Derivation of oral cancer slope factors for hexavalent chromium informed by pharmacokinetic models and in vivo genotoxicity data

Hexavalent chromium [Cr(VI)] is present in drinking water from natural and anthropogenic sources at approximately 1 ppb. Several regulatory bodies have recently developed threshold-based safety criteria for Cr(VI) of 30-100 ppb based on evidence that small intestine tumors in mice following exposure to ≥20,000 ppb are the result of a non-mutagenic mode of action (MOA). In contrast, U.S. EPA has recently concluded that Cr(VI) acts through a mutagenic MOA based, in part, on scoring numerous in vivo genotoxicity studies as having low confidence; and therefore derived a cancer slope factor (CSF) of 0.5 (mg/kg-day)-1, equivalent to ∼0.07 ppb. Herein, we demonstrate how physiologically based pharmacokinetic (PBPK) models and intestinal segment-specific tumor incidence data can form a robust dataset supporting derivation of alternative CSF values that equate to Cr(VI) concentrations ranging from below background to concentrations similar to those derived using threshold approaches-depending on benchmark response level and risk tolerance. Additionally, we highlight weaknesses in the rationale EPA used to discount critical in vivo genotoxicity studies. While the data support a non-genotoxic MOA, these alternative toxicity criteria require only PBPK models, robust tumor data, and fair interpretation of published in vivo genotoxicity data for Cr(VI).

Biogeographical survey of soil microbiomes across sub-Saharan Africa: structure, drivers, and predicted climate-driven changes

BACKGROUND

Top-soil microbiomes make a vital contribution to the Earth's ecology and harbor an extraordinarily high biodiversity. They are also key players in many ecosystem services, particularly in arid regions of the globe such as the African continent. While several recent studies have documented patterns in global soil microbial ecology, these are largely biased towards widely studied regions and rely on models to interpolate the microbial diversity of other regions where there is low data coverage. This is the case for sub-Saharan Africa, where the number of regional microbial studies is very low in comparison to other continents.

RESULTS

The aim of this study was to conduct an extensive biogeographical survey of sub-Saharan Africa's top-soil microbiomes, with a specific focus on investigating the environmental drivers of microbial ecology across the region. In this study, we sampled 810 sample sites across 9 sub-Saharan African countries and used taxonomic barcoding to profile the microbial ecology of these regions. Our results showed that the sub-Saharan nations included in the study harbor qualitatively distinguishable soil microbiomes. In addition, using soil chemistry and climatic data extracted from the same sites, we demonstrated that the top-soil microbiome is shaped by a broad range of environmental factors, most notably pH, precipitation, and temperature. Through the use of structural equation modeling, we also developed a model to predict how soil microbial biodiversity in sub-Saharan Africa might be affected by future climate change scenarios. This model predicted that the soil microbial biodiversity of countries such as Kenya will be negatively affected by increased temperatures and decreased precipitation, while the fungal biodiversity of Benin will benefit from the increase in annual precipitation.

CONCLUSION

This study represents the most extensive biogeographical survey of sub-Saharan top-soil microbiomes to date. Importantly, this study has allowed us to identify countries in sub-Saharan Africa that might be particularly vulnerable to losses in soil microbial ecology and productivity due to climate change. Considering the reliance of many economies in the region on rain-fed agriculture, this study provides crucial information to support conservation efforts in the countries that will be most heavily impacted by climate change. Video Abstract.

Evaluating cone-beam CT in the diagnosis of suspected scaphoid fractures in the emergency department: preliminary findings

OBJECTIVES

Scaphoid fractures are challenging to accurately diagnose with delayed and missed diagnoses risking poor patient outcomes. Cone beam CT (CBCT) is an emerging technology facilitating alternative access to multi-planar imaging. The aim of this study was to evaluate the use of early CBCT in the diagnosis of suspected scaphoid fractures presenting via the Emergency Department (ED).

METHODS

In this single centre the imaging pathway was adapted to include early CBCT in adult patients with a persisting high index of clinical suspicion for scaphoid fracture despite normal radiographs. Evaluation of referrals between September 2019 and February 2020 was undertaken. Statistical analysis and temporal pathway metrics were assessed including interrater agreement for CBCT and radiography examinations.

RESULTS

Over the six-month timeframe 100 CBCT wrist scans were performed on 99 adult patients. 94% of CBCT scans were performed within 1 day of referral. 25% of scans demonstrated acute injuries including 12 radius, 6 trapezium and 2 scaphoid fractures. For fracture, CBCT had a sensitivity of 96.2% and specificity of 100%. There was a highly significant difference in interobserver variation between fracture detection on CBCT and radiographs.

CONCLUSION

CBCT heralds the potential for early accurate diagnosis of radiocarpal fractures, at lower cost, shortening clinical pathways and reducing clinical risk in the ED.

Predictive modeling of biological responses in the rat liver using in vitro Tox21 bioactivity: Benefits from high-throughput toxicokinetics

Computational methods are needed to more efficiently leverage data from in vitro cell-based models to predict what occurs within whole body systems after chemical insults. This study set out to test the hypothesis that in vitro high-throughput screening (HTS) data can more effectively predict in vivo biological responses when chemical disposition and toxicokinetic (TK) modeling are employed. In vitro HTS data from the Tox21 consortium were analyzed in concert with chemical disposition modeling to derive nominal, aqueous, and intracellular estimates of concentrations eliciting 50% maximal activity. In vivo biological responses were captured using rat liver transcriptomic data from the DrugMatrix and TG-Gates databases and evaluated for pathway enrichment. In vivo dosing data were translated to equivalent body concentrations using HTTK modeling. Random forest models were then trained and tested to predict in vivo pathway-level activity across 221 chemicals using in vitro bioactivity data and physicochemical properties as predictor variables, incorporating methods to address imbalanced training data resulting from high instances of inactivity. Model performance was quantified using the area under the receiver operator characteristic curve (AUC-ROC) and compared across pathways for different combinations of predictor variables. All models that included toxicokinetics were found to outperform those that excluded toxicokinetics. Biological interpretation of the model features revealed that rather than a direct mapping of in vitro assays to in vivo pathways, unexpected combinations of multiple in vitro assays predicted in vivo pathway-level activities. To demonstrate the utility of these findings, the highest-performing model was leveraged to make new predictions of in vivo biological responses across all biological pathways for remaining chemicals tested in Tox21 with adequate data coverage (n = 6617). These results demonstrate that, when chemical disposition and toxicokinetics are carefully considered, in vitro HT screening data can be used to effectively predict in vivo biological responses to chemicals.

An adverse outcome pathway for small intestinal tumors in mice involving chronic cytotoxicity and regenerative hyperplasia: a case study with hexavalent chromium, captan, and folpet

Small intestinal (SI) tumors are relatively uncommon outcomes in rodent cancer bioassays, and limited information regarding chemical-induced SI tumorigenesis has been reported in the published literature. Herein, we propose a cytotoxicity-mediated adverse outcome pathway (AOP) for SI tumors by leveraging extensive target species- and site-specific molecular, cellular, and histological mode of action (MOA) research for three reference chemicals, the fungicides captan and folpet and the transition metal hexavalent chromium (Cr(VI)). The gut barrier functions through highly efficient homeostatic regulation of SI epithelial cell sloughing, regenerative proliferation, and repair, which involves the replacement of up to 10¹¹ cells per day. This dynamic turnover in the SI provides a unique local environment for a cytotoxicity mediated AOP/MOA. Upon entering the duodenum, cytotoxicity to the villous epithelium is the molecular initiating event, as indicated by crypt elongation, villous atrophy/blunting, and other morphologic changes. Over time, the regenerative capacity of the gut epithelium to compensate declines as epithelial loss accelerates, especially at higher exposures. The first key event (KE), sustained regenerative crypt proliferation/hyperplasia, requires sufficient durations, likely exceeding 6 or 12 months, due to extensive repair capacity, to create more opportunities for the second KE, spontaneous mutation/transformation, ultimately leading to proximal SI tumors. Per OECD guidance, biological plausibility, essentiality, and empirical support were assessed using modified Bradford Hill considerations. The weight-of-evidence also included a lack of induced mutations in the duodenum after up to 90 days of Cr(VI) or captan exposure. The extensive evidence for this AOP, along with the knowledge that human exposures are orders of magnitude below those associated with KEs in this AOP, supports its use for regulatory applications, including hazard identification and risk assessment.

