fertility decreased S leaf content, but increased the levels of Mg and Ca accumulation, two important minerals for human health. Levels of GS and MSCO decreased in response to a decreasing S level in nutrient solution. However, accumulation of lutein and beta-carotene was unaffected by S treatment. Lowering the S fertility in the production of kale should decrease the levels of negative flavors associated with high levels of GS and MCSO without affecting carotenoid pigment levels. Understanding the combined impact of fertility on flavor compounds and carotenoid pigments may help improve consumer acceptance of phytonutritionally enhanced vegetable crops.

DNA damage-mediated apoptosis induced by selenium compounds

Selenium (Se) compounds, which are the most extensively studied cancer chemopreventive agents, induce apoptotic death of tumor cells. In the current study, we show that selenite-induced apoptosis involves DNA damage. We showed that selenite-induced apoptosis as evidenced by cleavage of poly(ADP-ribose) polymerase was reduced in NIH 3T3 cells treated with ATM small interfering RNA, suggesting the involvement of the DNA damage regulator ATM. Consistent with ATM/ATR involvement, selenite was also shown to stimulate Ser-139 phosphorylation of the ATM/ATR substrate H2AX. Selenite-induced apoptosis was shown to involve DNA topoisomerase II (Top II) as selenite-induced apoptosis was reduced in Top II-deficient HL-60/MX2 cells and in HL-60 cells co-treated with the Top II catalytic inhibitor ICRF-193. Using purified human recombinant Top II, selenite was shown to induce reversible Top II cleavage complexes in vitro. In the aggregate, these results suggest that selenite-induced apoptosis, which involves ATM/ATR and Top II, is likely to be because of DNA damage.

Induction of tumor necrosis factor production and antitumor effect by cabbage extract

The effect of cabbage extract on the production of tumor necrosis factor and its implication in the antitumor effect were examined in vitro and in vivo. Cabbage extract stimulated the production of tumor necrosis factor by rat spleen cells and showed cytotoxic activity in a rat ascites hepatoma cell line (AH109A) when hepatoma cells were cultured with cabbage-stimulated spleen cells. When the extract was adminstered orally to AH109A-bearing rats in combination with lipopolysaccharide injection, the hepatoma weights were reduced to one-half of the vehicle control. The cytotoxic activity of tumor-infiltrating macrophages was induced by simultaneous treatment with cabbage extract and lipopolysaccharide. These results indicate that cabbage extract contains macrophage-stimulating component(s) and can implement the antitumor effect by stimulating the cytotoxicity of tumor-infiltrating macrophages.

Changes in broccoli (Brassica oleracea L. Var. italica) health-promoting compounds with inflorescence development

Changes in phenolic compounds, total glucosinolates, and vitamin C were monitored during the productive period along five inflorescence development stages of three broccoli commercial cultivars (Marathon, Monterrey, and Vencedor). In an attempt to identify differences due to agronomic factors, broccoli cultivars were grown under different sulfur fertilization with poor (15 kg/ha) and rich (150 kg/ha) rates. Phenolic compounds and vitamin C concentrations showed, in all broccoli cultivars, a rising trend from the first stage until the over-maturity stage, both for rich and poor sulfur fertilization. Significant differences were detected in the first two stages between rich and poor sulfur fertilization in total glucosinolates for all broccoli cultivars, where the highest concentration was always observed in the second development stage (used as minimally processed product) during poor fertilization. With regard to the last three stages, the glucosinolate concentration in the poor sulfur fertilization started to slope down until the over-maturity stage. Where rich sulfur fertilization is concerned, the highest level was reached during the third stage (used as minimally processed product also), and after that, glucosinolate concentration decreased until the fifth stage.

