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.

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.

N-glucuronidation of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and N_hydroxy-PhIP by specific human UDP-glucuronosyltransferases

Glucuronidation is a major metabolic pathway in the biotransformation of many xenobiotics. Recent studies have shown that in humans, UDP-glucuronosyltransferase (UGT)-mediated glucuronidation plays a critical role in the detoxification of food-borne carcinogenic heterocyclic amines. 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), the most abundant carcinogenic heterocyclic amine found in well-cooked meats, has been shown to be extensively glucuronidated in humans. To determine which UGT isozymes are involved in the biotransformation of PhIP and the cytochrome P4501A2-mediated reactive intermediate N-hydroxy-PhIP, microsomes expressing human UGT1A1, -1A4, -1A6 or -1A9 were incubated with PhIP and N-hydroxy-PhIP and the reaction products analyzed by HPLC and ESI-MS. Incubations containing N-hydroxy-PhIP and UGT1A1 expressing microsomes, with an apparent Km of 4.58 microM and a Vmax of 4.18 pmol/min/mg protein, had the highest capacity to convert N-hydroxy-PhIP to N-hydroxy-PhIP-N2-glucuronide. Microsomes expressing UGT1A9 produced N-hydroxy-PhIP-N3-glucuronide at the highest rate with an apparent Km and Vmax of 3.73 microM and 4.07 pmol/min/mg, respectively. A third previously undefined glucuronide accounted for 31% of the total glucuronides formed from the UGT1A4 expressing microsomes. No glucuronide conjugates were detected from microsomes expressing UGT1A6. Incubations containing PhIP as substrate formed direct PhIP-glucuronides in microsomes expressing UGT1A1, UGT1A4 and UGT1A9 but at levels averaging 53-fold lower than when N-hydroxy-PhIP was used as the substrate. Knowing the glucuronidation capacity of the specific UGT isozymes involved in PhIP and N-hydroxy-PhIP glucuronidation should help in determining the individual susceptibility to the potential cancer risk from exposure to PhIP.

Liquid chromatography–tandem mass spectrometry method of urine analysis for determining human variation in carcinogen metabolism

We developed a solid-phase extraction LC-MS-MS method for the analysis of the four major metabolites of PhIP (2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine) in human urine after a meal of well-done chicken. Ten volunteers each ate either 150 or 200 g of well-done chicken breast containing 9-21 microg of PhIP. Among the individual volunteers there is 8-fold variation in the total amount of metabolites and 20-fold variation in the relative amounts of individual metabolites, showing individual differences in carcinogen metabolism. PhIP metabolites were also detected in urine from a subject consuming chicken in a restaurant meal, demonstrating the method's sensitivity after real-life exposures.

Minimization of heterocyclic amines and thermal inactivation of Escherichia coli in fried ground beef

BACKGROUND

Heterocyclic amine carcinogens are formed during the cooking of a number of foods, especially well-done meats. Lower temperatures and shorter cooking times can minimize the formation of these carcinogens, yet a major food safety concern is that pathogens in the meat must be thermally inactivated. This study investigated cooking techniques that minimize heterocyclic amine formation while simultaneously destroying contaminating bacteria.

METHODS

Ground beef patties were inoculated with Escherichia coli K12 bacteria and fried to internal temperatures ranging from 35 degrees C to 70 degrees C in a skillet preheated to 160 degrees C, 180 degrees C, or 200 degrees C. Each patty was then analyzed for four common heterocyclic amines and for surviving bacteria. Additionally, the frequency of turning of the beef patty during cooking was varied (a single turn or multiple turns), length of time required for each patty to reach 70 degrees C was recorded, and heterocyclic amine levels were determined. An additional pan temperature of 250 degrees C was tested for its effect on heterocyclic amine formation but not on bacterial killing. Statistical tests were two-sided.

RESULTS

Colony-forming bacteria were reduced by five orders of magnitude at internal temperatures greater than 60 degrees C, regardless of cooking method, and were completely inactivated at 70 degrees C. For patties turned just once, heterocyclic amine levels increased as the cooking temperatures increased. However, levels of heterocyclic amines were statistically significantly lower with turning every minute. For each pan temperature, patties reached 70 degrees C internal temperature sooner when they were turned every minute than when they were turned just once during cooking.

CONCLUSION

Lowering the pan temperature and turning the patties frequently can greatly reduce the formation of heterocyclic amines and can simultaneously achieve bacterial inactivation with little or no increase in cooking time, ensuring a product that is safe for human consumption.

Identification of urine metabolites of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine following consumption of a single cooked chicken meal in humans

Many studies suggest that mutagenic/carcinogenic chemicals in the diet, like 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), may play a role in human cancer initiation. We have developed a method to quantify PhIP metabolites in human urine and have applied it to samples from female volunteers who had eaten a meal of cooked chicken. For this analysis, urine samples (5 ml) were spiked with a deuterium-labeled internal standard, adsorbed to a macroporous polymeric column and then eluted with methanol. After a solvent exchange to 0.01 M HCl, the urine extracts were passed through a filter, applied to a benzenesulfonic acid column, washed with methanol/acid and eluted with ammonium acetate and concentrated on a C(18) column. The metabolites were eluted from the C(18) column and quantified by LC/MS/MS. In our studies of human PhIP metabolism, eight volunteers were fed 200 g of cooked chicken containing a total of 27 microg PhIP. Urine samples were collected for 24 h after the meal, in 6 h aliquots. Although no metabolites could be found in urine collected from volunteers before eating the chicken, four major human PhIP metabolites, N:(2)-OH-PhIP-N:(2)-glucuronide, PhIP-N:(2)-glucuronide, 4'-PhIP-sulfate and N:(2)-OH-PhIP-N:3-glucuronide, were found in the urine after the chicken meal. The volunteers in the study excreted 4-53% of the ingested PhIP dose in the urine. The rate of metabolite excretion varied among the subjects, however, in all of the subjects the majority of the metabolites were excreted in the first 12 h. Very little metabolite was detected in the urine after 18 h. In humans, N:(2)-OH-PhIP-N:(2) glucuronide is the most abundant urinary metabolite, followed by PhIP-N:(2)-glucuronide. The variation seen in the total amount, excretion time and metabolite ratios with our method suggests that individual digestion, metabolism and/or other components of the diet may influence the absorption and amounts of metabolic products produced from PhIP.

