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E M Faustman

Publications and source records attributed to E M Faustman.

At least 37 records · Page 2Linked to original sources
PubMed1999

Quantitative mechanistically based dose-response modeling with endocrine-active compounds.

A wide range of toxicity test methods is used or is being developed for assessing the impact of endocrine-active compounds (EACs) on human health. Interpretation of these data and their quantitative use in human and ecologic risk assessment will be enhanced by the availability of mechanistically based dose-response (MBDR) models to assist low-dose, interspecies, and (italic)in vitro(/italic) to (italic)in vivo(/italic) extrapolations. A quantitative dose-response modeling work group examined the state of the art for developing MBDR models for EACs and the near-term needs to develop, validate, and apply these models for risk assessments. Major aspects of this report relate to current status of these models, the objectives/goals in MBDR model development for EACs, low-dose extrapolation issues, regulatory inertia impeding acceptance of these approaches, and resource/data needs to accelerate model development and model acceptance by the research and the regulatory community.

Dose-Response Relationship, Drug↗
PubMed1999

The role of intracellular glutathione in methylmercury-induced toxicity in embryonic neuronal cells.

Previous studies indicate that the ability of cells to up-regulate levels of intracellular glutathione (GSH) synthesis may determine their sensitivity to MeHg exposure. The purpose of the current study is two-fold. First, we determined whether the vulnerability of the developing central nervous system (CNS) to MeHg lies in its intracellular GSH content. The intracellular GSH content and the activity of gamma-glutamyl cysteine synthetase (GCS) were determined with and without MeHg exposure in primary cultures of rat embryonic CNS cells. In addition, the effect of GSH modulation on MeHg-induced cytotoxicity was determined. Second, we characterized the mechanism of GCS regulation, initially by studying the GCS heavy chain subunit (GCS-HC). Primary embryonic limb bud cells were used as a reference cell type for comparing the response of CNS cells. The results indicate that constitutive intracellular GSH content, GCS activity, and GCS-HC mRNA and protein levels of CNS cells were approximately ten-, two-, five-, and ten-fold higher, respectively, than those in limb bud cells. A dose-dependent increase in GSH levels and GCS activity was observed in CNS and limb bud cells following 1 and 2 microM MeHg exposure for 20 hr. Further characterization of GCS up-regulation in CNS cells showed that the increase in GCS activity following MeHg exposure, unlike limb bud cells, was not accompanied by an elevation of GCS-HC mRNA and protein levels. Pretreatment with N-acetylcysteine led to a significant increase in intracellular GSH, while L-buthionine-(S,R)-sulfoximine (BSO) resulted in decreased GSH levels, however neither pretreatment had a significant impact on MeHg-induced cytotoxicity in either cell type. Our results suggest that although oxidative stress may mediate aspects of MeHg toxicity, disruption of GSH homeostasis alone is not responsible for the sensitivity of embryonic CNS cells to MeHg.

Acetylcysteine↗
PubMed1998

Evaluation of P19 cells for studying mechanisms of developmental toxicity: application to four direct-acting alkylating agents.

