Botulinum toxin therapy: past, present and future developments

Five decades of the use of botulinum toxin in ophthalmology

Botulinum toxin (BoNT) has been known for over 50 years. It has conquered many areas of medicine and has become indispensable in contemporary medicine. Now, BoNT is used to treat at least 26 conditions in six medical specialties. Although the use of BoNT began in strabology, it became the gold standard for many ophthalmologic pathologies. The present review of the literature focuses on the use of BoNT in ophthalmology and treatment of the following conditions: blepharospasm, facial hemispasm, facial palsy, spastic entropion, strabismus, endocrine orbitopathy, convergence spasm, and facial trauma. We conclude that nearly half a century of experience in utilizing BoNT in ophthalmology ensured a satisfactory level of effectiveness and safety for patients with many pathologies. Areas of future research include the application of BoNT in new selected indications, the development of the route of application without injections, and the development of long-acting BoNT forms for patients who require repeated long-term treatment.

Botulinum toxin type a antinociceptive activity in trigeminal regions involves central transcytosis

OBJECTIVE

Botulinum toxin type A (BoNT-A) provides lasting pain relief in patients with craniofacial pain conditions but the mechanisms of its antinociceptive activity remain unclear. Preclinical research revealed toxin axonal transport to the central afferent terminals, but it is unknown if its central effects involve transsynaptic traffic to the higher-order synapses. To answer this, we examined the contribution of central BoNT-A transcytosis to its action in experimental orofacial pain.

MATERIAL AND METHODS

Male Wistar rats, 3-4 months old, were injected with BoNT-A (7 U/kg) unilaterally into the vibrissal pad. To investigate the possible contribution of toxin's transcytosis, BoNT-A-neutralizing antiserum (5 IU) was applied intracisternally. Antinocicepive BoNT-A action was assessed by duration of nocifensive behaviors and c-Fos activation in the trigeminal nucleus caudalis (TNC) following bilateral or unilateral formalin (2.5%) application into the vibrissal pad. Additionally, cleaved synaptosomal-associated protein of 25 kDa (cl-SNAP-25) immunoreactivity was analyzed in the bilateral TNC.

RESULTS

Unilaterally injected BoNT-A reduced the nocifensive behaviors and bilateral c-Fos activation induced by formalin, which was accompanied by the toxin's enzymatic activity on both sides of the TNC. BoNT-A antinociceptive or enzymatic activities were prevented by the specific neutralizing antitoxin. BoNT-A contralateral action occurred independently from ipsilateral side nociception or contralateral trigeminal nerve-mediated axonal traffic.

CONCLUSION

Herein, we demonstrate that antinociceptive action of pericranially administered BoNT-A involves transsynaptic transport to second order synapses and contralateral trigeminal nociceptive nuclei. These results reveal more complex central toxin activity, necessary to explain its clinical effectiveness in the trigeminal region-related pain states.

The Impact of Botulinum Toxin Injection on the Outcomes of Breast Surgeries: A Systematic Review and Meta-Analysis

BACKGROUND

Breast surgeries aim to restore the natural appearance of the breasts with acceptable functional and cosmetic outcomes. However, these surgical procedures may be associated with considerable adverse events. The present systematic review and meta-analysis was designed to reveal the functional and aesthetic outcomes of botulinum toxins (BTX) injection in patients subjected to breast surgeries.

METHODS

A literature review was performed up to 21 September 2022. All clinical studies included patients older than 18 years old and treated with BTX injection for breast surgeries were included.

RESULTS

The present study included 12 articles, encompassing 496 patients. The average dosage of BTX injection ranged from 20 to 100 units. Injecting BTX significantly reduced the mean post-operative opioid analgesics usage (SMD -1.577; 95% -2.087, -1.067; P < 0.001) and the risk of severe animation deformity (RR 12.37; 95% 1.76, 86.66; P = 0.01). There was a statistically significant higher mean expansion volume per visit in the BTX injection group (SMD 1.166; 95% 0.313, 2.018; P = 0.007). There was no statistically significant impact of BTX injection on the risk of surgical site infection (RR 0.59; 95% 0.15, 2.34; P = 0.45) and seroma (RR 0.51; 95% 0.03, 10.15; P = 0.66).

CONCLUSIONS

The present study revealed the potential benefits of BTX injection in breast surgeries. This included reduced post-operative analgesics, as well as the risk of severe animation deformity. This was accomplished with increased expansion volume per visit and a similar risk of BTX injection-related complications.

LEVEL OF EVIDENCE III

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Blocking insulin-like growth factor 1 receptor signaling pathway inhibits neuromuscular junction regeneration after botulinum toxin-A treatment

Botulinum toxin-A (BTX) administration into muscle is an established treatment for conditions with excessive muscle contraction. However, botulinum therapy has short-term effectiveness, and high-dose injection of BTX could induce neutralizing antibodies against BTX. Therefore, prolonging its effects could be beneficial in a clinical situation. Insulin-like growth factor-1 receptor (IGF1R) and its ligands, insulin-like growth factor (IGF) -I and II, regulate the physiological and pathological processes of the nervous system. It has been suggested that IGF1R is involved in the process after BTX administration, but the specific regeneration mechanism remains unclear. Therefore, this study aimed to determine how inhibition of IGF1R signaling pathway affects BTX-induced muscle paralysis. The results showed that anti-IGF1R antibody administration inhibited the recovery from BTX-induced neurogenic paralysis, and the synaptic components at the neuromuscular junction (NMJ), mainly post-synaptic components, were significantly affected by the antibody. In addition, the wet weight or frequency distribution of the cross-sectional area of the muscle fibers was regulated by IGF1R, and sequential antibody administration following BTX treatment increased the number of Pax7+-satellite cells in the gastrocnemius (GC) muscle, independent of NMJ recovery. Moreover, BTX treatment upregulated mammalian target of rapamycin (mTOR)/S6 kinase signaling pathway, HDAC4, Myog, Fbxo32/MAFbx/Atrogin-1 pathway, and transcription of synaptic components, but not autophagy. Finally, IGF1R inhibition affected only mTOR/S6 kinase translational signaling in the GC muscle. In conclusion, the IGF1R signaling pathway is critical for NMJ regeneration via specific translational signals. IGF1R inhibition could be highly beneficial in clinical practice by decreasing the number of injections and total dose of BTX due to the prolonged duration of the effect.

