Mutational specificity of 2-nitro-3,4-dimethylimidazo[4,5-f]quinoline in the lacI gene of Escherichia coli

2-Nitro-3,4-dimethylimidazo[4,5-f]quinoline (NO₂-MeIQ) is thenitro derivative of 2-amino-3,4-dimethylimi-dazo[4,5-f]quinoline(MeIQ), one of the food pyrolysis product mutagens and carcinogens.The mutational specificity of NO₂-MeIQ was determined usingthe lacI system in an Escherichia coli strain, EE125, harbouringthe plasmid pKM101. NO₂-MeIQ acts as a direct-acting mutagentowards this strain, and induces a broad range of mutationalalterations. At higher doses; G:C     

Isolation and identification of a new mutagen, 2-amino-4-hydroxy-methyl-3, 8-dimethylimidazo[4,5-f] quinoxaline (4-CH2OH-8-MeIQx), from beef extract

By monitoring the mutagenicity to a new Salmonella tester strain,YG1024, which has a much higher level of 0- acetyltransferaseactivity than S.typhimurium TA98, we found two new mutageniccompounds in bacteriological-grade beef extract. One of them(compound I), which had a similar UV spectrum to that of 2-amlno-3,4,8-trimethylimidazo[4,5-f]quinoxaline (4,8-DiMeIQx), was isolated and shown toaccount for {small tilde}2% of the total mutagenicity of thematerials adsorbed to blue cotton, and its concentration wasestimated to be 6.0 ng/g beef extract. This amount of compoundin beef extract was insufficient to allow measurements of variousspectra, but its level was increased {small tilde}9-fold byheating beef extract with creatine and threonine at 200°Cfor 5 h. From UV and mass spectra of the compound obtained frombeef extract heated with creatine plus threonine, it was deducedto be a hydroxymethyl derivative of anminodimethylimidazoquinoxaline.Compound I was isolated from the urine of rats given 4,8-DiMeIQxand identified as 2-amino-4-hydroxymethyl-3,8-dimethylimidazo[4,5-f]quinoxaline (4-CH₂OH-8-MeIQx) by ¹H-NMR analysis. 4-CH²OH-8-MeIQxinduced 326 000 revertants of YG1024 and 99 000 revertants ofTA98 per µg in the presence of S9 mix.     

Presence of N2-(deoxyguanosin-8-yl)-2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (dG-C8-MeIQx) in human tissues

One of the mutagenic and carcinogenic heterocyclic amines (HCAs),2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MelQx), is presentin cooked foods and we are chronically exposed to this compoundin our daily life. To study the role of HCAs in human carcinogenesis,we analyzed MelQx-DNA adducts in 38 DNA samples obtained fromsurgical and autopsy specimens by the ³²P-postlabeling methodunder adduct-intensification conditions with the modificationof additional digestion with nuclease P1 and phosphodiesteraseI after ³²P-labeling at 5' -hydroxyl termini. This modified³²P-postlabeling method can detect N²-(deoxyguanosin-8-yl)-2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline 5'-monophos-phate (5'-pdG-C8-MeIQx) at levelsdown to 1/10¹⁰ nucleo-tides. The DNA samples from colon andrectum surgical specimens and a kidney taken at autopsy werefound to contain an adduct spot corresponding to that of standard5'-pdG-C8-MeIQx on TLC at levels of 14, 18 and 1.8 per 10¹⁰nucleotides, respectively. Each adduct spot was extracted fromTLC and identified to be 5'-pdG-C8-MeIQx by HPLC. Thus, MelQx-DNAadducts actually exist in human tissues and this adduct formationmay be involved in human cancer development.     

Incorporation of carbon atoms from glucose into the food mutagens MeIQx and 4,8-DiMeIQx using 14C-labelled glucose in a model system

Mixtures of creatinine, glucose and threonine with the additionof a small amount, 250 µCi, of [U-¹⁴C]glucose, [1-¹⁴C]glucoseor [6-¹⁴C]glucose were heated at 180°C for 30 min in anaqueous model system. The mixtures were purified and analysedusing HPLC, scintillation and Ames tests. 2-Amino-3,8-dimethylimidazo[4,5-f]quinoxaline(MeIQx) and 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline(4,8-DiMeIQx) were detected as the main radioactive mutagens.The amount of MeIQx and 4,8-DiMeIQx produced from threoninewas estimated at 18 and 60 nmol/mmol glucose respectively. Radioactivecarbon atoms originating from glucose were also shown to beincorporated into 2-amino-3-methylimidazo[4,5-f]quinoxaline(IQx). The specific activity was calculated to be 0.6, 0.3 and0.1–0.3 mCi/mmol for MeIQx, 4,8-DiMeIQx and IQx respectivelyfor all three labelled forms of glucose. By the incorporationof carbon atoms originating from glucose into the imidazoquinoxalinemutagens it was clearly demonstrated that glucose is a precursorin the formation of these food mutagens.     

