Direct modification of the proinflammatory cytokine macrophage migration inhibitory factor by dietary isothiocyanates

Allyl Isothiocyanate Maintains DHA-Containing Glycerophospholipids and Ameliorates the Cognitive Function Decline in OVX Mice

Low-temperature-induced fatty acid desaturation is highly conserved in animals, plants, and bacteria. Allyl isothiocyanate (AITC) is an agonist of the transient receptor potential ankyrin 1 (TRPA1), which is activated by various chemophysiological stimuli, including low temperature. However, whether AITC induces fatty acid desaturation remains unknown. We showed here that AITC increased levels of glycerophospholipids (GP) esterified with unsaturated fatty acids, especially docosahexaenoic acid (DHA) in TRPA1-expressing HEK cells. Additionally, GP-DHA including phosphatidylcholine (18:0/22:6) and phosphatidylethanolamine (18:0/22:6) was increased in the brain and liver of AITC-administered mice. Moreover, intragastrical injection of AITC in ovariectomized (OVX) female C57BL/6J mice dose-dependently shortened the Δlatency time determined by the Morris water maze test, indicating AITC ameliorated the cognitive function decline in these mice. Thus, the oral administration of AITC maintains GP-DHA in the liver and brain, proving to be a potential strategy for preventing cognitive decline.

Exploring the anti-inflammatory activity of sulforaphane

Dysregulation of innate immune responses can result in chronic inflammatory conditions. Glucocorticoids, the current frontline therapy, are effective immunosuppressive drugs but come with a trade-off of cumulative and serious side effects. Therefore, alternative drug options with improved safety profiles are urgently needed. Sulforaphane, a phytochemical derived from plants of the brassica family, is a potent inducer of phase II detoxification enzymes via nuclear factor-erythroid factor 2-related factor 2 (NRF2) signaling. Moreover, a growing body of evidence suggests additional diverse anti-inflammatory properties of sulforaphane through interactions with mediators of key signaling pathways and inflammatory cytokines. Multiple studies support a role for sulforaphane as a negative regulator of nuclear factor kappa-light chain enhancer of activated B cells (NF-κB) activation and subsequent cytokine release, inflammasome activation and direct regulation of the activity of macrophage migration inhibitory factor. Significantly, studies have also highlighted potential steroid-sparing activity for sulforaphane, suggesting that it may have potential as an adjunctive therapy for some inflammatory conditions. This review discusses published research on sulforaphane, including proposed mechanisms of action, and poses questions for future studies that might help progress our understanding of the potential clinical applications of this intriguing molecule.

Beneficial Health Effects of Glucosinolates-Derived Isothiocyanates on Cardiovascular and Neurodegenerative Diseases

Neurodegenerative diseases (NDDs) and cardiovascular diseases (CVDs) are illnesses that affect the nervous system and heart, all of which are vital to the human body. To maintain health of the human body, vegetable diets serve as a preventive approach and particularly Brassica vegetables have been associated with lower risks of chronic diseases, especially NDDs and CVDs. Interestingly, glucosinolates (GLs) and isothiocyanates (ITCs) are phytochemicals that are mostly found in the Cruciferae family and they have been largely documented as antioxidants contributing to both cardio- and neuroprotective effects. The hydrolytic breakdown of GLs into ITCs such as sulforaphane (SFN), phenylethyl ITC (PEITC), moringin (MG), erucin (ER), and allyl ITC (AITC) has been recognized to exert significant effects with regards to cardio- and neuroprotection. From past in vivo and/or in vitro studies, those phytochemicals have displayed the ability to mitigate the adverse effects of reactive oxidation species (ROS), inflammation, and apoptosis, which are the primary causes of CVDs and NDDs. This review focuses on the protective effects of those GL-derived ITCs, featuring their beneficial effects and the mechanisms behind those effects in CVDs and NDDs.

Chemoinformatic Analysis of Isothiocyanates: Their Impact in Nature and Medicine

Isothiocyanates (ITCs) have a significant impact on food and natural product chemistry. Several dietary components and food chemicals contain the isothiocyanate moiety. In addition, many ITCs interact with macromolecules of biological relevance, making these compounds relevant for potential therapeutic applications and disease prevention. However, there is a lack of systematic analysis of ITCs in chemical and biological databases. Herein, we conducted a comprehensive analysis of ITCs present in public domain databases, including natural products, food chemicals, macromolecular targets of drugs, and the Protein Data Bank. A total of 154 ITCs were found, which can be classified into seven categories: acyclic, cyclic, polycyclic, aromatic, polyaromatic, indolic, and glycosylated. 24 ITCs were reported in 18 vegetable sources, mainly in cruciferous vegetables (Brassica oleracea L.). Calculated properties of pharmaceutical relevance indicated that 11 % of the 154 ITCs would be suitable to be orally absorbed and 48 % permeate the blood-brain-barrier. It was also found that seven molecular targets have been co-crystallized with ITCs and the most frequent is the macrophage migration inhibitory factor. It is expected that this work will contribute to the sub-disciplines of natural products and food informatics.

Targeting Macrophage Migration Inhibitory Factor in Acute Pancreatitis and Pancreatic Cancer

Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine implicated in the pathogenesis of inflammation and cancer. It is produced by various cells and circulating MIF has been identified as a biomarker for a range of diseases. Extracellular MIF mainly binds to the cluster of differentiation 74 (CD74)/CD44 to activate downstream signaling pathways. These in turn activate immune responses, enhance inflammation and can promote cancer cell proliferation and invasion. Extracellular MIF also binds to the C-X-C chemokine receptors cooperating with or without CD74 to activate chemokine response. Intracellular MIF is involved in Toll-like receptor and inflammasome-mediated inflammatory response. Pharmacological inhibition of MIF has been shown to hold great promise in treating inflammatory diseases and cancer, including small molecule MIF inhibitors targeting the tautomerase active site of MIF and antibodies that neutralize MIF. In the current review, we discuss the role of MIF signaling pathways in inflammation and cancer and summarize the recent advances of the role of MIF in experimental and clinical exocrine pancreatic diseases. We expect to provide insights into clinical translation of MIF antagonism as a strategy for treating acute pancreatitis and pancreatic cancer.

