Mammary gland carcinogenesis by food-derived heterocyclic amines and studies on the mechanisms of carcinogenesis of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)

Psychosocial stress and cancer risk: a narrative review

BACKGROUND

It is unclear which psychological factors (stressors, emotional correlates, and psychophysiological markers) induce cancer risk. This currently limits the potential for prevention strategies.

PURPOSE

The aim of this review is to bring forth evidence of stress as a determinant of cancer risk from a public health perspective, written for a broad public of practitioners and scientists.

METHODS

Based on a semisystematic literature search, the impact of different aspects/types of stress and the potential physiological and behavioral pathways are summarized, while highlighting further research, public health and clinical implications.

RESULTS

Between 2007 and 2020, 65 case-control or cohort studies have been identified. Apart from overall cancer ( N = 24), 12 cancer types have been associated with psychological stress with most for breast ( N = 21), colorectal ( N = 11) and lung/prostate/pancreas cancer ( N = 8 each). Although the evidence regarding the mechanisms is still scarce, cancer development in relation to stress might be due to interacting and combined effects of different stress(or) types, but such interaction has not really been tested yet. The path from stress towards cancer incidence consists of a biological pathway with endocrinology and immunology as well as stress-induced behavioral pathways, including smoking, alcoholism, sleep disruption, an unhealthy diet, and low physical activity together with the related phenomenon of obesity.

CONCLUSION

Not only the stress but also the stress-induced lifestyle should be targeted for cancer prevention and treatment. Future research should include a more diverse spectrum of cancer types (not only hormonal related like breast cancer) and of stress measures while also considering behavioral covariates.

Role of Human N-Acetyltransferase 2 Genetic Polymorphism on Aromatic Amine Carcinogen-Induced DNA Damage and Mutagenicity in a Chinese Hamster Ovary Cell Mutation Assay

Carcinogenic aromatic amines such as 4-aminobiphenyl (ABP) and 2-aminofluorene (AF) require metabolic activation to form electrophilic intermediates that mutate DNA leading to carcinogenesis. Bioactivation of these carcinogens includes N-hydroxylation catalyzed by CYP1A2 followed by O-acetylation catalyzed by arylamine N-acetyltransferase 2 (NAT2). To better understand the role of NAT2 genetic polymorphism in ABP- and AF-induced mutagenesis and DNA damage, nucleotide excision repair-deficient (UV5) Chinese hamster ovary (CHO) cells were stably transfected with human CYP1A2 and either NAT2*4 (rapid acetylator) or NAT2*5B (slow acetylator) alleles. ABP and AF both caused significantly (P < 0.001) greater mutagenesis measured at the hypoxanthine phosphoribosyl transferase (hprt) locus in the UV5/CYP1A2/NAT2*4 acetylator cell line compared to the UV5, UV5/CYP1A2, and UV5/CYP1A2/NAT2*5B cell lines. ABP- and AF-induced hprt mutant cDNAs were sequenced and over 80% of the single-base substitutions were at G:C base pairs. DNA damage also was quantified by γH2AX in-cell western assays and by identification and quantification of the two predominant DNA adducts, N-(deoxyguanosin-8-yl)-4-aminobiphenyl (dG-C8-ABP) and N-(deoxyguanosin-8-yl)-2-aminofluorene (dG-C8-AF) by liquid chromatography-mass spectrometry. DNA damage and adduct levels were dose-dependent, correlated highly with levels of hprt mutants, and were significantly (P < 0.0001) greater in the UV5/CYP1A2/NAT2*4 rapid acetylator cell line following treatment with ABP or AF as compared to all other cell lines. Our findings provide further clarity on the importance of O-acetylation in CHO mutagenesis assays for aromatic amines. They provide evidence that NAT2 genetic polymorphism modifies aromatic amine-induced DNA damage and mutagenesis that should be considered in human risk assessments following aromatic amine exposures. Environ. Mol. Mutagen. 61:235-245, 2020. © 2019 Wiley Periodicals, Inc.

Optimizing diet and nutrition for cancer survivors: A review

The number of cancer survivors is increasing and they are often highly motivated to search for information about nutrition and about physical activity in order to try to improve their treatment outcomes, quality of life and overall survival. In the light of these concerns, the World Cancer Research Fund (WCRF)/American Institute for Cancer Research (AICR) as well as the American Cancer Society recommend a largely plant-based diet with limited consumption of red and processed meat, and limited consumption of alcohol, as well as the maintenance of a healthy weight throughout life and regular engagement in physical activity. There is a need for well-designed large observational and intervention studies to shed more light on the association between diet and cancer survivorship, and to suggest additional means for the secondary prevention of cancer.

Diet and risk of breast cancer

Diet may play a role in both promoting and inhibiting human breast cancer development. In this review, nutritional risk factors such as consumption of dietary fat, meat, fiber, and alcohol, and intake of phytoestrogen, vitamin D, iron, and folate associated with breast cancer are reviewed. These nutritional factors have a variety of associations with breast cancer risk. Type of fat consumed has different effects on risk of breast cancer: consumption of meat is associated with heterocyclic amine (HCA) exposure; different types of plant fiber have various effects on breast cancer risk; alcohol consumption may increase the risk of breast cancer by producing acetaldehyde and reactive oxygen species (ROS); intake of phytoestrogen may reduce risk of breast cancer through genomic and non-genomic action; vitamin D can reduce the risk of breast cancer by inhibiting the process of cancer invasion and metastasis; intake of dietary iron may lead to oxidative stress, DNA damage, and lipid peroxidation; and lower intake of folate may be linked to a higher risk of breast cancer.

