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Logo of nihpaAbout Author manuscriptsSubmit a manuscriptHHS Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
 
Pharmacol Res. Author manuscript; available in PMC 2009 September 4.
Published in final edited form as:
PMCID: PMC2737735
NIHMSID: NIHMS22145

Cruciferous Vegetables and Human Cancer Risk: Epidemiologic Evidence and Mechanistic Basis

Abstract

Cruciferous vegetables are a rich source of glucosinolates and their hydrolysis products, including indoles and isothiocyanates, and high intake of cruciferous vegetables has been associated with lower risk of lung and colorectal cancer in some epidemiological studies. Glucosinolate hydrolysis products alter the metabolism or activity of sex hormones in ways that could inhibit the development of hormone-sensitive cancers, but evidence of an inverse association between cruciferous vegetable intake and breast or prostate cancer in humans is limited and inconsistent. Organizations such as the National Cancer Institute recommend the consumption of 5–9 servings of fruits and vegetables daily, but separate recommendations for cruciferous vegetables have not been established. Isothiocyanates and indoles derived from the hydrolysis of glucosinolates, such as sulforaphane and indole-3-carbinol (I3C), have been implicated in a variety of anticarcinogenic mechanisms, but deleterious effects also have been reported in some experimental protocols, including tumor promotion over prolonged periods of exposure. Epidemiological studies indicate that human exposure to isothiocyanates and indoles through cruciferous vegetable consumption may decrease cancer risk, but the protective effects may be influenced by individual genetic variation (polymorphisms) in the metabolism and elimination of isothiocyanates from the body. Cooking procedures also affect the bioavailability and intake of glucosinolates and their derivatives. Supplementation with I3C or the related dimer 3,3′-diindolylmethane (DIM) alters urinary estrogen metabolite profiles in women, but the effects of I3C and DIM on breast cancer risk are not known. Small preliminary trials in humans suggest that I3C supplementation may be beneficial in treating conditions related to human papilloma virus infection, such as cervical intraepithelial neoplasia and recurrent respiratory papillomatosis, but larger randomized controlled trials are needed.

Keywords: Brassica, glucosinolates, genetic polymorphisms, isothiocyanates, indole-3-carbinol, epigenetics

1. Introduction

Cruciferous or Brassica vegetables come from plants in the family known to botanists as Cruciferae or alternatively, Brassicaceae. Plants in the Cruciferae family have flowers with four equal-sized petals in the shape of a ‘crucifer’ cross. “Brassica” is the latin term for cabbage. Many commonly consumed cruciferous vegetables come from the Brassica genus, including broccoli, Brussels sprouts, cabbage, cauliflower, collard greens, kale, kohlrabi, mustard, rutabaga, turnips, bok choy and Chinese cabbage [1]. Although not in the Brassica genus, arugula, horseradish, radish, wasabi and watercress are also cruciferous vegetables. Like other vegetables, cruciferous vegetables contain a number of nutrients and phytochemicals with cancer chemopreventive properties, including folate, fiber, carotenoids and chlorophyll. However, cruciferous vegetables are unique in that they are rich sources of glucosinolates, sulfur-containing compounds that are responsible for their pungent aromas and spicy (some say bitter) taste [2]. The hydrolysis of glucosinolates by the plant enzyme myrosinase results in the formation of biologically active compounds, including indoles and isothiocyanates (Figure 1) [3]. More than 100 glucosinolates with unique hydrolysis products have been identified in plants. For example, broccoli is a good source of glucoraphanin, the glucosinolate precursor of sulforaphane (SFN), and glucobrassicin, the precursor of indole-3-carbinol (I3C) [4]. In contrast, watercress is a rich source of gluconasturtiin, the precursor of phenethyl isothiocyanate (PEITC). Table 1 lists some of the isothiocyanates and indoles that are currently under investigation for their cancer chemopreventive properties, along with their glucosinolate precursors. The purpose of this article is to review the available research on cruciferous vegetable intake and human cancer risk, with particular attention to those compounds that make cruciferous vegetables unique—glucosinolates and their biologically active hydrolysis products.

Figure 1
Breakdown of glucosinolates (adapted from [3])
Table 1
Some food sources of selected isothiocyanates and their glucosinolate precursors that are under investigation for their cancer chemopreventive properties.

2. Cruciferous Vegetables and Human Cancer Risk: Epidemiologic Evidence

Like most other vegetables, cruciferous vegetables are good sources of a variety of nutrients and phytochemicals that may work synergistically to help prevent cancer [5]. One challenge in studying the relationships between cruciferous vegetable intake and cancer risk in humans is separating the benefits of diets that are generally rich in vegetables from those that are specifically rich in cruciferous vegetables [6]. An extensive review of epidemiologic studies published prior to 1996 reported that the majority (67%) of 87 case-control studies found an inverse association between some type of cruciferous vegetable intake and cancer risk [7]. At that time, the inverse association appeared to be most consistent for cancers of the lung and digestive tract. The results of retrospective case-control studies are more likely to be distorted by bias in the selection of participants (cases and controls) and dietary recall than prospective cohort studies, which collect dietary information from participants before they are diagnosed with cancer [8]. In the past decade, results of large prospective cohort studies and studies taking into account individual genetic variation suggest that the relationship between cruciferous vegetable intake and the risk of several types of cancer is more complex than previously thought. Findings for lung, colorectal, breast and prostate cancer, which are the four major causes of cancer-related death in the US, are summarized next,

2.1. Lung Cancer

When evaluating the effect of cruciferous vegetable consumption on lung cancer risk, it is important to remember that the benefit of increasing cruciferous vegetable intake is likely to be small compared to the benefit of smoking cessation [9,10]. Although a number of case-control studies found that people diagnosed with lung cancer had significantly lower intakes of cruciferous vegetables than people in cancer-free control groups [7], the findings of more recent prospective cohort studies have been mixed. Prospective studies of Dutch men and women [11], U.S. women [12] and Finnish men [13] found that higher intakes of cruciferous vegetables (more than three weekly servings) were associated with significant reductions in lung cancer risk, but prospective studies of U.S. men [12] and European men and women [9] found no inverse association. The results of several studies suggest that genetic variation affecting the metabolism of glucosinolate hydrolysis products may influence the effects of cruciferous vegetable consumption on lung cancer risk[1417] (see Genetic Polymorphisms below).

2.2. Colorectal Cancer

A small clinical trial found that the consumption of 250 g/d (9 oz/d) of broccoli and 250 g/d of Brussels sprouts significantly increased the urinary excretion of a potential carcinogen found in well-done meat, namely 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) [18]. Walters et al. concluded that high cruciferous vegetable intake might decrease colorectal cancer risk by enhancing the elimination of PhIP and related dietary heterocyclic amine carcinogens. Although a number of case-control studies conducted prior to 1990 found that people diagnosed with colorectal cancer were more likely to have lower intakes of various cruciferous vegetables than people without colorectal cancer [1922], most prospective cohort studies have not found significant inverse associations between cruciferous vegetable intake and the risk of developing colorectal cancer over time [2326]. One exception was a prospective study of Dutch adults, which found that men and women with the highest intakes of cruciferous vegetables (averaging 58 g/d) were significantly less likely to develop colon cancer than those with the lowest intakes (averaging 11 g/d) [27]. Surprisingly, higher intakes of cruciferous vegetables were associated with increased risk of rectal cancer in women in that study. As with lung cancer, the relationship between cruciferous vegetable consumption and colorectal cancer risk may be complicated by genetic polymorphisms. The results of several recent epidemiological studies suggest that the protective effects of cruciferous vegetable consumption may be influenced by inherited differences in the capacity of individuals to metabolize and eliminate glucosinolate hydrolysis products [2831] (see Genetic Polymorphisms, next).

2.3. Breast Cancer

The endogenous estrogen 17β-estradiol can be metabolized to 16α-hydroxyestrone (16αOHE1) or 2-hydroxyestrone (2OHE1). In contrast to 2OHE1, 16αOHE1 is highly estrogenic and has been found to enhance the proliferation of estrogen-sensitive breast cancer cells in culture [32,33]. It has been hypothesized that shifting the metabolism of 17β-estradiol toward 2OHE1 and away from 16αOHE1 could decrease the risk of estrogen-sensitive cancers, such as breast cancer [34]. In a small clinical trial, increasing cruciferous vegetable intake of healthy postmenopausal women for four weeks increased urinary 2OHE1:16αOHE1 ratios, suggesting that high intakes of cruciferous vegetables can shift estrogen metabolism. However, the relationship between urinary 2OHE1:16OHE1 ratios and breast cancer risk is not clear. Several small case-control studies found that women with breast cancer had lower urinary ratios of 2OHE1:16αOHE1 [3537], but larger case-control and prospective cohort studies did not find significant associations between urinary 2OHE1:16αOHE1 ratios and breast cancer risk [3840]. The results of epidemiological studies of cruciferous vegetable intake and breast cancer risk are also inconsistent. Several recent case-control studies in the US, Sweden and China found that measures of cruciferous vegetable intake were significantly lower in women diagnosed with breast cancer than in cancer-free control groups [4143], but cruciferous vegetable intake was not associated with breast cancer risk in a pooled analysis of seven large prospective cohort studies [44].

