Urinary mutagenesis and fried red meat intake: influence of cooking temperature, phenotype, and genotype of metabolizing enzymes in a controlled feeding study

Meat cooked at high temperatures contains potential carcinogenic compounds, such as heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs). Samples from a 2-week controlled feeding study were used to examine the relationship between the intake of mutagenicity from meat fried at different temperatures and the levels of mutagenicity subsequently detected in urine, as well as the influence of the genotype of drug metabolizing enzymes on urinary mutagenicity. Sixty subjects consumed ground beef patties fried at low temperature (100 degrees C) for 1 week, followed by ground beef patties fried at high temperature (250 degrees C) the second week. Mutagenicity in the meat was assayed in Salmonella typhimurium TA98 (+S9), and urinary mutagenicity was determined using Salmonella YG1024 (+S9). Genotypes for NAT1, NAT2, GSTM1, and UGT1A1 were analyzed using blood samples from the subjects. Meat fried at 100 degrees C was not mutagenic, whereas meat fried at 250 degrees C was mutagenic (1023 rev/g). Unhydrolyzed and hydrolyzed urine samples were 22x and 131x more mutagenic, respectively, when subjects consumed red meat fried at 250 degrees C compared with red meat fried at 100 degrees C. We found that hydrolyzed urine was approximately 8x more mutagenic than unhydrolyzed urine, likely due to the deconjugation of mutagens from glucuronide. The intake of meat cooked at high temperature correlated with the mutagenicity of unhydrolyzed urine (r = 0.32, P = 0.01) and hydrolyzed urine (r = 0.34, P = 0.008). Mutagenicity in unhydrolyzed urine was not influenced by NAT1, NAT2, or GSTM1 genotypes. However, a UGT1A1*28 polymorphism that reduced UGT1A1 expression and conjugation modified the effect of intake of meat cooked at high temperature on mutagenicity of unhydrolyzed urine (P for interaction = 0.04). These mutagenicity data were also compared with previously determined levels of HCAs (measured as MeIQx, DiMeIQx, and PhIP) and polycyclic aromatic hydrocarbons (PAHs) in the meat, levels of HCAs in the urine, and CYP1A2 and NAT2 phenotypes. The levels of mutagenicity in the meat fried at low and high temperatures correlated with levels of HCAs, but not levels of PAHs, in the meat. Also, levels of mutagenicity in unhydrolyzed urine correlated with levels of MeIQx in unhydrolyzed urine (r = 0.36; P = 0.01), and the levels of mutagenicity of hydrolyzed urine correlated with levels of MeIQx (r = 0.34; P = 0.01) and PhIP (r = 0.43; P = 0.001) of hydrolyzed urine. Mutagenicity in unhydrolyzed urine was not influenced by either the CYP1A2 or NAT2 phenotype. The data from this study indicate that urinary mutagenicity correlates with mutagenic exposure from cooked meat and can potentially be used as a marker in etiological studies on cancer.     

Metabolic formation, synthesis and genotoxicity of the N-hydroxy derivative of the food mutagen 2-amino-1-methyl-6-phenylimidazo (4,5-b) pyridine (PhIP)

Hepatic microsomes from rats pretreated with PCB were found to metabolize the food mutagen 2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP) to two major metabolites, one of which was identified as the N-hydroxy derivative, 2-hydroxy-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (N-OH-PhIP). This identification was based on mass spectral (MS), UV and HPLC data by comparison with N-OH-PhIP prepared by chemical synthesis, as well as the specific activity of the compound in the Ames Salmonella test. Synthetic N-OH-PhIP was prepared by catalytic reduction of the nitro derivative of PhIP, which was synthesized from PhIP by diazotization and reaction with sodium nitrite. N-OH-PhIP was mutagenic to Salmonella typhimurium TA98 without metabolic activation and had a specific mutagenic activity of 2700 revertants/nmol. N-OH-PhIP thus seems to be a proximate mutagenic metabolite of PhIP. Other direct acting mutagens were not detected in the microsomal incubation mixture after HPLC separation. N-OH-PhIP also induced sister chromatid exchange (SCE) in Chinese hamster ovary cells (CHO cells) without metabolic activation. The specific activity of N-OH-PhIP in this assay was approximately 3 times higher than the activity of PhIP with microsomal activation.     

