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Yagishita Y.,Tohoku University | Fukutomi T.,Tohoku University | Sugawara A.,Tohoku University | Kawamura H.,Tohoku University | And 4 more authors.
Diabetes | Year: 2014

Mice Transcription factor Nrf2 (NF-E2-related factor 2) regulates wide-ranging cytoprotective genes in response to environmental stress. Keap1 (Kelch-like ECH-associated protein 1) is an adaptor protein for Cullin3-based ubiquitin E3 ligase and negatively regulates Nrf2. The Keap1-Nrf2 system plays important roles in the oxidative stress response and metabolism. However, the roles Nrf2 plays in prevention of pancreatic β-Cells damage remain elusive. To demonstrate the roles of Nrf2 in pancreatic β-Cellss, we used four genetically engineered mouse models: 1) β-Cells-specific Keap1- conditional knockout mice, 2) β-Cells-specific Nos2 transgenic mice, 3) conventional Nrf2-heterozygous knockout mice, and 4) β-Cells-specific Nrf2- conditional knockout mice. We found that Nrf2 induction suppressed the oxidative DNA-adduct formation in pancreatic islets of iNOS-Tg mice and strongly restored insulin secretion from pancreatic β-Cellss in the context of reactive species (RS) damage. Consistently, Nrf2 suppressed accumulation of intracellular RS in isolated islets and pancreatic β-Cells lines and also decreased nitrotyrosine levels. Nrf2 induced glutathione-related genes and reduced pancreatic β-Cells apoptosis mediated by nitric oxide. In contrast, Nrf2 depletion in Nrf2-heterozygous knockout and β-Cells-specific Nrf2-conditional knockout mice strongly aggravated pancreatic β-Cells damage. These results demonstrate that Nrf2 induction prevents RS damage in pancreatic β-Cellss and that the Keap1-Nrf2 system is the crucial defense pathway for the physiological and pathological protection of pancreatic β-Cellss. © 2014 by the American Diabetes Association.

Boekelheide K.,Brown University | Andersen M.E.,Hamner Institutes for Health Sciences
Altex | Year: 2010

The efforts of the committee that produced the report on Toxicity Testing in the 21st Century reflected the need to look at the issue of assessing risks to humans from exposure to various chemicals through a lens of 21st century biology. The problem - determining if there is a risk of specific exposures -is as old as humanity; every generation brings its own perspective and tools for examining the problem and coming to answers and solutions. Bringing this generation's tools to bear requires us to see the problem of chemical risk assessment in a different light, both in terms of testing of toxicity pathways in vitro and in the interpretation of the tests for estimating whether exposures will be safe. One key issue will be to assess when pathway perturbations are believed to be excessive, i.e., when they are deemed adverse. Redefinition of adversity based on in vitro testing will require a new perception of dose response functions as probabilities of failures, with multiple underlying processes acting sequentially and in parallel leading to failure at a cellular and an organism level. These dose response relationships for adversity will also require a computational systems biology approach for examining toxicity pathway dynamics and stress pathway overload. While the overall approach of defining adversity for in vitro endpoints and using this definition of adversity for risk assessment can be painted in broad brush strokes, as we have done here for DNA-reactive compounds, it will take implementation with a series of prototypes to show the process in practice.

Zhang Q.,Hamner Institutes for Health Sciences | Bhattacharya S.,Hamner Institutes for Health Sciences | Andersen M.E.,Hamner Institutes for Health Sciences
Open Biology | Year: 2013

Multi-component signal transduction pathways and gene regulatory circuits underpin integrated cellular responses to perturbations. A recurring set of network motifs serve as the basic building blocks of these molecular signalling networks. This review focuses on ultrasensitive response motifs (URMs) that amplify small percentage changes in the input signal into larger percentage changes in the output response. URMs generally possess a sigmoid input-output relationship that is steeper than the Michaelis-Menten type of response and is often approximated by the Hill function. Six types of URMs can be commonly found in intracellular molecular networks and each has a distinct kinetic mechanism for signal amplification. These URMs are: (i) positive cooperative binding, (ii) homo-multimerization, (iii) multistep signalling, (iv) molecular titration, (v) zero-order covalent modification cycle and (vi) positive feedback. Multiple URMs can be combined to generate highly switch-like responses. Serving as basic signal amplifiers, these URMs are essential for molecular circuits to produce complex nonlinear dynamics, including multistability, robust adaptation and oscillation. These dynamic properties are in turn responsible for higher-level cellular behaviours, such as cell fate determination, homeostasis and biological rhythm. © 2013 The Authors.