P19 cells are pluripotent murine embryonic carcinoma (EC) cells that can be induced by all-trans-retinoic acid (RA) to differentiate into cells that are biochemically and morphologically similar to cells of the central nervous system. We have established these cells as a reproducible cell system to evaluate potential effects of agents disrupting neuronal differentiation. The viability of P19 cells was assessed using a neutral red assay. Uptake of [3H]-gamma-amino butyric acid ([3H]GABA) was assessed as a marker of neuronal differentiation. We observed significant increases in [3H]GABA over time, corresponding with the appearance of cells with neuronal morphologies. 2,4-Diaminobutyric acid, a specific inhibitor of high affinity neuronal GABA uptake, reduced [3H]GABA uptake by approximately 75%. Additionally, [3H]GABA uptake in cells treated with dimethylsulfoxide (DMSO), which differentiate into mesodermal derivatives, was approximately 25% of uptake observed in RA-exposed, neuronally differentiated P19 cells. The morphology of P19 cell cultures correlated with [3H]GABA uptake: high [3H]GABA uptake was only observed in cultures with distinct neuronal morphologies. These results suggest that [3H]GABA uptake is a good indicator of neuronal differentiation in P19 cells. The responsiveness of P19 cells to developmental toxicants was assessed by comparing effects in P19 cells with effects observed previously in primary cultures of differentiating rat embryo midbrain (CNS) cells. Alkylating agents chosen for this investigation include methylnitrosourea (MNU), ethylnitrosourea (ENU), methyl methanesulfonate (MMS), and ethyl methanesulfonate (EMS). The rank order of potency of these alkylating agents in the CNS cells was MMS > MNU > ENU > EMS. With the exception of ENU, concentrations that caused effects on growth and differentiation in the P19 cells were very comparable to those causing similar effects in CNS cell cultures. Our results with P19 cells suggest that this EC cell line may also be a useful in vitro cell system for studying mechanisms of developmental toxicity, with the advantages of being an established cell line.

Alkylating Agents↗
PubMed1998

Contrasting associations of blood and semen lead concentrations with semen quality among lead smelter workers.

While blood lead concentration has been inversely associated with indicators of reproductive health in occupationally exposed male workers, the utility of lead concentration in semen as an indicator of lead exposure to the male reproductive system has not been fully explored. Blood and semen lead concentrations from 81 lead smelter workers were examined in relation to semen quality and endocrine function parameters. Mean blood and semen lead concentrations were 22.8 micrograms/dl (range 5-58) and 1.9 micrograms/dl (range 0.1-17.6), respectively. Total sperm count and concentration decreased with increasing blood lead concentration; p for trend was 0.003 and 0.009, respectively. Semen lead concentration was inversely related to total sperm count (p = 0.05), ejaculate volume (p = 0.001), and serum testosterone (p = 0.004), but not to sperm concentration. The association between semen lead concentration and total sperm count was eliminated when volume was included in the model. Blood lead concentration was more consistently associated with indicators of sperm production than was semen lead. In contrast, semen lead concentration was negatively associated with circulating testosterone concentrations. Our findings indicate that measurement of semen lead may not be a valuable adjunct to conventional blood lead monitoring for investigations of male reproductive system toxicity.

Adult↗
PubMed1998

Effects of O6-benzylguanine on growth and differentiation of P19 embryonic carcinoma cells treated with alkylating agents.

The purpose of this study was to evaluate the impact of modulating the repair of O6-alkylguanine adducts on the developmental toxicity of alkylating agents. Alkylating agents that have been shown to induce developmental toxicity following either in vitro or in vivo exposure were chosen for this investigation, and include methylnitrosourea (MNU), ethylnitrosourea (ENU), methyl methanesulfonate (MMS), and ethyl methanesulfonate (EMS). P19 cells are pluripotent murine embryonic carcinoma cells that can be induced by all trans retinoic acid (RA) to differentiate into cells that are biochemically and morphologically very similar to cells of the central nervous system. These cells are useful for studying the ability of chemicals to affect neuronal viability and differentiation. Neuronally differentiating P19 cells were pretreated with O6-benzylguanine (O6-Bg), a potent and specific inhibitor of the O6-alkylguanine-DNA-alkyltransferase (AT) protein that repairs lesions at the O6-position of guanine. In previous studies using micromass rat embryo midbrain cells, O6-Bg greatly potentiated the ability of MNU but not ENU to inhibit differentiation, and did not significantly alter the effects of either MNU or ENU on viability. In the P19 cells, we found that AT inhibition potentiated the effects of MMS, MNU, and EMS to inhibit both viability and differentiation. Additionally, AT inhibition had a much greater effect on toxicity of the methylating agents, as compared to the ethylating agents. These results suggest that O6-alkylguanine adducts can inhibit both viability and differentiation in P19 cells treated with alkylating agents.

Alkylating Agents↗
PubMed1998

Uncertainty analysis methods for comparing predictive models and biomarkers: A case study of dietary methyl mercury exposure.

