Enhancement by acrylamide of N-methyl-N-nitrosourea-induced rat mammary tumor development—possible application for a model to detect co-modifiers of carcinogenesis

Feeding a High-Fat Diet for a Limited Duration Increases Cancer Incidence in a Breast Cancer Model

High-fat intake by young Asian women impacts the risk of breast cancer. Understanding the underlying molecular mechanisms may be essential for disease prevention in Asia as well as globally. We aimed to examine the effects of corn oil- and animal fat-based high-fat diets (32.9 and 31.4%, respectively, of fat energy ratio as compared to 12.3% in the standard diet) on mammary carcinogenesis and alterations in gene expression and epigenetic statuses in the mammary gland during the growth stages in a rat model. An increased incidence of carcinomas was observed after the cessation of high-fat feeding. In addition, rapid tumor growth and elevations in Celsr2 expression, which may be a result of DNA hypomethylation patterns in the 3' untranslated region of the gene were noted in the animal fat group. In the human breast carcinoma cell line MCF7, a marginal decrease in cell viability was observed following the knockdown of Celsr2, suggesting that the animal fat-associated risk of cancer is partly due to the deregulation of mammary cell proliferation via non-metabolic gene functions. The present results will contribute to the development of strategies for controlling the food-associated risk of breast cancer, particularly in younger age groups.

The association between biomarkers of acrylamide and cancer mortality in U.S. adult population: Evidence from NHANES 2003-2014

The association between acrylamide (AA) and the development of cancer has been extensively discussed but the results remained controversial, especially in population studies. Large prospective epidemiological studies on the relationship of AA exposure with cancer mortality were still lacking. Therefore, we aimed to assess the association between AA biomarkers and cancer mortality in adult population from National Health and Nutrition Examination Survey (NHANES) 2003-2014. We followed 3717 participants for an average of 10.3 years. Cox regression models with multivariable adjustments were performed to determine the relationship of acrylamide hemoglobin adduct (HbAA) and glycidamide hemoglobin adduct (HbGA) with cancer mortality. Mediation analysis was conducted to demonstrate the mediated role of low-grade inflammation score (INFLA-score) in this correlation. Compared with the lowest quintile, participants with the highest quintile of HbAA, HbGA and HbAA+HbGA had increased cancer mortality risk, and the hazard ratios(HRs) were 2.07 (95%CI:1.04-4.14) for HbAA, 2.39 (95%CI:1.29-4.43) for HbGA and 2.48 (95%CI:1.28-4.80) for HbAA+HbGA, respectively. And there was a considerable non-linearity association between HbAA and cancer mortality (pfor non-linearity = 0.0139). We further found that increased INFLA-score significantly mediated 71.67% in the effect of HbGA exposure on increased cancer mortality risk. This study demonstrates that hemoglobin biomarkers of AA are positively associated with cancer mortality in adult American population and INFLA-score plays a mediated role in this process. Our findings can raise public awareness of environmental and dietary exposure to acrylamide and remind people to refrain from smoking or having acrylamide-rich foods.

Twist1 was detected in mesenchymal cells of mammary fibroadenoma and invasive components of breast carcinoma in rats

Fibroadenoma (FA) is a common mammary fibroepithelial tumor. The tumor size of the FA is increased by estrogen, progesterone, prolactin, and pregnancy, whereas it decreases after menopause. These observations in humans indicate that FA is hormone dependent. In rats, the most common mammary neoplasm is also FA. Expression levels of Twist1, a transcriptional regulator of epithelial-mesenchymal transition, were examined in paraffin-embedded tissue sections of an experimental rat breast model to find physiological alternations coincident with reproductive hormonal changes. Twenty-three Fischer 344/Brown Norway F1 hybrid rats were used as 14‐ to 16-week-old adolescent rats (n=3), pregnant rats (n=4), and lactating rats (n=6) in addition to rats over 100-weeks-old that exhibited aging (n=3) and FA (n=7). Seventy-six cases of chemically induced breast carcinoma and two cases of FA in Sprague Dawley rats were also examined. Using tissue sections, we observed that Twist1-positive mesenchymal cells were predominantly located in the periductal region in adolescent and pregnant rats and in the terminal duct lobular unit in pregnant and elderly rats. Twist1 was also expressed diffusely in the mesenchymal cells of FA rats. Twist1-positive cancer-associated mesenchymal cells were found more frequently in the invasive components of breast carcinomas than in intraductal components. The expressions of Twist1 in mesenchymal cells were induced by physiological and pathological stimuli, suggesting the biological role of Twist1 in tissue structure. Further study may reveal the role of Twist1 in mesenchymal cells of mammary glands in rats.