Magnetic Stimulus Responsive DDS Based on Chitosan Microbeads Embedded with Magnetic Nanoparticles

In this paper, we have presented a novel Drug Delivery Substrate (DDS) that that is responsive to external stimuli of high-frequency alternating magnetic fields. The DDS is constituted of chitosan crosslinked with PEGDMA (polyethylene glycol dimethacrylate), loaded with Fe₃O₄ magnetic nanoparticles and vancomycin. In another experiment, a 19-hour elution was observed where three magnetic stimuli of 25 mT, 109.9 kHz were given for 60 min to the test samples. The stimuli were separated by several hours. After excitation span, it was observed that the stimulated samples released a significantly higher amount of vancomycin by as much as 21% compared to non-stimulated samples. In another study, preliminary results showing the effect of different PEGDMA chain lengths have been discussed. These results show evidence of a smart, controllable DDS that allows modulation of its normal passive antibiotic elution by applying external stimuli per personalized needs.

Comparison of Gene Expression Responses in the Small Intestine of Mice Following Exposure to 3 Carcinogens Using the S1500+ Gene Set Informs a Potential Common Adverse Outcome Pathway

Carcinogenesis of the small intestine is rare in humans and rodents. Oral exposure to hexavalent chromium (Cr(VI)) and the fungicides captan and folpet induce intestinal carcinogenesis in mice. Previously (Toxicol Pathol. 330:48-52), we showed that B6C3F1 mice exposed to carcinogenic concentrations of Cr(VI), captan, or folpet for 28 days exhibited similar histopathological responses including villus enterocyte cytotoxicity and regenerative crypt epithelial hyperplasia. Herein, we analyze transcriptomic responses from formalin-fixed, paraffin-embedded duodenal sections from the aforementioned study. TempO-Seq technology and the S1500+ gene set were used to analyze transcription responses. Transcriptional responses were similar between all 3 agents; gene-level comparison identified 126/546 (23%) differentially expressed genes altered in the same direction, with a total of 25 upregulated pathways. These changes were related to cellular metabolism, stress, inflammatory/immune cell response, and cell proliferation, including upregulation in hypoxia inducible factor 1 (HIF-1) and activator protein 1 (AP1) signaling pathways, which have also been shown to be related to intestinal injury and angiogenesis/carcinogenesis. The similar molecular-, cellular-, and tissue-level changes induced by these 3 carcinogens can be informative for the development of an adverse outcome pathway for intestinal cancer.

Identifying Attributes That Influence In Vitro-to-In Vivo Concordance by Comparing In Vitro Tox21 Bioactivity Versus In Vivo DrugMatrix Transcriptomic Responses Across 130 Chemicals

Recent efforts aimed at integrating in vitro high-throughput screening (HTS) data into chemical toxicity assessments are necessitating increased understanding of concordance between chemical-induced responses observed in vitro versus in vivo. This investigation set out to (1) measure concordance between in vitro HTS data and transcriptomic responses observed in vivo, focusing on the liver, and (2) identify attributes that can influence concordance. Signal response profiles from 130 substances were compared between in vitro data produced through Tox21 and liver transcriptomic data through DrugMatrix, collected from rats exposed to a chemical for ≤5 days. A global in vitro-to-in vivo comparative analysis based on pathway-level responses resulted in an overall average percent agreement of 79%, ranging on a per-chemical basis between 41% and 100%. Whereas concordance amongst inactive chemicals was high (89%), concordance amongst chemicals showing in vitro activity was only 13%, suggesting that follow-up in vivo and/or orthogonal in vitro assays would improve interpretations of in vitro activity. Attributes identified to influence concordance included experimental design attributes (eg, cell type), target pathways, and physicochemical properties (eg, logP). The attribute that most consistently increased concordance was dose applicability, evaluated by filtering for experimental doses administered to rats that were within 10-fold of those related to likely bioactivity, derived using Tox21 data and high-throughput toxicokinetic modeling. Together, findings suggest that in vitro screening approaches to predict in vivo toxicity are viable particularly when certain attributes are considered, including whether activity versus inactivity is observed, experimental design, chemical properties, and dose applicability.

Assistant radiographer practitioners: Creating capacity or challenging professional boundaries?

INTRODUCTION

Over the last 2 decades the assistant radiographer practitioner (ARP) role has been introduced into NHS diagnostic imaging departments as a strategy to expand the workforce and create capacity. This skill mix initiative has not been implemented in a standardised way and there is limited knowledge of the current role scope within general radiography (X-Ray).

METHOD

An electronic survey of ARPs working within UK diagnostic imaging departments was conducted. Both open and closed questions sought information regarding basic demographic data (age category; gender; geographic region), scope of practice (patient groups; anatomical regions; imaging outside of the diagnostic imaging department), limitations placed on practice, supervision and additional roles.

RESULTS

A total of 108 responses, including 13 trainees, were received. Most sites employ three or less ARPs in general radiography (n = 43/66; 65.2%), although 11 sites have five (range 1-15). The majority undertake imaging of both adults and children (n = 85/108; 78.7%), although limitations on age were described. Their scope of practice covers a broad anatomical range and included some non-ambulant patients. The level of supervision varied with some sites empowering ARPs to check the referral prior to examination (n = 25) or images post acquisition (n = 32) (both n = 20/66; χ² = 16.003; 1df; p = 0.000).

CONCLUSION

ARPs are helping to maintain capacity in imaging departments but we suggest there is further scope for expansion. The practice described by the post holders suggests that many are working beyond the scope envisaged by the radiography professional body.

Integration of mechanistic and pharmacokinetic information to derive oral reference dose and margin-of-exposure values for hexavalent chromium

The current US Environmental Protection Agency (EPA) reference dose (RfD) for oral exposure to chromium, 0.003 mg kg-1  day-1 , is based on a no-observable-adverse-effect-level from a 1958 bioassay of rats exposed to ≤25 ppm hexavalent chromium [Cr(VI)] in drinking water. EPA characterizes the confidence in this RfD as "low." A more recent cancer bioassay indicates that Cr(VI) in drinking water is carcinogenic to mice at ≥30 ppm. To assess whether the existing RfD is health protective, neoplastic and non-neoplastic lesions from the 2 year cancer bioassay were modeled in a three-step process. First, a rodent physiological-based pharmacokinetic (PBPK) model was used to estimate internal dose metrics relevant to each lesion. Second, benchmark dose modeling was conducted on each lesion using the internal dose metrics. Third, a human PBPK model was used to estimate the daily mg kg-1 dose that would produce the same internal dose metric in both normal and susceptible humans. Mechanistic research into the mode of action for Cr(VI)-induced intestinal tumors in mice supports a threshold mechanism involving intestinal wounding and chronic regenerative hyperplasia. As such, an RfD was developed using incidence data for the precursor lesion diffuse epithelial hyperplasia. This RfD was compared to RfDs for other non-cancer endpoints; all RfD values ranged 0.003-0.02 mg kg-1  day-1 . The lowest of these values is identical to EPA's existing RfD value. Although the RfD value remains 0.003 mg kg-1  day-1 , the confidence is greatly improved due to the use of a 2-year bioassay, mechanistic data, PBPK models and benchmark dose modeling.

