Maria H. Traka

Glucosinolates, isothiocyanates and human health

Concurrent with the increase in our knowledge of the genetic and environmental factors that lead to glucosinolate accumulation in plants, and the role of these compounds and their derivatives in mediating plant–herbivore interactions, there has been significant advances in our understanding of how glucosinolates and their products may contribute to a reduction in risk of carcinogenesis and heart disease when consumed as part of the diet. In this paper, we review the epidemiological evidence for the health promoting effects of cruciferous vegetables, the processes by which glucosinolates and isothiocyanates are absorbed and metabolised by humans, with particular regard to the role of glutathione S-transferases, and the biological activity of isothiocyanates towards mammalian cells and tissues.

Broccoli Consumption Interacts with GSTM1 to Perturb Oncogenic Signalling Pathways in the Prostate

Background Epidemiological studies suggest that people who consume more than one portion of cruciferous vegetables per week are at lower risk of both the incidence of prostate cancer and of developing aggressive prostate cancer but there is little understanding of the underlying mechanisms. In this study, we quantify and interpret changes in global gene expression patterns in the human prostate gland before, during and after a 12 month broccoli-rich diet. Methods and Findings Volunteers were randomly assigned to either a broccoli-rich or a pea-rich diet. After six months there were no differences in gene expression between glutathione S-transferase mu 1 (GSTM1) positive and null individuals on the pea-rich diet but significant differences between GSTM1 genotypes on the broccoli-rich diet, associated with transforming growth factor beta 1 (TGFβ1) and epidermal growth factor (EGF) signalling pathways. Comparison of biopsies obtained pre and post intervention revealed more changes in gene expression occurred in individuals on a broccoli-rich diet than in those on a pea-rich diet. While there were changes in androgen signalling, regardless of diet, men on the broccoli diet had additional changes to mRNA processing, and TGFβ1, EGF and insulin signalling. We also provide evidence that sulforaphane (the isothiocyanate derived from 4-methylsuphinylbutyl glucosinolate that accumulates in broccoli) chemically interacts with TGFβ1, EGF and insulin peptides to form thioureas, and enhances TGFβ1/Smad-mediated transcription. Conclusions These findings suggest that consuming broccoli interacts with GSTM1 genotype to result in complex changes to signalling pathways associated with inflammation and carcinogenesis in the prostate. We propose that these changes may be mediated through the chemical interaction of isothiocyanates with signalling peptides in the plasma. This study provides, for the first time, experimental evidence obtained in humans to support observational studies that diets rich in cruciferous vegetables may reduce the risk of prostate cancer and other chronic disease. Trial Registration ClinicalTrials.gov NCT00535977

Glucosinolate and Amino Acid Biosynthesis in Arabidopsis

Enzymes that catalyze the condensation of acetyl coenzyme A and 2-oxo acids are likely to be important in two distinct metabolic pathways in Arabidopsis. These are the synthesis of isopropylmalate, an intermediate of Leu biosynthesis in primary metabolism, and the synthesis of methylthioalkylmalates, intermediates of Met elongation in the synthesis of aliphatic glucosinolates (GSLs), in secondary metabolism. Four Arabidopsis genes in the ecotype Columbia potentially encode proteins that could catalyze these reactions. MAM1 and MAML are adjacent genes on chromosome 5 at the Gsl-elong locus, while MAML-3 and MAML-4 are at opposite ends of chr 1. The isopropylmalate synthase activity of each member of the MAM-like gene family was investigated by heterologous expression in an isopropylmalate synthase-null Escherichia coli mutant. Only the expression of MAML-3 restored the ability of the mutant to grow in the absence of Leu. A MAML knockout line (KO) lacked long-chain aliphatic GSLs, which were restored when the KO was transformed with a functional MAML gene. Variation in expression of MAML did not alter the total levels of Met-derived GSLs, but just the ratio of chain lengths. MAML overexpression in Columbia led to an increase in long-chain GSLs, and an increase in 3C GSLs. Moreover, plants overexpressing MAML contained at least two novel amino acids. One of these was positively identified via MS/MS as homo-Leu, while the other, with identical mass and fragmentation patterns, was likely to be homo-Ile. A MAML-4 KO did not exhibit any changes in GSL profile, but had perturbed soluble amino acid content.