2.4. Prostate Cancer

Although glucosinolate hydrolysis products have been found to inhibit growth and promote death (apoptosis) of cultured prostate cancer cells [45,46], the results of epidemiological studies of cruciferous vegetable intake and prostate cancer risk are inconsistent. Four out of eight case-control studies published since 1990 found that some measure of cruciferous vegetable intake was significantly lower in men diagnosed with prostate cancer than men in a cancer-free control group [4750]. Of the 4 prospective cohort studies that have examined associations between cruciferous vegetable intake and the risk of prostate cancer, none found statistically significant inverse associations overall [5154]. However, the prospective study that included the longest follow-up period and the most cases of prostate cancer found a significant inverse association between cruciferous vegetable intake and the risk of prostate cancer when the analysis was limited to men who had a prostate specific antigen (PSA) test [51]. Since men who have PSA screening are more likely to be diagnosed with prostate cancer, limiting the analysis in this way is one way to reduce detection bias [55]. Presently, epidemiological studies provide only modest support for the hypothesis that high intakes of cruciferous vegetables reduce prostate cancer risk [1].

2.5. Other cancers

At the present time, there is no consistent epidemiological evidence to support a role for cruciferous vegetables as chemopreventive agents against cancers other than the four major types discussed above (lung, colorectal, breast and prostate). One exception may be pancreatic cancer. A recent multiethnic cohort study found no evidence for an inverse association between vegetable intake and pancreatic cancer overall, but inverse associations were seen for dark green vegetables in high-risk persons [56]. In another report [57], among specific subgroups of fruits and vegetables, a non-significant inverse association was observed with cruciferous vegetable consumption (3 or more servings per week versus less than one serving/wk: HR, 0.70; 95% CI, 0.43–1.13). Cabbage consumption was associated with a statistically significant lower risk of pancreatic cancer (1 or more servings/wk versus never consumption: HR, 0.62; 95% CI, 0.39–0.99). Findings from this prospective study do not support a relationship of overall fruit and vegetable consumption with pancreatic cancer risk, but the association between consumption of cruciferous vegetables and pancreatic cancer risk warrants further investigation. A prior study concluded that increasing vegetable and fruit consumption may impart some protection against developing pancreatic cancer [58].

3. Genetic Polymorphisms

There is increasing evidence that genetic differences in humans may influence the effects of cruciferous vegetable intake on cancer risk [59]. Glutathione S-transferases (GSTs) are a family of enzymes that metabolize a variety of compounds, including isothiocyanates, in a way that augments their elimination from the body. Genetic polymorphisms that affect the activity of GST enzymes have been identified in humans. Null variants of the GSTM1 gene and GSTT1 gene contain large deletions, and individuals who are homozygous for the GSTM1-null or GSTT1-null gene cannot produce the corresponding GST enzyme [60]. Lower GST activity in such individuals could result in slower elimination and longer exposure to isothiocyanates after cruciferous vegetable consumption [61]. In support of this idea, several epidemiological studies have found that inverse associations between isothiocyanate intake from cruciferous vegetables and the risk of lung cancer [1417] or colon cancer [2830] were more pronounced in GSTM1-null and/or GSTT1-null individuals. These findings suggest that the protective effects of high intakes of cruciferous vegetables may be enhanced in individuals that eliminate potentially protective compounds like isothiocyanates more slowly.

4. Cooking and Bioavailability of Glucosinolate Hydrolysis Products

Because most glucosinolates are chemically and thermally stable, enzymatic hydrolysis is required for the formation of biologically active isothiocyanates and indoles [3]. Myrosinase, a β-thioglucosidase, is physically separated from glucosinolates in intact plant cells. However, when raw cruciferous vegetables are chopped or chewed, myrosinase comes in contact with glucosinolates and catalyzes the hydrolysis of the glucosidic bond, yielding glucose and an unstable thiohydroxamate-O-sulfonate, which undergoes spontaneous rearrangement to form a number of possible products depending on the side chain structure and the reaction conditions (Figure 1). At neutral pH (6–7), the major glucosinolate hydrolysis products are stable isothiocyanates, with the exception of those with an indole moiety or a β-hydroxy side chain. Unstable β-hydroxy-isothiocyanates undergo spontaneous cyclization to form oxazolidine-2-thiones (e.g., goitrin), and indole isothiocyanates undergo lysis to their corresponding alcohols (e.g., I3C). Thorough chewing of raw cruciferous vegetables increases glucosinolate contact with plant myrosinase and increases the amount of isothiocyanates absorbed [62]. Even when plant myrosinase is completely inactivated by heat, the myrosinase activity of human intestinal bacteria allows for some formation and absorption of isothiocyanates [63].

Glucosinolates are water-soluble compounds that may be leached into cooking water. Boiling cruciferous vegetables for 9–15 minutes resulted in an 18–59% decrease in the total glucosinolate content of cruciferous vegetables [6]. Cooking methods that use less water, such as steaming or microwaving, may reduce glucosinolate losses. However, some cooking practices, including boiling [62], steaming [64] and microwaving at high power (850–900 watts) [65,66] can inactivate myrosinase, the enzyme that catalyzes glucosinolate hydrolysis. Several studies in humans have found that inactivation of myrosinase in cruciferous vegetables substantially decreases the bioavailability of isothiocyanates [62,64,65].

5. Fate of Isothiocyanates and Indoles

Isothiocyanates are metabolized primarily through the mercapturic acid pathway. Conjugation of isothiocyanates to glutathione is facilitated by GSTs. The glutathione conjugates are further metabolized to mercapturic acids by the sequential activity of γ-glutamyltranspeptidase, cysteinylglycinase and N-acetyltransferase (Figure 2). Isothiocyanate metabolites can be measured in the urine, and are highly correlated with dietary intake of cruciferous vegetables [61]. There is growing evidence that metabolites generated via the mercapturic acid pathway can contribute to the biological activity of dietary isothiocyanates, such as SFN (see below) [67,68].

Figure 2
Metabolism of isothiocyanates via the mercapturic acid pathway (adapted from [3,4])

Indoles from cruciferous vegetables have received considerable interest as cancer chemoprotective agents, including studies of their bioavailability in vivo. In the acidic environment of the stomach, I3C molecules can combine with each other to form a complex mixture of biologically active compounds, known collectively as acid condensation products [69]. Although numerous acid condensation products of I3C have been identified, some of the most prominent include the dimer 3,3′-diindolylmethane (DIM) and a cyclic trimer (CT) (Figure 3). The biological activities of individual acid condensation products differ from those of I3C and may be responsible for most of the biological effects attributed to I3C [70,71]. Information about the metabolism of I3C and its acid condensation products is limited. Oxidative metabolites indole-3-carboxylic acid and lesser amounts of indole-3-carboxaldehyde have been detected in the plasma of mice fed I3C [71].

Figure 3
Indole-3-carbinol and its acid condensation products

6. Effects on Xenobiotic Metabolism

Biotransformation enzymes play important roles in the metabolism and elimination of a variety of xenobiotics, including drugs, toxins and carcinogens. In general, phase I biotransformation enzymes catalyze reactions that increase the reactivity of hydrophobic (fat-soluble) compounds, preparing them for reactions catalyzed by phase II biotransformation enzymes. Reactions catalyzed by phase II enzymes generally increase water solubility and promote the elimination of the compound from the body [1]. Bifunctional and monofunctional inducers, including those from cruciferous vegetables, have been reviewed by Kensler and colleagues [72].

6.1. Modulation of Biotransformation by Isothiocyanates

Some chemical carcinogens require biotransformation by phase I enzymes, such as those of the cytochrome P450 (CYP) family, in order to become active carcinogens that are capable of binding DNA and inducing mutations. Inhibition of specific CYP enzymes involved in carcinogen activation inhibits the development of cancer in animal models [64]. Isothiocyanates, including PEITC and BITC, have been found to inhibit carcinogen activation by CYP enzymes in animal studies [73,74]. In human volunteers, ingestion of a watercress homogenate, which is rich in the glucosinolate precursor of PEITC, increased the area under the plasma concentration-time curve for the drug chlorzoxazone, suggesting that CYP2E1 activity was inhibited [74].

Many isothiocyanates, particularly SFN, are potent inducers of phase II enzymes in cultured human cells [4]. Phase II enzymes, including GSTs, UDP-glucuronosyl transferases (UGTs), NADPH quinone oxidoreductase (NQO) and glutamate cysteine ligase play important roles in protecting cells from DNA damage by carcinogens and reactive oxygen species [75]. The genes for these and other phase II enzymes contain a specific sequence of DNA called an antioxidant response element (ARE). Isothiocyanates have been shown to increase phase II enzyme activity by increasing the transcription of genes that contain an ARE [76]. Limited data from clinical trials suggests that glucosinolate-rich foods can increase phase II enzyme activity in humans. When smokers consumed 170 g/d (6 oz/d) of watercress, urinary excretion of glucuronidated nicotine metabolites increased significantly, suggesting UGT activity increased [77]. Brussels sprouts are rich in a number of glucosinolates, including precursors of AITC and SFN. Consumption of 300 g/d (11 oz/d) of Brussels sprouts for a week significantly increased plasma and intestinal GST levels in nonsmoking men [78].

