Clostridial toxins as therapeutic agents: benefits of nature's most toxic proteins

[Mode of action of botulinum neurotoxin: pathological, cellular and molecular aspect]

Several bacteria of the Clostridium genus (C. botulinum) produce 150 kDa di-chainal protein toxins referred as botulinum neurotoxins or BoNTs. They associate with non-toxic companion proteins and form a complex termed botulinum toxin or BoTx. The latter is used in clinic for therapeutic purpose. BoNTs affect cholinergic nerve terminals in periphery where they block acetylcholine release, thereby causing dysautonomia and motorparalysis (i.e. botulism). The cellular action of BoNTs can be depicted according to a three steps model: binding, internalisation and intraneuronal action. The toxins heavy chain mediates binding to specific receptors followed by endocytotic internalisation of BoNT/receptor complex. BoNT receptors may comprise gangliosides and synaptic vesicle-associated proteins as synaptotagmins. Vesicle recycling induces BoNT internalisation. Upon acidification of vesicles, the light chain of the neurotoxin is translocated into the cytosol. Here, this zinc-endopeptidase cleaves one or two among three synaptic proteins (VAMP-synaptobrevin, SNAP25, and syntaxin). As the three protein targets of BoNT play major role in fusion of synaptic vesicles at the release sites, their cleavage is followed by blockage of neurotransmitter exocytosis. The duration of the paralytic effect of the BoNTs is determined by 1) the turnover of their protein target; 2) the time-life of the toxin light chain in the cytosol, and 3) the sprouting of new nerve-endings that are retracted when the poisoned nerve terminal had recovered its full functionality.

East-west differences in the organization of botulinum toxin use in nine Central European countries

Availability and quality of expensive treatment modalities such as botulinum toxin (BTX) largely depend on organizational aspects such as costs, reimbursement by insurance companies, expertise and facilities for expert training, and the propagation of research. To investigate which determinants influence the organization of BTX' use throughout nine Central European countries (Austria, Croatia, Czech Republic, Germany, Hungary, Italy, Slovakia, Slovenia and Switzerland) we sent out questionnaires to leading BTX experts and consulted data banks of manufacturers and bulletins of international organizations. In Western European countries, there is a tendency for users to organize themselves in formal groups and to concentrate on research whereas the way how BTX is provided is diverse regarding qualifications of specialists and institutions. In the post-communist Eastern European countries, we found a tendency towards a centralized system of reimbursement and BTX treatment seems to be more in the hands of neurologists than any other specialists. Strong correlations were observed between the number of BTX centres, degree of organization of user groups and number of scientific publications, on the one hand, and parameters of healthcare performance and socioeconomic determinants, on the other. Our study suggests that in the nine countries surveyed, organizational aspects of BTX use vary considerably, whilst similarities are based mainly on socioeconomic rather than socio-demographic determinants.

Toxicity of botulinum neurotoxins in central nervous system of mice

Botulinum neurotoxins (BoNTs) act specifically on cholinergic nerve terminals, where they cause a sustained block of acetylcholine release, and therefore they are powerful tools to study the role of cholinergic neurons in neuronal processes. Peripheral effects of BoNTs are widely documented while central effects have not been studied. Here, we report for the first time on the central toxicity of BoNT serotypes A and B following their direct intracerebroventricular (icv) injection in CD1 mice. The LD50 values were found to be in the range 0.5-1.0 x 10(-6)mg/kg. We recorded the following signs preceding animal death: piloerection and weight decrease appear first, followed by temperature decrease, eyelid closure, loss of sensorimotor reflexes, dehydration, dyspnea. Mice died of heart or respiratory failure. The surviving mice recovered completely within 4-6 days and regained the initial healthy conditions. At sub-lethal doses, the same clinical signs appear in a lighter form and with a longer time course.

Silanediol-based inhibitor of thermolysin

The first silanediol inhibitor of thermolysin is reported, prepared by analogy with the Grobelny/Bartlett phosphinate inhibitor. A Cbz group on nitrogen proved to be unstable to the triflic acid mediated silanediol deprotection and was replaced with a dihydrocinnamoyl group. The silanediol was prepared in high purity by hydrolysis of a difluorosilane intermediate and proved to be an effective inhibitor, differing from the phosphinate by a factor of 4 (K(i)=41nM).

Botulinum and tetanus neurotoxins: structure, function and therapeutic utility

The toxic products of the anaerobic bacteria Clostridium botulinum, Clostridium butyricum, Clostridium barati and Clostridium tetani are the causative agents of botulism and tetanus. The ability of botulinum neurotoxins to disrupt neurotransmission, often for prolonged periods, has been exploited for use in several medical applications and the toxins, as licensed pharmaceutical products, now represent the therapeutics of choice for the treatment for several neuromuscular conditions. Research into the structures and activities of botulinum and tetanus toxins has revealed features of these proteins that might be useful in the design of improved vaccines, effective inhibitors and novel biopharmaceuticals. Here, we discuss the relationships between structure, mechanism of action and therapeutic use.

