An improved method for development of toxoid vaccines and antitoxins

Botulinum neurotoxins are the most potent toxins known and causative agents of human botulism. Treatment comprises of administering purified polyclonal antitoxin or the prophylactic use of a vaccine containing formaldehyde inactivated toxoid. Whilst formaldehyde inhibits toxin activity, it induces so many structural changes in the molecule that immunisation often results in low levels of neutralising antibodies. We describe here for the first time a simple, less time consuming, novel method for producing a non-toxic toxoid that is structurally and antigenically more similar to the native toxin. Toxin is chemically inactivated by alkylation with iodoacetamide in the presence of reversibly denaturing conditions. This reduces neurotoxic activity by at least 7-orders of magnitude to undetectable levels. Following immunisation, in vivo neutralising antibody levels were 600-times higher than those produced with formaldehyde toxoid, despite generating equivalent ELISA antitoxin binding titres. These studies demonstrate that the new toxoid retains more of the native toxins structure and critical epitopes responsible for inducing life-saving neutralising antibody. Toxoid produced by the new method should substantially improve both antitoxin and vaccine production and be applicable to other toxins and immunogens.

First report of homoanatoxin-a and associated dog neurotoxicosis in New Zealand

In November 2005, at least five dogs died rapidly after contact with water from the Hutt River (lower North Island, New Zealand). Necropsy performed 24h later on one of the dogs (a 20-month-old Labrador) revealed few findings of interest, except for copious amounts of froth in the respiratory tract down to the bifurcation of the trachea and large quantities of algal material in the dog's stomach. Low and relatively stable flows in the Hutt River during spring had resulted in the proliferation of benthic cyanobacteria that formed large black/brown mats along the river edge. Samples from the Labrador's stomach contents and cyanobacterial mats were analysed microscopically and screened using chemical and biochemical assays for cyanotoxins: anatoxin-a, homoanatoxin-a, cylindrospermopsins, saxitoxins and microcystins. Liquid chromatography-mass spectrometry (LC-MS) confirmed the presence of the neurotoxic cyanotoxins anatoxin-a and homoanatoxin-a and their degradation products, dihydro-anatoxin-a and dihydro-homoanatoxin-a. This is the first report of homoanatoxin-a and associated degradation product in New Zealand. Based on morphology, the causative species was identified as Phormidium sp. Subsequent phylogenetic analysis of 16S rRNA gene sequences demonstrated that the causative organism was most similar to Phormidium autumnale. Further investigations led to the detection of homoanatoxin-a and anatoxin-a in cyanobacterial mats from four other rivers in the Wellington region (lower North Island, New Zealand). Access restrictions were placed on over 60% of river catchments in the western Wellington region, severely affecting recreational users.

Changing a single amino acid in Clostridium perfringens beta-toxin affects the efficiency of heterologous secretion by Bacillus subtilis

Achieving efficient heterologous protein production and secretion by Bacillus subtilis is an attractive prospect, although often disappointingly low yields are reached. The expression of detoxified Clostridium perfringens beta-toxin (beta-toxoid) is exemplary for this. Although beta-toxin can be efficiently expressed and secreted by Bacillus subtilis, the genetically detoxified, and industrially interesting, beta-toxoid variant is difficult to obtain in high amounts. To optimize the expression of this putative vaccine component, we studied the differences in the global gene regulation responses of B. subtilis to overproduction of either beta-toxin or beta-toxoid by transcriptomics. A clear difference was the upregulation of the CssRS regulon, known to be induced upon secretion stress, when beta-toxoid is produced. YkoJ, a protein of unknown function, was also upregulated, and we show that its expression is dependent on cssS. We then focused on the heterologous protein itself and found that the major secretion bottleneck can be traced back to a single amino acid substitution between the beta-toxin and the beta-toxoid, which results in the rapid degradation of beta-toxoid following secretion across the cytoplasmic membrane. In contrast to beta-toxin, beta-toxoid protein is more prone to degradation directly after secretion, most likely due to poor folding characteristics introduced with point mutations. Our results show that although the host can be adapted in many ways, the intrinsic properties of a heterologous protein can play a decisive role when optimizing heterologous protein production.

Development of a carbohydrate binding assay for the B-oligomer of pertussis toxin and toxoid

Pertussis toxin (PTx) is a major virulence factor produced by Bordetella pertussis and, in its detoxified form PTd, is an important component of pertussis vaccines. The in vivo histamine sensitization test (HIST) is currently used for the safety testing of these vaccines. However, an alternative test is needed because of large assay variability and ethical concerns with regard to animal usage. PTx has two functionally distinct domains: the enzymatic A-protomer and the B-oligomer that facilitates host-cell binding and entry of PTx into the cell. The development of a quantitative PTx binding assay using glycoproteins or defined oligosaccharides is reported. PTx was found to bind preferentially to multiantennary N-glycans, with the highest binding toward the fully sialylated structures. In contrast, PTd lost the ability of PTx to bind to sialylated multiantennary structures but retained some capacity to bind to neutral multiantennary structures. The developed assay was shown to be specific, sensitive, and robust and could be used for investigating the mechanisms of PTx detoxification and for monitoring PTx binding activity in vaccine formulations. This assay could also be used to complement a PTx-enzymatic assay, developed recently, and together they may form the basis of a potential alternative in vitro assay to replace the in vivo HIST.

