Cancer potencies of heterocyclic amines found in cooked foods

Carcinogenic risk associated with popular Korean dishes: An approach of combined risk assessments using Oral Slope Factor and BMDL10 values

Cooking-related carcinogens are formed during the heating or processing of foods. To date, numerous studies analyzing carcinogens present in cooking ingredients or formed through different cooking methods have been conducted. However, combined risk assessment is important for practical reasons. The purpose of this study was to conduct a combined risk assessment of five cooking-related genotoxic carcinogens encompassing 25 chemicals: heterocyclic amines, acrylamide, furan, polycyclic aromatic hydrocarbons, and nitrosamines. Oral Slope Factor (OSF) and benchmark dose lower-bound confidence limit 10% (BMDL₁₀) of the compounds were obtained from public databases, and the values for the compounds that did not have published reference values were approximated using related toxicity values. The high-risk contributing food items and cooking methods for each carcinogen were selected for the study based on the Korean Total Diet Study (TDS) and Korea National Health and Nutrition Examination Survey (KNHANES). Exposure to the carcinogens from selected dishes per serving was estimated based on concentrations determined in TDS and consumption data gathered from 24-h recalls in the 2014 to 2016 KNHANES. The combined cancer risks were obtained by summing the risks of individual compounds in a dish, which were calculated by multiplying the OSF values by the concentrations of carcinogens per serving. The combined risks were used to compare the risk of different dishes, not to calculate the lifetime risk from the individual dishes. The risks of the dishes prepared with potatoes were found to be high, whereas namul (vegetable dish) had the lowest risk. Soup or stew dishes exhibited relatively high risks. Estimated combined risks based on BMDL₁₀ showed similar trends, except for fried potatoes and roasted or fried meat dishes. Combined risks of cooking-related carcinogens may vary based on the major contributors of individual carcinogens. The results of this study could provide an insightful guideline for selecting menus for consumers.

Generic Hockey-Stick Model for Estimating Benchmark Dose and Potency: Performance Relative to BMDS and Application to Anthraquinone

Benchmark Dose Model software (BMDS), developed by the U.S. Environmental Protection Agency, involves a growing suite of models and decision rules now widely applied to assess noncancer and cancer risk, yet its statistical performance has never been examined systematically. As typically applied, BMDS also ignores the possibility of reduced risk at low doses ("hormesis"). A simpler, proposed Generic Hockey-Stick (GHS) model also estimates benchmark dose and potency, and additionally characterizes and tests objectively for hormetic trend. Using 100 simulated dichotomous-data sets (5 dose groups, 50 animals/group), sampled from each of seven risk functions, GHS estimators performed about as well or better than BMDS estimators, and a surprising observation was that BMDS mis-specified all of six non-hormetic sampled risk functions most or all of the time. When applied to data on rodent tumors induced by the genotoxic chemical carcinogen anthraquinone (AQ), the GHS model yielded significantly negative estimates of net potency exhibited by the combined rodent data, suggesting that-consistent with the anti-leukemogenic properties of AQ and structurally similar quinones-environmental AQ exposures do not likely increase net cancer risk. In addition to its simplicity and flexibility, the GHS approach offers a unified, consistent approach to quantifying environmental chemical risk.

Flavonoids inhibit the genotoxicity of hydrogen peroxide (H(2)O(2)) and of the food mutagen 2-amino-3-methylimadazo[4,5-f]-quinoline (IQ) in lymphocytes from patients with inflammatory bowel disease (IBD)