6.2. Modulation of Biotransformation by Indoles

Aggarwal and Ichikawa recently reviewed [79] the molecular targets and anticancer potential of I3C and its indole derivatives, as well as the evidence for tumor promotion in some studies (see below). Acid condensation products of I3C, particularly DIM and indole[3,2-b]carbazole (ICZ), can bind in the cytoplasm to the aryl hydrocarbon receptor (Ahr) [70,80]. Binding allows the Ahr to enter the nucleus where it forms a complex with the AhR nuclear translocator (Arnt) protein. This Ahr/Arnt complex binds to specific DNA sequences in genes known as xenobiotic response elements (XRE) and enhances their transcription [81]. Genes for a number of CYP enzymes and several phase II enzymes are known to contain XREs. Thus, oral consumption of I3C results in the formation of acid condensation products that can increase the activity of certain phase I and phase II enzymes [8083]. Increasing the activity of biotransformation enzymes is generally considered a beneficial effect because the elimination of potential carcinogens or toxins is enhanced. However, there is a potential for adverse effects, because some procarcinogens require biotransformation by phase I enzymes to become active carcinogens [84].

7. Effects on Estrogen Metabolism and Activity

Estrogens, including 17β-estradiol, exert their estrogenic effects by binding to estrogen receptors (ERs). Within the nucleus, the estrogen-ER complex can bind to DNA sequences in genes known as estrogen response elements (EREs), and enhance the transcription of estrogen-responsive genes [85]. Some ER-mediated effects, such as those that promote cellular proliferation in the breast and uterus, can increase the risk of developing estrogen-sensitive cancers [86].

7.1. Effects of Indole-3-Carbinol on Estrogen Receptor Activity

When added to breast cancer cells in culture, I3C has been found to inhibit the transcription of estrogen-responsive genes stimulated by 17β-estradiol [87,88]. Acid condensation products of I3C that bind and activate Ahr may also inhibit the transcription of ER-responsive genes by competing for coactivators or increasing ER degradation [81,89]. In contrast, some studies in cell culture [90,91] and animal models [92] have found that acid condensation products of I3C enhance the transcription of ER-responsive genes. Further research is needed to determine the nature of the stimulatory and inhibitory effects of I3C and its acid-condensation products on ER-responsive gene transcription under conditions that are relevant to human cancer risk.

7.2. Effects of Indole-3-Carbinol on Estrogen Metabolism

As mentioned above, 17β-estradiol can be converted to 16α-hydroxyestrone (16αOHE1) or 2-hydroxyestrone (2OHE1), sometimes viewed as ‘bad’ and ‘good’ estrogenic metabolites, respectively. In controlled clinical trials, oral supplementation with 300–400 mg/d of I3C has consistently increased urinary 2OHE1 levels or urinary 2OHE1:16αOHE1 ratios in women [9397]. Supplementation with 108 mg/day of DIM also increased urinary 2OHE1 levels in postmenopausal women [98]. However, the relationship between urinary 2OHE1:16OHE1 ratios and breast cancer risk is not clear. Although women with breast cancer had lower urinary ratios of 2OHE1:16αOHE1 in several small case-control studies [3537], larger case-control and prospective cohort studies have not found significant associations between urinary 2OHE1:16αOHE1 ratios and breast cancer risk [3840].

8. Other Anticarcinogenic Properties

8.1. Induction of Cell Cycle Arrest and/or Apoptosis

After a cell divides, it passes through a sequence of stages known as the cell cycle before dividing again. Following DNA damage, the cell cycle can be transiently arrested to allow for DNA repair, or alternatively there can be activation of pathways leading to apoptosis if the damage cannot be repaired [99]. Defective cell cycle regulation may result in the propagation of mutations that contribute to the development of cancer. A number of isothiocyanates, including AITC, BITC, PEITC and SFN, have been found to induce cell cycle arrest in cultured cells [4], and similar findings have been reported for indoles, such as I3C [100,101]. However, the physiological relevance of these cell culture studies is unclear since it is not known how much I3C is available to the tissue after oral administration in humans (see Metabolism and Bioavailability above) [102]. Unlike normal cells, cancer cells proliferate rapidly and lose the ability to respond to cell death signals by undergoing apoptosis. I3C and DIM have been found to induce apoptosis when added to cultured prostate [100], breast [103,104] and cervical cancer cells [105]. Isothiocyanates has been found to inhibit proliferation and induce apoptosis in a number of cancer cell lines, as reviewed by Hecht [74].

8.2. Inhibition of Tumor Invasion and Angiogenesis

Limited evidence in cell culture experiments suggests that I3C and DIM can inhibit the invasion of normal tissue by cancer cells [88] and inhibit the development of new blood vessels (angiogenesis) required by tumors to fuel their rapid growth [106]. There is some evidence that isothiocyanates, such as SFN, might similarly affect tumor invasion and angiogenesis (reviewed in [107]), although further studies are warranted in vivo.

8.3. Anti-inflammatory Activity

The nuclear factor kappa B (NF-κB) has a pivotal role in cancer chemoprevention due to its involvement in tumor cell growth, proliferation, angiogenesis, invasion, apoptosis, and survival [108]. Inflammation promotes cellular proliferation and inhibits apoptosis, increasing the risk of developing cancer [109]. Among their reported anticancer properties, SFN and PEITC have been found to decrease the secretion of inflammatory signaling molecules by white blood cells and to decrease DNA binding of NF-κB, a pro-inflammatory transcription factor [107,110,111].

8.4. Epigenetic Modulation

In the nucleus, DNA is associated with basic proteins called histones. In general, acetylation of histones by histone acetyltransferases (HATs) makes DNA more accessible to transcription factors, which bind DNA and activate gene transcription. Deacetylation of histones by histone deacetylases (HDACs) restricts the access of transcription factors to DNA. Acetylation and deacetylation of nuclear histones is an important cellular mechanism for regulating gene transcription [112]. However, the balance between HAT and HDAC activities that exists in normal cells may be disrupted in cancer cells. Compounds that inhibit HDACs have the potential to induce the transcription of tumor suppressor proteins that promote differentiation and apoptosis in transformed (precancerous) cells [6]. AITC and SFN metabolites inhibit HDAC activity in cultured cancer cells and in animals models, and SFN-rich broccoli sprouts inhibited HDAC activity in peripheral blood mononuclear cells of human volunteers [68,113116].

There also is growing evidence for transplacental cancer chemopreventive effects of I3C and other dietary modulators, involving changes in DNA promoter methylation, chromatin remodeling, and expression of imprinted genes [117120]. This avenue of epigenetic research is likely to gain increasing interest in the future.

8.5. Anti-viral and Anti-bacterial Effects

Infection with certain strains of human papilloma virus (HPV) is an important risk factor for cervical cancer [19]. Transgenic mice that express cancer-promoting HPV genes develop cervical cancer with chronic 17β-estradiol administration. In this model, feeding I3C markedly reduced the number of mice that developed cervical cancer [121]. A small placebo-controlled trial in women examined the effect of oral I3C supplementation on the progression of precancerous cervical lesions classified as cervical intraepithelial neoplasia (CIN) [122]. After 12 weeks, 4 out of the 8 women who took 200 mg/d had complete regression of CIN and 4 out of the 9 who took 400 mg/d had complete regression, while none of the 10 women who took a placebo had complete regression. Although these preliminary results are encouraging, larger controlled clinical trials are needed to determine the efficacy of I3C supplementation for preventing the progression of precancerous lesions of the cervix [123].

Bacterial infection with H. pylori is associated with a marked increase in the risk of gastric cancer [124]. Purified SFN inhibited the growth and killed multiple strains of H. pylori in the test tube and in tissue culture, including antibiotic resistant strains [125]. In an animal model of H. pylori infection, SFN administration for 5 days eradicated H. pylori from 8 out of 11 xenografts of human gastric tissue implanted in immune-compromised mice [126]. However, in a small clinical trial, consumption of up to 56 g/d (2 oz/d) of glucoraphanin-rich broccoli sprouts for a week was associated with H. pylori eradication in only 3 out of 9 gastritis patients [127]. Further research is needed to determine whether SFN or foods rich in its precursor glucobrassicin will be helpful in the treatment of H. pylori infection in humans [128130].

