KatG catalase deficiency confers bedaquiline hyper-susceptibility to isoniazid resistant Mycobacterium tuberculosis.

Multidrug-resistant tuberculosis (MDR-TB) is a growing source of global mortality and threatens global control of tuberculosis (TB) disease. The diarylquinoline bedaquiline (BDQ) recently emerged as a highly efficacious drug against MDR-TB, defined as resistance to the first-line drugs isoniazid (INH) and rifampin. INH resistance is primarily caused by loss-of-function mutations in the catalase KatG, but mechanisms underlying BDQ's efficacy against MDR-TB remain unknown. Here we employ a systems biology approach to investigate BDQ hyper-susceptibility in INH-resistant Mycobacterium tuberculosis . We found hyper-susceptibility to BDQ in INH-resistant cells is due to several physiological changes induced by KatG deficiency, including increased susceptibility to reactive oxygen species and DNA damage, remodeling of transcriptional programs, and metabolic repression of folate biosynthesis. We demonstrate BDQ hyper-susceptibility is common in INH-resistant clinical isolates. Collectively, these results highlight how altered bacterial physiology can impact drug efficacy in drug-resistant bacteria.

Controlled Continuous Evolution of Enzymatic Activity Screened at Ultrahigh Throughput Using Drop-Based Microfluidics.

Enzymes are highly specific catalysts delivering improved drugs and greener industrial processes. Naturally occurring enzymes must typically be optimized which is often accomplished through directed evolution; however, this is still a labor- and capital-intensive process, due in part to multiple molecular biology steps including DNA extraction, in vitro library generation, transformation, and limited screening throughput. We present an effective and broadly applicable continuous evolution platform that enables controlled exploration of fitness landscape to evolve enzymes at ultrahigh throughput based on direct measurement of enzymatic activity. This drop-based microfluidics platform cycles cells between growth and mutagenesis followed by screening with minimal human intervention, relying on the nCas9 chimera with mutagenesis polymerase to produce in vivo gene diversification using sgRNAs tiled along the gene. We evolve alditol oxidase to change its substrate specificity towards glycerol, turning a waste product into a valuable feedstock. We identify a variant with a 10.5-fold catalytic efficiency.

Evaluation of potential health effects associated with occupational and environmental exposure to styrene - an update.

The potential chronic health risks of occupational and environmental exposure to styrene were evaluated to update health hazard and exposure information developed since the Harvard Center for Risk Analysis risk assessment for styrene was performed in 2002. The updated hazard assessment of styrene's health effects indicates human cancers and ototoxicity remain potential concerns. However, mechanistic research on mouse lung tumors demonstrates these tumors are mouse-specific and of low relevance to human cancer risk. The updated toxicity database supports toxicity reference levels of 20 ppm (equates to 400 mg urinary metabolites mandelic acid + phenylglyoxylic acid/g creatinine) for worker inhalation exposure and 3.7 ppm and 2.5 mg/kg bw/day, respectively, for general population inhalation and oral exposure. No cancer risk value estimates are proposed given the established lack of relevance of mouse lung tumors and inconsistent epidemiology evidence. The updated exposure assessment supports inhalation and ingestion routes as important. The updated risk assessment found estimated risks within acceptable ranges for all age groups of the general population and workers with occupational exposures in non-fiber-reinforced polymer composites industries and fiber-reinforced polymer composites (FRP) workers using closed-mold operations or open-mold operations with respiratory protection. Only FRP workers using open-mold operations not using respiratory protection have risk exceedances for styrene and should be considered for risk management measures. In addition, given the reported interaction of styrene exposure with noise, noise reduction to sustain levels below 85 dB(A) needs be in place.

Severe maternal morbidity during delivery hospitalisation in a large international administrative database, 2008-2013: a retrospective cohort.