Coordinate regulation of glutathione biosynthesis and release by Nrf2-expressing glia potently protects neurons from oxidative stress

Astrocytes have a higher antioxidant potential in comparison to neurons. Pathways associated with this selective advantage include the transcriptional regulation of antioxidant enzymes via the action of the Cap'n'Collar transcription factor Nrf2 at the antioxidant response element (ARE). Here we show that Nrf2 overexpression can reengineer neurons to express this glial pathway and enhance antioxidant gene expression. However, Nrf2-mediated protection from oxidative stress is conferred primarily by glia in mixed cultures. The antioxidant properties of Nrf2-overexpressing glia are more pronounced than those of neurons, and a relatively small number of these glia (< 1% of total cell number added) could protect fully cocultured naive neurons from oxidative glutamate toxicity associated with glutathione (GSH) depletion. Microarray and biochemical analyses indicate a coordinated upregulation of enzymes involved in GSH biosynthesis (xCT cystine antiporter, gamma-glutamylcysteine synthetase, and GSH synthase), use (glutathione S-transferase and glutathione reductase), and export (multidrug resistance protein 1) with Nrf2 overexpression, leading to an increase in both media and intracellular GSH. Selective inhibition of glial GSH synthesis and the supplementation of media GSH indicated that an Nrf2-dependent increase in glial GSH synthesis was both necessary and sufficient for the protection of neurons, respectively. Neuroprotection was not limited to overexpression of Nrf2, because activation of endogenous glial Nrf2 by the small molecule ARE inducer, tert-butylhydroquinone, also protected against oxidative glutamate toxicity.

Food matrix effects on bioactivity of broccoli-derived sulforaphane in liver and colon of F344 rats

Sulforaphane (SF) is considered to be the major anticarcinogenic component in broccoli. The effects of feeding rats purified SF (5 mmol/kg of diet), broccoli containing SF formed in situ during laboratory hydrolysis (broccoli-HP; 20% freeze-dried broccoli diet, 0.16 mmol of SF/kg of diet), and broccoli containing intact glucosinolates (broccoli-GS; 20% freeze-dried broccoli diet, 2.2 mmol of glucoraphanin/kg of diet) were compared. Rats (male F344 rats, five per group) were fed control (modified AIN-76 B-40), SF, broccoli-HP, or broccoli-GS for 5 days. In rats fed broccoli-GS, quinone reductase activities (QR) in the colon and liver were greater (4.5- and 1.4-fold over control, respectively) than in rats fed broccoli-HP (3.2- and 1.1-fold over control, respectively). Broccoli-GS and SF diets increased QR to the same extent, even though the broccoli-GS diet contained far less SF (as the unhydrolyzed glucosinolate, glucoraphanin) than the purified SF diet. In a second experiment, rats were fed one of six diets for 5 days: (1) control; (2) 20% broccoli-GS; (3) diet 2 + low SF (0.16 mmol/kg of diet); (4) diet 2 + high SF (5 mmol/kg of diet); (5) low SF (0.32 mmol/kg of diet); or (6) high SF (5.16 mmol/kg of diet). In both liver and colon, QR was increased most by high SF plus broccoli-GS; individually, high SF and broccoli-GS had similar effects, and adding the low-dose SF to broccoli-GS had either no effect or a negative effect. In both experiments, urinary SF-mercapturic acid correlated with QR activity, not with dietary intake. It was concluded that all diets were substantially more effective in the colon than in the liver and that broccoli-GS was more potent than SF or broccoli-HP.

Health-promoting compounds in broccoli as influenced by refrigerated transport and retail sale period

