Mutagens in human breast lipid and milk: the search for environmental agents that initiate breast cancer

Micronucleated Erythrocytes in Peripheral Blood from Neonate Rats Exposed by Breastfeeding to Cyclophosphamide, Colchicine, or Cytosine-Arabinoside

Genotoxic exposure to chemical substances is common, and nursing mothers could transmit harmful substances or their metabolites to their offspring through breast milk. We explored the possibility of determining genotoxic effects in the erythrocytes of breastfeeding rat pups whose mothers received a genotoxic compound while nursing. Ten groups of female rats and five pups per dam were studied. The control group received sterile water, and the experimental groups received one of three different doses of cyclophosphamide, colchicine, or cytosine-arabinoside. Blood smears were prepared from samples taken from each dam and pup every 24 h for six days. There were increased numbers of micronucleated erythrocytes (MNEs) and micronucleated polychromatic erythrocytes (MNPCEs) in the samples from pups in the experimental groups (P < 0.02) and increased MNPCE frequencies in the samples from the dams (P < 0.05). These results demonstrate the vertical transmission of the genotoxic effect of the compounds tested. In conclusion, assessing MNEs in breastfeeding neonate rats to assess DNA damage may be a useful approach for identifying genotoxic compounds and/or cytotoxic effects. This strategy could help in screening for therapeutic approaches that are genotoxic during the lactation stage and these assessments might also be helpful for developing preventive strategies to counteract harmful effects.

Identification of mammary epithelial cells subject to chronic oxidative stress in mammary epithelium of young women and teenagers living in USA: implication for breast carcinogenesis

Current knowledge of changes in the mammary epithelium relevant to breast carcinogenesis is limited to when histological changes are already present because of a lack of biomarkers needed to identify where such molecular changes might be ongoing at earlier during the of decades-long latent stages of breast carcinogenesis. Breast reduction tissues from young women and teenagers, representative of USA's high breast cancer incidence population, were studies using immunocytochemistry and targeted PCR arrays in order to learn whether a marker of chronic oxidative-stress [protein adducts of 4-hydroxy-2-nonenal (4HNE)] can identify where molecular changes relevant to carcinogenesis might be taking place prior to any histological changes. 4HNE-immunopositive (4HNE+) mammary epithelial cell-clusters were identified in breast tissue sections from most women and from many teenagers (ages 14-30 y) and, in tissues from women ages 17-27 y with many vs. few 4HNE+ cells, the expression of 30 of 84 oxidative-stress associated genes was decreased and only one was increased > 2-fold. This is in contrast to increased expression of many of these genes known to be elicited by acute oxidative-stress. The findings validate using 4HNE-adducts to identify where molecular changes of potential relevance to carcinogenesis are taking place in histologically normal mammary epithelium and highlight differences between responses to acute vs. chronic oxidative-stress. We posit that the altered gene expression in 4HNE+ tissues reflect adaptive responses to chronic oxidative-stress that enable some cells to evade mechanisms that have evolved to prevent propagation of cells with oxidatively-damaged DNA and to accrue heritable changes needed to establish a cancer.

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.

Umbuzeiro G, DeMarini DM. The Salmonella mutagenicity assay: the stethoscope of genetic toxicology for the 21st century

OBJECTIVES

According to the 2007 National Research Council report Toxicology for the Twenty-First Century, modern methods (e.g., "omics," in vitro assays, high-throughput testing, computational methods) will lead to the emergence of a new approach to toxicology. The Salmonella mammalian microsome mutagenicity assay has been central to the field of genetic toxicology since the 1970s. Here we document the paradigm shifts engendered by the assay, the validation and applications of the assay, and how the assay is a model for future in vitro toxicology assays.

DATA SOURCES

We searched PubMed, Scopus, and Web of Knowledge using key words relevant to the Salmonella assay and additional genotoxicity assays.

DATA EXTRACTION

We merged the citations, removing duplicates, and categorized the papers by year and topic.

