Office of Applied Research and Safety Assessment

Laurel, MD, United States

Office of Applied Research and Safety Assessment

Laurel, MD, United States
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Vinella D.,U.S. National Institutes of Health | Vinella D.,CNRS Institute of Chemistry | Vinella D.,Institute Pasteur Paris | Potrykus K.,U.S. National Institutes of Health | And 3 more authors.
Journal of Bacteriology | Year: 2012

It is well known that ppGpp and DksA interact with bacterial RNA polymerase (RNAP) to alter promoter activity. This study suggests that GreA plays a major role and GreB plays a minor role in the ppGpp-DksA regulatory network. We present evidence that DksA and GreA/GreB are redundant and/or share similar functions: (i) on minimal medium GreA overproduction suppresses the growth defects of a dksA mutant; (ii) GreA and DksA overexpression partially suppresses the auxotrophy of a ppGppdeficient strain; (iii) microarrays show that many genes are regulated similarly by GreA and DksA. We also find instances where GreA and DksA seem to act in opposition: (i) complete suppression of auxotrophy occurs by overexpression of GreA or DksA only in the absence of the other protein; (ii) PgadA and PgadE promoter fusions, along with many other genes, are dramatically affected in vivo by GreA overproduction only when DksA is absent; (iii) GreA and DksA show opposite regulation of a subset of genes. Mutations in key acidic residues of GreA and DksA suggest that properties seen here probably are not explained by known biochemical activities of these proteins. Our results indicate that the general pattern of gene expression and, in turn, the ability of Escherichia coli to grow under a defined condition are the result of a complex interplay between GreA, GreB, and DksA that also involves mutual control of their gene expression, competition for RNA polymerase binding, and similar or opposite action on RNA polymerase activity. © 2012, American Society for Microbiology.

Potrykus K.,U.S. National Institutes of Health | Murphy H.,Office of Applied Research and Safety Assessment | Philippe N.,French National Center for Scientific Research | Cashel M.,U.S. National Institutes of Health
Environmental Microbiology | Year: 2011

It is widely accepted that the DNA, RNA and protein content of Enterobacteriaceae is regulated as a function of exponential growth rates; macromolecular content increases with faster growth regardless of specific composition of the growth medium. This phenomenon, called growth rate control, primarily involves regulation of ribosomal RNA and ribosomal protein synthesis. However, it was uncertain whether the global regulator ppGpp is the major determinant for growth rate control. Therefore, here we re-evaluate the effect of ppGpp on macromolecular content for different balanced growth rates in defined media. We find that when ppGpp is absent, RNA/protein and RNA/DNA ratios are equivalent in fast and slow growing cells. Moreover, slow growing ppGpp-deficient cells with increased RNA content, display a normal ribosomal subunit composition although polysome content is reduced when compared with fast growing wild-type cells. From this we conclude that growth rate control does not occur in the absence of ppGpp. Also, artificial elevation of ppGpp or introduction of stringent RNA polymerase mutants in ppGpp-deficient cells restores this control. We believe these findings strongly argue in favour of ppGpp and against redundant regulation of growth rate control by other factors in Escherichia coli and other enteric bacteria. Published 2010. This article is a US Government work and is in the public domain in the USA.

Eppinger M.,University of Maryland Baltimore County | Mammel M.K.,Office of Applied Research and Safety Assessment | Leclerc J.E.,Office of Applied Research and Safety Assessment | Ravel J.,University of Maryland Baltimore County | Cebula T.A.,Johns Hopkins University
Proceedings of the National Academy of Sciences of the United States of America | Year: 2011

