The Therapeutic Potential of Botulinum Toxin

The Safety and Effect of Local Botulinumtoxin A Injections for Long-Term Management of Chronic Pain in Post-Herpetic Neuralgia: Literature Review and Cases Report Treated with Incobotulinumtoxin A

There are few reports on the safety and effectiveness of long-term botulinumtoxin A (BoNT A) therapy in severe chronic pain of post-herpetic neuralgia (PHN). The literature was searched with the term "neuropathic pain" and "botulinum" on PubMed (up to 29 February 2020). Pain was assessed with the Visual Analogue Scale (VAS) before and after BoNT A therapy. A total of 10 clinical trials and six case reports including 251 patients with PHN were presented. They showed that BoNT A therapy had significant pain reduction (up to 30-50%) and improvement in quality of life. The effect duration seems to be correlated with BoNT A doses injected per injection site. Intervals between BoNT A injections were 10-14 weeks. No adverse events were reported in cases and clinical studies, even in the two pregnant women, whose babies were healthy. The repeated (≥6 times) intra/subcutaneous injections of incobotulinumtoxin A (Xeomin®, Merz Pharmaceuticals, Germany) over the two years of our three cases showed marked pain reduction and no adverse events. Adjunctive local BoNT A injection is a promising option for severe PHN, as a safe and effective therapy in long-term management for chronic neuropathic pain. Its effect size and -duration seem to be depended on the dose of BoNT A injected per each point.

Botulinum Toxin and Neuronal Regeneration after Traumatic Injury of Central and Peripheral Nervous System

Botulinum neurotoxins (BoNTs) are toxins produced by the bacteria Clostridiumbotulinum, the causing agent for botulism, in different serotypes, seven of which (A-G) are well characterized, while others, such as H or FA, are still debated. BoNTs exert their action by blocking SNARE (soluble N-ethylmale-imide-sensitive factor-attachment protein receptors) complex formation and vesicle release from the neuronal terminal through the specific cleavage of SNARE proteins. The action of BoNTs at the neuromuscular junction has been extensively investigated and knowledge gained in this field has set the foundation for the use of these toxins in a variety of human pathologies characterized by excessive muscle contractions. In parallel, BoNTs became a cosmetic drug due to its power to ward off facial wrinkles following the activity of the mimic muscles. Successively, BoNTs became therapeutic agents that have proven to be successful in the treatment of different neurological disorders, with new indications emerging or being approved each year. In particular, BoNT/A became the treatment of excellence not only for muscle hyperactivity conditions, such as dystonia and spasticity, but also to reduce pain in a series of painful states, such as neuropathic pain, lumbar and myofascial pain, and to treat various dysfunctions of the urinary bladder. This review summarizes recent experimental findings on the potential efficacy of BoNTs in favoring nerve regeneration after traumatic injury in the peripheral nervous system, such as the injury of peripheral nerves, like sciatic nerve, and in the central nervous system, such as spinal cord injury.

Factors affecting the therapeutic effect of botulinum toxin A on trigeminal neuralgia: A follow-up retrospective study of 152 patients

Botulinum toxin A (BTX-A) is a promising therapeutic modality against trigeminal neuralgia (TN) with certain controversies pertaining to its application. To provide further information on factors influencing the treatment outcomes of BTX-A, a retrospective study with 152 patients with TN treated with BTX-A was performed. The starting time and duration of the therapeutic effect, as well as side effects, of BTX-A in the treatment of TN were analyzed by sex, age, course of disease, number of branches and injected dose. A total of 136 patients exhibited symptom improvement within 2 weeks following BTX-A treatment as evaluated using a visual analog scale (VAS). The effect of BTX-A was sustained throughout the initial 6 months of the follow-up and was demonstrated to persist for as long as 28 months. Female sex, short disease course and high injection dose (>70 units) were associated with lower long-term VAS scores. Patients receiving short-term medium-(50–70 units) or high-dose injections were more likely to be completely cured. Patients with a median disease course (1–10 years) or multiple branches were more likely to exhibit facial asymmetry. Based on the stratified analysis, female patients with a median disease course (1–10 years) exhibited a higher incidence of side effects and male patients achieved better treatment outcomes with high BTX-A doses. BTX-A effectively alleviated patients with TN in both short or long term, although the treatment efficacy may depend on patient characteristics.

