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The U.S. Environmental Protection Agency's Guidelines for Carcinogen Risk Assessment encourages the use of mechanistic data in the assessment of human cancer risk at low (environmental) exposure levels. The key events that define a particular mode of action for tumor formation have been concentrated to date more on mutational responses that are broadly the result of induced DNA damage and enhanced cell proliferation. While it is clear that these processes are important in terms of tumor induction, other modes that fall under the umbrella of epigenetic responses are increasingly being considered to play an important role in susceptibility to tumor induction by environmental chemicals and as significant modifiers of tumor responses. Alterations in gene expression, DNA repair, cell cycle control, genome stability and genome reprogramming could be the result of modification of DNA methylation and chromatin remodeling patterns as a consequence of exposure to environmental chemicals. These concepts are described and discussed.

The US Environmental Protection Agency recently released its new guidelines for carcinogen risk assessment together with supplemental guidance for assessing susceptibility from early-life exposure to carcinogens. In particular, these guidelines encourage the use of mechanistic data in support of dose-response characterization at doses below those at which an increase in tumor frequency over background levels might be detected. In this context of the utility of mechanistic data for human cancer risk assessment, the International Life Sciences Institute (ILSI) has developed a human relevance framework (HRF) that can be used to assess the plausibility of a mode of action (MoA) described for animal models operating in humans. The MoA is described as a sequence of key events and processes that result in an adverse outcome. A key event is a measurable precursor step that is in itself a necessary element of the MoA or is a bioindicator for such an element. A number of cellular and molecular perturbations have been identified as key events whereby DNA-reactive chemicals can produce tumors. These include DNA adducts in target tissues, gene mutations and/or chromosomal alterations in target tissues and enhanced cell proliferation in target tissues. This type of data integration approach to quantitative cancer risk assessment can be applied to 1,3-butadiene, for example, using data on biomarkers in exposed Czech workers [1]. For this study, an extensive range of biomarkers of exposure and response was assessed, including: polymorphisms in metabolizing enzymes; urinary concentrations of several metabolites of 1,3-butadiene; hemoglobin adducts; HPRT mutations in T-lymphocytes; chromosomal aberrations by FISH and conventional staining procedures; sister chromatid exchanges. Exposure levels were monitored in a comprehensive fashion. For risk assessment purposes, these data need to be considered in the context of how they inform the MoA for leukemia, the tumor type reported to be increased in synthetic rubber workers exposed to 1,3-butadiene. Also, for the HRF it is necessary to establish key events for a MoA in rodents for the induction of tumors by 1,3-butadiene. There is clearly a species difference in sensitivity to tumor induction, with mice being much more sensitive than rats; key events need to explain this difference. For butadiene, the MoA is DNA-reactivity and subsequent mutagenicity and so following the EPA's cancer guidelines, a linear extrapolation is used from the point of departure (POD), unless additional data support a non-linear extrapolation. For the present case, the human bioindicator data are not informative as far as dose-response characterization is concerned. Mouse chromosome aberration data for in vivo exposures might be used for establishing a POD, with linear extrapolation from this POD. The available cytogenetic data from rodent studies appear to be sufficiently extensive and consistent for this to be a viable approach. This approach of using MoA and key events to establish the human relevance can lead to the development of specific informative bioindicators of response that can be used as surrogates to predict the shape of the tumor dose response curve at low doses. Truly informative predictors of tumor responses should be able to provide estimates of human tumor frequencies at low, environmental exposures to 1,3-butadiene.

