Formation of 2-nitro-3-methylimidazo[4,5-f]quinoline, a directly mutagenic product, by near-ultraviolet irradiation of a mixture of 2-amino-3-methylimidazo[4,5-f]quinoline and N-nitrosodimethylamine

Direct-acting mutagens to Salmonella typhimurium TA98 were found to be formed from heterocyclic amines on exposure to near-ultraviolet light in the presence of N-nitrosodialkylamines. We have isolated the mutagenic photoproduct formed from 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and N-nitrosodimethylamine, and the product was identified as 3-methyl-2-nitromidazo[4,5-f]quinoline (IQ(NO₂)). The yield of IQ(NO₂) from IQ was estimated to be 17%. Similar light-dependent activation of IQ was noted with 4 different nitrosodialkylamines other than nitrosodimethylamine. Furthermore, MeIQ and MeIQx were also activated with nitrosamine and light. These reactions represent an example of interaction between 2 different classes of mutagens.     

Fate of the food mutagen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) in Sprague-Dawley rats. I. Mutagens in the urine

2-Amino-3-methylimidazo[4,5-f]quinoline (IQ) is a potent bacterial mutagen formed during cooking of beef. IQ was administered intravenously to Sprague-Dawley rats at concentrations ranging from 7.5-50 mg/kg body weight. Urine was collected and analyzed for mutagenicity. Urinary mutagens were found which required activation by S9 mix, and reverted Ames test strains TA98 and TA100, but not TA1535 or TA1537. The amount of urinary mutagen(s) were related to IQ dose administered and were excreted within 48 h. Additional mutagenic activity was not released after incubation with beta-glucuronidase or aryl sulfatase. Analysis of urinary mutagens by HPLC indicates that the majority of mutagenic activity is due to unchanged IQ, but a small peak of mutagenic activity may correspond to N-acetyl or 3-N-demethylated metabolite. Since only 1% of the administered mutagenic activity is recovered in the urine, IQ may be readily detoxified in vivo.     

Activated c-raf gene in a rat hepatocellular carcinoma induced by 2-amino-3-methylimidazo[4,5-f]quinoline

A rat hepatocellular carcinoma, IQ7, induced by 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) gave two transformants of NIH 3T3 cells on DNA mediated gene transfer. One of these transformants was examined further and secondary and tertiary transformants were obtained. The secondary transformant was tumorigenic in nude mice. The activated oncogene in this primary transformant was identified as rat c-raf by Southern blot analysis.     

Modulation of the mutagenic effects of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ) in bacteria with rat-liver 9000 x g supernatant or monolayers of rat hepatocytes as an activation system

An in vitro protocol was designed to separate the process of metabolic activation from the mutational events. Cultured rat hepatocytes were first incubated with the food mutagens 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) or 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ). After the incubation period the medium was removed and further incubated with Salmonella typhimurium TA98. A high direct mutagenic activity of the culture medium was then measured. The half-lives of the mutagenic metabolites formed from IQ and MeIQ were in the order of 45 min. The presence of the cytochrome P450 inhibitors alpha-naphthoflavone and metyrapone during the pre-incubation period reduced the accumulation of mutagenic metabolites. No effects of ascorbate on the mutagenic effects of IQ and MeIQ were seen. (+)-Catechin, another antioxidant and free-radical scavenger, markedly enhanced the number of IQ/MeIQ-induced revertants when added to the hepatocytes. In contrast, (+)-catechin clearly decreased the number of revertants when 9000 X g supernatant from rat liver (S9) was used as an activation system. No marked effect of pentachlorophenol, an inhibitor of hepatocyte sulfation and bacterial O-acetylation, was seen using hepatocytes as an activation system, while the mutagenic activity of both IQ and MeIQ was reduced by 90% in the S9/Salmonella system. The addition of an inhibitor of glucuronidation, galactosamine, or the nucleophile glutathione caused no or only minor decreases in the genotoxic effects of the IQ compounds. With both S9 and hepatocytes as activation systems the relative mutagenic effects observed in the S. typhimurium strains TA98 and TA98 NR were in the same order of magnitude, while a large decrease was seen with TA98/1,8-DNP6. The results show that this in vitro test protocol may be useful as a tool to study mechanisms involved in the formation of mutagenic metabolites.     

