Practical Media and Control Measures for Producing Highly Toxic Cultures of Clostridium botulinum, Type A

Clinical Safety and Tolerability of A2NTX, a Novel Low-Molecular-Weight Neurotoxin Derived from Botulinum Neurotoxin Subtype A2, in Comparison with Subtype A1 Toxins

All the botulinum type A neurotoxins available for clinical use are of the A1 subtype. We developed a subtype A2 low-molecular-weight (150 kD (kilo Dalton)) neurotoxin (A2NTX) with less spread and faster entry into the motor nerve terminal than A1 in vitro and in vivo. Preliminary clinical studies showed that its efficacy is superior to A1 toxins. We conducted an open study exploring its safety and tolerability profile in comparison with A1LL (LL type A1 toxin, or onabotulinumtoxinA) and a low-molecular-weight (150 kD) A1 neurotoxin (A1NTX). Those who had been using A1LL (n = 90; 50-360 mouse LD50 units) or A1NTX (n = 30; 50-580 units) were switched to A2NTX (n = 120; 25-600 units) from 2010 to 2018 (number of sessions ~27, cumulative doses ~11,640 units per patient). The adverse events for A2NTX included weakness (n = 1, ascribed to alcoholic polyneuropathy), dysphagia (1), local weakness (4), and spread to other muscles (1), whereas those for A1LL or A1NTX comprised weakness (n = 2, A1NTX), dysphagia (8), ptosis (6), local weakness (7), and spread to other muscles (15). After injections, 89 out of 120 patients preferred A2NTX to A1 for the successive sessions. The present study demonstrated that A2NTX had clinical safety up to the dose of 500 units and was well tolerated compared to A1 toxins.

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.

Recombination and insertion events involving the botulinum neurotoxin complex genes in Clostridium botulinum types A, B, E and F and Clostridium butyricum type E strains

Background

Clostridium botulinum is a taxonomic designation for at least four diverse species that are defined by the expression of one (monovalent) or two (bivalent) of seven different C. botulinum neurotoxins (BoNTs, A-G). The four species have been classified as C. botulinum Groups I-IV. The presence of bont genes in strains representing the different Groups is probably the result of horizontal transfer of the toxin operons between the species.

Results

Chromosome and plasmid sequences of several C. botulinum strains representing A, B, E and F serotypes and a C. butyricum type E strain were compared to examine their genomic organization, or synteny, and the location of the botulinum toxin complex genes. These comparisons identified synteny among proteolytic (Group I) strains or nonproteolytic (Group II) strains but not between the two Groups. The bont complex genes within the strains examined were not randomly located but found within three regions of the chromosome or in two specific sites within plasmids. A comparison of sequences from a Bf strain revealed homology to the plasmid pCLJ with similar locations for the bont/bv b genes but with the bont/a4 gene replaced by the bont/f gene. An analysis of the toxin cluster genes showed that many recombination events have occurred, including several events within the ntnh gene. One such recombination event resulted in the integration of the bont/a1 gene into the serotype toxin B ha cluster, resulting in a successful lineage commonly associated with food borne botulism outbreaks. In C. botulinum type E and C. butyricum type E strains the location of the bont/e gene cluster appears to be the result of insertion events that split a rarA, recombination-associated gene, independently at the same location in both species.

Conclusion

The analysis of the genomic sequences representing different strains reveals the presence of insertion sequence (IS) elements and other transposon-associated proteins such as recombinases that could facilitate the horizontal transfer of the bonts; these events, in addition to recombination among the toxin complex genes, have led to the lineages observed today within the neurotoxin-producing clostridia.

Regulation of neurotoxin complex expression in Clostridium botulinum strains 62A, Hall A-hyper, and NCTC 2916

The kinetics of botulinum toxin gene expression have been investigated in Clostridium botulinum type A strains 62A, Hall A-hyper, and type A(B) strain NCTC 2916 during the growth cycle. The analyses were performed in TPGY and type A Toxin Production Media (TPM). The mRNA transcript levels encoding the proteins of the neurotoxin complex were determined using Northern analyses. Neurotoxin concentrations in culture supernatants and lysed cell pellets were assayed using ELISA, Western blots, and mouse bioassay. Proteolytic activation of botulinum neurotoxin during the growth cycle was evaluated by Western blots. For all three strains, mRNA transcripts for the toxin complex genes were initially detected in early log phase, reached peak levels in early stationary phase, and rapidly decreased in mid-to-late stationary phase and during lysis. Toxin expression varied depending on the strain and growth medium. Toxin production was highest in strain Hall A-hyper, followed by NCTC 2916 and 62A. For C. botulinum strain Hall A-hyper, cell lysis and toxin release into the supernatant occurred rapidly for cells grown in TPM, while cells grown in TPGY remained in stationary phase with minimal lysis and toxin release through 96 h of growth. In contrast, strains 62A and NCTC 2916 lysed more extensively than Hall A-hyper in TPGY. TPM supported higher toxin production and activation than TPGY in strains 62A and Hall A-hyper. These data support that the genes of the botulinum neurotoxin complex are temporally expressed during late-log and early stationary phase and that toxin complex formation depends on the strain and growth medium. Botulinum toxin synthesis and activation appears to be a complex process that is highly regulated by nutritional and environmental conditions. Further research is needed to elucidate the sensing mechanisms and genetic regulatory factors controlling these processes.