Total aliphatic and indole glucosinolates, phenolic compounds (flavonoids and hydroxycinnamoyl derivatives), and vitamin C contents were evaluated in freshly harvested broccoli (Brassica oleracea L., var. italica, cv. Marathon) inflorescences. These were film-wrapped and stored for 7 days at 1 degrees C to simulate a maximum period of commercial transport and distribution. After cold storage, inflorescences were kept for 3 days at 15 degrees C to simulate a retail sale period. For wrapping, low-density polyethylene (LDPE) of 11 microm thickness was used. Gas composition was about 17% O(2) and 2% CO(2) during cold storage and about 16% O(2) and 3-4% CO(2) during shelf life within packages. The predominant glucosinolates were 4-methylsulfinylbutyl-glucosinolate (glucoraphanin), 3-indolylmethyl-glucosinolate (glucobrassicin), and 1-methoxy-3-indolylmethyl-glucosinolate (neoglucobrassicin). The predominant hydroxycinnamoyl derivatives were identified as 1,2,2'-trisinapoylgentiobiose, 1,2-diferuloylgentiobiose, 1,2'-disinapoyl-2-feruloylgentiobiose, and 3-O-caffeoyl-quinic (neochlorogenic acid). Results showed major losses at the end of both periods, in comparison with broccoli at harvest. Thus, the respective losses, at the end of cold storage and retail periods, were 71-80% of total glucosinolates, 62-59% of total flavonoids, 51-44% of sinapic acid derivatives, and 73-74% caffeoyl-quinic acid derivatives. Slight differences in all compound concentrations between storage and retail sale periods were detected. Distribution and retail periods had minimal effects on vitamin C. Weight loss was monitored at the end of both periods.

Translational strategies for cancer prevention in liver

Unlike many other types of human cancer, the aetiology of liver cancer is well understood. Infection with hepatitis viruses, coupled with dietary exposure to the fungal toxin aflatoxin, increases the risk of the disease. Although primary prevention, based on vaccination and avoiding exposure to these agents, is an appealing option, such strategies will require considerable investment of time and resources to be successful. In the developing world--where the burden of liver cancer is highest--immediate, practical and economical approaches are essential. So, targeted chemoprevention might be most appropriate for the present generation of individuals at risk.

Irradiation D-values for Escherichia coli O157:H7 and Salmonella sp. on inoculated broccoli seeds and effects of irradiation on broccoli sprout keeping quality and seed viability

Like alfalfa sprouts, broccoli sprouts can be a vehicle for bacterial pathogens, which can cause illness when they are consumed. The gamma irradiation process was used to reduce numbers of bacterial pathogens on broccoli sprouts and seeds, and the effect of this process on the seeds was studied. The irradiation destruct values for Salmonella sp. and for strains of Escherichia coli O157:H7 inoculated on broccoli seeds were determined. Results obtained in this study indicate that a dose of 2 kGy reduced total background counts for broccoli sprouts from 10(6) to 10(7) CFU/g to 10(4) to 10(5) CFU/g and increased the shelf life of the sprouts by 10 days. Yield ratio (wt/wt), germination percentage, sprout length, and thickness were measured to determine the effects of various irradiation doses on the broccoli seeds. Results show a decreased germination percentage at a dose level of 4 kGy, whereas the yield ratio (wt/wt), sprout length, and thickness decreased at the 2-kGy dose level. The radiation doses required to inactivate Salmonella sp. and strains of E. coli O157:H7 were higher than previously reported values. D-values, dose required for a 1-log reduction, for the nonvegetable and vegetable Salmonella sp. isolates were 0.74 and 1.10 kGy, respectively. The values for the nonvegetable and vegetable isolated strains of Escherichia coli O157:H7 were 1.43 and 1.11 kGy, respectively. With the irradiation process, a dose of up to 2 kGy can extend the shelf life of broccoli sprouts. A dose of > 2 kGy would have an adverse effect on the broccoli seed and decrease the yield of broccoli sprouts.

Coordinate regulation of glutathione biosynthesis and release by Nrf2-expressing glia potently protects neurons from oxidative stress