Characterisation of metabolites of the food mutagens 2-amino-3-methylimidazo[4,5-f]quinoline and 2-amino-3,4-dimethylimidazo[4,5-f]quinoline formed after incubation with isolated rat liver cells

The metabolism of 14C-labelled 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ) was studied in suspensions of hepatocytes isolated from PCB-pretreated rats. The metabolites found after incubation of IQ/MeIQ (0.1 mM) with PCB-pretreated hepatocytes for 3 h were separated into three principal groups: ethyl acetate-extractable metabolites (2-4%), water soluble metabolites (94-98%) and covalently bound metabolites (0.4-0.5%). The water soluble metabolites were separated by HPLC. The metabolites were evaluated by beta-glucuronidase lability, sulphate incorporation and compared with glucuronides formed by microsomes. Mass spectroscopy and proton NMR were also run. The major metabolites formed were a N2-sulphamate, an O-sulphate in position 5 for IQ and 5 for MeIQ and an O-glucuronide in the same position. The MeIQ N2-sulphamate was much less abundant than the IQ N2-sulphamate. When compared with hepatocytes from uninduced rats, it was found that primarily the formation of ring-hydroxylated conjugates increased after PCB-pretreatment. The major ethyl acetate-extractable metabolites were the N2-acetyl derivatives and an unidentified metabolite. A small peak representing the 5-hydroxy-IQ or 5-hydroxy-MeIQ could also be seen in the HPLC chromatogram of the ethyl acetate extractable metabolites. All major water soluble products described in hepatocytes were also found in urine and bile of uninduced rats exposed to IQ/MeIQ in vivo.     

Anaerobic metabolism of 2-amino-3-methyl-3H-imidazo[4,5-f]quinoline (IQ) by human fecal flora

Incubation of the heterocyclic cooked food mutagen IQ with mixed human fecal microflora under anaerobic conditions yielded 2-amino-3,6-dihydro-3-methyl-7H-imidazo[4,5-f]quinoline-7-one (2) as the major detectable metabolite.     

Nuclear damage of colon epithelial cells by the food carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) is modulated by dietary lipids

Intestinal damage in C57BL/6J female mice was quantified by measuring the frequency of nuclear aberrations in colonic crypts. The animals were maintained on the following diets: standard (5% lipids, 5% cellulose); low- and high-cellulose (0-20% cellulose); high lipids (20% maize oil or 20% olive oil). All groups of animals were treated by gavage either with saline or 250 mg/kg of the dietary carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ). After 24 h their colons were removed and stained and the nuclear aberrations scored under the microscope. The administration of IQ markedly increased the number of colon aberrations in all of the treated animals. Variations in dietary fiber did not modify the colon-damaging activity of this compound. Maize oil slightly increased the colon-damaging activity, whereas significant protection was observed in the animals on a high-lipid olive-oil diet. These results show that composition of the diet may vary the genotoxic effect of this dietary carcinogen.     

Antimutagenic activity of selenium-enriched green tea toward the heterocyclic amine 2-amino-3-methylimidazo[4,5-f]quinoline

Both selenium and green tea have been reported to exhibit antigenotoxic and cancer chemopreventive properties. We compared the antimutagenic activities of regular green tea and selenium-enriched green tea obtained from Hubei Province, China, toward the heterocyclic amine, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) in the Salmonella assay. Selenium-enriched green tea obtained by foliar application of selenite exhibited concentration-dependent inhibition of IQ-induced mutagenesis in the presence of rat liver S9 and was significantly more effective than regular green tea tested under the same conditions. Analytical studies revealed no major differences in the polyphenol or caffeine content between regular green tea and selenium-enriched green tea, but the latter tea contained approximately 60-fold higher concentrations of selenium compared with regular green tea. The only soluble form of selenium was identified as selenite. The antimutagenic effects of certain individual tea constituents, such as epicatechin gallate and catechin, were enhanced by the addition of selenite to the Salmonella assay. Sodium selenite, sodium selenate, seleno-dl-cysteine, seleno-l-methionine, and l-Se-methylselenocysteine were not antimutagenic toward IQ when tested alone, but augmented significantly the inhibitory potency of green tea. The results suggested an enhancing (“coantimutagenic”) effect of selenium in combination with green tea in vitro, but in vivo studies are needed to assess whether there is a synergistic effect of tea and selenium to protect against heterocyclic amine-induced mutagenesis and carcinogenesis.     

