Glucosinolates and Glucosinolate Derivatives: Implications for Protection Against Chemical Carcinogenesis

Nutrigenomic effects of glucosinolates on liver, muscle and distal kidney in parasite-free and salmon louse infected Atlantic salmon

Background

Reduction of Lepeophtheirus salmonis infection in Atlantic salmon achieved by glucosinolates (GLs) from Brassica plants was recently reported. However, wider application of functional feeds based on GLs requires better knowledge of their positive and adverse effects.

Methods

Liver, distal kidney and muscle transcriptomes of salmon exposed to the extreme dose of GLs were profiled by microarray, while qPCR analysis followed up selected hepatic and renal responses under the extreme and moderate GLs dose during the L. salmonis challenge. Transcriptional analysis were complemented with measurements of organ indices, liver steatosis and plasma profiling, including indicators of cytolysis and bilirubin. Finally, the third trial was performed to quantify the effect of lower GLs doses on growth.

Results

The extreme GLs dose caused a decrease in hepatic fat deposition and growth, in line with microarray findings, which suggested tissue remodeling and reduction of cellular proliferation in the skeletal muscle and liver. Lower GLs inclusion levels in a follow-up trial did not show negative effects on growth. Microarray analysis of the distal kidney pointed to activation of anti-fibrotic responses under the overexposure. However, analyses of ALT, CK and AST enzymes in plasma provided no evidence of increased cytolysis and organ damage. Prevalent activation of phase-2 detoxification genes that occurred in all three tissues could be considered part of beneficial effects caused by the extreme dose of GLs. In addition, transcriptomic evidence suggested GLs-mediated iron and heme withdrawal response, including increased heme degradation in muscle (upregulation of heme oxygenase-1), decrease of its synthesis in liver (downregulation of porphobilinogen deaminase) and increased iron sequestration from blood (hepatic induction of hepcidin-1 and renal induction of intracellular storage protein ferritin). This response could be advantageous for salmon upon encountering lice, which depend on the host for the provision of iron carrying heme. Most of the hepatic genes studied by qPCR showed similar expression levels in fish exposed to GLs, lice and their combination, while renal induction of leptin suggested heightened stress by the combination of extreme dose of GLs and lice. High expression of interferonγ (cytokine considered organ-protective in mammalian kidney) was detected at the moderate GLs level. This fish also showed highest plasma bilirubin levels (degradation product of heme), and had lowest number of attached lice, further supporting hypothesis that making heme unavailable to lice could be part of an effective anti-parasitic strategy.

Conclusions

Modulation of detoxification and iron metabolism in Atlantic salmon tissues could be beneficial prior and during lice infestations. Investigation of anti-lice functional feeds based on low and moderate GLs inclusion levels thus deserves further attention.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1921-7) contains supplementary material, which is available to authorized users.

The antibacterial properties of isothiocyanates

Isothiocyanates (ITCs) are natural plant products generated by the enzymic hydrolysis of glucosinolates found in Brassicaceae vegetables. These natural sulfur compounds and their dithiocarbamate conjugates have been previously evaluated for their anti-cancerous properties. Their antimicrobial properties have been previously studied as well, mainly for food preservation and plant pathogen control. Recently, several revelations concerning the mode of action of ITCs in prokaryotes have emerged. This review addresses these new studies and proposes a model to summarize the current knowledge and hypotheses for the antibacterial effect of ITCs and whether they may provide the basis for the design of novel antibiotics.

Glucosinolate profiling and antimicrobial screening of Aurinia leucadea (Brassicaceae)

