Background: Systemic sclerosis (SSc; also known as “scleroderma”) is an autoimmune disorder characterized by extensive fibrosis, vascular changes, and immunologic dysregulation. Baicalein (phenolic flavonoid derived from Scutellaria baicalensis Georgi) has been used to treat the pathological processes of various fibrotic and inflammatory diseases. In this study, we investigated the effect of baicalein on the major pathologic characteristics of SSc: fibrosis, B-cell abnormalities, and inflammation. Methods: The effect of baicalein on collagen accumulation and expression of fibrogenic markers in human dermal fibroblasts were analyzed. SSc mice were produced by injecting bleomycin and treated with baicalein (25, 50, or 100 mg/kg). The antifibrotic features of baicalein and its mechanisms were investigated by histologic examination, hydroxyproline assay, enzyme-linked immunosorbent assay, western blotting and flow cytometry. Results: Baicalein (5–120 μM) significantly inhibited the accumulation of the extracellular matrix and fibroblast activation in transforming growth factor (TGF)-β1- and platelet derived growth factor (PDGF)-induced human dermal fibroblasts, as evidenced by abrogated deposition of total collagen, decreased secretion of soluble collagen, reduced collagen contraction capability and downregulation of various fibrogenesis molecules. In a bleomycin-induced model of dermal fibrosis in mice, baicalein (25–100 mg/kg) restored dermal architecture, ameliorated inflammatory infiltrates, and attenuated dermal thickness and collagen accumulation in a dose-dependent manner. According to flow cytometry, baicalein reduced the proportion of B cells (B220⁺ lymphocytes) and increased the proportion of memory B cells (B220⁺CD27⁺ lymphocytes) in the spleens of bleomycin-induced mice. Baicalein treatment potently attenuated serum levels of cytokines (interleukin (IL)-1β, IL-2, IL-4, IL-6, IL-17A, tumor necrosis factor-α), chemokines (monocyte chemoattractant protein-1, macrophage inflammatory protein-1 beta) and autoantibodies (anti-scleroderma 70 (Scl-70), anti-polymyositis-scleroderma (PM-Scl), anti-centromeres, anti-double stranded DNA (dsDNA). In addition, baicalein treatment can significantly inhibit the activation of TGF-β1 signaling in dermal fibroblasts and bleomycin-induce mice of SSc, evidenced by reducing the expression of TGF-β1 and IL-11, as well as inhibiting both small mother against decapentaplegic homolog 3 (SMAD3) and extracellular signal-related kinase (ERK) activation. Conclusions: These findings suggest that baicalein has therapeutic potential against SSc, exerting modulating B-cell abnormalities, anti-inflammatory effects, and antifibrosis.

Background Scleroderma (Systemic sclerosis, SSc) is an autoimmune disorder characterized by multisystem extensive fibrosis, vascular changes and immunological dysregulation. B cell abnormalities play an essential role in the fibrotic pathogenesis of scleroderma by promoting autoantibodies and cytokines release as well as modulating the inflammatory processes. Baicalein, a phenolic flavonoid derived from the Chinese herb Scutellaria baicalensis Georgi, has been used in the treatment of the pathological processes of various fibrotic and inflammatory diseases. Here, we aimed to investigate the effect of baicalein on the major pathological characteristics of SSc both in vitro and in vivo, including fibrosis, B cell abnormalities and inflammation. Methods The effect of baicalein on collagen accumulation and expression of fibrogenic markers in human dermal fibroblasts were analyzed. The antifibrotic features of baicalein and its mechanisms were investigated in the bleomycin (BLM)-induced dermal fibrosis mice model by histologic examination, hydroxyproline assay, enzyme-linked immunosorbent assay and flow cytometry. Results 5-120 µM baicalein significantly abrogated total collagen deposition, decreased soluble collagen secretion, and inhibited the expression of various fibrogenesis molecules, including collagen(COL)1A1, COL1A2, COL3A1, connective tissue growth factor (CTGF), fibronectin, transforming growth factor β1 (TGF-β1) and alpha-smooth muscle actin (α-SMA) in both TGF β1- and PDGF-induced human CCC-ESF-1 dermal fibroblasts. In BLM-induced dermal fibrosis mice model, 25-100 mg/kg baicalein markedly attenuated dermal thickness and collagen accumulation in dose-dependent manners. Baicalein reduced the proportion of B220⁺ B cells, while increased the percentage of CD27⁺ memory B cells in the spleen of BLM-induced mice. Consistent with reversing B cell abnormalities, baicalein treatment potently attenuated serum levels of cytokines(IL-1β, IL-2, IL-4, IL6, IL-17A, TNF-α), chemokines (MCP-1, MIP-1β) and autoantibodies (anti-Scl-70, anti-PM-Scl, anti-centromeres and anti-dsDNA). Conclusions Baicalein inhibits TGF-β1 and PDGF- mediated ECM accumulation in human dermal fibroblasts and alleviates the development of experimental dermal fibrosis by reversing B cell abnormalities, reducing autoantibody production and ameliorating inflammation. Baicalein may have the potential to be further developed as a therapeutic candidate against SSc.