Metformin Alleviates DNCB-Induced Contact Dermatitis in vivo and in vitro by Inhibiting Necroptosis of Keratinocytes

Objective: Metformin is a well-known anti-diabetic drug that has also been reported to alleviate various inflammatory diseases. However, whether metformin can mitigate contact dermatitis and the underlying mechanisms remain unknown. Therefore, we conducted these in vitro and in vivo experiments to investigate the therapeutic effects of metformin on 2,4-dinitrochlorobenzene (DNCB)–induced contact dermatitis. Methods: The animal model used in the experiment was DNCB-induced contact dermatitis model, and HaCaT cells were used for in vitro experiments. Animal experiments were conducted in randomized groups. Patch tests were conducted to evaluate the irritation caused by different concentrations of metformin on mouse skin, and determined the optimal metformin concentration for following experiments. Propidium iodide staining was used to label dead cells, and western blotting was performed to assess changes in protein levels following metformin treatment. Immunofluorescence experiments were used to compare phosphorylated mixed lineage kinase domain-like protein levels before and after topical metformin administration in a DNCB-induced contact hypersensitivity mouse model. Data from the 2 groups were analyzed using the t test, and for comparisons involving 3 or more groups, a one-way analysis of variance was used. Results: In a DNCB-induced contact hypersensitivity mouse model, topical application of 4.0% metformin significantly alleviated skin inflammation (the dermatitis score reduced from 9.83 ± 0.29 to 5.17 ± 0.76, P < 0.05), and reduced the proportion of dead cells from 46.83% ± 9.25% to 9.77% ± 9.54% ( P < 0.05), and reduced phosphorylation levels of mixed lineage kinase domain-like protein in keratinocytes. In vitro experiments further demonstrated that metformin inhibited necroptosis in HaCaT cells under a contact dermatitis–like environment simulated by tumor necrosis factor-α and interferon-γ. Conclusions: These findings suggest that metformin inhibits keratinocyte necroptosis, thereby alleviating inflammation in contact dermatitis. The topical application of metformin may represent a potential therapeutic approach for contact dermatitis, which needs further in vitro and in vivo experiments for investigation.