Amelioration of oxidative stress, inflammation and liver function by nutraceuticals in rat model of hepatic cancer initiation induced by N-nitrosodiethylamine

Introduction: Nutraceuticals might serve as protective agent against liver cancer induced by pro-cancerous chemicals that initiate high oxidative stress, inflammation and affect DNA integrity. The aim of the present research was to study the prevention of hepatocellular carcinoma initiation induced by N-nitrosodiethylamine (NDEA) through treatment by nutraceuticals. Methods: Two nutraceuticals were prepared; the first (NI) was a mixture of different extracts of green tea, wheat germ and tomato, the second one (NII) was composed of extracts mixture of broccoli, hazelnuts and carrot. Total flavonoids and flavonols were determined in the nutraceuticals. Four groups of rats were run; the first served as control normal, the other three groups were treated by intraperitoneal injection of NDEA, one of these groups was designated as control NDEA, the other two groups (test groups) were treated daily with oral doses of NI and NII, respectively. The experiment continued for 8 weeks. Plasma transaminases, alkaline phosphatase and catalase activities, total protein, albumin, malondialdehyde (MDA) and tumor necrosis factor-α (TNF-α) along with liver MDA level and catalase activity were assessed. Results: NI showed higher flavonoids and lower flavonols than NII (P < 0.05). High oxidative stress and inflammation biomarkers, liver dysfunction, reduced plasma albumin and total protein were demonstrated in control NDEA compared to control normal (P < 0.05). Test groups showed significant improvement in all parameters (P < 0.05) compared to NDEA control. NI was superior in improving plasma transaminases and catalase activities, MDA and TNF-α levels and liver catalase activity compared to NII (P < 0.05). Conclusion: Both NI and NII might prevent liver cancer initiation during exposure to carcinogenic agents, NI being superior to NII.

The mother relationship between insulin resistance and non-alcoholic steatohepatitis: Glucosinolates hydrolysis products as a promising insulin resistance-modulator and fatty liver-preventer

Non-alcoholic fatty liver disease (NFLD) is one of the present public health problems which have no specific and effective treatment. The speed of the disease progression depends on the patient's lifestyle. Due to life stresses and lack of time, a high number of people depend on fast food containing a high amount of fats which one of the main causes of insulin resistance (IR). IR is one of the metabolic disorders which strongly intersected with molecular NAFLD and leading to its progression into non-alcoholic steatohepatitis (NASH). In this review, we introduced the updated statistics of NAFLD and NASH progression all over the world shows its importance, etiologies, and pathogenesis. Also, IR and its role in NASH initiation and progression explored, and current treatments with its limitations have been explained. Glucosinolates (GLS) is a group of phytochemicals which known by its potent hydrolysis products with promising anti-cancer effect. In this review, we have collected the recent experimental studies of different GLS hydrolysis products against IR and chronic liver diseases supported by our lab finding. Finally, we recommend this group of phytochemicals as promising molecules to be studied experimentally and clinically against a wide range of chronic liver diseases with an acceptable safety margin.

Therapeutic potential of sulfur-containing natural products in inflammatory diseases

Owing to the prevalence of chronic inflammation and its related disorders, there is a demand for novel therapeutic agents capable of preventing or suppressing inflammation. Natural products (NPs) are well established as an important resource for drug development and provide an almost infinite array of molecular entities. Sulfur-containing NPs (i.e., NPs containing one or more sulfur atoms) are abundant throughout nature, from bacteria to animals. The aim of this review was to survey the emerging evidence on role of sulfur-containing NPs, such as glutathione, garlic-derived sulfur compounds, Epipolythiodioxopiperazines (EPTs), Isothiocyanates (ITCs), and Ergothioneine (EGT), in the control of inflammation and to determine the possible underlying mechanisms. A discussion of how hydrogen sulfide (H₂S), an endogenous gaseous signaling molecule, links sulfur-containing NPs and their anti-inflammatory action is also performed. This review may help to further the development of sulfur-based compounds by providing a guide for structure-activity relationship-based modification for use in modern medicinal chemistry. However, as this field is still in its infancy, the review is concluded by an overview of the progression of these promising entities as therapeutic agents.

Immune modulation by the macrophage migration inhibitory factor (MIF) family: D-dopachrome tautomerase (DDT) is not (always) a backup system

Human macrophage migration inhibition factor (MIF) is a protein with cytokine and chemokine properties that regulates a diverse range of physiological functions related to innate immunity and inflammation. Most research has focused on the role of MIF in different inflammatory diseases. D-dopachrome tautomerase (DDT), a different molecule with structural similarities to MIF, which shares receptors and biological functions, has recently been reported, but little is known about its roles and mechanisms. In this review, we sought to understand the similarities and differences between these molecules by summarizing what is known about their different structures, receptors and mechanisms regulating their expression and biological activities with an emphasis on immunological aspects.

Metabolic targets of watercress and PEITC in MCF-7 and MCF-10A cells explain differential sensitisation responses to ionising radiation

PURPOSE

Watercress is a rich source of phytochemicals with anticancer potential, including phenethyl isothiocyanate (PEITC). We examined the potential for watercress extracts and PEITC to increase the DNA damage caused by ionising radiation (IR) in breast cancer cells and to be protective against radiation-induced collateral damage in healthy breast cells. The metabolic events that mediate such responses were explored using metabolic profiling.

METHODS

1H nuclear magnetic resonance spectroscopy-based metabolic profiling was coupled with DNA damage-related assays (cell cycle, Comet assay, viability assays) to profile the comparative effects of watercress and PEITC in MCF-7 breast cancer cells and MCF-10A non-tumorigenic breast cells with and without exposure to IR.

RESULTS

Both the watercress extract and PEITC-modulated biosynthetic pathways of lipid and protein synthesis and resulted in changes in cellular bioenergetics. Disruptions to the redox balance occurred with both treatments in the two cell lines, characterised by shifts in the abundance of glutathione. PEITC enhanced the sensitivity of the breast cancer cells to IR increasing the effectiveness of the cancer-killing process. In contrast, watercress-protected non-tumorigenic breast cells from radiation-induced damage. These effects were driven by changes in the cellular content of the antioxidant glutathione following exposure to PEITC and other phytochemicals in watercress.

CONCLUSION

These findings support the potential prophylactic impact of watercress during radiotherapy. Extracted compounds from watercress and PEITC differentially modulate cellular metabolism collectively enhancing the therapeutic outcomes of radiotherapy.

p53 mutant-type in human prostate cancer cells determines the sensitivity to phenethyl isothiocyanate induced growth inhibition

Background

We reported previously that phenethyl isothiocyanate (PEITC), a dietary compound, can reactivate p53^R175H mutant in vitro and in SK-BR-3 (p53^R175H) breast xenograft model resulting in tumor inhibition. Because of the diversity of human cancers with p53 mutations, these findings raise important questions whether this mechanism operates in different cancer types with same or different p53 mutations. In this study, we investigated whether PEITC recuses mutant p53 in prostate cancer cells harboring different types of p53 mutants, structural and contact, in vitro and in vivo.