Glucosinolates (GLs) were characterized in various aerial parts (stems, leaves, and flowers) of Aurinia leucadea (Guss.) C. Koch and quantified according to the ISO 9167-1 official method based on the HPLC analysis of desulfoglucosinolates. Eight GLs, i.e., glucoraphanin (GRA), glucoalyssin (GAL; 1), gluconapin (GNA; 2), glucocochlearin (GCC), glucobrassicanapin (GBN; 3), glucotropaeolin (GTL), glucoerucin (GER), and glucoberteroin (GBE) were identified. The total GL contents were 57.1, 37.8, and 81.3 μmol/g dry weight in the stems, leaves, and flowers, respectively. The major GL detected in all parts of the plant was 2, followed by 1 and 3. GC/MS Analysis of the volatile fractions extracted from the aerial parts of fresh plant material either by hydrodistillation or CH(2) Cl(2) extraction showed that these fractions mostly contained isothiocyanates (ITCs). The main ITCs were but-3-enyl- (55.6-71.8%), pent-4-enyl- (7.6-15.3%), and 5-(methylsulfinyl)pentyl ITC (0-9.5%), originating from the corresponding GLs 2, 3, and 1, respectively. The antimicrobial activity of the volatile samples was investigated by determining inhibition zones with the disk-diffusion method and minimal inhibitory concentrations (MIC) with the microdilution method. They were found to inhibit a wide range of bacteria and fungi, with MIC values of 2.0-32.0 μg/ml, indicating their promising antimicrobial potential, especially against the fungi Candida albicans and Rhizopus stolonifer as well as against the clinically important pathogen Pseudomonas aeruginosa.

Effect of the pasteurization process on the contents of ascorbigen, indole-3-carbinol, indole-3-acetonitrile, and 3,3'-diindolylmethane in fermented cabbage

The aim of the study was to investigate the effect of the pasteurization process on the content of ascorbigen, indole-3-carbinol, indole-3-acetonitrile, and 3,3'-diindolylmethane in fermented cabbage. Pasteurization was run at a temperature of 80 °C for 5-30 min. Significant changes were only observed in contents of ascorbigen and 3,3'-diindolylmethane. The total content of the compounds analyzed in cabbage pasteurized for 10-30 min was found to be decreased by ca. 20%, and the losses were due to thermal degradation of the predominating ascorbigen. Pasteurization was found not to exert any considerable effect on contents of indole-3-acetonitrile and indole-3-carbinol in cabbage nor did it affect contents of the compounds analyzed in juice.

Selenoglucosinolates and their metabolites produced in Brassica spp. fertilised with sodium selenate

Glucosinolates are sulphur-containing glycosides found in many Brassica spp. that are important because their aglycone hydrolysis products protect the plant from herbivores and exhibit anti-cancer properties in humans. Recently, synthetically produced selenium analogues have been shown to be more effective at suppressing cancers than their sulphur counterparts. Although selenium is incorporated into a number of Brassica amino acids and peptides, firm evidence has yet to be presented for the presence of selenium in the glucosinolates and their aglycones in planta. In this study broccoli and cauliflower florets, and roots of forage rape, all obtained from plants treated with sodium selenate, were analysed for the presence of organoselenides. GC-MS analysis of pentane/ether extracts identified six organoselenium compounds including selenium analogues of known myrosinase-derived Brassica volatiles: 4-(methylseleno)butanenitrile, 5-(methylseleno)pentanenitrile, 3-(methylseleno)propylisothiocyanate, 4-(methylseleno)butylisothiocyanate, and 5-(methylseleno)pentylisothiocyanate. LC-MS analysis of ethanolic extracts identified three selenoglucosinolates: 3-(methylseleno)propylglucosinolate (glucoselenoiberverin), 4-(methylseleno)butylglucosinolate (glucoselenoerucin), and 5-(methylseleno)pentylglucosinolate (glucoselenoberteroin). LC-MS/MS analysis was used to locate the position of the selenium atom in the selenoglucosinolate and indicates preferential incorporation of selenium via selenomethionine into the methylselenyl moiety rather than into the sulphate or β-thioglucose groups. In forage rape, selenoglucosinolates and their aglycones (mainly isothiocyanates), occurred at concentrations up to 10% and 70%, respectively, of their sulphur analogues. In broccoli, concentrations of the selenoglucosinolates and their aglycones (mainly nitriles) were up to 60% and 1300%, respectively of their sulphur analogues. These findings indicate the potential for the incorporation of high levels of selenium into Brassica glucosinolates.

Health benefits and possible risks of broccoli - an overview

Chemopreventive effects of broccoli, a highly valued vegetable, have been known for a long time. Several studies have demonstrated that broccoli might be beneficial by reducing the risk for the development of certain forms of cancer. These effects are generally attributed to glucosinolate-derived degradation products like isothiocyanates and indoles which are formed by the hydrolytic action of plant myrosinase and/or glucosidases deriving from the human microbial flora. However, recent in vitro and experimental animal studies indicate that broccoli, its extracts and the glucosinolate-derived degradation products might also have undesirable effects, especially genotoxic activities. However, the relevance of the genotoxic activities to human health is not known yet. This paper gives an overview on genotoxic, anti-genotoxic/chemopreventive, nutritive and antinutritive properties of broccoli, its ingredients and their degradation products. A qualitative comparison of the benefit and risk of broccoli consumption benefit-risk assessment shows that the benefit from intake in modest quantities and in processed form outweighs potential risks. For other preparations (fortified broccoli-based dietary supplements, diets with extraordinary high daily intake, consumption as a raw vegetable) further studies both for potential risks and beneficial effects are needed in order to assess the benefit and risk in the future.