Special Issue: Gram-Positive Bacterial Toxins

The Gram stain classifies most bacteria into one of two groups, Gram-negative or Gram-positive, based on the composition of their cell walls [...].

Biology activity and characterization of the functional L-HN fragment derivative of botulinum neurotoxin serotype E

OBJECTIVES

The mature botulinum neurotoxin (BoNT) is a long peptide chain consisting of a light chain (L) and a heavy chain (H) linked by a disulfide bond, where the heavy chain is divided into a translocation domain and an acceptor binding domain (Hc). In this study, we further explored the biology activity and characteristics of recombinant L-HN fragment (EL-HN) composed of the L and HN domains of BoNT/E in vivo and in vitro.

METHODS

Neurotoxicity of L-HN fragments from botulinum neurotoxins was assessed in mice. Cleavage of dichain EL-HN in vitro and in neuro-2a cells was assessed and compared with that of single chain EL-HN. Interaction of HN domain and the receptor synaptic vesicle glycoprotein 2C (SV2C) was explored in vitro and in neuro-2a cells only expressing SV2C.

RESULTS

We found that the 50% mouse lethal dose of the nicked dichain EL-HN fragment (EL-HN-DC) was 0.5 μg and its neurotoxicity was the highest among the L-HN's of the four serotypes of BoNT (A/B/E/F). The cleavage efficiency of EL-HN-DC toward synaptosome associated protein 25 (SNAP25) in vitro was 3-fold higher than that of the single chain at the cellular level, and showed 200-fold higher animal toxicity. The EL-HN-DC fragment might enter neuro-2a cells via binding to SV2C to efficiently cleave SNAP25.

CONCLUSIONS

The EL-HN fragment showed good biological activities in vivo and in vitro, and could be used as a drug screening model and to further explore the molecular mechanism of its transmembrane transport.

A Low Concentration of Citreoviridin Prevents Both Intracellular Calcium Deposition in Vascular Smooth Muscle Cell and Osteoclast Activation In Vitro

Vascular calcification (VC) and osteoporosis are age-related diseases and significant risk factors for the mortality of elderly. VC and osteoporosis may share common risk factors such as renin-angiotensin system (RAS)-related hypertension. In fact, inhibitors of RAS pathway, such as angiotensin type 1 receptor blockers (ARBs), improved both vascular calcification and hip fracture in elderly. However, a sex-dependent discrepancy in the responsiveness to ARB treatment in hip fracture was observed, possibly due to the estrogen deficiency in older women, suggesting that blocking the angiotensin signaling pathway may not be effective to suppress bone resorption, especially if an individual has underlying osteoclast activating conditions such as estrogen deficiency. Therefore, it has its own significance to find alternative modality for inhibiting both vascular calcification and osteoporosis by directly targeting osteoclast activation to circumvent the shortcoming of ARBs in preventing bone resorption in estrogen deficient individuals. In the present study, a natural compound library was screened to find chemical agents that are effective in preventing both calcium deposition in vascular smooth muscle cells (vSMCs) and activation of osteoclast using experimental methods such as Alizarin red staining and Tartrate-resistant acid phosphatase staining. According to our data, citreoviridin (CIT) has both an anti-VC effect and anti-osteoclastic effect in vSMCs and in Raw 264.7 cells, respectively, suggesting its potential as an effective therapeutic agent for both VC and osteoporosis.

How Does Botulinum Toxin Inhibit Itch?

Two decades after reports of the anti-pruritic effects of botulinum neurotoxins (BoNTs), there is still no approved product for the anti-itch indication of BoNTs, and most clinical case reports still focus on the off-label use of BoNTs for various itchy conditions. Few randomized clinical trials have been conducted with controversial results, and the beneficial effects of BoNTs against itch are mainly based on case studies and case series. These studies are valuable in presenting the potential application of BoNTs in chronic pruritic conditions, but due to the nature of these studies, they are categorized as providing lower levels of evidence or lower grades of recommendation. To obtain approval for the anti-pruritic indication of BoNTs, higher levels of evidence are required, which can be achieved through conducting large-scale and well-designed studies with proper control groups and established careful and reliable primary and secondary outcomes. In addition to clinical evidence, presenting the mechanism-based antipruritic action of BoNTs can potentially strengthen, accelerate, and facilitate the current efforts towards further investments in accelerating the field towards the potential approval of BoNTs for itchy conditions. This review, therefore, aimed to provide the state-of-the-art mechanisms underlying the anti-itch effect of BoNTs from basic studies that resemble various clinical conditions with itch as a hallmark. Evidence of the neuronal, glial, and immune modulatory actions of BoNTs in reducing the transmission of itch are presented, and future potential directions are outlined.