Effect of cooking time and temperature on the heterocyclic amine content of fried beef patties

Quantification of heterocyclic aromatic amines in fried meat by HPTLC/UV-FLD and HPLC/UV-FLD: a comparison of two methods

A recently developed HPTLC/UV-FLD method was compared to the routinely used HPLC/UV-FLD method for the quantification of heterocyclic aromatic amines (HAA) formed at trace levels during the heating process of meat. For formation of these process contaminants under normal cooking conditions, beef patties were fried in a double-contact grill at 230 degrees C for five different frying times and extracted by solid-phase extraction. The HAAs most frequently found, that is, 2-amino-1-methyl-6-phenylimidazo[4,5- b]pyridine (PhIP), 2-amino-3,8-dimethylimidazo[4,5- f]quinoxaline (MeIQx), 2-amino-3,4,8-trimethylimidazo[4,5- f]quinoxaline (4,8-DiMeIQx), 9 H-pyrido[3,4- b]indole (norharman), and 1-methyl-9 H-pyrido[3,4- b]indole (harman), were quantified by two chromatographic methods, which were orthogonal to each other (normal versus reversed phase system). Both methods showed a similar performance and good correlation of the results ( R (2) between 0.8875 and 0.9751). The comparison of running costs and run time in routine analysis proved HPTLC/UV-FLD to be more economical (factor of 3) and faster (factor of 4) due to its capability of parallel chromatography. The HAA findings calculated by standard addition increased with the heating time from <1 to 33 microg/kg related to 3-6 min of frying time. The precision (RSD) was between 7 and 49% (HPTLC) and between 5 and 38% (HPLC) at these very low HAA levels formed.

Quantitation of 13 heterocyclic aromatic amines in cooked beef, pork, and chicken by liquid chromatography-electrospray ionization/tandem mass spectrometry

The concentrations of heterocyclic aromatic amines (HAAs) were determined, by liquid chromatography-electrospray ionization/tandem mass spectrometry (LC-ESI-MS/MS), in 26 samples of beef, pork, and chicken cooked to various levels of doneness. The HAAs identified were 2-amino-3-methylimidazo[4,5- f]quinoline, 2-amino-1-methylimidazo[4,5- b]quinoline, 2-amino-1-methylimidazo[4,5- g]quinoxaline (I gQx), 2-amino-3-methylimidazo[4,5- f]quinoxaline, 2-amino-1,7-dimethylimidazo[4,5- g]quinoxaline (7-MeI gQx), 2-amino-3,8-dimethylimidazo[4,5- f]quinoxaline, 2-amino-1,6-dimethyl-furo[3,2- e]imidazo[4,5- b]pyridine, 2-amino-1,6,7-trimethylimidazo[4,5- g]quinoxaline, 2-amino-3,4,8-trimethylimidazo[4,5- f]quinoxaline, 2-amino-1,7,9-trimethylimidazo[4,5- g]quinoxaline, 2-amino-1-methyl-6-phenylimidazo[4,5- b]pyridine (PhIP), 2-amino-9 H-pyrido[2,3- b]indole, and 2-amino-3-methyl-9 H-pyrido[2,3- b]indole. The concentrations of these compounds ranged from <0.03 to 305 parts per billion (micrograms per kilogram). PhIP was the most abundant HAA formed in very well done barbecued chicken (up to 305 microg/kg), broiled bacon (16 microg/kg), and pan-fried bacon (4.9 microg/kg). 7-MeI gQx was the most abundant HAA formed in very well done pan-fried beef and steak, and in beef gravy, at concentrations up to 30 microg/kg. Several other linear tricyclic ring HAAs containing the I gQx skeleton are formed at concentrations in cooked meats that are relatively high in comparison to the concentrations of their angular tricyclic ring isomers, the latter of which are known experimental animal carcinogens and potential human carcinogens. The toxicological properties of these recently discovered I gQx derivatives warrant further investigation and assessment.

Tobacco smoking and urinary levels of 2-amino-9H-pyrido[2,3-b]indole in men of Shanghai, China

Carcinogenic heterocyclic aromatic amines (HAA) are formed in cooked meats, poultry, and fish and arise in tobacco smoke. We measured the concentrations of four prevalent HAAs in spot urine samples collected at baseline from 170 participants of the Shanghai Cohort study, a population-based cohort study of adult men recruited during 1986 to 1989 in Shanghai, China. Sixteen (18.6%) of 86 nonsmokers were positive for urinary 2-amino-9H-pyrido[2,3-b]indole (AalphaC) versus 41 (48.8%) of 84 cigarette smokers; the difference was statistically significant (P < 0.001). The number of cigarettes smoked per day was positively and significantly related to urinary levels of AalphaC in study subjects (P < 0.001); the mean level among nonsmokers was 2.54 ng/g creatinine, whereas the means for light (1-19 cigarettes per day) and heavy (20+ cigarettes per day) smokers were 7.50 and 11.92 ng/g creatinine, respectively. 2-Amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline was undetected in the urine of the 170 subjects. Only 5 (2.9%) and 6 (3.5%) subjects, respectively, showed detectable levels of urinary 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, and smoking status was unrelated to levels of either HAA. Quantitative measurements of HAAs in commonly eaten pork and chicken dishes in Shanghai showed low concentrations of HAAs (<1 ng/g meat). Our data indicate that AalphaC represents a major HAA exposure in adult men of Shanghai, China, and that tobacco smoke is an important point source of their AalphaC exposure.

