Analysis of DNA Adducts and Mutagenic Potency and Specificity in Rats Exposed to Acrylonitrile.

Acrylonitrile (ACN), which is a widely used industrial chemical, induces cancers in multiple organs/tissues of rats by unresolved mechanisms. For this report, evidence for ACN-induced direct/indirect DNA damage and mutagenesis was investigated by assessing the ability of ACN, or its reactive metabolite, 2-cyanoethylene oxide (CEO), to bind to DNA in vitro, to form select DNA adducts [N7-(2'-oxoethyl)guanine, ,3-ethenoguanine, 1,-ethenodeoxyadenosine, and 3,-ethenodeoxycytidine] in vitro and/or in vivo, and to perturb the frequency and spectra of mutations in the hypoxanthine-guanine phosphoribosyltransferase () gene in rats exposed to ACN in drinking water. Adducts and frequencies and spectra of mutations were analyzed using published methods.

Considerations for refining the risk assessment process for formaldehyde: Results from an interdisciplinary workshop.

Anticipating the need to evaluate and integrate scientific evidence to inform new risk assessments or to update existing risk assessments, the Formaldehyde Panel of the American Chemistry Council (ACC), in collaboration with the University of North Carolina, convened a workshop: "Understanding Potential Human Health Cancer Risk - From Data Integration to Risk Evaluation" in October 2017. Twenty-four (24) invited-experts participated with expertise in epidemiology, toxicology, science integration and risk evaluation. Including members of the organizing committee, there were 29 participants.

Evaluation of inhaled low-dose formaldehyde-induced DNA adducts and DNA-protein cross-links by liquid chromatography-tandem mass spectrometry.

As a widespread industrial chemical, formaldehyde carcinogenicity has been highly controversial. Meanwhile, formaldehyde is an essential metabolite in all living cells. Previously, we have demonstrated exogenous formaldehyde causes DNA adducts in a nonlinear manner between 0.

Understanding the importance of low-molecular weight (ethylene oxide- and propylene oxide-induced) DNA adducts and mutations in risk assessment: Insights from 15 years of research and collaborative discussions.

The interpretation and significance of DNA adduct data, their causal relationship to mutations, and their role in risk assessment have been debated for many years. An extended effort to identify key questions and collect relevant data to address them was focused on the ubiquitous low MW N7-alkyl/hydroxyalkylguanine adducts. Several academic, governmental, and industrial laboratories collaborated to gather new data aimed at better understanding the role and potential impact of these adducts in quantifiable genotoxic events (gene mutations/micronucleus).

Reevaluation of Hepatocellular Neoplasms in CD-1 Mice from a 2-year Oral Carcinogenicity Study with Permethrin.

A 24-month oral carcinogenicity study of permethrin was conducted by feeding male and female CD-1 mice diets containing concentrations of 0, 20, 500, and 2,000 ppm of permethrin (males) or 0, 20, 2,500, and 5,000 ppm of permethrin (females). After approximately two years on study, surviving mice were sacrificed for the evaluation of chronic toxicity and/or carcinogenicity. An expert panel of pathologists was convened as a Pathology Working Group (PWG) to review coded liver histology sections from male and female mice and to classify all liver neoplasms according to current nomenclature and diagnostic criteria guidelines.

Accurate Measurement of Formaldehyde-Induced DNA-Protein Cross-Links by High-Resolution Orbitrap Mass Spectrometry.

Genomic instability caused by DNA-protein cross-link (DPCs)-induced DNA damage is implicated in disease pathogenesis, aging, and cancer development. The covalent linkages between DNA and protein are induced by chemical reactions catalyzed by the endogenous metabolic intermediates and exogenous agents, such as aldehydes, chemotherapeutic agents, and ionizing radiation. Formaldehyde has been classified as a genotoxic carcinogen.

Exposure assessment of process-related contaminants in food by biomarker monitoring.

Exposure assessment is a fundamental part of the risk assessment paradigm, but can often present a number of challenges and uncertainties. This is especially the case for process contaminants formed during the processing, e.g.

Thrombocytopenia and disseminated histoplasmosis in immunocompetent adults.

Disseminated histoplasmosis among immunocompetent patients is rare, but may be associated with clinically significant refractory thrombocytopenia. Platelet counts often return to normal levels following antifungal therapy. Therefore, the most important management of this refractory thrombocytopenia is the recognition and treatment of histoplasmosis infection.

Editor's Highlight: High-Throughput Functional Genomics Identifies Modulators of TCE Metabolite Genotoxicity and Candidate Susceptibility Genes.

