Analysis of isothiocyanate mercapturic acids in urine: a biomarker for cruciferous vegetable intake

Naturally Derived Phenethyl Isothiocyanate Modulates Induction of Oxidative Stress via Its N-Acetylated Cysteine Conjugated form in Malignant Melanoma

Phenethyl isothiocyanate (PEITC) is a secondary metabolic product yielded upon the hydrolysis of gluconasturtiin and it is highly accumulated in the flowers of watercress. The aim of the current study was to assess the role of a naturally derived PEITC-enriched extract in the induction of oxidative stress and to evaluate its anti-melanoma potency through the regulation of its metabolism with the concurrent production of the N-acetyl cysteine conjugated by-product. For this purpose, an in vitro melanoma model was utilized consisting of human primary (A375) cells as well as metastatic (COLO-679) malignant melanoma cells together with non-tumorigenic immortalized keratinocytes (HaCaT). Cytotoxicity was assessed via the Alamar Blue assay whereas the antioxidant/prooxidant activity of PEITC was determined via spectrophotometric assays. Finally, kinetic characterization of the end-product of PEITC metabolism was monitored via UPLC coupled to a tandem mass spectrometry (MS/MS). Our results indicate that although PhEF showed very minor antioxidant activity in a cell-free system, in a cell-based system, it can modulate the activity of key enzyme(s) involved in cellular antioxidant defense mechanism(s). In addition, we have shown that PhEF induces lipid and protein oxidation in a concentration-dependent manner, while its cytotoxicity is not only dependent on PEITC itself but also on its N-acetylated cysteine conjugated form.

A novel set of volatile urinary biomarkers for late-life major depressive and anxiety disorders upon the progression of frailty: a pilot study

Mood and anxiety disorders are frequent in the elderly and increase the risk of frailty. This study aimed to identify novel biomarkers of major depressive disorder (MDD) and anxiety in the elderly. We examined 639 participants in the community-dwelling Otassha Study (518 individuals considered healthy control, 77 with depression, anxiety, etc.), mean age 75 years, 58.4% of female. After exclusion criteria, we analyzed VOCs from 18 individuals (9 healthy control, 9 of MDD/agoraphobia case). Urinary volatile and semi-volatile organic compounds (VOCs) were profiled using solid-phase microextraction and gas chromatography-mass spectrometry. Six urinary VOCs differed in the absolute area of the base peak between participants with MDD and/or agoraphobia and controls. High area under the receiver-operating characteristic curve (AUC) values were found for phenethyl isothiocyanate (AUC: 0.86, p = 0.009), hexanoic acid (AUC: 0.85, p = 0.012), texanol (AUC: 0.99, p = 0.0005), and texanol isomer (AUC: 0.89, p = 0.005). The combined indices of dimethyl sulfone, phenethyl isothiocyanate, and hexanoic acid, and texanol and texanol isomer showed AUCs of 0.91 (p = 0.003) and 0.99 (p = 0.0005) and correlated with the GRID-HAMD and the Kihon Checklist (CL score), respectively. These VOCs may be valuable biomarkers for evaluating MDD and/or agoraphobia in the elderly.

A Physiological-Based Model for Simulating the Bioavailability and Kinetics of Sulforaphane from Broccoli Products

There are no known physiological-based digestion models that depict glucoraphanin (GR) to sulforaphane (SR) conversion and subsequent absorption. The aim of this research was to make a physiological-based digestion model that includes SR formation, both by endogenous myrosinase and gut bacterial enzymes, and to simulate the SR bioavailability. An 18-compartment model (mouth, two stomach, seven small intestine, seven large intestine, and blood compartments) describing transit, reactions and absorption was made. The model, consisting of differential equations, was fit to data from a human intervention study using Mathwork’s Simulink and Matlab software. SR urine metabolite data from participants who consumed different broccoli products were used to estimate several model parameters and validate the model. The products had high, medium, low, and zero myrosinase content. The model’s predicted values fit the experimental values very well. Parity plots showed that the predicted values closely matched experimental values for the high (r² = 0.95), and low (r² = 0.93) products, but less so for the medium (r² = 0.85) and zero (r² = 0.78) myrosinase products. This is the first physiological-based model to depict the unique bioconversion processes of bioactive SR from broccoli. This model represents a preliminary step in creating a predictive model for the biological effect of SR, which can be used in the growing field of personalized nutrition.