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.     

Uptake of tobacco smoke constituents on exposure to environmental tobacco smoke (ETS)

Summary For the purpose of risk evaluation, passive smoking is frequently regarded as low-dose cigarette smoking. However, since the physical, chemical and biological properties of mainstream smoke (MS), which is inhaled by the smoker and environmental tobacco smoke (ETS), which is breathed by the passive smoker are quite different, risk extrapolation from active smoking to passive smoking is of doubtful value. In a series of experimental exposure studies we compared the uptake of tobacco smoke constituents by active and passive smoking. The results show that biomarkers which were found to be elevated after experimental ETS exposure, such as nicotine and cotinine in plasma and urine as well as thioethers in urine, indicate gas-phase exposure in passive smokers, but particle-phase exposure in active smokers. Biomarkers which should indicate the uptake of particle-bound, genotoxic substances with ETS, such as urinary mutagenicity, metabolites of polycyclic aromatic hydrocarbons (PAH) and DNA adducts, were not found to be elevated even after extremely high ETS exposure. From these results we conclude that a risk evaluation for passive smoking on the basis of dosimetric data is currently not possible.Abbreviations 1-ABP 4-aminobiphenyl - BaA benzo(a)anth-racene - BaP benzo(e)pyrene - BE butanol extraction - BeP benzo(e)pyrene - CO carbon monoxide - COHb carboxyhae-moglobin - DABS DNA binding substances - DRZ diagonal radioactive zone - ETS environmental tobacco smoke - GC gas chromatography - GC/MS gas chromatography coupled to mass spectrometry - HPLC high performance liquid chromatography - HPMA 3-hydroxypropylmercapturic acid - MS mainstream smoke - NNK 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone - NNN N-nitrosonornicotine - NO_xa nitrogen oxides (NO/NO₂) - PAH polycyclic aromatic hydrocarbons - PhIP 2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine - P1 nuclease P1 - RSP respirable particles     

Review: Putative mutagens and carcinogens in foods. VI. Protein pyrolysate products

Diet and nutrition may be responsible for 60% of the total cancer incidence for women and greater than 40% for men. Fat, animal protein, and meat consumption are highly correlated with colon cancer incidence. The charcoal broiling of meat and fish yield mutagenic substances. Many findings support the hypothesis that the predominant mutagens are formed by the Maillard reaction. A number of mutagenic compounds have been identified both from cooked foods and from protein pyrolysates. The identified compounds are N-heterocyclic primary amine derivatives of either carbolines, imidazoquinolines, or imidazoquinoxalines. The carboline-type mutagens are structurally related to the known carcinogens 2-acetylaminofluorene (AAF) and 2-aminofluorene (AF), while the imidazoquinoline and imidazoquinoxaline types are believed to resemble 3,2′-dimethyl-4-aminobiphenyl (DMAB). Studies support the theory that these compounds require metabolic activation and are carcinogenic. The major metabolites of several compounds have been identified as the N-hydroxy derivatives. DNA binding was found to be a necessary but not a sufficient condition for mutagenesis. The modified base products have been identified as C-8-guanyl derivatives, resembling adducts formed by the carcinogenic aromatic amines.     

Protein pyrolysate products

Diet and nutrition may be responsible for 60% of the total cancer incidence for women and greater than 40% for men. Fat, animal protein, and meat consumption are highly correlated with colon cancer incidence. The charcoal broiling of meat and fish yield mutagenic substances. Many findings support the hypothesis that the predominant mutagens are formed by the Maillard reaction. A number of mutagenic compounds have been identified both from cooked foods and from protein pyrolysates. The identified compounds are N-heterocyclic primary amine derivatives of either carbolines, imidazoquinolines, or imidazoquinoxalines. The carboline-type mutagens are structurally related to the known carcinogens 2-acetylaminofluorene (AAF) and 2-aminofluorene (AF), while the imidazoquinoline and imidazoquinoxaline types are believed to resemble 3,2'-dimethyl-4-aminobiphenyl (DMAB). Studies support the theory that these compounds require metabolic activation and are carcinogenic. The major metabolites of several compounds have been identified as the N-hydroxy derivatives. DNA binding was found to be a necessary but not a sufficient condition for mutagenesis. The modified base products have been identified as C-8-guanyl derivatives, resembling adducts formed by the carcinogenic aromatic amines.     