Trichloroethylene (TCE), an industrial chemical and environmental contaminant, is a human carcinogen. Reactive metabolites are implicated in renal carcinogenesis associated with TCE exposure, yet the toxicity mechanisms of these metabolites and their contribution to cancer and other adverse effects remain unclear. We employed an integrated functional genomics approach that combined functional profiling studies in yeast and avian DT40 cell models to provide new insights into the specific mechanisms contributing to toxicity associated with TCE metabolites.

N-Formyllysine as a Biomarker of Formaldehyde Exposure: Formation and Loss of N-Formyllysine in Nasal Epithelium in Long-Term, Low-Dose Inhalation Studies in Rats.

Exposure to both endogenous and exogenous formaldehyde has been established to be carcinogenic, likely by virtue of forming nucleic acid and proteins adducts such as N-formyllysine. To better assess N-formyllysine as a biomarker of formaldehyde exposure, we studied accumulation of N-formyllysine adducts in tissues of rats exposed by inhalation to 2 ppm [CH]-formaldehyde for 7, 14, 21, and 28 days (6 h/day) and investigated adduct loss over a 7-day postexposure period using liquid chromatography-coupled tandem mass spectrometry. Our results showed formation of exogenous adducts in nasal epithelium and to some extent in trachea but not in distant tissues of lung, bone marrow, or white blood cells, with a 2-fold increase over endogenous N-formyllysine over a 3-week exposure period.

Time-matched analysis of DNA adduct formation and early gene expression as predictive tool for renal carcinogenesis in methylazoxymethanol acetate treated Eker rats.

Genotoxic carcinogens pose great hazard to human health. Uncertainty of current risk assessment strategies and long latency periods between first carcinogen exposure and diagnosis of tumors have raised interest in predictive biomarkers. Initial DNA adduct formation is a necessary step for genotoxin induced carcinogenesis.

DNA Product Formation in Female Sprague-Dawley Rats Following Polyhalogenated Aromatic Hydrocarbon (PHAH) Exposure.

DNA oxidation damage has been regarded as one of the possible mechanisms for the hepatic carcinogenesis of dioxin-like compounds (DLCs). In this study, we evaluated the toxic equivalency factor (TEF) from the standpoint of induced DNA oxidation products and their relationship to toxicity and carcinogenicity. Nine DNA oxidation products were analyzed in the liver of female Sprague-Dawley rats exposed to 2,3,7,8-tetrachlorodibenzo-pdioxin (TCDD) alone or the tertiary mixture of TCDD, 3,3',4,4',5-pentachlorobiphenyl (PCB 126), and 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) by gavage for 14, 31, and 53 weeks (5 days/week) by LC-MS/MS: 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dGuo); 1,N-etheno-2'-deoxyadenosine (1,N-εdAdo); N,3-ethenoguanine (N,3-εG); 7-(2-oxoethly)guanine (7-OEG); 1,N-etheno-2'-deoxyguanosine (1,N-εdGuo); malondialdehyde (MdGuo); acrolein (AcrdGuo); crotonaldehyde (CrdGuo); and 4-hydroxynonenal (HNEdGuo) derived 2'-deoxyguanosine adducts.

Homologous Recombination and Translesion DNA Synthesis Play Critical Roles on Tolerating DNA Damage Caused by Trace Levels of Hexavalent Chromium.

Contamination of potentially carcinogenic hexavalent chromium (Cr(VI)) in the drinking water is a major public health concern worldwide. However, little information is available regarding the biological effects of a nanomoler amount of Cr(VI). Here, we investigated the genotoxic effects of Cr(VI) at nanomoler levels and their repair pathways.

Poor recognition of O6-isopropyl dG by MGMT triggers double strand break-mediated cell death and micronucleus induction in FANC-deficient cells.

Isopropyl methanesulfonate (IPMS) is the most potent genotoxic compound among methanesulfonic acid esters. The genotoxic potential of alkyl sulfonate esters is believed to be due to their alkylating ability of the O6 position of guanine. Understanding the primary repair pathway activated in response to IPMS-induced DNA damage is important to profile the genotoxic potential of IPMS.

Polychlorinated Biphenyls Induce Oxidative DNA Adducts in Female Sprague-Dawley Rats.

Polychlorinated biphenyls (PCBs) are organic chemicals that were traditionally produced and widely used in industry as mixtures and are presently formed as byproducts of pigment and dye manufacturing. They are known to persist and bioaccumulate in the environment. Some have been shown to induce liver cancer in rodents.

