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Kempher ML, Shadid TM, Larabee JL, Ballard JD. A sequence invariable region in TcdB2 is required for toxin escape from Clostridioides difficile. J Bacteriol 2024; 206:e0009624. [PMID: 38888328 PMCID: PMC11323933 DOI: 10.1128/jb.00096-24] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2024] [Accepted: 05/23/2024] [Indexed: 06/20/2024] Open
Abstract
Sequence differences among the subtypes of Clostridioides difficile toxin TcdB (2,366 amino acids) are broadly distributed across the entire protein, with the notable exception of 76 residues at the protein's carboxy terminus. This sequence invariable region (SIR) is identical at the DNA and protein level among the TcdB variants, suggesting this string of amino acids has undergone selective pressure to prevent alterations. The functional role of the SIR domain in TcdB has not been determined. Analysis of a recombinantly constructed TcdB mutant lacking the SIR domain did not identify changes in TcdB's enzymatic or cytopathic activities. To further assess the SIR region, we constructed a C. difficile strain with the final 228 bp deleted from the tcdB gene, resulting in the production of a truncated form of TcdB lacking the SIR (TcdB2∆2291-2366). Using a combination of approaches, we found in the absence of the SIR sequence TcdB2∆2291-2366 retained cytotoxic activity but was not secreted from C. difficile. TcdB2∆2291-2366 was not released from the cell under autolytic conditions, indicating the SIR is involved in a more discrete step in toxin escape from the bacterium. Fractionation experiments combined with antibody detection found that TcdB2∆2291-2366 accumulates at the cell membrane but is unable to complete steps in secretion beyond this point. These data suggest conservation of the SIR domain across variants of TcdB could be influenced by the sequence's role in efficient escape of the toxin from C. difficile. IMPORTANCE Clostridioides difficile is a leading cause of antibiotic associated disease in the United States. The primary virulence factors produced by C. difficile are two large glucosylating toxins TcdA and TcdB. To date, several sequence variants of TcdB have been identified that differ in various functional properties. Here, we identified a highly conserved region among TcdB subtypes that is required for release of the toxin from C. difficile. This study reveals a putative role for the longest stretch of invariable sequence among TcdB subtypes and provides new details regarding toxin release into the extracellular environment. Improving our understanding of the functional roles of the conserved regions of TcdB variants aids in the development of new, broadly applicable strategies to treat CDI.
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Affiliation(s)
- Megan L. Kempher
- Department of
Microbiology and Immunology, University of Oklahoma Health Sciences
Center, Oklahoma City,
Oklahoma, USA
- Department of
Chemistry and Biochemistry, University of
Oklahoma, Norman,
Oklahoma, USA
| | - Tyler M. Shadid
- Department of
Microbiology and Immunology, University of Oklahoma Health Sciences
Center, Oklahoma City,
Oklahoma, USA
| | - Jason L. Larabee
- Department of
Microbiology and Immunology, University of Oklahoma Health Sciences
Center, Oklahoma City,
Oklahoma, USA
| | - Jimmy D. Ballard
- Department of
Microbiology and Immunology, University of Oklahoma Health Sciences
Center, Oklahoma City,
Oklahoma, USA
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2
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Matylitsky J, Krieg A, Schumacher J, Borho J, Barth H, Papatheodorou P. Inhibition of Clostridioides difficile toxins TcdA and TcdB by the amiodarone derivative dronedarone. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 2024:10.1007/s00210-024-03248-8. [PMID: 38935126 DOI: 10.1007/s00210-024-03248-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/29/2024] [Accepted: 06/18/2024] [Indexed: 06/28/2024]
Abstract
The dreaded nosocomial pathogen Clostridioides difficile causes diarrhea and severe inflammation of the colon, especially after the use of certain antibiotics. The bacterium releases two deleterious toxins, TcdA and TcdB, into the gut, which are mainly responsible for the symptoms of C. difficile-associated diseases (CDADs). Both toxins are capable of entering independently into various host cells, e.g., intestinal epithelial cells, where they mono-O-glucosylate and inactivate Rho and/or Ras GTPases, important molecular switches for various cellular functions. We have shown recently that the cellular uptake of the Clostridioides difficile toxins TcdA and TcdB (TcdA/B) is inhibited by the licensed class III antiarrhythmic drug amiodarone (Schumacher et al. in Gut Microbes 15(2):2256695, 2023). Mechanistically, amiodarone delays the cellular uptake of both toxins into target cells most likely by lowering membrane cholesterol levels and by interfering with membrane insertion and/or pore formation of TcdA/B. However, serious side effects, such as thyroid dysfunction and severe pulmonary fibrosis, limit the clinical use of amiodarone in patients with C. difficile infection (CDI). For that reason, we aimed to test whether dronedarone, an amiodarone derivative with a more favorable side effect profile, is also capable of inhibiting TcdA/B. To this end, we tested in vitro with various methods the impact of dronedarone on the intoxication of Vero and CaCo-2 cells with TcdA/B. Importantly, preincubation of both cell lines with dronedarone for 1 h at concentrations in the low micromolar range rendered the cells less sensitive toward TcdA/B-induced Rac1 glucosylation, collapse of the actin cytoskeleton, cell rounding, and cytopathic effects, respectively. Our study points toward the possibility of repurposing the already approved drug dronedarone as the preferable safer-to-use alternative to amiodarone for inhibiting TcdA/B in the (supportive) therapy of CDADs.
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Affiliation(s)
- Jauheni Matylitsky
- Institute of Experimental and Clinical Pharmacology, Toxicology and Pharmacology of Natural Products, Ulm University Medical Center, Albert-Einstein-Allee 11, 89081, Ulm, Germany
| | - Anica Krieg
- Institute of Experimental and Clinical Pharmacology, Toxicology and Pharmacology of Natural Products, Ulm University Medical Center, Albert-Einstein-Allee 11, 89081, Ulm, Germany
| | - Judith Schumacher
- Institute of Experimental and Clinical Pharmacology, Toxicology and Pharmacology of Natural Products, Ulm University Medical Center, Albert-Einstein-Allee 11, 89081, Ulm, Germany
| | - Joscha Borho
- Institute of Experimental and Clinical Pharmacology, Toxicology and Pharmacology of Natural Products, Ulm University Medical Center, Albert-Einstein-Allee 11, 89081, Ulm, Germany
| | - Holger Barth
- Institute of Experimental and Clinical Pharmacology, Toxicology and Pharmacology of Natural Products, Ulm University Medical Center, Albert-Einstein-Allee 11, 89081, Ulm, Germany
| | - Panagiotis Papatheodorou
- Institute of Experimental and Clinical Pharmacology, Toxicology and Pharmacology of Natural Products, Ulm University Medical Center, Albert-Einstein-Allee 11, 89081, Ulm, Germany.
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3
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Papatheodorou P, Minton NP, Aktories K, Barth H. An Updated View on the Cellular Uptake and Mode-of-Action of Clostridioides difficile Toxins. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2024; 1435:219-247. [PMID: 38175478 DOI: 10.1007/978-3-031-42108-2_11] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2024]
Abstract
Research on the human gut pathogen Clostridioides (C.) difficile and its toxins continues to attract much attention as a consequence of the threat to human health posed by hypervirulent strains. Toxin A (TcdA) and Toxin B (TcdB) are the two major virulence determinants of C. difficile. Both are single-chain proteins with a similar multidomain architecture. Certain hypervirulent C. difficile strains also produce a third toxin, namely binary toxin CDT (C. difficile transferase). C. difficile toxins are the causative agents of C. difficile-associated diseases (CDADs), such as antibiotics-associated diarrhea and pseudomembranous colitis. For that reason, considerable efforts have been expended to unravel their molecular mode-of-action and the cellular mechanisms responsible for their uptake. Many of these studies have been conducted in European laboratories. Here, we provide an update on our previous review (Papatheodorou et al. Adv Exp Med Biol, 2018) on important advances in C. difficile toxins research.
