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Abstract
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.
Highlights
Pleurisy, which is caused by a variety of internal and external factors, such as immunological diseases, tumors and microbial infections, tends to threaten lung tissue and eventually leads to a series of respiratory diseases (Ryu et al, 2017; Leemans et al, 2018)
Under stress conditions, Nuclear factor erythroid 2-related factor 2 (Nrf2) is released from Keap1 and translocates into the nucleus, where it subsequently activates a variety of genes, including NAD(P)H-quinone oxidoreductase 1 (NQO-1), glutathione S-transferase (GST), heme oxygenase-1 (HO-1), and γ-glutamylcysteine ligase (GCL), to cope with stresses (Yamamoto et al, 2018)
Antibodies against mitogen-activated protein kinase (MAPK), NF-κB, p-signal transducer and activator of transcription 3 (STAT3), β-actin, Histone3.1, NOX2, and NOX4 were purchased from Cell Signaling (Boston, MA, United States), and antibodies against KEAP-1, Nrf2, GCLC, GCLM, HO-1, and NAD(P)H-quinone oxidoreductase 1 (NQO1) were acquired from Abcam (Cambridge, MA, United States)
Summary
Pleurisy, which is caused by a variety of internal and external factors, such as immunological diseases, tumors and microbial infections, tends to threaten lung tissue and eventually leads to a series of respiratory diseases (Ryu et al, 2017; Leemans et al, 2018). Amentoflavone Ameliorates Carrageenan-Induced Pleurisy occur in the pleural cavity, facilitating the inflammatory response and leading to lung injury (Gao et al, 2020). Oxidative stress and subsequent inflammation are the two main causes of Car-induced pleurisy and lung injury. Fighting against oxidative stress and subsequent inflammation is essential for treating Car-induced pleurisy and lung injury (Gao et al, 2020). Under stress conditions, Nrf is released from Keap and translocates into the nucleus, where it subsequently activates a variety of genes, including NAD(P)H-quinone oxidoreductase 1 (NQO-1), glutathione S-transferase (GST), heme oxygenase-1 (HO-1), and γ-glutamylcysteine ligase (GCL), to cope with stresses (Yamamoto et al, 2018). We hypothesize that Nrf may be a treatment target for Car-induced pleurisy and lung injury
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