Effects of enzymatically inactive recombinant botulinum neurotoxin type A at the mouse neuromuscular junctions

Potency Evaluations of Recombinant Botulinum Neurotoxin A1 Mutants Designed to Reduce Toxicity

Recombinant mutant holotoxin BoNTs (rBoNTs) are being evaluated as possible vaccines against botulism. Previously, several rBoNTs containing 2-3 amino acid mutations in the light chain (LC) showed significant decreases in toxicity (2.5-million-fold-12.5-million-fold) versus wild-type BoNT/A1, leading to their current exclusion from the Federal Select Agent list. In this study, we added four additional mutations in the receptor-binding domain, translocation domain, and enzymatic cleft to further decrease toxicity, creating 7M rBoNT/A1. Due to poor expression in E. coli, 7M rBoNT/A1 was produced in an endogenous C. botulinum expression system. This protein had higher residual toxicity (LD50: 280 ng/mouse) than previously reported for the catalytically inactive rBoNT/A1 containing only three of the mutations (>10 µg/mouse). To investigate this discrepancy, several additional rBoNT/A1 constructs containing individual sets of amino acid substitutions from 7M rBoNT/A1 and related mutations were also endogenously produced. Similarly to endogenously produced 7M rBoNT/A1, all of the endogenously produced mutants had ~100-1000-fold greater toxicity than what was reported for their original heterologous host counterparts. A combination of mutations in multiple functional domains resulted in a greater but not multiplicative reduction in toxicity. This report demonstrates the impact of production systems on residual toxicity of genetically inactivated rBoNTs.

Botulinum Neurotoxin Induces Neurotoxic Microglia Mediated by Exogenous Inflammatory Responses

Botulinum neurotoxin serotype A (BoNT/A) is widely used in therapeutics and cosmetics. The effects of multi-dosed BoNT/A treatment are well documented on the peripheral nervous system (PNS), but much less is known on the central nervous system (CNS). Here, the mechanism of multi-dosed BoNT/A leading to CNS neurodegeneration is explored by using the 3D human neuron-glia model. BoNT/A treatment reduces acetylcholine, triggers astrocytic transforming growth factor beta, and upregulates C1q, C3, and C5 expression, inducing microglial proinflammation. The disintegration of the neuronal microtubules is escorted by microglial nitric oxide, interleukin 1β, tumor necrosis factor α, and interleukin 8. The microglial proinflammation eventually causes synaptic impairment, phosphorylated tau (pTau) aggregation, and the loss of the BoNT/A-treated neurons. Taking a more holistic approach, the model will allow to assess therapeutics for the CNS neurodegeneration under the prolonged use of BoNT/A.

A Novel Catalytically Inactive Construct of Botulinum Neurotoxin A (BoNT/A) Directly Inhibits Visceral Sensory Signalling

Botulinum neurotoxin A (BoNT/A) is a potent neurotoxin that silences cholinergic neurotransmission through the cleavage of the synaptic protein SNAP-25. Previous studies have shown that, in addition to its paralytic effects, BoNT/A can inhibit sensory nerve activity. The aim of this study was to identify how BoNT/A inhibits afferent signalling from the bladder. To investigate the role of SNAP-25 cleavage in the previously reported BoNT/A-dependent inhibition of sensory signalling, we developed a recombinant form of BoNT/A with an inactive light chain, rBoNT/A (0), unable to paralyse muscle. We also developed recombinant light chain (LC)-domain-only proteins to better understand the entry mechanisms, as the heavy chain (HC) of the protein is responsible for the internalisation of the light chain. We found that, despite a lack of catalytic activity, rBoNT/A (0) potently inhibited the afferent responses to bladder distension to a greater degree than catalytically active rBoNT/A. This was also clear from the testing of the LC-only proteins, as the inactive rLC/A (0) protein inhibited afferent responses significantly more than the active rLC/A protein. Immunohistochemistry for cleaved SNAP-25 was negative, and purinergic and nitrergic antagonists partially and totally reversed the sensory inhibition, respectively. These data suggest that the BoNT/A inhibition of sensory nerve activity in this assay is not due to the classical well-characterised 'double-receptor' mechanism of BoNT/A, is independent of SNAP25 cleavage and involves nitrergic and purinergic signalling mechanisms.

