Transport of bacterial toxins into target cells: pathways followed by cholera toxin and botulinum progenitor toxin

Immunogenicity of botulinum toxin

Botulinum toxin treatment is the most common non-surgical cosmetic treatment. Although there are many available treatments using botulinum toxin, their effects are temporary and repeated injections are required. These frequent injections can trigger an immunological response. In addition, botulinum toxin acts as an antigen in the body; thus, its effect disappears progressively due to this immunological reaction, which may cause treatment failure. Active botulinum toxin consists of a core neurotoxin and complexing proteins, the exact effects of which remain unclear. However, the complexing proteins are closely related to the immune response and the formation of neutralizing antibodies. Since neutralizing antibodies can lead to treatment failure, their formation should be prevented. Furthermore, various methods of detecting neutralizing antibodies have been used to predict treatment failure.

Do complexing proteins provide mechanical protection for botulinum neurotoxins?

Botulinum toxin (BT) consists of botulinum neurotoxin and complexing proteins (CPs). CPs might provide mechanical protection for botulinum neurotoxin. As incobotulinumtoxinA (INCO, Xeomin®) does not contain CPs, we wanted to compare its mechanical stability to that of onabotulinumtoxinA (ONA, Botox®) containing CPs. For this, ONA and INCO were reconstituted without mechanical stress (NS) and with mechanical stress (WS) generated by a recently introduced stress test. Potencies were then measured by the paralysis times (PTs) in the mouse diaphragm assay. ONA-PT was 75.8 ± 10.3 min (n = 6) under NS and 116.7 ± 29.8 min (n = 6) under WS (two-tailed t test, p = 0.002). Mechanical stress increased the ONA-PT by 35.0% on the Growth Percentage Index. INCO-PT was 66.0 ± 7.0 min for NS and 76.0 ± 1.0 min for WS (t test, p = 0.129). Mechanical stress increased the INCO-PT by 13.2% on the Growth Percentage Index. Our data show that mechanical stress inactivates a CP-containing BT drug, but not a CP-free BT drug. We conclude that CPs do not provide protection against mechanical stress, supporting the view that CPs are not necessary for therapeutic purposes.

Shiga toxin-glycosphingolipid interaction: Status quo of research with focus on primary human brain and kidney endothelial cells

Shiga toxin (Stx)-mediated injury of the kidneys and the brain represent the major extraintestinal complications in humans upon infection by enterohemorrhagic Escherichia coli (EHEC). Damage of renal and cerebral endothelial cells is the key event in the pathogenesis of the life-threatening hemolytic uremic syndrome (HUS). Stxs are AB₅ toxins and the B-pentamers of the two clinically important Stx subtypes Stx1a and Stx2a preferentially bind to the glycosphingolipid globotriaosylceramide (Gb3Cer, Galα4Galβ4Glcβ1Cer) and to less extent to globotetraosylceramide (Gb4Cer, GalNAcβ3Galα4Galβ4Glcβ1), which are expected to reside in lipid rafts in the plasma membrane of the human endothelium. This review summarizes the current knowledge on the Stx glycosphingolipid receptors and their lipid membrane ensemble in primary human brain microvascular endothelial cells (pHBMECs) and primary human renal glomerular endothelial cells (pHRGECs). Increasing knowledge on the precise initial molecular mechanisms by which Stxs interact with cellular targets will help to develop specific therapeutics and/or preventive measures to combat EHEC-caused diseases.

Botulinum neurotoxin formulations: overcoming the confusion

Botulinum toxin A is produced by anaerobic spore-forming bacteria and is used for various therapeutic and cosmetic purposes. Botulinum toxin A injections are the most popular nonsurgical procedure worldwide. Despite an increased demand for botulinum toxin A injections, the clinical pharmacology and differences in formulation of commonly available products are poorly understood. The various products available in the market are unique and vary in terms of units, chemical properties, biological activities, and weight, and are therefore not interchangeable. For safe clinical practice and to achieve optimal results, the practitioners need to understand the clinical issues of potency, conversion ratio, and safety issues (toxin spread and immunogenicity). In this paper, the basic clinical pharmacology of botulinum toxin A and differences between onabotulinum toxin A, abobotulinum toxin A, and incobotulinum toxin A are discussed.