A 13-week dietary toxicity study in rats of a Napin-Rich Canola Protein Isolate

The objective was to study the safety of a Napin-Rich Canola Protein Isolate (NRCPI) fed to rats at various levels for 13-weeks. The study included four groups (20 animals/sex/group) of young Sprague Dawley rats. They were fed ad libitum with an AIN-93G based protein-free diet containing, respectively, 5%, 10% and 20% (w/w) NRCPI (test article) or 20% (w/w) vitamin-free casein (control article). Protein levels were adjusted at 18% in all groups with vitamin-free casein. Body weights, food consumption, locomotor activity and behavioral and clinical pathology parameters were recorded at various points in the study, followed by macroscopic examination, determination of organ weights and microscopic examination at termination. There were no test article-related effects on ophthalmology, functional observations, hematology, serum chemistry, urinalysis, organ weights and macroscopic or microscopic findings. Lower body weight gains were observed in the 10% NRCPI-treated males and the 20% NRCPI-treated males and females. The lower body weight gains were associated with significantly lower food consumption. Therefore, for NRCPI the No Observed Adversed Effect Level (NOAEL) was considered to be 20% (the highest fed level); equivalent to 12.46 g/kg BW/day for males and 14.95 g/kg BW/day for females. The NRCPI was considered safe under the tested conditions.

Effect of light conditions on the contents of glucosinolates in germinating seeds of white mustard, red radish, white radish, and rapeseed

The study was aimed at determining the effect of light conditions on contents of glucosinolates (GLS) in germinating seeds of white mustard, red radish, white radish, and rapeseed. The seeds were germinated in light and dark, at 25 degrees C, for up to 7 days. As compared to the nongerminated seeds, in seeds exposed to light and germinated for 4, 5, 6, and 7 days the content of total GLS was observed to decrease by 30 to 70% depending on the species. Germination in conducted the dark for the respective periods of time resulted in decreases of total GLS not exceeding 25%. The changes in the concentration of total GLS were attributed to aliphatic GLS predominating in seeds, yet in the case of white mustard to sinalbin belonging to aralkyl glucosinolates. Although seeds germinated in the dark, as compared to those exposed to light, were characterized by a higher total content of indole GLS, the percentage contribution of that group of compounds in white mustard, red radish, and white radish remained at a similar level, irrespective of germination time. Only in the case of rapeseed was the percentage of the sum of indole GLS observed to increase from 17 to up to 45% once the seeds were exposed to light and to 50% once they were germinated in the dark.

Influence of cabbage processing methods and prebiotic manipulationof colonic microflora on glucosinolate breakdown in man

Glucosinolate consumption from brassica vegetables has been implicated in reduction of cancer risk. The isothiocyanate breakdown products of glucosinolates appear to be particularly important as chemoprotective agents. Before consumption, brassica vegetables are generally cooked, causing the plant enzyme, myrosinase, to be denatured, influencing the profile of glucosinolate breakdown products produced. Some human intestinal microflora species show myrosinase-like activity (e.g. bifidobacteria). We aimed to increase bifidobacteria by offering a prebiotic (inulin) in a randomised crossover study. Six volunteers consumed inulin (10 g/d) for 21 d followed by a 21 d control period (no inulin). Treatment periods were reversed for the remaining six volunteers. During the last 5 d of each period two cabbage-containing meals were consumed. Total urine output was collected for 24 h following each meal. Cabbage was microwaved for 2 min (lightly cooked) or 5·5 min (fully cooked). Faecal samples were collected at the start and after the inulin and control treatments. Bifidobacteria were enumerated by real-time PCR. Allyl isothiocyanate production was quantified by measuring urinary excretion of allyl mercapturic acid (AMA). Bifidobacteria increased following prebiotic supplementation (P < 0·001) but there was no impact of this increase on AMA excretion. AMA excretion was greater following consumption of lightly cooked cabbage irrespective of prebiotic treatment (P < 0·001). In conclusion, the most effective way to increase isothiocyanate production may be to limit the length of time that brassica vegetables are cooked prior to consumption.

