Hemin potentiates nitric oxide-mediated nitrosation of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) to 2-nitrosoamino-3-methylimidazo[4,5-f]quinoline

Heme has been reported to be an important contributor to endogenous N-nitrosation within the colon and to the enhanced incidence of colon cancer observed with increased intake of red meat. This study uses the heterocyclic amine 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) as a target to evaluate hemin potentiation of nitric oxide (NO)-mediated nitrosation. Formation of 14C-2-nitrosoamino-3-methylimidazo[4,5-f]quinoline (N-NO-IQ) was monitored by HPLC following incubation of 10 microM IQ with the NO donor spermine NONOate (1.2 microM NO/min) at pH 7.4 in the presence or absence of hemin. N-NO-IQ formation due to autoxidation of NO was at the limit of detection (0.1 microM) and increased 22-fold in the presence of 10 microM hemin and an in situ system for generating H2O2 (glucose oxidase/glucose). A linear increase in N-NO-IQ formation was observed from 1 to 10 microM hemin. Significant nitrosamine formation occurred at fluxes of NO and H2O2 as low as 0.024 and 0.25 microM/min, respectively. Potentiation by hemin was not affected by a 400-fold excess flux of H2O2 over NO or a 4.8-fold excess flux of NO over H2O2. Reactive nitrogen species produced by hemin potentiation had a 46-fold greater affinity for IQ than those produced by autoxidation. Azide inhibited autoxidation, suggesting involvement of the nitrosonium ion, NO+. Hemin potentiation was inhibited by NADH, but not azide, suggesting oxidative nitrosylation with NO2* or a NO2*-like species. IQ and 2,3-diaminonaphthylene were much better targets for nitrosation than the secondary amine morpholine. Apc(min) mice with dextran sulfate sodium-induced colitis demonstrated increased levels of urinary nitrite and nitrate consistent with increased expression of iNOS and NO synthesis. As reported previously, identical conditions increased fecal N-nitroso compounds. Thus, hemin potentiation of NO-mediated nitrosation of heterocyclic amines provides a testable mechanism by which red meat consumption can generate N-nitroso compounds and initiate colon cancer under inflammatory conditions, such as colitis.     

Detection of PhIP (2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine) in the milk of healthy women.

An increased risk of breast cancer has been observed in women who consume "very well-done" meats. Heterocyclic amines are mutagenic and carcinogenic pyrolysis products formed during high temperature cooking of meats. In the present study, human milk samples were analyzed for PhIP, one of the most abundant dietary heterocyclic amine. A protocol was developed with a mixed-mode cation exchange sorbent for the extraction of heterocyclic amines from milk. Milk samples were acquired from healthy Canadian women. With LC/MS analysis and the method of isotope dilution for quantification, levels of PhIP were determined in human milk samples. PhIP was detected in 9 of the 11 milk samples, at levels as high as 59 pg/mL (ppt). No PhIP was detected in the milk of the vegetarian donor. Detection of PhIP in milk indicates that ductal mammary epithelial cells are directly exposed to this carcinogen, suggesting that heterocyclic amines are possible human mammary carcinogens.     

Prostaglandin-H synthase mediated metabolism and mutagenic activation of 2-amino-3-methylimidazo [4,5-f] quinoline (IQ)

 Prostaglandin-H synthase (PHS), a mammalian peroxidase of interest for the extrahepatic formation of reactive intermediates of carcinogens, catalyzes in vitro the metabolic activation of the mutagen and carcinogen 2-amino-3-methylimidazo-[4,5-f ]quinoline (IQ). Incubation of ¹⁴C-labeled IQ with ram seminal vesicle microsomes (RSVM), a rich source of PHS, resulted in protein binding and generated products mutagenic in S. typhimurium YG1024. The mutagenic activity produced in IQ/PHS incubations was stable and extractable with ethyl acetate. Upon fractionation of such extracts by HPLC and subsequent analysis, two metabolites were identified as 2,2′-azo-bis-3-methylimidazo[4,5-f ]quinoline (azo-IQ) and 3-methyl-2-nitro-imidazo[4,5-f ]quinoline (nitro-IQ) confirmed by comparison of HPLC retention times, UV/VIS-, ¹H-NMR-spectroscopy, and mass spectrometry of synthesized standards. Azo-IQ was obtained by chemical oxidation of IQ with metasodium periodate. It was the major metabolite in PHS incubations, but has not been detected in monooxygenase incubations. Azo-IQ, without metabolic activation, was much less mutagenic in S. typhimurium YG1024 (308 rev/nmol) than nitro-IQ and 3-methyl-2-nitroso-imidazo[4,5-f ]quinoline (nitroso-IQ), two other S9-independent mutagens which have been synthesized by chemical oxidation of IQ with sodium nitrite. Nitro-IQ was formed only in trace amounts but due to its potent mutagenicity in S. typhimurium YG1024 (2×10⁶ rev/nmol) it accounted for most of the mutagenic activity of the incubations. These data show that PHS-mediated in vitro metabolism of IQ results in its metabolic activation; thus PHS may contribute to the genotoxicity of IQ in extrahepatic tissues. Received: 25 July 1994/Accepted: 30 August 1994     

