Inhibitory effect of kaempferol on skin fibrosis in systemic sclerosis by the suppression of oxidative stress

Background There is growing evidence that vasculopathy-induced hypoxia and oxidative stress enhance the process of fibrosis in systemic sclerosis (SSc). Kaempferol is a natural flavonoid widely found in various vegetables and fruits, and has been reported to have excellent antioxidant activity. Objective Objective was to elucidate the effect of kaempferol on skin fibrosis and the mechanism of the inhibitory regulation of fibrosis by kaempferol. Methods We assessed the effect of intraperitoneally administered kaempferol on bleomycin-induced dermal fibrosis in mice. The effect of kaempferol on oxidative stress in bleomycin-treated mice and SSc fibroblasts was assessed in vivo and in vitro. Results We identified that kaempferol injection significantly inhibited bleomycin-induced dermal fibrosis in mice. The number of αSMA+ myofibroblasts, CD3+ T-cells, and CD68+ macrophages in lesional skin was significantly decreased by kaempferol injections. Kaempferol administration also significantly suppressed the bleomycin-induced oxidative stress signal in OKD48 mice. Additionally, mRNA levels of oxidative stress-associated factors, such as HO-1 and NOX2, as well as inflammatory and pro-fibrotic cytokines, including IL-6, TGF-β and TNFα in sclerotic skin were significantly decreased by kaempferol. Kaempferol also reduced bleomycin-induced TUNEL+ apoptotic cells in the lesional skin of bleomycin-treated mice. Furthermore, the oxidant-induced intracellular accumulation of reactive oxygen species (ROS) in SSc fibroblasts was inhibited by kaempferol treatment. In addition, the oxidant-induced apoptosis of SSc fibroblasts was decreased by kaempferol in vitro. Conclusion Kaempferol might improve bleomycin-induced fibrosis by reducing oxidative stress, inflammation, and oxidative cellular damage. Administration of kaempferol might be an alternative treatment for skin fibrosis in SSc.