Clonality, trafficking, and molecular alterations among Hprt mutant T lymphocytes isolated from control mice versus mice treated with N-ethyl-N-nitrosourea.

Mutations in T lymphocytes (T-cells) are informative quantitative markers for environmental mutagen exposures, but risk extrapolations from rodent models to humans also require an understanding of how T-cell development and proliferation kinetics impact mutagenic outcomes. Rodent studies have shown that patterns in chemical-induced mutations in the hypoxanthine-guanine phosphoribosyltransferase (Hprt) gene of T-cells differ between lymphoid organs. The current work was performed to obtain knowledge of the relationships between maturation events during T-cell development and changes in chemical-induced mutant frequencies over time in differing immune compartments of a mouse model.

SURROGATE SELECTION OVERSAMPLES EXPANDED T CELL CLONOTYPES.

Inference from immunological data on cells in the adaptive immune system may benefit from modeling specifications that describe variation in the sizes of various clonal sub-populations. We develop one such specification in order to quantify the effects of surrogate selection assays, which we confirm may lead to an enrichment for amplified, potentially disease-relevant cell clones. Our specification couples within-clonotype birth-death processes with an exchangeable model across clonotypes.

Acrylonitrile's genotoxicity profile: mutagenicity in search of an underlying molecular mechanism.

Acrylonitrile (ACN) is a known rodent and possible human carcinogen. There have also been concerns as to it causing adverse reproductive health effects. Numerous genotoxicity studies at the somatic level in a variety of test systems have demonstrated ACN's mutagenicity; its potential to induce mutations in germ cells has also been evaluated.

Molecular characterization of hypoxanthine guanine phosphoribosyltransferase mutant T cells in human blood: The concept of surrogate selection for immunologically relevant cells.

Somatic cell gene mutations arise in vivo due to replication errors during DNA synthesis occurring spontaneously during normal DNA synthesis or as a result of replication on a DNA template damaged by endogenous or exogenous mutagens. In principle, changes in the frequencies of mutant cells in vivo in humans reflect changes in exposures to exogenous or endogenous DNA damaging insults, other factors being equal. It is becoming increasingly evident however, that somatic mutations in humans have a far greater range of interpretations.

Using mechanistic information to support evidence integration and synthesis: a case study with inhaled formaldehyde and leukemia.

Formaldehyde is one of the most comprehensively studied chemicals, with over 30 years of research focused on understanding the development of cancer following inhalation. The causal conclusions regarding the potential for leukemia are largely based on the epidemiological literature, with little consideration of cancer bioassays, dosimetry studies, and mechanistic research, which challenge the biological plausibility of the disease. Recent reanalyzes of the epidemiological literature have also raised significant questions related to the purported associations between formaldehyde and leukemia.

Mutagenicity monitoring in humans: Global versus specific origin of mutations.

An underappreciated aspect of human mutagenicity biomonitoring is tissue specificity reflected in different assays, especially those that measure events that can only occur in developing bone marrow (BM) cells. Reviewed here are 9 currently-employed human mutagenicity biomonitoring assays. Several assays measure chromosome-level events in circulating T-lymphocytes (T-cells), i.

Genotoxicity as a toxicologically relevant endpoint to inform risk assessment: A case study with ethylene oxide.

The purpose of the present investigation is to analyze the in vivo genotoxicity dose-response data of ethylene oxide (EO) and the applicability of the derived point-of-departure (PoD) values when estimating permitted daily exposure (PDE) values. A total of 40 data sets were identified from the literature, and benchmark dose analyses were conducted using PROAST software to identify a PoD value. Studies employing the inhalation route of exposure and assessing gene or chromosomal mutations and chromosomal damage in various tissues were considered the most relevant for assessing risk from EO, since these effects are likely to contribute to adverse health consequences in exposed individuals.

1,3-Butadiene metabolite 1,2,3,4 diepoxybutane induces DNA adducts and micronuclei but not t(9;22) translocations in human cells.

Epidemiological studies of 1,3-butadiene (BD) exposures have reported a possible association with chronic myelogenous leukemia (CML), which is defined by the presence of the t(9;22) translocation (Philadelphia chromosome) creating an oncogenic BCR-ABL fusion gene. Butadiene diepoxide (DEB), the most mutagenic of three epoxides resulting from BD, forms DNA-DNA crosslink adducts that can lead to DNA double-strand breaks (DSBs). Thus, a study was designed to determine if (±)-DEB exposure of HL60 cells, a promyelocytic leukemia cell line lacking the Philadelphia chromosome, can produce t(9;22) translocations.