Biologically based markers (biomarkers) are currently used to provide information on exposure, health effects, and individual susceptibility to chemical and radiological wastes. However, the development and validation of biomarkers are expensive and time consuming. To determine whether biomarker development and use offer potential improvements to risk models based on predictive relationships or assumed values, we explore the use of uncertainty analysis applied to exposure models for dietary methyl mercury intake. We compare exposure estimates based on self-reported fish intake and measured fish mercury concentrations with biomarker-based exposure estimates (i.e., hair or blood mercury concentrations) using a published data set covering 1 month of exposure. Such a comparison of exposure model predictions allowed estimation of bias and random error associated with each exposure model. From these analyses, both bias and random error were found to be important components of uncertainty regarding biomarker-based exposure estimates, while the diary-based exposure estimate was susceptible to bias. Application of the proposed methods to a simple case study demonstrates their utility in estimating the contribution of population variability and measurement error in specific applications of biomarkers to environmental exposure and risk assessment. Such analyses can guide risk analysts and managers in the appropriate validation, use, and interpretation of exposure biomarker information.

Animals↗
PubMed1998

Interaction of blood lead and delta-aminolevulinic acid dehydratase genotype on markers of heme synthesis and sperm production in lead smelter workers.

The gene that encodes gamma-aminolevulinic acid dehydratase (ALAD) has a polymorphism that may modify lead toxicokinetics and ultimately influence individual susceptibility to lead poisoning. To evaluate the effect of the ALAD polymorphism on lead-mediated outcomes, a cross-sectional study of male employees from a lead-zinc smelter compared associations between blood lead concentration and markers of heme synthesis and semen quality with respect to ALAD genotype. Male employees were recruited via postal questionnaire to donate blood and urine for analysis of blood lead, zinc protoporphyrin (ZPP), urinary coproporphyrin (CPU), and ALAD genotype, and semen samples for semen analysis. Of the 134 workers who had ALAD genotypes completed, 114 (85%) were ALAD1-1 (ALAD1) and 20 (15%) were ALAD1-2 (ALAD2). The mean blood lead concentrations for ALAD1 and ALAD2 were 23.1 and 28.4 microg/dl (p = 0.08), respectively. ZPP/heme ratios were higher in ALAD1 workers (68.6 vs. 57.8 micromol/ml; p = 0.14), and the slope of the blood lead ZPP linear relationship was greater for ALAD1 (2.83 vs. 1.50, p = 0.06). No linear relationship between CPU and blood lead concentration was observed for either ALAD1 or ALAD2. The associations of blood lead concentration with ZPP, CPU, sperm count, and sperm concentration were more evident in workers with the ALAD1 genotype and blood lead concentrations >/= 40 microg/dl. The ALAD genetic polymorphism appears to modify the association between blood lead concentration and ZPP. However, consistent modification of effects were not found for CPU, sperm count, or sperm concentration.

Adult↗
PubMed1997

Induction of growth arrest and DNA damage-inducible genes Gadd45 and Gadd153 in primary rodent embryonic cells following exposure to methylmercury.

Methylmercury (MeHg) is recognized as a significant environmental hazard, particularly to the development of the nervous system. Studies on the mechanism of MeHg-induced toxicity reveal that inhibition of cell cycle progression may be one way by which MeHg interferes with normal development. In this study, we utilized primary rodent embryonic neuronal cell (CNS) and limb bud (LB) cultures to determine the mRNA expression level of two genes involved in cell cycle arrest, Gadd45 and Gadd153, both during cellular differentiation and in response to MeHg exposure. A differential expression pattern of Gadd45 and Gadd153 was observed during CNS and LB differentiation in culture. However, both CNS and LB cells responded to MeHg exposure with a concentration-dependent increase in Gadd45 and Gadd153 mRNA. Previous studies have shown that MeHg exposure (2 microm) of CNS cells for 24 hr causes a fourfold decrease in the number of cells passing through the cell cycle. The present study shows that at the same exposure concentration, a five- to eightfold increase in Gadd45 mRNA levels and a two- to fourfold increase of Gadd153 was observed. Induction of Gadd45 was also noted in adult female mice chronically exposed to 10 ppm MeHg, a dose that caused developmental toxicity in vivo. Based on the known involvement of the Gadd genes in cell cycle arrest, activation of these genes could be one mechanism by which MeHg interferes with the cell cycle in adult and developing organisms.