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Affiliation(s)
- Panagiotis Papatheodorou
- Institute of Experimental and Clinical Pharmacology, Toxicology and Pharmacology of Natural Products, Ulm University Medical Center, Ulm, Germany.
| | - Nigel P Minton
- BBSRC/EPSRC Synthetic Biology Research Centre, University of Nottingham, Nottingham, UK
| | - Klaus Aktories
- Institute of Experimental and Clinical Pharmacology and Toxicology, University of Freiburg, Freiburg, Germany
| | - Holger Barth
- Institute of Experimental and Clinical Pharmacology, Toxicology and Pharmacology of Natural Products, Ulm University Medical Center, Ulm, Germany
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4
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Schumacher J, Nienhaus A, Heber S, Matylitsky J, Chaves-Olarte E, Rodríguez C, Barth H, Papatheodorou P. Exploring the inhibitory potential of the antiarrhythmic drug amiodarone against Clostridioides difficile toxins TcdA and TcdB. Gut Microbes 2023; 15:2256695. [PMID: 37749884 PMCID: PMC10524773 DOI: 10.1080/19490976.2023.2256695] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/02/2023] [Accepted: 09/05/2023] [Indexed: 09/27/2023] Open
Abstract
The intestinal pathogen Clostridioides difficile is the leading cause of antibiotic-associated diarrhea and pseudomembranous colitis in humans. The symptoms of C. difficile-associated diseases (CDADs) are directly associated with the pathogen's toxins TcdA and TcdB, which enter host cells and inactivate Rho and/or Ras GTPases by glucosylation. Membrane cholesterol is crucial during the intoxication process of TcdA and TcdB, and likely involved during pore formation of both toxins in endosomal membranes, a key step after cellular uptake for the translocation of the glucosyltransferase domain of both toxins from endosomes into the host cell cytosol. The licensed drug amiodarone, a multichannel blocker commonly used in the treatment of cardiac dysrhythmias, is also capable of inhibiting endosomal acidification and, as shown recently, cholesterol biosynthesis. Thus, we were keen to investigate in vitro with cultured cells and human intestinal organoids, whether amiodarone preincubation protects from TcdA and/or TcdB intoxication. Amiodarone conferred protection against both toxins independently and in combination as well as against toxin variants from the clinically relevant, epidemic C. difficile strain NAP1/027. Further mechanistic studies suggested that amiodarone's mode-of-inhibition involves also interference with the translocation pore of both toxins. Our study opens the possibility of repurposing the licensed drug amiodarone as a novel pan-variant antitoxin therapeutic in the context of CDADs.
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Affiliation(s)
- Judith Schumacher
- Institute of Experimental and Clinical Pharmacology, Toxicology and Pharmacology of Natural Products, Ulm University Medical Center, Ulm, Germany
| | - Astrid Nienhaus
- Institute of Experimental and Clinical Pharmacology, Toxicology and Pharmacology of Natural Products, Ulm University Medical Center, Ulm, Germany
| | - Sebastian Heber
- Institute of Experimental and Clinical Pharmacology, Toxicology and Pharmacology of Natural Products, Ulm University Medical Center, Ulm, Germany
| | - Jauheni Matylitsky
- Institute of Experimental and Clinical Pharmacology, Toxicology and Pharmacology of Natural Products, Ulm University Medical Center, Ulm, Germany
| | - Esteban Chaves-Olarte
- Centro de Investigación en Enfermedades Tropicales and Facultad de Microbiología, Universidad de Costa Rica, San José, Costa Rica
| | - César Rodríguez
- Centro de Investigación en Enfermedades Tropicales and Facultad de Microbiología, Universidad de Costa Rica, San José, Costa Rica
| | - Holger Barth
- Institute of Experimental and Clinical Pharmacology, Toxicology and Pharmacology of Natural Products, Ulm University Medical Center, Ulm, Germany
| | - Panagiotis Papatheodorou
- Institute of Experimental and Clinical Pharmacology, Toxicology and Pharmacology of Natural Products, Ulm University Medical Center, Ulm, Germany
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5
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Bharathkar SK, Miller MJ, Stadtmueller BM. Engineered Secretory Immunoglobulin A provides insights on antibody-based effector mechanisms targeting Clostridiodes difficile. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.11.08.566291. [PMID: 37986930 PMCID: PMC10659285 DOI: 10.1101/2023.11.08.566291] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2023]
Abstract
Secretory (S) Immunoglobin (Ig) A is the predominant mucosal antibody, which mediates host interactions with commensal and pathogenic microbes, including Clostridioides difficile. SIgA adopts a polymeric IgA structure that is bound by secretory component (SC). Despite significance, how SIgA supports diverse effector mechanisms is poorly characterized and SIgA-based therapies nonexistent. We engineered chimeric (c) SIgAs, in which we replaced SC domain D2 with a single domain antibody or a monomeric fluorescent protein, allowing us to investigate and enhance SIgA effector mechanisms. cSIgAs exhibited increased neutralization potency against C. difficile toxins, promoted bacterial clumping and cell rupture, and decreased cytotoxicity. cSIgA also allowed us to visualize and/or quantify C. difficile morphological changes and clumping events. Results reveal mechanisms by which SIgA combats C. difficile infection, demonstrate that cSIgA design can modulate these mechanisms, and demonstrate cSIgA's adaptability to modifications that might target a broad range of antigens and effector mechanisms.
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Affiliation(s)
- Sonya Kumar Bharathkar
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, Illinois 61801 USA
| | - Michael J. Miller
- Carle R. Woese Institute of Genomic Biology
- Department of food science and Human Nutrition, University of Illinois Urbana-Champaign, Illinois 61801 USA
| | - Beth M. Stadtmueller
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, Illinois 61801 USA
- Department of Biomedical and Translational Sciences, Carle Illinois College of Medicine, University of Illinois Urbana-Champaign, Urbana, Illinois 61801 USA
- Carle R. Woese Institute of Genomic Biology
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6
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Schnizlein MK, Young VB. Capturing the environment of the Clostridioides difficile infection cycle. Nat Rev Gastroenterol Hepatol 2022; 19:508-520. [PMID: 35468953 DOI: 10.1038/s41575-022-00610-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 03/21/2022] [Indexed: 12/11/2022]
Abstract
Clostridioides difficile (formerly Clostridium difficile) infection is a substantial health and economic burden worldwide. Great strides have been made over the past several years in characterizing the physiology of C. difficile infection, particularly regarding how gut microorganisms and their host work together to provide colonization resistance. As mammalian hosts and their indigenous gut microbiota have co-evolved, they have formed a complex yet stable relationship that prevents invading microorganisms from establishing themselves. In this Review, we discuss the latest advances in our understanding of C. difficile physiology that have contributed to its success as a pathogen, including its versatile survival factors and ability to adapt to unique niches. Using discoveries regarding microorganism-host and microorganism-microorganism interactions that constitute colonization resistance, we place C. difficile within the fiercely competitive gut environment. A comprehensive understanding of these relationships is required to continue the development of precision medicine-based treatments for C. difficile infection.
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Affiliation(s)
- Matthew K Schnizlein
- Department of Microbiology and Immunology, University of Michigan, Ann Arbor, MI, USA
| | - Vincent B Young
- Department of Microbiology and Immunology, University of Michigan, Ann Arbor, MI, USA.
- Department of Internal Medicine/Division of Infectious Diseases, University of Michigan Medical School, Ann Arbor, MI, USA.
