Modulation of rat hepatic and pulmonary cytochromes P450 and phase II enzyme systems by erucin, an isothiocyanate structurally related to sulforaphane

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.

Molecular targets in cancer prevention by 4-(methylthio)butyl isothiocyanate - A comprehensive review

The consumption of cruciferous vegetables rich in isothiocyanates has long been associated with a reduced risk of various types of cancer. 4-(methylthio)butyl isothiocyanate also called erucin is an isothiocyanate present in appreciable quantity in the seeds of Eruca sativa Mill. plant. Although the literature has revealed its protective effects via inducing phase II enzymes and inhibiting carcinogen activating phase I enzymes, recent studies also suggest that, it inhibits the proliferation of cancer cells by altering the telomerase activity, dynamics of microtubules, expression of histone deacetylases, and other molecular pathways. With this in mind, the emphasis has been made to review the molecular targets involved in cancer prevention by 4-(methylthio)butyl isothiocyanate.

Induction of Apoptosis and Cytotoxicity by Raphasatin in Human Breast Adenocarcinoma MCF-7 Cells

Glucoraphasatin (GRH), a glucosinolate present abundantly in the plants of the Brassicaceae family, is hydrolyzed by myrosinase to raphasatin, which is considered responsible for its cancer chemopreventive activity; however, the underlying mechanisms of action have not been investigated, particularly in human cell lines. The aims of this study are to determine the cytotoxicity of raphasatin, and to evaluate its potential to cause apoptosis and modulate cell cycle arrest in human breast adenocarcinoma MCF-7 cells. The cytotoxicity was determined following incubation of the cells with glucoraphasatin or raphasatin (0–100 µM), for 24, 48, and 72 h. GRH displayed no cytotoxicity as exemplified by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. When myrosinase was added to the incubation system to convert GRH to raphasatin, cytotoxicity was evident. Exposure of the cells to raphasatin stimulated apoptosis, as was exemplified by cell shrinkage, membrane blebbing, chromatin condensation, and nuclear fragmentation. Moreover, using Annexin V-FITC assay, raphasatin induced apoptosis, as witnessed by changes in cellular distribution of cells, at different stages of apoptosis; in addition, raphasatin caused the arrest of the MCF-7 cells at the G₂ + M phase. In conclusion, raphasatin demonstrated cancer chemopreventive potential against human breast adenocarcinoma (MCF-7) cells, through induction of apoptosis and cell cycle arrest.

Paeonol exhibits anti-tumor effects by apoptotic and anti-inflammatory activities in 7,12-dimethylbenz(a)anthracene induced oral carcinogenesis

We investigated the preventive potential of paeonol on 7,12-dimethylbenz(a)anthracene (DMBA) induced oral carcinogenesis. Oral tumors were developed in the buccal pouches of Syrian golden hamsters using topical application of 0.5% DMBA three times/week for 10 weeks. DMBA treated hamsters developed hyperplasia, dysplasia and well-differentiated squamous cell carcinoma. The animals also exhibited increased lipid oxidation, decreased antioxidant status and altered levels of detoxification agents. Paeonol treatment of DMBA treated hamsters for 14 weeks decreased tumor incidence, volume and burden Paeonol treatment also increased antioxidant activity and decreased lipid oxidation to near normal levels. Histomorphology and the expression patterns of mutant p53, cyclo-oxygenase (COX-2) and caspase-9 were investigated in the oral buccal mucosa. Paeonol exhibited protective effects against DMBA induced oral carcinogenesis owing to its antitumor, antioxidant, anti-inflammatory and apoptosis inducing properties.

Chemoprevention with isothiocyanates - From bench to bedside

Isothiocyanates (ITCs) are naturally occurring hydrolization products from glucosinolates (GLSs) in brassicaceae and in epidemiological studies their intake has been weakly to moderately inversely correlated with the risk of colorectal cancer, prostate cancer and lung cancer. Numerous preclinical studies demonstrate chemopreventive mode of actions of ITCs, mainly related to a.) detoxification (induction of phase II enzymes), b.) anti-inflammatory properties by down-regulation of NFkappaB activity, c.) cyclin-mediated cell cycle arrest and d.) epigenetic modulation by inhibition of histone deacetylase activity. First prospective clinical trials were promising in patients with risk of prostate cancer recurrence. The glutathione-S-transferase gene expression seems to play a major role in the individual susceptibility towards ITCs. Safety issues are widely unclear and should be more addressed in future studies because ITCs can, in low concentrations, compromise the function of human immune cells and might impair genome stability.

