Systematic update to the mammalian relative potency estimate database and development of best estimate toxic equivalency factors for dioxin-like compounds

The World Health Organization (WHO) assesses potential health risks of dioxin-like compounds using Toxic Equivalency Factors (TEFs). This study systematically updated the relative potency (REP) database underlying the 2005 WHO TEFs and applied advanced methods for quantitative integration of study quality and dose-response. Data obtained from fifty-one publications more than doubled the size of the previous REP database (∼1300 datasets). REP quality and relevance for these data was assessed via application of a consensus-based weighting framework. Using Bayesian dose-response modeling, available data were modeled to produce standardized dose/concentration-response Hill curves. Study quality and REP data were synthesized via Bayesian meta-analysis to integrate dose/concentration-response data, author-calculated REPs and benchmark ratios. The output is a prediction of the most likely relationship between each congener and its reference as model-predicted TEF uncertainty distributions, or the 'best estimate TEF' (BE-TEF). The resulting weighted BE-TEFs were similar to the 2005 TEFs, though provide more information to inform selection of TEF values as well as to provide risk assessors and managers with information needed to quantitatively characterize uncertainty around TEF values. Collectively, these efforts produce an updated REP database and an objective, reproducible approach to support development of TEF values based on all available data.

A multi-tiered hierarchical Bayesian approach to derive toxic equivalency factors for dioxin-like compounds

In 2005, the World Health Organization (WHO) re-evaluated Toxic Equivalency factors (TEFs) developed for dioxin-like compounds believed to act through the Ah receptor based on an updated database of relative estimated potency (REP)(REP2004 database). This re-evalution identified the need to develop a consistent approach for dose-response modeling. Further, the WHO Panel discussed the significant heterogeneity of experimental datasets and dataset quality underlying the REPs in the database. There is a critical need to develop a quantitative, and quality weighted approach to characterize the TEF for each congener. To address this, a multi-tiered approach that combines Bayesian dose-response fitting and meta-regression with a machine learning model to predict REPS' quality categorizations was developed to predict the most likely relationship between each congener and its reference and derive model-predicted TEF uncertainty distributions. As a proof of concept, this 'Best-Estimate TEF workflow' was applied to the REP2004 database to derive TEF point-estimates and characterizations of uncertainty for all congeners. Model-TEFs were similar to the 2005 WHO TEFs, with the data-poor congeners having larger levels of uncertainty. This transparent and reproducible computational workflow incorporates WHO expert panel recommendations and represents a substantial improvement in the TEF methodology.

An updated mode of action and human relevance framework evaluation for Formaldehyde-Related nasal tumors

Formaldehyde is a reactive aldehyde naturally present in all plant and animal tissues and a critical component of the one-carbon metabolism pathway. It is also a high production volume chemical used in the manufacture of numerous products. Formaldehyde is also one of the most well-studied chemicals with respect to environmental fate, biology, and toxicology-including carcinogenic potential, and mode of action (MOA). In 2006, a published MOA for formaldehyde-induced nasal tumors in rats concluded that nasal tumors were most likely driven by cytotoxicity and regenerative cell proliferation, with possible contributions from direct genotoxicity. In the past 15 years, new research has better informed the MOA with the publication of in vivo genotoxicity assays, toxicogenomic analyses, and development of ultra-sensitive methods to measure endogenous and exogenous formaldehyde-induced DNA adducts. Herein, we review and update the MOA for nasal tumors, with particular emphasis on the numerous studies published since 2006. These new studies further underscore the involvement of cytotoxicity and regenerative cell proliferation, and further inform the genotoxic potential of inhaled formaldehyde. The data lend additional support for the use of mechanistic data for the derivation of toxicity criteria and/or scientifically supported approaches for low-dose extrapolation for the risk assessment of formaldehyde.

Development of a Range of Plausible Noncancer Toxicity Values for 2,3,7,8-Tetrachlorodibenzo-p-Dioxin Based on Effects on Sperm Count: Application of Systematic Review Methods and Quantitative Integration of Dose Response Using Meta-Regression

