Studies on immunity to toxins of Clostridium botulinum. VI. Purification and detoxification of type D toxin and the immunological response to toxoid

Light Chain Diversity among the Botulinum Neurotoxins

Botulinum neurotoxins (BoNT) are produced by several species of clostridium. There are seven immunologically unique BoNT serotypes (A⁻G). The Centers for Disease Control classifies BoNTs as 'Category A' select agents and are the most lethal protein toxins for humans. Recently, BoNT-like proteins have also been identified in several non-clostridia. BoNTs are di-chain proteins comprised of an N-terminal zinc metalloprotease Light Chain (LC) and a C-terminal Heavy Chain (HC) which includes the translocation and receptor binding domains. The two chains are held together by a disulfide bond. The LC cleaves Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs). The cleavage of SNAREs inhibits the fusion of synaptic vesicles to the cell membrane and the subsequent release of acetylcholine, which results in flaccid paralysis. The LC controls the catalytic properties and the duration of BoNT action. This review discusses the mechanism for LC catalysis, LC translocation, and the basis for the duration of LC action. Understanding these properties of the LC may expand the applications of BoNT as human therapies.

Yesterday and Today: The Impact of Research Conducted at Camp Detrick on Botulinum Toxin

Introduction

This review summarizes the research conducted on botulinum toxin (BoTx) from 1943 to 1956 by a small group of Camp Detrick investigators and their staff. A systematic, cross-disciplinary approach was used to develop effective vaccines against this biological warfare threat agent. In response to the potential need for medical countermeasures against BoTx during World War II, the refinement of isolation and purification techniques for BoTx successfully led to the large-scale production of botulinum toxoid vaccines. In addition, the work at Camp Detrick provided the foundation for the subsequent use of BoTx as a tool for studying the trophic regulation of skeletal muscle within motor neuron terminals and, more recently, for elucidation of the intricate details of neurotransmitter release at the molecular level. Indirectly, Camp Detrick investigators also played a significant role in studies that culminated in the use of BoTx as a pharmaceutical product that has been approved by the U.S. Food and Drug Administration for treating movement disorders, autonomic dysfunctions, and other conditions.

Methods

Online literature searches were performed with Google, Google Scholar, PubMed, the bibliography from the Camp Detrick technical library, and at the Defense Technical Information Center. Reference lists in some of the primary research publications and reviews also provided source material. Search terms included botulinum, botulinus, and Camp Detrick. References related to the subsequent impacts of the Camp Detrick results were selected and cited from reviews and primary references in the more recent literature. Notes on toxin nomenclature and potential sources of error in this study are presented.

Results

The literature searches returned 27 citations of Camp Detrick authors, 24 of which were articles in peer-reviewed journals. The publications by these investigators included several disciplines such as biochemistry, immunology, pharmacology, physiology, and toxicology. A fundamental finding was the identification of critical nutritional components for improved growth of Clostridium botulinum and the increased production of BoTx serotype A. The purification processes that were developed at Camp Detrick allowed for the production of crystalline material to be scaled up for the manufacture of toxoid vaccine. Based on the research by Camp Detrick scientists, a toxoid supply of over 1 million units was available to vaccinate ~300,000 troops before the large-scale operations of D-Day.

Conclusions

BoTx research during the period 1943 to 1956 resulted in refinements in the techniques for isolating and purifying the crystalline BoTx type A. These results led to the development and manufacture of a toxoid vaccine that was available in a sufficient quantity to protect ~300,000 warfighters in a large-scale military operation. One of the most important long-term consequences derived from the knowledge gained by the efforts at Camp Detrick was the development in the 1980s of safe and effective therapeutic uses for BoTx type A, the most lethal biological substance known.

Studies on immunity to toxins of Clostridium botulinum. VII. Purification and detoxification of trypsin-activated type E toxin

Fiock, Mary A. (Fort Detrick, Frederick, Md.), Allen Yarinsky, and James T. Duff. Studies on immunity to toxins of Clostridium botulinum. VII. Purification and detoxification of trypsin-activated type E toxin. J. Bacteriol. 82:66-71. 1961.-A procedure was described for production, purification, and conversion to toxoid of the Clostridium botulinum type E trypsin-treated toxin. A medium containing 1.5% trypticase, 0.5% yeast extract, 0.075% cysteine hydrochloride, and 1.0% glucose consistently yielded activated culture toxicities of 300,000 mouse intraperitoneal ld(50)/ml. Purification of the toxin was accomplished by precipitation with ammonium sulfate, extraction with calcium chloride, and reprecipitation with ethanol in the cold. The resulting partially purified toxin had a specific activity of 45,000,000 ld(50)/mg nitrogen. Purified toxins were converted to toxoid by incubation with formalin and adsorbed on aluminum phosphate. Good immune responses were obtained to the toxoids in mice, guinea pigs, and rabbits.