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7
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Heber S, Barthold L, Baier J, Papatheodorou P, Fois G, Frick M, Barth H, Fischer S. Inhibition of Clostridioides difficile Toxins TcdA and TcdB by Ambroxol. Front Pharmacol 2022; 12:809595. [PMID: 35058787 PMCID: PMC8764291 DOI: 10.3389/fphar.2021.809595] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2021] [Accepted: 12/10/2021] [Indexed: 02/04/2023] Open
Abstract
Clostridioides (C.) difficile produces the exotoxins TcdA and TcdB, which are the predominant virulence factors causing C. difficile associated disease (CDAD). TcdA and TcdB bind to target cells and are internalized via receptor-mediated endocytosis. Translocation of the toxins’ enzyme subunits from early endosomes into the cytosol depends on acidification of endosomal vesicles, which is a prerequisite for the formation of transmembrane channels. The enzyme subunits of the toxins translocate into the cytosol via these channels where they are released after auto-proteolytic cleavage. Once in the cytosol, both toxins target small GTPases of the Rho/Ras-family and inactivate them by mono-glucosylation. This in turn interferes with actin-dependent processes and ultimately leads to the breakdown of the intestinal epithelial barrier and inflammation. So far, therapeutic approaches to treat CDAD are insufficient, since conventional antibiotic therapy does not target the bacterial protein toxins, which are the causative agents for the clinical symptoms. Thus, directly targeting the exotoxins represents a promising approach for the treatment of CDAD. Lately, it was shown that ambroxol (Ax) prevents acidification of intracellular organelles. Therefore, we investigated the effect of Ax on the cytotoxic activities of TcdA and TcdB. Ax significantly reduced toxin-induced morphological changes as well as the glucosylation of Rac1 upon intoxication with TcdA and TcdB. Most surprisingly, Ax, independent of its effects on endosomal acidification, decreased the toxins’ intracellular enzyme activity, which is mediated by a catalytic glucosyltransferase domain. Considering its undoubted safety profile, Ax might be taken into account as therapeutic option in the context of CDAD.
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Affiliation(s)
- Sebastian Heber
- Institute of Pharmacology and Toxicology, Ulm University Medical Center, Ulm, Germany
| | - Lara Barthold
- Institute of Pharmacology and Toxicology, Ulm University Medical Center, Ulm, Germany
| | - Jan Baier
- Institute of Pharmacology and Toxicology, Ulm University Medical Center, Ulm, Germany
| | | | - Giorgio Fois
- Institute of General Physiology, Ulm University, Ulm, Germany
| | - Manfred Frick
- Institute of General Physiology, Ulm University, Ulm, Germany
| | - Holger Barth
- Institute of Pharmacology and Toxicology, Ulm University Medical Center, Ulm, Germany
| | - Stephan Fischer
- Institute of Pharmacology and Toxicology, Ulm University Medical Center, Ulm, Germany
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8
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Li Z, Lee K, Rajyaguru U, Jones CH, Janezic S, Rupnik M, Anderson AS, Liberator P. Ribotype Classification of Clostridioides difficile Isolates Is Not Predictive of the Amino Acid Sequence Diversity of the Toxin Virulence Factors TcdA and TcdB. Front Microbiol 2020; 11:1310. [PMID: 32636819 PMCID: PMC7318873 DOI: 10.3389/fmicb.2020.01310] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2019] [Accepted: 05/25/2020] [Indexed: 12/18/2022] Open
Abstract
Clostridioides (Clostridium) difficile is the most commonly recognized cause of infectious diarrhea in healthcare settings. Currently there is no vaccine to prevent initial or recurrent C. difficile infection (CDI). Two large clostridial toxins, TcdA and TcdB, are the primary virulence factors for CDI. Immunological approaches to prevent CDI include antibody-mediated neutralization of the cytotoxicity of these toxins. An understanding of the sequence diversity of the two toxins expressed by disease causing isolates is critical for the interpretation of the immune response to the toxins. In this study, we determined the whole genome sequence (WGS) of 478 C. difficile isolates collected in 12 countries between 2004 and 2018 to probe toxin variant diversity. A total of 44 unique TcdA variants and 37 unique TcdB variants were identified. The amino acid sequence conservation among the TcdA variants (≥98%) is considerably greater than among the TcdB variants (as low as 86.1%), suggesting that different selection pressures may have contributed to the evolution of the two toxins. Phylogenomic analysis of the WGS data demonstrate that isolates grouped together based on ribotype or MLST code for multiple different toxin variants. These findings illustrate the importance of determining not only the ribotype but also the toxin sequence when evaluating strain coverage using vaccine strategies that target these virulence factors. We recommend that toxin variant type and sequence type (ST), be used together with ribotype data to provide a more comprehensive strain classification scheme for C. difficile surveillance during vaccine development objectives.
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Affiliation(s)
- Zhenghui Li
- Vaccine Research and Development, Pfizer Inc., Pearl River, NY, United States
| | - Kwok Lee
- Vaccine Research and Development, Pfizer Inc., Pearl River, NY, United States
| | - Urvi Rajyaguru
- Vaccine Research and Development, Pfizer Inc., Pearl River, NY, United States
| | - C Hal Jones
- Vaccine Research and Development, Pfizer Inc., Pearl River, NY, United States
| | - Sandra Janezic
- National Laboratory for Health, Environment and Food, Maribor, Slovenia.,Faculty of Medicine, University of Maribor, Maribor, Slovenia
| | - Maja Rupnik
- National Laboratory for Health, Environment and Food, Maribor, Slovenia.,Faculty of Medicine, University of Maribor, Maribor, Slovenia
| | | | - Paul Liberator
- Vaccine Research and Development, Pfizer Inc., Pearl River, NY, United States
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9
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Pizarro-Guajardo M, Chamorro-Veloso N, Vidal RM, Paredes-Sabja D. New insights for vaccine development against Clostridium difficile infections. Anaerobe 2019; 58:73-79. [DOI: 10.1016/j.anaerobe.2019.04.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2018] [Revised: 04/17/2019] [Accepted: 04/25/2019] [Indexed: 02/08/2023]
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10
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Mileto S, Das A, Lyras D. Enterotoxic Clostridia: Clostridioides difficile Infections. Microbiol Spectr 2019; 7:10.1128/microbiolspec.gpp3-0015-2018. [PMID: 31124432 PMCID: PMC11026080 DOI: 10.1128/microbiolspec.gpp3-0015-2018] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2018] [Indexed: 12/17/2022] Open
Abstract
Clostridioides difficile is a Gram-positive, anaerobic, spore forming pathogen of both humans and animals and is the most common identifiable infectious agent of nosocomial antibiotic-associated diarrhea. Infection can occur following the ingestion and germination of spores, often concurrently with a disruption to the gastrointestinal microbiota, with the resulting disease presenting as a spectrum, ranging from mild and self-limiting diarrhea to severe diarrhea that may progress to life-threating syndromes that include toxic megacolon and pseudomembranous colitis. Disease is induced through the activity of the C. difficile toxins TcdA and TcdB, both of which disrupt the Rho family of GTPases in host cells, causing cell rounding and death and leading to fluid loss and diarrhea. These toxins, despite their functional and structural similarity, do not contribute to disease equally. C. difficile infection (CDI) is made more complex by a high level of strain diversity and the emergence of epidemic strains, including ribotype 027-strains which induce more severe disease in patients. With the changing epidemiology of CDI, our understanding of C. difficile disease, diagnosis, and pathogenesis continues to evolve. This article provides an overview of the current diagnostic tests available for CDI, strain typing, the major toxins C. difficile produces and their mode of action, the host immune response to each toxin and during infection, animal models of disease, and the current treatment and prevention strategies for CDI.