Animals↗
PubMed1997

Ras oncogene mutations in childhood brain tumors.

Although N-nitroso compounds (NNC) are ubiquitous in the human environment and are known neurocarcinogens in animal models, results of epidemiological studies have not yet convincingly associated NNCs with brain tumor occurrence in humans. Animal studies have suggested that specific codons (12, 13, and 61) in the ras family are mutable by exposure to NNCs. The purpose of this study was to measure the presence of mutations in the ras family of oncogenes in tissue from childhood brain (CB) tumors as a preliminary step toward investigating their potential use as biomarkers of chemical exposure. DNA was extracted from paraffin-embedded formalin-fixed CB tumors from tissues resected during neurosurgical operations. Using the PCR, designed RFLP-screening methods, and sequencing, we attempted to screen brain tumors from 46 children for the presence of H, K, and N-ras mutations at codons 12, 13, and 61. Screening for oncogene mutations using PCR, RFLP methods, and DNA sequencing was successfully completed for a high proportion of the available specimens. Astrocytoma specimens from three children for whom screening with PCR was successfully completed were found to contain CAA-->GAA point mutations in K-ras at codon 61. None of the specimens contained mutations at any of the other locations. These results, although preliminary, provide a potential clue for future mechanistic studies of CB tumors. The possible roles of NNCs in inducing this mutation, or of this mutation as an early or late event in tumor progression, however, remain unclear.

Adolescent↗
PubMed1996

Workshop overview. National Toxicology Program Studies: principles of dose selection and applications to mechanistic based risk assessment.

A workshop entitled "NTP Studies: Principles of Dose Selection and Applications to Mechanistic Based Risk Assessment" was held at the 34th Annual Meeting of the Society of Toxicology in Baltimore, Maryland. The purpose of the workshop was to provide an overview of factors currently considered important in the selection of doses for NTP studies, to describe some of the confounding factors that can result from the indiscriminate use of bioassay data in quantitative risk assessment, and to suggest ways in which information from mechanistic studies or studies of biomarkers of exposure or effect might be used to better advantage in risk assessment.

Biomarkers↗
PubMed1996

A biologically-based dose-response model for developmental toxicology.

The methods currently used to evaluate the risk of developmental defects in humans from exposure to potential toxic agents do not reflect biological processes in extrapolating estimated risks to low doses and from test species to humans. We develop a mathematical model to describe aspects of the dynamic process of organogenesis, based on branching process models of cell kinetics. The biological information that can be incorporated into the model includes timing and rates of dynamic cell processes such as differentiation, migration, growth, and replication. The dose-response models produced can explain patterns of malformation rates as a function of both dose and time of exposure, resulting in improvements in risk assessment and understanding of the underlying mechanistic processes. To illustrate the use of the model, we apply it to the prediction of the effects of methylmercury on brain development in rats.

Abnormalities, Drug-Induced↗
PubMed1996

Semen quality of men employed at a lead smelter.