Current analytical methods for determination of glucosinolates in vegetables and human tissues

Numerous epidemiological studies have indicated the potential effects of glucosinolates and their metabolites against cancer as well as other non-communicable diseases, such as cardiovascular disease and neurodegenerative disorders. However, information on the presence and quantity of glucosinolates in commonly consumed vegetables and in human fluids is sparse, largely because well-standardised methods for glucosinolate determination are not available, resulting in published data being inconsistent and conflicting. Thus, studies published since 2002 on the most recent developments of glucosinolate extraction and identification have been collected and reviewed with emphasis on determination of the intact glucosinolates by LC-MS and LC-MS/MS. This overview highlights the glucosinolate extraction methods used, the stability of glucosinolates during extraction, the availability of stable isotope labelled internal standards and the use of NMR for purity analysis, as well as the current analytical techniques that have been applied for glucosinolate analysis, e.g. liquid chromatography with mass spectrometric detection (LC-MS). It aims to interpret the findings with a focus on the development of a validated method, which will help to determine the glucosinolate content of vegetative plants and human tissues, and the identification and determination of selected glucosinolate metabolites.

Are Raw Brassica Vegetables Healthier Than Cooked Ones? A Randomized, Controlled Crossover Intervention Trial on the Health-Promoting Potential of Ethiopian Kale

The present human intervention trial investigated the health-promoting potential of B. carinata, with a focus on effects of thermal processing on bioactivity. Twenty-two healthy subjects consumed a B. carinata preparation from raw (allyl isothiocyanate-containing) or cooked (no allyl isothiocyanate) leaves for five days in a randomized crossover design. Peripheral blood mononuclear cells were exposed to aflatoxin B1 (AFB1), with or without metabolic activation using human S9 mix, and subsequently analyzed for DNA damage using the comet assay. Plasma was analyzed for total antioxidant capacity and prostaglandin E₂ (PGE₂) levels. Cooked B. carinata significantly reduced DNA damage induced by AFB1 as compared to baseline levels (+S9 mix: 35%, -S9 mix: 33%, p ≤ 0.01, respectively). Raw B. carinata only reduced DNA damage by S9-activated AFB1 by 21% (p = 0.08). PGE₂ plasma levels were significantly reduced in subjects after consuming raw B. carinata. No changes in plasma antioxidant capacity were detectable. A balanced diet, including raw and cooked Brassica vegetables, might be suited to fully exploit the health-promoting potential. These results also advocate the promotion of B. carinata cultivation in Eastern Africa as a measure to combat effects of unavoidable aflatoxin exposure.

Physiological relevance of covalent protein modification by dietary isothiocyanates

Isothiocyanates (ITCs), naturally occurring in abundance in cruciferous vegetables, are the most well-studied organosulfur compounds having an electrophilic reactivity. ITCs have been accepted as major ingredients of these vegetables that afford their health promoting potentials. ITCs are able to modulate protein functions related to drug-metabolizing enzymes, transporters, kinases and phosphatases, etc. One of the most important questions about the molecular basis for the health promoting effects of ITCs is how they modulate cellular target proteins. Although the molecular targets of ITCs remains to be validated, dietary modulation of the target proteins via covalent modification by ITCs should be one of the promising strategies for the protection of cells against oxidative and inflammatory damage. This review discusses the plausible target proteins of dietary ITCs with an emphasis on possible involvement of protein modification in their health promoting effects. The fundamental knowledge of ITCs is also included with consideration of the chemistry, intracellular behavior, and metabolism.

Sulforaphane epigenetically enhances neuronal BDNF expression and TrkB signaling pathways

SCOPE

Brain-derived neurotrophic factor (BDNF) is a neurotrophin that supports the survival of existing neurons and encourages the growth and differentiation of new neurons and synapses. We investigated the effect of sulforaphane, a hydrolysis product of glucoraphanin present in Brassica vegetables, on neuronal BDNF expression and its synaptic signaling pathways.