Diet and cancer: Risk factors and epidemiological evidence

Background

Diet represents 30–35% of risk factors that contribute to the onset of cancer. Some foods and dietary patterns have been linked to the risk of various cancers. However epidemiological available data are not consistent for many foods and the associations with cancer risk remain unclear. The concerns about this issue are considered like a “Hot topic” for oncologists and general population.

Objective

The aim of this report is to present a review of the published epidemiologic research to date reflecting the most current scientific evidence related to diet and cancer risk.

Design

EMBASE and PubMed-NCBI were searched for relevant articles up to October 2013 that identified potentials interactions between foods or dietary patterns with cancer risk.

Results

There is no conclusive evidence as an independent risk factor for isolated nutrients versus adoption of dietary patterns for cancer risk. Moderate physical activity after breast cancer diagnosis contributes to 40% reduction of recurrence/disease-specific mortality. Cancer colon risk derived from meat intake is influenced by both total intake and its frequency. The interaction of phenolic compounds on metabolic and signaling pathways like P450, MAP kinase, PI3 kinase, IGF-1, NF-kB and ROS seems to exert an inhibitory effect on cell proliferation and tumor metastasis and induces apoptosis in various types of cancer cells, including colon, lung, prostate, hepatocellular or breast cancer.

Conclusions

There is a direct relationship between unhealthy diet and lifestyle with the increase of tumor development and cancer risk. For this reason, a good nutritional status based on a balanced diet constitutes one of the main preventive factors from tumors. However the mixed results from epidemiologic studies hinder to get unequivocal and consistent evidence about the interaction between diet and cancer risk. More epidemiological studies will be needed in the future to clarify this issue.     

Carcinogen-DNA adducts in human breast epithelial cells

Diet and environmental exposures are often regarded as significant etiologic factors in human breast cancer. Chemicals that may be involved in these exposures include heterocyclic amines, aromatic amines, and polycyclic aromatic hydrocarbons, which also serve as strong mammary carcinogens in different animal models. In this study, we chose to quantify the major DNA adducts derived from one member of each of these classes of carcinogens, that is, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 4-aminobiphenyl (ABP), and benzo[a]pyrene (B[a]P), respectively, in DNA isolated from exfoliated ductal epithelial cells in human breast milk. Milk was collected from healthy, nonsmoking mothers. The isolated DNA was digested to 3' nucleotides and subjected to (32)P-postlabeling. Adduct enrichment was achieved using Oasis Sep-Paks and the analyses were conducted by HPLC using radiometric detection. Critical to the analyses were the syntheses of bis(phosphate) standards for the C8-dG adducts of PhIP and ABP, and the N(2)-dG adduct of B[a]P, which were added to each reaction as UV markers. Of the 64 samples analyzed, adducts were found in 31 samples. Thirty samples contained detectable levels of PhIP adducts, with a mean value of 4.7 adducts/10(7) nucleotides; 18 were positive for ABP adducts with a mean value of 4.7 adducts/10(7) nucleotides; and 13 were found to contain B[a]P adducts with a mean level of 1.9 adducts/10(7) nucleotides. These data indicate that women are exposed to several classes of dietary and environmental carcinogens and that these carcinogens react with DNA in breast ductal epithelial cells, the cells from which most breast cancers arise.     

An enzyme-linked immunosorbent assay (ELISA) for the major crustacean allergen, tropomyosin, in food

Shellfish are a common cause of food reactions in hypersensitive individuals and are among the eight foods that account for over 90% of food allergies. At present, the only way to prevent these serious consequences of food allergies is to avoid the foods that trigger the reactions. A sandwich-ELISA kit has been developed for the detection of crustacean meat in food, based on the major heat-stable shellfish allergen, tropomyosin. Tropomyosin was purified from whole prawn (Penaeus latisulcatus) and used to immunize rabbits after confirming its identity by MALDI-TOF MS. A sandwich-ELISA based on the rabbit antibodies takes less than 2 h to perform, including the food extraction, and has a detection limit of 1 ppm crustacean (prawn, lobster), without detectable cross-reactivity with fish or mammalian meat.     

