The mechanism of action of tetanus and botulinum neurotoxins

"Pseudo"-Secondary Treatment Failure Explained via Disease Progression and Effective Botulinum Toxin Therapy: A Pilot Simulation Study

BACKGROUND

The objective of this study was to provide evidence from a simple simulation. In patients with focal dystonia, an initial good response to botulinum neurotoxin (BoNT) injections followed by a secondary worsening does not necessarily arise from an antibody-induced secondary treatment failure (NAB-STF), but may stem from a "pseudo"-secondary treatment failure (PSEUDO-STF).

METHODS

The simulation of the outcome after BoNT long-term treatment was performed in four steps: 1. The effect of the first single BoNT injection (SI curve) was displayed as a 12-point graph, corresponding to the mean improvement from weeks 1 to 12. 2. The remaining severity of the dystonia during the nth injection cycle was calculated by subtracting the SI curve (weighted by the outcome after n - 1 cycles) from the outcome after week 12 of the (n - 1)th cycle. 3. A graph was chosen (the PRO curve), which represents the progression of the severity of the underlying disease during BoNT therapy. 4. The interaction between the outcome during the nth BoNT cycle and the PRO curve was determined.

RESULTS

When the long-term outcome after n cycles of BoNT injections (applied every 3 months) was simulated as an interactive process, subtracting the effect of the first cycle (weighted by the outcome after n - 1 cycles) and adding the progression of the disease, an initial good improvement followed by secondary worsening results. This long-term outcome depends on the steepness of the progression and the duration of action of the first injection cycle. We termed this response behavior a "pseudo"-secondary treatment failure, as it can be compensated via a dose increase.

CONCLUSION

A secondary worsening following an initial good response in BoNT therapy of focal dystonia might not necessarily indicate neutralizing antibody induction but could stem from a "PSEUDO"-STF (a combination of good response behavior and progression of the underlying disease). Thus, an adequate dose adaptation must be conducted before diagnosing a secondary treatment failure in the strict sense.

No Secondary Treatment Failure during Incobotulinumtoxin-A Long-Term Treatment Demonstrated by the Drawing of Disease Severity

The aim of this study was to detect clinical hints regarding the development of secondary treatment failure (STF) in patients with focal dystonia who were exclusively treated with incobotulinumtoxin/A (incoBoNT/A). In total, 33 outpatients (26 with idiopathic cervical dystonia, 4 with Meige syndrome and 3 with other cranial dystonia) who were treated with repeated injections of incoBoNT/A for a mean period of 6.4 years without interruptions were recruited to draw the course of their disease severity (CoD) from the onset of symptoms to the onset of BoNT therapy (CoDB graph) and from the onset of BoNT therapy to recruitment (CoDA graph). At the time of recruitment, the patients assessed the change in severity as a percentage of the severity at the onset of BoNT therapy. Blood samples were taken to test the presence of neutralizing antibodies (NABs) using the mouse hemidiaphragm assay (MHDA). Patients reported an improvement of about 70% with respect to the mean. None of the patients tested positive for MHDA. Three different types of CoDB and three different types of CoDA graphs could be distinguished. The patients with different CoDB graphs reported different long-term outcomes, but there was no significant difference in long-term outcomes between patients with different CoDA graphs. None of the patients produced a CoDA graph with an initial improvement and a secondary worsening as a hint for the development of STF. A primary non-response was not observed in any of the patients. During long-term treatment with BoNT/A, NABs and/or STF may develop. However, in the present study on patients with incoBoNT/A long-term monotherapy, no hints for the development of NABs or STF could be detected, underlining the low antigenicity of incoBoNT/A.

Structural Features of Clostridium botulinum Neurotoxin Subtype A2 Cell Binding Domain

Botulinum neurotoxins (BoNT) are a group of clostridial toxins that cause the potentially fatal neuroparalytic disease botulism. Although highly toxic, BoNTs are utilized as therapeutics to treat a range of neuromuscular conditions. Several serotypes (BoNT/A-/G, /X) have been identified with vastly differing toxicological profiles. Each serotype can be further sub-categorised into subtypes due to subtle variations in their protein sequence. These minor changes have been attributed to differences in both the duration of action and potency for BoNT/A subtypes. BoNTs are composed of three domains—a cell-binding domain, a translocation domain, and a catalytic domain. In this paper, we present the crystal structures of the botulinum neurotoxin A2 cell binding domain, both alone and in complex with its receptor ganglioside GD1a at 1.63 and 2.10 Å, respectively. The analysis of these structures reveals a potential redox-dependent Lys-O-Cys bridge close to the ganglioside binding site and a hinge motion between the H_CN and H_CC subdomains. Furthermore, we make a detailed comparison with the previously reported H_C/A2:SV2C structure for a comprehensive structural analysis of H_C/A2 receptor binding.

The Multispecialty Toxin: A Literature Review of Botulinum Toxin

Botulinum toxin (BoNT) is a potent biological exotoxin produced from Clostridium botulinum. Although it was first used therapeutically to treat strabismus, its clinical role has since expanded rapidly over the years to include treatment of a variety of head and neck, gastrointestinal, urogenital, musculoskeletal, neurological, dermatological, and cosmetic disorders. The main purpose of this review is to provide a brief updated overview of the history, mechanism of action, and clinical applications of BoNT therapy across multiple medical specialties, including the most common adverse effects and recommended Botox dosages.