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.

Analysis of heterocyclic aromatic amines

Heterocyclic aromatic amines are formed in protein and amino acid-rich foods at temperatures above 150 degrees C. Of more than twenty heterocyclic aromatic amines identified ten have been shown to have carcinogenic potential. As nutritional hazards, their reliable determination in prepared food, their uptake and elimination in living organisms, including humans, and assessment of associated risks are important food-safety issues. The concentration in foods is normally in the low ng g(-1) range, which poses a challenge to the analytical chemist. Because of the complex nature of food matrixes, clean-up and enrichment of the extracts are also complex, usually involving both cation-exchange (propylsulfonic acid silica gel, PRS) and reversed-phase purification. The application of novel solid-phase extraction cartridges with a wettable apolar phase combined with cation-exchange characteristics simplified this process--both the polar and apolar heterocyclic aromatic amines were recovered in one fraction. Copper phthalocyanine trisulfonate bonded to cotton ("blue cotton") or rayon, and molecular imprinted polymers have also been successfully used for one-step sample clean-up. For analysis of the heterocyclic aromatic amines, liquid chromatography with base-deactivated reversed-phase columns has been used, and, recently, semi-micro and capillary columns have been introduced. The photometric, fluorimetric, or electrochemical detectors used previously have been replaced by mass spectrometers. Increased specificity and sub-ppb sensitivities have been achieved by the use of the selected-reaction-monitoring mode of detection of advanced MS instrumentation, for example the triple quadrupole and Q-TOF instrument combination. Gas chromatography, also with mass-selective detection, has been used for specific applications; the extra derivatization step needed for volatilization has been balanced by the higher chromatographic resolution.

Heterocyclic amines in griddled beef steak analysed using a single extract clean-up procedure

Heterocyclic amines (HAs), which are potent mutagenic and carcinogenic substances, are formed in muscle meats during their cooking under ordinary conditions. In this work, we measured the concentration of 15 HAs in different samples of griddled beef steak, which is one of the most consumed meat items is Spain. Three samples were obtained from different restaurants, and the other sample was cooked under controlled conditions to a well-done degree of doneness. A low-time consuming solid-phase extraction procedure was used to purify the samples, and liquid chromatography-tandem mass spectrometry with an ion trap mass analyzer was used as determination technique. A second well-established purification procedure was used to demonstrate the applicability of the method to the analysis of these kind of samples. 8-MeIQx, 4,8-DiMeIQx, PhIP and the comutagens Harman and Norharman were found in all the samples, at levels ranging from 0.28 to 21.2ngg(-1). AalphaC was found in three samples (0.18-1.41ngg(-1)), whereas Trp-P-1 was detected in two samples (0.35ngg(-1)). MeAalphaC was found in three samples but could only be quantified in one (0.15ngg(-1)). Trp-P-2 and DMIP were also detected in some cases at levels below their limit of quantification. The remaining HAs analyzed were not detected in any of the samples.

Identification of 2-amino-1,7-dimethylimidazo[4,5-g]quinoxaline: an abundant mutagenic heterocyclic aromatic amine formed in cooked beef

A previously unknown isomer of the carcinogenic heterocyclic aromatic amine (HAA) 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (8-MeIQx) was recently discovered in the urine of meat eaters and subsequently detected in cooked ground beef (Holland, R.D., et al. (2004) Chem. Res. Toxicol. 17, 1121-1136). In this current investigation, the identity of the analyte was determined through a comparison of its chromatographic tR by HPLC and through UV and mass spectral comparisons to the synthesized isomers of 8-MeIQx. Angular tricyclic isomers of 8-MeIQx were excluded as potential structures of the newly discovered HAA, on the basis of dissimilar tR and product ion mass spectral data. The linear tricyclic isomers 2-amino-1,6-dimethylimidazo[4,5-g]quinoxaline (6-MeIgQx) and 2-amino-1,7-dimethylimidazo[4,5-g]quinoxaline (7-MeIgQx) were postulated as plausible structures. Both compounds were synthesized from 4-fluoro-5-nitro-benzene-1,2-diamine in five steps. The structure of the analyte was proven to be 7-MeIgQx, on the basis of co-injection of the compound with the synthetic isomers, and corroborated by comparisons of the UV and mass spectral data of the analyte and MeIgQx isomers. 7-MeIgQx induced 348 revertants/microg in the S. typhimurium tester strain YG1024, when liver S-9 homogenate of rats pretreated with polychlorinated biphenyls (PCBs) was used for bioactivation. This newly discovered 7-MeIgQx molecule is one of the most abundant HAAs formed in cooked ground beef patties and pan-fried scrapings. The human health risk of 7-MeIgQx requires investigation.

