Janice W. Yager

Guidelines for the communication of Biomonitoring Equivalents: Report from the Biomonitoring Equivalents Expert Workshop

Biomonitoring Equivalents (BEs) are screening tools for interpreting biomonitoring data. However, the development of BEs brings to the public a relatively novel concept in the field of health risk assessment and presents new challenges for environmental risk communication. This paper provides guidance on methods for conveying information to the general public, the health care community, regulators and other interested parties regarding how chemical-specific BEs are derived, what they mean in terms of health, and the challenges and questions related to interpretation and communication of biomonitoring data. Key communication issues include: (i) developing a definition of the BE that accurately captures the BE concept in lay terms, (ii) how to compare population biomonitoring data to BEs, (iii) interpreting biomonitoring data that exceed BEs for a specific chemical, (iv) how to best describe the confidence in chemical-specific BEs, and (v) key requirements for effective communication with health care professionals. While the risk communication literature specific to biomonitoring is sparse, many of the concepts developed for traditional risk assessments apply, including transparency and discussions of confidence and uncertainty. Communication of BEs will require outreach, education, and development of communication materials specific to several audiences including the lay public and health care providers.

Inhibition of poly(ADP-ribose) polymerase by arsenite.

Inorganic arsenic is considered a human carcinogen based principally on epidemiological evidence. Unlike most initiating chemicals, arsenic is inactive or extremely weak in its ability to directly induce gene mutations. Arsenite has been shown, however, to enhance mutagenicity when present with other agents such as UV radiation. Synergistic potentiation of chromosomal damage has been shown with co-treatment with DNA-crosslinking agents. Arsenite at low concentrations is known to be highly selective in reacting with closely spaced (vicinal) dithiol groups in proteins. Poly(ADP-ribose) polymerase (PARP) is known to contain such vicinal dithiol groups. Stimulation of PARP is an immediate response of eukaryotic cells to DNA strand breaks and has been implicated in DNA repair. The effect of treatment with sodium arsenite on PARP activity was assessed as follows: Molt-3 cells (a human T-cell lymphoma-derived cell line) in culture were treated for 24 h with concentrations of sodium arsenite ranging from 2.5 up to 25 microM. Speciation of inorganic arsenic and cell viability were determined. Cell cycle kinetics were measured by flow cytometry. Poly(ADP-ribose) synthesis was assayed using a palindromic decameric deoxynucleotide to stimulate enzyme activity. Results show that arsenite decreases PARP activity in a dose-dependent manner with an approximately 50% decrease in enzyme activity at 10 microM arsenite and 80% viability. The percent of cells in S-phase increases with increasing concentration of arsenite. These results provide further indication that arsenite may potentiate genetic damage through reaction with dithiols in DNA repair proteins such as PARP, perhaps resulting in interference with normal repair function.

Effect of hepatic methyl donor status on urinary excretion and DNA damage in B6C3F1 mice treated with sodium arsenite

This study evaluated the effect of hepatic methyl donor status on the ability of sodium arsenite (2.5, 5.0 and 10.0 mg/kg) administered by gavage once or on four consecutive days to induce DNA damage in male B6C3F1 mice. Maintenance on a choline-deficient (CD) diet prior to treatment resulted in mice with hepatic methyl donor deficiency (HMDD) and altered arsenical metabolism, as demonstrated by a decreased total urinary excretion of inorganic and organic arsenicals. The alkaline (pH > 13) Single Cell Gel (SCG) assay was used to evaluate for the induction of DNA damage (single strand breaks, alkali labile sites, DNA crosslinking) in blood leukocytes, liver parenchymal cells, and cells sampled from bladder, lung, and skin, while the bone marrow erythrocyte micronucleus (MN) assay was used to assess for the induction of chromosomal damage in bone marrow cells. Treatment with sodium arsenite once or four times induced a significant decrease in DNA migration (indicative of DNA crosslinking) in bladder and liver parenchymal cells of hepatic methyl donor sufficient (HMDS) mice, but in skin cells of HMDD mice. Both HMDD and HMDS mice exhibited a significant increase in the frequency of micronucleated polychromatic erythrocytes (MN-PCE) in bone marrow following four, but not following one, treatments. However, the positive response occurred at a lower dose for HMDS mice and, in these mice, bone marrow toxicity, as demonstrated by a significant reduction in the percentage of PCE, was present also. These results indicate that hepatic methyl donors deficiency significantly decreases the total urinary excretion of orally administered sodium arsenite and markedly modulates target organ arsenic-induced DNA damage, with an apparent shift from liver and bladder to skin.

Tissue distribution and urinary excretion of inorganic arsenic and its methylated metabolites in C57BL6 mice following subchronic exposure to arsenate in drinking water.

