Mutagenic and carcinogenic heterocyclic amines in Chinese cooked foods

Samples of 7 foods commonly eaten in the Northeast of China (i.e. fried and broiled fishes and broiled meat) were tested for mutagenicity on Salmonella typhimurium TA98 with S9 mix. The basic fractions of the samples were mutagenic, inducing 33-2930 revertants/g of cooked food. Fried walleye pollack (a kind of cod fish heated on a stainless steel pan) showed the highest mutagenicity, so attempts were made to isolate mutagens from the basic fraction of this food. The mutagens were purified by treatment with blue cotton and HPLC on a semi-preparative ODS column and analytical cation exchange and ODS columns. 5 mutagens were isolated and identified as 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (4,8-DiMeIQx) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). 1 g of fried fish was estimated to contain 0.16 ng of IQ, 0.03 ng of MeIQ, 6.44 ng of MeIQx, 0.10 ng of 4,8-DiMeIQx and 69.2 ng of PhIP. MeIQx and PhIP accounted for 24% and 4.7%, respectively, of the total mutagenicity. The other 3 heterocyclic amines were each responsible for only 0.3-1.2% of the total mutagenicity.     

Inhibition of the metabolism of mutagens occurring in food by arachidonic acid.

Hepatic microsomal fractions (microsomes) were prepared from male Sprague-Dawley rats. The effect of arachidonic acid on the conversion of the heterocyclic aromatic amine 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) to its genotoxic metabolites was investigated using a modified bacterial mutation assay (indicator: Salmonella typhimurium TA98). Arachidonic acid inhibited the mutagenicity of IQ without effect on the uptake of the active metabolites and/or on the DNA-repair processes within the bacterial cell. The activation of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and aflatoxin B1 (AFB1) was also inhibited by this polyunsaturated fatty acid.     

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.     

Regional mutagenicity of heterocyclic amines in the intestine: mutation analysis of the cII gene in lambda/lacZ transgenic mice

Transgenic mouse assays have revealed that the mouse intestine, despite its resistance to carcinogenesis, is sensitive to the mutagenicity of some heterocyclic amines (HCAs). Little is known, however, about the level and localization of that sensitivity. We assessed the mutagenicity of four orally administered (20 mg/kg per day for 5 days) HCAs-2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) hydrochloride, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), and 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) acetate-in the intestine of male MutaMice. Two weeks after the last administration, we isolated epithelium from the small intestine, cecum, and colon and analyzed lacZ and cII transgene mutations. PhIP increased the lacZ mutant frequency (MF) in all the samples, and in the small intestine, cII and lacZ MFs were comparable. In the cII gene, G:C to T:A and G:C to C:G transversions were characteristic PhIP-induced mutations (which has also been reported for the rat colon, where PhIP is carcinogenic). In the small intestine, PhIP increased the cII MF to four-fold that of the control, but IQ, MeIQ, and Trp-P-2 did not have a significant mutagenic effect. In the cecum, cII MFs induced by IQ and MeIQ were 1.9 and 2.7 times those in the control, respectively. The MF induced by MeIQ in the colon was 3.1 times the control value. Mutagenic potency was in the order PhIP>MeIQ>IQ; Trp-P-2 did not significantly increase the MF in any tissue. The cecum was the most susceptible organ to HCA mutagenicity.     

Inhibitory effect of dibenzoylmethane on mutagenicity of food-derived heterocyclic amine mutagens