Horseradish extract promotes urinary bladder carcinogenesis when administered to F344 rats in drinking water

Horseradish extract (HRE), consisting mainly of a mixture of allyl isothiocyanate and other isothiocyanates, has been used as a food additive. To evaluate the potential hazards of HRE, a 104-week chronic study, a 2-week analysis of cell proliferation in the urinary bladder and a medium-term promotion bioassay of HRE were conducted with administration at concentrations of up to 0.04% HRE in the drinking water to male F344 rats. In the 104-week chronic study with 32 male rats per group, no treatment-related increases in the incidences of neoplastic lesions in any organ, including urinary bladder, were observed, except for simple hyperplasia in the urinary bladder in rats treated with HRE at concentrations of more than 0.01% (5.0 mg kg^-1 body weight day^-1 ). In the promotion study, HRE treatment after N-butyl-N-(4-hydroxybutyl)nitrosamine initiation caused a clear increase in papillary or nodular hyperplasia, papilloma, and urothelial carcinoma of the urinary bladder in the groups given HRE for 13 weeks at doses higher than 0.005%, 0.01%, and 0.04% (2.7, 5.4 and 20.5 mg kg^-1 body weight day^-1 ), respectively. In the 2-week cell proliferation analysis, treatment with HRE at concentrations greater than 0.005% (3.9 mg kg^-1 body weight day^-1 ) caused transient increases in 5-bromo-2'-deoxyuridine labeling indices in the urothelium. Although clear tumor induction was not observed, administration of relatively low-dose HRE increased cell proliferation in the urothelium and exerted obvious promoting effects on rat urinary bladder carcinogenesis. Further studies are needed to elucidate the mode of action of HRE in the rat urinary bladder to facilitate data extrapolation from the present study and provide insights into risk assessment. Copyright © 2017 John Wiley & Sons, Ltd.

Chronic mesothelial reaction and toxicity of potassium octatitanate fibers in the pleural cavity in mice and F344 rats

Fiber‐shaped particles of potassium octatitanate (tradename TISMO; chemical formula K₂O·6TiO₂), which are morphologically similar to asbestos particles, were shown to induce severe proliferative reactions in the pleural mesothelium in a previous experiment carried out over 21 weeks. The present study aims to determine whether these fibers induce malignant mesotheliomas in rodents, and to examine chronic toxicity induced. Additionally, we investigated the specific differences observable between the biological responses to the direct infusion of the fibers alone into the pleural cavity and those induced by the co‐administration of the fibers with a known carcinogen. To detect the induction of malignant pleural mesotheliomas, two experiments were undertaken. In Experiment 1, four strains of mice, A/J, C3H, ICR, and C57BL, were examined for 52 weeks after experimental treatment with TISMO. In Experiment 2, the F344 rats were treated with TISMO alone, the lung carcinogen N‐bis (2‐hydroxypropyl) nitrosamine (DHPN) alone, both TISMO and DHPN, or left untreated and were then examined for 52 weeks. In this experiment, malignant lesion induction was expected in the co‐administration group. TISMO fibers were observed in the alveoli, indicating penetration through the visceral pleura in mice and rats. The histopathological detection of TISMO fibers in the liver and kidneys of mice and rats indicated migration of the fibers out of the pleural cavity. Atypical mesothelial cells with severe pleural proliferation were observed, but malignant mesotheliomas were not detected. Among the rats, there were no observed malignant alterations in the mesothelium induced by DHPN–TISMO co‐administration.

