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

Diet and breast cancer

The preponderance of evidence suggests a role for fat and alcohol as risk factors for breast cancer. The role of milk is more controversial with some studies suggesting that milk is a risk factor and others that consumption of milk is protective against breast cancer. No other major nutrient appears to play a significant role in increasing breast cancer risk. On the other hand, there is increasing evidence that a variety of micronutrients and hormones appear to have significant anticancer activity. These range from steroids such as dehydroepiandrosterone (DHEA) and its analysis to indoles, isothiocyanates, and isoflavone derivatives. These compounds act directly by interfering with cyclins and promoting apoptosis as well as indirectly by altering estrogen metabolism in a favorable direction. These effects are not merely theoretical actions in cell culture and tissue explants; they have been demonstrated in human patients as a range of studies have demonstrated.

Sulforaphane inhibits extracellular, intracellular, and antibiotic-resistant strains of Helicobacter pylori and prevents benzo[a]pyrene-induced stomach tumors

Gastric infection with Helicobacter pylori is a cosmopolitan problem, and is especially common in developing regions where there is also a high prevalence of gastric cancer. These infections are known to cause gastritis and peptic ulcers, and dramatically enhance the risk of gastric cancer. Eradication of this organism is an important medical goal that is complicated by the development of resistance to conventional antimicrobial agents and by the persistence of a low level reservoir of H. pylori within gastric epithelial cells. Moreover, economic and practical problems preclude widespread and intensive use of antibiotics in most developing regions. We have found that sulforaphane [(-)-1-isothiocyanato-(4R)-(methylsulfinyl)butane], an isothiocyanate abundant as its glucosinolate precursor in certain varieties of broccoli and broccoli sprouts, is a potent bacteriostatic agent against 3 reference strains and 45 clinical isolates of H. pylori [minimal inhibitory concentration (MIC) for 90% of the strains is Collapse

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MESH Headings

• Agaricales
• Amoxicillin/pharmacology
• Animals
• Anticarcinogenic Agents/pharmacology
• Benzo(a)pyrene
• Brassica
• Clarithromycin/pharmacology
• Drug Resistance, Microbial
• Female
• Helicobacter pylori/drug effects
• Helicobacter pylori/growth & development
• Helicobacter pylori/isolation & purification
• Humans
• Isothiocyanates
• Metronidazole/pharmacology
• Mice
• Mice, Inbred ICR
• Phytotherapy
• Stomach Neoplasms/chemically induced
• Stomach Neoplasms/microbiology
• Stomach Neoplasms/prevention & control
• Sulfoxides
• Thiocyanates/pharmacology

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Grants

• R01 CA094076 NCI NIH HHS
• CA 94076 NCI NIH HHS

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Affiliation(s)

Jed W Fahey Lewis B. and Dorothy Cullman Cancer Chemoprotection Center, Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21205-2185, USA.
Xavier Haristoy
Patrick M Dolan
Thomas W Kensler
Isabelle Scholtus
Katherine K Stephenson
Paul Talalay
Alain Lozniewski

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Collaborators Collapse

Direct analysis of single leaf disks for chemopreventive glucosinolates

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

Formation of methanethiol and dimethyl disulfide in crushed tissues of broccoli florets and their inhibition by freeze-thawing

The formation of methanethiol and dimethyl disulfide in crushed, homogenized, and frozen-thawed tissues of broccoli florets was investigated. These volatile sulfur compounds were produced in crushed florets, but their formation was inhibited in frozen-thawed tissues. Only dimethyl disulfide was formed in homogenized tissues. High pH treatment triggered the release of dimethyl disulfide in frozen-thawed tissues and also enhanced the action of cysteine sulfoxide lyase in all disrupted tissues. Methyl methanethiosulfinate and methyl methanethiosulfonate were not detected in crushed florets; thus, the favored mechanism for the formation of methanethiol and dimethyl disulfide is the chemical disproportionation of methanesulfenic acid. In contrast, the formation of dimethyl disulfide in frozen-thawed and homogenized tissues occurs from the chemical disproportionation of methyl methanethiosulfinate that was detected in these tissues. The inhibition of dimethyl disulfide production during freeze-thawing must be caused by a sudden drop in the pH of the tissue, adherence of dimethyl disulfide on the tissue surfaces, and weakening of the cysteine sulfoxide lyase activity under acidic conditions.

Flavonoids increase the intracellular glutathione level by transactivation of the gamma-glutamylcysteine synthetase catalytical subunit promoter

Fruits and vegetables protect against cancer by so far not well-characterized mechanisms. One likely explanation for this effect is that dietary plants contain substances able to control basic cellular processes such as the endogenous defense against oxidative stress. Oxidative stress is pivotal in many pathological processes and reduced oxidative stress is implicated in prevention of disease. Our results demonstrate that extract from onion and various flavonoids induce the cellular antioxidant system. Onion extract and quercetin were able to increase the intracellular concentration of glutathione by approximately 50%. Using a reporter construct where reporter expression is driven by the gamma-glutamylcysteine synthetase (GCS) heavy subunit (GCS(h)) promoter we show that onion extract, quercetin, kaempferol, and apigenin increased reporter gene activity, while a fourth flavonoid, myricetin and sugar conjugates of quercetin were unable to increase reporter expression. Quercetin was also able to induce a distal part of the GCS(h) promoter containing only two antioxidant-response/electrophile-response elements (ARE/EpRE). Our data strongly suggest that flavonoids are important in the regulation of the intracellular glutathione levels. This effect may be exerted in part through GCS gene regulation, and may also contribute to the disease-preventing effect of fruits and vegetables.

A systematic screening of total antioxidants in dietary plants

A predominantly plant-based diet reduces the risk for development of several chronic diseases. It is often assumed that antioxidants contribute to this protection, but results from intervention trials with single antioxidants administered as supplements quite consistently do not support any benefit. Because dietary plants contain several hundred different antioxidants, it would be useful to know the total concentration of electron-donating antioxidants (i.e., reductants) in individual items. Such data might be useful in the identification of the most beneficial dietary plants. We have assessed systematically total antioxidants in a variety of dietary plants used worldwide, including various fruits, berries, vegetables, cereals, nuts and pulses. When possible, we analyzed three or more samples of dietary plants from three different geographic regions in the world. Total antioxidants was assessed by the reduction of Fe(3+) to Fe(2+) (i.e., the FRAP assay), which occurred rapidly with all reductants with half-reaction reduction potentials above that of Fe(3+)/Fe(2+). The values, therefore, expressed the corresponding concentration of electron-donating antioxidants. Our results demonstrated that there is more than a 1000-fold difference among total antioxidants in various dietary plants. Plants that contain most antioxidants included members of several families, such as Rosaceae (dog rose, sour cherry, blackberry, strawberry, raspberry), Empetraceae (crowberry), Ericaceae (blueberry), Grossulariaceae (black currant), Juglandaceae (walnut), Asteraceae (sunflower seed), Punicaceae (pomegranate) and Zingiberaceae (ginger). In a Norwegian diet, fruits, berries and cereals contributed 43.6%, 27.1% and 11.7%, respectively, of the total intake of plant antioxidants. Vegetables contributed only 8.9%. The systematic analysis presented here will facilitate research into the nutritional role of the combined effect of antioxidants in dietary plants.