The rapid emergence of Escherichia coli O157:H7 from an unknown strain in 1982 to the dominant hemorrhagic E. coli serotype in the United States and the cause of widespread outbreaks of human food-borne illness highlights a need to evaluate critically the extent to which genomic plasticity of this important enteric pathogen contributes to its pathogenic potential and its evolution as well as its adaptation in different ecological niches. Aimed at a better understanding of the evolution of the E. coli O157:H7 pathogenome, the present study presents the high-quality sequencing and comparative phylogenomic analysis of a comprehensive panel of 25 E. coli O157:H7 strains associated with three nearly simultaneous foodborne outbreaks of human disease in the United States. Here we present a population genetic analysis of more than 200 related strains recovered from patients, contaminated produce, and zoonotic sources. High-resolution phylogenomic approaches allow the dynamics of pathogenome evolution to be followed at a high level of phylogenetic accuracy and resolution. SNP discovery and study of genome architecture and prophage content identified numerous biomarkers to assess the extent of genetic diversity within a set of clinical and environmental strains. A total of 1,225 SNPs were identified in the present study and are now available for typing of the E. coli O157:H7 lineage. These data should prove useful for the development of a refined phylogenomic framework for forensic, diagnostic, and epidemiological studies to define better risk in response to novel and emerging E. coli O157:H7 resistance and virulence phenotypes.

Steinsland H.,University of Bergen | Steinsland H.,Michigan State University | Lacher D.W.,Michigan State University | Lacher D.W.,Office of Applied Research and Safety Assessment | And 3 more authors.
Journal of Clinical Microbiology | Year: 2010

Enterotoxigenic Escherichia coli (ETEC) is a common cause of diarrhea among children living in and among travelers visiting developing countries. Human ETEC strains represent an epidemiologically and phenotypically diverse group of pathogens, and there is a need to identify natural groupings of these organisms that may help to explain this diversity. Here, we sought to identify most of the important human ETEC lineages that exist in the E. coli population, because strains that originate from the same lineage may also have inherited many of the same epidemiological and phenotypic traits. We performed multilocus sequence typing (MLST) on 1,019 ETEC isolates obtained from humans in different countries and analyzed the data against a backdrop of MLST data from 1,250 non-ETEC E. coli and eight ETEC isolates from pigs. A total of 42 different lineages were identified, 15 of which, representing 792 (78%) of the strains, were estimated to have emerged >900 years ago. Twenty of the lineages were represented in more than one country. There was evidence of extensive exchange of enterotoxin and colonization factor genes between different lineages. Human and porcine ETEC have probably emerged from the same ancestral ETEC lineage on at least three occasions. Our findings suggest that most ETEC strains circulating in the human population today originate from well-established, globally widespread ETEC lineages. Some of the more important lineages identified here may represent a smaller and more manageable target for the ongoing efforts to develop effective ETEC vaccines. Copyright © 2010, American Society for Microbiology. All Rights Reserved.

Mechold U.,U.S. National Institutes of Health | Mechold U.,CNRS Institute of Pharmacology and Structural Biology | Potrykus K.,U.S. National Institutes of Health | Potrykus K.,University of Gdansk | And 4 more authors.
Nucleic Acids Research | Year: 2013

Both ppGpp and pppGpp are thought to function collectively as second messengers for many complex cellular responses to nutritional stress throughout biology. There are few indications that their regulatory effects might be different; however, this question has been largely unexplored for lack of an ability to experimentally manipulate the relative abundance of ppGpp and pppGpp. Here, we achieve preferential accumulation of either ppGpp or pppGpp with Escherichia coli strains through induction of different Streptococcal (p)ppGpp synthetase fragments. In addition, expression of E. coli GppA, a pppGpp 5 0 -gamma phosphate hydrolase that converts pppGpp to ppGpp, is manipulated to fine tune differential accumulation of ppGpp and pppGpp. In vivo and in vitro experiments show that pppGpp is less potent than ppGpp with respect to regulation of growth rate, RNA/DNA ratios, ribosomal RNA P1 promoter transcription inhibition, threonine operon promoter activation and RpoS induction. To provide further insights into regulation by (p)ppGpp, we have also determined crystal structures of E. coli RNA polymerase-p 70 holoenzyme with ppGpp and pppGpp. We find that both nucleotides bind to a site at the interface between β′ and ω subunits. © 2013 The Author(s) 2013. Published by Oxford University Press.