Viral hemorrhagic septicemia virus glycoprotein production in tobacco

Viral hemorrhagic septicemia virus (VHSV) causes mortality in numerous marine and freshwater fish species resulting in heavy losses in fish farming. The glycoprotein gene of VHSV was fused with the cholera toxin B subunit (CTB) and expressed transiently in leaf tissues of Nicotiana benthamiana via the agroinfiltration method. The glycoprotein gene was divided into two parts to improve assembly of CTB fusion proteins (CTB-VHSV99-235 and CTB-VHSV258-417). Production of CTB fusion proteins was confirmed in the agroinfiltrated leaf tissue by western blot analysis. The plant-produced CTB fusion proteins showed biological activity to GM1-ganglioside, a receptor for biologically active CTB, on GM1-ELISA. The expression level of the CTB-VHSV fusion proteins was 0.86% (CTB-VHSV99-235) and 0.93% (CTB-VHSV258-417) of total proteins in agroinfiltrated leaf tissue, as determined by GM1-ELISA. These results suggest that Agrobacterium-mediated transient expression of CTB fusion antigens of VHSV is a rapid and convenient method and demonstrate the feasibility of using agroinfiltrated plant leaf tissues expressing CTB-fusion antigens as a plant-based vaccine to prevent VHSV infection.

Paclitaxel is an inhibitor and its boron dipyrromethene derivative is a fluorescent recognition agent for botulinum neurotoxin subtype A

We have successfully identified one new inhibitor and one new fluorescent recognition agent for the botulinum neurotoxin subtype A (BoNT/A) using the virtual screening protocol "protein scanning with virtual ligand screening" (PSVLS). Hit selection used an in-house developed holistic binding scoring method. Selected hits were tested experimentally for inhibitory activity using fluorescence resonance energy transfer (FRET) assays against the light chain (catalytic domain) of BoNT/A. Ligand binding was determined against the light and heavy chain BoNT/A complex through either radiolabeled ligand binding assays (nonfluorescent ligands) or fluorescence intensity assays (fluorescent ligands). These experimental assays have confirmed one compound (paclitaxel) to inhibit BoNT/A's proteolytic activity experimentally with an IC50 of 5.2 μM. A fluorescent derivative was also confirmed to bind to the toxin and therefore is a suitable candidate for the rational design of new detection agents and for the development of fluorescence-based multiprobe detection assays.

Facing glycosphingolipid-Shiga toxin interaction: dire straits for endothelial cells of the human vasculature

The two major Shiga toxin (Stx) types, Stx1 and Stx2, produced by enterohemorrhagic Escherichia coli (EHEC) in particular injure renal and cerebral microvascular endothelial cells after transfer from the human intestine into the circulation. Stxs are AB(5) toxins composed of an enzymatically active A subunit and the pentameric B subunit, which preferentially binds to the glycosphingolipid globotriaosylceramide (Gb3Cer/CD77). This review summarizes the current knowledge on Stx-caused cellular injury and the structural diversity of Stx receptors as well as the initial molecular interaction of Stxs with the human endothelium of different vascular beds. The varying lipoforms of Stx receptors and their spatial organization in lipid rafts suggest a central role in different modes of receptor-mediated endocytosis and intracellular destiny of the toxins. The design and development of tailored Stx neutralizers targeting the oligosaccharide-toxin recognition event has become a very real prospect to ameliorate or prevent life-threatening renal and neurological complications.

