Urinary total isothiocyanates and colorectal cancer: a prospective study of men in Shanghai, China

Validity of dietary isothiocyanate intake estimates from a food frequency questionnaire using 24 h urinary isothiocyanate excretion as an objective biomarker: the JPHC-NEXT protocol area

BACKGROUND/OBJECTIVES

Isothiocyanate (ITC) is formed via the hydrolysis of glucosinolates by myrosinase, found in cruciferous vegetables. Although myrosinase is inactivated by the cooking process, no studies have incorporated the effect of cooking into the estimation of dietary ITC intake or evaluated the validity. We evaluated the validity of dietary ITC intake estimated from a food frequency questionnaire (FFQ), and urinary ITC levels using 24 h urine samples or a WFR (weighed food record), and evaluated the reproducibility of dietary ITC in two FFQs administered at an interval of 1-year.

SUBJECTS/METHODS

The JPHC-NEXT Protocol Area included a total of 255 middle-aged participants across Japan. We calculated dietary ITC intake from WFR and two FFQs by assuming that cooked cruciferous vegetables contain zero ITC. Urinary ITC excretion was measured at two points during summer and winter. The validity and reproducibility of dietary ITC intake estimated by FFQ were assessed using Spearman's correlation coefficients.

RESULTS

Although we observed a moderate correlation between dietary ITC intake derived from a 12-day WFR and urinary ITC excretion, notwithstanding the cooking process, the correlation between dietary ITC intake estimated by FFQ and mean urinary ITC excretion was low. However, the correlation was improved when we compared urinary ITC excretion and a 3-day WFR or FFQ collected during winter. Our FFQ showed good reproducibility.

CONCLUSION

Although seasonality is a critical factor, dietary ITC intake estimated using an FFQ showed moderate validity and reproducibility and can be used in future epidemiological studies.

Metabolic Fate of Dietary Glucosinolates and Their Metabolites: A Role for the Microbiome

Robust evidence shows that phytochemicals from cruciferous vegetables, like broccoli, are associated with numerous health benefits. The anti-cancer properties of these foods are attributed to bioactive isothiocyanates (ITCs) and indoles, phytochemicals generated from biological precursor compounds called glucosinolates. ITCs, and particularly sulforaphane (SFN), are of intense interest as they block the initiation, and suppress the progression of cancer, through genetic and epigenetic mechanisms. The efficacy of these compounds is well-demonstrated in cell culture and animal models, however, high levels of inter-individual variation in absorption and excretion of ITCs is a significant barrier to the use of dietary glucosinolates to prevent and treat disease. The source of inter-individual ITC variation has yet to be fully elucidated and the gut microbiome may play a key role. This review highlights evidence that the gut microbiome influences the metabolic fate and activity of ITCs. Human feeding trials have shown inter-individual variations in gut microbiome composition coincides with variations in ITC absorption and excretion, and some bacteria produce ITCs from glucosinolates. Additionally, consumption of cruciferous vegetables can alter the composition of the gut microbiome and shift the physiochemical environment of the gut lumen, influencing the production of phytochemicals. Microbiome and diet induced changes to ITC metabolism may lead to the decrease of cancer fighting phytochemicals such as SFN and increase the production of biologically inert ones like SFN-nitrile. We conclude by offering perspective on the use of novel “omics” technologies to elucidate the interplay of the gut microbiome and ITC formation.

Composition of the Gut Microbiome Influences Production of Sulforaphane-Nitrile and Iberin-Nitrile from Glucosinolates in Broccoli Sprouts

Isothiocyanates, such as sulforaphane and iberin, derived from glucosinolates (GLS) in cruciferous vegetables, are known to prevent and suppress cancer development. GLS can also be converted by bacteria to biologically inert nitriles, such as sulforaphane-nitrile (SFN-NIT) and iberin-nitrile (IBN-NIT), but the role of the gut microbiome in this process is relatively undescribed and SFN-NIT excretion in humans is unknown. An ex vivo fecal incubation model with in vitro digested broccoli sprouts and 16S sequencing was utilized to explore the role of the gut microbiome in SFN- and IBN-NIT production. SFN-NIT excretion was measured among human subjects following broccoli sprout consumption. The fecal culture model showed high inter-individual variability in nitrile production and identified two sub-populations of microbial communities among the fecal cultures, which coincided with a differing abundance of nitriles. The Clostridiaceae family was associated with high levels, while individuals with a low abundance of nitriles were more enriched with taxa from the Enterobacteriaceae family. High levels of inter-individual variation in urine SFN-NIT levels were also observed, with peak excretion of SFN-NIT at 24 h post broccoli sprout consumption. These results suggest that nitrile production from broccoli, as opposed to isothiocyanates, could be influenced by gut microbiome composition, potentially lowering efficacy of cruciferous vegetable interventions.