Comparison of Toxicity and Recovery in the Duodenum of B6C3F1 Mice Following Treatment with Intestinal Carcinogens Captan, Folpet, and Hexavalent Chromium

High concentrations of hexavalent chromium (Cr(VI)), captan, and folpet induce duodenal tumors in mice. Using standardized tissue collection procedures and diagnostic criteria, we compared the duodenal histopathology in B6C3F1 mice following exposure to these 3 carcinogens to determine whether they share similar histopathological characteristics. B6C3F1 mice ( n = 20 per group) were exposed to 180 ppm Cr(VI) in drinking water, 12,000 ppm captan in feed, or 16,000 ppm folpet in feed for 28 days. After 28 days of exposure, villous enterocyte hypertrophy and mild crypt epithelial hyperplasia were observed in all exposed mice. In a subset of mice allowed to recover for 28 days, duodenal samples were generally indistinguishable from those of unexposed mice. Changes in the villi and lack of observable damage to the crypt compartment suggest that toxicity was mediated in the villi, which is consistent with earlier studies on each chemical. These findings indicate that structurally diverse agents can induce similar (and reversible) phenotypic changes in the duodenum. These intestinal carcinogens likely converge on common pathways involving irritation and wounding of the villi leading to crypt regenerative hyperplasia that, under protracted high-dose exposure scenarios, increases the risk of spontaneous mutation and tumorigenesis.

Estimating serum concentrations of dioxin-like compounds in the U.S. population effective 2005-2006 and 2007-2008: A multiple imputation and trending approach incorporating NHANES pooled sample data

Dioxin-like compounds (DLCs) are monitored in the U.S. population using data collected with the National Health and Nutrition Examination Survey (NHANES). Until recently, participants' serum samples have been analyzed individually, and summary statistics defining reference ranges by age, gender, and race/ethnicity have served as the background by which other biomonitoring data can be evaluated. In the most recent NHANES DLC data, 2005-2006 and 2007-2008, participants' sera have been physically pooled prior to laboratory analysis, introducing major challenges to their utility as a reference population: variability among individuals and relations with covariates are lost, and individual design effects cannot be applied. Further, the substantial drop in limits of detection (LODs) in pooled sample biennials prevents reliable comparisons to individual data, and has complicated estimates of change over time. In this study, we address the drawbacks introduced by pooled samples by generating U.S. population reference ranges based on individual-level data adjusted to 2005-2006 and 2007-2008 levels. Using publicly available data, multiple imputation (MI) generated four NHANES biennials (2001-2008) of individual DLC data; we then trended the change over time in each DLC by demographic stratum. NHANES 2003-2004 individuals were adjusted by the trended change over time. Population estimates of toxic equivalency (TEQ) concentrations were calculated using traditional MI survey analysis methods and reference tables provided for 2005-2006 and 2007-2008 by age, race, and gender. Demographic differences in TEQ concentrations and trended change are reported, e.g. TEQ continues to drop in young adults aged 20-39, but distributions appear stable in older adults 60+; Mexican Americans have consistently lowest dioxins, furans, and PCBs, with non-Hispanic Blacks dropping to the same levels as non-Hispanic Whites in dioxins and PCBs and significantly below non-Hispanic Whites in furans by 2007-2008. Additionally, the ratio of 95th percentile to mean in DLC distributions was found to vary by age, between dioxins, furans, and PCBs, and across mean, making a simple ratio approach impractical for describing population concentrations using pooled samples. We discuss the practical implications of the pooled sample method, the performance of this trending solution in the context of other methods, and expected effects of distribution assumptions on variability and TEQ estimates, particularly in largely undetected congeners. These updated reference populations of individuals, along with information on trending, provide a common and valid basis for interpreting other individually sampled biomonitoring data.

High-Throughput Screening Data Interpretation in the Context of In Vivo Transcriptomic Responses to Oral Cr(VI) Exposure

The toxicity of hexavalent chromium [Cr(VI)] in drinking water has been studied extensively, and available in vivo and in vitro studies provide a robust dataset for application of advanced toxicological tools to inform the mode of action (MOA). This study aimed to contribute to the understanding of Cr(VI) MOA by evaluating high-throughput screening (HTS) data and other in vitro data relevant to Cr(VI), and comparing these findings to robust in vivo data, including transcriptomic profiles in target tissues. Evaluation of Tox21 HTS data for Cr(VI) identified 11 active assay endpoints relevant to the Ten Key Characteristics of Carcinogens (TKCCs) that have been proposed by other investigators. Four of these endpoints were related to TP53 (tumor protein 53) activation mapping to genotoxicity (KCC#2), and four were related to cell death/proliferation (KCC#10). HTS results were consistent with other in vitro data from the Comparative Toxicogenomics Database. In vitro responses were compared to in vivo transcriptomic responses in the most sensitive target tissue, the duodenum, of mice exposed to ≤ 180 ppm Cr(VI) for 7 and 90 days. Pathways that were altered both in vitro and in vivo included those relevant to cell death/proliferation. In contrast, pathways relevant to p53/DNA damage were identified in vitro but not in vivo. Benchmark dose modeling and phenotypic anchoring of in vivo transcriptomic responses strengthened the finding that Cr(VI) causes cell stress/injury followed by proliferation in the mouse duodenum at high doses. These findings contribute to the body of evidence supporting a non-mutagenic MOA for Cr(VI)-induced intestinal cancer.

Transcriptomic responses in the oral cavity of F344 rats and B6C3F1 mice following exposure to Cr(VI): Implications for risk assessment

Exposure to hexavalent chromium [Cr(VI)] in drinking water was previously reported to increase oral tumor incidence in F344 rats. To investigate the mode of action for these tumors, transcriptomic profiles in oral mucosa samples of F344 rats and B6C3F1 mice were analyzed following exposure to 0.1-180 ppm Cr(VI) for 7 or 90 days. In rats, genome-wide microarray analyses identified no significantly differentially expressed genes (DEGs) at either time point. In mice, 14 and 1 DEGs were respectively identified after 7 and 90 days of exposure. Therefore, relaxed statistical criteria were employed to identify potential DEGs (pDEGs), followed by high-throughput benchmark dose modeling to identify responsive pDEGs for pathway enrichment analysis. This identified 288 and 168 pDEGs in the rat oral mucosa, of which only 20 and 7 showed evidence of dose-response. No significant pathway enrichment was obtained with either pDEG or dose-responsive pDEG lists. Similar results were obtained in mice. These analyses indicate a negligible transcriptional response in the oral mucosa of both species. Comparison of the total number of gene changes in the oral mucosa of rats and mice with responses in the duodenum of animals from the same study demonstrated remarkable dose-response concordance across tissues and species as a function of tissue chromium concentration. The low chromium levels in the oral mucosa and negligible transcript response are consistent with an absence of tissue lesions. These findings are used to compare the merits of linear and nonlinear approaches for deriving toxicity criteria based on the oral tumors in rats. Environ. Mol. Mutagen. 57:706-716, 2016. © 2016 The Authors. Environmental and Molecular Mutagenesis Published by Wiley Periodicals, Inc.

Consumer trust in Google’s top developers’ apps: an exploratory study

Purpose

This paper aims to investigate Google’s top developers’ apps with trust badges to see if they warrant an additional level of trust and confidence from consumers, as stated by Google.

Design/methodology/approach

Risky app permissions and in-app purchases (IAP) from Google’s top developers and traditional developers were investigated in several Google Play top app categories, including Editor’s Choice apps. Analysis was performed between categories and developer types.

Findings

Overall, Google’s top developers’ apps request more risky permissions and IAP than do traditional developers. Other results indicate that free apps are more dangerous than paid apps and star ratings do not signify safe apps.