Inflammatory bowel disease (IBD) including Crohn's disease (CD) and ulcerative colitis (UC) is a chronic inflammatory gastrointestinal autoimmune condition with an inappropriate immune response. We investigated DNA damage induced in vitro in lymphocytes from IBD patients caused by oxidative stress through H(2)O(2) and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and whether the plant flavonoids, quercetin and epicatechin, found in fruits, tea and soybeans could effectively reduce such stress. Lymphocytes from IBD patients and healthy volunteers were treated with 50 microg/ml H(2)O(2) or IQ in the presence of quercetin (0-250 microg/ml) or epicatechin (0-100 microg/ml). Flavonoid supplementation (250 microM quercetin or 100 microM epicatechin) caused an overall significant decrease of induced DNA damage resulting in a 48.6% (P < 0.001) reduction of H(2)O(2)-induced and a 43% (P < 0.001) reduction of IQ-induced DNA damage within the patient groups; for the control groups, reductions in DNA damage were 35.2 and 57.1%, respectively (both, P < 0.001). There was less induced DNA damage within lymphocytes from UC patients compared to CD patients for both series of experiments (H(2)O(2) and quercetin, IQ and epicatechin). In conclusion, flavonoids dramatically reduced oxidative stress in vitro in lymphocytes from IBD patients and healthy individuals. Thus, flavonoids could be very effective in the treatment of oxidative stress and encouraged in the diet of IBD patients.

Development of a meat frequency questionnaire for use in diet and cancer studies

OBJECTIVE

To develop a meat frequency questionnaire to assess dietary heterocyclic amine intake. The meat frequency questionnaire is designed to obtain information on meat types, cooking methods, and doneness preferences that predict heterocyclic amine concentrations in different meats.

DESIGN

Total and specific meat intakes were determined by a standard food frequency questionnaire (FFQ) and compared with that determined by the meat frequency questionnaire.

SUBJECTS/SETTING

Three-hundred fourteen African-American males participating in a clinic-based study of prostate disease and heterocyclic amine intake were administered the two questionnaires in a cancer education center prior to undergoing screening evaluations for prostate disease.

MAIN OUTCOME MEASURES

Fried, broiled, and grilled vs total meat intake was assessed using the meat frequency questionnaire vs FFQ, respectively. Specific meat items included in the meat frequency questionnaire were evaluated as factors potentially explaining discrepancies in meat intake estimated using the two questionnaires. Seasonal variation in meat intake was also examined.

STATISTICAL ANALYSIS

Correlation coefficients for intake of total meat and individual meat groups determined by FFQ vs meat frequency questionnaire were calculated. Seasonal differences in meat and estimated heterocyclic amine intakes were evaluated by t test, adjusted for multiple comparisons.

RESULTS

Meat intakes determined by the two questionnaires were well-correlated (Pearson r=0.69); however, total meat assessed by the meat frequency questionnaire exceeded total meat assessed by the FFQ in 30% of participants. Total energy and intake of heterocyclic amine-associated meat were greatest when the meat frequency questionnaire was administered during winter months.

CONCLUSIONS

The heterocyclic amine meat frequency questionnaire provided a fractional measure of total meat intake and identified specific heterocyclic amine-containing meat items underreported in a standard FFQ.

Highly elevated PSA and dietary PhIP intake in a prospective clinic-based study among African Americans

African-American men die from prostate cancer (PC) nearly twice as often as white US men and consume about twice as much of the predominant US dietary heterocyclic amine, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), a genotoxic rat-prostate carcinogen found primarily in well-cooked chicken and beef. To investigate the hypothesis that PhIP exposure increases PC risk, an ongoing prospective clinic-based study compared PC screening outcomes with survey-based estimates of dietary PhIP intake among 40-70-year-old African-American men with no prior PC in Oakland, CA. They completed food-frequency and meat-cooking/consumption questionnaires and had a prostate-specific antigen (PSA) test and digital-rectal exam. Results for 392 men indicated a 17 (+/-17) ng/kg day mean (+/-1 s.d.) daily intake of PhIP, about twice that of white US men of similar age. PhIP intake was attributable mostly to chicken (61%) and positively associated (R(2)=0.32, P<0.0001) with saturated fat intake. An odds ratio (95% confidence interval) of 31 (3.1-690) for highly elevated PSA > or =20 ng/ml was observed in the highest 15% vs lowest 50% of estimated daily PhIP intake (> or =30 vs < or =10 ng/kg day) among men 50+ years old (P=0.0002 for trend) and remained significant after adjustment for self-reported family history of (brother or father) PC, saturated fat intake and total energy intake. PSA measures were higher in African-American men with positive family history (P=0.007 all men, P<0.0001 highest PSA quartile). These preliminary results are consistent with a positive association between PhIP intake and highly elevated PSA, supporting the hypothesis that dietary intervention may help reduce PC risk.