Assessment of metastable atom bombardment (MAB) ionization mass spectrometry for the fast determination of heterocyclic aromatic amines in cooked meat

An investigation of metastable atom bombardment (MAB) ionization mass spectrometry for the fast characterization of mutagenic/carcinogenic heterocyclic aromatic amines (HAAs) formed during heating processes of meats is presented. The aim of our study was to use the selective ionization of MAB to develop a detection method for HAAs in non-purified meat extracts, thus avoiding purification and concentration steps and reducing analysis time. Sample introduction into the MAB ion source was achieved by pyrolysis, allowing the direct and fast insertion of complex food extracts into the mass spectrometer. Analysis conditions were optimized on standard HAAs by using different ionization gases for the MAB process. Metastable nitrogen was selected as the best MAB gas for the analysis of HAAs. Ionization selectivity is shown by the detection of heterocyclic amines in non-purified chicken meat extracts spiked with HAAs. A quantitative approach is also presented by using pyrograms as chromatograms for quantification purposes. HAAs determination using Py-MAB-ToF was finally performed on cooked chicken breast extracts and compared to an LC-APCI-MS/MS method. Although Py-MAB-ToF sensitivity remains to be improved in the present state of development of our prototype device, only 2 h from the cooking were required to obtain quantitative results in good agreement with HAAs concentrations measured by LC-MS/MS in 36 h. Figure Experimental set-up for pyrolysis-MAB-ToF mass spectrometry experiments.

Validation of a new planar chromatographic method for quantification of the heterocyclic aromatic amines most frequently found in meat

A new HPTLC method, in which all the HPTLC steps are performed automatically, has been established for quantification of the five most frequently found heterocyclic aromatic amines (HAA: PhIP, MeIQx, 4,8-DiMeIQx, norharmane, and harmane). The method was used for trace analysis (low microg kg(-1) range) of HAA in meat samples and found to be a cost-effective alternative to HPLC, because it enables simultaneous chromatography of up to 20 samples within 30 min. After preconditioning of the HPTLC silica gel layer with ammonia vapour the plate was developed with methanol-chloroform, 1:9 (v/v). At least 4ó separations were obtained and selectivity for the meat matrix was achieved. In repeatability tests relative standard deviations (RSD, n = 14, peak height) were less than or equal to +/-3.3%. In tests of intermediate precision (mean value for 14 tracks on six different plates on six different days) RSDs were better than +/-2% (peak height). Measurement of the reproducibility of migration distances on six different plates resulted in RSDs less than or equal to +/-1.3%. Limits of detection and quantification (S/N 3 and 10, respectively) for the five HAA ranged between 0.4 and 5 ng per band and between 0.8 and 14 ng per band, respectively. With paraffin-n-hexane, 3:7 (v/v), as fluorescence enhancer more sensitive determinations (up to 8.5-fold greater signal intensities) were achieved for PhIP, norharmane, and harmane. In the working range (1:10) polynomial regressions for PhIP, MeIQx, and 4,8-DiMeIQx and linear regressions for norharmane and harmane resulted in RSDs between +/-1.9 and 3.6%. To confirm the absence of potentially coeluting minor HAA, rarely formed in meat, mass spectra were occasionally recorded by online ESI-MS. Robustness tests showed that preconditioning with ammonia was essential for successful separation and that relative humidity had only a minor effect on the chromatography.

Formation and biochemistry of carcinogenic heterocyclic aromatic amines in cooked meats

Heteroyclic aromatic amines (HAAs) are a class of hazardous chemicals that are receiving heightened attention as a risk factor for human cancer. HAAs arise during the cooking of meats, fish, and poultry, and several HAAs also occur in tobacco smoke condensate and diesel exhaust. Many HAAs are carcinogenic and induce tumors at multiple sites in rodents. A number of epidemiologic studies have reported that frequent consumption of well-done cooked meats containing HAAs can result in elevated risks for colon, prostate, and mammary cancers. Moreover, DNA adducts of HAAs have been detected in human tissues, demonstrating that HAAs induce genetic damage even though the concentrations of these compounds in cooked meats are generally in the low parts-per-billion (ppb) range. With recent improvements in sensitivity of mass spectrometry instrumentation, HAAs, their metabolites, and DNA adducts can be detected at trace amounts in biological fluids and tissues of humans. The incorporation of HAA biomarkers in epidemologic studies will help to clarify the role of these dietary genotoxicants in the etiology of human cancer.

Heterocyclic aromatic amines in domestically prepared chicken and fish from Singapore Chinese households