Dibenzoylmethane (DBM), a structural analogue of curcumin (a bioactive phytochemical present in a widely used spice turmeric) was screened for its inhibitory effect against seven cooked food mutagens (heterocyclic amines): 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1), 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-amino-6-methyldipyrido[1,2-a:3',2'-d]imidazole (Glu-P-1), in both TA98 and TA100 strains of Salmonella typhimurium using Ames Salmonella/reversion assay in the presence of Aroclor1254-induced rat liver S9 homogenate. DBM has been reported to antagonize the mutagenicity of several chemical carcinogens in vitro and has recently been shown to be even more effective than curcumin in suppressing the 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary tumors in rats. But there are no reports regarding its antimutagenic properties against cooked food mutagens. Results of the present investigations clearly indicate that dibenzoylmethane is a very potent antimutagenic agent, that could effectively inhibit mutagenicity induced by all the tested cooked food mutagens in both the frame shift (TA98) as well as the base pair mutation sensitive (TA100) strains of S. typhimurium. These highly potent inhibitory effects of dibenzoylmethane against heterocyclic amines observed in our preliminary investigations strongly warrant further studies of its efficacy as a cancer chemopreventive agent.     

Binding activity of natto (a fermented food) and Bacillus natto isolates to mutagenic-carcinogenic heterocyclic amines.

The fermented food, whole meal Natto, viscous polymeric material from Natto, Natto bean, cooked soya bean, and 28 bacterial isolates from Natto were studied for their binding capacity to foodborne mutagenic-carcinogenic heterocyclic amines. The mutagenic heterocyclic amines used were Trp-P-1 (3-amino-1,4-dimethyl-5H-pyrido(4,3-b)indole); Trp-P-2 (3-amino-1-methyl-5H-pyrido(4,3-b)indole); Glu-P-1 (2-amino-6-methyldipyrido(1,2-a:3'2'-d)imidazole); PhIP (2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine); IQ (2-amino-3-methylimidazo(4,5-f)quinoline); MeIQ (2-amino-3,4-dimethylimidazo(4,5-f)quinoxaline); MeIQx (2-amino-3,8-dimethylimidazo(4,5-f)quinoxaline); and MeAalphaC (2-amino-3-methyl-9H-pyrido(2,3)indole). The lyophilized Natto and other fractions of Natto exhibited high binding activity towards Trp-P-1, Trp-P-2, PhIP, and MeAalphaC, while Glu-P-1, IQ, and MeIQ were not effectively bound. The binding capacity of bacterial isolates (Bacillus natto) were isolate-mutagen dependent. Heat treated lyophilized cells, cell wall, and cytoplasmic contents of the bacterial isolate with the highest binding capacity were analyzed for their ability to bind different heterocyclic amines. The results indicate the importance of the cell wall in binding to heterocyclic amines, whereas the cytoplasmic contents were less effective. Heat-treated cells were not much different from that of viable cells in their binding. The impact of different factors, such as pH, incubation time, metal ions, different concentrations of sodium chloride and alcohol, various enzymes, and acetylation of mutagens on binding of Trp-P-1 and IQ, were discussed. The significance of the present results is also discussed from the viewpoint that Natto, a fermented food, is able to scavenge dietary mutagenic heterocyclic amines through binding.     

Inhibitory effect of curcumin and its natural analogues on genotoxicity of heterocyclic amines from cooked food

Curcumin (C) and its natural analogues demethoxycurcumin (dmC) and bisdemethoxycurcumin (bdmC), known for their potent anti-inflammatory, antioxidant, antimutagenic and anticarcinogenic effects, were tested for their possible inhibitory effects against seven cooked food mutagens (heterocyclic amines): 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1), 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-amino-6-methyldipyrido[1,2-a:3',2'-d]imidazole (Glu-P-1), in both TA98 and TA100 strains of Salmonella typhimurium using Ames Salmonella/reversion assay in the presence of Aroclor induced rat liver S9 homogenate. In the present investigations, curcumin as well as its two natural analogues i.e., dmC and bdmC were found to be highly effective in suppressing genotoxicity of all the tested cooked food mutagens in a dose-dependent manner, in both the frame shift (TA98) as well as base pair mutation sensitive (TA100) strains of S. typhimurium. However, bdmC appeared to be a relatively less active antimutagen compared to C and dmC. More than 80% inhibition of mutagenicity was observed at 200 microg/plate in case of C and dmC in both TA98 and TA100 against all tested cooked food mutagens. Where as, bdmC showed 39-79% inhibition in TA100 and 60-80% inhibition in TA98, at a dose of 200 microg/plate. These findings warrant further biochemical, enzymatic and in vivo investigations in animal models as well as in humans to establish the chemoprotective effect of these agents against mutagenic heterocyclic amines found in cooked food.     