Sahu S.C.,Office of Applied Research and Safety Assessment | O'Donnell Jr. M.W.,Center for Food Safety and Applied Nutrition | Wiesenfeld P.L.,Office of Applied Research and Safety Assessment
Journal of Applied Toxicology | Year: 2010

The present study was undertaken to assess, in vitro, the hepatotoxic potential of the food-borne mycotoxin, deoxynivalenol (DON), using rat (Clone9 and MH1C1), mouse (NBL CL2) and human (WRL68 and HepG2) liver cells in culture. The cells were treated with DON for 24 h at 37°C in 5% CO 2 at concentrations of 0-25 μg ml -1. Following the treatment period, the cells were assayed for biochemical markers of hepatotoxicity that included three independent cytotoxicity assays, oxidative stress and mitochondrial dysfunction. Concentration-dependent cytotoxicity of DON was observed in each of the five different liver cells derived from three different species (rat, mouse and human) over the entire concentration range studied, beginning at 0.1 μg ml -1. At these concentrations DON did not induce a biologically significant increase in oxidative stress in these liver cells, and showed a significant decrease in the mitochondrial function only in the rat liver MH1C1 cells compared with the control. The results of this in vitro study suggest that DON is a potential hepatotoxin for the rat, mouse and human liver cells in the concentration range tested in this study. The liver cells used in this study showed distinct endpoint-sensitivity to DON related to the species.

Zhou W.,Center for Food Safety and Applied Nutrition | Wang P.G.,Center for Food Safety and Applied Nutrition | Ogunsola O.A.,Office of Applied Research and Safety Assessment | Kraeling M.E.K.,Office of Applied Research and Safety Assessment
Bioanalysis | Year: 2013

Background: A sensitive analytical method is needed for assessing penetration of topically applied peptides for in vitro skin-penetration studies. Results: A rapid hydrophilic interaction LC (HILIC)-MS/MS method for analyzing the polar peptides Ac-EEMQRR-amide and H2N-EEMQRR-amide in various skin layers and matrices has been developed and evaluated. The matrices included emulsion, receptor fluids, cotton-tipped applicators, stratum corneum tape strips, epidermis and dermis of the skin. Stable isotopically labeled analogues were used as internal standards to correct for recovery and matrix effects. A HILIC-SPE procedure was optimized to minimize significant ion suppression in the more complex matrices. Conclusion: This HILIC-MS/MS method is applicable to the determination of Ac-EEMQRR-amide and H2N-EEMQRR-amide in complex skin samples and other matrices generated during in vitro skin-penetration studies. © 2013 Future Science Ltd.

Chen Y.,Office of Applied Research and Safety Assessment | Reese D.H.,Office of Applied Research and Safety Assessment
Birth Defects Research Part B - Developmental and Reproductive Toxicology | Year: 2013

The pathway through which retinol (vitamin A) is converted to its active metabolite, all-trans-retinoic acid (atRA), and subsequent receptor-mediated regulation of gene transcription by atRA is essential for all mammal life stages. This pathway is required for normal embryonic development and maintenance of cellular phenotype in adult organisms; chemicals that cause even minor interference with its normal function are potential developmental and adult toxicants. A short-term (24 h) in vitro mode-of-action screen for detecting chemicals that disrupt this essential pathway is described. It uses the mouse pluripotent P19 stem cell in a 96-well format, RT-qPCR gene-expression assay that does not require RNA purification to detect chemicals that interfere with retinol-induced Hoxa1 gene expression, a target of retinol signaling in mammals. A total of 21 chemicals were screened at a single 45 μM concentration. Four chemicals known to disrupt the pathway in the rodent embryo (citral, disulfiram, and two rodent teratogens, nitrofen and bisdiamine) all significantly inhibited Hoxa1 upregulation by retinol. An additional four of seven chemicals with varying degrees of structural similarity to known disruptors or to the retinoid side chain, but not previously known to disrupt the pathway, were positive in the screen. The xenoestrogens, diethylstilbestrol, bisphenol A, 4-n-nonylphenol, and genistein and the phthalate esters, dibutyl phthalate and dipentyl phthalate, but not diethylhexyl phthalate, also significantly disrupted the pathway. Of the 21 chemicals tested, diethylstilbestrol was the only chemical that showed evidence in the MTT assay that cytotoxicity may have contributed to disruption of the pathway. © 2013 Wiley Periodicals, Inc.