Meat consumption and breast cancer: a case-control study in women

BACKGROUND

The relationship between meat intake and breast cancer has been inconsistent .

OBJECTIVE

The aim of this work was to evaluate the association between meat intake and breast cancer, in women.

DESIGN

A case-control study with 250 consecutive, newly diagnosed breast-cancer-female-patients (56 ± 12 years) and 250, one-to-one age-matched controls was conducted. A standardized, validated questionnaire assessing various socio-demographic, clinical, lifestyle and dietary characteristics was applied through face-to-face interviews. Data on consumption of red, white, processed and grilled meat were also recorded. Overall dietary habits were assessed through the level of adherence to the Mediterranean diet using the MedDietScore (theoretical range 0-55).

RESULTS

Processed meat intake, even for 1-2 times/week,was associated with a 2.7-fold (OR= 2.65, 95% CI 1.36, 5.14) (p= 0.004) higher likelihood of having breast cancer, while daily intake increased the likelihood by a 2.8-fold (OR = 2.81, 95% CI 1.13, 6.96) (p = 0.026), after various adjustments made. Red, white and grilled meat intake was not significantly associated with the outcome when the same adjustments were made.

CONCLUSIONS

This study suggested that only daily processed-meat intake was consistently associated with increased odds of breast-cancer.

Intake of red meat and heterocyclic amines, metabolic pathway genes and bladder cancer risk

We analyzed the association between meat intake, heterocyclic amines (HCAs) and bladder cancer (BC) risk in a large case-control study comprised of 884 BC cases and 878 healthy controls, recruited from 1999 to 2009. Epidemiologic and dietary data were collected via an in-person interview. Compared to the lowest quartile of red meat intake, the odds ratios (ORs) for the second, third and fourth quartiles were 1.17 (95% CI: 0.87-1.58), 1.47 (95% CI: 1.09-1.99) and 1.95 (95% CI: 1.41-2.68), respectively, (p-for trend <0.001). In a subset of participants with intakes of HCAs available, compared with those with the lowest quartile of intake, the ORs for the second, third and fourth quartiles were 1.47 (95% CI: 0.60-3.64), 2.58 (95% CI: 1.09-6.11) and 3.32 (95% CI: 1.37-8.01), respectively, (p for trend <0.001). In cumulative analysis of SNPs in the pathway, compared with subjects carrying 0-4 unfavorable genotypes, subjects carrying 5 and 6 or more unfavorable genotypes were at 1.60-fold (95% CI: 1.20-2.12) and 2.37-fold (95% CI: 1.82-3.10) increased risk, respectively. Moreover, subjects carrying six or more unfavorable genotypes and whose red meat intake was in the highest quartile were at 5.09-fold increased risk (95% CI: 2.89-8.96; p < 0.001). These results strongly support that high red meat intake, high intake of HCAs and carrying high number of unfavorable genotypes in the HCA metabolic pathways are associated with increased risk of BC in the study population.

DNA adducts of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and 4-aminobiphenyl are infrequently detected in human mammary tissue by liquid chromatography/tandem mass spectrometry

Some epidemiological investigations have revealed that frequent consumption of well-done cooked meats and tobacco smoking are risk factors for breast cancer in women. 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a heterocyclic aromatic amine that is formed in well-done cooked meat, and 4-aminobiphenyl (4-ABP) is an aromatic amine that arises in tobacco smoke and occurs as a contaminant in the atmosphere. Both compounds are rodent mammary carcinogens, and putative DNA adducts of PhIP and 4-ABP have been frequently detected, by immunohistochemistry (IHC) or (32)P-post-labeling methods, in mammary tissue of USA women. Because of these findings, PhIP and 4-ABP have been implicated as causal agents of human breast cancer. However, the biomarker data are controversial: both IHC and (32)P-post-labeling are non-selective screening methods and fail to provide confirmatory spectral data. Consequently, the identities of the lesions are equivocal. We employed a specific and sensitive liquid chromatography/mass spectrometry (MS) method, to screen tumor-adjacent normal mammary tissue for DNA adducts of PhIP and 4-ABP. Only 1 of 70 biopsy samples obtained from Minneapolis, Minnesota breast cancer patients contained a PhIP-DNA adduct. The level was three adducts per 10(9) nucleotides, a level that is 100-fold lower than the mean level of PhIP adducts reported by IHC or (32)P-post-labeling methods. The occurrence of 4-ABP-DNA adducts was nil in those same breast tissues. Our findings, derived from a specific mass spectrometry method, signify that PhIP and 4-ABP are not major DNA-damaging agents in mammary tissue of USA women and raise questions about the roles of these chemicals in breast cancer.

