Effect of enzyme inducers on the metabolism of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) in the rat

The effect of enzyme inducers 3-methylcholanthrene (3-MC) and Aroclor 1254 (A-1254) on the metabolic fate of the dietary mutagen and carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) in male F344 rats was studied in relation to single dose corn oil and untreated controls. The latter two groups were similar as regards metabolism of IQ. However, the ratio of total metabolites excreted in urine compared with those in feces was higher in A-1254 pretreated rats. In fact, this distinct excretory pattern stemmed from a lower level of IQ-N-sulfamate, and a considerably higher level of 5-OH-IQ sulfate ester, a major metabolite in urine of A-1254-injected rats. Interestingly, 5-OH-IQ glucuronide urinary levels were unaffected by the treatment. Thus, the direct 5-hydroxylation of IQ appears to be considerably increased by 3-MC and more so by A-1254, and under those conditions the resulting 5-OH-IQ is preferentially converted to the sulfate ester, in turn readily excreted in urine.     

The role of the human acetylation polymorphism in the metabolic activation of the food carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ).

The metabolic activation of the heterocyclic food carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) by two human cytochrome P450 monoxygenases (P4501A1 and P4501A2) and two human N-acetyltransferases (NAT1 and NAT2) was investigated. Various combinations of these enzymes were functionally expressed in COS-1 cells. DNA adducts resulting from the activation of IQ were assayed quantitatively by the 32P-postlabeling procedure. The highest adduct frequency was observed in cells expressing both CYP1A2 and NAT2. CYP1A2 in combination with NAT1 was 3-6 times less active. When expressed alone these enzymes gave rise to low adduct frequencies. Experiments with N-acetyl-IQ as substrate suggest that NAT1 and NAT2 in addition to their known role in N-acetylation display arylhydroxamic acid N, O-acetyltransferase (AHAT) activity. Quantitative differences in adduct formation between IQ and N-acetyl-IQ indicated that metabolic activation of these arylamines preferentially occurs by P4501A2-catalyzed N-hydroxylation followed by O-acetylation mediated through NAT1 and/or NAT2. These data, in combination with the known genetic polymorphism of NAT2, may explain the clinical observation that the acetylation polymorphism constitutes a risk factor in the carcinogenic activation of environmental mutagens.     

Organ-dependent susceptibility of p53 knockout mice to 2-amino-3-methylimidazo[4,5-f]quinoline (IQ)

p53 knockout mice are now being frequently used to identify the carcinogenic potential of chemicals, thus it is important to precisely assess the susceptibility of the animals to various test chemicals. In the present study the susceptibility of p53 nullizygous((-/-)), heterozygous((+/-)), and wild-type((+/+)) mice to 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) was investigated. Mice of all three genotypes were first fed a diet containing 100 or 300 p.p.m. IQ for 15 weeks in a short-term experiment. p53((+/-)) and ((+/+)) mice were then treated with IQ for 40 weeks and maintained without further treatment for an additional 12 weeks in the long-term experiment. In the forestomach, the incidence of squamous cell hyperplasia was significantly higher in p53((-/-)) than in ((+/-)) and ((+/+)) mice at 15 weeks and higher in ((+/-)) mice than ((+/+)) mice with long-term IQ treatment, indicating an elevated susceptibility of p53 knockout mice. In contrast, in the liver, various hepatocellular lesions developed mainly in female mice with long-term IQ exposure but no significant differences were evident between p53 knockout and wild-type mice, indicating a lack of elevated susceptibility in the knockout animals. Furthermore, polymerase chain reaction-single strand conformation polymorphism and sequencing analysis revealed relatively high (13/30) and low (1/15) incidences of p53 mutations (exons 5-8) in squamous cell hyperplasia and hepatocellular tumors, respectively. These results clearly indicate that the susceptibility of p53 knockout mice is organ-dependent, coinciding to some extent with the likelihood of p53 gene alteration in the induced tumors.     