Comparison of efficacy and toxicity between botulinum toxin subtypes A1 and A2 in cynomolgus macaques

Botulinum toxin type A (subtype A1) is used as therapeutic agent for some neurological disorders causing spasticity. The toxin products have an upper dosage limit, and their adverse events, such as side effects of diffusion following high-dose administration, have become serious issues. Therefore, a preparation with greater therapeutic efficacy at lower dosages and less diffusion in the body is desired. We have attempted to produce neurotoxin derived from subtype A2 (A2NTX), which has a different amino acid sequence from that of neurotoxin derived from subtype A1. In this study, to investigate whether A2NTX is applicable for treatment, we compared the muscle relaxation effects and the toxicity between A1LL and A2NTX in adult cynomolgus macaques. In the isometric muscle contraction test elicited by 30 Hz tetanus stimulation, the contractions observed in the 0.4 U/site A1LL-treated group were similar in value to those in the 0.13 U/site A2NTX-treated group. In the toxicity test, the 12 and 24 U/kg A1LL- and A2NTX-treated groups all exhibited similar signs of toxicity regarding symptoms, rate of weight loss, and decrease in the length of the right lower leg perimeter. Thus, A2NTX demonstrated approximately 3.0-times higher muscle relaxation activity than A1LL, and their toxicity was equivalent. This study suggested that A2NTX products are more suitable for the treatment of neurological disorders.

Interactions of a potent cyclic peptide inhibitor with the light chain of botulinum neurotoxin A: Insights from X-ray crystallography

The seven antigenically distinct serotypes (A-G) of botulinum neurotoxin (BoNT) are responsible for the deadly disease botulism. BoNT serotype A (BoNT/A) exerts its lethal action by cleaving the SNARE protein SNAP-25, leading to inhibition of neurotransmitter release, flaccid paralysis and autonomic dysfunction. BoNTs are dichain proteins consisting of a ∼ 100 kDa heavy chain and a ∼ 50 kDa light chain; the former is responsible for neurospecific binding, internalization and translocation, and the latter for cleavage of neuronal SNARE proteins. Because of their extreme toxicity and history of weaponization, the BoNTs are regarded as potential biowarfare/bioterrorism agents. No post-symptomatic therapeutic interventions are available for BoNT intoxication other than intensive care; therefore it is imperative to develop specific antidotes against this neurotoxin. To this end, a cyclic peptide inhibitor (CPI-1) was evaluated in a FRET assay for its ability to inhibit BoNT/A light chain (Balc). CPI was found to be highly potent, exhibiting a Ki of 12.3 nM with full-length Balc448 and 39.2 nM using a truncated crystallizable form of the light chain (Balc424). Cocrystallization studies revealed that in the Balc424-CPI-1 complex, the inhibitor adopts a helical conformation, occupies a high percentage of the active site cavity and interacts in an amphipathic manner with critical active site residues. The data suggest that CPI-1 prevents SNAP-25 from accessing the Balc active site by blocking both the substrate binding path at the surface and the Zn(2+) binding region involved in catalysis. This differs from linear peptide inhibitors described to date which block only the latter.

Establishment of alternative potency test for botulinum toxin type A using compound muscle action potential (CMAP) in rats

The biological activity of botulinum toxin type A has been evaluated using the mouse intraperitoneal (ip) LD50 test. This method requires a large number of mice to precisely determine toxin activity, and, as such, poses problems with regard to animal welfare. We previously developed a compound muscle action potential (CMAP) assay using rats as an alternative method to the mouse ip LD50 test. In this study, to evaluate this quantitative method of measuring toxin activity using CMAP, we assessed the parameters necessary for quantitative tests according to ICH Q2 (R1). This assay could be used to evaluate the activity of the toxin, even when inactive toxin was mixed with the sample. To reduce the number of animals needed, this assay was set to measure two samples per animal. Linearity was detected over a range of 0.1-12.8 U/mL, and the measurement range was set at 0.4-6.4 U/mL. The results for accuracy and precision showed low variability. The body weight was selected as a variable factor, but it showed no effect on the CMAP amplitude. In this study, potency tests using the rat CMAP assay of botulinum toxin type A demonstrated that it met the criteria for a quantitative analysis method.

Comparison of the immunogenicity of botulinum toxin type A and the efficacy of A1 and A2 neurotoxins in animals with A1 toxin antibodies

One issue with botulinum toxin type A products is a reduced therapeutic response in patients that have been injected with frequent dosing over a prolonged period. A possible cause of this is hemagglutinin, found in progenitor toxins, displaying adjuvant activity, enhancing antibody production against the toxin. We investigated whether there is any difference in immunogenicity between the LL toxin-derived subtype A1 (A1LL) and the neurotoxin-derived subtypes A1 and A2 (A1NTX and A2NTX, respectively), and investigated whether A2NTX is effective in animals which produce antibodies against A1LL. Neutralizing antibodies were detected in the A1LL-administered group; however, they were not detected in swine and rabbits administered multiple doses of A2NTX. These results indicate that A2NTX has a lower immunogenicity than A1LL. In rats with neutralizing antibodies, produced by the administration of A1LL, that were administered either A1NTX or A2NTX, A2NTX showed more potent inhibitory neuromuscular transmission than A1NTX. In human sera immunized with the botulinum toxoid vaccine (containing LL, L, and M toxoid derived subtype A1) reacted with either A1NTX or A2NTX, A2NTX showed more potent inhibitory neuromuscular transmission than A1NTX. This suggests that A2NTX has a greater therapeutic value in humans who have neutralizing antibodies against the A1 toxin.

Transsynaptic inhibition of spinal transmission by A2 botulinum toxin

Type A botulinum toxin blocks not only ACh release from motor nerve terminals but also central synaptic transmission, including glutamate, noradrenaline, dopamine, ATP, GABA and glycine. Neurotoxins (NTXs) are transported by both antero- and retrogradely along either motor or sensory axons for bidirectional delivery between peripheral tissues or the CNS. A newly developed type A2 NTX (A2NTX) injected into one rat foreleg muscle was transported to the contralateral muscle. This finding was consistent with the NTX traveling retrogradely via spinal neurons and then transsynaptically through motor neurons to the contralateral motor neurons within the spinal cord and on to the soleus muscle. In the present study we found that toxin injection into the rat left soleus muscle clearly induced bilateral muscle relaxation in a dose-dependent fashion, although the contralateral muscle relaxation followed the complete inhibition of toxin-injected ipsilateral muscles. The toxin-injected ipsilateral muscle relaxation was faster and stronger in A2NTX-treated rats than A1LL (BOTOX). A1LL was transported almost equally to the contralateral muscle via neural pathways and the bloodstream. In contrast, A2NTX was mainly transported to contralateral muscles via the blood. A1LL was more successfully transported to contralateral spinal neurons than A2NTX. We also demonstrated that A1LL and A2NTX were carried from peripheral to CNS and vice versa by dual antero- and retrograde axonal transport through either motor or sensory neurons.

