Indeed, in a previous study examining the effect of Tanshinone IIA (Tan IIA), a natural compound of traditional Chinese medicine in a silicosis rat model, Feng et al. found that Tan IIA could significantly alleviate the silica-induced pulmonary fibrosis, by reducing the silica-augmented NOX4 and enhancing Nrf2/ARE antioxidant activity in the lung of silicosis rats [42]. Here, NOX4 is linked to pulmonary fibrosis.