A hepatocarcinogenic tryptophan-pyrolyzate component, Trp-P-1, decreases serum total testosterone level and induces hepatic Cyp1a2 in male mice

Male (BALB/c x DBA/2) F(1) mice were given 3-amino-1,4-dimethyl-5H-pyrido [4,3-b] indole acetate (Trp-P-1; 20 mg/kg body weight) by gavage at 24-h intervals for 1 or 2 weeks, and the effects of Trp-P-1 on the levels of serum total testosterone and hepatic cytochrome P4501a2 (Cyp1a2) were examined. A significant decrease in serum total testosterone level was observed after treatment with Trp-P-1 for 2 weeks, but not for 1 week. Likewise, gene expression levels of testicular androgenic enzymes, including cholesterol side chain cleavage cytochrome P450, 3beta-hydroxysteroid dehydrogenase and steroid 17alpha-hydroxylase/C17-20 lyase, decreased only in the mice treated with Trp-P-1 for 2 weeks. In contrast, levels of the mRNA and apoprotein of hepatic Cyp1a2 and its enzyme activity for O-demethylation of methoxyresorufin significantly increased in the mice treated with Trp-P-1 for 2 weeks, but only a small increase was observed in mice treated for 1 week. In the present study, we demonstrate for the first time that treatment of male mice with Trp-P-1 results in a decrease in serum total testosterone level through suppression of the gene expression of testicular enzymes responsible for androgen biosynthesis, and this then leads to induction of hepatic Cyp1a2.

Interspecies metabolism of heterocyclic aromatic amines and the uncertainties in extrapolation of animal toxicity data for human risk assessment

Heterocyclic aromatic amines (HAAs) are potent bacterial mutagens that are formed in cooked meats, tobacco smokes condensate, and diesel exhaust. Many HAAs are carcinogenic in experimental animal models. Because of their wide-spread occurrence in the diet and environment, HAAs may contribute to some common types of human cancers. The extrapolation of animal toxicity data on HAAs to asses human health risk has many uncertainties, which can lead to tenuous risk assessment estimates. Perhaps the most critical and variable parameters in interspecies extrapolation are the effects of dose, species differences in catalytic activities of xenobiotic metabolism enzymes (XMEs), human XME polymorphisms that lead to interindividual differences in carcinogen metabolism and dietary constituents that may either augment or diminish the carcinogenic potency of these genotoxins. The impact of these parameters on the metabolism and toxicological properties of HAAS and uncertainties in extrapolation of animal toxicity data for human risk assessment are presented in this article.

Estimates of heterocyclic amine intake in the US population

HA-specific meat concentration estimates using a method that combines laboratory data to predict HA concentrations from meat type, cooking method and meat doneness were used with national dietary data to estimate daily HA intake for segments of the US population. PhIP was found to comprise approximately 70% of US mean dietary intake of total HAs, with pan-frying and chicken being the single cooking method and meat type contributing the greatest to total estimated HA exposures. This analysis demonstrated significantly higher concentrations in grilled/barbecued meats than in other cooked meats. African-American males were estimated to consume nearly twofold and approximately 35 to 40% more PhIP (and total HAs) than white males at ages <16 and >30 years, respectively.