Role of human CYP1A1 and NAT2 in 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine-induced mutagenicity and DNA adducts

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is carcinogenic in multiple organs and numerous species. Bioactivation of PhIP is initiated by PhIP N(2)-hydroxylation catalysed by cytochrome P450s. Following N-hydroxylation, O-acetylation catalysed by N-acetyltransferase 2 (NAT2) is considered a further possible activation pathway. Genetic polymorphisms in NAT2 may modify cancer risk following exposure. Nucleotide excision repair-deficient Chinese hamster ovary (CHO) cells stably transfected with human cytochrome P4501A1 (CYP1A1) and a single copy of either NAT2*4 (rapid acetylator) or NAT2*5B (slow acetylator) alleles were used to test the effect of CYP1A1 and NAT2 polymorphism on PhIP genotoxicity. Cells transfected with NAT2*4 had significantly higher levels of N-hydroxy-PhIP O-acetyltransferase (p = 0.0150) activity than cells transfected with NAT2*5B. Following PhIP treatment, CHO cell lines transfected with CYP1A1, CYP1A1/NAT2*4 and CYP1A1/NAT2*5B each showed concentration-dependent cytotoxicity and hypoxanthine phosphoribosyl transferase (hprt) mutagenesis not observed in untransfected CHO cells. dG-C8-PhIP was the primary DNA adduct formed and levels were dose dependent in transfected CHO cells in the order: CYP1A1 < CYP1A1 and NAT2*5B < CYP1A1 and NAT2*4, although levels did not differ significantly (p > 0.05) following one-way analysis of variance. These results strongly support activation of PhIP by CYP1A1 with little effect of human NAT2 genetic polymorphism on mutagenesis and DNA damage.

Inhibition of mutagenic PhIP formation by epigallocatechin gallate via scavenging of phenylacetaldehyde

Chemical model investigation showed that both epigallocatechin gallate (EGCG) and its peracetate, which has all the hydroxyl groups acetylated, effectively reduced the formation of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), the most abundant mutagenic heterocyclic amine found in foods. Mechanistic study was subsequently carried out to characterize the probable inhibitory mechanism involved. GC-MS analysis showed that EGCG in only one-fourth molar quantity of phenylalanine reduced formation of phenylacetaldehyde, a key PhIP intermediate by nearly 90%. Its peracetate also showed similar inhibitory activity. This further supported the existence of an antioxidant-independent mechanism contributing to the inhibition of PhIP formation by EGCG. Subsequent LC-MS analyses of samples from a wide range of model systems consisting of PhIP precursors showed the generation of characteristic analytes with molecular weight corresponding to the sum of EGCG and phenylalanine fragment(s) only in models where phenylalanine and EGCG were simultaneously present. An isotope-labeling study revealed that these analytes all contained fragment(s) of phenylalanine origin. Direct reaction employing phenylacetaldehyde and EGCG further confirmed the capability of EGCG to form adducts with phenylacetaldehyde, thus reducing its availability for PhIP formation. Finally, an investigation of the time course of the generation of postulated adduction products supported EGCG as an effective inhibitor of PhIP formation in prolonged heating processes.

Intake of meat, meat mutagens, and iron and the risk of breast cancer in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial

Background:

Epidemiological evidence on meat intake and breast cancer is inconsistent, with little research on potentially carcinogenic meat-related exposures. We investigated meat subtypes, cooking practices, meat mutagens, iron, and subsequent breast cancer risk.

Methods:

Among 52 158 women (aged 55–74 years) in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial, who completed a food frequency questionnaire, 1205 invasive breast cancer cases were identified. We estimated meat mutagen and haem iron intake with databases accounting for cooking practices. Using Cox proportional hazards regression, we calculated hazard ratios (HRs) and 95% confidence intervals (CIs) within quintiles of intake.

Results:

Comparing the fifth to the first quintile, red meat (HR=1.23; 95% CI=1.00–1.51, P trend=0.22), the heterocyclic amine (HCA), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), (HR=1.26; 95% CI=1.03–1.55; P trend=0.12), and dietary iron (HR=1.25; 95% CI=1.02–1.52; P trend=0.03) were positively associated with breast cancer. We observed elevated, though not statistically significant, risks with processed meat, the HCA 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx), mutagenic activity, iron from meat, and haem iron from meat.

Conclusion:

In this prospective study, red meat, MeIQx, and dietary iron elevated the risk of invasive breast cancer, but there was no linear trend in the association except for dietary iron.

Long-term meat intake and risk of breast cancer by oestrogen and progesterone receptor status in a cohort of Swedish women

Red meat intake has been postulated to increase the risk of breast cancer but epidemiologic studies have yielded inconsistent results. Data on meat intake in relation to hormone receptor-defined breast cancer are sparse. We examined the association of meat intake with incidence of breast cancer defined by oestrogen receptor (ER) and progesterone receptor (PR) status in the Swedish Mammography Cohort, a population-based cohort of 61,433 women. Dietary intake was assessed at baseline in 1987-1990 and again in 1997. Cox proportional hazards models were used to estimate relative risks for the association between long-term meat intake and breast cancer risk. During a mean follow-up of 17.4 years, 2952 incident cases of invasive breast cancer were ascertained. We found no association of total red meat, fresh red meat or processed meat intake with breast cancer risk. The multivariate relative risks (95% confidence interval) for the highest quintile of total red meat intake (98 g/d) compared with the lowest quintile (<46 g/d) were 0.98 (0.86-1.12) for overall breast cancer, 1.10 (0.90-1.34) for ER+/PR+ tumours, 0.86 (0.60-1.23) for ER+/PR- tumours and 1.12 (0.70-1.79) for ER-/PR- tumours. Intake of pan-fried meat was positively associated with a risk of ER+/PR- tumours; the multivariate relative risk for the highest compared with the lowest quartile of intake was 1.45 (95% confidence interval 1.03-2.03; P(trend)=0.03). These results do not support an association between red meat intake and overall breast cancer risk but suggest that fried meat intake may increase the risk of ER+/PR- breast cancer.