Chemical structure and mutagenic activity of aminoimidazoquinolines and aminonaphthimidazoles related to 2-amino-3-methylimidazo[4,5-f]quinoline

We have synthesized 11 heterocyclic aromatic amines with chemical structures related to that of 2-amino-3-methylimidazo [4,5-f] quinoline (IQ), a potent mutagen occurring in broiled sardines, fried beef and beef extract. The mutagenic activity of these IQ analogs was studied and compared with that of IQ using the Ames test with strain TA98 of Salmonella typhimurium in presence of a metabolic activation system (S9 mix) derived from rat liver. The mutagenic activities of the IQ analogs vary over a million-fold; structure-activity comparisons indicate major contributions of the methyl substitution in the imidazole ring and of the quinoline-N, and significant contributions of methylation of the exocyclic amino group and of the geometry of the entire ring system.     

One dose of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) or 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) induces tumours in Min/+ mice by truncation mutations or LOH in the Apc gene

The C57BL/6J-Min/+ (multiple intestinal neoplasia) mouse has a heterozygous nonsense Apc(Min) (adenomatous polyposis coli) mutation, and numerous adenomas spontaneously develop in the intestine. Neonatal exposure of Min/+ mice to the food carcinogens 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) or 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) (one injection of 50mg/kg) increased the number of small intestinal tumours about three- and two-fold, respectively. The number of colonic tumours was only increased in males. We examined whether the wild-type Apc allele was affected in intestinal tumours induced by either PhIP or IQ. In spontaneously formed and in IQ-induced small intestinal and colonic tumours from these mice, the main mechanism for tumour induction was loss of wild-type Apc allele, i.e. loss of heterozygosity (LOH). In contrast to the IQ-induced (84% LOH) and spontaneously (88% LOH) formed tumours, only 55% of the PhIP-induced small intestinal tumours from males showed LOH. Tumours that apparently had retained the wild-type Apc allele were further analysed for the presence of truncated Apc proteins by the in vitro synthesised protein (IVSP) assay. Truncated Apc proteins, indicating truncation mutations in exon 15 of the Apc gene, were detected in two of the 12 PhIP-induced tumours in segment 2 (codons 686-1217), and two of five IQ-induced tumours, one in segment 2 and the other in segment 3 (codons 1099-1693). Three of these four mutations, all in segment 2 of the Apc gene, were confirmed by sequencing. The PhIP-induced mutations were detected at codon 1125 (C deletion) and 1130 (G-T transversion), and the IQ-induced mutation was at codon 956 (C-T transition). Importantly, no truncated proteins were detected in tumours from unexposed mice with apparently retained wild-type Apc allele. These results show that one injection of either PhIP or IQ induces intestinal tumours in the Min/+ mice by inactivation of the wild-type Apc allele either by causing LOH or truncation mutations.     

Protective effects of epigallocatechin gallate on colon preneoplastic lesions induced by 2-amino-3-methylimidazo[4,5-f ] quinoline in mice

Epigallocatechin gallate (EGCG), a key active ingredient in green tea, has multiple anticarcinogenic effects. The aim of the present study was to investigate if EGCG could prevent the formation of colon aberrant crypt foci (ACF) induced by 2-amino-3-methylimidazo[4,5-f ]quinoline (IQ) and to explore possible mechanisms for resultant effects. Sixty male BALB/cA nude, immunodeficient mice were divided into six groups including a normal unexposed control, mice induced with IQ alone, three groups treated with varying doses of EGCG post-IQ induction, and a EGCG-treated control population. Six weeks later, the mice were killed, and tissues subjected to hematoxylin-eosin (H&E) and 0.2% methylene blue staining to observe histopathological alterations of colon mucus and the formation of ACF, respectively. Protein expression of NF-E2-related factor 2 (Nrf2) was assessed via immunohistochemistry (IHC) and Western analysis, and mRNA levels of Nrf2 and uridine 5'-diphosphate-glucuronosyltransferase (UGT)1A10 were determined in colon tissues. Our results demonstrate that, compared with IQ-induced controls, the degree of atypical hyperplasia decreased and the number of total ACF and total AC also decreased significantly (P < 0.05 and P < 0.01, respectively) in mice belonging to all EGCG dosing groups. At the same time, the protein levels of Nrf2 detected by IHC and Western blotting increased (both P < 0.01 compared with IQ group), and the mRNA levels of Nrf2 and UGT1A10 increased (both P < 0.01 compared with IQ group). In conclusion, EGCG had preventive effects on preneoplastic lesions induced by IQ. Our observations suggest that this effect may be the result of activation of the Nrf2-UGT1A10 signaling pathway.     