Astrocytes have a higher antioxidant potential in comparison to neurons. Pathways associated with this selective advantage include the transcriptional regulation of antioxidant enzymes via the action of the Cap'n'Collar transcription factor Nrf2 at the antioxidant response element (ARE). Here we show that Nrf2 overexpression can reengineer neurons to express this glial pathway and enhance antioxidant gene expression. However, Nrf2-mediated protection from oxidative stress is conferred primarily by glia in mixed cultures. The antioxidant properties of Nrf2-overexpressing glia are more pronounced than those of neurons, and a relatively small number of these glia (< 1% of total cell number added) could protect fully cocultured naive neurons from oxidative glutamate toxicity associated with glutathione (GSH) depletion. Microarray and biochemical analyses indicate a coordinated upregulation of enzymes involved in GSH biosynthesis (xCT cystine antiporter, gamma-glutamylcysteine synthetase, and GSH synthase), use (glutathione S-transferase and glutathione reductase), and export (multidrug resistance protein 1) with Nrf2 overexpression, leading to an increase in both media and intracellular GSH. Selective inhibition of glial GSH synthesis and the supplementation of media GSH indicated that an Nrf2-dependent increase in glial GSH synthesis was both necessary and sufficient for the protection of neurons, respectively. Neuroprotection was not limited to overexpression of Nrf2, because activation of endogenous glial Nrf2 by the small molecule ARE inducer, tert-butylhydroquinone, also protected against oxidative glutamate toxicity.

Oxathiolene oxides: a novel family of compounds that induce ferritin, glutathione S-transferase, and other proteins of the phase II response

Compounds that induce the synthesis of cytoprotective phase II enzymes have shown promise as cancer chemopreventive agents. Although chemically diverse, phase II enzyme inducers are capable of participating in Michael reaction chemistry. We have synthesized a novel class of organosulfur compounds, termed oxathiolene oxides (OTEOs). Based on their chemical properties, we hypothesized that these compounds could function as phase II enzyme inducers. Northern blot analysis showed that oxathiolene oxides induce the phase II enzymes glutathione S-transferase (GST), NAD(P)H:quinone oxidoreductase 1 (NQO1), and ferritin H and L mRNA in a concentration-dependent fashion in a normal embryonic mouse liver cell line, BNLCL.2. OTEO-562 (3-cyclohexenyl-4-methyl-1,2-oxathiol-3-ene-2-oxide) was the strongest inducer. Western blot analysis demonstrated that GST-alpha and ferritin H protein levels were also induced in cells treated with OTEO-562, as was total GST and NQO1 enzyme activity. Further, induction of NQO1 activity by OTEO-562 was equivalent in aromatic hydrocarbon (Ah) receptor wild-type and Ah receptor mutant cell lines, suggesting that oxathiolene oxides activate phase II enzymes by an Ah receptor-independent mechanism. Consistent with this observation, OTEO-562 failed to induce cytochrome P450 1A1 mRNA. These results suggest that oxathiolene oxides may merit further investigation as candidate chemopreventive agents.

Nutrition for health promotion: phytochemicals, functional foods, and alternative approaches to combat obesity

Functional foods are a new area of interest because of their potential health benefits. Functional foods may contain significant levels of biologically active components that impart health benefits when consumed in optimal serving sizes. Phytochemicals are components of plants that convey healthful properties beyond their use as macronutrients or micronutrients. Scientists have identified thousands of phytochemicals in vegetables, fruits, grains, legumes, and other plant sources. Even though the consumption of fat has steadily decreased over the past decade as Americans have became a fat-phobic society, body weight has continued to rise. Health professionals need to consider options or alternatives to the only recommendation currently being offered (ie, low-fat, low-calorie, portion-controlled diets) because the obesity problem is not being solved with current methods and recommendations. A new paradigm is needed. The controlled-carbohydrate diet is one viable alternative dietary approach. There also is emerging evidence to show that lipid profiles improve on a controlled-carbohydrate diet.