Desmutagenic effect of alpha-dicarbonyl and alpha-hydroxycarbonyl compounds against mutagenic heterocyclic amines

The desmutagenic effects of alpha-hydroxycarbonyl compounds, such as glyceraldehyde, glycolaldehyde, dihydroxyacetone, furfural, 5-hydroxymethylfurfural, maltol, acetol and acetoin and alpha-dicarbonyl compounds, such as diacetyl, glyoxal, methyl glyoxal and 2,3-pentanedione were investigated against the mutagenic heterocyclic amines, such as Trp-P-1, Trp-P-2, Glu-P-1, Glu-P-2 and IQ. Most of the carbonyl compounds suppressed the mutagenicity of heterocyclic amines for S. typhimurium TA98, alpha-dicarbonyl compounds showing a higher desmutagenic effect than alpha-hydroxycarbonyl compounds. Among the alpha-hydroxycarbonyl compounds, glyceraldehyde, glycolaldehyde and dihydroxyacetone showed more effective desmutagenicity, and diacetyl among the alpha-dicarbonyl compounds had the highest desmutagenic effect. These carbonyl compounds alone also showed mutagenicity to S. typhimurium TA100 without S9 mix. The reaction of carbonyl compounds with mutagenic heterocyclic amines also eliminated the mutagenicity of the former for S. typhimurium TA100.     

Phytoalexin resveratrol attenuates the mutagenicity of the heterocyclic amines 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline

Resveratrol is a phytoalexin, that belongs to a family of naturally occurring stilbenes. It has been reported that resveratrol can inhibit chemical carcinogenesis in experimental animals and although the mechanisms involved are unknown, an anti-mutagen mechanism has been proposed. We have explored this hypothesis using mutagenicity assays based on bacterial (Salmonella typhimurium) and eukaryotic cells (Chinese hamster V79 cells). We found resveratrol to be potent in both systems, blocking the mutagenicity of the food-derived heterocyclic amines (HA) 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) at micromolar concentrations. Furthermore, in cells capable of activating 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine to cytotoxic derivatives, resveratrol was able to attenuate cytotoxicity. Paradoxically, in cells lacking the ability to activate PhIP, resveratrol itself was toxic and co-incubation with PhIP reduced this toxicity. Our data confirm the potent anti-mutagenic activity of resveratrol and support its potential as a chemopreventative.     

Inhibition of mutagenicity of food-derived heterocyclic amines by sulforaphane--a constituent of broccoli

Sulforaphane, a constituent of broccoli was investigated for its antimutagenic potential against different classes of cooked food mutagens (heterocyclic amines). These include imidazoazaarenes such as 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP); pyridoindole derivatives such as 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) and 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2); and, dipyridoimidazole derivative such as 2-amino-6-methyldipyrido[1,2-a:3',2'-d]imidazole (Glu-P-1). Tests were carried out by Ames Salmonella/reversion assay using Salmonella typhimurium TA98 (frame shift mutation sensitive) and TA100 (base pair mutation sensitive) bacterial strains in the presence of Aroclor 1254-induced rat liver S9. Results of these in vitro antimutagenicity studies strongly suggest that sulforaphane is a potent inhibitor of the mutagenicity induced by imidazoazaarenes such as IQ, MeIQ and MeIQx (approximately 60% inhibition) and moderately active against pyridoindole derivatives such as Trp-P-1 and Trp-P-2 (32-48% inhibition), but ineffective against dipyridoimidazole derivative (Glu-P-1) in TA 100.     

Effects of seasoning and heating device on mutagenicity and heterocyclic amines in cooked beef.