Occupational health in the USA in the 21st century

Comparable to the confusion encountered in the birth of the machine age is the perplexing reconfiguration of the United States' health care system. Paralleling the advances in medicine have been the divesting mergers and downsizing of industry, coupled with globalization, which have released millions of long-time workers. The labour contingent is changing, with the addition of great numbers of women and immigrant workers, and the manufacturing economy has become one of service and information. Serving the occupational health (OH) needs of such a force have been the professional societies of physicians, nurses, and industrial hygienists, with their members providing care in a broad variety of facilities. It is possible that a national organization, including all these disciplines, would have a greater voice in the protection of workers' health. Immediate leadership of an occupational health service (OHS) can be rotated among the disciplines, so that competition for primacy among the professionals would end. The new workforce demands culture sensitivity among OH personnel and polylingual capabilities may be demanded in the future. Management skills will be required of all in OH, and greater participation of employees in OH policy will characterize the decades ahead. Nearly neglected up to now, occupational mental health programming will be required to meet the real needs of workers, and to counter the move to outsource OH services, where little patient contact results. Behavioural safety, total quality management, and application of the rapidly developing technologies in health care will define the 21st century efforts in OH. Remaining issues, such as violence, telecommuting injuries, the inclusion of alternative medicine, and women's health, among others, will see carry-over for resolution into the year 2000.

Genetically modified Chinese hamster ovary cells for investigating sulfotransferase-mediated cytotoxicity and mutation by 2-amino-1-methyl-6- phenylimidazo[4,5-b]pyridine

To test the hypothesis that the sulfotransferase gene plays a role in the phase II bioactivation of PhIP, a heterocyclic amine found in cooked meats, we transfected the UV5P3 cell line with cDNA plasmids of human aryl sulfotransferases (HAST1 and HAST3). UV5P3 is a nucleotide excision repair-deficient and P4501A2-expressing CHO cell line that we have previously developed. Functionally transformed clones were identified by the differential cytotoxicity (DC) assay that used PhIP as the cytotoxic agent. Two clones designated 5P3H1 and 5P3H3, expressing HAST1 and HAST3, respectively, were chosen for further characterization. Correct fragment sizes of the sulfotransferase cDNAs were identified in both cell lines by polymerase chain reaction. Immunoblot analysis confirmed the expression of the sulfotransferase proteins. The addition of the sulfotransferase inhibitor DCNP decreased the cytotoxic effects of PhIP in a dose-dependent manner. The increase in cell growth was 6. 5-fold for 5P3H1 and 2.4-fold for 5P3H3, relative to values obtained without DCNP. Based on D(50) values, the dose that reduced the survival to 50% relative to untreated controls, the cytotoxic effect of PhIP was increased threefold for 5P3H1 and 1.87-fold for 5P3H3 cell lines over the parental UV5P3 line. There was also a small increase in the mutation response at the aprt locus. These newly established 5P3H1 and 5P3H3 sulfotransferase-expressing cells provide valuable mechanistic information of the bioactivation of PhIP and related compounds. Environ. Mol. Mutagen. 35:57-65, 2000. Published 2000 Wiley-Liss, Inc.

Heterocyclic amine content of cooked meat and risk of prostate cancer

BACKGROUND

Some epidemiologic studies have described positive associations between prostate cancer risk and meat consumption, but underlying mechanisms have not been identified. Heterocyclic amines are mutagens formed during the cooking of meat. Well-done meat has been associated with increased risks of colorectal and breast cancers in humans. This study examined associations between prostate cancer risk and 1) estimated daily intake of heterocyclic amines from cooked meat and 2) level of cooked-meat doneness.

METHODS

A population-based, case-control study involving 317 case patients with prostate cancer and 480 age-matched control subjects was carried out in Auckland, New Zealand. Levels of meat doneness and daily intake of heterocyclic amines were determined from self-reported dietary data and experimentally measured heterocyclic amine levels in locally sourced meat samples cooked under controlled conditions to varying degrees of doneness.

RESULTS

The heterocyclic amines found in the highest concentrations in meat samples were 2-amino-1,6-dimethylfuro[3,2-e]imidazo[4,5-b]pyridine (IFP) and 2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine (PhIP) from well-done chicken and pork and very well-done beefsteak. Meat doneness was weakly and inconsistently associated with prostate cancer risk for individual types of meat, but increased risk was observed for well-done beefsteak (relative risk = 1.68; 95% confidence interval = 1.02-2.77; two-sided P for trend =.03). A weak positive gradient of increased risk was associated with estimated daily exposure to IFP but not with the other major heterocyclic amines.

CONCLUSIONS

Meat doneness and estimated intake of heterocyclic amines from cooked meat were not clearly associated with prostate cancer risk.

Macromolecular adduct formation and metabolism of heterocyclic amines in humans and rodents at low doses

2-Amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) are heterocyclic amines formed during the cooking of meat and fish. Both are genotoxic in a number of test systems and are carcinogenic in rats and mice. Human exposure to these compounds via dietary sources has been estimated to be under 1 microg/kg body wt. per day, although most laboratory animal studies have been conducted at doses in excess of 10 mg/kg body wt. per day. We are using accelerator mass spectrometry (AMS), a tool for measuring isotopes with attomole sensitivity, to study the dosimetry of protein and DNA adduct formation by low doses of MeIQx and PhIP in rodents and comparing the adduct levels to those formed in humans. The results of these studies show: 1, protein and DNA adduct levels in rodents are dose-dependent; 2, adduct levels in human tissues and blood are generally greater than in rodents administered equivalent doses; and 3, metabolite profiles differ substantially between humans and rodents for both MeIQx and PhIP, with more N-hydroxylation (bioactivation) and less ring oxidation (detoxification) in humans. These data suggest that rodent models do not accurately represent the human response to heterocyclic amine exposure.