DNA methylation on N(6)-adenine in mammalian embryonic stem cells.

It has been widely accepted that 5-methylcytosine is the only form of DNA methylation in mammalian genomes. Here we identify N(6)-methyladenine as another form of DNA modification in mouse embryonic stem cells. Alkbh1 encodes a demethylase for N(6)-methyladenine.

Measurement of Endogenous versus Exogenous Formaldehyde-Induced DNA-Protein Crosslinks in Animal Tissues by Stable Isotope Labeling and Ultrasensitive Mass Spectrometry.

DNA-protein crosslinks (DPC) arise from a wide range of endogenous and exogenous chemicals, such as chemotherapeutic drugs and formaldehyde. Importantly, recent identification of aldehydes as endogenous genotoxins in Fanconi anemia has provided new insight into disease causation. Because of their bulky nature, DPCs pose severe threats to genome stability, but previous methods to measure formaldehyde-induced DPCs were incapable of discriminating between endogenous and exogenous sources of chemical.

The bottom-up approach to bounding potential low-dose cancer risks from formaldehyde: An update.

In 2013, we proposed a novel bottom-up approach to bounding low-dose cancer risks that may result from small exogenous exposures to chemicals that are always present in the body as a result of normal biological processes. The approach utilizes the background cancer risk and the background (endogenous) concentration of a cancer-related exposure biomarker in specific target tissues. After allowing for statistical uncertainty in these two parameters, the ratio of the background risk to background exposure provides a conservative slope factor estimate that can be utilized to bound the added risk that may be associated with incremental exogenous exposures.

Endogenous Formaldehyde Is a Hematopoietic Stem Cell Genotoxin and Metabolic Carcinogen.

Endogenous formaldehyde is produced by numerous biochemical pathways fundamental to life, and it can crosslink both DNA and proteins. However, the consequences of its accumulation are unclear. Here we show that endogenous formaldehyde is removed by the enzyme alcohol dehydrogenase 5 (ADH5/GSNOR), and Adh5(-/-) mice therefore accumulate formaldehyde adducts in DNA.

Implication of a Chromosome 15q15.2 Locus in Regulating UBR1 and Predisposing Smokers to MGMT Methylation in Lung.

O(6)-Methylguanine-DNA methyltransferase (MGMT) is a DNA repair enzyme that protects cells from carcinogenic effects of alkylating agents; however, MGMT is silenced by promoter hypermethylation during carcinogenesis. A single-nucleotide polymorphism (SNP) in an enhancer in the MGMT promoter was previously identified to be highly significantly associated with risk for MGMT methylation in lung cancer and sputum from smokers. To further genetic investigations, a genome-wide association and replication study was conducted in two smoker cohorts to identify novel loci for MGMT methylation in sputum that were independent of the MGMT enhancer polymorphism.

Incorporation of metabolic activation potentiates cyclophosphamide-induced DNA damage response in isogenic DT40 mutant cells.

Elucidating the DNA repair pathways that are activated in the presence of genotoxic agents is critical to understand their modes of action. Although the DT40 cell-based DNA damage response (DDR) assay provides rapid and sensitive results, the assay cannot be used on genotoxic compounds that require metabolic activation to be reactive. Here, we applied the metabolic activation system to a DDR and micronucleus (MN) assays in DT40 cells.

Formation, Accumulation, and Hydrolysis of Endogenous and Exogenous Formaldehyde-Induced DNA Damage.

Formaldehyde is not only a widely used chemical with well-known carcinogenicity but is also a normal metabolite of living cells. It thus poses unique challenges for understanding risks associated with exposure. N(2-)hydroxymethyl-dG (N(2)-HOMe-dG) is the main formaldehyde-induced DNA mono-adduct, which together with DNA-protein crosslinks (DPCs) and toxicity-induced cell proliferation, play important roles in a mutagenic mode of action for cancer.

A gnotobiotic mouse model demonstrates that dietary fiber protects against colorectal tumorigenesis in a microbiota- and butyrate-dependent manner.

Unlabelled: Whether dietary fiber protects against colorectal cancer is controversial because of conflicting results from human epidemiologic studies. However, these studies and mouse models of colorectal cancer have not controlled the composition of gut microbiota, which ferment fiber into short-chain fatty acids such as butyrate. Butyrate is noteworthy because it has energetic and epigenetic functions in colonocytes and tumor-suppressive properties in colorectal cancer cell lines.