Effects of the bacterial status of rats on the changes in some liver cytochrome P450 (EC 1.14.14.1) apoproteins consequent to a glucosinolate-rich diet

The aim of the present work was to investigate the influence of the intestinal microflora on the changes in hepatic cytochrome P450 apoproteins induced by dietary glucosinolates. Ten rats harbouring a conventional digestive microflora were offered either a diet containing 390g myrosinase-free rapeseed meal/kg (n 5) or a control diet devoid of glucosinolates (n 5). A similar trial was performed using germ-free rats. After 4 weeks of exposure to the dietary regimens, animals were slaughtered and their livers removed for preparation of microsomes and analysis of cytochrome P450 (EC 1.14.14.1). The glucosinolate-rich diet decreased the concentration of total cytochrome P450 in conventional rats only (-34%). The bacterial status did not modify the concentration of apoproteins CYP1A2 and CYP2B1/B2, but greatly decreased the concentration of the male constitutive isoform CYP2C11 (-53 and -45% respectively in conventional and germ-free rats). Germ-free rats fed on the glucosinolate-rich diet had a greater concentration of CYP3A (+139%) and a lower concentration of CYP2E1 (-32%) than their counterparts fed on the control diet. However, these differences were absent in conventional animals. On the whole, the influence of the intestinal microflora on the changes in hepatic cytochrome P450 due to the consumption of cruciferous vegetables is very complex and obviously involves different mechanisms according to the apoprotein.

The activities of several detoxication enzymes are differentially induced by juices of garden cress, water cress and mustard in human HepG2 cells

It has been previously demonstrated in a human-derived hepatoma cell line (HepG2) that juices from cruciferous vegetables protect against the genotoxicity caused by dietary carcinogens. HepG2 cells possess different enzymes involved in the biotransformation of xenobiotics. Therefore, we investigated the effect of cruciferous juices on the activities of CYP 1A and several phase II enzymes in this cell model. For each experiment, 1 x 10(6) cells were seeded on Petri dishes. After 2 days, the juices (0.5-8 microl/ml of culture medium) were added for 48 h prior to cell harvesting. The addition of juice from water cress (Nasturtium officinalis R. Br) significantly increased the activities of ethoxyresorufin-O-deethylase at high doses only and NAD(P)H-quinone reductase in a dose-dependent manner (1.8- and 5-fold, respectively). The addition of juice from garden cress (Lepidum sativum L.) significantly increased the activities of NAD(P)H-quinone reductase and UDP-glucuronosyl-transferase with a maximal effect around the dose of 2 microl/ml juice (1.4- and 1.2-fold, respectively) while the other enzymes were not altered. Mustard (Sinapis alba L.) juice increased the activities of NAD(P)H-quinone reductase (2.6-fold at the dose of 8 microl/ml), and N-acetyl-transferase (1.4-fold at the dose of 8 microl/ml) in a dose-dependent manner while a maximal induction of UDP-glucuronosyl-transferase was obtained with a dose of 2 microl/ml (1.8-fold). These observations show that the three juices have different induction profiles: only water cress acted as a bifunctional inducer by enhancing both phase I and phase II enzymes. As a consequence, each juice may preferentially inhibit the genotoxicity of specific compounds.

Glucosinolate derivatives in stored fermented cabbage

The research focused on the glucosinolate (GLS) breakdown products formed during the fermentation of cabbage. A relationship between the contents of degradation products in fermented cabbage and native GLS in raw cabbage was investigated. The effect of fermented cabbage storage on the contents of individual compounds was also assayed. Ascorbigen formed from one of the degradation products of glucobrassicin (indole GLS) was found to be a dominating compound in fermented cabbage. Irrespective of the time of fermented cabbage storage, the content of ascorbigen reached approximately 14 micromol/100 g. Neither the content of isothiocyanates, the major degradation products of aliphatic GLS, nor that of cyanides exceeded 2.5 microM. Storage of cabbage caused periodical increases and decreases in the contents of cyanides and consequent declines in the contents of isothiocyanates. The highest relative contents (expressed as a percentage of the native GLS content) of degradation products--ranging from >70 to 96%--were reported for the products of glucoraphanin degradation, whereas the lowest-- <5% --were reported for the products of sinigrin degradation.