Plant Science and Human Nutrition: Challenges in Assessing Health-Promoting Properties of Phytochemicals

The rise in noncommunicable chronic diseases associated with changing diet and lifestyles throughout the world is a major challenge for society. It is possible that certain dietary components within plants have roles both in reducing the incidence and progression of these diseases. We critically review the types of evidence used to support the health promoting activities of certain phytochemicals and plant-based foods and summarize the major contributions but also the limitations of epidemiological and observational studies and research with the use of cell and animal models. We stress the need for human intervention studies to provide high-quality evidence for health benefits of dietary components derived from plants.

Genetic regulation of glucoraphanin accumulation in Beneforté® broccoli

Diets rich in broccoli (Brassica oleracea var italica) have been associated with maintenance of cardiovascular health and reduction in risk of cancer. These health benefits have been attributed to glucoraphanin that specifically accumulates in broccoli. The development of broccoli with enhanced concentrations of glucoraphanin may deliver greater health benefits. Three high-glucoraphanin F1 broccoli hybrids were developed in independent programmes through genome introgression from the wild species Brassica villosa. Glucoraphanin and other metabolites were quantified in experimental field trials. Global SNP analyses quantified the differential extent of B. villosa introgression The high-glucoraphanin broccoli hybrids contained 2.5–3 times the glucoraphanin content of standard hybrids due to enhanced sulphate assimilation and modifications in sulphur partitioning between sulphur-containing metabolites. All of the high-glucoraphanin hybrids possessed an introgressed B. villosa segment which contained a B. villosa Myb28 allele. Myb28 expression was increased in all of the high-glucoraphanin hybrids. Two high-glucoraphanin hybrids have been commercialised as Beneforté® broccoli. The study illustrates the translation of research on glucosinolate genetics from Arabidopsis to broccoli, the use of wild Brassica species to develop cultivars with potential consumer benefits, and the development of cultivars with contrasting concentrations of glucoraphanin for use in blinded human intervention studies.

Erucin, a new promising cancer chemopreventive agent from rocket salads, shows anti-proliferative activity on human lung carcinoma A549 cells.

Erucin (ER) is a dietary isothiocyanate present in cruciferous vegetables, such as rocket salads (Erucasativa Mill., Diplotaxis sp.), that has been recently considered a promising cancer chemopreventive phytochemical. Biological activity of ER was investigated on human lung adenocarcinoma A549 cells, analyzing its effects on molecular pathways involved in apoptosis and cell cycle arrest, such as PARP-1 cleavage, p53 and p21 protein expression. Our results show that ER affects the A549 cell proliferation, enhancing significantly p53 and p21 protein expression in a dose-dependent manner (p<0.001). PARP-1 cleavage occurs only after exposure to high concentrations of ER (50 microM), in accordance to previous studies showing similar bioactivity of other isothiocyanates (ITCs). Our study reports for the first time that the induction of p53, p21 and PARP-1 cleavage may participate in the anti-proliferative activity of ER in human lung adenocarcinoma A549 cells. Comparison of data with those obtained with the isothiocyanate sulforaphane (SF), structurally related to ER, underlines the strong relationship between structural analogy of ITCs and their biological activity. The ability of dietary compounds to modulate molecular mechanisms that affect cancer cell proliferation is certainly a key point of the cancer prevention potential by functional foods.

The dietary isothiocyanate sulforaphane modulates gene expression and alternative gene splicing in a PTEN null preclinical murine model of prostate cancer

BackgroundDietary or therapeutic interventions to counteract the loss of PTEN expression could contribute to the prevention of prostate carcinogenesis or reduce the rate of cancer progression. In this study, we investigate the interaction between sulforaphane, a dietary isothiocyanate derived from broccoli, PTEN expression and gene expression in pre malignant prostate tissue.ResultsWe initially describe heterogeneity in expression of PTEN in non-malignant prostate tissue of men deemed to be at risk of prostate cancer. We subsequently use the mouse prostate-specific PTEN deletion model, to show that sulforaphane suppresses transcriptional changes induced by PTEN deletion and induces additional changes in gene expression associated with cell cycle arrest and apoptosis in PTEN null tissue, but has no effect on transcription in wild type tissue. Comparative analyses of changes in gene expression in mouse and human prostate tissue indicate that similar changes can be induced in humans with a broccoli-rich diet. Global analyses of exon expression demonstrated that sulforaphane interacts with PTEN deletion to modulate alternative gene splicing, illustrated through a more detailed analysis of DMBT1 splicing.ConclusionTo our knowledge, this is the first report of how diet may perturb changes in transcription induced by PTEN deletion, and the effects of diet on global patterns of alternative gene splicing. The study exemplifies the complex interaction between diet, genotype and gene expression, and the multiple modes of action of small bioactive dietary components.