Major routes of metabolism of the food-borne carcinogen 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline in the rat

A metabolite of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline(MeIQx) was incorrectly characterized in this paper. The metabolitewas thought to be an acetyl conjugate of the 5-hydroxyl-atedderivative of MeIQx. This assignment is incorrect. The correctassignment is a sulfate conjugate of 5-hydroxy-MeIQx, 2-amino-3,8-dimethylirnidazo[4,5-f]quinoxaUn-5-yl-sulfate.This conclusion is based upon repurified sample analyzed by¹H NMR and ¹³C NMR, enzyme hydrolysis assays, IR spectro-scopyand FAB/MS (accurate mass measurement).     

32P-Post-labelling analysis of DNA adducts formed by food-derived heterocyclic amines: evidence for incomplete hydrolysis and a procedure for adduct pattern simplification

Food-derived aminoimidazoazarenes have been shown to be mutagenicand carcinogenic and to form covalent DNA adducts. ³²P-Post-labellinganalysis of DNA modified with these heterocyclic amines (HA),including 2-amino-3-methyl-imidazo[4,5-f]quinoline (IQ), 2-amino-1-methyl-6-phenylimid-azo[4,5-b]pyridine(PhIP), 2-amino-3,4-dimethylimidazo [4,5-fquinoline (MeIQ),2-amino-3,4,8-trimethylimidazo [4,5-f1 quinoxaline (4,8-DiMeIQx),2-amino-3,7,8-trimethylimidazo[4,5-f]quinoxaline (7,8-DiMeIQx)and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) hasresulted in considerable interlaboratory variation in the characteristicpatterns of DNA adduct spots, with up to six being detectedfor each compound. Similar complex patterns were observed whenazido-derivatives of HA were photoreacted with calf thymus DNA.When deoxyguanosine 3'-monophosphate was modified with the azidoderivatives and analysed using the ³²P-post-labelling procedure,one major spot was observed for IQ, 4,8-DilMeIQx, 7,8-DiMeIQxor PhIP and two major spots for MeIQ or MeIQx. In each case,these adducts were chromatographically indistinguishable fromthe major adducts formed with DNA. No major adduct spots wereobserved when 3'-phosphate derivatives of deoxyadenosine, deoxycytidineor thymidine were reacted with the azido-derivatives of HA.In an attempt to identify the additional spots, azido derivativesof PhIP or IQ were reacted with the synthetic homopolymer poly(dG)·poly(dC),the alternating copolymer poly(dC-dG) or a synthetic oligonucleotide(TTT-GTTTTTTCTTTCCCT): in each case a reduced number of adductspots were detected. The introduction of an additional nucleaseP1 hydrolysis step following the labelling reaction furtherreduced the number of adduct spots to only one or two majorspots. Reversed-phase HPLC analysis showed that the number ofpeaks of radioactivity was also reduced to one or two, presumablycorresponding to the [³²P]-5'-monophosphate deoxyguanosine adducts.We suggest that many of the additional spots commonly observedin conventional ³²P-post-labelling analysis of HA-modified DNAare adducted oligonucleotides that are partly resistant to hydrolysisby micrococcal nuclease and spleen phosphodiesterase but aresusceptible to hydrolysis by nuclease P1.     

Metabolism of the food carcinogen 2-amino-3, 8-dimethylimidazo[4, 5-f]quinoxaline in isolated rat liver cells

2-Amino-3, 8-dimethylimidazo[4, 5-f]quinoxaline (MelQx) wastransformed to at least 10 metabolites in suspensions of hepatocytesisolated from Aroclor 1254 treated rats. Combining biochemicaldata such as effects on MeIQx metabolism of metabolic modulatorsand incorporation of radioisotopic sulfur with UV, mass and¹H-NMR spectroscopy, we elucidated the structures of six metabolites.About 40% of the MeIQx was transformed to 2-amino-3, 8-dimethylimidazo[4,5-f]quinoxalin-4(or5)-yl sulfate. Other oxygenated metaboliteswere 2-amino-8-hydroxymethy1–3-methylimidazo[4, 5-f)quinoxalin-4(or5)-yl sulfate and 2-amino-4(or5)-ß-D-glucuronopyranosyloxy-3,8-dimethylimidazo[4, 5-f]quinoxaline. Evidence was obtainedthat a glutathione conjugate was formed. This metabolite, andthe other oxygenated metabolites were probably formed in P-450catalyzed reactions. Two metabolites, 2-ß-D-glucurono-pyranosylamino-3,8-dimethylimidazo[4, 5-f)quinoxaline and the N(3, 8-dimethylimidazo[4,5-f]quinoxaline-2-yl)sulfamate, were direct conjugates of MeIQx.     