Low-Dose Neubotulinum Toxin A versus Low-Dose Abobotulinum Toxin A Injection for the Treatment of Cervical Dystonia: A Multicenter, 48-Week, Prospective, Double-Blinded, Randomized Crossover Design Study

Various types of botulinum toxin (BoNT) have been studied to treat cervical dystonia (CD). Although high-dose BoNT has proven efficacy, it increases the risk of adverse events. For this reason, this study was planned to identify the non-inferiority efficacy, tolerability, and safety of low-dose neubotulinum toxin A (Neu-BoNT-A) versus low-dose abobotulinum toxin A (Abo-BoNT-A) in CD treatment. The 48-week, prospective, randomized, controlled crossover design study of CD treatment, with 50-unit Neu-BoNT-A and 250-unit Abo-BoNT-A injections at 12-week intervals, was conducted over a 24-week treatment period. This study used the following standardized rating scales to assess the efficacy of BoNT: the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS); health-related quality of life (HRQoL); the Cervical Dystonia Impact Profile (CDIP-58); the Short Form 36 health survey questionnaire (SF-36); and, for the depressive symptoms of CD patients, the Center for Epidemiological Studies-Depression Scale (CES-D) and the Patient Health Questionnaire-9 (PHQ-9). Fifty-two CD patients were enrolled from October 2019 to January 2021. The mean scores of the TWSTRS total at the post-treatments in both Neu-BoNT-A and Abo-BoNT-A had a significant reduction from baseline (p = 0.008 and 0.002, respectively). However, the mean changes of the TWSTRS total at the 12- and 24-week treatments between the two treatment groups were not significantly different (p = 0.284 and 0.129, respectively). The mean scores of the HRQoL questionnaires (the CIDP-58 and the SF-36) and the depressive symptoms (the CES-D and the PHQ-9) in both treated groups at the post-treatments did not significantly decrease from baseline and were comparable. Two patients treated with Abo-BoNT-A (250 units) reported cervical tension and benign paroxysmal positional vertigo (BPPV). There were no serious adverse events reported. Though both low-dose BoNT-As were effective at improving clinical symptoms without significant side effects, both treatments did not predict change in quality of life and depression. With the non-inferiority criteria, low-dose Neu-BoNT-A has a similar efficacy, safety, and tolerability to Abo-BoNT-A.

DD04107-Derived neuronal exocytosis inhibitor peptides: Evidences for synaptotagmin-1 as a putative target

The analgesic peptide DD04107 (Pal-EEMQRR-NH₂) and its acetylated analogue inhibit α-calcitonin gene-related peptide (α-CGRP) exocytotic release from primary sensory neurons. Examining the crystal structure of the SNARE-Synaptotagmin-1(Syt1) complex, we hypothesized that these peptides could inhibit neuronal exocytosis by binding to Syt1, hampering at least partially its interaction with the SNARE complex. To address this hypothesis, we first interrogate the role of individual side-chains on the inhibition of α-CGRP release, finding that E1, M3, Q4 and R6 residues were crucial for activity. CD and NMR conformational analysis showed that linear peptides have tendency to adopt α-helical conformations, but the results with cyclic analogues indicated that this secondary structure is not needed for activity. Isothermal titration calorimetry (ITC) measurements demonstrate a direct interaction of some of these peptides with Syt1-C2B domain, but not with Syt7-C2B region, indicating selectivity. As expected for a compound able to inhibit α-CGRP release, cyclic peptide derivative Pal-E-cyclo[EMQK]R-NH₂ showed potent in vivo analgesic activity, in a model of inflammatory pain. Molecular dynamics simulations provided a model consistent with K_D values for the interaction of peptides with Syt1-C2B domain, and with their biological activity. Altogether, these results identify Syt1 as a potential new analgesic target.

Neurotrophic effects of Botulinum neurotoxin type A in hippocampal neurons involve activation of Rac1 by the non-catalytic heavy chain (HCC/A)

Botulinum neurotoxins (BoNTs) are extremely potent naturally occurring poisons that act by silencing neurotransmission. Intriguingly, in addition to preventing presynaptic vesicle fusion, BoNT serotype A (BoNT/A) can also promote axonal regeneration in preclinical models. Here we report that the non-toxic C-terminal region of the receptor-binding domain of heavy chain BoNT/A (HCC/A) activates the small GTPase Rac1 and ERK pathway to potentiate axonal outgrowth, dendritic protrusion formation and synaptic vesicle release in hippocampal neurons. These data are consistent with HCC/A exerting neurotrophic properties, at least in part, independent of any BoNT catalytic activity or toxic effect.