Effect of Thyroid Function on MNU-Induced Mammary Carcinogenesis

Mammary cancer is a disease that affects many women. Extensive research has been conducted to elucidate which variables are involved in the development of this cancer. Studies have highlighted thyroid function as a modulator of tumor growth and development. Thyroxine and 3,3',5-triiodothyronine are responsible for regulating the development, differentiation, homeostasis, and metabolism of cells in the body including mammary tissue. Thyroid hormones also have estrogen-like effects on mammary cancer cell growth by regulating the estrogen receptor. The present study was designed to determine whether medically induced hyperthyroidism increases the multiplicity, prevalence, and mammary tumor burden in rats; and to elucidate whether surgically induced hypothyroidism conversely attenuates the rate of mammary cancer cell growth. Female Sprague-Dawley rats were randomly divided into three groups (euthyroid-control, hyperthyroid, and hypothyroid). Hyperthyroidism was induced via oral administration of levothyroxine; whereas, hypothyroidism was induced by thyroidectomy. Mammary carcinogenesis was induced with a single intraperitoneal injection of N-methyl-N-nitrosurea (MNU). Rats were sacrificed at 38 weeks, and the mammary tumors were excised, fixed for histology and analyzed. Analysis included evaluation of malignancy and immunohistochemistry for ER. MNU-induced mammary carcinogenesis among the groups resulted in a significant difference in tumor burden. The hyperthyroid group had a statistically higher tumor burden than did the euthyroid group, and the hypothyroid group had no tumors of mammary tissue origin at 38 weeks. All excised mammary tumors were ER alpha negative. These data support the hypothesis that thyroid function is one of potentially many factors that contribute to modulation of MNU-induced mammary tumor growth.

N-Methyl-N-nitrosourea as a mammary carcinogenic agent

The administration of chemical carcinogens is one of the most commonly used methods to induce tumors in several organs in laboratory animals in order to study oncologic diseases of humans. The carcinogen agent N-methyl-N-nitrosourea (MNU) is the oldest member of the nitroso compounds that has the ability to alkylate DNA. MNU is classified as a complete, potent, and direct alkylating compound. Depending on the animals' species and strain, dose, route, and age at the administration, MNU may induce tumors' development in several organs. The aim of this manuscript was to review MNU as a carcinogenic agent, taking into account that this carcinogen agent has been frequently used in experimental protocols to study the carcinogenesis in several tissues, namely breast, ovary, uterus, prostate, liver, spleen, kidney, stomach, small intestine, colon, hematopoietic system, lung, skin, retina, and urinary bladder. In this paper, we also reviewed the experimental conditions to the chemical induction of tumors in different organs with this carcinogen agent, with a special emphasis in the mammary carcinogenesis.

Negligible colon cancer risk from food-borne acrylamide exposure in male F344 rats and nude (nu/nu) mice-bearing human colon tumor xenografts

Acrylamide, a possible human carcinogen, is formed in certain carbohydrate-rich foods processed at high temperature. We evaluated if dietary acrylamide, at doses (0.5, 1.0 or 2.0 mg/kg diet) reflecting upper levels found in human foods, modulated colon tumorigenesis in two rodent models. Male F344 rats were randomized to receive diets without (control) or with acrylamide. 2-weeks later, rats in each group received two weekly subcutaneous injections of either azoxymethane (AOM) or saline, and were killed 20 weeks post-injections; colons were assessed for tumors. Male athymic nude (nu/nu) mice bearing HT-29 human colon adenocarcinoma cells-derived tumor xenografts received diets without (control) or with acrylamide; tumor growth was monitored and mice were killed 4 weeks later. In the F344 rat study, no tumors were found in the colons of the saline-injected rats. However, the colon tumor incidence was 54.2% and 66.7% in the control and the 2 mg/kg acrylamide-treated AOM-injected groups, respectively. While tumor multiplicity was similar across all diet groups, tumor size and burden were higher in the 2 mg/kg acrylamide group compared to the AOM control. These results suggest that acrylamide by itself is not a "complete carcinogen", but acts as a "co-carcinogen" by exacerbating the effects of AOM. The nude mouse study indicated no differences in the growth of human colon tumor xenografts between acrylamide-treated and control mice, suggesting that acrylamide does not aid in the progression of established tumors. Hence, food-borne acrylamide at levels comparable to those found in human foods is neither an independent carcinogen nor a tumor promoter in the colon. However, our results characterize a potential hazard of acrylamide as a colon co-carcinogen in association with known and possibly other environmental tumor initiators/promoters.