Differential mutagenic activity of IQ (2-amino-3-methylimidazo[4,5-f]quinoline) in Salmonella typhimurium strains in vitro and in vivo, in Drosophila, and in mice

IQ, a heterocyclic aromatic amine which is formed during the frying of meat, was prepared by chemical synthesis. Its genotoxic potential was studied in bacteria, Drosophila and in mice. A mutagenic effect of IQ (frameshift induction) was detected in Salmonella typhimurium in experiments without metabolic activation; this effect was several orders of magnitude lower than that observed in the presence of an activation system. Ames tests with liver-homogenate S9 fraction from PCB-induced mice and rats confirmed the high mutagenic potency of IQ metabolites (Kasai et al., 1980a). Comparative studies on diagnostic Salmonella strains revealed that the high frameshift-inducing activity is independent of the plasmid pkM101; it is, however, greatly reduced by an intact excision-repair system for DNA lesions. The mutagenic activity of the metabolite(s) formed in vitro by S9 mix has a half-life of ca. 14 min. In the fruit fly, Drosophila melanogaster, IQ induced when used at sublethal concentrations, X-chromosomal recessive lethal mutations in male germ cells in a dose-dependent manner. In mice, tests were performed to detect somatic mutations: chromosomal anomalies (micronuclei) in bone marrow, and gene mutations (affecting coat pigmentation) in mice exposed to IQ in utero. No genotoxic effects were observed in these assays. However, the formation of mutagenic metabolites in the liver of IQ-treated mice was unequivocally demonstrated in host-mediated assays using Salmonella as mutagen probes in mice. The data demonstrate genotoxic activity of IQ in prokaryotic and eukaryotic organisms. The possible reasons for the different response of mammalian systems in vivo and the Salmonella system are discussed.     

Inhibition of DNA adduct formation of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and 2-amino-3-methylimidazo[4,5-f]quinoline by dietary indole-3-carbinol in female rats.

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) are two important heterocyclic amines formed in proteinaceous foods during the cooking process. Both PhIP and IQ are carcinogenic in several strains of rats. PhIP induces mammary tumors in female F344 rats, while IQ induces principally mammary and liver tumors in female Sprague-Dawley rats. Both PhIP and IQ are activated enzymatically, first by N-hydroxylation, catalyzed by CYP1A1 and CYP1A2, and subsequently by esterification (O-acetylation or sulfation), to yield DNA adducts. Such DNA adduct formation, and persistence of adducts, is related to initiation of carcinogenesis, while inhibition of this process leads to prevention of carcinogenesis. Indole-3-carbinol (I3C), a constituent of cruciferous vegetables, has chemopreventive properties in various systems; it probably acts by induction of detoxification enzymes. We have examined the effect of dietary I3C on DNA adduct formation by PhIP in female F344 rats and on that by IQ in female Sprague-Dawley rats. In experiment 1, F344 rats were maintained on AIN-76A diet containing 0.1% (w/w) I3C and then given p.o. doses (10 or 50 mg/kg) of PhIP. These doses are known to induce CYP1A1 and CYP1A2. Groups of animals (4/time point) were euthanized 1, 2, 6, and 16 days later, and their blood (for isolation of white blood cells), mammary glands, liver, stomach, small intestine, cecum, colon, heart, lungs, kidneys, and spleen were removed for DNA isolation and quantitation of PhIP-DNA adducts by 32P-postlabeling. PhIP-DNA adduct formation was inhibited (40-100%) by I3C in virtually all organs, including the mammary gland (the target organ), at both doses of PhIP, and at almost all time points. In a second experiment, Sprague-Dawley rats were fed either control AIN-76A diet or this diet containing 0.02% I3C or 0.1% I3C for a total of 42 days. IQ was added to the diets (0.01%, w/w) from day 15 to day 42, after which all rats received diet free of IQ and I3C. Groups of animals (4/time point) were killed on days 43 and 57. In addition to the organs removed in experiment 1, the pancreas, uterus, and ovaries were also removed, and IQ-DNA adducts were quantitated by 32P-postlabeling. Both dietary concentrations of I3C inhibited IQ-DNA adduct formation in most organs (except in lungs, kidneys, and pancreas) on both days 43 and 57; in liver, stomach, mammary gland, and spleen, inhibition was evident only on day 43. Inhibitions ranged from 22.6 to 86.6% with the 0.02% I3C diet and from 32.2 to 89.6% with the 0.1% I3C diet. I3C diets did not affect rate of adduct removal in either experiment. It is concluded that dietary I3C inhibits PhIP- and IQ-DNA adduct formation in both target and nontarget organs of female rats, even with high doses of PhIP when CYP1A1 and CYP1A2, the enzymes responsible for the initial activation (N-hydroxylation) of PhIP, are expected to be induced.     