Role of critical elements in botulinum neurotoxin complex in toxin routing across intestinal and bronchial barriers

The highly potent botulinum neurotoxin serotype A (BoNT/A) inhibits neurotransmitter release at neuromuscular junctions resulting in flaccid muscle paralysis, respiratory arrest and death. In order to reach their neuronal cell targets, BoNT/A must cross epithelial cell barriers lining the intestines and airways. The toxin is produced as a large protein complex comprised of the neurotoxin and non-toxic neurotoxin-associated proteins (NAPs). Although NAPs are known to protect the toxin from harsh environments, their role in the movement of BoNT/A across epithelial barriers has not been fully characterized. In the current study, movement of the toxin across epithelial cells was examined macroscopically using a sensitive near infrared fluorescence transcytosis assay and microscopically using fluorescently labeled toxin and confocal microscopy. The studies show that the BoNT/A complex internalizes more rapidly than the pure toxin. The studies also show that one NAP protein, hemaglutinin 33 (Hn33), enhanced both the binding and movement of a deactivated recombinant botulinum neurotoxin A (DrBoNT) across epithelial cell monolayers and that the toxin associates with Hn33 on the cell surface. Collectively, the data demonstrate that, in addition to their protective role, NAPs and Hn33 play an important role in BoNT/A intoxication.

Perturbation to Cholesterol at the Neuromuscular Junction Confers Botulinum Neurotoxin A Sensitivity to Neonatal Mice

Botulinum neurotoxin A (BoNT/A) cleaves SNAP25 at the motor nerve terminals and inhibits stimulus evoked acetylcholine release. This causes skeletal muscle paralysis. However, younger neonatal mice (<P7; <7-days old) are resistant to the neuroparalytic effects of BoNT/A. That is, invivo injection of BoNT/A at the innervations of Extensor digitorum longus muscle in the hindlimbs inhibited the toe spread reflex within 24 hours following BoNT/A injection in adult mouse and in older (>P7) mice. However, neonatal mice younger than 7 days-age remained unaffected by BoNT/A injection. Also, BoNT/A inhibited stimulus evoked acetylcholine release and stimulus-evoked twitch tension of diaphragm nerve muscle preparations (NMPs) of adult mouse and >P7 neonates but not that of <P7. Moreover, NMPs of <P7 showed decreased uptake of fluorescent BoNT/A compared to >P7. However, cholesterol depletion using methyl-β-cyclodextrin (MβCD) sensitized <P7 neonates to BoNT/A and facilitated BoNT/A uptake into NMPs obtained from <P7 neonates. Further, MβCD (10 mM; 30 min pretreatment) increased the interaction between synaptic vesicle protein 2 and BoNT/A. Also, cholesterol depletion increased the miniature endplate current in adult NMPs. Interestingly, cholesterol replenishment, invitro, delayed the onset of inhibitory effect of BoNT/A. Collectively, our data suggest that cholesterol rich lipid microdomains are involved in BoNT/A uptake mechanisms during development. Our data demonstrate that cholesterol depletion sensitized neonatal mice (<P7) to BoNT/A while replenishing cholesterol delayed the onset of inhibitory actin of BoNT/A. This suggests that membrane cholesterol modulates neurotoxin sensitivity at the neuromuscular junction (NMJ).

Engineering of Botulinum Neurotoxins for Biomedical Applications

Botulinum neurotoxins (BoNTs) have been used as therapeutic agents in the clinical treatment of a wide array of neuromuscular and autonomic neuronal transmission disorders. These toxins contain three functional domains that mediate highly specific neuronal cell binding, internalization and cytosolic delivery of proteolytic enzymes that cleave proteins integral to the exocytosis of neurotransmitters. The exceptional cellular specificity, potency and persistence within the neuron that make BoNTs such effective toxins, also make them attractive models for derivatives that have modified properties that could potentially expand their therapeutic repertoire. Advances in molecular biology techniques and rapid DNA synthesis have allowed a wide variety of novel BoNTs with alternative functions to be assessed as potential new classes of therapeutic drugs. This review examines how the BoNTs have been engineered in an effort to produce new classes of therapeutic molecules to address a wide array of disorders.