OBJECTIVE: To evaluate the effects of recent and long term occupational lead exposure on indicators of male reproductive health. METHODS: In a cross sectional study of male employees of a lead smelter (n = 2469), blood samples were obtained from 152 workers including 119 who also provided semen samples. Semen analysis and serum concentrations of testosterone, follicle stimulating hormone, and luteinising hormone were used as indicators of reproductive health. Semen and hormone variables were examined in relation to measures of current and long term body lead burden estimated from current blood lead concentrations and historical blood lead monitoring data. RESULTS: For current blood lead concentration groups of < 15, 15-24, 25-39, > 40 micrograms/dl, the geometric mean sperm concentrations were, respectively, 79.1, 56.5, 62.7, and 44.4 million cells/ml and geometric mean total sperm counts were 186, 153, 137, and 89 million cells (P for trend 0.04). Compared with workers with blood lead concentrations less than 15 micrograms/dl, workers with current blood lead concentrations of 40 micrograms/dl or more had an increased risk of below normal sperm concentration (odds ratio (OR) 8.2, 95% confidence interval (95% CI) 1.2-57.9) and total sperm count (OR 2.6, 95% CI 0.4-15.7), based on World Health Organisation standards. Independent of current lead exposure, sperm concentration, total sperm count, and total motile sperm count were inversely related to measures of long term lead exposure. No association was found between lead exposure and measures of sperm motility, sperm morphology, or serum concentrations of reproductive hormones. CONCLUSIONS: Blood lead concentrations below the currently accepted worker protection criteria seem to adversely affect spermatogenesis.

Adult↗
PubMed1995

Toxicity of four alkylating agents on in vitro rat embryo differentiation and development.

The relative developmental toxicity of four direct acting, alkylating agents was determined in primary cultures of differentiating rat embryo midbrain (CNS) and limb bud (LB) cells and compared with that observed in the rat whole embryo postimplantation culture system. The alkylating agents tested include methylnitrosourea (MNU), ethylnitrosourea (ENU), methyl methanesulfonate (MMS), and ethyl methanesulfonate (EMS). These alkylating agents have been shown to produce developmental toxicity following either in vitro or in vivo exposure. Viability for both CNS and LB was assessed by a neutral red dye assay. Differentiation of CNS cells was assessed by hematoxylin staining of neurons; differentiation of LB cells was assessed by Alcian blue staining of extracellular proteoglycans. Relative potencies of these compounds in the cell culture system were not the same as those observed in the embryo culture system. Whereas rank order of potency in the cell culture system, for viability and differentiation, was MMS > MNU > ENU > EMS, rank order in the embryo culture system, for embryo lethality and malformations, was MNU > ENU > MMS > EMS. Effective concentrations for cell culture viability and differentiation by MNU and ENU in cell culture were about three to nine times higher than comparable values previously reported for embryos, while effective concentrations for MMS and EMS were two to seven times lower than those observed in the embryos. Differences in potency between the two culture systems may be related to differences in formation and repair of DNA adducts, as well as differences in culture conditions.

Abnormalities, Drug-Induced↗
PubMed1995

Dose-response assessments for developmental toxicity. IV. Benchmark doses for fetal weight changes.

Recently, most attention on the application of benchmark dose (BMD) techniques to toxicology data has focused on quantal measures of response. Before the advantages of the BMD approach can be exploited in the risk assessment process, it is important that continuous measures of response also be modeled appropriately. In this study, we examined a variety of approaches to estimating BMDs for a change in fetal weight following chemical exposure from a total of 85 developmental toxicity experiments. We modeled the change in the mean fetal weight of a litter in response to treatment using a continuous power model, as well as reductions in the weight of individual fetuses within litters (defined as falling below a preset level) using a log-logistic model which incorporates litter size as a covariable and considers intralitter correlations. For the litter-based approach, several methods of defining a benchmark effect (BME) were considered, including a percentage change in mean litter weight, a change in mean litter weight relative to variability in the control group, and a reduction in the mean litter weight to some point on the control group distribution curve. For the fetus-based approach, we examined several BME options on the cumulative frequency distribution of the control fetuses for defining a low weight fetus and calculated several levels of additional risk. BMDs for four litter-based BMEs (a difference of 5% in mean fetal weight, a decrease to the 25th percentile mean weight of control litters, a decrease in the mean weight by 2 standard errors, and a decrease of 0.5 standard deviation units) and two fetus-based BMEs (a 5% added risk of weighing less than the 5th percentile of control weights and a 10% added risk of weighing less than the 10th percentile) showed strong similarities to each other and to statistically derived NOAELs. In addition to providing comparison with the NOAEL as a reference value, these analyses provided confirmation of the advantages of the BMD approach over the NOAEL in terms of the influence of dose spacing and dose selection. Combined with our previous analyses of quantal endpoints of fetal effects, this information provides a firm basis upon which to implement the benchmark dose concept in developmental toxicity risk assessments.