OBJECTIVE: This study utilized the Dr. Foster Global Comparators database to identify pregnancy complications and associated risk factors that led to severe maternal morbidity during delivery hospitalisations in large university hospitals based in the USA, Australia, and England. DESIGN: Retrospective cohort. SETTING: Births in the USA, England and Australia from 2008 to 2013. SAMPLE: Data from delivery hospitalisations between 2008 and 2013 were examined using the Dr. Foster Global Comparators database. METHODS: We identified delivery hospitalisations with life-threatening diagnoses or use of life-saving procedures, using algorithms for severe maternal morbidity from the Center for Disease Control. Frequency of severe maternal morbidity was calculated for each country. MAIN OUTCOME MEASURES: Multivariable analysis was used to examine the association between morbidity and socio-demographic and clinical characteristics within each country. Chi-square tests assessed differences in covariates between countries. RESULTS: From 2008 to 2013, there were 516 781 deliveries from a total of 18 hospitals: 24.5% from the USA, 57.0% from England and 18.4% from Australia. Overall severe maternal morbidity rate was 8.2 per 1000 deliveries: 15.6 in the USA, 5.0 in England, and 8.2 in Australia. The most common codes identifying severe morbidity included transfusion, disseminated intravascular coagulation, acute renal failure, cardiac events/procedures, ventilation, hysterectomy, and eclampsia. Advanced maternal age, hypertension, diabetes, and substance abuse were associated with severe maternal morbidity in all three countries. CONCLUSION: Rates of severe maternal morbidity differed by country. Identification of geographical, socio-demographic, and clinical differences can help target modifications of practice and potentially reduce severe maternal morbidity. TWEETABLE ABSTRACT: Rates of severe maternal morbidity vary, but risk factors associated with adverse outcomes are similar in developed countries.

Challenges and Opportunities for Occupational Epidemiology in the Twenty-first Century.

PURPOSE OF REVIEW: There are many opportunities and challenges for conducting occupational epidemiologic studies today. In this paper, we summarize the discussion of a symposium held at the Epidemiology in Occupational Health (EPICOH) conference, Chicago 2014, on challenges for occupational epidemiology in the twenty-first century. RECENT FINDINGS: The increasing number of publications and attendance at our conferences suggests that worldwide interest in occupational epidemiology has been growing. There are clearly abundant opportunities for new research in occupational epidemiology. Areas ripe for further work include developing improved methods for exposure assessment, statistical analysis, studying migrant workers and other vulnerable populations, the use of biomarkers, and new hazards. Several major challenges are also discussed such as the rapidly changing nature and location of work, lack of funding, and political/legal conflicts. As long as work exists there will be occupational diseases that demand our attention, and a need for epidemiologic studies designed to characterize these risks and to support the development of preventive strategies. Despite the challenges and given the important past contribution in this field, we are optimistic about the importance and continued vitality of the research field of occupational epidemiology.

Mortality risk among workers with exposure to dioxins.

BACKGROUND: In several studies, dioxin exposure has been associated with increased risk from several causes of death. AIMS: To compare the mortality experience of workers exposed to dioxins during trichlorophenol (TCP) and pentachlorophenol (PCP) production to that of the general population and to examine mortality risk by estimated exposure levels. METHODS: A retrospective cohort study which followed up workers' vital status from 1940 to 2011, with serum surveys to support estimation of historical dioxin exposure levels. RESULTS: Among the 2192 study subjects, there were nine deaths in TCP workers from acute non-lymphatic leukaemia [standardized mortality ratio (SMR) = 2.88, 95% confidence interval (CI) 1.32-5.47], four mesothelioma deaths (SMR = 5.12, 95% CI 1.39-13.10) and four soft tissue sarcoma (STS) deaths (SMR = 3.08, 95% CI 0.84-7.87). In PCP workers, there were eight deaths from non-Hodgkin's lymphoma (SMR = 1.92, 95% CI 0.83-3.79), 150 from ischaemic heart disease (SMR = 1.20, 95% CI 1.01-7.89) and five from stomach ulcers (SMR = 3.38, 95% CI 1.10-7.89). There were no trends of increased mortality with increased dioxin exposure except for STS and 2,3,7,8-tetrachlorodibenzo-p-dioxin levels. This finding for STS should be interpreted with caution due to the small number of deaths and the uncertainty in diagnosis and nosology. CONCLUSIONS: While some causes of death were greater than expected, this study provides little evidence of increased risk when dioxin exposures are considered.

"Intrinsic" elimination rate and dietary intake estimates for selected indicator PCBs: toxicokinetic modeling using serial sampling data in US subjects, 2005-2010.