Quantitative determination of dithiocarbamates in human plasma, serum, erythrocytes and urine: pharmacokinetics of broccoli sprout isothiocyanates in humans

BACKGROUND

Humans are exposed to substantial quantities of isothiocyanates and glucosinolates from vegetables. Since dietary isothiocyanates are widely regarded as potentially important chemoprotectors against cancer, reliable methods for measuring the plasma and tissue pharmacokinetics of isothiocyanates and their dithiocarbamate metabolites are essential for defining dosing regimens.

METHODS

Isothiocyanates (ITC) and dithiocarbamates (DTC) react quantitatively with 1,2-benzenedithiol to produce 1,3-benzodithiole-2-thione that can be quantified spectroscopically. Although this cyclocondensation reaction has been highly useful for analyzing plant material and urine samples, the determination of DTC/ITC (the total quantity of DTC and ITC components in a sample that react in the cyclocondensation reaction) in blood and tissues has been hampered by their low levels and the high concentrations of proteins that interfere with the cyclocondensation reaction. The protein content of blood and tissues was reduced by the precipitation with polyethylene glycol (PEG) or ultrafiltration, and the sensitivity of the method was increased substantially by the solid phase extraction of the cyclocondensation product.

RESULTS

Pharmacokinetic measurements were made in four human volunteers who received single doses of about 200 micromol of broccoli sprout isothiocyanates (largely sulforaphane, with lesser amounts of iberin and erucin). Isothiocyanates were absorbed rapidly, reached peak concentrations of 0.943-2.27 micromol/l in plasma, serum and erythrocytes at 1 h after feeding and declined with first-order kinetics (half-life of 1.77+/-0.13 h). The cumulative excretion at 8 h was 58.3+/-2.8% of the dose. Clearance was 369+/-53 ml/min, indicating active renal tubular secretion.

CONCLUSION

A sensitive and specific method for quantifying DTC levels in human plasma, serum, and erythrocytes has been devised. Determinations of ITC/DTC levels are important because: (i) dietary isothiocyanates are of potential value in reducing the risk of cancer, and (ii) humans are extensively exposed to DTC as fungicides, insecticides, pesticides and rubber vulcanization accelerators.

Disposition of glucosinolates and sulforaphane in humans after ingestion of steamed and fresh broccoli

The cancer-chemopreventive effects of broccoli may be attributed, in part, to isothiocyanates (ITCs), hydrolysis products of glucosinolates. Glucosinolates are hydrolyzed to their respective ITCs by the enzyme myrosinase, which is inactivated by heat. In this study, the metabolic fate of glucosinolates after ingestion of steamed and fresh broccoli was compared in 12 male subjects in a crossover design. During each 48-hour baseline period, no foods containing glucosinolates or ITCs were allowed. The subjects then consumed 200 g of fresh or steamed broccoli; all other dietary sources of ITCs were excluded. Blood and urine samples were collected during the 24-hour period after broccoli consumption. Total ITC equivalents in broccoli and total ITC equivalents in plasma and urine were assayed by high-performance liquid chromatography as the cyclocondensation product of 1,2-benzenedithiol. The content of ITCs in fresh and steamed broccoli after myrosinase treatment was found to be virtually identical (1.1 vs. 1.0 micromol/g wet wt). The average 24-hour urinary excretion of ITC equivalents amounted to 32.3 +/- 12.7% and 10.2 +/- 5.9% of the amounts ingested for fresh and steamed broccoli, respectively. Approximately 40% of total ITC equivalents in urine, 25.8 +/- 13.9 and 6.9 +/- 2.5 micromol for fresh and steamed broccoli, respectively, occurred as the N-acetyl-L-cysteine conjugate of sulforaphane (SFN-NAC). Total ITC metabolites in plasma peaked between 0 and 8 hours, whereas urinary excretion of total ITC equivalents and SFN-NAC occurred primarily between 2 and 12 hours. Results of this study indicate that the bioavailability of ITCs from fresh broccoli is approximately three times greater than that from cooked broccoli, in which myrosinase is inactivated. Considering the cancer-chemopreventive potential of ITCs, cooking broccoli may markedly reduce its beneficial effects on health.

Powerful and prolonged protection of human retinal pigment epithelial cells, keratinocytes, and mouse leukemia cells against oxidative damage: the indirect antioxidant effects of sulforaphane

Mammalian cells are equipped with elaborate systems for protection against the toxicity of reactive oxygen and nitrogen species and electrophiles that are constant dangers to the integrity of their DNA. Phase 2 enzymes (e.g., glutathione transferases, NAD(P)H:quinone reductase) and glutathione synthesis are widely recognized as playing major protective roles against electrophilic carcinogens, but their antioxidant functions have attracted far less attention. The cytotoxicities of four oxidative stressors (menadione, tert-butyl hydroperoxide, 4-hydroxynonenal, and peroxynitrite) for human adult retinal pigment epithelial cells (ARPE-19) were quantified by measuring the concentration dependence of cell death and were expressed as the median effect dose (D(m)) for each oxidant. After treatment of ARPE-19 cells for 24 h with 0-5 microM concentrations of sulforaphane (the powerful Phase 2 enzyme inducer isolated from broccoli), the toxicities of the oxidants were markedly reduced as shown by 1.5- to 3-fold increases in D(m) values. The magnitude of protection was a function of the nature of the oxidants and the concentrations of both the oxidants and sulforaphane. Protection was prolonged and persisted for several days after removal of sulforaphane before returning to control levels. The sulforaphane-dependent increases in specific activities of cytosolic quinone reductase and the glutathione levels were highly significantly correlated with the degree of protection as measured by D(m) values. Antioxidant protection was also demonstrated for human HaCaT keratinocytes and L1210 murine leukemia cells. It is therefore highly likely that the multifaceted and prolonged antioxidant protection provided by sulforaphane is a general phenomenon that is mediated through induction of the Phase 2 enzyme response.

Preneoplastic prostate lesions: an opportunity for prostate cancer prevention

Environmental factors, especially the diet, play a prominent role in the epidemic of prostate cancer (PCA), in the United States. Many candidate dietary components have been proposed to influence human prostatic carcinogenesis, including fat, calories, fruits and vegetables, anti-oxidants, and various micronutrients, but the specific roles dietary agents play in promoting or preventing PCA remain controversial. We have collected evidence to suggest that GSTP1, the gene encoding the pi-class glutathione S-transferase (GST), may serve a "caretaker" function for prostatic cells. Although GSTP1 can be detected in normal prostatic epithelium, in almost all PCA cases, PCA cells fail to express GSTP1 polypeptides, and lack of GSTP1 expression most often appears to be the result of somatic "CpG island" DNA methylation changes. Loss of GSTP1 function also appears to be characteristic of prostatic epithelial neoplasia (PIN) lesions, thought to represent PCA precursors. We have recently learned that a new candidate early PCA precursor lesion, proliferative inflammatory atrophy (PIA), characterized by proliferating prostatic cells juxtaposed to inflammatory cells, contains epithelial cells that express high levels of GSTP1. These findings have formed the basis for a new model of prostatic carcinogenesis, in which prostatic cells in PIA lesions, subjected to a barrage of inflammatory oxidants, induce GSTP1 expression as a defense against oxidative genome damage. When cells with defective GSTP1 genes appear amongst the PIA cells, such cells become vulnerable to oxidants and electrophiles that inflict genome damage that tends to promote neoplastic transformation to PIN and PCA cells. Subsequently, PIN and PCA cells with defective GSTPI genes remain vulnerable to similar stresses tending to promote malignant progression. This new model for prostatic carcinogenesis has implications for the design of new prostate cancer prevention strategies. Rational prevention approaches might include: (i) restoration of GSTPI expression via treatment with inhibitors of CpG methylation, (ii) compensation for inadequate GSTPI activity via treatment with inducers of general GST activity, and (iii) abrogation of genome-damaging stresses via avoidance of exogenous carcinogens and/or reduction of endogenous carcinogenic (particularly oxidant) stresses.