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Affiliation(s)
- S Mileto
- Infection and Immunity Program, Monash Biomedicine Discovery Institute and Department of Microbiology, Monash University, Clayton, Victoria, Australia, 3800
| | - A Das
- Infection and Immunity Program, Monash Biomedicine Discovery Institute and Department of Microbiology, Monash University, Clayton, Victoria, Australia, 3800
| | - D Lyras
- Infection and Immunity Program, Monash Biomedicine Discovery Institute and Department of Microbiology, Monash University, Clayton, Victoria, Australia, 3800
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11
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Beer LA, Tatge H, Reich N, Tenspolde M, Olling A, Goy S, Rottner K, Alekov AK, Gerhard R. Early cell death induced by Clostridium difficile TcdB: Uptake and Rac1-glucosylation kinetics are decisive for cell fate. Cell Microbiol 2018; 20:e12865. [PMID: 29904993 DOI: 10.1111/cmi.12865] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2018] [Revised: 05/23/2018] [Accepted: 05/26/2018] [Indexed: 12/29/2022]
Abstract
Toxin A and Toxin B (TcdA/TcdB) are large glucosyltransferases produced by Clostridium difficile. TcdB but not TcdA induces reactive oxygen species-mediated early cell death (ECD) when applied at high concentrations. We found that nonglucosylated Rac1 is essential for induction of ECD since inhibition of Rac1 impedes this effect. ECD only occurs when TcdB is rapidly endocytosed. This was shown by generation of chimeras using the trunk of TcdB from a hypervirulent strain. TcdB from hypervirulent strain has been described to translocate from endosomes at higher pH values and thus, meaning faster than reference type TcdB. Accordingly, intracellular delivery of the glucosyltransferase domain of reference TcdB by the trunk of TcdB from hypervirulent strain increased ECD. Furthermore, proton transporters such as sodium/proton exchanger (NHE) or the ClC-5 anion/proton exchanger, both of which contribute to endosomal acidification, also affected cytotoxic potency of TcdB: Specific inhibition of NHE reduced cytotoxicity, whereas transfection of cells with the endosomal anion/proton exchanger ClC-5 increased cytotoxicity of TcdB. Our data suggest that both the uptake rate of TcdB into the cytosol and the status of nonglucosylated Rac1 are key determinants that are decisive for whether ECD or delayed apoptosis is triggered.
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Affiliation(s)
| | - Helma Tatge
- Institute of Toxicology, Hannover Medical School, Hannover, Germany
| | - Nicole Reich
- Institute of Toxicology, Hannover Medical School, Hannover, Germany
| | - Michel Tenspolde
- Institute of Toxicology, Hannover Medical School, Hannover, Germany
| | - Alexandra Olling
- Institute of Toxicology, Hannover Medical School, Hannover, Germany
| | - Sebastian Goy
- Institute of Toxicology, Hannover Medical School, Hannover, Germany
| | - Klemens Rottner
- Division of Molecular Cell Biology, Zoological Institute, Braunschweig, Germany.,Molecular Cell Biology Group, Helmholtz Centre for Infection Research, Braunschweig, Germany
| | | | - Ralf Gerhard
- Institute of Toxicology, Hannover Medical School, Hannover, Germany
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12
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Cellular Uptake and Mode-of-Action of Clostridium difficile Toxins. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2018; 1050:77-96. [DOI: 10.1007/978-3-319-72799-8_6] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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13
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Chandrasekaran R, Lacy DB. The role of toxins in Clostridium difficile infection. FEMS Microbiol Rev 2017; 41:723-750. [PMID: 29048477 PMCID: PMC5812492 DOI: 10.1093/femsre/fux048] [Citation(s) in RCA: 210] [Impact Index Per Article: 30.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2017] [Accepted: 10/10/2017] [Indexed: 02/06/2023] Open
Abstract
Clostridium difficile is a bacterial pathogen that is the leading cause of nosocomial antibiotic-associated diarrhea and pseudomembranous colitis worldwide. The incidence, severity, mortality and healthcare costs associated with C. difficile infection (CDI) are rising, making C. difficile a major threat to public health. Traditional treatments for CDI involve use of antibiotics such as metronidazole and vancomycin, but disease recurrence occurs in about 30% of patients, highlighting the need for new therapies. The pathogenesis of C. difficile is primarily mediated by the actions of two large clostridial glucosylating toxins, toxin A (TcdA) and toxin B (TcdB). Some strains produce a third toxin, the binary toxin C. difficile transferase, which can also contribute to C. difficile virulence and disease. These toxins act on the colonic epithelium and immune cells and induce a complex cascade of cellular events that result in fluid secretion, inflammation and tissue damage, which are the hallmark features of the disease. In this review, we summarize our current understanding of the structure and mechanism of action of the C. difficile toxins and their role in disease.
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Affiliation(s)
- Ramyavardhanee Chandrasekaran
- Department of Pathology, Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
| | - D. Borden Lacy
- Department of Pathology, Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
- The Veterans Affairs Tennessee Valley Healthcare System, Nashville, TN 37232, USA
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Gupta P, Zhang Z, Sugiman-Marangos SN, Tam J, Raman S, Julien JP, Kroh HK, Lacy DB, Murgolo N, Bekkari K, Therien AG, Hernandez LD, Melnyk RA. Functional defects in Clostridium difficile TcdB toxin uptake identify CSPG4 receptor-binding determinants. J Biol Chem 2017; 292:17290-17301. [PMID: 28842504 DOI: 10.1074/jbc.m117.806687] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2017] [Revised: 08/11/2017] [Indexed: 12/11/2022] Open
Abstract
Clostridium difficile is a major nosocomial pathogen that produces two exotoxins, TcdA and TcdB, with TcdB thought to be the primary determinant in human disease. TcdA and TcdB are large, multidomain proteins, each harboring a cytotoxic glucosyltransferase domain that is delivered into the cytosol from endosomes via a translocation domain after receptor-mediated endocytosis of toxins from the cell surface. Although there are currently no known host cell receptors for TcdA, three cell-surface receptors for TcdB have been identified: CSPG4, NECTIN3, and FZD1/2/7. The sites on TcdB that mediate binding to each receptor are not defined. Furthermore, it is not known whether the combined repetitive oligopeptide (CROP) domain is involved in or required for receptor binding. Here, in a screen designed to identify sites in TcdB that are essential for target cell intoxication, we identified a region at the junction of the translocation and the CROP domains that is implicated in CSPG4 binding. Using a series of C-terminal truncations, we show that the CSPG4-binding site on TcdB extends into the CROP domain, requiring three short repeats for binding and for full toxicity on CSPG4-expressing cells. Consistent with the location of the CSPG4-binding site on TcdB, we show that the anti-TcdB antibody bezlotoxumab, which binds partially within the first three short repeats, prevents CSPG4 binding to TcdB. In addition to establishing the binding region for CSPG4, this work ascribes for the first time a role in TcdB CROPs in receptor binding and further clarifies the relative roles of host receptors in TcdB pathogenesis.
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Affiliation(s)
- Pulkit Gupta
- From Merck & Co., Inc., Kenilworth, New Jersey 07033
| | - Zhifen Zhang
- Molecular Medicine, The Hospital for Sick Children, Ontario M5G 0A4, Canada.,the Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada, and
| | | | - John Tam
- Molecular Medicine, The Hospital for Sick Children, Ontario M5G 0A4, Canada
| | - Swetha Raman
- Molecular Medicine, The Hospital for Sick Children, Ontario M5G 0A4, Canada
| | - Jean-Phillipe Julien
- Molecular Medicine, The Hospital for Sick Children, Ontario M5G 0A4, Canada.,the Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada, and
| | - Heather K Kroh
- the Departments of Pathology, Microbiology, and Immunology, Vanderbilt University School of Medicine, Nashville, Tennessee 37212
| | - D Borden Lacy
- the Departments of Pathology, Microbiology, and Immunology, Vanderbilt University School of Medicine, Nashville, Tennessee 37212
| | | | | | | | | | - Roman A Melnyk
- Molecular Medicine, The Hospital for Sick Children, Ontario M5G 0A4, Canada, .,the Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada, and
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Amino Acid Differences in the 1753-to-1851 Region of TcdB Influence Variations in TcdB1 and TcdB2 Cell Entry. mSphere 2017; 2:mSphere00268-17. [PMID: 28776043 PMCID: PMC5541160 DOI: 10.1128/msphere.00268-17] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2017] [Accepted: 07/13/2017] [Indexed: 01/24/2023] Open
Abstract
Clostridium difficile TcdB2 enters cells with a higher efficiency than TcdB1 and exhibits an overall higher level of toxicity. However, the TcdB2-specific sequences that account for more efficient cell entry have not been reported. In this study, we examined the contribution of carboxy-terminal sequence differences to TcdB activity by comparing the binding, uptake, and endosomal localization of TcdB1 and TcdB2 or selected recombinant fragments of these proteins. Our findings suggest that sequence differences in the amino acid 1753 to 1851 region proximal to the combined repetitive oligopeptide domain (CROP) support enhanced uptake of TcdB2 and localization of toxin in acidified endosomes. In the absence of this region, the CROP domains of both forms of the toxin exhibited similar levels of cell interaction, while the addition of amino acids 1753 to 1851 greatly increased toxin binding by only TcdB2. Moreover, the amino acid 1753 to 2366 fragment of TcdB2, but not TcdB1, accumulated to detectable levels in acidified endosomes. Unexpectedly, we discovered an unusual relationship between endocytosis and the efficiency of cell binding for TcdB1 and TcdB2 wherein inhibition of endocytosis by a chemical inhibitor or incubation at a low temperature resulted in a dramatic reduction in cell binding. These findings provide information on sequence variations that may contribute to differences in TcdB1 and TcdB2 toxicity and reveal a heretofore unknown connection between endocytosis and cell binding for this toxin. IMPORTANCE TcdB is a major virulence factor produced by Clostridium difficile, a leading cause of antibiotic-associated diarrhea. Hypervirulent strains of C. difficile encode a variant of TcdB (TcdB2) that is more toxic than toxin derived from historical strains (TcdB1). Though TcdB1 and TcdB2 exhibit 92% overall identity, a 99-amino-acid region previously associated with cell entry and spanning amino acids 1753 to 1851 has only 77% sequence identity. Results from the present study indicate that the substantial sequence variation in this region could contribute to the differences in cell entry between TcdB1 and TcdB2 and possibly explain TcdB2's heightened toxicity. Finally, during the course of these studies, an unusual aspect of TcdB cell entry was discovered wherein cell binding appeared to depend on endocytosis. These findings provide insight into TcdB's variant forms and their mechanisms of cell entry.