METHODS AND RESULTS

Mouse primary cortical neurons and a triple-transgenic mouse model of Alzheimer's disease (3 × Tg-AD) were used to study the effect of sulforaphane. Sulforaphane enhanced neuronal BDNF expression and increased levels of neuronal and synaptic molecules such as MAP2, synaptophysin, and PSD-95 in primary cortical neurons and 3 × Tg-AD mice. Sulforaphane elevated levels of synaptic TrkB signaling pathway components, including CREB, CaMKII, ERK, and Akt in both primary cortical neurons and 3 × Tg-AD mice. Sulforaphane increased global acetylation of histone 3 (H3) and H4, inhibited HDAC activity, and decreased the level of HDAC2 in primary cortical neurons. Chromatin immunoprecipitation analysis revealed that sulforaphane increased acetylated H3 and H4 at BDNF promoters, suggesting that sulforaphane regulates BDNF expression via HDAC inhibition.

CONCLUSION

These findings suggest that sulforaphane has the potential to prevent neuronal disorders such as Alzheimer's disease by epigenetically enhancing neuronal BDNF expression and its TrkB signaling pathways.

Phytochemical Compounds and Protection from Cardiovascular Diseases: A State of the Art

Cardiovascular diseases represent a worldwide relevant socioeconomical problem. Cardiovascular disease prevention relies also on lifestyle changes, including dietary habits. The cardioprotective effects of several foods and dietary supplements in both animal models and in humans have been explored. It was found that beneficial effects are mainly dependent on antioxidant and anti-inflammatory properties, also involving modulation of mitochondrial function. Resveratrol is one of the most studied phytochemical compounds and it is provided with several benefits in cardiovascular diseases as well as in other pathological conditions (such as cancer). Other relevant compounds are Brassica oleracea, curcumin, and berberine, and they all exert beneficial effects in several diseases. In the attempt to provide a comprehensive reference tool for both researchers and clinicians, we summarized in the present paper the existing literature on both preclinical and clinical cardioprotective effects of each mentioned phytochemical. We structured the discussion of each compound by analyzing, first, its cellular molecular targets of action, subsequently focusing on results from applications in both ex vivo and in vivo models, finally discussing the relevance of the compound in the context of human diseases.

Glucosinolates Are Mainly Absorbed Intact in Germfree and Human Microbiota-Associated Mice

Chemoprotective or genotoxic effects of glucosinolates occurring in Brassica vegetables are attributed to their hydrolysis products formed upon tissue damage by plant myrosinase. Since Brassica vegetables, in which myrosinase has been heat-inactivated, still display bioactivity, glucosinolate activation has been attributed to intestinal bacteria. The aim of this study was to investigate whether this is true. Glucoraphanin (172 mg/kg body weight) and neoglucobrassicin (297 mg/kg body weight) were administered intragastrically to germ free and human microbiota associated (HMA) mice. Approximately 30% of the applied doses of glucoraphanin and neoglucobrassicin were excreted unchanged in the urine of both germ free and HMA mice. Isothiocyanates, sulforaphane, and erucin, formed from glucoraphanin, were mainly excreted as urinary N-acetyl-l-cysteine conjugates. N-Methoxyindole-3-carbinol formed from neoglucobrassicin was observed in small amounts in both germ free and HMA mice. Formation of DNA adducts from neoglucobrassicin was also independent from bacterial colonization of the mice. Hence, intestinal bacteria are involved in the bioactivation of glucosinolates in the gut, but their contribution to glucosinolate transformation in HMA mice is apparently very small.

A Facile One-pot Synthesis and Heterocyclisation of (R)-2-amino-3-((aroylcarbamothioyl)thio)propanoic Acids

A series of ( R)-2-amino-3-((aroylcarbamothioyl)thio)propanoic acid derivatives have been synthesised by a one-pot, three-component reaction of L-cysteine with ammonium thiocyanate in the presence of various acid chlorides under solvent-free conditions in excellent yields. These compounds were converted to ( R)-2-thioxothiazolidine-4-carboxylic acid in water under reflux conditions.

