A study of botulinum toxin type A for the treatment of ultraviolet B-induced hyperpigmentation: a prospective, randomized, controlled trial

Botulinum neurotoxin type DC (BoNT/DC) cleavage of VAMP3 reduces melanin production in melanocytes

Melanin in skin and hair protects cells from UV damage; however, uneven skin color or hyperpigmentation is a common aesthetic concern. Melanin is synthesized in melanosomes, organelles within melanocytes, where tyrosinase converts tyrosine to melanin. Trafficking of tyrosinase or other cargo (eg, premelanosome protein [PMEL]) may depend on vesicle-associated membrane proteins (VAMPs); interfering with VAMPs has been reported to impact melanogenesis. Botulinum neurotoxin type DC (BoNT/DC) is a naturally occurring mosaic serotype that cleaves the SNARE proteins VAMP1-3. This study evaluated BoNT/DC as a potential treatment for hyperpigmentation by testing if it affects melanogenesis. In melanocytes, BoNT/DC cleaved VAMP2 and VAMP3, and knockdown of VAMP3, but not VAMP2, reduced melanin content, which suggests that BoNT/DC may affect melanogenesis via VAMP3 cleavage. Indeed, BoNT/DC (5 nM) produced a ∼50 % reduction in melanin content in melanocytes, and in 2 human melanocyte models, BoNT/DC, but not BoNT/A, significantly reduced melanin content (∼40-50 %) without cytotoxicity. Electron microscopy showed that BoNT/DC-treated melanocytes contained more early-stage (II) and fewer late-stage (IV) melanosomes than vehicle- or BoNT/A-treated melanocytes. Overall, BoNT/DC reduced melanin content in multiple melanocyte models, and its lightening effects are likely due to VAMP3 cleavage interfering with trafficking of cargo (eg, tyrosinase, PMEL) required for melanogenesis.

Melasma Management: A Comprehensive Review of Treatment Strategies Including BTX-A

BACKGROUND

Botulinum toxin A (BTX-A) is a widely utilized protein derived from the bacterium Clostridium botulinum, known for its effectiveness in treating various medical conditions involving muscle spasticity, involuntary muscle movements, and pain disorders. Beyond its therapeutic applications, BTX-A is also commonly used in cosmetic procedures to address dynamic wrinkles, hyperhidrosis, sebum production, pore size, and overall skin texture. While the use of neurotoxins like BTX-A for treating conditions such as UVB-induced hyperpigmentation, specifically melasma, is an emerging area of interest, it is not yet a widely recognized treatment for this dermatologic condition. This literature review serves to provide a consolidated overview of the current therapeutic implications of BTX-A treatment for melasma and explore its proposed mechanisms of action.

OBJECTIVE

This review aims to provide a comprehensive analysis of the current evidence base for the efficacy of BTX-A treatment on melasma.

METHODS

To gain a comprehensive understanding on the current theories regarding BTX-A treatment on melasma, a literature review was conducted on all the available information using PubMed. A combination of keywords was used to maximize the search results, including "botulinum toxin," "melasma," "melanogenesis," "neurotoxin," "cholinergic system," "BTX-A," and "UV-induced melasma." The search was not restricted by date, allowing for the inclusion of articles offering historical context and those providing the most recent findings. Ninety-eight articles were reviewed to provide a consolidated update on the effectiveness of botulinum toxin A in reducing the appearance of melasma and potential mechanisms of action involved in doing so.

CONCLUSION

Melasma is a challenging dermatologic condition due to its chronicity and various intrinsic and extrinsic factors that influence its pathogenesis. While current treatment options for melasma include topical, oral, and light-based therapies, recent studies suggest that BTX-A may hold potential as a viable treatment modality for melasma. Despite the mechanism of action remaining unclear, it is hypothesized that BTX-A inhibition of Ach receptors on melanocytes could play a role in the reduction of melanogenesis. BTX-A treatment in melasma-affected skin demonstrates statistically significant reduction in hyperpigmented lesions associated with melasma.

Incobotulinum Toxin Type A for Treatment of Ultraviolet-B-Induced Hyperpigmentation: A Prospective, Randomized, Controlled Trial

Incobotulinum toxin A (IncoBoNT-A) is effective in preventing ultraviolet B (UVB)-induced hyperpigmentation. This prospective, randomized, controlled study aimed to evaluate the effect of IncoBoNT-A on the treatment of UVB-induced hyperpigmentation in 15 volunteers. Five hyperpigmentation squares (2 × 2 cm) were induced by local UVB on the abdomen at baseline. At Day 7, each site was randomized to receive no treatment (control), normal saline, or intradermal IncoBoNT-A injection with 1:2.5, 1:5, and 1:7.5 dilutions (12, 6, and 4 units, respectively). The mean lightness index (L*), hyperpigmentation improvement score evaluated by blinded dermatologists, and participant satisfaction scores were obtained at Days 21, 28, and 35. At Day 21, improvements in mean L* of 1:2.5, 1:5, and 1:7.5 IncoBoNT-A-treated, saline-treated, and control sites were 14.30%, 12.28%, 6.62%, 0.32%, and 4.98%, respectively (p = 0.86). At Day 28, the improvement in mean L* in IncoBoNT-A-treated groups was superior to that in the other groups. In terms of the hyperpigmentation improvement score, 12 participants (80%) experienced better outcomes with the IncoBoNT-A-injected site compared with the other sites. IncoBoNT-A, especially at higher concentrations, showed some positive effects on the treatment of UVB-induced hyperpigmentation. This may serve as an adjuvant treatment for hyperpigmentary conditions that are aggravated by UVB.