Tissue distribution of DNA adducts in CDF1 mice fed 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ)

Male and female CDF1 mice were administered a single oral dose of 3 mumol of the food mutagens 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) or 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ) and killed 24 h later. DNA was isolated from the livers, lungs, kidneys, colon and forestomach and analysed by 32P-postlabelling for the presence of IQ and MeIQ adducts. Several adduct-enrichment procedures were investigated, including ATP-deficient labelling conditions, butanol extraction and nuclease P1 digestion, and only the ATP-deficient procedure was found to produce the same adduct pattern on polyethyleneimine--cellulose TLC as the standard procedure. Up to nine adduct spots were detected in liver DNA from IQ-treated mice, two of which were not detected in other tissues. The levels of binding in both male and female mice were in the order liver greater than kidney greater than colon greater than forestomach greater than lung. Analysis of DNA from MeIQ-treated mice revealed the presence of up to seven adducts, one of which was detected in liver but not in other tissues. The relative order of DNA binding was kidney greater than liver greater than or equal to colon greater than forestomach greater than lung. As dietary feeding of IQ induces liver, lung and forestomach tumours, and MeIQ induces liver and forestomach tumours in this mouse strain, these binding levels do not correlate with the susceptibility of the organs to carcinogenesis induced by these compounds; the results may indicate the importance of additional factors in determining organ specificity of carcinogenicity.     

Metabolic activation of the food mutagens 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ) to DNA binding species in human mammary epithelial cells.

When incubated in suspension with the heterocyclic aromatic amine food mutagens 2-amino-3-methylimidazo [4,5-f]-quinoline (IQ) and 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), human mammary epithelial cell aggregates were found, by 32P-postlabelling analysis, to yield DNA that contained adducts. Analysis by HPLC of the 32P-labelled digests of mammary cell DNA indicated that in each case a major adduct peak corresponded to that produced in DNA in vitro by activated derivatives of the two compounds. The patterns of adducts obtained when DNA digests were separated by TLC on polyethyleneimine-cellulose plates were found to resemble those previously shown to be present in DNA of tissues of mice fed IQ or MeIQ. These results demonstrate the ability of human mammary epithelial cells to activate carcinogenic heterocyclic compounds known to be present in the human diet to DNA binding derivatives.     

Multipotential carcinogenicity of the fried food mutagen 2-amino-3-methylimidazo[4,5-f]quinoline in rats

The carcinogenicity of the mutagenic compound 2-amino-3-methylimidazo[4,5-f]-quinoline (IQ), identified in fried and broiled foods, was investigated in female Sprague-Dawley rats. Administration by gavage of IQ (0.4 mmol/kg body weight) on a weekly regimen for 31 weeks starting with 6-week-old animals induced a high yield of multiple mammary gland carcinomas in a limited bioassay lasting a total of 52 weeks. In a positive control group receiving 4-aminobiphenyl (4-AB), the expected carcinomas in the mammary gland developed. IQ, but not 4-AB, also yielded neoplasms in the ear duct and to a lesser degree, in the liver, pancreas, and urinary bladder. In addition, with IQ, a high incidence of preneoplastic lesions in the pancreas was observed. Vehicle and untreated controls did not have any lesions. These findings demonstrate that IQ is a powerful multipotent carcinogen in the rat.     

Comparison of initiation potential of 2-amino-3-methylimidazo[4,5-f]quinoline and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline in an in vivo carcinogen bioassay system

A new approach to low-dose assessment of carcinogenic potential was applied to food contaminant pyrolysis products. Single intragastric doses of the carcinogenic pyrolysates, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) or 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline MeIQx), were given 12 h after two-thirds partial hepatectomy (PH) to F344 male rats. Two weeks thereafter the animals were placed on a basal diet containing 0.05% phenobarbital (PB) for 6 weeks combined with an i.p. administration of D-galactosamine (300 mg/kg) to facilitate growth of initiated cells. Both IQ and MeIQx clearly caused initiation of hepatocarcinogenesis as revealed by induction of preneoplastic placental-form glutathione-S-transferase-positive (GST-P+) hepatocyte foci composed of more than three cells (approximately 30 microns in diameter). A similar protocol without performance of PH before pyrolysate administration gave a positive result only for the IQ-treated group indicating that cell proliferation is essential during the low-dose, one-shot initiation step. IQ was found to be two to three times more potent in inducing GST-P+ foci using both protocols. The current approach could find application in practical carcinogenicity screening of chemicals, for which only small amounts are available.     