In vivo human metabolism of [2-14C]2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)

To better understand the interactions of the pathways of activation and detoxification on the metabolism of the putative carcinogen, PhIP, we administered a dose of 70-84 microg [2-14C] PhIP (17.5 [microCi 14C) 48-72 h before scheduled colon surgery. Blood and urine collected for the next 48-72 h was evaluated by linear accelerator mass spectroscopy (AMS) and scintillation counting LC-MS to identify specific PhIP metabolites. The thermostable phenol sulfotransferase (SULT1A1) phenotype was correlated with the 4'-PhIP-SO4 levels in the urine at 0-4 h (R = 0.86, P = 0.059). The CYP1A2 activity had a negative correlation with PhIP serum levels at 1 h (R = 0.94, P = 0.06) and a positive correlation with urine N-OH-PhIP levels at 0-4 h (R = 0.85, P = 0.15). This low level radioisotope method of determining the influence of phenotype on metabolism will significantly improve our understanding of the interrelationships of these pathways and provide a critical foundation for the development of individual risk assessment.

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.

Effects of a chargrilled meat diet on expression of CYP3A, CYP1A, and P-glycoprotein levels in healthy volunteers

BACKGROUND & AIMS

Carcinogenic heterocyclic amines and polycyclic aromatic hydrocarbons present in chargrilled meat are substrates for inducible CYP1A and CYP3A enzymes and for P-glycoprotein. We examined whether consumption of a chargrilled meat diet results in induction of these proteins.

METHODS

Ten healthy adults were fed a diet enriched with chargrilled meat for 7 days. Duodenal biopsy specimens were obtained on days 1, 5, and 12 and analyzed for CYP1A, CYP3A, and P-glycoprotein messenger RNA (mRNA) and protein. On days 5 and 12, hepatic CYP3A4 and CYP1A2 activities were measured and colon biopsies were performed. The levels of polycyclic aromatic hydrocarbon DNA adducts in peripheral blood mononuclear cells were measured on days 1, 4, 11, and 26.

RESULTS

There was no detectable induction of CYP3A4, CYP3A5, or P-glycoprotein mRNAs or protein in small intestine or colon and no induction of hepatic CYP3A4 enzyme activity. In contrast, the chargrilled meat diet resulted in unequivocal induction of CYP1A enzymes in the liver and small intestine of each subject. There was an inverse correlation between the level of peripheral polycyclic aromatic hydrocarbon DNA adducts measured on day 11 and both liver CYP1A2 activity (P = 0.027) and enterocyte CYP1A1 protein concentration (P = 0.046).

CONCLUSIONS

Ingestion of chargrilled meat results in induction of CYP1A enzymes but not CYP3A4 or P-glycoprotein. This observation, combined with the correlation between adduct levels and CYP1A expression, supports an adaptive role for CYP1A but not CYP3A4 or P-glycoprotein.

DNA and protein adduct formation in the colon and blood of humans after exposure to a dietary-relevant dose of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine

Epidemiology studies have indicated that certain dietary components, including well-cooked meat, are risk determinants for colon cancer. Cooked meat can contain significant quantities of heterocyclic aromatic amines (HCAs), which have been established as carcinogens in laboratory animals. 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is usually the most mass-abundant HCA, with concentrations up to 480 ppb. We used accelerator mass spectrometry to establish whether DNA and protein adducts can be detected in humans exposed to a quantity of PhIP comparable with levels of exposure that occur in the diet. Five human volunteers were administered a dietary-relevant dose of [14C]PhIP (70-84 microg) 48-72 h before surgery for removal of colon tumors. Blood samples were collected at various time points, and albumin, hemoglobin, and WBC DNA were extracted for analysis by accelerator mass spectrometry. Tissue samples were collected during surgery and used to assess either tissue available doses of [14C]PhIP or adduct levels. The results of this study show: (a) PhIP is activated to a form that will bind to albumin, hemoglobin, and WBC DNA in peripheral blood. WBC DNA adducts were unstable and declined substantially over 24 h; (b) PhIP is bioavailable to the colon, with levels in normal tissue in the range 42-122 pg PhIP/g tissue; and (c) PhIP binds to both protein and DNA in the colon. DNA adduct levels in the normal tissue were 35-135 adducts/10(12) nucleotides, which was significantly lower than tumor tissue. The results of this study demonstrate that PhIP is bioavailable to the human colon following defined dietary-relevant doses and forms DNA and protein adducts.

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.

The identification of [2-(14)C]2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine metabolites in humans

[2-(14)C]2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine ([14C]PhIP), a putative human carcinogenic heterocyclic amine found in well-done cooked meat, was administered orally to three colon cancer patients undergoing a partial colonectomy. Forty-eight to seventy-two hours prior to surgery, subjects received a 70-84 microg dose of 14C. Urine and blood were analyzed by HPLC for PhIP and PhIP metabolites. Metabolites were identified based on HPLC co-elution with authentic PhIP metabolite standards, mass spectral analysis and susceptibility to enzymatic cleavage. In two subjects, approximately 90% of the administered [14C]PhIP dose was eliminated in the urine, whereas in the other, only 50% of the dose was found in the urine. One subject excreted three times more radioactivity in the first 4 h than did the others. Twelve radioactive peaks associated with PhIP were detected in the urine samples. The relative amount of each metabolite varied by subject, and the amounts of each metabolite within subjects changed over time. In all three subjects the most abundant urinary metabolite was identified as 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine-N2-glucuron ide (N-hydroxy-PhIP-N2-glucuronide), accounting for 47-60% of the recovered counts in 24 h. PhIP accounted for <1% of the excreted radiolabel in all three patients. Other metabolites detected in the urine at significant amounts were 4-(2-amino-1-methylimidazo[4,5-b]pyrid-6-yl)phenyl sulfate, N-hydroxy-PhIP-N3-glucuronide and PhIP-N2-glucuronide. In the plasma, N-hydroxy-PhIP-N2-glucuronide accounted for 60, 18 and 20% of the recovered plasma radioactivity at 1 h post PhIP dose in subjects 1, 2 and 3 respectively. Plasma PhIP was 56-17% of the recovered dose at 1 h post exposure. The relatively high concentration of N-hydroxy-PhIP-N2-glucuronide and the fact that it is an indicator of bioactivation make this metabolite a potential biomarker for PhIP exposure and activation. Determining the relative differences in PhIP metabolites among individuals will indicate metabolic differences that may predict individual susceptibility to carcinogenic risk from this suspected dietary carcinogen.