Sulforaphane retards the growth of UM-UC-3 xenographs, induces apoptosis, and reduces survivin in athymic mice

Sulforaphane (SFN), an isothiocyanate that exists exclusively in cruciferous vegetables, may be the most promising preventive agent for bladder cancer (BC) to date. We previously observed that SFN dramatically inhibits human BC T24 cells in vitro. Our hypothesis is that SFN may attenuate BC growth. To test our hypothesis, we investigated the effect of SFN on human BC UM-UC-3 cell xenografts implanted into athymic mice. Sulforaphane extract was routinely prepared in our laboratory, and its content was measured with high-performance liquid chromatography. Athymic mice were injected subcutaneously with a UM-UC-3 cell suspension (2.0×10(6) cells/200 μL per mouse) and randomly divided into 2 groups. The positive control group was orally gavaged with water, and the treatment group was orally administered SFN from broccoli sprout (12 mg/kg body weight) for 5 weeks. At the end of the experiment, tumor tissues were harvested and processed for hematoxylin and eosin staining and immunohistochemistry. The average tumor volume decreased from 4.1±1.67 cm(3) in the positive control mice to 1.5±0.72 cm(3) in the SFN-treated mice, evidencing an inhibitory rate of 63%. The SFN extract also reduced the appearance of tumors, including karyopyknosis and angiogenesis. Sulforaphane extract induced caspase 3 and cytochrome c expression but reduced the expression of survivin. Sulforaphane extract retards the growth of UM-UC-3 xenografts in vivo, confirming its future potential in BC therapy.

Bioavailability and kinetics of sulforaphane in humans after consumption of cooked versus raw broccoli

The aim of this study was to determine the bioavailability and kinetics of the supposed anticarcinogen sulforaphane, the hydrolysis product of glucoraphanin, from raw and cooked broccoli. Eight men consumed 200 g of crushed broccoli, raw or cooked, with a warm meal in a randomized, free-living, open cross-over trial. Higher amounts of sulforaphane were found in the blood and urine when broccoli was eaten raw (bioavailability of 37%) versus cooked (3.4%, p ) 0.002). Absorption of sulforaphane was delayed when cooked broccoli was consumed (peak plasma time ) 6 h) versus raw broccoli (1.6 h, p ) 0.001). Excretion half-lives were comparable, 2.6 and 2.4 h on average, for raw and cooked broccoli, respectively (p ) 0.5). This study gives complete kinetic data and shows that consumption of raw broccoli results in faster absorption, higher bioavailability, and higher peak plasma amounts of sulforaphane, compared to cooked broccoli.

Sulforaphane protects against cytokine- and streptozotocin-induced beta-cell damage by suppressing the NF-kappaB pathway

Sulforaphane (SFN) is an indirect antioxidant that protects animal tissues from chemical or biological insults by stimulating the expression of several NF-E2-related factor-2 (Nrf2)-regulated phase 2 enzymes. Treatment of RINm5F insulinoma cells with SFN increases Nrf2 nuclear translocation and expression of phase 2 enzymes. In this study, we investigated whether the activation of Nrf2 by SFN treatment or ectopic overexpression of Nrf2 inhibited cytokine-induced beta-cell damage. Treatment of RIN cells with IL-1beta and IFN-gamma induced beta-cell damage through a NF-kappaB-dependent signaling pathway. Activation of Nrf2 by treatment with SFN and induction of Nrf2 overexpression by transfection with Nrf2 prevented cytokine toxicity. The mechanism by which Nrf2 activation inhibited NF-kappaB-dependent cell death signals appeared to involve the reduction of oxidative stress, as demonstrated by the inhibition of cytokine-induced H(2)O(2) production. The protective effect of SFN was further demonstrated by the restoration of normal insulin secreting responses to glucose in cytokine-treated rat pancreatic islets. Furthermore, pretreatment with SFN blocked the development of type 1 diabetes in streptozotocin-treated mice.

Quantification of sulforaphane mercapturic acid pathway conjugates in human urine by high-performance liquid chromatography and isotope-dilution tandem mass spectrometry