9. Adverse effects

In vivo, naturally occurring isothiocyanates and their metabolites have been found to inhibit the development of chemically-induced cancers of the lung, liver, esophagus, stomach, small intestine, colon and mammary gland (breast) in a variety of animal models [67,73]. When administered before or at the same time as the carcinogen, oral I3C has been found to inhibit the development of cancer in a variety of animal models and tissues, including cancers of the mammary gland (breast) [131,132], stomach [133], colon [134,135], lung [136] and liver [137]. However, a number of studies found that I3C actually promoted or enhanced the development of cancer when administered chronically after the carcinogen (post initiation). The cancer promoting effects of I3C were first reported in a trout model of liver cancer [138,139]. However, I3C also has been found to promote or enhance cancer of the liver [140,141], thyroid [142], colon [143] and uterus [144] in rats. The long-term effects of I3C supplementation on cancer risk in humans are not known, but the contradictory results of animal studies have led some to caution against the widespread use of I3C and DIM supplements in humans until the potential risks versus benefits are better understood [141,145,146].

10. Future Perspectives

Although epidemiological studies provide some evidence that higher intakes of cruciferous vegetables are associated with decreased cancer risk in humans [7], it is difficult to determine whether such protective effects are related to isothiocyanates or other factors associated with cruciferous vegetable consumption. Investigators have attempted to calculate human isothiocyanate exposure based on assessments of cruciferous vegetable intake and measurements of the maximal amounts of isothiocyanates that can be liberated from various cruciferous vegetables in the laboratory [61]. Case-control studies using this technique found that dietary isothiocyanate intakes were significantly lower in Chinese women [14] and US men [16] diagnosed with lung cancer than in cancer-free control groups. Assessing dietary intake of cruciferous vegetables may not accurately measure an individual’s exposure to isothiocyanates, since other factors may alter the amount of isothiocyanates formed and absorbed (see Metabolism and Bioavailability above). Measuring urinary excretion of isothiocyanates and their metabolites may provide a better assessment of isothiocyanate exposure [42,61], but few studies have examined relationships between urinary isothiocyanate excretion and cancer risk. In a prospective study, Chinese men with detectable levels of urinary isothiocyanates at baseline were at significantly lower risk of developing lung cancer over the next ten years than men with undetectable levels [17]. A case-control study found that urinary isothiocyanate excretion was significantly lower in Chinese women diagnosed with breast cancer than in a cancer-free control group [147]. In contrast, cruciferous vegetable intake estimated from a food frequency questionnaire was not associated with breast cancer risk in the same study. One important frontier in the study of cruciferous vegetables and health is to obtain better assessment of physiologically-relevant concentrations of individual vegetable constituents and their tissue metabolites. This difficult area is being developed in human trails, facilitated by such analytical techniques as LC-MS-MS and accelerator mass spectrometry [148150].

11. Intake Recommendations

Although many organizations, including the National Cancer Institute, recommend the consumption of 5–9 servings (2½–4½ cups) of fruits and vegetables daily [151], separate recommendations for cruciferous vegetables have not been established. Much remains to be learned regarding cruciferous vegetable consumption and cancer prevention, but the results of some prospective cohort studies suggest that adults should aim for at least 5 weekly servings of cruciferous vegetables [12,51,152].

12. Summary

Cruciferous vegetables are unique in that they are rich sources of sulfur-containing compounds known as glucosinolates. Chopping or chewing cruciferous vegetables results in the formation of bioactive glucosinolate hydrolysis products, such as isothiocyanates and indole-3-carbinol. High intake of cruciferous vegetables has been associated with lower risk of lung and colorectal cancer in some epidemiological studies, but there is evidence that genetic polymorphisms may influence the effective of cruciferous vegetables on human cancer risk. Although glucosinolate hydrolysis products may alter the metabolism or activity of sex hormones in ways that could inhibit the development of hormone-sensitive cancers, evidence of an inverse association between cruciferous vegetable intake and breast or prostate cancer in humans is limited and inconsistent. Many organizations, including the National Cancer Institute, recommend the consumption of 5–9 servings (2½–4 ½ cups) of fruits and vegetables daily, but separate recommendations for cruciferous vegetables have not been established.

For specific constituents of cruciferous vegetables, isothiocyanates are derived from the hydrolysis of glucosinolates, and compounds such as sulforaphane may help prevent cancer by enhancing the elimination of potential carcinogens from the body and increasing the transcription of tumor suppressor proteins, including those silenced by epigenetic mechanisms. Epidemiological studies provide some evidence that human exposure to isothiocyanates through cruciferous vegetable consumption may decrease cancer risk, but the protective effects may be influenced by individual genetic variation in the metabolism and elimination of isothiocyanates from the body. Glucosinolates are present in relatively high concentrations in cruciferous vegetables, but cooking, particularly boiling and microwaving at high power, may decrease the bioavailability of isothiocyanates.

Among indoles, indole-3-carbinol is derived from the hydrolysis of glucobrassicin, and in the acidic environment of the stomach it forms a number of biologically active indole acid condensation products, such as 3,3′-diindolylmethane (DIM) and related oligomers. I3C has been found to inhibit the development of cancer in animals when given before or at the same time as a carcinogen. However, in some cases, I3C enhanced the development of cancer in animals when administered after a carcinogen. The contradictory results of animal studies have led some experts to caution against the widespread use of I3C and DIM supplements for cancer prevention in humans until their potential risks and benefits are better understood. Although I3C and DIM supplementation have been found to alter urinary estrogen metabolite profiles in women, the effects of I3C and DIM on breast cancer risk are not known. Small preliminary trials in humans suggest that I3C supplementation may be beneficial in treating conditions related to human papilloma virus infection, such as cervical intraepithelial neoplasia and recurrent respiratory papillomatosis, but larger randomized controlled trials are needed.