Chicken and fish samples prepared by 42 Singapore Chinese in their homes were obtained. Researchers were present to collect data on raw sample weight, cooking time, maximum cooking surface temperature, and cooked sample weight. Each participant prepared one pan-fried fish sample and two pan-fried chicken samples, one marinated, one not marinated. The cooked samples were analyzed for five heterocyclic aromatic amine (HAA) mutagens, including MeIQx (2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline); 4,8-DiMeIQx (2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline); 7,8-DiMeIQx (2-amino-3,7,8-trimethylimidazo[4,5-f]quinoxaline); PhIP (2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine), and IFP (2-amino-(1,6-dimethylfuro[3,2-e]imidazo[4,5-b])pyridine). A paired Student's t-test showed that marinated chicken had lower concentrations of PhIP (p<0.05), but higher concentrations of MeIQx (p<0.05) and 4,8-DiMeIQx (p<0.001) than non-marinated chicken, and also that weight loss due to cooking was less in marinated chicken than in non-marinated chicken (p<0.001). Interestingly, the maximum cooking surface temperature was higher for fish than for either marinated or non-marinated chicken (p<0.001), yet fish was lower in 4,8-DiMeIQx per gram than marinated or non-marinated chicken (p<0.001), lower in PhIP than non-marinated chicken (p<0.05), and lost less weight due to cooking than either marinated or non-marinated chicken (p<0.001). Fish was also lower in MeIQx and 7,8-DiMeIQx than marinated chicken (p<0.05). This study provides new information on HAA content in the Singapore Chinese diet.

Meat cooking habits and risk of colorectal cancer in Córdoba, Argentina

OBJECTIVE

Colorectal cancer is the third cause of death among women and the fifth among men in Córdoba, Argentina. We previously reported colorectal cancer to be associated with a high intake of fatty meats and bovine viscera and inversely associated with dietary fiber intake. In this study, we investigated the role of method of cooking meat and preferences in browned surfaces in the risk of colorectal cancer.

METHODS

A case-control retrospective study was carried out by interviewing 296 patients and 597 control subjects with a food-frequency questionnaire. Meat consumption and preferred cooking procedures (boiled, roasted, barbecued, cooked in a flat iron-pan without fat, and fried) were investigated. Odds ratios and 95% confidence intervals were obtained by unconditional logistic regression analysis.

RESULTS

Barbecuing was the cooking method preferred by men, whereas iron-pan cooking was favored by women; frying was the least favored method. Fatty beef, sausages, and bovine viscera were preferentially barbecued or boiled, whereas lean beef was mainly roasted, iron-pan cooked, or fried. Chicken was barbecued or roasted. The multivariate relative risks (adjusted by age, sex, social stratum, and total energy intake) for preferring darkly browned surfaces were significantly associated with an increased risk for all cooking procedures (odds ratio, 4.57; 95% confidence interval, 3.10 to 6.73). No associations were found for red roasted or for boiled meats.

CONCLUSION

Increased risk seems to be related to cooking temperature and close contact of the food to the heating source, because higher risks were observed for heavily browned surfaces when meats were barbecued or iron-pan cooked.

CYP1A2 and NAT2 genotype/phenotype relations and urinary excretion of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in a human dietary intervention study

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a mutagenic and carcinogenic heterocyclic amine formed during ordinary cooking, and is subsequently metabolically activated by cytochrome P4501A2 (CYP1A2) and N-acetyltransferase 2 (NAT2). Respective genes encoding for these enzymes, display polymorphic distribution in the human population and are thus believed to cause interindividual differences in cancer risk susceptibility. The present study investigated the influence of dietary exposure and CYP1A2 and NAT2 genotypes and phenotypes on differential urinary PhIP excretion levels in 71 human volunteers after consumption of either a high (7.4 ng/g) or low (1.7 ng/g) dose of PhIP. Urinary PhIP excretion levels were found to reflect recent dietary exposure levels, with average levels of 174% (high dose group) and 127% (low dose group), as compared to pre-feed levels. Urinary caffeine metabolite ratios were significantly different between the two NAT2 genotypes, whereas for CYP1A2, the apparent difference in metabolic ratios between the genotypes was statistically non-significant. Significant correlations were firstly found between the CYP1A2-164A-->C (CYP1A2*1F) polymorphism and differential urinary PhIP excretion levels. Although the found correlations are driven primarily by a small number of subjects possessing the homozygous variant constellation, the strong influence of this genotype indicates that the CYP1A2*1F polymorphism could play an important role in human cancer risk susceptibility.

Impact of environmental exposures on the mutagenicity/carcinogenicity of heterocyclic amines

Carcinogenic heterocyclic amines are produced from overcooked foods and are highly mutagenic in most short-term test systems. One of the most abundant of these amines, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), induces breast, colon and prostate tumors in rats. Human dietary epidemiology studies suggest a strong correlation between either meat consumption or well-done muscle meat consumption and cancers of the colon, breast, stomach, lung and esophagus. For over 20 years our laboratory has helped define the human exposure to these dietary carcinogens. In this report we describe how various environmental exposures may modulate the risk from exposure to heterocyclic amines, especially PhIP. To assess the impact of foods on PhIP metabolism in humans, we developed an LC/MS/MS method to analyze the four major PhIP urinary metabolites following the consumption of a single portion of grilled chicken. Adding broccoli to the volunteers' diet altered the kinetics of PhIP metabolism. At the cellular level we have found that PhIP itself stimulates a significant estrogenic response in MCF-7 cells, but even more interestingly, co-incubation of the cells with herbal teas appear to enhance the response. Numerous environmental chemicals found in food or the atmosphere can impact the exposure, metabolism, and cell proliferation response of heterocyclic amines.