We report validation of the first high-pressure liquid chromatography isotope-dilution mass spectrometry method to measure sulforaphane (SFN) and its glutathione-derived conjugates in human urine. As epidemiological evidence continues to mount that the consumption of a diet rich in cruciferous vegetables may reduce the risk of certain cancers, the development of analytical methodologies to accurately measure isothiocyanates (ITCs) and their subsequent metabolic products becomes paramount. SFN, the principal ITC produced by broccoli, is an effective chemopreventive agent with multiple modes of action. SFN and SFN conjugates have often been measured collectively utilizing a cyclocondensation assay with 1,2-benzenedithiol. More recently, some of the major SFN conjugates have been determined using mass spectrometry. Here, triple-quadrupole mass spectrometry has been coupled with the use of stable isotope-labeled internal standards of D8-SFN and all four D8-SFN mercapturic acid pathway conjugates to provide an accurate, precise, sensitive, and specific method for analysis of these compounds. Using urine samples collected during an earlier intervention with broccoli sprouts, the concentrations of SFN, SFN-cysteine, and the mercapturic acid SFN- N-acetylcysteine were sufficiently high such that as little as 50 nL of urine was required for analysis. Although each study participant received an equivalent dose of broccoli sprout preparation, the interindividual conversion of the precursor glucosinolate to SFN varied over 100-fold. These 98 urines provided an ideal sample set for examining the robustness of the assay. The mean urinary concentrations +/- standard deviations in overnight voids following ingestion of the first dose were 4.7 +/- 5.1, 0.03 +/- 0.05, 0.06 +/- 0.06, 18 +/- 15, and 42 +/- 23 nmol/mg creatinine for SFN, SFN-glutathione, SFN-cysteine-glycine, SFN-cysteine, and SFN- N-acetylcysteine, respectively. This method determines SFN and all four SFN glutathione-derived metabolites with minimal sample preparation and will be extremely useful in understanding the role of SFN-rich foods in preventing cancer and other chronic diseases.

Antiproliferative activity of sulforaphane in Akt-overexpressing ovarian cancer cells

Epidemiologic studies show a correlation between increased consumption of fruits and vegetables with reduced risk of ovarian cancer. One major bioactive compound found in cruciferous vegetables, particularly broccoli, is sulforaphane, derived from the breakdown of glucoraphanin. We observed potent antiproliferative effects of sulforaphane on human ovarian cancer cell line SKOV3 (IC(50) 40 micromol/L) and mouse ovarian cancer cell lines C3 and T3 (IC(50) 25 micromol/L each) by cell viability assays. The loss of viability is reflected by a down-regulation of cell cycle transition regulators cyclin D1, cyclin-dependent kinase 4 (cdk4), and cdk6. The upstream mediators of sulforaphane effects on the cell cycle in ovarian cancer are still unknown. However, because the Akt signal transduction pathway is overactivated in ovarian cancer, we investigated the effects of sulforaphane on this prosurvival pathway. Both total Akt protein and active phosphorylated levels of Akt (Ser(473)) and phosphoinositide 3-kinase were significantly decreased in sulforaphane-treated SKOV3, C3, and T3 cells with a concomitant inhibition of Akt kinase activity by sulforaphane in SKOV3 and C3 cells. This inhibitory effect of sulforaphane leads to a potent induction of apoptosis in all three cell lines, along with the cleavage of poly(ADP)ribose polymerase. Our study is the first to report the antiproliferative effects of sulforaphane in ovarian cancer and identifying the Akt pathway as a target of sulforaphane, with implications for the inhibition of carcinogenesis by diet-based chemoprevention.

Improved synthesis methods of standards used for quantitative determination of total isothiocyanates from broccoli in human urine

A well-known method for quantification of isothiocyanates (ITCs) and their metabolites is the condensation reaction with 1,2-benzenedithiole to produce 1,3-benzodithiole-2-thione, which can be quantified by high-performance liquid chromatography. Standards of an ITC metabolite and 1,3-benzodithiole-2-thione are required for this assay but are not commercially available. In the present study, we report on an improved synthesis of the ITC metabolite N-acetyl-S-(N-4-methylsulfinylbutylthiocarbamoyl)-L-cysteine and 1,3-benzodithiole-2-thione. The standards were used to quantify the urinary excretion of ITCs from 10 healthy subjects who consumed 350 g broccoli. The excretion was investigated throughout 48 h showing a cumulative urinary ITC excretion of 49.1+/-25.2% of the dose.