Construction of recombinant lactobacilli expressing the core neutralizing epitope (COE) of porcine epidemic diarrhea virus and a fusion protein consisting of COE and Escherichia coli heat-labile enterotoxin B, and comparison of the immune responses by orogastric immunization

The core neutralizing epitope (COE) region of porcine epidemic diarrhea virus (PEDV) plays an important role in the development of the subunit vaccine against PEDV infection. To enhance the vaccine's immunogenicity, Escherichia coli heat-labile enterotoxin B (LTB) has usually been adopted as a molecular adjuvant. In this study, the COE and LTB-COE genes were engineered into the Lactobacillus -Escherichia coli shuttle vectors pSAPG1 (surface-displaying) and pSAPG2 (secreting) followed by electrotransformation into Lactobacillus casei (Lc) to yield the following recombinant strains: Lc:PG1-LTB-COE, Lc:PG2-LTB-COE, Lc:PG1-COE, and Lc:PG2-COE. Our results showed that mice immunized orogastrically with L. casei expressing COE or LTB-COE produced secretory immunoglobulin A and immunoglobulin G with the ability to neutralize PEDV in sera and mucus. Moreover, higher levels of interleukin-4 and gamma interferon were also exhibited compared with negative control. These data displayed the tendency of Lc:PG2-LTB-COE > Lc:PG1-LTB-COE > Lc:PG2-COE > Lc:PG1-COE at the same time point. Taken together, LTB-COE is more suitable for Lactobacillus expressing system to engineer mucosal vaccine against PEDV infection.

Analysis of the mechanisms that underlie absorption of botulinum toxin by the inhalation route

Botulinum toxin is a highly potent oral and inhalation poison, which means that the toxin must have an efficient mechanism for penetration of epithelial barriers. To date, three models for toxin passage across epithelial barriers have been proposed: (i) the toxin itself undergoes binding and transcytosis; (ii) an auxiliary protein, HA35, transports toxin from the apical to the basal side of epithelial cells; and (iii) an auxiliary protein, HA35, acts on the basal side of epithelial cells to disrupt tight junctions, and this permits paracellular flux of toxin. These models were evaluated by studying toxin absorption following inhalation exposure in mice. Three types of experiments were conducted. In the first, the potency of pure neurotoxin was compared with that of progenitor toxin complex, which contains HA35. The results showed that the rate and extent of toxin absorption, as well as the potency of absorbed toxin, did not depend upon, nor were they enhanced by, the presence of HA35. In the second type of experiment, the potencies of pure neurotoxin and progenitor toxin complex were compared in the absence or presence of antibodies on the apical side of epithelial cells. Antibodies directed against the neurotoxin protected against challenge, but antibodies against HA35 did not. In the final type of experiment, the potency of pure neurotoxin and toxin complex was compared in animals pretreated to deliver antibodies to the basal side of epithelial cells. Once again, antibodies directed against the neurotoxin provided resistance to challenge, but antibodies directed against HA35 did not. Taken collectively, the data indicate that the toxin by itself is capable of crossing epithelial barriers. The data do not support any hypothesis in which HA35 is essential for toxin penetration of epithelial barriers.

Five-year experience with incobotulinumtoxinA (Xeomin(®) ): the first botulinum toxin drug free of complexing proteins

In 2005, incobotulinumtoxinA (Xeomin(®) ), a new botulinum toxin (BT) type A drug without complexing proteins (CPs), became available. This paper reviews the specific features of Xeomin(®) and the experience gathered with it during the last 5 years. Compared with conventional BT drugs, Xeomin(®) 's extended shelf live and its simplified temperature restrictions indicate that CPs are not necessary for BT drug stability. Its reduced molecular size does not translate into diffusion differences, and its potency labelling is identical to that of onabotulinumtoxinA (Botox(®) ). With a reduced content of inactivated botulinum neurotoxin, Xeomin(®) should have reduced antigenicity. Lack of CP's may further reduce antigenicity. Xeomin(®) 's therapeutic efficacy against cervical dystonia, blepharospasm and spasticity has been proven in large randomised, double-blind and placebo-controlled studies leading to registrations in many countries. Additional successful clinical use in axillary hyperhidrosis, hemifacial spasm, re-innervation synkinesias and hypersalivation as well as in dystonia and spasticity in extended doses and throughout extended observation periods has been documented meanwhile. Lack of reported cases of antibody-induced therapy failure (ABF), as to date, support the hypothesis of an improved antigenicity.