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Abstract
Clostridium difficile is the cause of antibiotics-associated diarrhea and pseudomembranous colitis. The pathogen produces three protein toxins: C. difficile toxins A (TcdA) and B (TcdB), and C. difficile transferase toxin (CDT). The single-chain toxins TcdA and TcdB are the main virulence factors. They bind to cell membrane receptors and are internalized. The N-terminal glucosyltransferase and autoprotease domains of the toxins translocate from low-pH endosomes into the cytosol. After activation by inositol hexakisphosphate (InsP6), the autoprotease cleaves and releases the glucosyltransferase domain into the cytosol, where GTP-binding proteins of the Rho/Ras family are mono-O-glucosylated and, thereby, inactivated. Inactivation of Rho proteins disturbs the organization of the cytoskeleton and affects multiple Rho-dependent cellular processes, including loss of epithelial barrier functions, induction of apoptosis, and inflammation. CDT, the third C. difficile toxin, is a binary actin-ADP-ribosylating toxin that causes depolymerization of actin, thereby inducing formation of the microtubule-based protrusions. Recent progress in understanding of the toxins' actions include insights into the toxin structures, their interaction with host cells, and functional consequences of their actions.
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Affiliation(s)
- Klaus Aktories
- Institute of Experimental and Clinical Pharmacology and Toxicology, University of Freiburg, 79104 Freiburg, Germany; , ,
| | - Carsten Schwan
- Institute of Experimental and Clinical Pharmacology and Toxicology, University of Freiburg, 79104 Freiburg, Germany; , ,
| | - Thomas Jank
- Institute of Experimental and Clinical Pharmacology and Toxicology, University of Freiburg, 79104 Freiburg, Germany; , ,
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Orrell KE, Zhang Z, Sugiman-Marangos SN, Melnyk RA. Clostridium difficile toxins A and B: Receptors, pores, and translocation into cells. Crit Rev Biochem Mol Biol 2017; 52:461-473. [DOI: 10.1080/10409238.2017.1325831] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Kathleen E. Orrell
- Molecular Medicine Program, The Hospital for Sick Children Research Institute, Toronto, ON, Canada
- Department of Biochemistry, University of Toronto, Toronto, ON, Canada
| | - Zhifen Zhang
- Molecular Medicine Program, The Hospital for Sick Children Research Institute, Toronto, ON, Canada
- Department of Biochemistry, University of Toronto, Toronto, ON, Canada
| | | | - Roman A. Melnyk
- Molecular Medicine Program, The Hospital for Sick Children Research Institute, Toronto, ON, Canada
- Department of Biochemistry, University of Toronto, Toronto, ON, Canada
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Ruhe F, Olling A, Abromeit R, Rataj D, Grieschat M, Zeug A, Gerhard R, Alekov A. Overexpression of the Endosomal Anion/Proton Exchanger ClC-5 Increases Cell Susceptibility toward Clostridium difficile Toxins TcdA and TcdB. Front Cell Infect Microbiol 2017; 7:67. [PMID: 28348980 PMCID: PMC5346576 DOI: 10.3389/fcimb.2017.00067] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2016] [Accepted: 02/21/2017] [Indexed: 12/30/2022] Open
Abstract
Virulent C. difficile toxins TcdA and TcdB invade host intestinal epithelia by endocytosis and use the acidic environment of intracellular vesicles for further processing and activation. We investigated the role of ClC-5, a chloride/proton exchanger expressed in the endosomes of gastrointestinal epithelial cells, in the activation and processing of C. difficile toxins. Enhanced intoxication by TcdA and TcdB was observed in cells expressing ClC-5 but not ClC-4, another chloride/proton exchanger with similar function but different localization. In accordance with the established physiological function of ClC-5, its expression lowered the endosomal pH in HEK293T cells by approximately 0.6 units and enhanced approximately 5-fold the internalization of TcdA. In colon HT29 cells, 34% of internalized TcdA localized to ClC-5-containing vesicles defined by colocalization with Rab5, Rab4a, and Rab7 as early and early-to-late of endosomes but not as Rab11-containing recycling endosomes. Impairing the cellular uptake of TcdA by deleting the toxin CROPs domain did not abolish the effects of ClC-5. In addition, the transport-incompetent mutant ClC-5 E268Q similarly enhanced both endosomal acidification and intoxication by TcdA but facilitated the internalization of the toxin to a lower extent. These data suggest that ClC-5 enhances the cytotoxic action of C. difficile toxins by accelerating the acidification and maturation of vesicles of the early and early-to-late endosomal system. The dispensable role of electrogenic ion transport suggests that the voltage-dependent nonlinear capacitances of mammalian CLC transporters serve important physiological functions. Our data shed light on the intersection between the endocytotic cascade of host epithelial cells and the internalization pathway of the large virulence C. difficile toxins. Identifying ClC-5 as a potential specific host ion transporter hijacked by toxins produced by pathogenic bacteria widens the horizon of possibilities for novel therapies of life-threatening gastrointestinal infections.