Pan-roasted beef showed a lower mutagenicity after various degrees of cooking than charcoaled one. The high mutagenicity of charcoaled beef was due to the formation of more heterocyclic amines, especially AalphaC (2-amino-9H-pyrido- [2,3-b]indole) and PhIP (2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine) because of rapid and direct heating on the surface of the meat at a high temperature. Seasoning decreased mutagenicity of pan-roasted beef except the very well done sample with unchanged heterocyclic amine contents, but increased mutagenicity of charcoaled beef with decreased levels of AalphaC and PhIP, probably due to the change of heterocyclic amine precursors or alternatively to the occurrence of other mutagens.     

Effects of Seasoning and Heating Device on Mutagenicity and Heterocyclic Amines in Cooked Beef

Pan-roasted beef showed a lower mutagenicity after various degrees of cooking than charcoaled one. The high mutagenicity of charcoaled beef was due to the formation of more heterocyclic amines, especially AαC (2-amino-9 H-pyrido- [2,3-b]indole) and PhIP (2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine) because of rapid and direct heating on the surface of the meat at a high temperature. Seasoning decreased mutagenicity of pan-roasted beef except the very well done sample with unchanged heterocyclic amine contents, but increased mutagenicity of charcoaled beef with decreased levels of AαC and PhIP, probably due to the change of heterocyclic amine precursors or alternatively to the occurrence of other mutagens.     

Mutagenic activity and heterocyclic amine carcinogens in commercial pet foods

Twenty-five commercial pet foods were analyzed for mutagenic activity using the Ames/Salmonella test with strain TA98 and added metabolic activation. All but one gave a positive mutagenic response. Fourteen of these samples were analyzed for heterocyclic amine mutagens/carcinogens and all but one contained 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and 10 of 14 contained 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) as analyzed by HPLC and confirmed by photodiode array peak matching. From these findings it is hypothesized that there is a connection between dietary heterocyclic amines and cancer in animals consuming these foods.     

Establishment of ten strains of genetically engineered Salmonella typhimurium TA1538 each co-expressing a form of human cytochrome P450 with NADPH-cytochrome P450 reductase sensitive to various promutagens

We newly developed 10 Salmonela typhimurium TA1538 strains each co-expressing a form of human cytochrome P450s (P450 or CYP) together with NADPH-cytochrome P450 reductase (CPR) for highly sensitive detection of mutagenic activation of mycotoxins, polycyclic aromatic hydrocarbons, heterocyclic amines, and aromatic amines at low substrate concentrations. Each form of P450 (CYP1A1, CYP1A2, CYP2A6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4 or CYP3A5) expressed in the TA1538 cells efficiently catalyzed the oxidation of a representative substrate. Aflatoxin B1 was mutagenically activated effectively by CYP1A1, CYP1A2, and CYP3A4 and weakly by CYP2A6 and CYP2C8 expressed in S. typhimurium TA1538. CYP1A1 and CYP1A2 were responsible for the mutagenic activation of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-acetylaminofluorene. Benzo[a]pyrene was also activated efficiently by CYP1A1 and weakly by CYP1A2, CYP2C9, CYP2C19, and CYP3A4 expressed in TA1538. These results suggest that the newly developed S. typhimurium TA1538 strains are applicable for detecting the activation of promutagens of which mutagenic activation is not or weakly detectable with N-nitrosamine-sensitive YG7108 strains expressing human P450s.     

