Effect of Botulinum Toxin Type A on Differentiation of Fibroblasts Derived from Scar Tissue

Background: Although botulinum toxin type A has been shown to inhibit the formation of hypertrophic scars, little is known about the underlying mechanisms of action. Studies have reported that botulinum toxin type A is able to inhibit fibroblast proliferation and transforming growth factor (TGF)-beta 1 expression; therefore, in this study, the authors evaluated its effect on the differentiation of fibroblasts derived from normal and hypertrophic scar tissue. Methods: Under local anesthesia, tissue specimens from 10 scars (five normal mature scars and five hypertrophic scars) were obtained from nine patients who visited the authors' department for scar revision. Fibroblasts isolated from the tissue specimens were cultured until confluent and pretreated with TGF-beta 1 to induce differentiation before treatment with botulinum toxin type A. Expression of the myofibroblast marker alpha-smooth muscle actin in cell cultures was evaluated by enzyme-linked immunosorbent assay and quantitative reverse transcription polymerase chain reaction. Fibroblast-to-myofibroblast differentiation was further evaluated by immunocytochemistry and confocal microscopy. Results: The authors' results showed that alpha-smooth muscle actin mRNA and protein levels were significantly lower in the botulinum toxin type A-treated group than in the control group (treated with TGF-beta 1 only) of fibroblasts derived from hypertrophic scars, but not fibroblasts derived from normal scars. Immunocytochemistry results also showed that fibroblast-to-myofibroblast differentiation was significantly decreased after botulinum toxin type A treatment in fibroblasts derived from hypertrophic scars. Conclusion: The authors' results show that botulinum toxin type A directly inhibits fibroblast-to-myofibroblast differentiation in vitro, and indicate its potential for use in treating wounds expected to develop into hypertrophic scars after trauma, burn, or surgery.