Changes in measured concentrations of persistent compounds such as polychlorinated biphenyls (PCBs) in an individual over time reflect not only intrinsic elimination rates but also any ongoing intake of the compounds and changes in the volume of distribution. Thus, "apparent" elimination rates calculated from data on changes in serum lipid-adjusted concentration may over- or under-estimate the "intrinsic" elimination rates for such compounds. Serum PCB concentrations were measured in 43 individuals approximately 5years apart. Changes in measured concentrations and body weights were used to estimate mass-based apparent elimination rates. The changes in estimated body mass of PCBs 105, 118, 138, 153, and 180 were input into a simple first-order model employing previously estimated intrinsic elimination rates to estimate congener-specific average dietary intake rates over the period between samples. Calculated median dietary intakes were compared to previous estimates. Intrinsic elimination rates were adjusted for two congeners. The analyses support central tendencies of intrinsic elimination rates of approximately 5years for PCBs 105 and 118, 11years for PCB 138, 14.4years for PCB 153, and 20years or more for PCB 180. Estimated dietary intakes for this population and time period depend on the assumed intrinsic elimination rates and range from 0.1ngkg(-1)d(-1) for PCB 105 to approximately 1-2ngkg(-1)d(-1) for PCB 180. Estimated body burdens of PCB 180 changed very little over the five-year period, suggesting near steady-state exposure levels. As a result, estimates for both elimination half-life and ongoing intake rates for this congener are highly uncertain.

Slips, trips and falls at a chemical manufacturing company.

BACKGROUND: Slips, trips and falls (STF) are a major cause of workplace injury. AIMS: To examine risk factors for STF at a large US chemical manufacturing company. METHODS: We conducted a case-control study of occupational STF. Cases were identified from company injury records between 1 April 2009 and 1 May 2011. Four controls per case were randomly selected from all active company workers employed during the same time. Data were collected through a questionnaire and from company medical examinations. Logistic regression was used to calculate odds ratio (OR) and 95% confidence intervals (95% CI) for personal, environmental and health-related risk factors for STF. RESULTS: There were 74 cases and 309 controls. The response rate was 65% for the cases and 68% for the controls. Most STF were unrelated to production activities. When examining all factors in a logistic regression model, increased OR were observed for increased body mass index (OR = 1.44, 95% CI: 1.03-2.02), having arthritis (OR = 2.11, 95% CI: 1.01-4.37), lack of exercise (OR = 2.25, 95% CI: 1.01-5.05), carrying materials (OR = 3.01, 95% CI: 1.41-6.43) and being female (OR = 2.46, 95% CI: 1.17-5.19). Reduced risk of STF was observed for never having smoked (OR = 0.48, 95% CI: 0.24-0.95), long service (OR = 0.53, 95% CI: 0.34-0.81) and persons working over 8h a day (OR = 0.42, 95% CI: 0.20-0.88). CONCLUSIONS: Risk factors for STF in a large US chemical company are similar to those reported from other workplaces, but we found that staying fit and healthy is important for reducing risk.

Antenatal ureaplasma infection impairs development of the fetal ovine gut in an IL-1-dependent manner.

Ureaplasma infection of the amniotic cavity is associated with adverse postnatal intestinal outcomes. We tested whether interleukin-1 (IL-1) signaling underlies intestinal pathology following ureaplasma exposure in fetal sheep. Pregnant ewes received intra-amniotic injections of ureaplasma or culture media for controls at 3, 7, and 14 d before preterm delivery at 124 d gestation (term 150 d). Intra-amniotic injections of recombinant human interleukin IL-1 receptor antagonist (rhIL-1ra) or saline for controls were given 3 h before and every 2 d after Ureaplasma injection. Ureaplasma exposure caused fetal gut inflammation within 7 d with damaged villus epithelium and gut barrier loss. Proliferation, differentiation, and maturation of enterocytes were significantly reduced after 7 d of ureaplasma exposure, leading to severe villus atrophy at 14 d. Inflammation, impaired development and villus atrophy of the fetal gut was largely prevented by intra-uterine rhIL-1ra treatment. These data form the basis for a clinical understanding of the role of ureaplasma in postnatal intestinal pathologies.

Screening-level risk assessment for styrene-acrylonitrile (SAN) trimer detected in soil and groundwater.

