The mechanisms of action and use of botulinum neurotoxin type A in aesthetics: Key Clinical Postulates II

Overview of popular cosmeceuticals in dermatology

The eternal pursuit to prevent ageing and maintain a youthful appearance has resulted in a rapidly expanding cosmeceutical industry. Cosmeceutical products, particularly of natural origin, are in high demand due to claims of efficacy for signs of ageing and other skin conditions. Consumers often include cosmeceutical products in their skin care regime as they are readily available, and a more affordable option compared to prescription products. However, many cosmeceutical ingredients lack clinical evidence regarding their efficacy and safety as these products are not regulated by the U.S. Food and Drug Administration. This review provides a brief overview of several popular cosmeceutical ingredients with regards to their potential indications, targets and mechanisms of action.

Real-World Patient Experience With PrabotulinumtoxinA in the United Kingdom: A Single-Center Survey and Analysis of 254 Patients

Background

Botulinum toxin Type A (BoNT-A) injection is the most widely performed nonsurgical cosmetic procedure in the United Kingdom. PrabotulinumtoxinA is a new BoNT-A, recently licensed in the United Kingdom, for treating moderate-to-severe glabellar lines in adults under 65. Although clinical trials have established safety and efficacy, real-world data can help clinicians translate study findings into practice and support prabotulinumtoxinA use in a more diverse patient population.

Objectives

To understand the real-world patient experience and patient perceptions of prabotulinumtoxinA performance for treatment of the glabellar region.

Methods

In this single-center survey study, a single injector administered prabotulinumtoxinA for the treatment of glabellar lines to real-world patients presenting for BoNT-A treatment. Two weeks later, patients received surveys asking about their experience through email. There were no incentives for participation. Responses returned within 5 weeks of treatment were included.

Results

From February to June 2023, 457 patients received prabotulinumtoxinA injections for glabellar line treatment. Survey response rate was 56% (254/457 patients). For most patients, treatment onset was 2 to 3 days following injection and peak response occurred after 7 to 10 days. Adverse effects were minimal, with 67% of patients experiencing none. Among survey respondents, 83% rated their treatment positively (5-point satisfaction scale), and 72% would choose prabotulinumtoxinA again.

Conclusions

These data support safety and effectiveness of prabotulinumtoxinA in a diverse, real-world population, and confirm patient satisfaction among experienced BoNT-A patients, as well as suggest a rapid time to onset and peak effect.

Level of Evidence 4

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.

Contemporary treatment techniques for excessive gingival display caused by altered passive eruption or lip hypermobility

OBJECTIVES

Excessive gingival display (EGD), also known as gummy smile, has various causes, including altered passive eruption (APE) and hypermobile upper lip (HUL). This state-of-the art narrative review explores current concepts regarding soft tissue EGD etiologies and the contemporary modalities available for APE or HUL treatment.

DATA, SOURCES, STUDY SELECTION

Literature search was conducted for a narrative review on the etiology, diagnosis, and treatment of EGD caused by APE and HUL. Searching for articles was carried out in PubMed and Google Scholar. Published articles, including case reports, case series, observational and interventional clinical trials, and critical appraisals of the literature (e.g., systematic reviews) on the etiology, diagnosis, and treatment of EGD caused by APE and HUL were retrieved and reviewed. Particular focus was placed on novel treatment modalities introduced in the last five years.

CONCLUSIONS

Recent research evidence indicates that APE and HUL are the two major soft tissue-based EGD etiologies. Aesthetic crown lengthening (ACL) and lip repositioning surgery (LRS) are the established surgical treatment modalities for APE and HUL, respectively. The last few years have seen the introduction of new techniques for APE and HUL management, an expansion of the available ACL and LRS technique variations, and additional evidence further supporting the effectiveness of these two procedures. Several of the recently introduced approaches offer unique, innovative, and potentially impactful concepts. However, for many of these newly described treatments the available evidence is limited to case reports and the exact indications remain to be adequately defined.

CLINICAL SIGNIFICANCE

Altered passive eruption and hypermobile upper lip are the common soft tissue causes of gummy smile and can be successfully managed through aesthetic crown lengthening and lip repositioning surgery, respectively. A wide range of newly introduced approaches promises to further facilitate gummy smile treatment and improve outcomes.