Meat intake and meat preparation in relation to risk of postmenopausal breast cancer in the NIH-AARP diet and health study

A number of studies have reported that intake of red meat or meat cooked at high temperatures is associated with increased risk of breast cancer, but other studies have shown no association. We assessed the association between meat, meat-cooking methods, and meat-mutagen intake and postmenopausal breast cancer in the NIH-AARP Diet and Health Study cohort of 120,755 postmenopausal women who completed a food frequency questionnaire at baseline (1995-1996) as well as a detailed meat-cooking module within 6 months following baseline. During 8 years of follow-up, 3,818 cases of invasive breast cancer were identified in this cohort. Cox proportional hazards models were used to estimate hazard ratios (HR) and 95% confidence intervals (95% CI). After adjusting for covariates, intake of total meat, red meat, meat cooked at high temperatures, and meat mutagens showed no association with breast cancer risk. This large prospective study with detailed information on meat preparation methods provides no support for a role of meat mutagens in the development of postmenopausal breast cancer.

Meat consumption, heterocyclic amines, NAT2, and the risk of breast cancer

Meat consumption and heterocyclic amine (HCA) intake have been inconsistently associated with breast cancer risk in epidemiologic studies. Genetic variation in N-acetyltransferase2 (NAT2) has been suggested to modify the association of meat intake with breast cancer through its influence on metabolism of HCAs. We examined associations between meat intake, HCA exposure, acetylator genotype, and breast cancer risk in a case-control study of 2,686 case women and 3,508 controls. Women were asked to report their usual intake, cooking method, and preferred doneness of specific meats. We observed no association between total meat, red meat, or chicken with breast cancer risk. Women who consumed 5 or more servings of meat per week had no increased risk of breast cancer compared to women consuming fewer than 2 servings per week (OR = 0.99, 95% CI 0.84-1.15). No statistically significant associations with breast cancer were found for individual HCAs or for total estimated mutagenic activity of meat. Results varied modestly according to menopausal status. There were no statistically significant interactions with NAT2 genotype. Results do not support an important association of HCAs with breast cancer risk, although potential biases in case-control studies should be considered.

GST polymorphism and excretion of heterocyclic aromatic amine and isothiocyanate metabolites after Brassica consumption

Brassica vegetable intake has been associated with decreased risk and well-done meat intake has been associated with increased risk of cancers at multiple organ sites in epidemiologic studies. Experimental studies suggest a role of modulation of phase I and phase II metabolizing enzymes as one mechanism for these associations. Heterocyclic aromatic amines (HAAs) are carcinogens formed in meat that has been cooked to well-done and at high temperatures. Phase I metabolizing enzymes catalyze the activation of HAAs, and phase II metabolizing enzymes serve to detoxify the active carcinogens. The glutathione S-transferases (GSTs) are a family of phase II metabolizing enzymes that are induced by, and act to conjugate, isothiocyanates (ITCs), phytochemicals found in Brassica vegetables. This review summarizes the results of feeding studies in humans that examine effects of polymorphisms in GSTs on ITC metabolite excretion, reviews the evidence for modulation of HAA mutagenicity by ITCs, and discusses the need for feeding studies examining potential interactions among polymorphic genes encoding phase I and phase II metabolizing enzymes, meat intake, and Brassica intake to elucidate their role in cancer etiology.

4-Aminobiphenyl downregulation of NAT2 acetylator genotype-dependent N- and O-acetylation of aromatic and heterocyclic amine carcinogens in primary mammary epithelial cell cultures from rapid and slow acetylator rats

Aromatic and heterocyclic amine carcinogens present in the diet and in cigarette smoke induce breast tumors in rats. N-acetyltransferase 1 (NAT1) and N-acetyltransferase 2 (NAT2) enzymes have important roles in their metabolic activation and deactivation. Human epidemiological studies suggest that genetic polymorphisms in NAT1 and/or NAT2 modify breast cancer risk in women exposed to these carcinogens. p-Aminobenzoic acid (selective for rat NAT2) and sulfamethazine (SMZ; selective for rat NAT1) N-acetyltransferase catalytic activities were both expressed in primary cultures of rat mammary epithelial cells. PABA, 2-aminofluorene, and 4-aminobiphenyl N-acetyltransferase and N-hydroxy-2-amino-1-methyl-6-phenylimidazo[4,5-b] pyridine and N-hydroxy-2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline O-acetyltransferase activities were two- to threefold higher in mammary epithelial cell cultures from rapid than slow acetylator rats. In contrast, SMZ (a rat NAT1-selective substrate) N-acetyltransferase activity did not differ between rapid and slow acetylators. Rat mammary cells cultured in the medium supplemented 24 h with 10muM ABP showed downregulation in the N-and O-acetylation of all substrates tested except for the NAT1-selective substrate SMZ. This downregulation was comparable in rapid and slow NAT2 acetylators. These studies clearly show NAT2 acetylator genotype-dependent N- and O-acetylation of aromatic and heterocyclic amine carcinogens in rat mammary epithelial cell cultures to be subject to downregulation by the arylamine carcinogen ABP.