Methods

Cell proliferation, cell apoptosis and cell cycle arrest assays were performed to examine the effects of PEITC on prostate cancer cell lines with p53 mutation(s), wild-type p53, p53 null or normal prostate cells in vitro. Western blot analysis was used to monitor the expression levels of p53 protein, activation of ATM and upregulation of canonical p53 targets. Immunoprecipitation, subcellular protein fraction and qRT-PCR was performed to determine change in conformation and restoration of transactivation functions/ inhibition of gain-of-function (GOF) activities to p53 mutant(s). Mice xenograft models were established to evaluate the antitumor efficacy of PEITC and PEITC-induced reactivation of p53 mutant(s) in vivo. Immunohistochemistry of xenograft tumor tissues was performed to determine effects of PEITC on expression of Ki67 and mutant p53 in vivo.

Results

We demonstrated that PEITC inhibits the growth of prostate cancer cells with different “hotspot” p53 mutations (structural and contact), however, preferentially towards structural mutants. PEITC inhibits proliferation and induces apoptosis by rescuing mutant p53 in p53^R248W contact (VCaP) and p53^R175H structural (LAPC-4) mutant cells with differential potency. We further showed that PEITC inhibits the growth of DU145 cells that co-express p53^P223L (structural) and p53^V274F (contact) mutants by targeting p53^P223L mutant selectively, but not p53^V274F. The mutant p53 restored by PEITC induces apoptosis in DU145 cells by activating canonical p53 targets, delaying cells in G1 phase and phosphorylating ATM. Importantly, PEITC reactivated p53^R175H and p53^P223L/V274F mutants in LAPC-4 and DU145 prostate xenograft models, respectively, resulting in significant tumor inhibition.

Conclusion

Our studies provide the first evidence that PEITC’s anti-cancer activity is cancer cell type-independent, but p53 mutant-type dependent.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1267-z) contains supplementary material, which is available to authorized users.

Phenethyl isothiocyanate stimulates glucose uptake through the Akt pathway in C2C12 myotubes

Phenethyl isothiocyanate (PEITC) is an aromatic isothiocyanate present in cruciferous vegetables. Several studies have shown that isothiocyanates regulate various intracellular signaling pathways, and thereby show anti-inflammatory and detoxifying activities. However, little is known about the effects of PEITC on glucose metabolism. In this study, we examined whether PEITC promotes glucose utilization in mouse skeletal muscle cells, C2C12 myotubes. PEITC induced glucose uptake, glucose transporter 4 (Glut4) translocation to the plasma membrane, and activation of Akt and ERK in C2C12 cells. Inhibition of Akt suppressed PEITC-induced Glut4 translocation and glucose uptake, whereas ERK inhibition did not. Furthermore, PEITC increased phosphorylation of ErbB2 and ErbB3. Treatment with a pan-ErbB inhibitor reduced Akt activation and the subsequent glucose uptake induced by PEITC. These results indicate that PEITC promotes glucose utilization through the ErbB/Akt pathway in C2C12 myotubes. PEITC may therefore serve as a dietary constituent with beneficial effects on the carbohydrate metabolism.

Abbreviations: PEITC: phenethyl isothiocyanate; Glut4: glucose transporter 4; PI3K: phosphatidylinositide 3-kinase; Nrf2: erythroid−2-related factor; ARE: antioxidant response element; HO−1: heme oxygenase−1; NRG: neuregulin

Yeast screening system reveals the inhibitory mechanism of cancer cell proliferation by benzyl isothiocyanate through down-regulation of Mis12

Benzyl isothiocyanate (BITC) is a naturally-occurring isothiocyanate derived from cruciferous vegetables. BITC has been reported to inhibit the proliferation of various cancer cells, which is believed to be important for the inhibition of tumorigenesis. However, the detailed mechanisms of action remain unclear. In this study, we employed a budding yeast Saccharomyces cerevisiae as a model organism for screening. Twelve genes including MTW1 were identified as the overexpression suppressors for the antiproliferative effect of BITC using the genome-wide multi-copy plasmid collection for S. cerevisiae. Overexpression of the kinetochore protein Mtw1 counteracts the antiproliferative effect of BITC in yeast. The inhibitory effect of BITC on the proliferation of human colon cancer HCT-116 cells was consistently suppressed by the overexpression of Mis12, a human orthologue of Mtw1, and enhanced by the knockdown of Mis12. We also found that BITC increased the phosphorylated and ubiquitinated Mis12 level with consequent reduction of Mis12, suggesting that BITC degrades Mis12 through an ubiquitin-proteasome system. Furthermore, cell cycle analysis showed that the change in the Mis12 level affected the cell cycle distribution and the sensitivity to the BITC-induced apoptosis. These results provide evidence that BITC suppresses cell proliferation through the post-transcriptional regulation of the kinetochore protein Mis12.

Covalent Modification of Phosphatidylethanolamine by Benzyl Isothiocyanate and the Resultant Generation of Ethanolamine Adduct as Its Metabolite

Benzyl isothiocyanate (BITC), a dietary isothiocyanate (ITC) derived from cruciferous vegetables, has anticancer properties. It is believed that the ITC moiety (-N═C═S) that reacts predominantly with thiol compounds plays a central role in triggering the activities resulting from these properties. Recent studies have demonstrated that ITCs also covalently modify amino moieties in a protein. In this study, we examined the chemical reaction between BITC and the aminophospholipid, phosphatidylethanolamine (PE), in the cell membrane or lipoprotein particle. To detect the BITC-modified PE, the bond between ethanolamine (EA) and phosphatidic acid in PE was cleaved using phospholipase D to form the BITC-EA adduct, which was then measured. BITC-EA was detected from the BITC-treated unilamellar liposome and low-density lipoprotein even with only a few micromoles of BITC treatment, suggesting that BITC might react with not only a thiol/amino group of a protein but also an amino moiety of an aminophospholipid. Moreover, after incorporating BITC-PE included in the liposomes into the cultured cells or after direct exposure of BITC to the cells, free BITC-EA was excreted and accumulated in the medium in a time-dependent manner. It indicates that an intracellular enzyme catalyzes the cleavage of BITC-PE to produce BITC-EA. Because the ITC-amine adduct is stable, the ITC-EA adduct could be a promising indicator of ITC exposure in vivo.