The Eskimo diet. Prophylactic effects ascribed to the balanced presence of natural cis unsaturated fatty acids and to the absence of unnatural trans and cis isomers of unsaturated fatty acids

In addition to the well recognised roles of eicosapentaenoic acid and possibly docosahexaenoic acid, there are two other major important, but unrecognised, features of the traditional Eskimo staple diet namely that it contains the unsaturated fatty acids (UFA) cis oleic, cis linoleic and cis alpha-linolenic as well as their respective C20 and C22 metabolites in physiologically optimal concentrations and, it is virtually totally devoid of unnatural and potentially hazardous trans and cis isomers of these fatty acids. Large quantities of unnatural trans and cis isomers of UFA are found in the Western diet as partially hydrogenated UFA in many foods. These isomers are formed during the manufacture of margarines and related compounds, as food contaminants during excessive heating of cooking oils for deep-frying and other excessive heat-requiring mass food preparation procedures and it is suggested, as the result of excessive feeding with an unnatural diet of ruminants and non-ruminants for increased meat and/or milk production and of poultry for increased egg and/or meat production. These isomers have been shown to display potentially hazardous metabolic effects which include the competitive inhibition of UFA metabolism at various steps and have been causally implicated in the etiology of ischemic heart disease and cancer. It is suggested that the myth of the safety of trans fatty acids arises from misinterpretation of the observation that increasing dietary cis linoleic acid reduces the toxic effects of trans UFA. It is suggested that the decrease of 20% in the ischemic heart disease mortality in the USA during the past two decades is directly related to a shift in the dietary ratio of unnatural trans and cis UFA isomers: cis linoleic acid in favour of the latter. It is predicted that this ratio will be found to correlate with ischemic heart disease patterns in other countries. Eskimos consume the bulk of their food frozen, raw or dried, seldom boiled, but never deep-fried or after exposure to excessive heat. Moreover the proportionality of cis UFA and their metabolites in their traditional staple diet would render gross tissue UFA utilization relatively independent of desaturase enzyme activity. In the Eskimo tissues these enzymes would function to make the minute, critical UFA metabolic adjustments required to ensure the presence of structural UFA in membranes in functionally optimal quantities and, ensure the synthesis of eicosanoids from dihomogamma-linolenic acid, arachidonic acid and eicosapentaenoic acid in balanced, optimal physiological concentrations for the genetic make-up of Eskimos.(ABSTRACT TRUNCATED AT 400 WORDS)     

Studies on mammary carcinogenesis induced by a heterocyclic amine, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, in mice and rats

Ten heterocyclic amines (HCAs) that are produced by heating amino acids, proteins, or proteinaceous food such as fish and meat were examined for carcinogenicity in rats and mice. Three of them, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), have been shown to induce mammary cancer in female F344 and/or SD rats, but none of the HCAs induced mammary cancer in CDF(1) mice. This report reviews our recent studies on mammary carcinogenesis of PhIP in various strains of mice and on the roles of genomic instability in the rat mammary carcinogenesis of PhIP. We demonstrated that the survival time from mammary adenocarcinomas was shorter in PhIP-treated BALB/c mice than that in the untreated control, and with a significantly higher incidence in the C.B-17 strain of mice compared with that of the control. To clarify mechanisms of mammary carcinogenesis, we examined genomic instability in rat mammary cancer induced by PhIP. Mammary cancers were induced in F344 x SD F(1) rats harboring the lacI transgene, and two cell lines were established from two adenocarcinomas. They showed a greater than 10-fold higher frequency of spontaneous mutations than that of the primary culture of normal mammary epithelial cells, in the lacI transgene and the hprt endogenous gene during cell replication. Nucleotide sequencing revealed that almost all types of mutations were increased, with a remarkable increase of A:T --> C:G mutation. This genomic instability was not attributed either to alterations of mismatch-repair enzymes or to p53. These mutational characteristics were also observed in the original tumors. Single-nucleotide instability (SNI) might be implicated in the mammary cancer induced by PhIP.     