Botulinum toxin type A induces protective autophagy in human dermal microvascular endothelial cells exposed to an in vitro model of ischemia/reperfusion injury

Botulinum toxin type A (BTXA) has been reported to increase the survival of ischemic skin flaps; however, the exact mechanism underlying this effect remains unclear and needs to be further established. The present study aimed to elucidate whether autophagy caused by BTXA functions as a protection mechanism and to identify the mechanisms of its regulation by BTXA in human dermal microvascular endothelial cells (HDMECs) subjected to hypoxia/reoxygenation (H/R)-induced injury. HDMECs were harvested from the upper eyelid tissues of female blepharoplasty patients. HDMECs were exposed to BTXA treatment for 12 h and then subjected to hypoxia for 8 h, followed by reoxygenation for 24 h. Chloroquine diphosphate salt (CQ) was used as an autophagy inhibitor. H/R led to extreme injury to the HDMECs as indicated by the rise in the apoptosis rate, which was significantly attenuated by BTXA pretreatment. The outcomes demonstrated that H/R caused autophagy, as evidenced by a higher type II/type I ratio of light chain 3 (LC3), increased expression of Beclin-1 and increased autophagosome formation. BTXA enhanced autophagy and attenuated apoptosis in a dose-dependent manner, whereas CQ attenuated the BTXA antiapoptotic effects and inhibited the formation of autophagolysosomes, which caused clustering of the LC3-II in cells. In conclusion, autophagy promoted by BTXA serves as a potential protective effect on ischemia/reperfusion injury.

Botulinum Toxin Type A-A Modulator of Spinal Neuron-Glia Interactions under Neuropathic Pain Conditions

Neuropathic pain represents a significant clinical problem because it is a chronic condition often refractory to available therapy. Therefore, there is still a strong need for new analgesics. Botulinum neurotoxin A (BoNT/A) is used to treat a variety of clinical diseases associated with pain. Glia are in continuous bi-directional communication with neurons to direct the formation and refinement of synaptic connectivity. This review addresses the effects of BoNT/A on the relationship between glia and neurons under neuropathic pain. The inhibitory action of BoNT/A on synaptic vesicle fusion that blocks the release of miscellaneous pain-related neurotransmitters is known. However, increasing evidence suggests that the analgesic effect of BoNT/A is mediated through neurons and glial cells, especially microglia. In vitro studies provide evidence that BoNT/A exerts its anti-inflammatory effect by diminishing NF-κB, p38 and ERK1/2 phosphorylation in microglia and directly interacts with Toll-like receptor 2 (TLR2). Furthermore, BoNT/A appears to have no more than a slight effect on astroglia. The full activation of TLR2 in astroglia appears to require the presence of functional TLR4 in microglia, emphasizing the significant interaction between those cell types. In this review, we discuss whether and how BoNT/A affects the spinal neuron–glia interaction and reduces the development of neuropathy.

Botulinum Toxin A for Controlling Obesity

Rapid growth of the overweight population and the number of obese individuals in recent decades suggests that current strategies based on diet, exercise, and pharmacological knowledge are not sufficient to address this epidemic. Obesity is the result of a high caloric intake and energy storage, not counterbalanced by an equally important energy expense. Botulinum toxin type A (BoNT-A) use is rapidly expanding to include treatment of a variety of ophthalmological, gastrointestinal, urological, orthopedic, dermatological, secretory, painful, and cosmetic disorders. Many studies evaluating the effect of BoNT-A in gastric antrum e/o fundus for the treatment of obesity have been published. This treatment modality was based on the observation that gastric injection of BoNT-A in laparatomized rats induced a significant reduction of food intake and body weight. These studies have been published yielding debated results. Differences in the selection of patients, the doses of BoNT-A, the method of administration of the toxin, and the instruments of evaluation of some parameters among these studies may be the cause. In this review, it will study the state-of-the-art use of BoNT-A in obesity basic science models and review the clinical evidence on the therapeutic applications of BoNT-A for obesity.

Botulinum toxin for neuropathic pain and spasticity: an overview

In recent years, a large body of data has surfaced reporting the therapeutic benefit of botulinum toxin injection in multiple conditions. The aim of this review is: to summarize the highest quality literature pertaining to clinical application of botulinum toxin in neuropathic pain conditions including postherpetic neuralgia, trigeminal neuralgia, diabetic polyneuropathy, post-traumatic neuralgia, carpal tunnel syndrome, complex regional pain syndrome, phantom limb and stump pain, and occipital neuralgia; to provide an overview of the clinical trials using botulinum toxin in adult spasticity; and to assign levels of evidence according to the American Academy of Neurology guidelines. In summary, there is level A evidence for established efficacy in postherpetic neuralgia and adult spasticity; level B evidence for probable efficacy in trigeminal neuralgia and post-traumatic neuralgia; level B evidence for probable lack of efficacy in carpal tunnel syndrome; level C evidence for possible efficacy in diabetic polyneuropathy; and level U (insufficient) evidence in complex regional pain syndrome, phantom limb and stump pain, and occipital neuralgia.