Formation of mutagenic/carcinogenic heterocyclic amines in dry-heated model systems, meats, and meat drippings

Mixtures of amino acids, creatine, and glucose simulating the composition of six different kinds of meats (beef, chicken breast, chicken thigh, turkey breast, pork, and fish) were dry-heated to simulate the formation of heterocyclic amines in meats. The presence of 16 heterocyclic amines was investigated in the model systems and in the six meats and their corresponding meat drippings to determine the importance of meat composition to heterocyclic amine formation. Nine mutagenic amines (IQ, MeIQ, 8-MeIQx, 4,8-DiMeIQx, PhIP, IQx, IFP, DMIP, and TMIP) were found to be present at concentrations >0.1 ng/g in some of the model systems and in some of the meats or pan residues. Heterocyclic amine concentrations clearly are affected by precursor composition in this model system, and the same nine heterocyclic amines formed in the meat and in the model system show that this is a well-controlled surrogate for the reaction conditions that occur in meats during cooking.

School nursing: a study of perceptions and visions

The complex and changing health needs of students and lack of consistency between school districts have led to some role confusion among school nurses. Ten school nurses participated in this qualitative, descriptive study, which elicited their perceptions and visions of their practice. Constant comparative analysis was used to find meaning in the data. Five conceptual categories--preparation for school nursing practice, essence of school nursing, scope of practice perceptions, powerlessness, and future outlook--emerged from the data. The results indicated the need for specialty education and peer mentoring as participants developed in their autonomous role as school nurses. The collective data from the categories provide direction for school nurses, for university school nursing educators, and the national association in advancing role development for school nursing practice.

Chemical and biological factors affecting mutagen potency

This review surveys the chemical and biological factors that are correlated with the mutagenic activity of the aromatic and heterocyclic amines. Particular attention is given to the predicted quantum chemical properties of the parent amines and their metabolites. A number of chemical properties have been found to correlate well with measured mutagenic potency, including log P, the energies of the frontier orbitals of the parent amines, and the thermodynamic stability of the nitrenium ion, possibly the ultimate DNA-binding species. These correlations are intriguing clues to the mutagenic activity of the aromatic amines; however, many factors still await final explanation, including the exact mechanisms of the metabolic enzymes, the identity(s) of the ultimate DNA-binding species, the reaction mechanism in the DNA-adduction, the role of sequence context in the covalent and non-covalent binding of the adducts, and the role of DNA repair.

Burnout as a clinical entity--its importance in health care workers

Burnout, viewed as the exhaustion of physical or emotional strength as a result of prolonged stress or frustration, was added to the mental health lexicon in the 1970s, and has been detected in a wide variety of health care providers. A study of 600 American workers indicated that burnout resulted in lowered production, and increases in absenteeism, health care costs, and personnel turnover. Many employees are vulnerable, particularly as the American job scene changes through industrial downsizing, corporate buyouts and mergers, and lengthened work time. Burnout produces both physical and behavioural changes, in some instances leading to chemical abuse. The health professionals at risk include physicians, nurses, social workers, dentists, care providers in oncology and AIDS-patient care personnel, emergency service staff members, mental health workers, and speech and language pathologists, among others. Early identification of this emotional slippage is needed to prevent the depersonalization of the provider-patient relationship. Prevention and treatment are essentially parallel efforts, including greater job control by the individual worker, group meetings, better up-and-down communication, more recognition of individual worth, job redesign, flexible work hours, full orientation to job requirements, available employee assistance programmes, and adjuvant activity. Burnout is a health care professional's occupational disease which must be recognized early and treated.

Heterocyclic amine content in beef cooked by different methods to varying degrees of doneness and gravy made from meat drippings

Meats cooked at high temperatures sometimes contain heterocyclic amines (HCAs) that are known mutagens and animal carcinogens, but their carcinogenic potential in humans has not been established. To investigate the association between HCAs and cancer, sources of exposure to these compounds need to be determined. Beef is the most frequently consumed meat in the United States and for this study we determined HCA values in beef samples cooked in ways to represent US cooking practices, the results of which can be used in epidemiological studies to estimate HCA exposure from dietary questionnaires. We measured five HCAs [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 (DiMeIQx) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)] in different types of cooked beef using solid-phase extraction and HPLC. Steak and hamburger patties were pan-fried, oven-broiled, and grilled/barbecued to four levels of doneness (rare, medium, well done or very well done), while beef roasts were oven cooked to three levels of doneness (rare, medium or well done). The measured values of the specific HCAs varied with the cut of beef, cooking method, and doneness level. In general, MeIQx content increased with doneness under each cooking condition for steak and hamburger patties, up to 8.2 ng/g. PhIP was the predominant HCA produced in steak (1.9 to 30 ng/g), but was formed only in very well done fried or grilled hamburger. DiMeIQx was found in trace levels in pan-fried steaks only, while IQ and MeIQ were not detectable in any of the samples. Roast beef did not contain any of the HCAs, but the gravy made from the drippings from well done roasts had 2 ng/g of PhIP and 7 ng/g of MeIQx. Epidemiological studies need to consider the type of meat, cooking method and degree of doneness/surface browning in survey questions to adequately assess an individual's exposure to HCAs.

Heterocyclic amine content of pork products cooked by different methods and to varying degrees of doneness

Heterocyclic amines (HCAs) are known mutagens and animal carcinogens produced in meats cooked at high temperature. As pork is the second most frequently consumed meat in the United States, five predominant HCAs [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 (DiMeIQx) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)] were measured in various pork products, cooked by different techniques and to varying doneness levels. Pork chops and ham slices were pan-fried and oven-broiled; bacon was pan-fried, oven-broiled or microwaved; hot dogs were pan-fried, oven-broiled, grilled/barbecued or boiled; sausage links and patties were pan-fried. All the products were cooked to three levels of doneness: just until done, well done or very well done. HCA type and level varied substantially by pork product, cooking method and doneness level. The highest PhIP levels were found in well done and very well done oven-broiled bacon; for very well done 30.3 and 4.0 ng per gram of meat of PhIP and MeIQx, respectively. Pan-fried very well done sausage patties contained 5.4 ng of MeIQx per gram of meat, while sausage links contained 1.3 ng per gram of meat. MeIQx was formed in well done and very well done pan-fried but not broiled pork chops. Hot dogs or ham slices had low or undetectable levels of HCAs. These results demonstrate that epidemiological studies investigating the relationship between HCA intake and cancer risk need to incorporate type of meat, cooking method and degree of doneness/surface browning into questions to assess adequately an individual's HCA exposure.