Antiproliferative Activity of the Dietary Isothiocyanate Erucin, a Bioactive Compound from Cruciferous Vegetables, on Human Prostate Cancer Cells

It is becoming increasingly clear that many dietary agents, such as isothiocyanates (ITCs) from cruciferous vegetables, can retard or prevent the process of prostate carcinogenesis. Erucin (ER) is a dietary ITC, which has been recently considered a promising cancer chemopreventive phytochemical. The potential protective activity of ER against prostate cancer was investigated using prostate adenocarcinoma cells (PC3), to analyze its effects on pathways involved in cell growth regulation, such as the cyclin-dependent kinase (CDKs) inhibitor p21WAF1/CIP1 (p21), phosphatidylinositol-3 kinase/AKT, and extracellular signal-regulated kinases (ERK)1/2 signaling pathways. We have shown for the first time that ER increases significantly p21 protein expression and ERK1/2 phosphorylation in a dose-dependent manner to inhibit PC3 cell proliferation (P ≤ 0.01). Compared to the structurally related sulforaphane, a well-studied broccoli-derived ITC, ER showed lower potency in inhibiting proliferation of PC3 cells, as well as in modulating p21 and pERK1/2 protein levels. Neither of the naturally occurring ITCs was able to affect significantly pAKT protein levels in prostate cells at all concentrations tested (0–25 μM). It is clearly important for the translation of laboratory findings to clinical approaches to investigate in animal and cell studies the molecular mechanisms by which ITCs may exert health promoting effects.

Involvement of KLF4 in sulforaphane- and iberin-mediated induction of p21waf1/cip1.

Sulforaphane (SF; 4-methylsulfinylbutyl isothiocyanate), a dietary compound derived from broccoli, may exhibit chemopreventive properties by inducing cell cycle arrest via induction of cyclin-dependent kinase inhibitor 1A (p21 waf1/cip1 ), but the exact molecular mechanism has not been determined. Here we evaluate the role of the transcription factor Krüppel-like factor 4 (KLF4) in mediating the induction of p21 waf1/cip1 and cellular differentiation by SF and iberin (IB; 3-methylsulphinyl propyl isothiocyanate), also derived from broccoli. Exposure of Caco-2 and Caco-2/TC7 cells to SF and IB increased expression of both KLF4 and p21 waf1/cip1 , whereas exposure of HT29 cells resulted only in induction of p21 waf1/cip1 . In Caco-2 cells, small interfering RNA knock down of KLF4 expression attenuated induction of p21 waf1/cip1 in response to either SF or IB treatment. Contrary to expectation, prolonged exposure to SF reduced sucrase isomaltase activity, a marker of small intestinal differentiation in Caco-2 cells. Additional support for the SF-mediated induction of p21 waf1/cip1 by KLF4 was obtained from analyses of gastric tissue of Apc Min/+ mice following acute intervention with SF but not from the analyses of other tissue of the intestinal tract. These results suggest that induction of p21 waf1/cip1 by SF or IB may be partly mediated by KLF4 in some colon cancer cells and tissues.

Diet rich in high glucoraphanin broccoli reduces plasma LDL cholesterol: Evidence from randomised controlled trials.

Scope Cruciferous-rich diets have been associated with reduction in plasma LDL-cholesterol (LDL-C), which may be due to the action of isothiocyanates derived from glucosinolates that accumulate in these vegetables. This study tests the hypothesis that a diet rich in high glucoraphanin (HG) broccoli will reduce plasma LDL-C. Methods and results One hundred and thirty volunteers were recruited to two independent double-blind, randomly allocated parallel dietary intervention studies, and were assigned to consume either 400 g standard broccoli or 400 g HG broccoli per week for 12 weeks. Plasma lipids were quantified before and after the intervention. In study 1 (37 volunteers), the HG broccoli diet reduced plasma LDL-C by 7.1% (95% CI: –1.8%, –12.3%, p = 0.011), whereas standard broccoli reduced LDL-C by 1.8% (95% CI +3.9%, –7.5%, ns). In study 2 (93 volunteers), the HG broccoli diet resulted in a reduction of 5.1% (95% CI: –2.1%, –8.1%, p = 0.001), whereas standard broccoli reduced LDL-C by 2.5% (95% CI: +0.8%, –5.7%, ns). When data from the two studies were combined the reduction in LDL-C by the HG broccoli was significantly greater than standard broccoli (p = 0.031). Conclusion Evidence from two independent human studies indicates that consumption of high glucoraphanin broccoli significantly reduces plasma LDL-C.