Occurrence of heterocyclic amines in several home-cooked meat dishes of the Spanish diet

Heterocyclic amines (HAs) were determined in several of the most frequently eaten meat dishes in Spain such as fried beef hamburger, fried pork loin, fried chicken breast, fried pork sausages, griddled chicken breast, griddled lamb steak and griddled beef steak. All of the products tested were household cooked. The HAs were analysed in the selected meat dishes using an analytical method based on solid-phase extraction followed by liquid chromatography coupled to tandem mass spectrometry. DMIP, MeIQx, 4,8-DiMeIQx, Norharman, Harman, PhIP, Trp-P-1, AalphaC and MeAalphaC were the amines most frequently found at concentrations of up to 47 ng g(-1) of cooked meat. Glu-P-2, IQ, MeIQ, Glu-P-1, 7,8-DiMeIQx and Trp-P-2 were only found in a few of the meat dishes and their concentrations were lower than 1 ng g(-1) of cooked meat. The highest amounts of HAs, especially PhIP and DMIP, were formed in fried chicken breast and the lowest were formed in fried beef hamburger and in fried pork sausages. Daily intake of HAs in Spain was estimated at 606 ng of mutagenic HAs per capita and day, DMIP and PhIP being the main contributors.

PhIP metabolites in human urine after consumption of well-cooked chicken

We devised an assay to quantify the metabolites of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in human urine following a single exposure to well-cooked meat. Our method uses LC/MS/MS to detect four metabolites and four deuterated internal standard peaks in a single chromatographic run. N2-OH-PhIP-N2-glucuronide was the most abundant urinary metabolite excreted by the 12 individuals who participated in our study. N2-PhIP glucuronide was the second most abundant metabolite for 8 of the 12 volunteers. The stability of PhIP metabolism over time was studied in three of the volunteers who repeated the assay eight times over a 2.5 year-period. PhIP metabolite excretion varied in each subject over time, although the rate of excretion was more constant. Our results suggest that quantifying PhIP metabolites should make future studies of individual susceptibility and dietary interventions possible.

Effects of heating time and antioxidants on the formation of heterocyclic amines in marinated foods

The effect of heating time and antioxidants on the heterocyclic amine (HAs) formation in marinated foods were studied. Food samples were cooked at 98 +/- 2 degrees C for 1, 2, 4, 8, 16 and 32 h in a closed pan in the presence of water, soy sauce and rock candy with or without antioxidants. The various HAs in marinated food samples and juice were analyzed by HPLC with photodiode-array detection. Results showed that the amount of HAs formed during heating followed an increased order for each increasing heating time. A larger variety and higher amount of HAs were generated in marinated pork when compared to marinated eggs and bean cake. In marinated juice, the levels of HAs were present in greater amount than in marinated foods. The incorporation of antioxidants Vitamin C, Vitamin E and BHT were found to be effective towards HAs inhibition, however, the effect was minor.

Meat-related mutagens/carcinogens in the etiology of colorectal cancer

Diets containing substantial amounts of red or preserved meats may increase the risk of various cancers, including colorectal cancer. This association may be due to a combination of factors such as the content of fat, protein, iron, and/or meat preparation (e.g., cooking or preserving methods). Red meat may be associated with colorectal cancer by contributing to N-nitroso compound (NOC) exposure. Humans can be exposed to NOCs by exogenous routes (from processed meats in particular) and by endogenous routes. Endogenous exposure to NOCs is dose-dependently related to the amount of red meat in the diet. Laboratory results have shown that meats cooked at high temperatures contain other potential mutagens in the form of heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs). To investigate the role of these compounds, we have created separate databases for HCAs and PAHs, which we have used in conjunction with a validated meat-cooking food frequency questionnaire. The role of meat type, cooking methods, doneness levels, and meat-cooking mutagens has been examined in both case-control studies and prospective cohort studies, with mixed results. Here, we review the current epidemiologic knowledge of meat-related mutagens, and evaluate the types of studies that may be required in the future to clarify the association between meat consumption and colorectal cancer.

Influence of antioxidants in virgin olive oil on the formation of heterocyclic amines in fried beefburgers

An association between the intake of heterocyclic amines (HAs) and the development of cancer has been observed in some epidemiological studies, while in other studies no such correlation has been found. HAs are mutagenic/carcinogenic compounds formed at low levels via the Maillard reaction and a free radical mechanism during cooking of animal tissue. The addition of pure antioxidants or foods containing antioxidants has previously been shown to decrease the amount of HAs formed during cooking. In this study, beefburgers were fried in six different oils: refined olive oil, virgin olive oil, virgin olive oil depleted of phenols, rapeseed oil, virgin olive oil with rosemary extract and refined olive oil with rosemary extract. The content of antioxidative compounds in the virgin olive oil and the rosemary extract was determined. The beefburgers were analysed with regards to 12 different HAs by solid phase extraction and HPLC analysis. MeIQx, 4,8-DiMeIQx, PhIP, Harman and Norharman were detected in all beefburgers fried in the different oils, but the relative amounts varied. Frying in virgin olive oil reduced the formation of HAs compared with refined olive oil. This effect is probably due to the content of phenols in the virgin olive oil. The HA-reducing effect of virgin olive oil decreased during storage, but the addition of rosemary extract may prevent this decrease.