The cruciferous nitrile crambene has bioactivity similar to sulforaphane when administered to Fischer 344 rats but is far less potent in cell culture

The anticarcinogenic properties of broccoli are believed to be due to modification of detoxification enzymes by a group of isothiocyanates, hydrolysis products of glucosinolates, particularly sulforaphane. We previously showed that the nitrile crambene (1-cyano-2-hydroxy-3-butene), present in most Brassica vegetables, induces hepatic quinone reductase activity when administered to rats. In this study, we compared the effects of seven daily oral doses of crambene (50 mg/kg rat/day) and sulforaphane (50 mg/kg rat/day) on induction of hepatic quinone reductase activity in Fischer 344 rats. The two treatments produced similar effects, with crambene and sulforaphane producing 1.5- and 1.7-fold induction in hepatic quinone reductase activity, respectively. Additionally, we evaluated the effect of crambene on quinone reductase activity in Hepa 1c1c7 cells, because this system had been shown to possess high sensitivity to sulforaphane and is commonly used for screening anticarcinogenic compounds. Crambene (5 mM) induced quinone reductase activity and caused cell cycle arrest in the G2/M phase in mouse Hepa 1c1c7 cells, rat H4IIEC3 cells, and human Hep G2 cells (> 95% viability). Doses of crambene needed for induction of quinone reductase in cell culture were approximately 100-fold greater than effective doses of sulforaphane. These findings indicate that hepatoma cell lines may not accurately reflect relative potency of anticarcinogens in Fischer 344 rats.

Brassica vegetables and prostate cancer risk: a review of the epidemiological evidence

Epidemiological studies have yielded conflicting results on the associations of diet with prostate cancer. We review evidence that Brassica vegetables are associated with reduced prostate cancer risk. Brassica vegetables, which include broccoli, cabbage, mustard and collard greens, and bok choy, contain glucosinolates, the metabolic breakdown products of which are potent modulators of xenobiotic-metabolizing enzymes that protect DNA from damage. Twelve published studies give some information about Brassica vegetables and prostate cancer risk; six of these studies can be clearly interpreted. Of these, three reported statistically significant reduced risks (P < 0.05) and one reported a borderline significant reduced risk (P = 0.06) with high Brassica vegetable consumption. The epidemiological literature provides modest support for the hypothesis that high intakes of Brassica vegetables reduce prostate cancer risk.

Benzyl isothiocyanate: an effective inhibitor of polycyclic aromatic hydrocarbon tumorigenesis in A/J mouse lung

Polycyclic aromatic hydrocarbons (PAH) are an important group of carcinogens that are likely to be involved as one of the causes of lung cancer in smokers and occupationally exposed individuals. Previous studies have shown that benzyl isothiocyanate (BITC), administered by gavage, is a good inhibitor of lung tumorigenesis in A/J mice induced by benzo[a]pyrene (BaP), a typical PAH carcinogen. In this study, we evaluated the effects of BITC on lung tumor induction in A/J mice by two other carcinogenic PAH in cigarette smoke - 5-methylchrysene (5-MeC) and dibenz[a,h]anthracene (DBahA). We also compared the effects of BITC with two other well known chemopreventive agents - butylated hydroxyanisole (BHA) and sulforaphane. In experiment 1, groups of A/J mice were treated by gavage once weekly for 8 weeks with BaP (3 micromol) or 5-MeC (2 micromol) or DBahA (1 micromol) in 0.1 ml cottonseed oil. Fifteen minutes before each treatment, the mice were gavaged with 0.1 ml cottonseed oil or 0.1 ml cottonseed oil containing 13.4 micromol or 6.7 micromol of BITC. The experiment was terminated 19 weeks after the final carcinogen treatment. BITC significantly reduced lung tumor multiplicity in all PAH-treated groups by 63.5-90.6%. In experiment 2, groups of A/J mice were treated with BaP or BITC and BaP as in experiment 1, or with BHA or sulforaphane at doses equimolar to those of BITC. BITC was significantly more effective as an inhibitor of lung tumor induction than either BHA or sulforaphane. These results firmly establish gavaged BITC as a strong inhibitor of lung tumorigenesis induced in A/J mice by PAH, and support its further development for chemoprevention of smoking-induced lung cancer.