Quantitative measurement of sulforaphane, iberin and their mercapturic acid pathway metabolites in human plasma and urine using liquid chromatography-tandem electrospray ionisation mass spectrometry

A quantitative liquid chromatography positive ion electrospray tandem mass spectrometric method for the simultaneous determination of sulforaphane, iberin and their metabolites in human urine and plasma is described. The stability of the metabolites was determined in aqueous solution and in human plasma. Gradient liquid chromatographic separation was performed on a Zorbax SB-Aq 3.5 microm (100 x 2.1mm) column, using a mobile phase (flow rate 0.25 mL/min) consisting of ammonium acetate buffer at pH 4 and acetonitrile. Butyl thiocarbamoyl l-cysteine was used as internal standard. The assay was linear (r(2)>0.99) over the range of 0.03-300 microM in urine and 0.03-15 microM in plasma with intra- and inter-day assay precision (<10% CV) and accuracy (<20%). The lower limits of quantitation were in the range of 10-150 nmol/L. The method has been used to report, for the first time, individual quantitative measurement of each of the mercapturic acid pathway metabolites of sulforaphane and iberin in both human plasma and urine following a dietary study of broccoli consumption.

Simultaneous determination of sulforaphane and its major metabolites from biological matrices with liquid chromatography–tandem mass spectroscopy

A simple, sensitive and specific LC-MS/MS method for the simultaneous determination of sulforaphane (SFN) and its major metabolites, the glutathione (SFN-GSH) and N-acetyl cysteine conjugates (SFN-NAC) from biological matrices was developed and validated. The assay procedure involved solid-phase extratcion of all three analytes from rat intestinal perfusate using C2 extraction cartridges, whereas from rat plasma, metabolites were extracted by solid-phase extraction and SFN was extracted by liquid-liquid extraction with ethyl acetate. Chromatographic separation of SFN, SFN-GSH and SFN-NAC was achieved on a C8 reverse phase column with a mobile phase gradient (Mobile Phase A: 10mM ammonium acetate buffer, pH: 4.5 and Mobile Phase B: acetonitrile with 0.1% formic acid) at a flow rate of 0.3 mL/min. The Finnigan LCQ LC-MS/MS was operated under the selective reaction monitoring mode using the electrospray ionization technique in positive mode. The nominal retention times for SFN-GSH, SFN-NAC and SFN were 8.4, 11.0, and 28.2 min,, respectively. The method was linear for SFN and its metabolites with correlation coefficients >0.998 for all analytes. The limit of quantification was 0.01-0.1 microm depending on analyte and matrix, whereas the mean recoveries from spiked plasma and perfusate samples were approximately 90%. The method was further validated according to U.S. Food and Drug Administration guidance in terms of accuracy and precision. Stability of compounds was established in a battery of stability studies, i.e., bench top, auto-sampler and long-term storage stability as well as freeze/thaw cycles. The utility of the assay was confirmed by the analysis of intestinal perfusate and plasma samples from single-pass intestinal perfusion studies with mesenteric vein cannulation in rats.

Chemical and biological characterisation of nutraceutical compounds of broccoli

People's diet offers a greater and more diverse group of plant bioactives than do drugs, and they often do not realise that many drugs are derived from the compounds originally discovered in plant foods. Numerous epidemiological studies indicate that Brassica vegetables in general, and broccoli in particular, protect humans against cancer since they are rich sources of glucosinolates as well as possessing a high content of flavonoids, vitamins and mineral nutrients. One unusual phytotherapeutic role of broccoli is for skin diseases--the juice of the leaves is used to treat warts. However, the main use of broccoli stems from its health-promoting properties. Some criteria have been proposed to evaluate the possibilities of developing new "functional foods" to reduce the risk of specific cancers; largely in broccoli, which is associated with cancer protection. Processing conditions, transport, domestic cooking, etc., affect the health-promoting properties of broccoli and these have been widely studied. This review makes an in-depth study of the chemical and biological characterization of the phytochemicals of broccoli and the effects on the bioactive composition of broccoli.

The principal urinary metabolites of dietary isothiocyanates, N-acetylcysteine conjugates, elicit the same anti-proliferative response as their parent compounds in human bladder cancer cells