Anatoxins and degradation products, determined using hybrid quadrupole time-of-flight and quadrupole ion-trap mass spectrometry: forensic investigations of cyanobacterial neurotoxin poisoning

The potent neurotoxins from cyanobacteria, anatoxin-a (AN), its methyl analogue, homoanatoxin-a (HMAN), and their degradation products, have been studied using nano-electrospray hybrid quadrupole time-of-flight mass spectrometry (QqTOF-MS). The anatoxin degradation products, which are readily produced in vivo by either reduction or epoxidation, were also examined in this study. The high mass accuracy QqTOF-MS data was used to confirm formula assignments for major product ions and quadrupole ion-trap (QIT)-MS was used to construct fragmentation pathways for anatoxins. Significant differences between these fragmentation pathways were observed. Comparisons between the spectra of compounds that differ in side-chain length (the AN and HMAN series) were used to identify ions that are characteristic of the homologues. The application to forensic samples in which the principal neurotoxin had undergone rapid biodegradation has been demonstrated and used to confirm anatoxin poisoning of dogs.

Production of Secondary Metabolites by Freshwater Cyanobacteria

Freshwater cyanobacteria produce lethal toxins such as microcystins and anatoxins. During the purification of microcystins in bloom samples we found that a toxic cyanobacterium produced not only microcystins but also other types-peptides in early 1990. Since then we have isolated approximately thirty peptides from freshwater cyanobacteria. In this manuscript we focused on the following topics concerning the isolated peptides: 1) how to isolate desired compounds and to determine their structures, 2) structural classification of isolated compounds, 3) isolation of similar peptides from laboratory strains and bloom materials, 4) structurally related peptides from freshwater and marine origins, 5) beta-amino acid containing peptides from cyanobacteria, 6) comprehensive analysis system for the biosynthetic study of peptides produced by cyanobacteria, 7) biological activities of isolated compounds.

Microbial transformation of baccatin VI and 1β-Hydroxy baccatin I by aspergillus niger

The biotransformation of baccatin VI (1) and 1beta-hydroxybaccatin I (2) with the filamentous fungus Aspergillus niger produced four new taxane diterpenoids taxumairol S(1) (3), taxumairol T(1) (4) and taxumairol S (5), taxumairol T (6), respectively. 1beta-Dehydroxybaccatin VI (7) remained unreacted under the same condition.

Effects of adsorption of acellular pertussis antigens onto different aluminium salts on the protective activity in an intranasal murine model of Bordetella pertussis infection

Adsorption of the pertussis antigens, pertussis toxoid (PT), filamentous hemagglutinin (FHA) and pertactin (PRN) onto aluminium phosphate rather than aluminium hydroxide leads to a lower humoral response and poorer protection against intranasal pertussis challenge in mice. These effects could be reversed by inclusion of fimbriae (FIM) 2 and 3 in the formulation. These data emphasis the importance of correct formulation for such vaccines.

Molecular basis for the cross-reactivity of antibodies elicited by a natural anatoxin with alpha- and beta-toxins from the venom of Tityus serrulatus scorpion

A non-toxic protein (TsNTxP) isolated from the venom of the noxious scorpion Tityus serrulatus (Ts) induces polyclonal antibodies cross-reactive with several toxins from the venom, in sharp contrast to anti-toxin antibodies which are toxin specific. To try to uncover the molecular basis for these unusual properties, peptide scanning experiments were performed and indicated that the N- and C-terminal parts of TsNTxP enclose continuous epitopes (residues 1-15 and 47-61). Antibodies raised against peptides corresponding to these two regions were found to have neutralizing properties against a mixture of all toxic proteins from the T. serrulatus venom, indicating that residues 1-15 and 47-61 correspond to neutralizing epitopes. The identification of key antigenic residues within these two epitopes revealed that several of them are well conserved in the amino-acid sequences of the three main toxins (Ts II, Ts IV and Ts VII) from the venom: Glu 3, Tyr 5, Asp 8, Asp 50, Trp 55 and Lys 61. A single key-residue (Glu 58) is unique to TsNTxP. By using homology modeling, a model of the three-dimensional structure of TsNTxP was obtained. The antigenically important residues from TsNTxP were found to be surface exposed, with five of them clustered on the facet of the protein reported to enclose the active site of toxins. Residues equivalent to the seven key-residues of the anatoxin were also found to be exposed in the active toxins from T. serrulatus venom. These results show that antibodies elicited by the non-toxic protein TsNTxP recognized, within the N- and C-terminal parts of toxins of T. serrulatus, conserved and surface exposed residues which might also be involved in the toxic action of the proteins.