Inhibition of heterocyclic aromatic amine formation in fried ground beef patties by garlic and selected garlic-related sulfur compounds

The effects of garlic and selected organosulfur compounds (diallyl disulfide, dipropyl disulfide, diallyl sulfide, allyl methyl sulfide, allyl mercaptan, cysteine, and cystine) on the formation of heterocyclic aromatic amines (HAAs) in fried ground beef patties were evaluated. Minced garlic cloves (ca. 4.8 to 16.7%, wt/wt) or organosulfur compounds (0.67 mmol) were added directly to ground beef. Patties (100 g) were fried at 225 degrees C (surface temperature) for 10 min per side. Two patties were fried for each replication, and five replicates were analyzed for each treatment. For each replicate, four subsamples were analyzed (two unspiked subsamples for concentration and two spiked subsamples for the recovery of HAA standards). The volatile sulfur compounds significantly (P < 0.05) reduced concentrations of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine by reductions of 46 to 81%, while average reductions of 35, 22, and 71%, were achieved with cystine, cysteine, and whole garlic, respectively. The volatile sulfur compounds reduced concentrations of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline by 34 to 67%, while reductions of 25, 19, and 63% (P < 0.05) were achieved with cystine, cysteine, and whole garlic, respectively. These studies confirm that garlic and some organosulfur compounds have the potential to reduce HAA formation incooked beef patties.

A critical evaluation of the application of biomarkers in epidemiological studies on diet and health

One of the problems which may beset epidemiological studies is the difficulty of accurately measuring the dietary intakes of participants. Biomarkers of diet promise to provide a more accurate measure of dietary intake and a more objective one in that they are not reliant on the subject's memory. This review considers some issues of importance in epidemiology when information is obtained from biomarkers. The approach taken is to use examples both of normal dietary constituents and of contaminants in relation to a range of diet and health questions to illustrate these points. A brief overview of the role of sample collection, processing and storage is given including some generic recommendations for maximising the reliability of subsequent analytical data. Using the examples of phytoestrogens and iodine the question of whether biomarkers can accurately reflect the intake of the dietary constituents of interest at the population level or at the individual level is considered. The relationship of the biomarker to the natural history of the disease is exemplified using the role of folate in neural tube defects. Finally, intakes of vitamin D and heterocyclic amines are used to illustrate the integration of biomarkers into epidemiological studies of prostate and colorectal cancer, respectively. It is concluded that biomarkers may provide a more accurate and objective measure of diet than estimates of current or usual intake but that this approach also has limitations. A combination of methods will probably prove to be most valuable and this approach is being taken in current large prospective studies.

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.

Separation of heteroaromatic amines in food products

In recent years, many studies have dealt with the role of certain heteroaromatic amines (HAs) as mutagenic compounds, and their occurrence in foodstuffs. Here we examine the determination of HAs, focusing on the analytical strategies for their extraction and preconcentration from several matrices. We summarise the properties of heteroaromatic amines and the main drawbacks involved in their analysis, and then concentrate on the separation procedures, sorbents and solvents used in the sample treatment. We discuss the requirements of the analytical techniques and the strategies most frequently followed to achieve accurate results.

Creatine and creatinine metabolism

The goal of this review is to present a comprehensive survey of the many intriguing facets of creatine (Cr) and creatinine metabolism, encompassing the pathways and regulation of Cr biosynthesis and degradation, species and tissue distribution of the enzymes and metabolites involved, and of the inherent implications for physiology and human pathology. Very recently, a series of new discoveries have been made that are bound to have distinguished implications for bioenergetics, physiology, human pathology, and clinical diagnosis and that suggest that deregulation of the creatine kinase (CK) system is associated with a variety of diseases. Disturbances of the CK system have been observed in muscle, brain, cardiac, and renal diseases as well as in cancer. On the other hand, Cr and Cr analogs such as cyclocreatine were found to have antitumor, antiviral, and antidiabetic effects and to protect tissues from hypoxic, ischemic, neurodegenerative, or muscle damage. Oral Cr ingestion is used in sports as an ergogenic aid, and some data suggest that Cr and creatinine may be precursors of food mutagens and uremic toxins. These findings are discussed in depth, the interrelationships are outlined, and all is put into a broader context to provide a more detailed understanding of the biological functions of Cr and of the CK system.

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%.

Determination of heterocyclic aromatic amines in meat extracts by liquid chromatography-ion-trap atmospheric pressure chemical ionization mass spectrometry

When protein-rich foods are processed under normal cooking conditions, heterocyclic aromatic amines (HAAs) can be generated at a few parts per billion level. In this work, we have analyzed the HAAs present in a lyophilized meat extract by means of a simplified solid-phase extraction procedure. All the analytes were collected in a single extract with recoveries in the range of 45.6-75.2%, so the analysis time has been greatly reduced. Problems derived from the less exhaustive purification of the extract have been solved by using MS(ion trap) detection. The RSD for quantification ranged from 2.1% to 5.1% for run-to-run precision and from 5.2% to 11% for day-to-day precision. The limits of detection for standard solutions ranged from 20 to 150 pg injected. For the meat extract analyzed limits of detection from 0.9 to 11.2 ng g(-1) were obtained. Results of the quantification are in agreement with those obtained using different clean-up procedures.