Critical review of dose-response options for F344 rat mammary tumors for acrylamide - additional insights based on mode of action

Previous risk assessment reviews analyzed the potential for dietary acrylamide to increase breast cancer risk. Here, we critically review acrylamide animal bioassay data on mammary tumors for human relevance. We applied a systematic evaluation using reasonable standards of scientific certainty and a systematic weight of evidence (WOE) approach to evaluate several hypothesized modes of action (MOA), including (1) genotoxicity related to glycidamide formation and oxidative stress, (2) endocrine effects due to age-related hyperprolactinemia or secondary to neurotoxicity, and (3) epigenetic effects. We conclude that the appropriate approach for low-dose extrapolation of the rat mammary tumors can be narrowed to two options: (1) linear low-dose extrapolation (i.e., based on a MOA of mutagenicity from direct DNA interaction) from a point of departure (POD) for the combined incidence of adenomas and adenocarcinomas, since these tumor types are related; or (2) non-linear extrapolation, using uncertainty factors to estimate a Reference Dose (RfD) from a POD for tumor promotion derived using the combined fibroadenoma, adenoma and adenocarcinoma data. Non-linear extrapolation is used in the latter approach because these combined tumor types are unlikely to be exclusively caused by mutagenicity. Comparison of the WOE for each alternative MOA indicates that a non-linear approach (option 2) is more appropriate for evaluation of acrylamide-induced mammary tumors; a linear approach (option 1) is shown for comparison.

Dietary acrylamide does not increase colon aberrant crypt foci formation in male F344 rats

Acrylamide, a known rodent and a probable human carcinogen, is spontaneously formed in foods cooked at high temperature. We studied the role of dietary acrylamide in modulating the early stages of colon carcinogenesis and assessed if dietary fat level was critical in altering the effects of acrylamide. Male F344 rats were subcutaneously injected with azoxymethane and were simultaneously randomized into 8 dietary groups (n=8 rats/group). Diets were based on AIN-93G semi-synthetic formula modified to contain either low fat (7% corn oil) or high fat (23.9% corn oil) and acrylamide at 0, 5, 10 or 50 mg/kg diet (wt/wt). All rats received the experimental diets ad libitum for 8 weeks, after which they were killed and their colons assessed for aberrant crypt foci (ACF), putative precancerous lesions. Irrespective of dietary fat level, rats with the highest tested dose of acrylamide (50 mg/kg diet) had significantly lower total ACF (p<0.05) and lower large ACF (those with 4 or more crypts/focus; p<0.001) compared with their respective controls (0 mg/kg diet). A significantly lower number of large ACF (p=0.046) was noted in rats treated with 10 mg/kg diet acrylamide exclusively in the high fat group, compared to the high fat control. This short-term bio-assay to test carcinogenicity of dietary acrylamide in the colon demonstrates that acrylamide, when administered through the diet at doses known to cause rat tumors, does not increase the risk of developing azoxymethane-induced precancerous lesions of the colon in rats. On the contrary, a high dose of dietary acrylamide decreased the growth of precancerous lesions in both low and high fat diet regimens in this model.

Lack of modifying effects of prepubertal exposure to acrylamide (AA) on N-methyl-N-nitrosourea (MNU)-induced multi-organ carcinogenesis in F344 rats