Occurrence of heterocyclic aromatic amines in the Swiss diet: analytical method, exposure estimation and risk assessment

A total of 86 meat samples, prepared in restaurants or homes, ready to eat (including poultry and fish) and 16 commercial samples such as bouillon (cubes) were analysed for heterocyclic aromatic amines (HAA). The analytical method consisted of an acidic extraction, clean-up on a cation exchange cartridge followed by an analogous HPLC step to recover the following HAA: IQ, MeIQ, MeIQx, 4,8-DiMeIQx, PhIP and 7,8-DiMeIQx. The HAA containing HPLC-fractions were collected, the HAA identified and quantified using two RP-HPLC-systems of different retention properties (UV-detection). The limit of quantitation was in the range of 0.2-0.4 ng/g and the relative repeatability 6-15%. The recovery of PhIP was lower than for the other HAA analysed (less than 80%) and a correction factor was applied. No significant differences of the HAA-concentration were found in samples from homes and restaurants, half of the total samples contained HAA at the following frequencies: PhIP and MeIQx 33% (each), 4,8-DiMeIQx 11% and MeIQ 4%; 7,8-DiMeIQx and IQ were not detected. The frequencies in commercial products were for MeIQx 31%, 7,8-DiMeIQx 19%, IQ 13% and PhIP 6%; MeIQ and 4,8-DiMeIQx were not found. Based on these data, the average exposure of Swiss adults to HAA was estimated to be 5 ng/kg body mass per day, commercial products contributing less than 10%. The theoretical excess cancer risk due to this intake was estimated on the base of the carcinogenic potency of the HAA in long-term animal experiments by linear extrapolation. The resulting risk in the order of 10(-4) at the maximum is discussed in terms of Swiss epidemiological data.

U.S. dietary exposures to heterocyclic amines

Heterocyclic amines (HAs) formed in fried, broiled or grilled meats are potent mutagens that increase rates of colon, mammary, prostate and other cancers in bioassay rodents. Studies of how human dietary HA exposures may affect cancer risks have so far relied on fairly crudely defined HA-exposure categories. Recently, an integrated, quantitative approach to HA-exposure assessment (HAEA) was developed to estimate compound-specific intakes for particular individuals based on corresponding HA-concentration estimates that reflect their meat-type, intake-rate, cooking-method and meat-doneness preferences. This method was applied in the present study to U.S. national Continuing Survey of Food Intakes by Individuals (CSFII) data on meats consumed and cooking methods used by >25,000 people, after adjusting for underreported energy intake and conditional on meat-doneness preferences estimated from additional survey data. The U.S. population average lifetime time-weighted average of total HAs consumed was estimated to be approximately 9 ng/kg/day, with 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) estimated to comprise about two thirds of this intake. Pan-fried meats were the largest source of HA in the diet and chicken the largest source of HAs among different meat types. Estimated total HA intakes by male vs. female children were generally similar, with those by (0- to 15-year-old) children approximately 25% greater than those by (16+-year-old) adults. Race-, age- and sex-specific mean HA intakes were estimated to be greatest for African American males, who were estimated to consume approximately 2- and approximately 3-fold more PhIP than white males at ages <16 and 30+ years, respectively, after considering a relatively greater preference for more well-done items among African Americans based on national survey data. This difference in PhIP intakes may at least partly explain why prostate cancer (PC) kills approximately 2-fold more African American than white men, in view of experimental data indicating that PhIP mutates prostate DNA and causes prostate tumors in rats.

Methods for estimating heterocyclic amine concentrations in cooked meats in the US diet

Heterocyclic amines (HAs) are formed in numerous cooked foods commonly consumed in the diet. A method was developed to estimate dietary HA levels using HA concentrations in experimentally cooked meats reported in the literature and meat consumption data obtained from a national dietary survey. Cooking variables (meat internal temperature and weight loss, surface temperature and time) were used to develop relationships for estimating total HA concentrations in six meat types. Concentrations of five individual HAs were estimated for specific meat type/cooking method combinations based on linear regression of total and individual HA values obtained from the literature. Using these relationships, total and individual HA concentrations were estimated for 21 meat type/cooking method combinations at four meat doneness levels. Reported consumption of the 21 meat type/cooking method combinations was obtained from a national dietary survey and the age-specific daily HA intake calculated using the estimated HA concentrations (ng/g) and reported meat intakes. Estimated mean daily total HA intakes for children (to age 15 years) and adults (30+ years) were 11 and 7.0 ng/kg/day, respectively, with 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) estimated to comprise approximately 65% of each intake. Pan-fried meats were the largest source of HA in the diet and chicken the largest source of HAs among the different meat types.