Easy expression of the C-terminal heavy chain domain of botulinum neurotoxin serotype A as a vaccine candidate using a bi-cistronic baculovirus system

Clostridial botulinum neurotoxin (BoNT) is one of the most toxic proteins causing the food borne disease, botulism. In previous studies, recombinant BoNT production by Escherichia coli and yeast Pichia pastoris has been hampered by high AT content and codon bias in the gene encoding BoNT and required a synthetic gene to resolve this intrinsic bottleneck. This paper reports the simultaneous expression of the C-terminal heavy chain domain of BoNT (rBoNT/A-HC-6h) and enhanced green fluorescent protein (EGFP) using a bi-cistronic baculovirus-insect cell expression system. The expression of EGFP facilitated the monitoring of viral infection, virus titer determination, and isolation of the recombinant virus. Protein fusion with hexa-His-tag and one-step immobilized metal-ion affinity chromatography (IMAC) purification produced a homogenous, stable, and immunologically active 55-kDa rBoNT/A-HC-6h (about 3mg/L) with >90% purity. Furthermore, measured levels of serum titers were 8-folds for mice vaccinated with the purified rBoNT/A-HC-6h (2μg) than for mice administered with botulinum toxoid after initial immunization. Challenge experiment with botulinum A toxin demonstrated the immunoprotective activity of purified rBoNT/A-HC-6h providing the mice full protection against 10(2) LD50 botulinum A toxin with a dose as low as 0.2μg. This study provided supportive evidence for the use of a bi-cistronic baculovirus-Sf21 insect cell expression system in the facile expression of an immunogenically active rBoNT/A-HC.

Effect of botulinum neurotoxin treatment in the lateral spread monitoring of microvascular decompression for hemifacial spasm

INTRODUCTION

Botulinum neurotoxin (BtNtx) treatment for hemifacial spasm (HFS) prior to microvascular decompression (MVD) is hypothesized to be a factor in the variability of intraoperative neurophysiological monitoring (IONM) during this procedure.

METHODS

We analyzed 282 MVDs performed at the University of Pittsburgh Medical Center between January 1, 2000 and December 31, 2007. We retrospectively compared the lateral spread response (LSR) in the mentalis muscle when stimulus-triggered electromyography (EMG) was elicited from the facial nerve. Previous BtNtx treatment was the grouping factor.

RESULTS

Baseline LSR amplitudes during MVD (prior BtNtx: mean = 341.47 μV; no BtNtx: mean = 241.81 μV) were significantly different between groups (df = 1,281; t = -2.463; P = 0.014). Comparisons of latency and current threshold at baseline, as well as HFS disappearance or LSR persistence after the procedure, did not achieve statistical significance.

CONCLUSIONS

HFS patients treated with BtNtx prior to MVD demonstrated higher LSR baseline amplitudes during IONM. This could be related to muscle poly-reinnervation after recovery from repeated BtNtx use.

Lipid-mediated endocytosis

Receptor-mediated endocytosis is used by a number of viruses and toxins to gain entry into cells. Some have evolved to use specific lipids in the plasma membrane as their receptors. They include bacterial toxins such as Shiga and Cholera toxin and viruses such as mouse polyoma virus and simian virus 40. Through multivalent binding to glycosphingolipids, they induce lipid clustering and changes in membrane properties. Internalization occurs by unusual endocytic mechanisms involving lipid rafts, induction of membrane curvature, trans-bilayer coupling, and activation of signaling pathways. Once delivered to early endosomes, they follow diverse intracellular routes to the lumen of the ER, from which they penetrate into the cytosol. The role of the lipid receptors is central in these well-studied processes.

Comparison of effects of botulinum toxin subtype A1 and A2 using twitch tension assay and rat grip strength test

Botulinum toxin type A is used as a therapeutic agent for some spastic neurological disorders. Type A organisms have been classified into four subtypes (A1 to A4) based on the amino acid sequence variability of the produced neurotoxin. At present, commercially available preparations of the toxin belong to subtype A1. To date, no study has compared the characteristics of the biological activity of toxins from different subtypes. We compared the efficacy of A1 toxin (LL toxin or neurotoxin: NTX) with that of A2 toxin (NTX) employing the twitch tension assay using the mouse phrenic nerve hemidiaphragm and grip strength test in rats. The inhibitory effects on neuromuscular transmission of A2NTX at pH 7.4 and pH 6.8 were 1.95 and 3.73 times more potent than those of A1LL, respectively. The 50% effective doses for the administered limb, the dose which caused a 50% reduction in grip strength, i.e. ED(50), of A1LL, A1NTX, and A2NTX were calculated as 0.087, 0.060, and 0.040 U/head, respectively. These doses for the contralateral limb, i.e. TD(50), of A1LL, A1NTX, and A2NTX were calculated as 6.35, 7.54, and 15.62 U/head, respectively. In addition, the time required for A2NTX-injected rats to recover the grip strength of the contralateral limb was 17 days, while that for rats injected with A1LL was 35 days. The results indicated that A2NTX is a more potent neuromuscular blocker than A1 toxins, and suggested that A2NTX will provide a preferentical therapeutic agent for neurological disorders.

