Pro-Inflammatory Signaling in Dermal Fibroblasts: A Possible Role of Different Botulinum Toxin Formulations on IL-6 Expression

Background: Botulinum toxin type A (BoNT-A) formulations are extensively employed in aesthetic and therapeutic dermatology. However, their immunomodulatory and pro-inflammatory properties remain incompletely characterized, particularly concerning dermal fibroblasts. Aims: This study aimed to evaluate and compare the effects of three commercially available BoNT-A formulations-Bocouture, Vistabex, and Azzalure-on the expression of interleukin-6 (IL-6), a key pro-inflammatory cytokine, in cultured adult human dermal fibroblasts. Patients/methods: Human dermal fibroblasts were cultured in vitro and treated with increasing concentrations of Bocouture, Vistabex, and Azzalure. IL-6 expression was measured at 24, 48, and 72 h posttreatment using an enzyme-linked immunosorbent assay (ELISA). Cell viability was assessed by MTT assay to exclude cytotoxic effects. Each condition was tested in triplicate. Data were analyzed using one-way ANOVA with Bonferroni's multiple comparisons posttest. Results: Vistabex significantly increased IL-6 expression at multiple time points, with the most marked elevation observed at 0.5 U/mL after 24 h (p ≤ 0.0001). Conversely, Bocouture and Azzalure did not induce significant changes in IL-6 levels across all tested concentrations and time intervals. No formulation reduced fibroblast viability below 80%, confirming the absence of relevant cytotoxicity. Conclusions: These findings suggest a formulation-specific inflammatory response to BoNT-A in dermal fibroblasts, with Vistabex eliciting a notable upregulation of IL-6. The observed differences may be attributed to distinct structural or excipient-related properties and warrant further investigation to clarify their clinical implications, especially in patients with a predisposition to inflammatory skin responses.