32P-Postlabeling analysis of IQ, MelQx and PhIP adducts formed in vitro in DNA and polynucleotides and found in vivo in hepatic DNA from IQ-, MelQx- and PhIP-treated monkeys

The ³²P-postlabeling method was used to examine the adductsin DNA, polynucleotides, and mononucleotides reacted in vitrowith the N-hydroxy and N-acetoxy derivatives of 2-amino-3-methylimidazo[4,5-f]quinoline(IQ), 2-amino-3, 8-dimethylimidazo[4,5-f]quinoxaline (MelQx)or 2-amino-1-methy1-6-phenylimidazo[4,5-b]pyridine (PhIP). Adductprofiles were compared to those found in vivo in liver of cynomolgusmonkeys fed IQ, MeIQx or PhIP. The N-acetoxy derivatives ofIQ, MelQx and PhIP (generated in situ from the correspondingN-hydroxylamine in the presence of acetic anhydride) each formedthree principal adducts in DNA. Adduct 1 of IQ, MeIQx and PhlPwas chromatographically identical to the ³²P-labeled bis(phosphate)derivative of N-(deoxyguanosin-8-yI)-IQ, N-(deoxyguanosin-8-yI)-MeIQx,and N-(deoxyguanosin-8-yl)-PhIP respectively, and this adductcomprised     

Identification of N2-(deoxyguanosin-8-yl)-2-amino-3,8-dimethylimidazo[4,5-f)quinoxaline 3',5'-diphosphate, a major DNA adduct, detected by nuclease P1 modification of the 32P-postlabeling method, in the liver of rats fed MeIQx

The carcinogenic heterocyclic amine 2-amino-3,8-dimethyl-imidazo[4,5-f]quinoxaline(MeIQx) is widely distributed in cooked foods. The nucleaseP1 method increased the sensitivity of the standard ³²P-postlabelinganalysis about 1000-fold for detection of MeIQx-DNA adducts.The recovery of MeIQx-DNA adducts by the nuclease P1 methodwas determined to be about 50% using liver DNA of a rat treatedwith [¹⁴C]MeIQx intragastrically. By the nuclease P1 methodfive adducts were detected in the liver DNA of rats fed MeIQxand two of them, including the most abundant one, were identifiedas MeIQx-deoxyguanosine adducts by comparison with the adductsformed in in vitro reactions of N-acetoxy-2-amino-3,8-dimethylimidazo[4,5-f)quinoxalinewith the four 2'-deoxyribonucleotides. The most abundant adductin vivo was identified as N²-(deoxyguanosin-8-yl)-MeIQx 3',5'-diphosphate(3',5'-pdGp-C8-MeIQx). MeIQx-DNA adduct levels in human tissuescould be determined by the nuclease P1 modification of the ³²P-postlabelingmethod in combination with HPLC, and thus provide informationon the roles of MeIQx in human carcinogenesis.     

Major routes of metabolism of the food-borne carcinogen 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline in the rat

The metabolic fate of 2-amino-3,8-dimethylimidazo[4,5-f] quinoxaline(MeIQx), a carcinogen formed in cooked meat and fish, has beeninvestigated in male Sprague-Dawley rats. Five metabolites wererecovered from bile of animals given an intragastric dose of{2-¹⁴C]MeIQx. These accounted for nearly all of the radioactivityin bile. The chemical structures of these metabolites were elucidatedby proton NMR, UV and mass spectroscopy. Three structures maybe assigned unambiguously: two sulfamates, N-(3,8.dimethylimidazo[4,5f]quinoxalin-2-yl)sulfamic acid and N-(8-hydroxymethyl-3-methylimidazo[4,5f]quinoxalin-2-yl)sulfamic acid, and N-(8-one glucuronide, N²(ß-1-glucosiduronyl)-2-amino-3,8-dimelhyliinidazo[4,5f]quinoxaline In addition, an acetyl and a glucosiduronylconjugate of 5-hydroxy-MeIQx were observed. The spectral evidencedid not allow an unambiguous assignment of the site of conjugation.The two glucuronides were excreted in urine and the sulfamateof MeIQx was found in feces as well as urine. All five metaboliteswere found to be non-mutagenic to Salmonella typhimurium TA98with or without metabolic activation. The glucuronide conjugateswere found also to be non-mutagenic when ß- glucuronidasewas incorporated with S-9 mixture in the mutation assay, andthus all appear to be detoxification products. The previouslyreported metabolite, 2-amino-8-hydroxymethyl-3-methylimidazo[4,5f]quinoxalinewhich is mutagenic to Salmonella typhimurium TA98 with metabolicactivation, was identified as a minor component in both urineand feces.     