Diversity and impact of prokaryotic toxins on aquatic environments: a review

Microorganisms are ubiquitous in all habitats and are recognized by their metabolic versatility and ability to produce many bioactive compounds, including toxins. Some of the most common toxins present in water are produced by several cyanobacterial species. As a result, their blooms create major threats to animal and human health, tourism, recreation and aquaculture. Quite a few cyanobacterial toxins have been described, including hepatotoxins, neurotoxins, cytotoxins and dermatotoxins. These toxins are secondary metabolites, presenting a vast diversity of structures and variants. Most of cyanobacterial secondary metabolites are peptides or have peptidic substructures and are assumed to be synthesized by non-ribosomal peptide synthesis (NRPS), involving peptide synthetases, or NRPS/PKS, involving peptide synthetases and polyketide synthases hybrid pathways. Besides cyanobacteria, other bacteria associated with aquatic environments are recognized as significant toxin producers, representing important issues in food safety, public health, and human and animal well being. Vibrio species are one of the most representative groups of aquatic toxin producers, commonly associated with seafood-born infections. Some enterotoxins and hemolysins have been identified as fundamental for V. cholerae and V. vulnificus pathogenesis, but there is evidence for the existence of other potential toxins. Campylobacter spp. and Escherichia coli are also water contaminants and are able to produce important toxins after infecting their hosts. Other bacteria associated with aquatic environments are emerging as toxin producers, namely Legionella pneumophila and Aeromonas hydrophila, described as responsible for the synthesis of several exotoxins, enterotoxins and cytotoxins. Furthermore, several Clostridium species can produce potent neurotoxins. Although not considered aquatic microorganisms, they are ubiquitous in the environment and can easily contaminate drinking and irrigation water. Clostridium members are also spore-forming bacteria and can persist in hostile environmental conditions for long periods of time, contributing to their hazard grade. Similarly, Pseudomonas species are widespread in the environment. Since P. aeruginosa is an emergent opportunistic pathogen, its toxins may represent new hazards for humans and animals. This review presents an overview of the diversity of toxins produced by prokaryotic microorganisms associated with aquatic habitats and their impact on environment, life and health of humans and other animals. Moreover, important issues like the availability of these toxins in the environment, contamination sources and pathways, genes involved in their biosynthesis and molecular mechanisms of some representative toxins are also discussed.

Pain behavior measures to quantitate joint pain and response to neurotoxin treatment in murine models of arthritis

OBJECTIVE

To evaluate the validity of newly developed pain behavior measures in two murine models of inflammatory arthritis and to determine the ability of these measures to evaluate the analgesic effectiveness of intra-articular (IA) botulinum toxin type A (BoNT/A) for treatment of arthritis pain.

DESIGN

Acute inflammatory arthritis was produced in adult female mice by IA injection of carrageenan and chronic inflammatory arthritis by IA injection of CFA. The presence of arthritis was confirmed by the presence of swelling and erythema. A menu of pain behavior measures was devised for quantitating pain in these models including tenderness, and spontaneous nocturnal wheel running. Toxicity due to neurotoxin was measured as gross limb weakness and impaired functional ability during wheel running.

RESULTS

Tenderness measures and spontaneous nocturnal wheel-running are valid measures of arthritis pain and are sensitive to the effects of analgesia. Narcotic analgesics are effective, but in fully analgesic doses impair wheel-running. IA BoNT/A is an effective analgesic for chronic arthritis pain, but not for acute arthritis pain. High doses can produce local limb muscle weakness, which impairs wheel-running function. Doses of botulinum toxin that are not toxic retain their analgesic function.

CONCLUSIONS

Tenderness and spontaneous pain behavior measures are valid and sensitive for the measurement of pain and analgesia in murine models of inflammatory arthritis. Effective narcotic analgesia produces a decline in function in mice similar to that seen in humans. IA neurotoxin is a promising therapy for chronic inflammatory arthritis but may not be effective for acute arthritis pain.

Investigations into small molecule non-peptidic inhibitors of the botulinum neurotoxins

Botulinum neurotoxins (BoNTs), proteins secreted by the bacteria genus Clostridium, represent a group of extremely lethal toxins and a potential bioterrorism threat. As the current therapeutic options are of a predominantly prophylactic nature and cannot be used en masse, new strategies and ultimately potential treatments are desperately needed to combat any widespread release of these neurotoxins. In these regards, our laboratory has been working on developing new alternatives to treat botulinum intoxication through the development of inhibitors of the light chain proteases, the etiological agent which causes BoNT intoxication. Such a strategy has required the construction of two high-throughput screens and small molecule non-peptidic libraries; excitingly, inhibitors of the BoNT/A protease have been uncovered and are being optimized via structure activity relationship studies.

Molecular mechanisms of presynaptic differentiation

Information processing in the nervous system relies on properly localized and organized synaptic structures at the correct locations. The formation of synapses is a long and intricate process involving multiple interrelated steps. Decades of research have identified a large number of molecular components of the presynaptic compartment. In addition to neurotransmitter-containing synaptic vesicles, presynaptic terminals are defined by cytoskeletal and membrane specializations that allow highly regulated exo- and endocytosis of synaptic vesicles and that maintain precise registration with postsynaptic targets. Functional studies at multiple levels have revealed complex interactions between the transport of vesicular intermediates, the presynaptic cytoskeleton, growth cone navigation, and synaptic targets. With the advent of finer anatomical, physiological, and molecular tools, great insights have been gained toward the mechanistic dissection of functionally redundant processes controlling the specificity and dynamics of synapses. This review highlights the recent findings pertaining to the cellular and molecular regulation of presynaptic differentiation.

Structure- and substrate-based inhibitor design for Clostridium botulinum neurotoxin serotype A

The seven antigenically distinct serotypes of Clostridium botulinum neurotoxins cleave specific soluble N-ethylmaleimide-sensitive factor attachment protein receptor complex proteins and block the release of neurotransmitters that cause flaccid paralysis and are considered potential bioweapons. Botulinum neurotoxin type A is the most potent among the clostridial neurotoxins, and to date there is no post-exposure therapeutic intervention available. To develop inhibitors leading to drug design, it is imperative that critical interactions between the enzyme and the substrate near the active site are known. Although enzyme-substrate interactions at exosites away from the active site are mapped in detail for botulinum neurotoxin type A, information about the active site interactions is lacking. Here, we present the crystal structures of botulinum neurotoxin type A catalytic domain in complex with four inhibitory substrate analog tetrapeptides, viz. RRGC, RRGL, RRGI, and RRGM at resolutions of 1.6-1.8 A. These structures show for the first time the interactions between the substrate and enzyme at the active site and delineate residues important for substrate stabilization and catalytic activity. We show that OH of Tyr(366) and NH(2) of Arg(363) are hydrogen-bonded to carbonyl oxygens of P1 and P1' of the substrate analog and position it for catalytic activity. Most importantly, the nucleophilic water is replaced by the amino group of the N-terminal residue of the tetrapeptide. Furthermore, the S1' site is formed by Phe(194), Thr(215), Thr(220), Asp(370), and Arg(363). The K(i) of the best inhibitory tetrapeptide is 157 nm.