Effects of acetylcholinesterase inhibitor paraoxon denote the possibility of non-quantal acetylcholine release in myocardium of different vertebrates

Effects of organophosphorous acetylcholinesterase inhibitor paraoxon were studied in the isolated atrial and ventricular myocardium preparations of a fish (cod), an amphibian (frog) and a mammal (rat) using the microelectrode technique. Incubation of isolated atrium with paraoxon (5 × 10(-6)-5 × 10(-5) M) caused significant reduction of action potential duration and marked slowing of sinus rhythm. These effects were abolished by muscarinic blocker atropine and therefore are caused by acetylcholine, which accumulates in the myocardium due to acetylcholinesterase inhibition even in the absence of vagal input. Hemicholinium III is a blocker of high affinity choline-uptake transporters, which are believed to mediate non-quantal release of acetylcholine from cholinergic terminals in different tissues. In the atrial myocardium of all the three studied species, hemicholinium III (10(-5) M) significantly suppressed all the effects of paraoxon. Blocker of parasympathetic ganglionic transmission hexamethonium bromide (10(-4) M) and inhibitor of vesicular acetylcholine transporters vesamicol (10(-5) M) failed to attenuate paraoxon effects. Among ventricular myocardium preparations of three species paraoxon provoked marked cholinergic effects only in frog, hemicholinium III abolished these effects effectively. We conclude that paraoxon stops degradation of acetylcholine in the myocardium and helps to reveal the effects of acetylcholine, which is continuously secreted from the cholinergic nerves in non-quantal manner. Thus, non-quantal release of acetylcholine in the heart is not specific only for mammals, but is also present in the hearts of different vertebrates.

Expression of a cholera toxin B subunit-neutralizing epitope of the porcine epidemic diarrhea virus fusion gene in transgenic lettuce (Lactuca sativa L.)

Transgenic plants have been used as a safe and economic expression system for the production of edible vaccines. A synthetic cholera toxin B subunit gene (CTB) was fused with a synthetic neutralizing epitope gene of the porcine epidemic diarrhea virus (sCTB-sCOE), and the sCTB-sCOE fusion gene was introduced into a plant expression vector under the control of the ubiquitin promoter. This plant expression vector was transformed into lettuce (Lactuca sativa L.) using the Agrobacterium-mediated transformation method. Stable integration and transcriptional expression of the sCTB-sCOE fusion gene was confirmed using genomic DNA PCR analysis and northern blot analysis, respectively. The results of western blot analysis with anti-cholera toxin and anti-COE antibody showed the synthesis and assembly of CTB-COE fusion protein into oligomeric structures with pentameric sizing. The biological activity of CTB-COE fusion protein to its receptor, G(M1)-ganglioside, in transgenic plants was confirmed via G(M1)-ELISA with anti-cholera toxin and anti-COE antibody. Based on G(M1)-ELISA, the expression level of CTB-COE fusion proteins reached 0.0065% of the total soluble protein in transgenic lettuce leaf tissues. Transgenic lettuce successfully expressing CTB-COE fusion protein will be tested to induce efficient immune responses against porcine epidemic diarrhea virus infection by administration with raw material.

Profile of Xeomin® (incobotulinumtoxinA) for the treatment of blepharospasm

Even though conventional botulinum neurotoxin (BoNT) products have shown successful treatment results in patients with benign blepharospasm (BEB), the main, potential long-term side effect of BoNT use is the development of immunologic resistance due to the production of neutralizing antibody to the neurotoxin after repeated injections. Xeomin^® (incobotulinumtoxinA), a unique botulinum neurotoxin type A (BoNT/A) drug free of complexing proteins otherwise contained in all conventional BoNT/A drugs, was recently approved by US Food and Drug Administration for the treatment of cervical dystonia or blepharospasm in adults. The newly approved BoNT/A drug may overcome this limitation of previous conventional products, since it contains pure neurotoxin (150 kDa) through a manufacturing process that separates it from complexing proteins such as hemagglutinins produced by fermentation of Clostridium botulinum. Many studies have also shown that Xeomin^® has the same efficacy and safety profile as complexing protein-containing products such as Botox^® and is exchangeable with Botox^® using a simple 1:1 conversion ratio. Xeomin^® represents a new treatment option for the repeated treatment of patients with blepharospasm in that it may reduce antibody-induced therapy failure. But, long-term comparative trials in naïve patients between Xeomin^® and conventional BoNT/A drugs are required to confirm the low immunogenicity of Xeomin^®.