Phenethyl Isothiocyanate, a Dual Activator of Transcription Factors NRF2 and HSF1

Cruciferous vegetables are rich sources of glucosinolates which are the biogenic precursor molecules of isothiocyanates (ITCs). The relationship between the consumption of cruciferous vegetables and chemoprotection has been widely documented in epidemiological studies. Phenethyl isothiocyanate (PEITC) occurs as its glucosinolate precursor gluconasturtiin in the cruciferous vegetable watercress (Nasturtium officinale). PEITC has multiple biological effects, including activation of cytoprotective pathways, such as those mediated by the transcription factor nuclear factor erythroid 2 p45-related factor 2 (NRF2) and the transcription factor heat shock factor 1 (HSF1), and can cause changes in the epigenome. However, at high concentrations, PEITC leads to accumulation of reactive oxygen species and cytoskeletal changes, resulting in cytotoxicity. Underlying these activities is the sulfhydryl reactivity of PEITC with cysteine residues in its protein targets. This chemical reactivity highlights the critical importance of the dose of PEITC for achieving on-target selectivity, which should be carefully considered in the design of future clinical trials.

Advances and Insights for Small Molecule Inhibition of Macrophage Migration Inhibitory Factor

Macrophage migration inhibitory factor (MIF) is an upstream regulator of the immune response whose dysregulation is tied to a broad spectrum of inflammatory and proliferative disorders. As its complex signaling pathways and pleiotropic nature have been elucidated, it has become an attractive target for drug discovery. Remarkably, MIF is both a cytokine and an enzyme that functions as a keto-enol tautomerase. Strategies including in silico modeling, virtual screening, high-throughput screening, and screening of anti-inflammatory natural products have led to a large and diverse catalogue of MIF inhibitors as well as some understanding of the structure-activity relationships for compounds binding MIF's tautomerase active site. With possible clinical trials of some MIF inhibitors on the horizon, it is an opportune time to review the literature to seek trends, address inconsistencies, and identify promising new avenues of research.

The Fate of a Hapten - From the Skin to Modification of Macrophage Migration Inhibitory Factor (MIF) in Lymph Nodes

Skin (contact) allergy, the most prevalent form of immunotoxicity in humans, is caused by low molecular weight chemicals (haptens) that penetrate stratum corneum and modify endogenous proteins. The fate of haptens after cutaneous absorption, especially what protein(s) they react with, is largely unknown. In this study the fluorescent hapten tetramethylrhodamine isothiocyanate (TRITC) was used to identify hapten-protein conjugates in the local lymph nodes after topical application, as they play a key role in activation of the adaptive immune system. TRITC interacted with dendritic cells but also with T and B cells in the lymph nodes as shown by flow cytometry. Identification of the most abundant TRITC-modified protein in lymph nodes by tandem mass spectrometry revealed TRITC-modification of the N-terminal proline of macrophage migration inhibitory factor (MIF) – an evolutionary well-conserved protein involved in cell-mediated immunity and inflammation. This is the first time a hapten-modified protein has been identified in lymph nodes after topical administration of the hapten. Most haptens are electrophiles and can therefore modify the N-terminal proline of MIF, which has an unusually reactive amino group under physiological conditions; thus, modification of MIF by haptens may have an immunomodulating role in contact allergy as well as in other immunotoxicity reactions.

Physiological relevance of covalent protein modification by dietary isothiocyanates

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

Post-translational regulation of macrophage migration inhibitory factor: Basis for functional fine-tuning

Macrophage migration inhibitory factor (MIF) is a chemokine-like protein and an important mediator in the inflammatory response. Unlike most other pro-inflammatory cytokines, a number of cell types constitutively express MIF and secretion occurs from preformed stores. MIF is an evolutionarily conserved protein that shows a remarkable functional diversity, including specific binding to surface CD74 and chemokine receptors and the presence of two intrinsic tautomerase and oxidoreductase activities. Several studies have shown that MIF is subject to post-translational modification, particularly redox-dependent modification of the catalytic proline and cysteine residues. In this review, we summarize and discuss MIF post-translational modifications and their effects on the biological properties of this protein. We propose that the redox-sensitive residues in MIF will be modified at sites of inflammation and that this will add further depth to the functional diversity of this intriguing cytokine.

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MIF is a pro-inflammatory cytokine with tautomerase and oxidoreductase activity.

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MIF is susceptible to post-translational modifications, including redox modification.

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Oxidants and electrophiles generated at inflammatory sites can modify MIF.

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The biological consequences of redox modification need detailed characterization.

Translational opportunities for broad-spectrum natural phytochemicals and targeted agent combinations in breast cancer

Breast cancer (BC) prevention and therapy in the context of life-style risk factors and biological drivers is a major focus of developmental therapeutics in oncology. Obesity, alcohol, chronic estrogen signaling and smoking have distinct BC precipitating and facilitating effects that may act alone or in combination. A spectrum of signaling events including enhanced oxidative stress and changes in estrogen-receptor (ER)-dependent and -independent signaling drive the progression of BC. Breast tumors modulate ERα/ERβ ratio, upregulate proliferative pathways driven by ERα and HER2 with a parallel loss and/or downregulation of tumor suppressors such as TP53 and PTEN which together impact the efficacy of therapeutic strategies and frequently lead to emergence of drug resistance. Natural phytochemicals modulate oxidative stress, leptin, integrin, HER2, MAPK, ERK, Wnt/β-catenin and NFκB signaling along with regulating ERα and ERβ, thereby presenting unique opportunities for both primary and combinatorial interventions in BC. In this regard, this article focuses on critical analyses of the evidence from multiple studies on the efficacy of natural phytochemicals in BC. In addition, areas in which the combinations of such effective natural phytochemicals with approved and/or developing anticancer agents can be translationally beneficial are discussed to derive evidence-based inference for addressing challenges in BC control and therapy.

Brassica-Derived Plant Bioactives as Modulators of Chemopreventive and Inflammatory Signaling Pathways

A high consumption of vegetables belonging to the Brassicaceae family has been related to a lower incidence of chronic diseases including different kinds of cancer. These beneficial effects of, e.g., broccoli, cabbage or rocket (arugula) intake have been mainly dedicated to the sulfur-containing glucosinolates (GLSs)-secondary plant compounds nearly exclusively present in Brassicaceae-and in particular to their bioactive breakdown products including isothiocyanates (ITCs). Overall, the current literature indicate that selected Brassica-derived ITCs exhibit health-promoting effects in vitro, as well as in laboratory mice in vivo. Some studies suggest anti-carcinogenic and anti-inflammatory properties for ITCs which may be communicated through an activation of the redox-sensitive transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) that controls the expression of antioxidant and phase II enzymes. Furthermore, it has been shown that ITCs are able to significantly ameliorate a severe inflammatory phenotype in colitic mice in vivo. As there are studies available suggesting an epigenetic mode of action for Brassica-derived phytochemicals, the conduction of further studies would be recommendable to investigate if the beneficial effects of these compounds also persist during an irregular consumption pattern.