SAMCEP Society consensus on the treatment of upper facial lines with botulinum neurotoxin type A: A tailored approach

BACKGROUND

The safety and efficacy of botulinum neurotoxin type A (BoNTA) treatments are well established, but injection techniques, target muscles, and toxin doses continue to evolve, with each refinement producing improvements in treatment outcomes. The recommendations in this consensus move away from standard templates and illustrate how to tailor treatments to individual patterns and strengths of muscle activity, and patient preferences.

METHODS

Seventeen experts in the fields of plastic surgery, dermatology, ophthalmology, otorhinolaryngology, and neurology convened in 2022 to develop consensus-based recommendations for the use of botulinum toxin A for the treatment of horizontal forehead lines, glabellar frown lines, and crow's feet lines that reflect current clinical practice. The focus was on how to tailor injections to individual patients to optimize treatment outcomes.

RESULTS

For each upper face indication, consensus members describe how to perform a dynamic assessment to optimize the dose and injection technique for each patient. A tailored treatment protocol is presented for commonly observed patterns of dynamic lines. Units of Inco are defined and the precise location of injection points, illustrated with the use of anatomical images.

CONCLUSION

This consensus provides up-to-date recommendations on the tailored treatment of upper facial lines based on the latest research and collective clinical experience of the expert injectors. Optimal outcomes require thorough patient evaluation, both at rest and during animation, using both visual and tactile cues; detailed understanding of facial muscular anatomy and how opposing muscles interact; and use of a BoNTA with high precision to target identified zones of excess muscle activity.

A Double-Blinded, Randomized, Dose-Comparison Pilot Study to Comparatively Evaluate Efficacy and Safety of Two Doses of Botulinum Toxin Type A Injection for Deltoid Muscle Hypertrophy

BACKGROUND

Botulinum toxin type A (BTX-A) injection is being widely used off-label for muscular hypertrophy, including deltoid muscle hypertrophy. However, very few studies have evaluated the optimal dosage and its clinical response.

OBJECTIVE

This study aimed to assess the efficacy and safety of different doses of Prabotulinum toxin A (PBoNT) for treating deltoid muscle hypertrophy.

METHODS

Twelve particiapants with bilateral deltoid muscle hypertrophy were enrolled and randomly received either 16 U or 32 U of PBoNT. In each participant, the same dose was administered to both deltoid muscles. Both participants and evaluators were blinded. Deltoid muscle thickness and upper arm circumference were measured on day 0, and weeks 2, 4, and 12 after the PBoNT injection.

RESULTS

Upper arm circumference significantly decreased in both groups; however, deltoid muscle thickness was reduced in the 16 U group only. No major complications were reported in both groups. However, a few minor complications were reported in the 16 U injection group.

CONCLUSION

Both 16 U and 32 U of PBoNT intramuscular injections are safe and effective in treating deltoid hypertrophy.

Management of Severe Botulinum-Induced Eyelid Ptosis With Pretarsal Botulinum Toxin and Oxymetazoline Hydrochloride 0.1

BACKGROUND

Eyelid ptosis following periocular onabotulinumtoxinA (BoNT-A) treatment is a known complication that can be frustrating for both patients and practitioners. Iatrogenic blepharoptosis occurs due to local spread of the BoNT-A from the periocular region into the levator palpebrae superioris muscle. Although injectors should have a thorough understanding of the relevant anatomy in order to prevent it, BoNT-A induced ptosis can occur even in the most experienced hands.

OBJECTIVES

The aim of this study was to describe a case series of patients treated effectively with topical oxymetazoline HCl 0.1% and pretarsal BoNT-A injections in the setting of botox-induced ptosis.

METHODS

The study group consisted of 8 patients who had undergone recent cosmetic BoNT-A treatment preceding the sudden onset of unilateral upper eyelid ptosis.

RESULTS

A diagnosis of severe ptosis (>3 mm) was made in all the cases in this series. Pretarsal BoNT-A injections alone or in association with topical administration of Upneeq eyedrops (Upneeq, Osmotica Pharmaceuticals, Marietta, GA) significantly reversed the ptosis in all treated cases.