Recognition that children are a potentially susceptible subpopulation has led to the development of child-specific sensitivity factors. Establishing reliable sensitivity factors in support of risk assessment of early-life stage exposures can be aided by evaluating studies that enhance our understanding both of the biological basis of disease processes and the potential role of environmental exposures in disease etiology. For these reasons, we evaluated childhood acute lymphocytic leukemia (ALL) studies from the point of view of mechanism and etiology. ALL is the most common form of childhood cancer proposed to result from a prenatal primary event and a postnatal second event. This multi-stage model is supported by the observation that chromosomal translocations/fusion genes (e.g., TEL-AML1) involved in producing ALL are detected at birth (prenatal event), and a postnatal event (e.g., TEL deletion) is required for disease manifestation. It appears that a proportion of ALL cases are the result of environmental exposures, in which case preconceptional, prenatal, and postnatal stages are likely to be critical exposure windows. To this end, we recognized postnatal infection-related risk factors as potential candidates associated with the ALL second event. Additionally, we discuss use of ALL-associated fusion genes and genetic polymorphisms, together or separately, as indicators of ALL susceptibility and increased risk. The possibility of using fusion genes alone as biomarkers of response is also discussed because they can serve as predictors of key events in the development of a mode of action (a sequence of key events, starting with interaction of an agent with a cell, ultimately resulting in cancer formation) for particular environmental exposures. Furthermore, we discuss use of an initiated animal model for ALL, namely transgenic mice with TEL-AML1 expression, for exploring mechanisms by which different classes of environmental exposures could be involved in inducing the postnatal step in ALL formation.

In April 2004, the Health and Environmental Sciences Institute, a branch of the International Life Sciences Institute, with support from the National Institute of Environmental Health Sciences, organized a workshop to discuss the biological significance of DNA adducts. Workshop speakers and attendees included leading international experts from government, academia, and industry in the field of adduct detection and interpretation. The workshop initially examined the relationship between measured adduct levels in the context of exposure and dose. This was followed by a discussion on the complex response of cells to deal with genotoxic insult in complex, interconnected, and interdependent repair pathways. One of the major objectives of the workshop was to address the recurring question about the mechanistic and toxicological relevance of low-concentration measured adducts and the presentations in the session entitled "Can low levels of DNA adducts predict adverse outcomes?" served as catalysts for further discussions on this subject during the course of the workshop. Speakers representing the regulatory community and industry reviewed the value, current practices, and limitations of utilizing DNA adduct data in risk assessment and addressed a number of practical questions pertaining to these issues. While no consensus statement emerged on the biological significance of low levels of DNA adducts, the workshop concluded by identifying the need for more experimental data to address this important question. One of the recommendations stemming from this workshop was the need to develop an interim "decision-logic" or framework to guide the integration of DNA adduct data in the risk assessment process. HESI has recently formed a subcommittee consisting of experts in the field and other key stakeholders to address this recommendation as well as to identify specific research projects that could help advance the understanding of the biological significance of low levels of DNA adducts.

In trying to decide what type of scientific paper I could prepare as a tribute to Jim Neel, I thought back over the discussions that we had over some 25 years. Sometimes these discussions were on specific topics such as how to extrapolate from mutation data in mice to those for humans following radiation or chemical exposures. On other occasions, our discussions were of a more philosophical nature, particularly on where the field of epidemiology might or needed to go. For example, what types of data are needed for assessing the public health impact of exposure to environmental agents. Perhaps because I enjoyed these discussions so much, I have chosen to take a look from a current perspective at the field of molecular epidemiology. Jim Neel would have loved to have entered into this discussion; he would have enhanced it in is own inimitable way.

Few writers have commented on how seaside leisure spaces are socially constructed, who competes for their use, and how they may change. This paper discusses how these spaces have been identified and partitioned at Durban, South Africa, as new tourist populations discover them. Given the history of ethnic separation and contemporary social and political change in this country, attention is focussed on the extent to which groups retain and express a sense of identity in the construction of leisure spaces. Selected spaces are discussed to illustrate how they may be constructed around notions of cultural identity, the possession of particular skills, or access to scarce spatial and material resources.