Occurrence of mutagenic/carcinogenic heterocyclic amines in meat and fish products, including pan residues, prepared under domestic conditions

Some typical Swedish meat and fish products, e.g. bacon, beefburgers,meatballs, Baltic herring, salmon, smoked fish, black puddingand sausages, and their corresponding pan residues, were analysedby HPLC for their content of mutagenic/carcinogenic heterocyclicamines (HAs). The products were cooked using recommended domesticcooking conditions concerning temperature, time and frying equipmentThe amount of HAs was low in most products, though the amountwas higher in the pan residues, especially in the pan residuefrom the frying of Falun sausage, which contained 18.5 ng HAs/gcooked product Mostly MelQx (2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline)and 4,8-DiMeIQx (2-amino-3,4,8-trimethylimidazo[4,5-f]-quinoxaline)were found, being 0.03–2.8 ng MelQx/g and n.d.-3.4 ng4,8-DiMeIQx/g cooked product in the food products and 0.05–73ng MelQx/g and n.d.-2.8 ng 4,8-DiMelQx/g cooked product in thepan residues. High levels of IQ (2-amino-3-methylimidazo[4,5-f]quinoline),10.5 ng/g, were only found in well-done bacon and a correlationwas seen between fat content and IQ formation. Low levels ofMelQ (2-amino-3,4-dimethylimidazo[4,5-f]quinoline) and PhIP(2-amino-l-methyl-6-phenylimidazo[4,5-b]pyridine) were foundin the foods.     

Structural determination of a new mutagenic heterocydic amine, 2-amino-1,7,9-trimethylimidazo[4,5-g]quinoxaline (7,9-DiMeIgQx), present in beef extract

We previously found two new mutagens, compounds I and II, inbacteriological-grade beef extract by monitoring the mutagenicityto a new Salmonella strain, YG1024; compound I was identifiedas 2-amino-4-hydroxymethyl-3,8-dimethyli-midazo[4,5-f]quinoxaline(4-CH₂OH-8-MeIQX) In the present study, we isolated compoundII from the beef extract, which accounted for 2% of the totalmutagenicity of materials adsorbed on blue cotton. Further,we found that a large quantity of compound II was produced byheating a mixture of creatine, threonine and glucose (1:1:0.5)at 200^°C for 5 h, the level being 860-fold of that in thebeef extract. The structure of this compound was determinedto be 2-amino-1,7,9-trimethylimidazo[4,5-g]quinoxaline (7,9-DiMeIgQx)by X-ray crystallography. The amount of 7,9-DiMeIgQx in bacteriological-gradebeef extract was estimated to be 53 ng/g. This compound induced13 800 and 670 revertants of S.typhimurium YG1024 and TA98 respectively,per µg in the presence of S9 mix.     

Heterocyclic aromatic amine formation in grilled bacon, beef and fish and in grill scrapings

The heterocyclic aromatic amines (HAAs) 2-amino-l-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 2-amino-3, 8-di-methylimidazo[4,5-f)quinoxaline(MelQx), 2-amino-3, 4, 8-tri-methylimidazo[4, 5-f)quinoxaline(4, 8-DiMeIQx) and 2-amino     

Identification of N-(deoxyguanosin-8-yl)-2-amino-3,4-dimethylimidazo[4,5-f]quinoline (dG-C8-MeIQ) as a major adduct formed by MeIQ with nucleotides in vitro and with DNA in vivo