Comparison of the bioactivity of two glucoraphanin hydrolysis products found in broccoli, sulforaphane and sulforaphane nitrile

Epidemiological and laboratory studies suggest that dietary broccoli may prevent or delay a variety of cancers. Broccoli and other crucifers contain a relatively unique family of secondary metabolites called glucosinolates. Glucoraphanin, the major glucosinolate in broccoli, is hydrolyzed by an endogenous plant myrosinase to form either the potent anticarcinogen sulforaphane (SF) or sulforaphane nitrile (SF nitrile). The bioactivities of SF and SF nitrile were compared in rats and in mouse hepatoma cells. Male, 4-week-old, Fischer 344 rats were administered SF or SF nitrile (200, 500, or 1000 micromol/kg) by gavage daily for 5 days. Hepatic, colonic mucosal, and pancreatic quinone reductase and glutathione S-transferase activities were induced by high doses of SF, but not by SF nitrile. When Hepa 1c1c7 cells were exposed to increasing levels of each compound for 24 h, quinone reductase showed a 3-fold maximal induction over control at 2.5 microM SF and a 3.5-fold maximal induction over control at 2000 microM SF nitrile, the highest concentration tested. These results demonstrate that SF nitrile is substantially less potent than SF as an inducing agent of phase II detoxification enzymes. Therefore, glucoraphanin hydrolysis directed toward the production of SF rather than SF nitrile could increase the potential chemoprotective effects of broccoli.

A gene controlling variation in Arabidopsis glucosinolate composition is part of the methionine chain elongation pathway

Arabidopsis and other Brassicaceae produce an enormous diversity of aliphatic glucosinolates, a group of methionine (Met)-derived plant secondary compounds containing a beta-thio-glucose moiety, a sulfonated oxime, and a variable side chain. We fine-scale mapped GSL-ELONG, a locus controlling variation in the side-chain length of aliphatic glucosinolates. Within this locus, a polymorphic gene was identified that determines whether Met is extended predominantly by either one or by two methylene groups to produce aliphatic glucosinolates with either three- or four-carbon side chains. Two allelic mutants deficient in four-carbon side-chain glucosinolates were shown to contain independent missense mutations within this gene. In cell-free enzyme assays, a heterologously expressed cDNA from this locus was capable of condensing 2-oxo-4-methylthiobutanoic acid with acetyl-coenzyme A, the initial reaction in Met chain elongation. The gene methylthioalkylmalate synthase1 (MAM1) is a member of a gene family sharing approximately 60% amino acid sequence similarity with 2-isopropylmalate synthase, an enzyme of leucine biosynthesis that condenses 2-oxo-3-methylbutanoate with acetyl-coenzyme A.

A gene controlling variation in Arabidopsis glucosinolate composition is part of the methionine chain elongation pathway

Arabidopsis and other Brassicaceae produce an enormous diversity of aliphatic glucosinolates, a group of methionine (Met)-derived plant secondary compounds containing a beta-thio-glucose moiety, a sulfonated oxime, and a variable side chain. We fine-scale mapped GSL-ELONG, a locus controlling variation in the side-chain length of aliphatic glucosinolates. Within this locus, a polymorphic gene was identified that determines whether Met is extended predominantly by either one or by two methylene groups to produce aliphatic glucosinolates with either three- or four-carbon side chains. Two allelic mutants deficient in four-carbon side-chain glucosinolates were shown to contain independent missense mutations within this gene. In cell-free enzyme assays, a heterologously expressed cDNA from this locus was capable of condensing 2-oxo-4-methylthiobutanoic acid with acetyl-coenzyme A, the initial reaction in Met chain elongation. The gene methylthioalkylmalate synthase1 (MAM1) is a member of a gene family sharing approximately 60% amino acid sequence similarity with 2-isopropylmalate synthase, an enzyme of leucine biosynthesis that condenses 2-oxo-3-methylbutanoate with acetyl-coenzyme A.

Phytochemicals from cruciferous plants protect against cancer by modulating carcinogen metabolism

Several epidemiologic studies suggest that consumption of cruciferous vegetables may be particularly effective (compared with total fruit and vegetable consumption) in reducing cancer risk at several organ sites. Crucifers that are widely consumed are especially rich in glucosinolates, which are converted by plant myrosinase and gastrointestinal microflora to isothiocyanates. A number of isothiocyanates and a limited number of glucosinolates that were examined effectively block chemical carcinogenesis in animal models. Many isothiocyanates are also potent inducers of phase 2 proteins. Substantial evidence supports the view that phase 2 enzyme induction is a highly effective strategy for reducing susceptibility to carcinogens. This conclusion has recently received strong molecular support from experiments on mice in which the specific transcription factor, nrf2, which is essential for induction of phase 2 proteins, was deleted. In these knock-out mice, the basal levels of phase 2 enzymes are very low and not inducible. Accordingly, these mice are much more susceptible than their wild-type counterparts to benzo[a]pyrene forestomach carcinogenesis and are not protected by phase 2 inducers. These experiments provide very strong evidence for a major role of phase 2 enzymes in controlling the risk of exposure to carcinogens. An increasing number of phase 2 proteins that exert a variety of protective mechanisms are being identified. Thus, in addition to detoxifying electrophiles, these proteins exercise versatile, long-lasting and catalytic antioxidant protection.

The impaired glutathione system and its up-regulation by sulforaphane in vascular smooth muscle cells from spontaneously hypertensive rats

The glutathione (GSH) system plays an important role in reducing oxidative stress, the increase of which has been linked to the pathogenesis of hypertension. The aims of this study were to investigate: (1) whether the GSH system was impaired in aortic smooth muscle cells (SMCs) from spontaneously hypertensive rats (SHR), and (2) whether this system could be up-regulated by the phase-2 enzyme inducers, sulforaphane and t-butylhydroquinone (t-BHQ). Basal levels of cellular GSH, GSH-reductase and GSH-peroxidase were significantly lower in SMCs from SHR than from normotensive Wistar-Kyoto (WKY) rats. Heme oxygenase-1 (HO-1) was significantly higher in SHR SMCs, which correlated with the higher oxidative stress experienced by these cells. No differences were observed in the basal activity of GSH-S-transferase nor in the ability to synthesize GSH between SMCs from these two strains. Sulforaphane (0.05-1 micromol/l) and t-BHQ (10-100 micromol/l) induced significant and concentration-dependent increases in cellular GSH levels, HO-1 protein content and activities of GSH-reductase and GSH-peroxidase in SMCs from both rat strains. Upregulation of phase 2 enzymes correlated with a decrease in oxidative stress experienced by the SMCs, particularly with SHR. We conclude that SHR SMCs experience greater oxidative stress than WKY SMCs and that malfunction of the GSH system contributes to the enhanced oxidative stress in SHR SMCs.