Footnotes

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References

1. Kristal AR, Lampe JW. Brassica vegetables and prostate cancer risk: a review of the epidemiological evidence. Nutr Cancer. 2002;42:1–9. [PubMed]
2. Drewnowski A, Gomez-Carneros C. Bitter taste, phytonutrients, and the consumer: a review. Am J Clin Nutr. 2000;72:1424–35. [PubMed]
3. Holst B, Williamson G. A critical review of the bioavailability of glucosinolates and related compounds. Nat Prod Rep. 2004;21:425–47. [PubMed]
4. Zhang Y. Cancer-preventive isothiocyanates: measurement of human exposure and mechanism of action. Mutat Res. 2004;555:173–90. [PubMed]
5. Liu RH. Potential synergy of phytochemicals in cancer prevention: mechanism of action. J Nutr. 2004;134:3479S–85S. [PubMed]
6. McNaughton SA, Marks GC. Development of a food composition database for the estimation of dietary intakes of glucosinolates, the biologically active constituents of cruciferous vegetables. Br J Nutr. 2003;90:687–97. [PubMed]
7. Verhoeven DT, Goldbohm RA, van Poppel G, Verhagen H, van den Brandt PA. Epidemiological studies on brassica vegetables and cancer risk. Cancer Epidemiol Biomarkers Prev. 1996;5:733–48. [PubMed]
8. Willett W. Oxford University Press; New York: 1998. pp. 148–56.
9. Miller AB, Altenburg HP, Bueno-de-Mesquita B, Boshuizen HC, Agudo A, Berrino F, et al. Fruits and vegetables and lung cancer: findings from the european prospective investigation into cancer and nutrition. Int J Cancer. 2004;108:269–76. [PubMed]
10. Smith-Warner SA, Spiegelman D, Yaun SS, Albanes D, Beeson WL, van den Brandt PA, et al. Fruits, vegetables and lung cancer: a pooled analysis of cohort studies. Int J Cancer. 2003;107:1001–11. [PubMed]
11. Voorrips LE, Goldbohm RA, Verhoeven DT, van Poppel GA, Sturmans F, Hermus RJ, et al. Vegetable and fruit consumption and lung cancer risk in the Netherlands Cohort Study on diet and cancer. Cancer Causes Control. 2000;11:101–15. [PubMed]
12. Feskanich D, Ziegler RG, Michaud DS, Giovannucci EL, Speizer FE, Willett WC, et al. Prospective study of fruit and vegetable consumption and risk of lung cancer among men and women. J Natl Cancer Inst. 2000;92:1812–23. [PubMed]
13. Neuhouser ML, Patterson RE, Thornquist MD, Omenn GS, King IB, Goodman GE. Fruits and vegetables are associated with lower lung cancer risk only in the placebo arm of the beta-carotene and retinol efficacy trial (CARET) Cancer Epidemiol Biomarkers Prev. 2003;12:350–8. [PubMed]
14. Zhao B, Seow A, Lee EJ, Poh WT, Teh M, Eng P, et al. Dietary isothiocyanates, glutathione S-transferase -M1, -T1 polymorphisms and lung cancer risk among Chinese women in Singapore. Cancer Epidemiol Biomarkers Prev. 2001;10:1063–7. [PubMed]
15. Lewis S, Brennan P, Nyberg F, Ahrens W, Constantinescu V, Mukeria A, et al. Re: Spitz, M. R., Duphorne, C. M., Detry, M. A., Pillow, P. C., Amos, C. I., Lei, L., de Andrade, M., Gu, X., Hong, W. K., and Wu, X. Dietary intake of isothiocyanates: evidence of a joint effect with glutathione S-transferase polymorphisms in lung cancer risk. Cancer Epidemiol. Biomark. Prev. 9: 1017–1020, 2000. Cancer Epidemiol Biomarkers Prev. 2001;10:1105–6. [PubMed]
16. Spitz MR, Duphorne CM, Detry MA, Pillow PC, Amos CI, Lei L, et al. Dietary intake of isothiocyanates: evidence of a joint effect with glutathione S-transferase polymorphisms in lung cancer risk. Cancer Epidemiol Biomarkers Prev. 2000;9:1017–20. [PubMed]
17. London SJ, Yuan JM, Chung FL, Gao YT, Coetzee GA, Ross RK, et al. Isothiocyanates, glutathione S-transferase M1 and T1 polymorphisms, and lung-cancer risk: a prospective study of men in Shanghai, China. Lancet. 2000;356:724–9. [PubMed]
18. Walters DG, Young PJ, Agus C, Knize MG, Boobis AR, Gooderham NJ, et al. Cruciferous vegetable consumption alters the metabolism of the dietary carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in humans. Carcinogenesis. 2004;25:1659–69. [PubMed]
19. Benito E, Obrador A, Stiggelbout A, Bosch FX, Mulet M, Munoz N, et al. A population-based case-control study of colorectal cancer in Majorca. I. Dietary factors. Int J Cancer. 1990;45:69–76. [PubMed]
20. West DW, Slattery ML, Robison LM, Schuman KL, Ford MH, Mahoney AW, et al. Dietary intake and colon cancer: sex- and anatomic site-specific associations. Am J Epidemiol. 1989;130:883–94. [PubMed]
21. Young TB, Wolf DA. Case-control study of proximal and distal colon cancer and diet in Wisconsin. Int J Cancer. 1988;42:167–75. [PubMed]
22. Graham S, Dayal H, Swanson M, Mittelman A, Wilkinson G. Diet in the epidemiology of cancer of the colon and rectum. J Natl Cancer Inst. 1978;61:709–14. [PubMed]
23. Kojima M, Wakai K, Tamakoshi K, Tokudome S, Toyoshima H, Watanabe Y, et al. Diet and colorectal cancer mortality: results from the Japan Collaborative Cohort Study. Nutr Cancer. 2004;50:23–32. [PubMed]
24. McCullough ML, Robertson AS, Chao A, Jacobs EJ, Stampfer MJ, Jacobs DR, et al. A prospective study of whole grains, fruits, vegetables and colon cancer risk. Cancer Causes Control. 2003;14:959–70. [PubMed]
25. Michels KB, Edward G, Joshipura KJ, Rosner BA, Stampfer MJ, Fuchs CS, et al. Prospective study of fruit and vegetable consumption and incidence of colon and rectal cancers. J Natl Cancer Inst. 2000;92:1740–52. [PubMed]
26. Steinmetz KA, Kushi LH, Bostick RM, Folsom AR, Potter JD. Vegetables, fruit, and colon cancer in the Iowa Women’s Health Study. Am J Epidemiol. 1994;139:1–15. [PubMed]
27. Voorrips LE, Goldbohm RA, van Poppel G, Sturmans F, Hermus RJ, van den Brandt PA. Vegetable and fruit consumption and risks of colon and rectal cancer in a prospective cohort study: The Netherlands Cohort Study on Diet and Cancer. Am J Epidemiol. 2000;152:1081–92. [PubMed]
28. Turner F, Smith G, Sachse C, Lightfoot T, Garner RC, Wolf CR, et al. Vegetable, fruit and meat consumption and potential risk modifying genes in relation to colorectal cancer. Int J Cancer. 2004;112:259–64. [PubMed]
29. Seow A, Yuan JM, Sun CL, Van Den Berg D, Lee HP, Yu MC. Dietary isothiocyanates, glutathione S-transferase polymorphisms and colorectal cancer risk in the Singapore Chinese Health Study. Carcinogenesis. 2002;23:2055–61. [PubMed]
30. Slattery ML, Kampman E, Samowitz W, Caan BJ, Potter JD. Interplay between dietary inducers of GST and the GSTM-1 genotype in colon cancer. Int J Cancer. 2000;87:728–33. [PubMed]
31. Lin HJ, Probst-Hensch NM, Louie AD, Kau IH, Witte JS, Ingles SA, et al. Glutathione transferase null genotype, broccoli, and lower prevalence of colorectal adenomas. Cancer Epidemiol Biomarkers Prev. 1998;7:647–52. [PubMed]
32. Telang NT, Suto A, Wong GY, Osborne MP, Bradlow HL. Induction by estrogen metabolite 16 alpha-hydroxyestrone of genotoxic damage and aberrant proliferation in mouse mammary epithelial cells. J Natl Cancer Inst. 1992;84:634–8. [PubMed]
33. Yuan F, Chen DZ, Liu K, Sepkovic DW, Bradlow HL, Auborn K. Anti-estrogenic activities of indole-3-carbinol in cervical cells: implication for prevention of cervical cancer. Anticancer Res. 1999;19:1673–80. [PubMed]
34. Bradlow HL, Telang NT, Sepkovic DW, Osborne MP. 2-hydroxyestrone: the ‘good’ estrogen. J Endocrinol. 1996;150 Suppl:S259–65. [PubMed]
35. Ho GH, Luo XW, Ji CY, Foo SC, Ng EH. Urinary 2/16 alpha-hydroxyestrone ratio: correlation with serum insulin-like growth factor binding protein-3 and a potential biomarker of breast cancer risk. Ann Acad Med Singapore. 1998;27:294–9. [PubMed]
36. Kabat GC, Chang CJ, Sparano JA, Sepkovie DW, Hu XP, Khalil A, et al. Urinary estrogen metabolites and breast cancer: a case-control study. Cancer Epidemiol Biomarkers Prev. 1997;6:505–9. [PubMed]
37. Schneider J, Kinne D, Fracchia A, Pierce V, Anderson KE, Bradlow HL, et al. Abnormal oxidative metabolism of estradiol in women with breast cancer. Proc Natl Acad Sci USA. 1982;79:3047–51. [PubMed]
38. Cauley JA, Zmuda JM, Danielson ME, Ljung BM, Bauer DC, Cummings SR, et al. Estrogen metabolites and the risk of breast cancer in older women. Epidemiology. 2003;14:740–4. [PubMed]