Specificity of base substitution mutations induced by the dietary carcinogens 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhlP) and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) in Salmonella

The base pair substitution mutational profiles induced by the heterocyclic amine cooked food mutagens PhlP and IQ in Salmonella typhimurium strains TA100 and TA1535 were determined by colony hybridization analysis. Both PhlP and IQ induced predominantly GC-->TA transversions in strain TA100 (rfa,delta uvrB/pKM101) with a pronounced preference for the second codon position (CCC--> CAC; 72% of total). PhlP also reverted strain TA1535 (rfa, delta uvrB) efficiently at concentrations similar to those required for strain TA100. In contrast to the PhlP-induced mutational profile observed in strain TA100, in strain TA1535 PhlP induced exclusively GC-->AT transitions at the second codon position (CCC-->CTC; 96-99% of total). Base substitution mutagenesis induced by heterocyclic amines related to PhlP is generally SOS-dependent, requiring the presence of plasmid pKM101 in Salmonella hisG46 strains. Thus, the SOS dependent reversion of S. typhimurium strain TA100 probably reflects error-prone lesion bypass at the major PhlP- guanosine adduct at the C-8 position. The GC-->AT transition mutations induced by PhlP in strain TA1535 appear to be SOS-independent, however, suggesting that these mutations may arise from the formation of PhlP-DNA adducts other than the replication-blocking C8-dG lesion.

Pilot study of free and conjugated urinary mutagenicity during consumption of pan-fried meats: possible modulation by cruciferous vegetables, glutathione S-transferase-M1, and N-acetyltransferase-2

Epidemiological and experimental evidence indicates that consumption of fried meats in conjunction with certain genotypes of phase I and II metabolism genes poses an elevated risk for colorectal cancer. Parallel to this, the consumption of cruciferous vegetables is associated with a reduced risk of colon cancer. Therefore, we designed a 6-week pilot feeding study to evaluate the effect of these variables on urinary mutagenicity, which is a biomarker associated with fried-meat consumption. Eight subjects were fed fried meats daily for six weeks; four ate cruciferous vegetables, and four ate non-cruciferous vegetables. Urinary mutagenicity was evaluated in the presence of S9 in strain YG1024 of Salmonella, which is a frameshift strain that overproduces acetyltransferase. C18/methanol extracts of 24-h urines collected once each week were tested unhydrolyzed (free mutagenicity) and hydrolyzed (total mutagenicity); the difference between the two was the conjugated mutagenicity. Although not significant, the levels of conjugated urinary mutagenicity doubled among crucifera consumers and decreased to 30% of the initial levels among non-crucifera consumers, suggesting the possibility that crucifera may enhance the level of conjugated urinary mutagenicity resulting from consumption of fried meats. Such an effect would be consistent with the documented ability of cruciferous vegetables to induce phase II enzymes. The NAT2 rapid phenotype was significantly associated with approximately 2-fold increases in conjugated (p = 0.05) and total (p = 0.004) urinary mutagenicity relative to NAT2 slow subjects, consistent with the elevated risk confirmed by the NAT2 rapid phenotype for colorectal cancer among meat consumers. An approximately 2-fold increase in urinary mutagenicity among the GSTM1- subjects relative to the GSTM1+ subjects approached significance for free (p = 0.18) and total (p = 0.13) urinary mutagenicity. This is the first report on (a) the mutagenicity of hydrolyzed urine, which was consistently more mutagenic than unhydrolyzed urine; (b) the potential enhancement of conjugated urinary mutagenicity by crucifera; and (c) the association of the rapid NAT2 and possibly the GSTM1- phenotype with elevated levels of fried meat-associated urinary mutagenicity.

Violence prevention at the health care site

Dr. Felton discusses risk factors for violence in the health care setting and recommends worksite analysis procedures, hazard prevention controls, and training and education programs for the greatest protection possible. An appendix offers three contacts for additional materials on devising preventive programs.

Analysis of cooked muscle meats for heterocyclic aromatic amine carcinogens

A number of related heterocyclic amines that are mutagenic in bacterial test systems and carcinogenic in animals are formed during the cooking of food. The most commonly reported and abundant compounds are PhIP, MeIQx, DiMeIQx, IQ and A alpha C. Using analysis by solid-phase extraction and HPLC, amounts found in foods range from less than one ng/g for products from fast-food restaurants, up to 14 ng/g in commercially cooked products and over 300 ng/g for well done flame-grilled chicken breast meat. Interestingly, marinating meat for 4 h greatly reduces the amount of PhIP produced during cooking, but not MeIQx. Comparing mutagenic activity in meat samples to the mutagenic activity accounted for by the known heterocyclic amines shows that most samples have activity that cannot be accounted for by the aromatic amines we can currently identify. This suggests that additional compounds are present in these foods and need to be investigated, particularly those grilled over open flames.

Health risks of heterocyclic amines

Common cooking procedures such as broiling, frying, barbecuing (flame-grilling), heat processing and pyrolysis of protein-rich foods induce the formation of potent mutagenic and carcinogenic heterocyclic amines. These same compounds produce tumors at multiple organ sites in both mice and rats. One example of these induced tumors has also been seen in nonhuman primates. Risk assessment for the human population consuming these compounds requires the integration of knowledge of dosimetry, metabolism, carcinogenic potency, and epidemiology. When this integration is done in even a preliminary way as is done here, the range of risk for an individual from these compounds is enormous. Exposure contributes a range of 200-fold or more and metabolism and DNA repair differences among individuals could easily be an additional 10-fold between individuals. This indicates that differences in human cancer risk for heterocyclic amines could range more than a thousandfold between individuals based on exposure and genetic susceptibility.

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.

