This joint study by Imavita and the biopharmaceutical group Ipsen, published in late 2023 in Toxicon, compares the effects of a single injection of aboBoNT-A (botulinum toxin) with those of daily treatment using adapalene. The trial was conducted in “Rhino” mice, a commonly used preclinical animal model for studying acne. This model allows for rigorous exploration of the effects of novel therapeutic approaches on the skin.
From acne to skin aging: an innovative therapeutic approach
The main objective was to determine whether BoNT/A could serve as an alternative or complement to standard acne treatments, while also providing an overall benefit to skin quality. To achieve this, the team compared the effects of a single intradermal injection of aboBoNT-A with those of a daily topical application of adapalene for two weeks. This third-generation retinoid is commonly prescribed as a first-line treatment for moderate acne.
Experimental data and methodology
The experiments were conducted on 6- to 8-week-old female RHJ/LeJ mice (Rhino model). After an acclimation period, animals received, under anesthesia, an intradermal injection of aboBoNT-A (0.1 U, 0.3 U, or 1 U) at four sites on the back, or a daily topical application of adapalene 0.1% gel for 15 days. Skin thickness, erythema, desquamation, and body weight were monitored throughout the study.
The following biochemical and histopathological parameters were assessed:
- Macro- and microscopic skin analysis (skin thickness, erythema, desquamation)
- Quantification of inflammatory markers, particularly IL-1α (a key marker of skin inflammation)
- Lipid composition of sebum
- Tissue levels of substance P
- Cellular integrity of major skin cell populations (keratinocytes, fibroblasts, sebocytes).
All procedures were carried out in accordance with European regulations (Directive 2010/63/EU) and approved by an independent ethics committee (APAFIS #3495–2016010816311469).
➡️ Also discover how Imavita implements the 3Rs principles in its preclinical studies (Replace, Reduce, Refine).
Why use the rhino mouse as a preclinical dermatology model?
The rhino mouse (RHJ/LeJ) is a well-established preclinical model for testing dermatological treatments. It has genetic traits that lead to the formation of pseudo-comedones filled with keratin and sebum, resembling human blackheads. Although no animal model fully replicates human acne, the Rhino mouse presents altered sebaceous follicles, making it a relevant tool to evaluate the effects of molecules on the skin, such as retinoids or botulinum toxin.
The following biochemical and histopathological parameters were assessed:
- Macro- and microscopic skin analysis (skin thickness, erythema, desquamation)
- Quantification of inflammatory markers, particularly IL-1α (a key marker of skin inflammation)
- Lipid composition of sebum
- Tissue levels of substance P
- Cellular integrity of major skin cell populations (keratinocytes, fibroblasts, sebocytes).
All procedures were carried out in accordance with European regulations (Directive 2010/63/EU) and approved by an independent ethics committee (APAFIS #3495–2016010816311469).
➡️ Also discover how Imavita implements the 3Rs principles in its preclinical studies (Replace, Reduce, Refine).
Skin benefits achieved with botulinum toxin AboBoNT-A
Administration of aboBoNT-A led to several positive effects on the skin of treated mice compared to adapalene. These effects include better local tolerance, reduced inflammation, cellular stability, and improved lipid quality of the skin.
Reduction in skin thickness without erythema or desquamation in mice
AboBoNT-A caused a moderate decrease in dorsal skin thickness (a beneficial therapeutic effect) without inducing erythema or desquamation, unlike adapalene treatment. Although adapalene produced a similar reduction in skin thickness, it was accompanied by visible signs of skin irritation.
Decrease in dermal inflammation without epidermal thickening
Histological analyses revealed a significant, dose-dependent reduction in immune cell infiltration in the dermis with AboBoNT-A. This effect was not associated with epidermal hyperplasia (abnormal proliferation of epidermal layers), in contrast to adapalene. In fact, adapalene caused significant epidermal hyperplasia (+188%), along with parakeratosis and dermal inflammation (+23%).