The effect of post-harvest and packaging treatments on glucoraphanin concentration in broccoli (Brassica oleracea var. italica)

The effects of post-harvest and packaging treatments on glucoraphanin (4-methylsulfinylbutyl glucosinolate), the glucosinolate precursor of anticancer isothiocyanate sulforaphane [4-methylsulfinylbutyl isothiocyanate], were examined in broccoli (Brassica oleracea var. italica) during storage times. The results showed that at 20 degrees C, 55% loss of glucoraphanin concentration occurred in broccoli stored in open boxes during the first 3 days of the treatment and 56% loss was found in broccoli stored in plastic bags by day 7. Under both air and controlled atmosphere (CA) storage, glucoraphanin concentration appeared to fluctuate slightly during 25 days of storage and the concentrations under CA was significantly higher than those stored under air treatment. In modified atmosphere packaging (MAP) treatments, glucoraphanin concentration in air control packaging decreased significantly whereas there were no significant changes in glucoraphanin concentration in MAP with no holes at 4 degrees C and two microholes at 20 degrees C for up to 10 days. Decreases in glucoraphanin concentration occurred when the broccoli heads deteriorated. In the present study, the best method for preserving glucoraphanin concentration in broccoli heads after harvest was storage of broccoli in MAP and refrigeration at 4 degrees C. This condition maintained the glucoraphanin concentration for at least 10 days and also maintained the visual quality of the broccoli heads.

Pinostrobin from honey and Thai ginger (Boesenbergia pandurata): a potent flavonoid inducer of mammalian phase 2 chemoprotective and antioxidant enzymes

Over 60 different samples comprising 35 distinct honeys were evaluated for their ability to induce mammalian phase 2 detoxication enzymes using a microtiter plate assay of quinone reductase (QR) induction with murine hepatoma cells in microtiter plates. This assay has been used extensively to identify and isolate a variety of natural and synthetic inducers from plants. All 35 honeys examined induced elevations of mammalian QR activity ranging from 153 to 2155 units/g with a mean of 630 and a median of 417 units/g. The concentrations for doubling the QR activity (CD) of certain of the prominent flavonoids found in honey were also assessed (pinostrobin, 0.5 microM; pinocembrin, 110 microM; chrysin, 25 microM) and compared to those of related, more commonly described flavonoids such as quercetin (2.7 microM) and myricetin (58 microM). On the basis of the extremely high QR inducing potency of one of these compounds, pinostrobin (5-hydroxy-7-methoxyflavanone), a bioassay-guided search was conducted which revealed a dietary source of pinostrobin, Boesenbergia pandurata (fingerroot), with extraordinarily high ability to induce mammalian phase 2 detoxication enzymes. Although the QR inducing activity of buckwheat honeys was 2155 +/- 951 units/g (n = 8 samples), which is less than 10% of the average values obtained from fresh broccoli, the potency of fingerroot rhizomes (ca. 110,000 units/g) is even higher than that of broccoli and the potencies of fingerroot oil and powdered rhizome (ca. 500,000 units/g) rival that of broccoli sprouts.

Chemoprevention of colorectal cancer: problems, progress, and prospects

Chemoprevention holds great promise as a complement to traditional CRC screening and treatment. Effective chemopreventive agents might improve patient outcomes by reducing the number of missed lesions, the morbidity associated with their identification and treatment, and their malignant potential. In addition, chemoprevention may reduce neoplastic potential simultaneously in several organs and improve clinical outcomes for persons at risk for cancers at multiple sites (e.g., colorectal and extracolonic cancers in HNPCC cohorts). Complex molecular circuits underlie the disease mosaic that is associated with aging. Several of these diseases share common mechanisms against which preventive interventions appear to be effective, such as NSAIDs for colorectal neoplasia and neurodegenerative disease, and statins for cardiovascular disease and colorectal neoplasia. Understanding these mechanisms and effects could raise prevention science to an entirely new level. The number of trials that are investigating chemopreventives against CR neoplasia is relatively small; if these agents live up to a fraction of their promise, the public health impact may be great (see Table 6).