The N-hydroxylamine of a carcinogenic heterocyclic amine, 2-amino-3,4-dimethylimidazo[4,5-f]quinoline(MeIQ), was reacted with four 2'-deoxynucleoside 3'-monophosphatesafter O-acetylation. ³²P-Postlabeing analysis demonstrated thatthe adduct was formed with only the guanine nucleotide, andthe structure of the compound in the obtained adduct spot wasdetermined to be N-(deoxyguanosin-8-yl)-MeIQ 3',5'-diphosphate(3',5'-pdGp-C8-MeIQ). DNA samples from livers of mice fed MelQwere also ³²P labeled under standard conditions and additionallytreated with nuclease P1 and phosphodiesterase I. A single adductspot was obtained and the structure of the adduct was identifiedas 5'-pdG-C8-MeIQ. Thus, MelQ binds at the C-8 position of guaninein vitro and in vivo, like other heterocyclic amines.     

SHORT COMMUNICATION: Metabolic activation and DNA binding of food mutagens and other environmental carcinogens in human mammary epithelial cells

Cultures of human mammary epithelial cells were treated withone of seven heterocyclic amine food mutagens [2-amino-3-methylimidazo[4,5-f)quinoline (IQ), 2-amino-3, 4-dimethylimidazo[4, 5-f)quinoline(MelQ), 2-amino-3, 8-di-methylimidazo[4, 5-f]quinoxaline (MeIQx),2-amino-3, 4, 8-trimethylimidazo[4, 5-f]quinoxaline (4, 8-DiMelQx)2-amino-3, 7, 8-trimethylimidazo[4, 5-f]quinoline (7, 8-DiMelQx),2-amino-3, 4, 7, 8-tetramethylimidazo[4, 5-f]quinoxaline (4,7, 8-TriMelQx) or 2-amino-1-methy1–6-phenylimidazo[4,5-b] pyridine (PhlP)], four nitropyrenes (1-nitropyrene (1-NP),1, 3-dinitropyrene (1, 3-DNP), 1, 6-dinitropyrene (1, 6-DNP)or 1, 8-dinitropyrene (1, 8-DNP) or the Polycyclic aromatichydrocarbon dibenzo[a, l]pyrene (DB[a, l]P). DNA isolated fromthe cultures was analysed by ³²P-post-labelling and in eachcase the presence of carcinogen-DNA adducts was detected. Thepatterns and numbers of adducts obtained when human mammarycell DNA digests were separated on polyethyleneimine-celluloseTLC were found to closely resemble those previously demonstratedto be present in the DNA of tissues from rodents and other primatestreated with the same agents. Up to six DNA adducts were detectedin human breast cells treated with IQ and MelQ. Fewer adducts(1–3) were detected following treatment with MelQx orits methylated derivatives, whilst PhIP gave rise to at leastfour distinct adduct spots. Five adduct spots were detectedin breast cells treated with DB[a, l]P or with 1-NP, but feweradduct spots were formed by 1, 3-, 1, 6- and 1, 8-DNP. Thesedata demonstrate the ability of human breast epithelial cellsto activate to DNA binding species a range of carcinogenic compoundsknown to be present in the human diet or to which humans areknown to be exposed environmentally.     

Formation of DNA adducts by the food mutagen 2-amino-3,4,8-trimethyl-3H-imidazo [4,8-f]quinoxaline (4,8-DiMeIQx) in vitro and in vivo. Identification of a N-(2'-deoxyguanosin-8-yl)-4,8-DiMeIQx adduct

The covalent binding of the mutagenic N²-hydroxy metaboilteof the food mutagen 2-amino-3,4,8-trimethyl-3H-lmldazo[4,5-f]quinoxaline(4,8-DiMeIQx) to 2'-deoxy-nudeosides and DNA was investigatedin vitro and in vivo. N²-Hydroxy-4,8-DiMeIQx reacted to a smallextent spontaneously with 2-deoxyguanosine. However, acetylatlonof N²-hydroxy-4,8-DiMeIqx with acetic anhydride to form theN²-acetoxy derivative prior to reaction with 2-deoxyguanosineresulted in much higher yield of adduct. N²-Acetoxy-4,8-DiMeIQxdid not form adducts with 2'-deoxy- adenosine, 2'-deoxycytldlneor 2'-deoxythymldlne. The adduct formed between the N metaboliteof 4,8- DiMeIQx and 2-deoxyguanosine was analysed by mass spectrometryand NMR spectroscopy and the structure of the adduct was shownto be N²-Acetoxy-4,8-DiMeIQx. N²-Acetoxy-4,8-DiMeIQx. reactedwith calf thymus DNA and formed a covalently bound 4,8-DiMeIQxresidue, which could not be removed by repeated precipita tionsor solvent extractions. The 4,8-DiMeIQx-DNA was hydrolysed enzymaticallywith nuclease P1/acid phosphat ase and HPLC analysis showedthat 70% of the bound mutagen was recovered as N²-Acetoxy-4,8-DiMeIQx.An additional minor adduct accounting for     

