Endotoxins

11 Key excerpts on "Endotoxins"

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  eBook - ePub

  Membrane Structure in Disease and Drug Therapy

  • Svante Cornell(Author)
  • 2000(Publication Date)
  • CRC Press

    (Publisher)

  13 Lipopolysaccharide

  A Membrane-Forming and Inflammation-Inducing Bacterial Macromolecule

  Ulrich Seydel, Artur J. Ulmer, Stefan Uhlig, and Ernst Theodor Rietschel Research Center Borstel, Borstel, Germany

  I. INTRODUCTION

  Endotoxins are formed by a certain group of bacteria, the gram-negative bacteria, which differ from other microorganisms by the unique architecture of their cell wall and thus their staining behavior as devised by Hans-Christian Gram (1 ). Endotoxins were originally described as heat-stable components of Vibrio chol-erae by Richard Pfeiffer (2 ) and are known today to be generally present in the cell envelope of gram-negative bacteria. Here they are major and integral components of the outer membrane, being exclusively located in its outer leaflet facing the bacterial environment. Endotoxins participate in the physiological membrane functions and are therefore essential for bacterial growth and viability (3 ). At the same time, Endotoxins represent a primary target for interaction with antibacterial drugs and components of the immune system of the host. They have therefore attracted the interest of microbiologists and bacterial geneticists, who initiated studies to understand the biosynthesis and the molecular basis of the vital function of Endotoxins for bacteria.

  Further, Endotoxins were recognized as potent toxins that, in higher organisms, elicit a broad spectrum of biological activities. They play an important role in the pathogenesis and manifestation of gram-negative infection in general and of septic shock in particular. As a result, Endotoxins intrigued clinical and biological researchers, who set out to elucidate their mode of action and to devise strategies aiming at control of the detrimental endotoxin effects observed during severe bacterial infection and sepsis. In addition, Endotoxins are capable of producing beneficial effects in higher organisms depending upon their amount and route of introduction (4

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  Handbook of Toxinology

  • W. T. Shier(Author)
  • 2020(Publication Date)
  • CRC Press

    (Publisher)

  9 Bacterial Endotoxins JAROSLAV HOFMAN Institute of Microbiology, Czechoslovakian Academy of Science, Prague, Czechoslovakia

  1. INTRODUCTION
  2. LOCALIZATION AND STRUCTURE
     1. Localization of Endotoxins in the cell membrane
     2. Isolation
     3. Chemical structure and assay
        1. Chemical structure of Endotoxins
        2. Synthetic lipid A
        3. Depyrogenation or detoxification of endotoxin
        4. Assay of Endotoxins: Limulus amebocyte lysate (LAL) test
  3. BIOLOGICAL ACTIVITIES
     1. Lethality
     2. Endotoxin-complement system interaction
     3. Interaction with the blood coagulation system
     4. Antibody response to endotoxin
     5. Stimulating and suppressive effect on the immune response
     6. Endotoxin effects on nonspecific resistance to infection
     7. Endotoxin and tumors
     8. Endotoxin-induced release of mediators
  4. CONCLUSION
  5. REFERENCES

  I. Introduction

  Endotoxin is a historical term for high-molecular substances from gram-negative bacteria. The name indicates that endotoxin is a constitutive part of a bacterial cell (“endo”) which, when applied to an organism, induces pathological changes (“toxin”). The term arose from observations that endotoxin is released from cells only with difficulty, either after breakdown or digestion of the cell. Together with relative thermostability, these properties distinguish endotoxin from thermolabile exotoxins, which, on the other hand, are spontaneously released by the microorganisms into the growth medium or during infection. Although the term “endotoxin,” which originated at the beginning of this century, has been replaced by other names expressing its partial properties, it is still used, and it denotes the most complex definition of the substance. An endotoxin is not only toxic, but it exhibits various other biological activities when administered to higher organisms or when added to humoral or cellular components in vitro. The spectrum of activities is unusually broad and unique among toxins. On the other hand, it is a substance present in very small but definite amounts in our body during our whole lifespan. It is not known what biological functions are affected by these low concentrations.