Onions--a global benefit to health

Onion (Allium cepa L.) is botanically included in the Liliaceae and species are found across a wide range of latitudes and altitudes in Europe, Asia, N. America and Africa. World onion production has increased by at least 25% over the past 10 years with current production being around 44 million tonnes making it the second most important horticultural crop after tomatoes. Because of their storage characteristics and durability for shipping, onions have always been traded more widely than most vegetables. Onions are versatile and are often used as an ingredient in many dishes and are accepted by almost all traditions and cultures. Onion consumption is increasing significantly, particularly in the USA and this is partly because of heavy promotion that links flavour and health. Onions are rich in two chemical groups that have perceived benefits to human health. These are the flavonoids and the alk(en)yl cysteine sulphoxides (ACSOs). Two flavonoid subgroups are found in onion, the anthocyanins, which impart a red/purple colour to some varieties and flavanols such as quercetin and its derivatives responsible for the yellow and brown skins of many other varieties. The ACSOs are the flavour precursors, which, when cleaved by the enzyme alliinase, generate the characteristic odour and taste of onion. The downstream products are a complex mixture of compounds which include thiosulphinates, thiosulphonates, mono-, di- and tri-sulphides. Compounds from onion have been reported to have a range of health benefits which include anticarcinogenic properties, antiplatelet activity, antithrombotic activity, antiasthmatic and antibiotic effects. Here we review the agronomy of the onion crop, the biochemistry of the health compounds and report on recent clinical data obtained using extracts from this species. Where appropriate we have compared the data with that obtained from garlic (Allium sativum L.) for which more information is widely available.

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.

In vitro induction of benzo(a)pyrene cell-transforming activity by the glucosinolate gluconasturtiin found in cruciferous vegetables

Cytotoxic and cell-transforming activity of gluconasturtiin (GNST), a promising chemopreventive agent commonly found in human diet, was studied in a medium-term bioassay utilizing BALB/c 3T3 cells. We also assessed whether GNST coupled with myrosinase, thus yielding product phenylethyl isothiocyanate (as shown by gas chromatography-mass spectral analysis), can affect the transforming potential of benzo(a)pyrene (B(a)P). Neither cytotoxicity nor cell-transforming activity was recorded. On the contrary, a marked increase (up to sevenfold) of the transforming activity of B(a)P was seen. This cocarcinogenic potential could be ascribed to an imbalance among bioactivation/detoxication during cell growth. These results indicate the need for an overall toxicological characterization of a chemopreventive agent prior to large-scale use.

Chemoprotective potential of phase 2 enzyme inducers

In this review we summarize recent data on the use of phase 2 enzyme inducers as cancer chemopreventive agents in preclinical and clinical studies. These agents elevate the expression of genes involved in the detoxication of electrophiles and free radicals that contribute to carcinogenesis. Their mechanisms of action, efficacy and limitations are discussed. Particular attention is paid to isothiocyante and dithiolethione classes of agents, as these are the most developed.

Direct evidence that sulfhydryl groups of Keap1 are the sensors regulating induction of phase 2 enzymes that protect against carcinogens and oxidants