A screening-level risk assessment was conducted for styrene-acrylonitrile (SAN) Trimer detected at the Reich Farm Superfund site in Toms River, NJ. Consistent with a screening-level approach, on-site and off-site exposure scenarios were evaluated using assumptions that are expected to overestimate actual exposures and hazards at the site. Environmental sampling data collected for soil and groundwater were used to estimate exposure point concentrations. Several exposure scenarios were evaluated to assess potential on-site and off-site exposures, using parameter values for exposures to soil (oral, inhalation of particulates, and dermal contact) and groundwater (oral, dermal contact) to reflect central tendency exposure (CTE) and reasonable maximum exposure (RME) conditions. Three reference dose (RfD) values were derived for SAN Trimer for short-term, subchronic, and chronic exposures, based upon its effects on the liver in exposed rats. Benchmark (BMD) methods were used to assess the relationship between exposure and response, and to characterize appropriate points of departure (POD) for each RfD. An uncertainty factor of 300 was applied to each POD to yield RfD values of 0.1, 0.04, and 0.03 mg/kg-d for short-term, subchronic, and chronic exposures, respectively. Because a chronic cancer bioassay for SAN Trimer in rats (NTP 2011a) does not provide evidence of carcinogenicity, a cancer risk assessment is not appropriate for this chemical. Potential health hazards to human health were assessed using a hazard index (HI) approach, which considers the ratio of exposure dose (i.e., average daily dose, mg/kg-d) to toxicity dose (RfD, mg/kg-d) for each scenario. All CTE and RME HI values are well below 1 (where the average daily dose is equivalent to the RfD), indicating that there is no concern for potential noncancer effects in exposed populations even under the conservative assumptions of this screening-level assessment.

[Effects of antenatal inflammation on the developing lung]. / Pathogenetische Effekte der prä- und postnatalen Inflammationsreaktion in den Lungen.

The developing lung and immune systems are very plastic and their developmental pathway can be influenced by various endogenous and/or exogenous factors. In the last years translational research with various animal models has been helpful to answer some basic questions about the effect of chorioamnionitis on maturation and development of the foetal lung and immune system. Chorioamnionitis can induce a cascade of lung injury, pulmonary inflammation and remodelling in the foetal lung. Chorioamnionitis-induced IL-1 production is consistently associated with lung maturation, induced by enhancing surfactant protein and lipid synthesis. IL-1 therefore seems to be the main link between lung inflammation and lung maturation, which largely prevents RDS in preterm infants. On the other hand, chorioamnionitis can also cause structural lung changes and affect the expression of growth factors, like TGF-ß, CTGF, FGF-10 or BMP-4, which are crucial for branching morphogenesis. These changes result in alveolar and microvascular simplification similar to BPD. Neonatal outcome may also be affected by chorioamnionitis by modulating the efficacy of the immune system. Chorioamnionitis can induce LPS-tolerance (endotoxin hyporesponsiveness/immunoparalysis), which may prevent further foetal lung damage but increases susceptibility to postnatal infections. The inflammatory and developmental signalling pathways affected by chorioamnionitis form delicately regulated networks, which interact with each other to control lung development. In addition to chorioamnionitis, these pathways can be affected by other prenatal (steroid) or postnatal factors (mechanical ventilation, oxygen exposure, infection, steroids). Because the postnatal response to injury appears to be highly dependent on prenatal exposures, the "secondary hit" hypothesis is very plausible, in which exposure to chorioamnionitis is a predisposition for the development of adverse neonatal outcomes.

The healthy worker effect in US chemical industry workers.

BACKGROUND: Occupational studies typically observe a 20% deficit in overall mortality, broadly characterized as the healthy worker effect (HWE). Components of the HWE may be addressed by various analytical approaches. AIMS: To explore the HWE in a modern industrial cohort. METHODS: Standardized mortality ratios (SMRs) were calculated for 114,683 US chemical industry employees, who worked at least 3 days between 1960 and 2005. RESULTS: SMRs were 79 (95% confidence interval 78-80) for all causes, 81 (95% confidence interval 79-82) for heart disease, 70 (95% confidence interval 67-73) for non-malignant respiratory disease, 83 (95% confidence interval 81-85) for smoking-related cancers (buccal, cervix, oesophagus, stomach, pancreas, lung, larynx, bladder and kidney) combined and 97 (95% confidence interval 95-100) for other cancers. CONCLUSIONS: The low SMRs observed in this study are likely due to differential smoking between the cohort and the background population. Future considerations to control for the HWE should take this into account.

Correlates of serum dioxin to self-reported exposure factors.

The aim of the current analysis was to examine the determinates of lipid-adjusted body levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) from occupational histories, age, body mass index, and self-reported information from a questionnaire. We collected serum from 346 workers at a New Zealand chemical plant that manufactured and formulated the herbicide, 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). Age, body mass index, and employment history were significant determinates of TCDD. The self-reported data on occupation, residence, and general diet were not predictive of serum levels and we observed no evidence of increased TCDD levels from living close to the site. For participants with putative occupational exposure, employment history and personal factors were important to understand the range of TCDD serum levels. For employees without direct occupational exposure, and resulting lower dioxin levels, we recommend further efforts to develop and validate questionnaires to better evaluate environmental sources of dioxins.