Phenethyl Isothiocyanate-Containing Carbomer Gel for Use against Squamous Cell Carcinoma

It is currently estimated that one in every five Americans will develop skin cancer during their lifetime. Squamous cell carcinoma (SCC) is a common type of skin cancer that can develop due to the skin’s exposure to the sun. Herein, we prepared a topical gel containing 0.5% v/w phenethyl isothiocyanate (PEITC) for the treatment of SCC. PEITC is a naturally occurring isothiocyanate that has been shown to have efficacy against various types of cancer in preclinical studies. We first incorporated PEITC into a carbomer gel. A uniform formulation was prepared, and its viscosity was appropriate for topical application. We then demonstrated the release of PEITC from the gel into and through a Strat-M skin-like membrane. Finally, the effects of the PEITC-containing gel were tested against SCC and normal keratinocytes skin cells in culture, and these results were compared to those obtained for free 5-fluoruracil (5-FU), a commonly used skin-cancer drug. Our results show that a homogeneous PEITC-containing topical gel can be prepared and used to kill SCC cells. Thus, our formulation may be useful for treating SCC in the clinic.

Cruciferous vegetables and colorectal cancer risk: a hospital-based matched case-control study in Northeast China

BACKGROUND/OBJECTIVES

Conflicting results have been reported on the association of cruciferous vegetable intake and colorectal cancer risk. This study aimed to clarify the relationship of cruciferous vegetables and colorectal cancer among individuals in Northeast China, where large amounts of cruciferous vegetables are consumed habitually.

SUBJECTS/METHODS

We conducted a hospital-based case-control study in the First Hospital of China Medical University, the Shengjing Hospital of China Medical University and the First Hospital of Dalian Medical University from 2009 to 2011. Patients in the study were matched individually by age, gender, and city of residence. The study ultimately included 833 case-control pairs. A structured questionnaire was applied to collect data on general characteristics, dietary habits, and selected dietary intake. Differences between cases and controls were ascertained with the chi-square test or the Mann-Whitney U test. Unconditional logistic regression was employed to compute odds ratios (ORs) and 95% confidence intervals (CIs). Stratified analyses were conducted by gender.

RESULTS

In the total study cohort, no significant association was found between total cruciferous vegetable intake and colorectal cancer risk. The adjusted OR for the highest versus the lowest intake was 0.83 (95% CI: 0.59-1.18). In stratification analyses by gender, reduced colorectal cancer risk was related to higher consumption of total cruciferous vegetables in women but not in men. Significant inverse correlations were found in analyses of individual cruciferous vegetables, including greens (OR = 0.47; 95% CI: 0.32-0.68), cabbage (OR = 0.61; 95% CI: 0.44-0.86), and cauliflower (OR = 0.66; 95% CI: 0.48-0.92).

CONCLUSIONS

No significant association was found between total cruciferous vegetable intake and colorectal cancer risk. However, specific types of cruciferous vegetables might have protective roles against colorectal cancer.