Regulatory agencies have derived noncancer toxicity values for 2,3,7,8-tetrachlorodibenzo-p-dioxin based on reduced sperm counts relying on single studies from a large body of evidence. Techniques such as meta-regression allow for greater use of the available data while simultaneously providing important information regarding the uncertainty associated with the underlying evidence base when conducting risk assessments. The objective herein was to apply systematic review methods and meta-regression to characterize the dose-response relationship of gestational exposure and epididymal sperm count. Twenty-three publications (20 animal studies consisting of 29 separate rat experimental data sets, and 3 epidemiology studies) met inclusion criteria. Risk of bias evaluation was performed to critically appraise study validity. Low to very low confidence precluded use of available epidemiological data as candidate studies for dose-response due to inconsistencies across the evidence base, high risk of bias, and general lack of biological coherence, including lack of clinical relevance and dose-response concordance. Experimental animal studies, which were found to have higher confidence following the structured assessment of confidence (eg, controlled exposure, biological consistency), were used as the basis of a meta-regression. Multiple models were fit; points of departure were identified and converted to human equivalent doses. The resulting reference dose estimates ranged from approximately 4 to 70 pg/kg/day, depending on model, benchmark response level, and study validity integration approach. This range of reference doses can be used either qualitatively or quantitatively to enhance understanding of human health risk estimates for dioxin-like compounds.

A hypothesis-driven weight-of-evidence analysis to evaluate potential endocrine activity of perfluorohexanoic acid

Perfluorohexanoic acid (PFHxA) is a potential impurity and environmental degradation product of C6-based fluorotelomer products. Considering the potential endocrine activity of perfluoroalkyl acids, a hypothesis-driven weight-of-evidence (WoE) analysis was conducted to evaluate the potential endocrine disruptor activity of PFHxA, as defined by World Health Organization (WHO), across estrogen (E), androgen (A), thyroid (T), and steroidogenesis (S) pathways. A comprehensive literature search identified primary and secondary studies across species for review. The ToxCast/Tox21 database provided in vitro data. Studies identified were reviewed for reliability, and relevance, with endocrine endpoints ranked, and lines of evidence evaluated across pathways. Overall, PFHxA showed no endocrine effects in Japanese medaka, juvenile rainbow trout, chickens or reproductive parameters in northern bobwhite with no significant activity in rodent repeated-dose toxicity, lifetime cancer, or reproductive and developmental studies. In vitro, there was weak or negative activity for T transport protein or activation of E, A or T receptors. PFHxA was also negative in vitro and in vivo for disrupting steroidogenesis. Based on this WoE endocrine analysis, PFHxA exposure did not cause adverse effects associated with alterations in endocrine activity in these models, as such would not be characterized as an endocrine disruptor according to the WHO definition.

Assessing the risk of venous thromboembolism in psychiatric in-patients

Introduction

Venous thromboembolism (VTE) is a potentially fatal condition. Hospital-associated VTE leads to more than 25,000 deaths per year in the UK. Therefore identification of at-risk patients is crucial. Psychiatric in-patients have unique factors which may affect their risk of VTE (antipsychotic prescription, restraint) however there are currently no UK guidelines which specifically address VTE risk in this population.

Objectives

We assessed VTE risk among psychiatric inpatients in Cardiff and Vale university health board, Wales, UK, and whether proformas currently provided for VTE risk assessment were being completed.

Methods

All acute adult in-patient and old age psychiatric wards were assessed by a team of medical students and a junior doctor over three days. We used the UK department of health VTE risk assessment tool which was adapted to include factors specific for psychiatric patients. We also assessed if there were concerns about prescribing VTE prophylaxis (compression stockings or anticoagulants), because of a history of self-harm or ligature use.

Results

Of the 145 patients included, 0% had a completed VTE risk assessment form. We found 38.6% to be at an increased risk of VTE and there were concerns about prescribing VTE prophylaxis in 31% of patients.

Conclusions

Our findings suggest that VTE risk assessment is not being carried out on psychiatric wards. Staff education is needed to improve awareness of VTE. Specific guidance for this population is needed due to the presence of unique risk factors in psychiatric in-patients and concerns regarding VTE prophylaxis.

Disclosure of interest

The authors have not supplied their declaration of competing interest.

Mouse bone marrow and peripheral blood erythroid cell counts are regulated by different autosomal genetic loci

Erythropoiesis is under fine control and genetic loci that affect it are likely to be important in a range of conditions. To assess the relative contributions of different genetic loci to parameters of erythropoiesis, we have measured RBC counts in the peripheral circulation and committed erythroid cells (RBC and small normoblasts) in the bone marrow in a cohort of (CBA/H x C57BL/6) F2 mice to map quantitative trait loci (QTL). Candidate genes were assessed using bioinformatics and DNA sequencing. Different autosomal loci affect bone marrow (chromosomes 5, 11 and 19) and peripheral blood (chromosome 4) erythroid cell counts but there may be a common chromosome X locus. Spleen weight QTL were found on chromosomes 3, 15 and 17. Surprisingly, erythropoietin (Epo) is the best candidate quantitative trait gene (QTG) in the chromosome 5 locus that affects bone marrow but not peripheral blood erythroid cell counts. Epo gene expression is known to be genetically regulated in mice, but our data suggest a tissue-specific role for epo in mouse erythropoiesis that is also genetically determined. The identity of the other QTG will be important both to further knowledge of the control of erythropoiesis and as potential modifier genes for haematological disorders.