Complexing proteins in botulinum toxin type A drugs: a help or a hindrance?

Botulinum toxin type A is a high molecular weight protein complex containing active neurotoxin and complexing proteins, the latter of which, it is believed, protect the neurotoxin when in the gastrointestinal tract, and may facilitate its absorption. Comparisons of conventional botulinum toxin type A drugs that include complexing proteins with the complexing protein-free formulation of Xeomin^® strongly suggest that complexing proteins do not affect diffusion of the active neurotoxin. Studies of Xeomin have also shown that complexing proteins do not enhance product stability in storage. However, complexing proteins may stimulate antibody development against botulinum toxin type A. Numerous observational studies have been published showing that some patients receiving conventional botulinum toxin may develop neutralizing antibodies, leading to antibody-induced therapy failure. Studies have shown that Xeomin is not associated with the development of neutralizing antibodies in animal models or in patients. In conclusion, complexing proteins do not contribute to the stability of botulinum toxin type A drugs and do not contribute to their therapeutic effects, but may be associated with a secondary nonresponse due to the development of neutralizing antibodies.

Advances on the compositional analysis of glycosphingolipids combining thin-layer chromatography with mass spectrometry

Glycosphingolipids (GSLs), composed of a hydrophilic carbohydrate chain and a lipophilic ceramide anchor, play pivotal roles in countless biological processes, including infectious diseases and the development of cancer. Knowledge of the number and sequence of monosaccharides and their anomeric configuration and linkage type, which make up the principal items of the glyco code of biologically active carbohydrate chains, is essential for exploring the function of GSLs. As part of the investigation of the vertebrate glycome, GSL analysis is undergoing rapid expansion owing to the application of novel biochemical and biophysical technologies. Mass spectrometry (MS) takes part in the network of collaborations to further unravel structural and functional aspects within the fascinating world of GSLs with the ultimate aim to better define their role in human health and disease. However, a single-method analytical MS technique without supporting tools is limited yielding only partial structural information. Because of its superior resolving power, robustness, and easy handling, high-performance thin-layer chromatography (TLC) is widely used as an invaluable tool in GSL analysis. The intention of this review is to give an insight into current advances obtained by coupling supplementary techniques such as TLC and mass spectrometry. A retrospective view of the development of this concept and the recent improvements by merging (1) TLC separation of GSLs, (2) their detection with oligosaccharide-specific proteins, and (3) in situ MS analysis of protein-detected GSLs directly on the TLC plate, are provided. The procedure works on a nanogram scale and was successfully applied to the identification of cancer-associated GSLs in several types of human tumors. The combination of these two supplementary techniques opens new doors by delivering specific structural information of trace quantities of GSLs with only limited investment in sample preparation.

Toxins-useful biochemical tools for leukocyte research

Leukocytes are a heterogeneous group of cells that display differences in anatomic localization, cell surface phenotype, and function. The different subtypes include e.g., granulocytes, monocytes, dendritic cells, T cells, B cells and NK cells. These different cell types represent the cellular component of innate and adaptive immunity. Using certain toxins such as pertussis toxin, cholera toxin or clostridium difficile toxin, the regulatory functions of Gα_i, Gαs and small GTPases of the Rho family in leukocytes have been reported. A summary of these reports is discussed in this review.