Development of a food composition database for the estimation of dietary intakes of glucosinolates, the biologically active constituents of cruciferous vegetables

Evidence indicates that cruciferous vegetables are protective against a range of cancers with glucosinolates and their breakdown products considered the biologically active constituents. To date, epidemiological studies have not investigated the intakes of these constituents due to a lack of food composition databases. The aim of the present study was to develop a database for the glucosinolate content of cruciferous vegetables that can be used to quantify dietary exposure for use in epidemiological studies of diet-disease relationships. Published food composition data sources for the glucosinolate content of cruciferous vegetables were identified and assessed for data quality using established criteria. Adequate data for the total glucosinolate content were available from eighteen published studies providing 140 estimates for forty-two items. The highest glucosinolate values were for cress (389 mg/100 g) while the lowest values were for Pe-tsai chinese cabbage (20 mg/100 g). There is considerable variation in the values reported for the same vegetable by different studies, with a median difference between the minimum and maximum values of 5.8-fold. Limited analysis of cooked cruciferous vegetables has been conducted; however, the available data show that average losses during cooking are approximately 36 %. This is the first attempt to collate the available literature on the glucosinolate content of cruciferous vegetables. These data will allow quantification of intakes of the glucosinolates, which can be used in epidemiological studies to investigate the role of cruciferous vegetables in cancer aetiology and prevention.

Urinary excretion of dithiocarbamates and self-reported Cruciferous vegetable intake: application of the 'method of triads' to a food-specific biomarker

OBJECTIVE

Greater intake of Cruciferous vegetables (e.g. broccoli) may prevent cancer at several sites. Urinary excretion of isothiocyanate conjugates (dithiocarbamates, DTC) provides a specific biomarker of Cruciferous vegetable consumption suitable for epidemiological investigations. However, no gold-standard referent is available for evaluating urinary DTC levels as an estimator of Cruciferous vegetable consumption. We compared urinary DTC levels to intake as measured by two self-reported dietary assessment techniques.

DESIGN

Cruciferous vegetable consumption was measured before and after a behavioural dietary intervention using multiple 24-hour recalls (24HR), a food-counting questionnaire (VFQ) and urinary DTC excretion levels. Analysis included a structural equation approach (Method of Triads) combining these three assessment techniques to estimate the relationship between DTC level and the study population's 'true' Cruciferous vegetable intake.

SETTING

The intervention curriculum assisted participants in consuming about 2 servings per day for a 6-week period. Participants attended four classes emphasising problem-solving skills, dietary counselling and vegetable preparation skills. There were no dietary restrictions.

SUBJECTS

Thirty-three healthy, free-living, post-menopausal women.

RESULTS

Although few participants reported Cruciferae consumption prior to the intervention, 30 participants reported Cruciferae consumption after the intervention (Post-intervention). Urinary DTC levels were correlated with estimated intake derived from either the 24HR (r = 0.57; 95% confidence interval (95% CI) 0.28, 0.76) or VFQ (r =0.49; 95% CI 0.17, 0.71). The validity coefficient (Method of Triads) between urinary DTC excretion and an index of true Cruciferous intake was stronger than the Pearson correlation (r(v) = 0.65; 95% CI 0.35, 0.90), and comparable to estimates derived from the 24HR (r(v) = 0.82; 95% CI 0.65, 1.00) or VFQ (r(v) = 0.76; 95% CI 0.47, 0.92) method. These associations were not affected by adjustment for body mass index, energy intake, or social approval or desirability response sets.

CONCLUSIONS

Food-frequency questionnaires (FFQ) suitable for large epidemiological studies may not be designed to measure all Cruciferae, and cannot capture exposure to phytochemicals derived from those vegetables. Urinary DTC measurement was significantly correlated with Cruciferae intake derived from two dietary assessment approaches, and urinary DTC levels could supplement traditional FFQ data by providing an index of recent Cruciferous vegetable intake not susceptible to reporting biases.