Campbell Jr. J.L.,Hamner Institutes for Health Sciences
Methods in molecular biology (Clifton, N.J.) | Year: 2012

Physiologically based pharmacokinetic (PBPK) models differ from conventional compartmental pharmacokinetic models in that they are based to a large extent on the actual physiology of the organism. The application of pharmacokinetics to toxicology or risk assessment requires that the toxic effects in a particular tissue are related in some way to the concentration time course of an active form of the substance in that tissue. The motivation for applying pharmacokinetics is the expectation that the observed effects of a chemical will be more simply and directly related to a measure of target tissue exposure than to a measure of administered dose. The goal of this work is to provide the reader with an understanding of PBPK modeling and its utility as well as the procedures used in the development and implementation of a model to chemical safety assessment using the styrene PBPK model as an example.

Pi J.,Hamner Institutes for Health Sciences | Collins S.,Sanford Burnham Institute for Medical Research
Diabetes, Obesity and Metabolism | Year: 2010

Growing evidence indicates that reactive oxygen species (ROS) are not just deleterious by-products of respiratory metabolism in mitochondria, but can be essential elements for many biological responses, including in pancreatic β-cells. ROS can be a 'second-messenger signal' in response to hormone/receptor activation that serves as part of the 'code' to trigger the ultimate biological response, or it can be a 'protective signal' to increase the levels of antioxidant enzymes and small molecules to scavenge ROS, thus restoring cellular redox homeostasis. In pancreatic β-cells evidence is emerging that acute and transient glucose-dependent ROS contributes to normal glucose-stimulated insulin secretion (GSIS). However, chronic and persistent elevation of ROS, resulting from inflammation or excessive metabolic fuels such as glucose and fatty acids, may elevate antioxidant enzymes such that they blunt ROS and redox signalling, thus impairing β-cell function. An interesting mitochondrial protein whose main function appears to be the control of ROS is uncoupling protein 2 (UCP2). Despite continuing investigation of the exact mechanism by which UCP2 is 'activated', it is clear that UCP2 levels and/or activity impact the efficacy of GSIS in pancreatic islets. This review will focus on the paradoxical roles of ROS in pancreatic β-cell function and the regulatory role of UCP2 in ROS signalling and GSIS. © 2010 Blackwell Publishing Ltd.

Grimes J.H.,Hamner Institutes for Health Sciences | O'Connell T.M.,Hamner Institutes for Health Sciences | O'Connell T.M.,University of North Carolina at Chapel Hill
Journal of Biomolecular NMR | Year: 2011

Increasing the sensitivity and throughput of NMR-based metabolomics is critical for the continued growth of this field. In this paper the application of micro-coil NMR probe technology was evaluated for this purpose. The most commonly used biofluids in metabolomics are urine and serum. In this study we examine different sample limited conditions and compare the detection sensitivity of the micro-coil with a standard 5 mm NMR probe. Sample concentration is evaluated as a means to leverage the greatly improved mass sensitivity of the micro-coil probes. With very small sample volumes, the sensitivity of the micro-coil probe does indeed provide a significant advantage over the standard probe. Concentrating the samples does improve the signal detection, but the benefits do not follow the expected linear increase and are both matrix and metabolite specific. Absolute quantitation will be affected by concentration, but an analysis of relative concentrations is still possible. The choice of the micro-coil probe over a standard tube based probe will depend upon a number of factors including number of samples and initial volume but this study demonstrates the feasibility of high-throughput metabolomics with the micro-probe platform. © 2011 Springer Science+Business Media B.V.

Krewski D.,University of Ottawa | Westphal M.,University of Ottawa | Al-Zoughool M.,University of Ottawa | Croteau M.C.,University of Ottawa | Andersen M.E.,Hamner Institutes for Health Sciences
Annual Review of Public Health | Year: 2011

In 2007, the U.S. National Research Council (NRC) published a groundbreaking report entitled Toxicity Testing in the 21st Century: A Vision and a Strategy. The purpose of this report was to develop a long-range strategic plan to update and advance the way environmental agents are tested for toxicity. The vision focused on the identification of critical perturbations of toxicity pathways that lead to adverse human health outcomes using modern scientific tools and technologies. This review describes how emerging scientific methods will move the NRC vision forward and improve the manner in which the potential health risks associated with exposure to environmental agents are assessed. The new paradigm for toxicity testing is compatible with the widely used four-stage risk assessment framework originally proposed by the NRC in 1983 in the so-called Red Book. The Nrf2 antioxidant pathway provides a detailed example of how relevant pathway perturbations will be identified within the context of the new NRC vision for the future of toxicity testing. The implications of the NRC vision for toxicity testing for regulatory risk assessment are also discussed. © 2011 by Annual Reviews. rights reserved.