CONCLUSIONS

This is the first documented case series of patients treated effectively with topical oxymetazoline HCl 0.1% and pretarsal BoNT-A injections in the setting of botox-induced ptosis. This treatment combination is a safe and effective option in these cases.

LEVEL OF EVIDENCE: 4

A Preclinical Study Comparing the Activity and Potency of OnabotulinumtoxinA and PrabotulinumtoxinA

Objective

The goal of this study was to compare the unit-to-unit biological activity of the vacuum-dried formulation of prabotulinumtoxinA (prabotA) and onabotulinumtoxinA (onabotA) in preclinical assays.

Methods

Reconstituted 100 U vials of prabotA and onabotA were tested in 3 distinct assays: plate-capture light chain activity (PC-LCA), measuringlight chain enzymatic activity after recovery of toxin from reconstituted product using a proprietary toxin capture step; cell-based potency assay (CBPA), measuring the intoxication steps of binding, translocation, and light chain activity (synaptosomal-associated protein 25 [SNAP25] cleavage); and mouse Digit Abduction Score (DAS), evaluating muscle paresis. Each assay tested 3 separate prabotA and onabotA lots on several independent test dates.

Results

Multiple orthogonal assays established that when assessed on a unit-to-unit basis, the biological activity of prabotA is lower than that of onabotA. In the PC-LCA and CBPA assays, onabotA displayed 1.51 ± 0.14-fold higher (mean ± SD) and 1.33 ± 0.07-fold higher (mean of pooled lots ± SEM) activity than prabotA, respectively. Similarly, the mouse DAS data showed that onabotA had 1.4 ± 0.1-fold higher (mean ± SEM) potency than prabotA. Results of all 3 assays demonstrated differences in potency, efficacy, and duration of action between onabotA and prabotA on a unit-to-unit basis.

Conclusion

Preclinical assays established differences in the biological activity of onabotA and prabotA, supporting that the units of biological activity are not interchangeable.

Discrimination of the Activity of Low-Affinity Wild-Type and High-Affinity Mutant Recombinant BoNT/B by a SIMA Cell-Based Reporter Release Assay

Botulinum neurotoxin (BoNT) is used for the treatment of a number of ailments. The activity of the toxin that is isolated from bacterial cultures is frequently tested in the mouse lethality assay. Apart from the ethical concerns inherent to this assay, species-specific differences in the affinity for different BoNT serotypes give rise to activity results that differ from the activity in humans. Thus, BoNT/B is more active in mice than in humans. The current study shows that the stimulus-dependent release of a luciferase from a differentiated human neuroblastoma–based reporter cell line (SIMA-hPOMC1-26-Gluc) was inhibited by clostridial and recombinant BoNT/A to the same extent, whereas both clostridial and recombinant BoNT/B inhibited the release to a lesser extent and only at much higher concentrations, reflecting the low activity of BoNT/B in humans. By contrast, the genetically modified BoNT/B-MY, which has increased affinity for human synaptotagmin, and the BoNT/B protein receptor inhibited luciferase release effectively and with an EC50 comparable to recombinant BoNT/A. This was due to an enhanced uptake into the reporter cells of BoNT/B-MY in comparison to the recombinant wild-type toxin. Thus, the SIMA-hPOMC1-26-Gluc cell assay is a versatile tool to determine the activity of different BoNT serotypes providing human-relevant dose-response data.

Botulinum toxin-induced blepharoptosis: Anatomy, etiology, prevention, and therapeutic options

Background

Botulinum toxin A (BoNT‐A) has grown tremendously in aesthetic dermatology since 2002 when the United States Food and Drug Administration (FDA) first approved its use for treating moderate‐to‐severe glabellar lines. Blepharoptosis, due to local spread of toxin, is a reported side effect of BoNT‐A which, although rare, more frequently occurs among inexperienced practitioners.

Objectives

The purpose of this review is to highlight the causes and management of eyelid ptosis secondary to BoNT‐A administration including new anatomic pathways for BoNT‐A spread from the brow area to the levator palpebrae superioris muscle.