DATA SYNTHESIS

The Salmonella assay led to two paradigm shifts: that some carcinogens were mutagens and that some environmental samples (e.g., air, water, soil, food, combustion emissions) were mutagenic. Although there are > 10,000 publications on the Salmonella assay, covering tens of thousands of agents, data on even more agents probably exist in unpublished form, largely as proprietary studies by industry. The Salmonella assay is a model for the development of 21st century in vitro toxicology assays in terms of the establishment of standard procedures, ability to test various agents, transferability across laboratories, validation and testing, and structure-activity analysis.

CONCLUSIONS

Similar to a stethoscope as a first-line, inexpensive tool in medicine, the Salmonella assay can serve a similar, indispensable role in the foreseeable future of 21st century toxicology.

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.

Prenatal Multivitamin Supplementation and Rates of Pediatric Cancers: A Meta-Analysis

Prenatal supplementation of folic acid has been shown to decrease the risk of several congenital malformations. Several studies have recently suggested a potential protective effect of folic acid on certain pediatric cancers. The protective role of prenatal multivitamins has not been elucidated. We conducted a systematic review and meta-analysis to assess the potential protective effect of prenatal multivitamins on several pediatric cancers. Medline, PubMed, EMBASE, Toxline, Healthstar, and Cochrane databases were searched for studies published in all languages from 1960 to July 2005 on multivitamin supplementation and pediatric cancers. References from all articles collected were reviewed for additional articles. Two blinded independent reviewers assessed the articles for inclusion and exclusion. Rates of cancers in women supplemented with multivitamins were compared with unsupplemented women using a random effects model. Sixty-one articles were identified in the initial search, of which, seven articles met the inclusion criteria. There was an apparent protective effect for leukemia (odds ratio (OR)=0.61, 95% confidence interval (CI)=0.50-0.74), pediatric brain tumors (OR=0.73, 95% CI=0.60-0.88) and neuroblastoma (OR=0.53, 95% CI=0.42-0.68). In conclusion, maternal ingestion of prenatal multivitamins is associated with a decreased risk for pediatric brain tumors, neuroblastoma, and leukemia. Presently, it is not known which constituent(s) among the multivitamins confer this protective effect.

Signs of proinflammatory/genotoxic switch (adipogenotoxicosis) in mammary fat of breast cancer patients: Role of menopausal status, estrogens and hyperglycemia

The abundance of fat tissue surrounding normal and malignant epithelial mammary cells raises the questions whether such "adipose milieu" is important in the local proinflammatory/genotoxic shift, which apparently promotes tumor development and worsens prognosis, and what conditions stimulate this shift, or "adipogenotoxicosis." We studied 95 mammary fat samples from 70 postmenopausal and 25 premenopausal breast cancer (BC) patients at a distance of 1.5-2.0 cm from tumors. The levels of leptin, adiponectin, TNFalpha and IL-6 release after 4-hr incubation of the samples were evaluated with ELISA, nitric oxide (NO) production by Griess reaction and lipid peroxidation by determination of thiobarbiturate-reactive products (TBRP). Infiltration of fat with macrophages (CD68-positive cells) and expression of cytochrome P450 1B1/estrogen 4-hydroxylase (CYP1B1) were detected by immunohistochemistry. Aromatase (CYP19) activity in mammary fat was measured by (3)H(2)O release from (3)H-1beta-androstenedione. In the postmenopausal BC patients, NO and TNFalpha production by adipose tissue explants increased independent of BMI and in parallel with decreasing leptin and, especially, adiponectin release. In the premenopausal patients, higher CYP1B1 expression and TBRP level were found in mammary fat, while higher aromatase activity was combined with higher CYP1B1 expression as well as NO and IL-6 production. In the postmenopausal group, impaired glucose tolerance was associated with higher IL-6 release production by fat and with higher IL-6/adiponectin ratio. Thus, signs of adipogenotoxicosis in mammary fat can be found in both pre- and postmenopausal BC patients. This condition is likely being maintained through estrogen- and glucose-related factors and mechanisms presumably associated with less favorable types of hormonal carcinogenesis.