Non-quantal release of acetylcholine from parasympathetic nerve terminals in the right atrium of rats

Acetylcholinesterase (AChE) inhibitors provoke typical cholinergic effects in the isolated right atrium of the rat due to the accumulation of acetylcholine (ACh). Our study was designed to show that in the absence of vagal impulse activity, ACh is released from the parasympathetic nerve fibres by means of non-quantal secretion. The conventional microelectrode technique was used to study changes in action potential (AP) configuration in the right atrium preparation of rats during application of AChE inhibitors. Staining with the lipophilic fluorescent dye FM1-43 was used to demonstrate the presence of endocytosis in cholinergic endings. The AChE inhibitors armin (10(7)-10(5)m) and neostigmine (10(7) to 5 x 10(6)m) caused a reduction of AP duration and prolonged the cycle length. These effects were abolished by atropine and were therefore mediated by ACh accumulated in the myocardium during AChE inhibition. Putative block of impulse activity of the postganglionic neurons by tetrodotoxin (5 x 10(7)m) and blockade of ganglionic transmission by hexomethonium (2 x 10(4)m), as well as blockade of all forms of quantal release with Clostridium botulinum type A toxin (50 U ml(1)), did not alter the effects of armin. Experiments with FM1-43 dye confirmed the effective block of exocytosis by botulinum toxin. Selective inhibition of the choline uptake system using hemicholinium III (10(5)m), which blocks non-quantal release at the neuromuscular junction, suppressed the effects of AChE inhibitors. Thus, accumulation of ACh is likely to be caused by non-quantal release from cholinergic terminals. We propose that non-quantal release of ACh, shown previously at the neuromuscular junction, is present in cholinergic postganglionic fibres of the rat heart in addition to quantal release.

The HA proteins of botulinum toxin disrupt intestinal epithelial intercellular junctions to increase toxin absorption

The type B botulinum neurotoxin (BoNT) elicits flaccid paralysis and death in humans by intoxicating peripheral nerves after oral absorption. Here, we examine the function of the haemagglutinin (HA), a non-toxic component of the large 16S BoNT complex. We find that the HA acts in the intestine to disrupt epithelial barrier function by opening intercellular tight and adherens junctions. This allows transport of BoNT and other large solutes into the systemic circulation and explains how the type B BoNT complexes are efficiently absorbed. In vitro, HA appears to act on the epithelial cell via the basolateral membrane only, suggesting the possibility of another step in the absorptive process. These studies show that the 16S BoNT complex is a multifunctional protein assembly equipped with the machinery to efficiently breach the intestinal barrier and act systemically on peripheral nerves.

ER chaperones in mammalian development and human diseases

The field of endoplasmic reticulum (ER) stress in mammalian cells has expanded rapidly during the past decade, contributing to understanding of the molecular pathways that allow cells to adapt to perturbations in ER homeostasis. One major mechanism is mediated by molecular ER chaperones which are critical not only for quality control of proteins processed in the ER, but also for regulation of ER signaling in response to ER stress. Here, we summarized the properties and functions of GRP78/BiP, GRP94/gp96, GRP170/ORP150, GRP58/ERp57, PDI, ERp72, calnexin, calreticulin, EDEM, Herp and co-chaperones SIL1 and P58(IPK) and their role in development and diseases. Many of the new insights are derived from recently constructed mouse models where the genes encoding the chaperones are genetically altered, providing invaluable tools for examining the physiological involvement of the ER chaperones in vivo.

Human milk SIgA binds to botulinum type B 16S toxin and limits toxin adherence on T84 cells

Botulinum neurotoxin produced by Clostridium botulinum type B is in the form of a complex of 12S and 16S toxins. Food-borne botulism is caused by these complex toxins which are ingested orally and absorbed from the digestive tract. Here, we show that the human milk SIgA binds to the type B16S toxin. The binding of SIgA to 16S toxin and HA was inhibited by carbohydrates such as galactose, suggesting that the interaction of carbohydrate side chain of the SIgA with the HA of the 16S toxin is important for SIgA-16S complex formation. We also demonstrate that SIgA inhibits the attachment of 16S toxin to intestinal epithelial cells. These data suggest that the interaction of antigen nonspecific SIgA with 16S toxin has a large influence on the absorption of 16S toxin from the intestinal epithelium, and that SIgA may provide insight into developing a therapeutic agent for type B food-borne botulism.