Derivation of noncancer reference values for acrylonitrile.

Dose-response assessments were conducted for the noncancer effects of acrylonitrile (AN) for the purposes of deriving subchronic and chronic oral reference dose (RfD) and inhalation reference concentration (RfC) values. Based upon an evaluation of available toxicity data, the irritation and neurological effects of AN were determined to be appropriate bases for deriving reference values. A PBPK model, which describes the toxicokinetics of AN and its metabolite 2-cyanoethylene oxide (CEO) in both rats and humans, was used to assess the dose-response data in terms of an internal dose measure for the oral RfD values, but could not be used in deriving the inhalation RfC values. Benchmark dose (BMD) methods were used to derive all reference values. Where sufficient information was available, data-derived uncertainty factors were applied to the points of departure determined by BMD methods. From this assessment, subchronic and chronic oral RfD values of 0.5 and 0.05 mg/kg/day, respectively, were derived. Similarly, subchronic and chronic inhalation RfC values of 0.1 and 0.06 mg/m(3), respectively, were derived. Confidence in the reference values derived for AN was considered to be medium to high, based upon a consideration of the confidence in the key studies, the toxicity database, dosimetry, and dose-response modeling.

A report on location of death in paediatric palliative care between home, hospice and hospital.

This retrospective study analysed data for 703 children who died from 2000 to 2006 to examine where children with a broad range of progressive, life-limiting illnesses actually die when families are able to access hospital, paediatric hospice facility and care at home. There was an overall even distribution for location of death in which 35.1% of children died at home, 32.1% died in a paediatric hospice facility, 31.9% in hospital and 0.9% at another location. Previous research suggests a preference for home as the location of death, but these studies have primarily focused on adults, children with cancer or settings without paediatric hospice facilities available as an option. Our results suggest that the choice of families for end-of-life care is equally divided amongst all three options. Given the increasing numbers of children's hospices worldwide, these findings are important for clinicians, care managers and researchers who plan, provide and evaluate the care of children with life-limiting illness.

A pathway and genetic factors contributing to elevated gene expression noise in stationary phase.

Previous studies have identified factors associated with transcription and translation efficiency, such as promoter strength and mRNA sequences, that can affect stochasticity in gene expression. Here we present evidence for a pathway and associated genetic factors (namely, the ribosome modulation factor RMF and ppGpp) in Escherichia coli that contribute to heightened levels of gene expression noise during stationary phase. Endogenous cellular mechanisms that globally affect gene expression noise, such as those identified in this study, could provide phenotypic diversity under adverse conditions such as stationary phase.

Ovulation suppression for endometriosis.

BACKGROUND: Endometriosis is the finding of endometrial glands or stroma in sites other than the uterine cavity. Endometriosis appears to be an oestrogen dependent condition. This hormonal dependency has prompted the therapeutic use of ovulation suppression agents, in an effort to improve subsequent fertility. OBJECTIVES: To assess the effectiveness of ovulation suppression agents, including danazol, progestins and oral contraceptives, in the treatment of endometriosis-associated subfertility in improving pregnancy outcomes including live birth. SEARCH STRATEGY: We searched the Cochrane Menstrual Disorders and Sub-fertility Group's specialised register of trials (searched October 5th, 2007) the Cochrane Register of Controlled Trials (The Cochrane Library, Issue 3, 2007), MEDLINE (1966-October 2007), EMBASE (1980 - October 2007) and reference lists of articles. SELECTION CRITERIA: Randomised trials comparing an ovulation suppression agent with placebo or no treatment, or a suppressive agent with danazol or a GnRH with oral contraception in women with endometriosis. A total of twenty three RCTs comparing an ovulation suppression agent with placebo or no treatment, or a suppressive agent with danazol or a GnRH with oral contraception were identified. DATA COLLECTION AND ANALYSIS: Two review authors independently extracted data and assessed quality. We contacted study authors for additional information. Quality was assessed by of method of randomization,allocation concealment, blinding, completeness of follow-up, presence or absence of crossover and co-intervention. 2 x 2 tables were generated for all relevant outcomes. Odds ratios were generated using the Peto modified Mantel-Haenszel technique. Statistical heterogeneity was assessed using the I(2) test of heterogeneity. Subgroup analysis was conducted on those couples clearly identifiable as infertile or wanting to conceive. MAIN RESULTS: Twenty four trials were included. The odds ratio for pregnancy following ovulation suppression versus placebo or no treatment for all women randomised was 0.79 (95% CI 0.54 to 1.14), P = 0.21 and 0.80 (95% CI 0.51 to 1.24), P = 0.32 respectively for subfertile couples only despite the use of a variety of suppression agents. There was no evidence of benefit from the treatment. The common odds ratio for pregnancy following all agents versus danazol for all women randomised was 1.38 (95% CI 1.05 to 1.82), P = 0.02 and OR 1.37 (95% CI 0.94 to 1.99), P = 0.10 for subfertile couples only. When GnRHa and danazol were directly compared, OR was 1.45 (95% CI 1.08 to 1.95) P = 0.01 for all women randomised and OR 1.63( 95% CI 1.12 to 2.37), P = 0.01 for subfertile couples only in favour of GnRH. No effect was observed for GnRH compared with oral contraception; OR 0.99 (95% CI 0.52 to 1.89), P = 0.98 for all women randomised and OR 0.79 ( 95% CI 0.37 to 1.69), P = 0.55. In all analyses the data were statistically homogeneous (I(2)=0%). AUTHORS' CONCLUSIONS: There is no evidence of benefit in the use of ovulation suppression in subfertile women with endometriosis who wish to conceive.