Role of Botulinum Toxin Type-A (BTX-A) in the Management of Trigeminal Neuralgia

Trigeminal neuralgia (TN) is a clinical condition characterized by paroxysmal attacks of severe and electric shock-like pain along the distribution of one or more branches of the trigeminal nerve. Various medicinal or surgical modalities have been employed in the past with variable success. Newer methods were tried in search of permanent cure or long-lasting pain relief. The purpose of this paper is to present the review of the literature regarding the use of botulinum toxin type-A (BTX-A) in the management of trigeminal neuralgia.

Botulinum neurotoxin for pain management: insights from animal models

The action of botulinum neurotoxins (BoNTs) at the neuromuscular junction has been extensively investigated and knowledge gained in this field laid the foundation for the use of BoNTs in human pathologies characterized by excessive muscle contractions. Although much more is known about the action of BoNTs on the peripheral system, growing evidence has demonstrated several effects also at the central level. Pain conditions, with special regard to neuropathic and intractable pain, are some of the pathological states that have been recently treated with BoNTs with beneficial effects. The knowledge of the action and potentiality of BoNTs utilization against pain, with emphasis for its possible use in modulation and alleviation of chronic pain, still represents an outstanding challenge for experimental research. This review highlights recent findings on the effects of BoNTs in animal pain models.

Molecular basis of activation of endopeptidase activity of botulinum neurotoxin type E

Botulinum neurotoxins (BoNTs) are a group of large proteins that are responsible for the clinical syndrome of botulism. The seven immunologically distinct serotypes of BoNTs (A-G), each produced by various strains of Clostridium botulinum, act on the neuromuscular junction by blocking the release of the neurotransmitter acetylcholine, thereby resulting in flaccid muscle paralysis. BoNTs are synthesized as single inactive polypeptide chains that are cleaved by endogenous or exogenous proteases to generate the active dichain form of the toxin. Nicking of the single chain BoNT/E to the dichain form is associated with 100-fold increase in toxicity. Here we investigated the activation mechanism of botulinum neurotoxin type E upon nicking and subsequent reduction of disulfide bond. It was observed that nicking of BoNT/E significantly enhances its endopeptidase activity and that at the physiological temperature of 37 degrees C the reduced form of nicked BoNT/E adopts a dynamically flexible conformation resulting from the exposure of hydrophobic segments and facilitating optimal cleavage of its substrate SNAP-25. Such reduction-induced increase in the flexibility of the polypeptide folding provides a rationale for the mechanism of BoNT/E endopeptidase against its intracellular substrate, SNAP-25, and complements current understanding of the mechanistics of interaction between the substrate and BoNT endopeptidase.

Immunological characterization of the subunits of type A botulinum neurotoxin and different components of its associated proteins

Botulinum neurotoxins (BoNTs) constitute a family of seven structurally similar but antigenically distinct proteins produced by different strains of Clostridium botulinum. Type A botulinum neurotoxin (BoNT/A) is produced along with 6 neurotoxin associated proteins (NAPs) including hemagglutinin (Hn-33) through polycistronic expression of a clustered group of genes to form a complex (BoNT/AC). The presence of NAPs enhances the oral toxicity of the neurotoxin significantly. Hn-33 makes up the largest fraction of NAPs in BoNT/AC and strongly protects BoNT/A against proteases of the GI tract. BoNT in its complex form is also used in therapeutic and cosmetic applications to treat several neuromuscular disorders. In this study immunological reactivity of BoNT/A in its purified and complex forms, neurotoxin associated proteins, and Hn-33 have been examined using enzyme-linked immunosorbent assay (ELISA). Antibodies raised against the whole complex reacted 60 times better with the complex and 35 times better with Hn-33 and NAPs compared to the purified neurotoxin suggesting stronger immunogenicity of NAPs over that of purified neurotoxin and a higher potential of BoNT/AC and its associated proteins to induce host immune response. This observation also suggests that Hn-33 and other NAPs could potentially be employed as adjuvants for development of vaccines against botulism and could be a good surrogate for botulinum diagnostics. ELISA binding curves of BoNT/AC and BoNT/A with antibodies raised against BoNT/A indicate that BoNT/A in its purified and complex forms induces equal immunogenic response and a 2.5-fold higher immunogenic response compared to BoNT/A light and heavy chains. We have also discovered a new protein, an intimin analog, present within the complex preparation of BoNT/A which shows dramatically high immunoreactivity.