Cruciferous Vegetables, Isothiocyanates, and Bladder Cancer Prevention

Bladder cancer is a significant health burden due to its high prevalence, risk of mortality, morbidity, and high cost of medical care. Epidemiologic evidence suggests that diets rich in cruciferous vegetables, particularly broccoli, are associated with lower bladder cancer risk. Phytochemicals in cruciferous vegetables, such as glucosinolates, which are enzymatically hydrolyzed to bioactive isothiocyanates, are possible mediators of an anticancer effect. In vitro studies have shown inhibition of bladder cancer cell lines, cell cycle arrest, and induction of apoptosis by these isothiocyanates, in particular sulforaphane and erucin. Although not yet completely understood, many mechanisms of anticancer activity at the steps of cancer initiation, promotion, and progression have been attributed to these isothiocyanates. They target multiple pathways including the adaptive stress response, phase I/II enzyme modulation, pro-growth, pro-survival, pro-inflammatory signaling, angiogenesis, and even epigenetic modulation. Multiple in vivo studies have shown the bioavailability of isothiocyanates and their antitumoral effects. Although human studies are limited, they support oral bioavailability with reasonable plasma and urine concentrations achieved. Overall, both cell and animal studies support a potential role for isothiocyanates in bladder cancer prevention and treatment. Future studies are necessary to examine clinically relevant outcomes and define guidelines on ameliorating the bladder cancer burden.

Role of Urinary Biomarkers in the Diagnosis of Adenoma and Colorectal Cancer: A Systematic Review and Meta-Analysis

The growing interest in enhancing and spreading colorectal cancer (CRC) screening has been stimulating the exploration of novel biomarkers with greater sensitivity and specificity than immunochemical faecal occult blood test (iFOBT). The present study provides i) a systematic review of the urinary biomarkers that have been tested to achieve early CRC diagnosis and assess the risk of colorectal adenoma and adenocarcinoma, and ii) a meta-analysis of the data regarding the urinary prostaglandin (PG) metabolite PGE-M. As regard to gene markers, we found significantly different percent methylation of the vimentin gene in CRC patients and healthy controls (HC) (p<0.0001). Respect to metabolism of nitrogenous bases, cytidine, 1-methyladenosine, and adenosine, have higher concentrations in CRC patients than in HC (respectively, p<0.01, p=0.01, and p<0.01). As regard to spermine we found that N1,N12 diacetyl spermine (DiAcSpm) and N1, N8 diacetylspermidine (DiAcSpd) were significantly higher in CRC than in HC (respectively p=0.01 and p<0.01). Respect to PGE-M, levels were higher in CRC than in those with multiple polyposis (p<0.006) and HC subjects (p<0.0004). PGE-M seems to be the most interesting and promising urinary marker for CRC and adenoma risk assessment and for CRC screening. In conclusion, evidence suggests that urinary biomarker could have a potential role as urinary biomarkers in the diagnosis of colorectal cancer. Particularly, PGE-M seems to be the most promising urinary marker for CRC early detection.

Nutrients, foods, and colorectal cancer prevention

Diet has an important role in the development of colorectal cancer. In the past few decades, findings from extensive epidemiologic and experimental investigations have linked consumption of several foods and nutrients to the risk of colorectal neoplasia. Calcium, fiber, milk, and whole grains have been associated with a lower risk of colorectal cancer, and red meat and processed meat have been associated with an increased risk. There is substantial evidence for the potential chemopreventive effects of vitamin D, folate, fruits, and vegetables. Nutrients and foods also may interact, as a dietary pattern, to influence colorectal cancer risk. Diet likely influences colorectal carcinogenesis through several interacting mechanisms. These include the direct effects on immune responsiveness and inflammation, and the indirect effects of overnutrition and obesity-risk factors for colorectal cancer. Emerging evidence also implicates the gut microbiota as an important effector in the relationship between diet and cancer. Dietary modification therefore has the promise of reducing colorectal cancer incidence.

Cruciferous vegetables and risk of colorectal neoplasms: a systematic review and meta-analysis

Evidence shows cruciferous vegetables exhibit chemoprotective properties, commonly attributed to their rich source of isothiocyanates. However, epidemiological data examining the association between cruciferous vegetable intake and colorectal neoplasms have been inconclusive. This meta-analysis examines the epidemiological evidence to characterize the association between cruciferous vegetable intake and risk of developing colorectal neoplasms. Thirty-three articles were included in the meta-analysis after a literature search of electronic databases. Subgroup analysis for individual cruciferae types (n = 8 studies) and GST polymorphism (n = 8 studies) were performed. Pooled adjusted odds ratios (ORs) comparing highest and lowest categories of dietary pattern scores were calculated. Results show a statistically significant inverse association between cruciferous vegetable intake and colon cancer [OR = 0.84; 95% confidence interval (CI): 0.72-0.98; P value heterogeneity < 0.001]. Broccoli in particular exhibited protective benefits against colorectal (CRC) neoplasms (OR = 0.80; 95% CI: 0.65-0.99; P value heterogeneity = 0.02). Stratification by GST genotype reveals that the GSTT1 null genotype confers a reduction in CRC risk (OR = 0.78; 95% CI: 0.64-0.95; P value heterogeneity = 0.32). This study provides support to the hypothesis that cruciferous vegetable intake protects against cancer of the colon. This study also demonstrates the significance of gene-diet interactions and the importance of assessing individual cruciferous vegetables.