The relationship of exposure and tissue concentration of parent chemical and metabolites over prolonged exposure is a critical issue for chronic toxicities mediated by metabolite(s) rather than parent chemical alone. This is an issue for AsV because its trivalent metabolites have unique toxicities and relatively greater potency compared to their pentavalent counterparts for many endpoints. In this study, dose-dependency in tissue distribution and urinary excretion for inorganic arsenic and its methylated metabolites was assessed in female C57Bl/6 mice exposed to 0, 0.5, 2, 10 or 50 ppm arsenic (as arsenate, AsV) in their drinking water for 12 weeks. No adverse effects were observed and body weight gain did not differ significantly among groups. Urinary excretion of arsenite monomethylarsonous acid (MMA(III)), dimethylarsinous acid (DMA(III)), dimethylarsinic acid (DMAV), and trimethylarsine oxide (TMAO) increased linearly with dose, whereas AsV and monomethylarsonic acid (MMAV) excretion was non-linear with respect to dose. Total tissue arsenic accumulation was greatest in kidney > lung > urinary bladder >>> skin > blood > liver. Monomethyl arsenic (MMA, i.e. MMA(III)+MMAV) was the predominant metabolite in kidney, whereas dimethylarsenic (DMA, i.e., DMA(III)+DMAV) was the predominant metabolite in lung. Urinary bladder tissue had roughly equivalent levels of inorganic arsenic and dimethylarsenic, as did skin. These data indicate that pharmacokinetic models for arsenic metabolism and disposition need to include mechanisms for organ-specific accumulation of some arsenicals and that urinary metabolite profiles are not necessarily reflective of target tissue dosimetry.

Analysis of genomic dose-response information on arsenic to inform key events in a mode of action for carcinogenicity.

A comprehensive literature search was conducted to identify information on gene expression changes following exposures to inorganic arsenic compounds. This information was organized by compound, exposure, dose/concentration, species, tissue, and cell type. A concentration‐related hierarchy of responses was observed, beginning with changes in gene/protein expression associated with adaptive responses (e.g., preinflammatory responses, delay of apoptosis). Between 0.1 and 10 μM, additional gene/protein expression changes related to oxidative stress, proteotoxicity, inflammation, and proliferative signaling occur along with those related to DNA repair, cell cycle G2/M checkpoint control, and induction of apoptosis. At higher concentrations (10–100 μM), changes in apoptotic genes dominate. Comparisons of primary cell results with those obtained from immortalized or tumor‐derived cell lines were also evaluated to determine the extent to which similar responses are observed across cell lines. Although immortalized cells appear to respond similarly to primary cells, caution must be exercised in using gene expression data from tumor‐derived cell lines, where inactivation or overexpression of key genes (e.g., p53, Bcl‐2) may lead to altered genomic responses. Data from acute in vivo exposures are of limited value for evaluating the dose‐response for gene expression, because of the transient, variable, and uncertain nature of tissue exposure in these studies. The available in vitro gene expression data, together with information on the metabolism and protein binding of arsenic compounds, provide evidence of a mode of action for inorganic arsenic carcinogenicity involving interactions with critical proteins, such as those involved in DNA repair, overlaid against a background of chemical stress, including proteotoxicity and depletion of nonprotein sulfhydryls. The inhibition of DNA repair under conditions of toxicity and proliferative pressure may compromise the ability of cells to maintain the integrity of their DNA. Environ. Mol. Mutagen., 2010.

Case study report. Business case for implementing battery-powered tools for direct-bury line workers at an electric power utility.

C utting cable and crimping compression connectors are the two most commonly performed tasks by direct-bury line workers who repair and bury underground cable for electric power utilities. Battery-powered tools, rather than manual (Figure 1), do the demanding work of cutting cable and crimping connectors while the worker holds the tool in place.(1) The focus of this case study is whether the cost of batterypowered tools for direct-bury line workers can be justified based on injury and illness data and other factors.

Biomonitoring Equivalents (BE) dossier for cadmium (Cd) (CAS No. 7440-43-9)

Recent efforts by the US Centers for Disease Control and Prevention and other researchers have resulted in a growing database of measured concentrations of chemical substances in blood or urine samples taken from the general population. However, few tools exist to assist in the interpretation of the measured values in a health risk context. Biomonitoring Equivalents (BEs) are defined as the concentration or range of concentrations of a chemical or its metabolite in a biological medium (blood, urine, or other medium) that is consistent with an existing health-based exposure guideline. This document reviews available pharmacokinetic data and models for cadmium and applies these data and models to existing health-based exposure guidance values from the US Environmental Protection Agency, the Agency for Toxic Substances and Disease Registry, Health Canada, and the World Health Organization, to estimate corresponding BE values for cadmium in blood and urine. These values can be used as screening tools for evaluation of biomonitoring data for cadmium in the context of existing risk assessments for cadmium and for prioritization of the potential need for additional risk assessment and risk management efforts for cadmium.

Concentration- and time-dependent genomic changes in the mouse urinary bladder following exposure to arsenate in drinking water for up to 12 weeks.