Identification of N-(Deoxyguanosin-8-yl)-2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine as the major adduct formed by the food-borne carcinogen, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, with DNA.

The covalent binding of the N-acetoxy-, N-hydroxy-, and nitro derivatives of the food-borne carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) to 2'-deoxyribonucleosides or DNA was investigated in vitro and in vivo. N-Acetoxy-PhIP reacted with deoxyguanosine (dG), but not with the other deoxyribonucleosides, to form N-(deoxyguanosin-8-yl)-PhIP (dG-C8-PhIP), whose structure was determined by NMR and mass spectral analyses and by ultraviolet absorption and pH-solvent partitioning characteristics. While reaction of N-acetoxy-PhIP with calf thymus DNA at pH 5.0 yielded 5.38 +/- 1.16 nmol of bound PhIP residues/mg of DNA, N-hydroxy-PhIP gave only 0.13-0.23 nmol binding/mg of DNA under identical reaction conditions. Nitro-PhIP produced no detectable binding under these conditions. HPLC analysis of 1-butanol extracts of enzymatically hydrolyzed DNA that had been modified by N-acetoxy-PhIP in vitro showed a major adduct which coeluted with and had an ultraviolet absorption and a mass spectrum that were identical to that of authentic dG-C8-PhIP. 32P-Postlabeling analysis of DNA isolated from colon, pancreas, lung, heart, and liver of rats treated orally with PhIP revealed the presence of a major PhIP-DNA adduct. This adduct had chromatographic properties identical to that of the 32P-labeled bis(phosphate) derivative of dG-C8-PhIP and represented 35-45% of the total adducts.(ABSTRACT TRUNCATED AT 250 WORDS)     

Oral administration of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) yields PhIP-DNA adducts but not tumors in male Syrian hamsters congenic at the N-acetyltransferase 2 (NAT2) locus.

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a heterocyclic amine carcinogen present in well-done meat. PhIP must undergo host-mediated bioactivation to exert its mutagenic and carcinogenic effects. Following N-hydroxylation, N-acetyltransferases catalyze the O-acetylation (activation) of N-hydroxy-PhIP to an electrophile causing DNA damage. A well-defined genetic polymorphism in N-acetyltransferase 2 (NAT2) activity exists in humans and the Syrian hamster. Since some human epidemiological studies suggest an association between acetylator genotype and cancer susceptibility in individuals who consume well done meats, this study was designed to investigate the specific role of acetylator genotype in PhIP-induced tumors using a Syrian hamster model congenic at the NAT2 locus. Following oral administration of PhIP to male rapid and slow acetylator Syrian hamsters, DNA adducts were identified in each tissue examined with levels in the relative order: pancreas > heart and urinary bladder > prostate, small intestine and transverse colon > ascending colon, liver, cecum, descending colon, and rectum. However, no tumors were observed in male rapid and slow acetylator congenic hamsters administered 11 oral doses of PhIP (75 mg/kg) and maintained on a high fat diet for one year.     