The therapeutic use of botulinum toxin

Since Alan Scott's research, botulinum toxin (BoNT) has been used in several diseases or conditions characterised by muscular overactivity. BoNT acts on either neuromuscular or autonomic cholinergic junctions. Seven different serotypes are known, with antigenic specificity and different therapeutic profiles. BoNT is made up of a heavy chain, involved in binding and membrane translocation, and a light chain, involved in blocking neuroexcytosis. Each serotype shares a specific acceptor on the presynaptic membrane of a cholinergic junction. The available BoNT preparations differ in toxicity, purity and stability. Injection of the neurotoxin produces several modifications at a neuromuscular junction. Axonal sprouting, muscular fibre atrophy, and new end-plates are the most evident histological events after BoNT treatment. They appear to be reversible in untreated muscles. Diffusion can occur at first by haematogeneous or local BoNT spread. Several factors, such as dose, volume, site of injection, muscle size, and muscular fascia, can influence the amount of diffusion and possible side-effects. After prolonged BoNT treatment patients can become unresponsive. Antibodies directed against BoNT have been observed with ELISA or mouse bioassay. Different serotypes have been used to treat non-responder patients. Novel toxins with lower immunogenicity and prolonged clinical efficacy are required for more effective treatment.

Properties and use of botulinum toxin and other microbial neurotoxins in medicine

Crystalline botulinum toxin type A was licensed in December 1989 by the Food and Drug Administration for treatment of certain spasmodic muscle disorders following 10 or more years of experimental treatment on human volunteers. Botulinum toxin exerts its action on a muscle indirectly by blocking the release of the neurotransmitter acetylcholine at the nerve ending, resulting in reduced muscle activity or paralysis. The injection of only nanogram quantities (1 ng = 30 mouse 50% lethal doses [U]) of the toxin into a spastic muscle is required to bring about the desired muscle control. The type A toxin produced in anaerobic culture and purified in crystalline form has a specific toxicity in mice of 3 x 10(7) U/mg. The crystalline toxin is a high-molecular-weight protein of 900,000 Mr and is composed of two molecules of neurotoxin (ca. 150,000 Mr) noncovalently bound to nontoxic proteins that play an important role in the stability of the toxic unit and its effective toxicity. Because the toxin is administered by injection directly into neuromuscular tissue, the methods of culturing and purification are vital. Its chemical, physical, and biological properties as applied to its use in medicine are described. Dilution and drying of the toxin for dispensing causes some detoxification, and the mouse assay is the only means of evaluation for human treatment. Other microbial neurotoxins may have uses in medicine; these include serotypes of botulinum toxins and tetanus toxin. Certain neurotoxins produced by dinoflagellates, including saxitoxin and tetrodotoxin, cause muscle paralysis through their effect on the action potential at the voltage-gated sodium channel. Saxitoxin used with anaesthetics lengthens the effect of the anaesthetic and may enhance the effectiveness of other medical drugs. Combining toxins with drugs could increase their effectiveness in treatment of human disease.

Regulation of neurotoxin and protease formation in Clostridium botulinum Okra B and Hall A by arginine

Supplementation of a minimal medium with high levels of arginine (20 g/liter) markedly decreased neurotoxin titers and protease activities in cultures of Clostridium botulinum Okra B and Hall A. Nitrogenous nutrients that are known to be derived from arginine, including proline, glutamate, and ammonia, also decreased protease and toxin but less so than did arginine. Proteases synthesized during growth were rapidly inactivated after growth stopped in media containing high levels of arginine. Separation of extracellular proteins by electrophoresis and immunoblots with antibodies to toxin showed that the decrease in toxin titers in media containing high levels of arginine was caused by both reduced synthesis of protoxin and impaired proteolytic activation. In contrast, certain other nutritional conditions stimulated protease and toxin formation in C. botulinum and counteracted the repression by arginine. Supplementation of the minimal medium with casein or casein hydrolysates increased protease activities and toxin titers. Casein supplementation of a medium containing high levels of arginine prevented protease inactivation. High levels of glucose (50 g/liter) also delayed the inactivation of proteases in both the minimal medium and a medium containing high levels of arginine. These observations suggest that the availability of nitrogen and energy sources, particularly arginine, affects the production and proteolytic processing of toxins and proteases in C. botulinum.

Toxin production by Clostridium botulinum type A under various fermentation conditions

The time of appearance and the quantity of toxin produced by the Hall strain of Clostridium botulinum type A were examined under various conditions. A 70-liter fermentor and a complex medium consisting of 2% casein hydrolysate and 1% yeast extract plus an appropriate concentration of glucose were employed. Optimal conditions for toxin production were as follows: a nitrogen overlay at a rate of 5 liters/min, an agitation rate of 50 rpm, a temperature of 35 degrees C, and an initial glucose concentration of 1.0% with the pH uncontrolled. Under these conditions, the maximum toxin concentration (6.3 x 10(5) mouse median lethal doses/ml) was attained within 24 h. Cell lysis was apparently not required to obtain maximum toxin concentrations under the fermentation conditions described.

PREPARATION AND ASSAY OF THE INTERNATIONAL STANDARDS FOR CLOSTRIDIUM BOTULINUM TYPES A, B, C, D AND E ANTITOXINS

The National Institute for Medical Research, London, was authorized in 1962 by the WHO Expert Committee on Biological Standardization to establish the International Standards for Clostridium botulinum Types A, B, C, D and E Antitoxins and to define the International Units. For this purpose use was made of the material accepted in 1954 as the British reference preparations and reconstituted in 1960 for establishment as the first British standards.The author describes the methods of preparation of this material and results of examinations, including estimates of the quality of the antitoxins (assessed as an "efficiency ratio") and of the specificity of the sera.The International Unit is defined as the specific activity contained in a known weight of dried antitoxin of each Cl. botulinum type: for Type A, 0.1360 mg; for Type B, 0.1740 mg; for Type C, 0.0800 mg; for Type D, 0.0121 mg; and for Type E, 0.0691 mg.