Differential effect of acetyltransferase expression on the genotoxicity of heterocyclic amines in CHO cells

We earlier developed the Chinese hamster ovary UV5P3 cell line that expresses cytochrome P4501A2 and lacks nucleotide excision repair for studying metabolism and mutagenicity of heterocyclic amines. The Chinese hamster ovary UV5P3 cells are approximately 50-fold more sensitive to the cooked food mutagen, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) than 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), another genotoxic compound found in cooked food, with respect to cytotoxicity and mutation induction at the adenine phosphoribosyltransferase (aprt) locus. To test the hypothesis that the important missing activity in our CHO system for IQ genotoxicity was acetyltransferase, we transfected the UV5P3 cells with cDNA plasmids of either the human NAT2 N-acetyltransferase gene or a bacterial O-acetyltransferase gene. Functionally transformed clones were determined by the differential cytotoxicity assay using IQ, and confirmed by measuring the enzyme activity with isoniazid as substrate. Two clones designated 5P3NAT2 and 5P3YG (expressing human and bacterial transferases, respectively) were characterized. Both cell lines were sensitive to killing by IQ at concentrations as low as 4 ng/ml. Based on the D37 value, the dose that reduced the survival to 37% relative to untreated controls, the acetyltransferase expressing lines showed approximately 1000-fold increase in sensitivity to the killing effect of IQ over the parental UV5P3 cell line. The same dramatic change in sensitivity was also seen in mutation response at the aprt locus and with chromosomal aberrations and sister chromatid exchanges. In contrast, these cell lines showed cytotoxicity to PhIP similar to that of the parental line UV5P3. These results suggest that PhIP does not require acetyltransferase for metabolic activation leading to genotoxicity in these cells. These new cell lines constitute a sensitive cell system for assessing genotoxicity of compounds requiring metabolic activation by both P450IA2 and acetyltransferase, as well as for studying the molecular processes by which DNA damage can lead to mutation and cancer.

Agreement of mutational characteristics of heterocyclic amines in lacI of the Big Blue mouse with those in tumor related genes in rodents

The mutational spectra of carcinogenic heterocyclic amines (HCAs), 2-amino-3,4-dimethylimidazo[4,5-b]quinoline (MeIQ), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-amino-9H-pyrido[2,3-b]indole (A alphaC) were studied in the colon of Big Blue mice. In 90, 115 and 105 lacI mutants from mice fed 300 p.p.m. MeIQ, 400 p.p.m. PhIP and 800 p.p.m. A alphaC, respectively, 92, 115 and 105 mutations were identified. G:C-->T:A transversions predominated with these HCAs. Mutational hot spots for base-substitution mutations caused by MeIQ, PhIP and A alphaC were in distinct sequence contexts; at 5'-GC-3', in runs of guanine and in 5'-CGT-3', respectively. Further, 30 of 115 (26%) PhIP-induced mutations were G:C base pair deletions, and eight of these deletions were in 5'-GGGA-3'. The mutational characteristics of MeIQ in the lacI gene coincided well with those in the Ha-ras gene of MeIQ-induced mouse forestomach tumors and rat Zymbal gland tumors. The characteristic single-base deletion induced by PhIP in the lacI gene also coincided well with those in the Apc gene of PhIP-induced rat colon tumors. These results suggest that the mutational characteristics of each chemical are conserved across different genes in different species.

The heritage of Bernardino Ramazzini

Although the seminal work in what was to become the specialty of occupational medicine appeared in 1700 as written by the Italian physician, Bernardino Ramazzini and titled De Morbis Artificum Diatriba, it was through the English translation by Wilmer Cave Wright in 1940 and and the subsequent scholarship of Dr Pericle Di Pietro of Modena, Italy, that this monograph became widely known. Ramazzini has been cited by innumerable medical authors and his volume has undergone many translations from the mid-18th century to the present day. References to this early observations of persons and work and their subsequent disease patterns repeatedly infuse today's description of work-related illness. That his pioneering efforts continue to receive adulation is seen in the organizations bearing his name, many eponymous awards, the striking Ramazzini Hall in Japan, and the continuing appearance of new reprintings of Diseases of Workers world-wide. The name Ramazzini marks the beginning of society's concern with the well-being and physical and emotional health of its workers from the shops of the crafts to the offices of the executives.

Analysis of foods for heterocyclic aromatic amine carcinogens by solid-phase extraction and high-performance liquid chromatography

Carcinogenic and mutagenic heterocyclic aromatic amines (HAA) are natural products often present at ng/g levels in muscle meats when they are cooked at temperatures over 150 degrees C. Using solid-phase extraction and high performance liquid chromatography (HPLC) with photodiode array UV detection, samples were analyzed for the following heterocyclic amines: DiMeIQx (2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline); IQ (2-amino-3-methylimidazo[4,5-f]quinoline); MelQx (2- amino-3,8-dimethylimidazo[4,5-f]quinoxaline); and PhIP (2-amino-1-methyl- 6-phenylimidazo[4,5-b]pyridine). Quality control samples, analyzed periodically over two years in a blind study, show relative standard deviations ranging from 22 to 38% for the compounds found, variations typical for analysis at ng/g levels. Amounts range from undetectable levels (less than 0.1 ng/g) to hundreds of ng/g of PhIP for frying or grilling at high meat surface temperatures. Beef, chicken, pork and lamb can all have greater than 10 ng/g of PhIP. Ground chicken breast meat has lower amounts of heterocyclic amines than intact muscle pieces of the same size cooked identically. Restaurant prepared samples that we analyzed contained undetectable levels up to 14 ng/g total heterocyclic amines for a beef steak sample. Not extracted with the above method are related mutagenic heterocyclic amines, which have been reported in cooked foods in our laboratory and others. Method development using ion exchange on an SCX solid-phase extraction cartridge shows promise in providing a method for the quantitation of these mutagenic dimethyl-, trimethyl- and furo-imidazopyridines where a practical analysis method is needed.

How the occupational physician works with the unions

A few attitudinal and behavioural principles will bring about a productive liaison between the occupational physician and trade unions. An effective working relationship with these organizations and employee associations can be developed, provided the occupational health care professionals are impartial in their practice, the loyalty to medicine replacing any bias toward the favouring of a managerial view. Respect must be given union officials, for in their organization they have status and can advance or defeat various health programs. Union representation on an occupational health committee will gain union support and minimize the filing of health-based grievances. The presentation of occupational health information at union meetings will communicate the goals of in-plant programs and familiarize workers, through their accustomed channels, with the objectives of health care policies and procedures.

