The consumption of cruciferous vegetables has long been associated with a reduced risk in the occurrence of cancer at various sites, including the prostate, lung, breast and colon. This protective effect is attributed to isothiocyanates present in these vegetables, and sulforaphane (SF), present in broccoli, is by far the most extensively studied to uncover the mechanisms behind this chemoprotection. The major mechanism by which SF protects cells was traditionally thought to be through Nrf2-mediated induction of phase 2 detoxification enzymes that elevate cell defense against oxidative damage and promote the removal of carcinogens. However, it is becoming clear that there are multiple mechanisms activated in response to SF, including suppression of cytochrome P450 enzymes, induction of apoptotic pathways, suppression of cell cycle progression, inhibition of angiogenesis and anti-inflammatory activity. Moreover, these mechanisms seem to have some degree of interaction to synergistically afford chemoprevention.

Glucosinolates (GLSs) are found in Brassica vegetables. Examples of these sources include cabbage, Brussels sprouts, broccoli, cauliflower and various root vegetables (e.g. radish and turnip). A number of epidemiological studies have identified an inverse association between consumption of these vegetables and the risk of colon and rectal cancer. Animal studies have shown changes in enzyme activities and DNA damage resulting from consumption of Brassica vegetables or isothiocyanates, the breakdown products (BDP) of GLSs in the body. Mechanistic studies have begun to identify the ways in which the compounds may exert their protective action but the relevance of these studies to protective effects in the human alimentary tract is as yet unproven. In vitro studies with a number of specific isothiocyanates have suggested mechanisms that might be the basis of their chemoprotective effects. The concentration and composition of the GLSs in different plants, but also within a plant (e.g. in the seeds, roots or leaves), can vary greatly and also changes during plant development. Furthermore, the effects of various factors in the supply chain of Brassica vegetables including breeding, cultivation, storage and processing on intake and bioavailability of GLSs are extensively discussed in this paper.

Whole genome DNA sequencing was used to decrypt the phylogeny of multiple samples from distinct areas of cancer and morphologically normal tissue taken from the prostates of three men. Mutations were present at high levels in morphologically normal tissue distant from the cancer reflecting clonal expansions, and the underlying mutational processes at work in morphologically normal tissue were also at work in cancer. Our observations demonstrate the existence of on-going abnormal mutational processes, consistent with field-effects, underlying carcinogenesis. This mechanism gives rise to extensive branching evolution and cancer clone mixing as exemplified by the coexistence of multiple cancer lineages harboring distinct ERG fusions within a single cancer nodule. Subsets of mutations were shared either by morphologically normal and malignant tissue or between different ERG-lineages, indicating earlier or separate clonal cell expansions. Our observations inform on the origin of multifocal disease and have implications for prostate cancer therapy in individual cases.

The glucosinolates are a large group of sulphur‐containing compounds which occur in all the economically important varieties of Brassica vegetable. Their common structure comprises a β‐D‐thioglucose group, a sulphonated oxime moiety and a variable side‐chain derived from methionine, tryptophan or phenylalanine. When the plant tissue is damaged the glucosinolates are hydrolysed by the endogenous enzyme ‘myrosinase’ (thioglucoside glycohydrolase EC 3:2:3:1), to release a range of breakdown products including the bitter, biologically active isothiocyanates. Although these compounds exert antinutritional effects in animals there is also substantial evidence that they are the principal source of anticarcinogenic activity in Brassica vegetables, and this provides a strong motive for the manipulation of glucosinolate levels in vegetables for human consumption. This review provides an overview of the evidence for a beneficial role for glucosinolates in human health, and describes the current state of knowledge regarding the genetics and biosynthesis of glucosinolates, their chemical analysis, their behaviour during cooking and processing, and their bioavailability to humans. As the genetic basis of glucosinolate biosynthesis becomes more apparent, and tools for marker‐assisted plant breeding become more available, the selective breeding of horticultural brassicas with different levels and types of glucosinolates, whether by conventional means or genetic manipulation, is becoming a practical possibility. However before this strategy becomes commercially viable, the health benefits of glucosinolates for human beings must be unequivocally established. © 2000 Society of Chemical Industry

Twenty eight Brassica napus lines were developed which had contrasting leaf glucosinolate profiles to those found in commercial oilseed rape cultivars. The lines varied both in the total amount of aliphatic glucosinolates and in the ratio of different side chain structures. The lines were used in field experiments to assess the manner by which glucosinolates mediate the interactions between Brasssica and specialist pests (Psylliodes chrysocephala and Pieris rapae) and generalist pests (pigeons and slugs). Increases in the level of glucosinolates resulted in greater damage by adult flea beetles ( P . chrysocephala) and a greater incidence of Pieris rapae larvae, but reduced the extent of grazing by pigeons and slugs. Decreasing the side chain length of aliphatic glucosinolates and reducing the extent of hydroxylation of butenyl glucosinolates increased the extent of adult flea beetle feeding. The implications of modifying the glucosinolate content of the leaves of oilseed rape and the role of these secondary metabolites in plant/herbivore interactions are discussed.

In some cruciferous plants, epithiospecifier protein (ESP) directs myrosinase (EC 3.2.3.1)-catalyzed hydrolysis of alkenyl glucosinolates toward epithionitrile formation. Here, for the first time, we show that ESP activity is negatively correlated with the extent of formation of the health-promoting phytochemical sulforaphane in broccoli (Brassica oleracea L. ssp. italica). A 43 kDa protein with ESP activity and sequence homology to the ESP of Arabidopsis thaliana was cloned from the broccoli cv. Packman and expressed in Escherichia coli. In a model system, the recombinant protein not only directed myrosinase-dependent metabolism of the alkenyl glucosinolate epi-progoitrin [(2S)-2-hydroxy-3-butenyl glucosinolate] toward formation of an epithionitrile but also directed myrosinase-dependent hydrolysis of the glucosinolate glucoraphanin [4-(methylsulfinyl)butyl glucosinolate] to form sulforaphane nitrile, in place of the isothiocyanate sulforaphane. The importance of this finding is that, whereas sulforaphane has been shown to have anticarcinogenic properties, sulforaphane nitrile has not. Genetic manipulation designed to attenuate or eliminate expression of ESP in broccoli could increase the fractional conversion of glucoraphanin to sulforaphane, enhancing potential health benefits.

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.

Glucosinolates are a major class of sulphur-containing secondary metabolites involved in plant defence against pathogens. Recently many regulatory links between glucosinolate biosynthesis and sulphate assimilation were established. Since sulphate assimilation undergoes diurnal rhythm and is light regulated, this study analysed whether the same is true for glucosinolate biosynthesis. The levels of glucosinolates and glutathione were found to be higher during the day than during the night. This agreed with variation in sulphate uptake as well as activity of the key enzyme of the sulphate assimilation pathway, adenosine 5’-phosphosulphate reductase. Correspondingly, the flux through sulphate assimilation was higher during the day than during the night, with the maximum flux through primary assimilation preceding maximal incorporation into glucosinolates. Prolonged darkness resulted in a strong reduction in glucosinolate content. Re-illumination of such dark-adapted plants induced accumulation of mRNA for many genes of glucosinolate biosynthesis, leading to increased glucosinolate biosynthesis. The light regulation of the glucosinolate synthesis genes as well as many genes of primary sulphate assimilation was controlled at least partly by the LONG HYPOCOTYL5 (HY5) transcription regulator. Thus, glucosinolate biosynthesis is highly co-regulated with sulphate assimilation.