Animals↗
PubMed1995

Modulation of nitrosourea toxicity in rodent embryonic cells by O6-benzylguanine, a depletor of O6-methylguanine-DNA methyltransferase.

Micromass culture systems of mesencephalon (CNS) and limb bud (LB) regions were used to evaluate the impact of the O6-methylguanine-DNA methyltransferase (MGMT) inhibitor, O6-benzylguanine (BG), on ethylnitrosourea (ENU) and methylnitrosourea (MNU)-induced in vitro toxicity. These primary rat embryo cells were preincubated with BG (2.5 microM for CNS; 10 microM for LB) for 24 hr and then ENU (0-1708 microM) or MNU (0-1600 microM) was added. Five days after culture initiation, cell survival was assessed using neutral red uptake and cell differentiation was assessed using selective staining (Alcian blue in LB cultures and hematoxylin in CNS) and image analysis. In both LB and CNS cultures, preexposure to BG resulted in a significant increase in inhibition of differentiation following MNU exposure but no increase in cytotoxicity. There were no statistically significant changes in the toxicity induced by ENU in these differentiating cells consequent to BG preexposure. Our observations lend support to the idea of a specific role for DNA adducts in defining MNU's toxic effects on cell viability and differentiation.

Animals↗
PubMed1995

The application of benchmark dose methodology to data from prenatal developmental toxicity studies.

The benchmark dose (BMD) concept was applied to 246 prenatal-developmental toxicity (DT) datasets from government, industry and commercial laboratories. Five modeling approaches were used, 2 generic and 3 specific to DT models. BMDs for both quantal and continuous data were compared with statistically derived no observed adverse effect levels (NOAELs) to determine similarities. Quantal (Q) endpoints included litter responses (e.g., one or more dead or malformed implants), and QBMDs were calculated using a Q Weibull (QW) model. Two types of continuous (C) data were modeled, the proportion of implants affected per litter, and the change in fetal weight (both mean and distribution); continuous power (CP) and DT models were used to calculate CBMDs. QBMDs for a 5% change in response (QBMD05) were 6-fold lower, on average, than the corresponding NOAEL. CBMD05s on average were similar to the corresponding NOAELs, and CBMD05s from different models were similar to each other. Including litter size but not threshold improved the fit of the DT models. For fetal weight data, specific cutoff values were used to calculate BMDs that were similar on average to the corresponding NOAELs: (1) changes from the control mean (5% of the mean, 25th percentile of the control distribution, or a decrease of 0.5 standard deviation), and (2) a 5 or 10% decrease in the proportion of fetuses below the 5th or 10th percentile, respectively, of the control distribution. These results support the use of BMDs as providing a more consistent basis for risk assessment than do NOAELs.

Animals↗
PubMed1995

Formation of N-7-(2-carbamoyl-2-hydroxyethyl)guanine in DNA of the mouse and the rat following intraperitoneal administration of [14C]acrylamide.

Acrylamide is an alkylating agent which reacts very slowly in direct reactions with DNA and is negative in the Ames test, but is carcinogenic in mice and rats. In order to explain the cancer-initiating properties of acrylamide we have studied DNA adduct formation in vitro with a metabolizing system and in vivo in mice and rats following i.p. administration of 14C-labeled acrylamide. A major adduct found in both species was N-7-(2-carbamoyl-2-hydroxy-ethyl)guanine, formed by reaction of the DNA with the epoxide metabolite glycidamide. The levels of this adduct were similar in the different organs of the two rodent species, which supports the notion that glycidamide is relatively evenly distributed among tissues and that the organ-specificity in acrylamide carcinogenesis cannot be explained by a selective accumulation of the DNA-reactive metabolite in target organs.

Acrylamide↗