Comparison between intramuscular and perimuscular injections of botulinum toxin type A

BACKGROUND

Botulinum toxin type A (BTX-A) must be injected in the intramuscular area to exert its paralytic effect. The durability of the BTX-A effect varies in different patients, and this fact can result from different locations of the drug injection, for example, the muscle peripheral area (perimuscular). This study aimed to evaluate whether a difference exists in the effect duration of the muscle paralysis between intramuscular and perimuscular injections of BTX-A.

METHODS

This study used 18 male New Zealand rabbits divided into two groups (A and B) based on the location of the BTX-A injection. The group A animals received 10 units of BTX-A diluted with 0.1 ml of normal saline injected perimuscularly. The group B animals received the same dosage injected in the intramuscular area of the left masseter muscle. An electroneurophysiologic study was performed 1 week before the experiment for all the animals, then repeated 1, 4, and 8 weeks after the toxin injection.

RESULTS

The amplitude values recorded in the masseter muscle were significantly lower in both groups throughout the study than the physiologic amplitude. The comparison between groups A and B did not show any statistically significant amplitude variations throughout the 8 weeks.

CONCLUSION

No significant difference in the neuromuscular blockade induced by botulinum toxin type A was observed between injections into the muscle peripheral area and intramuscular injections.

Expression, Purification and Transduction of PEP-1-Botulinum Neurotoxin Type A (PEP-1-BoNT/A) into Skin

Botulinum neurotoxin A (BoNT/A) has been used therapeutically to treat muscular hypercontractions and sudomotor hyperactivity and it has been reported that BoNT/A might have analgesic properties in headache. PEP-1 peptide is a known carrier peptide that delivers full-length native proteins in vitro and in vivo. In this study, a BoNT/A gene were fused with PEP-1 peptide in a bacterial expression vector to produce a genetic in-frame PEP-1-BoNT/A fusion protein. The expressed and purified PEP-1-BoNT/A fusion proteins were efficiently transduced into cells in a time- and dose-dependent manner when added exogenously in a culture medium. In addition, immunohistochemical analysis revealed that PEP-1-BoNT/A fusion protein efficiently penetrated into the epidermis as well as the dermis of the subcutaneous layer, when sprayed on mice skin. These results suggest that PEP-1-BoNT/A fusion protein provide an efficient strategy for therapeutic delivery in various human diseases related to this protein.

Expanding use of botulinum toxin

Botulinum toxin type A (BTX-A) is best known to neurologists as a treatment for neuromuscular conditions such as dystonias and spasticity and has recently been publicized for the management of facial wrinkles. The property that makes botulinum toxin type A useful for these various conditions is the inhibition of acetylcholine release at the neuromuscular junction. Although botulinum toxin types A and B (BTX-A and BTX-B) continue to find new uses in neuromuscular conditions involving the somatic nervous system, it has also been recognized that the effects of these medications are not confined to cholinergic neurons at the neuromuscular junction. Acceptors for BTX-A and BTX-B are also found on autonomic nerve terminals, where they inhibit acetylcholine release at glands and smooth muscle. This observation led to trials of botulinum neurotoxins in various conditions involving autonomic innervation. The article reviews the emerging use of botulinum neurotoxins in these and selected other conditions, including sialorrhea, primary focal hyperhidrosis, pathological pain and primary headache disorders that may be of interest to neurologists and related specialists.

Urologic applications of botulinum toxin therapy for voiding dysfunction

Botulinum toxin is primarily a presynaptic neuromuscular blocking agent inducing selective and reversible muscle weakness up to several months when injected intramuscularly in small quantities. The clinical use of botulinum toxin type-A has gained widespread acceptance and application for numerous adult and pediatric spasticity syndromes. This has led to the urologic adoption of this minimally invasive therapy for the treatment of idiopathic and neurogenic detrusor overactivity, interstitial cystitis, detrusor-sphincter dyssynergia, urinary retention, and prostatic conditions. Outlined below is an overview of the clinical adoption of this therapy for the treatment of various dysfunctions of the lower urinary tract.

Injectable neuromodulatory agents: botulinum toxin therapy

Botulinum toxin therapy is a diverse treatment option for various dysfunctions of the lower urinary tract. The limited but growing clinical experience reveals that temporary chemodenervation with reduction or loss of neuronal activity at the target organ may be achieved with minimal risk. This highly favorable risk-benefit ratio in urology is derived from the clinical ability to treat an end-organ condition effectively with controllable site-specific delivery (eg, subcutaneous, intramuscular, or instillation) combined with high affinity for toxin uptake by the peripheral cholinergic nerves. Although many questions remain regarding the optimal use of this minimally invasive option for urologic applications, the opportunity for expanding indications will provide urologists with more options for addressing difficult challenges in voiding dysfunction.