Do both heterocyclic amines and omega-6 polyunsaturated fatty acids contribute to the incidence of breast cancer in postmenopausal women of the Malmö diet and cancer cohort?

Heterocyclic amines (HAs), formed when meat and fish are cooked at high temperatures, have been linked to mammary gland cancer in rats, and some epidemiological studies indicate increased breast cancer risk by consumption of well-done meat. The epidemiological evidence linking HAs per se to breast cancer is however sparse, especially from prospective studies. Moreover, high-fat diets rich in omega-6 polyunsaturated fatty acids (PUFAs) have produced higher frequencies of HA-induced mammary gland tumors in rats compared to those fed low-fat diets. The aim was to evaluate prospectively if intake of HAs is associated with breast cancer incidence, and if the association is independent of omega-6 PUFA intakes. Among women 50 years or older at baseline from the population-based prospective Malmö Diet and Cancer cohort (n = 11,699), 430 women were diagnosed with incident invasive breast cancer during a mean follow-up of 10.4 years. Information on dietary habits was collected by a modified diet history method. Cox proportional hazards regression estimated hazard ratios (HRs) and 95% confidence intervals (CIs) of breast cancer associated with energy-adjusted intakes of HAs and omega-6 PUFA. Intakes of HAs were not associated with breast cancer incidence (HR, 0.94; 95% CI, 0.69-1.28, for highest compared to lowest quintile). In individuals with low HA intakes, a significant increased risk was observed among those with high intakes of omega-6 PUFAs. In conclusion, intakes of HAs are not associated with breast cancer incidence in this Swedish cohort, but dietary patterns very high in omega-6 PUFA may promote breast cancer development.

New insights in the formation of deoxynucleoside adducts with the heterocyclic aromatic amines PhIP and IQ by means of ion trap MSn and accurate mass measurement of fragment ions

The formation of adducts by reaction of active metabolites of two heterocyclic aromatic amines (NHOH-PhIP and NHOH-IQ) at nucleophilic sites of deoxynucleosides has been studied by LC-MS(n) analyses of the obtained reaction mixtures. Sequential MS(3) experiments were carried out on an ion trap mass spectrometer to gain extensive structural information on each adduct detected in the first MS step. Attribution of ions was supported by accurate mass measurements performed on an Orbitrap mass analyzer. Particular attention was given to ions diagnostic of the linking between the heterocyclic aromatic amine (HAA) and the deoxynucleoside. By this way, the structures of five adducts have been characterized in this study, among which two are new compounds: dG-N7-IQ and dA-N(6)-IQ. No depurinating adduct was found in the reactions investigated therein. As expected, the C8 and N(2) atoms of dG were found as the most reactive sites of deoxynucleosides, resulting in the formation of two different adducts with IQ and one adduct with PhIP. An unusual non-depurinating dG-N7-IQ adduct has been characterized and a mechanism is proposed for its formation on the basis of the reactivity of arylamines. A dA-N(6)-IQ adduct has been identified for the first time in this work, showing that HAAs can generate DNA adducts with bases other than dG.

The cooked meat derived genotoxic carcinogen 2-amino-3-methylimidazo[4,5-b]pyridine has potent hormone-like activity: mechanistic support for a role in breast cancer

The cooked meat-derived heterocyclic amine 2-amino-3-methylimidazo[4,5-b]pyridine (PhIP) is activated by CYP1A2 to the N-hydroxy metabolite, then esterified by acetyl transferase and sulfur transferase into unstable DNA-reactive products that can lead to mutation. The genotoxicity of PhIP has been implicated in its carcinogenicity. Yet, CYP1A2-null mice are still prone to PhIP-mediated cancer, inferring that alternative mechanisms must be operative in tumor induction. PhIP induces tumors of the breast, prostate, and colon in rats and lymphoma in mice. This profile of carcinogenicity is indicative of hormonal involvement. We recently reported that PhIP has potent estrogenic activity inducing transcription of estrogen (E2)-regulated genes, proliferation of E(2)-dependent cells, up-regulation of progesterone receptor, and stimulation of mitogen-activated protein kinase signaling. In this report, we show for the first time that PhIP at doses as low as of 10(-11) mol/L has direct effects on a rat pituitary lactotroph model (GH3 cells) and is able to induce cell proliferation and the synthesis and secretion of prolactin. This PhIP-induced pituitary cell proliferation and synthesis and secretion of prolactin can be attenuated by an estrogen receptor (ER) inhibitor, implying that PhIP effects on lactotroph responses are ERalpha mediated. In view of the strong association between estrogen, progesterone, prolactin, and breast cancer, the PhIP repertoire of hormone-like activities provides further mechanistic support for the tissue-specific carcinogenicity of the chemical. Furthermore, the recent epidemiology studies that report an association between consumption of cooked red meat and premenopausal and postmenopausal human breast cancer are consonant with these observations.