Genotoxicity of the food mutagen 2-amino-3-methylimidazo-[4,5-f]quinoline (IQ) and analogs

The food mutagen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ)is an analogue of quinoline, a hepatocarcinogen. 2-Aminofluorene,benzldine and 3,2'-dimethyl-4-aminobiphenyl (DMAB) are potentinducers of unscheduled DNA repair in primary culture rat liverhepatocytes, as was IQ (151 grains/ nucleus at 1 x 10^–6M). Quinoline, on the other hand, is only weakly positive inthis assay (15 grains/nucleus at 1 x 10^–3 M). IQ, quinolineand DMAB were applied topically to shaved skin of Sencar micewith promotion by 12-O-tetradecanoylphorbol 13-acetate (TPA)for 20 weeks, when 14 of 20 mice in the quinoline group had25 tumors, but only one of 30 animals in the IQ group and fiveof 30 in the DMAB group were tumor-bearing. Analogs of IQ synthesizedby substitution at the 2- or 3-position with amino or methylgroups were assayed with the Ames Salmonella typhimurium testerstrains TA98 and TA100. Mutagenicity for TA98 is reduced inthe absence of the 3-methyl group and is completely abolishedwith removal of the 2-amino moiety. None of these analogs arestrong mutagens for TA100. Exocyclic N-oxidation is a likelyobligatory step in the activation of IQ to a mutagen.     

Mutagenicity of 2-amino-3-methylimidazo[4,5-f]quinoline in human lymphoblastoid cells

2-Amino-3-methylimidazo[4,5-f]quinoline (IQ), a heterocyclic aromatic amine that has been identified in cooked meats and cigarette condensates, is mutagenic in human lymphoblastoid TK6 cells at the thymidine kinase and hypoxanthine-guanine phosphoribosyl transferase (hprt) loci. Treatment of the cells with IQ following activation with either an exogenous metabolizing mixture (S9) or following photoactivation of the azido-derivative of IQ (N3-IQ) showed that the photolytic-derivative of N3-IQ was more active. This observation is consistent with other reports that indicate that the weak mutagenicity of IQ in mammalian cells is caused by the lack of enzymes required for the ultimate activation of the compound within the cells. Two DNA adducts were found by 32P-post-labelling in the cells treated with the photoactivated N3-IQ. The major adduct was identified as N- (deoxyguanosin-8-yl)-2-amino-3-methylimidazo[4,5-f]quinoline (dG-C8-IQ) and the minor adduct as 5-(deoxyguanosin-N2-yl)-2-amino-3- methylimidazo[4,5-f]quinoline (dG-N2-IQ). The ratio of the dG-C8IQ to the dG-N2-IQ adducts was approximately 3:1 and did not significantly change in cultures treated with different concentrations of the mutagen. Approximately 50% of the adducts were removed 9 h after treatment with IQ and <10% of these adducts remained after 24 h. There was no significant preferential repair of either adduct under the experimental conditions used. The identification of 15 mutations induced at the hprt locus (of the 44 mutants analysed) showed IQ to be efficient at inducing single base deletions in a run of guanines. Six single guanine deletions were observed in the run of six guanines in exon III and one deletion of a single guanine was observed in a non- repetitive sequence in exon VI. Other mutations observed were two GC-- >TA transversions, two GC-->CG transversions, one AT-->TA transversion and one GC-->AT transition. In addition, two multiple mutations were found. The majority of the identified mutations (12/15) occurred at GC base pairs and suggests either the dG-C8-IQ or the dG-N2-IQ adduct to be the pre-mutagenic lesion.      

Detection of 2-amino-3-methylimidazo[4,5-f]quinoline in cigarette smoke condensate

2-Amino-3-methylimidazo[4,5-f]quinoline (IQ), which is mutagenic and carcinogenic, was found to be present in cigarette smoke condensate by liquid chromatography with an electrochemical detector and a photodiode-array detector. The amount of IQ was estimated to be 0.26 ng per cigarette.     

Fluorometric detection of 2-amino-3-methylimidazo[4,5-f]quinoline, 2-amino-3,4-dimethylimidazo[4,5-f]quinoline and their N-acetylated metabolites excreted by the rat

A sensitive fluorometric method has been developed for the determinationof carcinogenic amino imidazoazaarenes (AIA compounds) whichare formed during the cooking of food. They are separated byt.l.c. followed by spraying with dimethylsulfoxide and visualizationby long-wave u.v. light. Quantification is done by fluorescencescanning. This method was applied to the determination of themetabolites in urine and feces from rats given 5 mg/kg bodywt i.p. of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ). Metabolitesextractable by organic solvents were identified as the parentcompound and their N-acetylated derivatives (AcIQ, AcMeIQ).Between 0.1 and 1% of the administered dose was recovered asthese metabolites in urine during 24 h. The amounts of MeIQand AcMeIQ found in feces were 1 and 3% respectively. AcIQ wasnot detected in feces while IQ, MeIQ and their N-acetylatedderivatives were found in bile. The metabolites in urine wereidentified by m.s. and in feces by t.l.c. and their fluorescentproperties. When IQ or MeIQ were incubated with rat liver cytosolin the presence of acetyl-CoA, N-acetylated derivatives wereformed. The reverse reaction, deacetylation, also took placein the liver cytosol, with K_m values of 67 and 32 µM forAcIQ and AcMeIQ respectively.     