Comparative mutagenic efficiencies of the DNA adducts from the cooked-food-related mutagens Trp-P-2 and IQ in CHO cells

The relationship between DNA-adduct formation and mutagenicity of two heterocyclic aromatic amines associated with cooked foods was determined in a CHO cell strain lacking nucleotide excision repair. Cells were exposed to tritiated IQ (2-amino-3-methylimidazo[4,5-f]quinoline) or Trp-P-2 (3-amino-1-methyl-5H-pyrido[4,3-b]indole) supplemented with hamster S9 microsomal fraction for metabolic activation. DNA from nuclei was isolated by DNAase-mediated elution from polycarbonate filters after RNAase and proteinase treatment. The presumed metabolites of both compounds bound to DNA in a dose-dependent fashion. Although the dose required to produce 50% cell killing was 15 times higher for IQ than Trp-P-2, the amount of radioactive material bound to DNA at that dose was about 10-fold lower with IQ. When mutations at the hprt and aprt loci were compared with the estimated levels of adducts, the calculated mutagenic efficiency of the adducts was about 4 mutations per 1000 adducts for both compounds, assuming a target sequence of 1000 base pairs for either locus. We conclude that IQ is acting as a weak mutagen in this system because its extracellular metabolites either do not reach or do not react efficiently with the DNA of the CHO cells.     

Purified prostaglandin synthase activates aromatic amines to derivatives that are mutagenic to Salmonella typhimurium.

Prostaglandin H synthase (PHS) is widely distributed in mammalian tissues and has the ability to oxidize a variety of mutagens and carcinogens. It may therefore play a key role in the metabolic activation of xenobiotics. The present study documents that highly purified PHS can be used in conjunction with 5-phenyl-4-pentenyl-1-hydroperoxide (PPHP), a relatively stable and non-mutagenic hydroperoxide substrate, for the metabolic activation of aromatic amines to mutagenic derivatives that can be detected in short-term Salmonella typhimurium mutagenesis assays. The PHS-based activation system alone was not mutagenic for these tester strains, nor were the test compounds significantly toxic for the bacteria over the concentration range tested. When used in conjunction with Salmonella strains TA98 and TA100 in a modified Ames assay, this system should prove useful for screening of a wide range of compounds for metabolic activation by this mammalian peroxidase. The potential broad utility of this purified PHS-dependent metabolic activation system was investigated by evaluating the activation of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), which are representative of a group of mutagenic and carcinogenic heterocyclic arylamines to which humans are exposed via their diet. Both IQ and MeIQ were activated by PHS to potent mutagens and confirm the utility of the PPHP/PHS system for the activation of premutagens. Whereas the extent of activation of aromatic amines by S9-based systems is significantly greater than for the PHS activation system described herein, PHS may play a significant role in target tissues in which it is present at significantly greater levels than P450 isoenzymes. Moreover, it is likely that the substrate specificity of PHS differs sufficiently from that of P450 isoenzymes so that PHS may activate some compounds that are not efficiently activated by mixed-function oxidase based systems.     

Meat-derived carcinogens,genetic susceptibility and colorectal adenoma risk

Exposure to heterocyclic aromatic amines (HAAs), carcinogens produced when meat is cooked at high temperatures, is an emerging risk factor for colorectal cancer (CRC). In a cross-sectional study of 342 patients undergoing a screening colonoscopy, the role of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx), the three most abundant HAAs found in cooked meats, and total mutagenic activity in cooked meats were examined in relation to colorectal adenoma risk. Given that genetic differences in the ability to biotransform HAAs and repair DNA are postulated to modify the HAA–CRC relationship, gene–diet interactions were also examined. Among the total study population, no relationships were observed between dietary HAAs or meat mutagenicity, and colorectal adenoma risk; however, in males, positive associations between dietary HAAs/meat mutagenicity exposures and adenoma risk were suggestive of a relationship. In a separate analysis, polymorphisms in CYP1B1 were found to be associated with colorectal adenoma risk. Additionally, gene–diet interactions were observed for dietary PhIP and polymorphisms in CYP1B1 and XPD, dietary DiMeIQx and XPD polymorphisms, and meat mutagenicity exposure and CYP1B1 polymorphisms. Overall, increased colorectal adenoma risk was observed with higher HAA/meat mutagenicity exposures among those with polymorphisms which confer greater activity to biotransform HAAs and/or lower ability to repair DNA. This research supports the link between dietary HAAs and genetic susceptibility in colorectal adenoma etiology. The vast majority of CRCs arise from colorectal adenomas; thus, the results of this study suggest that changes in meat preparation practices limiting the production of HAAs may be beneficial for CRC prevention.     