Coordinate induction of phase 2 proteins and elevation of glutathione protect cells against the toxic and carcinogenic effects of electrophiles and oxidants. All inducers react covalently with thiols at rates that are closely related to their potencies. Inducers disrupt the cytoplasmic complex between the actin-bound protein Keap1 and the transcription factor Nrf2, thereby releasing Nrf2 to migrate to the nucleus where it activates the antioxidant response element (ARE) of phase 2 genes and accelerates their transcription. We cloned, overexpressed, and purified murine Keap1 and demonstrated on native gels the formation of complexes of Keap1 with the Neh2 domain of Nrf2 and their concentration-dependent disruption by inducers such as sulforaphane and bis(2-hydroxybenzylidene)acetone. The kinetics, stoichiometry, and order of reactivities of the most reactive of the 25 cysteine thiol groups of Keap1 have been determined by tritium incorporation from [(3)H]dexamethasone mesylate (an inducer and irreversible modifier of thiols) and by UV spectroscopy with sulforaphane, 2,2'-dipyridyl disulfide and 4,4'-dipyridyl disulfide (titrants of thiol groups), and two closely related Michael reaction acceptors [bis(2- and 4-hydroxybenzylidene)acetones] that differ 100-fold in inducer potency and the UV spectra of which are bleached by thiol addition. With large excesses of these reagents nearly all thiols of Keap1 react, but sequential reaction with three successive single equivalents (per cysteine residue) of dipyridyl disulfides revealed excellent agreement with pseudo-first order kinetics, rapid successive declines in reaction velocity, and the stoichiometric formation of two equivalents of thiopyridone per reacted cysteine. This finding suggests that reaction of cysteine thiols is followed by rapid formation of protein disulfide linkages. The most reactive residues of Keap1 (C(257), C(273), C(288), and C(297)) were identified by mapping the dexamethasone-modified cysteines by mass spectrometry of tryptic peptides. These residues are located in the intervening region between BTB and Kelch repeat domains of Keap1 and probably are the direct sensors of inducers of the phase 2 system.

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.

The Taste of Health: Nature's Bitter Gifts

A plant-based diet is said to protect against aging, heart disease, and cancer. Yet, the given advice to eat more vegetables and fruit often goes unheeded. Some consumers have turned instead to dietary supplements that provide plant-based antioxidants in a more concentrated form. Although these supplements are beneficial to human health in small doses, such compounds can sometimes be toxic. Biologically active phytochemicals also tend to be bitter, acrid, or astringent. The food industry has been removing them from plant foods through selective breeding and debittering processes, in response to consumer demand. Concerning bitter phytonutrients, the consumer faces competing demands of taste, health, and food safety.

Diet and colorectal cancer: an investigation of the lectin/galactose hypothesis

BACKGROUND & AIMS

Mucosal expression of terminal unsubstituted galactose is increased in colon cancer and precancer and allows interaction with mitogenic galactose-binding lectins of dietary or microbial origin. This study tests the hypothesis that galactose, which is variably plentiful in fruit and vegetable but not cereal fibers, might prevent cancer by binding and inhibiting such lectins.

METHODS

Colorectal cancer cases (512) and controls (512) were matched for age, sex, primary care practitioner, and postal code. A 160-item food-frequency questionnaire was used to estimate their usual pre-illness (6 months previous) diet, aspirin intake, and exercise.

RESULTS

Neither cereal fiber nor fruit and vegetable fiber were protective when assessed by univariate analysis, whereas dietary fiber galactose content showed a dose-related protective effect (odds ratio [OR] highest quartile/lowest quartile, 0.67; confidence interval [CI], 0.47-0.95) that remained protective when adjusted for energy, red meat, alcohol, calcium, protein and fat intake, regular aspirin usage, and exercise. Intake of nonlegume green vegetables, assessed because of the high lectin content of legumes, was also protective (OR, 0.54; CI, 0.35-0.81), but this was not independent of galactose. Protective effects of exercise and regular daily aspirin consumption and harmful effects of high energy consumption and high red meat intake were confirmed.

CONCLUSIONS

The protective effect of fruit and vegetable fibers may be related to their galactose content. This provides further evidence that the association between diet and colon cancer is mediated via specific food components and may explain the discrepant results of studies addressing the protective effects of fiber.

Glucosinolate research in the Arabidopsis era

The wide range of biological activities of products derived from the glucosinolate-myrosinase system is biologically and economically important. On the one hand, the degradation products of glucosinolates play an important role in the defence of plants against herbivores. On the other hand, these compounds have toxic (e.g. goitrogenic) as well as protective (e.g. cancer-preventing) effects in higher animals and humans. There is a strong interest in the ability to regulate and optimize the levels of individual glucosinolates tissue-specifically to improve the nutritional value and pest resistance of crops. Recent advances in our understanding of glucosinolate biosynthesis have brought us closer to this goal.