Evaluation of fecal mutagenicity and colorectal cancer risk

Colorectal cancer is one of the most common internal malignancies in Western society. The cause of this disease appears to be multifactorial and involves genetic as well as environmental aspects. The human colon is continuously exposed to a complex mixture of compounds, which is either of direct dietary origin or the result of digestive, microbial and excretory processes. In order to establish the mutagenic burden of the colorectal mucosa, analysis of specific compounds in feces is usually preferred. Alternatively, the mutagenic potency of fecal extracts has been determined, but the interpretation of these more integrative measurements is hampered by methodological shortcomings. In this review, we focus on exposure of the large bowel to five different classes of fecal mutagens that have previously been related to colorectal cancer risk. These include heterocyclic aromatic amines (HCA) and polycyclic aromatic hydrocarbons (PAH), two exogenous factors that are predominantly ingested as pyrolysis products present in food and (partially) excreted in the feces. Additionally, we discuss N-nitroso-compounds, fecapentaenes and bile acids, all fecal constituents (mainly) of endogenous origin. The mutagenic and carcinogenic potency of the above mentioned compounds as well as their presence in feces, proposed mode of action and potential role in the initiation and promotion of human colorectal cancer are discussed. The combined results from in vitro and in vivo research unequivocally demonstrate that these classes of compounds comprise potent mutagens that induce many different forms of genetic damage and that particularly bile acids and fecapentaenes may also affect the carcinogenic process by epigenetic mechanisms. Large inter-individual differences in levels of exposures have been reported, including those in a range where considerable genetic damage can be expected based on evidence from animal studies. Particularly, however, exposure profiles of PAH and N-nitroso compounds (NOC) have to be more accurately established to come to a risk evaluation. Moreover, lack of human studies and inconsistency between epidemiological data make it impossible to describe colorectal cancer risk as a result of specific exposures in quantitative terms, or even to indicate the relative importance of the mutagens discussed. Particularly, the polymorphisms of genes involved in the metabolism of heterocyclic amines are important determinants of carcinogenic risk. However, the present knowledge of gene-environment interactions with regard to colorectal cancer risk is rather limited. We expect that the introduction of DNA chip technology in colorectal cancer epidemiology will offer new opportunities to identify combinations of exposures and genetic polymorphisms that relate to increased cancer risk. This knowledge will enable us to improve epidemiological study design and statistical power in future research.

Formation and inhibition of heterocyclic aromatic amines in fried ground beef patties

The effect of vitamin E and oleoresin rosemary on heterocyclic aromatic amine (HAA) formation in fried ground beef patties was studied. Patties were fried at three temperatures (175 degrees C, 200 degrees C, 225 degrees C) for 6 and 10 min/side to determine the conditions for optimum HAA formation. HAAs were isolated by solid phase extraction and quantitated by HPLC. Greatest concentrations were generated when patties were fried at 225 degrees C for 10 min/side, 31.4 ng/g 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 5.8 ng/g 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx). Vitamin E, when used at two concentrations (1% and 10% based on fat content) and added directly to the ground beef patties, reduced PhIP concentrations in the cooked patties by 69% and 72%, respectively. Smaller but more variable reductions were achieved for MeIQx. Comparable inhibition of HAA formation was achieved by the direct addition of vitamin E (1% based on fat content) to the surface of the patties before frying. Concentrations of five HAAs studied were all significantly reduced (P<0.006), with average reductions ranging from 45% to 75%. Oleoresin rosemary, when used at two concentrations (1% and 10% based on fat content), reduced PhIP formation by 44%.