Research limitations/implications

Because of a limited number of Google’s top developers and Editor’s Choice apps, conclusions are drawn from a small sample of apps and not the entire market.

Practical implications

Google’s top developers’ apps are suited well for increasing revenue for Google and developers at the consumer’s expense. Consumers should be wary of top developer trust badges.

Social implications

As the lure for “top free” and “top developer” software is strong among consumers, this research contributes to societal welfare in that it makes consumers aware that Google top developer app trust badges and free apps are more dangerous than traditional developer and paid apps, as they request risky permissions at a much higher frequency. Therefore, consumers should be very careful when downloading apps that are advertised as “top free” or “top developer”.

Originality/value

Google’s top developers’ apps and Editors’ Choice apps have not been investigated from the perspective of permissions and IAP before.

Assessment of the mutagenic potential of Cr(VI) in the oral mucosa of Big Blue® transgenic F344 rats

Exposure to high concentrations of hexavalent chromium [Cr(VI)] in drinking water was associated with an increased incidence of oral tumors in F344 rats in a 2-year cancer bioassay conducted by the National Toxicology Program. These tumors primarily occurred at 180 ppm Cr(VI) and appeared to originate from the gingival mucosa surrounding the upper molar teeth. To investigate whether these tumors could have resulted from a mutagenic mode of action (MOA), a transgenic mutation assay based on OECD Test Guideline 488 was conducted in Big Blue(®) TgF344 rats. The mutagenic oral carcinogen 4-nitroquinoline-1-oxide (4-NQO) served as a positive control. Mutant frequency was measured in the inner gingiva with adjacent palate, and outer gingiva with adjacent buccal tissue. Exposure to 10 ppm 4-NQO in drinking water for 28 days increased mutant frequency in the cII transgene significantly, from 39.1 ± 7.5 × 10(-6) to 688 ± 250 × 10(-6) in the gingival/buccal region, and from 49.8 ± 17.8 × 10(-6) to 1818 ± 362 × 10(-6) in the gingival/palate region. Exposure to 180 ppm Cr(VI) in drinking water for 28 days did not significantly increase the mutant frequency in the gingival/buccal (44.4 ± 25.4 × 10(-6)) or the gingival/palate (57.8 ± 9.1 × 10(-6)) regions relative to controls. These data indicate that high (∼180,000 times expected human exposure), tumorigenic concentrations of Cr(VI) did not significantly increase mutations in the gingival epithelium, and suggest that Cr(VI) does not act by a mutagenic MOA in the rat oral cavity.

Duodenal crypt health following exposure to Cr(VI): Micronucleus scoring, γ-H2AX immunostaining, and synchrotron X-ray fluorescence microscopy

Lifetime exposure to high concentrations of hexavalent chromium [Cr(VI)] in drinking water results in intestinal damage and an increase in duodenal tumors in B6C3F1 mice. To assess whether these tumors could be the result of a direct mutagenic or genotoxic mode of action, we conducted a GLP-compliant 7-day drinking water study to assess crypt health along the entire length of the duodenum. Mice were exposed to water (vehicle control), 1.4, 21, or 180 ppm Cr(VI) via drinking water for 7 consecutive days. Crypt enterocytes in Swiss roll sections were scored as normal, mitotic, apoptotic, karyorrhectic, or as having micronuclei. A single oral gavage of 50mg/kg cyclophosphamide served as a positive control for micronucleus induction. Exposure to 21 and 180 ppm Cr(VI) significantly increased the number of crypt enterocytes. Micronuclei and γ-H2AX immunostaining were not elevated in the crypts of Cr(VI)-treated mice. In contrast, treatment with cyclophosphamide significantly increased numbers of crypt micronuclei and qualitatively increased γ-H2AX immunostaining. Synchrotron-based X-ray fluorescence (XRF) microscopy revealed the presence of strong Cr fluorescence in duodenal villi, but negligible Cr fluorescence in the crypt compartment. Together, these data indicate that Cr(VI) does not adversely effect the crypt compartment where intestinal stem cells reside, and provide additional evidence that the mode of action for Cr(VI)-induced intestinal cancer in B6C3F1 mice involves chronic villous wounding resulting in compensatory crypt enterocyte hyperplasia.

Synchrotron-based imaging of chromium and γ-H2AX immunostaining in the duodenum following repeated exposure to Cr(VI) in drinking water

Current drinking water standards for chromium are for the combined total of both hexavalent and trivalent chromium (Cr(VI) and Cr(III)). However, recent studies have shown that Cr(III) is not carcinogenic to rodents, whereas mice chronically exposed to high levels of Cr(VI) developed duodenal tumors. These findings may suggest the need for environmental standards specific for Cr(VI). Whether the intestinal tumors arose through a mutagenic or non-mutagenic mode of action (MOA) greatly impacts how drinking water standards for Cr(VI) are derived. Herein, X-ray fluorescence (spectro)microscopy (µ-XRF) was used to image the Cr content in the villus and crypt regions of duodena from B6C3F1 mice exposed to 180 mg/l Cr(VI) in drinking water for 13 weeks. DNA damage was also assessed by γ-H2AX immunostaining. Exposure to Cr(VI) induced villus blunting and crypt hyperplasia in the duodenum--the latter evidenced by lengthening of the crypt compartment by ∼2-fold with a concomitant 1.5-fold increase in the number of crypt enterocytes. γ-H2AX immunostaining was elevated in villi, but not in the crypt compartment. µ-XRF maps revealed mean Cr levels >30 times higher in duodenal villi than crypt regions; mean Cr levels in crypt regions were only slightly above background signal. Despite the presence of Cr and elevated γ-H2AX immunoreactivity in villi, no aberrant foci indicative of transformation were evident. These findings do not support a MOA for intestinal carcinogenesis involving direct Cr-DNA interaction in intestinal stem cells, but rather support a non-mutagenic MOA involving chronic wounding of intestinal villi and crypt cell hyperplasia.

A chronic oral reference dose for hexavalent chromium-induced intestinal cancer

High concentrations of hexavalent chromium [Cr(VI)] in drinking water induce villous cytotoxicity and compensatory crypt hyperplasia in the small intestines of mice (but not rats). Lifetime exposure to such cytotoxic concentrations increases intestinal neoplasms in mice, suggesting that the mode of action for Cr(VI)-induced intestinal tumors involves chronic wounding and compensatory cell proliferation of the intestine. Therefore, we developed a chronic oral reference dose (RfD) designed to be protective of intestinal damage and thus intestinal cancer. A physiologically based pharmacokinetic model for chromium in mice was used to estimate the amount of Cr(VI) entering each intestinal tissue section (duodenum, jejunum and ileum) from the lumen per day (normalized to intestinal tissue weight). These internal dose metrics, together with corresponding incidences for diffuse hyperplasia, were used to derive points of departure using benchmark dose modeling and constrained nonlinear regression. Both modeling techniques resulted in similar points of departure, which were subsequently converted to human equivalent doses using a human physiologically based pharmacokinetic model. Applying appropriate uncertainty factors, an RfD of 0.006 mg kg(-1) day(-1) was derived for diffuse hyperplasia-an effect that precedes tumor formation. This RfD is protective of both noncancer and cancer effects in the small intestine and corresponds to a safe drinking water equivalent level of 210 µg l(-1). This concentration is higher than the current federal maximum contaminant level for total Cr (100 µg l(-1)) and well above levels of Cr(VI) in US drinking water supplies (typically ≤ 5 µg l(-1)).