N-Acetyltransferase polymorphism and human cancer risk

Because of the important role ofN-acetyltransferase (NAT) enzymes in both metabolic activation and detoxification of certain precarcinogens, such as homo-and heterocyclic arylamines, extensive research in the past has focused on the relationship between the distribution of different variants of these enzymes and cancer susceptibility. In this context, we examined the relationship between the acetylator type of two NAT isozymes (NAT1 and NAT2) and cancer risk. It was shown that any independent overall association of those diseases with acetylation for eitherNATl orNAT2 is likely to be weak at most. Besides individual genetic profile, differences in the degree of exposure to environmental precarcinogens should also be considered. It was suggested that smoking and red meat intake were associated with bothNATl andNAT2 genotype in the carcinogenesis. A gene-gene interaction, even linkage betweenNATl andNAT2 may also exist.

Effects of marinating with Asian marinades or western barbecue sauce on PhIP and MeIQx formation in barbecued beef

Heterocyclic aromatic amines (HAAs), a group of chemicals formed during high-temperature cooking of meat and fish, are potent mutagens and are suspected to play a role in colorectal cancer. A recent study suggested that marinating meat may offer a way to reduce HAA formation. Hawaii's diverse ethnic populations, which are at various risks of colorectal cancer, often use traditional marinades when cooking meat. We compared the HAA content of beef steaks marinated overnight with teriyaki sauce, turmeric-garlic sauce, or commercial honey barbecue sauce with that of unmarinated steaks. The levels of 2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine (PhIP) and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) were determined by liquid-liquid extraction and gas chromatography-mass spectrometry. Beef steaks marinated with teriyaki sauce had 45% and 67% lower PhIP level at 10 minutes (p = 0.002) and 15 minutes (p = 0.001) of cooking time as well as 44% and 60% lower MeIQx levels at 10 minutes (p = 0.008) and 15 minutes (p = 0.001), respectively, than unmarinated meat. Lower levels of PhIP and MeIQx were also observed in meat marinated with turmeric-garlic sauce. In contrast, marinating with barbecue sauce caused a 2.9- and 1.9-fold increase in PhIP (p < or = 0.005) and a 4- and 2.9-fold increase in MeIQx (p < or = 0.001) at 10 and 15 minutes, respectively. Differences in the mutagenic activities of marinated and unmarinated steaks, as measured by the Ames assay, paralleled the differences in PhIP and MeIQx levels. Future studies should test the effects of specific ingredients, including the water content of marinades, and the effect of reapplying barbecue sauce during cooking (to reduce charring) on HAA formation.

Heterocyclic amine formation and the impact of structure on their mutagenicity

The occurrence and formation of heterocyclic amines in foods is discussed in light of the consistent finding of a new class of imidazopyridines. In addition, a quantitative structure-activity relationship will be presented correlating the potency of these imidazopyridines to predicted chemical properties. Although no strong linear correlation is found between the potency and the chemical properties, a low dipole moment is found to be a qualitative predictor of high mutagenic potency.

Factors determining dietary intakes of heterocyclic amines in cooked foods

The identification of heterocyclic amines (HCAs) in cooked foods has focused attention on the potential health effects from their consumption in the diet. Recent studies have estimated daily dietary intakes of HCAs that vary 10-fold and implicated different cooked meats as the prime source of HCAs in the diet. These varied estimates can be attributed to the different dietary assessment methods used in these studies, as well as the different levels of HCAs ascribed to the most commonly consumed cooked meats. Epidemiological studies utilizing information on dietary practice and food intake have found higher risks for several cancers among individuals consuming the highest levels of HCAs. These studies have highlighted the importance of using information on cooking methods in addition to food intake to accurately estimate dietary exposure to HCAs.

Food heating and the formation of heterocyclic aromatic amine and polycyclic aromatic hydrocarbon mutagens/carcinogens

Heterocyclic aromatic amines (HAA) and polycyclic aromatic hydrocarbons (PAH) are mutagens and animal carcinogens sometimes formed when foods are heated or processed. Determining their role in cancer etiology depends on comparing human exposures and determining any significant dose-related effects. Chemical analysis of foods shows that flame-grilling can form both PAH and HAA, and that frying forms predominantly HAA. With detection limits of about 0.1 ng/g, amounts found in commercially processed or restaurant foods range from 0.1 to 14 ng/g for HAA, and levels of PAH up to 1 ng/g in a liquid smoke flavoring. Laboratory fried samples have greater amounts of PAH, up to 38 ng/g in hamburgers, and high levels of HAA, over 300 ng/g, are measured in grilled chicken breast. Understanding the processing conditions that form PAH and HAA can lead to methods to greatly reduce their occurrence in processed foods.