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  Large Animal Internal Medicine - E-Book

  • Bradford P. Smith, David C Van Metre, Nicola Pusterla(Authors)
  • 2019(Publication Date)
  • Mosby

    (Publisher)

  Endotoxemia and Sepsis

  Kelsey A. Hart • Erin McConachie Beasley • Robert J. MacKay

  ■ Definitions

  The term endotoxin was originally coined to describe toxic bacterial components that were contained within or on the bacterial cell, in comparison with exotoxins that were secreted from outside bacterial cells. The heat-stable endotoxic activity of Vibrio cholera, identified by Richard F. J. Pfeiffer in the late nineteenth century, resides in lipopolysaccharide (LPS), the principal component of the outer leaflet of the outer membrane of all Gram-negative bacteria1 (Fig. 32.55 ). Today, the terms endotoxin (the activity) and LPS (the molecule) are used synonymously to refer to this specific Gram-negative bacterial membrane component, except when purified LPS is being referenced.2 Each LPS molecule has three structural domains: a polar polysaccharide O region, which projects into the aqueous extracellular environment; a hydrophobic lipid A region, which is largely buried in the bacterial outer membrane; and a core acidic oligosaccharide region connecting the other two. The O-region is highly variable, consisting of repeating units each of one to eight glycosyl residues, and contains antigens specific for each bacterial strain; the core glycolipid region is relatively constant among bacteria and mediates most of the toxic effects of endotoxin. On bacterial death or during bacterial proliferation, large (molecular mass > 106 D) aggregates of LPS and membrane protein are released. It is these protein-lipid micelles that constitute native endotoxin.

  FIG. 32.55

  Illustration of a cross-section of the double lipid bilayer that forms the cell membrane of Gram-negative bacteria. Lipopolysaccharide (LPS) is the principal component of the outer leaflet of the outer membrane. The insert

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  Concepts in Bacterial Virulence

  • W. Russell, H. Herwald, A. Schmidt, H. Herwald(Authors)
  • 2004(Publication Date)
  • S. Karger

    (Publisher)

  Russell W, Herwald H (eds): Concepts in Bacterial Virulence. Contrib Microbiol. Basel, Karger, 2004, vol 12, pp 1–27 Fundamentals of Endotoxin Structure and Function Russell E. Bishop Departments of Laboratory Medicine and Pathobiology, and Biochemistry, University of Toronto, Toronto, Canada In 1892, Richard Pfeiffer first defined endotoxin as a heat-stable toxic sub-stance that was released upon disruption of microbial envelopes [1]. The toxic-ity is now known to be a consequence of the host inflammatory response, which appears to be optimally adapted for the clearance of most local infections. However, when severe infections become distributed systemically, the inflam-matory response can lead to septic shock and death. Most of the early efforts to determine the signal transduction events that occur between the presentation of endotoxin to the myeloid cells of the immune system and the production of inflammatory cytokines have utilized lipopolysaccharide (LPS) from gram-negative bacteria [2]. The bioactive lipid A component of LPS is arguably the most potent of the substances that fit Pfeiffer’s endotoxin definition, and lipid A has become synonymous with endotoxin. However, many other inflammatory mediators derived from bacteria can also be regarded as Endotoxins, including peptidoglycan, the diacylglycerylcysteine moiety of bacterial lipoproteins, and bacterial nucleic acid signatures, to name only a few. The recent discovery that Toll-like receptor 4 (TLR4) is the lipid A inflammatory signal transducer has been followed by the identification of signal transducers for different inflam-matory mediators [3, 4]. Coincident with these developments in endotoxin signaling has been the revelation that pathogenic gram-negative bacteria can modulate the structure of lipid A in order to evade detection by the host immune system.