DNA damage response pathways coordinate the cellular response to DNA damage. To investigate the roles of tumor suppressor genes in these pathways, human lymphoblastoid cells (wild-type, p53−/− , ATM−/− ) were treated for 1 h with 0–3 μg/ml of the radiomimetic compound bleomycin (BLM), and cells treated in G 2 were analyzed for chromatid aberrations. BLM-induced aberration frequencies were significantly increased, to the greatest extent in the ATM−/− cells and, to a lesser extent, in the p53−/− cells compared to wild-type cells. These observations are consistent with p53 and ATM acting in a damage response pathway activated by DNA strand breaks. The consequences of disrupting this pathway were further investigated by studies using wortmannin, a PI-3 kinase and DNA repair inhibitor. Wortmannin significantly increased the BLM-induced aberration frequencies in all but the ATM−/− cells, elevating the sensitivity of p53−/− cells to ATM−/− levels and that of wild-type cells to intermediate levels. These differential sensitivities suggest that the ATM phenotype is the result of dual cellular defects, one involving p53 and the other a wortmannin-sensitive component. Similar studies in Brca1+/− and Brca2+/− human lymphoblasts showed no increased sensitization to BLM in the absence of inhibitor, and differential sensitization by wortmannin. To determine if there was any substrate specificity for p53- and ATM-mediated DNA damage responses, chromatid aberrations were assessed in wild-type, p53−/− , and ATM−/− cells exposed to 0–0.4 μg/ml neocarzinostatin (NCS) for 1 h. In contrast to results with BLM, the p53−/− cells exhibited a low sensitivity to NCS-induced aberrations, similar to wild-type, while ATM−/− cells remained highly sensitive. This suggests that the response to BLM- and NCS-induced lesions involves different mechanisms.

In the past few years, our knowledge of mammalian genomes has increased enormously. Our understanding of the molecular basis of the normal cellular processes of DNA replication and repair and cell cycle control, together with how their fidelity malfunctions as part of tumor development, has increased in parallel. This has led to a clearer appreciation that there are subpopulations that have been generically described as being genetically or otherwise susceptible to the induction of cancer or birth defects. The term susceptibility is a default option, since there clearly will be a very broad range of sensitivities among the so-called susceptible populations, dependent upon the specific underlying mechanism. This could lead to the conduct of risk assessments for each specific situation, involving both genotypes of individuals and agents of concern. This would ideally take into account the effects on response of various modifying factors, genetic and other. One advantage to be gained from this approach is the ability to determine if a particular susceptibility places subpopulations at extreme risk as compared to the overall normal distribution of risk in the population, or whether such a susceptible population presents a slight extension of the upper bound of the risk distribution or lies within the normal distribution. In addition, the specific mechanism of the susceptibility as related to exposure scenarios and the magnitude and demographics of the susceptible populations need to be taken into account. Thus, the management of risk has to be linked to the specific risk assessment. For many of the so-called susceptible populations an uncertainty factor of less than 10, even including 1, would be predicted to bring the risk within the normal distribution. It is hoped that as more mechanistic information on susceptibility becomes available and a specific risk can be defined, the practice of risk management will be considerably improved.

A Silicon Microstrip Spectrometer has been installed and successfully operated in experiment E789 at Fermilab. The main physics goal of the experiment is to search for charged particle decays of B and D Mesons. Damage effects due to ionizing radiation exposure to the silicon during the experiment are reported.

Rule, D.C., Preston, R.L., Koes, R.M. and McReynolds, W.E., 1986. Feeding value of sprouted wheat (Triticum aestivum) for beef cattle finishing diets. Anita. Feed Sci. Technol., 15: 113--121. The feeding value of sprouted, soft white wheat was compared with that of sound (unsprouted) wheat and barley in the diets of 95 Simmental-Hereford beef cattle. There were no differences (P > 0.05) in daily gains, feed intakes or feed/gain ratios of cattle fed on either sound wheat, wheat with 9% sprouted kernels (low-sprout) or wheat with 58% sprouted kernels (high-sprout), when the wheat was included at 25 or 50% of the diet. When sound and sprouted wheats were given to 44-kg sheep, at 75% of the diet, dry matter intake of the sound-wheat diet was 21% less than that of the high-sprout-wheat diet; dry matter digestibility and the digestible energy content of the former diet were slightly greater (74.3 vs 70.7% and 3.2 and 3.0 kcal g- '), but neither difference was significant (P > 0.05). It was concluded that sprouting does not affect the feeding value of wheat for finishing beef cattle when offered at 50% of the diet, and reduces it only slightly for sheep when given at 75% of the diet.