Conformational differences of the C8-deoxyguanosine adduct of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) within the NarI recognition sequence

2-amino-3-methylimidazo[4,5-f]quinoline (IQ) is a highly mutagenic heterocyclic amine found in cooked meats. The major DNA adduct of IQ is at the C8-position of dGuo. We have previously reported the incorporation of the C8-IQ adduct into oligonucleotides, namely, the G1-position of codon 12 of the N-ras oncogene sequence (G1G2T) and the G3-position of the NarI recognition sequence (G1G2CG3CC) (Elmquist et al. (2004) J. Am. Chem. Soc. 126, 11189-11201). Ultraviolet spectroscopy and circular dichroism studies indicated that the conformation of the adduct in the two oligonucleotides was different, and they were assigned as groove-bound and base-displaced intercalated, respectively. The conformation of the latter was subsequently confirmed through NMR and restrained molecular dynamics studies (Wang et al. (2006) J. Am. Chem. Soc. 128, 10085-10095). We report here the incorporation of the C8-IQ adduct into the G1- and G2-positions of the NarI sequence. A complete analysis of the UV, CD, and NMR chemical shift data for the IQ protons are consistent with the IQ adduct adopting a minor groove-bound conformation at the G1- and G2-positions of the NarI sequence. To further correlate the spectroscopic data with the adduct conformation, the C8-aminofluorene (AF) adduct of dGuo was also incorporated into the NarI sequence; previous NMR studies demonstrated that the AF-modified oligonucleotides were in a sequence-dependent conformational exchange between major groove-bound and base-displaced intercalated conformations. The spectroscopic data for the IQ- and AF-modified oligonucleotides are compared. The sequence-dependent conformational preferences are likely to play a key role in the repair and mutagenicity of C8-arylamine adducts.     

Characterization of a peptide adduct formed by N-acetoxy-2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), a reactive intermediate of the food carcinogen PhIP.

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a member of a class of compounds known as the heterocyclic amines (HCAs) that are formed in meat during cooking. It is a multi-organ carcinogen in rodents forms adducts and with DNA and protein. Although protein adducts are not thought to be involved in cancer development, they may be useful as internal dosimeters of PhIP exposure and bioactivation. Towards the goals of characterizing the adducts formed in humans and the development of an assay for quantitation of adduct levels, we have characterized a peptide adduct formed by the putative genotoxic metabolite, N-acetoxy-PhIP. A model peptide with the internal sequence Leu-Gln-Lys-Cys-Pro-Tyr, which is homologous to a potential target sequence for HCAs in human serum albumin, was reacted with N-acetoxy-PhIP and an adduct was identified and further characterized by LC-ESI-MS/MS. N-acetoxy-PhIP is covalently bound to the peptide via cysteine and the exocyclic amino group of PhIP. Future work is needed to establish if this adduct is formed and is stable in vivo in humans following exposure to PhIP.     

Biomonitoring of urinary metabolites of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) following human consumption of cooked chicken

Human risk assessment of exposure to 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) through the diet may be improved by conducting biomonitoring studies comparing metabolism in humans and rodents. Eleven volunteers ingested a meal of cooked chicken containing 4 -OH-PhIP and PhIP in amounts of 0.6 and 0.8mug/kg, respectively and urine was collected for the next 16h. The large number of PhIP metabolites was by treatment of the urine samples with hydrazine hydrate and hydrolytic enzymes reduced to three substances, 4'-OH-PhIP, PhIP and 5-OH-PhIP of which the first is a biomarker for detoxification and the last a biomarker for activation. The eleven volunteers eliminated large amounts of 4'-OH-PhIP in the urine. The majority of which could be accounted for by the presence of 4'-OH-PhIP in the fried chicken, showing that PhIP only to a small extent (11%) was metabolised to 4'-OH-PhIP. A larger fraction of the PhIP exposure, 38%, was recovered as PhIP and the largest fraction (51%) was recovered as 5-OH-PhIP suggesting that PhIP in humans to a large extent is metabolised to reactive substances. In rats, less than 1% of the dose of PhIP was eliminated as 5-OH-PhIP, suggesting that human cancer risk from exposure to PhIP is considerable higher than risk estimations based on extrapolation from rodent bioassays.     

Eumelanin is a major determinant for 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) incorporation into hair of mice

Mice with different hair pigmentation were studied to evaluate the role of melanin in the incorporation of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) into hair. Mice C57BL/6J-c2j/+ (white), C57BL/6J-Ay (yellow), C57L/J (grey), C57BR/cdJ (brown) and C57BL/6J (black) were dosed with PhIP: 7-9 days old (total amount: 0.006 or 0.58 mg/kg b.wt., for 4 days) and adults (total amount 50 mg/kg b.wt. during 8 weeks). Hair was collected either 30 days after the last PhIP administration (new-born mice) or 8 weeks after the first administration (adult mice). PhIP was incorporated into black hair to a greater extent than into brown, grey, yellow and non-pigmented hair. The concentration of PhIP in the hair of new-born mice exposed to 0.58 mg PhIP/kg b.wt. were (mean+/-S.D.): 328+/-135 (black), 134+/-41 (brown), 9.1+/-1.2 (yellow) and 5.2+/-1.4 (white) ng/g hair. The PhIP concentrations in the hair of adult mice exposed to 50 mg/kg b.wt. were: 4750+/-1449 (black), 810+/-235 (brown), 541+/-119 (grey), 35.5+/-4.6 (yellow) and 21.6+/-8.8 (white) ng/g, and the eumelanin hair concentration in the same animals decreased in a similar pattern. A linear relationship (r2= 1.00, P<0.0001) between the relative PhIP incorporation and the eumelanin concentration in hair was found.     