Mutant yields and mutational spectra of the heterocyclic amines MeIQ and PhIP at the S1 locus of human-hamster AL cells with activation by chick embryo liver (CELC) co-cultures

Cooking meat and fish at high temperature creates heterocyclic amines (HA) including 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). Several HA are mutagens in the Ames' S9/Salmonella assay. While PhIP is a substantial Ames' test mutagen, it is 1000-fold less active than the extraordinarily potent MeIQ. In contrast, MeIQ is significantly less mutagenic than PhIP in several mammalian cell assays, especially in repair-deficient Chinese hamster ovary (CHO) cells. HA are suspect human carcinogens on the basis of (i) epidemiological evidence, (ii) induction of tumors in rodents and monkeys, (iii) DNA adduct formation and (iv) mutagenic capacity. In this study, MeIQ and PhIP were significant mutagens at the S1 locus of co-cultivated human/hamster hybrid AL cells following metabolic activation by beta-napthoflavone (betaNF)-induced chick embryonic liver cultures (CELC). MeIQ was more mutagenic than PhIP in the CELC+AL cell assay. The mutant response curves increase with dose and then plateau (PhIP), or decrease (MeIQ). The inflections in these response curves coincide with dose-dependent decreases in cytochrome CYP1A1 activity. Molecular analysis of S1- mutants indicates that a substantial fraction, >65%, of the mutations induced by PhIP are deletions of 4.2 to 133 (Mbp); half are larger than 21 Mbp. Mutations induced by MeIQ were smaller, most (56%) being less than 5.7 Mbp. When appropriate metabolic activation is combined with a target locus, which can detect both small and large chromosomal mutations, both MeIQ and PhIP are significant mutagens and clastogens in repair proficient mammalian cells.

Effects of marinating on heterocyclic amine carcinogen formation in grilled chicken

This study compared heterocyclic aromatic amines in marinated and unmarinated chicken breast meat flame-broiled on a propane grill. Chicken was marinated prior to grilling and the levels of several heterocyclic amines formed during cooking were determined by solid-phase extraction and HPLC. Compared with unmarinated controls, a 92-99% decrease in 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) was observed in whole chicken breast marinated with a mixture of brown sugar, olive oil, cider vinegar, garlic, mustard, lemon juice and salt, then grilled for 10, 20, 30 or 40 min. Conversely, 2-amino-3, 8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) increased over 10-fold with marinating, but only at the 30 and 40 min cooking times. Marinating reduced the total detectable heterocyclic amines from 56 to 1.7 ng/g, from 158 to 10 ng/g and from 330 to 44 ng/g for grilling times of 20, 30 and 40 min, respectively. The mutagenic activity of the sample extracts was also measured, using the Ames/Salmonella assay. Mutagenic activity was lower in marinated samples cooked for 10, 20 and 30 min, but higher in the marinated samples cooked for 40 min, compared with unmarinated controls. Although a change in free amino acids, which are heterocyclic amine precursors, might explain the decrease in PhIP and increase in MeIQx, no such change was detected. Marinating chicken in one ingredient at a time showed that sugar was involved in the increased MeIQx, but the reason for the decrease in PhIP was unclear. PhIP decreased in grilled chicken after marinating with several individual ingredients. This work shows that marinating is one method that can significantly reduce PhIP concentration in grilled chicken.