Human breast biomonitoring and environmental chemicals: use of breast tissues and fluids in breast cancer etiologic research

Extensive research indicates that the etiology of breast cancer is complex and multifactorial and may include environmental risk factors. Breast cancer etiology and exposure to xenobiotic compounds, diet, electromagnetic fields, and lifestyle have been the subject of numerous scientific inquiries, but research has yielded inconsistent results. Biomonitoring has been used to explore associations between breast cancer and levels of environmental chemicals in the breast. Research using breast tissues and fluids to cast light on the etiology of breast cancer is, for the most part, predicated on the assumption that the tissue or fluid samples either contain measurable traces of the environmental agent(s) associated with the cancer or that they retain biological changes that are biomarkers of such exposure or precursors of carcinogenic effect. In this paper, we review breast cancer etiology research utilizing breast biomonitoring. We first provide a brief synopsis of the current state of understanding of associations between exposure to environmental chemicals and breast cancer etiology. We then describe the published breast cancer research on tissues and fluids, which have been used for biomonitoring, specifically human milk and its components, malignant and benign breast tissue, nipple aspirate fluid (NAF) and breast cyst fluid. We conclude with a discussion on recommendations for biomonitoring of breast tissues and fluids in future breast cancer etiology research. Both human milk and NAF fluids, and the cells contained therein, hold promise for future biomonitoring research into breast cancer etiology, but must be conducted with carefully delineated hypotheses and a scientifically supportable epidemiological approach.

2-amino-1-methyl-6-phenylimidazo [4,5-b] pyridine-induced DNA adducts and genotoxicity in chinese hamster ovary (CHO) cells expressing human CYP1A2 and rapid or slow acetylator N-acetyltransferase 2

Heterocyclic amine carcinogens such as 2-amino-1-methyl-6-phenylimidazo [4,5-b] pyridine (PhIP) are present in diet and cigarette smoke. Bioactivation in humans includes N-hydroxylation catalyzed by cytochrome P4501A2 possibly followed by O-acetylation catalyzed by N-acetyltransferase 2 (NAT2). Nucleotide excision repair-deficient Chinese hamster ovary (CHO) cells were stably transfected with human CYP1A2 and either NAT2*4 (rapid acetylator) or NAT2*5B (slow acetylator) alleles. CYP1A2 and NAT2 catalytic activities were undetectable in untransfected CHO cell lines. CYP1A2 catalytic activity levels did not differ significantly (P > 0.05) among the CYP1A2-transfected cell lines. Cells transfected with NAT2*4 had significantly higher levels of N-acetyltransferase (P = 0.0001) and N-hydroxy-PhIP O-acetyltransferase (P = 0.0170) catalytic activity than cells transfected with NAT2*5B. PhIP caused dose-dependent decreases in cell survival and significant (P < 0.001) increases in mutagenesis measured at the hypoxanthine phosphoribosyl transferase (hprt) locus in all the CYP1A2-transfected cell lines. Transfection with NAT2*4 or NAT2*5B did not further increase hprt mutagenesis. PhIP-induced hprt mutant cDNAs were sequenced, and 80% of the mutations were single base substitutions at G:C base pairs. dG-C8-PhIP DNA adduct levels were dose-dependent in the order: untransfected < transfected with CYP1A2 < transfected with CYP1A2 and NAT2*5B < transfected with CYP1A2 and NAT2*4. Following incubation with 1.2 microM PhIP, DNA adduct levels were significantly (P < 0.05) higher in CHO cells transfected with CYP1A2/NAT2*4 versus CYP1A2/NAT2*5B. These results strongly support an activation role for CYP1A2 in PhIP-induced mutagenesis and DNA damage and suggest a modest effect of human NAT2 and its genetic polymorphism on PhIP DNA adduct levels.

Cooked meat and risk of breast cancer--lifetime versus recent dietary intake

BACKGROUND

Polycyclic aromatic hydrocarbons (PAHs) and heterocyclic amines (HCAs) are carcinogens formed in or on the surface of well-done meat, cooked at high temperature.

METHODS

We estimated breast cancer risk in relation to intake of cooked meat in a population-based, case-control study (1508 cases and 1556 controls) conducted in Long Island, NY from 1996 to 1997. Lifetime intakes of grilled or barbecued and smoked meats were derived from the interviewer-administered questionnaire data. Dietary intakes of PAH and HCA were derived from the self-administered modified Block food frequency questionnaire of intake 1 year before reference date. Unconditional logistic regression was used to estimate adjusted odds ratios (ORs) and 95% confidence intervals (CIs).

RESULTS

Modest increased risk was observed among postmenopausal, but not premenopausal, women consuming the most grilled or barbecued and smoked meats over the life course (OR = 1.47; CI = 1.12-1.92 for highest vs. lowest tertile of intake). Postmenopausal women with low fruit and vegetable intake, but high lifetime intake of grilled or barbecued and smoked meats, had a higher OR of 1.74 (CI = 1.20-2.50). No associations were observed with the food frequency questionnaire-derived intake measures of PAHs and HCAs, with the possible exception of benzo(alpha)pyrene from meat among postmenopausal women whose tumors were positive for both estrogen receptors and progesterone receptors (OR = 1.47; CI = 0.99-2.19).