Cruciferous vegetables, glutathione S-transferase polymorphisms, and the risk of colorectal cancer among Chinese men

PURPOSE

To assess the associations between cruciferous vegetable (CV) intake, GST gene polymorphisms, and colorectal cancer (CRC) in a population of Chinese men.

METHODS

Using incidence density sampling, CRC cases (N = 340) diagnosed before December 31, 2010 within the Shanghai Men's Health Study were matched to noncases (N = 673). CV intake was assessed from a food frequency questionnaire and by isothiocyanate levels from spot urine samples. GSTM1 and GSTT1 were categorized as null (0 copies) versus non-null (1 or 2 copies). Conditional logistic regression was used to calculate odds ratios and 95% confidence intervals for the association between CV intake and GST gene variants with CRC, and statistical interactions were evaluated.

RESULTS

CRC risk was not associated with CV intake, whether measured by self-report or by urinary isothiocyanate nor with GST gene variants. No statistical interactions were detected between CV intake and GST gene variants on the odds of CRC. Stratifying by timing of urine sample collection and excluding CRC cases diagnosed in the first 2 years did not materially alter the results.

CONCLUSIONS

This study provides no evidence supporting the involvement of CV intake in the development of CRC in Chinese men.

Phenethyl isothiocyanate suppresses EGF-stimulated SAS human oral squamous carcinoma cell invasion by targeting EGF receptor signaling

Phenethyl isothiocyanate (PEITC) is a natural compound that is involved in chemoprevention as well as inhibition of cell growth and induction of apoptosis in several types of cancer cells. Previous studies have revealed that PEITC suppresses the invasion of AGS gastric and HT-29 colorectal cancer cells. However, the effects of PEITC on the metastasis of SAS oral cancer cells remain to be determined. Our results showed that PEITC treatment inhibited the invasion of EGF-stimulated SAS cells in a concentration-dependent manner, but appeared not to affect the cell viability. The expression and enzymatic activities of matrix metalloprotease-2 (MMP-2) and matrix metalloprotease-9 (MMP-9) were suppressed by PEITC. Concomitantly, we observed an increase in the protein expression of both tissue inhibitor of metalloproteinase-1 (TIMP-1) and -2 (TIMP-2) in treated cells. Furthermore, PEITC treatments decreased the protein phosphorylation of epidermal growth factor receptor (EGFR) and downstream signaling proteins including PDK1, PI3K (p85), AKT, phosphorylated IKK and IκB to inactivate NF-κB for the suppression of MMP-2 and MMP-9 expression. In addition, PEITC can trigger the MAPK signaling pathway through the increase in phosphorylated p38, JNK and ERK in treated cells. Our data indicate that PEITC is able to inhibit the invasion of EGF-stimulated SAS oral cancer cells by targeting EGFR and its downstream signaling molecules and finally lead to the reduced expression and enzymatic activities of both MMP-2 and MMP-9. These results suggest that PEITC is promising for the therapy of oral cancer metastasis.

Notch2 activation by benzyl isothiocyanate impedes its inhibitory effect on breast cancer cell migration

