Botulinum Toxin Type A Attenuates Hypertrophic Scars Formation by Preventing Macrophage M1 Polarization

Field: Medicine (Health Sciences)

BACKGROUND: Botulinum toxin type A has been shown to be a promising therapy for hypertrophic scars by alleviating muscle tension, inhibiting fibroblasts proliferation, and influencing transforming growth factor-β1 expression.1 However, persistent inflammation in wound healing is one of the main causes of hypertrophic scars.2 The severity of the inflammatory response is determined in large part by pro-inflammatory M1 macrophages.3 Studies have reported that botulinum toxin type A had an anti-inflammatory effect and could induce innate immune cell activation such as macrophages.4 Therefore, we hypothesized that botulinum toxin type A may reduce inflammation and inhibited the hypertrophic scars formation by preventing macrophage M1 polarization. MATERIALS AND METHODS: Murine macrophage RAW264.7 cells were cultured and treated with LPS (to induce M1 polarization) and botulinum toxin type A for 24 hours. M1-type markers such as iNOS, tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6 were determined by reverse transcription-quantitative polymerase chain reaction. The mouse model of hypertrophic scars was prepared by a mechanical stretch device5 and treated with botulinum toxin type A. Histologic studies were performed to evaluate scar hypertrophy by hematoxylin and eosin and Masson's trichrome staining. The pro-inflammatory cytokines such as TNF-α, IL-1β, and IL-6 were observed by immunohistochemistry. The M1 macrophages (F4/80+ iNOS+ cells) in vivo were further evaluated by immunofluorescence staining. RESULTS: The mRNA levels of iNOS, TNF-α, IL-1β, and IL-6 of RAW264.7 cells were significantly decreased in the botulinum toxin type A treated group than in the controls. In addition, histologic studies and immunohistochemistry showed that local administration of botulinum toxin type A significantly inhibited hypertrophic scars formation and reduced inflammatory response with decreased expression of TNF-α, IL-1β, and IL-6. Besides, botulinum toxin type A administration led to a decrease in the percentage of M1 macrophages in the scar tissue. CONCLUSION: Botulinum toxin type A inhibits macrophage M1 polarization during wound healing and attenuates hypertrophic scars formation. REFERENCES: 1. Chen HC, Yen CI, Yang SY, et al. Comparison of steroid and botulinum toxin type A monotherapy with combination therapy for treating human hypertrophic scars in an animal model. Plast Reconstr Surg. 2017;140:43e–49e. 2. Finnerty CC, Jeschke MG, Branski LK, et al. Hypertrophic scarring: the greatest unmet challenge after burn injury. The Lancet. 2016;388:1427–1436. 3. Chen L, Wang J, Li S, et al. The clinical dynamic changes of macrophage phenotype and function in different stages of human wound healing and hypertrophic scar formation. Int Wound J. 2018;16:360–369. 4. Yoo KY, Lee HS, Cho YK, et al. Anti-inflammatory effects of botulinum toxin type A in a complete Freund's adjuvant-induced arthritic knee joint of hind leg on rat model. Neurotox Res. 2014;26:32–39. 5. Wong VW, Rustad KC, Akaishi S, et al. Focal adhesion kinase links mechanical force to skin fibrosis via inflammatory signaling. Nat Med. 2012;18:148.