A bottom-up approach to gene regulation.

The ability to construct synthetic gene networks enables experimental investigations of deliberately simplified systems that can be compared to qualitative and quantitative models. If simple, well-characterized modules can be coupled together into more complex networks with behaviour that can be predicted from that of the individual components, we may begin to build an understanding of cellular regulatory processes from the 'bottom up'. Here we have engineered a promoter to allow simultaneous repression and activation of gene expression in Escherichia coli. We studied its behaviour in synthetic gene networks under increasingly complex conditions: unregulated, repressed, activated, and simultaneously repressed and activated. We develop a stochastic model that quantitatively captures the means and distributions of the expression from the engineered promoter of this modular system, and show that the model can be extended and used to accurately predict the in vivo behaviour of the network when it is expanded to include positive feedback. The model also reveals the counterintuitive prediction that noise in protein expression levels can increase upon arrest of cell growth and division, which we confirm experimentally. This work shows that the properties of regulatory subsystems can be used to predict the behaviour of larger, more complex regulatory networks, and that this bottom-up approach can provide insights into gene regulation.

Cancer dose--response assessment for acrylonitrile based upon rodent brain tumor incidence: use of epidemiologic, mechanistic, and pharmacokinetic support for nonlinearity.

A cancer dose-response assessment was conducted for acrylonitrile (AN) using updated information on mechanism of action, epidemiology, toxicity, and pharmacokinetics. Although more than 10 chronic bioassays indicate that AN produces multiple tumors in rats and mice, a number of large, well-conducted epidemiology studies provide no evidence of a causal association between AN exposure and cancer mortality of any type. The epidemiological data include early industry exposures that are far higher than occur today and that approach or exceed levels found to be tumorigenic in animals. Despite the absence of positive findings in the epidemiology data, a dose-response assessment was conducted for AN based on brain tumors in rats. Mechanistic studies implicate the involvement of oxidative stress in rat brain due to a metabolite (2-cyanoethylene oxide or CEO, cyanide), but do not conclusively rule out a potential role for the direct genotoxicity of CEO. A PBPK model was used to predict internal doses (peak CEO in brain) for 12 data sets, which were pooled together to provide a consistent characterization of the dose-response relationship for brain tumor incidence in the rat. The internal dose corresponding to a 5% increase in extra risk (ED 05=0.017 mg/L brain) and its lower confidence limit (LED 05=0.014 mg/L brain) was used as the point of departure. The weight-of-evidence supports the use of a nonlinear extrapolation for the cancer dose-response assessment. A quantitative comparison of the epidemiology exposure-response data (lung and brain cancer mortality) to the rat brain tumor data in terms of internal dose adds to the confidence in the nonlinear extrapolation. Uncertainty factors of 200 and 220 (for the oral and inhalation routes, respectively) were applied to the LED 05 to account for interspecies variation, intraspecies variation, and the severity of the response measure. Accordingly, oral doses below 0.009 mg/kg-day and air concentrations below 0.1mg/m(3) are not expected to pose an appreciable risk to human populations exposed to AN.