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Affiliation(s)
- Frederike Ruhe
- Institute for Neurophysiology, Hannover Medical SchoolHannover, Germany
| | - Alexandra Olling
- Institute for Toxicology, Hannover Medical SchoolHannover, Germany
| | - Rasmus Abromeit
- Institute for Neurophysiology, Hannover Medical SchoolHannover, Germany
| | - Dennis Rataj
- Institute for Toxicology, Hannover Medical SchoolHannover, Germany
| | | | - Andre Zeug
- Institute for Neurophysiology, Hannover Medical SchoolHannover, Germany
| | - Ralf Gerhard
- Institute for Toxicology, Hannover Medical SchoolHannover, Germany
| | - Alexi Alekov
- Institute for Neurophysiology, Hannover Medical SchoolHannover, Germany
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Chandrasekaran R, Kenworthy AK, Lacy DB. Clostridium difficile Toxin A Undergoes Clathrin-Independent, PACSIN2-Dependent Endocytosis. PLoS Pathog 2016; 12:e1006070. [PMID: 27942025 PMCID: PMC5152916 DOI: 10.1371/journal.ppat.1006070] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2016] [Accepted: 11/17/2016] [Indexed: 12/18/2022] Open
Abstract
Clostridium difficile infection affects a significant number of hospitalized patients in the United States. Two homologous exotoxins, TcdA and TcdB, are the major virulence factors in C. difficile pathogenesis. The toxins are glucosyltransferases that inactivate Rho family-GTPases to disrupt host cellular function and cause fluid secretion, inflammation, and cell death. Toxicity depends on receptor binding and subsequent endocytosis. TcdB has been shown to enter cells by clathrin-dependent endocytosis, but the mechanism of TcdA uptake is still unclear. Here, we utilize a combination of RNAi-based knockdown, pharmacological inhibition, and cell imaging approaches to investigate the endocytic mechanism(s) that contribute to TcdA uptake and subsequent cytopathic and cytotoxic effects. We show that TcdA uptake and cellular intoxication is dynamin-dependent but does not involve clathrin- or caveolae-mediated endocytosis. Confocal microscopy using fluorescently labeled TcdA shows significant colocalization of the toxin with PACSIN2-positive structures in cells during entry. Disruption of PACSIN2 function by RNAi-based knockdown approaches inhibits TcdA uptake and toxin-induced downstream effects in cells indicating that TcdA entry is PACSIN2-dependent. We conclude that TcdA and TcdB utilize distinct endocytic mechanisms to intoxicate host cells. Clostridium difficile is a bacterial pathogen that causes nearly half a million infections each year in the United States. It infects the human colon and causes diarrhea, colitis and, in some cases, death. C. difficile infection is mediated by the action of two large homologous toxins, TcdA and TcdB. Disruption of host cell function by these toxins requires entry into cells. There are multiple ways for pathogens and virulence factors such as viruses and toxins to enter host cells. The entry mechanism is often directed by a cell surface receptor and can impact the trafficking and virulence properties of the pathogenic factor. Investigating the internalization strategy can provide critical insight into the mechanism of action for specific pathogens and virulence factors. In our current study, we sought to determine the strategy utilized by TcdA to enter host cells. We show that TcdA uptake occurs by a clathrin- and caveolae-independent endocytic mechanism that is mediated by PACSIN2 and dynamin. We also show that TcdA and TcdB can utilize different routes of entry, which may have implications regarding their cytotoxic mechanisms. In summary, our results provide new insights into the mechanism of cellular intoxication by TcdA and the role of PACSIN2 in endocytosis.
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Affiliation(s)
- Ramyavardhanee Chandrasekaran
- Department of Pathology, Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, TN, United States of America
| | - Anne K. Kenworthy
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN, United States of America
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN, United States of America
- Epithelial Biology Program, Vanderbilt University School of Medicine, Nashville, TN, United States of America
| | - D. Borden Lacy
- Department of Pathology, Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, TN, United States of America
- Epithelial Biology Program, Vanderbilt University School of Medicine, Nashville, TN, United States of America
- The Veterans Affairs Tennessee Valley Healthcare System, Nashville, TN, United States of America
- * E-mail:
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Lambert GS, Baldwin MR. Evidence for dual receptor-binding sites in Clostridium difficile toxin A. FEBS Lett 2016; 590:4550-4563. [PMID: 27861794 DOI: 10.1002/1873-3468.12487] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2016] [Revised: 10/10/2016] [Accepted: 10/24/2016] [Indexed: 12/24/2022]
Abstract
TcdA (308 kDa) and TcdB (270 kDa) disrupt the integrity of the intestinal epithelial barrier and provide an environment favorable for Clostridium difficile colonization. Recent evidence suggests that entry of TcdA into cells is mediated by at least two domains. Here, we report the characterization of a second receptor-binding domain (RBD2) for TcdA. While both the isolated combined repetitive oligopeptides (CROPs) and RBD2 fragments are rapidly internalized into cells under physiologic conditions, only the CROPs domain appreciably accumulates at the cell surface. Once internalized, CROPs and RBD2 are trafficked to late endosomal compartments. An internal deletion of RBD2 from TcdA holotoxin ablated toxicity in HT29 cells. These data are consistent with the recently proposed dual receptor model of cellular entry.
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Affiliation(s)
- Gregory S Lambert
- Department of Molecular Microbiology and Immunology, University of Missouri School of Medicine, Columbia, MO, USA
| | - Michael R Baldwin
- Department of Molecular Microbiology and Immunology, University of Missouri School of Medicine, Columbia, MO, USA
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21
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Janoir C. Virulence factors of Clostridium difficile and their role during infection. Anaerobe 2016; 37:13-24. [DOI: 10.1016/j.anaerobe.2015.10.009] [Citation(s) in RCA: 77] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2015] [Revised: 10/16/2015] [Accepted: 10/21/2015] [Indexed: 02/08/2023]
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Frädrich C, Beer LA, Gerhard R. Reactive Oxygen Species as Additional Determinants for Cytotoxicity of Clostridium difficile Toxins A and B. Toxins (Basel) 2016; 8:toxins8010025. [PMID: 26797634 PMCID: PMC4728547 DOI: 10.3390/toxins8010025] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2015] [Revised: 01/07/2016] [Accepted: 01/13/2016] [Indexed: 12/18/2022] Open
Abstract
Clostridium difficile infections can induce mild to severe diarrhoea and the often associated characteristic pseudomembranous colitis. Two protein toxins, the large glucosyltransferases TcdA and TcdB, are the main pathogenicity factors that can induce all clinical symptoms in animal models. The classical molecular mode of action of these homologous toxins is the inhibition of Rho GTPases by mono-glucosylation. Rho-inhibition leads to breakdown of the actin cytoskeleton, induces stress-activated and pro-inflammatory signaling and eventually results in apoptosis of the affected cells. An increasing number of reports, however, have documented further qualities of TcdA and TcdB, including the production of reactive oxygen species (ROS) by target cells. This review summarizes observations dealing with the production of ROS induced by TcdA and TcdB, dissects pathways that contribute to this phenomenon and speculates about ROS in mediating pathogenesis. In conclusion, ROS have to be considered as a discrete, glucosyltransferase-independent quality of at least TcdB, triggered by different mechanisms.
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Affiliation(s)
- Claudia Frädrich
- Postgraduate Course for Toxicology and Environmental Toxicology, Institute for Legal Medicine, University of Leipzig, Johannisallee 28, Leipzig 04103, Germany.
| | - Lara-Antonia Beer
- Institute of Toxicology, Hannover Medical School, Carl-Neuberg-Str. 1, Hannover 30625, Germany.
| | - Ralf Gerhard
- Postgraduate Course for Toxicology and Environmental Toxicology, Institute for Legal Medicine, University of Leipzig, Johannisallee 28, Leipzig 04103, Germany.
- Institute of Toxicology, Hannover Medical School, Carl-Neuberg-Str. 1, Hannover 30625, Germany.
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Manse JS, Baldwin MR. Binding and entry of Clostridium difficile toxin B is mediated by multiple domains. FEBS Lett 2015; 589:3945-51. [PMID: 26602083 DOI: 10.1016/j.febslet.2015.11.017] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2015] [Revised: 10/24/2015] [Accepted: 11/09/2015] [Indexed: 11/26/2022]
Abstract
Clostridium difficile is responsible for a number of serious gastrointestinal diseases caused primarily by two exotoxins, TcdA and TcdB. These toxins enter host cells by binding unique receptors, at least partially via their combined repetitive oligopeptides (CROPs) domains. Our study investigated structural determinants necessary for binding and entry of TcdB. Deletion analyses identified TcdB residues 1372-1493 as essential for cytotoxicity in three cell lines. Consistent with this observation, overlapping TcdB fragments (residues 1372-1848, 1372-1493 and 1493-1848) were able to independently bind cells. Our data provide new evidence supporting a more complex model of clostridial glucosylating toxin uptake than previously suggested.
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Affiliation(s)
- Jared S Manse
- Department of Molecular Microbiology and Immunology, University of Missouri School of Medicine, Columbia, MO, USA
| | - Michael R Baldwin
- Department of Molecular Microbiology and Immunology, University of Missouri School of Medicine, Columbia, MO, USA.