39. Meilahn EN, De Stavola B, Allen DS, Fentiman I, Bradlow HL, Sepkovic DW, et al. Do urinary oestrogen metabolites predict breast cancer? Guernsey III cohort follow-up Br J Cancer. 1998;78:1250–5. [PMC free article] [PubMed]
40. Ursin G, London S, Stanczyk FZ, Gentzschein E, Paganini-Hill A, Ross RK, et al. Urinary 2-hydroxyestrone/16alpha-hydroxyestrone ratio and risk of breast cancer in postmenopausal women. J Natl Cancer Inst. 1999;91:1067–72. [PubMed]
41. Ambrosone CB, McCann SE, Freudenheim JL, Marshall JR, Zhang Y, Shields PG. Breast cancer risk in premenopausal women is inversely associated with consumption of broccoli, a source of isothiocyanates, but is not modified by GST genotype. J Nutr. 2004;134:1134–8. [PubMed]
42. Fowke JH, Chung FL, Jin F, Qi D, Cai Q, Conaway C, et al. Urinary isothiocyanate levels, brassica, and human breast cancer. Cancer Res. 2003;63:3980–6. [PubMed]
43. Terry P, Wolk A, Persson I, Magnusson C. Brassica vegetables and breast cancer risk. JAMA. 2001;285:2975–7. [PubMed]
44. Smith-Warner SA, Spiegelman D, Yaun SS, Adami HO, Beeson WL, van den Brandt PA, et al. Intake of fruits and vegetables and risk of breast cancer: a pooled analysis of cohort studies. JAMA. 2001;285:769–76. [PubMed]
45. Singh AV, Xiao D, Lew KL, Dhir R, Singh SV. Sulforaphane induces caspase-mediated apoptosis in cultured PC-3 human prostate cancer cells and retards growth of PC-3 xenografts in vivo. Carcinogenesis. 2004;25:83–90. [PubMed]
46. Sarkar FH, Li Y. Indole-3-carbinol and prostate cancer. J Nutr. 2004;134:3493S–8S. [PubMed]
47. Cohen JH, Kristal AR, Stanford JL. Fruit and vegetable intakes and prostate cancer risk. J Natl Cancer Inst. 2000;92:61–8. [PubMed]
48. Jain MG, Hislop GT, Howe GR, Ghadirian P. Plant foods, antioxidants, and prostate cancer risk: findings from case-control studies in Canada. Nutr Cancer. 1999;34:173–84. [PubMed]
49. Joseph MA, Moysich KB, Freudenheim JL, Shields PG, Bowman ED, Zhang Y, et al. Cruciferous vegetables, genetic polymorphisms in glutathione S-transferases M1 and T1, and prostate cancer risk. Nutr Cancer. 2004;50:206–13. [PubMed]
50. Kolonel LN, Hankin JH, Whittemore AS, Wu AH, Gallagher RP, Wilkens LR, et al. Vegetables, fruits, legumes and prostate cancer: a multiethnic case-control study. Cancer Epidemiol Biomarkers Prev. 2000;9:795–804. [PubMed]
51. Giovannucci E, Rimm EB, Liu Y, Stampfer MJ, Willett WC. A prospective study of cruciferous vegetables and prostate cancer. Cancer Epidemiol Biomarkers Prev. 2003;12:1403–9. [PubMed]
52. Hsing AW, McLaughlin JK, Schuman LM, Bjelke E, Gridley G, Wacholder S, et al. Diet, tobacco use, and fatal prostate cancer: results from the Lutheran Brotherhood Cohort Study. Cancer Res. 1990;50:6836–40. [PubMed]
53. Key TJ, Allen N, Appleby P, Overvad K, Tjonneland A, Miller A, et al. Fruits and vegetables and prostate cancer: no association among 1104 cases in a prospective study of 130544 men in the European Prospective Investigation into Cancer and Nutrition (EPIC) Int J Cancer. 2004;109:119–24. [PubMed]
54. Schuurman AG, Goldbohm RA, Dorant E, van den Brandt PA. Vegetable and fruit consumption and prostate cancer risk: a cohort study in The Netherlands. Cancer Epidemiol Biomarkers Prev. 1998;7:673–80. [PubMed]
55. Kristal AR, Stanford JL. Cruciferous vegetables and prostate cancer risk: confounding by PSA screening. Cancer Epidemiol Biomarkers Prev. 2004;13:1265. [PubMed]
56. Nothlings U, Wilkens LR, Murphy SP, Hankin JH, Henderson BE, Kolonel LN. Vegetable intake and pancreatic cancer risk: the multiethnic cohort study. Am J Epidemiol. 2006 Oct 26; epub ahead of print. [PubMed]
57. Larsson SC, Hakansson N, Naslund I, Bergkvist L, Wolk A. Fruit and vegetable consumption in relation to pancreatic cancer: a prospective study. Cancer Epidemiol Biomarkers Prev. 2006;15:301–305. [PubMed]
58. Chan JM, Wang F, Holly EA. Vegetable and fruit intake and pancreatic cancer in a population-based case-control study in the San Francisco bay area. Cancer Epidemiol Biomarkers Prev. 2005;14:2093–7. [PubMed]
59. Lampe JW, Peterson S. Brassica, biotransformation and cancer risk: genetic polymorphisms alter the preventive effects of cruciferous vegetables. J Nutr. 2002;132:2991–4. [PubMed]
60. Coles BF, Kadlubar FF. Detoxification of electrophilic compounds by glutathione S-transferase catalysis: determinants of individual response to chemical carcinogens and chemotherapeutic drugs? Biofactors. 2003;17:115–30. [PubMed]
61. Seow A, Shi CY, Chung FL, Jiao D, Hankin JH, Lee HP, et al. Urinary total isothiocyanate (ITC) in a population-based sample of middle-aged and older Chinese in Singapore: relationship with dietary total ITC and glutathione S-transferase M1/T1/P1 genotypes. Cancer Epidemiol Biomarkers Prev. 1998;7:775–81. [PubMed]
62. Shapiro TA, Fahey JW, Wade KL, Stephenson KK, Talalay P. Chemoprotective glucosinolates and isothiocyanates of broccoli sprouts: metabolism and excretion in humans. Cancer Epidemiol Biomarkers Prev. 2001;10:501–8. [PubMed]
63. Shapiro TA, Fahey JW, Wade KL, Stephenson KK, Talalay P. Human metabolism and excretion of cancer chemoprotective glucosinolates and isothiocyanates of cruciferous vegetables. Cancer Epidemiol Biomarkers Prev. 1998;7:1091–100. [PubMed]
64. Conaway CC, Getahun SM, Liebes LL, Pusateri DJ, Topham DK, Botero-Omary M, et al. Disposition of glucosinolates and sulforaphane in humans after ingestion of steamed and fresh broccoli. Nutr Cancer. 2000;38:168–78. [PubMed]
65. Rouzaud G, Young SA, Duncan AJ. Hydrolysis of glucosinolates to isothiocyanates after ingestion of raw or microwaved cabbage by human volunteers. Cancer Epidemiol Biomarkers Prev. 2004;13:125–31. [PubMed]
66. Verkerk R, van der Gaag MS, Dekker M, Jongen WM. Effects of processing conditions on glucosinolates in cruciferous vegetables. Cancer Lett. 1997;114:193–4. [PubMed]
67. Hecht SS, Carmella SG, Kenney PM, Low SH, Arakawa K, Yu MC. Effects of cruciferous vegetable consumption on urinary metabolites of the tobacco-specific lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in Singapore Chinese. Cancer Epidemiol Biomarkers Prev. 2004;13:997–1004. [PubMed]
68. Myzak MC, Karplus PA, Chung FL, Dashwood RH. A novel mechanism of chemoprotection by sulforaphane: inhibition of histone deacetylase. Cancer Res. 2004;64:5767–74. [PubMed]
69. Shertzer HG, Senft AP. The micronutrient indole-3-carbinol: implications for disease and chemoprevention. Drug Metabol Drug Interact. 2000;17:159–88. [PubMed]
70. Bjeldanes LF, Kim JY, Grose KR, Bartholomew JC, Bradfield CA. Aromatic hydrocarbon responsiveness-receptor agonists generated from indole-3-carbinol in vitro and in vivo: comparisons with 2,3,7,8-tetrachlorodibenzo-p-dioxin. Proc Natl Acad Sci USA. 1991;88:9543–7. [PubMed]
71. Anderton MJ, Manson MM, Verschoyle RD, Gescher A, Lamb JH, Farmer PB, et al. Pharmacokinetics and tissue disposition of indole-3-carbinol and its acid condensation products after oral administration to mice. Clin Cancer Res. 2004;10:5233–41. [PubMed]
72. Kensler TW, Curphey TJ, Maxiutenko Y, Roebuck BD. Chemoprotection by organosulfur inducers of phase 2 enzymes: dithiolethiones and dithiins. Drug Metabol Drug Interact. 2000;17:3–22. [PubMed]
73. Conaway CC, Yang YM, Chung FL. Isothiocyanates as cancer chemopreventive agents: their biological activities and metabolism in rodents and humans. Curr Drug Metab. 2002;3:233–55. [PubMed]
74. Hecht SS. Inhibition of carcinogenesis by isothiocyanates. Drug Metab Rev. 2000;32:395–411. [PubMed]
75. Kensler TW, Egner PA, Wang JB, Zhu YR, Zhang BC, Lu PX, et al. Chemoprevention of hepatocellular carcinoma in aflatoxin endemic areas. Gastroenterology. 2004;127:S310–8. [PubMed]
76. Dinkova-Kostova AT, Holtzclaw WD, Cole RN, Itoh K, Wakabayashi N, Katoh Y, et al. Direct evidence that sulfhydryl groups of Keap1 are the sensors regulating induction of phase 2 enzymes that protect against carcinogens and oxidants. Proc Natl Acad Sci U S A. 2002;99:11908–13. [PubMed]