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  Endotoxin in Health and Disease

  • Helmut Brade(Author)
  • 2020(Publication Date)
  • CRC Press

    (Publisher)

  11A Biophysical View on the Function and Activity of Endotoxins Ulrich Seydel, Andre Wiese, Andra B. Schromm, and Klaus Brandenburg

  Research Center Borstel, Borstel, Germany

  INTRODUCTION

  Lipopolysaccharides (LPS) are known to constitute amphiphilic macromolecules located on the surface of gram-negative bacteria (1 ,2 ). They participate in the physiological membrane functions of the bacterial organism and are essential for its growth and survival (3 ). LPS are, at the same time, the primary target for interaction with antibacterial drugs and components of the immune system of the host.

  Released from the bacterial surface or in isolated form, LPS evoke an overwhelming spectrum of biological activities when administered to animals or humans or in vitro. They play an important role in the pathogenesis and manifestation of gram-negative infection in general and of septic shock in particular. Thus, lipopolysaccharides are also termed Endotoxins (4 ) and are among the most potent agents capable of inducing local or generalized inflammatory reactions in both humans and experimental animals.

  In gram-negative bacteria, the composition of the lipid matrix of the outer membrane is extremely asymmetric with respect to chemical structure and charge of the lipids. Thus, the outer leaflet is built up from LPS and the inner from a mixture of phospholipids (5 ). Chemically, LPS consist of a hydrophilic heteropolysaccharide, which is covalently linked to a hydrophobic lipid portion, termed lipid A, which anchors the molecule in the outer membrane. In wild-type strains, the polysaccharide portion consists of an O-specific chain and the core oligosaccharide (S-form LPS). Rough mutant strains do not express the O side chain but retain core oligosaccharides of varying length. The LPS of the various rough mutants are characterized by chemotypes in the sequence of decreasing length of the core sugar as Ra (complete core), Rb, Rc, Rd, and Re, the latter representing the minimal structure of LPS consisting only of lipid A and two 2-keto-3-deoxyoctonate (Kdo) monosaccharides. Lipid A is composed of a ±-glucosaminyl-(1 →6 )-α-D

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  Food Microbiology

  Principles into Practice

  • Osman Erkmen, T. Faruk Bozoglu(Authors)
  • 2016(Publication Date)
  • Wiley

    (Publisher)

  Endotoxins are released from lysed bacterial cells as a result of effective host defense. However, structural components of cells can be released as soluble Endotoxins from the growing bacteria. Endotoxins are pyrogenic (fever producing) lipopolysaccharides released from the outer membrane of the lysed Gram-negative bacterial cell wall. Endotoxins are cell-associated substances that are structural components of bacteria. Most Endotoxins are located in the cell wall. Endotoxin refers specifically to the lipopolysaccharide or lipooligosaccharide (LOS) located in the outer membrane of Gram-negative bacteria. LPS consists of lipid A, polysaccharide, and core oligosaccharide. Oligosaccharide attaches directly to lipid A, and contains sugar and noncarbohydrate components (such as phosphate and amino acids). Polysaccharide is the O-antigen that can induce specific immunity. The term LOS is used to refer to a low molecular weight substance of bacterial LPS. LOS lacks O-antigens and has only lipid A and an oligosaccharide core. Endotoxins generally indicate bacterial growth. Bacterial Endotoxins, both soluble and cell associated, may be transported by blood and lymph and can cause cytotoxic effects on tissue. Some bacterial Endotoxins may also act at the site of colonization and play a role in invasion. Toxicity is not destroyed above 60 °C for hours. Endotoxins are weakly antigenic and not converted to toxoid. Endotoxins are synthesized directly by chromosomal genes.