Antioxidative and antitumor promoting effects of [6]-paradol and its homologs

Recently, considerable attention is focused on anti-carcinogenic phytochemicals, particularly those derived from medicinal or edible plants. [6]-Paradol, a pungent phenolic compound present in certain Zingiberaceae plants, is known to have antimicrobial and analgesic activities. The compound has been reported to attenuate promotion of skin carcinogenesis and TPA-induced ear edema in female ICR mice, and to induce apoptosis in cultured human promyelocytic leukemia (HL-60) cells. In this study, we performed several biochemical studies to evaluate and compare the cancer chemopreventive potential of [6]-paradol and its synthetic derivatives. [6]-Paradol and its synthetic nonpungent analog, [6]-dehydroparadol significantly decreased the incidence and the multiplicity of skin tumors initiated by 7,12-dimethylbenz[a]anthracene (DMBA) and promoted by 12-O-tetradecanoylphorbol-13-acetate (TPA). Topical application of [6]-paradol and its derivatives inhibited TPA-induced ear edema and H(2)O(2) production and myeloperoxidase activity in the dorsal skin of mice. Induction of TPA-induced mouse epidermal ornithine decarboxylase (ODC) activity and H(2)O(2)- and UV-induced formation of oxidized DNA bases in vitro were also attenuated by the above compounds. These results indicate that [6]-paradol and its derivatives possess the cancer chemopreventive potential.

Role of phase 2 enzyme induction in chemoprotection by dithiolethiones

One of the major mechanisms of protection against carcinogenesis, mutagenesis, and other forms of toxicity mediated by carcinogens is the induction of enzymes involved in their metabolism, particularly phase 2 enzymes such as glutathione S-transferases (GSTs), UDP-glucuronosyl transferases, and quinone reductases. Animal studies indicate that induction of phase 2 enzymes is a sufficient condition for obtaining chemoprevention and can be achieved by administering any of a diverse array of naturally-occurring and synthetic chemopreventive agents. Indeed, monitoring of enzyme induction has led to the recognition or isolation of novel, potent chemopreventive agents such as 1,2-dithiole-3-thiones, terpenoids and the isothiocyanate sulforaphane. For example, oltipraz, a substituted 1,2-dithiole-3-thione originally developed as an antischistosomal agent, possesses chemopreventive activity against different classes of carcinogens targeting multiple organs. Mechanistic studies in rodent models for chemoprevention of aflatoxin B(1) (AFB(1))-induced hepatocarcinogenesis by oltipraz indicates that increased expression of phase 2 genes is of central importance, although inhibition of phase 1 activation of AFB(1) can also contribute to protection. Exposure of rodents to 1,2-dithiole-3-thiones triggers nuclear accumulation of the transcription factor Nrf2 and its enhanced binding to the "antioxidant response element" (ARE), leading to transcriptional activation of a score of genes involved in carcinogen detoxication and attenuation of oxidative stress. Nrf2-deficient mice fail to induce many of these genes in response to dithiolethiones; moreover, basal expression of these genes is typically repressed. To test the hypothesis that enzyme induction is a useful strategy for chemoprevention in humans, three key elements are necessary: a candidate agent, an at-risk population and modulatable intermediate endpoints. Towards this end, a placebo-controlled, double blind clinical trial of oltipraz was conducted in residents of Qidong, PR China who are exposed to dietary aflatoxins and who are at high risk for the development of liver cancer. Oltipraz significantly enhanced excretion of a phase 2 product, aflatoxin-mercapturic acid, a derivative of the aflatoxin-glutathione conjugate, in the urine of study participants administered 125 mg oltipraz by mouth daily. Administration of 500 mg oltipraz once a week led to a significant reduction in the excretion of the primary oxidative metabolite of AFB(1), AFM(1), when measured shortly after drug administration. While this study highlighted the general feasibility of inducing phase 2 enzymes in humans, a longer term intervention is addressing whether protective alterations in aflatoxin metabolism can be sustained for extended periods of time in this high-risk population.

Rapid isolation and purification of 1-cyano-2-hydroxy-3-butene (crambene) from Crambe abyssinica seed meal using immiscible solvent extraction and high-performance liquid chromatography

1-Cyano-2-hydroxy-3-butene (crambene) is a nitrile found in cruciferous vegetables that causes significant upregulation of quinone reductase and glutathione S-transferases in vivo and in vitro, making it a likely candidate as a cancer chemopreventive compound. To investigate further the putative anticarcinogenic mechanisms of crambene, a compound of the highest possible purity is vital. Therefore, a rapid and effective method of purification of crambene is necessary to continue studies of its beneficial health effects. A rapid method to isolate and purify natural crambene from either Crambe abyssinica (crambe) seed or commercially processed crambe seed meal was developed using immiscible solvent extraction followed by high-performance liquid chromatography. Use of this methodology eliminated the need for time-consuming and relatively inefficient column chromatography, improved extraction efficiency, and resulted in higher purity than previously used methodologies. Elimination of trace amounts of fatty acid residues, unachievable with previous methodologies, also was accomplished.

Induction of histone acetylation in mouse erythroleukemia cells by some organosulfur compounds including allyl isothiocyanate

In previous studies we observed that some allyl sulfides can cause increased acetylation of histones and differentiation in DS19 mouse erythroleukemia cells. In the present work we observed increased acetylation of histones with allyl isothiocyanate and butanethiol but not with butyl sulfide or butyl disulfide. Increased acetylation of histones was established by change in electrophoretic mobility, incorporation of [3H]acetate or immunoblotting. Histone deacetylase in nuclei of DS19 cells was inhibited 74% by 0.5 mM allyl mercaptan and 43% by 0.5 mM butanethiol but was not significantly affected by 0.5 mM allyl isothiocyanate. There was some degree of reversibility in the effect of allyl isothiocyanate when the cells were incubated for 15 hr in fresh medium. The data suggested that allyl isothiocyanate may stimulate histone acetylation rather than inhibit histone deacetylation. Addition of allyl isothiocyanate, however, had very little or no additional effect on the induction of histone acetylation caused by trichostatin A. Histone acetyltransferase activity determined in cell homogenates was not increased by preincubation of cells with allyl isothiocyanate or inclusion of allyl isothiocyanate in the assay medium. It was concluded that treatment of mouse erythroleukemia cells with allyl isothiocyanate can cause increased acetylation of histones but the mechanism for this effect requires further elucidation.

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

While methods for the identification and quantification of total plant glucosinolate content typically utilize desulfation of glucosinolates followed by reversed-phase chromatography, the analysis of intact glucosinolates has been problematic. Hydrophilic interaction chromatography offers a novel method for analyzing intact glucosinolates and when performed along with ion-pair reversed-phase chromatography offers a powerful and complementary method for glucosinolate analysis.