Primary lymphoma of bone in children

Primary lymphoma of bone (PLB) occurs infrequently in children. Between January 1962 and November 1988, 395 children with non-Hodgkin's lymphoma (NHL) were treated at St. Jude Children's Research Hospital. Eleven of these patients (2.8%) presented with a bone primary, usually in the femur (eight of 11 patients). The median age of these seven boys and four girls at presentation was 13 years (range, 5.5 to 19 years). Seven patients had one or more additional bones involved. All patients had high-grade lymphomas based on the National Institutes of Health (NIH) Working Formulation. The histologic subtypes included six large-cell lymphomas, three lymphoblastic lymphomas, one small-noncleaved, non-Burkitt's lymphoma, and one unclassifiable lymphoma. Treatment consisted of multiagent chemotherapy combined with local radiation therapy in seven of 11 patients. Six of 10 children who received chemotherapy as a component of their initial therapy, including all who presented with localized tumor, are alive with no evidence of disease 2+ to 85+ months (median, 42.5 months) after cessation of treatment; one patient has just completed chemotherapy. Each of the four patients who died showed leukemic conversion 5 to 11 months after diagnosis, and three died of progressive disease. One patient died of sepsis during chemotherapy-induced neutropenia with no evidence of disease at necropsy. We conclude that optimal therapy for PLB, as with all other forms of NHL, should focus on the histologic subtype and stage of disease.

Significance of pulmonary computed tomography at diagnosis in Wilms' tumor

Pulmonary lesions were found by computed tomography (CT) despite normal chest roentgenograms (CXR) at diagnosis in 11 of 124 patients with Wilms' tumor. All patients were entered on a treatment protocol at St Jude Children's Research Hospital from 1978 to 1986. The 11 patients all had favorable histology Wilms' tumor. Staging and therapy were based on interpretation of the CXR and abdominal findings. Excluding CT findings, one patient had stage I disease, two stage II, seven stage III, and one stage IV on the basis of multiple liver metastases. Four patients have relapsed: one with stage II and three with stage III. All relapses have been pulmonary. Overall, 4/11 (36%) relapsed. This relapse rate is considerably greater than the 20% overall relapse rate of patients treated according to this protocol though not statistically significant. These relapses suggest that such patients may be at increased risk for pulmonary recurrence. The results also indicate that small lesions initially noted only on CT scans of the chest in children with Wilms' tumor frequently represent metastatic tumor. Further studies of larger numbers of patients will be necessary to confirm these findings.

Influence of human muscle length on fatigue

The effect of muscle length on susceptibility to fatigue has been examined in human ankle dorsiflexor muscles. The fatiguing procedure consisted of either indirect tetanic stimulation at 20 Hz or maximal voluntary contraction; each procedure lasted 90 s. The amplitude of the evoked muscle compound action potential (M-wave) increased during the first 30 s or so of the tetanic fatiguing procedure and then decreased. The torque developed by the dorsiflexor muscles declined throughout the period of tetanization. A significantly greater reduction in twitch and tetanic torque was found after the fatiguing procedure had been conducted at the optimum muscle length rather than with the muscle in a shortened position. Relaxation after tetanic stimulation was slower after fatigue had been induced at the optimum muscle length. It is concluded that muscle fatigue is related to the number of actin-myosin cross-bridge interactions and is unlikely to be accounted for solely on the basis of changes in the ionic composition of the transverse tubular fluid.

Developmental cystic renal neoplasms in children. Diagnostic imaging characteristics

We report diagnostic imaging and histopathologic findings in four children with different cystic renal neoplasms. The features discerned with computed tomography (CT), as well as ultrasound, correlated well with gross histologic findings, although a definitive diagnosis could not be made on the basis of CT and ultrasound alone. Because the most malignant variants of these lesions cannot be excluded preoperatively, we advocate complete diagnostic imaging studies, followed by nephrectomy, for all cases of cystic renal neoplasms in infants and children.