Inhibition of release of neurotransmitters from rat dorsal root ganglia by a novel conjugate of a Clostridium botulinum toxin A endopeptidase fragment and Erythrina cristagalli lectin

Clostridial neurotoxins potently and specifically inhibit neurotransmitter release in defined cell types. Here we report that a catalytically active derivative (termed LH(N)/A) of the type A neurotoxin from Clostridium botulinum has been coupled to a lectin obtained from Erythrina cristagalli to form a novel conjugate. This conjugate exhibits an in vitro selectivity for nociceptive afferents compared with the anatomically adjacent spinal neurons, as assessed using in vitro primary neuronal culture systems to measure inhibition of release of neurotransmitters. Chemical conjugates prepared between E. cristagalli lectin and either natively sourced LH(N)/A or recombinant LH(N)/A purified from Escherichia coli are assessed, and equivalence of the recombinant material are demonstrated. Furthermore, the dependence of inhibition of neurotransmitter release on the cleavage of SNAP-25 is demonstrated through the use of an endopeptidase-deficient LH(N)/A conjugate variant. The duration of action of inhibition of neurotransmitter released by the conjugate in vitro is assessed and is comparable with that observed with Clostridium botulinum neurotoxin. Finally, in vivo electrophysiology shows that these in vitro actions have biological relevance in that sensory transmission from nociceptive afferents through the spinal cord is significantly attenuated. These data demonstrate that the potent endopeptidase activity of clostridial neurotoxins can be selectively retargeted to cells of interest and that inhibition of release of neurotransmitters from a neuronal population of therapeutic relevance to the treatment of pain can be achieved.

Botulinum neurotoxin A activity is dependent upon the presence of specific gangliosides in neuroblastoma cells expressing synaptotagmin I

Botulinum neurotoxin A (BoNT/A) is the deadliest of all known biological substances. Although its toxicity makes BoNT/A a biological warfare threat, its biologic activity makes it an increasingly useful therapeutic agent for the treatment of muscular disorders. However, almost 200 years after its discovery, the neuronal cell components required for the activity of this deadly toxin have not been unequivocally identified. In this work, neuroblastoma cells expressing synaptotagmin I, a protein shown to be bound by BoNT/A, were used to determine whether specific gangliosides were necessary for BoNT/A activity as measured by synaptosomal-associated protein of 25 kDa (SNAP-25) cleavage. Ganglioside GT1b was found to support BoNT/A activity significantly more effectively than GD1a, which was far more effective than GM1 when added to ganglioside-deficient murine cholinergic Neuro 2a or to human adrenergic SK-N-SH neuroblastoma cells. Whereas both cell lines expressed synaptotagmin I, SNAP-25 cleavage was not observed in the absence of complex gangliosides. These results indicate that 1) gangliosides are required for BoNT/A activity, 2) synaptotagmin I in the absence of gangliosides does not support BoNT/A activity, and 3) Neuro 2a cells are an efficient model system for studying the biological activity of BoNT/A.

The crystal structure of tetanus toxin Hc fragment complexed with a synthetic GT1b analogue suggests cross-linking between ganglioside receptors and the toxin

Tetanus toxin, a member of the family of Clostridial neurotoxins, is one of the most potent toxins known. The crystal structure of the complex of the COOH-terminal fragment of the heavy chain with an analogue of its ganglioside receptor, GT1b, provides the first direct identification and characterization of the ganglioside-binding sites. The ganglioside induces cross-linking by binding to two distinct sites on the Hc molecule. The structure sheds new light on the binding of Clostridial neurotoxins to receptors on neuronal cells and provides important information relevant to the design of anti-tetanus and anti-botulism therapeutic agents.

Botulinum toxin therapy for pain and inflammatory disorders: mechanisms and therapeutic effects

Botulinum toxin (BTX) injections are a well-recognised therapeutic modality for the treatment of regional involuntary muscle disorders and recently BTX has been used for treatment of pain and inflammatory disorders. The primary purpose of this review is to discuss the mechanism of action of therapeutic BTX in light of both the traditional understanding of BTX pharmacological effects as well as new observations. The review will deal with clinical observations and relevant animal experimentation. The data and hypotheses presented are not only relevant to botulinum toxin technology but will certainly prove important in the basic mechanisms of some of the diseases where botulinum toxin has been successfully applied. BTX used clinically comprises botulinum neurotoxin (BoNT) complexed with non-toxic proteins. The non-toxic components of the BTX complexes stabilise the labile BoNT during purification and formulation as a therapeutic. The complex proteins may also have unrecognised clinical significance such as slowing diffusion in tissues or imparting stability. The mechanisms of BTX formulations acting on SNARE proteins are briefly reviewed providing a basis for BTX clinical applications. The potential for design of improved botulinum toxins and formulations is addressed.