Benzyl isothiocyanate is the chief or sole anthelmintic in papaya seed extracts

Papaya (Carica papaya) seeds were extracted in an aqueous buffer or in organic solvents, fractionated by chromatography on silica and aliquots tested for anthelmintic activity by viability assays using Caenorhabditis elegans. For all preparations and fractions tested, anthelmintic activity and benzyl isothiocyanate content correlated positively. Aqueous extracts prepared from heat-treated seeds had no anthelmintic activity or benzyl isothiocyanate content although both appeared when these extracts were incubated with a myrosinase-containing fraction prepared from papaya seeds. A 10 h incubation of crude seed extracts at room temperature led to a decrease in anthelmintic activity and fractionated samples showed a lower benzyl isothiocyanate content relative to non-incubated controls. Benzyl thiocyanate, benzyl cyanide, and benzonitrile were not detected in any preparations and cyanogenic glucosides. which were present, could not account for the anthelmintic activity detected. Thus, our results are best explained if benzyl isothiocyanate is the predominant or sole anthelmintic agent in papaya seed extracts regardless of how seeds are extracted.

Prevention of prostate cancer

Strategies for reducing the occurrence of prostate cancers will be critical in limiting the morbidity and mortality of this disease. The long latency period of prostate tumors and improved understanding of prostate carcinogenesis suggest opportunities for effective preventive measures. Because androgen is integral to prostatic carcinogenesis, several preventive strategies under investigation target the androgen axis. Epidemiologic and basic studies implicate dietary factors in prostate cancer development and suggest that altering diet may influence prostate cancer risk and progression. Many of the micronutrients with preventive potential have antioxidant properties; cellular defenses against oxidative stresses are likely to be crucial in reducing prostate carcinogenesis. This article summarizes the current status and opportunities in prostate cancer prevention.

Chemopreventive effect of 2-(allylthio)pyrazine (2-AP) on rat colon carcinogenesis induced by azoxymethane (AOM)

An investigation was conducted to assess the chemopreventive effects of 2-(allylthio)pyrazine (2-AP), synthesized for potential use as a chemopreventive agent, after administration during the pre-initiation and post-initiation stages in a rat colon carcinogenesis model with azoxymethane (AOM). One hundred, 5-week-old, male F344 rats were randomly divided into two experiments (n = 50 each). Experiment 1 rats were randomly divided into three groups: Group 1 rats were pre-treated with 2-AP (25 or 50 mg/kg body weight, 3 consecutive days through the route of intragastric intubations) before AOM (20 mg/kg body weight, single subcutaneous (s.c.) injection) initiation. Group 2 rats were treated with AOM alone. Group 3 rats were given 2-AP alone without AOM initiation. The animals were killed at the end of each experiment (week 5) and the aberrant crypt foci (ACF) of the colonic mucosa were assessed after staining with methylene blue. Experiment 2 rats were randomly divided into three groups: Group 1 rats were given 2-AP (10, 25 or 50 mg/kg body weight, five-times intragastric intubations per week for 5 weeks from week 3) after AOM (15 mg/kg body weight, three s.c. injections) initiation for 2 weeks. Group 2 rats were treated with AOM alone. Group 3 rats were given 2-AP alone without AOM initiation. The animals were killed at the end of the experiment (week 8) and the ACF of the colonic mucosa were quantified. Total numbers of ACF/colon in Group 1 rats (pre-treated with 2-AP) tended to decrease (2-AP, 50 mg/kg body weight) or increase (2-AP, 100 mg/kg body weight) depending on the dose level. Total numbers of ACF/colon in Group 1 rats (treated with AOM followed by 2-AP, all subgroups; 160.8 +/- 38.0; 161.8 +/- 38.1; 137.1 +/- 48.4) were decreased significantly compared with the values in Group 2 rats (AOM alone; 214.8 +/- 48.1) (P < 0.05 or 0.01). The highest dose group (2-AP, 50 mg/kg body weight) had the lowest levels of total numbers of ACF/colon among the three subgroups. Total numbers of aberrant crypts (AC)/colon of the highest dose group (340.1+/- 117.9) decreased significantly compared with the value for Group 2 rats (AOM alone; 545.1 +/- 38.3). These results thus suggest that 2-AP may have potential as a chemopreventive agent against rat colon carcinogenesis after administration of AOM during the post-initiation stage.

Cancer-protective properties of high-selenium broccoli

Selenium (Se) from high-Se garlic reduces the incidence of chemically induced mammary tumors, and Se from high-Se broccoli reduces colon cancer. However, the ability of Se from high-Se broccoli to protect against mammary cancer has not been tested. Also, the sprout form of broccoli contains many secondary plant compounds that are known to reduce cancer risk, but the anticarcinogenic activity of broccoli sprouts has not been investigated. The present studies examined the ability of high-Se broccoli or high-Se broccoli sprouts to protect against chemically induced mammary or colon cancer. In one experiment, Sprague--Dawley rats that consumed diets containing 3.0 microg of Se/g supplied as high-Se broccoli had significantly fewer mammary tumors than rats fed 0.1 microg of Se as selenite with or without the addition of regular broccoli. In the second experiment, Fisher F-344 rats fed 2.0 microg of Se/g of diet supplied as either high-Se broccoli florets or high-Se broccoli sprouts had significantly fewer aberrant colon crypts than rats fed 0.1 or 2 microg of Se/g of diet supplied as selenite with or without the addition of low-Se broccoli. These data demonstrate that the cancer-protective effect of Se in high-Se broccoli extends to mammary cancer and the protective forms of broccoli against colon cancer include high-Se broccoli sprouts.

Cytochrome p450 CYP79F1 from arabidopsis catalyzes the conversion of dihomomethionine and trihomomethionine to the corresponding aldoximes in the biosynthesis of aliphatic glucosinolates

Glucosinolates are natural plant products that have received rising attention due to their role in interactions between pests and crop plants and as chemical protectors against cancer. Glucosinolates are derived from amino acids and have aldoximes as intermediates. We report that cytochrome P450 CYP79F1 catalyzes aldoxime formation in the biosynthesis of aliphatic glucosinolates in Arabidopsis thaliana. Using recombinant CYP79F1 functionally expressed in Escherichia coli, we show that both dihomomethionine and trihomomethionine are metabolized by CYP79F1 resulting in the formation of 5-methylthiopentanaldoxime and 6-methylthiohexanaldoxime, respectively. 5-methylthiopentanaldoxime is the precursor of the major glucosinolates in leaves of A. thaliana, i.e. 4-methylthiobutylglucosinolate and 4-methylsulfinylbutylglucosinolate, and a variety of other glucosinolates in Brassica sp. Transgenic A. thaliana with cosuppression of CYP79F1 have a reduced content of aliphatic glucosinolates and a highly increased level of dihomomethionine and trihomomethionine. The transgenic plants have a morphological phenotype showing loss of apical dominance and formation of multiple axillary shoots. Our data provide the first evidence that a cytochrome P450 catalyzes the N-hydroxylation of chain-elongated methionine homologues to the corresponding aldoximes in the biosynthesis of aliphatic glucosinolates.