CONCLUSIONS

These results support the accumulating evidence that consumption of meats cooked by methods that promote carcinogen formation may increase risk of postmenopausal breast cancer.

Functional characterization of single-nucleotide polymorphisms and haplotypes of human N-acetyltransferase 2

Human N-acetyltransferase 2 (NAT2) is polymorphic in humans and may associate with cancer risk by modifying individual susceptibility to cancers from carcinogen exposure. Since molecular epidemiological studies investigating these associations usually include determining NAT2 single-nucleotide polymorphisms (SNPs), haplotypes or genotypes, their conclusions can be compromised by the uncertainty of genotype-phenotype relationships. We characterized NAT2 SNPs and haplotypes by cloning and expressing recombinant NAT2 allozymes in mammalian cells. The reference and variant recombinant NAT2 allozymes were characterized for arylamine N-acetylation and O-acetylation of N-hydroxy-arylamines. SNPs and haplotypes that conferred reduced enzymatic activity did so by reducing NAT2 protein without changing NAT2 mRNA levels. Among SNPs that reduced catalytic activity, G191A (R64Q), G590A (R197Q) and G857A (G286E) reduced protein half-life but T341C (I114T), G499A (E167K) and A411T (L137F) did not. G857A (G286E) and the major haplotype possessing this SNP (NAT2 7B) altered the affinity to both substrate and cofactor acetyl coenzyme A, resulting in reduced catalytic activity toward some substrates but not others. Our results suggest that coding region SNPs confer slow acetylator phenotype by multiple mechanisms that also may vary with arylamine exposures.

In vitro mutagenicity of anti-inflammatory parsalmide analogues PA7, PA10, and PA31 triggered by biotransformation into hydroxy derivatives

In this study, the mutagenicity of the anti-inflammatory parsalmide [5-amino-N-butyl-2-(2-propynyloxy)-benzamide] analogues PA7 [5-amino-N-butyl-2-cyclohexyloxy-benzamide], PA10 [5-amino-N-butyl-2-phenoxy-benzamide] and PA31 [5-amino-N-butyl-2-(p-tolyloxy)-benzamide] was determined by an Ames Salmonella assay. The experiments were performed by preincubating the compounds in the absence and presence of a post-mitochondrial fraction (S9) of rat liver homogenate from phenobarbital/beta-naphtoflavone treated rats. No mutagenic effect was observed after direct testing (no S9 added) in Salmonella typhymurium strains TA98, TA100, TA102, TA1535 and TA1537. However, in the presence of S9, the test substances triggered mutagenic responses in strains TA100 and TA98. PA31 presented the strongest mutagenic potential. The reversion rates in the presence of PA31 were about 2-19 fold higher than spontaneous mutation rates. In the presence of PA7, the reversion increased 2-14-fold over spontaneous rates. While PA10 showed a relatively mild mutagenic potential, as the number of revertants did not exceed 2.5 times the number of spontaneous mutations. Mass spectrometric analysis of the in vitro biotransformation showed that S9 converted (%), regioselectively, PA7 (19%), PA10 (7%) and PA31 (12%) into hydroxy-derivatives.

Gene expression profiling of chemically induced rat mammary gland cancer

Exposure to carcinogens through diet, the atmosphere and other means is generally regarded as influencing human cancer risk, but the impact of specific environmental carcinogens on human breast cancer incidence is still unknown. We examined whether distinct chemical carcinogens induce a unique transcriptional profile in mammary gland cancer that is characteristic of the etiologic agent. Rat mammary gland cancers (n = 34) were generated by various carcinogens, including the food-derived heterocyclic amines 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, 7,12-dimethylbenz[a]anthracene, N-nitrosomethylurea and 4-aminobiphenyl. The histopathology of the carcinomas was graded using a modified Scarff-Bloom-Richardson scheme and the gene expression profiles in the carcinomas were evaluated on a 10K cDNA microarray. Unsupervised hierarchical clustering analysis revealed two major clusters of carcinomas irrespective of the carcinogenic agent that distinguished two groups with different histopathological parameters (degree of differentiation, nuclear grade, mitotic activity, epithelial cell growth pattern and necrosis). Using class comparison analysis and hierarchical clustering of all carcinomas irrespective of histopathology, gene expression profiles were further shown to be statistically differentially expressed according to the carcinogenic agent. These findings indicate that the transcriptional program in carcinomas is unique to the etiologic agent and can be observed among a diverse set of carcinogens despite variations in carcinoma histopathology. The ability to use microarray analysis to discern an etiology-specific profile among a pathologically heterogeneous group of breast carcinomas may ultimately be valuable in determining the role of environmental chemical carcinogens in human breast cancer risk.