Methods

A literature search was conducted using electronic databases (PubMed, Science Direct, MEDLINE, Embase, CINAHL, EBSCO) regarding eyelid anatomy and the underlying pathogenesis, presentation, prevention, and treatment of eyelid ptosis secondary to BoNT‐A. Anatomic dissection has been performed to assess the role of neurovascular pedicles and supraorbital foramen anatomic variations.

Results

Blepharoptosis occurs due to weakness of the levator palpebrae superioris muscle. Mean onset is 3–14 days after injection and eventually self‐resolves after the paralytic effect of BoNT‐A wanes. Administration of medications, such as oxymetazoline hydrochloride or apraclonidine hydrochloride eye drops, anticholinesterase agents, or transdermal BoNT‐A injections to the pre‐tarsal orbicularis, can at least partially reverse eyelid ptosis. Anatomic study shows that a supraorbital foramen may be present in some patients and constitutes a shortcut from the brow area directly into the orbital roof, following the supraorbital neurovascular pedicle.

Conclusion

Providers should understand the anatomy and be aware of the causes and treatment for blepharoptosis when injecting BoNT‐A for the reduction of facial wrinkles. Thorough anatomic knowledge of the supraorbital area and orbital roof is paramount to preventing incorrect injection into “danger zones,” which increase the risk of eyelid ptosis.

Botulinum Toxin Type A for Glabellar Frown Lines: What Impact of Higher Doses on Outcomes?

Botulinum toxin serotype-A (BoNT-A) preparations are widely used to improve the appearance of wrinkles. While effective and well tolerated, patients require retreatment over time to re-establish the effects. There is growing interest from patients as to whether higher doses can prolong response without significantly increasing side effects. We reviewed the efficacy and safety evidence for high-dose BoNT-A treatment of glabellar lines, by evaluating high-dose studies published since 2015. Toxins approved for glabellar line treatment in the US or Europe were considered. "High-dose" indicated doses above the licensed dose for each BoNT-A preparation. Five studies met the inclusion criteria and most were randomized, double-blind trials; designs and population sizes varied. Findings suggested that higher-dose BoNT-A treatment is feasible and may improve response duration without increased safety issues. Around 9 months' median duration was achieved with a 2-2.5-fold increase of the abobotulinumtoxinA on-label dose, or with a 5-fold increase in incobotulinumtoxinA dose. A 2-4-fold increase of the onabotulinumtoxinA on-label dose yielded a median duration of around 6 months. Importantly, patient satisfaction and natural look remained with increasing abobotulinumtoxinA doses. While more data are needed, these findings may lead to more effective, individually tailored treatment plans to meet patient expectations.

The mechanisms of action and use of botulinum neurotoxin type A in aesthetics: Key Clinical Postulates II

BACKGROUND

The literature on botulinum neurotoxin type A (BoNT-A) is extensive, often contradictory, and confounded by a competitive market of products and research attempting to distinguish brand individuality.

METHODS

A comprehensive review of literature on the principles of BoNT-A in aesthetics as well as clinical examples.

RESULTS

In 2017, the Eight Key Clinical Postulates were formulated as a guide for the aesthetic practitioner in understanding BoNT-A pharmacodynamics and to compare different toxins. These are now updated to include (a) All type A toxins act identically; (b) The mathematical relationship between toxin and receptor is the basis of efficacy, and clinical efficacy is influenced by molecular potency and patient attributes including muscle mass, gender, age, and ethnicity; (c) Efficacy, onset, and duration are functions of "molecular potency" defined as the number of active 150 kDa molecules available for binding; (d) "Molecular potency" is difficult to objectively quantify for commercially available toxins; (e) Up to a point, increased molecular potency decreases time to onset and increases duration of effect, and the "Molecular Potency Quotient" is a construct for comparing molecular potency commercial cost; (f) The area of effect of a toxin injection is dependent upon molecular potency, diffusion (passive), and spread (active); (g) Differing reconstitution volumes; and (h) Increased number of injection sites can affect spread, onset, and duration of effect.

CONCLUSIONS

The principles of BoNT-A use in aesthetics are complex yet understandable as outlined in the framework of the updated Eight Key Clinical Postulates and serves as a useful tool for providing the most effective treatment and interpreting research on present and future toxin formulations.