Intestinal mutagenicity of two carcinogenic food mutagens in transgenic mice: 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and amino(alpha)carboline

The heterocyclic amines produced during the cooking of meat, including amino(alpha)carboline (AalphaC) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), are potent bacterial mutagens and are carcinogenic in rodents. PhIP is mutagenic in the small intestine, but its mutagenicity in the colon, where most human intestinal cancers arise, has not been reported, nor has the mutagenicity of AalphaC. In this study, AalphaC (800 p.p.m.) was fed for 30 and 45 days and PhIP (100 and 400 p.p.m.) was fed for 30, 60 and 90 days to groups of F1 (C57BL/6 x SWR) mice hemizygous for multiple tandem copies of a lacI transgene (the Big Blue mouse) and heterozygous at the endogenous Dlb-1 locus. The mutant frequencies were assayed at Dlb-1 and at lacI in the small intestine and at lacI in the colon. PhIP induced mutations at both loci in the small intestine and induced slightly fewer mutations in the colon. The accumulation of mutations at both loci appears to be linear with both PhIP concentration and duration of exposure and, thus, with dose (concentration x duration). The linear increase with time is in agreement with predictions about the effectiveness of chronic treatment protocols for tests of in vivo mutagenicity. Unlike PhIP, AalphaC induced mutations specifically in the colon and not in the small intestine, thereby showing a dramatic tissue specificity. The rate (mutations/p.p.m. day) was similar to PhIP.

How to meet the media

Occupational physicians on occasion will have to respond to inquiries from the print and broadcast media, particularly in situations involving the health or death of workers. They must be prepared concerning the issue at hand, be factual, be cooperative, and be careful of questions that are 'just off the record'. As representatives of organizations at times of corporate stress, they must be truthful in the presentation of explanations concerning the causes of mishaps and the means of averting future repetitions of comparable hazardous episodes. A set of principles is offered which will aid physicians in their discussion of serious health and safety issues at the worksite.

The capability of rat colon tissue slices to metabolize the cooked-food carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine

A major target tissue for carcinogenesis from the cooked-food carcinogen 2-amino-l-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in rodents is the colon, yet the role of colon metabolism on the carcinogenicity of PhIP is not clearly understood. The mutagenic potency of PhIP is highly dependent upon cytochrome P450 N-hydroxylation. In the present study, the ability of rat colon tissue to activate PhIP to a mutagen was investigated in Salmonella typhimurium (strains TA98 and YGI024) and rat colon tissue slices. In the Ames/Salmonella assay, using rat colon S9 as the activating system, no mutations were evident from bacteria exposed to PhIP at any concentration tested. However, mutations were observed when bacteria were exposed to 2-aminoanthracene (2AA) and colon S9, indicating sufficient P450 activity in the S9 to activate 2AA but not PhIP. In rat colon slice preparations, the sulfotransferase and acetyltransferase inhibitors pentachlorophenol (PCP) and 2,6-dichloro-4-nitrophenol (DCNP) were used to modulate DNA adduct and metabolite formation. Incubations of 3-methylcholanthrene-induced colon slices dosed with 50 microMolar [(3)H]PhIP produced no detectable metabolites. However, incubations of uninduced slices exposed to 10 microMolar of the reactive intermediate, [(3)H]2-(hydroxyamino)-l-methyl-6-phenylimidazo[4,5-b]pyridine (N-hydroxy-PhIP), produced a single detectable metabolite, a glucuronide conjugate of N-hydroxy-PhIP. This metabolite decreased when PCP or DCNP was added to the incubation medium. DNA adducts were detected in colon slices exposed to N-hydroxy-PhIP at approximately 33 adducts/10(7) nucleotides. Interestingly, when PCP was added to the incubation mixture, an increase in DNA adduct levels was detected, whereas DCNP produced a decrease in adducts. Because these inhibitors are thought to have similar mechanisms with regard to sulfotransferase inhibition, the inverse relationship in DNA adduct levels due to PCP or DCNP treatment is at present unexplainable. The formation of DNA adducts and metabolites from colon slices exposed to N-hydroxy-PhIP but not PhIP implies that there is insufficient P450 activity in the rat colon to activate PhIP to hydroxylated metabolites, suggesting that the rat colon is a site of Phase II metabolism for PhIP and that the liver is the primary source for hydroxylation.

Comparison of crystal structure and theory for 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine

The crystal structure of the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b] pyridine (PhIP) has been determined by single-crystal X-ray crystallography. Crystals grown by evaporation of an aqueous solution form in the monoclinic space group P2(1)/n with two molecules of PhIP per asymmetric unit, along with six water molecules. The phenyl groups of these two PhIP molecules have torsion angles of different magnitude with respect to the plane of the imidazopyridine moiety. To maintain centrosymmetry, the crystal also contains an oppositely torsioned symmetry equivalent of each. The amino groups of both PhIP molecules take part in an extensive hydrogen bond network with the water of crystallization, forming long channels through the crystals parallel to the crystallographic b axis. The diffraction results are compared to theoretical calculations of the optimized geometry for a single PhIP molecule in vacuo as well as with water hydrogen-bonded to the exocyclic amine. In general, the agreement between the X-ray crystal structure of PhIP and its theory-derived counterpart in vacuo is within the combined experimental-theoretical uncertainty. The C-N bond to the exocyclic amine and the neighboring C=N imidazole bond are exceptions. This is attributed to the combined neglect of the crystal environment, waters of hydration, and the lack of coplanarity between the imidazole ring and the amine group in the calculations. To address the effect of waters of hydration, additional calculations were performed to optimize the geometry of a PhIP molecule with two water molecules hydrogen-bonded to the exocyclic amine. The resulting C-N exocyclic amine and C=N imidazole bond lengths were closer to those obtained by X-ray diffraction. The accord between theory and experiment demonstrates the utility of applying theory to (1) accurately predict structures of PhIP metabolites and intermediates that are too labile for study by conventional structural techniques such as X-ray crystallography and (2) assist in studying the mechanisms by which PhIP and its metabolites interact with proteins and DNA.

Problem-based learning as a training modality in the occupational medicine curriculum

Problem-based learning has been used as a curricular modality in the academic year of the Occupational Medicine Residency Program. The method was applied to the resolution of problems presented by patients referred to a university clinic specifically for the determination of possible work-relatedness of the syndrome or symptoms presented. Following the usual development of the occupational and medical histories, physical examination, and determination of certain clinical laboratory values, the resident would then have to seek assistance through consultation with related specialists, a perusal of the pertinent toxicology, epidemiology, or other discipline literature, and ultimately prepare a university-level report, following case conferences with fellow residents and faculty members. No formal direction was given the student, the problems of diagnosis, occupational etiology and medicolegal acceptance of the resulting report having to be resolved through self-perusal of informational sources. The knowledge gained from the exercise would be longer-lasting than that attained strictly from lecture attendance.