Stability of Russell's viper venom toxoid (lyophilized form) on storage

A previously developed Russell's viper venom toxoid in Myanmar is in a liquid form that shows reversion in the form of a reduced number of formaldehyde linkages and toxicity during storage at 37 degrees C and at room temperature. In order to have a safe, potent and stable toxoid, a lyophilized form was prepared in the present study from the liquid toxoid through the use of a freeze dryer. Both the liquid and lyophilized forms were then stored at 4 degrees C and at room temperature, and in addition to safety and immunogenicity tests, biochemical parameters such as the protein content, the activity of venom enzymes (proteinase, phospholipase A, phosphodiesterase, and arginine esterase), and the released free formalin amounts were assessed at 3-month intervals over a period of 1 year. The results indicate that under both conditions, the lyophilized toxoid shows minimum changes in enzyme activity, a reduced tendency toward formaldehyde linkage, no toxicity, and more immunogenicity in comparison with the respective liquid toxoids. It could therefore be hypothesized that Russell's viper venom toxoid in a lyophilized form is more promising in terms of efficacy and stability for prophylactic use in human immunization than the conventional toxoid in a liquid form.

Transformation of a non-enzymatic toxin into a toxoid by genetic engineering

Curaremimetic toxins are typical non-enzymatic toxins that bind to their target [the nicotinic acetylcholine receptor (AChR)] through multiple residues. Nevertheless, we show that the concomitant substitutions of only three of the ten functionally important residues of such a toxin sufficed to cause an affinity decrease of the toxin for AChR that is higher than four orders of magnitude. Despite these triple mutations, the overall conformation of the mutated protein remains similar to that of a related recombinant toxin, as judged from both circular dichroism analysis and investigation of antigenicity, using monoclonal and polyclonal antibodies. Furthermore, we show that the detoxified toxin is capable of eliciting antibodies that neutralize the binding of a wild-type toxin to AChR. Therefore, transformation of a non-enzymatic toxin into a toxoid can be achieved, like in the case of enzymatic toxins, by introducing a small number of mutations at positions identified to be critical for expression of toxicity.

Molecular characterization, antigenicity and immunogenicity of anatoxic polymeric forms conferring protection against scorpion venoms

Two polymeric forms of Buthus occitamus tunetanus (Bot) G-50 and Androctonus australis hector (Aah) G-50 were obtained by controlled polymerization with glutaraldehyde. Their mol. wts, determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and exclusion high-performance liquid chromatography using radiolabelled toxin, ranged from 14,000 to 90,000 and 90,000 to 100,000 for Aah G-50 and Bot G-50, respectively. Modification of about 20% of the lysine residues yielded completely detoxified Bot G-50 fractions which retained the antigenic cross-reactivity with the native G-50 fraction, venom and toxins. High levels of specific antibodies against venoms and toxins were generated by immunization with prepared polymeric forms because absorbance values higher than 3 units were regularly observed by enzyme-linked immunosorbent assay with immune sera dilutions of 1/10,000. In vitro protection experiments demonstrated that immune sera from mice, horse and monkeys efficiently neutralized either Aah or Bot venom. Depending on the adjuvant and animal model species used, the neutralizing titre estimated by subcutaneous injection in mice varied between 20 and 40 LD50/ml. The in vivo protection assays showed that immunized mice could resist the challenge by six times the LD50 amounts of the toxic fraction. This protection was found to be long-lived. It was concluded that G-50 polymeric forms are highly detoxified and immunogenic, and should be useful for the production of potent polyvalent antivenom against scorpion toxins. They could also be considered for further studies towards the development of vaccine candidates.

The nucleotide and deduced amino acid sequences of EcoRI fragment containing the 5'-terminal region of Clostridium botulinum type E toxin gene cloned from Mashike, Iwanai and Otaru strains

Chromosomal DNAs were extracted from toxigenic three Clostridium botulinum type E strains isolated from food-borne botulism. After digestion by EcoRI, the fragments were cloned into Escherichia coli by using bacteriophage lambda gt11 and screened with monoclonal antibody recognizing the light chain component of botulinum type E toxin. The fragments (about 1 kbp size) cloned from each strain were recloned into a plasmid vector pUC118. The E. coli cells transformed with the recombinant plasmids produced 33 kDa protein with or without IPTG (isopropyl-beta-D-thiogalactopyranoside) which reacted with the monoclonal antibody. The nucleotide sequences of the cloned EcoRI fragments from the three type E strains were identical and contain the 5'-terminal region of the type E toxin gene. It was also found that there exist several highly homologous nucleotide sequences among the botulinum types A, C and E, and tetanus toxin genes in both translated and untranslated regions.