4-OI ameliorates bleomycin-induced pulmonary fibrosis by activating Nrf2 and suppressing macrophage-mediated epithelial-mesenchymal transition.

ABSTRACT

OBJECTIVES: Pulmonary fibrosis (PF) is a chronic and refractory interstitial lung disease with limited therapeutic options. 4-octyl itaconate (4-OI), a cell-permeable derivative of itaconate, has been shown to have anti-oxidative and anti-inflammatory properties. However, the effect and the underlying mechanism of 4-OI on PF are still unknown. METHODS: WT or Nrf2 knockout (Nrf2-/-) mice were intratracheally injected with bleomycin (BLM) to establish PF model and then treated with 4-OI. The mechanism study was performed by using RAW264.7 cells, primary macrophages, and conditional medium-cultured MLE-12 cells. RESULTS: 4-OI significantly alleviated BLM-induced PF and EMT process. Mechanism studies have found that 4-OI can not only directly inhibit EMT process, but also can reduce the production of TGF-ß1 by restraining macrophage M2 polarization, which in turn inhibits EMT process. Moreover, the effect of 4-OI on PF and EMT depends on Nrf2. CONCLUSION: 4-OI ameliorates BLM-induced PF in an Nrf2-dependent manner, and its role in alleviating PF is partly due to the direct inhibition on EMT, and partly through indirect inhibition of M2-mediated EMT. These findings suggested that 4-OI has great clinical potential to develop as a new anti-fibrotic agent for PF therapy.