Benzyl isothiocyanate (BITC) is a promising anticancer constituent of edible cruciferous vegetables with in vivo efficacy against chemically induced as well as oncogene-driven breast cancer in experimental rodents. However, the mechanism underlying anticancer effect of BITC is not fully understood. This study was undertaken to determine the role of Notch signaling in anticancer responses to BITC as this pathway is often hyperactive in human breast cancer. Exposure of MCF-7, MDA-MB-231, and SUM159 human breast cancer cells to pharmacologic concentrations of BITC (2.5 and 5 μM) resulted in cleavage (activation) of Notch1, Notch2, and Notch4, which was accompanied by induction of γ-secretase complex components Presenilin1 and/or Nicastrin. The BITC-mediated cleavage of Notch was associated with its transcriptional activation as revealed by RBP-Jk and Hes-1A/B luciferase reporter assays. Inhibition of cell migration or cell viability resulting from BITC exposure was not influenced by pharmacological suppression of Notch1 using a γ-secretase inhibitor or RNA interference of Notch1 as well as Notch4. On the other hand, the BITC-mediated inhibition of cell migration, but not cell viability, was significantly augmented by siRNA and shRNA knockdown of Notch2 protein. Furthermore, the BITC-mediated inhibition of MDA-MB-231 xenograft growth in vivo was associated with a significant increase in nuclear levels of cleaved Notch2 and Hes-1 proteins. In conclusion, the results of this study indicate that (a) BITC treatment activates Notch2 in cultured and xenografted human breast cancer cells, and (b) Notch2 activation impedes inhibitory effect of BITC on cell migration.

Cancer chemoprevention mechanisms mediated through the Keap1-Nrf2 pathway

The cap'n'collar (CNC) bZIP transcription factor Nrf2 controls expression of genes for antioxidant enzymes, metal-binding proteins, drug-metabolising enzymes, drug transporters, and molecular chaperones. Many chemicals that protect against carcinogenesis induce Nrf2-target genes. These compounds are all thiol-reactive and stimulate an adaptive response to redox stress in cells. Such agents induce the expression of genes that posses an antioxidant response element (ARE) in their regulatory regions. Under normal homeostatic conditions, Nrf2 activity is restricted through a Keap1-dependent ubiquitylation by Cul3-Rbx1, which targets the CNC-bZIP transcription factor for proteasomal degradation. However, as the substrate adaptor function of Keap1 is redox-sensitive, Nrf2 protein evades ubiquitylation by Cul3-Rbx1 when cells are treated with chemopreventive agents. As a consequence, Nrf2 accumulates in the nucleus where it heterodimerizes with small Maf proteins and transactivates genes regulated through an ARE. In this review, we describe synthetic compounds and phytochemicals from edible plants that induce Nrf2-target genes. We also discuss evidence for the existence of different classes of ARE (a 16-bp 5'-TMAnnRTGABnnnGCR-3' versus an 11-bp 5'-RTGABnnnGCR-3', with or without the embedded activator protein 1-binding site 5'-TGASTCA-3'), species differences in the ARE-gene battery, and the identity of critical Cys residues in Keap1 required for de-repression of Nrf2 by chemopreventive agents.

Isothiocyanate exposure, glutathione S-transferase polymorphisms, and colorectal cancer risk

BACKGROUND

Isothiocyanates, compounds found primarily in cruciferous vegetables, have been shown in laboratory studies to possess anticarcinogenic activity. Glutathione S-transferases (GSTs) are involved in the metabolism and elimination of isothiocyanates; thus, genetic variations in these enzymes may affect in vivo bioavailability and the activity of isothiocyanates.

OBJECTIVE

The objective was to prospectively evaluate the association between urinary isothiocyanate concentrations and colorectal cancer risk as well as the potential modifying effect of GST genotypes on the association.

DESIGN

A nested case-control study of 322 cases and 1251 controls identified from the Shanghai Women's Health Study was conducted.

RESULTS

Urinary isothiocyanate concentrations were inversely associated with colorectal cancer risk; the inverse association was statistically significant or nearly significant in the GSTM1-null (P for trend = 0.04) and the GSTT1-null (P for trend = 0.07) genotype groups. The strongest inverse association was found among individuals with both the GSTM1-null and the GSTT1-null genotypes, with an adjusted odds ratio of 0.51 (95% CI: 0.27, 0.95), in a comparison of the highest with the lowest tertile of urinary isothiocyanates. No apparent associations between isothiocyanate concentration and colorectal cancer risk were found among individuals who carried either the GSTM1 or GSTT1 gene (P for interaction < 0.05).

CONCLUSION

This study suggests that isothiocyanate exposure may reduce the risk of colorectal cancer, and this protective effect may be modified by the GSTM1 and GSTT1 genes.

Dietary chemopreventive phytochemicals: too little or too much?