DNA adduct formation of the food carcinogen 2-amino-3-methylimidazo[4, 5-f]quinoline (IQ) in liver, kidney and colo-rectum of rats

DNA adducts of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ)have been measured in the liver, kidney, and colorectum of maleFischer-344 rats given a single oral dose of IQ (20 mg/kg).The pattern and distribution of DNA adducts examined by ³²P-postlabelingwas similar in all tissues. N-(Deoxyguanosin-8-yl)-2-amino-3-methylimidazo-[4,5-f]quinoline(dG-C8-IQ) was the principal adduct identified and it accountedfor     

Purification of the food-borne carcinogens 2-amino-3-methylimidazo [4,5-f]quinoline and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline in heated meat products by immunoaffinity chromatography

A rapid and simple scheme has been developed for the isolation and purification of two of the major mutagenic heterocyclic amines formed in heated beef products by affinity chromatography using monoclonal antibodies which recognize 2-amino-3-methylimidazo[4,5-f]quinoline (IQ). Two cell lines producing IgG antibodies were established following fusion of Sp2 or P3x.63 myeloma cells with spleen cells of immunized BALB/cby mice. The antigen was bovine gamma globulin haptenized with 2-(3-carboxypropylthio)-3-methylimidazo-[4,5-f]quinoline. The antibodies were immobilized on CNBr-activated Sepharose 4B. IQ and MeIQx formed in heated beef products were partially purified by XAD-2 chromatography and then applied to the affinity columns. Purification by affinity chromatography was adequate for subsequent quantitative analysis by HPLC with UV detection. With this purification scheme as little as 1 g of beef extract or 15 g of fried beef could be assayed for IQ and MeIQx at the part per billion level. Both antibodies had similar affinity constants for IQ (9.3 X 10(6) and 6.7 X 10(6) M-1) and for MeIQx (7.1 X 10(5) and 2.7 X 10(5) M-1) and both were suitable for immunoaffinity purification of IQ from complex mixtures. MAb2 could be used as well to selectively remove MeIQx from meat products after partial purification by XAD-2. MAb1, despite having a 3-fold higher affinity than MAb2 for MeIQx, could not be used for affinity chromatography for this mutagen.     

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

The presence of activated oncogenes in several rat hepatocellular carcinomas induced by 2-amino-3-methylimidazo[4,5-f]-quinoline (IQ) was examined by NIH 3T3 cell transfection assay and Southern blot analysis. In one tumor, IQ4, rat H-ras-1 and another oncogene that did not belong to the ras family were found to be activated.     

Quantitation of 2-amino-3-methylimidazo[4,5-f]quinoline and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline DNA adducts in specific sequences using alkali or uvrABC excinuclease

2-Amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MelQx) are carcinogens found in cooked meats that form DNA adducts upon metabolic activation. Purified DNA from Chinese hamster ovary (CHO) cells was reacted in vitro with the active metabolites N-acetoxy-lQ or N-acetoxy-MelQx, and the adduct levels in the 5′ dihydrofolate reductase (DHFR) gene and downstream region were quantitated by Southern hybridization. Adducted and restricted DNA was treated with Escherichia coli uvrABC excinuclease or alkali (0.1 N NaOH, 37°C, 60 min) to incise DNA at IQ and MeIQx adduct sites. The DNA was then denatured with formamide, electrophoresed on a neutral agarose gel, transferred to a support membrane, and hybridized with sequence-specific DNA probes. Both uvrABC and alkali reduced the intensity of Southern hybridization in proportion to the number of IQ or MeIQx adducts in DNA, indicating that these adducts are substrates for uvrABC and that they form alkali-labile lesions in DNA. IQ and MeIQx adduct levels were the same in the 5′ DHFR gene and in the downstream region. Southern hybridization analysis of pBR322 containing known levels of IQ or MeIQx adducts showed that the efficiency of cutting IQ or MeIQx adducts by uvrABC excinuclease and alkali was approximately 30% and 15%, respectively. ³²P-postlabeling studies examining adduct level in bulk DNA further showed that the adduct profiles were identical in pBR322, CHO DNA, and cultured CHO cells exposed to the reactive metabolites of IQ or MeIQx. The results indicate that IQ and MeIOx adducts can be quantitated in specific genomic sequences and that this method should be directly applicable to studies of gene-specific repair of these adducts in cultured cells.     