Susceptibility of rats to mammary gland carcinogenesis by the food-derived carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) varies with age and is associated with the induction of differential gene expression

2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), a heterocyclic amine found in cooked meat, induces mammary gland cancer when administered to adolescent female rats (43-day-old). In contrast, mature virgin rats (150-day-old) were resistant to mammary carcinogenesis by PhIP. To explore the possible mechanisms for the age-related differences in susceptibility, PhIP-DNA adduct levels, mutations, and gene expression were examined in glands from 43-day and 150-day-old PhIP-treated rats. In rats of different ages, PhIP-DNA adduct levels detected by the (32)P-post-labeling assay and mutant frequency measured in the lacI reporter gene of Big Blue rats were not statistically different. PhIP-DNA adduct levels, adduct removal, and mutation burden did not appear to account for the variation in carcinogen susceptibility with age. However, cDNA microarray analysis indicated that PhIP treatment differentially altered the profile of gene expression in glands from 43-day-old and 150-day-old rats. In 150-day-old rats, PhIP enhanced the expression of genes associated with differentiation (eg, beta-casein, kappa-casein, whey acidic protein) and induced morphological differentiation. In contrast, in 43-day-old rats, PhIP inhibited the expression of differentiation genes and enhanced cellular proliferation. From 3 hours to 6 weeks after PhIP dosing, the number of clones showing altered expression declined more than 50% in 150-day-old rats but increased fourfold in 43-day-old rats (29 clones versus 194, respectively) suggesting that PhIP induced a cascade of gene expression alterations only in susceptible rats. Genes showing altered expression specifically in 43-day-old rats included the Ras superfamily genes and genes associated with protein synthesis/degradation (lysosomal proteins, heat shock proteins, and proteasomes). The microarray data support the notion that the mechanism of age-dependent susceptibility to mammary gland cancer is largely associated with differential responses in expression of genes involved in cellular differentiation, proliferation, and protein homeostasis.

In utero effects of chemicals on reproductive tissues in females

Chemicals found in the environment as industrial byproducts or pollutants as well as those that are prescribed or part of our daily lives can have multiple effects on the human body. The manner in which we are exposed, and the levels we are exposed to are significant contributing factors. Adults have the bodily defense mechanisms in place to combat exposures to adverse toxicants and general pollution at a variety of levels. However, developing organisms may not have adequate defense mechanisms, and toxicants can have a significant effect on their health and development. In this review, we take particular note of the toxicities of chemicals on the developing female reproductive system as a result of in utero exposure. Environmental and prescribed chemicals such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), diethylstilbestrol, and genistein, as well as others, will be reviewed for their in utero toxicity in the neuroendocrine system, the ovary, oviduct, placenta, uterus, vagina, cervix, and mammary gland.

Mutagenic activity and heterocyclic amine carcinogens in commercial pet foods

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

Contrasting effects of non-starch polysaccharide and resistant starch-based diets on the disposition and excretion of the food carcinogen, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), in a rat model

It has commonly been believed that increasing fibre in the diet should reduce the incidence of cancers, especially those of the colon and rectum. The earliest definitions of dietary fibre restricted the term to plant cell walls in which non-starch polysaccharides are key chemical components. However, new definitions encompass a wider range of materials, including starches resistant to digestion in the colon (resistant starches). Nevertheless, most definitions require that "dietary fibres" show physiological effects considered beneficial against cancer, including enhanced laxation and faecal bulking. On theoretical grounds, such properties might be expected to dilute the concentration of any carcinogen present and move it more rapidly through the colon, thereby reducing bioavailability. We have compared the properties of two dietary fibre preparations that are primarily non-starch polysaccharides with two resistant starch preparations for effects on carcinogen disposition in a rodent model. Although both preparations enhanced laxation and faecal bulking, only the non-starch polysaccharide preparation reduced carcinogen biovailability. Indeed, carcinogen biovailability was significantly enhanced by resistant starch. We suggest that there may be fundamental differences in the manner by which non-starch polysaccharides or resistant starches affect carcinogen disposition, and express concern that the events seen with the resistant starches [RS] are unlikely to be beneficial with respect to protection against cancer by exogenous carcinogens. Furthermore, the data reveal that the observation of enhanced laxation and faecal bulking does not necessarily imply a reduction in carcinogen bioavailability.

Highlights of the eighth international conference on carcinogenic/mutagenic N-substituted aryl compounds

Research in the 20th century initially identified arylamines as causative factors in occupational carcinogenesis, especially bladder cancer, and subsequently identified arylamines as a major class of mutagens/carcinogens in the environment and diet that are potential risk factors in a variety of human cancers. Current research focuses on understanding of mechanisms of arylamine carcinogenesis, such as the role of metabolic processing, DNA adduct formation, and mutagenesis, and learning more about the molecular alterations in carcinomas induced by these compounds. Furthermore, research to identify human exposures, including developing more sensitive methods for analyzing environmental samples and identifying suitable biomarkers are important aspects of contemporary investigations. In addition, better evaluation of the risk of these compounds in human cancer especially with regard to the impact of genetic polymorphisms is a major focus of research in this field. Although current population studies have sometimes been described as equivocal, improved tools for epidemiology, refined human biomonitoring methods and collaborative endeavors to study multiple population groups now provide a better means to ultimately define the role of arylamines in human carcinogenesis. The purpose of the Eighth International Conference on Carcinogenic/Mutagenic N-Substituted Aryl Compounds, held in Washington, DC, 12-14 November 2001, was to explore the current scope of studies on arylamine carcinogenesis among scientists in basic research and epidemiology and to discuss future research priorities. With the intent of providing a view to the current field of research on aromatic amines, this review presents a synopsis of the Proceedings of the Eighth International Conference and highlights the manuscripts contained in this special issue of Mutation Research.