This report presents an assessment made by the U.S. Environmental Protection Agency Gene-Tox Program's Work Group on mammalian cytogenetics of the clastogenic effects of chemicals in in vivo and in vitro mammalian cell assays. This assessment is based on information provided by the Environmental Mutagen Information Center, Oak Ridge National Laboratory, with the proviso that the experimental protocol used in these papers was adjudged to be acceptable by standards outlined by the Work Group. Some data were accepted as "qualitative only" because the protocol used was fairly close to that proposed as suitable. Using these criteria, 177 papers were selected for review. 6 assays were reviewed: bone marrow (32 papers, 31 chemicals), spermatogonial (10 papers, 10 chemicals), spermatocyte (25 papers, 25 chemicals), oocyte or early embryo (18 papers, 19 chemicals), in vitro cell culture (30 papers, 66 chemicals), and leukocyte (66 papers, 53 chemicals). Each assay was considered separately, and comparisons were then made between them for their similarities or differences in producing a positive or negative clastogenic effect of a particular chemical or chemical class. A large proportion of the available cytogenetic data was not suitable for inclusion in the final data base because of poor experimental design or unsatisfactory reporting of the information. It was not possible to recommend any one assay for determining potential clastogenicity because each had its own particular advantages and limitations and provided unique information. For demonstrating in vivo effects, the bone-marrow assay is probably the simplest and most economical. If only in vitro exposures were considered, leukocytes or cultured mammalian cell lines would be suitable. However, there are advantages to using leukocytes because they are a synchronous population, at least through their cell division, and because of the ready availability of human cells. In general, there was good agreement between clastogenicity and carcinogenicity.

80 papers published between 1970 and 1984 were evaluated for results pertaining to chemical-induced aneuploidy in mammalian male germ cells. Diverse assays and end points were represented. The assays considered to involve direct measures of aneuploidy were based upon chromosome counts in premeiotic, meiotic, and embryonic cells, and the male pronucleus, or upon phenotypic expression of X-linked genetic markers. Assays in which indirect measures were interpreted as evidence for aneuploidy included those primarily assessing chiasma frequencies, univalent frequencies, and spermatid/sperm sex chromosome body counts. An initial screening to reject studies with insufficient data and those which did not involve a single chemical test agent led to the elimination of 39 papers from further review. The remaining 41 papers reported effects from 46 different chemicals. These papers were rigorously assessed for adequacy of experimental protocols, relevance of end points as direct measures of aneuploidy, and completeness of data presentation and statistical analysis. Criteria specific to each assay were also considered. 4 chemical tests were considered to provide reliable positive or negative aneuploidy data. Cyclophosphamide and chloral hydrate each caused metaphase II hyperploidy when injected into mice. Very limited analyses of trenimon and isoniazid provided negative results. Test findings for 44 chemicals were viewed as inconclusive. It was concluded that standardization of tests to evaluate chemical-induced aneuploidy in male germ cells and the application of these tests towards increasing the data base are badly needed.

Acrylamide, a widely used vinyl monomer, is well known as a neurotoxin but inactive as a mutagen in bacterial test systems. The experiments reported demonstrate that after subchronic oral dosing in the male rat, acrylamide induced significant elevations in both pre- and post-implantation loss following dominant lethal testing. These effects were seen at doses which failed to produce clinical or pathological evidence of neurotoxicity. In an accompanying cytogenetic study, no increase in chromosome aberrations was observed in spermatogonia or spermatocytes of treated animals. When spermatocytes from treated spermatogonial stem cells were analyzed, reciprocal translocations (4) were observed in the treated animals and not in the control, but the significance of this result still needs to be established.