Macrophage migration inhibitory factor deficiency enhances immune response to Nippostrongylus brasiliensis

Infections with helminth parasites are endemic in the developing world and are a target for intervention with new therapies. Macrophage migration inhibitory factor (MIF) is a cytokine with pleiotropic effects in inflammation and immune responses. We investigated the role of MIF in a naturally cleared model of helminth infection in rodents, Nippostrongylus brasiliensis. At day 7 postinfection, MIF-deficient (MIF^-/-) mice had reduced parasite burden and mounted an enhanced type 2 immune response (Th2), including increased Gata3 expression and interleukin-13 (IL-13) production in the mesenteric lymph nodes (MLNs). Bone marrow reconstitution demonstrated that MIF produced from hematopoietic cells was crucial and Rag1^-/- reconstitution provided direct evidence that MIF^-/- CD4⁺ T cells were responsible for the augmented parasite clearance. MIF^-/- CD4⁺ T cells produced less IL-6 postinfection, which correlated with enhanced Th2 responses. MIF^-/- CD4⁺ T cells exhibited lower nuclear factor-κB activation, potentially explaining the reduction in IL-6. Finally, we demonstrated enhanced clearance of the parasite and Th2 response in wild-type mice treated with the MIF tautomerase inhibitor, sulforaphane, a compound found naturally found in cruciferous vegetables. These results are the first to describe the importance of the tautomerase enzyme activity in MIF function in N. brasiliensis infection.

Prevention and treatment of cancers by immune modulating nutrients

Epidemiological and laboratory data support the protective effects of bioactive nutrients in our diets for various diseases. Along with various factors, such as genetic history, alcohol, smoking, exercise, and dietary choices play a vital role in affecting an individual's immune responses toward a transforming cell, by either preventing or accelerating a neoplastic transformation. Ample evidence suggests that dietary nutrients control the inflammatory and protumorigenic responses in immune cells. Immunoprevention is usually associated with the modulation of immune responses that help in resolving the inflammation, thus improving clinical outcome. Various metabolic pathway-related nutrients, including glutamine, arginine, vitamins, minerals, and long-chain fatty acids, are important components of immunonutrient mixes. Epidemiological studies related to these substances have reported different results, with no or minimal effects. However, several studies suggest that these nutrients may have immune-modulating effects that may lower cancer risk. Preclinical studies submit that most of these components may provide beneficial effects. The present review discusses the available data, the immune-modulating functions of these nutrients, and how these substances could be used to study immune modulation in a neoplastic environment. Further research will help to determine whether the mechanistic signaling pathways in immune cells altered by nutrients can be exploited for cancer prevention and treatment.

Chemical alterations and regulations of biomolecules in lifestyle-related diseases

We know experientially that not only nutrient factors but also non-nutritive functional food factors are playing important roles in maintenance of homeostasis, health promotion, and disease prevention. Although some of these effective behaviors are supported by accumulating scientific evidences, it is in general difficult to determine properly in human. Therefore, the discovering of novel biomarker and developments of the analytical method are one of the prudent strategies to understand disease etiology and evaluate efficacies of functional food factors via monitoring the pathophysiological alteration in live body, tissue, and cells. This review describes recent our findings on (1) formation mechanism, bioactivities, quantitative determination of cholesterol ozonolysis product, secosterol as possible biomarker for lifestyle-related disease, and (2) chemical biology approach for the investigating molecular mechanisms of most promising cancer chemopreventive food factors, isothiocyanate-inducing bioactivities.

Targeting MIF in Cancer: Therapeutic Strategies, Current Developments, and Future Opportunities

Strong evidence has been presented linking chronic inflammation to the onset and pathogenesis of cancer. The multifunctional pro-inflammatory protein macrophage migration inhibitory factor (MIF) occupies a central role in the inflammatory pathway and has been implicated in the tumorigenesis, angiogenesis, and metastasis of many cancer phenotypes. This review highlights the current state of the art, which presents MIF, and the second member of the MIF structural superfamily, D-DT (MIF2), as significant mediators in the inflammatory-cancer axis. Although the mechanism by which MIF asserts its biological activity has yet to be fully understood, it has become clear in recent years that for certain phenotypes of cancer, MIF represents a valid therapeutic target. Current research efforts have focused on small molecule approaches that target MIF's unique tautomerase active site and neutralization of MIF with anti-MIF antibodies. These approaches have yielded promising results in a number of preclinical murine cancer models and have helped to increase our understanding of MIF biological activity. More recently, MIF's involvement in a number of key protein-protein interactions, such as with CD74 and HSP90, has been highlighted and provides a novel platform for the development of anti-MIF chemotherapeutic strategies in the future.

Macrophage migration inhibitory factor (MIF) is rendered enzymatically inactive by myeloperoxidase-derived oxidants but retains its immunomodulatory function

Macrophage migration inhibitory factor (MIF) is an important player in the regulation of the inflammatory response. Elevated plasma MIF is found in sepsis, arthritis, cystic fibrosis and atherosclerosis. Immunomodulatory activities of MIF include the ability to promote survival and recruitment of inflammatory cells and to amplify pro-inflammatory cytokine production. MIF has an unusual nucleophilic N-terminal proline with catalytic tautomerase activity. It remains unclear whether tautomerase activity is required for MIF function, but small molecules that inhibit tautomerase activity also inhibit the pro-inflammatory activities of MIF. A prominent feature of the acute inflammatory response is neutrophil activation and production of reactive oxygen species, including myeloperoxidase (MPO)-derived hypochlorous acid and hypothiocyanous acid. We hypothesized that MPO-derived oxidants would oxidize the N-terminal proline of MIF and alter its biological activity. MIF was exposed to hypochlorous acid and hypothiocyanous acid and the oxidative modifications on MIF were examined by LC-MS/MS. Imine formation and carbamylation was observed on the N-terminal proline in response to MPO-dependent generation of hypochlorous and hypothiocyanous acid, respectively. These modifications led to a complete loss of tautomerase activity. However, modified MIF still increased CXCL-8/IL-8 production by peripheral blood mononuclear cells (PBMCs) and blocked neutrophil apoptosis, indicating that tautomerase activity is not essential for these biological functions. Pre-treatment of MIF with hypochlorous acid protected the protein from covalent modification by the MIF inhibitor 4-iodo-6-phenylpyrimidine (4-IPP). Therefore, oxidant generation at inflammatory sites may protect MIF from inactivation by more disruptive electrophiles, including drugs designed to target the tautomerase activity of MIF.

