Tetanus neurotoxin system

A second example of a toxin that has been used as targeting device is tetanus toxin. Tetanus toxin is a potent neurotoxin, which can undergo uptake in the nerve endings of motor neurones and subsequent retrograde transport into the central nervous system. The nontoxic C-fragment of tetanus toxin (TTC,451 amino acids), has been used to increase the neuronal uptake of the therapeutic protein SOD [57]. Following intravenous infusion, the recombinant hybrid protein reduced the occurrence of ischaemia-induced cerebral infarction in rats [58]. 

Tetanus is characterised by a prolonged contraction of skeletal muscle fibres the neurotoxin responsible is from Clostridium tetani. The toxin initially binds to peripheral nerve terminals and is then transported within the axon and across synaptic junctions until it reaches the central nervous system (CNS). Here it attaches to ganghosides at the presynaptic inhibitory motor nerve endings and is taken up into the axon by endocytosis. The effect of the toxin is to block the release of inhibitory neurotransmitters (glycine and gamma-amino butyric acid), which are required to check the nervous impulse, leading to the generalised muscular spasms characteristic of tetanus. 

Clostridial neurotoxins are very toxic. However they are ineffective in individuals immunized with the corresponding toxoids. In most countries children are vaccinated with tetanus toxoid and this is sufficient to provide full protection against tetanus for decades. A booster injection of tetanus toxoid (available from health authorities) before starting research with TeTx is advisable. On the other hand, the vaccine for BoNT/A, B, C, D and E is not commercially available, but can be obtained from the Center for Disease Control (CDC, Atlanta, GA). Due to the rather low efficacy of the BoNTs vaccine, a protective serum anti-BoNT titre is generally, but not always, achieved. Human anti-TeTx antibodies and horse anti-BoNT antibodies are also available from health authorities, and their injection immediately after accidental penetration of the toxin into the circulatory system is sufficient to prevent the disease. 

Kistner A, Habermann E (1992) Reductive cleavage of tetanus toxin and botulinum neurotoxin A by the thioredoxin system from brain. Evidence for two redox isomers of tetanus toxin. Naunyn. Schmiedebergs Arch. Pharmacol. 345 227-34... 

Clostridium tetani, produces another deadly neurotoxin. Tetanus toxin causes severe paralysis by blocking neurotransmitter release (primarily glycine and y-aminobutyric acid) in the central nervous system. 

Habermann E. Clostridial neurotoxins and the central nervous system Functional studies on isolated preparations. In Simpson LL, ed. Botulinum Neurotoxin and Tetanus Toxin. New York, NY Academic Press, Inc 1989 53-67. 

Primary cultures of spinal cord represent a convenient and sensitive system to study mechanisms of neurotransmitters release [11,12]. Internalized neurotransmitters by spinal cord neurons in culture were released quantitatively in response to depolarization and Ca2+. This release is inhibited by tetanus toxin and bot-ulinum neurotoxins in a concentration- and time-dependent manner [13-17]. Therefore, this system serves as a suitable model to examine the efficacy of prospective BoNT countermeasures. Sheridan and Adler indicated that the evoked release of neurotransmitters, notably glycine, in this system was time-dependently increased [18]. In our studies, there was a pronounced time-dependent increase of the drug carrier separation from DDV, which paralleled an enhancement of transmitter release. 

Tetanus Toxin (TTFC) The tetanus toxin is a neurotoxin produced by Clostridium tetani under certain conditions. The use of L. lactis as a live protein delivery vector was first published by Wells et al. with the fragment C of tetanus toxin (TTFC) to provide a proof-of-concept (Wells et al. 1993a). Mice immunized with subcutaneous injection of L. lactis strains producing TTFC were successfully protected against lethal challenge with tetanus toxin. Both oral (Robinson et al. 1997) and nasal (Norton et al. 1997) administration strategies induced similar systemic antibody responses at protective levels, albeit oral immunization produced lower serum IgG and mucosal IgA antibodies compared to nasal immunization. 

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