Neurologic uses of botulinum neurotoxin type A

This article reviews the current and most neurologic uses of botulinum neurotoxin type A (BoNT-A), beginning with relevant historical data, neurochemical mechanism at the neuromuscular junction. Current commercial preparations of BoNT-A are reviewed, as are immunologic issues relating to secondary failure of BoNT-A therapy. Clinical uses are summarized with an emphasis on controlled clinical trials (as appropriate), including facial movement disorders, focal neck and limb dystonias, spasticity, hypersecretory syndromes, and pain.

Intramuscular botulinum toxin-A reduces hemiplegic shoulder pain: a randomized, double-blind, comparative study versus intraarticular triamcinolone acetonide

BACKGROUND AND PURPOSE

Shoulder pain is frequent after stroke and interferes with the rehabilitative process and outcome. However, treatments used for hemiplegic shoulder pain are limited and largely ineffective. This prospective, randomized, double-blind controlled study was conducted to compare the efficacies of botulinum toxin type A (BoNT-A) and triamcinolone acetonide (TA) on hemiplegic shoulder pain and their effects on arm function in patients with stroke.

METHODS

Twenty-nine hemiplegic stroke patients with shoulder pain (duration <or=24 months, pain on numeric rating scale >or=6/10) were randomized into 2 groups. One group received intramuscular injections of BoNT-A (BOTOX 100 U total) during one session to the infraspinatus, pectoralis and subscapularis muscles in conjunction with an intraarticular injection of normal saline to painful shoulder joint, whereas the other group received an intraarticular injection of TA (40 mg) and an intramuscular injection of normal saline to the same muscles. Outcome measures were pain (measured using a numeric rating scale), physician's global rating scale, shoulder range of motion (ROM) in 4 directions, arm function measured using Fugl-Meyer score, and spasticity measured using the modified Ashworth scale. Measurements were made at baseline and 2, 6, and 12 weeks after injection.

RESULTS

At 12 weeks after treatment mean decrease in pain was 4.2 in the BoNT-A-treated group versus 2.5 in the TA-treated group (P=0.051), and improvements in overall ROM were 82.9 degrees versus 51.8 degrees in these groups (P=0.059), showing a strong trend toward there being less pain and better ROM among those treated with BoNT-A than with TA. However, no significant differences were observed between the 2 groups in terms of improvement in physician global rating, Fugl-Meyer score or modified Ashworth scales. No adverse effect was observed in either group.

CONCLUSIONS

Results from this study suggest that injection of BoNT-A into selected muscles of the shoulder girdle might provide more pain relief and ROM improvement than intraarticular steroid in patients with hemiplegic shoulder pain. A larger clinical trial needs to be undertaken to confirm the benefits of this approach.

Structures of Clostridium botulinum Neurotoxin Serotype A Light Chain complexed with small-molecule inhibitors highlight active-site flexibility

The potential for the use of Clostridial neurotoxins as bioweapons makes the development of small-molecule inhibitors of these deadly toxins a top priority. Recently, screening of a random hydroxamate library identified a small-molecule inhibitor of C. botulinum Neurotoxin Serotype A Light Chain (BoNT/A-LC), 4-chlorocinnamic hydroxamate, a derivative of which has been shown to have in vivo efficacy in mice and no toxicity. We describe the X-ray crystal structures of BoNT/A-LC in complexes with two potent small-molecule inhibitors. The structures of the enzyme with 4-chlorocinnamic hydroxamate or 2,4-dichlorocinnamic hydroxamate bound are compared to the structure of the enzyme complexed with L-arginine hydroxamate, an inhibitor with modest affinity. Taken together, this suite of structures provides surprising insights into the BoNT/A-LC active site, including unexpected conformational flexibility at the S1' site that changes the electrostatic environment of the binding pocket. Information gained from these structures will inform the design and optimization of more effective small-molecule inhibitors of BoNT/A-LC.

A non-viral vector for targeting gene therapy to motoneurons in the CNS

Gene therapy vectors that can be targeted to motoneuronal cells are required in the field of neurodegenerative diseases. We propose the use of the atoxic fragment C of tetanus toxin (TTC) as biological activity carrier to the motoneurons. Naked DNA encoding beta-galactosidase-TTC hybrid protein was used to transfect muscle cells in vivo, resulting in a selective gene transfer of the enzymatic activity to the CNS. In the muscle, level expression of beta-galactosidase was readily detectable 24 h after injection, reaching a maximum after 4 days and gradually decreasing thereafter. Labelling in the hypoglossal motoneurons and motor cortex was observed from 4 days after injection. In this paper, we show that TTC works as an enzymatic activity carrier to the CNS when muscle cells are transfected in vivo. We have also shown that the presence of TTC does not have any influence on the expression of the transfected gene. Both these results warrant further studies of TTC as a means of treating motoneuron diseases in the field of gene therapy.

Long term effects of intra-articular botulinum toxin A for refractory joint pain

The purpose of this case series review is to describe our 12 month clinical experience with intra-articular injections of Botulinum toxin Type A (BoNT/A) for refractory joint pain. Eleven patients with chronic arthritis who had failed treatment with oral and/or intra-articular medications and were not surgical candidates were referred to us for management of moderate to severe refractory joint pain in 15 joints. The use of BoNT/A to treat joint pain is a non-FDA approved "off label" treatment with potential side effects. After a detailed explanation of the joint injection procedure, signed informed consent was obtained for the procedure. Fifteen joints were injected with BoNT/A (Allergan, Inc): six lower extremity joints (3 knees, 3 ankles) with 25-50 units and nine shoulders with 50-100 units. Patients were followed for one year or longer. Maximum relief of pain was measured by comparing baseline pain on a numeric rating scale (0-10) to pain at the time of maximum relief (paired t-test). Maximum improvement in function was assessed using paired t-tests for improvement in active flexion and abduction for the shoulder joint, and by the time to perform sit to stand ten times (the timed stands test, TST) for the lower extremity joints.