The food mutagen 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline: a conformational analysis of its major DNA adduct and comparison with the 2-amino-3-methylimidazo[4,5-f]quinoline adduct

The heterocyclic amine 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) is one of a group of heterocyclic amine carcinogens that exists in cooked meat and fish. It causes mutations in bacterial and mammalian assays and induces tumors in mammals. MeIQx is converted within cells to a reactive derivative which forms a major covalent adduct at carbon-8 of guanine in DNA. This adduct may alter the DNA conformation at critical stages of the replicative process, and cause mutations which initiate the carcinogenic process. Atomic resolution structures of the MeIQx-damaged DNA are not yet available experimentally. We have carried out an extensive molecular mechanics/energy minimization search to locate feasible structures for the major MeIQx adduct in DNA, using the sequence d(5'-C1-G2-C3-G4[IQ]-C5-G6-C7-3').d(5'-G8-C9-G10-C11-G12-C13-G14-3') with MeIQx modification at G4. We have created 1152 starting conformations which uniformly sampled each of the three flexible torsion angles that govern the MeIQx-DNA orientation at 15 degrees intervals, and minimized their energy. A mixture of conformations was generated, which were separated into families according to the position of the ring system of the carcinogenic amine: major groove, minor groove, and base-displaced-intercalated. While a generally similar mixture had been generated previously for the related carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) [Wu, X., et al. (1999) Chem. Res. Toxicol. 12, 895-905], differences were found which could be rationalized in terms of the additional methyl group in the MeIQx.     

Metabolism of 2-amino-3-methylimidazo[4,5-f]quinoline in the male rat

The metabolism of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) was studied in the male rat using the radiochemical labels 14C and 3H at positions 2 and 5 of the molecule, respectively. Adult male Fischer 344 rats were administered [2-14C]IQ or [5-3H]IQ by oral gavage at dose levels of 20 or 40 mg/kg body weight. Rats were also given [2-14C]IQ in the diet at a dose level of 300 ppm for 2 days and after administration of unlabelled IQ (300 ppm) in the diet for approximately 6.5 wk for an additional 2 days. In the initial 48 hr following oral administration of 20 or 40 mg [2-14C]IQ/kg body weight, about 40-50% radioactivity was recovered in the urine, and about 30-38% radioactivity was recovered in the faeces. In the initial 72 hr following consumption of [2-14C]IQ (300 ppm) in the diet about 26% radioactivity was recovered in the urine and about 61% radioactivity was recovered in the faeces. Following cannulation of the bile ducts, rats administered a single dose of [2-14C]IQ (40 mg/kg body weight) by oral gavage excreted about 15% of the administered dose in the bile over a period of 2 days. Urine from rats given [2-14C]IQ contained three main polar metabolites that included a glucuronide, a sulphate ester and IQ sulphamate, and a number of less polar metabolites that included IQ, 2-acetylamino-3-methylimidazo[4,5-f]quinoline, 2-aminoimidazo[4,5-f]quinoline and 2-amino-3,6-dihydro-3-methyl-7H-imidazo[4,5-f]quinoline-7-one (7-OH-IQ). Administration of [2-14C]IQ by oral gavage or in the diet gave the same metabolites, but in different amounts. In the faeces of rats given [2-14C] by oral gavage, IQ-sulphamate was the major metabolite in the polar fraction. Non-polar metabolites similar to those found in the urine were also present, but in different amounts. A major, non-polar faecal metabolite, 7-OH-IQ was probably formed as a result of the activity of the intestinal bacterial flora. In rats given a single gavage dose of [2-14C]IQ, excretion of metabolites was higher in the urine and lower in the faeces compared with that in animals fed [2-14C]IQ in the diet. One polar metabolite present in the urine, IQ-sulphamate (39%), was found at considerably higher levels in rats dosed orally with IQ compared with those fed IQ (less than 6%). Thus, IQ is extensively metabolized to give a number of polar and non-polar metabolites, the amounts of which depend, in part, on the mode of dosing.     