The utilization of nitrogen contained in soybean meal, casein, zein, and urea was studied in 12 mature wethers. Net microbial synthesis rates during the 6-hour period after feeding corresponded to ruminai ammonia concentrations, suggesting that the ruminai ammonia level in these experiments was a limiting factor in microbial protein synthesis. Maximum conversion of dietary nitrogen to microbial nitrogen in the rumen during a 24-hour period was estimated to be 62.5, 85.3, 40.9, and 90.1%, respec tively, for soybean meal, casein, zein, and urea. Estimated production rates of acetic, pro- pionic, butyric, isovaleric, and valeric acids during the first 6 hours after feeding suggested that zein supported the lowest microbial activity in the rumen, and that urea supplemen tation resulted in isovaleric and valeric acids production rates equivalent to or greater than rates when the other nitrogen supplements were present in the diet. Daily endoge nous urinary and metabolic fecal nitrogen determined by regression analysis utilizing soybean meal as the only nitrogen supplement were 72 mg/kg body weight075 and 340 mg/100 g of dry matter intake. Biological values of 84.8, 78.3, 84.3, and 76.4 were ob tained for soybean meal, casein, zein, and urea, respectively. J. Nutr. 105: 267-273, 1975.

Our aquatic environment contains 5-chlorouracil and 5-chlorouridine among other chloro-organics as a result of chlorination of sewage. Mice ingesting 5-chlorouracil in their drinking water incorporate the base heavily in the liver and testes DNA. Another related metabolite, 5-chlorodeoxyuridine, is 5 times more potent than 5-bromodeoxyuridine in inducing sister-chromatid exchanges in Chinese hamster ovary cells.

Our initial objective was to develop an in vivo mammalian, female aneuploid assay that is consistent, time efficient, and that yields a large number of oocytes amenable to objective analyses. Subsequently, we desired to use such an assay for identifying chemicals and dosages that could increase the incidence of aneuploidy in mouse metaphase II oocytes. The experimental protocol involved superovulating CD-1 mice with PMS; HCG was given 48 h later. At the time of HCG injection, different dosages od diethylstilbestrol diphosphate, cadmium chloride, chloral hydrate, or colchicine were injected intraperitoneally. 17 h later, oocytes were collected and fixed prior to C-banding the chromosomes. The procedure required about 3 h to process oocytes from 25 mice and yielded over 100 analyzable metaphase II oocytes. Colchicine was the only compound tested that resulted in a statistically significant (P less than 0.01) increase in hyperploid (N greater than 20) oocytes over controls. The incidence of hyperploid oocytes in the colchicine group was 2/167, 1/182, 21/220, and 38/202, for control, 0.1 mg/kg, 0.2 mg/kg, and 0.3 mg/kg, respectively. This assay appears sensitive for aneuploidy detection but requires further validation.

Crystal structures have been studied in a series of alloys in the RFe2-RAl 2 system in which R includes Sc, Y, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm and Lu. X-ray studies were made by the Debye-Scherrer method for arcmelted and annealed alloys. Earlier work had shown that where the composition is close to RFe2 or RAl2, the compounds are MgCu2-type (cubic) Laves phases, but that in a composition region intermediate between RFe2 and RAl2 the compounds are MgZn2-type (hexagonal) Laves phases. The present work defines the composition limits of the MgCu2- and MgZn2-type structures and reports the existence of a new MgCu2-type compound based on ScFe2. In general, the range of stability of the hexagonal compounds is shifted to higher aluminum concentration as the identity of the rare earth changes from Sm to Lu, although anomalous behavior is exhibited by Sc. When the regions of phase stability are depicted in a plot of volume per formula weight vs. composition, the phase boundaries between cubic and hexagonal phases are curved, but have similar shapes at both the iron-rich and aluminum-rich end of the diagram. The tendency to order into the Mg2Cu3 Si-type structure in the hexagonal phase has been studied by X-ray diffraction; various models of this ordering are treated. Both the cubic and the hexagonal phases have been studied by the Mossbauer effect with 57Fe. The hexagonal phases exhibit magnetic order at low temperatures but not at room temperature. At room temperature the cubic phases of Ho33AlxFe66−x are magnetic for x = 10 and nonmagnetic for x = 20 or greater.

The wall structure of the growth zone of Phycomyces has been further investigated by means of X-rays, the polarizing microscope, and the electron microscope. Material has been used which has been subjected to no chemical treatment whatever, and it has been established that the flat spiral structure which occurs in the growth zone is sinistral. When the cells were treated with solutions of vital dyes, or subjected to mechanical injury, abnormal growths were obtained which appear to shed light on wall formation in the cell. Spirals in the protoplasm have been photographed.