Preservation of cellular integrity in skin tissues
Cellular analyses showed that botulinum toxin does not impair the essential functions of key skin cell types. There was no observed effect on the proliferation of sebocytes, fibroblasts, or keratinocytes
Dose-dependent increase in substance P levels in skin without inflammatory response
AboBoNT-A induced a significant, dose-dependent increase in the neuropeptide substance P in skin tissue, without an increase in inflammatory cytokines such as IL-1α. This suggests a neuromodulatory rather than an inflammatory mechanism.
What is substance P?
Substance P is a neuropeptide released by nerves and certain immune cells. It plays an important role in pain transmission, inflammatory responses, and blood vessel dilation. In the skin, it can also influence sebum production. When it accumulates without triggering inflammation, it may indicate that nerve signals are being modulated without aggressive reactions or adverse effects on the skin.
Improved skin quality and potential protective effect through modification of sebum composition
Unlike retinoids, aboBoNT-A did not reduce the amount of sebum produced on the skin’s surface. Lipidomic analyses revealed a marked increase in certain protective lipids: squalene, cholesterol, fatty acids (FA4), and cholesterol esters (up to +440% at the highest doses of aboBoNT-A). These components are known for their moisturizing, antioxidant, and skin barrier-protective properties.
Overall, the results suggest that aboBoNT-A may help improve overall skin quality and provide a protective effect against environmental stressors or age-related changes. Indeed, maintaining high-quality sebum secretion plays an important role in preventing premature skin aging.
How can the skin effects of aboBoNT-A be explained?
The results observed in this study—reduction of inflammation, improvement in the lipid profile of sebum, and absence of irritating effects—suggest that aboBoNT-A acts beyond its well-known neuromuscular effect. We propose several mechanistic hypotheses to explain these outcomes.
Overall, the results suggest that aboBoNT-A may help improve overall skin quality and provide a protective effect against environmental stressors or age-related changes. Indeed, maintaining high-quality sebum secretion plays an important role in preventing premature skin aging.
Blockade of neuropeptide exocytosis
A dose-dependent increase in substance P concentration was observed in the treated skin tissues, without any rise in IL-1α levels. This accumulation of neuropeptides may result from an inhibition of exocytosis, a mechanism well-documented for botulinum toxin.
By blocking exocytosis, the toxin reduces the release of pain and inflammation mediators such as substance P. This may contribute to improved skin tolerance, reduced redness, and overall soothing of the tissue, without triggering an excessive inflammatory response.
Overall, the results suggest that aboBoNT-A may help improve overall skin quality and provide a protective effect against environmental stressors or age-related changes. Indeed, maintaining high-quality sebum secretion plays an important role in preventing premature skin aging.
How does botulinum toxin inhibit exocytosis?
To release certain molecules like substance P, cells use a transport system called exocytosis, in which vesicles fuse with the cell membrane. This process relies on the SNARE complex—a kind of molecular “zipper” made up of several proteins, including SNAP25. By cleaving SNAP25, botulinum toxin blocks this mechanism, thereby preventing the release of neuropeptides into the extracellular space.
Interaction with skin receptors
BoNT/A may bind to various receptors expressed on the surface of skin cells: SV2 (the classic neuronal receptor), TRPV1 (involved in sebocyte regulation), and FGFR3 (found on fibroblasts and keratinocytes).
These local interactions could contribute to the observed improvement in skin quality following treatment.
Modulation of lipid synthesis and sebum composition
BoNT/A may act directly or indirectly on enzymes involved in lipid production by sebocytes. Some studies suggest a possible interaction at the cell surface without internalization or SNARE (Soluble N-ethylmaleimide-Sensitive Factor Attachment protein Receptor) cleavage, indicating a non-conventional mechanism of action.
Indirect effects via non-neuronal cells: keratinocytes or fibroblasts
BoNT/A could also exert indirect effects on the skin through keratinocytes, fibroblasts, or smooth muscle cells. These cells play essential roles in skin structure, lipid regulation, and inflammatory responses.
Although these hypotheses require further validation, they broaden our understanding of BoNT/A’s skin-related effects, offering new perspectives in dermatology beyond its traditional aesthetic applications.
Reference :
Maignel J, Albinet V, Chusseau M, Lacoste E. AbobotulinumtoxinA improves skin properties and sebum quality in the rhino mouse. Toxicon. 2023 Sep;233:107230. doi: 10.1016/j.toxicon.2023.107230.