Genetically modified Chinese hamster ovary (CHO) cells for studying the genotoxicity of heterocyclic amines from cooked foods

We have developed metabolically competent Chinese hamster ovary (CHO) cells to evaluate the genotoxicity associated with heterocyclic amines, such as those that are present in cooked foods. Into repair-deficient UV5 cells we introduced cDNAs for expressing cytochrome P450IA2 and acetyltransferases. We then genetically reverted these transformed lines to obtain matched metabolically competent repair-deficient/proficient lines. For a high mutagenic response, we find a requirement for acetyltransferase with 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) but not with 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). This system allows for both quantifying mutagenesis and analyzing the mutational spectra produced by heterocyclic amines.

High concentrations of the carcinogen 2-amino-1-methyl-6-phenylimidazo- [4,5-b]pyridine (PhIP) occur in chicken but are dependent on the cooking method

Heterocyclic aromatic amines (HAAs) are mutagenic and carcinogenic compounds found in meats cooked at high temperatures. Although chicken is consumed in large quantities in the United States, there is little information on its HAA content. The objective of this study was to measure the five predominant HAAs (IQ, MeIQ, MeIQx, DiMeIQx, and PhIP) in chicken cooked by various methods to different degrees of doneness. Chicken breasts were panfried, oven-broiled, or grilled/barbecued. Whole chickens were roasted or stewed. Skinless, boneless chicken breasts were cooked to three degrees of doneness: just until done, well done, or very well done. High levels of PhIP (ranging from 12 to 480 ng/g cooked meat) were found in chicken breasts when panfried, oven-broiled, and grilled/barbecued but not in while roasted or stewed chicken. PhIP concentration increased in skinless, boneless chicken breast with longer cooking time, higher internal temperature, and greater degree of surface browning. PhIP concentration was also high in chicken breasts cooked with skin and bones. MeIQx and DiMeIQx levels increased with the degree of doneness, whereas IQ and MeIQ were not detectable in any of these chicken samples. Certain cooking methods produce PhIP, a known colon and breast carcinogen in rodents and possibly a human carcinogen, at substantially higher levels in chicken than has been reported previously in red meat.

Airborne mutagens produced by frying beef, pork and a soy-based food

Airborne cooking by-products from frying beef (hamburgers), pork (bacon strips) and soybean-based food (tempeh burgers) were collected, extracted, tested for mutagenicity and chemically analysed. The fumes generated by frying pork and beef were mutagenic, with 4900 and 1300 revertants/g of food cooked, respectively. No mutagenicity was detected in fumes from frying tempeh burgers. Bacon fried to a well-done but non-charred state was eight times more mutagenic in a microsuspension Ames/Salmonella test (TA98 with S-9) than hamburgers and about 350 times more mutagenic than tempeh burgers. Among food samples cooked to a well-done, non-charred state, bacon strips had almost 15-fold more mass (109.5 ng/g) than that of the beef, whereas no heterocyclic amine (HCA) was detected in the fried tempeh burgers. 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) was the most abundant HCA, followed by 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx). No 2-amino-9H-pyrido[2,3-b]indole (A alpha C) was detected in the food samples fried at about 200 degrees C, although it was present in the collected airborne products. The total amounts of HCAs in the smoke condensates were 3 ng/g from fried bacon, 0.37 ng/g from fried beef and 0.177 ng/g from fried soy-based food. This study indicates that cooks are potentially exposed to relatively high levels of airborne mutagens and carcinogens and that long-term sampling inside restaurants and kitchens may be warranted in order to assess the potential risk of prolonged exposure.

A correlation of Salmonella mutagenicity with DNA adducts induced by the cooked-food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine

The correlation of bacterial mutagenicity with DNA adducts from the heterocyclic amine cooked-food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) was investigated in Salmonella typhimurium strains TA98 (uvrB deficient) and TA1978 (uvrB proficient). Bacterial cells were exposed to PhIP using a modification of the Ames/Salmonella microsuspension assay. Half of the cells, generated from a 90 min pre-incubation and washing, were plated for revertant formation while the remaining half was subjected to DNA adduct analysis via 32P-postlabeling. In TA98, DNA adducts were detected at an RAL (relative adduct labeling) of 10 x 10(-7) and 21 x 10(-7) at PhIP concentrations of 5.5 and 17 microM, respectively. This corresponded to 28.8 and 20.9 adducts/revertant, respectively. These values were based on the assumption that only four repeating GC bases within a 75 DNA base region is the gene target site for PhIP induced mutations. In TA1978, no revertants above background were detected at any concentration of PhIP tested. DNA adducts, however, were detected at 11 x 10(-7) and 21 x 10(-7) adducts per nucleotide at 223 and 1116 microM PhIP, respectively. The lack of detectable revertants, but the presence of DNA adducts, suggests pre-mutational lesions did occur during the 90 min pre-incubation. Presumably, when the S9 activating system and PhIP were removed (via washing with phosphate buffered saline) prior to plating, the cells containing an intact uvrB repair system repaired the lesions during the incubation time on the plates. In conclusion, the induction of revertants by adducts appears quite efficient, as approximately 25 adducts are required for one mutational event in the excision repair deficient bacteria.

Heterocyclic amine content in fast-food meat products

Heterocyclic aromatic amines are sometimes formed during the cooking of muscle meats, and their mutagenic and carcinogenic effects are of potential concern in the aetiology of human cancer. In a large survey of the heterocyclic amine content of foods, fried or charbroiled hamburgers, fried chicken, chicken breast sandwiches, fish sandwiches and breakfast sausages were purchased from fast-food restaurants. At least three different chains were visited per product and samples from five stores from each chain were pooled. The solid-phase extraction and HPLC method was used to analyse pooled samples for heterocyclic amine content and mutagenic activity with the Ames/Salmonella assay. Samples were analysed in a blind study which also contained quality control samples of two types, one high and one low in heterocyclic amine content and mutagenic activity. Results from the fast-food products showed undetectable levels of heterocyclic amines in 10 of 17 samples and only low levels [< or = 1 ng/g total of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx)] in the remaining samples. Compared with literature values based primarily on laboratory and home cooking conditions, fast-food meat products appear to contribute only a small percentage of the estimated daily dietary intake of heterocyclic amines.