Effect of commercial marinades on the mutagenic activity, sensory quality and amount of heterocyclic amines in chicken grilled under different conditions

The effect of processing conditions on the mutagenic activity and sensory quality of everyday food was studied by investigating grilled chicken samples seasoned with four different marinades and grilled at temperatures of about 110, 170 and 220 degrees C. The amounts of the heterocyclic amines 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline and 2-amino-1-methyl-6-phenylimidazo[4,5,-b]pyridine were determined only in samples grilled at 220 degrees C, using a gas chromatography-mass spectrometry technique with negative-ion chemical ionization. Sensory quality was determined using the extended ranking test method and the mutagenic activity using the Ames Salmonella assay. At 220 degrees C one of the marinades decreased the mutagenic activity in the chicken samples compared with the unseasoned control or samples treated with the other marinades. Great variations, without any clear correlation with mutagenicity, were observed in the amounts of heterocyclic amines between chicken samples treated with the same or different marinades. At the grilling temperatures of 170 degrees C and 110 degrees C the mutagenic activities of the chicken samples were lower or they were non-mutagenic. There was no correlation between mutagenic activity and sensory quality of the products. The samples with high mutagenic activity were ranked to be as good as the samples with lower or no mutagenicity. The results show that it is possible to prepare grilled products with reduced mutagenicity without compromising their sensory quality. It was also evident that marinades can have a reducing effect on the mutagenicity of grilled chicken. Variation observed in the amounts of heterocyclic amines between equivalent products makes it difficult to estimate their concentration in everyday foods.

Interplay between heterocyclic amines in cooked meat and metabolic phenotype in the etiology of colon cancer

Although the etiology of colon cancer remains uncertain, an increasing body of epidemiologic evidence indicates that red meat consumption is an important risk factor. The cooking of red meat produces a class of potent experimental carcinogens, the heterocyclic aromatic amines (HAA). These induce cancers in several different sites, including the colon, in rats and mice. Other epidemiologic studies indicate that an individual's genetically determined metabolic phenotype (polymorphisms for N-acetyltransferase and N-hydroxylase) modulates the risk of colon cancer. Both N-acetyltransferase and N-hydroxylase are involved in the metabolism of HAA. An increased risk of colon cancer has been observed in rapid acetylators in four of five studies; further, in two of these the association was found only in meat eaters. The latter observation supports the hypothesis that HAA are involved in colon carcinogenesis. Considerable progress has been made in the study of the molecular pathogenesis of colon cancer, which typically entails the cumulation of several genetic events (mutations and deletions) in oncogenes and tumor suppressor genes. It would now be a crucial contribution to elucidating the causation of colon cancer to show that such mutations are induced in human colonic mucosa by food-borne heterocyclic aromatic amines.

Extrapolation of heterocyclic amine carcinogenesis data from rodents and nonhuman primates to humans

Twenty different heterocyclic amines have been isolated and identified from cooked foods especially beef, fish, pork and fowl. Other HCAs have also been isolated but their structure remains to be elucidated and new HCAs are likely to be identified in the future. The HCAs are highly mutagenic and all ten HCAs that have been tested for carcinogenic activity, produce tumors in mice and rats. For humans the average daily intake of HCAs is in quantities of 10-20 mg/person/day. The HCAs are procarcinogens and are activated by the cytochrome P450 system especially CYP 1A2. Rodents, monkeys and humans have the capacity to activate HCAs. Studies using hepatic microsomes demonstrated that humans have a greater capacity to activate the majority of HCAs tested than rodents or cynomolgus monkeys. Three HCAs are currently under evaluation in nonhuman primates for carcinogenic activity and one, IQ, is highly carcinogenic inducing primary hepatocellular carcinomas in the majority of cynomolgus monkeys treated. Epidemiological studies, although not definitive, are supportive of an association of HCAs intake to the etiology of human cancer. Risk assessments from animal data show a risk of HCAs to humans in the range of 10(-3) to 10(-4) which is an order of magnitude greater than compounds currently regulated by the U.S. Food and Drug Administration or the Environmental Protection Agency. Taken together evidence from mutagenicity data, activation by various species including humans, carcinogenicity in animals, human consumption data, epidemiological studies and risk assessment, supports the conclusion that HCAs are probable human carcinogens.