Nutritional fats and the risk of type 2 diabetes and cancer

Dietary factors are important predictors for the risk of diabetes type 2. Increased consumption of fibre-rich foods, fruits and vegetables as well as limited amounts of total and saturated fats are essential elements in the prevention of diabetes type 2. The association between these dietary factors and the appearance of diabetes was not only present in cohort studies but were also major elements in the dietary part of the two large diabetes prevention trials (Finnish Diabetes Prevention Study, Diabetes Prevention Program). There is also strong evidence for a relation between obesity and total fat intake and the incidence of certain types of cancers. There is a significant correlation between total fat intake and the risk of cancer; however, it is much weaker than that of the effect of red meat. Recommendations to decrease red meat intake, particularly processed meat, may decrease the risk of colorectal and prostate cancer and may have beneficial effects on breast cancer as well, although this evidence is less compelling. Overall, recommendations focused on controlling or reducing body weight by regular physical activity and avoidance of excessive energy intake from all sources, particularly from fat and saturated fats, by increasing consumption of fibre-rich carbohydrates, vegetables and fruits are effective in decreasing the risk for type 2 diabetes by more than 50% in high-risk individuals. Similar dietary patterns are likely to diminish the manifestation of certain forms of cancers. These conclusions are in agreement with current recommendations for cancer prevention as propagated by the American Cancer Society.     

Physical activity,diet, adiposity and female breast cancer prognosis: A review of the epidemiologic literature

Given the increasing numbers of long-term survivors of breast cancer, research specific to prevention of recurrence, new breast cancer events, and mortality is of considerable public health importance. The objective of this report is to present a review of the published epidemiologic research on lifestyle and breast cancer outcomes among women with a history of breast cancer. This review focused on physical activity, diet, and adiposity; and the primary outcomes were additional breast cancer events and mortality. The most consistent finding from observational studies was that adiposity was associated with a 30% increased risk of mortality. Although the observational data were not as consistent (or abundant), physical activity appeared to be associated with a 30% decreased risk of mortality. These data do not indicate that alcoholic drinks are a risk factor. Based only on the observational studies, total dietary fat appeared to be a risk factor, fiber was protective, and information on micronutrients and specific foods was sparse. However, the null results of 2 dietary intervention trials in survivors suggests that lowering fat intake or increasing consumption of fruits, vegetables, and fiber will not lead to improved prognosis in breast cancer survivors. Given that a high proportion of breast cancer patients appear to be both sedentary and obese/overweight, clinical trials are needed to investigate whether the combination of increased physical activity and reduced adiposity can improve breast cancer prognosis.     

IgE-mediated allergy to peanut, cow's milk, and egg in children with special reference to maternal diet

Nineteen children with IgE-mediated allergy associated with strongly positive prick skin tests and RASTs to peanut or cow's milk and/or egg were studied. Seventeen of the children had been breast fed, ten had been exclusively breast fed for a minimum of 5 months. Reactions to these foods occurred on first exposure to the food in all but one instance, suggesting that in 18 instances sensitization had occurred antenatally or via the breast. A retrospective inquiry indicated that most of the mothers had had a generous intake of the food(s) to which their children were sensitized, but mothers of sensitized children did not consume more of these foods than the mothers of non-sensitized children; moreover, avoidance of the foods (peanut in two instances and egg in one) did not ensure freedom from sensitization to peanut and/or egg. Breast feeding by itself cannot be guaranteed to protect against the development of food allergy.     

Genetic predisposition and environmental factors leading to the development of insulin-dependent diabetes mellitus in Chilean children

This study was designed to examine the hypothesis that some environmental factors increase the risk for insulin-dependent diabetes mellitus. Data on dietary history was collected from 80 diabetic children from the Santiago de Chile Registry and from 85 nondiabetic control subjects who were comparable in terms of age, sex, and ethnic characteristics. Early exposure was defined as the ingestion of food sources other than maternal milk before 3 months of age. To define genetic susceptibility to insulin-dependent diabetes mellitus each subject was typed in terms of HLA DQA1 and DQB1, and the possible conformation of susceptible heterodimers was considered as a risk marker. Fewer children were exclusively breast fed in the diabetic group than in the control group (21.55±15.05 vs. 33.95±20.40 weeks, P<0.01). In addition, exposure to cow's milk and solid foods occurred earlier in the diabetic group than in the control group (15.90±10.95 vs. 21.15 13.65 and 16.85±10.25 vs. 21.20±12.35 weeks, P<0.05). Our data show that a short duration of breast-feeding and early exposure to cow's milk and solid foods may be important factors in the development of insulin-dependent diabetes mellitus. The high relative risk observed in individuals genetically predisposed indicates an interaction effect between genetic and environmental components.Abbreviations IDDM Insulin-dependent diabetes mellitus - RR Relative risk     

The role of aromatic hydrocarbons in the genesis of breast cancer.