RESULTS

Two patients were female and nine were male, aged 42-82 years. Five had osteoarthritis (OA), five had rheumatoid arthritis (RA) and one had psoriatic arthritis. All patients were on analgesic and/or anti-inflammatory medications and all joints had previous intra-articular steroid or viscosupplement injections with inadequate or unsatisfactory benefit. A clinically and statistically significant improvement was noted after IA-BoNT/A injections. The mean maximum decrease in lower extremity joint pain was 55% (p =0.02) and the 36% (p =0.044) improvement in the Timed Stands Test was noted at four to ten weeks after injection. There was a 71% mean maximum reduction in shoulder pain severity from 8.2 +/- 1.1 to 2.4 +/- 1.9 (p <0.001). Active range of motion increased 67% in flexion (from 67.8 +/- 27.6 to 113.3 +/- 46.6 degrees, p =0.001) and 42% in abduction (from 50 +/- 18.5 degrees to 71.1 +/- 23.1 degrees p =0.01). No immediate or delayed adverse effects related to BoNT/A were noted after the injection. Duration of pain relief was variable and ranged from 3 to 12 months. Five joints were re-injected with IA-Bont/A and had a similar decrease in joint pain that lasted 3 to 12 months.

CONCLUSIONS

This is the first report of the long term effects of intra-articular BoNT/A injections to treat chronic joint pain and the efficacy of repeated injections. Although this study was small, and uncontrolled the results suggest that IA-BoNT/A injections are an effective and safe treatment for chronic joint pain disorders.

Recombinant C fragment of botulinum neurotoxin B serotype (rBoNTB (HC)) immune response and protection in the rhesus monkey

Botulinum neurotoxin B (BoNTB) is a distinct protein subtype of a family of neurotoxins with the potential for use in biological warfare or terrorist attacks. This study is one in a series evaluating the immunogenicity and protective effects of recombinant vaccines against the different subtypes of botulinum toxin. The recombinant subunit vaccines encoding the C fragment portion ( approximately 50 kDa) of the toxins are produced in the yeast, Pichia pastoris. In this study, groups of rhesus monkeys were vaccinated with three doses (1 and 5microg per dose) of rBoNTB(H(c)) vaccine. Total and neutralizing antibody titers were determined at various times during and postvaccination. Two groups of vaccinated monkeys plus non-vaccinated controls were actively challenged with B toxin by aerosol exposure. All monkeys receiving vaccine were protected from the toxin and no clinical signs of disease were observed, while controls displaying classic signs of botulism succumbed to the toxin challenge. Two additional groups of monkeys receiving the same vaccine regiment as the first two groups had significant levels of circulating neutralizing antibody titers up to 24 months postvaccination. This non-human primate study demonstrated the short- and long-term immunity afforded by the rBoNTB(H(c)) vaccine.

Basic immunological aspects of botulinum toxin therapy

Previous studies in this laboratory had mapped the immune recognition profile of the regions recognized antibodies (Abs) and by T cells on the protective H(C) domain (C-terminal fragment corresponding to residues 855-1296 of the heavy chain) of botulinum neurotoxin serotype A (BoNT/A). The localization of these regions has several potential applications and has provided a basis for the understanding of immunoresistance to treatment. We briefly outline these localized regions and discuss the impact of these findings on the immunotherapeutic applications of BoNT/A. Immunoresistance to toxin therapy can appear in some patients after a few injections with the toxin. Our epitope mapping studies have shown that several factors can influence the immune response to the toxin. These factors include dose, duration of treatment, frequency of immunization, and quality of the toxin. The immune response to the whole toxin is under genetic control, and the response to each epitope is under separate genetic control. Therefore, the appearance of blocking Abs (i.e., immunoresistance) in patients might be controlled by the major histocompatability of the host. Once a patient becomes immunoresistant to one toxin then switching to another toxin will most often be of limited and short-lived benefit, because the patient becomes rapidly immunoresistant to the second toxin. Finally, because of the considerable structural homology between tetanus neurotoxin (TeNT) and BoNTs, it is possible, although not certain, that a prior active immune response to TeNT might play some role in the early appearance on anti-BoNT Abs in some patients.

Botulinum toxins in neurological disease

Botulinum toxins are among the most potent neurotoxins known to humans. In the past 25 years, botulinum toxin has emerged as both a potential weapon of bioterrorism and as a powerful therapeutic agent, with growing applications in neurological and non-neurological disease. Botulinum toxin is unique in its ability to target peripheral cholinergic neurons, preventing the release of acetylcholine through the enzymatic cleavage of proteins involved in membrane fusion, without prominent central nervous system effects. There are seven serotypes of the toxin, each with a specific activity at the molecular level. Currently, serotypes A (in two preparations) and B are available for clinical use, and have been shown to be safe and effective for the treatment of dystonia, spasticity, and other disorders in which muscle overactivity gives rise to symptoms. This review focuses on the pharmacology, electrophysiology, immunology, and application of botulinum toxin in selected neurological disorders.