Intestinal microflora plays a crucial role in the genotoxicity of the cooked food mutagen 2-amino-3-methylimidazo [4,5-f]quinoline

We investigated the impact of the intestinal microflora on the genotoxicity of 2-amino-3-methylimidazo[4,5-f] quinoline (IQ), a mutagenic/carcinogenic heterocyclic amine commonly found in fried meats and fish. In parallel, we also examined the effect of the microflora on the protective effect of glucotropaeolin (GT), a glucosinolate contained in cruciferous vegetables, towards IQ-induced genotoxic effect. Conventional (NF), human flora associated (HFA) and germ free (GF) rats were treated either with 90 mg/kg IQ alone, 150 mg/kg GT alone or a combination of the two by gavage and DNA damage was determined in liver and colon cells using the alkaline single cell gel electrophoresis (SCGE) or comet assay. IQ caused a significant effect in both organs of all groups. However, DNA damage was most pronounced in NF animals. In colon cells, DNA migration was 6-fold more in IQ-exposed rats as compared with untreated controls. The effect measured with liver cells was similar. In comparison to NF rats, in HFA rats, tail length of the comets was 22 and 53% lower in liver and colon cells, respectively. Significantly weaker effects were seen in GF animals (66 and 75% lower damage in hepatocytes and colonocytes, respectively, than in NF animals). Pretreatment with GT led to a complete reduction of IQ-induced DNA damage regardless of the microbial status of the animals. In addition, a moderate decrease in spontaneous DNA damage was seen in animals that received GT alone. Our results show that the microflora has a strong impact on the genotoxic effects of IQ. We conclude that the alkaline SCGE assay with rats harbouring different flora opens new possibilities to investigate the role of intestinal bacteria on health risks caused by dietary carcinogens.     

Efficient method for the isolation by HPLC, of a major metabolite of the carcinogen 2-amino-3-methylimidazo [4,5-f]quinoline (IQ), the 5-hydroxy derivative

Previous difficulties in the standard HPLC separation of the 5-hydroxy derivative, a major metabolite of the food mutagen and carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), with the properties of a chelating agent, were resolved by utilizing a nonmetallic tubing and column and a BRP-1 stationary phase. This system separates the already known metabolites by reverse phase mode, but presents the unique advantage of resolving chelating compounds like 5-hydroxy-IQ as a single, clean peak. The procedure may be generally applicable to this class of chemicals.     

Inhibitory effect of dietary 4-ipomeanol on DNA adduct formation by the food mutagen 2-amino-3-methylimidazo [4,5-f]quinoline (IQ)in male CDF1 mice

The food mutagen 2-amino-3-methlimidazo[4,5-f]quinoline (IQ)is carcinogenic in the CDF₁ mouse liver, lungs and stomach.IQ Is activated to its ultimate carcinogenic form by N-hydroxylation,catalyzed principally by hepatic microsomal cytochrome P450IA2,and further esterification, resulting in the formation of N-(deoxyguanosin-8-yl)-IQand other adducts. The furanoterpenold 4-ipomeanol (IPO) isa naturally occurring pneumotoxin which exerts its specifictoxicity in Clara cells of the lung after activation by microsomalcytochrome P450. Because IPO is activated in the liver by acytochrome P450IA2 enzyme, we evaluated IPO as a possible chemopreventiveagent by assessing its ability to inhibit IQ-DNA adduct formationin the CDF₁ mouse. Mice were put on an AIN-76A diet with orwithout 0.075% IPO from day 0 to 54. IQ (0.01%) was added tothe diets from day 22 to 41 and animals were killed (four animals/timepoint) on days 42, 44, 46, 48, 50 and 54. Blood (for white bloodcell isolation), liver, lungs, stomach, small intestine, cecun,colon, kidneys, spleen and heart were collected for analysisof IQ-DNA adducts by .³²P-post-labeling. During the 12 day periodafter cessation of IQ exposure (days 42–54) IQ-DNA adductformation was significantly inhibited in the liver (33.6–46.4%),lungs (29.9–58.6%), stomach (33.2–51.5%) and whiteblood cells (24.5–63.7%), but not in the other organs.Except in the colon, adduct removal from organs during days42–54 was relatively slow (36.0–81.9% of day 42levels remaining on day 54, 9.4–16.7% in the colon), butthe presence of IPO in the diet did not influence the rate ofadduct removal. Measurement of hepatic microsomal ethoxyresorufindeethylase, an activity specific for cytochrome P450IA isozymes,showed that the enzyme could be inhibited (14.1–68.1%)by IPO (0.05–10.0 mM) in vitro. It is concluded that IPOinhibits IQ-DNA adduct formation in target organs of the CDF₁mouse and that IPO may act by inhibiting N-hydroxylation ofIQ. It is therefore possible that IPO may be a candidate chemopreventiveagent against IQ-induced carcinogenesis.     