Purification and Characterization of Recombinant Botulinum Neurotoxin Serotype FA, Also Known as Serotype H

We have purified and characterized recombinant botulinum neurotoxin serotype FA (BoNT/FA). This protein has also been named as a new serotype (serotype H), but the classification has been controversial. A lack of well-characterized, highly pure material has been a roadblock to study. Here we report purification and characterization of enzymatically active, and of inactive nontoxic, recombinant forms of BoNT/FA as tractable alternatives to purifying this neurotoxin from native Clostridium botulinum. BoNT/FA cleaves the same intracellular target proteins as BoNT/F1 and other F serotype BoNTs; the intracellular targets are vesicle associated membrane proteins (VAMP) 1, 2 and 3. BoNT/FA cleaves the same site in VAMP-2 as BoNT/F5, which is different from the cleavage site of other F serotype BoNTs. BoNT/FA has slower enzyme kinetics than BoNT/F1 in a cell-free protease assay and is less potent at inhibiting ex vivo nerve-stimulated skeletal muscle contraction. In contrast, BoNT/FA is more potent at inhibiting neurotransmitter release from cultured neurons.

High Yield Preparation of Functionally Active Catalytic-Translocation Domain Module of Botulinum Neurotoxin Type A That Exhibits Uniquely Different Enzyme Kinetics

Botulinum neurotoxins (BoNTs) are the most toxic proteins known to cause flaccid muscle paralysis as a result of inhibition of neurotransmitter release from peripheral cholinergic synapses. BoNT type A (BoNT/A) is a 150 kDa protein consisting of two major subunits: light chain (LC) and heavy chain (HC). The LC is required for the catalytic activity of neurotoxin, whereas the C and N terminal domains of the HC are required for cell binding, and translocation of LC across the endosome membranes, respectively. To better understand the structural and functional aspects of BoNT/A intoxication we report here the development of high yield Escherichia coli expression system (2-20-fold higher yield than the value reported in the literature) for the production of recombinant light chain-translocation domain (rLC-TD/A) module of BoNT/A which is catalytically active and translocation competent. The open reading frame of rLC-TD/A was PCR amplified from deactivated recombinant BoNT/A gene (a non-select agent reagent), and was cloned using pET45b (+) vector to express in E. coli cells. The purification procedure included a sequential order of affinity chromatography, trypsinization, and anion exchange column chromatography. We were able to purify > 95% pure, catalytically active and structurally well-folded protein. Comparison of enzyme kinetics of purified LC-TD/A to full-length toxin and recombinant light chain A suggest that the affinity for the substrate is in between endopeptidase domain and botulinum toxin. The potential application of the purified protein has been discussed in toxicity and translocation assays.

In Vivo Toxicity and Immunological Characterization of Detoxified Recombinant Botulinum Neurotoxin Type A

PURPOSE

A double-mutant E224A/E262A full-length botulinum neurotoxin (BoNT) Type A with structural similarity to native BoNT/A but lacking the endopeptidase activity provides an ideal surrogate for testing pharmacokinetics and immunochemical characteristics of BoNT.

METHODS

We determined lethality (LD50) of deactivated recombinant botulinum neurotoxin (drBoNT/A) to be 24.0 μg by intraperitoneal route (i.p). The polypeptide drBoNT/A labeled with near infra-red dye 800 (NIR 800) was used to examine its distribution to different organs using whole body imaging when administered to mice via intravenous (i.v) or i.p route. Also, drBoNT/A was used to evaluate its immunogenicity in Balb/C mice model.

RESULTS

drBoNT/A was found to be highly immunogenic when tested under various in vivo conditions in Balb/C mice model. For the first time we have demonstrated that a full length 150 kDa drBoNT/A, by administering via inhalation route in mice model, has evoked both circulating immunoglobulin levels of IgG and secretory IgA at the mucosal surface. The immunoglobulin levels were sufficient enough to protect against the challenge dose of native BoNT toxin in mice model. Tissue distribution of drBoNT/A seems to be similar to that of native toxin.