  O-polysaccharide is responsible for the property of “smoothness” of bacterial cells, which may contribute to their resistance to phagocytosis. O-polysaccharide is hydrophilic and may allow diffusion of the toxic lipid in the hydrophilic environment. O-polysaccharide can act as a specific ligand (adhesion) for bacterial colonization that is essential for virulence characteristic. O-polysaccharide is antigenic, and the usual basis for antigenic variation in Gram-negative bacteria rests in differences in their O-polysaccharides.

  Physiological, pathological, and clinical effects of Endotoxins of different Gram-negative bacteria are similar. (i) The endotoxin causes liberation of interleukin-1. Interleukin-1 acts on thermoregulatory center and causes fever. (ii) Leukopenia occurs early with onset of fever. It may be followed by leukocytosis. (iii) Endotoxin enhances glycolysis in many cell types and can lead to hypoglycemia. (iv) Hypotension occurs early in Gram-negative bacteremia. (v) Endotoxic (septic) shock may develop in severe Gram-negative bacteremia. (v) Endotoxin activates complement system. (vi) Endotoxin causes coagulation of blood. (vii) Death may occur due to shock and bacteremia. (viii) Peptidoglycan of Gram-positive bacteria may produce similar activities as LPS of Gram-negative bacteria. However, peptidoglycan is much less potent toxic than LPS.

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  Pharmaceutical Dosage Forms - Parenteral Medications

  Volume 2: Facility Design, Sterilization and Processing

  • Sandeep Nema, John D. Ludwig(Authors)
  • 2016(Publication Date)
  • CRC Press

    (Publisher)

  Endotoxin is almost universally present in the natural environment, and it is resilient and persistent. Stringent and specific steps must be taken to ensure that parenteral products are not significantly contaminated with endotoxin, either from component materials or by introduc-tion during the manufacturing process. Finished parenteral products must not contain quantities of endotoxin in excess of the limits specified in either compendial monographs or approved submissions. Low levels of endotoxin, below these limits, are tolerated by humans (and other species). This chapter begins with a review of the nature of endotoxin and its role in bacterial cells. The biochemistry of endotoxin; its effects and properties; the practical implications of the properties of endotoxin for parenteral products; and standard endotoxin preparations are then discussed. The Limulus amebocyte lysate (LAL) reagent is introduced and the various LAL test methodologies for the detection of endotoxin are described. The regulatory context for the endotoxin testing is addressed with particular emphasis on the harmonized pharmacopeial Endotoxins test chapters and the United States Food and Drug Administration (FDA) Guideline on the Limulus amebocyte lysate test (2). Practical information is presented on testing parenteral products and a brief section on testing medical devices is included. The chapter finishes with an overview of depyrogenation. ENDOTOXIN Endotoxin Structure Endotoxin is a structural component of the cell envelope of gram-negative bacteria, which consists of an inner and an outer membrane. The inner (cytoplasmic) membrane is a typical biological membrane consisting of a phospholipid bilayer with embedded proteins and is similar in structure to the cytoplasmic membrane of gram-positive cells. The outer membrane comprises an inner phospholipid leaflet (layer) and an outer leaflet, of which the principal component is lipopolysaccharide (LPS), not phospholipid.

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  Microbial Contamination Control in the Pharmaceutical Industry

  • Luis Jimenez(Author)
  • 2004(Publication Date)
  • CRC Press

    (Publisher)