The expression of xenobiotic-metabolizing enzymes in human prostate and in prostate epithelial cells (PECs) derived from primary cultures

BACKGROUND

Dietary heterocyclic amines (HCAs) are carcinogenic in rodent prostate requiring activation by enzymes such as cytochrome P450 (CYP) and N-acetyltransferase (NAT).

METHODS

We investigated by Western blotting and immunohistochemistry the expression of CYP1A1, CYP1A2, and NAT1 in human prostate and in prostate epithelial cells (PECs) derived from primary cultures and tested their ability to activate the dietary carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and its N-hydroxy metabolite (N-OH-IQ) to DNA-damaging moieties.

RESULTS

Western blotting identified CYP1A1, CYP1A2, and NAT1. Immunohistochemistry localized NAT1 to the cytoplasm of PECs. Inter-individual variation was observed in the expression levels of CYP1A1, 1A2, and NAT1 (11, 75, and 35-fold, respectively). PECs expressed CYP1A1 and NAT1 but not CYP1A2. When incubated with IQ or N-OH-IQ, PECs formed DNA adducts indicating their ability to metabolically activate these compounds.

CONCLUSIONS

Prostate cells possess the capacity to activate dietary carcinogens. PECs may provide a useful model system to study their role in prostate carcinogenesis.

Aetiology of childhood leukemia

Leukemia is the most common cancer to affect children, accounting for approximately a third of all childhood cancers. The major morphological subtypes of leukemia, acute lymphoblastic leukemia (ALL), and acute myeloblastic leukemia (AML), are characterized by chromosomal translocations involving over 200 genes including mixed lineage leukemia (MLL), TEL, and AML1. Chromosomal translocations involving the MLL gene at 11q23 are a common feature of infant acute leukemia, found in up to 80% of all cases, and there is strong evidence that rearrangements involving the MLL gene or the TEL-AML1 gene fusion can originate in utero. As with most other cancers, the mechanism by which leukemia arises is likely to involve gene-environment interactions. Accordingly, it is important to identify exposures that cause DNA damage and induce chromosome breaks which are inadequately repaired, ultimately leading to the initiation and disease progression. Exposures acting before birth and early in life has long been thought to be important determinants of leukemia, and the list of suspected chemical, physical, and biological agents continues to increase. Unfortunately, the evidence regarding the majority of suggested exposures is limited and often contradictory, and there are areas, which clearly warrant further investigation in order to further our understanding of the aetiology of childhood leukemia.

Causes of childhood leukaemia and lymphoma

Childhood cancer is rare comprising less than 1% of all malignancies diagnosed each year in developed countries. Leukaemia is the commonest form of cancer in children accounting for around a third of all childhood cancer, with acute lymphoblastic leukaemia (ALL) being the most prevalent. Biologically specific subtypes of ALL and acute myeloblastic leukaemia (AML), the other major morphological type of childhood leukaemia, are characterised by chromosomal changes. Whilst over 200 genes have been associated with chromosomal translocations, to date, only MLL, TEL, and AML1 have been linked with childhood leukaemia. Interestingly, there is increasing evidence to support the theory that gene rearrangements such as these may originate in utero. As with many other human diseases, both genetic and environmental factors have been implicated in the aetiology of the disease. Although much has been documented with regard to diet, smoking, alcohol consumption and recreational and prescription drug use during pregnancy, there is no consistent evidence to support a link with any of these factors and childhood leukaemia. However, findings from studies investigating prenatal and early life exposures are often based on small numbers of cases as both the type of cancer and exposure are rare. Furthermore, accurate information relating to past exposures can be difficult to obtain and is often reliant on self-reporting. To further our understanding of the aetiology of childhood leukaemia and lymphoma, there are areas which clearly warrant investigation. These include collection of parental dietary folate data combined with genetic analysis of the folate related genes, in utero exposure to DNA topoisomerase II inhibitors, and the possible effects of assisted reproduction technology on disease susceptibility.