The formation of heart DNA adducts in F344 rat following dietary administration of heterocyclic amines

Most heterocyclic amines formed during the cooking of meat and fish have been shown to form adducts in the livers of rats. Recently, however, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), administered in the diet to Fischer 344 (F344) rats for 4 weeks, was shown to produce the highest levels of adducts in the heart. In the present study 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,8-dimethylimidazo [4,5-f]quinoxaline (MeIQx), 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) and 2-amino-6-methyldipyrido[1,2-a:1',2'-d]imidazole (Glu-P-1) were given to F344 rats at carcinogenic dose levels (IQ 0.03%, MeIQx 0.04%, Trp-P-1 0.015%, Glu-P-1 0.05%) in the diet for 4 weeks. DNA adducts in the liver and heart were analyzed by 32P-postlabeling. DNA adducts were demonstrated to appear in the hearts of all animals exposed to heterocyclic amines at the following levels: IQ, 1.8 adducts/10(7) nucleotides, MeIQx, 3.8/10(7) ntd, Trp-P-1, 20/10(7) ntd and Glu-P-1, 7.2/10(7) ntd. Values for the heart were 10-20% of the respective liver adduct levels. Heart adducts increased linearly throughout the observed period when MeIQx was administered for up to 40 weeks. When MeIQx feeding was discontinued after 20 weeks and the animals subsequently given the basal diet, the adduct level at 20 weeks did not change during the following 20 weeks. A possible role for heart DNA alterations caused by food-borne heterocyclic amines in the development of age-related myopathies and cardiovascular disease is not inconceivable.     

Effects of industrially produced flavours with pro- and antioxidative properties on the formation of the heterocyclic amine PhIP in a model system

PhIP (2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine) is a heterocyclic aromatic amine belonging to a class of mutagens found in food. This project studied the effects of commercially available flavours of spices on the formation of PhIP, one of the most common heterocyclic aromatic amines in heated meat and fish products. The model reactions were carried out in diethylene glycol. Highest amounts of PhIP were obtained at 200 degrees C, a heating time of 60 min and an equivalent molar ratio of phenylalanine and creatinine. With this model system, the influence of Monascus red and flavours extracted from thyme, marjoram and rosemary on the formation of PhIP was tested. The flavours were added to the model system in different amounts. The oxidative properties were determined with the rancimat method. It was shown that all tested products, independent of their pro- or antioxidative properties, increased PhIP in the model system.     

Mutagenicity modulating effect of quercetin on aromatic amines and acetamides

The effect of quercetin on the mutagenicity of 32 kinds of aromatic amines and their acetamides were investigated using Salmonella typhimurium TA98 with a mammalian metabolic activation system (S9 mix). Quercetin enhanced the mutagenicity of the tricyclic aromatic amines (aminofluorene, aminoanthracene and aminophenanthrene) and their acetamides by 1.2-5.9-fold. Whereas, quercetin depressed the mutagenicity of aniline derivatives, biphenyl derivatives, and bi- and tetra-cyclic amino derivatives. The modulation of mutagenicity of Trp-P-1, Trp-P-2, Glu-P-1 and Glu-P-2 (heterocyclic amines) by quercetin were liable to be affected by the content of S9 in the S9 mix. It seems that quercetin does not have the same effect as norharman, because quercetin did not enhance the mutagenicity of aniline. It is suggested that the modulation of the mutagenicity of aromatic amines and acetamides is caused by the modulation of the balance between the mutagenic activation and inactivation in the metabolism of these amines and acetamides in the presence of quercetin. In this modulation, quercetin may participate through its effects on the promotion of N-hydroxylation and the inhibition of arylhydroxylation and transacylation. The presence of tricyclic aromatic rings of amines and acetamides is a structural requirement for the mutagenicity enhancement by quercetin.