  This chapter seeks to provide an overview for endotoxin as both a parenteral contaminant and as a standard used in modern assays. 2. ENDOTOXIN NOMENCLATURE AND CLASSIFICATION AS A PYROGEN Although used interchangeably, Hitchcock et al. have proposed reserving the term ‘‘ lipopolysaccharide ’’ (LPS) for ‘‘ purified bacterial extracts which are reasonably free of detectable contaminants, particularly protein ’’ and the term ‘‘ endotoxin ’’ for ‘‘ products of extraction procedures which result in macromolecular complexes of LPS, protein, and phospholipid. ’’ Any study of endotoxin requires definition as to relative position as one of many pyrogens. Pyrogens include any substance capable of eliciting a febrile (or fever) re-sponse on injection or infection (as in endotoxin released in vivo by infecting gram-negative bacteria (GNB). Endotoxin is a subset of pyrogens that are strictly of GNB origin; they occur (virtually) nowhere else in nature. The definition of endotoxin as ‘‘ lipopolysaccharide–protein complexes contained in cell walls of GNB, including noninfectious gram negatives ’’ has also been used to denote its heterogenous nature [2]. Exogenous pyrogens include any substance foreign to the body that are capable of inducing a febrile response on injection or infection and, of course, include microbial pyrogen—the most potent and predominant of which is endotoxin. Nonmicrobial exogenous pyrogen includes certain pharmaco-logical agents or, for a sensitized host, antigens such as human serum albumen [3].

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  Endotoxins

  Pyrogens, LAL Testing and Depyrogenation

  • Kevin L. Williams(Author)
  • 2007(Publication Date)
  • CRC Press

    (Publisher)

  J Biol Chem 1999; 274(48):34116–34122. 52. Shands JW. Affinity of endotoxin for membranes. J Infect Dis 1973; 128(suppl):197 – 201. 53. Shands JW. Morphological structures of isolated bacterial lipopolysaccharide. J Mol Biol 1967; 25:15–21. 54. Brandenburg K, Rietschel ET, Brade H. Conformation of lipid A-the endotoxic center of bacterial lipopolysaccharide. J Endotoxin Res 1996; 313:173 – 178. 55. Tanford C. The hydrophobic effect: formation of micelles and biological membranes. 2nd ed. New York: John Wiley & Sons, 1980. 56. Sikkema J, De Bont JAM, Poolman B. Mechanisms of membrane toxicity of hydrocar-bons. Microbiol Rev 1995; 59(2):201 – 222. 57. Shands JW, Chun PW. The dispersion of gram-negative lipopolysaccharide by deoxy-cholate. J Biol Chem 1980; 255(3):1221 – 1226. 58. Luhm J et al. Hypothermia enhances the biological activity of lipopolysaccharide by altering its fluidity state. Eur J Biochem 1988; 256:325 – 333. Endotoxin Structure, Function, and Activity 89 59. Falk MC et al. Aggregation of serum proteins with lipopolysaccharide (LPS): character-ization of the precipitable LPS-protein complex. J Endotoxin Res 1996; 3(2):129 – 142. 60. Din ZZ et al. Effect of pH on solubility and ionic state of lipopolysaccharide obtained from the deep rough mutant of Escherichia coli . Biochemistry 32:4579 – 4586. 61. Takayama et al. Physiochemical properties of the lipopolysaccharide unit that activates B lymphocytes. J Biol Chem 1990; 265(23):14023 – 14029. 62. Mueller M, Linder B, Kusumoto S, Fukase K, Andra B Schromm, Ulrich Seydel. Aggregates are the biologically active units of endotoxin. J Biol Chem 2004; 279(25):26307 – 26313. 63. Brandenburg KJ, Rietschel ET, Mayer H, Koch MH, Weckesser J, Seydel U. Influence of the supramolecular structure of free lipid A on its biological activities. FEBS J Eur Biochem 1993; 218:555 – 563. 64. Kato H et al. Chemical structure of lipid A isolated from Flavobacterium meningosepticum lipopolysaccharide.

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  Carbohydrates in Drug Design and Discovery

  • Jesus Jimenez-Barbero, F. Javier Canada, Sonsoles Martin-Santamaria(Authors)
  • 2015(Publication Date)
  • Royal Society of Chemistry

    (Publisher)