Isothiocyanates (ITCs) are a class of well-known cancerpreventive phytochemicals, but are primarily disposed of and concentrated in the urine as N-acetylcysteine conjugates (NAC-ITCs) in vivo. Because human urinary bladder cancers occur almost exclusively in the bladder epithelium, which is directly exposed to the urine stored in the bladder, we undertook to examine the anti-cancer activity of NAC-ITCs in cultured human bladder cancer cells. In this paper, we report that the NAC conjugates of four naturally occurring ITCs, including allyl ITC, benzyl ITC (BITC), phenethyl ITC and sulforaphane, potently inhibited the growth of cells derived from both low-grade superficial and high-grade invasive human bladder cancers and drug-resistant bladder cancer cells. Moreover, the growth-inhibitory potencies were similar between the conjugates and their parent compounds. Further study of NAC-BITC and BITC as model compounds showed that both compounds accumulated in cells predominantly as the glutathione conjugate of BITC, but the accumulation of the former was slower. Moreover, both compounds also demonstrated the same anti-proliferative mechanisms: causing the cleavage of the same set of caspases (caspase-3, -8 and -9) in apoptosis induction, arresting cells in the same phases (S and G2/M) and targeting the same cell cycle regulator (Cdc25C), although a longer treatment time or slightly higher doses were needed for NAC-BITC to achieve the same effect as BITC, presumably due to slower cellular uptake of NAC-BITC. These data show that the NAC-ITCs are biologically similar to their parent compounds and are highly effective against human bladder cancer cells.

Isothiocyanates in cancer prevention

Isothiocyanates are sulfur-containing compounds which are largely responsible for the typical flavor of cruciferous vegetables. In animals and humans they are conjugated with glutathione; the first product of this reaction is a dithiocarbamate, which can be ultimately metabolized to the corresponding mercapturic acid, excreted in urine. Aliphatic and aromatic isothiocyanates, as well as dithiocarbamates, can react quantitatively with an excess of 1,2-benzenedithiol giving rise to a cyclic condensation product readily measured in biological fluids. The use of this assay as a biomarker of isothiocyanate or cruciferous vegetable intake can offer several advantages over food frequency questionnaires, mainly in the objectivity and accuracy of the measure and the lack of bias. Epidemiological studies on the relationship between cancer risk with isothiocyanate intake or excretion have shown inverse associations, mainly with lung cancer. The studies are also consistent in reporting a gene-environment interaction, with a stronger protective effect in persons null for the GSTM1 or GSTT1 genotype. However, further research is needed to better clarify the importance of these polymorphisms in modulating the effect of isothiocyanates in cancer development.

Cancer-preventive isothiocyanates: measurement of human exposure and mechanism of action

Numerous studies in rodents have documented the cancer-preventive activity of a significant number of isothiocyanates (ITCs), the majority of which occur in plants, especially in cruciferous vegetables. Dietary ITCs may play an important role in the prevention of human cancers. Several recent epidemiological studies have already shown that dietary consumption of ITCs inversely correlates with the risk of developing lung, breast and colon cancers. ITCs are principally metabolized through the mercapturic acid pathway in vivo, giving rise to N-acetylcysteine conjugates, which are excreted in the urine. Analytical methods have been developed to allow detection of ITCs and their metabolites formed in the mercapturic acid pathway. Studies show that total urinary level of ITC equivalent is an excellent biomarker of human exposure to ITCs. Moreover, these methods also have made it possible to learn the bioavailability of ITCs from cruciferous vegetables. ITCs possess multiple anticarcinogenic mechanisms, including inhibition of carcinogen-activating enzymes, induction of carcinogen-detoxifying enzymes, increase of apoptosis, arrest of cell cycle progression, as well as several other mechanisms that are not yet fully described. These mechanisms, which are discussed in detail in this review, illustrate the remarkable ability of ITCs to inhibit cancer development-effective against both developing and developed cancer cells.

A novel mechanism of chemoprotection by sulforaphane: inhibition of histone deacetylase

Sulforaphane (SFN), a compound found at high levels in broccoli and broccoli sprouts, is a potent inducer of phase 2 detoxification enzymes and inhibits tumorigenesis in animal models. SFN also has a marked effect on cell cycle checkpoint controls and cell survival and/or apoptosis in various cancer cells, through mechanisms that are poorly understood. We tested the hypothesis that SFN acts as an inhibitor of histone deacetylase (HDAC). In human embryonic kidney 293 cells, SFN dose-dependently increased the activity of a beta-catenin-responsive reporter (TOPflash), without altering beta-catenin or HDAC protein levels. Cytoplasmic and nuclear extracts from these cells had diminished HDAC activity, and both global and localized histone acetylation was increased, compared with untreated controls. Studies with SFN and with media from SFN-treated cells indicated that the parent compound was not responsible for the inhibition of HDAC, and this was confirmed using an inhibitor of glutathione S-transferase, which blocked the first step in the metabolism of SFN, via the mercapturic acid pathway. Whereas SFN and its glutathione conjugate (SFN-GSH) had little or no effect, the two major metabolites SFN-cysteine and SFN-N-acetylcysteine were effective HDAC inhibitors in vitro. Finally, several of these findings were recapitulated in HCT116 human colorectal cancer cells: SFN dose-dependently increased TOPflash reporter activity and inhibited HDAC activity, there was an increase in acetylated histones and in p21(Cip1/Waf1), and chromatin immunoprecipitation assays revealed an increase in acetylated histones bound to the P21 promoter. Collectively, these findings suggest that SFN may be effective as a tumor-suppressing agent and as a chemotherapeutic agent, alone or in combination with other HDAC inhibitors currently undergoing clinical trials.