Metabolism of sinigrin (2-propenyl glucosinolate) by the human colonic microflora in a dynamic in vitro large-intestinal model

Cruciferous vegetables, such as Brassica, which contain substantial quantities of glucosinolates, have been suggested to possess anticarcinogenic activity. Cutting and chewing of cruciferous vegetables releases the thioglucosidase enzyme myrosinase, which degrades glucosinolates to isothiocyanates and other minor metabolites. Cooking of cruciferous vegetables inactivates the myrosinase enzyme, allowing intact glucosinolates to reach the large intestine, where they can be degraded by the indigenous microflora into isothiocyanates. This local release of isothiocyanates may explain the protective effect of cruciferous vegetables on the colon epithelium. However, little is known about the amounts and identities of glucosinolate metabolites produced by the human microflora. The production of allyl isothiocyanate from sinigrin was investigated in a dynamic in vitro large-intestinal model, after inoculation with a complex microflora of human origin. Sinigrin and allyl isothiocyanate concentrations were analysed in the lumen and dialysis fluid of the model. Peak levels of allyl isothiocyanate were observed between 9 and 12 h after the addition of sinigrin. The model was first set up with a pooled and cultured human microflora, in which 1 and 4% of, respectively, 1 and 15 mM sinigrin, was converted into AITC. However, the conversion rate was remarkably higher if different individual human microflora were used. Between 10% and 30% (mean 19%) of the sinigrin was converted into allyl isothiocyanate. The results of this study suggest that allyl isothiocyanate is converted further into other, yet unknown, metabolites.

Using isothiocyanate excretion as a biological marker of Brassica vegetable consumption in epidemiological studies: evaluating the sources of variability

OBJECTIVE

Brassica vegetable consumption (e.g. broccoli) leads to excretion of isothiocyanates (ITC) in urine. We evaluated the consistency of ITC as a biomarker for dietary Brassica vegetable consumption across the types of vegetables and methods of preparation used in Western societies, and across consumption levels.

DESIGN

A single-armed behavioural intervention with duplicate baseline assessment and post-intervention assessment. Urinary ITC excretion and estrogen metabolites were measured from 24-hour urine samples. Dietary intake was measured by a 24-hour recall.

SETTING

The behavioural intervention facilitated daily Brassica intake among participants by providing peer support, food preparation instruction, guided practice in a teaching kitchen, and other information.

SUBJECTS

Thirty-four healthy free-living postmenopausal women who recently had a negative screening mammogram at the University of Massachusetts Medical Center.

RESULTS

Urinary ITC excretion and total Brassica intake followed the same pattern over the intervention. The ITC biomarker significantly predicted Brassica intake when Brassica consumption averaged about 100 g day-1, but not when Brassica consumption averaged about 200 g day-1. Urinary ITC levels were somewhat higher when more raw vegetables were consumed as compared to lightly cooked vegetables, while the types of Brassica consumed appeared to have only a small, non-significant effect on urinary ITC levels.

CONCLUSION

Urinary ITC excretion would be a good exposure biomarker among populations regularly consuming a vegetable serving/day, but may be less accurate among populations with greater intake levels or a wide range of cooking practices.

Content of glucosinolates in cruciferous vegetables grown at the same site for two years under different climatic conditions

Individual glucosinolates (GLS) were determined in vegetables of three Cruciferae species: Brassica oleracea L. (white cabbage, red cabbage, Savoy cabbage, Brussels sprouts, cauliflower, kale, kohlrabi), Brassica rapa L. (turnip), and Raphanus sativus L. (red radish, black radish, and white radish) produced in two years. The cultivars were compared for the contents of total-, indole-, and aliphatic GLS. In both years, the total content of GLS was highest in black radish, and all examined R. sativus vegetables contained the greatest amount of aliphatic GLS. Neither the level nor the identity of GLS differentiated among the vegetables of the other cultivars grown in the same year. Comparison of the GLS contents of the same cultivar in two production years, which differed in temperature and rainfall rate, showed that low average 10-day rainfall and high average temperature during the vegetation period significantly increased the GLS content of vegetables. This suggests that the year x cultivar interaction modified the GLS content of vegetables.