Sulforaphane improves the bronchoprotective response in asthmatics through Nrf2-mediated gene pathways

Background

It is widely recognized that deep inspiration (DI), either before methacholine (MCh) challenge (Bronchoprotection, BP) or after MCh challenge (Bronchodilation, BD) protects against this challenge in healthy individuals, but not in asthmatics. Sulforaphane, a dietary antioxidant and antiinflammatory phytochemical derived from broccoli, may affect the pulmonary bronchoconstrictor responses to MCh and the responses to DI in asthmatic patients.

Methods

Forty-five moderate asthmatics were administered sulforaphane (100 μmol daily for 14 days), BP, BD, lung volumes by body-plethsmography, and airway morphology by computed tomography (CT) were measured pre- and post sulforaphane consumption.

Results

Sulforaphane ameliorated the bronchoconstrictor effects of MCh on FEV₁ significantly (on average by 21 %; p = 0.01) in 60 % of these asthmatics. Interestingly, in 20 % of the asthmatics, sulforaphane aggravated the bronchoconstrictor effects of MCh and in a similar number was without effect, documenting the great heterogeneity of the responsiveness of these individuals to sulforaphane. Moreover, in individuals in whom the FEV₁ response to MCh challenge decreased after sulforaphane administration, i.e., sulforaphane was protective, the activities of Nrf2-regulated antioxidant and anti-inflammatory genes decreased. In contrast, individuals in whom sulforaphane treatment enhanced the FEV₁ response to MCh, had increased expression of the activities of these genes. High resolution CT scans disclosed that in asthmatics sulforaphane treatment resulted in a significant reduction in specific airway resistance and also increased small airway luminal area and airway trapping modestly but significantly.

Conclusion

These findings suggest the potential value of blocking the bronchoconstrictor hyperresponsiveness in some types of asthmatics by phytochemicals such as sulforaphane.

Multiple binding modes of isothiocyanates that inhibit macrophage migration inhibitory factor

Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine that has roles in the innate immune response, and also contributes to inflammatory disease. While the biological properties of MIF are closely linked to protein-protein interactions, MIF also has tautomerase activity. Inhibition of this activity interferes with the interaction of MIF with protein partners e.g. the CD74 receptor, and tautomerase inhibitors show promise in disease models including multiple sclerosis and colitis. Isothiocyanates inhibit MIF tautomerase activity via covalent modification of the N-terminal proline. We systematically explored variants of benzyl and phenethyl isothiocyanates, to define determinants of inhibition. In particular, substitution with hydroxyl, chloro, fluoro and trifluoro moieties at the para and meta positions were evaluated. In assays on treated cells and recombinant protein, the IC50 varied from 250 nM to >100 μM. X-ray crystal structures of selected complexes revealed that two binding modes are accessed by some compounds, perhaps owing to strain in short linkers between the isothiocyanate and aromatic ring. The variety of binding modes confirms the existence of two subsites for inhibitors and establishes a platform for the development of potent inhibitors of MIF that only need to target one of these subsites.

Phenethyl isothiocyanate: a comprehensive review of anti-cancer mechanisms

The epidemiological evidence suggests a strong inverse relationship between dietary intake of cruciferous vegetables and the incidence of cancer. Among other constituents of cruciferous vegetables, isothiocyanates (ITC) are the main bioactive chemicals present. Phenethyl isothiocyanate (PEITC) is present as gluconasturtiin in many cruciferous vegetables with remarkable anti-cancer effects. PEITC is known to not only prevent the initiation phase of carcinogenesis process but also to inhibit the progression of tumorigenesis. PEITC targets multiple proteins to suppress various cancer-promoting mechanisms such as cell proliferation, progression and metastasis. Pre-clinical evidence suggests that combination of PEITC with conventional anti-cancer agents is also highly effective in improving overall efficacy. Based on accumulating evidence, PEITC appears to be a promising agent for cancer therapy and is already under clinical trials for leukemia and lung cancer. This is the first review which provides a comprehensive analysis of known targets and mechanisms along with a critical evaluation of PEITC as a future anti-cancer agent.

Potent inhibition of macrophage migration inhibitory factor (MIF) by myeloperoxidase-dependent oxidation of epicatechins

We report the ability of oxidized epicatechins to modify the N-terminal proline of the pro-inflammatory cytokine MIF at equimolar concentrations.

Cruciferous vegetable intake is inversely correlated with circulating levels of proinflammatory markers in women

BACKGROUND

Higher intakes of cruciferous vegetables or their constituents have been shown to lower inflammation in animal studies. However, evidence for this anti-inflammatory effect of cruciferous vegetable consumption in humans is scarce.

OBJECTIVE/DESIGN

In this cross-sectional analysis, we evaluated associations of vegetable intake with a panel of inflammatory and oxidative stress markers among 1,005 middle-aged Chinese women. Dietary intake of foods was assessed by a food frequency questionnaire.

RESULTS

Multivariable-adjusted circulating concentrations of tumor necrosis factor-α (TNF-α), interlukin-1β (IL-1β), and IL-6 were lower among women with higher intakes of cruciferous vegetables. The differences in concentrations of inflammatory biomarkers between extreme quintiles of cruciferous vegetable intake were 12.66% for TNF-α (Ptrend=0.01), 18.18% for IL-1β (Ptrend=0.02), and 24.68% for IL-6 (Ptrend=0.02). A similar, but less apparent, inverse association was found for intakes of all vegetables combined but not for noncruciferous vegetables. Levels of the urinary oxidative stress markers F2-isoprostanes and their major metabolite, 2,3-dinor-5,6-dihydro-15-F2t-IsoP, were not associated with intakes of cruciferous vegetables or all vegetables combined.

CONCLUSIONS

This study suggests that the previously observed health benefits of cruciferous vegetable consumption may be partly associated with the anti-inflammatory effects of these vegetables.

Spirohexenolide A targets human macrophage migration inhibitory factor (hMIF)

Spirohexenolides A and B comprise a unique family of spirotetronate natural products. We report on the identification of their binding to and modulation of human macrophage migration inhibitor factor (hMIF). Using an immunoaffinity-fluorescent labeling method, the properties of this interaction are detailed and evidence is provided that hMIF plays a key role in the cytostatic activity of the spirohexenolides.