A principal mechanism for the cancer chemopreventive activity of phenethyl isothiocyanate is modulation of carcinogen metabolism

Isothiocyanates are small molecules characterized by high chemical reactivity that allows them to interact readily with cellular constituents eliciting a plethora of biological activities. They are present exclusively in cruciferous vegetables, as glucosinolates, the intake of which has been associated with cancer chemoprevention. When the physical structure of these vegetables is disturbed, e.g. during mastication, the enzyme myrosinase is released and converts the glucosinolates to isothiocyanates (R-N=C=S), where R can be aliphatic or aromatic. Although sulforaphane, an aliphatic isothiocyanate, has received most attention worldwide, the most extensively studied aromatic isothiocyanate is phenethyl isothiocyanate (PEITC), and there are substantial differences in biological activity between the two sub-classes. In animal cancer models, PEITC effectively antagonized the carcinogenicity of chemicals, especially nitrosocompounds. A principal mechanism of their action is to protect the integrity of DNA by decreasing the levels of the genotoxic metabolites of chemical carcinogens. Extensive studies established that PEITC modulates the metabolism of the tobacco-specific carcinogenic nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) by inhibiting its cytochrome P450-mediated bioactivation. Moreover, PEITC is a potent inducer of detoxification enzymes such as quinone reductase, glutathione S-transferase and glucuronosyl transferase. PEITC is rapidly absorbed and is characterized by a large bioavailability; Cmax concentrations achieved in plasma after dietary intake are sufficient to modulate carcinogen metabolism. PEITC is primarily metabolized by glutathione conjugation and is excreted in the urine and bile as the mercapturate. The ability of PEITC to perturb carcinogen metabolism through modulation of cytochrome P450 and phase II detoxification enzymes is comprehensively and critically reviewed.

Sulforaphane is superior to glucoraphanin in modulating carcinogen-metabolising enzymes in Hep G2 cells

Glucoraphanin is the main glucosinolate found in broccoli and other cruciferous vegetables (Brassicaceae). The objective of the study was to evaluate whether glucoraphanin and its breakdown product sulforaphane, are potent modulators of various phase I and phase II enzymes involved in carcinogen-metabolising enzyme systems in vitro. The glucosinolate glucoraphanin was isolated from cruciferous vegetables and exposed to human hepatoma cell line HepG2 at various concentrations (0-25 μM) for 24 hours. Glucoraphanin at higher concentration (25 μM) decreased dealkylation of methoxyresorufin, a marker for cytochrome P4501 activity; supplementation of the incubation medium with myrosinase (0.018 U), the enzyme that converts glucosinolate to its corresponding isothiocyanate, showed minimal induction in this enzyme activity at concentration 10 μM. Quinone reductase and glutathione S-transferase activities were unaffected by this glucosinolate; however, supplementation of the incubation medium with myrosinase elevated quinone reductase activity. It may be inferred that the breakdown product of glucoraphanin, in this case sulforaphane, is superior than its precursor in modulating carcinogen- metabolising enzyme systems in vitro and this is likely to impact on the chemopreventive activity linked to cruciferous vegetable consumption.

Cruciferous vegetables: dietary phytochemicals for cancer prevention

Relationships between diet and health have attracted attention for centuries; but links between diet and cancer have been a focus only in recent decades. The consumption of diet-containing carcinogens, including polycyclic aromatic hydrocarbons and heterocyclic amines is most closely correlated with increasing cancer risk. Epidemiological evidence strongly suggests that consumption of dietary phytochemicals found in vegetables and fruit can decrease cancer incidence. Among the various vegetables, broccoli and other cruciferous species appear most closely associated with reduced cancer risk in organs such as the colorectum, lung, prostate and breast. The protecting effects against cancer risk have been attributed, at least partly, due to their comparatively high amounts of glucosinolates, which differentiate them from other vegetables. Glucosinolates, a class of sulphur- containing glycosides, present at substantial amounts in cruciferous vegetables, and their breakdown products such as the isothiocyanates, are believed to be responsible for their health benefits. However, the underlying mechanisms responsible for the chemopreventive effect of these compounds are likely to be manifold, possibly concerning very complex interactions, and thus difficult to fully understand. Therefore, this article provides a brief overview about the mechanism of such compounds involved in modulation of carcinogen metabolising enzyme systems.

