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In vitro determination of specific toxicity in tetanus vaccines
B Kegel1, U Bonifas, K Silberbach
1Paul-Ehrlich-Institute, Federal Agency for Sera and Vaccines, Langen, Germany.
Abstract:
Tetanus vaccine is prepared from detoxified tetanus neurotoxin. To ensure the absence of residual toxin activity or to exclude the reversion to toxicity reliable control testing is based on in vivo methods, because no in vitro assay provides the required specificity and sensitivity. Tetanus neurotoxin is a 150 kDa protein produced by Clostridium tetani. The 50 kDa light chain of this neurotoxin belongs to the family of zinc metalloproteases. It cleaves synaptobrevin, a small synaptic vesicle protein, which is involved in neuroexocytosis, at the single Q76-F77 peptide bond. To develop a sensitive in vitro assay capable of quantifying the proteolytic activity of this toxin, we used as substrate a recombinant fragment of synaptobrevin2 (1-97). For detecting the cleavage products a peptide antibody raised against the N-terminal cleavage site was used. In Western Blot analysis only the cleaved substrate was detected while the uncleaved substrate showed no signal. In different approaches, recombinant synaptobrevin was either (i) bound to a microtitre plate, reduced toxin was added and the N-terminal cleavage product was detected by a specific antibody or (ii) the cleavage was performed in test tubes, the samples were transferred to a microtitre plate and immobilised cleavage products were detected. When toxoid or crude toxin is used, non-specific cleavage of synaptobrevin substrate occurs. Depending on the toxoid used different patterns of degradation of substrate are visible in Western Blots. Different protease inhibitors and reaction conditions seem to have an effect on the inhibition of this non-specific cleavage.
Insights
Researchers developed a sensitive in vitro assay to quantify tetanus neurotoxin activity. This assay detects the toxin
Area of Science:
- Biochemistry
- Neuroscience
- Immunology
Background:
- Tetanus vaccines rely on detoxified tetanus neurotoxin, with current safety testing primarily using in vivo methods due to limitations in in vitro assays.
- Tetanus neurotoxin, a 150 kDa protein from Clostridium tetani, features a 50 kDa light chain with zinc metalloprotease activity.
- This light chain specifically cleaves synaptobrevin, a key protein in neuroexocytosis, at the Q76-F77 peptide bond.
Purpose of the Study:
- To develop a sensitive in vitro assay for quantifying the proteolytic activity of tetanus neurotoxin.
- To establish a reliable method for detecting residual toxin activity in vaccines, overcoming the limitations of current in vivo testing.
Main Methods:
- Utilized a recombinant fragment of synaptobrevin2 (amino acids 1-97) as a substrate to detect tetanus neurotoxin's enzymatic activity.
- Employed a peptide antibody targeting the N-terminal cleavage site of synaptobrevin for sensitive detection of cleavage products.
- Investigated two approaches: immobilizing the substrate on a microtitre plate or performing cleavage in solution followed by plate immobilization and detection.
Main Results:
- Western Blot analysis successfully detected only cleaved substrate, indicating high specificity for the toxin's activity.
- The developed assay demonstrated sensitivity in quantifying proteolytic activity, distinguishing between cleaved and uncleaved synaptobrevin.
- Observed non-specific cleavage of the synaptobrevin substrate when using toxoid or crude toxin, influenced by reaction conditions and protease inhibitors.
Conclusions:
- A sensitive and specific in vitro assay for quantifying tetanus neurotoxin proteolytic activity has been successfully developed.
- This assay holds potential for improving vaccine safety by reliably detecting residual toxin activity, complementing or potentially replacing in vivo methods.
- Further research is needed to optimize conditions and address non-specific cleavage observed with toxoids and crude toxins.