Enhanced in vitro biological activity of synthetic 2-(2-pyridyl) ethyl isothiocyanate compared to natural 4-(methylsulfinyl) butyl isothiocyanate

Dietary isothiocyanates (ITC) derived from cruciferous vegetables have been shown to have numerous biological effects consistent with chemoprotective activity. In this study we synthesized a novel ITC, 2-(2-pyridyl) ethyl ITC (PY-ITC), and assessed its chemopreventive ability in comparison to sulforaphane (SF), the ITC derived from broccoli. PY-ITC suppressed cancerous cell growth and proliferation at lower concentrations than SF and was more potent at inducing p21 protein. Through the use of whole genome arrays we demonstrate that prostate cells exposed to PY-ITC or SF have similar biological response, albeit PY-ITC alters a greater number of genes, and to a greater extent. In the presence of a phosphatidylinositol-3-kinase (PI3K) inhibitor PY-ITC had a more pronounced effect on gene expression, emphasizing the important role of PI3K/AKT signaling in mediating the chemopreventive effects of ITCs. These results highlight the importance of the ITC side chain in bioactivity.

Neuroprotective effects of sulforaphane after contusive spinal cord injury

Traumatic spinal cord injury (SCI) leads to oxidative stress, calcium mobilization, glutamate toxicity, the release of proinflammatory factors, and depletion of reduced glutathione (GSH) at the site of injury. Induction of the Keap1/Nrf2/ARE pathway can alleviate neurotoxicity by protecting against GSH depletion, oxidation, intracellular calcium overload, mitochondrial dysfunction, and excitotoxicity. Sulforaphane (SF), an isothiocyanate derived from broccoli, is a potent naturally-occurring inducer of the Keap1/Nrf2/ARE pathway, leading to upregulation of genes encoding cytoprotective proteins such as NAD(P)H: quinone oxidoreductase 1, and GSH-regulatory enzymes. Additionally, SF can attenuate inflammation by inhibiting the nuclear factor-κB (NF-κB) pathway, and the enzymatic activity of the proinflammatory cytokine macrophage inhibitory factor (MIF). Our study examined systemic administration of SF in a rat model of contusion SCI, in an effort to utilize its indirect antioxidant and anti-inflammatory properties to decrease secondary injury. Two doses of SF (10 or 50 mg/kg) were administered at 10 min and 72 h after contusion SCI. SF (50 mg/kg) treatment resulted in both acute and long-term beneficial effects, including upregulation of the phase 2 antioxidant response at the injury site, decreased mRNA levels of inflammatory cytokines (i.e., MMP-9) in the injured spinal cord, inactivation of urinary MIF tautomerase activity, enhanced hindlimb locomotor function, and an increased number of serotonergic axons caudal to the lesion site. These findings demonstrate that SF provides neuroprotective effects in the spinal cord after injury, and could be a candidate for therapy of SCI.

Engineering glucosinolates in plants: current knowledge and potential uses

Glucosinolates (GSL) and their derivatives are well known for the characteristic roles they play in plant defense as signaling molecules and as bioactive compounds for human health. More than 130 GSLs have been reported so far, and most of them belong to the Brassicaceae family. Several enzymes and transcription factors involved in the GSL biosynthesis have been studied in the model plant, Arabidopsis, and in a few other Brassica crop species. Recent studies in GSL research have defined the regulation, distribution, and degradation of GSL biosynthetic pathways; however, the underlying mechanism behind transportation of GSLs in plants is still largely unknown. This review highlights the recent advances in the metabolic engineering of GSLs in plants and discusses their potential applications.

Structural interactions dictate the kinetics of macrophage migration inhibitory factor inhibition by different cancer-preventive isothiocyanates

Regulation of cellular processes by dietary nutrients is known to affect the likelihood of cancer development. One class of cancer-preventive nutrients, isothiocyanates (ITCs), derived from the consumption of cruciferous vegetables, is known to have various effects on cellular biochemistry. One target of ITCs is macrophage migration inhibitory factor (MIF), a widely expressed protein with known inflammatory, pro-tumorigenic, pro-angiogenic, and anti-apoptotic properties. MIF is covalently inhibited by a variety of ITCs, which in part may explain how they exert their cancer-preventive effects. We report the crystallographic structures of human MIF bound to phenethylisothiocyanate and to l-sulforaphane (dietary isothiocyanates derived from watercress and broccoli, respectively) and correlate structural features of these two isothiocyanates with their second-order rate constants for MIF inactivation. We also characterize changes in the MIF structure using nuclear magnetic resonance heteronuclear single-quantum coherence spectra of these complexes and observe many changes at the subunit interface. While a number of chemical shifts do not change, many of those that change do not have features similar in magnitude or direction for the two isothiocyanates. The difference in the binding modes of these two ITCs provides a means of using structure-activity relationships to reveal insights into MIF biological interactions. The results of this study provide a framework for the development of therapeutics that target MIF.

Macrophage migration inhibitory factor covalently complexed with phenethyl isothiocyanate

Macrophage migration inhibitory factor is irreversibly inhibited via covalent modification by phenethyl isothiocyanate, a naturally occurring compound with anti-inflammatory and anticancer properties. The structure of the modified protein obtained from X-ray diffraction data to 1.64 Å resolution is presented. The inhibitor sits within a deep hydrophobic pocket between subunits of the homotrimer and is highly ordered. The secondary structure of macrophage migratory inhibitory factor is unchanged by this modification, but there are significant rearrangements, including of the side-chain position of Tyr37 and the main chain of residues 31-34. These changes may explain the decreased binding of the modified protein to the receptor CD74. Together with the pocket, the areas of conformational change define specific targets for the design of more selective and potent inhibitors as potential therapeutics.

Development and application of a method for identification of isothiocyanate-targeted molecules in colon cancer cells

In this study, we have developed a novel method to identify isothiocyanate (ITC)-targeted molecules using two well-studied ITCs: benzyl ITC (BITC) and phenethyl ITC (PEITC). The principle of this method is based on identifying a pattern of differences between BITC and PEITC given that they show similar chemical and biological behaviors. For method validation, dithiothreitol-reduced bovine insulin as a model molecule was incubated with either BITC or PEITC, and digested peptides were analyzed by ultra-performance liquid chromatography time-of-flight mass spectrometry (UPLC-TOF-MS) and liquid chromatography quadrupole TOF-MS (LC-Q-TOF-MS). Three peptides-NYCN, FVNQHLCGSHLVE, and ALYLVCGE-were identified as being adducted with BITC or PEITC on their cysteine residues. Each set of peptides adducted with either BITC or PEITC showed retention times (RT(BITC)<RT(PEITC)) by reverse-phase column chromatography with a difference of molecular mass (Δ14.01565). On the basis of these findings, computational mathematical schemes were constructed to extract sets of MS ions satisfying the above criteria. Application of the developed method to an extract of ITC-treated human colon cancer HCT116 cells, thiocarbamoylation of cysteine residues of glutathione, and the N-terminal proline residues of PMFIVNTNVPR from macrophage migration inhibitory factor were successfully identified as one of the intracellular targets of ITCs. Moreover, the method also detected the thiocarbamoylated conjugates of ITCs with intracellular free cysteines and lysines.

