Manuela Bagatta

Intact glucosinolates modulate hepatic cytochrome P450 and phase II conjugation activities and may contribute directly to the chemopreventive activity of cruciferous vegetables

The currently accepted view is that the chemopreventive activity of glucosinolates is exclusively mediated by their degradation products, such as isothiocyanates. In the present study, evidence is presented for the first time that intact glucosinolates can modulate carcinogen-metabolising enzyme systems. The glucosinolates glucoraphanin and glucoerucin were isolated from cruciferous vegetables and incubated with precision-cut rat liver slices. Both glucosinolates elevated the O-dealkylations of methoxy- and ethoxyresorufin, markers for CYP1 activity; supplementation of the incubation medium with myrosinase, the enzyme that converts glucosinolates to their corresponding isothiocyanates, abolished these effects. Moreover, both glucoerucin and glucoraphanin increased the apoprotein levels of microsomal CYP1A1, CYP1A2 and CYP1B1. At higher concentrations, both glucosinolates enhanced quinone reductase activity, whereas glucoraphanin also elevated glutathione S-transferase; in this instance, however, supplementation of the incubation medium with myrosinase exacerbated the inductive effect. Finally, both glucosinolates increased modestly cytosolic quinone reductase, GSTα and GSTμ protein levels, which became more pronounced when myrosinase was added to the incubations with the glucosinolate. It may be inferred that intact glucosinolates can modulate the activity of hepatic carcinogen-metabolising enzyme systems and this is likely to impact on the chemopreventive activity linked to cruciferous vegetable consumption.

Up-regulation of cytochrome P450 and phase II enzyme systems in rat precision-cut rat lung slices by the intact glucosinolates, glucoraphanin and glucoerucin

It is believed that the chemopreventive activity of cruciferous vegetables in the lung and other tissues is exclusively the result of exposure to degradation products of glucosinolates, such as the isothiocyanates, and that the parent glucosinolates make no contribution. In the present study, evidence is presented for the first time that, in rat lung, the intact glucosinolates, glucoraphanin and glucoerucin, can modulate carcinogen-metabolising enzyme systems. The glucosinolates were isolated from cruciferous vegetables and incubated (1-25 μM) with precision-cut rat lung slices for 24h. Both glucosinolates, at concentrations as low as 1 μM, up-regulated the O-deethylation of ethoxyresorufin and the apoprotein levels of CYP1A1 and CYP1B1; supplementation of the incubation medium with myrosinase, the enzyme that converts glucosinolates to their corresponding isothiocyanates, abolished the rise in ethoxyresorufin O-deethylase activity. In contrast, neither glucosinolate, at the concentrations studied, influenced quinone reductase activity in the lung slices, but addition of myrosinase to the glucosinolate incubations led to a marked rise in activity. Glutathione S-transferase activity, monitored using 1-chloro-2,4-dinitrobenzene as the accepting substrate, was elevated in lung slices exposed to glucoraphanin. GSTα protein levels were increased by glucoraphanin and, to a much lesser extent, glucoerucin. It may be concluded that intact glucosinolates can modulate the activity of pulmonary carcinogen-metabolising enzyme systems, and can thus contribute to the documented chemopreventive activity of cruciferous vegetables in the lung.

Comparison of bioactive phytochemical content and release of isothiocyanates in selected brassica sprouts

The consumption of brassica sprouts as raw vegetables provides a fair amount of glucosinolates (GLs) and active plant myrosinase, which enables the breakdown of GLs into health-promoting isothiocyanates (ITCs). This study reports the determination of the main constituents related to human health found in edible sprouts of two Brassica oleracea varieties, broccoli and Tuscan black kale, and two Raphanus sativus varieties, Daikon and Sango. Radish sprouts exhibited the highest ability to produce ITCs, with Daikon showing the greatest level of conversion of GLs into bioactive ITCs (96.5%), followed by Sango (90.0%). Tuscan black kale gave a value of 68.5%, whereas broccoli displayed the lowest with 18.7%. ITCs were not the exclusive GL breakdown products in the two B. oleracea varieties, since nitriles were also produced, thus accounting for the lower conversion observed. Measuring the release of plant ITCs is a valuable tool in predicting the potential level of exposure to these bioactive compounds after the consumption of raw brassica sprouts.