Bhattacharya S.,Hamner Institutes for Health Sciences | Zhang Q.,Hamner Institutes for Health Sciences | Andersen M.E.,Hamner Institutes for Health Sciences
BMC Systems Biology | Year: 2011

Background: The image of the "epigenetic landscape", with a series of branching valleys and ridges depicting stable cellular states and the barriers between those states, has been a popular visual metaphor for cell lineage specification - especially in light of the recent discovery that terminally differentiated adult cells can be reprogrammed into pluripotent stem cells or into alternative cell lineages. However the question of whether the epigenetic landscape can be mapped out quantitatively to provide a predictive model of cellular differentiation remains largely unanswered.Results: Here we derive a simple deterministic path-integral quasi-potential, based on the kinetic parameters of a gene network regulating cell fate, and show that this quantity is minimized along a temporal trajectory in the state space of the gene network, thus providing a marker of directionality for cell differentiation processes. We then use the derived quasi-potential as a measure of "elevation" to quantitatively map the epigenetic landscape, on which trajectories flow "downhill" from any location. Stochastic simulations confirm that the elevation of this computed landscape correlates to the likelihood of occurrence of particular cell fates, with well-populated low-lying "valleys" representing stable cellular states and higher "ridges" acting as barriers to transitions between the stable states.Conclusions: This quantitative map of the epigenetic landscape underlying cell fate choice provides mechanistic insights into the "forces" that direct cellular differentiation in the context of physiological development, as well as during artificially induced cell lineage reprogramming. Our generalized approach to mapping the landscape is applicable to non-gradient gene regulatory systems for which an analytical potential function cannot be derived, and also to high-dimensional gene networks. Rigorous quantification of the gene regulatory circuits that govern cell lineage choice and subsequent mapping of the epigenetic landscape can potentially help identify optimal routes of cell fate reprogramming. © 2011 Bhattacharya et al; licensee BioMed Central Ltd.

Wetmore B.A.,Hamner Institutes for Health Sciences
Toxicology | Year: 2015

High-throughput in vitro toxicity screening provides an efficient way to identify potential biological targets for environmental and industrial chemicals while conserving limited testing resources. However, reliance on the nominal chemical concentrations in these in vitro assays as an indicator of bioactivity may misrepresent potential in vivo effects of these chemicals due to differences in clearance, protein binding, bioavailability, and other pharmacokinetic factors. Development of high-throughput in vitro hepatic clearance and protein binding assays and refinement of quantitative in vitro-to-. in vivo extrapolation (QIVIVE) methods have provided key tools to predict xenobiotic steady state pharmacokinetics. Using a process known as reverse dosimetry, knowledge of the chemical steady state behavior can be incorporated with HTS data to determine the external in vivo oral exposure needed to achieve internal blood concentrations equivalent to those eliciting bioactivity in the assays. These daily oral doses, known as oral equivalents, can be compared to chronic human exposure estimates to assess whether in vitro bioactivity would be expected at the dose-equivalent level of human exposure. This review will describe the use of QIVIVE methods in a high-throughput environment and the promise they hold in shaping chemical testing priorities and, potentially, high-throughput risk assessment strategies. © 2014 Elsevier Ireland Ltd.

Clewell R.A.,Hamner Institutes for Health Sciences | Andersen M.E.,Hamner Institutes for Health Sciences
Mutagenesis | Year: 2016

Assessing the shape of dose-response curves for DNA-damage in cellular systems and for the consequences of DNA damage in intact animals remains a controversial topic. This overview looks at aspects of the pharmacokinetics (PK) and pharmacodynamics (PD) of cellular DNA-damage/repair and their role in defining the shape of dose-response curves using an in vivo example with formaldehyde and in vitro examples for micronuclei (MN) formation with several test compounds. Formaldehyde is both strongly mutagenic and an endogenous metabolite in cells. With increasing inhaled concentrations, there were transitions in gene changes, from activation of selective stress pathway genes at low concentrations, to activation of pathways for cell-cycle control, p53-DNA damage, and stem cell niche pathways at higher exposures. These gene expression changes were more consistent with dose-dependent transitions in the PD responses to formaldehyde in epithelial cells in the intact rat rather than the low-dose linear extrapolation methods currently used for carcinogens. However, more complete PD explanations of non-linear dose response for creation of fixed damage in cells require detailed examination of cellular responses in vitro using measures of DNA damage and repair that are not easily accessible in the intact animal. In the second section of the article, we illustrate an approach from our laboratory that develops fit-for-purpose, in vitro assays and evaluates the PD of DNA damage and repair through studies using prototypical DNA-damaging agents. Examination of a broad range of responses in these cells showed that transcriptional upregulation of cell cycle control and DNA repair pathways only occurred at doses higher than those causing overt damage fixed damage-measured as MN formation. Lower levels of damage appear to be handled by post-translational repair process using pre-existing proteins. In depth evaluation of the PD properties of one such post-translational process (formation of DNA repair centers; DRCs) has indicated that the formation of DRCs and their ability to complete repair before replication are consistent with threshold behaviours for mutagenesis and, by extension, with chemical carcinogenesis. © 2016 The Author.

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