Metformin Inhibits Transforming Growth Factor β-Induced Fibrogenic Response of Human Dermal Fibroblasts and Suppresses Fibrosis in Keloid Spheroids

Accumulation of excessive extracellular matrix (ECM) and aberrant transforming growth factor beta (TGF-beta) signaling pathway function can be potential therapeutic targets for keloid treatment. In this study, we examined the antifibrotic effect of metformin as a suppressor of TGF-beta signaling pathways in human dermal fibroblasts (HDFs) and keloid spheroids. Human dermal fibroblasts were stimulated with TGF-beta (10 ng/mL) and treated with metformin (10 mM). The mRNA and protein expression of ECM components were evaluated by quantitative polymerase chain reaction, western blot, and immunofluorescence assay. In addition, we immunohistochemically examined the expression levels of ECM proteins in keloid spheroids. After addition of metformin (10 mM), collagen types I and III and elastin mRNA levels were significantly decreased in HDFs, and collagen type I protein level was significantly decreased. In addition, the expression levels of collagen types I and III, fibronectin, and elastin were significantly reduced in keloid spheroids after treatment with metformin (100 mM). Collagen types I and III and p-Smad2/3 complex proteins were decreased in metformin-treated keloid spheroids. These findings indicated that metformin inhibits the expression of ECM components in TGF-beta-stimulated HDFs and keloid spheroids. Therefore, we suggest the potential of metformin as an effective agent for the treatment of keloids.