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.

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.

4-Methylsulfanyl-3-butenyl isothiocyanate derived from glucoraphasatin is a potent inducer of rat hepatic phase II enzymes and a potential chemopreventive agent

The objective of this study was to establish whether the phytochemical glucoraphasatin, a glucosinolate present in cruciferous vegetables, and its corresponding isothiocyanate, 4-methylsulfanyl-3-butenyl isothiocyanate, up-regulate enzymes involved in the detoxification of carcinogens and are thus potential chemopreventive agents. Glucoraphasatin and myrosinase were isolated and purified from Daikon sprouts and Sinapis alba L., respectively. Glucoraphasatin (0-10 μM) was incubated for 24 h with precision-cut rat liver slices in the presence and absence of myrosinase, the enzyme that converts the glucosinolate to the isothiocyanate. The intact glucosinolate failed to influence the O-dealkylations of methoxy- and ethoxyresorufin or the apoprotein expression of CYP1 enzymes. Supplementation with myrosinase led to an increase in the dealkylation of methoxyresorufin, but only at the highest concentration of the glucosinolate, and CYP1A2 expression. In the absence of myrosinase, glucoraphasatin caused a marked increase in epoxide hydrolase activity at concentrations as low as 1 μM paralleled by a rise in the enzyme protein expression; at the highest concentration only, a rise was also observed in glucuronosyl transferase activity, but other phase II enzyme systems were unaffected. Addition of myrosinase to the glucoraphasatin incubation maintained the rise in epoxide hydrolase and glucuronosyl transferase activities, further elevated quinone reductase and glutathione S-transferase activities, and increased total glutathione concentrations. It is concluded that at low concentrations, glucoraphasatin, either intact and/or through the formation of 4-methylsulfanyl-3-butenyl isothiocyanate, is a potent inducer of hepatic enzymes involved in the detoxification of chemical carcinogens and merits further investigation for chemopreventive activity.

Differential response of four human livers to modulation of phase II enzyme systems by the chemopreventive phytochemical phenethyl isothiocyanate

A principal mechanism of the chemopreventive activity of isothiocyanates is detoxification of the genotoxic metabolites of chemical carcinogens through up-regulation of enzymes such as quinone reductase and the glutathione-S-transferases. In this study we report, for the first time, the potential of the aromatic isothiocyanate, phenethyl isothiocyanate (PEITC) to modulate these enzymes in human liver from four donors, in comparison with rat liver. Precision-cut human and rat liver slices were incubated with PEITC at concentrations that can be achieved in plasma following dietary intake. Glutathione-S-transferase activity increased in rat slices whereas in human slices activity rose only in three of the four donors. At the protein level, a marked rise in GSTα was seen in one of the human donors whereas much less pronounced elevation was noted in the other three. Quinone reductase activity doubled in rat liver slices incubated with PEITC, and was accompanied by an increase in protein expression. Only in one of the human donors was activity and expression of quinone reductase elevated. These studies illustrate that there are very pronounced differences in the response of human liver to PEITC, indicating that the chemopreventive effect of isothiocyanates may not be manifested in all individuals.

Pharmacokinetics of dietary cancer chemopreventive compound dibenzoylmethane in rats and the impact of nanoemulsion and genetic knockout of Nrf2 on its disposition