2-Amino-1-methyl-6-(5-hydroxy-)phenylimidazo[4,5-b]pyridine (5-OH-PhIP), a biomarker for the genotoxic dose of the heterocyclic amine, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP).

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a mutagenic and carcinogenic heterocyclic amine formed during ordinary cooking. PhIP is metabolically activated by CYP P450 mediated N-hydroxylation followed by phase II esterification. The ultimate mutagenic metabolite reacts with DNA resulting in formation of adducts, and with proteins and other cellular constituents resulting in unstable products which are degraded to 5-hydroxy-PhIP. Rats were dosed orally with PhIP and urine and faeces were collected to 24, 48 and 72 h. Urine and faeces samples were hydrolysed with glucuronidase/sulfatase in order to release conjugated metabolites, followed by purification on C18 columns. The rats excreted 0.88% of the dose as 5-hydroxy-PhIP with the urine to 24 h and 0.04 and 0.01% to 48 and 72 h, respectively. The amounts of 5-hydroxy-PhIP found in faeces were 0.03, 0.1 and 0% to 24, 48 and 72 h. Urinary excretion of 5-hydroxy-PhIP showed a linear dose-response relationship in rats dosed orally with PhIP. This shows that 5-hydroxy-PhIP is also formed in vivo and that 91% is excreted with the urine in 24 h, indicating the possible use of 5-hydroxy-PhIP as a urinary biomarker for the bioactive dose of PhIP. In a preliminary study, using molecular imprinted polymer a specific sorbent for purification, after enzymatic hydrolysis and purification on a C18 column, we have identified 5-OH-PhIP in a 24-h urine sample from a male volunteer who had ingested a fried beef. This indicates that urinary 5-OH-PhIP could be used as an easily obtainable marker for the genotoxic dose of PhIP in human biomonitoring studies.     

Prenatal toxicity and lack of carcinogenicity of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) following transplacental exposure.

Accumulating evidence from human and experimental animal studies indicates that consumption of heterocyclic amines (HA), derived from cooked meat and fish, may be associated with an increased incidence of cancer. Experiments were initiated to assess the role of one of these compounds, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), as a potential transplacental carcinogen, as well as to evaluate whether in utero exposure to IQ results in the induction of fetal cytochrome P4501A1 (Cyp1a1), P4501B1 (Cyp1b1), and/or glutathione S-transferase (GST). Inducible, or responsive, backcrossed fetuses resulting from a cross between congenic C57BL/6 (Ah(d)Ah(d)) nonresponsive female mice and C57BL/6 (Ah(b)Ah(b)) responsive male mice were transplacentally exposed to olive oil or 6.25, 12.5, or 25 mg/kg of IQ on day 17 of gestation. No macroscopically or microscopically visible liver, lung, or colon tumors were found in the transplacentally treated offspring by one year after birth. Ethoxyresorufin O-deethylase (EROD) and 1-chloro-2,4-dinitrobenzene assays were performed to evaluate whether transplacental exposure to IQ results in the induction of fetal Cyp1a1 and GST, respectively, in lung and liver tissues. Results showed levels of EROD and GST activity in tissues of IQ-treated mice to be very close, if not identical, to those of mice treated with olive oil. Similarly, ribonuclease protection assay data showed that the levels of Cyp1a1 and Cyp1b1 RNA in tissues of IQ-treated mice were not significantly different from those of oil-treated controls. Previous studies have shown that the developing organism expresses very low levels of Cyp1a2. Thus, in utero exposure to IQ does not lead to induction of Cyp1a1, Cyp1a2, or Cyp1b1 in the fetal compartment, thereby maintaining the low levels of these activating enzymes in the developing organism. Taken together, these data imply that, at least under the conditions employed for these experiments, IQ may not play an important role in transplacentally induced tumorigenesis.     

The cooked meat-derived mammary carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) elicits estrogenic-like microRNA responses in breast cancer cells

The cooking of meat results in the generation of heterocyclic amines (HCA), the most abundant of which is 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). Data from epidemiological, mechanistic, and animal studies indicate that PhIP could be causally linked to breast cancer incidence. Besides the established DNA damaging and mutagenic activities of PhIP, the chemical is reported to have oestrogenic activity that could contribute to its tissue specific carcinogenicity. In this study we investigated the effect of treatment with PhIP and 17-β-estradiol (E2) on global microRNA (miRNA) expression of the oestrogen responsive MCF-7 human breast adenocarcinoma cell line.     