77. Hecht SS, Carmella SG, Murphy SE. Effects of watercress consumption on urinary metabolites of nicotine in smokers. Cancer Epidemiol Biomarkers Prev. 1999;8:907–13. [PubMed]
78. Verhagen H, de Vries A, Nijhoff WA, Schouten A, van Poppel G, Peters WH, et al. Effect of Brussels sprouts on oxidative DNA-damage in man. Cancer Lett. 1997;114:127–30. [PubMed]
79. Aggarwal BB, Ichikawa H. Molecular targets and anticancer potential of indole-3-carbinol and its derivatives. Cell Cycle. 2005;4:1201–15. [PubMed]
80. Bonnesen C, Eggleston IM, Hayes JD. Dietary indoles and isothiocyanates that are generated from cruciferous vegetables can both stimulate apoptosis and confer protection against DNA damage in human colon cell lines. Cancer Res. 2001;61:6120–30. [PubMed]
81. Safe S. Molecular biology of the Ah receptor and its role in carcinogenesis. Toxicol Lett. 2001;120:1–7. [PubMed]
82. Nho CW, Jeffery E. The synergistic upregulation of phase II detoxification enzymes by glucosinolate breakdown products in cruciferous vegetables. Toxicol Appl Pharmacol. 2001;174:146–52. [PubMed]
83. Wallig MA, Kingston S, Staack R, Jefferey EH. Induction of rat pancreatic glutathione S-transferase and quinone reductase activities by a mixture of glucosinolate breakdown derivatives found in Brussels sprouts. Food Chem Toxicol. 1998;36:365–73. [PubMed]
84. Baird WM, Hooven LA, Mahadevan B. Carcinogenic polycyclic aromatic hydrocarbon-DNA adducts and mechanism of action. Environ Mol Mutagen. 2005;45:106–14. [PubMed]
85. Jordan VC, Schafer JM, Levenson AS, Liu H, Pease KM, Simons LA, et al. Molecular classification of estrogens. Cancer Res. 2001;61:6619–23. [PubMed]
86. Liehr JG. Is estradiol a genotoxic mutagenic carcinogen? Endocr Rev. 2000;21:40–54. [PubMed]
87. Ashok BT, Chen Y, Liu X, Bradlow HL, Mittelman A, Tiwari RK. Abrogation of estrogen-mediated cellular and biochemical effects by indole-3-carbinol. Nutr Cancer. 2001;41:180–7. [PubMed]
88. Meng Q, Goldberg ID, Rosen EM, Fan S. Inhibitory effects of indole-3-carbinol on invasion and migration in human breast cancer cells. Breast Cancer Res Treat. 2000;63:147–52. [PubMed]
89. Chen I, McDougal A, Wang F, Safe S. Aryl hydrocarbon receptor-mediated antiestrogenic and antitumorigenic activity of diindolylmethane. Carcinogenesis. 1998;19:1631–9. [PubMed]
90. Leong H, Riby JE, Firestone GL, Bjeldanes LF. Potent ligand-independent estrogen receptor activation by 3,3′-diindolylmethane is mediated by cross talk between the protein kinase A and mitogen-activated protein kinase signaling pathways. Mol Endocrinol. 2004;18:291–302. [PubMed]
91. Riby JE, Feng C, Chang YC, Schaldach CM, Firestone GL, Bjeldanes LF. The major cyclic trimeric product of indole-3-carbinol is a strong agonist of the estrogen receptor signaling pathway. Biochemistry. 2000;39:910–8. [PubMed]
92. Shilling AD, Carlson DB, Katchamart S, Williams DE. 3,3′-Diindolylmethane, a major condensation product of indole-3-carbinol, is a potent estrogen in the rainbow trout. Toxicol Appl Pharmacol. 2001;170:191–200. [PubMed]
93. Bradlow HL, Michnovicz JJ, Halper M, Miller DG, Wong GY, Osborne MP. Long-term responses of women to indole-3-carbinol or a high fiber diet. Cancer Epidemiol Biomarkers Prev. 1994;3:591–5. [PubMed]
94. McAlindon TE, Gulin J, Chen T, Klug T, Lahita R, Nuite M. Indole-3-carbinol in women with SLE: effect on estrogen metabolism and disease activity. Lupus. 2001;10:779–83. [PubMed]
95. Michnovicz JJ, Adlercreutz H, Bradlow HL. Changes in levels of urinary estrogen metabolites after oral indole-3-carbinol treatment in humans. J Natl Cancer Inst. 1997;89:718–23. [PubMed]
96. Michnovicz JJ. Increased estrogen 2-hydroxylation in obese women using oral indole-3-carbinol. Int J Obes Relat Metab Disord. 1998;22:227–9. [PubMed]
97. Wong GY, Bradlow L, Sepkovic D, Mehl S, Mailman J, Osborne MP. Dose-ranging study of indole-3-carbinol for breast cancer prevention. J Cell Biochem Suppl. 1997;28–29:111–6. [PubMed]
98. Dalessandri KM, Firestone GL, Fitch MD, Bradlow HL, Bjeldanes LF. Pilot study: effect of 3,3′-diindolylmethane supplements on urinary hormone metabolites in postmenopausal women with a history of early-stage breast cancer. Nutr Cancer. 2004;50:161–7. [PubMed]
99. Stewart ZA, Westfall MD, Pietenpol JA. Cell-cycle dysregulation and anticancer therapy. Trends Pharmacol Sci. 2003;24:139–45. [PubMed]
100. Chinni SR, Li Y, Upadhyay S, Koppolu PK, Sarkar FH. Indole-3-carbinol (I3C) induced cell growth inhibition, G1 cell cycle arrest and apoptosis in prostate cancer cells. Oncogene. 2001;20:2927–36. [PubMed]
101. Cover CM, Hsieh SJ, Tran SH, Hallden G, Kim GS, Bjeldanes LF, et al. Indole-3-carbinol inhibits the expression of cyclin-dependent kinase-6 and induces a G1 cell cycle arrest of human breast cancer cells independent of estrogen receptor signaling. J Biol Chem. 1998;273:3838–47. [PubMed]
102. Stresser DM, Williams DE, Griffin DA, Bailey GS. Mechanisms of tumor modulation by indole-3-carbinol. Disposition and excretion in male Fischer 344 rats. Drug Metab Dispos. 1995;23:965–75. [PubMed]
103. Hong C, Kim HA, Firestone GL, Bjeldanes LF. 3,3′-Diindolylmethane (DIM) induces a G(1) cell cycle arrest in human breast cancer cells that is accompanied by Sp1-mediated activation of p21(WAF1/CIP1) expression. Carcinogenesis. 2002;23:1297–305. [PubMed]
104. Howells LM, Gallacher-Horley B, Houghton CE, Manson MM, Hudson EA. Indole-3-carbinol inhibits protein kinase B/Akt and induces apoptosis in the human breast tumor cell line MDA MB468 but not in the nontumorigenic HBL100 line. Mol Cancer Ther. 2002;1:1161–72. [PubMed]
105. Chen D, Carter TH, Auborn KJ. Apoptosis in cervical cancer cells: implications for adjunct anti-estrogen therapy for cervical cancer. Anticancer Res. 2004;24:2649–56. [PubMed]
106. Chang X, Tou JC, Hong C, Kim HA, Riby JE, Firestone GL, et al. 3,3′-Diindolylmethane inhibits angiogenesis and the growth of transplantable human breast carcinoma in athymic mice. Carcinogenesis. 2005;26:771–8. [PubMed]
107. Myzak MC, Dashwood RH. Histone deacetylases as targets for dietary cancer preventive agents: lessons learned with butyrate, diallyl disulfide, and sulforaphane. Curr Drug Targets. 2006;7:443–52. [PubMed]
108. Xu C, Shen G, Chen C, Gelinas C, Kong AN. Suppression of NFκB and NFκB-regulated gene expression by sulforaphane and PEITC through IkappaBalpha, IKK pathway in human prostate cancer PC-3 cells. Oncogene. 2005;24:4486–95. [PubMed]
109. Steele VE, Hawk ET, Viner JL, Lubet RA. Mechanisms and applications of non-steroidal anti-inflammatory drugs in the chemoprevention of cancer. Mutat Res. 2003;523–524:137–44. [PubMed]
110. Gerhauser C, Klimo K, Heiss E, Neumann I, Gamal-Eldeen A, Knauft J, et al. Mechanism-based in vitro screening of potential cancer chemopreventive agents. Mutat Res. 2003;523–524:163–72. [PubMed]
111. Heiss E, Herhaus C, Klimo K, Bartsch H, Gerhauser C. Nuclear factor kappa B is a molecular target for sulforaphane-mediated anti-inflammatory mechanisms. J Biol Chem. 2001;276:32008–15. [PubMed]
112. Mei S, Ho AD, Mahlknecht U. Role of histone deacetylase inhibitors in the treatment of cancer (Review) Int J Oncol. 2004;25:1509–19. [PubMed]
113. Lea MA, Rasheed M, Randolph VM, Khan F, Shareef A, desBordes C. Induction of histone acetylation and inhibition of growth of mouse erythroleukemia cells by S-allylmercaptocysteine. Nutr Cancer. 2002;43:90–102. [PubMed]
114. Myzak MC, Dashwood WM, Orner GA, Ho E, Dashwood RH. Sulforaphane inhibits histone deacetylase in vivo and suppresses tumorigenesis in Apcmin mice. FASEB J. 2006;20:506–8. [PMC free article] [PubMed]
115. Myzak MC, Hardin K, Wang R, Dashwood RH, Ho E. Sulforaphane inhibits histone deacetylase activity in BPH-1, LnCaP and PC-3 prostate epithelial cells. Carcinogenesis. 2006;27:811–9. [PMC free article] [PubMed]
116. Dashwood RH, Myzak MC, Ho E. Dietary HDAC inhibitors: time to rethink weak ligands in cancer chemoprevention? Carcinogenesis. 2006;27:344–9. [PMC free article] [PubMed]