The molecular pathogenesis of prostate cancer: Implications for prostate cancer prevention

Prostate cancer has become 1 of the most commonly diagnosed cancers in the United States and 1 of the leading causes of cancer death in North America and Western Europe. Survey studies of prostate tissues obtained at autopsy indicate that the development of life-threatening prostate cancer in the US likely occurs over decades. Insights from epidemiologic studies implicate environmental factors, principally dietary components, as major risk factors for prostate cancer development. An accumulating body of basic research data suggests that normal and neoplastic prostate cells may be subjected to a relentless barrage of genome-damaging stresses, and that dietary components and male sex steroids might modulate the level of genome threatening insults. Finally, over the past 5 years, analyses of somatic genome alterations in prostatic carcinoma cells have revealed that somatic inactivation of GSTP1, encoding the carcinogen-detoxification enzyme glutathione S-transferase pi, may serve as an initiating genome lesion for prostatic carcinogenesis. These diverse observations can be integrated into a transcendent mechanistic hypothesis for the pathogenesis of prostate cancer: normal prostate cells acquiring somatic GSTP1 defects may suffer chronic genome damage, influenced by dietary practices, that promote neoplastic transformation, while prostatic carcinoma cells, which characteristically contain defective GSTP1 alleles, remain susceptible to further genome-damaging stresses that promote malignant cancer progression. This hypothesized critical role for GSTP1 inactivation in the earliest steps of prostatic carcinogenesis provides several attractive opportunities for prostate cancer prevention strategies, including (1) restoration of GSTP1 function, (2) compensation for inadequate GSTP1 activity (via use of therapeutic inducers of other glutathione S-transferases (GST), and (3) abrogation or attenuation of genome-damaging stresses.

Preparative HPLC method for the purification of sulforaphane and sulforaphane nitrile from Brassica oleracea

An extraction and preparative HPLC method has been devised to simultaneously purify sulforaphane and sulforaphane nitrile from the seed of Brassica oleracea var. italica cv. Brigadier. The seed was defatted with hexane, dried, and hydrolyzed in deionized water (1:9) for 8 h. The hydrolyzed seed meal was salted and extracted with methylene chloride. The dried residue was redissolved in a 5% acetonitrile solution and washed with excess hexane to remove nonpolar contaminants. The aqueous phase was filtered through a 0.22-microm cellulose filter and separated by HPLC using a Waters Prep Nova-Pak HR C-18 reverse-phase column. Refractive index was used to detect sulforaphane nitrile, and absorbance at 254 nm was used to detect sulforaphane. Peak identification was confirmed using gas chromatography and electron-impact mass spectrometry. Each kilogram of extracted seed yielded approximately 4.8 g of sulforaphane and 3.8 g of sulforaphane nitrile. Standard curves were developed using the purified compounds to allow quantification of sulforaphane and sulforaphane nitrile in broccoli tissue using a rapid GC method. The methodology was used to compare sulforaphane and sulforaphane nitrile content of autolyzed samples of several broccoli varieties.

Induction of cytochrome P4501A1

Cytochrome P4501A1 is a substrate-inducible microsomal enzyme that oxygenates polycyclic aromatic hydrocarbons, such as the carcinogen benzo(a)pyrene, as the initial step in their metabolic processing to water-soluble derivatives. Enzyme induction reflects increased transcription of the cognate CYP1A1 gene. The environmental toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin is the most potent known cytochrome P4501A1 inducer. Two regulatory proteins, the aromatic (aryl) hydrocarbon receptor (AhR) and the AhR nuclear translocator (Arnt), mediate induction. AhR and Arnt are prototypical members of the basic helix-loop-helix/Per-Arnt-Sim class of transcription factors. Mechanistic analyses of cytochrome P4501A1 induction provide insights into ligand-dependent mammalian gene expression, basic helix-loop-helix/Per-Arnt-Sim protein function, and dioxin action; such studies also impact public health issues concerned with molecular epidemiology, carcinogenesis, and risk assessment.

Potency of Michael reaction acceptors as inducers of enzymes that protect against carcinogenesis depends on their reactivity with sulfhydryl groups

Induction of phase 2 enzymes and elevations of glutathione are major and sufficient strategies for protecting mammals and their cells against the toxic and carcinogenic effects of electrophiles and reactive forms of oxygen. Inducers belong to nine chemical classes and have few common properties except for their ability to modify sulfhydryl groups by oxidation, reduction, or alkylation. Much evidence suggests that the cellular "sensor" molecule that recognizes the inducers and signals the enhanced transcription of phase 2 genes does so by virtue of unique and highly reactive sulfhydryl functions that recognize and covalently react with the inducers. Benzylidene-alkanones and -cycloalkanones are Michael reaction acceptors whose inducer potency is profoundly increased by the presence of ortho- (but not other) hydroxyl substituent(s) on the aromatic ring(s). This enhancement correlates with more rapid reactivity of the ortho-hydroxylated derivatives with model sulfhydryl compounds. Proton NMR spectroscopy provides no evidence for increased electrophilicity of the beta-vinyl carbons (the presumed site of nucleophilic attack) on the hydroxylated inducers. Surprisingly, these ortho-hydroxyl groups display a propensity for extensive intermolecular hydrogen bond formation, which may raise the reactivity and facilitate addition of mercaptans, thereby raising inducer potencies.

The importance of using scientific principles in the development of medicinal agents from plants

The authors review the major scientific milestones and the legislative framework that have made possible the spectacular successes of many modern therapies that trace their origins to plants. They emphasize that drugs used in mainstream medicine, in contrast to most of those used in alternative medicine, are required to meet stringent federal requirements for purity, safety, and efficacy before they can be distributed to the public, and that the necessary testing requires much time and effort. Yet alternative medicines based on plant substances are extremely popular, even though their safety and efficacy have not been scientifically proven. Reasons for this are reviewed and numerous examples and case histories are cited illustrating both successes in the scientific development of drugs from plants and the dangers of unregulated drugs. Such drugs are more easily available because of the deregulating effect of the 1994 Dietary Supplement Health and Education Act (DSHEA), which has substantially weakened the authority of the Food and Drug Administration to ensure the safety of dietary supplements. The authors describe the rigorous scientific investigations of curcumin, from the ginger family, and of sulforaphane, from crucifers, to illustrate the long and demanding scientific process that is required to establish the safety and effectiveness of potential drugs from plants. They re-emphasize the necessity for strict scientific review of all drugs. They also recommend that all providers of care be required to question patients about their intakes of dietary supplements. The authors close by saying that the DSHEA is "a disaster waiting to happen," but warn that any attempts to strengthen current legislation will be opposed by special interests.

Therapeutic potential of dietary phase 2 enzyme inducers in ameliorating diseases that have an underlying inflammatory component

Many diseases associated with ageing have an underlying oxidative stress and accompanying inflammatory component, for example, Alzheimer's disease or atherosclerosis. Reviewed in this manuscript are: the role of oxidative stress in activating the transcription factor nuclear factor kappa B (NFκB), the role of NFκB in activating pro-inflammatory gene transcription, strong oxidants produced by cells, anti-oxidant defense systems, the central role of phase 2 enzymes in the anti-oxidant defense, dietary phase 2 enzyme inducers and evidence that dietary phase 2 enzymes decrease oxidative stress. It is likely that a diet containing phase 2 enzyme inducers may ameliorate or even prevent diseases that have a prominent inflammatory component to them. Research should be directed into the potential therapeutic effects of dietary phase 2 enzyme inducers in ameliorating diseases with an underlying oxidative stress and inflammatory component to them.Key words: Alzheimer's disease, atherosclerosis, diet, glutathione, inflammation, stroke.

