Synergistic protection of Schizandrin B and Glycyrrhizic acid against bleomycin-induced pulmonary fibrosis by inhibiting TGF-β1/Smad2 pathways and overexpression of NOX4

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Pulmonary fibrosis, a progressive and lethal lung disease, is a major therapeutic challenge for which new therapeutic strategies are warranted. Schisandrin B (Sch B) and Glycyrrhizic acid (GA) are the principal active ingredients of Schisandra chinensis and Glycyrrhiza glabra respectively, which have been reported to protect against lung injures. The present study was aimed at exploring the combinatorial therapeutic effects on bleomycin-induced pulmonary fibrosis. Lung fibrotic injuries were induced in mice by a single intratracheal instillation of 5 mg/kg bleomycin (BLM). Then, these mice were administered with Sch B (100 mg/kg) or/and GA (75 mg/kg) for 28 days. BLM-triggered structure distortion, collagen overproduction, excessive inflammatory infiltration, pro-inflammatory cytokine release, and oxidative stress damages in lung tissues were attenuated to a higher degree by combinatorial treatment than by treatment of the individual agents. The expression of TGF-β1 and the phosphorylation of its downstream target, Smad2 were enhanced by BLM, but weakened by Sch B or/and GA. Furthermore, the significant overexpression of NADPH oxidase 4 (NOX4) was observed in BLM-induced pulmonary fibrosis, which was inhibited by Sch B or/and GA. Our study reveals that the synergistic protection by Sch B and GA against BLM-induced pulmonary fibrosis is correlated to its anti-inflammatory, anti-oxidative and anti-fibrotic properties, involving inhibition of TGF-β1/Smad2 signaling pathways and overexpression of NOX4.

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