The pharmacokinetic disposition of a dietary cancer chemopreventive compound dibenzoylmethane (DBM) was studied in male Sprague-Dawley rats after intravenous (i.v.) and oral (p.o.) administrations. Following a single i.v. bolus dose, the mean plasma clearance (CL) of DBM was low compared with the hepatic blood flow. DBM displayed a high volume of distribution (Vss). The elimination terminal t1/2 was long. The mean CL, Vss and AUC0-∞/dose were similar between the i.v. 10 and 10 mg/kg doses. After single oral doses (10, 50 and 250 mg/kg), the absolute oral bioavailability (F*) of DBM was 7.4%-13.6%. The increase in AUC was not proportional to the oral doses, suggesting non-linearity. In silico prediction of oral absorption also demonstrated low DBM absorption in vivo. An oil-in-water nanoemulsion containing DBM was formulated to potentially overcome the low F* due to poor water solubility of DBM, with enhanced oral absorption. Finally, to examine the role of Nrf2 on the pharmacokinetics of DBM, since DBM activates the Nrf2-dependent detoxification pathways, Nrf2 wild-type (+/+) mice and Nrf2 knockout (-/-) mice were utilized. There was an increased systemic plasma exposure of DBM in Nrf2 (-/-) mice, suggesting that the Nrf2 genotype could also play a role in the pharmacokinetic disposition of DBM. Taken together, the results show that DBM has low oral bioavailability which could be due in part to poor water solubility and this could be overcome by a nanotechnology-based drug delivery system and furthermore the Nrf2 genotype could also play a role in the pharmacokinetics of DBM.

The natural chemopreventive phytochemical R-sulforaphane is a far more potent inducer of the carcinogen-detoxifying enzyme systems in rat liver and lung than the S-isomer

The chemopreventive activity of the phytochemical sulforaphane, (-)1-isothiocyanato-4R-(methylsulfinyl)-butane, present in cruciferous vegetables in substantial amounts in the form of glucosinolate, was demonstrated in animal models of cancer using the racemate, despite the fact that humans are exposed only to the R-enantiomer through the diet. Since a principal mechanism of the chemopreventive activity of sulforaphane is modulation of the carcinogen-metabolising enzyme systems, a study was conducted in precision-cut rat liver and lung slices, and in FAO cells comparing the ability of R- and S-sulforaphane to modulate these enzyme systems. R-sulforaphane elevated hepatic glutathione S-transferase and quinone reductase whereas the S-enantiomer had no effect; moreover, the R-enantiomer was more effective in up-regulating GSTα, GSTμ and quinone reductase protein levels. In the lung, both enantiomers increased the same enzyme activities with the R-enantiomer being more potent; in addition, the R-enantiomer was more effective in up-regulating GSTα and quinone reductase protein levels. Both isomers increased glutathione levels in both tissues, with R-sulforaphane being more potent. Finally, R-sulforaphane was the more effective of the two isomers in up-regulating CYP1A1/1B1 apoprotein levels in both liver and lung, and CYP1A2 in the liver. Similarly, in FAO cells the R-enantiomer was far more effective in up-regulating quinone reductase and glutathione S-transferase activities and protein levels compared with the S-isomer. These studies demonstrate clearly the superiority of R-sulforaphane, when compared with the S-enantiomer, in stimulating detoxification enzymes, and raises the possibility that the animal studies that employed the racemate may have underestimated the chemopreventive activity of this isothiocyanate.

Repeated oral administration modulates the pharmacokinetic behavior of the chemopreventive agent phenethyl isothiocyanate in rats

The principal objective of this study was to evaluate whether repeated oral administration influences the pharmacokinetic behavior of the chemopreventive agent phenethyl isothiocyanate (PEITC) in rat. Animals were treated orally with 0.5, 1.0 and 5.0 mg/kg of the isothiocyanate for 4 days, and plasma levels at various times post-administration were determined by LC/MS after the first and last day. To determine absolute bioavailability, a group of animals was treated with a single (0.5 mg/kg) intravenous dose of PEITC. Following single oral dose administration, PEITC was rapidly absorbed, peak plasma concentrations being attained within the hour, and achieved an absolute bioavailability of 77%, but displayed dose-dependent pharmacokinetics, with bioavailability decreasing and clearance increasing moderately with dose; C(max) values did not rise proportionately to the dose and volume of distribution increased. At the higher doses of 1.0 and 5.0 mg/kg, repeated administration led to higher PEITC plasma C(max) concentrations and decreased plasma clearance of the isothiocyanate leading to enhanced bioavailability.