117. Yu Z, Mahadevan B, Lohr CV, Fischer KA, Louderback MA, Krueger SK, et al. Indole-3-carbinol in the maternal diet provides chemoprotection for the fetus against transplacental carcinogenesis by the polycyclic aromatic hydrocarbon, dibenzo[a,l]pyrene. Carcinogenesis. 2006 May 16; [epub ahead of print] [PubMed]
118. Hilakivi-Clarke L, Cho E, Cabanes A, DeAssis S, Olivo S, Helferich W, et al. Dietary modulation of pregnancy estrogen levels and breast cancer risk among female rat offspring. Clin Cancer Res. 2002;8:3601–10. [PubMed]
119. Ghoshal K, Li X, Datta J, Bai S, Pogribny I, Pogribny M, et al. A folate- and methyl-deficient diet alters the expression of DNA methyltransferases and methyl CpG binding proteins involved in epigenetic gene silencing in livers of F344 rats. J Nutr. 2006;136:1522–7. [PMC free article] [PubMed]
120. Dolinoy DC, Weidman JR, Waterland RA, Jirtle RL. Maternal genistein alters coat color and protects Avy mouse offspring from obesity by modifying the fetal epigenome. Environ Health Perspect. 2006;114:567–72. [PMC free article] [PubMed]
121. Jin L, Qi M, Chen DZ, Anderson A, Yang GY, Arbeit JM, et al. Indole-3-carbinol prevents cervical cancer in human papilloma virus type 16 (HPV16) transgenic mice. Cancer Res. 1999;59:3991–7. [PubMed]
122. Bell MC, Crowley-Nowick P, Bradlow HL, Sepkovic DW, Schmidt-Grimminger D, Howell P, et al. Placebo-controlled trial of indole-3-carbinol in the treatment of CIN. Gynecol Oncol. 2000;78:123–9. [PubMed]
123. Stanley M. Chapter 17: Genital human papillomavirus infections--current and prospective therapies. J Natl Cancer Inst Monogr. 2003:117–24. [PubMed]
124. Normark S, Nilsson C, Normark BH, Hornef MW. Persistent infection with Helicobacter pylori and development of gastric cancer. Adv Cancer Res. 2003;90:63–89. [PubMed]
125. Fahey JW, Haristoy X, Dolan PM, Kensler TW, Scholtus I, Stephenson KK, et al. Sulforaphane inhibits extracellular, intracellular, and antibiotic-resistant strains of Helicobacter pylori and prevents benzo[a]pyrene-induced stomach tumors. Proc Natl Acad Sci U S A. 2002;99:7610–5. [PubMed]
126. Haristoy X, Angioi-Duprez K, Duprez A, Lozniewski A. Efficacy of sulforaphane in eradicating Helicobacter pylori in human gastric xenografts implanted in nude mice. Antimicrob Agents Chemother. 2003;47:3982–4. [PMC free article] [PubMed]
127. Galan MV, Kishan AA, Silverman AL. Oral broccoli sprouts for the treatment of Helicobacter pylori infection: a preliminary report. Dig Dis Sci. 2004;49:1088–90. [PubMed]
128. Sato K, Kawakami N, Ohtsu T, Tsutsumi A, Miyazaki S, Masumoto T, et al. Broccoli consumption and chronic atrophic gastritis among Japanese males: an epidemiological investigation. Acta Med Okayama. 2004;58:127–33. [PubMed]
129. Haristoy X, Fahey JW, Scholtus I, Lozniewski A. Evaluation of the antimicrobial effects of several isothiocyanates on Helicobacter pylori. Planta Med. 2005;71:326–30. [PubMed]
130. Hara M, Hanaoka T, Kobayashi M, Otani T, Adachi HY, Montani A, et al. Cruciferous vegetables, mushrooms, and gastrointestinal cancer risks in a multicenter, hospital-based case-control study in Japan. Nutr Cancer. 2003;46:138–47. [PubMed]
131. Grubbs CJ, Steele VE, Casebolt T, Juliana MM, Eto I, Whitaker LM, et al. Chemoprevention of chemically-induced mammary carcinogenesis by indole-3-carbinol. Anticancer Res. 1995;15:709–16. [PubMed]
132. Bradlow HL, Michnovicz J, Telang NT, Osborne MP. Effects of dietary indole-3-carbinol on estradiol metabolism and spontaneous mammary tumors in mice. Carcinogenesis. 1991;12:1571–4. [PubMed]
133. Wattenberg LW, Loub WD. Inhibition of polycyclic aromatic hydrocarbon-induced neoplasia by naturally occurring indoles. Cancer Res. 1978;38:1410–3. [PubMed]
134. Wargovich MJ, Chen CD, Jimenez A, Steele VE, Velasco M, Stephens LC, et al. Aberrant crypts as a biomarker for colon cancer: evaluation of potential chemopreventive agents in the rat. Cancer Epidemiol Biomarkers Prev. 1996;5:355–60. [PubMed]
135. Guo D, Schut HA, Davis CD, Snyderwine EG, Bailey GS, Dashwood RH. Protection by chlorophyllin and indole-3-carbinol against 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-induced DNA adducts and colonic aberrant crypts in the F344 rat. Carcinogenesis. 1995;16:2931–7. [PubMed]
136. Morse MA, LaGreca SD, Amin SG, Chung FL. Effects of indole-3-carbinol on lung tumorigenesis and DNA methylation induced by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and on the metabolism and disposition of NNK in A/J mice. Cancer Res. 1990;50:2613–7. [PubMed]
137. Dashwood RH, Arbogast DN, Fong AT, Hendricks JD, Bailey GS. Mechanisms of anti-carcinogenesis by indole-3-carbinol: detailed in vivo DNA binding dose-response studies after dietary administration with aflatoxin B1. Carcinogenesis. 1988;9:427–32. [PubMed]
138. Dashwood RH, Fong AT, Williams DE, Hendricks JD, Bailey GS. Promotion of aflatoxin B1 carcinogenesis by the natural tumor modulator indole-3-carbinol: influence of dose, duration, and intermittent exposure on indole-3-carbinol promotional potency. Cancer Res. 1991;51:2362–5. [PubMed]
139. Oganesian A, Hendricks JD, Pereira CB, Orner GA, Bailey GS, Williams DE. Potency of dietary indole-3-carbinol as a promoter of aflatoxin B1-initiated hepatocarcinogenesis: results from a 9000 animal tumor study. Carcinogenesis. 1999;20:453–8. [PubMed]
140. Kim DJ, Lee KK, Han BS, Ahn B, Bae JH, Jang JJ. Biphasic modifying effect of indole-3-carbinol on diethylnitrosamine-induced preneoplastic glutathione S-transferase placental form-positive liver cell foci in Sprague-Dawley rats. Jpn J Cancer Res. 1994;85:578–83. [PubMed]
141. Stoner G, Casto B, Ralston S, Roebuck B, Pereira C, Bailey G. Development of a multi-organ rat model for evaluating chemopreventive agents: efficacy of indole-3-carbinol. Carcinogenesis. 2002;23:265–72. [PubMed]
142. Kim DJ, Han BS, Ahn B, Hasegawa R, Shirai T, Ito N, et al. Enhancement by indole-3-carbinol of liver and thyroid gland neoplastic development in a rat medium-term multiorgan carcinogenesis model. Carcinogenesis. 1997;18:377–81. [PubMed]
143. Pence BC, Buddingh F, Yang SP. Multiple dietary factors in the enhancement of dimethylhydrazine carcinogenesis: main effect of indole-3-carbinol. J Natl Cancer Inst. 1986;77:269–76. [PubMed]
144. Yoshida M, Katashima S, Ando J, Tanaka T, Uematsu F, Nakae D, et al. Dietary indole-3-carbinol promotes endometrial adenocarcinoma development in rats initiated with N-ethyl-N′-nitro-N-nitrosoguanidine, with induction of cytochrome P450s in the liver and consequent modulation of estrogen metabolism. Carcinogenesis. 2004;25:2257–64. [PubMed]
145. Dashwood RH. Indole-3-carbinol: anticarcinogen or tumor promoter in brassica vegetables? Chem Biol Interact. 1998;110:1–5. [PubMed]
146. Lee BM, Park KK. Beneficial and adverse effects of chemopreventive agents. Mutat Res. 2003;523–524:265–78. [PubMed]
147. Fowke JH, Shu XO, Dai Q, Shintani A, Conaway CC, Chung FL, et al. Urinary isothiocyanate excretion, brassica consumption, and gene polymorphisms among women living in Shanghai, China. Cancer Epidemiol Biomarkers Prev. 2003;12:1536–9. [PubMed]
148. Mullen W, Edwards CA, Crozier A. Absorption, excretion and metabolite profiling of methyl-, glucuronyl-, glucosyl- and sulpho-conjugates of quercetin in human plasma and urine after ingestion of onions. Br J Nutr. 2006;96:107–16. [PubMed]
149. Vermeulen M, van den Berg R, Freidig AP, van Bladeren PJ, Vaes WH. Association between consumption of cruciferous vegetables and condiments and excretion in urine of isothiocyanate mercapturic acids. J Agric Food Chem. 2006;54:5350–8. [PubMed]
150. Brown K, Dingley KH, Turteltaub KW. Accelerator mass spectrometry for biomedical research. Methods Enzymol. 2005;402:423–43. [PubMed]
151. National Cancer Institute (2005), Vol. 2005.
152. Michaud DS, Spiegelman D, Clinton SK, Rimm EB, Willett WC, Giovannucci EL. Fruit and vegetable intake and incidence of bladder cancer in a male prospective cohort. J Natl Cancer Inst. 1999;91:605–13. [PubMed]