Preferential expression of antioxidant response element mediated gene expression in astrocytes

Transcriptional control of target genes by antioxidant/electrophile response elements has been well described in peripheral tissues. Genes that are regulated by this mechanism include the antioxidant enzymes NAD(P)H:quinone oxidoreductase, gamma-glutamyl cystine synthetase and glutathione-S-transferase. Antioxidant/electrophile response elements within a gene's promoter confer induction by low-molecular-weight electrophilic compounds such as tert-butylhydroquinone and dimethyl fumarate. We have now examined the ability of antioxidant/electrophile response elements to elicit gene expression in neurons and astrocytes in both brain slices and primary cultures using transient transfection of promoter reporter constructs. Our results using a heat-stable human placental alkaline phosphatase reporter indicate that antioxidant/electrophile response element mediated gene expression is largely restricted to astrocyte cell populations. Placental alkaline phosphatase expression was significantly elevated in astrocytes treated with the antioxidant/electrophile response element inducer dimethyl fumarate. Mutant constructs lacking a functional antioxidant/electrophile response element abolished all placental alkaline phosphatase expression in astrocytes. We suggest that astrocytic metabolic processes that normally aid and/or protect neurons may be controlled via this inducible system.

Synthesis, analysis and rearrangement of novel unnatural glucosinolates

As part of a structure activity study to examine the interaction of glucosinolates with leaf surfaces, a number of glucosinolates were synthesised bearing novel side chain functionalities. These included 7-carboxyheptyl, heptyl, and naphthyl side chains. For the carboxyheptyl glucosinolate, a novel intramolecular rearrangement reaction was observed during the final deprotection step, which generated an ester attached to the C-3 of glucose. Studies by 1H NMR spectroscopy showed that the hydrophobic side chain associated with one face of the glucose ring and it was proposed that this was the driving force for the rearrangement. Similar hydrophobic interactions were also observed between the heptyl and naphthyl side chains and the glucose.

Current prospects for controlling cancer growth with non-cytotoxic agents--nutrients, phytochemicals, herbal extracts, and available drugs

In animal or cell culture studies, the growth and spread of cancer can be slowed by many nutrients, food factors, herbal extracts, and well-tolerated, available drugs that are still rarely used in the clinical management of cancer, in part because they seem unlikely to constitute definitive therapies in themselves. However, it is reasonable to expect that mechanistically complementary combinations of these measures could have a worthwhile impact on survival times and, when used as adjuvants, could improve the cure rates achievable with standard therapies. The therapeutic options available in this regard include measures that: down-regulate serum free IGF-I; suppress the synthesis of mevalonic acid and/or certain derivatives thereof; modulate arachidonate metabolism by inhibiting 5-lipoxygenase, 12-lipoxygenase, or COX-2; antagonize the activation of AP-1 transcription factors; promote the activation of PPAR-gamma transcription factors; and that suppress angiogenesis by additional mechanisms. Many of these measures appear suitable for use in cancer prevention.

Rapid polyubiquitination and proteasomal degradation of a mutant form of NAD(P)H:quinone oxidoreductase 1

The NAD(P)H:quinone oxidoreductase 1 (NQO1)*2 polymorphism is characterized by a single proline-to-serine amino acid substitution. Cell lines and tissues from organisms genotyped as homozygous for the NQO1*2 polymorphism are deficient in NQO1 activity. In studies with cells homozygous for the wild-type allele and cells homozygous for the mutant NQO1*2 allele, no difference in the half-life of NQO1 mRNA transcripts was observed. Similarly, in vitro transcription/translation studies showed that both wild-type and mutant NQO1 coding regions were transcribed and translated into full-length protein with equal efficiency. Protein turnover studies in NQO1 wild-type and mutant cell lines demonstrated that the half-life of wild-type NQO1 was greater than 18 h, whereas the half-life of mutant NQO1 was 1.2 h. Incubation of NQO1 mutant cell lines with proteasome inhibitors increased the amount of immunoreactive NQO1 protein, suggesting that mutant protein may be degraded via the proteasome pathway. Additional studies were performed using purified recombinant NQO1 wild-type and mutant proteins incubated in a rabbit reticulocyte lysate system. In these studies, no degradation of wild-type NQO1 protein was observed; however, mutant NQO1 protein was completely degraded in 2 h. Degradation of mutant NQO1 was inhibited by proteasome inhibitors and was ATP-dependent. Mutant NQO1 incubated in rabbit reticulocyte lysate with MG132 resulted in the accumulation of proteins with increased molecular masses that were immunoreactive for both NQO1 and ubiquitin. These data suggest that wild-type NQO1 persists in cells whereas mutant NQO1 is rapidly degraded via ubiquitination and proteasome degradation.

Risk factors for pancreatic cancer: a case-control study based on direct interviews

The etiology of pancreatic cancer is poorly understood, partly because of the inconsistency of findings among case-control studies of pancreatic cancer. Because of the unfavorable prognosis for pancreatic cancer, many case-control studies have been based largely on interviews with next of kin, who are known to report less reliable information on potential risk factors than original respondents. The purpose of this study was to estimate the effects of speculative risk factors such as dietary/nutritional factors and alcohol drinking, as well as those of established risk factors such as cigarette smoking, diabetes mellitus, and family history of pancreatic cancer, on pancreatic cancer risk based solely on direct interviews. This investigation was a population-based case-control study of pancreatic cancer diagnosed in Atlanta (GA), Detroit (MI), and ten New Jersey counties from August 1986 through April 1989. Direct interviews were conducted with 526 incident cases and 2,153 population controls. This study revealed a significant interaction between body mass index and caloric intake that was consistent by both race and gender. Subjects with elevated body mass index and caloric intake had increased risk, whereas those with elevated values for one of these factors but not the other experienced no increased risk. This finding suggests that energy balance may play a major role in pancreatic carcinogenesis. Diabetes mellitus was also a risk factor for pancreatic cancer, as well as a possible complication of the tumor. Our data are consistent with a key role for hyperinsulinemia in pancreatic carcinogenesis, particularly among non-diabetics with an elevated body mass index. A three-fold risk of pancreatic cancer among first-degree relatives of affected individuals was apparent. An increased risk also was associated with a family history of colon, endometrial, ovary, and breast cancer, suggesting a possible link to hereditary non-polyposis colon cancer. Our findings support a causal role for cigarette smoking in pancreatic carcinogenesis. Alcohol drinking at levels typically consumed by the general population of the United States did not appear to be a risk factor for pancreatic cancer, although heavy drinking may be related to risk, particularly in blacks.

Inhibition of CYP2E1 with natural agents may be a feasible strategy for minimizing the hepatotoxicity of ethanol

CYP2E1, induced in hepatocytes by heavy consumption of ethanol and certain other drugs, is a potent generator of superoxide, and is thereby thought to mediate the gravest aspects of alcoholic hepatotoxicity. Certain drugs such as the sedative chlormethiazole are effective inhibitors of CYP2E1, and may have clinical potential in the treatment of alcoholics. A number of phytochemicals can also potently inhibit CYP2E1 - most notably certain isothiocyanates found in crucifera, such as sulforaphane and phenethylisothiocyanate. Preparation of these compounds from crucifera seeds or sprouts should enable commercial production of supplements that would protect the livers of social drinkers while concurrently reducing risk for carcinogen-induced cancers.