Evaluation of impact of shale gas operations in the Barnett Shale region on volatile organic compounds in air and potential human health risks

Shale gas exploration and production (E&P) has experienced substantial growth across the U.S. over the last decade. The Barnett Shale, in north-central Texas, contains one of the largest, most active onshore gas fields in North America, stretching across 5000 square miles and having an estimated 15,870 producing wells as of 2011. Given that these operations may occur in relatively close proximity to populated/urban areas, concerns have been expressed about potential impacts on human health. In response to these concerns, the Texas Commission on Environmental Quality established an extensive air monitoring network in the region. This network provides a unique data set for evaluating the potential impact of shale gas E&P activities on human health. As such, the objective of this study was to evaluate community-wide exposures to volatile organic compounds (VOCs) in the Barnett Shale region. In this current study, more than 4.6 million data points (representing data from seven monitors at six locations, up to 105 VOCs/monitor, and periods of record dating back to 2000) were evaluated. Measured air concentrations were compared to federal and state health-based air comparison values (HBACVs) to assess potential acute and chronic health effects. None of the measured VOC concentrations exceeded applicable acute HBACVs. Only one chemical (1,2-dibromoethane) exceeded its applicable chronic HBACV, but it is not known to be associated with shale gas production activities. Annual average concentrations were also evaluated in deterministic and probabilistic risk assessments and all risks/hazards were below levels of concern. The analyses demonstrate that, for the extensive number of VOCs measured, shale gas production activities have not resulted in community-wide exposures to those VOCs at levels that would pose a health concern. With the high density of active wells in this region, these findings may be useful for understanding potential health risks in other shale play regions.

High concentrations of hexavalent chromium in drinking water alter iron homeostasis in F344 rats and B6C3F1 mice

Hexavalent chromium [Cr(VI)] induces hematological signs of microcytic anemia in rodents. Considering that Cr(VI) can oxidize ferrous (Fe(2+)) to ferric (Fe(3+)) iron, and that only the former is transported across the duodenum, we hypothesize that, at high concentrations, Cr(VI) oxidizes Fe(2+) in the lumen of the small intestine and perturbs iron absorption. Herein we report that 90-day exposure to Cr(VI) in drinking water resulted in dose-dependent decreases in Fe levels in the duodenum, liver, serum, and bone marrow. Toxicogenomic analyses from the duodenum indicate responses consistent with Fe deficiency, including significant induction of divalent metal transporter 1 (DMT1, Slc11a2) and transferrin receptor 1 (TFR1, Tfr1). In addition, at ⩾20mg Cr(VI)/L in drinking water, Cr RBC:plasma ratios in rats were increased and exceeded unity, indicating saturation of reductive capacity and intracellular absorption of Cr(VI) into red blood cells (RBCs). These effects occurred in both species but were generally more severe in rats. These data suggest that high concentrations of Cr(VI) in drinking limit Fe absorption and alter iron homeostasis. Furthermore, some effects observed at high doses in recent Cr(VI) chronic and subchronic bioassays may be explained, at least in part, by iron deficiency and disruption of homeostasis.

A review of background dioxin concentrations in urban/suburban and rural soils across the United States: implications for site assessments and the establishment of soil cleanup levels

Over the last several decades, dioxin releases have decreased >90%, leading to a corresponding decrease in human body burdens. In addition, the weight-of-evidence indicates that soil exposures have little impact on human body burdens of dioxin-like compounds (DLCs), with dietary sources being the greatest contributor. In spite of this, USEPA recently proposed substantially lower preliminary remediation goals (PRGs) for soil based on their new oral reference dose (RfD) for dioxin. As such, it is important to understand how these lower soil PRGs compare to background concentrations in urban/suburban and rural soils. The objective of this evaluation was to conduct a comprehensive review of available data concerning background levels of DLCs in U.S. soils. There was substantial variability in how the soil dioxin data were presented (e.g., raw vs. summary data, congener vs. toxic equivalency [TEQ] concentration, number of DLC congeners reported, etc.). In cases where TEQ estimates were based on outdated TEFs and congener-specific data was provided, TEQ concentrations were recalculated using the current WHO2006 TEFs. The data available for rural soils were generally more robust than for urban/suburban soils. Not surprisingly, background levels of DLCs in urban/suburban soils were higher and more variable than in rural soils: 0.1-186 vs. 0.1-22.9 ng/kg TEQ, respectively. In several cases, incomplete soil DLC data were available (e.g., DL-PCBs not included) and, as such, calculated TEQ concentrations likely underestimate actual background levels. Though the current data are somewhat limited, these findings indicate that background DLC concentrations in urban/suburban soils may exceed the USEPA's updated PRGs based on the oral RfD, and are expected to substantially exceed future PRGs to be developed based on the forthcoming dioxin cancer slope factor. This demonstrates a need to characterize anthropogenic background DLCs in non-rural areas across the US to avoid establishing soil screening levels and PRGs that are lower than background concentrations.

Central sleep-disordered breathing and the effects of oxygen therapy in infants with Prader-Willi syndrome

OBJECTIVES

To describe breathing patterns in infants with Prader-Willi Syndrome (PWS), as well as the effects of supplemental oxygen (O2) on breathing patterns. Children with PWS commonly have sleep-disordered breathing, including hypersomnolence and obstructive sleep apnoea, as well as central sleep breathing abnormalities that are present from infancy.

DESIGN

Retrospective cohort study.

PATIENTS

Infants with a diagnosis of PWS.

SETTING

Tertiary children's hospital.

INTERVENTIONS

Infants with PWS underwent full polysomnography, and in those with frequent desaturations associated with central events, supplemental O2 during sleep was started and followed with regular split-night studies (periods in both air and O2).

RESULTS

Thirty split-night studies on 10 infants (8 female) aged 0.06-1.79 (median 0.68, IQR 0.45, 1.07) years were undertaken. At baseline (ie, air), children with PWS had a median (IQR) central apnoea index (CAI) of 4.7 (1.9, 10.6) per hour, with accompanying falls in oxygen saturation (SpO2). O2 therapy led to statistically significant reductions in CAI to 2.5/hour (p=0.002), as well as a reduced central event index (CEI) and improved SpO2. No change in the number of obstructive events was noted. Central events were more prevalent in rapid-eye movement/active sleep.

CONCLUSIONS

It is concluded that infants with PWS may have central sleep-disordered breathing, which, in some children, may cause frequent desaturations. Improvements in CAI and CEI as well as oxygenation were noted with O2 therapy. Longitudinal work with this patient group would help to establish the timing of onset of obstructive symptoms.

Assessment of K-Ras mutant frequency and micronucleus incidence in the mouse duodenum following 90-days of exposure to Cr(VI) in drinking water

Chronic exposure to high concentrations of hexavalent chromium [Cr(VI)] as sodium dichromate dihydrate (SDD) in drinking water induces duodenal tumors in mice, but the mode of action (MOA) for these tumors has been a subject of scientific debate. To evaluate the tumor-site-specific genotoxicity and cytotoxicity of SDD in the mouse small intestine, tissue pathology and cytogenetic damage were evaluated in duodenal crypt and villus enterocytes from B6C3F1 mice exposed to 0.3-520mg/L SDD in drinking water for 7 and 90 days. Allele-competitive blocker PCR (ACB-PCR) was used to investigate the induction of a sensitive, tumor-relevant mutation, specifically in vivo K-Ras codon 12 GAT mutation, in scraped duodenal epithelium following 90 days of drinking water exposure. Cytotoxicity was evident in the villus as disruption of cellular arrangement, desquamation, nuclear atypia and blunting. Following 90 days of treatment, aberrant nuclei, occurring primarily at villi tips, were significantly increased at ≥60mg/L SDD. However, in the crypt compartment, there were no dose-related effects on mitotic and apoptotic indices or the formation of aberrant nuclei indicating that Cr(VI)-induced cytotoxicity was limited to the villi. Cr(VI) caused a dose-dependent proliferative response in the duodenal crypt as evidenced by an increase in crypt area and increased number of crypt enterocytes. Spontaneous K-Ras codon 12 GAT mutations in untreated mice were higher than expected, in the range of 10(-2) to 10(-3); however no treatment-related trend in the K-Ras codon 12 GAT mutation was observed. The high spontaneous background K-Ras mutant frequency and Cr(VI) dose-related increases in crypt enterocyte proliferation, without dose-related increase in K-Ras mutant frequency, micronuclei formation, or change in mitotic or apoptotic indices, are consistent with a lack of genotoxicity in the crypt compartment, and a MOA involving accumulation of mutations late in carcinogenesis as a consequence of sustained regenerative proliferation.