Chen Y.,Office of Applied Research and Safety Assessment | Reese D.H.,Office of Applied Research and Safety Assessment
PLoS ONE | Year: 2016

A spectrum of reproductive system anomalies (cryptorchidism, hypospadias, dysgenesis of Wolffian duct-derived tissues and prostate, and reduced sperm production) in male rats exposed in utero to phthalate esters (PEs) are thought to be caused by PE inhibition of fetal testosterone production. Recently, dibutyl and dipentyl phthalate (DBuP, DPnP) were shown to disrupt the retinol signaling pathway (RSP) in mouse pluripotent P19 embryonal carcinoma cells in vitro. The RSP regulates the synthesis and cellular levels of retinoic acid (RA), the active metabolite of retinol (vitamin A). In this new study, a total of 26 di- and mono-esters were screened to identify additional phthalate structures that disrupt the RSP and explore their mechanisms of action. The most potent PEs, those causing > 50% inhibition, contained aryl and cycloalkane groups or C4-C6 alkyl ester chains and were the same PEs reported to cause malformations in utero. They shared similar lipid solubility; logP values were between 4 and 6 and, except for PEs with butyl and phenyl groups, were stable for prolonged periods in culture. Mono- and cognate di-esters varied in ability to disrupt the RSP; e.g., DEHP was inactive but its monoester was active while DBuP was active yet its monoester was inactive. DBuP and dibenzyl phthalate both disrupted the synthesis of RA from retinol but not the ability of RA to activate gene transcription. Both PEs also disrupted the RSP in C3H10T1/2 multipotent mesenchymal stem cells. Based on this in vitro study showing that some PEs disrupt retinol signaling and previous in vivo studies that vitamin A/RA deficiency and PEs both cause strikingly similar anomalies in the male rat reproductive system, we propose that PE-mediated inhibition of testosterone and RA synthesis in utero are both causes of malformations in male rat offspring. This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.

Gao X.,Office of Applied Research and Safety Assessment | Yourick J.J.,Office of Applied Research and Safety Assessment | Sprando R.L.,Office of Applied Research and Safety Assessment
PLoS ONE | Year: 2014

The Tox21 program calls for transforming toxicology testing from traditional in vivo tests to less expensive and higher throughput in vitro methods. In developmental toxicology, a spectrum of alternative methods including cell line based tests has been developed. In particular, embryonic stem cells (ESCs) have received widespread attention as a promising alternative model for developmental toxicity assessment. Here, we characterized gene expression changes during mouse ESC differentiation and their modulation by developmental toxicants. C57BL/6 ESCs were allowed to differentiate spontaneously and RNA of vehicle controls was collected at 0, 24, 48, 72, 96, 120 and 168 h after embryoid body (EB) formation; RNA of compound-exposed EBs were collected at 24 h. Samples were hybridized to Affymetrix Mouse Gene 2.0 ST Array; using stringent cut-off criteria of Bonferroni-adjusted p<0.05 and fold change >2.0, a total of 1996 genes were found differentially expressed among the vehicle controls at different time points. Gene ontology (GO) analysis showed these regulated genes were mostly involved in differentiation-related processes such as development, morphogenesis, metabolism, cell differentiation, cell organization and biogenesis, embryonic development, and reproduction. Biomarkers of all three germ layers or of their derivative early cell types were identified in the gene list. Principal component analysis (PCA) based on these genes showed that the unexposed vehicle controls appeared in chronological order in the PCA plot, and formed a differentiation track when connected. Cultures exposed to thalidomide, monobutyl phthalate, or valproic acid deviated significantly from the differentiation track, manifesting the capacity of the differentiation track to identify the modulating effects of diverse developmental toxicants. The differentiation track defined in this study may be further exploited as a baseline for developmental toxicity testing, with compounds causing significant deviation from the differentiation track being predicted as potential developmental toxicants.

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