Specific induction of hepatic cytochrome p4501a-2 in C57BL/6 and DBA/2 mice treated with 2-amino-3-methylimidazo[4,5-f]quinoline (IQ)

The food mutagen/carcinogen amino-3-methylimidazo[4,5-f]quinoline (IQ) is activated by cytochrome p4501a-2 via N-hydrox-ylation; various P450s may contribute to detoxification via ring hydroxylation. Alterations in P450 levels by IQ treatment might therefore influence its toxicity. To examine the role of Ah locus genotype on the biochemical effects of IQ, C57BL/6 (Ah^bAh^b; p450Ia-½ inducible) and DBA/2 (Ah_dAh_d, noninducible) mice of both sexes were given IQ at varying doses, with different vehicles and routes of administration. Livers taken after 24 hours were assessed for total cytochrome p450 and activities of ethoxyresorufin-O-deethylase (EROD, a p4501a-l activity, inducible in Ah^b mice), meth-oxyresorufin-O-demethylase (MROD, a p4501a-2 activity), and benzyloxyresorufin-O-dealkylase (BzROD, an activity of p4502b). There was little effect on total cytochrome p450, but all three enzyme activities were often induced, a maximum of 2.5-fold, in both sexes and in DBA/2 as well as C57BL/6 mice. However, Western immunoblot analysis with monoclonal antibodies demonstrated an increase only in p4501a-2 protein. p4501a-l remained undetectable. A monoclonal antibody to p4502-b recognized one protein band in liver mi-crosomes from males and two bands in female mice of both strains. Amounts of these proteins were not altered by IQ treatment. Thus, IQ specifically, if moderately, induces its activating enzyme, p4501a-2, in a process that was not clearly related to Ah responsiveness.     

Mutagenic activation of 2-amino-3-methylimidazo[4,5-f]-quinoline (IQ) and 2-amino-3,4-dimethylimidazo[4,5-f]-quinoline (MeIQ) by subcellular fractions and cells isolated from small intestine,kidney and liver of the rat

The mutagenic activity of the pyrolysis products 2-amino-3-methylimidazo[4,5-f]-quinoline and 2-amino-3,4-dimethylimidazo[4,5-f]-quinoline in Salmonella typhimurium TA98 using rat intestinal and renal subcellular fractions as activation systems was approximately 1 and 5 revertants per nmol, respectively. This was 1,000 times less than the activity with a subcellular fraction from rat liver. The mutagenic activity of both compounds was considerably increased using intestinal, renal and hepatic preparations isolated from PCB (Aroclor 1254)-pretreated rats, compared to preparations from control animals. In addition, both compounds displayed a moderate direct-acting mutagenic activity at concentrations above 10^-5 M. Isolated cells from small intestine, kidney and liver incubated in nucleopore chambers were able to convert both compounds into products which mutated bacteria outside the chambers. The concentrations of chemicals required to yield responses of a similar magnitude were approximately 3 orders of magnitude higher in the intestinal and renal systems compared to the hepatic system. The formation of metabolites mutagenic for Salmonella typhimurium by hepatic subcellular and cellular systems was shown to be superior to the respective intestinal and renal systems.Abbreviations AHH arylhydrocarbon hydroxylase - IQ 2-amino-3-methylimidazo[4,5-f]-quinoline - MC 3-methylcholanthrene - MeIQ 2-amino-3,4-dimethylimidazo[4,5-f]-quinoline - PCB polychlorinated biphenyls (Aroclor 1254) - S9 the 9,000 g supernatant tissue fraction - TCDD 2,3,7,8-tetrachlorodibenzo-p-dioxin     