Assessment of the mode of action underlying development of rodent small intestinal tumors following oral exposure to hexavalent chromium and relevance to humans

Abstract Chronic exposure to high concentrations of hexavalent chromium (Cr(VI)) in drinking water causes intestinal adenomas and carcinomas in mice, but not in rats. Cr(VI) causes damage to intestinal villi and crypt hyperplasia in mice after only one week of exposure. After two years of exposure, intestinal damage and crypt hyperplasia are evident in mice (but not rats), as are intestinal tumors. Although Cr(VI) has genotoxic properties, these findings suggest that intestinal tumors in mice arise as a result of chronic mucosal injury. To better understand the mode of action (MOA) of Cr(VI) in the intestine, a 90-day drinking water study was conducted to collect histological, biochemical, toxicogenomic and pharmacokinetic data in intestinal tissues. Using MOA analyses and human relevance frameworks proposed by national and international regulatory agencies, the weight of evidence supports a cytotoxic MOA with the following key events: (a) absorption of Cr(VI) from the intestinal lumen, (b) toxicity to intestinal villi, (c) crypt regenerative hyperplasia and (d) clonal expansion of mutations within the crypt stem cells, resulting in late onset tumorigenesis. This article summarizes the data supporting each key event in the MOA, as well as data that argue against a mutagenic MOA for Cr(VI)-induced intestinal tumors.

Pumpers, skypers, surfers and texters: technology to improve the management of diabetes in teenagers

A variety of innovative technologies are available to assist with the management of diabetes in teenagers. Technologies include devices that assist with the direct day-to-day management of diabetes including insulin pumps and continuous glucose monitors. These devices are being used more and more with teenagers as a means of improving treatment adherence and glycaemic control. In addition, telehealth is being used to deliver care and support around diabetes management issues for teens with diabetes. Telehealth used in diabetes care for teens includes cell phones and video-conferencing. The goal of this telehealth technology is to support health behaviours and implement behavioural change strategies in a way that is more integrated into the everyday lives of patients and even in the context in which the behaviours occur in 'real time'. Finally, information and support via the Internet are gaining acceptance and use among teens with diabetes as an effective means of strategies for improved diabetes self-care. All three of these broad uses of technology in diabetes in teens represent flexible, innovative, and accessible approaches to improving both diabetes management and glycaemic control in this 'at risk' population.

Hexavalent chromium reduction kinetics in rodent stomach contents

Reduction of hexavalent chromium (Cr(VI)) to trivalent chromium (Cr(III)) in the stomach prior to absorption is a well-recognized detoxification process thought to limit the toxicity of ingested Cr(VI). However, administration of high concentrations of Cr(VI) in drinking water cause mouse small intestinal tumors, and quantitative measures of Cr(VI) reduction rate and capacity for rodent stomach contents are needed for interspecies extrapolation using physiologically-based toxicokinetic (PBTK) models. Ex vivo studies using stomach contents of rats and mice were conducted to quantify Cr(VI) reduction rate and capacity for loading rates (1-400 mg Cr(VI)L(-1) stomach contents) in the range of recent bioassays. Cr(VI) reduction was measured with speciated isotope dilution mass spectrometry to quantify dynamic Cr(VI) and Cr(III) concentrations in stomach contents at select time points over 1 h. Cr(VI) reduction followed mixed second-order kinetics, dependent upon concentrations of both Cr(VI) and the native reducing agents. Approximately 16 mg Cr(VI)-equivalents of reducing capacity per L of fed stomach contents (containing gastric secretions, saliva, water and food) was found for both species. The second-order rate constants were 0.2 and 0.3 L mg(-1) h(-1) for mice and rats, respectively. These findings support that, at the doses that caused cancer in the mouse small intestine (≥ 20 mg Cr(VI)L(-1) in drinking water), the reducing capacity of stomach contents was likely exceeded. Thus, for extrapolation of target tissue dose in risk assessment, PBTK models are necessary to account for competing kinetic rates including second order capacity-limited reduction of Cr(VI) to Cr(III).

Physiologically based pharmacokinetic model for rats and mice orally exposed to chromium

A multi-compartment physiologically based pharmacokinetic (PBPK) model was developed to describe the behavior of Cr(III) and Cr(VI) in rats and mice following long-term oral exposure. Model compartments were included for GI lumen, oral mucosa, forestomach/stomach, small intestinal mucosa (duodenum, jejunum, ileum), blood, liver, kidney, bone, and a combined compartment for remaining tissues. Data from ex vivo Cr(VI) reduction studies were used to characterize reduction of Cr(VI) in fed rodent stomach fluid as a second-order, pH-dependent process. For model development, tissue time-course data for total chromium were collected from rats and mice exposed to Cr(VI) in drinking water for 90 days at six concentrations ranging from 0.1 to 180 mg Cr(VI)/L. These data were used to supplement the tissue time-course data collected in other studies with oral administration of Cr(III) and Cr(VI), including that from recent NTP chronic bioassays. Clear species differences were identified for chromium delivery to the target tissue (small intestines), with higher concentrations achieved in mice than in rats, consistent with small intestinal tumor formation, which was observed upon chronic exposures in mice but not in rats. Erythrocyte:plasma chromium ratios suggest that Cr(VI) entered portal circulation at drinking water concentrations equal to and greater than 60 mg/L in rodents. Species differences are described for distribution of chromium to the liver and kidney, with liver:kidney ratios higher in mice than in rats. Overall, the PBPK model provides a good description of chromium toxicokinetics, with model predictions for tissue chromium within a factor of 3 for greater than 80% of measurements evaluated. The tissue data and PBPK model predictions indicate a concentration gradient in the small intestines (duodenum > jejunum > ileum), which will be useful for assessing the tumor response gradient observed in mouse small intestines in terms of target tissue dose. The rodent PBPK model presented here, when used in conjunction with a human PBPK model for Cr(VI), should provide a more robust characterization of species differences in toxicokinetic factors for assessing the potential risks associated with low-dose exposures of Cr(VI) in human populations.

Assessment of Cr(VI)-induced cytotoxicity and genotoxicity using high content analysis

Oral exposure to high concentrations of hexavalent chromium [Cr(VI)] induces intestinal redox changes, villus cytotoxicity, crypt hyperplasia, and intestinal tumors in mice. To assess the effects of Cr(VI) in a cell model relevant to the intestine, undifferentiated (proliferating) and differentiated (confluent) Caco-2 cells were treated with Cr(VI), hydrogen peroxide or rotenone for 2-24 hours. DNA damage was then assessed by nuclear staining intensity of 8-hydroxydeoxyguanosine (8-OHdG) and phosphorylated histone variant H2AX (γ-H2AX) measured by high content analysis methods. In undifferentiated Caco-2, all three chemicals increased 8-OHdG and γ-H2AX staining at cytotoxic concentrations, whereas only 8-OHdG was elevated at non-cytotoxic concentrations at 24 hr. Differentiated Caco-2 were more resistant to cytotoxicity and DNA damage than undifferentiated cells, and there were no changes in apoptotic markers p53 or annexin-V. However, Cr(VI) induced a dose-dependent translocation of the unfolded protein response transcription factor ATF6 into the nucleus. Micronucleus (MN) formation was assessed in CHO-K1 and A549 cell lines. Cr(VI) increased MN frequency in CHO-K1 only at highly cytotoxic concentrations. Relative to the positive control Mitomycin-C, Cr(VI) only slightly increased MN frequency in A549 at mildly cytotoxic concentrations. The results demonstrate that Cr(VI) genotoxicity correlates with cytotoxic concentrations, and that H2AX phosphorylation occurs at higher concentrations than oxidative DNA damage in proliferating Caco-2 cells. The findings suggest that in vitro genotoxicity of Cr(VI) is primarily oxidative in nature at low concentrations. Implications for in vivo intestinal toxicity of Cr(VI) will be discussed.