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Biochemical and Immunological Characterization of Truncated Fragments of the Receptor-Binding Domains of C. difficile Toxin A. PLoS One 2015; 10:e0135045. [PMID: 26271033 PMCID: PMC4536038 DOI: 10.1371/journal.pone.0135045] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2014] [Accepted: 07/17/2015] [Indexed: 12/18/2022] Open
Abstract
Clostridium difficile is an emerging pathogen responsible for opportunistic infections in hospitals worldwide and is the main cause of antibiotic-associated pseudo-membranous colitis and diarrhea in humans. Clostridial toxins A and B (TcdA and TcdB) specifically bind to unknown glycoprotein(s) on the surface of epithelial cells in the host intestine, disrupting the intestinal barrier and ultimately leading to acute inflammation and diarrhea. The C-terminal receptor-binding domain (RBD) of TcdA, which is responsible for the initial binding of the toxin to host glycoproteins, has been predicted to contain 7 potential oligosaccharide-binding sites. To study the specific roles and functions of these 7 putative lectin-like binding regions, a consensus sequence of TcdA RBD derived from different C. difficile strains deposited in the NCBI protein database and three truncated fragments corresponding to the N-terminal (residues 1–411), middle (residues 296–701), and C-terminal portions (residues 524–911) of the RBD (F1, F2 and F3, respectively) were designed and expressed in Escherichia coli. In this study, the recombinant RBD (rRBD) and its truncated fragments were purified, characterized biologically and found to have the following similar properties: (a) are capable of binding to the cell surface of both Vero and Caco-2 cells; (b) possess Toll-like receptor agonist-like adjuvant activities that can activate dendritic cell maturation and increase the secretion of pro-inflammatory cytokines; and (c) function as potent adjuvants in the intramuscular immunization route to enhance immune responses against weak immunogens. Although F1, F2 and F3 have similar repetitive amino acid sequences and putative oligosaccharide-binding domains, they do not possess the same biological and immunological properties: (i) TcdA rRBD and its fragments bind to the cell surface, but only TcdA rRBD and F3 internalize into Vero cells within 15 min; (ii) the fragments exhibit various levels of hemagglutinin (HA) activity, with the exception of the F1 fragment, which demonstrates no HA activity; and (iii) in the presence of alum, all fragments elicit various levels of anti-toxin A-neutralizing antibody responses, but those neutralizing antibodies elicited by F2 did not protect mice against a TcdA challenge. Because TcdA rRBD, F1 and F3 formulated with alum can elicit immune protective responses against the cytotoxicity of TcdA, they represent potential components of future candidate vaccines against C. difficile-associated diseases.
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Tam J, Beilhartz GL, Auger A, Gupta P, Therien AG, Melnyk RA. Small molecule inhibitors of Clostridium difficile toxin B-induced cellular damage. ACTA ACUST UNITED AC 2015; 22:175-85. [PMID: 25619932 DOI: 10.1016/j.chembiol.2014.12.010] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2014] [Revised: 11/25/2014] [Accepted: 12/06/2014] [Indexed: 02/04/2023]
Abstract
Clostridium difficile causes life-threatening diarrhea through the actions of its homologous toxins TcdA and TcdB on human colonocytes. Therapeutic agents that block toxin-induced damage are urgently needed to prevent the harmful consequences of toxin action that are not addressed with current antibiotic-based treatments. Here, we developed an imaging-based phenotypic screen to identify small molecules that protected human cells from TcdB-induced cell rounding. A series of structurally diverse compounds with antitoxin activity were identified and found to act through one of a small subset of mechanisms, including direct binding and sequestration of TcdB, inhibition of endosomal maturation, and noncompetitive inhibition of the toxin glucosyltransferase activity. Distinct classes of inhibitors were used further to dissect the determinants of the toxin-mediated necrosis phenotype occurring at higher doses of toxin. These findings validate and inform novel targeting strategies for discovering small molecule agents to treat C. difficile infection.
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Affiliation(s)
- John Tam
- Molecular Structure & Function, The Hospital for Sick Children, 686 Bay Street, Toronto, ON M5G 0A4, Canada
| | - Greg L Beilhartz
- Molecular Structure & Function, The Hospital for Sick Children, 686 Bay Street, Toronto, ON M5G 0A4, Canada
| | - Anick Auger
- Molecular Structure & Function, The Hospital for Sick Children, 686 Bay Street, Toronto, ON M5G 0A4, Canada
| | - Pulkit Gupta
- Merck & Co. Inc., 2000 Galloping Hill Road, K15, Kenilworth, NJ 07033, USA
| | - Alex G Therien
- Merck & Co. Inc., 2000 Galloping Hill Road, K15, Kenilworth, NJ 07033, USA
| | - Roman A Melnyk
- Molecular Structure & Function, The Hospital for Sick Children, 686 Bay Street, Toronto, ON M5G 0A4, Canada; Department of Biochemistry, University of Toronto, Toronto, ON M5S 1A8, Canada.
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Yuan P, Zhang H, Cai C, Zhu S, Zhou Y, Yang X, He R, Li C, Guo S, Li S, Huang T, Perez-Cordon G, Feng H, Wei W. Chondroitin sulfate proteoglycan 4 functions as the cellular receptor for Clostridium difficile toxin B. Cell Res 2014; 25:157-68. [PMID: 25547119 PMCID: PMC4650570 DOI: 10.1038/cr.2014.169] [Citation(s) in RCA: 133] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2014] [Revised: 11/06/2014] [Accepted: 11/19/2014] [Indexed: 02/06/2023] Open
Abstract
As a gram-positive, spore-forming anaerobic bacillus, Clostridium difficile (C. difficile) is responsible for severe and fatal pseudomembranous colitis, and poses the most urgent antibiotic resistance threat worldwide. Epidemic C. difficile is the leading cause of antibiotic-associated diarrhoea globally, especially diarrhoea due to the emergence of hypervirulent strains associated with high mortality and morbidity. TcdB, one of the key virulence factors secreted by this bacterium, enters host cells through a poorly understood mechanism to elicit its pathogenic effect. Here we report the first identification of the TcdB cellular receptor, chondroitin sulfate proteoglycan 4 (CSPG4). CSPG4 was initially isolated from a whole-genome human shRNAmir library screening, and its role was confirmed by both TALEN- and CRISPR/Cas9-mediated gene knockout in human cells. CSPG4 is critical for TcdB binding to the cell surface, inducing cytoskeleton disruption and cell death. A direct interaction between the N-terminus of CSPG4 and the C-terminus of TcdB was confirmed, and the soluble peptide of the toxin-binding domain of CSPG4 could protect cells from the action of TcdB. Notably, the complete loss of CSPG4/NG2 decreased TcdB-triggered interleukin-8 induction in mice without significantly affecting animal mortality. Based on both the in vitro and in vivo studies, we propose a dual-receptor model for TcdB endocytosis. The discovery of the first TcdB receptor reveals a previously unsuspected role for CSPG4 and provides a new therapeutic target for the treatment of C. difficile infection.