Activation of the food-derived mutagen 2-amino-3-methylimidazo[4, 5-f]quinoline by human-liver microsomes

The ability of human-liver microsomes to metabolically activate the food-derived heterocyclic amine, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), and the model mutagen, 2-aminofluorene (AF), has been investigated using Salmonella typhimurium TA98. In 6 subjects tested the number of revertants produced by 0.1 micrograms IQ per mg microsomal protein varied from 11, 830 +/- 320 to 42, 830 +/- 290 (mean +/- SD). With the same livers and a dose of 10 micrograms AF per plate the number of revertants varied from 15,770 +/- 1600 to 29,380 +/- 810 per mg microsomal protein. Metyrapone and alpha-naphthoflavone caused differential inhibition of the mutagenesis of both IQ and AF indicating the involvement of different forms of cytochrome P450 in the metabolic activation of these amines in human-liver microsomes. In presence of human-liver microsomes IQ produced no detectable increase in mutations at the hypoxanthine phosphoribosyl transferase locus in lymphocytes and caused no increase in micronuclei formation at realistic exposure levels.     

Effect of intestinal microfloras from vegetarians and meat eaters on the genotoxicity of 2-amino-3-methylimidazo[4,5-f]quinoline, a carcinogenic heterocyclic amine

Aim of this study was to investigate the impact of intestinal microfloras from vegetarians and non-vegetarians on the DNA-damaging activity of 2-amino-3-methyl-3H-imidazo[4,5-f]quinoline (IQ), a carcinogenic heterocyclic amine that is found in fried meats. Floras from four vegetarians (Seventh Day Adventists) and from four individuals who consumed high amounts of meats were collected and inoculated into germfree F344 rats. The rats were kept on isocaloric diets that either contained animal derived protein and fat (meat consumers group) or proteins and fat of plant origin (vegetarian groups). IQ (90 mg/kg bw) was administered orally, after 4 h the extent of DNA-damage in colon and liver cells was determined in single cell gel electrophoresis assays. In all groups, the IQ induced DNA-migration was in the liver substantially higher than in the colon. In animals harbouring floras of vegetarians, the extent of damage was in both organs significantly (69.2% in the liver, P<0.016 and 64.7%, P<0.042 in the colon, respectively) lower than in the meat consumer groups. Our findings show that diet related differences in the microfloras have a strong impact on the genotoxic effects of IQ and suggest that heterocyclic amines are less genotoxic and carcinogenic in individuals that consume mainly plant derived foods.     

Effect of common Brassica vegetables (Brussels sprouts and red cabbage) on the development of preneoplastic lesions induced by 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) in liver and colon of Fischer 344 rats

Aim of the present study was the investigation of effects of juices from commonly consumed Brassica vegetables (two cultivars of Brussels sprouts and two cultivars of red cabbage) on formation and development of preneoplastic lesions in colons (aberrant crypt foci, ACF) and livers (glutathione-S-transferase placental form, GST-P+) in male F344 rats. The foci were induced by 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), a widespread carcinogenic heterocyclic aromatic amine which is found in fried meats. Recently, we reported on pronounced protective effects in the two-organ foci model when the vegetable juices were given during the carcinogen treatment but several findings by other groups indicated that breakdown products of glucosinolates contained in Brassica vegetables cause tumour promotion in various organs of laboratory rodents. In the present study, the animals received the juices in the drinking water (5%) over a period of 20 days after treatment with IQ (100 mg/kg bw on 10 alternate days). To increase the foci yield (which facilitates the detection of modifying effects), the animals were fed with a modified (high fat, fibre free) AIN-76 diet. With exception of the sprout variety "Cyrus", all juices lowered the number of GST-P+ foci as well as the foci area in the liver, but none of these effects was statistically significant. In the colon, none of the juices had an impact on crypt multiplicity (number of crypts/focus), whereas the number of ACF was decreased; only with the sprout variety Maximus the protective effect was significant (reduction 49%). The present findings show that administration of vegetable juices to the animals after the carcinogen does not increase the number and size of IQ-induced preneoplastic lesions in liver and colon.