Benefits and risks of pharmacological treatments for essential tremor

Essential tremor can cause significant functional disability in some patients. The arms are the most common body part affected and cause the most functional disability. The treatment of essential tremor includes medications, surgical options and other forms of therapy. Presently there is no cure for essential tremor nor are there any medications that can slow the progression of tremor. Treatment for essential tremor is recommended if the tremor causes functional disability. If the tremor is disabling only during periods of stress and anxiety, propranolol and benzodiazepines can be used during those periods when the tremor causes functional disability. The currently available medications can improve tremor in approximately 50% of the patients. If the tremor is disabling, treatment should be initiated with either primidone or propranolol. If either primidone or propranolol do not provide adequate control of the tremor, then the medications can be used in combination. If patients experience adverse effects with propranolol, occasionally other beta-adrenoceptor antagonists (such as atenolol or metoprolol) can be used. If primidone and propranolol do not provide adequate control of tremor, occasionally the use of benzodiazepines (such as clonazepam) can provide benefit. Other medications that may be helpful include gabapentin or topiramate. If a patient has disabling head or voice tremor, botulinum toxin injections into the muscles may provide relief from the tremor. Botulinum toxin in the hand muscles for hand tremor can result in bothersome hand weakness and is not widely used. There are other medications that have been tried in essential tremor and have questionable efficacy. These drugs include carbonic anhydrase inhibitors (e.g. methazolamide), phenobarbital, calcium channel antagonists (e.g. nimodipine), isoniazid, clonidine, clozapine and mirtazapine. If the patient still has disabling tremor after medication trials, surgical options are usually considered. Surgical options include thalamotomy and deep brain stimulation of the thalamus. These surgical options provide adequate tremor control in approximately 90% of the patients. Surgical morbidity and mortality for these procedures is low. Deep brain stimulation and thalamotomy have been shown to have comparable efficacy but fewer complications have been reported with deep brain stimulation. In patients undergoing bilateral procedures deep brain stimulation of the thalamus is the procedure of choice to avoid adverse effects seen with bilateral ablative procedures. The use of medication and/or surgery can provide adequate tremor control in the majority of the patients.

Granule stores from cellubrevin/VAMP-3 null mouse platelets exhibit normal stimulus-induced release

It is widely accepted that the platelet release reaction is mediated by heterotrimeric complexes of integral membrane proteins known as SNAREs (SNAP receptors). In an effort to define the precise molecular machinery required for platelet exocytosis, we have analyzed platelets from cellubrevin/VAMP-3 knockout mice. Cellubrevin/VAMP-3 has been proposed to be a critical v-SNARE for human platelet exocytosis; however, data reported here suggest that it is not required for platelet function. Upon stimulation with increasing concentrations of thrombin, collagen, or with thrombin for increasing time there were no differences in secretion of [3H]-5HT (dense core granules), platelet factor IV (alpha granules), or hexosaminidase (lysosomes) between null and wild-type platelets. There were no gross differences in bleeding times nor in agonist-induced aggregation measured in platelet-rich plasma or with washed platelets. Western blotting of wild-type, heterozygous, and null platelets confirmed the lack of cellubrevin/VAMP-3 in nulls and showed that most elements of the secretion machinery are expressed at similar levels. While the secretory machinery in mice was similar to humans, mice did express apparently higher levels of synaptobrevin/VAMP-2. These data show that the v-SNARE, cellubrevin/VAMP-3 is not a requirement for the platelet release reaction in mice.

Characterization of a cytotoxic factor in culture filtrates of Serratia marcescens

Serratia marcescens culture filtrates have been reported to be cytotoxic to mammalian cells. Using biochemical and genetic approaches, we have identified a major source of this cytotoxic activity. Both heat and protease treatments abrogated the cytotoxicity of S. marcescens culture filtrates towards HeLa cells, suggesting the involvement of one or more protein factors. A screen for in vitro cytotoxic activity revealed that S. marcescens mutant strains that are deficient in production of a 56-kDa metalloprotease are significantly less cytotoxic to mammalian cells. Cytotoxicity was significantly reduced when culture filtrates prepared from wild-type strains were pretreated with either EDTA or 1,10-phenanthroline, which are potent inhibitors of the 56-kDa metalloprotease. Furthermore, cytotoxic activity was restored when the same culture filtrates were incubated with zinc divalent cations, which are essential for enzymatic activity of the 56-kDa metalloprotease. Finally, recombinant expression of the S. marcescens 56-kDa metalloprotease conferred a cytotoxic phenotype on the culture filtrates of a nonpathogenic Escherichia coli strain. Collectively, these data suggest that the 56-kDa metalloprotease contributes significantly to the in vitro cytotoxic activity commonly observed in S. marcescens culture filtrates.

Safety factor at the neuromuscular junction

Reliable transmission of activity from nerve to muscle is necessary for the normal function of the body. The term 'safety factor' refers to the ability of neuromuscular transmission to remain effective under various physiological conditions and stresses. This is a result of the amount of transmitter released per nerve impulse being greater than that required to trigger an action potential in the muscle fibre. The safety factor is a measure of this excess of released transmitter. In this review we discuss the practical difficulties involved in estimating the safety factor in vitro. We then consider the factors that influence the safety factor in vivo. While presynaptic transmitter release may be modulated on a moment to moment basis, the postsynaptic features that determine the effect of released transmitter are not so readily altered to meet changing demands. Different strategies are used by different species to ensure reliable neuromuscular transmission. Some, like frogs, rely on releasing a large amount of transmitter while others, like man, rely on elaborate postsynaptic specialisations to enhance the response to transmitter. In normal adult mammals, the safety factor is generally 3-5. Both pre- and postsynaptic components change during development and may show plasticity in response to injury or disease. Thus, both acquired autoimmune and inherited congenital diseases of the neuromuscular junction (NMJ) can significantly reduce, or even transiently increase, safety factor.

Identification of the characteristics that underlie botulinum toxin potency: implications for designing novel drugs

Botulinum toxin is a uniquely potent substance whose natural site of action is the peripheral cholinergic nerve ending. A substantial amount of information on the cellular, subcellular and molecular aspects of toxin action has been accumulated, and as a result a sound understanding of the basis for toxin potency has been developed. The principal characteristics of the toxin molecule that account for its potency are its ability: a) to be absorbed from the gut with minimal degradation; b) to bind to receptors that maximize the prospects of a pathophysiologic outcome; c) to act by a multiplicative (viz., enzymatic) mechanism; and d) to modify a substrate that is essential for neuronal function. Interestingly, the same properties that account for potency can also be exploited to utilize the toxin as a research tool and as a therapeutic agent. Several specific examples of ways to use the toxin advantageously are presented, including: a) development of oral medications and vaccines; b) analysis of subcellular mechanisms that govern transcytosis; c) identification of cell surface markers characteristic of cholinergic nerve endings; and d) analysis of specific aspects of exocytosis, such as spontaneous quantal release and synchronous quantal release. In all likelihood, further studies on the mechanism of botulinum toxin action will reveal yet further opportunities for utilizing it as a research tool or therapeutic agent.