There is a large body of evidence that the consumption of fruit and vegetables can decrease the risk of cancer. However, the link between diet and health is extremely complex. Some dietary phytochemicals seem to offer protection in an exposure-related manner and many molecular targets and signaling pathways affected by phytochemicals have been discovered. Although in vitro studies have contributed significantly to our understanding, quite a number use concentrations orders of magnitude greater than those achievable in humans or toxic to normal tissues (exemplified by toxic concentrations of indole-3-carbinol, epigallocatechin-3-gallate, curcumin, and genistein for breast cells). Such studies may produce results that are physiologically irrelevant, thus hindering predictions of efficacy. Here, we argue for careful consideration to be given to the in vitro experimental conditions under which dietary phytochemicals are investigated. Design features, such as the use of appropriate nontoxic concentrations, extended treatment times, three-dimensional cultures, primary tumor cultures, and comparison of susceptibility of various cancer subtypes, should improve our understanding of their molecular targets. This in turn would facilitate predictions as to their potential usefulness in the clinic.

Nutrition and colon cancer prevention

PURPOSE OF REVIEW

In spite of improvements in care of colon cancer patients, prevention may enable potential patients to avoid cancer therapy. Although screening is direct and effective, dietary modification or low-risk chemopreventive agents might prevent colon cancer development. In this article, we review recent developments in colon cancer prevention, emphasizing nutrition.

RECENT FINDINGS

Epidemiologic findings continue to suggest that diet is related to colon cancer risk. These findings, although, are inconsistent enough to render dietary recommendations premature. An exciting recent discovery is that the combination of diflouromethylornithine and sulindac substantially decreases adenomatous polyp recurrence. Reliance upon clinical trials continues to grow as a means of testing prevention strategies.

SUMMARY

Prevention remains an important goal for reducing the burden of colon cancer. Screening has an important role, although it will probably not eliminate all colon cancer. Nutritional modification remains potentially valuable, although research has not yet identified the objects of nutritional intervention. NSAIDs hold promise as chemopreventive agents.

Ab initio investigation of the fragmentation of 5,5-diamino-substituted 1,4,2-oxathiazoles

The mechanism for the fragmentation of 5,5-diamino-1,4,2-oxathiazole derivatives has been studied at the CCSD(T)/6-311+G(3df,2p)//MP2/6-31+G(2df,p) level of theory. The calculations suggest that the fragmentation occurs via a stepwise process involving the formation of polar intermediates that lie in shallow potential wells. We find a large thermodynamic driving force for fragmentation, which together with a weakening of the C-S bond through electron donation by the amino substituents provides the impetus for a low-barrier fragmentation.

Urinary isothiocyanates; glutathione S-transferase M1, T1, and P1 polymorphisms; and risk of colorectal cancer: the Multiethnic Cohort Study

Although an association between diet, especially cruciferous vegetables, and colorectal cancer has been hypothesized, recent studies have been inconsistent with their findings. One possibility for the discrepant results is that the interaction with related genes has not generally been considered. The present study examined the associations among urinary isothiocyanates, glutathione S-transferase (GST) polymorphisms, and colorectal cancer risk in a case-control study nested within the Multiethnic Cohort Study, based in Hawaii and Los Angeles, California. We measured prediagnositic urinary isothiocyanate levels adjusted for creatinine and analyzed GSTM1, GSTT1, and GSTP1 polymorphisms in 173 cases and 313 matched controls, with biospecimens collected between 2001 and 2006. Conditional logistic regression was used to compute odds ratios and 95% confidence intervals (95% CI). A detectable amount of urinary isothiocyanates was associated with a 41% decrease in colorectal cancer risk (95% CI, 0.36-0.98). No significant, main-effect associations were seen with a homozygous deletion of the GSTM1 or GSTT1 polymorphism, or with the AG or GG genotypes for GSTP1 rs1695. There was a weak suggestion that for individuals with the GSTP1 AG or GG genotype, a detectable amount of isothiocyanates further decreases one's risk of colorectal cancer compared with those with the GSTP1 AA genotype, but the interaction term was not statistically significant (P = 0.09). This is only the second study published on the association between urinary isothiocyanates and colorectal cancer risk. The results suggest that further studies, with larger numbers, examining a possible interaction with the GSTP1 polymorphisms are warranted.