The incidence of breast cancer in women has increased dramatically over the last decade. Epidemiological markers of this increased incidence include: endocrine related phenomena (early menarche, age of first parity and age of menopause); exposure of the breast to X-radiation; and a group of seemingly disparate factors--urban residence, dietary selection and alcohol consumption. Although experimental breast cancer may be induced by estrogenic hormones, X-radiation and aromatic hydrocarbons, only aromatic hydrocarbons have not been previously implicated in human mammary carcinogenesis. The seemingly unrelated human factors can best be understood by examining the role of breast tissue in aromatic hydrocarbon metabolism. Aromatic hydrocarbons are important environmental chemicals produced by the incomplete combustion of hydrocarbons for use in energy production. Benzene, benz(a)pyrene, dibenz(ah)anthracene and 1-nitropyrene, known experimental breast carcinogens, are produced in this way. Human exposure to aromatic hydrocarbon metabolites induces and promotes altered DNA by mechanisms described as increased intracellular pro-oxidant production as well as direct adduction to DNA. The breast is anatomically embedded in a major fat depot which stores and concentrates aromatic hydrocarbons and can metabolize these hydrocarbons to carcinogenic metabolites. Ductal cells concentrate these metabolites and themselves become target cells for carcinogenesis. Some lifestyle factors increase the amount of carcinogens produced or enhance their activity. A unitary model for mammary carcinogenesis in humans as well as in experimental carcinogenesis is hypothesized. If correct, the hypothesis would account for some of the increase in breast cancer incidence in industrial countries--and would suggest environmental and dietary modifications that would inhibit hydrocarbon induced mammary carcinogenesis.     

Intestinal tumours induced by the food carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine in multiple intestinal neoplasia mice have truncation mutations as well as loss of the wild-type Apc(+) allele.

C57BL/6J-Min/+ (multiple intestinal neoplasia) is a murine model for familial adenomatous polyposis (FAP), where the mice are heterozygous for a nonsense Apc(Min) (adenomatous polyposis coli) mutation, and therefore develop numerous spontaneous adenomas in the small intestine and colon. Neonatal exposure of Min/+ mice to the food carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) (eight subcutaneous injections of 25 or 50 mg/kg PhIP to pups or 50 mg/kg PhIP to lactating dams) markedly increased (2--9-fold) the number of intestinal tumours, especially in the small intestine. We examined whether the Apc gene was affected in small intestinal and colonic tumours induced by PhIP. In spontaneous tumours formed in these mice, the main mechanism for tumour induction is loss of the wild-type Apc(+) allele, i.e. loss of heterozygosity (LOH). Also in the PhIP-induced tumours, this is a major mechanism, since large fractions of PhIP-induced tumours had LOH in APC: However, mechanisms other than LOH must also prevail, since a lower frequency of LOH was found in the small intestinal tumours from male mice exposed to PhIP either via breast milk (65%) or by direct injection (68%), compared with the untreated controls (92%). Tumours that had retained the wild-type Apc(+) allele were further analysed for presence of truncated Apc proteins with in vitro synthesized protein (IVSP) assay. Truncated Apc proteins, indicating truncation mutations in exon 15 of the Apc gene, were detected in 20% (8 of 40) of the tumours not showing LOH from the small intestine after PhIP exposure, all in segment 2 (codons 686--1217). Seventeen percent (2 of 12) of the colonic tumours had a truncated Apc protein in segment 3 (codons 1099--1693). Importantly, no truncated proteins were detected in tumours from unexposed mice with apparently retained wild-type Apc(+) allele. These results show that PhIP induces intestinal tumours in the Min/+ mice both by causing LOH and truncation mutations in the wild-type Apc(+) allele.     