Vitexin-2-O-xyloside, raphasatin and (-)-epigallocatechin-3-gallate synergistically affect cell growth and apoptosis of colon cancer cells.

Cytotoxic effects of the combination of the food components vitexin-2-O-xyloside (X), raphasatin (4-methylsulphanyl-3-butenyl isothiocyanates; G) and (-)-epigallocatechin-3-gallate (E) were investigated in colon (LoVo and CaCo-2) and breast (MDA-MB-231 and MCF-7) cancer cells. Breast cancer cells were more resistant than colon cells to X, G and E inhibition. On the contrary, marked synergistic effects among X, G and E on cell growth were found in both colon cancer cells. Further analysis revealed a G0/G1 arrest of the phase cell progression and apoptosis, linked to modulation of Bax, Bcl2, caspase-9 and poly(ADP-ribose) polymerase as well as Reactive Oxygen Species (ROS) generation in both colon cancer cells, whereas apoptosis and ROS were not significantly detected in normal human lymphocytes. We conclude that the X, G and E mixture might act by mitochondrial pathway activation of apoptosis, possibly elicited by ROS and the mixture may be effective in the chemoprevention of colon cancer.

Characterization of the temporal induction of hepatic xenobiotic-metabolizing enzymes by glucosinolates and isothiocyanates: requirement for at least a 6 h exposure to elicit complete induction profile.

A mechanism of action of chemopreventive glucosinolates/isothiocyanates, established largely in vitro, is to modulate carcinogen-metabolizing enzymes. Extrapolation in vivo involves relating in vitro concentrations to plasma/tissue concentrations attained in vivo, thus assuming that even transient exposure modulates enzyme activity. To test this hypothesis, precision-cut rat liver slices were incubated with glucosinolates for up to 24 h, and the O-dealkylation of methoxyresorufin and ethoxyresorufin was determined; increased activities were observed only at incubations of at least 6 h. To evaluate phase II enzymes, isothiocyanates, namely, sulforaphane, erucin, and phenethyl isothiocyanate, were similarly incubated; quinone reductase increased after incubation for 6 h or longer. When glutathione S-transferase was monitored, the phenethyl isothiocyanate-manifested rise necessitated at least a 6 h incubation, whereas in the case of sulforaphane and erucin, the activity was elevated after only 2 h. It is inferred that a rise in carcinogen-metabolizing enzymes by glucosinolates/isothiocyanates necessitates tissue exposure of at least 6 h.

Isatis canescens is a rich source of glucobrassicin and other health-promoting compounds

BACKGROUND Glucobrassicin (GBS), a glucosinolate contained in many brassica vegetables, is the precursor of chemopreventive compounds such as indole-3-carbinol. Large amounts of GBS would be needed to perform studies aimed at elucidating its role in the diet. This study was mainly undertaken to evaluate the flower buds of Isatis canescens as a source for GBS purification. In order to investigate the health-promoting potential of this species, glucosinolate, phenol and flavonoid content as well as the whole antioxidant capacity were also determined. Flower bud samples were collected in four localities around Mount Etna in Sicily, Italy, where I. canescens is widespread, as they are locally traditionally eaten. RESULTS I. canescens flower buds displayed high GBS concentrations, up to 60 µmol g(-1) dry weight. The purification method consisted of two chromatographic steps, which made it possible to obtain GBS with a purity of 92-95%, with a yield of 21 g kg(-1) . The total glucosinolates, phenols, flavonoids and antioxidant activity were considerable, with the southern locality showing the highest concentrations for all the phytochemicals. CONCLUSION I. canescens flower buds represent a naturally rich source of GBS, at a level suitable for its purification. Furthermore, flower bud consumption could provide an intake of health-promoting compounds, with possible antioxidant and chemopreventive properties.