  CHAPTER 3 Lipopolysaccharides as Microbe-associated Molecular Patterns: A Structural Perspective FLAVIANA DI LORENZO, CRISTINA DE CASTRO, ROSA LANZETTA, MICHELANGELO PARRILLI, ALBA SILIPO AND ANTONIO MOLINARO* Department of Chemical Sciences, University of Naples Federico II, Via Cinthia 4, 80126, Naples, Italy *Email: [email protected] 3.1 Introduction The history of the lipopolysaccharide (LPS) macromolecule, also known as ‘‘endotoxin’’, starts in the year 1892 from a work on Vibrio cholerae 1,2 executed by Richard Pfeiffer, a disciple of Robert Koch, who showed that heat-killed cholera bacteria were able to cause toxic shock reactions in guinea pigs, thus demonstrating that they were themselves toxic, unlike the previous dogma regarding the toxicity belonging to secreted products from living microorganisms, known as ‘‘exotoxins’’. 1,2 Later, the endo-bacterial nature of this toxic material was further confirmed by Florence Seibert in 1923, 2 identifying the bioactive material contaminating infusion fluids and pharmaceutical drugs. 2 In 1943, the pharmacologist Murray J. Shear intro-duced the current term ‘‘lipopolysaccharide’’, highlighting the glycolipid RSC Drug Discovery Series No. 43 Carbohydrates in Drug Design and Discovery Edited by Jesu ´s Jime ´nez-Barbero, F. Javier Can ˜ada and Sonsoles Martı ´n-Santamarı ´a r The Royal Society of Chemistry 2015 Published by the Royal Society of Chemistry, www.rsc.org 38 nature of the Endotoxins, 2 although it took several years to reach the complete elucidation of the structure of the macromolecule; this was obtained in 1952 by Otto Lu ¨deritz and Otto Westphal, who were the first to isolate the endotoxic material in sufficiently pure amounts required for structural studies. 3 Their protocol of LPS extraction from bacterial dried cells is currently used in the lipopolysaccharide research field.

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  The Equine Acute Abdomen

  • Anthony T. Blikslager, Nathaniel A. White, James N. Moore, Tim S. Mair, Anthony T. Blikslager, Nathaniel A. White, II, James N. Moore, Tim S. Mair(Authors)
  • 2017(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  Chapter 31 ), a primary focus of this chapter will be on the manner in which the body senses and responds to Gram‐negative and Gram‐positive bacteria. Gram‐negative bacteria generate ligands such as lipopolysaccharides, flagellin, peptidoglycan, and methylated DNA, whereas Gram‐positive bacteria give rise to peptidoglycan, bacterial lipoproteins, methylated DNA, and lipoteichoic acid.

  Receptors for Gram‐negative Bacteria and Bacterial Ligands

  Endotoxin, the bacterial ligand commonly associated with gastrointestinal diseases in adult horses and sepsis in foals, is recognized by TLR‐4 in a large protein complex containing lipopolysaccharide‐binding protein (LBP), CD14, and MD2 (Figure 16.1 ) (Bryant et al., 2015). TLR‐4 is only expressed on the cell surface when it is bound to MD2; otherwise it is located within the cell in the endoplasmic reticulum. Endotoxin binds to LBP, which then binds to CD14. The role of CD14 and LBP is to increase the sensitivity of the cell to the presence of endotoxin by presenting the bound endotoxin to the complex consisting of TLR‐4 and MD2. At this point, endotoxin binds to MD2, thereby causing a conformational change in TLR‐4. This conformational change allows the receptor complex to dimerize with another complex of MD2 and TLR‐4 presumably also complexes with endotoxin. Dimerization of TLR‐4 initiates the intracellular signaling pathways that result in the production of pro‐inflammatory mediators, such as cytokines, and inducible enzymes.

  Figure 16.1

  Ligand bound structures for the Toll‐like receptors (TLRs). LPS, lipopolysaccharide, endotoxin; ds, double stranded; ss, single stranded.

  Because the cytoplasmic domain of TLR‐4 is similar to the cytoplasmic domain of the interleukin‐1 receptor, stimulation of TLR‐4 activates many of the same intracellular signaling cascades activated by interleukin‐1 through its own receptor (Figure 16.2

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