Glucosinolates and isothiocyanates in health and disease

Glucosinolates and isothiocyanates have both been objects of research for more than half a century. Interest in these unique phytochemicals escalated following the discovery that sulforaphane, an isothiocyanate from broccoli, potently induces mammalian cytoprotective proteins through the Keap1-Nrf2-ARE pathway. In parallel with the advances in understanding the molecular regulation of this pathway and its critical role in protection against electrophiles and oxidants, there have been increased efforts toward translating this knowledge to improve human health and combat disease. This review focuses on the animal studies demonstrating the beneficial effects of glucosinolates and isothiocyanates in models of carcinogenesis, and cardiovascular and neurological diseases, as well as on the intervention studies of their safety, pharmacokinetics, and efficacy in humans.

Natural isothiocyanates: genotoxic potential versus chemoprevention

Isothiocyanates, occurring in many dietary cruciferous vegetables, show interesting chemopreventive activities against several chronic-degenerative diseases, including cancer, cardiovascular diseases, neurodegeneration, diabetes. The electrophilic carbon residue in the isothiocyanate moiety reacts with biological nucleophiles and modification of proteins is recognized as a key mechanism underlying the biological activity of isothiocyanates. The nuclear factor-erythroid-2-related factor 2 system, which orchestrates the expression of a wide array of antioxidant genes, plays a role in the protective effect of isothiocyanates against almost all the pathological conditions reported above. Recent emerging findings suggest a further common mechanism. Chronic inflammation plays a central role in many human diseases and isothiocyanates inhibit the activity of many inflammation components, suppress cyclooxygenase 2, and irreversibly inactivate the macrophage migration inhibitory factor. Due to their electrophilic reactivity, some isothiocyanates are able to form adducts with DNA and induce gene mutations and chromosomal aberrations. DNA damage has been demonstrated to be involved in the pathogenesis of various chronic-degenerative diseases of epidemiological relevance. Thus, the genotoxicity of the isothiocyanates should be carefully considered. In addition, the dose-response relationship for genotoxic compounds does not suggest evidence of a threshold. Thus, chemicals that are genotoxic pose a greater potential risk to humans than non-genotoxic compounds. Dietary consumption levels of isothiocyanates appear to be several orders of magnitude lower than the doses used in the genotoxicity studies and thus it is highly unlikely that such toxicities would occur in humans. However, the beneficial properties of isothiocyanates stimulated an increase of dietary supplements and functional foods with highly enriched isothiocyanate concentrations on the market. Whether such concentrations may exert a potential health risk cannot be excluded with certainty and an accurate evaluation of the toxicological profile of isothiocyanates should be prompted before any major increase in their consumption be recommended or their clinical use suggested.

The molecular basis that unifies the metabolism, cellular uptake and chemopreventive activities of dietary isothiocyanates

Organic isothiocyanates (ITCs), which are characterized by the presence of an -N=C=S group, are among the most extensively studied cancer chemopreventive agents and show highly promising chemopreventive activities. Numerous studies have shown that ITCs can inhibit both carcinogenesis and cancer growth in a variety of animal models. Many cruciferous vegetables, which are commonly consumed by humans, are rich sources of these compounds. Of particular interest are their high bioavailability, their shared metabolic profile and their ability to target a wide array of cancer-related cellular proteins. This review is focused on discussing the molecular basis of these intriguing properties of ITCs, with a particular emphasis on the concept that cellular uptake and metabolism of ITCs and at least some of their major chemopreventive activities are all initiated through direct reaction of the carbon atom of the -N=C=S group of the ITCs with cysteine sulfhydryl groups of glutathione (GSH) and of proteins. This knowledge deepens our understanding about the biological activities of ITCs and may facilitate further research and development of these compounds for cancer prevention and treatment.

Identification of potential protein targets of isothiocyanates by proteomics

Isothiocyanates (ITCs), such as phenethyl isothiocyanate (PEITC) and sulforaphane (SFN), are effective cancer chemopreventive compounds. It is believed that the major mechanism for the cancer preventive activity of ITCs is through the induction of cell cycle arrest and apoptosis. However, the upstream molecular targets of ITCs have been underexplored until recently. To identify proteins that are covalently modified by ITCs, human non-small cell lung cancer A549 cells were treated with (14)C-PEITC and (14)C-SFN, and the cell lysates were extracted for analysis by 2-D gel electrophoresis and mass spectrometry. After superimposing the colloidal Coomassie blue protein staining pattern with the pattern of radioactivity obtained from X-ray films, it was clear that only a small fraction of cellular proteins contained radioactivity, presumably resulting from selective binding with PEITC or SFN via thiocarbamation. More than 30 proteins with a variety of biological functions were identified with high confidence. Here, we report the identities of these potential ITC target proteins and discuss their biological relevance. The discovery of the protein targets may facilitate studies of the mechanisms by which ITCs exert their cancer preventive activity and provide the molecular basis for designing more efficacious ITC compounds.

Proteins as binding targets of isothiocyanates in cancer prevention

Isothiocyanates are versatile cancer-preventive compounds. Evidence from animal studies indicates that the anticarcinogenic activities of ITCs involve all the major stages of tumor growth: initiation, promotion and progression. Epidemiological studies have also shown that dietary intake of ITCs is associated with reduced risk of certain human cancers. A number of mechanisms have been proposed for the chemopreventive activities of ITCs. To identify the molecular targets of ITCs is a first step to understand the molecular mechanisms of ITCs. Studies in recent years have shown that the covalent binding to certain protein targets by ITCs seems to play an important role in ITC-induced apoptosis and cell growth inhibition and other cellular effects. The knowledge gained from these studies may be used to guide future design and screen of better and more efficacious compounds. In this review, we intend to cover all potential protein targets of ITCs so far studied and summarize what are known about their binding sites and the potential biological consequences. In the end, we also offer discussions to shed light onto the relationship between protein binding and reactive oxygen species generation by ITCs.