The presence of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline in smoked dry bonito (katsuobushi)

Smoked dry bonito (katsuobushi), an everyday food item for most Japanese people, was found to contain 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), the content of which was estimated at about 2 ng/g. This content is similar to the known MeIQx content of cooked beef. The katsuobushi also contained another mutagenic component, the total activity of which was 1/6-1/3 that of the MeIQx. This component was similar to 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (4,8-DiMeIQx) with respect to its behavior in high-pressure liquid chromatography and its ultraviolet absorption spectrum.     

Excretion of food-derived heterocyclic amine carcinogens into breast milk of lactating rats and formation of DNA adducts in the newborn

The distribution, DNA adduction and excretion into breast milkof 2-amino-3-methylimidazo[4, 5-f)quinoline (IQ), 2-amino-3,8-dimethylimidazo[4, 5-f)quinoxaline (MeIQx) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) were examined in lactating female F344 ratswith 5 day old pups. Six hours after a single dose (10 mg/kg,p.o.) of radiolabeled IQ, MelQx or PhIP to lactating dams, radioactivityin the dams was highest in the liver and kidney followed, indescending order, by the mammary gland, omental fat and brain.By 24 h after carcinogen administration, all tissues of thedams showed significantly reduced levels of radioactivity exceptfor omental fat which changed only marginally from 6 to 24 h.³²P-Postlabeling analysis showed that the level of DNA adductsin mammary gland 6 h after dosing was 2.2, 0.7 and 0.2 adducts/10⁷nucleotides for PhIP, IQ and MelQx respectively. In contrast,in hepatic DNA, the levels of IQ-DNA adducts (5.5 adducts/10⁷nucleotides) were 11-fold higher than those of PhIP or MelQx.The stomach contents, liver, kidney and urine of pups nursedby dams given radiolabeled IQ, MelQx or PhIP were radioactive,indicating that these carcinogens (and/or metabolites) wereexcreted into breast milk and absorbed by the pups. After a6 h suckling period, the amount of PhlP-derived radioactivityin the stomach contents of the pups was     

In vitro formation and degradation of 2-amino-1-methyl-6-phenyliinidazo[4,5-b]pyridine(PhIP) protein adducts

Adduct formation between the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b](PhIP)and rat serum albumin (RSA) was studied in vitro using hepaticmicrosomes isolated from polychiorinated biphenyl induced rats.With 1-methyl-2-nitro-6-phenylimidazo[4,5-b]pyridine (2-nitro-PhIP)as starting material, four main products were formed. Pretreatmentof RSA with ß-mercaptoethanol markedly increased theyield of one of them. In this adduct, the C-2 of PhIP was linkedto cysteine of RSA at position 34 in a C-S linkage. With N²-acetoxy-PhIPas starting material, unstable conjugates were formed with RSAas well as with glutathione (GSH) and cysteine. The suggestedstructures of the GSH-S-n² and cysteine conjug ates, GSH-S-N²-PhIPand cysteine-S-N²-PhIP respectively, are based on mass spectraand UV spectra. The degradation of the conjugates of GSH andcysteine as well as of the protein adduct were monitored. Theyall resulted in the same degradation product, identified as2-amino-5 hydroxy-1-methyl-6-phenylimidazo[4,5b]pyridine (5-hydroxy-PhIP).     

Metabolism of the food-derived carcinogen 2-amino-3,8-dimethylimidazo[4,5,-f)quinoxaline (MeIQx) in nonhuman primates

The metabolism and disposition of the food mutagen and rodentcarcinogen 2-amino-3, 8-dimethylimidazo[4, 5-f)quinoxaline wasinvestigated in cynomolgus monkeys. Monkeys were administereda single dose of radiolabeled [¹⁴C]MeIQx (2.2 or 50 µmol/kg).Peak blood levels of radioactivity were observed within 1–3h after dosing and declined rapidly thereafter. By 72 h afterdosing, approximately 50% and 70% of the 2.2 µmol/kg,and 50 µmol/kg dose, respectively, was excreted in theurine. Approximately 15–20% of either dose was recoveredin the feces. Eight metabolites and the parent compound weredetected in urine by HPLC. The parent compound accounted for