Inorganic arsenic (As(i)) is a known human bladder carcinogen. The objective of this study was to examine the concentration dependence of the genomic response to As(i) in the urinary bladders of mice. C57BL/6J mice were exposed for 1 or 12 weeks to arsenate in drinking water at concentrations of 0.5, 2, 10, and 50 mg As/l. Urinary bladders were analyzed using gene expression microarrays. A consistent reversal was observed in the direction of gene expression change: from predominantly decreased expression at 1 week to predominantly increased expression at 12 weeks. These results are consistent with evidence from in vitro studies of an acute adaptive response that is suppressed on longer exposure due to downregulation of Fos. Pathways with the highest enrichment in gene expression changes were associated with epithelial-to-mesenchymal transition, inflammation, and proliferation. Benchmark dose (BMD) analysis determined that the lowest median BMD values for pathways were above 5 mg As/l, despite the fact that pathway enrichment was observed at the 0.5 mg As/l exposure concentration. This disparity may result from the nonmonotonic nature of the concentration-responses for the expression changes of a number of genes, as evidenced by the much fewer gene expression changes at 2 mg As/l compared with lower or higher concentrations. Pathway categories with concentration-related gene expression changes included cellular morphogenesis, inflammation, apoptosis/survival, cell cycle control, and DNA damage response. The results of this study provide evidence of a concentration-dependent transition in the mode of action for the subchronic effects of As(i) in mouse bladder cells in the vicinity of 2 mg As(i)/l.

Evaluation of uncontrolled confounding in studies of environmental exposures and neurobehavioral testing in children.

Background: Neurobehavioral tests are commonly used in studies of children exposed to low-level environmental concentrations of compounds known to be neurotoxic at higher levels. However, uncontrolled or incomplete control for confounding makes interpretation of results problematic because effects of confounders are often stronger than the effects of primary interest. We examined a priori the potential impact of confounding in a hypothetical study evaluating the association of a potentially neurotoxic environmental exposure with neurobehavioral function in children. Methods: We used 2 outcome measures: the Bayley Scales of Infant Development Mental Development Index and the Stanford-Binet Intelligence Scale Composite Score. We selected 3 potential confounders: maternal intelligence, home environment, and socioeconomic status as measured by years of parental education. We conducted 3 sets of analyses measuring the effect of each of the 3 confounding factors alone, 2 confounders acting simultaneously, and all 3 confounders acting simultaneously. Results: Relatively small differences (0.5 standard deviations) in confounding variables between “exposed” and “unexposed” groups, if unmeasured and unaccounted for in the analysis, could produce spurious differences in cognitive test scores. The magnitude of this difference (3–10 points) has been suggested to have a meaningful impact in populations. The method of measuring confounders (eg, maternal intelligence) could also substantially affect the results. Conclusions: It is important to carefully consider the impact of potential confounders during the planning stages of an observational study. Study-to-study differences in neurobehavioral outcomes with similar environmental exposures could be partially explained by differences in the adjustment for confounding variables.

Physiologically Based Pharmacokinetic Modeling of Arsenic in the Mouse

A remarkable feature of the carcinogenicity of inorganic arsenic is that while human exposures to high concentrations of inorganic arsenic in drinking water are associated with increases in skin, lung, and bladder cancer, inorganic arsenic has not typically caused tumors in standard laboratory animal test protocols. Inorganic arsenic administered for periods of up to 2 yr to various strains of laboratory mice, including the Swiss CD-1, Swiss CR:NIH(S), C57Bl/6p53(+/−), and C57Bl/6p53(+/+), has not resulted in significant increases in tumor incidence. However, Ng et al. (1999) have reported a 40% tumor incidence in C57Bl/6J mice exposed to arsenic in their drinking water throughout their lifetime, with no tumors reported in controls. In order to investigate the potential role of tissue dosimetry in differential susceptibility to arsenic carcino-genicity, a physiologically based pharmacokinetic (PBPK) model for inorganic arsenic in the rat, hamster, monkey, and human (Mann et al., 1996a, 1996) was extended to describe the kinetics in the mouse. The PBPK model was parameterized in the mouse using published data from acute exposures of B6C3F1 mice to arsenate, arsenite, monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA) and validated using data from acute exposures of C57Black mice. Predictions of the acute model were then compared with data from chronic exposures. There was no evidence of changes in the apparent volume of distribution or in the tissue-plasma concentration ratios between acute and chronic exposure that might support the possibility of inducible arsenite efflux. The PBPK model was also used to project tissue dosimetry in the C57Bl/6J study, in comparison with tissue levels in studies having shorter duration but higher arsenic treatment concentrations. The model evaluation indicates that pharmacokinetic factors do not provide an explanation for the difference in outcomes across the various mouse bioassays. Other possible explanations may relate to strain-specific differences, or to the different durations of dosing in each of the mouse studies, given the evidence that inorganic arsenic is likely to be active in the later stages of the carcinogenic process.