Quercetin increases the bioavailability of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in rats

This study investigates whether the previous observation that quercetin increases the transport of PhIP through Caco-2 monolayers in vitro could be confirmed in an in vivo rat model.     

No effects of chlorophyllin on IQ (2-amino-3-methylimidazo[4,5-f]-quinoline)-genotoxicity and -DNA adduct formation in Drosophila

Previously we demonstrated that chlorophyllin suppressed the genotoxicities of many carcinogens. However, the genotoxicity of IQ (2-amino-3-methylimidazo[4,5-f]quinoline), a carcinogenic heterocyclic amine, was not suppressed in Drosophila. On the contrary, it has been reported that chrolophyllin suppressed the genotoxicity of IQ in rodents, rainbow trout and Salmonella. We demonstrated that the chlorophyllin-induced suppression of MeIQx (2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline)-genotoxicity was associated with a decrease in MeIQx-DNA adduct formation in Drosophila larval DNA. MeIQx represents another type of heterocyclic amine and is similar to IQ in structure. In this study we utilized (32)P-postlabeling to examine whether chlorophyllin reduced IQ-DNA adduct formation in Drosophila DNA in the same way as MeIQx. The results revealed that the formation of IQ-DNA adducts was unaffected by treatment with chlorophyllin. This was consistent with the absence of any inhibitory effect on genotoxicity as observed in the Drosophila repair test. These results suggest that IQ-behavior in Drosophila is not affected by chlorophyllin, indicating that the process of IQ-DNA adduct formation followed by expression of genotoxicity in Drosophila may be different from that in other organisms.     

Synthesis of oligonucleotides containing the N2-deoxyguanosine adduct of the dietary carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline

2-amino-3-methylimidazo[4,5-f]quinoline (IQ) is a highly mutagenic heterocyclic amine formed in all cooked meats. IQ has been found to be a potent inducer of frameshift mutations in bacteria and carcinogenic in laboratory animals. Upon metabolic activation, IQ forms covalent adducts at the C8- and N2-positions of deoxyguanosine with a relative ratio of up to approximately 4:1. We have previously incorporated the major dGuo-C8-IQ adduct into oligonucleotides through the corresponding phosphoramidite reagent. We report here the sequence-specific synthesis of oligonucleotides containing the minor dGuo-N2-IQ adduct. Thermal melting analysis revealed that the dGuo-N2-IQ adduct significantly destabilizes duplex DNA.     

A comprehensive investigation of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) metabolism in the mouse using a multivariate data analysis approach

2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a potent rodent carcinogen and a potential human carcinogen because of its existence in the normal human diet. N2-OH-PhIP, a major PhIP metabolite, has been identified as a precursor of genotoxic species. In vitro data supported the view that CYP1A2 is the major enzyme responsible for the formation of N2-OH-PhIP. However, disruption of the CYP1A2 gene in mouse failed to inhibit PhIP-induced carcinogenesis. To investigate the mechanism underlying this observation, the metabolism of PhIP in wild-type, Cyp1a2-null, and CYP1A2-humanized mice was examined in detail using a metabolomic approach. Following data acquisition in a high-resolution LC-MS system, urinary metabolomes of the control and PhIP-treated mice were characterized in a principal component analysis (PCA) model. Comprehensive metabolite profiles of PhIP in high dose (10 mg/kg) and low dose (100 microg/kg) were established through analyzing urinary ions contributing to the separation of three mouse lines in the multivariate model and by measuring radiolabled PhIP metabolite in a radio-HPLC assay, respectively. The genotoxicity of PhIP to three mouse lines was evaluated by measuring DNA adduction levels in liver, lung, colon, and mammary gland. On the basis of the chemical identities of 17 urinary PhIP metabolites, including eight novel metabolites, multivariate data analysis revealed the role of CYP1A2 in PhIP metabolism and a human-mouse interspecies difference in the catalytic activity of CYP1A2. In addition, the results also showed that Cyp1a2-null mice still possess significant N2-hydroxylation and DNA adduction activities, which may be partially attributed to mouse CYP2C enzymes according to the results from in vitro microsome and Supersome incubations and antibody inhibition experiments.