Longitudinal study of t-cell somatic mutations conferring glycosylphosphatidylinositol-anchor deficiency in gulf war I veterans exposed to depleted uranium.

Fifty Veterans of the first Gulf War in 1991 exposed to depleted uranium (DU) were studied for glycosylphosphatidylinositol-anchor (GPIa) deficient T-cell mutants on three occasions during the years 2009, 2011, and 2013. GPIa deficiency was determined in two ways: cloning assays employing aerolysin selection and cytometry using the FLAER reagent for positive staining of GPIa cell surface proteins. Subsequent molecular analyses of deficient isolates recovered from cloning assays (Nicklas JA et al.

Molecular analysis of glycosylphosphatidylinositol anchor deficient aerolysin resistant isolates in gulf war i veterans exposed to depleted uranium.

During the First Gulf War (1991) over 100 servicemen sustained depleted uranium (DU) exposure through wound contamination, inhalation, and shrapnel. The Department of Veterans Affairs has a surveillance program for these Veterans which has included genotoxicity assays. The frequencies of glycosylphosphatidylinositol anchor (GPIa) negative (aerolysin resistant) cells determined by cloning assays for these Veterans are reported in Albertini RJ et al.

Frequencies of micronucleated reticulocytes, a dosimeter of DNA double-strand breaks, in infants receiving computed tomography or cardiac catheterization.

The use of computed tomography (CT scans) has increased dramatically in recent decades, raising questions about the long-term safety of CT-emitted x-rays especially in infants who are more sensitive to radiation-induced effects. Cancer risk estimates for CT scans typically are extrapolated from models; therefore, new approaches measuring actual DNA damage are needed for improved estimations. Hence, changes in a dosimeter of DNA double-strand breaks, micronucleated reticulocytes (MN-RETs) measured by flow cytometry, were investigated in mice and infants exposed to CT scans.

The lower alkyl methacrylates: Genotoxic profile of non-carcinogenic compounds.

All of the lower alkyl methacrylates are high production chemicals with potential for human exposure. The genotoxicity of seven mono-functional alkyl esters of methacrylic acid, i.e.

Do chromosome changes in blood cells implicate formaldehyde as a leukemogen?

Formaldehyde (FA) is a mutagenic chemical - a property mitigated in vivo by rapid detoxification and limited tissue distribution following inhalation of the free agent. Endogenously produced FA is necessary for life and required for one-carbon transfer reactions; however, FA derived from external sources (exogenous FA), which may be in the form of methanol, may increase in vivo concentrations above naturally occurring physiological levels. Both endogenous and exogenous FA produce DNA monoadducts, DNA-DNA and DNA-protein cross-links (DDX and DPX) but, when exposed to exogenously-derived free FA, DNA monoadducts, DDX, and DPX are only produced at initial sites of contact.

1,3-Butadiene, CML and the t(9:22) translocation: A reality check.

Epidemiological studies of 1,3-butadiene have suggest that exposures to humans are associated with chronic myeloid leukemia (CML). CML has a well-documented association with ionizing radiation, but reports of associations with chemical exposures have been questioned. Ionizing radiation is capable of inducing the requisite CML-associated t(9:22) translocation (Philadelphia chromosome) in appropriate cells in vitro but, thus far, chemicals have not shown this capacity.

Both PIGA and PIGL mutations cause GPI-a deficient isolates in the Tk6 cell line.

Molecular analysis of proaerolysin selected glycosylphosphatidylinositol anchor (GPI-a) deficient isolates in the TK6 cell line was performed. Initial studies found that the expected X-linked PIGA mutations were rare among the spontaneous isolates but did increase modestly after ethyl methane sulfate (EMS) treatment (but to only 50% of isolates). To determine the molecular bases of the remaining GPI-a deficient isolates, real-time analysis for all the 25 autosomal GPI-a pathway genes was performed on the isolates without PIGA mutations, determining that PIGL mRNA was absent for many.

Mutagenicity monitoring following battlefield exposures: Molecular analysis of HPRT mutations in Gulf War I veterans exposed to depleted uranium.

Molecular studies that involved cDNA and genomic DNA sequencing as well as multiplex PCR of the HPRT gene were performed to determine the molecular mutational spectrum for 1,377 HPRT mutant isolates obtained from 61 Veterans of the 1991 Gulf War, most of whom were exposed to depleted uranium (DU). Mutant colonies were isolated from one to four times from each Veteran (in 2003, 2005, 2007, and/or 2009). The relative frequencies of the various types of mutations (point mutations, deletions, insertions, etc.

Mutagenicity monitoring following battlefield exposures: Longitudinal study of HPRT mutations in Gulf War I veterans exposed to depleted uranium.