Ready-to-use introduction schedules for first exposure to allergenic foods in children at home

Background:  The vast majority of children will undergo their first exposure to common allergenic foods at home. However, the first exposure may lead to clinical reactions. It has been proposed to introduce allergenic foods gradually into the diets of children at risk for food allergy, but no practical dietary advice has been devised.
Objective:  The aim of this study was to devise safe introduction schedules for common allergenic foods for use at home, based on the challenge doses as administered in double-blind, placebo-controlled food challenge (DBPCFCs) in children who were never exposed previously to these foods.
Methods:  Seventy-two DBPCFCs were performed in 63 children as a first known exposure. The incrementing challenge doses were converted into equivalent portions of these foods in their usual household form and incorporated in introduction schedules. The feasibility of the introduction scales was tested in parents of the children attending our clinic.
Results:  Based on the results of the positive challenges (37) in which severe reactions did not occur, detailed introduction schedules and a reference photograph of the required increasing amounts of food were devised for use at home. Feasibility testing showed that, when using these introduction schedules, parents portioned the initial doses significantly lower than without detailed instructions.
Conclusions:  The introduction schedules and reference photograph provide information for parents to introduce the required amounts of allergenic foods in initial low doses at home. This is expected to improve the safety of this procedure.     

Intake of dietary fat and vitamin in relation to breast cancer risk in Korean women: a case-control study

To investigate association between breast cancer risk and nutrients intake in Korean women, a case-control study was carried out, at Seoul, Korea. Incident cases (n=224) were identified through the cancer biopsy between February 1999 and December 2000 at two University hospitals in Seoul. Hospital-based controls (n=250) were selected from patients in the same hospitals, during the same periods. Food intake was investigated semiquantitative frequency questionnaire (98 items) by trained dietitian. Subjects were asked to indicate the average food intake and vitamin supplement for a 12 months period of 3-yr prior to the baseline phase. In investigation of vitamin supplement use, subjects were asked the average frequency of use, duration, dose and the brand name of vitamin supplement (multivitamins, vitamin A, vitamin C and vitamin E). And nutrients were calorie adjusted by the residuals method. In this study, higher breast cancer risk incidence was not observed with higher intake of total fat and saturated fatty acids, however statistically significant trends with breast cancer incidence for total saturated fatty acids were found (ptrend=0.0458). In analyses of vitamins, beta-carotene and vitamin C were significantly associated with decreasing risk of breast cancer. In analyses, results from dietary plus supplement of vitamin was not associated with breast cancer risk in this study. In conclusion, our findings suggest that antioxidant vitamins such as beta-carotene and vitamin C intake could lower the breast cancer risk in Korean women.     

Conjugated linoleic acid inhibits mutagenesis by 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine in the prostate of Big Blue rats

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a potent mutagen and carcinogen formed at high temperature during the cooking of meat. PhIP induces tumors in the colon and prostate of male rats and in the mammary gland of female rats and has been associated with the etiology of human cancers. We have recently demonstrated that PhIP induces mutations in the prostate in Big Blue transgenic rats. In the current study we have examined the effect of a dietary anti-carcinogen, conjugated linoleic acid (CLA), on PhIP-induced mutagenesis in the prostate. CLA is a mixture of positional and geometric isomers of linoleic acid and has been reported to inhibit various chemical-induced cancers in rodent models. Fifty day old male Big Blue rats were fed a standard diet containing 100 p.p.m. PhIP for 47 days, which induced a mutation frequency of 14.6 x 10(-5) in the prostate, 5.1-fold higher than that of controls. The addition of 1% CLA (w/w) in the diet starting 1 week prior to exposure to PhIP decreased PhIP-induced mutagenesis by 38% (P = 0.03). The predominant class of mutation induced by PhIP is -1 frameshifts involving the loss of G:C base pairs, followed by G:C-->T:A transversions and G:C-->A:T transitions. Addition of CLA to the diet significantly changed the PhIP-induced mutation spectrum; notably, -1 frameshifts and G:C-->A:T transitions were selectively inhibited, suggesting involvement of mismatch repair. This is the first report to show the protective effect of CLA against PhIP-induced mutagenesis in the prostate on both mutation frequency and mutational spectrum. The inhibitory effect of CLA against PhIP-induced mutagenicity suggests a possibility for its application in human chemoprevention studies.