Acrylamide (AA) has been reported to be formed in fried and baked foods with various concentrations, and exposure levels to AA from cooked foods in children are estimated to be higher than those in adults. In order to evaluate the carcinogenicity of AA exposure during childhood, we conducted a medium-term carcinogenicity study with prepubertal administration of AA followed by treatments of a multi-organ-targeted genotoxic carcinogen and a promoting agent for thyroid carcinogenesis in rats. A total of 36 postpartum F344 rats were given drinking water containing AA at 0, 20, 40 or 80 ppm for 3 weeks during the lactation period, and their weaned offspring received the same AA-containing water for 3 more weeks. Offspring were then injected with N-methyl-N-nitrosourea (MNU; 40 mg/kg body weight, i.p.) once at week 7 after birth. Half the animals of the 0 and 40 ppm groups were additionally treated with the anti-thyroid agent sulfadimethoxine (SDM; 125 ppm) in the drinking water thereafter. Offspring were subjected to complete necropsy at week 50. All the major organs and macroscopic abnormalities were excised and examined histopathologically. There was no significant difference in the incidences of hyperplastic and neoplastic lesions in the target organs of AA and/or MNU, such as the brain, spinal cord, pituitary gland, thyroid, adrenal glands, uterus, mammary glands, clitoral gland and tunica vaginalis. In conclusion, no significant modifying actions of AA on MNU-induced multi-organ carcinogenesis were exhibited in any organs of rats when exposed prepubertally under the present experimental conditions.

Increased H-ras mutation frequency in mammary tumors of rats initiated with N-methyl-N-nitrosourea (MNU) and treated with acrylamide

We recently demonstrated the incidence and multiplicity of N-methyl-N-nitrosourea (MNU)-induced mammary tumors to be increased by administration of acrylamide (AA) in post-initiation in rats. In the present study, to clarify the mechanisms of enhancement, H-ras gene mutations in mammary tumors induced in MNU-initiated rats with or without subsequent AA administration were investigated. Frequencies of mutations in codon 12 from GGA to GAA were significantly (p < 0.05) higher in rats with AA administration (82%, 23 out of 28 tumors) as compared to those without AA (50%, 9 out of 18 tumors), but the latency and volume of H-ras mutation-harboring tumors were similar to those of the mutation-lacking tumors. No mutations in codons 13 or 61 were detected in either treatment groups. The results thus indicate that H-ras gene mutations in codon 12 play a pivotal role in initiation of carcinogenesis and it appears possible that AA administration may selectively co-stimulate and/or maintain initiated cells via other genomic or non-genomic events in MNU-treated rats.

Quantitation of mercapturic acids from acrylamide and glycidamide in human urine using a column switching tool with two trap columns and electrospray tandem mass spectrometry

A sensitive and specific electrospray tandem mass spectrometry method using a column switching unit with two trap columns was established to quantify the mercapturates (MAs) of acrylamide (AA) and glycidamide (GA) in human urine. A specially endcapped material was applied for trapping the hydrophilic MAs and a pre-trap column was used to remove lipophilic compounds from the directly injected urine to protect the trap column. The limits of quantitation for AA-MA and GA-MA in urine were 0.5 microg/L and 1 microg/L, respectively. Urine was spiked with deuterated internal standards and injected directly into LC-MS/MS. Urine of smokers (n=13) revealed the highest concentrations of AA-MA and GA-MA in the range of 61-706 microg/L and 5-54 microg/L, respectively. Lower levels for AA-MA (14-102 microg/L) and GA-MA (1-11 microg/L) were detected in non-smokers (n=13).

Acrylamide, an in vivo thyroid carcinogenic agent, induces DNA damage in rat thyroid cell lines and primary cultures

Chronic treatment of rats with acrylamide induces various tumors among which thyroid tumors are the most frequent. The aim of the present study was to develop an in vitro model of acrylamide action on thyroid cells to allow the investigation of the mechanism of this tumorigenic action. The first part of the study considered as targets, characteristics of thyroid metabolism, which could explain the thyroid specificity of acrylamide action: the cAMP mitogenic effect and the important H2O2 generation by thyroid cells. However, acrylamide did not modulate H2O2 or cAMP generation in the thyroid cell models studied. No effect on thyroid cell proliferation was observed in the rat thyroid cell line FRTL5. On the other hand, as shown by the comet assay, acrylamide induced DNA damage, as the positive control H2O2 in the PC Cl3 and FRTL5 rat thyroid cell lines, as well as in thyroid cell primary cultures. The absence of effect of acrylamide on H2AX histone phosphorylation suggests that this effect does not reflect the induction of DNA double strand breaks. DNA damage leads to the generation of mutations. It is proposed that such mutations could play a role in the carcinogenic effect of acrylamide. The mechanism of this effect can now be studied in this in vitro model.