Contrast ureteropyelography in theatre: standardised flowchart reporting

INTRODUCTION

Urologists perform retrograde contrast studies of the ureters and pelvicalyceal systems in the operating theatre, both for diagnostic purposes and to guide instrumentation. We describe the development of a set of guidelines that aim to standardise the diagnostic quality of these studies and to reduce radiation dose to the patient and theatre staff. The guidelines incorporate a reporting template that allows a urologist's written report to be made available on the picture archiving and com- munication system (PACS) for subsequent multidisciplinary review.

METHODS

Three cycles of audit were conducted to assess the implementation of the guidelines. An independent reviewer rated image quality and screening times. During the audit cycle, the presentation of the guidelines was honed. The end prod- uct is a flowchart and reporting template for use by urologists in the operating theatre.

RESULTS

Phase 1 of the audit included 63 studies, phase 2 included 42 studies and phase 3 included 46 studies. The results demonstrate significant improvements in the number of good quality studies and in the recording of control, contrast and post-procedure images. The mean screening time decreased from 5.0 minutes in phase 1 to 3.2 minutes in phase 3. In phase 3, when in-theatre reporting of the studies by the urologist was added, the handwritten report was scanned in and made available on PACS in 43 of 46 cases (93%). CONCLUSIONS Introduction of guidelines improved retrograde contrast study quality and reduced screening times. A system has been developed to store appropriate pictures and a urologist's report of the study on PACS.

Assessment of genotoxic potential of Cr(VI) in the mouse duodenum: an in silico comparison with mutagenic and nonmutagenic carcinogens across tissues

In vitro studies on hexavalent chromium [Cr(VI)] indicate that reduced forms of this metal can interact with DNA and cause mutations. Recently, Cr(VI) was shown to induce intestinal tumors in mice; however, Cr(VI) elicited redox changes, cytotoxicity and hyperplasia - suggesting involvement of tissue injury rather than direct mutagenesis. Moreover, toxicogenomic analyses indicated limited evidence for DNA damage responses. Herein, we extend these toxicogenomic analyses by comparing the gene expression patterns elicited by Cr(VI) with those of four mutagenic and four nonmutagenic carcinogens. To date, toxicogenomic profiles for mutagenic and nonmutagenic duodenal carcinogens do not exist, thus duodenal gene changes in mice were compared to those elicited by hepatocarcinogens. Specifically, duodenal gene changes in mice following exposure to Cr(VI) in drinking water were compared to hepatic gene changes previously identified as potentially discriminating mutagenic and nonmutagenic hepatocarcinogens. Using multivariate statistical analyses (including logistic regression classification), the Cr(VI) gene responses clustered apart from mutagenic carcinogens and closely with nonmutagenic carcinogens. These findings are consistent with other intestinal data supporting a nonmutagenic mode of action (MOA). These findings may be useful as part of a full weight of evidence MOA evaluation for Cr(VI)-induced intestinal carcinogenesis. Limitations to this analysis will also be discussed.

Comparison of the effects of hexavalent chromium in the alimentary canal of F344 rats and B6C3F1 mice following exposure in drinking water: implications for carcinogenic modes of action

Exposure to high concentrations of hexavalent chromium (Cr[VI]) in drinking water is reported to induce oral mucosa tumors in F344 rats and intestinal tumors in B6C3F1 mice. To investigate the modes of action underlying these tumors, 90-day drinking water studies (with interim necropsy at day 8) were conducted with concentrations of 0.1-182 mg/l Cr(VI), administered as 0.3-520 mg/l sodium dichromate dihydrate. Blood and tissue samples were analyzed for chromium content, oxidative stress, iron levels, and gross and microscopic lesions. Results for the F344 rats are described herein and compared with results from B6C3F1 mice published previously. After 90 days of exposure, total chromium concentrations in the rat and mouse oral mucosae were comparable, yet significant dose-dependent decreases in the reduced-to-oxidized glutathione ratio (GSH/GSSG) were observed only in rats. In the duodenum, changes in GSH/GSSG were only observed in mice. Levels of 8-hydroxydeoxyguanosine were not increased in the oral or duodenal mucosae of either species. Glutathione levels were increased in the duodenum but decreased in the jejunum of both species, indicating potential differential responses in the intestinal segments. Histiocytic infiltration was observed in the duodenum of both species, yet duodenal cytokines were repressed in mice but increased in rats. Serum and bone marrow iron levels were more decreased in rats than mice. Collectively, these data suggest that Cr(VI)-induced carcinogenesis in the rodent alimentary canal involves oxidative stress; however, differences in histopathology, cytokines, and iron status suggest potential contributions from other factors as well.

Bmp2 is required for odontoblast differentiation and pulp vasculogenesis

Using the Bmp2 floxed/3.6Col1a1-Cre (Bmp2-cKO(od)) mouse model, we have observed severe defects in odontogenesis and dentin formation with the removal of the Bmp2 gene in early-polarizing odontoblasts. The odontoblasts in the Bmp2-cKO(od) do not mature properly and fail to form proper dentin with normal dentinal tubules and activate terminal differentiation, as reflected by decreased Osterix, Col1a1, and Dspp expression. There is less dentin, and the dentin is hypomineralized and patchy. We also describe an indirect effect of the Bmp2 gene in odontoblasts on formation of the vascular bed and associated pericytes in the pulp. This vascular niche and numbers of CD146+ pericytes are likely controlled by odontogenic and Bmp2-dependent VegfA production in odontoblasts. The complex roles of Bmp2, postulated to be both direct and indirect, lead to permanent defects in the teeth throughout life, and result in teeth with low quantities of dentin and dentin of poor quality.

Investigation of the mode of action underlying the tumorigenic response induced in B6C3F1 mice exposed orally to hexavalent chromium

Chronic ingestion of high concentrations of hexavalent chromium [Cr(VI)] in drinking water induces intestinal tumors in mice. To investigate the mode of action (MOA) underlying these tumors, a 90-day drinking water study was conducted using similar exposure conditions as in a previous cancer bioassay, as well as lower (heretofore unexamined) drinking water concentrations. Tissue samples were collected in mice exposed for 7 or 90 days and subjected to histopathological, biochemical, toxicogenomic, and toxicokinetic analyses. Described herein are the results of toxicokinetic, biochemical, and pathological findings. Following 90 days of exposure to 0.3–520 mg/l of sodium dichromate dihydrate (SDD), total chromium concentrations in the duodenum were significantly elevated at ≥ 14 mg/l. At these concentrations, significant decreases in the reduced-to-oxidized glutathione ratio (GSH/GSSG) were observed. Beginning at 60 mg/l, intestinal lesions were observed including villous cytoplasmic vacuolization. Atrophy, apoptosis, and crypt hyperplasia were evident at ≥ 170 mg/l. Protein carbonyls were elevated at concentrations ≥ 4 mg/l SDD, whereas oxidative DNA damage, as assessed by 8-hydroxydeoxyguanosine, was not increased in any treatment group. Significant decreases in the GSH/GSSG ratio and similar histopathological lesions as observed in the duodenum were also observed in the jejunum following 90 days of exposure. Cytokine levels (e.g., interleukin-1β) were generally depressed or unaltered at the termination of the study. Overall, the data suggest that Cr(VI) in drinking water can induce oxidative stress, villous cytotoxicity, and crypt hyperplasia in the mouse intestine and may underlie the MOA of intestinal carcinogenesis in mice.