Dietary isothiocyanates inhibit the growth of human bladder carcinoma cells

Many isothiocyanates (ITCs), some of which are abundant in cruciferous vegetables, have been repeatedly shown to inhibit carcinogenesis in a variety of rodent organs. However, several naturally occurring ITCs also promoted bladder tumorigenesis in rodents, raising the question of whether ITCs behave differently in bladder cells. Alternatively, the observed carcinogenic effects of ITCs may result from prolonged exposure of the bladder epithelium, where the tumors originate, to high concentrations of electrophilic ITCs in the urine. Ingested ITCs are almost exclusively excreted and highly concentrated in the urine as N-acetylcysteine conjugates (NAC-ITC). While several NAC-ITCs also are known anticarcinogens, they are unstable and readily dissociate into parent ITCs. In this study, ITCs, including those that have carcinogenic potential in the rodent bladders, induced apoptosis and/or arrested cell-cycle progression in 2 human bladder carcinoma lines (UM-UC-3 and T24) at 7.5-30 micromol/L. Multiple caspases, including caspase-9, -8, and -3, as well as poly(ADP-ribose)polymerase, were cleaved upon ITC exposure. The ITCs blocked cell-cycle progression at the G(2)/M and/or S phases in these cells and downregulated several cell-cycle regulators. However, further increases in ITC concentrations abolished their activities, described above. These findings show that urinary ITC concentrations may need to be maintained at low micromolar concentrations for bladder cancer prevention.

Evaluation of urinary N-acetyl cysteinyl allyl isothiocyanate as a biomarker for intake and bioactivity of Brussels sprouts

Isothiocyanates (ITC), glucosinolate hydrolysis products from Brussels sprouts (BS) and other cruciferous vegetables, are considered to protect the body from cancer by induction of detoxification enzymes such as quinone reductase (QR). Urinary N-acetyl-cysteine (NAC) conjugates of ITC have been proposed as biomarkers of crucifer intake. Here we asked if dietary intake and induction of detoxification enzymes are dose-related to urinary NAC conjugate appearance. Male F344 rats (4/group) received an AIN 76B-40 diet containing 0, 10 or 20% freeze-dried BS for 6 days. A human subject ingested 500 g BS. Urinary AITC-NAC was identified in human and rat urine. Ten and 20% BS diets caused a 1.4- and 2.3-fold induction of QR in the pancreas, a 1.5- and 2.5-fold induction in liver and a 3.1- and 3.6-fold induction in colonic epithelium, respectively. Liver and pancreatic QR induction was dose-related, whereas induction of QR in colon was less different between the two doses. Excretion of the conjugate was dose-related only on day 1, and unrelated to dose after day 2. These results suggest that urinary NAC-AITC is a qualitative biomarker for ingestion and bioactivity of BS, but that it may not be dose-related when rats are fed continuously for 2 or more days.

Synthesis of isothiocyanate-derived mercapturic acids

Twelve mercapturic acids derived from saturated and unsaturated aliphatic and aromatic isothiocyanates were synthesised, by adding isothiocyanate to a solution of N-acetyl-L-cysteine and sodium bicarbonate, in a typical yield of 77%. Isothiocyanates were synthesised first by adding the corresponding alkyl bromide to phthalimide potassium salt. The obtained N-alkyl-phthalimide was hydrazinolysed yielding the alkyl amine, which subsequently was reacted with thiophosgene yielding the isothiocyanate with an overall yield of 16%. Mercapturic acids in urine can serve as a biomarker of intake to determine the health promoting potential of isothiocyanates present in cruciferous vegetables.