Carcinogenic heterocyclic amines in model systems and cooked foods: a review on formation, occurrence and intake

Frying or grilling of meat and fish products may generate low ppb levels of mutagenic/carcinogenic heterocyclic amines (HAs). Many heterocyclic amines are formed via the Maillard reaction from creatine, free amino acids and monosaccharides; compounds naturally occurring in protein-rich foods of animal origin. The formation and yield of HAs are dependent on physical parameters, such as cooking temperature and time, cooking technique and equipment, heat and mass transport, and on chemical parameters, especially the precursors to HAs. This paper reviews the current knowledge on the formation of HAs in cooked foods and model systems, and summarizes data on the content of HAs in various cooked foods, and estimates of the dietary intake of HAs. It should be noted that the presence of carcinogens of other types in food (e.g. nitrosamines, aromatic amines, cholesterol oxide products) and that their generation during frying and grilling are outside the scope of this review.

Feeding of a well-cooked beef diet containing a high heterocyclic amine content enhances colon and stomach carcinogenesis in 1,2-dimethylhydrazine-treated rats

Epidemiologic studies have linked the consumption of red meat and the consumption of highly browned meats containing high levels of heterocyclic aromatic amines (HCAs) to increased risk of colorectal cancer or polyps. The present study determined the effects of long-term feeding of beef-containing diets with low and high levels of HCAs (in the context of a low or high beef tallow diet) on a standard 1,2-dimethylhydrazine (DMH)-induced colon tumorigenesis protocol. Very lean beef was cooked by a variety of methods at different temperatures, and the levels of the major HCAs (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-f]pyridine) were measured by high-performance liquid chromatography. Diets incorporating beef containing low or high levels of HCAs were fed for 12 weeks, during which DMH was administered to induce colon tumors, followed by various dietary regimens as promotional stimuli. Feeding of a beef diet high in HCAs resulted in more DMH-induced colon adenocarcinomas, but only in the context of a low-fat diet. The high-HCA diets increased stomach tumors in all DMH-treated rats. An apparent interaction of high HCA with a high fat level reduced the colon tumor incidence and tumor numbers in those diets containing both factors. These results support the epidemiologic data linking well-cooked meat to increased risk for colon and stomach cancer, but the role of dietary fat level remains puzzling.

Thomas G. Orr Memorial Lectureship. Colon cancer from etiology to prevention

BACKGROUND

Recent changes in healthcare have resulted in a general malaise among physicians leading to negative advice to young people about career choices in the medical field. The author uses his experiences in academic surgery to show that medicine continues to be an exciting and desirable career choice.

DATA SOURCES

Relevant literature from surgery, toxicology, molecular biology, carcinogenesis, and epidemiology fields.

CONCLUSIONS

Significant advances have occurred in the understanding of colon cancer. These advances have occurred because of extensive collaborations across many different scientific fields. The methods used and the collaborations involved provide a model for other physicians to unravel the mysteries of disease and to make academic medicine fun and exciting. The risk of colon cancer depends on genetically determined factors that combine with environmental exposure (diet) to determine risk. Microwaving meat before cooking and eating more cruciferous vegetables may reduce this risk. Additional prevention steps are in the planning stages.

Heterocyclic aromatic amines in human urine following a fried meat meal

In a search for suitable biomarkers for human dietary exposure to heterocyclic aromatic amines (HAAs), we have investigated the concentrations of three common fried food mutagens in food and urine after consumption of a fried meat meal. In this connection we developed a method for the determination of HAAs and have investigated the common fried red meat HAAs 2-amino-1-methyl-6-phenylimidazo[4,5-beta]pyridine (PhIP), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx). Eight volunteers participated in the study, each consuming a meal of fried minced beef patties (295 g), boiled potatoes, and a green salad. Urine was collected for two 12-hr periods prior to and following the meal. HAAs were determined in cooked meat and in untreated and acid hydrolysed urine by a series of liquid/liquid extractions, followed by Blue cotton adsorption and finally by a novel derivatized technique for gas chromatography-mass spectrometry (GC-MS). The primary amino groups were derivatized by acylation with heptafluorobutyric acid anhydride, and the resulting amide methylated using diazomethane. Phenolic hydroxyl groups were also methylated by this procedure, making it possible to detect hydroxylated HAAs, possible metabolites or constituents of the fried meat. 4'-Hydroxy-PhIP ¿2-amino-1-methyl-6-(4-hydroxyphenyl)imidazo[4,5-beta]pyridine¿ (4'-OH-PhIP) was indeed found in meat as well as in urine. The contents of PhIP, MeIQx and DiMeIQx in meat were 4.0 +/- 2.6, 3.5 +/- 0.9 and 0.3 +/- 0.1 ng g-1 (mean +/- SD, n = 4), from which the mean amounts ingested were calculated to be 1180, 1030 and 90 ng, respectively. Total amounts of HAAs in the 0-24-hr post-meal untreated urine (and percent of ingested dose) were 6-23 ng PhIP (0.5-2%) and 10-63 ng MeIQx (1-6%). In hydrolysed urine, the levels of HAAs were higher, totalling 24-100 ng PhIP (2-8.5%) and 133-329 ng of MeIQx (13-32%). DiMeIQx was below detection limit in all urine samples. Judged from our study, there were rather large inter-individual variations in the amounts of excreted HAAs, possibly caused by variations in the activities of enzymes taking part in HAA metabolism.