Sulforaphane and alpha-lipoic acid upregulate the expression of the pi class of glutathione S-transferase through c-jun and Nrf2 activation

The anticarcinogenic effect of dietary organosulfur compounds has been partly attributed to their modulation of the activity and expression of phase II detoxification enzymes. Our previous studies indicated that garlic allyl sulfides upregulate the expression of the pi class of glutathione S-transferase (GSTP) through the activator protein-1 pathway. Here, we examined the modulatory effect of sulforaphane (SFN) and alpha-lipoic acid (LA) or dihydrolipoic acid (DHLA) on GSTP expression in rat Clone 9 liver cells. Cells were treated with LA or DHLA (50-600 micromol/L) or SFN (0.2-5 micromol/L) for 24 h. Immunoblots and real-time PCR showed that SFN, LA, and DHLA dose dependently induced GSTP protein and mRNA expression. Compared with the induction by the garlic organosulfur compound diallyl trisulfide (DATS), the effectiveness was in the order of SFN > DATS > LA = DHLA. The increase in GSTP enzyme activity in cells treated with 5 micromol/L SFN, 50 micromol/L DATS, and 600 micromol/L LA and DHLA was 172, 75, 122, and 117%, respectively (P < 0.05). A reporter assay showed that the GSTP enhancer I (GPEI) was required for GSTP induction by the organosulfur compounds. Electromobility gel shift assays showed that the DNA binding of GPEI to nuclear proteins reached a maximum at 0.5-1 h after SFN, LA, and DHLA treatment. Super-shift assay revealed that the transcription factors c-jun and nuclear factor erythroid-2 related factor 2 (Nrf2) were bound to GPEI. These results suggest that SFN and LA in either its oxidized or reduced form upregulate the transcription of the GSTP gene by activating c-jun and Nrf2 binding to the enhancer element GPEI.

Phenethyl isocyanate is not the metabolite of phenethyl isothiocyanate responsible for mechanism-based inhibition of cytochrome P450

Phenethyl isothiocyanate is a chemopreventive phytochemical present in cruciferous vegetables where it exists as the glucosinolate gluconasturtiin. It is a mechanism-based inhibitor of both rat and human cytochrome P450 enzymes. The principal objective of the present study was to ascertain whether phenethyl isocyanate, formed by the cytochrome P450-mediated oxidative desulphuration of phenethyl isothiocyanate, is the metabolite responsible for the mechanism-based inhibition. Phenethyl isothiocyanate, following incubation with Aroclor 1254-induced rat liver microsomes in the presence of NADPH, markedly suppressed the CYP1A-mediated O-deethylation of ethoxyresorufin; extent of inhibition was directly related to the pre-incubation time and was antagonised by reduced glutathione. When human liver microsomes were used, the inhibitory effect of phenethyl isothiocyanate, which was once again related to the pre-incubation time, was even more pronounced. When the ability of phenethyl isothiocyanate and phenethyl isocyanate to directly inhibit the O-deethylation of ethoxyresorufin in rat microsomes was compared, the latter compound was only moderately more effective. In human microsomes, both compounds were equipotent. In phenobarbital-induced lung microsomes, phenethyl isothiocyanate was a direct and potent inhibitor of the O-depentylation of pentoxyresorufin; pre-incubation of the isothiocyanate had no impact. Human precision-cut liver slices were more effective than rat slices in metabolising phenethyl isothiocyanate. Pre-treatment of rats, however, with phenobarbitone significantly enhanced the metabolism of isothiocyanate. It may be inferred from the present studies that: (a) phenethyl isocyanate is not the metabolite of phenethyl isothiocyanate responsible for its mechanism-based inhibition, and (b) CYP2B is an important catalyst of the metabolism of phenethyl isothiocyanate.

Antioxidant and pro-oxidant capacities of ITCs

Isothiocyanates (ITCs) are breakdown products of glucosinolates contained in cruciciferous vegetables. This heterogeneous family of molecules has the -N=C=S group as its common structural feature and possesses important cytoprotective properties. Their biological interactions are strongly related to modulation of cellular redox status, and a number of studies have documented their indirect antioxidant properties, particularly related to induction of phase-2 enzymes. On the other hand, some direct antioxidant behavior has also been observed for a limited number of ITCs. Paradoxically relevant pro-oxidant properties have also been documented, possibly related to the simultaneous induction of phase-1 enzymes. In this review, we will summarize and discuss the prevailing mechanisms for the antioxidant and pro-oxidant activity of ITCs, both in vivo and in vitro.