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Affiliation(s)
- Pengfei Yuan
- Biodynamic Optical Imaging Center (BIOPIC), State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing 100871, China
| | - Hongmin Zhang
- Biodynamic Optical Imaging Center (BIOPIC), State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing 100871, China
| | - Changzu Cai
- Biodynamic Optical Imaging Center (BIOPIC), State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing 100871, China
| | - Shiyou Zhu
- Biodynamic Optical Imaging Center (BIOPIC), State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing 100871, China
| | - Yuexin Zhou
- Biodynamic Optical Imaging Center (BIOPIC), State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing 100871, China
| | - Xiaozhou Yang
- Biodynamic Optical Imaging Center (BIOPIC), State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing 100871, China
| | - Ruina He
- Biodynamic Optical Imaging Center (BIOPIC), State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing 100871, China
| | - Chan Li
- Biodynamic Optical Imaging Center (BIOPIC), State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing 100871, China
| | - Shengjie Guo
- Biodynamic Optical Imaging Center (BIOPIC), State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing 100871, China
| | - Shan Li
- School of Bioscience and Biotechnology, South China University of Technology, Guangzhou, Guangdong 510006, China
| | - Tuxiong Huang
- Department of Microbial Pathogenesis, University of Maryland Dental School, Baltimore, Maryland 21201, USA
| | - Gregorio Perez-Cordon
- Department of Microbial Pathogenesis, University of Maryland Dental School, Baltimore, Maryland 21201, USA
| | - Hanping Feng
- Department of Microbial Pathogenesis, University of Maryland Dental School, Baltimore, Maryland 21201, USA
| | - Wensheng Wei
- Biodynamic Optical Imaging Center (BIOPIC), State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing 100871, China
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27
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Genth H, Pauillac S, Schelle I, Bouvet P, Bouchier C, Varela-Chavez C, Just I, Popoff MR. Haemorrhagic toxin and lethal toxin from Clostridium sordellii strain vpi9048: molecular characterization and comparative analysis of substrate specificity of the large clostridial glucosylating toxins. Cell Microbiol 2014; 16:1706-21. [PMID: 24905543 DOI: 10.1111/cmi.12321] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2014] [Revised: 05/12/2014] [Accepted: 05/29/2014] [Indexed: 12/16/2022]
Abstract
Large clostridial glucosylating toxins (LCGTs) are produced by toxigenic strains of Clostridium difficile, Clostridium perfringens, Clostridium novyi and Clostridium sordellii. While most C. sordellii strains solely produce lethal toxin (TcsL), C. sordellii strain VPI9048 co-produces both hemorrhagic toxin (TcsH) and TcsL. Here, the sequences of TcsH-9048 and TcsL-9048 are provided, showing that both toxins retain conserved LCGT features and that TcsL and TcsH are highly related to Toxin A (TcdA) and Toxin B (TcdB) from C. difficile strain VPI10463. The substrate profile of the toxins was investigated with recombinant LCGT transferase domains (rN) and a wide panel of small GTPases. rN-TcsH-9048 and rN-TcdA-10463 glucosylated preferably Rho-GTPases but also Ras-GTPases to some extent. In this respect, rN-TcsH-9048 and rN-TcdA-10463 differ from the respective full-length TcsH-9048 and TcdA-10463, which exclusively glucosylate Rho-GTPases. rN-TcsL-9048 and full length TcsL-9048 glucosylate both Rho- and Ras-GTPases, whereas rN-TcdB-10463 and full length TcdB-10463 exclusively glucosylate Rho-GTPases. Vero cells treated with full length TcsH-9048 or TcdA-10463 also showed glucosylation of Ras, albeit to a lower extent than of Rho-GTPases. Thus, in vitro analysis of substrate spectra using recombinant transferase domains corresponding to the auto-proteolytically cleaved domains, predicts more precisely the in vivo substrates than the full length toxins. Except for TcdB-1470, all LCGTs evoked increased expression of the small GTPase RhoB, which exhibited cytoprotective activity in cells treated with TcsL isoforms, but pro-apoptotic activity in cells treated with TcdA, TcdB, and TcsH. All LCGTs induced a rapid dephosphorylation of pY118-paxillin and of pS144/141-PAK1/2 prior to actin filament depolymerization indicating that disassembly of focal adhesions is an early event leading to the disorganization of the actin cytoskeleton.
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Affiliation(s)
- Harald Genth
- Institute of Toxicology, Medical School Hannover, Hannover, Germany
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28
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Olling A, Hüls C, Goy S, Müller M, Krooss S, Rudolf I, Tatge H, Gerhard R. The combined repetitive oligopeptides of clostridium difficile toxin A counteract premature cleavage of the glucosyl-transferase domain by stabilizing protein conformation. Toxins (Basel) 2014; 6:2162-76. [PMID: 25054784 PMCID: PMC4113749 DOI: 10.3390/toxins6072162] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2014] [Revised: 07/03/2014] [Accepted: 07/04/2014] [Indexed: 11/25/2022] Open
Abstract
Toxin A (TcdA) and B (TcdB) from Clostridium difficile enter host cells by receptor-mediated endocytosis. A prerequisite for proper toxin action is the intracellular release of the glucosyltransferase domain by an inherent cysteine protease, which is allosterically activated by inositol hexaphosphate (IP6). We found that in in vitro assays, the C-terminally-truncated TcdA1–1065 was more efficient at IP6-induced cleavage compared with full-length TcdA. We hypothesized that the C-terminally-located combined repetitive oligopeptides (CROPs) interact with the N-terminal part of the toxin, thereby preventing autoproteolysis. Glutathione-S-transferase (GST) pull-down assays and microscale thermophoresis confirmed binding between the CROPs and the glucosyltransferase (TcdA1–542) or intermediate (TcdA1102–1847) domain of TcdA, respectively. This interaction between the N- and C-terminus was not found for TcdB. Functional assays revealed that TcdB was more susceptible to inactivation by extracellular IP6-induced cleavage. In vitro autoprocessing and inactivation of TcdA, however, significantly increased, either by acidification of the surrounding milieu or following exchange of its CROP domain by the homologous CROP domain of TcdB. Thus, TcdA CROPs contribute to the stabilization and protection of toxin conformation in addition to function as the main receptor binding domain.
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Affiliation(s)
- Alexandra Olling
- Institute of Toxicology, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany.
| | - Corinna Hüls
- Institute of Toxicology, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany.
| | - Sebastian Goy
- Institute of Toxicology, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany.
| | - Mirco Müller
- Institute for Biophysical Chemistry, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany.
| | - Simon Krooss
- Institute of Toxicology, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany.
| | - Isa Rudolf
- Institute of Toxicology, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany.
| | - Helma Tatge
- Institute of Toxicology, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany.
| | - Ralf Gerhard
- Institute of Toxicology, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany.
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29
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Chen C, Doll NK, Casadei G, Bremner JB, Lewis K, Kelso MJ. Diarylacylhydrazones: Clostridium-selective antibacterials with activity against stationary-phase cells. Bioorg Med Chem Lett 2014; 24:595-600. [PMID: 24360560 PMCID: PMC3912389 DOI: 10.1016/j.bmcl.2013.12.015] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2013] [Revised: 11/26/2013] [Accepted: 12/02/2013] [Indexed: 12/30/2022]
Abstract
Current antibiotics for treating Clostridium difficile infections (CDI), that is, metronidazole, vancomycin and more recently fidaxomicin, are mostly effective but treatment failure and disease relapse remain as significant clinical problems. The shortcomings of these agents are attributed to their low selectivity for C. difficile over normal gut microflora and their ineffectiveness against C. difficile spores. This Letter reports that certain diarylacylhydrazones identified during a high-throughput screening/counter-screening campaign show selective activity against two Clostridium species (C. difficile and Clostridium perfringens) over common gut commensals. Representative examples are shown to possess activity similar to vancomycin against clinical C. difficile strains and to kill stationary-phase C. difficile cells, which are responsible for spore production. Structure-activity relationships with additional synthesised analogues suggested a protonophoric mechanism may play a role in the observed activity/selectivity and this was supported by the well-known protonophore carbonyl cyanide m-chlorophenyl hydrazone (CCCP) showing selective anti-Clostridium effects and activity similar to diarylacylhydrazones against stationary-phase C. difficile cells. Two diarylacylhydrazones were shown to be non-toxic towards human FaDu and Hep G2 cells indicating that further studies with the class are warranted towards new drugs for CDI.
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Affiliation(s)
- Chao Chen
- Antimicrobial Discovery Center, Department of Biology, Northeastern University, Boston, MA 02115, USA
| | - Naveen K. Doll
- Antimicrobial Discovery Center, Department of Biology, Northeastern University, Boston, MA 02115, USA
- School of Chemistry, University of Wollongong, NSW 2522, Australia
| | - Gabriele Casadei
- Antimicrobial Discovery Center, Department of Biology, Northeastern University, Boston, MA 02115, USA
| | - John B. Bremner
- School of Chemistry, University of Wollongong, NSW 2522, Australia
| | - Kim Lewis
- Antimicrobial Discovery Center, Department of Biology, Northeastern University, Boston, MA 02115, USA
| | - Michael J. Kelso
- School of Chemistry, University of Wollongong, NSW 2522, Australia
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