Biological neurotoxins

The authors divide biological toxins into animal, plant, and bacterial classes and discuss each within a context of demographic, clinical and research examples. Advances in our knowledge are highlighted, and the authors relate the implications of this knowledge to target-specific neurologic involvement.

The effects of tetanus toxin on the orbicularis oculi muscle

PURPOSE

Tetanus toxin can cause localized neuromuscular weakness, but it also can produce systemic tetany. The action of tetanus toxin on the orbicularis muscle has not been studied in animals immunized to prevent systemic tetany. Our objective was to determine whether tetanus toxin could be used to treat orbicularis oculi muscle spasms.

METHODS

We analyzed the clinical, electrophysiologic, and histopathologic effects of tetanus toxin injected into the orbicularis oculi muscle of rabbits with passive immunity to tetanus toxin. In six rabbits, the orbicularis oculi function in both eyes was assessed clinically, and the baseline orbicularis oculi muscle action potential was measured physiologically with electromyography (EMG). The rabbits then were immunized against tetanus toxin with tetanus immunoglobulin for immediate and definitive immunity. Tetanus toxin was injected into the left orbicularis oculi muscles, leaving the right eyes as controls. Ten days later, the rabbits were again assessed by clinical examination and with EMGs on both the injected side and the noninjected side. The animals were killed at 14 days, and the orbicularis muscle was removed from both sides. The injected and control tissues were examined microscopically for signs of neuromuscular denervation.

RESULTS

All six rabbits showed weakness in eye closure on the side injected with tetanus toxin. In addition, four rabbits developed complete ear ptosis on the tetanus toxin injected side because of spread of the toxin to adjacent ear muscles. EMGs showed both a denervation of the orbicularis oculi muscle and a poor blink potential on the side injected with tetanus toxin. Histopathologic studies of the orbicularis oculi muscle injected with tetanus toxin showed angulation of both slow and fast types of muscle fibers compatible with neuromuscular denervation.

CONCLUSIONS

Tetanus toxin can cause localized orbicularis oculi weakness, as documented clinically, physiologically, and microscopically, without producing systemic tetany in immunized rabbits. Tetanus toxin may have a potential application in the treatment of blepharospasm and hemifacial spasm.

Pure botulinum neurotoxin is absorbed from the stomach and small intestine and produces peripheral neuromuscular blockade

Clostridium botulinum serotype A produces a neurotoxin composed of a 100-kDa heavy chain and a 50-kDa light chain linked by a disulfide bond. This neurotoxin is part of a ca. 900-kDa complex, formed by noncovalent association with a single nontoxin, nonhemagglutinin subunit and a family of hemagglutinating proteins. Previous work has suggested, although never conclusively demonstrated, that neurotoxin alone cannot survive passage through the stomach and/or cannot be absorbed from the gut without the involvement of auxiliary proteins in the complex. Therefore, this study compared the relative absorption and toxicity of three preparations of neurotoxin in an in vivo mouse model. Equimolar amounts of serotype A complex with hemagglutinins, complex without hemagglutinins, and purified neurotoxin were surgically introduced into the stomach or into the small intestine. In some experiments, movement of neurotoxin from the site of administration was restricted by ligation of the pylorus. Comparison of relative toxicities demonstrated that at adequate doses, complex with hemagglutinins, complex without hemagglutinins, and pure neurotoxin can be absorbed from the stomach. The potency of neurotoxin in complex was greater than that of pure neurotoxin, but the magnitude of this difference diminished as the dosage of neurotoxin increased. Qualitatively similar results were obtained when complex with hemagglutinins, complex without hemagglutinins, and pure neurotoxin were placed directly into the intestine. This work establishes that pure botulinum neurotoxin serotype A is toxic when administered orally. This means that pure neurotoxin does not require hemagglutinins or other auxiliary proteins for absorption from the gastrointestinal system into the general circulation.

Binding and transcytosis of botulinum neurotoxin by polarized human colon carcinoma cells

T-84 and Caco-2 human colon carcinoma cells and Madin-Darby canine kidney (MDCK) cells were used to study binding and transcytosis of iodinated Clostridium botulinum neurotoxin serotypes A, B, and C, as well as tetanus toxin. Specific binding and transcytosis were demonstrated for serotypes A and B in intestinal cells. Using serotype A as an example, the rate of transcytosis by T-84 cells was determined in both apical to basolateral (11.34 fmol/h/cm2) as well as basolateral to apical (8.98 fmol/h/cm2) directions, and by Caco-2 cells in the apical to basolateral (8.42 fmol/h/cm2) direction. Serotype A retained intact di-chain structure during transit through T-84 or Caco-2 cells, and when released on the basolateral side was toxic in vivo to mice and in vitro on mouse phrenic nerve-hemidiaphragm preparations. Serotype C and tetanus toxin did not bind effectively to T-84 cells, nor were they efficiently transcytosed (8-10% of serotype A). MDCK cells did not bind or efficiently transcytose (0.32 fmol/h/cm2) botulinum toxin. Further characterization demonstrated that the rate of transcytosis for serotype A in T-84 cells was increased 66% when vesicle sorting was disrupted by 5 microM brefeldin A, decreased 42% when microtubules were disrupted by 10 microM nocodazole, and decreased 74% at 18 degreesC. Drugs that antagonize toxin action at the nerve terminal, such as bafilomycin A1 (which prevents acidification of endosomes) and methylamine HCl (which neutralizes acidification of endosomes), produced only a modest inhibitory effect on the rate of transcytosis (17-22%). These results may provide an explanation for the mechanism by which botulinum toxin escapes the human gastrointestinal tract, and they may also explain why specific serotypes cause human disease and others do not.