A total of 70 military Veterans have been monitored for HPRT T-cell mutations in five separate studies at 2-year intervals over an 8-year period. Systemic depleted uranium (DU) levels were measured at the time of each study by determining urinary uranium (uU) excretion. Each HPRT study included 30-40 Veterans, several with retained DU-containing shrapnel.

A proposal for assessing study quality: Biomonitoring, Environmental Epidemiology, and Short-lived Chemicals (BEES-C) instrument.

The quality of exposure assessment is a major determinant of the overall quality of any environmental epidemiology study. The use of biomonitoring as a tool for assessing exposure to ubiquitous chemicals with short physiologic half-lives began relatively recently. These chemicals present several challenges, including their presence in analytical laboratories and sampling equipment, difficulty in establishing temporal order in cross-sectional studies, short- and long-term variability in exposures and biomarker concentrations, and a paucity of information on the number of measurements required for proper exposure classification.

Nonlinear responses for chromosome and gene level effects induced by vinyl acetate monomer and its metabolite, acetaldehyde in TK6 cells.

Vinyl acetate monomer (VAM) produced rat nasal tumors at concentrations in the hundreds of parts per million. However, VAM is weakly genotoxic in vitro and shows no genotoxicity in vivo. A European Union Risk Assessment concluded that VAM's hydrolysis to acetaldehyde (AA), via carboxylesterase, is a critical key event in VAM's carcinogenic potential.

Vinyl acetate monomer (VAM) genotoxicity profile: relevance for carcinogenicity.

Vinyl acetate monomer (VAM) is a site-of-contact carcinogen in rodents. It is also DNA reactive and mutagenic, but only after its carboxylesterase mediated conversion to acetaldehyde (AA), a metabolic reaction that also produces acetic acid and protons. As VAM's mutagenic metabolite, AA is normally produced endogenously; detoxification by aldehyde dehydrogenase (ALDH) is required to maintain intra-cellular AA homeostasis.

Formaldehyde exposure and leukemia: critical review and reevaluation of the results from a study that is the focus for evidence of biological plausibility.

A recent study (Zhang et al., 2010) has provided results attributed to aneuploidy in circulating stem cells that has been characterized as providing potential support for proposed mechanisms for formaldehyde to impact bone marrow. A critical review of the study, as well as a reanalysis of the underlying data, was performed and the results of this reanalysis suggested factors other than formaldehyde exposure may have contributed to the effects reported.

Formation of 1,2:3,4-diepoxybutane-specific hemoglobin adducts in 1,3-butadiene exposed workers.

1,3-Butadiene (BD) is an important industrial chemical that is classified as a human carcinogen. BD carcinogenicity has been attributed to its metabolism to several reactive epoxide metabolites and formation of the highly mutagenic 1,2:3,4-diepoxybutane (DEB) has been hypothesized to drive mutagenesis and carcinogenesis at exposures experienced in humans. We report herein the formation of DEB-specific N,N-(2,3-dihydroxy-1,4-butadiyl)valine (pyr-Val) in BD-exposed workers as a biomarker of DEB formation.

Measures of genotoxicity in Gulf war I veterans exposed to depleted uranium.

Exposure to depleted uranium (DU), an alpha-emitting heavy metal, has prompted the inclusion of markers of genotoxicity in the long-term medical surveillance of a cohort of DU-exposed Gulf War veterans followed since 1994. Using urine U (uU) concentration as the measure of U body burden, the cohort has been stratified into low-u (<0.10 μg U/g creatinine) and high-u groups (≥ 0.

1,3-Butadiene: Biomarkers and application to risk assessment.

1,3-Butadiene (BD) is a known rodent and human carcinogen that is metabolized mainly by P450 2E1 to three epoxides, 1,2-epoxy-3-butene (EB), 1,2:3,4-diepoxybutane (DEB) and 1,2-epoxy-3,4-butanediol (EB-diol). The individual epoxides vary up to 200-fold in their mutagenic potency, with DEB being the most mutagenic metabolite. It is important to understand the internal formation of the individual epoxides to assign the relative risk for each metabolite and to understand the molecular mechanisms responsible for major species differences in carcinogenicity.

1,3-Butadiene: III. Assessing carcinogenic modes of action.

1,3-Butadiene (BD) is a multisite carcinogen in laboratory rodents following lifetime exposure, with greater potency in the mouse than the rat, and is associated with an increase in leukemia mortality in highly exposed workers. Species differences in the formation of reactive metabolites underlie observed species differences in sensitivity to the carcinogenic effects of BD. The modes of action (MOAs) for human leukemia and rodent tumors are both likely related to mutagenic potencies of one or more of these metabolites.