Dietary low-glucosinolate rapeseed meal affects thyroid status and nutrient utilization in rainbow trout (Oncorhynchus mykiss)

Two rapeseed (Brassica napus) meals, RM1 and RM2, with two levels of glucosinolates (GLS; 5 and 41 mumol/g DM respectively) were incorporated at the levels of 300 and 500 g/kg of the diets of juvenile rainbow trout (Oncorhynchus mykiss) in replacement of fish meal, and compared with a fish-meal-based diet. A decrease in the digestibility of the DM, protein, gross energy and P was observed with high-rapeseed meal (RM) incorporation. In trout fed on RM-based diets, growth performance was reduced even after only 3 weeks of feeding. Feed efficiency was adversely affected by RM and GLS intake. Protein and energy retention coefficients were significantly lower in fish fed on the diet containing the higher level of GLS. P retention was significantly lower with all the RM-based diets than with the fish-meal diet. Irrespective of the degree of growth inhibition, fish fed on RM-based diets exhibited similar typical features of hypothyroid condition due to GLS intake, expressed by lower plasma levels of triiodothyronine and especially thyroxine and a hyperactivity of the thyroid follicles. This hypothyroidal condition led to a strong adjustment of the deiodinase activities in the liver, the kidney and the brain. A significant increase of the outer ring deiodinase activities (deiodinases type I and II respectively) and a decrease of the inner ring deiodinase activity (deiodinase type III) were observed. It is concluded that the observed growth depression could be attributed to the concomitant presence of GLS, depressing the thyroid function, and of other antinutritional factors affecting digestibility and the metabolic utilization of dietary nutrients and energy.

Chemoprevention of DMBA-induced transplacental and translactational carcinogenesis in mice by oil from mustard seeds (Brassica spp.)

The present study reports the chemopreventive potential of the oil from mustard seed on 7,12-dimethylbenz[a]anthracene-induced transplacental and translactational carcinogenesis in Swiss albino mice. Gestating females were treated with mustard oil at dose levels of 0.05 and 0.10 ml per day from days 13 to 19 of gestation. In addition, they were given DMBA (3 mg/animal) on days 15-17 of gestation. The percentage of tumour incidence in the F1 progeny was reduced significantly at both dose levels from 65% in the control group to 29% and 16%, respectively, in the experimental groups. The mean number of tumours per effective F1 progeny was reduced from 1.56 in the control group to 0.93 and 0.41 in the animals treated with lower and higher doses of mustard oil, respectively. When lactating mothers were given the mustard oil at dose levels of 0.05 and 0.10 ml per day for the first 15 days of lactation in addition to DMBA given on days 3, 6, 9, 12 and 15 of lactation, the multiple site tumour incidence was brought down significantly from a control value of 70% to 32% and 18%, respectively, in lower and higher dose groups. The mean number of tumours in the F1 mouse was reduced from a control value of 1.71 to 0.96 at the lower dose level and to 0.34 at the higher dose level. From earlier studies done in our laboratory, it appears that mustard oil exerts its effect by inducing the enzymes of drug detoxification and also by changing the profile of the antioxidant defence system. The quantitative and qualitative nature of the active principles and their passage into the F1 progeny remains to be seen.

Modulation of the biological effects of glucosinolates by inulin and oat fibre in gnotobiotic rats inoculated with a human whole faecal flora

The influence of dietary fibre on the biological effects of glucosinolates was investigated in gnotobiotic rats harbouring a human whole faecal flora. Animals were fed for 6 wk with diets containing 12% rapeseed meal (RSM) supplemented or not supplemented with 10% inulin (INL) or oat fibre. Both fibre types enhanced the liver hypertrophy due to RSM to equal extents, but had different effects on the other glucosinolate-related toxic effects. INL partially restored a normal thyroid hormone status whereas kidney weight, goitre and growth deficit were increased on exposure to the diet containing oat fibre. Oat fibre and, to a lesser extent, INL modulated the alterations of digestive xenobiotic-metabolizing enzymes (XME) induced by RSM. They counter-balanced the induction of hepatic cytochrome P-450 and lessened the induction of uridine diphosphate-glucuronosyltransferase in the liver but did not modify depletion of its activity in the small intestine. On the other hand, they enhanced the induction of glutathione S-transferase in the liver and the large intestine but not in the small intestine. These findings give new evidence that the biological effects of naturally occurring non-nutrient compounds are closely dependent on the composition of the diet. Two mechanisms are proposed to explain the different influence of INL and oat fibre on RSM toxicity. Their different fermentative characteristics could lead to a modulation of the bacterial metabolism of glucosinolates in the caecum. Alternatively, their own action on the digestive XME could modify the subsequent metabolism of bacterial glucosinolate derivatives.