Production of toxic antigens in dialyzed cultures of microorganisms

Data on the production of clostridial toxins in dialyzed cultures are summarized. Principal modifications of this cultivation technique suitable for both research and production are shown. If toxins are released from the cells by autolysis (neurotoxins of Clostridium tetani, C. botulinum; lethal factors of C. novyi and C. sordellii), a 10-fold increase of the antigen concentration in filtrates of dialyzed cultures is found in comparison with normal cultures. If toxins are excreted already during growth (lethal factors of C. perfringens type A, C. septicum), the positive effect of the technique is less significant. A dialyzed culture ensures a well-balanced production of toxic filtrates that contain highly concentrated, relatively pure and strongly immunogenic antigens.

Preparation of Clostridium septicum antigen for hyperimmunization of horses using a dialyzed culture

The preparation of toxic cultures of Clostridium septicum is described, using an apparatus with a straight dialysis tubing, where the medium is filled both into the nutrition and cultivation space of the apparatus. Using the cultivation to nutrition volume rate 1:2, mean titre of lethal antigen in filtrates 3.86 limes mortis per mL and 300 dosis lethalis minima per Lm was obtained in comparison with the values of 2.22 and 150 respectively in flask filtrates. Native filtrates of dialyzed cultures were better antigens for hyperimmunization of horses than the culture filtrates from flasks.

Acid precipitation of Clostridium botulinum type C and D toxins from whole culture by addition of ribonucleic acid as a precipitation aid

The ratios of ribonucleic acid to protein contents of Clostridium botulinum type C, D, and E cultures were lower than those of type A, B, and F cultures. Addition of ribonucleic acid at 0.4 mg/ml to culture satisfactorily aided acid precipitation of type C and D toxins, but not that of type E toxin.

Clostridium botulinum type D toxin: purification, molecular structure, and some immunological properties

Clostridium botulinum type D progenitor toxin was purified. The addition of ribonucleic acid to the whole culture helped initial acid precipitation of the toxin. As with type B, both L (16S) and M toxins (12S) obtained from a hemagglutinin-positive strain, whereas M toxin only was produced by a hemagglutinin-negative strain. M toxin (molecular weight, 300,000) consisted of one molecule each of a toxic (molecular weight, 170,000) and a nontoxic component (molecular weight, 130,000); L toxin consisted of both components plus hemagglutinin. The specific toxicity of M toxin was 5 X 10(8) mean lethal doses per mg of N; that of L toxin was 2.4 X 10(8) mean lethal doses per mg of N. These toxins were fully or nearly fully active, but in un-nicked form. Trypsinization caused nicking in the toxic component, forming a molecule made up of two peptide chains with molecular weights of 110,000 and 60,000; there was little or no increase in toxicity. The toxic component of type D was not antigenically related to that of type C, whereas the nontoxic component was antigenically indistinguishable from that of type C. The toxicities of both L nad M toxins of the hemagglutinin-positive strain were increased twofold by trypsinization. Neither toxin contained the C2 toxic factor elaborated by C and D strain.

Toxoid of Clostridium botulinum type F: purification and immunogenicity studies

Toxin from Clostridium botulinum type F was recovered from dialysis cultures and partially purifed by: (i) ammonium sulfate and ethanol precipitation; (ii) O-(diethylaminoethyl)-cellulose chromatography; or (iii) diethylaminoethyl-cellulose chromatography followed by O-(carboxymethyl)-cellulose chromatography. Toxin purities as reflected by specific activity were 1.83 X 10(6), 9.8 X 10(6), and 2.0 X 10(7) mouse 50% lethal doses (LD50)/mg of N, respectively, for toxins purified by the three methods. The toxins were converted to toxoids by incubation at 35 C in the presence of 0.3 to 0.45% formalin for 21 to 35 days. Toxoids were immunogenic in guinea pigs, as demonstrated by serum antitoxin response and the immunized animals' resistance to challenge by type F botulinal toxin. The immune response to type F toxoids was lower when toxoids of serotypes A, B, C, D, and E were combined with the type F toxoid than when the type F toxoid only was administered. The toxoid prepared from the most highly purified toxin (method [iii]) conferred the highest immunity in guinea pigs at a given dose level. A relation between serum antitoxin level and resistance to challenge was observed. At least 50% of the groups of guinea pigs with 0.015 antitoxin units or more per ml survived challenge by 10(5) mouse LD50 of type F botulinal toxin. A dose of 3.75 mug of N of the most highly purified type F toxoid in combination with the other five serotypes of botulinal toxoid invoked an immune response in guinea pigs comparable to that considered adequate for the other toxoids.

Purification of Clostridium botuliunum type F progenitor toxin

Clostridium botulinum type F progenitor toxin was purified to a homogeneous state as judged by gel filtration on Sephadex G-200, ultracentrifugation, and disc electrophoresis. The sedimentation constant, corrected to water at 20 C, of type F progenitor toxin was determined to be 10.3 and the molecular weight to be 235,000 by ultracentrifugation at pH 6.0. The purified toxin contained a toxicity of 1.2 x 10(8) 50% lethal doses/mg of N. In agar gel double diffusion, it formed two precipitin lines at pH 6.0. The progenitor toxin of type F differs from that of type A in that it contains no hemagglutinin and from that of type E in that it is not activable.