Sex differences in the formation and persistence of DNA adducts of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) in CDF1 mice

The potent food mutagen 2-amino-3-methylimidazo[4,5-f]-quinoline (IQ) is carcinogenic in the CDF1 mouse, affecting the liver, lungs and forestomach. Females are approximately twice as sensitive as males to liver tumor induction. Using 32P-postlabeling assays, the dose-response of IQ-DNA adduct formation was determined in various organs of male and female CDF1 mice after single p.o. doses of IQ. To determine the possible correlation between IQ-DNA adduct formation, persistence and tumorigenicity in target organs, young adult male and female CDF1 mice were treated with a single p.o. dose (50 mg/kg) of IQ, and IQ-DNA adducts were isolated and quantitated in liver, lungs, forestomach, small intestine and large intestine over a 24 day period. In the range of 5-50 mg IQ/kg, IQ-DNA adduct formation was related to dose in all organs examined (liver, lungs, stomach, small intestine, large intestine). Total adduct formation (expressed as relative adduct labeling, RAL) 24 h after administration was highest in the liver (6.4-6.9 x 10(-7)) with lower levels, in decreasing order, in the large intestine, small intestine (non-target organs), forestomach and lungs (target organs). In all cases the major adduct, comprising 68-79% of the total, co-chromatographed with standard N-(deoxyguanosin-8-yl)-IQ. Up to three additional IQ-specific adducts could be detected. Except in the liver, adduct levels 24 h after administration of IQ were 2- to 3-fold higher in females than in males. There was no preferential retention of any one of the four adducts 1-24 days after administration of IQ. Beyond day 4 after administration, total adducts in the liver of females were approximately 2-fold higher than those in males, and the rate of removal from female lung was approximately 2-fold faster than that from male lung during the 1-24 day time period. Both these findings correspond to the known sex differences in IQ-induced tumor incidences in these organs. The higher adduct levels in non-target organs (intestines) as compared to target organs (lungs and stomach), combined with the absence of differential persistence of any individual adduct indicates that, in addition to adduct formation and persistence, other factors contribute to the target organ specificity of IQ in CDF1 mice.     

Effect of methyl substitution on mutagenicity of 2-amino-3-methylimidazo[4,5-f]quinoline isolated from broiled sardine

2-Amino-3-methylimldazo [4,5-f]quinoline [I] is a potent mutagenisolated from broiled sun-dried sardine. [I] and its seven ofderivatives, (two isomers, one demethylated derivative and fourmethyl-substituted derivatives), were tested for mutagenicityon Salmonella typhimurium TA98 and TA100 in the presence ofS9 mix. 2-Amino-1,4-dlmethylimldazo [4,5-f]quinoline was thestrongest mutagen of these 8 compounds on TA98, giving 159,000revertants/nmol (750,000 revertants/µg). The demethylatedderivative, 2-aminoimidazo [4,5-f]quinoline, had very weak mutagenicity,inducing only 55 revertants/nmol (200 revertants/µg).Compounds having a methyl group at position N-1 or N-3 of 2-aminoimidazo[4,5-f]quinoline were strong mutagens. The 1,5-dimethyl-derivativewas more mutagenic than 3,5-dimethyl-derivative. Introductionof a methyl group at position 4 and position 5 enhanced andreduced the mutagenicity, respectively. All the compounds testedwere more mutagenic to TA98 than to TA100, but their relativeorders of mutgenlcity with TA98 and TA100 were the same.