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Background and PurposeOur previous research showed that ferroptosis plays a crucial role in the pathophysiology of PM2.5‐induced lung injury. The present study aimed to investigate the protective role of the Nrf2 signalling pathway and its bioactive molecule tectoridin in PM2.5‐induced lung injury by regulating ferroptosis.Experimental ApproachWe examined the regulatory effect of Nrf2 on ferroptosis in PM2.5‐induced lung injury and Beas‐2b cells using Nrf2‐knockout (KO) mice and Nrf2 siRNA transfection. The effects and underlying mechanisms of tectoridin on PM2.5‐induced lung injury were evaluated in vitro and in vivo.Key ResultsNrf2 deletion increased iron accumulation and ferroptosis‐related protein expression in vivo and vitro, further exacerbating lung injury and cell death in response to PM2.5 exposure. Tectoridin activated Nrf2 target genes and ameliorated cell death caused by PM2.5. In addition, tectoridin prevented lipid peroxidation, iron accumulation and ferroptosis in vitro, but in siNrf2‐treated cells, these effects almost disappeared. In addition, tectoridin effectively mitigated PM2.5‐induced respiratory system damage, as evaluated by HE, PAS, and inflammatory factors. Tectoridin also augmented the antioxidative Nrf2 signalling pathway and prevented changes in ferroptosis‐related morphological and biochemical indicators, including MDA levels, GSH depletion and GPX4 and xCT downregulation, in PM2.5‐induced lung injury. However, the effects of tectoridin on ferroptosis and respiratory injury were almost abolished in Nrf2‐KO mice.Conclusion and ImplicationsOur data proposed the protective effect of Nrf2 activation on PM2.5‐induced lung injury by inhibiting ferroptosis‐mediated lipid peroxidation and highlight the potential of tectoridin as a PM2.5‐induced lung injury treatment.

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Many natural flavonoids can activate nuclear factor erythroid 2-related factor 2 (Nrf2), which is pivotal for alleviating various diseases related to inflammation and oxidative stress, including pleurisy. Amentoflavone (AMF), a biflavonoid extracted from many plants, has some beneficial bioactivities, especially anti-inflammatory and antioxidative activities. We aimed to investigate whether AMF protects against pleurisy and lung injury induced by carrageenan (Car) by activating Nrf2. Pleurisy was induced in wild-type (WT) and Nrf2-deficient (Nrf2-/-) mice. Then, pleural exudate and lung tissue were collected for biochemical analysis, H&E staining, immunocytochemistry and western blotting. Our results indicated that AMF protected against Car-induced pleurisy and lung injury. The Wright-Giemsa and H&E staining results showed that AMF alleviated inflammatory effusion and pathological injury. In addition, AMF decreased SOD and GSH depletion and MDA and MPO generation in the lung tissue of mice. AMF activated Nrf2 through keap-1 dissociation and subsequently increased heme oxygenase-1 (HO-1), NAD(P)H-quinone oxidoreductase 1 (NQO1), and γ-glutamylcysteine ligase (GCL) levels. Furthermore, AMF suppressed IL-1β and TNF-α levels and increased IL-10 levels in pleural exudate by blocking the proinflammatory NF-κB, signal transducer and activator of transcription 3 (STAT3) and extracellular signal-regulated kinase (ERK) pathways induced by Car. However, these antioxidative and anti-inflammatory effects were weakened in Nrf2-/- mice. Moreover, AMF failed to suppress the NF-κB and STAT3 pathways in Nrf2-/- mice. Our results demonstrated that AMF exerted anti-inflammatory and antioxidative effects in Car-induced lung injury and pleurisy in a Nrf2-dependent manner.

Oxidative stress and inflammation play important roles in pleurisy. Leonurine (Leo) has been confirmed to exert antioxidative and antiinflammatory effects in many preclinical experiments, but these effects have not been studied in pleurisy. The aim of this study was to explore the therapeutic effect and mechanism of Leo in a carrageenan (CAR)‐induced pleurisy model. In this study, we found that the increase of reactive oxygen species (ROS), myeloperoxidase (MPO), and malondialdehyde (MDA) and decrease of glutathione (GSH) induced by CAR could be reversed by the treatment of Leo. Leo effectively reduced the levels of proinflammatory cytokines interleukin‐1β (IL‐1β), tumor necrosis factor‐α (TNF‐α), and the percentages of mature macrophages and increased the levels of antiinflammatory cytokines (IL‐10). Furthermore, Western blotting revealed that Leo significantly activated the Nrf2 pathway to restrain the thioredoxin‐interacting protein/NOD‐like receptor protein 3 (TXNIP/NLRP3) and nuclear factor kappa‐B (NF‐κB) pathways. However, the protective effect of Leo was significantly weakened in Nrf2‐deficient mice. These results indicate that Leo confers potent protection against CAR‐induced pleurisy by inhibiting the TXNIP/NLRP3 and NF‐κB pathways dependent on Nrf2, which may serve as a promising agent for attenuating pleurisy.