Application of the U.S. EPA mode of action Framework for purposes of guiding future research: a case study involving the oral carcinogenicity of hexavalent chromium

Mode of action (MOA) analysis provides a systematic description of key events leading to adverse health effects in animal bioassays for the purpose of informing human health risk assessment. Uncertainties and data gaps identified in the MOA analysis may also be used to guide future research to improve understanding of the MOAs underlying a specific toxic response and foster development of toxicokinetic and toxicodynamic models. An MOA analysis, consistent with approaches outlined in the MOA Framework as described in the Guidelines for Carcinogen Risk Assessment, was conducted to evaluate small intestinal tumors observed in mice chronically exposed to relatively high concentrations of hexavalent chromium (Cr(VI)) in drinking water. Based on review of the literature, key events in the MOA are hypothesized to include saturation of the reductive capacity of the upper gastrointestinal tract, absorption of Cr(VI) into the intestinal epithelium, oxidative stress and inflammation, cell proliferation, direct and/or indirect DNA modification, and mutagenesis. Although available data generally support the plausibility of these key events, several unresolved questions and data gaps were identified, highlighting the need for obtaining critical toxicokinetic and toxicodynamic data in the target tissue and in the low-dose range. Experimental assays that can address these data gaps are discussed along with strategies for comparisons between responsive and nonresponsive tissues and species. This analysis provides a practical application of MOA Framework guidance and is instructive for the design of studies to improve upon the information available for quantitative risk assessment.

Reduction of a large fish tissue analyte database: identifying and assessing data specific to a remediation site for risk assessment application

The Lower Passaic River (LPR) is one of the most heavily industrialized waterways in the US with both historical and continuing discharges of chemicals from point and non-point sources. Significant efforts have been initiated on behalf of public, private, and regulatory entities to restore this degraded urban river. Considerable attention has been devoted to characterizing environmental media with respect to human and ecological risk. As part of these efforts, a wealth of environmental data have been collected and analyzed for a variety of metals, pesticides, organic compounds, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), polychlorinated dibenzodioxins/furans (PCDD/Fs), and dioxin-like compounds. The objectives of the study described in this paper were two-fold: (1) to generate LPR-specific data for use in human health risk assessment by characterizing concentrations of contaminants in LPR fish tissue samples based on publicly available data using a methodical and transparent approach, and (2) using the resulting data, to calculate the contaminant concentrations in a "Representative Fish," which is a representation of proportional fish tissue concentrations calculated based upon consumption patterns of LPR anglers. The data reduction, processing, and analyses described provide a representative dataset for the conduct of a human health assessment associated with fish consumption from the LPR.

New roles and mechanism of action of BMP4 in postnatal tooth cytodifferentiation

During the phase of overt tooth cytodifferentiation that occurs after birth in the mouse and using the 3.6Collagen1a-Cre and the BMP4 floxed and BMP4 knockout mice, the BMP4 gene was deleted in early collagen producing odontoblasts around postnatal day 1. BMP4 expression was reduced over 90% in alveolar osteoblasts and odontoblasts. There was decreased rate of predentin to dentin formation and decreased mature odontoblast differentiation reflected in reduced DMP1 expression and proper dentinal tubule formation, as well as reduced Collagen type I and Osteocalcin expression. We observed mutant dysmorphogenic odontoblasts that failed to properly elongate and differentiate. The consequence of this failed differentiation process leads to permanent loss of dentin thickness, apparent enlarged pulp chambers in the molars and reduced bone supporting the tooth structures in mice as old as 10-12 months. Deletion of the BMP4 gene in odontoblasts also indirectly disrupted the process of enamel formation that persisted throughout life. The mechanism for this altered differentiation program in the absence of the BMP4 gene in odontoblasts is from decreased BMP signaling, and decreased expression of three key transcription factors, Dlx3, Dlx5, and Osterix. BMP signaling, as well as Dlx3 and Amelogenin expression, is also indirectly reduced in the ameloblasts of the odontoblast BMP4 cKO mice. This supports a key paracrine or endocrine postnatal role of odontoblast derived BMP4 on the proper amelogenesis and formation of the enamel.

Assessment of human health risks posed by consumption of fish from the Lower Passaic River, New Jersey

The Lower Passaic River (LPR) in New Jersey has been impacted by variety of human activities over the course of the last two centuries. In this risk assessment, we assessed potential human health risks associated with consumption of fish from the LPR, the human exposure pathway of greatest concern when addressing contaminated sediments. Our risk assessment incorporates fish consumption information gathered during a year-long, intercept-style creel angler survey and representative fish tissue concentrations for 156 chemicals of potential concern (COPCs) obtained from USEPA's public database (OurPassaic website: http://www.ourpassaic.org/projectsites/premis_public/index.cfm?fuseaction=contaminants). Due to the large number of COPCs investigated, this risk assessment was divided into two phases: (1) identification of COPCs that contribute to the majority of overall excess cancer risk and hazard estimates using deterministic and probabilistic methods, and (2) probabilistic characterization of risk using distributions of chemical concentration and cooking loss for those compounds identified in Phase 1. Phase 1 relied on point estimates of COPC concentrations and demonstrated that PCDD/Fs and PCBs (dioxin-like and non-dioxin-like) are the greatest contributors to cancer risk, while non-dioxin-like PCBs are the primary contributors to non-cancer hazard estimates. Total excess cancer risks for adult and child and receptors estimated in Phase 1 were within USEPA's acceptable excess cancer risk range, with the exception of RME child (3.0 x 10(-4) and 1.3 x 10(-4) for deterministic and probabilistic approaches, respectively). Phase 2 focused on PCDD, PCDF, and PCBs and used distributions of chemical concentrations in fish. The results showed that all excess cancer risk estimates were within the acceptable risk range, although non-cancer hazard estimates for PCBs slightly exceeded a Hazard Index of 1. This HHRA of LPR fish ingestion represents the most comprehensive evaluation conducted to date, and demonstrates that measured concentrations of COPCs are not likely to pose a health risk to people who currently consume fish from the LPR.

Levels of polychlorinated dibenzo-p-dioxins, dibenzofurans, and biphenyls in southern Mississippi catfish and estimation of potential health risks

Fish consumption has been classified as one of the primary pathways of exposure to polychlorinated dibenzo-p-dioxins, dibenzofurans (PCDD/Fs) and biphenyls (PCBs). In this study, we evaluated tissue levels of the 17 laterally substituted PCDD/Fs, 12 dioxin-like PCBs, and 97 non-dioxin-like PCBs in a number of wild-caught and farm-raised catfish collected throughout southern Mississippi. Total lipid-adjusted TEQ and non-dioxin-like PCB concentrations in wild-caught catfish fillets were significantly higher than concentrations in farm-raised fillet samples. The percent contribution of PCDDs, PCDFs, and dioxin-like PCBs to mean total TEQ varied between wild-caught and farm-raised samples as well as by collection site for wild-caught catfish. The non-dioxin-like PCBs that contributed the most to total PCB concentrations also differed between wild-caught and farm-raised samples. Regardless of whether samples were farm-raised or wild-caught, estimated cancer risks associated with consumption of these catfish were less than 27.0E-06. Overall, results of this study indicate that levels of dioxin-like compounds and PCBs in Mississippi catfish are similar to those measured in more recent studies in the US and that levels of these compounds appear to be decreasing in this food source.