The chemical diversity and distribution of glucosinolates and isothiocyanates among plants

Glucosinolates (beta-thioglucoside-N-hydroxysulfates), the precursors of isothiocyanates, are present in sixteen families of dicotyledonous angiosperms including a large number of edible species. At least 120 different glucosinolates have been identified in these plants, although closely related taxonomic groups typically contain only a small number of such compounds. Glucosinolates and/or their breakdown products have long been known for their fungicidal, bacteriocidal, nematocidal and allelopathic properties and have recently attracted intense research interest because of their cancer chemoprotective attributes. Numerous reviews have addressed the occurrence of glucosinolates in vegetables, primarily the family Brassicaceae (syn. Cruciferae; including Brassica spp and Raphanus spp). The major focus of much previous research has been on the negative aspects of these compounds because of the prevalence of certain "antinutritional" or goitrogenic glucosinolates in the protein-rich defatted meal from widely grown oilseed crops and in some domesticated vegetable crops. There is, however, an opposite and positive side of this picture represented by the therapeutic and prophylactic properties of other "nutritional" or "functional" glucosinolates. This review addresses the complex array of these biologically active and chemically diverse compounds many of which have been identified during the past three decades in other families. In addition to the Brassica vegetables, these glucosinolates have been found in hundreds of species, many of which are edible or could provide substantial quantities of glucosinolates for isolation, for biological evaluation, and potential application as chemoprotective or other dietary or pharmacological agents.

Bitter taste, phytonutrients, and the consumer: a review

Dietary phytonutrients found in vegetables and fruit appear to lower the risk of cancer and cardiovascular disease. Studies on the mechanisms of chemoprotection have focused on the biological activity of plant-based phenols and polyphenols, flavonoids, isoflavones, terpenes, and glucosinolates. Enhancing the phytonutrient content of plant foods through selective breeding or genetic improvement is a potent dietary option for disease prevention. However, most, if not all, of these bioactive compounds are bitter, acrid, or astringent and therefore aversive to the consumer. Some have long been viewed as plant-based toxins. As a result, the food industry routinely removes these compounds from plant foods through selective breeding and a variety of debittering processes. This poses a dilemma for the designers of functional foods because increasing the content of bitter phytonutrients for health may be wholly incompatible with consumer acceptance. Studies on phytonutrients and health ought to take sensory factors and food preferences into account.

Functional detection of chemopreventive glucosinolates in Arabidopsis thaliana

Natural isothiocyanates, derived from glucosinolates by myrosinase-catalyzed hydrolysis, are potent chemopreventive agents that favorably modify carcinogen metabolism in mammals by inhibiting metabolic activation of carcinogens and/or by inducing carcinogen-detoxifying enzymes. Methylsulfinylalkyl isothiocyanates are potent selective inducers of mammalian Phase 2 detoxification enzymes such as quinone reductase [NADP(H):quinone-acceptor oxidoreductase, EC 1.6.99.2]. Members of the Cruciferae family, including the model plant species Arabidopsis thaliana (L.) Heyhn, synthesize methylsulfinylalkyl glucosinolates. We have adapted a colorimetric bioassay for quinone reductase activity in Hepa 1c1c7 murine hepatoma cells as a versatile tool to rapidly monitor methylsulfinylalkyl glucosinolate content in A. thaliana leaf extracts. Using wild type plants and mutant plants defective in the synthesis of 4-methylsulfinylbutyl glucosinolate (glucoraphanin), we have demonstrated that A. thaliana (ecotype Columbia) is a rich source of Phase 2 enzyme inducers and that methylsulfinylalkyl glucosinolates, predominantly glucoraphanin, account for about 80% of the quinone reductase inducer potency of Columbia leaf extracts. We have optimized leaf extraction conditions and the quinone reductase bioassay to allow for screening of large numbers of plant extracts in a molecular genetic approach to dissecting glucosinolate biosynthesis in A. thaliana.

Persuasive evidence that quinone reductase type 1 (DT diaphorase) protects cells against the toxicity of electrophiles and reactive forms of oxygen

An extensive body of evidence supports the conclusion that by catalyzing obligatory two-electron reductions of quinones to hydroquinones, NAD(P)H:quinone reductase (QR1) protects cells against the deleterious effects of redox cycling of quinones, their ability to deplete glutathione, and to produce neoplasia. The effects of elevation of QR1 levels by various enzyme inducers, inhibition of the enzyme by dicumarol, and genetic deletion of the enzyme (knockout mouse) are all consistent with the proposed protective functions. Measurement of QR1 activity in murine hepatoma cells grown in 96-well microtiter plates has provided a rapid and quantitative method for detecting inducer activity and determining inducer potency. This constitutes a strategy for the identification of potential chemoprotectors against cancer. Epidemiological studies show that humans who are genetically deficient in QR1 are more susceptible to the hematological toxicity and carcinogenicity of benzene exposure, and may be more susceptible to the development of a number of malignant tumors.

Antiplatelet and anticancer isothiocyanates in Japanese domestic horseradish, Wasabi

6-Methylsulfinylhexyl isothiocyanate (MS-ITC) was isolated from wasabi (Wasabia japonica, Japanese domestic horseradish) as a potential inhibitor of human platelet aggregation in vitro through our extensive screening of vegetables and fruits. In the course of an another screening for the induction of glutathione S-transferase (GST) activity in RL34 cells, MS-ITC was inadvertently isolated from wasabi as a potential inducer of GST. MS-ITC administered to rats or mice also showed both activities in vivo. As a result from elucidation of the platelet aggregation inhibition and the GST induction mechanisms of MS-ITC, the isothiocyanate moiety of MS-ITC plays an important role for antiplatelet and anticancer activities because of its high reactivity with sulfhydryl (RSH) groups in biomolecules (GSH, cysteine residue in a certain protein, etc.).

Cytochrome P450 CYP79A2 from Arabidopsis thaliana L. Catalyzes the conversion of L-phenylalanine to phenylacetaldoxime in the biosynthesis of benzylglucosinolate

Glucosinolates are natural plant products gaining increasing interest as cancer-preventing agents and crop protectants. Similar to cyanogenic glucosides, glucosinolates are derived from amino acids and have aldoximes as intermediates. We report cloning and characterization of cytochrome P450 CYP79A2 involved in aldoxime formation in the glucosinolate-producing Arabidopsis thaliana L. The CYP79A2 cDNA was cloned by polymerase chain reaction, and CYP79A2 was functionally expressed in Escherichia coli. Characterization of the recombinant protein shows that CYP79A2 is an N-hydroxylase converting L-phenylalanine into phenylacetaldoxime, the precursor of benzylglucosinolate. Transgenic A. thaliana constitutively expressing CYP79A2 accumulate high levels of benzylglucosinolate. CYP79A2 expressed in E. coli has a K(m) of 6.7 micromol liter(-1) for L-phenylalanine. Neither L-tyrosine, L-tryptophan, L-methionine, nor DL-homophenylalanine are metabolized by CYP79A2, indicating that the enzyme has a narrow substrate specificity. CYP79A2 is the first enzyme shown to catalyze the conversion of an amino acid to the aldoxime in the biosynthesis of glucosinolates. Our data provide the first conclusive evidence that evolutionarily conserved cytochromes P450 catalyze this step common for the biosynthetic pathways of glucosinolates and cyanogenic glucosides. This strongly indicates that the biosynthesis of glucosinolates has evolved based on a cyanogenic predisposition.