CONCLUSIONS

Based on the characteristics described in this report this nontoxic holotoxin protein will assist us to explore the window of opportunity available for therapeutic treatment in case of unnatural poisoning, and also it can be an effective vaccine candidate.

The Inhibitory Effect of Botulinum Toxin Type A on Rat Pyloric Smooth Muscle Contractile Response to Substance P In Vitro

A decrease in pyloric myoelectrical activity and pyloric substance P (SP) content following intrasphincteric injection of botulinum toxin type A (BTX-A) in free move rats have been demonstrated in our previous studies. The aim of the present study was to investigate the inhibitory effect of BTX-A on rat pyloric muscle contractile response to SP in vitro and the distributions of SP and neurokinin 1 receptor (NK1R) immunoreactive (IR) cells and fibers within pylorus. After treatment with atropine, BTX-A (10 U/mL), similar to [D-Arg¹, D-Phe⁵, D-Trp^7,9, Leu¹¹]-SP (APTL-SP, 1 μmol/L) which is an NK1R antagonist, decreased electric field stimulation (EFS)-induced contractile tension and frequency, whereas, subsequent administration of APTL-SP did not act on contractility. Incubation with BTX-A at 4 and 10 U/mL for 4 h respectively decreased SP (1 μmol/L)-induced contractions by 26.64% ± 5.12% and 74.92% ± 3.62%. SP-IR fibers and NK1R-IR cells both located within pylorus including mucosa and circular muscle layer. However, fewer SP-fibers were observed in pylorus treated with BTX-A (10 U/mL). In conclusion, BTX-A inhibits SP release from enteric terminals in pylorus and EFS-induced contractile responses when muscarinic cholinergic receptors are blocked by atropine. In addition, BTX-A concentration- and time-dependently directly inhibits SP-induced pyloric smooth muscle contractility.

Novel therapeutic uses and formulations of botulinum neurotoxins: a patent review (2012 - 2014)

INTRODUCTION

Botulinum neurotoxins (BoNTs) are among the most toxic of known biological molecules and function as acetylcholine release inhibitors and neuromuscular blocking agents. Paradoxically, these properties also make them valuable therapeutic agents for the treatment of movement disorders, urological conditions and hypersecretory disorders. Greater understanding of their molecular mechanism of action and advances in protein engineering has led to significant efforts to improve and expand their function with a view towards broadening their therapeutic potential.

AREAS COVERED

Searches of Espacenet and Google Patent have revealed a number of patents related to BoNTs. This review will focus on novel therapeutic uses and formulations disclosed during 2012 - 2014. The seven patents discussed will include nanoformulations of FDA-approved BoNTs, additional BoNT subtypes and novel BoNT variants and chimeras created through protein engineering. Supporting patents and related publications are also briefly discussed.

EXPERT OPINION

The clinical and commercial success of BoNTs has prompted investigation into novel BoNTs or BoNT-mediated chimeras with promising in vitro results. Distinct strategies including the use of nanoformulations and targeted delivery have been implemented to identify new indication and improved functionality. Greater understanding of their systemic exposure, efficacy and safety profiles will be required for further development.

Novel pharmacological approaches for the treatment of acne vulgaris

INTRODUCTION

Acne vulgaris is the most common skin disease worldwide; yet, current treatment options, although effective, are associated with unwanted side effects, chronicity, relapses and recurrences. The adequate control of the four pathogenic mechanisms, involved in the appearance of acne lesions, is paramount to treatment success.

AREAS COVERED

The authors discuss and evaluate the pathogenic pathways related to the mechanisms of action of novel molecules, which are currently under investigation for the treatment of acne vulgaris. The manuscript is based on comprehensive searches made through PubMed, GoogleScholar and ClinicalTrial.gov, using different combination of key words, which include acne vulgaris, pathogenesis, treatment, sebogenesis and Propionibacterium acnes.

EXPERT OPINION

In the near future, more effective treatments with fewer side effects are expected. The use of topical antiandrogens, acetylcholine inhibitors and PPAR modulators seem to be promising options for controlling sebum production. Retinoic acid metabolism-blocking agents and IL-1α inhibitors have the potential to become legitimate alternative options to retinoid therapy in the management of infundibular dyskeratosis. Indeed, the authors believe that there will likely be a decline in the use of antibiotics for controlling P. acnes colonization and targeting the inflammation cascade.